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Home My WebLink AboutGeology & Mineral Deposits of Southeastern Alaska est 1929Geology and mineral deposits of southeastern Alaska by A.F. Buddington and Theodore Chapin USGS Bulletin No. 800 Washington 1929 ABSTRACT: Within southeastern Alaska the dominating feature of the mainland is the Coast Range, a high mountain mass many peaks of which rise to altitudes of 6,000 to 8,000 feet. Clarence Strait, Revillagigedo Channel, Nichols Passage, and the lowlands bordering them occupy the site of a down-warped trough. This trough extends northwestward beneath the Tertiary formations of Eagle, Zarembo, Kashevarof, Prince of Wales, Kupreanof, Kuiu, and Admiralty Islands. It is evidently one of the series of basins constituting the Pacific coast downfold. Tertiary formations are exposed at least locally in or on the borders of all the basins of the downfold that are not completely submerged. The mountainous islands and penisulas to the east of this Tertiary belt may, in the absence of more definite knowledge, be grouped with the Coast Range of the mainland. To the west of the trough lies what is here named the Prince of Wales Range, dom- inated by a complex group of short, rugged mountains that reach an altitude of about 4,000 feet. This range includes Prince of Wales Island, all of Kuiu Island except the eastern part, and the island groups lying west of Prince of Wales Island, with the possible exception of Forrester Island. The Prince of Wales Range is composed almost wholly of Paleozoic formations with associated intru- sive rocks of Upper Jurassic or Lower Cretaceous age, The trough between the Coast Range and the Prince of Wales Range appears to be terminated by Chatham Strait. Chatham Strait and Lynn Canal constitute a great fiord eroded along a faulted zone. This fiord is 250 miles long, 3 to 6 miles broad, and 1,000 to 2,900 feet deep. It traverses the general trend of the mountain ranges and of the bedrock structure at an angle of about 30 degrees. To the north there is no satisfactory means of discriminating between the Coast Range on the one side and the mountain ranges of Admiralty and Chichagof Islands, the Glacier Bay region, and the penisula west of Lynn Canal on the other. Mount Fairweather and the associated mountains, which are part of the St. Elias Range, lie along the line of trend of the ranges of the Alexander Archipelago, but are much higher, 8,000 to 15,000 feet, and probably in part of later origin. Their youth is indicated by the fact that in the vicinity of Mount St. Elias Pleistocene beds have been uplifted on their flnaks and folded and faulted. Se The predominant features of the bedrock geology of southeastern Alaska comprise the composite Coast Range batholith of the mainland and the as- sociated outlying intrusive bodies on the islands of the Alexander Archi- pelago and in the Glacier Bay region; a metamorphic complex belt that lies adjacent to the Coast Range batholith and consists of injection gneiss, crystalline schist, marble, phyllite, and highly schistose greenstone; three belts of Mesozoic formations—one through Juneau and Mitkof Island, one through Keku Straits and Gravina Island, and one through the west coast of Chichagof and Baranof Islands; a belt of Tertiary formations on Zarembo, Kupreanof, Kuiu, and Admiralty Islands, and another along the outside main- land coast northwest of Icy Point; and Paleozoic formations which form pro- bably two-thirds of the country rock of the Alexander Archipelago and the Glacier Bay region. The metamorphic complex is in part of Carboniferous age but may include beds ranging from Ordovician to Upper Jurassic or Lower Cretaceous. Recent lava flows from Mount Edgecombe, on Kruzof Island, and are found in several small separated areas in the vicinity of Thorne Bay, on Revillagigedo Island, and the east side of Behm Canal and along the Lava Fork of Unuk River. Paleozoic beds form practically all of the Prince of Wales Range, the northeastern part of Chichagof Island, and the area in the vicinity of Glacier Bay. These beds are of pre-Ordovician (?), Ordovician, Silurian, and Devonian age. A considerable part of Kupreanof and Zarembo Islands is composed of middle Paleozoic formations. Carboniferous formations are found within the Alexander Archipelago, in the Keku synclinorium on the northeast end of Kiziu and the norhtwest end of Kupreanof Island and on Admi- ralty Island. They are also exposed on the mainland along both borders of the Juneau synclinorium in the Juneau and Skagway districts and locally along the borders of the Gravina synclinorium in the Ketchikan district. The Prince of Wales Range and the mountain ranges on the northeast end of Chicagof Island ' and in the Glacier Bay region are characterized by the predominance of middle and lower Paleozoic formations, in contrast to the Queen Charlotte Range of Graham Island, where only Mesozoic formations are reported to be present, and the Vancouver Range, where there are Mesozoic and upper Paleozoic formations. Tertiary formations are found in and adjacent to the great trough between the Coast Range and the Prince of Wales Range. This trough must have originated in late Cretaceous or early Tertiary time, for its northwestward continuation forms the lowland area upon which lies the belt of Tertiary beds of Union Bay, on the Cleveland Penisula, Eagle Island, the west side of Zarembo Island, the Kasherof Islands, the northeast side of Prince of Wales Island, the west side of Kupreanof Island, the east half of Kuiu Island, and the southwest end of Admiralty Island. The Tertiary deposits of Kasaan Bay, Duncan Canal, and Ernest Sound indieate the sites of Tertiary erosion valleys which lead into the major trough. Geology of Hyder and vicinity, southeastern Alaska by A.F. Buddington USGS Bulletin No. 807 Washington 1929 ABSTRACT: The predomiant rocks of the area consist of (1) a great central mass of gray granodiorite composing the Texas Creek batholith intrusive into (2) the Hazelton group, of probable Jurassic age, comprising greenstone, tuff, volcanic breccia, graywacke, slate, argillite, quartzite, and rare limestone, which borders the Texas Creek batholith on the east and west; into both the Texas Creek granodiorite and the Hazelton group are intruded (3) a pinkish quartz monzonite, the Hyder quartz monzonite, composing the Hyder batholith, which forms the northeastern border portion of the main Coast Range batholith and which here lies along the southern border of the Texas Creek batholith, and (4) a pink granodiorite, the Boundary granodio- rite, composing the Boundary stock or apophysis, which occurs along the northern border of the Texas Creek granodiorite and the Hazelton group and is a facies of the main Coast Range batholith. Small stocks and dikes of gray sheared porphyry, genetically allied with the Texas Creek grano- diorite, occur in the beds of the Hazelton group. At many places dikes of pink to white granodiorite or dark diorite porphyry intrude both the Texas Creek batholith and the volcanic-sedimentary rocks of the Hazelton group. These are genetically associated with the Hyder quartz monzonite and the Boundary granodiorite. The Texas Creek and associated stocks and dikes, the Hyderbatholith and associated dikes, the Boundary stock and associated dikes, and the rocks of the Hazelton group are all cut by narrow dikes of dark to black lamprophyre and malchite. The major river valleys are floored with recent gravel and sand and locally with morainal deposits. Here and there benches along the river at a considerable height above their flhors are covered with morainal gravel, clay, and sand of Recent age. A thin veneer of glacial drift occurs locally in some of the valleys and on the gentler mountain slopes. In southeastern Alaska the dominant structural features of the formations older than the Coast Range intrusive rocks consist of northwestward striking folds, in part overturned or isoclinal. The gneissic structure of the Coast Range batholith similarly has a northwest strike. The folds immediately ad- Pema |(2||| oe jacent to the batholith on the southwest border are closely folded and in part overturned toward the southwest, and the foliation of the batholith dips uniformly steeply to the northeast. Similarly in the Salmon River area in British Columbia, just to the north of the area considered in this re- port, the formations are folded into a series of anticlines and synclines with a north-northwest strike. In the Salmon River area of the Hyder dis- trict there are beds along the international boundary east of Salmon River that strike north-northwest and dip steeply southwest; but in general with- in the area covered by this report the trend of the folds of the bedded rocks, of the gneissic structure of the Texas Creek batholith, and of the schistose structure of the greenstones is within 20 degrees of true east and is therefore completely out of harmony with the prevailing structure of the surrounding country. Mineral industry of Alaska in 1927 by Philip S. Smith USGS Bulletin No. 810 Mineral Resources of Alaska 1927 NOTES: Summarizes the economic atatus of the Alaskan mining industry during 1927 and tabulates total mineral production. The Chandalar-Sheenjek district by J.B. Mertie, Jr. USGS Bulletin No. 810 Mineral Resources of Alaska 1927 ABSTRACT: , The sedimentary rocks of the Chandalar-Sheenjek district are mainly of Paleozoic age. Six sedimentary formations are represented, ranging in age from pre-Silurian to Carboniferous. Igneous rocks also are present but are confined mainly to Sheenjek Valley, where they occur as intrusive bodies in the late Devonian or early Mississippian sediments. Tertiary lavas are present in the southwest corner of the mapped area. The oldest sedimentary rocks are a group of schists of early Paleozoic and possibly in part of pre-Paleozoic age. These schists are overlain by the Skajit limestone, of Silurian age, and this in turn is followed by a group of rocks that are believed to belong in the Devonian system. Three younger formations are also mapped, of which the lower one is here considered to be of Upper Devonian or early Mississippian age. The intermediate formation is regarded as lower Mississippian. The youngest of these three formations is the Lisburne limestone, of Upper Mississippian age. Triassic rocks are known also to exist to the northwest and northeast but have not been recognized as such in this district. To the west Cretaceous rocks also are known to exist south of the Brooks Range, and such rocks may indeed be present in the mnmapped country in the south- central part of this area, especially near the Christian River. The Mount Spurr region, Alaska by Stephen R. Capps USGS Bulletin No. 810 Mineral Resources of Alaska 1927 ABSTRACT: Probably the oldest rocks of the region are certain banded schistose rocks that occur on the mountain ridge 6 or 8 miles northwest of Mount Spurr and between the crest of that ridge and the Nagishlamina River. These rocks were not seen in place and are not represented on the geologic map, but their general location is known because of their abundance on the mo- raines of the southwestward flowing Harpoon Glacier, which terminates in the Nagishlamina Valley 11 miles above the mouth of that stream. The age of these schists is not known, but they are believed to be of pre-Mesozoic age. Next younger is a group of basaltic flows, andesitic, dacitic, and ba- saltic tuffs, and metamorphosed sedimentary rocks that include banded schists and rocks that were formerly shale, sandstone, and limestone. The rocks of this group are unfossiliferous but are believed to be Mesozoic and are pro- bably of Jurassic and Cretaceous age. A large part of the area here consi- dered is occupied by granitic rocks that form a notable element of the-Alaska Range from Lake Clark northward to Mount McKinley and beyond. Quite possibly granites of several ages are represented, but in the Mount Spurr region there is evidence for the belief that the major intrusions took place in late Meso- zoic time, though earlier granites are present also. Tertiary sedimentary rocks of Eocene age are present in the widespread deposits between the east flank of the mountains and the coast. These rocks include clay, sandstone, tuff, and lignitic coal. The volcanic rocks of Mount Spurr range in age from early Tertiary to Recent. Tuffs and beds of lava pebbles included in the Eocene sedi- ments indicate that this volcano was active in Eocene time, and lava beds inter- bedded with glacial deposits, deposits of volcanic as, and fumaroles that still exist on the mountain give evidence of'at least intermittent activity up to the present time. A widespread mantle of glacial till and boulders over the piedmont area and the deeply excavated glacial troughs within the mountains testify to the great development of glacial ice within the region in Pleisto- cene time, and the remnants of those ancient glaciers are still vigorous ice streams that occupy the higher mountain valleys. Mineral industry of Alaska in 1928 by Philip S. Smith USGS Bulletin No. 813 Mineral Resources of Alaska 1928 NOTES: Summarizes the economic status of the Alaskan mining industry during 1928 and tabulates total mineral preduction. The Chakachamna-Stony region by Stephen R. Capps USGS Bulletin No. 813 Mineral Resources of Alaska 1928 ABSTRACT: Probably the oldest rocks in this area are a group that includes fragmental volcanic material now consolidated into tuff, lava flows, and associated clastic sediments, all considerably metamorphosed. This group has yielded no fossils in this region but is believed to be Mesozoic and probably of Lower Jurassic age.It is associated with and overlain by metamorphosed sediments that were originally sand and mud, but are now altered to argillite, slate, graywacke, and quartzite. These rocks are probably of Jurassic or Cretaceous age. A third group, younger than those already mentioned, consists largely of black argillite and slate, with minor amounts of graywacke. The rocks of this group have locally been severely metamorphosed to form black fissile schist penetrated in all directions by long andalusite crystals. From this group a single fossil was collected that indicates an Upper Cretaceous age. A large proportion of the Alaska Range in this region is composed of granitic rocks. To the north, west, and south— west of Kenibuna Lake the granitic materials show a pronounced gneissic chara- cter, and these granitic or dioritic gneisses may be older than the surround- ing unaltered granite, though definite proof of this was not obtained. The alternate view is that the granite gneisses are of the same age as the asso- ciated unaltered granite, but that they were changed to gneisses through fairly local metamorphism. There is evidence that granitic intrusion has taken place in this part of the Alaska Range during more than one period. Nevertheless, the great bulk of the granitic rocks are believed to have been intruded in late late Mesozoic time, for they cut rocks of know Tertiary age. Tertiary sediments are present on the east bank of the Alaska Range in this latitude and are known to occur on the north and northwest flank north of this region. No Tertiary bedswere observed in the present investigation. Un- consolidated materials of Pleistocene and Recent age are widely distributed in this region, particularly in the valley of the Stony River. These materials include glacial morainal deposits, alluvial fans, talus accumulations, and the gravel, sand, and silt of the present streams. Mining in the Fortymile district by J.B. Mertie, Jr. USGS Bulletin No. 813 Mineral Resources of Alaska 1928 NOTES : Sketches present progress of mining development in the district. For a description of the geology see USGS Bulletins No. 251 and 375. Notes on the geology of Upper Nizina River by Fred H. Moffit USGS Bulletin No. 813 Mineral Resources of Alaska 1928 EBSTRACT: The rocks that are most widely distributed in this district are sedi- mentary rocks and bedded tuffs and lava flows. Massive intrusive rocks are not well represented in the area studied and are confined to a small area near Frederika Mountain, another on Skolai Creek, and possibly one other locality. Similar rocks are found in the mountains of lower McCarthy Creek but lie outside the area to which most attention was given. The oldest rocks that have been recognized are of Permian age and include a great thickness of lava flows, bedded tuffs, massive limestone, shale, limy sandstone, and grit. The next younger formation is the Nikolai greenstone, of Permian or Triassic age, which is overlain by rocks of Upper Triassic age, which in- clude the Chitistone, Nizina, and McCarthy formations and reach a thickness of at least 5,500 feet. Possibly the Permian rocks underwent some folding before the Upper Triassic sediments were deposited, but the evidence for this is not yet complete. However that may be, both the Permian and the Upper Triassic rocks were folded and subjected to weathering and erosion before the next younger beds, the Cretaceous sandstone and shale, were formed. The Cretaceous beds are largely of marine origin and are widely distributed in the Chitina Valley. Their thickness in the Nizina district is probably not less than 2,000 feet. They also are folded but much less so than the older formations. The folds as a rule are open and broad, and in places the beds show only a moderate tilting. After the Cretaceous beds were deposited a period of volcanism began in Eocene time, which yielded possibly 3,000 feet of lava flows and tuffs. These surface effusive rocks and fragmental deposits are extensively developed in the Wrangell Mountains, where they make up much of the highland area. Originally they formed a continuous sheet of great ex- tent that hid all the older rocks beneath, yet erosion has not only cut through them but has earved deep valleys in the underlying formations. In Se 2 eee a few localities fresh-water leaf-bearing beds of sandstone and shale containing thin coal seams have been found at the base of these Tertiary volcanic rocks and furnish evidence for assigningthem to the Eocene. These beds appear to be small in extent and local in their distribution. The Tertiary volcanic rocks, like the Cretaceous sediments, do not lie in their original horizonal position but are slightly tilted in most places. Stream gravel and glacial morainic material, together with loose waste on the mountain slopes and a little volcanic "ash" complete the list of geologic formations known in the district. Geology and mineral resources of northwestern Alaska by Philip S. Smith and J.B. Mertie, Jr. USGS Bulletin No. 815 Washington 1930 ABSTRACT: Stratigraphy of northwestern Alaska Era Period Epoch Description ' Recent Sand, gravel, silt, and ice wedges or masses, of Bp, Pleistocene fluviatile, marine, glacial, and lacustrine origin 38 laid down on the land and in the shallow waters 38 e off the coast. Nonindurated stratified slate-colored or ash- a Pliocene colored calcareous sediments near mouth of Colville 3 P Formerly treated as upper part of Colville series. 8 3 Miocene Conglomerate,sand, and shale, dominantly of terri- & Eocene genous origin, containing small coal beds. Poorly consolidated except in Kobuk Valley. Sandstone and shale of marine origin with some bentonite beds near the top. Upper Dominantly sandstone and shale of terrigenous origi: 3 with numerous thick coal beds. 8 pene eS ee eee ee ea ete ase 3 Sandstone and shale principally of marine origin. oO mememenen ewer snemenssionmen: a eee ee eee eee eee eee eee eee ee ee ee ee ee 8 Sandstone and shale with minor beds of grit. Marine. a Lower Universally much deformed. Massive conglomerate g member near base. eee o a a Upper Sedimentary representatives believed to be absent o Middle throughout northwestern Alaska but possibly pre- 4 Lower sent as Corwin formation in Lisburne region. 45 KR NRT |? +o; C CEES ESET EH EES EEE HEHE EES EEE HES EEE E HEED a 2 Era Period Epoch Description Upper Chert, limestone, and shale. Marine. Highly de- ° formed. oO Ad 5 a rnc ccc ccc ccc cee n cc cscccccec secs enseccescccses N 9 Middle Unknown anywhere in Alaska ef a ser ical 3 ai Lower Unknown anywhere in Alaska Permian ‘Not recognized in region but may be present and Pennsylvanian overlapped by later rocks of Mesozoic age. a ra TST ae 3 Upper Missi- Lisburne limestone, of marine origin. (Limestone & ssippian and chert.) 3 Lower Noatak formation. (Sandstone and shale, principally 4 Mississipp- of marine origin but contains small coal beds. In- Oo ian cludes chert conglomerate formerly called Stuver "series", Upper Sandstone, grit, and shale. a Not specifically identified but probably present g 8 Middle and included with the general group of Devonian 3 q rocks. S > rman mmm ccc ccc ccc ccc cece cece cece ccc c ces cccecscece cecoeee ’ a Lower Not recognized anywhere in Alaska and probably ab- sent in this region. Slate, schist, and metamorphic limestone desig- a nated undifferentiated Silurian rocks. 3 Skajit limestone. (Metamorphosed and recrystallized a limestone). -— § Era Period Epoch Description ia Upper Early Paleozoic or older rocks: Quartzite, quartz- iS ------------ ite schist, quartz-mica schist, cacareous schist, 5 Middle carbonaceous schist, chloritic schist, phyllite, 2 ------------ hornblende schist, albite schist, interbedded cry- ° a Lower stalline limestone, and undifferentiated basic vol- Qo rere nnoo----- ~canic rocks of greenstone habit. Includes part of Upper former "Totsen series" of John River region and cer- & 3 ------------ tain of the so-called "undifferentiated schists" of = B Middle the Kobuk and Noatak Valleys. At least one strongly q ------------ indicated unconformity is present, and doubtless o Lower others occur but have not been distinguished. © q pal 4 9. oO a Note: The dotted line indicates that the two units are separated by a strati- graphic break, either an angular unconformity or a gap in which certain beds represented elsewhere are absent. Geology of the Hagle-Circle district, Alaska by J.B. Mertie, Jr. USGS Bulletin No. 816 Washington 1930 ABSTRACT: Stratigraphy of the Eagle-Circle district Sedimentary and volcanic rocks: Period Epoch Rock types and formations Recent and Alluviun Quaternary Pleistocene Pleistocene Morainal deposits Eocene and Upper Sandstone, shale, and conglomerate Tertiary and Cretaceous Cretaceous = -------~-----------------~--------------_ +--+ Lower Cretaceous Kandik formation (Sandstone and slate) Triassic Upper Triassic Limestone and shale Permian Tahkandit limestone Pennsylvanian or Nation River formation (Sandstone, shale, Mississippian and conglomerate) Carboniferous Shale, argillite, conglomerate, and grit. Upper Mississippian Calico Bluff formation (Limestone and shale) Lower Mississippian Circle volcanics (Basaltic greenstone inter- bedded with chert and argillite). Chert, slate, and shale = 2 a! Period Epoch Rock types and formations Woodchopper volcanics (Basaltic greenstone with Devonian Middle interbedded limestone, slate, and chert) Devonian won +~--- -- - Argillite, chert, and cherty grit Silurian Limestone, slate, and chert Upper Cambrian Limestone Cambrian Middle Cambrian Limestone Middle Cambrian Limestone, shale, and argillite or older Lower (?) Cambrian Red beds Cambrian or pre-Cambrian or tern tne penn ne Pre-Cambrian Tindir group (Dolomite, limestone, quartzite, shale, and interbedded flows; also dikes and sills of greenstone). Limestones Undifferentiated ---- Paleozoic Non calcareous rocks, including some rocks of igneous origin. Pre—Cambrian Birch Creek schist (Quartzite and schist) Igneous rocks: Tertiary Rhyolite and dacite flows, mainly rhyolite. Tertiary and Mesozoic Granite, diorite, and related rocks Paleozoic Undifferentiated greenstone, in part ultra basic Mineral industry of Alaska in 1929 by Philip S. Smith USGS Bulletin NO. 824 Mineral Resources of Alaska NOTES: Summarizes the economic status of the Alaskan mining industry during 1929 and tabulates total mineral production. The Slana district, upper Copper River region by Fred H. Moffit USGS Bulletin No. 824 Mineral Resources of Alaska 1929 ABSTRACT: Bothe sedimentary and igneous rocks, together with large areas of stream and lake gravel and morainal deposits are present in the region. In general the mountains south of the Mankomen Valley, between the Chisto- china and Slana Rivers, are made up of igneous rocks, which include coarse- grained granitic rocks, dark fine-grained lava flows, intrusive rocks, and tuffs. They also include beds of limestone in a few places and possibly some other sediments. The mountains north of the Slana River are composed dominantly of sedimentary rocks but include considerable amounts of dark fine-grained igneous rock and some granitic rocks. Near the axis of the range most of these rocks have been altered to schist. The age of most of the formations has not been established yet. Mining in the Circle district by J.B. Mertie, Jr. USGS BULLETIN No. 824 Mineral Resources of Alaska 1929 NOTES: Sketches present mining development in the district, with brief notes on the bedrock of the most important localities. For detailed regional geology see USGS Bulletins 251, 295, and 538. The occurrence of gypsum at Iyoukeen Cove, Chichagof Island, Alaska by B.D. Stewart USGS Bulletin No. 824 Mineral Resources of Alaska 1929 ABSTRACT: As the deposit at Gypsum Creek underlies the creek valley the surface is so thickly covered by modern stream gravel that bedrock outcrops are searce. For this reason and because old mine workings were confined almost wholly to the gypsum beds, the geology in the immediate vicinity of that deposit is somewhat obscure. It is known, however, that the underlying bed- rock is cherty limestone and that a chert conglomerate overlies the gypsum beds. The Lake Clark-Mulchatna region, Alaska by Stephen R. Capps USGS Bulletin No. 824 Mineral Resources of Alaska 1929 ABSTRACT: ' The oldest:rocks in this area comprise a group of volcanic materials with which are associated large quanities of sediments, all more or less metamorphosed. These rocks occupy the foothills northwest of Lake Clark and are present near the face of the Alaska Range as far north as the basin of the Stony River. The volcanic rocks include andesite and basalt flows and large volumes of water-laid fragmental volcanic rocks that may be included under the general term "tuff". Interbedded with the tuff there is locally much sedimentary material that was originally mud and impure sand but is now indurated and metamorphosed to form shale, argillite, and graywacke. It is believed that the lower part of this group is composed dominantly of me- dium basic to basic lava flows, with the fragmental volcanic material and sediments increasing in abundance toward the upper limit of the group. The age of this undifferentiated group of rocks is somewhat uncertain, but it is here tentatively assigned mainly to the Lower Jurassic, though it may in- clude materials as young as Upper Jurassic or even Cretaceous. The next young- er rocks in this region consist of a series of argillites and graywackes, cut by numerous dikes and sills, but containing only minor amounts of lava and tuff, that occurs west of the Koksetna River and in the vicinity of Telaquana Lake. These rocks lie along the strike of a similar series of rocks in the Stony Basin, from which a fossil has been determined as probably of Upper Cretaceous age. A third group, composed almost exclusively of lava flows and tuff of andesitic, rhyolitic, and basaltic composition covers a considerable area of the foothill region in the upper basin of the Chilikadrotna River. These rocks are locally faulted and mildly folded but in general are not greatly deformed and are obviously younger than the Upper Cretaceous sediments. They are no doubt of Tertiary age, though it is as yet impossible to determine to what part of the Tertiary system they belong. Granitic rocks form a prominent element in the Alaska Range from Iliamna Lake northward to and beyond Mount McKinley, being present in bodies of large area and also in smaller outliers. In the Lake Clark-Mulchatna region granitic rocks occur in both small outliers —- 2 -— and as part of the larger masses that are present in the main range, though it happens that the region here covered lies a little too far west to in- clude extensive areas of granite. Such an area occurs, however, not far east of this region, and studies in the Iliamna-Lake Clark area and in the Chaka- chatna Basin, farther north, indicate that the main range is composed mainly of granitic rock. Still farther north, in the Stony and Skwentna Basins, these granites are found to cut Upper Cretaceous sediments, though they are nowhere known to intrude Eocene sediments, and they are there fore thought to be of late Mesozoic age. Un consolidated materials of Pleistocene and Recent age are abundantly present in this region and include conspicuous glacial moraine de- posits, glacial outwash gravel, and the deposits of the present streams. Almost the entire foothill belt was formerly buried by glaciers that moved out from the high range and spread over the lowlands. This area is characterized by wide gravel-floored valleys, whose filling, in part at least, has been derived from the outwash left behind by the Pleistocene glaciers during their retreat. In many places the gravel has been partly removed by the streams, and the remnants now occupy terraces at various heights above the present flood plains. The Slana district, Upper Copper River region, Alaska by Fred H. Moffit USGS Bulletin No. 824-B Washington 1931 NOTES: The above report is an extract from USGS Bulletin No. 824: Mineral Resources of Alaska 1929, which see for abstract. The occurrence of gypsum at Iyoukeen Cove, Chichagof Island, Alaska by B.D. Stewart USGS Bulletin No. 824-8 Washington 1931 NOTES: The above report is an extract from USGS Bulletin No. 824: Mineral Resources of Alaska 1929, which see for an abstract. A geologic reconnaissance of the Dennison Fork district, Alaska by J.B. Mertie, Jr. i USGS Bulletin No. 827 Washington 1931 ABSTRACT: Stratigraphy of the Dennison Fork district: Age Description Quaternary Alluvial deposits , Cretaceous or Tertiary Sandstone, shale, and conglomerate. Carboniferous Wellesley formation (Conglomerate and slate) , Paleozoic Undifferentiated Paleozoic rocks (Phyllite, - Slate, quartzite, limestone, and greenstone) | Pre-Cambrian Birch Creek schist and associated igneous rocks, chiefly if not wholly. pre—Cambrian. IGNEOUS ROCKS: Late Tertiary and Quaternary Later volcanic rocks (Rhyolite, dacite, and basalt), Late Mesozoic or early Tertiary arly volcanic rocks (Rhyolite and dacite) Mesozoic Granitic rocks (Granite, quartz diorite, and basic differentiates). Devonian or Carboniferous Greenstone (Basic and ultrabasic intrusive rocks of greenstone habit). Mineral industry of Alaska in 1930 by Philip S. Smith USGS Bulletin No. 836 Mineral Resources of Alaska 1930 NOTES : Summarizes the economic status of the Alaskan mining industry during 1930 and tabulates total mineral production. Notes on the geography and geology of Lituya Bay by J.B. Mertie, Jr. USGS Bulletin No. 836 Mineral Resources of Alaska 1930 ABSTRACT: The hard rocks of Lituya Bay and vicinity may be divided broadly into five groups, as follows: Amphibolite and chlorite schists, the oldest rocks exposed. A group of rocks composed of argillite, slate, and limestone with asso- ciated greenstone, of pre-Tertiary age. Sandstone, shale, and conglomerate of Tertiary age. Quaternary deposits. Granitic rocks, probably of Mesozoic age. Upon the basis of only three days' work the writer naturally is not pre- pared to present a geologic map of these stratigraphic groups, but their gene- ral distribution can be indicated by a brief description. Surface water supply of southeastern Alaska, 1909-1930 by Fred F. Henshaw USGS Bulletin No. 836 Mineral Resources of Alaska 1930 NOTES: Contains a general description of southeastern Alaska with special em- phasis on those factors affecting the water power development of the region, including precipitation, topography and drainage, glaciation, vegetation, etc. The gaging station discharge records are given for the preceding decade. The eastern portion of Mount Mckinley National Park by Stephen R. Capps USGS Bulletin No. 836 Mineral Resources of Alaska 1930 ABSTRACT: In the Mount McKinley region there are two rock groups that are believed to be definitely of pre-Devonian age. One of these is considered to be pre-Cam- brian, and the other pre-Devonian Paleozoic. A group of rocks lying near the _ center of the range contains limestone of Middle Devonian age, and also a great thickness of sediments both above and below the horizon at which the Middle Devonian fossils have been found. These associated rocks have so far failed to yield fossils. They are believed to be in part pre-Devonian and in part later than Middle Devonian, but all are definitely younger than the pre-Cambrian schist and also younger than the group of schist, limestone, slate, and serpentine of pre-Devonian Paleozoic age. Furthermore, they are definitely pre-Triassic. Along the north flank of the range there is another group of metamorphic sediments whose age is not accurately known. They are here grouped as undifferentiated Paleozoic rock. To the south, in the Thorofare Pass—Divide Mountain region, is another group of Paleozoic rocks of undetermined age which may be equivalent to or younger or older than the undifferentiated Paleozoic rocks on the north flank of the range. Their relations to the rocks of Middle Devonian age have not been determined. The rocks of the region that are here referred to the Mesozoic include greenstone flows and tuffs that underlie a series of Triassic rocks and may pos- sibly be in part of late Paleozoic (Permian) age; a Triassic group that includes slate, argillite, graywacke, tuff, and some limestone; and a thick group com- posed mainly of black shale but containing also graywacke beds and a little limy shale that is, in part at least, of Upper Jurassic or Cretaceous age. All these sediments are cut by dikes, sills, and stocks of intrusive rocks, including coarse-grained granitic materials. The Tertiary deposits of the region include a thick series of shale, conglomerate, and sandstone—-the Cantwell formation-- that has yielded fossils identified as ef Hocene age. It is succeeded unconform- ably by a series of softer shale, sandstone, and conglomerate that also contains lignitic coal. This coal formation