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Home My WebLink AboutE-Scan Resistivity Survey Makusin Colcano 1984--LR Reduced from 1:24000 original plot,Scale of this plot:1:37500 (approx.) a r T r T T rT r T Y T 7 T g g g g g g g 4 a a q 0 ®R SECTION 10 SECTIONS CROSS:\°°|\°|>{°° e-1 sT-4 1000 . a e 8200”4 9 o 5 <@F7 "--- 500 .®3 s 3 HY e fe)o i a w 8 +4 "YY My n ( awl n l A "a o 'Oo o a ns 8 "i)Ra pe A 0 ©pw a °. 20 o 100 500 2000 fle,1000 MEAN |300 1000 LEVEL 50 7 ;500 ;Y 700 /°500SHoposte7ae3i .-1000 500 , -REPUBLIC GEOTHERMAL INC. f 7 UNALASKA GEOTHERMALiv500EXPLORATIONPROJECT q Porarus awa I Perenran wearer an" UNALASKA ISLAND,ALASKA JULY,AUGUST,1864 E-SCAN RESISTIVITY SUAVEY MAKUSHIN VOLCANO AREA INTERPRETED TRUE RESISTIVITY SECTION SECTION #{10 RESISTIVITIES:OHM-METERS PLOT SCALE UNITS:METERS ORIGINAL DWE SCALE:{:24000 LIMIT OF MODEL CONFIDENCE:..... PREMIER GEOPHYSICS INC. VANCOUVER,CANADA -.|ery ara Greer ee anran aa Fare ware -2000J A i +ee _ & Meteors water dhoride hot so ryNearneuteetptWater"/ Sw <+ GLACIER VALLEY 2X VERTICAL EXAGGERATION MAKUSHIN VALLEY Fumarole Field MemesAPPENDIX A Fluid Geochemistry Data Tables for Fumaroles and Hot Springs e a AlTable18,Chemical analyses of sulfate-carbonate spring waters in the Makushin geothermal area.” '(Values in mg/1 unless otherwise specified). Site Name Date 7 pu?Na K Ca Mg Li Sr HCO?S03 F Cc}siop B Fe TDS sc GV-Gdl 8-11-80 97 6.4 52 4.8 12 4.0 £0.01 0.1 37 125 0.1 10.0 94"<0.5 0.10 325 360 GV-Gd2 8-11-80 82 6.5 87 5.7 32 1 0.02 0.3 288 95 0.3 5.0 125 <0.5 0.01 504 580 GV-Gd3 7-05-81 78 4.3 62 5.2 25 8.0 0.01 0.2 3 218 <0.1 6.1 120 <0.5 nd 447 9250 GV-Ge 7-05-81 68 nd 61 3.3 260 9.6 0.04 1.1 nd 491 0.3 2.3 138 =6¢0.5 0.02 nd 1400 GV-GE 8-11-80 70 6.1 78 4.5 nd nd nd nd nd 42 nd 10.0 125 nd nd nd nd GV-Gf 7-05-81 79 6.4 81 4.8 210 7.8 0.03 Ll 256 476 0.2 7.5 142 <0.5 0.21 1050 1200 'GV-Gh 7-11-82 61 6.0 64 3.8 240 1]0.03 1.2 358 472,¢1.0 5.8 445 <0.5 0.40 1120 1320 GV-Gj 7-10-82 41 6.1 53 3.4 280 il 0.03 1.4 332 581 <1.0 6.6 120)=<0.5 0.70 1220 1430 GV-G1L 7-13-82 62 6.0 63 4.5 260 10 0.03 1.2 325 542 <1.0 6.6 135 <¢0.5 0.50 1190 1370 MV-Ma 7-17-82 84 6.0 54 9.0 65 13 0.02 0.3 nd 344 <1.0 nd 155 ¢90.5 2.5 nd nd MV-Mb 8-13-80 87 5.5 28 5.9 67 12 0.01 0.3 191 155 0.1 5.0 140 nd 0.09 508 600 MV-Mc 7-04-81 58 5.3 24 3.2 23 5.5 0.01 0.1 nd 25 0.1 7.8 88 0.5 0.07 nd 250 MV-Mc 7-18-82 55 6.8 32 4.3 34 6.1 <0.01 Ost 201 15 1.0 7.9 105 ¢0.5 0.10 305 351 MV-Md 8-13-80 67 5.3 14 3.4 23 8.0 0.01 0.1 116 21 0.1 5.0 88 nd 0.03 220 255 NY-Na 8-20-83 23 6.1 88 4.2 390 36 0.14 3.1 678 710 0.7 5.6 110 ¢0.5 nd 1680 nd GV =Glacter Valley,MV =Makushin Valley,NV =Nateekin Valley § a)Alaska