is in turn overlain unconformably by e heavy deposit of Tertiary gravel--the Nenan gravel. The Cantwell formation and the coal-bearing series are cut by dikes and sills of various sorts of granular intrusive rocks and interbedded with lava flows. Quaternary deposits include glacial morainal material of at least two stages of Pleistocene glaciation, present glacier deposits, outwash gravel, terrace deposits, and the deposits of present strems, as well as accumulations of talus, products of rock disin- tegration and decomposition in place, soils, and peat. All these materials except those of Pleistocene and Recent age have suffered varying degrees of —- 2 --- metamorphism. The main structural features of the Alaska Range lie parallel to the axis of the range, and the region has been the scene of repeated mountain-building processes that have recurred at intervals from pre-Cambrian time to the middle of the Tertiary time. There was probably intense pre-Cam- brian deformation and metamorphism of the preexisting rocks, perhaps at many times, and the structure of the pre-Cambrian schists is parallel to the more recent folding and faulting. The pre-Devonian Paleozoic schists, slates, and serpentines on the south flank of the range indicate another period of defor- mation. The group of Devonian and associated rocks is recrystallized, folded, and crumpled, in lesser degree than the pre-Devonian Paleozoic schists and Slates, but more than the Triassic beds, which are somewhat more metamorphosed than the overlying Mesozoic shale series. Possibly some folding occurred be- tween the deposition of the late Mesozoic and the earliest Tertiary rocks here represented, but this has not been definitely established. Close folding, crumpling, and faulting occurred after the deposition of the Cantwell, but before the coal-bearing formation was laid down, and intense metamorphism took place along the zone of the great fault that accompanied this period of mountain building, so that Tertiary conglomerates were stretched and sheared and became schistose. The final upthrust of this region occurred after the coal—bearing formation was laid down and involved also at least a part of the overlying gravel. Since this period of Tertiary deformation the region has re- mained relatively stable. The Kantishna district by Fred H. Moffit USGS Bulletin No. 836 Mineral Resources of Alaska 1930 ABSTRACT: Two principal groups of metamorphosed, dominantly sedimentary rocks are represented in the Kantishna Hills and the lower slopes of Mount McKinley south of McKinley Fork. These sediments are intruded by igneous rocks, which in the form of granite and quartz diorite are especially abundant in the vicinity of Mount McKinley and include some lava flows of rather minor importance. In addition to these two main groups, several areas of unaltered or only slightly altered younger sedimentary rocks are present. The unconsolidated deposits in- clude the usual stream deposits and glacial debris of glaciated mountain areas and also older, slightly weathered gravel deposits, which locally attain a great thickness. The Tatonduk-Nation district, Alaska by J.B. Mertie USGS Bulletin No. 836 Mineral Resources of Alaska 1930 ABSTRACT: Geologically, as well as geographically, the Yukon River in this part of Alaska forms a significant boundary, for south of the river are great granitic batholiths of Mesozoic age, whereas north of the river such intrusive bodies are absent. Likewise, south of the river the pre-Cambrian rocks have been pro- foundly metamorphosed, and even rocks as young as Devonian have locally been rendered schistose. North of the river, on the other hand, rocks considered to be pre-Cambrian occur practically unaltered. Conditions of sedimentation have also been different north of the river, for the pre-Cambrian dolomite, red beds, and lavas and the Cambrian and Ordovician limestone have no known counterpart elsewhere in Alaska. In eddition, sedimentary rocks of every geologic system except the Jurassic are found in the same general vicinity, so that the Taton- duk-Nation district affords an unusual opportunity for compiling a complete geologic section. The Carboniferous and younger rocks of this section, however, have been described by the writer in some detail in an earlier publication, and therefore in this bulletin emphasis has been laid on the less well known lower Paleozoic and pre-Cambrian rocks of this district. The oldest rocks in Alaska, known as the Birch Creek schist and considered by the writer to be the basal part of the pre-Cambrian sequence, are not present in this district. The oldest rocks exposed consist of an assemblage of sediments and lavas called the Tindir group, which sre know on stratigraphic grounds to be older than Middle Cambrian and which are believed by the writer to be probably of Algonkian age. The Tindir group is divided into seven units, designated by letters and described as follows: Unit A. Principally thin-bedded limestone. Top of sequence. Unit B. Principally siliceous dolomite and shale, with beds of dolomitic conglomerate near bhe base. Unit C. Upper red beds, consisting of hematitic dolomite, shale, flint, tuff, and lava, with a red basal conglomerate. Unit DB. Amygdaloidal and ellipsoidal lavas of greenstone habit. Unit EH. Thin-bedded dolomite, shale, argillite, and quartzite, with here and there beds of more massive dolomite and quartzite. Also basic dikes and sill. flows, and a prominent horizon of red beds. Unit F. Massive magnesian limestone and dolomite. Unit G. An incompletely differentiated group of thin—bedded dolomite and argillaceous rocks that includes also a horizon of lava and an equally well defined horizon of red beds. A part of these rocks is believed to overlie unit F. The upper rocks of the Tindir group underlie early Middle Cambrian rocks without any recognizable discordance in structure. Open folding, modified by later fault displacements, characterizes these upper beds. The lower beds are more intricately folded, but this may be a matter of local variation rather than an indication of greater metamorphism. The total thickness of the Tindir rocks is estimated by the author to be between 20,000 and 25,000 feet. The Cambrian section is divided into four parts, as follows: 1. Upper Cambrian limestone that grades upward, without any noticeable stratigraphic or lithologic break, into Ordovician limestone. 2. An upper plate of Middle Cambrian limestone. 5. A thin formation of slate and quartzite. 4. A lower plate of Middle Cambrian limestone. Both the Middle and Upper Cambrian rocks of the Tatonduk River lie in an anticline that plunges southeastward to the Yukon River. The Middle Cam- brian are believed to have a thickness of 1,300 feet and the Upper Cambrian limestone about 2,000 feet. The Ordovician rocks consist of about 1,000 feet of limestone, essentially similar to the underlying Upper Cambrian limestone, and 250 feet or more of graptolitic shale, which appears to be of approximately the same age as the limestone. The Silurian rocks have not been well differentiated in the Tatonduk-Nation district, but fossil collections show that both middle and late Silurian are resent. i As a result of studies in the Tatonduk-Nation district and other parts of Alaska, the writer presents a generalized Devonian section, composed of four groups of rocks, of which three are found in this district. This sequence is as follows: ; a Bae 1. Upper Devonian, characterized by Spirifer disjunctus and other in- vertebrates. These rocks sre found in the Brooks Range, of northern Alaska, and on Prince of Wales and Chichagof Islands, in southeastern Alaska. ®. High Middle Devonian, typified by siliceous and slaty beds in the Tatonduk-Nation district and by the Woodchopper volcanics farther north on the Yukon. 5. Middle Devonian proper, exemplified by thin-bedded limestone and shale, found. in many parts of Alaska, including the Tatonduk-Nation district. 4. Salmontrout limestone, of lowest Middle Devonian age, typically on the Porcupine River, and also in the Tatonduk-Nation district. Five Carboniferous formations, together with Triassic, Cretaceous, and Tertiary rocks and Quaternary unconsolidated deposits, are also described, but these formations are more fully discussed in an earlier publication, and the author has merely presented a summary of the post-Devonian formations, amplified by new material of later date. : The principal igneous rocks of this district are the Tindir lavas and intrusive rocks, which are for the most part normal basaltic rocks, ranging in granularity from holocrystalline to glassy. Some of the intrusive types contain a small percentage of orthoclase and quartz. Undifferentiated green- stone from the highly altered rocks south of the Yukon is also described. These rocks, though much more altered than the Tindir lavas, are probably Devonain in age. Mineral industry of Alaska in 1930 and Administrative report by Philip S. Smith USGS Bulletin No. 836-A Washington 1931 NOTES: The above reports are extracts from USGS Bulletin No. 836: Mineral Resources of Alaska 1930. Notes on the geography and geology of Lituya Bay, Alaska by J.B. Mertie, Jr. USGS Bulletin No. 836-B Washington 1931 NOTES: The above report is an extract from USGS Bulletin No. 836: Mineral Re- . sources of Alaska 1930, which see for abstract. The eastern portion of Mount McKinley National Park by S.R. Capps The Kantishna district and Mining development in the Tatlanika and Totatlanika basins by Fred H. Moffit USGS Bulletin No. 836-D Washington 1932 NOTES: The above reports are extracts from USGS Bulletin No. 836: Mineral Re- sources of Alaska 19350, which see for abstracts. The Tatonduk-Nation district by J.B. Mertie, Jr. USGS Bulletin No. 836-E Washington 1932 NOTES: The above report is an extract from USGS Bulletin No. 836: Mineral Resources of Alaska 1930, which see for abstract. Mineral industry of Alaska in 1931 and Administrative report by Philip S. Smith USGS Bulletin No. 844-A Mineral Resources of Alaska 1951 NOTES: Summarizes the economic status of the Alaskan mining industry during 1931 and tabulates total mineral production. Mineral investigations in the Alaska railroad belt, 1931 byS.R. Capps USGS Bulletin No. 344-B Mineral Resources of Alaska 1931 NOTES : Contains an account of investigations at the following points along the Alaska Railroad: Anthracite Ridge coal basin Moose Pass-Hope district, Kenai Penisula Girdwood district Willow Creek district Valdez Creek district West Fork of Chulitna River Mount Hielson district Eureka and vicinity, Kantishna district Fairbanks district The Suslota Pass district, upper Copper River region, Alaska by Fred H. Moffit USGS Bulletin No. 844-C Mineral Resources of Alaska 1931 ABSTRACT : The bedrock geology is apparently simple insofar as the number and distribution of formations is concerned. Metamorphosed tuffs and lava flows with a minor proportion of sediments, chiefly limestone, form a belt about 10 miles wide along the southwest side of the area. This belt of rocks, of Permian age, trends northwestward and forms the foothills of the range. It is bordered on the northeast by a wider belt of Mesozoic sedimentary beds, including ribbon-banded argillite, slate, sandstone, quartzite, conglomerate, and limestone. These beds are folded, and the folds trend northwestward with the axis of the Alaska Range in this vicinity. In places the sediments have been altered by the intrusion of igneous rocks of from other causes, but they show much less metamorphism than the Permian rocks, which they overlie uncon- formably. The Mesozoic sediments, like the Permian volcanic rocks, are intru- ded by granular igneous rocks that belong in large part to the diorite family and in places are extensively displayed. Fossils collected from the Mesozoic limestone show that Upper Triassic and Lower Cretaceous beds are present, and although no Jurassic beds were identified it appears probable from evidence afforded in nearby areas that they may be present also. Unconsolidated glacial and stream-laid deposits are widely distributed within the area. Mineral deposits of the Rampart and Hot Springs districts, Alaska by J.B. Mertie, dr. USGS Bulletin No. 844-D Mineral Resources of Alaska 1951 ABSTRACT: Bedded rocks of Paleozoic, Mesozoic, and Cenozoic age and granitic rocks of Cenozoic age compose the geologic column in the Rampart and Hot Springs districts. The bedded rocks that lie in the zones where intrusion and mineral- ization have occurred are locally much metamorphosed, although some of these are as young as Cretaceous. On the other hand, some of the older Paleozoic rocks that do not lie in such zones are relatively metamorphosed, considering their age. The oldest sedimentary rocks are a group of rocks termed the Nilkoka for- mation. These rocks form most of the highland area between Baker Creek and the Tolovana River and consist essentially of ferruginous sandstones and slates. They are now considered to be of pre-Ordovician age. Stratigraphically above the Nilkoka formation lies a thick formation of crystalline limestone, which also crops out in the hills between Baker Creek and the Tolovana River. This limestone represents the same horizon as the limestone in the White Mountains, northeast of Fairbanks, and is known to be of middle Silurian age. Two groups of later Paleozoic rocks are recognized. Am older group of undifferentiated Paleozoic rocks crops out in a narrow belt north of the Silurian limestone and in a much wider belt that extends from Troublesome Creek west-southwest almost to Tanana. This older group is made up of slate, quartzite, chert, chert conglomerate, lime- stone, greenstone, and their metamorphic equivalents. These rocks are mainly of Middle Devonian and Mississippian age, bub some of them may be as old as upper Silurian. The youngest of the Paleozoic rocks is an assemblage of volcanic and sedimentary rocks known as the Rampart group, which crops out along the Yukon River from Fort Hamlin to a point below Rampart and extends back into the hills several miles on both sides of the river. These rocks consist mainly of diabasic and basaltic lava flows and tuffs but inélude also interbedded chert, shale, slate, sandstone, and a few beds of limestone. The Rampart group is of Mississippian age. The Mesozoic bedded rocks lie in a belt from 12 to 20 miles wide, extending from the headwaters of Hutlinana and Hutlitakwa Creeks west- southwest to the Tanana River. These rocks consist of argillite, slate, quartz- Ieee anna ose sandstone, and their metamorphic equivalents. They are mainly of Lower Cretaceous age, but some Upper Cretaceous rocks are also found in the vici- nity of Wolverine and Elephant Mountains. The Cenozoic bedded formations include the early Tertiary coal measures and unconsolidated deposits of Plio- cene (?), Pleistocene, and Recent age. The coal-bearing rocks occur only along the Yukon River, chiefly at and above Rampart. The coal is a black lignite. The Pliocene (2) deposits consist of high gravel that lies.on the ridge tops east of Minook Creek and south of Hunter Creek, in the Rampart district. Pleisto- cene and Recent gravel deposits are present in the Eureka and Tofty areas. The principal igneous rocks of the Rampart and Hot Springs districts are intrusive masses of granitic rock, which are found chiefly at Hot Springs Dome, Roughtop Mountain, Elephant Mountain, Wolverine Mountain, and along the Yukon River at the rapids, or "Ramparts". The intrusive rocks at Roughtop, Elephant, and Saw- tooth Mountains are monzonite; the intrusives at or near Wolverine Mountain are quartz monzonite; and the mass at Hot Springs Dome is a biotite granite. All the granitic rocks of the Rampart and Hot Springs districts are of Tertiary age. Placer concentrates of the Rampart and Hot Springs districts by A.E. Waters, Jr. USGS Bulletin No. 844-D Mineral Resources of Alaska 1931 ABSTRACT: The Tertiary granitic rocks of the Rampart and Hot Springs districts are of particular importance in the present study, because they are believed to be connected genetically with the mineralization in this region and thus to have been the source of the heavy minerals of the concentrates. Masses of such rocks of considerable size occur at Hot Springs Dome, Roughtop Mountain, Elephant Mountain, Wolverine Mountain, the Sawtooth Mountains, and along the Yukon River below Stevens Creek. The intrusive mass at Hot Springs Dome shows little variation in mineral composition and consists essentially of quartz, potash feldspar, basic orthoclase, and biotite, with accessory iron ores, zir- con, muscovite, and tourmaline. The main intrusive mass at Roughtop Mountain is a monzonite, which, however, grades into syenite and olivine monzonite. NOTES: Contains a listing of nine samples of placer concentrates from the Ram- part area. Reconnaissance of the northern Koyukuk Valley, Alaska by Robert Marshall USGS Bulletin No. 844-2 Mineral Resources of Alaska 1931 NOTES : Contains notes on the geography and system of nomenclature in the region. The writer is not a trained geologist and he makes no geological observations. Progress of surveys in the Anthracite Ridge district, Alaske by Ralph W. Richards and Gerald A. Waring USGS Bulletin No. 849-A Investigations in Alaska Railroad belt, 1931 ABSTRACT: Anthracite Ridge is in south-central Alaska, on the north side of the Matanuska River Valley, about 200 miles north of Seward. The coal basin is about 4 miles wide and 7 miles long and lies between the ridge and the Mata- nuska River. The basin is in general synclinal, sharply folded and faulted along its north border. The coal beds are in the Chickaloon formation, of Tertiary fresh-water deposits, intruded by igneous dikes and sills and un- conformably overlying marine Upper Cretaceous beds. The geologic section as partly exposed in the valleys of the creeks crossing the coal basin show that the coal—bearing formation consists chiefly of shales, with minor len- ticular beds of sandstone and conglomerate. A dozen or more coal beds are found in a zone of several hundred feet, belonging to either the lower or the middle portion of the Chickaloon formation. Many of the coal beds range from a few inches to about 8 feet in thickness; but in one locality on the northwest border of the basin exceptional thicknesses of 34 and 24 feet were measured. These beds and others near by are of low-rand anthracite or semi- anthracite and are found in closely folded and faulted sediments further com- plicated by igneous intrusions. Most of the coal exposed in the southern and eastern parts of the basin is found in relatively thin beds and is of semi- bituminous to bituminous grade. Lode deposits of the Fairbanks district by James M. Hill USGS Bulletin No. 849-B Investigations in Alaska Railroad belt ABSTRACT: The Fairbanks district is underlain by pre-Cambrian metamorphic schists of sedimentary origin having a considerable range in composition. The schists are overlain by extensive gold—bearing gravel and muck in the valleys, and natural exposures on the hillsides and even on the summits are extremely rare, because of the heavy cover of moss and bushes. The cleavage of the schists has a general well-defined structural trend; which in the eastern part of the dis-— trict, or Pedro Dome area, strikes about east and dips 15 to 45 degrees both north and south. In the western part of the area, in the vicinity of Ester Dome, the trend is slightly east of north, and this has influenced both intru- sion and mineralization in that area. The schists have been intruded by igneous rocks of various types. The earliest is a fine-grained quartz diorite, which is well exposed on Pedro Dome. The diorite was followed by a coarse-grained biotite granite porphyry and this by finer-grained quartz porphyry, which in some dikes is represented by aplitic rock. These intrusive rocks occur in two principal areas as elongated nearly parallel bodies following the general structural trend, one north and one south of the Goldstream valley northeast of Fairbanks. There are probably a large number of small offshoots or dikes from these large masses, but the deep surface cover has obscured most of them, and only a few of them have been traced and mapped. Ester Dome has relatively little igneous rock in the more highly mineralized area on its southeast side, but a few small outcrops of these rocks show that the dikes follow the northward-trending structure. The principal mineral deposits of economic interest, aside from the extensive gold placers, are the gold quartz veins, from a few inches to 15 feet wide. The Willow Creek gold. lode district, Alaska by James C. Ray USGS Bulletin No. 849-C Investigations in Alaska Railroad belt 1931 ABSTRACT: The principal hard rocks exposed within the Willow Creek district are quartz diorite, probably of late Mesozoic age; very old mica schist of sedi- mentary origin, probably pre-Cambrian; a thoroughly cemented arkosic conglo- merate, possibly of Cretaceous age, which is exposed at several localities along the southern limits of the granitic rocks; a series of early Tertiary sedimentary beds; and Quaternary glacial debris and more recent Quaternary stream deposits partly fill the valleys to varying depths. The productive gold veins of the district occur within the quartz diorite, which occupies the northern half of the area. The quartz diorite is part of a large granitic mass that forms most of the Talkeetna Mountains. It grades locally into mon- zonite and in the eastern part into gabbro. This igneous mass is cut by dikes of dacite, dacitic aplite, and pegmatite. Flow structure and groups of sharply angular fragments of fine-grained dioritic rock included in the quartz diorite suggest that the portion in which they are found lies within the peripheral zone of the intrusive mass. The rock is much fractured and faulted as a result of stresses that were in operation before, during, and after the formation of the mineral deposits. The Mount Eielson district, Alaska by John C. Reed USGS Bulletin No. 849-D Investigations in Alaska Railroad belt 1931 ABSTRACT : The Mount Eielson district lies in south-central Alaska, on the north side of the Alaska Range, about 30 miles east of Mount McKinley. A thick series of limy sediments is distributed widely and constitutes the formation that is undoubtedly the oldest in the district. The formation is composed principally of light to dark bluish-gray thin to medium bedded limestone, interbedded here and there with graywacke and with black fissile shale. No recognizable fossils have been found in the formation in the vicinity of Mount Eielson. It is believed to be Paleozoic, and probably Devonian. The portion of the formation displayed within the Mount Eielson district is at least a mile thick, and neither the top nor bottom is exposed. A greenstone formation several hundred feet thick and in part ellipsoidal, appears to be the next younger formation than the Paleozoic limestone. This formation is probably Triassic. The Paleozoic limestone and the Triassic (?) greenstone have been intruded by a group of plutonic and hypabyssal rocks which display a wide range of composition and texture. There is evidence that all members of the group are genetically related and collectively represent a differentiation series. The oldest member is gabbro, which has a small areal development. The bulk of the intrusive rock is porphyritic granodiorite, which occurs in large masses and also as dikes and sills in the greenstone and in the Limestone, A third widespread member of the group is even-grained to slightly porphyritic granodiorite, which has not been found intruding the greenstone but only as stocklike masses in the limestone. Ore deposition appears to have been controlled by this member. The group was intruded during the Mesozoic era, and its intrusion period may cover a considerable span of Mesozoic time. A great unconformity separates the rocks already described from those which remain. The latter are all Tertiary or younger, the one possible exception being a group of basalts, tuffs, and obsidians, which has been correlated with the Cantwell formation. A lignite-bearing group of sandstone, shale, and gravel, which is younger than the rocks of Cantwell age, is found locally in the area. These rocks may be correlated with the Eocene lignite-bearing beds of the Nenana coal field. The lignite-bearing formation is succeeded by a deposit of yellow or buff gravel, the Nenana gravel, which is also Tertiary. The Quaternary deposits mapped include accumulations of morainic material of Pleistocene glaciers and some morainic material of present glaciers, alluvial deposits of fluvial and glaciofluvial origin, and talus and fanglomerate deposits, which are formaing at the present time. Material given off by the granodiorite has permeated the enclosing sediments and selectively replaced them with minerals of the epidote group and to a somewhat. lesser extent with sphalerite, galena, chaleopyrite, and pyrite. South of Mount Eielson the regional strike is about N. 55 E. and the dip is low toward the southeast. North of the mountain the strike of the sediments conforms in general to the curve of the base of the mountain and is about N.65 W. on Bald Mountain and north of the eastern peak of Mount Eielson, nearly east north of the central peak, and about N. 50 &. on the northern slopes of Copper Mountain. In most places the dip is steep toward the north. A normal fault of large displacement abruptly terminates the granitic area on the south. An ore-bearing zone can be definitely traced for about 4 miles along the north side of thegranodiorite mass. Its width on the surface is not uniform , but its thickness is about 2,000 feet, Sphalerite is the most abundant sulfide and is several times as abundant as galeha. Chalcopyrite is present in minor quanities. The small amount of silver in the ore appears to be irregu- larly distributed. Mineral deposits near the west fork of the Chulitna River, Alaska by Clyde P. Ross USGS Bulletin No. 849-# Investigations in Alaska Railroad belt, 1951 ABSTRACT: Both stratigraphically and structurally the area has features which distinguish it from others in this part of Alaska. The presence of strata of Carboniferous (probable Permian) age and of thrust faults are among the more striking of these features. Many of the rocks are distinctively colored, per- mitting subdivision into relatively small stratigraphic units. Fossils at several horizons help to date these units. Faulting, not completely understood, causes minor uncertainties in correlation. The lowest stratigraphic unit com- prises ancient, possibly Devonian, metamorphosed sedimentary rocks in which silicified limestone is prominent. Unconformably above these are tuff, lava, limestone, chert,-and argillite of probable Permian age, succeeded, with some unconformity, by Triassic limestone, followed by Triassic argillite with some limestone, pyroclastic rocks, and lava. There are some small dikes and bosses of moderately silicic porphyritic rocks of undetermined, presumably Tertiary - age, and Tertiary sediments of late Hocene or later age. The lodes, which are genetically related to the porphyry, are of three interrelated and intergra- dational kinds--(1) disseminated deposits, mainly in the porphyry, (2) re- placement deposits along the bedding in calcareous rocks, (3) tabular and lenticular lodes with conspicuous vein quartz, along fissures end shear zones. The principal metallic minerals are arsenopyrite, pyrite, pyrrhotite, chalco- pyrite, sphalerite, and galena. Lode deposits of Eureka and vicinity, Kantishma district, Alaska by Francis G. Wells USGS Bulletin No. 849-F Investigations in the Alaska Railroad belt, 1931 ABSTRACT: The bedrock of the Kantishma mining district is mainly a metamorphic series of rocks which within the area has been differentiated into a quartz-— muscovite schist and a calcareous facies that ranges from limestone to chlo- rite schist. A few small dikes of quartz porphyry and diabase intrude the schist. The general structure trends N. 70 E., and from an axis that extends from Eldorado Creek northeastward to Spruce Peak the schistosity dips to the northwest and southeast. It is along this axis that the heaviest mineralization has occurred. All the veins in the area strike N. 50-70 E., and most of them dip at high angles toward the southeast, though a few dip toward the northwest. The veins are rudely tabular, swelling and pinching along both the strike and dip, and range in thickness from 23 feet to a fraction of an inch. The veins are of three types--gold quartz veins, silver-bearing galena veins, and stib- nite veins. The gold quartz veins consist of white quartz containing small amounts of arsenopyrite and pyrite with scattered nests of galena or sphalerite. The gold is largely associated with the sulfide minerals except in the oxidized parts of the vein, where it is found as free gold. The galena-sphalerite veins are composed predominantly of sulfides carrying only small amounts of quartz and carbonate gangue. The stibnite veins are composed of stibnite with some quartz gangue, and many are massive stibnite. Enrichment appears to be almost totally lacking in all the veins, and they have been only superficially oxi- dized. The Girdwood district, Alaska by C.F. Park, dr. USGS Bulletin No. 849-G Investigations in Alaska Railroad belt, 1931 ABSTRACT: The predominant sedimentary rocks of the region is a series of thinly banded argillite and graywacke, containing some conglomerate, impure lime- stone, and partly indurated sandstone. On the basis of fossils, obtained at six different localities within the district, the rocks are considered of Upper Cretaceous age. The thickness of the argillite and graywacke is unknowm but must be 4 or 5 miles. These Upper Cretaceous rocks apparently were de- posited unconformably above an undifferentiated metamorphosed series of lava, tuff, agglomerate, intrusive rocks, and sedimentary rocks of undetermined age. The metamorphic rocks, whose thickness is unknown, are found in the western part of the district. Greenstone tuff several thousand feet thick, probably of Upper Cretaceous age, unconformably overlies the argillite-graywacke series. The rocks intruded into the argillite-graywacke series are classified as quartz diorite, dacite, and dacitic aplite. The igneous rocks are in the form of dikes, sills, and exceedingly erratic pipes that are composed essentially of a network of thin medium-grained dikes. Some of the individual dikes are only an inch or even less in thickness, but they are granitoid in texture, and several have been traced on the surface for 100 feet or more. The district is peculiar in that the details of the intrusions are apparently independent of any observed structu- ral control. The region has been the site of considerable widespread structural deformation, and the beds are highly tilted, folded, and faulted. The main axes of deformation follow the general trend of the Chugach Mountains, 10 to 20 de- grees east of north. Both normal and reverse faults occur, and their strikes also tend to align themselves with the main axes of folding. A minor system of tear faulting is developed in a general east-west direction. Much but not all of the faulting was earlier than the intrusions, and in places dikes tend to follow the fault planes for short distances. The rocks of the region are not greatly altered, although some recrystallization due to processes of rock de- formation has begun. Fine brown tourmaline needles and small reddish-brown gar- nets have been observed in argillite bordering an irregular intrusive pipe. ee ate Near the dike contacts silicification has taken place, but the introduction of silica is much more intense within an inch or two of the intrusive mass than farther away. Silification is intense in the vicinity of the pipelike intrusions and extends 20 feet or more from the contact; chlorite, muscovite, sericite, and some epidote are also usually developed. The ore deposits are small arsenopyrite-gold-quartz veins and the placer deposits derived from these veins. The most prominent vein deposits are grouped in a small area near the headwaters of Crow Creek. The veins are thin and irregular, but in places contain small pockets of rich gold ere with minor quanities of sulfides-- chalcopyrite, galena, sphalerite, pyrrhotite, and molybdenite. Most of the deposits lie approximately parallel to the bedding planes or cross them at low angles. There has been considerable postmineral movement along many of the veins, and the quartz and sulfides in places form a breccia in gouge and sheared wall rock. It is thought that the veins will continue in depth with essentially the same mineral composition. The veins are all grouped around the irregular pipelike intrusive rocks, and owing to the hydrothermally al- tered condition of these rocks and the noticeable contact action, as well as the constant association of these intrusive rocks with the veins, it is thought that the two have a closely related history. The fine-grained dikes and sills are apparently not closely associated with the ores. The Moose Pass-Hope district, Kenai Penisuia, Alaska by Ralph Tuck USGS Bulletin No. 849-I Investigations in Alaska Railroad belt, 1931 ABSTRACT: The bedrock throughout most of the district consists of a series of interbedded slate and graywacke, probably of late Cretaceous age. The bed- rock in the northwest corner of the district is a series of tuff and agglo- merate whose age is not definitely known. The only intrusive rocks in the area are fine-grained acidic dikes that are remarkable for their continuity across the country in spite of their small width. The region has been glaciated up to an elevation of about 4,000 feet, and glacial outwash aand and gravel cover the valley bottom and walls. The structure is highly complex, and the lack of any recognizable horizons makes interpretation difficult. Close folds.with over- turning are the rule. Numerous strike faults occur, and transverse faulting of unknown displacement has taken place. Two types of lode deposits are recognized—- mineralized dikes and fissure veins. Both types are identical in mineralization and have the same origin. The mineralized dikes are the acidic dikes that in places have been fractured and the fractures subsequently filled with vein ma- terial. The gold content of the dikes is erratically distributed, and they have not .yet been found to have sufficient value to be worked at a profit. The fissure veins have been worked profitably in a few places but only on a small