Division of Geological and Geophysical Surveys,Fairbanks,Alaska,M.A.Moorman,analyst. b)Determined in the field. Av Table 19.Chemical analyses of chloride spring waters in the Makushin geothermal area.” .Values in mg/l unless otherwise specified). b b Cations :b Anions « Site Name Date T pt _Na K Ca Mg Li Sr _eof”ssohy oF C)siqj]B Fe TDS sc DV -stream 8-21-83 14 6.9 36 3 8.8 2 0.15 ¢0.7 35”bond 56 43.6 0.7 nd 175 nd GV -Gm 7-20-82 39 5.9 180 19 200.0 15 0.48 1.1 463 360 ¢€1.0 160 113 4.2 1.7 1290 1380 Gav -Gn 7-20-82 27 5.8 180 19 180.9 23 0.40 41.0 563 320 <¢1.0 140 119 4.0 1.9 1260 1760 GV -Gp 7-20-82 40 6.3 300 31 160.0 39 0.66 1.4 590 180 <1!.0 380 104 9.9 2.1 1500 nd DV =Driftwood Valley,GV =Glacier Valley a)Alaska Division of Geological and Geophysical Surveys,Fairbanks,Alaska,M.A.Moorman,analyst. b)Determined in the field. Table 20.Chemical analyses of cold waters in the Makushin geothermal area.°(Values in mg/l unless otherwise specified) b b Cations b AnionsSitenameDateTph__Na K Ca Mg Li Sr ucof sof F Cci_siBr siod,B As Fe TDS SC DV -stream 8-21-83 14 6.9 36 3.4 8.8 2.0 0.15 <o.1 35 6"nd 56 nd 43.6 0.7 0.10 nd 175 nd Gd spring 7-05-81 5 od 4.7 0.8 8.9 1.90.01 40.1 nd 29 ¢€0.1 5.6 nd 20.0 <0.5 nd nd nd 100 -Gd stream 8-11-80 7 6.0 78 "4.5 nd 0.1 O.Ot nd nd 418 nd 10 nd 125.0 nd nd nd nd nd -Gk spring 7-15-82 16 6.6 4.1 0.3 20 1.1¢0.0L 0.1 38 27 41.0 5.9 nd 9.4 <0.5 nd 0.10 88 141 -Gl stream 7-18-82 5 6.5 8.5 1.4 52 6.6 ¢0.01 O.L 13 150 (1.0 12 nd 28.0 <0.5 nd 0.40 264 375 -Gn spring 7-09-83 6 .6.4 5.6 0.2 6.4 1.0 ¢0.01 0.2 26 4 nd 5.5 nd 6.0 0.10 06.002 nd 42 nd -clear river month 7-19-83 7 6.4 7.5 0.5 53 1.8 0.01 <0.)37 14 «nd 8.8 nd 14,2 0.02 0.001 nd 117 nd -kettle pond 8-19-84 nd nod 1.9 0.1 0.5 0.3 0.01 <0.1 nd 1 nd 2.0 O.1 3.0 0.04 ¢90.001 nds nd nd -muddy river mouth 7-19-83 5 6.5 6.3 0.7 12 2.2 0.01 o.t lt 36-So nd 7.0 nd 12.0 0.16 0.001 nd 82 nd -spring 7-19-82 6 6.6 2.6 0.2 1.8 0.6<¢0.01 <0.1,11 3 ¢1.0 3.7 nd 13.0 <0.5 nd 0.1 325 34 =Driftwood Valley,GV =Glacier Valley,MV =Makushin Valley Alaska Division of Geological and Geophysical Surveys,Fairbanks,M.A.Moorman,analyst. Determined in the field. ieTable21.Stable isotope analyses of sulfate-carbonate spring waters in the Makushin geothermal area.c-coteact Cole mm 2 Site Name Date Tes D/H £01440" GV -Ga 7+05-81 nd -83 -11.9 GV -'Gb 7-05-81 nd -80 -12.2 GV -Ge 7-05-81 nd -83 -12.5 GV -Gdl 8-11-80 97 -70 -8.9 GV -Gd2 8-11-80 82 -80 11.6 GV -Gd3 7-05-81 78 -83 11.9 GV -Ge 7-05-81 68 80 -12.2 GV -Gf 7-05-81 79 -83 -12.5 GV -Gh 7-11-82 61 -82 -11.7 GV -Gj 7-10-82 41 -79 -11.0 GV -Gl 7-13-82 62 -83 -11.9 MV -Ma 7-17-82 84 -77 -ll.1 MV -Mb 7-04-81 nd -81 -12.4 MV =Mb 8-13-80 87 -78 -11.9 MV -Mc 7-04-81 58 -81 -12.4 MV -Mc 7-18-82 55 84 -11.7 MV =-Md 8-13-80 67 -81 -12.1 NV -Na 8-20-83 23 -78 -11.3 GV- MV = NV - Glacier Valley Makushin Valley Nateekin Valley a)Analyzed at Stable Isotope Laboratory,Southern Methodist U.,Dallas,Texas. b)Values are in permil with respect to SMOW. Table 22.Stable isotope analyses of chloride spring waters in the Makushin geothermal area. Site Name Date T°p/H?A$o Aho" DV -stream 8-21-83 14 -76 -9.9 GV -Gm 7-20-82 39 80 -1ll.1 GV -Gn 7-20-82 27 82 -li.l GV -Gp 7-20-82 40 -78 -10.9 GV -Gp 7-16-83 44 -80 -11.2 DV -Driftwood Valley GV -Glacier Valley a)Analyzed at State Isotope Laboratory,Southern Methodist U.,Dallas,Texas. b)Values are in permil with respect to SMOW.i a fb Table 23.Stable isotope analyses of cold waters in the Makushin geothermal area. Site Name Date TC p/H $6 AMO DV -stream 8-21-83 14 -76 -9.9 FF 1 -stream 7-18-83 nd -81 -11.2 FF 3 -stream 7-11-83 nd -89 -13.5 FF 6 -snow 7-18-82 nd =-121 -15.9 FF 7 -snow melt 8-20-83 nd -88 -12.7 FF 9 =snow melt 7-11-83 nd -65 -11.0 GV -Gd spring 7-05-81 5 -93 -14.2 GV -Gd spring 8-11-80 nd -77 -11.1 GV -Gd stream 8-11-80 7 -87 -12.0 GV -Gk spring 7-15-82 16 -77 -10.0 GV -Gl stream 7-18-82 5 -88 -12.6 GV -Gn spring 7-09-83 nd -78 -11.3 GV -West Fork River 7-05-81 5 -93 -14.2 GV -clear river mouth 7-19-83 7 -77 -11.5 GV -muddy river mouth 7-19-83 5 -85 -12.8 GV -snow melt 8-11-80 nd -76 -11.2 MV -Camp spring 7-19-82 nd -67 -9.7 MV -Mb stream 8-13-80 nd -89 -13.0 MV -Mc stream 7-04-81 nd -82 -11.9 MV --Md stream 8-11-80 nd -83 -11.3 MV -spring 7-19-82 6 -82 -11.9 NV -'stream 8-20-83 nd -88 -12.7 DV -Driftwood Valley FF -Fumarole field GV -Glacier Valley MV -Makushin Valley NV -Nateekin Valley a)Analyzed at Stable Isotope Laboratory,Southern Methodist U.,Dallas,Texas. Values are in permil with respect to SMOW. AT sy Table 25.Geothermometry of chloride spring waters in Makushin geothermal area. (Temperatures in °C), Site Name Date Qz.cond.(1)Chal.cond.(2)Na/K (3) Na/K (4)Na/K (5)Na-K-Ca (6)Na-K-Ca (7)Ni/Li (8) DV -stream 8-21-83 96 65 210 178 187 157 71 171 GV -Gm 7-20-82 144 118 225 '197 205 166 129 139 GV -Gn 7-20-82 °147 122 225 "197 204 167 99 126 GV -Gp 7-20-82 139 113 221 192 200 175 64 143 DV =Driftwood Valley,GV =Glacier ValleyCindPott>(1)Fournier,19887 improved $102,Covert2 ): (2)Fournier,198%,impreved=ftOG +hy leedony i (3)Fournier,1981,Na/K.7 \(4)Truesdell,1976,Na/K.wa (5)Arnorsson,1983,Na/K,Basalt. (6)Fournier &Truesdell,1973. (7)Fournier &Potter,1979.ol(8)Fouillic &Michard,1981.J hg Coated) Ag :Preawt Table 26.Analyses of gases collected from fumaroles and hot springs,Makushin geothermal area,Jn mole X%.Analyses corrected