scale. The veins have well-defined walls but are narrow and have not been found to be con- tinuous for more than a few hundred feet. The tenor of the ore in the veins is usually good. In both the dikes and the veins the chief value lies in gold, which occurs free and also combined with the sulfides. The gangue is predomi- nantly quartz, with small amounts of calcite; the sulfides present are arseno- pyrite, pyrite, galena, sphalerite, and chalcopyrite, but the total forms only a small percentage of the vein material. The genesis of the ores is closely associated with the origin of the dikes, as both ores and dikes were probably derived from the same parent magma. After the intrusion of the dikes the region was subjected to stresses that fractured the dikes and the country rock. Subse- quently mineral-bearing solutions from an underlying source filled the fissures and deposited the present vein material. The Valdez Creek mining district, Alaska by Clyde P. Ross USGS Bulletin No. 849-H Investigations in Alaska Railroad belt, 1931 ABSTRACT: The Valdez Creek mining district is underlain by argillite, schist, tuff, tuffaceous conglomerate, limestone, and greenstone, listed in approximate stra- tigraphic.order beginning with the youngest. These rocks are probably all of Upper Triassic age and form part of the north limb of a large fold that trends east to northeast but is locally broken by faults and minor flexures. There are a number of stocklike intrusions, mainly quartz diorite and similar rock, and small basic dikes, all of Upper Jurassic or later age. One small mass of Ter- tiary (Eocene?) coal-bearing beds and considerable Quaternary alluvium and gla- cial deposits are present. The district contains numerous auriferous quartz veins, which range in size from stringers along joints and similar openings to lodes more than 1,000 feet long and several feet wide. The larger masses lie in shear zones in which the altered country rock is itself mineralized, and such bodies are of possible commercial value, although apparently not of high grade. Along the eastern border of the area examined during the pre- sent study limestone, schist, and greenstone have suffered igneous metamor- phism, including the deposition of metallic minerals. This part of the area appears to justify more prospecting than it has yet received. Sufficient coal exists here to be of some local value if a metal mine were established. Mineral industry of Alaska in 1932 by Philip S. Smith USGS Bulletin No. 857-A Minéral Resources of Alaska 1932 NOTES : Summarizes the economic status of the Alaskan mining industry during 1932 and tabulates total mineral production. Past placer-gold production from Alaska by Philip S. Smith USGS Bulletin No. 8574B Mineral Resources of Alaska 1932 NOTES : Gives the statistics of Alaskan placer-gold production since 1880, with the total values itemized by regions. The Curry district, Alaska by Ralph Tuck USGS Bulletin No. 857-C Mineral Resources of Alaska 1932 ABSTRACT: The oldest rocks of the region consist of thin-bedded chert, quartzite, and argillite that are exposed in only a small part of the area. Lying un- conformably on these rocks is a volcanic formation composed of tuff and agglo- merate, exposed only in the northern part of the area. Later another series of sediments, now exposed as chiefly slate, graywacke, and schist, was depo- sited, and all the rocks were folded, faulted, and changed to their present highly metamorphosed condition. Subsequent to the regional metamorphism, or as its last phase, the district was invaded by a granitic bathbdlith that now occupies its greater part. This igneous intrusion further altered the metamor- phic rocks and along its margin sent acidic dikes and sills ramifying into the surrounding sediments. The last phase of igneous activity was the intru- sion of a few basic dikes that but the granite as well as the me vamorphosed sediments. The formation of the ore deposits in the district was probably as- sociated with the granitic intrusion, in that the vein minerals were brought in by the granite magma and were liberated during its crystallization. The intrusion of the granite batholith was followed by 2 long period of erosion, in which a topography with a general similarity to that of today was carved into the metamorphosed sediments and granite. At the end of this period much of the region, particularly what are now the valleys, was a low-lying region close to sea level, with many swamps. In this low region vegetation grew rank for long periods of time. Then folhowed periods of rapid deposition which re- sulted in the covering of the vegetation by clay, sand, and gravel. This cycle reccurred several times, as is indicated by the different coal seams, separa— ted by deposits of clay, sand, or gravel. After the deposition of the coal- bearing rocks was completed a sheet of gravel many hundreds of feet thick com- pletely covered the coal series. At the end of this period of active sedimen— tation an uplift of the land mass slightly tilted the coal-bearing rocks and rejuvenated the streams, which onee more began to erode actively. After a long period of erosion climatic changes resulted in the accumulation of ice at several centers in the hgiher parts of the Alaska Range. From these centers the ice moved down the valleys and modified the earlier stream-carved topo- graphy. Still later, with a return to milder climactic conditions, the gla- ciers retreated, leaving behind morainal material liverated by the melting ice. Most of the morainal material has since been removed by erosion, but a great thickness of glacial outwash gravel remains in the valleys in the form of well- defined terraces. Still more recently the present streams have been engaged in transporting and depositing silt, sand, and gravel. Notes on the geology of the Alaska Penisula and Aleutian Islands by Stephen R. Capps USGS Bulletin No. 857-D Mineral Resources of Alaska 1932 ABSTRACT: The islands west of Unimak Pass are composed mainly of basic volcanic lavas and fragmental materials, into which have later been injected dikes, sills, and considerable masses of intrusive rocks, some of which are of acidic types and of granitic texture. These westward islands are bordered both to the north and south by depressions 2,000 fathoms or more in depth, and the islands have apparently been built up from that depth by the ejection and extrusion of volcanic materials since early Tertiary time. No rocks of proved pre-Tertiary age were seen, and the only sedimentary materials present may well have been derived from the erosion of the volcanic islands after they were built up above sea level. On the Alaska Penisula pre-Tertiary sediments through which the volcanic materials broke to the surface are abundantly pre- sent. There is evidence that all the larger islands and the higher portions of the penisula were severely glaciated during Pleistocene time. Each of the larger islands was the center of ice accumulation and dispersal, and the pre- sent topography, except upon recently active volcanic cones, shows strongly the effects of glacial sculpture. Core drilling for coal in the Moose Creck area, Alaska by Gerald A. Waring USGS Bulletin No. 857-E Mineral Resources of Alaska 1932 ABSTRACT: The Moose Creek area is bordered on the north by the Talkeetna Mountains, which are composed chiefly of granitic and gneissic rocks. From their relation to other rocks farther north and east, these crystalline rocks were assigned to a period of intrusion during the Middle Jurassic. Along the south side of the Matanuska River and also in bluffs in bluffs on the north side both above and below the mouth of Moose Creek, dark indurated shale and sandstone are exposed. These beds.in places contain fossils which show them to be of marine deposition and Upper Cretaceous age. They have for several years been known as the "Mata- nuska formation." On the flank of the Talkectna Mountains, restind directly on the granitic rocks, there is a series of highly indurated arkose, conglomerate, and shale. Poorly preserved plant remains show that the beds are of Tertiary age, probably Eocene. Much of the Moose Creek area is covered by a series of unaltered shale, sandstone, and conglomerate. This has for many years been known as the "Chickaloon formation", from prominent exposures along the Shicka- loon River, farther east in the Matanuska Valley. In the western area the sandy and coarse-grained materials predominate and for the most part are poorly con- solidated, though there are some beds of hard sandstone. Within the formation there are coal beds; and most of the shales are black and carbonaceous and carry veinlets of coal. The carbonaceous beds also contain plant remains which show that the deposits are of fresh-water origin and Eocene age. At Wishbone Hill, between Moose and Eska Creeks, the Chickaloon beds are overlain by a series of thick beds of coarse conglomerate, separated by minor beds of coarse sandstone and sandy shale. This formation is known as the "Zska conglomerate," and al- though it lies without noticeable unconformity on the Chickaloon formation, it has been considered to be a later formation, questionably of Miocene age. It contains no coal beds and very little fossil material. About 20 miles east of Eska fully 3,000 feet of the conglomerate is exposed in the cliffs of Castle Mountain. The formation is more than 1,000 feet thick in the eastern part of Wishbone Hill, but thence westward it either thins rapidly or the upper portion has been removed by erosion. Along the valley of Moose Creek a thickness of only 200 or 300 feet of the conglomerate is exposed. --- 2 --- In. the western part of the Matanuska Valley the rocks have been greatly folded and faulted. On the north side of the valley there is a great fault, which has been described and mapped by Martin. The dominant structure of the Moose Creek area is a broad, shallow syncline, of which Wishbone Hill is the most prominent portion. A mile east of the hill the syncline is exposed along Eska Creek, where it is broken by minor cross faults. The eastern part of Wishbone Hill seems to be unbroken by large faults; but along its northwest base the beds of the hill have been uplifted. In some places the beds there dip northward and indicate tilted fault blocks of considerable size. The axis of the syncline plunges southwestward, approximately with the slope of the hill, and the dips of its limbs flatten so that the area included between the lifibs widens in that direction. Along the southern course of Moose Creek the dip flattens to only 2 or 3 degrees near the synclinal axis, but steepens again to 20 to 40 degrees on the south limb of the fold, near the moubh of the creek. On the south side, as well as on the north side, the syncline is broken by faults, but these have not been mapped in detail. Geology of the Anthracite Ridge Coal district, Alaska by Gerald A. Waring USGS Bulletin No. 861 Washington 1936 ABSTRACT: The Anthracite Ridge coal district is in south-central Alaska, about 200 miles by rail from the coast at Seward. The district lies between Anthra- cite Ridge on the north and the Matanuska River on the south. It is about 4 miles wide and extends for 7 miles along the flank of the ridge. The older rocks of the district are overlain by the coal-bearing Chickaloon formation, consisting of fresh-water deposits of Eocene age; and these are intruded by sills and dikes of igneous rock. Structurally, the district consists of a block formed of these sediments and intrusive rocks, faulted down between the ridge and the river and limited on the east and west by beds upturned around the ends of a general synclinal trough. Within this syncline there is minor ‘folding and faulting. Along the middle slopes of the ridge the surficial struc- ture is that of two minor anticlines, which are in places sharply compressed and locally faulted. This northern folded zone is cut off by a fault along the base of the ridge, marked by cliffs and waterfalls. The zone thence south- ward toward the river is in the main a broad syncline, but it contains a few minor anticlinal folds and slice faults. Coal beds are exposed in three main areas within the district--at the north, on the central part of the ridge; at the east, in the basin of Muddy Creek; and at the southwest, along lower Pu- rington Creek. About 90 coal outcrops in the district were examined and numerous geologic sections were measured and compared. All the coal beds are of moderate extent. Some pinch out, and others grade within short distances into shales. The observations on the structure of the rocks indicate that there are three coal-bearing zones, all low in the Chickaloon formation. The thickest beds of coal, which are also those of highest rank, are -in the northern area. The principal beds there are in the highest zone and in two exposures show 34 and 24 feet of clean coal, but this is considerably shat- tered. To the eas t and west this coal zone thins rapidly. The middle zone lies about 120 feet deeper and locally shows coal and bone as much as 10 feet in thickness. Westward this zone thins rapidly, but eastward it thickens and con- tains several beds of coal. This zone seems to be 600 or 700 feet above the base of the Chickaloon formation, which overlies marine deposits of Upper Cretaceous age. The lowest coal zone is not present in this area. These coals are semianthra- cite to anthracite, having been altered from coals of lower rank. Probably the sec alt change was produced chiefly by heat from the intruding masses of igneous rock, which drove off some of the volatile matter from the coal. The heat resulting from the later compression and folding of the beds may also in some places have been an agent in their alteration. The coal beds of the eastern areabelong mainly to the middle zone and consist of four or five beds with a’total of about 10 feet of coal ina zone 50 feet thick. Although these coals have been in places closely folded, they have not been appreciably altered and are of bituminous rank. On middle Muddy Creek the lowest coal zone is exposed and consists of a 6-foot bed of bituminous coal 140 feet below the middle zone. In the southwest area there are about six coal beds, distributed through a thickness of nearly 400 feet of sediments. The uppermost bed seems to be about equivalent to the upper coals of the northern area, and the others accord appro- ximately with the middle and lower coal zones. These southwestern coals are bi- tuminous to semwibituminous in rank. Except for a few locally altered lenses, all the known coalcof anthra- cite rank in the district is confined to an area half a mile long and a quarter of a mile wide, on the south flank of the ridge. This area is folded and faulted, and the coal beds are much shattered, with inclusions of bone and shale and in- trusions of igneous rock. The amount of coal in the most promising 20 acres of this area has been estimated at 750,000 tons. The tract lies high on the side of the ridge, 2,500 to 3,000 feet above the river and nearly 20 miles from the former railroad terminus at Chickaloon. All the other beds of workable thickness in the district are of semibituminous and bituminous coals. Their outcrops are of small extent, and the beds are so irregular in thickness that estimates of available tonnage cannot be made on the basis of present information. Although the district probably contains several million tons of bituminous coal, in add- ition to the 780,000 tons of anthracite and semianthracite, the beds are ir- regular in thickness and much fractured, and much dead work would be involved. The southern Alaska Range by Stephen R. Capps USGS Bulletin No. 862 Washington 1935 ABSTRACT: The southern Alaska Range, as here defined, extends from the Skwentna River and Rainy Pass on the north to Iliamna Lake on the south. It comprises an area of more than 25,000 square miles, of which much was unexplored until . 1926, when the surveys here described were begun. Within that area there are still many unsurveyed patches, but the major topographic and geologic features of this great mountain area are now known. This portion of the Alaska Range, though nowhere reaching the altitude of Mount McKinley, is nevertheless of impressive grandeur, with many peaks reaching heights of 10,000 to 12,000 feet, and includes a labyrinth of ragged mountain crests that nourish great valley glaciers, interspersed with timbered valleys studded with magnificent glacial lakes. Geologically the region has a complex history, as represented by rock formations that range in age from Paleozoic to Recent. These formations in- clude ancient gneiss, schist, and crystalline limestone, less highly meta- morphosed Mesozoic sediments, cut by tremendous intrusive masses of granitic rocks, little-altered Tertiary coal-bearing beds, extensive deposits of gla- cial moraines and outwash gravel, and the present stream, lake, and beach deposits. One of the highest mountains of the region, Mount Spurr, was found to be a volcano that still shows signs of mild activity, and other volcanoes, such as Mounts Iliamna and Augustine, lie just east of the region here treated. These mountains are the northern members of that great line of volcanic vents that stretches along the Alaska Penisula and Aleutian Islands. So few white men have visited this region that its potential mineral resources have not been determined. A little placer gold has been recovered at several localities, but no large areasof workable ground have yet been found. Lodes carrying pro- mising amounts of copper, silver, and lead have been located in the southern part of the region, but lack of transportation has retarded their development. Near the shores of Cook Inlet there are extensive deposits of lignitic coal that may sometime be minable. Mineral industry of Alaska in 1933 by Philip S. Smith USGS Bulletin No. 864-A Mineral Resources of Alaska, 1933 NOTES: Summarizes the economic status of the Alaskan mining industry during 1933 and tabulates total mineral production. The Willow Creek-Kashwitna district, Alaska by S.R. Capps and Ralph Tuck USGS Bulletin No. 864-B Mineral Resources of Alaska, 1933 ABSTRACT: It has long been known that most of the southwestern part of the Tal- keetna Mountains is composed of and is a part of the Talkeetna Mountain grano- diorite batholith. Early reconnaissances by Paige and Knopf and by Capps showed the presence of granodiobite and related rocks along the west face of the range, and from examination of float from the streams they inferred that the interior mass of the mountains was also predominantly granodiobite. The present detailed investigation confirmed these inferences. Conclusive evidence of more than one intrusive mass is lacking, and although several types of intrusive rocks are present, they all probably represent one general magmatic period. No other consolidated deposits were found in the area, as the field work did not extend into the Susitna Valley beyond the west face of the range. However, as Tertiary (Eocene) lignite is present at numerous localities through- out the Susitna Valley, and as several coal seams have been reported from lo- calities bordering the western margin of the field visited, it seems probable that Tertiary sediments overlap the western margin of the granodiorite batholith, as they do the southern margin, both in the Willow Creek district and farther east in the Matanuska Valley. The only other formations in thearea are Quaternary glacial deposits and Recent stream and talus deposits, which are confined chief- ly to the present valleys and valley walls. Mineral deposits of the Ruby-—Kuskokwim region, Alaska by J.B. Mertie, Jr. USGS Bulletin No. 864-C Mineral Resources of Alaska, 1933 ABSTRACT: The Ruby-Kuskokwim region lies in west-central Alaska, between the Yukon and Kuskokwim Rivers. Gold was discovered in this region in 1906, and in the following 10 or 12 years several gold placer-mining camps were located, most of which are still producing gold. These mining districts, named from north to south, are the Ruby, Cripple, Ophir, Tolstoi, Nimon Fork, McGrath, Iditarod, and Georgetown districts. Valuable gold lodes were located in the Nixon Fork district in 1918, and these have been mined continuously since that date. Other gold lodes have been located in the Ophir and Iditarod districts, and silver- lead ores have been prospected in the Ruby district, but none of these lodes have been commercially successful. In the Georgetown district, however, cinna- bar ores have been known for many years and have been mined intermittently since 1906. The following report is essentially a description of the mineral deposits that have been found in this region and of the status of mining in 1933. The geologic features of this region have been described in some detail in earlier reports, and here only a generalized statement of the general geolopy is presented, adequate for an understanding of the history and character of mineralizabion in this region. Gold mineralization is believed to have occurred both in the Mesozoic era and during the Tertiary period, but the ores of cinna- bar are believed to have originated only during the Tertiary. The age of the silver-lead ores has not been determined. The gold placers, derived from such preexisting lodes, range in age from early Pleistocene to Recent. Geology of the Tonsina district, Alaska by Fred H. Moffit USGS Bulletin No. 866 Washington 1935 ABSTRACT: The Tonsina district is a part of the north slope of the Chugach Mountains that includes the headwaters of the Klutina, Tonsina, and Tiekel Rivers and their upper valleys. This district is an area of rugged mountains, which reach a height of over 8,000 feet in its southwestern portion but are lower and less rugged toward the north, where they meet the Copper River lowland. This part of the Chugach Mountain area is made up of two principal groups of rocks, which are dominantly of sedimentary origin, are folded and metamorphosed in varying degree, and have the same general trend as the mountains themselves—-that is, slightly north of west. The oldest rocks of the Tonsina district are in its northern part, adjacent to the Copper River lowland, and include argillite, graywacke, quartzite, oanded argillite and quartzite, and limestone. These sediments are interbedded with lava flows and tuffs and are intruded by granitic rocks that are chiefly granite and quartz diorite. All are metamorphosed in some degree and in places schistose. The bedded rocks, at least in part, are believed to have been deposited in early Car- boniferous (Mississippian) time. The southern and larger part of the district is occupied by a great thickness of slate and graywacke in alternating beds which are much folded, seamed with quartz veins, and intruded’ by sills and dikes of granite and quartz diorite. The sedimentary beds are believed to be of Mesozoic age, being later than the Triassic and belonging in part to late Cretaceous time. If this assignment is correct the Chugach Mountains themselves were formed during the Tertiary period, and at least a part of the intrusive granite and quartz diorite of the district are also of that age. In much more recent time the district has undergone profound glaciation, not yet ended, during which the topographic forms were modified, old deposits of gravel were swept from the valleys, and new deposits of glacial debris and waterborne material were laid down. The Tonsina district has produced a small quantity of gold and holds promise of further production. The time of intru- sion by igneous rocks was also a time of formation of mineralized quartz veins. Mineral industry of Alaska in 1934 by Philip S. Smith USGS Bulletin No. 868-A Mineral Resources of Alaska 1934 NOTES : Summarizes the economic status of the mining industry in Alaska during 1934 and tabulates total mineral production. Kodiak and vicinity, Alaska by Stephen R. Capps USGS Bulletin No. 868-B Mineral Resources of Alaska 1934 ABSTRACT: The geology of this part of Kodiak Island consists essentially of a great series of upper Mesozoic slates and graywackes that have a prevailing northeast strike and steep northwest dip. The apparent thickness of this series of beds is much greater than the actual thickness, for there has been much reduplication by close folding and by faulting. These rocks were intruded in later Mesozoic or early Tertiary time by granitic masses that now appear as a great and nearly continuous mass lying along the axis of the island, as outlying satellites of this mass, and as numerous dikes and sills. At a few points in this district Ter- tiary sandstones lie unconformably upon the Mesozoic sediments or in fault con- tact with them. Kodiak Island during Pleistocene time was a vigorous center of glaciation, and from its higher mountains glaciers that almost completely covered the island pushed out to sea in all directions. The present topographic form of the island, with its glacially carved valleys and fiorded coast line, is largely the product of severe glacial erosion. Glacial deposits are present, but in relatively small amounts, most of the glacial debris having been carried out to sea. Within the last few years there has been a reviavl of interest in prospect- ing in this district. It is believed by the writer that the most promising sites for prospecting for gold lodes lie along the contact between the granitic intru- sive masses and the sediments and in both granites and sediments for some distance on each side of such contacts. Some areas not plainly related to such contacts also show mineralization, but in these areas there is some indisation that granitic intrusive rocks are present in depth. The placer gold in the beach deposits at many places on Kodiak and adjacent islands was doubtless derived from the lodes within the islands. Upper Copper and Tanana Rivers, Alaska by Fred H. Moffit USGS Bulletin No. 868-C Mineral Resources of Alaska 1934 ABSTRACT: The area under consideration gives a complete cross section of the rocks that make up this part of the Alaska Range. These rocks are dominantly sedi- ments, showing varying degrees of metamorphism, but locally include lava flows and granitic intrusives. Although the age of the sediments is imperfectly know, rocks of Devonian, Permian or Mississippian, Upper Triassic, and Cretaceous age are present. Further, more detailed field study may extend or fill out this strati- graphic section. In general the structure is characterized by several major folds, the most prominent of which is a great syncline, trending west-northwest, that includes the Mesozoic sediments and makes the backbone of the range. On the north- east side of the area the rocks dip to the northeast and rarely show any reversal. The Kaiyuh Hills, Alaska by J.B. Mertie, Jr. USGS Bulletin No. 868-D Mineral Resources of Alaska 1934 ABSTRACT: The oldest rocks of the Kaiyuh Hills are a group of. undifferentiated metamorphic rocks, of pre-Paleozoic or early Paleozoic age, which include various types of sedimentary and igneous schists, phyllite, and slate, to- gether with a minor proportion of chert and limestone. So far as practicable the areas of limestone have been separately mapped. These metamorphic rocks constitute more than half of the exposed bedrock, both in the Kaiyuh Hills and in the Ruby district. The next younger geologic unit is a group composed mainly of basic igneous rocks of greenstone habit, which are in part surficial and in part intrusive. With these igneous rocks, however, are included some sedimentary rocks that it has not been practicable to separate. This group of rocks, which are considered to be probably of Carboniferous age, form the bedrock in nearly half of the Kaiyuh Hills and in about a third of the Ruby district. Both the undifferentiated metamorphic rocks and the later greenstones have been intruded by granitic rocks, which are mainly of Mesozoic (?) age. Three small areas of such granitic intrusives are shown on the geologic map, together with two smaller areas that may be younger. A small area of Tertiary basaltic lavas is mapped in the vicinity of Poorman. The youngest sedimentary rocks of this region are sandstone, shale, and conglomerate; most of which are considered to be of Cretaceous age. The low hills that form the extreme south- western continuation of the Kaiyuh Hills are composed of such rocks, and a similar area is present southeast of Poorman. The latter area is in the northern limit of a much larger body of such rocks which occupies much of the area be- tween Poorman and the Kuskokwim River. Alluvial deposits of various types, of both Pleistocene and Recent age, occupy large areas in this region, covering the bedrock deeply in the larger valleys and extending upstream into the upper- most headwater tributaries. In addition to those deposits, most of which are of fluviatile or lacustrine origin, much of the bedrock in the hills is over- lain by a mantle of residual and semiresidual deposits. The Yukon-Tanana region by J.B. Mertie USGS Bulletin No. 872 Washington 1937 ABSTRACT: The Yukon-Tanana region and contiguous areas north of the Yukon River present one of the most complete geologic sections now known in Alaska. Bed- ded rocks of every geologic period except one have been identified, and a variety of igneous rocks, both intrusive and extrusive in origin, are also present. This diversified assemblage of rocks indicates that the region has had a long and intricate geologic history. The reconnaissance studies of the last 50 years have resulted in the accumulation of a great mass of information about this region, and although many of these data are even yet thoroughly correlated, nevertheless they serve to indicate the major events in the geo- logic history. There remain, however, many unsolved geologic problems in this region, not the least of which is a better understanding of the regional struc- ture. The bedded rocks range in age from pre-Cambrian to Recent, and in the explanation accompanying the geologic map 22 map units of bedded rocks have been differentiated. The oldest sedimentary rocks are assembled in a group of crystalline schists, known as the Birch Creek schist, of pre-Cambrian age. Later pre-Cambrian rocks are also present, of which the least metamorphosed and best known are comprised in the Tindir group, of pre-Cambrian and Lower Cambrian (?) age, which is roughly correlative with the pre-Cambrian Belt series. The Tindir group, however, is typically developed in the contiguous area north of the Yukon River and therefore outside of the Yukon-Tanana region proper. South of the Yukon most of the younger pre-Cambrian rocks are assembled into a group of undifferentiated rocks, which also includes some rocks of early Pale- ozoic age. The calcareous members of the post-Birch Creek rocks are separately mapped, though few such rocks occur south of the Yukon. The Cambrian system is developed, so far as now known, only in the belt along the international boun- dary northof the Yukon, but the proximity of these rocks to the Yukon River renders it desirable to give a brief outline of their general character. Some of the rocks of the Ordovician period are included with the pre-Cambrian in the assemblage here mapped as undifferentiated pre-Middle Ordovician rocks, but one formation of basic lavas, here designated the "Fossil Creek volcanics", has been differentiated and mapped. The Silurian system, so far as known at present, is represented by only one formation, which is composed of a great thickness of limestone and dolomite here named the "Tolovana limestone", The Devonian system, like the Ordovician, is largely undifferentiated, but one formation, composed a 22) largely of lavas and known as the "Woodchopper volcanics", has been differentia- ted and separately mapped. The undifferentiated Devonian rocks have been divided into a calcareous and a noncalcareous unit, which are separately delineated on the accompanying map. The Carboniferous system includes a great diversity of bedded rocks. These have been divided into five well-defined mappable units and also into two less well-defined groups of undifferentiated rocks, one of calcareous and one of noncalcareous character. Three of the well-defined units (the Liven- good chert, the Rampart group, and the Calico Bluff formation) are of Miss- issippian age, and two groups of undifferentiated rocks are also Mississippian. The Rampart group is an assemblage of sedimentary rocks, lava flows, tuffs, and breccias, associated with which are masses of intrusive rocks. Another litho- logic unit, known as the "Nation River formation", comprises a group of unique continental deposits, which are believed to be of Pennsylvanian age. The young- est of the Carboniferous rocks is a marine limestone of Permian age, the Tah- kandit limestone. The Mesozoic rocks include a series of Upper Triassic rocks, and also rocks of Lower and Upper Cretaceous age. No Jurassic sedimentary rocks have been recognized in this region, though some may be present, as a Callovian fauna correlative with the lower part of the Upper Jurassic of Alaska has re- cently been found on the Porcupine River, about 25 miles below the international boundary. The apparent absence of Jurassic rocks in the Yukon-Tanana region, however is interpreted to mean that a great unconformity exists at the base of the Lower Cretaceous sequence. In an earlier report the writer mapped the Lower Cretaceous rocks of part of this area as a separate unit, designated as the Kan- dik formation, but in the present report the Lower and Upper Cretaceous rocks are mapped as a unit, with no formal designations. The youngest of the consolida- ted rocks are a group of Tertkary rocks of estuarine and continental origin. Overlying all the hard rocks of the region are a variety of unconsolidated or alluvial deposits, which range in age from late Pliocene to Recent. Many igneous rocks are present in the Yukon-Tanana region. Some of these, such as the meta-igneous rocks that are associated with the crystalline schists, are not separately mapped. Others, such as the Fossil Creek and Woodchopper vol- eanics and the Rampart group with its associated intrusives, are mapped with the bedded rocks. In addition to these, five units of igneous rocks are separately mapped. The two most important of these, from their economic relations, are the Mesozoic and Tertiary granitic rocks, which are the ultimate source of most of the metalliferous ores of this region. A group of Devonian intrusive rocks, main- ly of ultra+basic character, has also been differentiated. Finally, two