for air contamination using ratio of of in sample to Qp in air (Ro}). Gas geothermometer(c) Sample code Location Date sample RO Xe cop nis ni cud wud Ne Ar NZ/Ar_C/S Tl T2 Sodium-hydroxide charged flasks:(a)v Vv °¥bd Ml "v RM 83-46 FFFL 7-17-83 0.01 0.17 82.19 2.28 0.21 0.039 0.38 14.73 0.17 86.4 36.1 227 206 RM 83-GVI-A FF#3 Superheated 7-08-83 0.00 0.16 8B.04 6.38 0.95 0.010 0.13 4.43 0.06 80.2 13.8 298 272 RM 83-L1b FF#3 West 7-10-83 0.06 0.50 83.72 1.69 0.22 0.001 0.04 14.16 0.17 84.1 49.4 256 234 RM 83-31 FF#3 Far west 7-13-83 0.05 0.36 88.10 4.58 0.25 0.001 0.01 6.94 0.14 51.3 19.3 273 249 RM 83-57 FF#7 8-20-83 0.01 2.63 82.15 1.81 1.10 2.482 0.18 12.21 0.08 161.9 46.7 230 210 RM 83-19 FFA9 .7-11-83 0.00 0.78 91.55 3.94 0.85 0.004 0.03 3.63 0.02 146.3 23.2 294 268 DS 83 RN7 DS FF#3 superheated (98)8-29-83 0.00 0.18 88.93 6.85 0.88 0.006 0.08 3.22 0.03 113.1 13.0 302 275 DS 83 BNI13 DS FF#3 Far west 8-29-83 0.00 0.25 84,93 6.25 0.66 0.003 0.06 8.06 0.01 --13.6 299 273 RM 82-GV1L FF#3 Superheated 7-09-82 0.02 0.15 82.29 12.25 1.84 0.070 nd 3.56 0.07 54.7 6.7 313 285 RM 82-Ma sum FF#6 Summit 7-18-82 0.00 1,67 87.47 5.53 0.21 0.047 nd 6.63 0.11 60.2 15.8 235 214 RM 82-MV FF#2 FF#2 7-17-82 0.00 - 90.40 2.92 0.35 0.012 nd 6.24 0.07 87.8 30.9 252 229 RM 82 Ma west fl.FFAS 7-13-82 0.01 1.39 91.16 0.95 0.5!0.004 0.03 7.29 0.05 137.0 96.4 257 234 RP 81-AL3 FFA2 .7-14-81 0.00 0.00 87.17 5.26 0.75 0.002 nd 6.76 0.06 120.2 16.6 308 280 RP 81-A15 FFE#3 7-05-81 0.00 0.00 87.42 1.23 1.80 0.002 nd 9.43 0.11 86,4 70.9 309 281 § RM 80-MV2 FF#L 8-13-80 0.00 0.41 91.68 2.63 0.24 0.029 nd 5.36 0.07 78.4 34.9 231 210 5 0.54 0.002 nd 8.81 0.09 95.4 33.2 283 258RM80-MV1 FFA2 8-13-80 0.00 0.59 87.90 2.6 Uncharged,evacuated fJasks:(b) RM 83 G-p Spring G-p 7-16-83 ----98.22 0.02 0.005 0.052 nd 0.96 0.02 48.0 ------ RM 83 G-j Spring G-j 7-21-83 0.04 --25.43 0.02 0.02 0.010 nd 74.13 1.02 72.4 0 ==---- RM 82 GV UW FF#4 7-14-82 0.01 --92.73 0.82 1.21 0.01 nd 5.50 0.05 104.8 4813.5 295 269 RM 82 Ma WF FFAS 7-13-82 0.00 --94.89 0.68 0.59 0.01 nd 3.78 0.05 77.6 139.3 268 244 RM 82 Ma Sum FFI6 7-18-82 0.00 --90.60 5.68 0.12 0.02 nd 3.43 0.01 --16.0 226 206 RM 82 GV W FF#9 r)7-14-82 0.00 --93.36 2.01 0.72 0.01 nd 4.33 0.04 108.3 46.4 293 267 analyz-d by J.Whelan,(S1I0}La Jolla,and R.J.Motyka,APEGS)Fairbanks.(b)Analy-ed by W.Evans,U663)Menlo Park,and R.J.Motyka,ABGES Fnisbamhs |.\ (c)D'tAmere and Panicht,1980./TI uses P cop =1 bar;T2 uses P CO 5 bar.Dapnat mad |Scbubi fee tJ Tr duster Cceiel Trililul of Ocseme pighy Alo Divoivn fosmtehohbalyicedfeGrplyedf-Aviy (a)Sampler RM 83 and RM 82 analyzed 'by R.J.Motyka,ADGGS;samples DS 83 analyzed by D.S.Sheppard,v New Zealand;samples RP 81 and RM 80 |UA.(rheyit#(utr yiTable27.Makushin geothermal area,analyses of Mc/The in coe,emanating from fumaroles and hot springs. Pa *Year Location Coltttea)”Ke,PDB Type Analyst -- Fum.field #1 1983 -14.3 SrCOf/NaOH USGS 1983 -13.9 SrCOP/NaOH USGS Fum.field #2 1981 12.2 SrC0}$/Na0H GC -12.5 SrCO}/Na0H SMU 1982 -11.6 SrCO}/NaOH USGS Fum.field #3,sp 1981 -11.8 SrCOW/NaOH GC -12.4 SrCOg/NaOH SMU lower 1981 -13.0 CcOv-gas GC super heated 1982 -10.2 COf-gas siIo 1983 -13.4 SrCO$/NaOH USGS west 1983 -11.3 SrCO$¢/NaOH USGS Fum.field #4 1982 -12.3 co¢-gas USGS Fum.field #5 1982 12.4 SrCO}/NaOH USGS -12.4 CO¢-gas USGS Fum.field #6 1982 -10.0 COf-cas USGS -11.5 SrCO¥/NaOH SMU Fum.field #9 1982 -12.1 cod-gas USGS Spring G-j 1983 -15.4 CO¢-gas USGS Spring G-p 1983 -13.3 COf-gas USGS USGS =U.S.Geological Survey,Menlo Park,California. SMU =Southern Methodist University,Stable Isotope Laboratory,Dallas, Texas. GC =Global Geochemistry,Inc.,Canoga Park,California. SIO =Scripps Institute of Oceanography,Stable Isotope Laboratory, La Jolla,Claifornia. PoeeRY Table 29.Makushin geothermal area,miscellaneous stable isotope analyses. AVWart-Hoos,thermal i Year Location Collected 440,PDB Spring G-h 1982 -ll.l Test well ST-1 1984 23.0 atten?,§feAcand{to Abo in cacog,calcite sinter deposized on downholeinstrumentcableintestwellST-l,mid-July,1984y ((cAbc,PDB RA',PDB:cay RM84-MVTW cacog, 12.5 29.3 AX Abc in methane,fumarole gases. Year Location Collected hho »PDB Analyst Fum.field #2 ....1982...-42.3 ly Ad Fum.field #6 1982 -30.6 iv D/H in hydrogen and methane,fumarole gases. Year Location Collected D/H -Hp,SMOW D/H -cud,SMOW Analyst Fum.field #3,sp 1981 -601 ---[v AdFum.field #3,' superheated 1982 -582 ---(Fum field #6,,'J summit 1982 -719 -132.6 "Crate I Ah . dik)>type SMS ffrileAG | 7.5 Calcite Saturation log(Ca*HCO3*2/PCO2) 7 4b + 7 b+ 295 + a+ 7]1+ U 4 q J 't 'LI ''q LU LJ q La L 't ' 100 120 140 160 180 200 220 240 +260 £280 T,deg C 300 Anhydrite Saturation -Log(Ca++S04=)40 80 120 160 200 240 280 T,deg.C. -30 -40 - -50 - -60 +Adak precip.line -70 -+D/H-90 +A A -100- --110 -Craig meteoric water --120 t q 'i JS u ''u ]a -17 -15 -13 -11 --9 7 180/160 °oO ST-1 +low Cl CI A meteor. \'TritiumUnits6O. 50 40 30 20 10 O MAKUSHIN GEOTHERMAL AREA Tritium ay 4 | o a o a) | 0 oO Oo th 5 ot J |t |is 'Ef LJ ST1 ST1 str Mc Gj Gl Gm Gp min ave Site O CO,dissolved in NaOH @ @ L\CO»5 gas 1984_|® @ ® @ @ t .asS1983_|iA,©Ace © _ 1 ©Ay ;a ©summit -E |A®A 1982 _|A®Ash A,OD 1981_|@) -Organjc -sedimentary Volcanic -magmatic »-Marine limestone [||||{t |||} ||{}|\1 |||1 -20 -16 -12 -8 -4 0 é 136 -CO,,permil2 Makushin Geothermal Helium Isotope Data © a9 @ @ ©Summit