groups of lavas, one of early Tertiary and one of late Tertiary and Quaternary age, are mapped as separate units. The mineral industry of Alaska in 1935 by Philip S. Smith USGS Bulletin No. 880-A Mineral Resources of Alaska 1935 NOTES: Summarizes the economie status of the Alaskan mining industry during 1935 and tabulates total mineral production. Recent mineral developments in the Copper River region, Alaska by Fred H. Moffit USGS Bulletin No. 880-3 Mineral Resources of Alaska 1935 NOTES: Describes recent mining activity in the Copper River region. Kodiak and adjacent islands, Alaska by Stephen R. Capps USGS Bulletin No. 880-C Mineral Resources of Alaska 1935 ABSTRACT: Although the islands of the Kodiak group are the structural southwestward continuation of the Kenai Mountains of Kenai Penisula, and the dominant elements off the geology are similar, nevertheless there are also considerable differences between the two provinces. In both the preponderant rock group consists of slates and graywackes, probably in the main of upper Mesozoic age, highly metamorphosed, generally of steep dip, much faulted and folded, and largely devoid of fossils. To the west of these rocks throughout the island group, and locally on the east of them as well, there is an older series that includes ellipsoidal lava, crumpled cherts, limestone, and argillaceous sediments, all in various degrees of meta- morphism and alteration and lying unconformably below the slate and graywacke or separated from them by faults. On the islands these materials seem to be locally more highly altered than on Kenai Penisula and include greenstone schist, schist composed of greenstone and shaly and sandy sediments intricately kneaded together, crumpled cherts, limestone, and locally even mica schists. Though their contact with the slate-graywacke group is in most places along profound vertical faults, they are evidently older and are correlated with the Triassic and Jurassic of Kenai Penisula, though the mica schists may be older still. Next younger than the slates and graywackes in this region and unconformably above them are fresh- water or subaerial Tertiary beds that include sandstone, shale, and conglomerate, generally well indurated and steeply dipping and locally much crumpled, crushed, and contorted. These beds contain carbonaceous bits of plant remains and even thin coaly streaks, though identifiable leaves have been collected at only one locality. They are tentatively correlated with the Eocene fresh-water sedimentary rocks of Cook Inlet. Still younger than the fresh-water Tertiary beds and proba- bly lying unconformably above them are marine sandstones that have been recognized only at Narrow Point, on the west coast of Kodiak Island. These beds consist of gently folded and moderately indurated buff sandstones that carry a marine Miocene or Pliocene fauna. They are the youngest consolidated rocks of the region. ete Granitic masses were injected into the rocks of this region after the slates and graywackes were laid dow, but before the deposition of the Ter- tiary beds.The granite is now exposed as one long, narrow body that extends along the axis of Kodiak Island for almost its full length and as many smaller satellitic masses that by their distribution suggest that not far below the present surface the granites are more extensive than at the surface. The gra- nites are of late Mesozoic or early Tertiary age. The latest geologic event of major importance on these islands was the accumulation, during Pleistocene time, of an ice mass that extended in all di- rections to the borders of the island group, completely submerged the lower- lying areas, and left only a few of the highest peaks and ridges projecting above its surface. Erosion by this glacier or by possible Pleistocene predecessors of it deeply affected the topography of the region by rounding and smoothing the over- ridden surfaces, deepening and straightening the valleys, and scouring out deep fiords that, on the retreat of the ice, left the land mass cut into numerous islands and furrowed by deep bays. The present topography has been altered from the form given it by glacial ice only in a minor way, stream erosion having ac- complished little and the attack of waves on the exposed coast line having only fairly begun. The Eska Creek coal deposits, Matanuska Valley, Alaska by Ralph Tuck USGS Bulletin No. 880-D Mineral Resources of Alaska 1935 ABSTRACT: The coal deposits in the vicinity of Eska Creek, a small tributary from the north to the Matanuska River, are a part of the Matanuska coal field. One of the two commercial coal-producing districts in Alaska, this field is in the south-central part of the Territory at the head of Cook Inlet. It is 170 miles from. Seward, the ocean terminus of the Government-owned and -operated Alaska Railroad, and is served by a branch line of that railroad. A high-volatile bituminous coal has been produced in the vicinity of Eska Creek since 1917. The coal occurs in the Chickaloon formation (Eocene), which, in this area, is composed of over 2,000 feet of sandstone, shale, and inter bedded coal seams. The Eska conglomerate, more than 1,100 feet thick, overlies the Chickaloon formation. Both the coal beds and the intervening sandstone and shale, comprising the Chickaloon formation, vary in thickness and composition within short distances. Over 20 coal beds having a thickness of more than 3 feet are known to occur. Most of the coal beds are from 3 to 5 feet thick. : The underlying rock structure is expressed by much of the topography. Wishbone Hill, the dominant topographic feature, reflects the major structural feature, which is a southwestward-plunging syncline. Strikes and transverse faults are numerous. The transverse faults are usually normal and have the greater dis- placement, some of them more than 300 feet. The structure has strongly affected mining operations; it has increased the cost of development and mining and has decreased the quantity of recoverable coal and the production of lump coal. Most of the coal reserves are west of Eska Creek, on the north side of Wishbone Hill. In spite of the detrimental effect of faulting, there are reserves of many million tons of recoverable coal above the present tunnel levels and an equal if not greater amount below. Geology of the Chitina Valley and adjacent area, Alaska by Fred H. Moffit USGS Bulletin No. 894 Washington 1938 ABSTRACT: The Chitina Valley and adjoining area form part of a rugged alpine re- gion in the southeast corner of the main body of Alaska and include a portion of the Chugach Mountains and most of the southern half of the Wrangell Moun- tains to the north. The Chitina River is an eastern branch of the Copper ‘iver and rises in ice fields and valley glaciers occupying most of the country near the international boundary north of Mount St. Elias. The adjoining area descri- bed in this report includes the Hanagita and Bremner River district and the west- ward continuation of the north side of the Chugach Mountains as far as Valdez Arm and Klutina Lake. In addition, the geology of the upper White River district is described because of its relation to that of the Chitina Valley. The rocks of the area are dominantly bedded and are largely of sedimentary origin, although extensive areas of lava flows and tuff are included with the bedded rocks. Granitic and dioritic intrusive rocks are widely distributed in the area, yet they occupy only a relatively small part of it, The rocks described range in age from late Paleozoic to Recent and show all stages of metamorphism between schist and gneiss, on the one hand, and fresh lava flows and unconsolidated clay, sand, and gravel, on the other. The oldest rocks that have been recognized are of Mississippian age. They include altered lava flows and tuffs and extensive areas of schistose sedimentary rocks, slate, and limestone, all cut by granular igneous intrusives of varied character. They occupy the axial part of the Chitina Valley and the north slope of the Chugach Mountains. The older Paleozoic sediments and volcanic rocks were followed by a thick accumulation of Permian lavas and tuffs in which there are highly fossiliferous limestone beds and a little slate. Such rocks are widely distributed in the upper Nizina and White River areas and bear evidence of a time when the forces of vol- canism dominated over the more ordinary processes of weathering and accumulation. The violent outbursts that yielded the alternating tuff beds and thin lava flows - of the lower part of the section were followed by a more quiet welling forth of lavas that yielded the next succeeding formation. The Nikolai greenstone, well known because of its copper prospects, is a great accumulation of lava flows representing, at least in part, the final stages of Permian volcanic activity in this district. Possibly also it may represent a continuation of the same kind of activity into Mesozoic time and is therefore partly of Mesozoic age. The Nikolai greenstone is exposed chiefly along the north side of the Chitina Valley. Rocks of unquestioned Mesozoic age were laid down in Upper Triassic, Jurassic, and Lower Cretaceous time. The oldest of them are the Chitistone and Nizina limestones and the overlying McCarthy shale, which together con- stitute the finest section of Upper Triassic rocks in Alaska. The Chitistone limestone is an excellent horizon marker but is best known because it is the host rock for the Kennecott copper ores and other similar copper deposits in the Chitina Valley. The limestones and shale have much the same distribution as the Nikolai greenstone, which they overlie with structural conformity but with a probable conformity but with a probable discontinuity in time. A great unconformity marks the boundary between Triassic and Cretaceous sedimentary rocks and probably also the boundary between Triassic and Jurassic. The Jurassic sedimentary rocks are much less extensive than the Cretaceous, oc- cur in small scattered areas, and are imperfectly known, so that a clear under- standing of their relations to the older and younger rocks is lacking. The Ju- rassic rocks include a small area of tuffaceous slate and conglomerate near the mouth of the Chitina River, containing the Middle Jurassic Tuxedni fauna; two small areas of black slate on McCarthy Creek, with the Upper Jurassic Naknek fauna; and isolated areas of sandstone, conglomerate, and limestone of probable Upper Jurassic age in the Kotsina-Kuskulana district. Considerable areas of rocks that were once referred to the Upper Jurassic are now regarded as younger and are included with the Cretaceous. Rocks of Cretaceous age are widely distributed in the area but are most abundant in the part of it on the north side of the Chitina Valley that extends eastward from the Kuskulana River. They include thick deposits of shale, sand- stone, and conglomerate and are now referred to the Lower;Cretaceous epoch, con- trary to the former assignment of part of them. In general these rocks are less folded than the Upper Triassic and other underlying, on the beveled edges of which they rest, but the softer shale members show much more distortion than the sandstone and conglomerate, which, especially in the localities where the great- est accumulation took place, are only slightly tilted. A very widespread group of sediments, including the great succession of slate and graywacke beds that make up most of the Chugach Mountains and have been known as the Valdez and Orca groups of Prince William Sound, are provision- ally assigned to the Mesozoic, because the work of recent years has indicated that probability, and definite evidence of Cretaceous age for part of the rocks north of Prince William Sound has been found. In Tertiary time an outpouring of lavas began in the Wrangell Mountain area. The first of the molten lavas flowed over an old land surface of probable moderate relief that resulted from a long period of subaerial erosion. Succeed- ing flows buried the old surface to a depth of several thousand fect, and the extrusion of melted rock and ejection of fragmental material have continued to the present time. The lava beds and the tuff associated with them cap not only the high mountains between Mount Wrangell and Nizina Glacier but extend far to the east over the lower hills in the White River Valley. The nature of the Ter- —- 5 — tiary land over which the first flows spread is inferred from the fresh-water leaf-bearing clays and gravel deposits that accumulated in the depressions of the old surface. The latest of the volcanic materials were extruded through Quaternary gravel deposits and therefore are of Recent date. All the bedded rocks of the area, including even the Tertiary lava flows, are cut by intrusive rocks ranging in age from Mississippiam or post-Mississippian to Recent. Gabbro and other coarse-grained basic intrusives cut the older Car- boniferous sedimentary rocks but are uncommon in those of Mesozoic and later age. The most conspicuous and widespread of the igneous intrusives are dikes and sills of granite and diorite, or closely related Species, that are distributed through the entire area and invaded the Lower Cretaceous and all older bedded rocks. Pro- bably the granitic rocks represent several periods of intrusion and are connected with more than one period of mineralization. The most outstanding of the later events in the geologic history of the area is the glaciation that began after most of the Wrangell lava had been erupt- ed and is still in progress. Its most conspicuous effects are the result of its influence in the forming of the present topography and include, among others, mountain sculpturing, morainal deposition, and stream diversion. The Chitina Valley is important as a producer of copper and gold and has possibilities for the production of other mineral wealth. This report describes the mode of occurrence of the mineral deposits and makes suggsstions for pros— pectors in search for them, but it does not contain detailed descriptions of mines and prospects, as information of that kind has been given in earlier reports in a more extended form than is suitable for this summary statement. Mineral industry of Alaska in 1936 by Philip S. Smith USGS Bulletin No. 897-A Mineral Resources of Alaska 1936 NOTES: Summarizes the economic status of the Alaskan mining industry during 1936 and tabulates total mineral production. The Valdez Creek mining district, Alaska, in 1936 by Ralph Tuck USGS Bulletin No. 897-B Mineral Resources of Alaska, 1956 ABSTRACT: The Valdez Creek district is on the south flank of the Alaska Range, about 50 miles east of the line of the Government-owned and -operated Alaska Railroad. This report is a result of a short investigation of the current min- ing activities in the district in 1936, as a part of the cooperative program of the Alaska Railroad and the Geological Survey in furthering the mineral industry in the area tributary to the railroad. e district is underlain by metamorphosed sedimentary rocks, principally argillite, slate, schist, tuff, and greenstone, which have been intruded by small stocks of diorite and quartz diorite. Stream and glacial deposits of clay, sand, gravel, and boulders are present in all the valleys. Placer mining has been carried on in this district since the first dis- covery of gbld here in 1903. Placer-gold deposits of two types have been worked-- a buried-channel type, formed before the last period of glaciation; and a type in which the gold has been concentrated since the glacial epoch by the present streams. Deposits of both types have produced a considerable amount of gold. Placer gold will continue to be produced for many years, and will probably increas in value, as many of the creeks have not yet been thoroughly prospected, and some of the producing properties are capable of a greater production. A number of gold-quartz prospects have been located and are being prospected, particularly in recent years. The gold lodes have a wide variety of occurrence and are found in both the metamorphosed sediments and in the intrusive rocks. None of these prospects have as yet produced gold in important amounts, but conditions are con- sidered favorable for their doing so, and further prospecting and exploitation is well justified. i Gold placers of the Fortymile, Eagle, and Circle districts, Alaska by J.B. Mertie, Jr. USGS Bulletin No. 897-B Mineral Resources of Alaska, 1936 ABSTRACT: The Fortymile, Eagle, and Circle districts lie in east-central Alaska, mainly between the Yukon and Tanana Rivers, but closer to the Yukon. Placer gold was discovered in these districts in the last two decades of the nine- teenth century, and since that time they have been the sites of continuous gold placer mining. At the present time the Circle district is the largest pro- ducer of placer gold among these three districts, and the Eagle district is the smallest producer. The geographic and geologic features of the Fortymile, Eagle, and Circle districts have been described in earlier reports, and in the present report only those salient features that have a bearing on the mining activities are presented. Special emphasis is laid upon the granitic rocks, because they are ' considered to be the primary source of the gold in this region, and upon the bedded rocks of Tertiary age, which are believed to be a secondary and proximate source of much of the gold found in certain of the placers. The conglomerates of these Tertiary deposits, in fact, are considered to be genetically analogous with those of the Witwatersrand district, of South Africa. The following report is mainly a description of the mining activities in these three districts in 1936, together with any information and deductions of a general character that such mining operations have revealed. \Where the infor- mation could be obtained, however, a historical background of the older mining activities has also been presented; and in this connection special attention has been given to the history of older dredging operations, from 1900 6n. Nickel content of an Alaskan basic rock by John C. Reed USGS Bulletin No. 897-D Mineral Resources of Alaska, 1936 ABSTRACT: A nickel-bearing sill, about 126 feet thick, lies in a thick sequence of greenstone schists, graphitic phyllites, and quartzites near the north end of Admiralty Island not far from Juneau, Alaska. Petrographic measurements show that volumetrically the rock is made up of about 62.07 percent labradorite, 54.22 percent olivine, 2.42 percent pyro- xene, 0.79 percent pyrrhotite, 0.21 percent magnetite, 0.14 percent chalcopyrite, and 0.06 percent pentlandite. By weight the rock contains about 0.20 percent chalcopyrite and 0.10 percent pentlandite. The copper content in chalcopyrite therefore is about 0.067 percent and the nickel content in pentlandite about 0.025 percent. Chemical analyses of the representative samples show the rock as a whole to contain about 0.350 percent copper and 0.344 perce t nickel. The differences between the petrographic and the chemical results are believed to be due only in part to the fact that the few thin and polished sections studied may not be re- presentative of the rock, The large differences appear to indicate that much of the nickel is present in the rock in some other mineral than pentlandite, pre- sumably. in olivine. The Nushagak district, Alaska by J.B. Mertie, Jr. USGS Bulletin No. 903 Washington 1938 ABSTRACT: The Nushagak district, as here defined, is an area of about 14,000 square miles in southwestern Alaska which extends northward from Nushagak and Kvichak Bays for a distance of about 100 miles. This region is drained by the Nushagak River, and the mapped area includes mainly the western part of the Nushagak Val- ley. Except in its southern part, little was known regarding this district until 1930 and 1931, when a topographic map was prepared by the Geological Survey. The geologic mapping was done in 1931 and 1935. The district comprises three rather well-defined geographic units. The first of these is known as the Tikchik Mountains, which form the eastern part of a large mountainous province that constitutes the western part of this dis- trict. The Tikchik Mountains form a rugged highland that is isolated from the main mountain ranges of southern Alaska and was the site of extensive Pleistocene ice fields. These mountains are bordered on their east side by a system of 12 more or less parallel deep glacial lakes, which now occupy essentially bedrock basins. The second unit, called the Nushagak Hills, is a group of low rounded hills that form the northeastern part of the district. The third unit is the lowland of the Nushagak River and Bay, which comprises the eastern and southern parts of the district. The geologic sequence consists of sedimentary and igneous rocks, which range in age from Carboniferous to Recent. The Carboniferous rocks consist of Mississippian (?) and Permian sedimentary rocks and Permian volcanic rocks. The Mississippian (?) strata comprise mainly cherty and quartzitic rocks but include also some argillaceous and calcareous beds. The Permian strata consist of fossil- iferous limestone. The Permian volcanics comprise basic lavas, which have develop- ed a greenstone habit. A few fossiliferous Upper Triassic rocks have also been recognized, but such rocks appear to constitute only a very small part of the geologic column. No Jurassic rocks are known to be present, but the Cretaceous system is represented in the Tikchik Mountains by a great volume of rocks, which crop out for more than 60 miles normal to their strike. From lithologic and structural evidence, this sequence has been divided into two unconformable groups, which are correlated roughly with the Upper and Lower Cretaceous epocfis. In the 8 aes Nushagak Hills fossiliferous Upper Cretaceous rocks have also been recognized and mapped. The Tertiary system is represented by marine beds of Pliocene age, which occur only along the seacoast. The Quaternary deposits consist of older sedimentary beds, including glacial, glaciofluviatile, and fluviatile deposits, which were laid down during the period of active glaciation; and younger flu- viatile and beach deposits, mainly of Recent age. The Carboniferous and Meso- zoic sedimentary rocks are intruded by granitic and monzonitic rocks of Tertiary age. No metalliferous deposits of commercial value have yet been found in the Nushagak district, but the presence of small bodies of granitic rocks suggests that the country rock is probably more or less mineralized. The occurrence of gold in small quantities at widely separated localities materially strengthens this probability. It is concluded that the Tikchik Mountains, because they have been extensively glaciated, are not a favorable sibe for the occurrence of commerc ial placers, though lode deposits may be present. The northeastern part of the district and contiguous areas to the north and esastiare regarded as more favorable sites for prospecting for gold placers. Geology of the Slana-Tok district, Alaska by Fred H. Moffit USGS Bulletin No. 904 Washington 1938 ABSTRACT: The Slana-Tok district includes part of the Alaska Range lying between the headwaters of the Copper River and the Tanana River. The trend of the Alaska Range in this area is approximately northwest, and although the average altitude of the mountains is somewhat less than it is in the western part of the range the relief is nevertheless considerable, reaching a maximum of about 8,500 feet. The principal streams of the district are the Slana River and Indian Creek, which flow into the Copper River, and three tributaries of the Tanana River--the Robert- son River, the Tok River together with its branches, the Little Tok and the Dry Tok, and the Tetling River, which flows through the large Tetling Lake. The rocks of the district are prevailingly sedimentary but include tuff beds and lava flows and many masses of intruded granitic rocks, most of which are dio- rite and related types rather than granite. Some of these rocks are highly metamor phic. Others are greatly folded yet not notably altered. The structure is complex and not clearly understood. The rocks range in age from pre—Cambrian or early Paleozoic to late Mesozoic. In places they are concealed by Recent unconsolidated water-laid and glacial deposits. : The oldest rocks are siliceous and micaceous schists, which occupy nearly all the northern half of the district. They are in part altered sandstone and mudrock but probably include altered siliceous igneous rocks as well. Their age is unknown, but they are probably to be correlated with some of the metamorphic rocks of the Yukon-Tanana region, which range in age from pre-Cambrian.to early Paleozoic. the next younger rocks are of Middle Devonian age and include gray and black slate, hard gray siliceous beds, yellowish sandy and gritty beds, limestone, and brown mica schist that is a contact-metamorphic phase of the sedimentary beds. They occupy only a small area in the southeastern part of the district, yet they : attract attention because of the forms into which the limestone weathers. Although they are closely folded they are not greatly altered except in the vicinity of the intrusive diorite. Permian rocks come next in the stratigraphic sequence. They include both sedimentary and igneous rocks——limestone, sandstone, arkosic and black shale, tuff beds, and lava flows--which make up the Mankomen formation. They are typically developed north of Mankomen Lake near the heads of the Slana and Chistochina Rivers but extend intermittently southeastward along the south fac of the mountains to the Nabesna River. A large area of the district is occupied by slate, conglomerate, and other sedimentary beds that are mainly of Permian age but include an unknown proportion of ididdle Devonian and possibly some early Carboniferous rocks. The youngest of the consolidated deposits consist of an assemblage of Mesozoic slate, argillite, sandstone, conglomerate, and limestone beds that formthe mountains of the southeastern part of the district. They are strongly folded but are unmetamorphosed and range in age from Upper Triassic to Lower Cretaceous. l All the sedimentary and volcanic beds so far mentioned are intruded by igneous rocks that are dominantly of the diorite family but include more basic and more acidic rock types. These intrusive rocks range in age from Paleozoic or older to Lower Cretaceous or younger. The more recent geolgic history of the district includes a period of in- tense glaciation which is not yet ended, although the area occupied by the ice is now only a small fraction of its former extent. This glaciation left evidence of its occurrence in the forms of its mountains and in glacial deposits that in most piaces are readily distinguishable by their form and composition from the gravel deposited by water. The Slana-Tok district exhibits many evidences of mineralization by the precious metals, yet thus far no lode mine has been brougiit to production, al- though one placer gold-mining operation is established on Ahtell Creek. Geology of the Alaska Railroad region by Stephen R. Capps USGS Bulletin No. 907 Washington 1940 ABSTRACT: The Alaska Railroad region, as here defined, covers an area about 140 miles wide and 450 miles long from north to south, reaching from the Gulf of Alaska northward into the Yukon Basin. The Government-owned and operated Alaska Railroad lies along the axis of this belt. The region contains impor- tant mineral deposits, particularly gold and coal, and has produced some $150,000,000 worth of minerals in the last 40 years. Its known reserves of minerals are large, and the possibilities of future discoveries have by no means been exhausted. It also contains extensive areas that are suitable for agriculture and for grazing. A considerable portion of the Mount McKinley Na- tional Park falls within this area. The railroad region includes portions of seven rather distinct geographic provinces and thus exhibits a wide range of geologic formations and structures. During the last 40 years more than 100 parties of the Geological Survey have carried out studies in this region, and the results of that work have appeared in an even larger number of maps and writte reports published by the Survey or in the technical press. Many of these pub- lications are now out of print and not easy of reference. Furthermore, as know- ledge of the region has grown, many of the earlier conclusions with regard to the stratigraphic sequence and structure have been changed. The present report is an attempt to bring together in condensed form the present state of knowledge of the geology of the region. Limitations of space have necessitated great condensation of the material available, but references are given to the published works of the original authors, and a chronologic list is presented of field work that has been done. It has been necessary to generalize the geology in such a way as to bring into accord the results of different workers, but in almost all instances where that has been done, or where changes in age assignment of formations have been made, it has been with the concurrence of the original authors, on the basis of more recent information. Brief descriptions are given of the history of exploration, climate, ve- getation, animal life, population, routes of travel, agriculture, and of Mount McKinley National Park. A study of the geologic maps at once discloses the fact that most of this region is occupied by rocks of only moderate geologic age. So far as is now known , pre-Cambrian rocks occur here only north of the Alaska Range and perhaps in a small area in the Willow Creek district. The great Paleozoic era is also rather scantily represented south of the Alaska Range, where only a few areas of undifferentiated metamorphic rocks that are possibly of Paleozoic age, a few small areas of Carboniferous sediments and tuffs in the Chulitna region, and some Devonian limestones and associated sediments are known. North of the range Paleozoic rocks are better represented, for there are extensive belts of mica schists, or metamorphosed sedimentary rocks, and of ancient lavas and associated sedimentary beds, all now greatly altered from their original state. The prevailing rocks from Seward to Broad Pass are believed to be for the most part of Mesozoic age. They include great areas of slates, shales, and gray- wackes of somewhat uncertain age but in part Cretaceous; some fossiliferous sandstones and shales, a little limestone and quartzite, and great areas of basic lavas and tuffs. The Cantwell formation composed of hard mountain—building conglomerates and shales is now also believed to be of Cretaceous age. Conspi- cuous also are the masses of granitic intrusive rocks that have penetrated the earlier Mesozoic materials and now lie as great batholiths, such as that which forms most of the western Talkeetna Mountains, or as smaller and more widely scattered masses. Tertiary rocks are also present in abundance and include the generally unconsolidated sands, clays, and gravels of the coal-bearing beds. Widespread ancient gravels also belong with the Tertiary or early Quaternary. Quaternary deposits cover a large portion of the region and include the uncon- solidated lowland deposits of the streams and shore lines and the glacially deposited materials. Both stream and glacial deposits and estuarine accumulations in the upper part of Cook Inlet are today being formad In an area so large and including so many distinct geographic and geologic provinces as the one here described, a systematic description of the rock for- mations in chronologic order would require the reader to focus his attention on first one locality and then on another far away, and by so doing to become confused as to the sequence of earth history and formations at any one place. In the geologic history of the area the sequence of events was not the same for any two geologic provinces. It therefore seems desirable to describe the rocks by provinces rather than oy geologic periods. The area is naturally divided into four major subdivisions, which include distinct mountain masses, as well as the bordering lowlands. These divisions are (1) the Kenai-Chugach Mountains, (2) the Talkeetna Mountains, (3) the Alaska Range, and (4) the Yukon-Tanana Plateau. During the last great time division, the Quaternary, the mountain masses have all stood approximately in their present locations and at about their present altitudes, and the geologic events, including the shaping of the surface forms by erosion and deposition and the great ice invasions, have affected this area to a greater or less degree. A special section of this report therefore deals with the Quaternary history as it has affected the area as a whole. Mineral industry of Alaska in 1937 by Philip S. Smith USGS Bulletin No. 910-A Mineral Resources of Alaska 1937 NOTES: Summarizes the economic status of the Alaskan mining industry during 1937 and tabulates total mineral production. Platinum deposits of the Goodnews Bay district, Alaska by J.B. Mertie, Jr. USGS Bulletin No. 910-B Mineral Resources of Alaska, 1937 ABSTRACT: Platinum metals have been found in earlier years at several localities in Alaska, but with the exception of a palladium-copper lode in southeastern Alaska none off these deposits has been of commercial importance. The platinum deposits described in this report are placers. They were discovered in 1926 and are now being worked on a large scale. The area containing these deposits is located in southwestern Alaska, close to Kuskokwim Bay. The bedded rocks consist of sedimentary and volcanic rocks of late Paleozoic (?) age, which have been intruded by ultrabasic and granitic rocks, and overlying all of these is a variety of unconsolidated de- posits of Quaternary age. The bedded rocks have an intricate structure and are more or less recrystallized. The ultrabasic intrusive rocks consist of several varieties of peridotite and perknite, but other specialized types of igneous rocks are closely associated with them. The Quaternary deposits reveal a long and intricate geomorphic history, which is likewise a history of the deposition of the platinum-bearing gravels. The mineral industry of Alaska in 1938 by Philip S. Smith USGS Bulletin No. 917-A Mineral Resources of Alaska, 1938 NOTES: Summarizes the economic status of the Alaskan mining industry during 1938 and tabulates total mineral production. Geology of the Upper Tetling River district, Alaska by Fred H. Moffit USGS Bulletin No. 917-3 Mineral Resources of Alaska, 1938 ABSTRACT: The