rscee +MOH ,Hot spot ||| 5 10 15 Ro/Ra R =3He /4He i 20 1V T,degC260 250 240 230 220 210 GEOTHERMOMETRY ST-1 + 4 + : _ + 3 a a it A 8 4 I 7 x Vv 10} 8 9 A o it] a 0 A x ro) P|B . T T T T T T ST1 Qz Na/K NokKCa No /LI S04 G1 G2 G3 Geothermometer EXPLANATION OF LOG SYMBOLS Homogeneous Volcanics =[tists Gravel,Lahar,Till ospioe: Cinders | Unalaska Hornfels Gabbronorite ++ +ae swe. Unalaska Clastics Unalaska Flows Hydrothermal Breccia av Sharp Contact a FEETTEMPERATURE(°C)METERS Rgg8ggg l i t ! ll !i t t f +-8+-3 _ r Fs - rs a - ba ° ------a eo N3s i ___ 2 3 -_--F "os - T T OORT TT28&§& Chli-ActLaumMontEpMtPyAnhCaQtz D-1Well TEMPERATURE (°C)'METERS rrTyprrrryprrrr yp rrr ry 20 50 100 150 200 ' ' ' ' \ \ t 4 ;L t { ' t 1 t '-'- ' a = H i '|Temp. (7/2/83) : ” a :4 {= |* =- Level 7 4 |_. >+ry e¢64380+"tbe 1 ++ ++t = oe +|*4 >+> +420 -|+"+||7 o - ++|++ -"+-3¢#4 'wee --i Po PEI TERE>3 §=F39 Well FEET 200 400 1000 1200 1400 FEET 200 800 -1200 -+400 Temp. (6/30/83) TEMPERATURE (°C)METERS atMorditliteMontEpPyAnhCaQtz I-14Well METERS *TEMPERATURE (°C)FEET a ee a 20 Bed 50 100 150 200 60 +*.''1.200 1004 » r-499 140 7." 180 +.at ta *Temp.Td,.ot 17/3/84) ry,|||. = 220 pb,Watero¢t 'a Level "|+«'|800 2604 + --600 ita+ec 't3004«|:-+me ee 1000 @aeodi1200 420 4*,°1 -3400 450 -+|*,*L. *,':r 1600 5004 .«,' 540 +° !evel -1800 580 4,°,' L WO> La Well ST-17 no|-egquy|--AdwWa3wowM418, onaMETERS WELL A- 1 TEMPERATURE (°C)FEET re ee 50 yt 100 l I -1200 r-1800 210eDAdJNd3|juowwney QUARTZ CALCITE ANHYDRITE CHLORITE- ACTINOLITE ANTHOPHYLLITE- CUMMINGTONITE BIOTITE EPIDOTE ALBITE WAIRAKITE OTHER ZEOLITES MONTMORILLONITE PYRITE MAGNETITE 'HEMATITE MARCASITE SPHALERITE DEUTERIC.HYDROTHERMAL EARLY LATE Paragenetic Chart of Makushin Alteration Minerals =-a"os 20 &£5 yypta ae -FI Fig,11: =-=TEMPERATURE OF LAST ICE MELTINGn=80 =p =tebe X= 037 So*0.13 -o 10 = > =2 Cc jal TTTTTT1 Pott -1.0 0.0 TEMPERATURE,IN DEGREES CELSIUS TEMPERATURE OF INCLUSION HOMOGENIZATION TEMPERATURE,IN DEGREES CELSIUS i a U q ==80 al >200 250 +++¢ P ++¢ +¢ + &100 4 t Fig.120 "a , w 200 >WELL 1-1 -MTG z 2=«= 3 ted r=} 300 = 400 = TEMPERATURE,IN DEGREES CELSIUS SH3L3W Ni 'H1d3a WELL ST=1 SHILIW NI 'H1d3C )oN Fig.12¢ WELL E-1 +ooee 3 |2 +4o+4 -8 ass -on ++4 =” $4444 uaNy ogee ; ++ one or au +44 +++ +4 33 sal Ba ch +44 ++ + $444 . Doi be AH on ttt 4464+ +o28 2 + Ftttettt) em +4444 +++ +4444 ++ 5 « aa wowot+ + a ett + : . Lg $4 teteeseres M 5ft 2 +ee 44444444404 __ + $4eeees+4 oon eee on [et $404 i.