term upper Tetling River district is here applied to a small part of the Alaska Range lying northeast of the Wrangell Mountains and extending from Suslota Pass to the Nabesna River. However, the geologic map and the de- scription of the rocks include adjacent areas, which are needed to give a bet- ter understanding of the general setting. This part of the Alaska Range shows a maximum relief of about 6,000 feet between the bars of the Nabesna Hiver and the high peaks of the divide which separates the drainage of the Copper and Tanana Rivers at the head of the Tetling River. The rocks of the district are predominantly sedimentary--shale or slate, sandstone, conglomerate, and limestone-—-but include lava flows and tuffs, all of which make up a succession of bedded deposits ranging in age from liiddle De- vonian to Tertiary or younger. In addition to the bedded rocks there are areas of granitic intrusives. ‘ The oldest rocks comprise slate, quartzite, limestone, and conglomerate of liddle Devonian age, which are intruded by large bodies of granitic rock and are locally schistose. The limestone outcrops are particularly numerous and are sparingly fossiliferous. : Following the Devonian rocks in the stratigraphic column are old lava flows and limestone, which are referred to the Permian on the evidence of fossils collected from the limestone and the association of the limestone with the lava flows. The Permian lava flows and limestones are the latest of the Paleozoic formations. They are overlain by a great mass of sediments, including chiefly limestone, shale, sandstone, and conglomerate, which occupies a great synclinal basin that extends northwest and southeast and separates the areas of Devonian and Permian deposits. They include Upper Triassic, Upper Jurassic, and Lower Cretaceous beds, which are strongly folded and are intruded by dikes and sills of granitic rock. Their relation to both the underlying and the overlying rocks is that of structural unconformity. The youngest of the consolidated rocks are lava flows and tuffs, which began to accumulate in early Tertiary time and now cover most of the Wrangell Mountain area. Although the lava flows have been ex- — 2 tensively eroded, they, unlike all the older rocks, are not folded and are only slightly tilted. The district is strongly glaciated, and its unconsolidated deposits therefore include morainal material as well as the usual sand, silt, and gravel of the streams and lakes. The upper Tetling River district has received some attention from pros- pectors, and evidences of gold and molybdenum have been found. However, aside from the Nabesna mine at White Mountain, on the Nabesna River, which is now one of the leading gold mines of Alaska but which is not described in this report, the results of prospecting have not been encouraging. Tertiary deposits of the Hagle-Circle district, Alaska by J.B. Mertie, Jr. USGS Bulletin No. 917-D Mineral Resources of Alaska 1938 ABSTRACT: A belt of sedimentary rocks of Tertiary age lies south of the Yukon River, between the international boundary and Circle. Conglomerate forms a large part of this series of rocks. All the streams that drain northward to the Yukon, flow- across these Tertiary rocks, contain more or less gold in their valleys, and some of these valleys contain important gold placers, which have been mined for many years. Recently, under the stimulus of a higher price for gold, dredges have been installed in the valleys of Coal and Woodchopper Creeks, and these dredges ar now recovering a large quantity of gold. Miners and geologists have thought for many years that these workable gold placers were derived from gold that was contained in the Tertiary conglomerates. The present investigation proves that these conglomerates are the proximate source of this placer gold, but also suggests that the original sources of the gold were the granitic rocks that form the bedrock farther south. The gold has been found to be so sparsely distributed in the Tertiary rocks that such rocks cannot be regarded as possible sites for gold lode mining, under present economic conditions As a result of complex geologic agencies, operating over a long period of time, the gold is also found to be erraticaaly distributed in the Tertiary rocks, thus explaining the presence of placers in a certain few stream valleys and their ab- sence in most of the valleys incised in the Tertiary rocks. One of the interesting results of the investigation, of possible economic value, is the discovery of a significant amount of platinum, which is alloyed with the placer gold derived from the Tertiary rocks. The presence of platinum had been unsuspected, even by the producers of a large volume of such placer gold. The platinum metals constitute as much as 0.42 percent of the placergola, but at present no payment is made for small quantities of platinum in placer gold. With a market price of platinum higher than now exists, however, it is possible that it may pay to separate the~platinum before the bullion is sent to the Federal mints or assay offices. The Goodnews Platinum deposits, Alaska by J.B. Mertie, Jr. USGS Bulletin No. 918 Washington 1940 ABSTRACT: Platinum metals have been found in earlier years at several localities in Alaska, but, except a palladium-copper lode in southeastern Alaska, none of these deposits has been of much commercial importance. The platinum placers described in this report were discovered in 1926 and are now being worked on a large scale. The area containing these deposits is in southwestern Alaska, close to Kuskokwim Bay. The bedded rocks consist of sedimentary and volcanic rocks of late Paleozoic (?) age that have been intruded by ultrabasic and granitic rocks; and overlying all of these is a variety of unconsolidated deposits of Quaternary age. The bedded rocks have an intricate structure and are more or less recry- stallized. The ultrabasic intrusive rocks consist of several varieties of peri- dotite and perknite, but more specialized types of igneous rocks are closely as- sociated with them. The Quaternary deposits reveal a long and intricate geomor- phic history, which is likewise a history of the deposition of the platinun- bearing gravels. The platinum placers occur principally in the valleys of the Salmon River and its tributaries Platinum and Clara Creeks, which drain the east side of Red Mountain. The bedrock of Red Mountain consists of ultrabasic rocks; and the gene- tic connection betwwen these rocks and the platinum placers is definite and in- disputable. The platinum metals consistof alloys of platinum, iridium, osmium, ruthenium, rhodium, and palladium. Some of these alloys are notable for their high content of iridium, but others are low in iridium. These differences have been traced to original differences in the proportions of the alloys in the bed- rock sources. The percentage of platinum increases and the percentages of iri- dium and osmium decrease from the head of Platinum Creek northeastward along the flanks of the ultrabasic intrusive of Red Mountain. A small amount of free gold also occurs in these placers, and a part of this is related genetically to the platinum metals. A larger part has been introduced from outside the area through the medium of glacial deposits, which were transported to the head of the Salmon River and were subsequently concentrated by fluviatile action. Past lode-gold production from Alaska by Philip S. Smith USGS Bulletin No. 917-C Mineral Resources of Alaska, 1938 ABSTRACT: This report presents an analysis of the statistical records of the Geo- logical Survey regarding the production of lode gold from the Territory of Alaska for the period 1882 to 1937, inclusive. During that time lode gold to the value of $172,368,000 had been mined. The history of the discovery of lode gold and the early developments in lode-gold mining in each of the va- rious districts is outlined briefly, and the production of lode gold in each of the geographic subdivisions is tabulated fully for each year, as far as the records and the practices of the Geological Survey permit. The records for the larger geographic subdivisions show that lode gold to the value of $150,775,000 or 87.5 percent of the total production of the Territory, came from mines in southeastern Alaska. The Cook Inlet-Susitna region stands second, with a pro- duction for the period of nearly 39,774,000, or about 5.7 percent. The remainder, approximately $12,820,000, equal to 6.8 percent of the total, came from mines in the following regions, named in order of their standing as producers of lode gold: Yukon, Prince William Sound, southwestern Alaska, Kuskokwim, Seward Penis— ula, and Copper River. The mineral industry of Alaska in 1939 by Philip S. Smith USGS Bulletin No. 926-A Mineral Resources of Alaska, 1939 NOTES: Summarizes the economic status of the Alaskan mining industry in 1939 and tabulates total mineral production for the year. Occurrences of molybdenum minerals in Alaska by Philip S. Smith USGS BULLETIN No. 926-C Mineral Resources of Alaska, 1939 ABSTRACT: In the accompanying report reference is made to all the deposits in Alaska in which molybdenum minerals have been definitely recognized and re- ported. None of the deposits have been mined commercially, and none of them have been prospected thoroughly enough to afford quantitative estimates as to their tenor and potential reserves; in fact, at only a few of the localities has there been more than surficial testing. Forty-one separate and distinct localities where molybdenum minerals occur are listed, and the available in- formation on factors of geologic significance regarding each occurrence is given. A small-scale map of Alaska on which the various localities are indica- ted forms part of the bulletin, and in the text are extensive references to the various published reports and records of the Survey upon which the state- ments are based. In spite of the widespread distribution of molybdenum mine- ralization in Alaska, the remoteness of many of the localities, their handicap through dearth of transportation facilities and labor supplies, and the already well-supplied condition of the American market for molybdenum ores discourage the early development of any of the known deposits or search for them in unsur- veyed areas. These drawbacks will doubtless become less important factors as the settlement and development of Alaska as a whole takes place. It is therefore, with a view to the future that one must consider these deposits, and from that standpoint it becomes evident that some of them merit watchful consideration. Geology of the Gerstle River district, Alaska with a report on the Black Rapids Glacier by Fred H. Moffit USGS Bulletin No. 926-B Mineral Resources of Alaska, 1939 ABSTRACT: The area here described includes most of the north side of the Alaska Range between the Delta and Johnson Rivers, in one direction, and the axis of the Alaska Range and the Tanana River in the other. Besides the Delta River, its principal streams are Jarvis Creek, the Gerstle and Little Gerstle Hivers, and, at the extreme east, the Johnson River, all of which have glacial sources. On the south are high, rugged mountains with snowcaps and icecaps that feed not only many small glaciers but also several glaciers of much greater size. On the north are the lowlands of the Tanana River. Between the high mountains and the lowlands is an elevated plateau of varying width and with a smooth, rolling sur- face through which the principal streams, aided by glacial ice, have cut deep valleys. The lower country, up to approximately 2,500 feet above sea level, is covered with timber. Most of the district is occupied by schist and gneiss that are in large part altered sedimentary beds of prevailingly quartzitic character and practically lacking in limestone members. The schist and gneiss are tentatively correlated with the pre-Cambrian Birch Creek schist, but the possibility of their being part- or wholly of Paleozoic age is recognized. These metamorphic rocks are intruded by light-colored granitic rocks in the form of dikes, sills, and larger bodies of irregular shapes, some of which occupy areas of considerable size. The intru- sive rocks may represent more than one period of intrusion, but whatever their age or ages may be they were exposed to weathering and were deeply eroded before the Tertiary coal-bearing beds were laid down. No sedimentary rocks shat are definitely recognized as of either Paleozoic or Mesozoic age are known in the area. Tertiary time is represented by a thick accumulation of fine gravel, sand, and sandy clay or shale containing many seams of lignitic coal, and by beds of coarser gravel and sand tentatively correlated with the Nenana gravel. The coal-bearing beds, of Eocene or possibly later age, are tilted in places but are only slightly consolidated, although theyare older and more consolidated than the Nenana gravel. | The youngest unconsolidated deposits include glacial moraines, glacial outwash gravel that occupies much of the Tanana lowland, the sand, gravel, and silt of the present streams and lakes, and extensive deposits of wind-blow sand. The district was prospected in the early days by men in search of placer gold and other valuable metals, and although it has not been commercially pro- ductive it shows evidence of mineralization. Black Rapids Glacier: The Black Rapids Glacier is one of the many glaciers of the Alaska Range. It belongs to the Delta River drainage and occupies a basinlike valley with an area of approximately 150 square miles west of the Rapids Roadhouse on the Richardson Highway. In the winter of 1936-37 the active front of this glacier made a sensational advance of more than 4 miles, ancadvance which clear- ly is a recurring event, as the evidence of several former advances is seen in old terminal moraines outside the present front. These advances take place after intervals of many years, during which snow and ice accumulate in the upper val- ley at a greater rate than that at which they are dissipated, till at last they overcome resistance to pressure and begin a brief, rapid movement. The pressure required to initiate the movement is greater. than that required to maintain it after it has been started, and the advance of the glacier continues until, under diminishing force, it finally ceases and a new cycle begins. Geology of the Portage Pass area, Alaska by F.F. Barnes USGS Bulletin No. 926-D Mineral Resources of Alaska, 1939 ABSTRACT: The Portage Pass area is in south-central Alaska, and includes part of the narrow neck of land that joins the Kenai Penisula with the mainland to the north. This region is in general mountainous, elevations ranging from sea level to more than 4,000 feet on the peaks bordering the area. Several glaciers, all of which are apparently receding, extend into the area. Vegetation, chiefly al- der and cottonwood on the valley lowlands and some spruce and hemlock on the lower slopes, extends to an elevation of about 1,000 feet, above which the slopes are bare except for occasional clumps of brush. | The bedrock of the entire area is slate, argillite, and graywacke, ap- parently part of the same great series that extends from the Kenai Penisula into the Prince William Sound region and is at least in part of Cretaceous age. The only igneous rocks recognized in the area are a few acidic dikes and a small dia- base dike. Small irregular quartz veinlets are widespread. The structure is not only complex but, owing to extensive metamorphism, is in many places obscure. A general northeast strike and steep to vertical dips of both bedding and cleavage planes are the rule, but there appears to be some broad folding along steeply northeast-pitching axes. Although no large faults have been recognized, much movement has occurred along many small faults, shear zones, and bedding planes. All observed faults and shear zones trend northeastward. There are no mines in the area. Some mineralization of quartz veins was noted at a few places, and some prospecting has been done, but no workable deposits are known. Geology and ore deposits of the Chicagof mining district, Alaska by John C. Reed and Robert R. Coats USGS Bulletin No. 929 Washington 1941 ABSTRACT: The Chichagof mining district lies on the west side of Chicagof Island, one of the larger islands of the Alexander Archipelago of southeastern Alaska, about 50 miles northwest of Sitka. From its discovery in 1905 through 1938 the district produced about $16, 250,000 worth of gold and about $170,000 worth of silver, practically all of which came from two mines, the Chichagoff and the Hirst-Chichagof. Much of Chichagof Island, including parts of the Chichagof mining dis- trict is made up of granitic rocks in masses that are believed to be parts of the very extensive Coast Range batholith, which, in some places at least, was intruded probably late in Jurassic or early in Cretaceous time. Other bedrocks of the district include slightly to intensely metamorphosed sedimentary, intru- sive, and extrusive rocks, some of which are probably of Triassic age and others probably of Lower Cretaceous age. The oldest rocks of the district may be Paleo- zoic. Except the surficial deposits, which include glacial moraine, volcanic ash, and alluvium, the bedded rocks are grouped into five units or formations--green- stone-schist; greenstone, limestone, and schist of probable Triassic age; and Lower Cretaceous (?) graywacke. Each of the formations contains rocks other than the diagnostic rocks that characterizes it. i The intrusive rocks embrace three distinct groups--diorite, albite granite and granodiorite, and dike rocks. Each of the groups is made up of several rock types. The rocks of the diorite group were intruded first and the dikes probably last, although the age relations between the albite granite and granodiorite are not clear. All the intrusive rocks may be related to the Coast Range batholith. The Chichagof district lies on the western limb of the Chichagof-Glacier Bay anticlinorium, one of the major anticlinoria of southeastern Alaska. The gen- eral trend of the rocks is west of north, and the general dip is steep to the southwest. Locally the rocks dip dip steeply northeast. The average trend in the district is N.50 W. With local exceptions the bedding and the foliation of the rocks are parallel. -— 2 --- Many faults cut the rocks of the district. Practically all the ore so far mined has come from quartz bodies that occupied one or the other of the most prominent fault zones of the district, the Hirst fault and the Chicha- gof fault. In general the faults trend about parallel to the rocks, but lo- cally the faults and the bedding diverge considerably considerably. In the vicinity of Doolth Mountain, for example, the bedding in general strikes about N.62 W. and dips 67 degrees SW., whereas the strike of the Hirst and Chichagof fault there approaches N.34 W., and the dip 75 degrees SW. Such deviations from parallelism may have been an important factor in the formation of ore bodies. Characteristic features of the fault zones are the splits or branches that diverge from main faults to enter either the hanging wall or the footwall. The splits range from tiny cracks that penetrate the wall rocks for only a few inches to strong faults that rival the main fault zones. Two types of splits are recognized—-a more common type whose members diverge from the main faults parallel to the bedding and foliation surfaces, and a less common type whose members diverge from the main faults across or against the bedding and foliation surfaces. Many split faults connect main faults. The most recent movements on the faults appear to have been soucthwestward and downward at an angle of about 30 degrees for the northeast or footwall sides, relative to the southwest sides. For the most part the movements on the faults followed the intrusion of the dikes, but at some places eikea have been intruded into preexisting fault zones. Within the district all the ore so far mined has come from fault zones in the Lower Cretaceous graywacke. Other faults in the graywacke and in the older formations may be worthy of further prospecting. The ore deposits are quartz bodies in the fault zones. Many of them have been formed at places along the faults where large splits diverge from main faults and in or adjacent to distinct warps in the faults. The quartz bodies are steep- ly inclined and tabular in form. Commonly the thickness is only a few feet, the horizonal length a few hundred feet, and the pitch length from many hundred to a few thousand feet. Many shoots pitch steeply southeastward in the southwest- ward-dipping fault zones. Most of the vein quartz is "ribbon quartz," but some is massive. Much of the quartz has been crushed by fault movements that followed the quartz deposi- tion, but these later movements are believed to have been of minor magnitude. The metallic minerals, which include pyrite, arsenopyrite, galena, sphalerite, chaleopyrite, and gold, commonly form less than 3 percent of the ore. Of the ~ metallic minerals, pyrite is by far the most abundant and arsenopyrite is next. The record of production for the district indicates that the ore so far mined has contained on the average a little more than ounce of gold to the ton. The Hirst and Chichagof faults may contain other ore bodies not yet found, and similar faults in the district may be ore-bearing. Because of the sporadic distribution of the ore bodies in the fault zones much of the future prospecting will probably be done by relatively expensive underground methods. In this report the Chicagoff and Hirst-Chichagof mines are described in detail. About 35 prospects and one small mine within the district are described more briefly. In addition the report includes short descriptions of three imines-- the Apex, the El Nido, and that of Cox, Bolyan & Loberg; and four other pros- pects on Chicagof Island, one west and the others either north or south of the district as mapped. Nickel deposits of Bohemia Basin and vicinity, Yakobi Island, Alaska by John C. Reed and John Van N. Dorr 2d USGS Bulletin No. 931-F Strategic Minerals Investigations, 1941 ABSTRACT: The nickel deposits of Bohemia Basin and vicinity are on Yakobi Island, about 130 miles by water west of Juneau. The district is readily accessible by boat or airplane. The oldest rocks in the vicinity consist of a thick sequence of strata that is thought to be in part of Upper Triassic and in part of Lower Cretaceous age. The Triassic (?) rocks are largely volcanic with some sedimentary material, whereas the Cretaceous (7?) rocks are largely graywacke. Within the district, these rocks have been metamorphosed to various kinds of schist. : The stratified rocks were invaded, probably in Cretaceous time, by gneissic rocks which are thought to be related to the Coast Range batholith of the main- land farther east. These intrusive rocks are principally gneissic albite granite and amphibolite. i Along the west coast of Chichagof Island and on Yakobi Island are several stocks of unfoliated intrusive rocks of unknown age which are younger than the intrusive rocks mentioned above. These stocks consist of norite, gabbro, diorite, quartz diorite, granite, and albite granite. The nickel deposits of Yakobh Island are several stocks of unfoliated in- trusive rocks of unknown age which are younger than the intrusive rocks mention- ed above. These stocks consist of norite, gabbro, diorite, quartz diorite, gra- nite, and albite granite. The nickel deposits of Yakobi Island are sulfide-bearing bodies containing pyrrhotite, pentlandite, and chalcopyrite, and are confined to the more calcic rocks, principally norite, of the younger intrusive stocks. They are believed to be segregated material that crystallized early from the magma from which all the rocks of the stock eventually consolidated. Individual sulfide-bearing bodies reach a maximum of several hundred feet in length. Bight of these bodies have been partly opened by 19 prospect trenches and a tunnel. At least four additional known bodies have not been prospected and there probably are others not yet discovered. The eight prospected sulfide-bearing bodies are estimated to contain about 6,000,000 tons of rock that contains about 0.36 percent of nickel and 0.27 percent of copper. The estimate of tonnage is based on the assumption that each of the bodies extends to a depth below its lowest outcrop equal to one-half of its length. Further prospecting will probably show that the ton- nage is much greater than this, but it probably will not greatly change the estimate of the grade. Rough calculations indicate that, under ecomomic conditions similar to those existing in the early part of 1941, the deposits are marginal, especially since there is now no smelter on the Pacific Coast equipped to handle nickel ores. Chromite deposits of Kenai Penisula, Alaska by Philip W. Guild USGS Bulletin No. 931-G Strategic Minerals Investigations, 1941 ABSTRACT: Chromite deposits occur at the south end of Kenai Penisula, Alaska, in two areas, Claim Point and Red Mountain. They are contained in masses of ultramafic rocks (those with unusually large contents of magnesium and iron), which are intrusive into a complex series of graywackes, slates, and cherts of Paleozoic (?) age. Dunite is the predominant intrusive; pyroxe- nite, garnet pyroxenite, and serpentine derived from the alteration of dunite are also present. Chromite grains are distributed in small quantity throughout the dunite ; the ore deposits are parts of the dunite and serpentine masses in which chro- mite has been concentrated by magmatic segregation. These deposits are tabular, strongly banded bodies, which range in size from stringers to bodies contain- ing more than 50,000 tons, and in grade from a few percent to 50 percent of chromic oxide (Cr20z). Analyses of the chromite alone, separated from the sili- cate gangue, show that it usually contains 54 to 59 percent of Cre0z and has a chrome~iron ratio of 3:1 or greater. The reserves are estimated to contain 150,000 tons of chromite. About 73,000 tons of the chromite is in shipping ore, containing 40 percent or more of Cro0z3; the remaining 77,000 tons is in some 170,000 tons of lower-grade ore, which will require concentration to produce a marketable pro- duct. Transportation difficulties have retarded the development of the Red Moun- tain area, which is 6 miles from tidewater, and they will add to the cost of mining. Claim Point is easily accessible by boat. Mineral industry of Alaska in 1940 by Philip S. Smith USGS Bulletin No. 933-A Mineral Resources of Alaska, 1940 NOTES: Summarizes the economic status of the Alaskan mining industry during 1940 and tabulates total mineral production over that period. Geology of the Nutzotin Mountains, Alaska by Fred H. Moffit USGS Bulletin No. 933-B Mineral Resources of Alaska, 1940 ABSTRACT: The Nutzotin Mountains constitute the eastern end of the Alaska Range, which extends in a great arc across southern Alaska and either merges with the Coast Range or dies out as an independent range in the vicinity of the inter- national boundary. The part of the Nutzotin Mountains considered in this report lies on the northeast side of the Wrangell Mountains and extends from the Na- besna River southeastward across the Chisana River to Beaver Creek. It is an area of rugged mountains, many peaks being between 6,000 and 7,000 feet in alti- tude and one, Mount Allen, reaching 9,478 feet. Many of the higher mountains are covered with perpetual snow and so become the gathering ground of the ice that feeds numerous glaciers. The two largest streams of the area are the Nabesna and Chisana Rivers, which originate in huge glaciers on the slopes of the Wrangell Mountains and flow in narrow, canyon-like valleys cut diredtly through the Nut- zotin Mountains, finally uniting to form the Tanana River. Two smaller streams, the Snag River and Beaver Creek, rise within the area, but they are tributary to the White River, which flows into the Yukon. The oldest rocks of the district form a small area of schist and phy- llites associated with altered granitic intrusives along the southwest border of the Tanana lowland. The next oldest rocks include basaltic flows, intrusives, and: volcanics, which are interbedded or associated with a minor proportion of limestone, shale, and other clastic beds that are in part of Devonian and in part of Permian age. However, the dominant rocks of the district, which form most of the Nutzotin Mountains, are of Mesozoic age and include Upper Triassic limestone, Upper Jurassic, Lower Cretaceous, and Upper Cretaceous shale, arkose, graywacke, conglomerate, limestone, and other clastic deposits. These beds are much folded and faulted but are not schistose. Unconformities or discontinuities probably separate the groups of deposits belonging to each of the different epoctis. Moreover, with the possible exception of the Upper Cretaceous sandstone, shale, and conglomerate, the bedded rocks were intruded by dikes, sills, and large irregular bodies of granitic rock, belonging to the granodiorite family for the most part. --- 2 --- Finally, a thick series of basaltic and andesitic lavas and other vol- canics rests unconformably on the older rocks in places and completes the stratigraphic section of consolidated deposits. Extrusion of these younger volcanics began in Tertiary time and has continued intermittently to the present. The flows are tilted but are not folded and have been eroded extensively by glacial ice and the processes of normal erosion. Prospecting for gold and copper began in the district at an early date and led to the discovery of the Chisana gold placers, which have been in con- tinuous production since 1913, and the lode-gold deposit of the Nabesna Mine, at White Mountain, on the Nabesna River, where gold production began in 1931. Gold deposits near Nabesna by Russell G. Wayland USGS Bulletin No. 933-B Mineral Resources of Alaska, 1940 ABSTRACT: The Nabesna mine is in the north border of the Wrangell Mountains, 236 miles by highway northeast of Valdez. Since operations began, in 1930, the mine has produced about $1,870,000, chiefly in gold. The principal ore body was exhausted in 1940, but summer work is expected to continue on nearby minor lowvalities. The Nabesna limestone dips gently or moderately westward and is invaded by an irregular, elongated stock of quartz diorite and a number of minor dio- ritic and andesitic dikes, Ore bodies and tactite were formed in the limestone along the east contact of the main stock. A large area of minor intrusives and much contact metamorphism lies just south of the principal ore bodies. The do- minant tactitic minerals are andradite, vesuvianite, diopside-hedenbergite, and magnetite. Tertiary lavas overlie the intrusive rocks and the limestone unconfor- mably. The mineralized area has been exposed by erosion of the prominent lime- stone cliffs of White Mountain. Three types of mineralization are present: (1) Bodies of magnetite with pyrite and calcite, (2) veins and masses of pyrrhotite with or without pyrite, and (3) veins of pyrite with calcite. Of these, only the third type has thus far been important, but a body of the second type is being prospected. The pyrite veins are formed by replacement of the limestone, but they are localized by pre-existing fractures and contacts, especially by the contact of tactite and limestone. Most of the veins are parallel to the stesp, eastward- dipping contact between the quartz diorite and limestone. Their average width is about 5 feet. Other sulfides are chalcopyrite, galena, and sphalerite. Quartz is present in the upper parts of some veins. No ore has been found below the 550 foot level of the mine. Preglacial oxidation was effective to depths of several tens of feet. Relations of structure to mineral deposition at the Independence mine, Alaska by Walter Clericus Stoll USGS Bulletin No. 933-C Mineral Resources of Alaska, 1940 ABSTRACT: The gold quartz vein at the Independence mine in the Willow Creek dis-. trict is one of several occurring in the quartz diorite batholith of late Mesozoic or early Tertiary age that forms the Talkeetna Mountain range of south-central Alaska. The vein proper, which occurs in a fault zone, has a maximum known thickness of 8 feet. The average strike is N.10 W. and the aver- age dip is 25 degrees W. The maximum observed dip is 55 degrees W. The attitude of the vein is modified by three undulations or rolls trending NW-SE. The in= ternal vein structure is a result of minor faulting that occurred during and after mineralization. Ascending solutions along the fault zone caused intense alteration of the wall rock followed by deposition of quartz and minor amounts of pyrite, arsenopyrite, calcite, scheelite, sphalerite, galena, and native gold. Three types of vein areas occur in the mine: Areas of compression, typi- fied by absence of quartz, areas typified by the presence of a varying thickness of vein quartz, and transitional areas typified by alternating bands of vein quartz and country rock or by inclusions of wall rock in the quartz vein. These three types of areas are found in parts of the mine where the dip of the vein is high, low, and intermediate, respectively. The maximum thickness of quartz occurs where the dip is lowest. The maximum tenor of gold occurs where the dip, as compared with immediately adjacent areas, is greatest. Study of thin sections of the vein material shows that the gold occurs in zones of microbrecciation within the quartz. These were caused by faulting subsequent to the deposition of the quartz and are most prevalent in areas of steepest dip. It is suggested that the hori- zonal stress tending to crush the vein would be most effective in areas where steeper dips caused the vein to be more nearly normal to the direction of the horizonal force. At two places where the quartz was present, but having low gold tenor, it was noted that late shearing had taken place in the wall rock instead of in the quartz. At another place late shearing had provided a "by- pass" which may have prevented the gold-bearing solutions from reaching the quartz vein. Reconnaissance of Porcupine Valley, Alaska by Gerald Fitzgerald USGS Bulletin No. 933-D Mineral Resources of Alaska 1940 ABSTRACT: The term Porcupine Valley is applied in this report to the part of the drainage basin of the Porcupine River that lies in northeastern Alaska be- tween the Alaska-Canada boundary and the confluence of the Porcupine and Yukon Rivers. It includes an area of approximately 3,000 square miles. The main Porcupine River is probably more than 500 miles long, but less than half this length is in Alaska. Its principal tributaries upstream from its junction with the Yukon are the Little Black River, Black River, Sheenjek River, Coléen River, Rapid River, Campbell River, Salmon Trout River, and Sunagun Creek. The Porcupine Valley comprises the following physiographic units: An alluvial basin called the Yukon Flats; an area of moderate relief, the Co leen Hills; an intermediate basin, the Coleen Lowland; and bordering the international boundary, a Highland province in which the highest summits are more than 4,000 feet above sea level. The area was first explored in 1842 by members of the Hudson's Bay Co., which for nearly 60 years controlled the fur trade along the Porcupine River between Fort Yukon and Rampart House on the international boundary. Members of the Geological Survey first visited the river in 1889 and since then sev- eral Survey parties have carried on field work in parts of the valley. The transportation needs of the inhabitants of Porcupine Valley are ser- ved during the summer by river steamer from the Yukon, by small river boats, and by airplanes; and in winter airplanes on skis and dog teams are used for travel and transportation of supplies and equipment. The climate is sub-Arctic and is marked by great seasonal variations in temperatitre, scant rainfall, and few severe storms. The forests consist mainly of spruce, with scattered cottonwood, birch, willow, and alder brush. Some of the ordinary garden vegetables are success-— fully grown. The animal life is varied and includes bear, moose, caribou, mountain sheep, and most of the fur-bearing animals common to interior Alaska. Lee el eal Ducks and geese are plentiful, especially at the time of the fall migration, and several kinds of food fish are found in the Porcupine River and its tributa- ries. The area here described has less than a dozen permanent white inhabitants; these are trappers living on tributary streams. Fort Yukon, which is near the junction of the Porcupine and the Yukon, the point of entrance to the Porcupine Valley, had a population of 274 in 1940. A few natives live in small settlements along the river and its tributaries. Chromite deposits of Red Bluff Bay and vicinity, Baranof Island by Philip W. Guild and James R. Balsley, Jr. USGS Bulletin No. 936-G Strategic Minerals Investigations, 1942 ABSTRACT: Small deposits of chromite occur in serpenized ultramafic intrusive masses on Baranof Island, southeastern Alaska. The body of greatest importance as a possible source of chromite is at Red Bluff Bay, on the east coast of the island; seven others are known about 10 miles west-northwest, in the rugged interior. The ultramafic rocks are dunite and pyroxenite, largely altered to serpentine or talc. They are intruded into phyllite and green- stone schist of Triassic (?) age, and are cut by dikes that are probably related to the Coast Range batholith. The ore deposits are lenticular concentrations of chromite ( (ig, Fe) (Cr, Fe, Al) 0 ), a normal accessory mineral of dunite. The chromite differs Widely in composition in different deposits, or even in the same deposit, but in general it has a low ratio of chromium to iron, an undesirable feature in chromite ores. Eight deposits at Red Bluff Bay are known, of which five con- tain ore of shipping grade and three contain material that may be of concentrating grade; but the estimated reserves amount to only 570 tons of ore containing 40 percent or more of chromic oxide (Cro0,), and about 29,000 tons of low-grade material averaging 12 percent of chromic oxide. No deposits of economic importance are known to occur in the interior of the island. Nickel-Copper deposits on the west coast of Chichagof Island by William T. Pecora USGS Bulletin No. 936-I Strategic Minerals Investigations, 1942 ABSTRACT: On the west coast of Chichagof Island, southeastern Alaska, are three nickel-copper deposits that consist of norite contain- ing the sulfide minerals pyrrhotite, pentlandite, and chalcopyrite. The deposits are within less than a mile of each other and are, by water, 160 miles southwest of Juneau and 70 miles northwest of Sitka. The norite is part of a stock, about 5 square miles of which is above sea level. Other rocks of the stock are amphibolite, amphibolitic norite, gabbro, diorite, quartz diorite, monzonite, granite, pegma- tites, quartz veins, and schist inclusions. The stock is intrusive into a Lower Cretaceous (?) graywacke formation and an Upper Triassic (?) greenstone formation, both of which are now metamorphosed to schis The deposits are of two kinds: (1) A disseminated-sulfide de- posit, in which the sulfide minerals are distributed throughout the mass of the norite, and (2) concentrated-sulfide deposits, in which the sulfide minerals are in distinct podlike masses of sulfide-rich norite. The deposits of type 2 are coarser-grained, smaller, and high- er in nickel and copper than those of type l. Two of the three deposits described are of the concentrated- sulfide variety. One of these, the Fleming Island deposit, has been partly developed by means of a 175-foot shaft, now flooded, by 71 feet of underground openings on a 75-foot level, of which 37 feet are _eported to be in ore, and by &5 feet of openings on the 175-foot level, of which 14 feet are reported to be in ore. A sample represent- ing 400 soquare feet, or half the surface outcrop, contains 0.58 per- cent of nickel and 1.15 percent of copper. It is reported that 37 feet of sulfide ore on the 75-foot level has an average content of 3.42 percent of nickel and 1.15 percent of copper, and that a half-ton sample from the 175-foot level contained 2.41 percent of nickel and 1.00 percent of copper. If the ore body is continuous between the sur- face and the 175-foot level, the deposit is a steepiy aipping ore snoo wnicn contains more unan 10,000 tons of ore. The ore contains possibly 4 percent ol nickel ana L percent ol copper. A second outcrop of concentrated sulfides is near tne water's eage, about 5,UuUU Leet’ soutneast of tne one mentionea avove. Its area 1s apout 500 square Leet, anda tne material exposed resembies tnav or tne Fleming Island deposit; tnougn tne samples taken, wnicn were naraly aqgequate in number, indicate that 1t 18 of somewnat Lower graae. No sudsuriace exploration nas peen done here. Tne depositcomposea or noritve with disseminated sulfides is exposed about 1,000 feet soutneast oi tne second deposit oi concen- trated suitiaes. It probably contains a LeW Mliiion tons ol Low-grade maverlaiL witn pernaps 0.2 percent of nicket ana 0.1 percent of copper. Nickel-Copper deposit at Snipe Bay, Baranof Island, Alaska by John C. Reed and George 0. Gates USGS Bulletin No. 936-M Strategic Minerals Investigations, 1942 ABSTRACT: At Snipe Bay, on the outer coast oi Baranoi Isiand, about 46 miles soutneast ot Sitka in soutneastvern Alaska, 1s a nickel- copper aeposlt that consists ol a4 mass Ol basic rock intruaea into quartzite ana quarts scnist. Neither tne size nortne grade or tne deposit 1s adequateiy known. Natural exposures and tnose in a rew prospect openings indicate that to an assumed depth of about 130 feet below the lowest point on the outcrop there is a reserve of about 430,000 tons oft Low-graae nickei-pearing materia, which, to juage Irom avaiitabie assays ana Lrom comparison witn simiiar mater- lai Irom other piaces, probably goes not contain more tnan 0.3 per- cent each of nickel and copper. The deposit thus appears too small and of too low grade to permit the recovery of the nickel and copper except at a considerable financial loss; but as the location is favorable for large-scale, Low-cost aevelopment, Lurtner prospecting may ve justiitlea, in tne nope that a moaerate amount ol suriace sUrlpping, pius a lew Glamond-driii noies, mignt indicate wnat tne ageposit 1s Larger, ana possibiy ol higher graae, tnan 10 1s sale to infer from the available data. Antimony deposits of tne Stampeae Creek area, Kantisnna aistrict oy Donaia E. White USGS Buitetin No. y50-N Strategic Minerais Investigation, Ly4z ABSTRACT: Tne Stampeae Creek area 1les about iéu mlies soutnwest or Fairbanks, Alaska, It is uost reaagity accessible by air during the summer and by tractor road during the winter. Since 1936 approximately 2,400 tons of shipping-grade anti- mony ore and concentrates, containing about 1,300 tons of metallic antimony, have been produced at the Stampede mine. The mine was closed down in the spring of 1941, principally because of the high cost of transportation. The area is underlain largely by metamor- phosea rocks ol tne Birch Creek scnist. The scnist nas veen warpea ana crumpieaq into many broaa, open iloias wnicn strike nortneast ana also piuge to tne nortneast. The Stampede mine is in tne scnistose quartzite memoer or tne Biren Creek scnist. Tne antimony occurs princlpailty as tne minerai stipnite. It is founa in veins, in tenses, ana in velniets in shear zones whnicn are propabDiy retated to tne Stampede rauit, a Large nortneast-trend— ing fauit wnicn cuts a nortneast=piunging anticiilne at a smaiit angie. The vein rractures were rormea near tne axis olf tne anticiine wnere tne strixe ol tne Lauitv cnanges trom N.ou E. to N.&O E. Tne pest ore is Louna av tne intersections of tne veins witn cross fauits, anda at tne acute-angied junction of one ol tne principai veins witn tne Stam- peae tauit. Tne veins strike from aque nortn to N.&u E., and dip trom SU vo (> aegrees to tne east ana south. The cross faults strike about at right angles to the veins, and dip steeply to the east and north. The low-grade ore bodies consist of stibnite disseminated in quartz veins as much as 7 feet wide, and of stringer veinlets in schist. Stringer vBinlets in zones as much as 30 feet wiae rorm ilow- graae ore pdoagles with assay boundaries. Tne nign-graae snipping ore we 2 mre Consists of Lenses ana velns ol stibnite up to > feet wide, except for one exceptional body which was 26 feet wide. The low-grade: mill ore assays from 10 to 20 percent antimony, and the high-grade ship- ping ore over 50 percent antimony. The blocked out reserves, as in nearly all antimony deposits, are small. The estimated reserves, including both proved and pro- bable ore, are 70 tons of 50-percent or better ore, 6,000 tons of 10- to 15-percent ore, 1,000 tons of 20-percent ore as loose material below the suriace ore body, and 5,000 tons of mill tailings which carry, about 6 percent of antimony. Two or tne ore podies wnicn nave been developed oniy very siigntiy may contain mucn more antimony Unan present estimates indicate, The geoLogicai reiations are sucn as to suggest tne presence ol undiscovered ore bodies, Nickei-Copper deposit atv Funter Bay, Aamiraity Isianda, Alaska by John C. Reed USGS Bulletin No. 936-0 Strategic Minerals Investigations, 1942 ABSTRACT: The nickel-copper deposit near the north end of Admiralty Island, about 18 miles in an airline west of Juneau, in south- eastern Alaska, consists of a basic sill which averages somewhat more than 100 feet in thickness, The sill, which dips eastward, is intrusive into a thick sequence of phyllite and various types of schist. The rock of the sill consists principally of the silicate minerals labradorite and olivine, but it also contains magnetite and the sulfides pyrrhotite, pentlandite, and chalcopyrite. It assays, on he average, about 0.34 percent nickel and 0.35 percent copper, which are doubtless: mostly in the pentlandite and chalco- pyrite respectively but are probably constituents of other minerals also. A significant portion of nickel and copper is probably contvain- eq in tne olivine ana pernaps in tne pyrrnovite. The incompiete gata avaliable indicate a reserve of approxi- mately 56U,UUU tons. Further exploration wouid probabiy show that the quantity is ratner greater than tnis; put tne average graae wouLa probabiy not prove higher than that inaicated above, aitvnough some ore of relatively nigh grade mignt weii ve found in places. Aitnough mining conditions are generaiiy good, tne nickei and Copper convent of tne rock is so LOW tnat 1 appears very aouptius wnetner tne Geposlt can pe expiolvea successiuliy or contribute sig- nilicantiy to tune Nation's nickei supply. Any Lurtner stuay ana aeve- topment of the aeposlt snouig be directead toward determining 1ts rulL emvent and towara more compiete KNowLeage ol tne amount, distripution, and availability of the nickel and copper in the rock and in each of its constituent minerals, Mineral industry of Alaska in 1941 and 1942 by Philip S. Smith USGS Bulletin No. 943-A Mineral Resources of Alaska, 1941 and 1942 NOTES: Summarizes the economic status of the Alaskan mining industry during 1941 and 1942, and tabulates total mineral »sroduction. Mining in the northern Copper River region, Alaska by Fred H. Moffit USGS Bulletin No. 943-B Mineral Resources of Alaska, 1941-42 NOTES: Describes mining activity in the northern Copper River region during 1941 and 1942. Nickel-Copper prospect near Spirit Mountain, Copper River region by Jack Kingston and Don J. Miller USGS Bulletin No. 943-C Mineral Resources of Alaska, 1941 and 1942 ABSTRACT: The Spirit Mountain nickel-copper prospect, near the head of Canyon Creek, 15 miles south-southeast of Chitina in the Copper River region of Alaska, is accessioie by boav or trait From Cnitina, or py pontoon piane Irom Cnitina or more distant points, Bedded metamorpnic rocxs or Carbonirerous (Mississippian) age an Unis area nave peen intruded oy generaity concoraant igneous poaies anciuaging severat Slii-ilke masses oF suililde-pearing aiterea perido- tite and pyroxenite. Two o1 tnese bodies on tne west siae ot Canyon Creek constitute tne principal nickei aeposit. Here tne suiiide min- erais bravoite, pyrrnotite, chaicopyrite, pentlandite, ana pyrite are present 1n tne perildotvite and pyroxenite as disseminated grains ana as massive Lenses, The deposit probabdiy 1s ol magmatic origin, The deposit 1s estimated to contain avout 6,500 tons of material ranging in grade from 0.22 percent of nickel and 0.12 percent of cop- per for the lowest grade disseminated-sulfide material to 7.61 per- cent of nickel and 1.56 percent of copper for the massive sulfide ma- terial. Because of the small size and almost inaccessible location of the deposit, the authors do not believe that it can be minea pro- Iivaply, even 11 tne price of nickel snouia rise consilaerapiy above ats present LeveL, Additional deposits, 11 any, wouLa pe alizicuLt to lina ana are not i1ikeLy to ve Larger or richer tnan tne Known ae- posit. Mineral investigations of the Geological Survey in Alaska in 1943 and 1944 by John C. Reed USGS Bulletin No. 947-A Mineral Resources of Alaska, 1943 and 1944 NOTES: Describes the investigations undertaken during 1943 and 1944, principally in the search for vital wartime mineral deposits. Molybdenite investigations in southeastern Alaska by W.S. Twenhofel, G.D. Robinson, and H.R. Gault USGS Bulletin No. 947-B Mineral Resources of Alaska, 1943 and 1944 ABSTRACT: Four moiybaenite aeposits in soutneasvern Alaska were exa- minea oy tne Geologicas Survey in 1ty4é ana 1y45. Tne aevosits are an tne Nunatak area, near tne neaa or Muir Iniet, Giacier Bay; near Snaxan, Kosciusko Isiana; on Baker Isiana; ana in Grounanog Basin, on tne mainiana east of Wrangell. In tne Nunatak area tne bedrock inciudes tigntiy toLaea PaLeo- zole nornieis ana Limestone, imtruaed py a smalt boay or quartz mon- zonlte porpnyry, wnicn 1s surrounded py myrlaa quartz veiniets. Among tne nonmetaiilec minerais are Leiadspar, nornolende, alopside, ana ciino zolsite. Tne metaiilc minerals inciuae molypaenive, pyrite, magnetite, and cnaicopyrite, oi Wnlcn aii Dut moiyodenite are inconspicuous. Two types of motybaenite aeposits are recognized. Tne stockwork type in- cLuaes tune miadiLe part of tne gone ol quartz veiniets surrounding the intrusive core; 1U crops out over an area oi avout 2,170,000 square feet and probably extends many nunarea iteetv pelow tne suriace. The rauLt-zone type 18 similiar, but tne rock witoin 1 contains many open Iractures, Tne Nunatak rauit aeposit, tne Largest of tnav type, crops out over a Lengtn of <,UuUU Leet, has a Known verticaL range of about duu reet, ana averages about y feet in widtn., All tne MoLyoaenite ae- posits ot tne Nunatak area are tow graae. The 177 chip, drill, and channel samples collected by the United States Bureau of Mines from the part of the stockwork mapped as containing conspicuous molybdenite contain from 0.02 to 0.21 percent of molybdenum, with an average of about 0.075 percent. The 56 samples collected by the Bureau of Mines from the part containing inconspicuous molybdenite contain from 0.02 to 0.11 percent of molybdenum, with an average of 0.046 percent. The samples from the Nunatak fault deposit contain from 0.04 to 0.34 per- cent of molybdenum, with an average of about 0.102 percent. Assuming that the fault deposit extends to an average depth of 300 feet and the stockwork to an average depth of 500 feet, it is estimated that the Nunatak fault deposit contains about 500,000 tons of indicated molybdenite-bearing rock, of which 260,000 tons contain conspicuous molybdenite, and that the stogkwork contains more than 100,000,000 tons, of which about 8,500,000 tons contain conspicuous molybdenite. Tne moLyoaenite aeposits near Snaxan, Kosciusko Istana, are in @ narrow, Low-cipping LauLtv sone ana constitute a composites vein un nornbdienae aiorive. Breccia piocks ol nornbienae alorive are tne principal vein Iiiiing. The dpiocxs are commoniy separatea ana Lo- Cally repiacea aiLong tne margins by bandas ana small ilrreguiar masses oL granite pegmatite, Lampropnyre, apiite, quartz, quartz-aauiaria, calclte, zeolites, and lron, copper, and zine suiilaes, in addition to moLybdente. Tne introaucea vein materldis appear to nave been ae- posived over a cConslaerapie range ol temperature put at relatively 1ow pressure. Molybaenite was aeposited near tne ena ol une minerail- zation sequence. Inconciusive evidence indicates tnavt tne aisvriou- ULon OL wmoLlybaenlte was probably controliea princlipaisiy py openings aeveiopea ln une more steeply dadlipping parts ol tne Laut zone as a consequence ol Sid4it-scaie normat LIauiting. Surtace anda unaergrouna Workings expose one ore snoovt tnat 1s estimated to contain petween 4U,UUU ana £v,UUU tons ol measurea and inaicatvea ore containing abou 1.5 percent or MoSo- A few tens of thousands oI tons of additionaL ore flay be inlerrea in extensionsor tne Known ore shoot ana in snoots not now exposed. Tne east-centrat part o1 Baxer Istana 1s unaeriain py quartz aio- rive intrusive into siigntiy recrystaitizea Devonian (?) argiisite and quartzite. Tne quartz aloritve, originaiiy a ratner uniform ierro- magneslan-poor rock, has peen varlabiy precclatved and universaissy but unequaity siiicitiea. The intensity of sliliication, aistnougn ranging widely witnin snort alsvances, in generat increases towara tne nortneast. The intensity of precclation ana ol siiiiication are reLlavea to tne aegree ol aevelopment of joints strixing apout N.ood Wy and dipping Yu-/> degrees S. Joints oi otner prominent sets strike apout N. 15 We, N. su E., ana N.&> W., ana aip very sveepiy. Many gray or oiuisn glassy quartz velniets, mostly occupying tne Nod W. joints, cul tne siilcifrieda quartz ailoritve. In most places tne veiniets are quantitatively insignificant, put 1n tne smait area convaining une 1argest moLyodaenite aeposlts tney Ltorm a reticuLating network tnav Collprises Irom Luv to dU percent ofr tne rock voiume, Motyoaenite commoniy occurs 1n smait paper-tnin pavenes aiong tne margins o1 quartz veiniets ang in Iractures cutting tne veinievs. Associatea WLUN Molyoadenivte are smali amounts ol pyrive, arsenopyrite, ana py- rrnovitve (?). The oniy novewortny aeposits are on tne east coast about 1 miLe soutn ol tne entrance to Port San Antonio, where mosy- paenite 1s exposea in relative apunaance tor apout /vu reet aiong tne beacn ang in most ol tune outcrops 4uUU tO bUU Teev back OL tne snore, wltn an exposed vertical range of avout Zuu ieet. The average moiy- oaenitve content of tne rocks wltnin tnis area Irom tne suriace bo a deptn ol about idu Leet’ DeLow sea Level 1S Delleved to ve tess tnan U.iL percent py welgnt ana probably Less tnan vu.ud percent. Because oi unelr extremely poor graae, Lurtner aeveLopment oz tne Baxer Istana moLybaenlve deposits does not appear warrantvea at present. --- 3 --+ In Groundnog Basin, Wrangeil aistrict, a nortnwestwarda-trend- ang granite siiit at seast 1,000 eet wiae ana perpaps severai miles 4ong contains sparse wolypaenive near its soutn ena. Tne moltyoaenite aS irreguLariy Gistriputea as iracture Iliiings ana in quartz velniets Nickel investigations in soutneastern Alaska oy George C. Kenneay ana Matt S. Waiton, Jr. USGS Buitetin No. 947-C Mineral Resources of Alaska, 1943 and 1944 ABSTRACT: During Ly4Z and 1y45 tne nicke1-copper aeposits on Yakobi Istana, tne west coast of Cnicnagor Isiana, ana a smait prospect on Baranot Istana near Sitka were Lurther stvuaieda by tne GeotogicaLr Survey ln connection witn investigations on strategic ana .crivicar war minerais in Alaska. Yakobi Istana aeposits. The o1daest rocks on Yakopi Isiana con- slSt of a tnick sequence ol voicanic rocks ana graywacke. These were antrudea py piLutonic rocks, wihicn were Later snearea ana mevamorpnosea aargeLy to aibite granite gneiss and ampniboiive. The iargest Known nickei-copper aeposits are in Bonemia Basin ana are segregavions trom norite voales, parts of a postiletamorpnic composite rock. The nicxei-copver aeposits on whicn expioratory work nas veen concentrated are parts ol a noritve pody wnabv’ Contains pentianaivte, chaicopyrite, ana pyrrnotitve. The noritve poay 1s surrounaea py norn- Leis, gaooro, ana quartz Qiorite, ana une suiillae-vearing parts of the poay crop out near its peripnery. Driidi notes ana magnetic aata anaicave tnav une norite poay is basin shaped and tbnat 1t 1s under-= dain sargeiy oy gapbro and-nornieis, Tne suiiiae-pearing rock Lorns a trougnh=snapea aepositl tying above tne iower contact ol tne norive. Avaliavie eviagence indicates that tne suiliae winerais in tne Iorm OL lmmiscloOLe aropietl[S were Concentravea DY gravity in tne 10- wer parts of tne noritve voay at a time when most ol tne siticatve min- erais in tne norive naa crystaiiizea. Eariier estimates on tne pasis of tne scant aatva tnen aval- uacie were Uhat £,4UU,UUU ons OL Maverias CoNtalning v.44 percent ol nicxet ana 0.29 percent of copper were present in the Tunnel, East Tripod, and West Tripod bodies;:1,042,000 tons of material containing ---- 2 ---- 0.25 percent of nickel and 0.25 percent of copper in the Muskeg and Side Hill bodies; and 2,400,000 tons of material containing 0.31 percent of nickel and 0.25 percent of copper in the Takanis bodies. The interpretations of drill tests by the Bureau of Mines furnish the basis for a revised estimate of 10,300,000 tons of in- dicated material in the Tunnel and Tripod bodies, with an average grad of 0.37 percent of nickel aid 0.20 percent of copper. Drill data from the Bureau of Mines work and magnetic data furnish the basis for a revised estinate of 8,100,000 tons of inferred material in the Muskeg and Side Hill bodies, with an average grade of about 0.27 percent of nickel and 0.20 percent and 0.20 percent of copper. No additional data are available on the Takanis bodies. Estimated re- serves therefore total 20,700,000 tons of indicated and inferred ma- terial. The average grade is about 0.33 percent of nickel and 0.21 percent of copper. Approximately 35 percent of the material included in estimates of tonnage in the Tunnel ana Tripoa bodies is virtuaily barren; 1% tnis were exciudgea py some process ol seiective mining, Une graae wouia ove increasea to avout 0.51 percent of nickel and 0.27 percent of copper. Presumably similar percentages of barren ma- terial are present in the other bodies. Chicnagor Istana aeposits. Severat nicxei-copper aeposits are Known ln @ Sildit area ln tne vicinity or Mirror Harbor on tne west coast of Cnicnagor Isiana. Tne ceposits are suLiiae-vearing parts ol a noratve boay which 18 part of a much sarger composite stock in- trusive into metamorpnosea greenstone ana graywacke, Tne sustiae minerais in tne norive are pentianaive, pyrrnovlte ana cnaicopyrite. In one piace unese minerais are alsseminatea tnrougn tune noritve, Lorming a Large GQeposit ol very sow graae. Numerous smais reLativeiry ricn pods, ranging in tengtn Lrom a Lew inenes to a iew ieetv, torm pooles of solewnal higner graae, Tne sargest concentravea-suLiiae aeposit crops out on tne nortn snore ot Fieming Isaana. Tnis aeposit 1s of ovat outcrop, 1s plpeilke ana extendas to a aepin oL apout 110 Leet, wnere 1U 1s probabiy cuv O1L vy a raust. The body contains about &,000 tons of material with an average grade of about 1.57 percent of nickel and 0.88 percent.of Three other concentrated-sulfide deposits lie near the head of Davison Bay about 3,000 feet from the Fleming Island deposit. The largest of these contains only a few tons of concentrated sulfide material. The large disseminated-sulfide deposit, about 1,000 feet long and a hundred or more feet thick, crops out about 1,000 feet south- east of the concentrated-sulfide deposits at Davison Bay. Meager evi- dence indicates that the body dips west at about 20 degrees. This deposit probabiy contains several miiition tons olf matveriai with an average graae oi apout 0.2 percent ot nickei ana 0.1 of copper. Baranof Island deposit. The deposit on Baranof Island near Sitka contains only a few tons of nickel-bearing rock and was not studied in detail. Geology ana assoclatea winerai Geposits ol some uLtrapasic rock boales in soutneastern Alaska by George C. Kenneay ana Matt S. Waiton, Jr. USGS Buisetin No. 947-D Minerai Resources o1 Alaska, 1943 ana 1944 ABSTRACT: In connection witn a Geological Survey project to investigate tne occurrence oi Nickel, chromium, ana retractory-gradge o1lvine in soutneastern Alaska, tne authors examineq severaéi uLtrabasic rock boales during the summer ol 1945. Among these were tne boaies in tne Lituya Bay-Mount Criiion area, centrai Baranot Isiana, Rea Biurr Bay, tne Biasnxe Isiands, Kane Peak, ana Mount Burnett. In tne Lituya Bay-Mount Criiton area tne o1gest group ofr rocks 1s a tnick sequence of nigniy mevamorpnosea seaqimentary ana voicanic rocks which are separatea by a major LauLtl Irom a younger group ot beaded siate ana greenstone.Overiying tne siatve and greenstone is a Unick sequence oi Miocene rocks consisting of unsortea congiomerate, Sanastone, snaie, a Lew thin seams or coai, and some turraceous peas, A targe iayerea basic igneous poay with tne puik composition of a nyperstnene gabbro or norite intruaes whe mevamorpnosea sedimentary and voicanic rocks. This boay is composea Lor tne most part or ai“ vernating sayers ol norite, olivine norite, dunite, troctoiite, anor- TnoOSlLlB, Dronz1ltite, anda Llinenite, Beacn sands in tne vicinity or Lituya Bay nave yieiaed a isimited amount ol goia and some piatinul; tne pLatinum may nave been aerivea Irom tne basic intrusive, Tne Lowermost outcrops of tne basic boay contain abundant suilide minerais, principaiiy cnaicopyrite and pyrr- notite, and tne limenitic sneets in une boay are rich in suLridae min- erais. No chromite was observed 1n piace, aitnougn chromite Iioat nas peen reported on tne giaciers, In tne centvrai part of Baranoi Isiana, in tne area petween Rea Biurr Bay ana Siiver Bay, numerous aiscontinuous slits o1 higniy ser- pentinizea agunite crop out. Chromite 1s abundant in the siiis, occur- ring as scatvvered grains, as crystai aggregates as mucn as tnree inene tong, ana as streaks and seals as much as 3 Leet tong ana a trew incnes wide. No concentration of chromite was found of sufficient size and grade to constitute an ore body. At Red Blufi Bay, Baranoit Isiana, a boay o1 chromite crops out in tne northeastern part of tne uitrabasic mass. This chromite con- valns suilillclent lron to be appreciabiy magnetic. A series ol mag— nevometer observations was mage in a smail area lmmedilateiy soutn ol tne nortnern segment of tne aeposit to aetect, 11 possibie, a soutnwardad exvension oi tne poay peneatn a Llauit. A distinct hnign Was noted 1n the magnetometer reaaings, wnlcn tends to inalicate a supsurrace southward extension of tne northern segment ol tne ore boay. A smaii cnromite aeposit, nitvnervto unreportea, crops out in a guich a lew nunared Leet west of tne ageposit expiorea by tne magnev- ometer. This deposit contains about &U tons ol chromite with an ave- rage graae ot 45.2u percent or Cr,0.,. The Blashke Islands are a gfotp of 16 smait 1siands maue up o1 agetormea rocks, wnhichare intruaea by an uLtrabasic body of rougniy circular outcrop. The bedded rocks are 1targely graywacke anda pyro- clastic rocks ot Silurian age, whicn generally strike northwestward, bul Locally tney rougniy coniorm in attltuae to the margin ot tne uitrabasic intrusive poay. The core oi tne ultrabasic intrusive is an ovai dunitve mass apout 6,000 by 8,000 reet in outcrop dimensions, Encirciing tne aunite core 1s a ring ol pyroxenite ana wenriite 500 to 2,000 feet wide, which in turn is encirciea py a ring ot gabbro wltn 10cal variants ol hornbienaite, alorite, augitite, and anortho- site. Tne gabbro pnase is gradationai into the surrounding rocks. Con- tacts petween tne various units ol tne uLvrabasic poay are approxi- mateiy vertical, A smait percentage of suitide minerais, princlpaiiy pyrrnovive ana chaicopyrive, 1s Locally present in the pyroxenite ana tune gabpro. Tnree anaiyses of samples of the suitide-pearing maveriaL indicate tnat 10 contains U.Uu4 tO U.s.i OUNCE OL pLalinum-group mevais per ton. In tne Kane Peax area, Kupreanoi Istana, an uitrapasic in- Urusive rock boay 1s surrounaea py graywacke ot Cretaceous age ana by DlotUlte-quartz gneiss and monzoqdiorite. Tne uitrabasic rocks range 1N Collposltion irom gabdbro vo aunite, Wenriite, pyroxenite, norn- Dienaivtve, ana mica-ricn varlants or these rocks are Locaiity apun- aant, Tne aistribpution ana rocks in tne Kane Peak area are rougniy Slmliar to tnose atv tne BLasnkxe Isianads,. In tne Mount Burnett area an ultrabasic rock mass apout / miies tong and 4 to < mites wilde Lntrudges pnyisite and scnist ofr tne Wrangeii—~Reviliagigeao peiv ol mevamorpnic rocks, Some Tertiary conglomerate overiles tne ultrabasic intrusive rock voay. The uLtrabasic rocks lorm a targe composite stock maae up oi dio- rite, gabpro, nornbiendive, pyroxenite, wenrilte, ana daunite,. A cruae panaing was notea wltnin tne uitrabasic poay. In some places tne qgunite 1s nigniy serpentinizea; eisewnere in the voay 1tU 1s very iresnh, Witn no aiteration. Tne oLivine approximates iorsterite 1n composition. A rew tons ol chromite ofr inierior graae are present. Uitrabasic rocks in souvneastern Aiaska are known to contain nickel, copper, piatinum, ana cnromite. In most of tne uitrabasic roc: in tnis region nickel’ ana copper are present ln minor quanities ana are peileved to be oi no economic imporvance. A Lturthner investigation or the piatinum content of some of the ultrabasic podles may reveaL minapie quantities of piatinum—-bearing rock. A lew smait boaies ofr chromite are Known, but these are ol relatively 11ttLe Importance, Large quanitles ol serpentine-ftree qunitve are known, and tnese may be ol vaiue as a reiractory. Almost unilmlted quanitvies olf aunite are avaisadie, ang wiit be OL Vaiue li eliorts to periect a process tror oovaining mevaiitlc magnesium Lrom oilvine are successful. Copper bullion claims, Rua Cove, Knight Island ~by Karl Stefansson and Robert M. Moxham USGS Bulletin No. 947-E Mineral Resources of Alaska, 1943 and 1944 ABSTRACT: The Copper Builion Claims are near Rua Cove, about midway in the east coast of Knight Island, Prince William Sound. The pro- perty consists of 18 claims controlled by F. H. Dickey, of Seattle, Washington. Development includes numerous open-cuts, 2,850 feet of tunnel and crosscuts, and a number of diamond-drill holes. The rocks of Rua Cove are of igneous origin and probably of late Mesozoic age. Three distinct types of igneous rocks have been recognized, Mineralization occurred in a shear zone, with sulfide minerals replacing the sountry rock along fault and fracture planes. Reserves of ore with an average content of 1.25 percent or more of copper are: Measured ore, 25,000 tons; indicated ore, 1,125, 000 tons; inferred ore, 264,000 tons or more. It is estimated that the shear zone contains also several million tons of ore with an average content of about 0.6 percent of copper. Copper deposits of the Nizina district, Alaska by Don J. Miller USGS Bulletin No. 947-F Mineral Resources of Alaska, 1943 and 1944 ABSTRACT: The Nizina district lies on the southeast flank of the Wran- gell Mountains, about 60 miles east of Chitina and about 200 miles by automobile road and rail from the port of Valdez. The first cop- per claims were located in 1899. From 1911 to 1938 the district pro- duced more than a billion pounds of copper, nearly all from the Kennecott mines. When the Kennecott mines closed and the railroad to Cordova was abandoned, in 193&, copper production ceased, except for a few tons of copper nuggets recovered as a byproduct of gold- placer operations. The host rocks of the copper deposits are the Nikolai green- stone, consisting of altered basaltic lava flows of Permian and Tri- assic (?) age, and the overlying Chitistone limestone, consisting of massive thick-bedded limestone of Upper Triassic age. The greenstone and limestone are folded into a broad syncline trending northwest. The deposition of the ore bodies was controlled in part by minor cross folds, steeply dipping faults that strike at a large angle to the axis of the major fold, and bedding faults. Chalcocite is the principal copper mineral in most of the depo- sits in limestone, and bornite and chalcocite are the principal cop- per minerals in the deposits in greenstone. Native copper also occurs in the greenstone. Nearly all the ore has come from the lowest 300 feet of the Chitistone limestone. In this report 7 mines and about 13 prospects, comprising near- ly all of the known copper deposits of the district, are described briefly. None of the known deposits is believed to offer sufficient promise of significant production or profit to warrant the cost of reestablégshing a practicable means of transportation to the district solely for the cipper. Copper deposits of the Kotsina-Kuskulana district, Alaska by Ralph E. Van Alstine and Robert F. Black USGS Bulletin No. 947-G