& \ N 4 irag= + wo B 3e= & bu T t| L } ' LJ T s = 8=83 8g 3 g Ncao11 GIBBSITE PREHNITE WAIRAKITE KAQOLINITEMORDENITE YUGAWARALITEPREHNITE | 10 +AU NLCALEITESATURATION. =MAAGARITE !a9-j____CALCITE SATURATIONPCO,*1.0} 3 4 WAIRAKITE 7 _ GIBBSITE 6 7 KAOLINITE S!l57=|=> S| {if Ty T i }1 i 3.5 3 25 2 -1.5 "1 0.0 LOG aSi0,(aq) fo 2 200°C 117 t+10-PREHNITE i+ om a\e S febdg|=2(LAUMONTITE)oF9*s MUSCOVITE oxoxo|”KAOLINITE )MAKUSHIN . 8 q if qT J 1.0 2.0 3.0 4.0 +> LOG a H* 200°C 10- PREHNITE : om ZZole96sLAUMONTITE./ALBITE 4 (LOW) J MAKUSHIN @ KAOLINITE PARAGONITE8T]I 42.0 3.0 40 5.0LOGaN2'a Hr 0ial I] ke oe | Table8.Makushin Valley test well ST-1l,stable isotope analyses corrected to reservoir conditions. (Parts per mil with respect to SMOW). ere ae 1983 n 1 75 76 7 Average D/H (SMU)-81 -78.5 -79 -78.5 78.5 -79 1857/16 (smu)-10.3 -10.4 -10.3 (-8.8)?10.1 10.3 185/165 (yscsy.10.2 -9.9 -10.0 --9.9 -9.9 -10.0 1984 g4-1>84-2 D/H (SMU)-69 -83 18/16,(SMU)10.4 -10.2 a)Suspect value;not used in computing average.} b)A large amount of chloride was detected in the 84-1 condensate indicating incomplete separation. Values for this sample are therefore not considered to accurately represent reservoir isotope composition. 4Table30.St-1 whole rock oxygen isotope data.* Sample #185/18 Description 19 §T-1-201 -4.0 Gabbro.Plagiclase altered to clays. | ST-1-664 -2.7 Gabbro altered to wairakite.Steam entry. ST-1-1066 -2.0 Albite-K spar-biotite-epidote vein. ST-1-1638 +2.8 '""Unaltered"gabbro.Pyroxenes altered to anthophyllite-cumtegtonite. ;Sa gt Pat ST-1-1937 -0.1 Chloritically altered gabbro. --+6.4 Average of 11 Makushin area volcanic rocks. a)Analyzed at U.S.Geological Survey,Menlo Park,CA.,I.Barnes lab. [5 Table 24.Analyses of tritium in waters from Makushin geothermal area. Sample code Locality Date collected TU MVTW-3 ST-1 9-02-83 0.4640.08 MVTW-5 ST-1 -9-03-83 0.29+0.08 RM82MV-cs cold str.,Mk.Val 7-21-82 11.3+0.3 RM82MV-ru hot spr.Mec 7-22-82 16.440.4 RM82GV-E hot spr.G-j 7-20-82 36.520.8 RM8 2GV-wv hot spr.G-1 7-20-82 28.220.7 RM82GV--24 hot spr.G-m 7-20-82 10.54+0.3 RM82PV hot spr.G-p 7 20-82 6,140.2 Analyst:H.Gote Ostlund,U.of Miami,Miami,Florida. TU =Tritium units Table 16.Makushin Valley test well ST-1,Unalaska Island,Alaska,carbon isotope analyses,CO,in gas and steam,2 ©13Sample#Date Collected T,°C Sep &Copp MVTW-1 8/27/83 120 -13.3MVTW-3 9/02/83 134 . @13.5 MVTW-4 9/02/83 148 -13.3 MVTW-5-9/03/83 148 -13.3 MVTW-1G-C 8/04/84 130 15.1 MVTW-2G-A 8/07/84 131 -15.0 MVTIW-2G-B 8/07/84 131 -15.1 a)C.Janik,U.S.Geological Survey,Menlo Park,analyst. 7 Table 28.Helium isotope data,Makushin geothermal aread.* Year Location Collected R/Ra?