Mineral Resources of Alaska, 1943 and 1944 ABSTRACT: The Kotsina-Kuskulana district of the Copper River region is between the Chitina River and the crest of the Wrangell Mountains. The principal prospects are those on Copper Creek, Clear Creek, Nugget Creek, MacDougall Creek, Berg Creek, and Elliott Creek and the Big Horn and Pierson prospects. A brief description of the lo- cation, stratigraphy, geologic structure, and mineralogy is given for each prospect. Detailed maps of the accessible underground work- ings at Copper Creek and Clear Creek are included. The prospects are in the Nikolai greenstone and to a less extent in the overlying Chitistone limestone. No large or high-grade depo- sits of copper ore are known. Two carloads of hand-sorted material and 160 tons of concentrates from Nugget Creek constitute the total shipments of copper ore from the district. Some Mineral Investigations in southeastern Alaska by W.S. Twenhofel, J.C. Reed, and G.O. Gates USGS Bulletin No. 963-A Washington 1949 ABSTRACT: About a dozen mines, principally gold mines, were operating in southeastern Alaska in 1940, but by 1944 the Riverside tungsten mine in the Hyder district was the only active mine in the region ex- cept for a little mining and prospecting by a few groups of a few men each, During the samé interval the exploration for and appraisal of mineral deposits in southeastern Alaska by the Geological Survey and the Bureau of Mines was greatly increased, and many of the ex- aminations were of deposits of the strategic and critical minerals. In 1940 and 1941 the Geological Survey made a detailed invest- igation of the nickel-copper deposits on Yakobi Island, and in 1941 the chromite deposits at Red Bluff Bay on Baranof Island and the nickel-copper deposits on the west Coast of Chichagof Island were studied. Late in 1941 the Bureau of Mines started a sampling and drilling project on the Yakobi Island deposits and completed it in 1942 and later in 1942 also tested the denosits on Chichagof Island. In the summer of 1942 the Geotogicai Survey examinea tungsten aepo- slts in tne Hyaer alstrict, ana tne aeposits were ariitsea ana sampiec by tne Bureau ot Mines in ty4Z ana iy45. Tne Geoiogicai Survey in 1942 stualea molybdaenite deposits in Glacier Bay ana started a syste- matic investigation or tne 1lron-copper aeposits ofr Prince ot Waies Istand. The molypdenite aeposits and some oi tne bron-copper aeposits were tater arlited and sampieda by tne Bureau ot Mines. Some ot tne zine ageposlts of soutneastern Alaska and an antimony aeposit on the CleveLana Penisula were investigatea py tne Geotogicai Survey in iy4é, and 4 starv was made on a stuay of the copper—paiiaadium deposit atv tne Sait Chuck mine. In 1y45 tne Geotogicas Survey continuea its studies of tne iron copper deposits oi Prince ot Waites Isiana ana compLetea its project av tne Sait Chuck wine. Tne gine investigations were expanded in 1943 In addition some ultrabasic rocks were explored for nickel, chro- mium, and refractory grade olivine, and two molybdenite deposits were examined, In 1944 the Survey continued its investigations or tne lron-copper ana zinc aeposits. Tne resuits of mucn o1 tne Geotogicas Survey work outsinea above nave appearea in puiietins or ln mimeograpnea reports. How- ever,some of Une stuaies, especiaiiy vrier exaulnatlons made Largeiy Ior planning purposes, nave nov nitnerto peen preparea itor pubic aistripbution. In this report are recoraea tor tne Iirst time tne re- sUuLUS OL many ot Unese investigations, Tne report inciudes iniormat1 gatnerea in 1939 through 1944 and contains descriptions of six coppe deposits or group of deposits; three goid aeposits; ana one deposit ol eacn of tne Loitowing; Copper-Leaa, 1Leaa, parite, tungsten, iron, gypsum, asbestos, ana witneritve, Preiiminary report on tne Ketchikan mining aistraict, Alaska by Alfred H. Brooks USGS Professional Paper No. 1 Washington 1902 ABSTRACT: The Ketchikan mining district embraces an area of about 7,200 square miles in southeastern Alaska, and is the southern- most of the several recording districts into which southeastern Alaska has been divided, The district includes Prince of Wales, Revillagigedo, and many smaller islands as well as a part of the mainland, The international boundary marks its southern and east- ern limits. The north boundary of the district follows Sumner Strait, Clarence Strait, Ernest Sound, the Eastern Passage, and Bradfield Canal to its head, from which latter point it runs due east to the international boundary. To the west the district is bounded by the Pacific Ocean, and includes all of the small is- lands lying adjacent to Prince of Wales Island. A little less than a third of the area of the district is mainland, the rest being included in the islands. Prince of Wales Island is the largest of the islands, and Revillagigedo Island is second in size. From a topographic standpoint the Ketchikan district falls naturally into two subdivisions, one lying east and one lying west of Clarence Strait. The easterly portion embraces Gravina, Annette, Duke, and Revillagigedo islands and the adjacent portions of the mainland. The westerly portion includes Prince of Wales and the smaller adjacent islands. The easterly part of the district falls within the Coast Range province. This part of the Coast Range consists of a rather rugged mountain mass having no well-defined crest line. The highest peaks reach altitudes of 5,000 to 6,000 feet. Among the higher mountains are not uncommon, but they are insignificant in size compared with those in the northern part of the range. Prince of Wales Island is 140 miles in length and has an extreme width of about 40 miles. With its contiguous islands on the west it forms a distinct group, which has a rectangular out- line and is separated from the islands and mainland to the east by Clarence Strait. The Coast line of Prince of Wales Island is 22. 3 im broken by many deep embayments which run far inland. At a number of localities such embayments approach each other from opposite sides of the island and reduce its width to but a few miles. At many places broad valleys with very low divides connect these op- posing fiords. A depression of a few hundred feet would flood these divices and resolve Prince of Wales Island into an archi- pelago. The relief on the island varies from 1,500 to 3,600 feet. The shore line is generally abrupt and the mountains have very steep slopes. The larger valleys have the U-shaped cross sections typi- cal of glaciated regions. In the valley bottoms the streams have incised post-Glacial gorges. Lakes occupying rock-bound basins, which have been scooped out by glacial action, are found through- out the district. Of the drainage but few detaila are known, as the interior of the island is entirely unmapped. Generally speaking, the streams have east-west courses. The drainage system seems to be very irregular, the watershed being in some places near the eastern, in others near the western coast of the island. The mountains, the highest of which reach altitudes of about 3,500 feet, form no well- defined ridges, but, broadly speaking, have a northwest-southeast linear arrangement. The islands on the west side of Prince of Wales were not visited by the writer and but little information was ob- tained in regard to them. Their relief is probably less than that of Prince of Wales. The easterly province, in its relief and general topographic character, can not be properly separated from the Coast Range. Mi- nor ranges extend in a northwest-southeast direction through Gra- vina, Annette, and Duke Islands. The mountains of Revillagigedo Island and the mainland in general parallel the coast, and also the dominant structural lines, They are divided into many minor groups, within which there is no systematic arrangement or corres- pondence to rock structure. On these islands and on the Cleveland Penisula to the north the drainage follows northerly and southerly courses, parallel to the trend of the mountains. On the mainland to the east the principal water courses lie transverse to the axes of the ranges as a whole. The chief rivers empty into the heads of the fiords, whose directions are the continuation of their approxi- mately northeast-southwest courses. The Unuk River is the largest of these transverse streams. Only a part of its course has been map- ped, but its source must Lie near une eastern 1imit or tne Coast Range or witnin tune Platcau region veyona. In 1ts upper course iv is said to occupy a narrow, rock-floored valley, but about 20 miles from the coast it broadens out and is floored with gravel to its mouth at the head of Burroughs Bay. Twenty miles south of Burroughs em 3 uu Bay the Chickamin River enters Behm Canal from the east. It has a broad delta at its mouth, and for some miles up a wide, gravel- floored valley. Its source lies within the Coast Range among high mountains which give rise to a number of glaciers. The other main- land streams of the Ketchikan district are comparatively small and rise with in the Coast Range. The largest are those which are tri- butary to the head of Portland Canal. The oldest rocks of the district are crystalline limestones and phyllites, which occupy a large area on Prince of Wales Island and have been called the Wales series. They are believed to be of Silurian or pre-Silurian age. Succeeding these is a series of bluish limestones, calcareous schists, and black slates, which was found along the western part of Gravina Island. It has been named the Vallenar series, from its typical exposures on the bay of that same name. Fossil evidence goes to show that this series is, at part at least, of Middle Devonian age. The name Ketchikan series has been applied to a succession of argillites with some limestones and arenaceous beds which are found along the eastern margin of Gravina Island and along the western margin of Revillagigedo Island. These rocks are believed to be in part Paleozoic and in part Mesozoic. On the southern end of Gravina Island massive conglomerates were found unconformably overlying the Vallenar rocks. These have been termed the Gravina series, and are provisionally assigned to the Mesozoic. At Coal Bay, an arm of the Kasaan Bay, some lignite- bearing beds occur, which are believed to be Tertiary. Igneous rocks have a wide distribution in the region, granite being amorig the most abundant. The eastern part of the district is occupied by a broad, batholithic belt of granite, which is the prin- cipal constituent formation of the adjacent portion of the Coast Range. This is found cutting the Ketchikan series. At various lo- calities granite stocks werge found. Pegmatite is not uncommon in dikes, and syenite was found in one locality. Diorites are widely distributed as stocks , dikes, and sills. Gabbros and amphiboles also occur among the intrusives. Greenstone-schists are widely dis- tributed and are found associated with all the sedimentary beds ex- cept the Gravina series, They are made up chiefly of chlorite, with some actinolite, epidote, and other schists. Diabases are very com- mon, and belong to the latest intrusions in the region. Of the ef- fusive rocks, which are also well represented in the district, the most abundant is the porphyritic rock which has been termed the Kasaan greenstone. Its general character is that of an andesite, but it shows great local variations, and probably includes some intrusive rocks. A reconnaissance of the northwestern portion of Seward Penisula by Arthur J. Collier USGS Professional Paper No. 2 Washington 1902 ABSTRACT: Seward Penisula is an irregular land mass, comprising ap- proximately 20,000 square miles, and extending from the western coast of Alaska westward to within 60 miles of the Asiatic coast, from which it is separated by Bering Strait. It separates Bering Sea from the Arctic Ocean, and is itself cut off from the mass of the continent on the south by Norton Bay, a deep indentation of Bering Sea, and on the north by Kotzebue Sound, an inlet from the Arctic Ocean. Ammountain axis, represented in the Kigluaik and Ben- deleben ranges, divides the penisula naturally into a southern and northern part. This axis has an area of depression, partly occupied by the sea, on its northern side. The southern part of the penis- ula was investigated by the United States Geological Survey in the season of 1900, and is the subject of a report entitled Reconnai- ssances in the Cape Nome and Norton Bay Regions, Alaska, in 1900. The present report deals with the northwestern part of the penisula, comprising an area of approximately 5,000 square miles lying west of the one hundred and sixty-fourth meridian and north of Port Cla- rence and Imuruk Bay. Four subdivisions have been made of the sedimentary bed rocks of the northern portion of the Seward Penisula. The Kigluaik series is the oldest, and is made up of white crystalline limestones and mica-schists. Succeeding this, apparently conformably, is the Kuzi- trin series, made up of arenaceous and argillaceous sediments. These two series are identical with those described by Brooks. The Kuzi- trin series is overlain by the Nome series, probably unconformably, as suggested by Brooks. The Nome series has been here subdivided into two conformable grouns, the lower named the Port Clarence limestone and the upper called the Kugruk group. The Port Clarence limestone, which is blue and almost unaltered, was found to contain Lower Silurian fossils. The Kugruk group is made up of limestones and calcareous beds, with some argillites, which are locally consi- derably altered. The unconsolidated sediments which have been assign- ed to the Pleistocene include sands, gravels, and aluvium, and need no special mention here. Loe lee Three classes of igneous rocks have been recognized in the region and indicated on the map. The oldest are intrusives of va- rious types, which are usually schistose, and these have been grouped together under the field term greenstone. The granites form a second group, and probably represent Mesozoic intrusions. These two classes were recognized by Brooks, but the third, which comprises Pleistocene lavas was not represented in the region map- ped in 1901. In the northern part of the penisula the earliest crustal movements produced a series of folds whose axes run approximately north and south. This deformation probably took place in Paleozoic times, and was accompanied by extensive intrusions of greenstone. A later period of disturbance, probably during the Mesozoic, pro- duced folds whose axes are transverse to the earlier system. This was accompanied by the intrusion of some large masses of granite. Reconnaissance from Fort Hamlin to Kotzebue Sound, Alaska by Walter C. Mendenhall USGS Professional Paper No. 10 Washington 1902 ABSTRACT: The most important physical feature of that portion of Alaska lying north of the Yukon is a great mountain range extending from the Arctic Coast just north of Kotzebue Sound east and northeast to the international boundary in the region between the Porcupine River and the Arctic Ocean. To this range, whose central portion he could see from Lookout Mounvtain on the Middle Koyukuk, Lieutenant Allen, in 1885, applied the name Endicott Mountains. These moun- tains extend from the vicinity of the Mulgrave Hills east and north- east to Demarcation Point and the British Mountains in the vicinity of the international boundary. The mountains nave a north-soutn wiatn olf 5U or 4U miies. At their western ena tney are narrow and comparativeiy tow, reacning neignts or 3,000 or 4,000 treet, but near tne neaa or the Kowak, peaks reacn aitituaes or 6,000 feet, and in the vicinity of the Totsenbet River portage and eastward to the boundary 7,000 feet is not unusual. The mountain belt is broader, too, toward the east, where it may have a maximum nortn-soutn extension ot 100 miies. In Canadian territory 1t benas to tne south near tne Mackenzie River, and 1s conslaered a continuation or tne Canadian Rockies. Between this mountain peit ana tne Arctic Ocean tnere is a triangular area of relatively Low country, with Point Barrow forming 1ts northern angie. On 1ts coastward side tnils region 1s a true ebastal plain, and adjacent to the mountains it is a low, roiiing plateau Witn an elevation of between 1,uUuU and Z,UUU Leet above sea Level. Physicaily, tne peit of country Lying between the Endicott Mountains ana tne Yukon 18 much more diverse, as weit as more ex- tensive, tnan tnat to the north of the mountains. More or Less 1s0- iatea groups anda ranges reach in exceptional cases altitudes of over 5,000 feet. Generally, however, the ridges have altitudes be- tween 1,000 and 3,000 feet and are separated by river vaileys which here and there open out into broad flats, comparable, except in ex- tent , to the well-known basin of the Yuxon, whose center is in tne vicinity of tne mouth of tne Porcupine River. Tne most important streams rise, as 1s to be expected, in the Endicott Mountains, wnich iorm a generai divide between whe Arctic drainage proper ana wnat or tne Bering Sea and Kotzebue Sound. The dargest oI tnese rivers is tne Koyukuk. Tnis is about /UU milies in dength and, by 1ts numerous lmportvant northern tributaries, among which may be mentioned the Dietricn, Totsenpet, and Allen rivers, arains tne soutnern slopes of tne Endicott Mountains petween the meridians ot 149 and 154 degrees west Longitude. East or the one hundred ana tifty-fourth meridian the southern siopes are drained by une Chandalar and Porcupine rivers, ana west of the one nunarea and forvy-ninth meridian py the Kowak ana its branches. The Noatak River, rising near the one hundred and it1lity-i11lith meriaian, in a high mountain group, whose arainage is shared by the Kowak, Alashuk, Coiviitie, and Noatak, ILows west aiong the sixty-elgnth paraiiel to witnin 4U or 5U mites of the Arctic Coast, then turns south through tne range and empties into Kotzebue Sound near the entrance to Hothan Iniet. The position or the Colvilie on the north siope or the Endi- cott Range corresponds to that or the Koyukuk, opposite 1t, on the south siope, and its drainage basin 1s aimost as extensive. It enters the Arctic about midway between Point Barrow anda the international boundary. East or tne Coivilie the streams which reach the Arctic coast Within United States territory are smaii, Turner River, pernaps idu miies in Length, being tne Largest known, West of tne Colviite, how- ever, severai streams IrLow northward, tne Chipp, tne Meade, tne Otu- kan, ana the Pitmegea belng tne most 1lmportant. The writer nas groupea together a diverse compiex of oider rock whicn probabiy incluae partial equivaients ot Spurr's Birch Creek ana Fortymite series, and ot Brook's Nome, Kuzitrin and pernaps of his Kigiuailk rocks and which are round near tne base of the geologic column in tne region traversed. The rocks described here are regaraed as in a general way equivaient to tnose aescripea py tne writer ina previous paper as tne Metamorphic series, They present many oi the same characteristics and general ieatures, aitnougn exnipiting some- whab greater dlverslty iltnotogicaiity. This 1s to be expectea as a much more extenaed area nas peen stualea this season tnan in iyuu. Tne grouping oi these rocks 1n the present report 1s aetermined by tne same conditions observed in the Seward PenisuLa in 1yvUu; name- iy, a generai ana considerabie, aithougn varying, metamorpnisu, wnhicn affects ait tne rock types, nowever diverse, ana gives a ciear pbasks for the separation of the group from younger unaltered or but little altered sediments and lavas which are found at widely separated point in the field. Overlying portions of the Metamorphic complex are recent un- altered beds with basal conglomerates in some cases derived di- rectly from the schists, and containing no other material than that furnished by them. Some of these beds are of Tertiary age, as deter- by plant remains collected in them, and others are regarded on some- what less definite grounds as Cretaceous or at least Mesozoic. The members of tne Metamorphic compiex are, of course, older tnan wnese. In his section across tne Arctic Rockies, Mr. Schrader round Quartzltves ana pnyiiltes or Carbonirerous and iimestones ot Devonian and Silurian age. Tnese exnioit the errects ol mevamoronic action, ana probaviy are represented among the diverse beds inciudea nere, Messrs. Brooks ana Coitiler round iossiis or Devonian ana Siiuriar age 1m tne rocks oir tne Nome series or Seward Penisuia. In Lyuu tne Writer Iouna on Seward Penisuia rfossiis which are Lower Mesozoic or Carboniferous. These Sewara Penisula Rocks, as nas peen stated, are regarded as tune general equivaients ol tnose under consideration, because ol tnelr slmliarity 1n metamorphism ana in reLations to otner seaqiments ana 1tavas, Thus the eviaence at nana tends to tne conciusic that tne rocks here consiaerea are cnieity Paleozoic, probabiy rang- ang generaity through this era; vtney may an some iocaiities inciuae Lower Mesozoic beads. The mineral resources of the Mount Wrangell district, Alaska by Walter ©. Mendenhall and Frank C. Schrader USGS Professional Paper No. 15 Washington 1903 ABSTRACT: Southern area: This area lies in the foothills that form the southern flanks of the Wrangell Mountains. It is drained by the Cheshnina, the Kot- sina, and the Chitina and its tributaries. Since it is largely in the drainage basin of the latter stream itv is Irequenvtiy reLterrea to as tune Cnitina copper vei. Tne rock Lormatilons ol tne aistrict inciuae tne Nikotai green- svone, the Chitistone limestone, Triassic shales and limestones, the Kennicott formation, as well as intrusive gabbroic and dioritic masses. The copper deposits everywhere witnin tne Chitvina aistrict are closely associated witn tne doay of aiterea igneous rocks whicn nas peen aescrivea as tne Nikoiai greenstone. It 1s veilevea tnav une copper was originaity alssemlnatea ln minuve quantities tnrougnour Unis Lormation ana tnatv une vaiuadie aeposits now recognized are concentrations, in various Llorus, irom this originai wiaeiy aisse- minaved conartion. These concentrations have been made at different horizons, but the richer ore bodies seem generally to have formed near the contact with the overlying limestone, usually in the upper part of the greenstone, but in one or two notable instances in the limestone itself, a short distance above the contact. This contact is easily followed and has been recognized by prospectors as mark- ing an important economic horizon throughout the district. Northern area$ The northern copper area bears about the same relation to the north slope of the Wrangell Mountains that the southern area does to the south slope--that is , it forms an ill-defined belt extending approximately east and west through the foothills of the range. Four --- 2 --- large streams rise in glaciers that flow down from the Wrangell Mountains and cross this belt; they are the Copper, the Nabesna, the Chisana, and the White Rivers. Were it nob for the fact that much of economic value has been expected from that part of the upper Copper River Valley lying on the north slope’‘of the Wrangell Mountains, it would not be referred to in this report. From the meager and indefinite accounts that could be obtained of the region, it had been somewhat widely suppo- sed that the copper-bearing rocks and consequently copper ores would be found to occur here as on the Chitina side of the mountains. The past season's work (1902), however has shown that the Wrangell por- tion of the upper Copper River Valley consists of a waste of ande- sitic and basaltic lavas. These lavas, which in general lie nearly horizonal or dip gently northward, consist of innumerable sheets or flows superposed one upon the other. They are varicolored and all apparently much younger than the copper-bearing Nikolai greenstone, of which no exposures were seen, nor do the moraine gravels brought down by the glaciers denote the occurrence of this rock in any con- siderable quantity in the unvisited portions of the mountains above snow line. A reconnaissance in northern Alaska by Frank Charles Schrader USGS Professional Paper No. 20 Washington 1904 ABSTRACT: Geographically the region consists of three well-marked pro- vinces--the mountain or middle, the Koyukuk or southern, and the Arctic slope or northern. Orographically the mountain range, forming the middle province, is regarded as a northwestern continuation of the Rocky Mountain system of the United States, which, extending northwestward through Canada nearly to the Arctic Ocean, bends abruptly to the west be- yond the Arctic Circle and trends nearly westward across northern Alaska, forming the great trans-Alaskan watershed between the Yukon Basin on the south and the Arctic Ocean on the north. In its north- ward and finally westward course the range forms a prominent feature of the "concentric" orography of Alaska, and embraces in its south- ward-facing curve the great basin of the Yukon and the well-known, but not always well-defined, Yukon Plateau. From its character and relation to the range, it seems probable that the gently rolling plain bordering the mountains on the north and sloping gently to the Arctic Ocean may be physiographically cor- related with the Great Plains in western United States, while the _basin of the Yukon-corresponds to the great Interior Basin of the West, lying between the Rocky Mountains and the Coast Range. In their trend across Alaska the mountains agree with those in the Canadian territory adjacent to the east, which extend nearly to Mackenzie River. In the region north of the mountains, both in Can- ada and in Alaska, the valleys trend northward toward the Arctic coast, while those on the south trend southwestward toward the Yukon. Considering the country more in detail, we may note that the line of profile extending through the region as a whole, in a north- south direction, beginning on the south, at the sixty-sixth parallel, traverses for the first 120 miles of its course an undulating country whose low, rounded hills attain elevations of from 1,000 to 3,000 feet. It then crosses a rugged range of mountains 100 miles wide and about 6,000 feet high, whence it descends steeply to the elevation of 2,500 feet at the inland edge of a gently sloping plateau or rol- --- 2 --- ling plains country stretching to the northward. It then traverses this rolling plain for 80 miles, and thence passes for about 80 miles through a nearly flat, tundra country or coastal plain to the Arctic Coast. Table of geologic formations. Sedimentary rocks. Pleistocene .eeveeeccccccccccceecvesees Recent stream gravels, dune Tertiary (Colville series) Mesozoic Paleozoic sands, mud flats, silts, beach gravels, Gubik sand, ground ice, and glacial drift. Pliocene ......... Nearly horizonally stratified, fine-grained calcareous silts. Oligocene ........ Sand, clay, shale soft sand- stone and limestone with lig- nites, hard ferruginous sand- stone, and conglomerate, Upper Cretaceous Soft sandstone, limestone, (Nanushuk series). shale, and coal. Cretaceous (?) (Bergman series)... Sandstone, slate, grit, con- glomerate, and coal. Lower Cretaceous Impure limestone, sandstone, (Koyukuk series). slate, and associated igneous rocks. Lower Cretaceous © Principally impure sandstone (Anaktuvuk series) or arkose, with some conglo- merate or grit. Jura-Cretaceous Sandstone, impure limestone, (Corwin series) shale, and bituminous coal. Lower Carboniferous Phyllites, slate, limestone, (Fickett series) sandstone, quartzite, grit, and conglomerate. Devonian (Lisburne Limestone and shale. formation). Silurian (probably)Mica-schists and quartz-mica- (Totsen series). schists. Upper Silurian Schistose and micaceous lime- (Skajit formation). stone. Pre-Devonian (pro- Conglomerate, quartzite, bably(Stuver series) slate, and shale. Geology of the central Copper River region, Alaska by Walter C. Mendenhall USGS Professional Paper No. 4l Washington 1905 ABSTRACT: The earliest rocks recognized in the central Copper River re- gion are the Tanana and Dadina schists, which include both sedi- mentary and igneous members, and are regarded tentatively as pre- Silurian. The Silurian system may be represented in the conglome- rates, arkoses, shales, and schists of the Valdez formation. These rocks constitute the chieZ part of the Chugach Range. Sediments and volcanics, which are supposed to be Carboniferous or Devonian, are found in the northern edge of the Cooper basin. They are somewhat altered, but the alteration is not comparable in intensity with that affecting the older rocks, although greater than that observed in those of later age, The upper Carboniferous is probably represent- ed in the geologic column by the Nikolai greenstone, a series of flows of basic lavas. These seem to close a period of Paleozoic land or shoal-water conditions, which gave way in the Permian to wide- spread marine influences that continued well into the Triassic. This marine deposition was closed by a period of folding and general ero- sion, followed in Jura-Cretaceous time by the deposition of coarse materials. Another period of folding and erosion ensued, and when, in the upper Eocene, sedimentation was resumed it was of the fresh- water type, probably in isolated or nearly isolated water bodies of limited extent. The principal post-Eocene events have been the uplift of the mountain ranges, the outpouring of the Wrangell lavas, and the ac- cumulation of the Pleistocene silts, sands, and gravels. NOTES: The Paper includes a section on economic geology originally published in Professional Paper No. 15. The Geography and Geology of Alaska by Alfred H. Brooks USGS Professional Paper No. 45 Washington 1906 ABSTRACT: Geography: The broad cordillera which stretches northwestward through the western United States traverses western Canada, and extends into Alaska, where it swings west and southwest parallel to the great bend in the shore line of the northern Pacific. This cres-— centic sweep has a wide import, for in Alaska the trend of the cordillera maintained from Mexico for 3,000 miles to the north- west changes its direction and turns to meet the northeastern ex- tension of the Asiatic continent, and, as this feature is repeated in the bedrock terranes, it can be said to mark the change from Americah to Asiatic structure. The extension of the structural and physiographic provinces of Alaska are to be sought in Siberia to the west of Bering Sea and Strait. This cordillera is outlined by two mountainous zones separa- ted by a broad upland of relatively low relief, called the Central Plateau region. The southern highland belt--the Pacific Mountain system--is a rugged mass 100 to 200 miles wide, which in many places rises almost sheer from the waters of the Pacific, while inland it often descends with almost equal abruptness to the upland region. The northern highlands, a northwestern extension of the Rocky Moun- tain system, are of lesser relief, though they also form a rugged mass 100 to 200 miles in width. Their inland slopes appear to merge with the highlands of the central upland region, but on the north they fall off abruptly to the fourth province--the Arctic Slope regic The coasts of northern and southern Alaska are in striking contrast. Innumerable waterways and islands break the shores of the Pacific, and the land ascent is usually steep from tide water, while seaward the descent to deep water is equally abrupt. On the other hand, the shores of Bering Sea and the Arctic Ocean are even, the land slopes up gently inland, and the sea is shoal for a long dis- tance from the coast. --- 2 --- The Pacific Mountain system of Alaska trends northwesterly to about the one hundred and forty-ninth meridian, where it makes an almost right-angled bend, continues southwest, but with decreased relief, to Bering Sea. The system comprises four dominant ranges-- the Coast, St. Elias, Alaska, and Aleutian--together with some les- ser highland masses and two areas of low relief, the Copper River Plateau and the Susitna Valley. The Central Plateau region is very different from the border- ing mountains, for here bold ranges and sharp peaks give way to a much dissected rolling upland with flat-topped, interstream areas having a general accord of summit level. These mark the surface of a dissected plateau, which has given to this province its name. In its narrowest part, near the one hundred and fifty-second meridian, the plateau province has a width of but 200 miles, but broadens out both to the southwest, where it presents a frontage to Bering Sea of nearly 500 miles, and to the southeast in Canada, where it widens to 300 or 400 miles, The altitude of the plateau remnants, varying from 1,500 to 6,000 feet, is greatest along the margin, and its surface also shows a general incline to the north and west. Several broad lowlands lie within the plateau region, and near Bering Sea it gives way to a wide coastal plain. The Rocky Mountain system of Alaska, called the Endicott Moun- tains by Schrader, is formed of several high ranges which stretch from the international boundary westward to the Arctic Ocean, and constitute the divide between the polar and Bering Sea waters. These ranges are little explored, but near the boundary probably reach altitudes of 5,000 to 8,000 feet, while to the west they decrease in height and near the Arctic appear to be separated into a number of minor ranges by broad valleys. On the north the Rocky Mountains fall off abruptly to the Arc- tic Slope region, which is of relatively low relief and divisible into two subprovinces, the Anaktuvuk Plateau and the Coastal Plain. The Anaktuvuk Plateau has an altitude of 2,500 feet at the base of the mountains and slopes gently for 60 miles to the north to a scarp which marks the beginning of the Coastal Plain. The drainage of Alaska flows southerly to the Pacific Ocean, westerly to Bering Sea, and northerly and westerly into the Arctic Ocean. Several trunk streams, such as the Stikine, Taku, Chilkat, and Alsek rivers, which rise in broad, open valleys within the Cen- tral Plateau region and then traverse the coastal ranges by steep- walled canyons, drain the southern part of the Pacific Mountain sys- tem. A broad depression lying within the Pacific Mountains is drain- ed by another group of rivers, including the Copper, Matanuska, and Susitna. fo! 3 \o42 The Central Plateau region sends nearly all its waters to Bering Sea through the Yukon, the master stream, but the Kusko- kwim also drains a part of this province. These and their many large tributaries usually occupy broad valleys, with gently slop- ing walls, sometimes opening out into large lowland basins. The waters of the southern slope of the Rocky Mountain system go to tributaries of the Yukon, while those of the northern slope flow into the Arctic Ocean through north-south valleys which tra- verse the Arctic Slope region. The western drainage of these mount- ains goes to the Arctic through the Noatak and Kobuk valleys. Geology: As the physiographic provinces of Alaska are continuations of those of the western United States and Canada, and as they are in a measure but an expression of the bed-rock geology, it would be inferred that the same general horizons which form the cordillera of western United States and Canada extend into Alaska. Such has been found to be the case. The trend of the structure is northwest, parallel to shore line and the mountain ranges. It is thus northwest-southeast in south- eastern Alaska, and then southwest-northeast. The parallelism of the structural features of the Paleozoic and older rocks makes it evident that this marked change in direction of the axes has domina- ted the deformation of this province since very early geologic time. Dawson has stated that there is a marked continuity and litho- logic uniformity along the strike of the various terranes in this cordilleran belt, and as to a certain extent this holds true in Ala- ska, it is possible to delineate on the map some of the larger geo- logic features throughout the entire province. Several areas of gneissoid rocks, including gneisses, mica- schists, and igneous intrusives, with probably some altered sedi- ments, are provisionally referred to the Archean, though their pre- Cambrian age is open to question. The sedimentary rocks have been divided into four groups, in the oldest of which are placed the beds which have been more of less metamorphosed, and which are probably, for the most part, Paleozoic, though it is known to include some Triassic. All the rocks of this division, which embraces a number of unconformable series, were closely folded and considerably altered before the deposition of the second group which embraces the higher terranes of the Mesozoic and Cee are chiefly Cretaceous, though it includes some Jurassic. The beds of this second group have also been subjected to stresses and are closely folded, but not to anything like the extent of the underlyin; metamorphic terranes. Beds of Tertiary age, probably chiefly Eocene, form the third of these large subdivisions but in most cases to a much less extent than the Mesozoic. The Pleistocene unconsolidated gravels, sands, and silts are the highest of the groups and also the best defined. The igneous rocks fall into two groups, the intrusives and extrusives. The extrusives are especially abundant in the southern part of the field and decrease to the north, though evidences of recent volcanic activity are far from being absent in Alaska. The igneous complex of the Coast Range is the only extensive area of intrusive rocks in the field. Intrusive rocks are, however, very common throughout the province, especially in the areas of meta- morphic terranes. In general the rocks are distributed as follows: A belt of metamorphic sediments, ehiefly Paleozoic, but with some Triassic, skirts the shore of the Pacific and is the bedrock of the islands of British Columbia and of southeastern Alaska, as well as part of the mainland. This is bounded on the east by the great zone of Coast Range intrusives. East of the Coast Range is a second belt of meta- morphic terranes, probably Chiefly Paleozoic, of irregular form, about 300 miles in width and stretching from Washington to the north- west into Alaska, a distance of 1,000 miles, and occupying in a gene- ral way the intermontane belt between the Rocky Mountains on the east and the Pacific Mountains on the west. This zone is interrupted by a number of elongated gneissic areas (Archean?), which have a roughly linear arrangement along a northwest-southeast axis, and by irregular belts of intrusives, of Mesozoic sediments, and of Ter- tiary lavas. A belt of Mesozoic sediments forms the eastern boundary of the metamorphic rocks south of the sixtieth parallel of latitude. These include not only the undisturbed Mesozoic beds which underlie the Tertiary of the Great Plains region to the east, but also some older terranes of this system, which, infolded with Paleozoic sedi- ments, make up the Rocky Mountains. Tracing these groups northward, it is found that the western belt of metamorphics skirts the coast line, and following the bend at Prince William Sound, is continued in the Kenai Penisula. The Coast Range complex is extended to the north by a series of intru- sives along the axis of the Alaska Range. The interior belt of meta- morphic sediments broadens into a fan-shaped area in Alaska, but is interrupted near Bering Sea by extensive areas of Mesozoic rocks. The eastern belt of Mesozoic and Tertiary rocks of British Cdumbia finds its couterpart in the rocks of similar age in the Arctic Slope region. The Yakutat Bay region, Alaska by Ralph S. Tarr USGS Professional Paper No. 64 Washington 1909 ABSTRACT: Part I. Physiography and glacial geology Chapter I. General physiography Chapter II. Previous explorations Chapter III. General physiographic history Chapter IV. Existing valley glaciers. Turner Glacier Haenke Glacier Hubbard Glacier Variegated Glacier Orange Glacier Nunatak Glacier Cascading Glacier Hidden Glacier Fallen Glacier Black Glacier Galiano Glacier Atrevida Glacier Lucia Glacier Chapter V. Malaspina Glacier General description Haydeh Glacier Marvine Glacier Blossom Island region Chapter VI. Advance of the glaciers sate |2)- once Chapter VII. Morainic deposits of formerly expanded glaciers Chapter VIII. Glacial erosion Chapter IX. Gravel deposits Chapter X. Distribution of plants and animals Part II. Areal geology The problem of the stratigraphy of the Yakutat Bay region was found to be a most difficult one. The rocks are mostly barren of fossils, and except in the youngest beds none were found that promised to throw definite light on their age. This rendered it difficult to fix upon beds which could be used as a datum plane in determining the order of succession or the thickness of the strata. Moreover, the region has been subjected to profound dis- turbance, including both folding and faulting. Many of the faults are thrust faults, and many of the folds are overturned. This dis- turbance of the layers is on both a large and a small scale, in- troducing an extraordinary degree of complexity in the region. Scores of faults and small folds could be seen in a single small outcrop. Under these conditions it was utterly impossible to hope to work out with definiteness an order of succession of strata in the limited time at our diposal. The strata throughout most of the region are an assemblage of sedimentary beds beds complexly folded and faulted, but ordi- narily not notably metamorphosed. These beds are included under the term Yakutat group; they are very barren of fossils, but there are reasons for assigning them tentatively to Mesozoic age, as is shown in a later section. The Yakutat beds consist in the main of a peculiar graywacke, in part, at least, a tuff; very fragile and fissile black shale; and rapidly alternating thin-bedded black shale and sandstone. There is also a blue limestone in one or two places; and there are two different kinds of conglomerate, one a massive conglomerate of normal kind, though often including large boulders, the other a conglomerate whose matrix is black shale and whose peb- bles are often boulders of very large size. This we have called a black conglomeratic argillite. It appears to be the basal member of the Yakutat group. ao — 3 2oae The beds of the Yakutat group form practically the entire penisula, the mountains west of Disenchantment Bay as far at least as Blossom Island, and the mountains east of the South Arm of Russell Fiord south of the Hidden Glacier. The only excep- tions discovered are the basement crystalline rocks, mentioned in the next paragraph, and some basic dikes. The basement crystalline rocks appear at several points along the coast, and also were found in the interior of the penisula. So far as could be seen, the black conglomeratic argillite rests on these crystalline rocks unconformably, but in a complex relation, evidently due to faulting and folding. Both large and small frag- ments of the crystalline rocks are included in the black argillite. The basement rocks are mainly greenstone and white crystalline mar- ble; but there are also quartz diorite and granodiorite, besides other rock phases. These rocks were found over so wide an area that it is believed they form the platform on which the strata of the Yakutat group were deposited, A fault separates the Yakutat group from a complex of meta- morphic and crystalline rocks. This fault was definitely located on the southern shore of Nunatak Fiord, and its extension, as plottec on the map, would carry it to Hidden Glacier and down the Northwest Arm of Russell Fiord. On one side of this fault line the Yakutat group and the greenstone-limestone series only were found; on the other, crystalline rocks only, and no beds like those found south of the fault line. The metamorphic and crystalline rocks include clay slates with cleavage parallel to the bedding, gneissoid conglomerates, a great variety of gneiss and schist, and intrusive granites, both in dikes and in large masses. The slate outcrops along the entire northeastern shore of the Northwest Arm or Russell Fiord, and also in smaller area on Nunatak Fiord and in the Hidden Glacier valley. Back of the slates are gneisses, schists, and granites, which also form the main rocks on the two sides of Nunatak Fiord; but here on both sides, gneissoid conglomerate was found. These beds of metamorphic and crystalline rock are tentatively assigned to the Paleozoic era; they are certainly older than the Ya- kutat group. In all probability, too, they include beds of more than one age. It seems reasonably certain, for instance, that the clay slates and gneissoid conglomerates are younger than the gneisses and schists. By far the greater part of the region is made up of rocks of these kinds. In one place, however, along and near Esker Stream, on the west side of Yakutat Bay, near Bancas Point, rocks of Tertiary age were found. These, which are probably Pliocene in age, consist of cross-—bedded sandstones, clays, shales, and lignitic beds. They are far less disturbed than the strata of the Yakutat group, from which they are apparently separated by a fault. In these beds a fairly good flora was found. The Tertiary strata outcrop in but a small area, evidently extending westward under Atrevida Glacier. The earthquakes at Yakutat Bay, Alaska in September, 1899 by Ralph S. Tarr and Lawrence Martin USGS Professional Paper No. 69 Washington 1912 ABSTRACT: Chapter I. Introduction Chapter II. Changes in shore lines in 1899 Chapter III. Faulting Chapter IV. Surficial effects of the shock Chapter V. Observations of the earthquake Chapter VI. Earthquakes before and since September, 1899 Chapter VII. Instrumental records of the earthquake Chapter VIII. Magnitude of Yakutat Bay earthquakes of September, 1899. Summary: During the month of September, 1699, the region near Yakutat Bay, Alaska, was shaken by a series of severe earthquakes--so se- vere, indeed, that it seems probable that in the minds of geologists the name Yakutat will always be associated with these earthquakes rather than with the grand glaciers, fiords, mountain scenery, or any other features of the bay. The cause of these shocks was undoubt edly the renewal of growth in the St. Elias Range, one of the young- est and loftiest of mountain ranges. --- 2 --- These earthquakes were attended by two notable results-- great changes in the level of the land, incidental to faulting, and remarkable accompanying and subsequent changes in the adjac- ent glaciers. The changes in level are the greatest recorded in historical times, the maximum uplift amounting to over 47 feet. The changes in the glaciers include a rapid retreat of Muir Gla- cier, 150 miles to the southeast, and a general advance of several glaciers near Yakutat Bay. By 1903 Muir Glacier had retreated from 23 to 3 miles, and by 1907 from 74 to 8 miles, perhaps in part as an indirect result of this earthquake, and had lost much of its scenic interest. The advance of the glaciers near Yakutat Bay in- cluded the eastern or Marvine lobe of the great Malaspina Glacier and rendered that highway of glacier travel inaccessible through intricate crevassing. These and other effects have been discussed in detail in this paper following a brief topographic and geologic of the region itself. The Mount McKinley region, Alaska by Alfred H. Brooks USGS Professional Paper No. 70 Washington 1911 ABSTRACT: Geography: The Pacific margin of the North American continent is mark- ed by a broad mountainous belt which extends northwestward from Mexico through the United States and Canada into Alaska as far as the one hundred and iiftieth meridian, where, paralleling the coast line, it makes an abrupt bend to the southwest and continues toward Asia in the highlands of the Alaska Penisula and the Aleutian Is- lands. The western part of this cordillera, embracing many distinct ranges, together with transverse lines of considerable height and some areas of lesser relief, but in general forming a rugged moun- tainous belt 50 to 200 miles in width, has been called the Pacific mountain system. In Alaska this system is bounded on the inland side by the central plateau region, which may be broadly correlated with the plateau or great basin region of western Canada and the United States. The Pacific mountain system at the international boundary includes the great mass of snow-clad paaks and connecting ridges, about 80 miles in width and from 8,000 to over 19,000 feet in alt- itude, to which the name St. Elias Range has been given. To the northwest this highland mass widens and is divided by the Copper River and upper Tanana drainage systems into two divergent mountain ranges. The Nutzotin Mountains, 5,000 to 8,000 feet high, form the northern fork of the system and connect the St. Elias Mountains with Range, 8,000 to 20,000 feet in height. These ranges encircle the northern and western margins of the Copper and Susitna basins. The southern fork of the St. Elias system, extending westward, is formed by the Chugach Mountains, 6,000 to &,000 feet high, and their exten- sion, the Kenai Mountains, 5,000 to 6,000 feet high, and these ranges together constitute the rugged coastal barrier stretching from St. Elias to Cook Inlet. --- 2 --- Two rugged mountain masses lie within the reentrant formed by the two forks of the St. Elias Range. One, on the east--a group of irregularly distributed snow-covered volcanic peaks &,000 to 16,000 feet in altitude, called the Wrangell Mountains--is between Chitina River on the south and Copper River on the north. The other range, on the west, called the Talkeetna Mountains, is a roughly circular area of high relief, 5,000 to 8,600 feet in height, lying in the region tributary to Cook Inlet. The axes of all these ranges have the northwesterly trend characteristic of the Pacific mountain system of Canada and the United States about as far west as the one hundredth and forty- eighth meridian, then bend sharply to the southwest to meet the northeasterly extension of the Asiatic continent. In other words, these axes are in general parallel to the Pacific shore line, form- ing a crescentic curve around the Gulf of Alaska. The drainage of the ranges above described is carried for the most part southward to the Pacific Ocean. Among the larger rivers are the Copper, flowing directly into the Pacific, and the Susitna and Matanuska, tributary to Cook Inlet. A broad, flat, silt-covered area standing about 3,000 feet above sea level, called the Copper River plateau, lies between the westerly tributaries of the Copper and the headwaters of the Matanuska and Susitna. The northerly slopes of the Pacific ranges descend in most places abruptly to a gravel-floored plateau which, stretching around their margins, slopes gradually to the valley of the Kuskokwim on the west and to that of the Tanana on the north. Both these rivers meander through broad lowlands which, in turn, are delimited on the north and west by an abrupt rise of land marking the southern bound- ary of an upland. This upland, best described north of the Tanana Valley, is characterized by level, flat-topped interstream areas 2,000 to 3,000 feet in altitude, and forms part of the central pla- teau region. The Mount McKinley region lies,for the most part, in the Pacific mountain system, but also stretches northward into the cen- tral plateau region. It is roughly bounded by meridians 148 and 154 degrees west and parallels 61 degrees and 65 degrees 20' north and has an area of about 40,000 square miles. This report, however, deals more specially with the Alaska Range proper, and the detailed discu- ssion will be confined largely to the region, embracing about 10,000 square miles, lying between the Susitna basin on the south and the Kuskokwim and Tanana basins on the west and north. w~-- 3 --- Geology: What are believed to be the oldest rocks in this region are a series of closely folded schists and quartzites, with subor- dinate crystalline limestone masses and considerable igneous ma- terial, which stretch as a broad zone westward from the internationa boundary nearly to the Yukon below the big bend. These are mantled by the younger Paleozoic rocks. Within these metamorphic schists oc- cur many bodies of intrusive granites of at least two ages, The younger granites (to be discusses below) are shown on the map; the older, which are represented by gneisses and gneissoid granites, are not differentiated from the other metamorphic rocks. These rocks extend to the southwest in a narrow zone which which forms the east end of the Alaska Range and, continuing westwar¢ are found in a foothill belt north of the mountains, finally passing underneath the Quaternary deposits of the Kuskokwim lowlands. A second area of metamorphic rocks, probably equivalent in age to those described above, lies north of the Yukon. Both are provision- ally correlated with the pre-Ordovician quartzites and slates ex- posed along the Porcupine Valley near the international boundary. Another broad belt of closely folded metamorphic sediments skirts the Pacific seaboard and forms the southern boundary of the region. These comprise slates, phyllites, quartzites, conglomerates, and graywackes, and are considerably less altered than the metamor- phic rocks of the Yukon. This metamorphic belt includes some Meso- zoic, but most of the series is known to be pre-Jurassic and is pro- bably Paleozoic. Rocks of the same character occur in the upper Susitna basin, where they probably occupy a considerable area. The largest areas of Paleozoic rocks of the province occur in the Yukon basin, where Ordovician, Silurian, Devonian, and Car- boniferous formations have been recognized. It should be noted, however, that the data regarding the stratigraphy of the rocks be- low the Middle Devonian are very fragmentary. These older formations are much altered and are more closely folded than the Middle Devo- nian or later Paleozoic rocks. The Paleozoic strata above described lie north of the metamorphic belt, and another area, probably made up of the same terranes, bounds the metamorphic rocks on the south. The Paleozoic rocks exposed along the northwestern front of the Alaska Range are known to include Ordovician, Devonian, and probably some Silurian and Carboniferous strata, and are intensely folded and fadted. At the head of Copper River the Paleozoic is re- presented chiefly by Carbonigerous rocks. The Mesozoic strata are extensively developed in central Alaska. On the upper Yukon occur slates and quartzites of Lower Cretaceous age, and in the Rampart region are some small areas of Upper Cretaceous sandstones and shales. At the head of Copper River and in the adjacent areas Triassic and later Mesozoic rocks are extensively developed. These beds appear to form a broad belt caught up in the synclinorium which marks the structure-of the Nutzotin Mountains. The same formations are exposed on the south side of the Wrangell Mountains, whose structurecis probably syn- clinal. In the Matanuska basin and in the eastern part of the Susitna basin two Jurassic formations and one of Lower Cretaceous age have been found. Middle Jurassic beds also occur in the Alaska Range, where they occupy a broad synclinorium in the heart of the mountains. In the coastal region of Kenai Penisula and Prince Wil- liam Sound the Orca group, made up of slates and graywackes and provisionally referred to the Mesozoic, is extensively developed. The Tertiary deposits of central Alaska probably belong chiefly to the Kenai formation (upper Eocene) and are fresh-water beds, in large part of fluviatile origin. A series of such deposits occurring along the Yukon and in the Cook Inlet region is believed to mark the position of the Tertiary drainage. On Alaska Penisula some marine Eocene beds have been found. Though most of these Eo- cene deposits are only slightly deformed, some are intensely folded and faulted, In addition to these fresh-water Eocene beds, a closely folded series of Tertiary deposits occurs east of the Copper and near the Pacific coast which carries a marine fauna provisionally assigned to the Miocene. Rocks of Miocene age have also been found on the Alaska Penisula. Quaternary deposits occupy large areas in central Alaska, including preglacial, glacial and postglacial material. The most extensive are the silts, sands, and gravels deposited during the retreat of the ice sheet, and these are probably of Pleistocene age. Since their deposition they have been deeply dissected. In the Yukon basin there are some high gravels which may be Pleistocene or older. The Recent deposits comprise chiefly those of the present watercourses. The intrusive rocks shown on the map are chiefly granites, granodiorites, and diorites. For convenience of description they will be referred to here as granite. South of the Yukon basin they are distributed along two general axes. One of these passes through the central part of the Alaska Range and is continued southeastward by the granite stocks of the upper part of the Copper River basin. A further extension of this axis would carry it into the Coast Range intrusive belt of southeastern Alaska.A second axis is defined by the granites of the Iliamna Lake region, the Mount Susitna stock near the upper end of Cook Inlet, the batholith of the Talkeetna Mountains, and the stocks lying near the southern margin of the Cop- per River basin. A third axis may be defined by the granitic rocks which are intrusive in the metamorphic belt south of Fairbanks. The granites of the Alaska Range and the Talkeetna Mountains are in part er ee ie ns us Middle Jurassic, and it seems probable that the others repre- sent about the same epoch of intrusion. It should be noted, however, that granites cut the Upper Cretaceous rocks of the Rampart region and that there is no proof that the granites of the upper Copper basin are later than the upper Carboniferous. It is perhaps fair to assume that there was a general period of intrusion, beginning possibly in late Paleozoic time and in some parts of the province extending through to the Upper Cretaceous, but having its maximum devel»pment late in the Jurassic period. In the Yukon-Tanana region, as already stated, there are some gneissoid granites which belong to an older period of intrusion. The trend of the bedrock in this region is parallel to the Pacific Coast line and to the dominant mountain axes. In the western part of the province it is northeastward, then gradually bends to the east and finally to the southeast. In other words, the dominant strike lines mark a crescent opening toward the Pa- cific. The metamorphic sediments of the Chugach and Kenai moun- tains are closeiy folded and east of the Copper River are flanked on the seaward side by closely folded and intricately deformed Miocene beds. The scant evidence indicates that the structure of the coastal system of mountains is of a general synclinal character. North of these are the Mesozoic beds, thrown into braad, open folds, broken in the Talkeetna Mountains by a huge granite batholith, and in the Wrangelkl Mountains covered in part by thousands of feet of Tertiary and recent volcanic rocks. The structure of the Alaska Range is synclinal, accompanied by profound faulting in the western limb. Mesozoic formations are involved in this folding and also some Tertiary beds. A belt of metamorphic rocks lying south of and adjacent to the Tanana Valley probably marks another anticlinal axis. North of this valley lies the main zone of metamorphic rocks, which are closely folded byt are believed to have the structure of an anti- clinorium, and are bounded on the northwest by Paleozoic rocks. These Paleozoic strata are less intricately folded than the metamor- phic rocks. They comprise at least two unconformable series, the lower of which is more intricately folded than the upper. The Jurassic flora of Cape Lisburne, Alaska by F.H. Knowlton USGS Professional Paper 85 Shorter Contributions to General Geology 1913 ABSTRACT: The material considered in this paper was collected in .1904 by Arthur J. Collier, of the United States Geological Survey, while engaged in a study of the geology and coal resources of the Cape Lisburne region. The coal deposits are extensive and are the only mineral resources of the region known to be of com- mercial importance. Collier describes the locality as follows: "Cape Lisburne is the bold headland which marks the north- western extremity of a land mass projecting into the Arctic Ocean from the western coast of Alaska between latitudes 68 and 69 de- grees. It lies 160 miles north of the Arctic Circle, about 300 miles directly north of Nome, and is the only point in Alaska north of Bering Strait where hills above 1,000 feet in height approach the sea." So far as known, the rocks of the Cape Lisburne region are all sedimentary, with the following ages and approximate thick- nesses: Devonian (?), 2,000 feet; Lower Carboniferous (Mississi- ppian), 4,500 feet; Upper Jurassic, 15,000 feet; Lower Cretaceous (7), 10,000 feet; Pleistocene, 50 feet. Geology and ore deposits of Copper Mountain and Kasaan Penisula by Charles Will Wright USGS Professional Paper 87 Washington 1915 ABSTRACT: The geology of the Ketchikan district is bu. imperfectly known, for, except in the two areas to be described in detail below, observations have been confined almost entirely to the shore lines, and this limitation, together with the gaps in the information regarding continuity of formations and stratigraphic relations caused by. the many broad waterways, has prevented the exact dtermination of either stratigraphic sequence or structure. Hence the sedimentary rocks of the region, which range in age from Silurian to Jurassic or Cretaceous, will be described in only a general way, but as the knowledge of the igneous rocks is more exact and comprehensive, these will be described in greater detail. The geologic map shows that the intrusives of the Coast Range occupy a larger area than any other of the rocks units that have beer discriminated. The main batholiths of these intrusives occupy the eastern part of the district and form a convenient starting point for a geologic dsscription, though they by no means represent the oldest rocks of the district. Adjacent to these intrusives on the west and in part included within their area lies a series of cry- stalline schists which, though in places showing igneous phases, are for the most part sedimentary. The seaward and western boun- daries of these schists are marked by a belt of argillites--either slates or phyllites--in part interbedded, in part succeeded by an- cient lavas and tuffs that are here grouped together as greenstones. Some semicrystalline limestone bands occur in the slate and green- stone series, and as Carboniferous fossils have been found in these limestones the entire sequence has heretofore been referred to the Carboniferous period. This determination of the age of the se- ries accords with Spencer's provisional determination of the age of similar rocks that apparently represent a northern extension of the same belt.Knopf's recent studies north of Juneau have shown, Sls 1D) jee however, that these rocks are in part, at least, of Jurassic or Lower Cretaceous age. This series of slates, phyllites, schists, and greenstones may therefore be Mesozoic, though it may include some infolded Carboniferous limestones. On the map the sedimentary rocks adjacent to the Caast Range are not differentiated from the sedimentary rocks that lie farther west, most of which are older than those near the Coast Range. But few correlations have been made between the rocks of Prince of Wales and adjacent islands and those of the mainland belt described above. Igneous rocks like those found in the Coast Range occur as intrusives in this western province. Some of the sedimentary rocks here are also lithologically the same as some of those found farther east, and the likeness suggests certain correlations which can not yet be definitely established. The sedi- mentary rocks of Prince of Wales Island include slates, quartzites, arkoses, and conglomerates, and locally alarge amount of limestone. The fossils found in these rocks indicate the presence of strata ranging in age from Silurian to Carboniferous. The rocks of the island include also a serteés of volcanic deposits and another of graywackes and conglomerates, which on stratigraphic grounds have been assigned to the Mesozoic. The Paleozoic formations have not been differentiated on the geologic map which therefore indicates a sameness in the geology of Prince of Wales Island that is by no means in accord with the facts. The continuity along strike lines that is characteristic of the mainland does not prevail on Prince of Wales Island, where the rocks show close folding, which, with the presence of many large stocks of igneous rocks, has given great variety to the geology. The Tertiary period is represented in the district by one small area of conglomerate, sandstone, and shale; the Quaternary by many widely distributed basaltic lava flows, though none of any great areal extent. Of the igneous rocks the intrusives of the Coast Range, made up of granite, diorite, granodiorite, and peridotite, are most abun- dant and most widely distributed and are probably later intrusives. Copper Mountain area: The most striking geologic feature of the area is the ir- regular granitic intrusive mass that occupies its central part. From this mass spurs or dikes 300 to 600 feet wide diverge into the surrounding series of metamorphic schists and the interstra- tified beds of limestone. The schists are much wrinkled and sheared and include both calcareous and siliceous varieties, and the limeston is generally marmarized. The rocks nearer the intrusive contact are further altered to hornfels or amphibolite, which is usually banded with parallel beds containing much granite and diopside. The principal limestone belt extends from Copper Harbor north- westward into Jumbo Basin, and another belt occurs on Green Monster Mountain and Hetta Mountain. Narrow bands of schist are interstratified with these limestones, and in turn narrow beds of limestone are interstratified with the schists. Southwest of the main limestone belt on the west slope of Copper Mountain the limestone is overlain by a considerable thickness of altered siliceous schists, which lie conformably on the limestone and grade upward into a succession of amphibole and chlorite schists that are interstratified with quartzites and show no limestone. These chlorite and amphibole schists are interstratified with guartzites, slates, and here and there beds of a massive greenstone that probably represents an ancient lava. They border the east and west shores of Hetta Inlet and are the most recent bedded rocks in the area. Kasaan Penisula: The geology of Kasaan Penisula displays strikingly the pheno- mena of igneous intrusion and contact metamorphism. The geologic problems are numerous, but in this report it is possible to consider only the questions that directly bear on the occurrence of ore. The relations of the geology of the penisula to that of the Ketchikan mining district have been already described. The follow- ing discussion will be confined to the stratified rocks, which com- prise those of sedimentary and volcanic origin; the intrusive rocks, which apparently underlie the penisula and consist essentially of granitic and porphyritic rocks; and the ore deposits. The stratified rocks are of interest to the miner because they determine the character and composition of the ore bodies. The intrusive rocks are of even greater interest because they are believed to be the original sources of the ores. As the principal ore deposits are found at or near contacts between certain intrusive and stratified rocks, it is desirable to determine the particular intrusive or intruded rocks with which &he ore deposits are most commonly associated. Notes on the geology of Gravina Island, Alaska by Philip S. Smith USGS Professional Paper 95 Shorter Contributions to General Geology 1915 ABSTRACT: Gravina Island is in the extreme southern part of Alaska and is about 20 miles long and 10 miles wide, It lies about 30 miles north of the international boundary and is separated by a narrow channel from the town of Ketchikan, the southernmost port of call in Alaska. Ansopportunity of studying the coast exposures of this island was afforded the writer in the summer of 1913. This work, amplified by the earlier investigations of Brooks and the Wrights, showed the presence of Triassic rocks, which previously had been reported definitely at only one other locality in southeastern Alaska. Inasmuch as the structure and general relations of Gravina Island furnish an insight into the geology of this region, the fol- lowing notes are presented. Little of the island away from the seacoast has been studied, and therefore the geology of the interior is practically unknown. Both igneous and sedimentary rocks are represented in the re- gion. The sedimentary rocks range in character from thoroughly re- erystallized schists to unmetamorphosed conglomerates, sandstones, and limestones. The igneous rocks include both deep-seated intru- sives and lava flows.