(He/Ne)/air®Re/Ra® Fum.field #1°1980 6.6 110.0 6.6 Fum.field #2 1980 4.9 37.0 5.1 Fum.field #2 1981 5.0 94.0 5.1 Fum.field #3,sp 1981 3.8 24.0 4.0 Fum.field #3 1981 4.4 53.0 4.5 Fum.field #3,SH 1982 4.1 11.4 4.4 Fum.field #5 1982 5.0 50.0 5.1 Fum.field #6,SU 1982 7.8 1500.0 7.8 Fum.field #7 1983 5.9 300.0 5.9 Spring G-p 1983 (1.3)°(1.5)(1.9)® Test well ST-1l 1983 3.6 41.0 3.7 R.Poreda analyst,Scripps Institute of Oceanography,Stable Isotope Lab. R =Pie Aue ratio in sample. Ra =$ue/4Me ratio in air.Re =Sample ratio corrected for air contamination using He/Ne ratios: Helium concentration in sample was extremely low. I? Table 3.Geothermometry for Webre separator waters from Makushin Valley test well ST-1 corrected for reservoir conditions.(Temperatures in °C). Sample #Date Qz.cond (1)Chal.cond (2)Na/K (3)Na/K (4)Na/K (5)Na-K-Ca (6)Na/ii (7) RM83-71 8-27-83 208 19%240 216 222 224 193 RM83-74 9-01-83 208 192 247 226 231 229 194 RM83-75 9-02-83.209 193 243 221 227 227 196 RM83-76 9-02-83 203 186 241 218 224 225 194 RM83-77 9-03-83 208 191 238 213 220 223 193 RM84-01 8-04-84 nd nd 245 223 229 227 194 RM84-02 8-07-84 206 189 240 217 223 224 193 amd fall #: (1)Fournier,1983,improved S102,(gue )i(2)Fournier,1989,imp .Cn(3)Fournter,1981,vie NN Chalcedony(4)Truesdell,1976,Na/K. (5)Arnorsson,1983,Na/K,Basalt.1 (6) (7) Fournier &Truesdell,1973. Foufllic &Michard,1981.faa 9TableIl.Sulfate-water {forth isotope temperatures,Makushin Valley test well,sT-1.° Date Temp §fo/fho-so4,WGo/fho-abo,hor fPo-uho,Sample #Collected sep,WRT SMOW WRT SMOW at sep WRT SMOW,res T1,°C T2,°C MVTW-74 9-01-83 135 -3.8 "29.5 9.9 245 256 MVTW-75 9-02-83 134 -3.4 -9.6 10.0 235 245 MVTW-76 9-02-83 148 -3.4 -9.6 -9.9 235 248 MVIW-77 9-03-83 148 -3.3 -9.6 -9.9 235 244 MVTW-1W 8-04-84 130 -3.9 -10.3?-10.4 230 246 MVTW-2W 8-07-84 -131 -3.6 -10.0 -10.2 232 246 a)Isotope analyses performed at U.S.Geological Survey,Menlo Park,except as noted. b)Analysis performed at Southern Methodist University,Stable Isotope Laboratory. c)Temperature calculated using method described in McKenzie and Truesdell (1977)for the case of single-stopsteam-loss.The separator water composition was used for fto/f4qo -H,0. d)Temperature calculated using the {5/10 -H fractionation equation of Mizutani and Rafter (0 value determined for the gesgrvoir water and the equilibrium1000In=2.88 (10 /T')-4.1,T=°K. go Table 15.Gas geothermometers applied to Makushin test well. Sample #Date Sampled T°c (a)T°(b)TC (c) MVTW-1 DS/CJ 8-27-83 228 212 220 MVTW-2A DS/CJ 9-01-83 250 222 227 'MVTW-3B DS/CJ 9-02-83 217 216 222 MVTW-4B DS/CJ 9-02-83 213 223 223 MVTW-5A DS/CJ -9-03-83 204 216.222 MVTW-1G+C RM/CJ 8-04-84 218 220 225 MVTIW-2G-A RM/CJ 8-07-84 216 211 199 MVTW-2G-B RM/CJ 8-07-84 190 212 213 (a)Gas geothermometer of D'Amore and Panachi,1980. (b)nes geothermometer of D'Amore and Truesdell,198), (c)cop,geothermometer of Arnorsson and others,1983. FIGURES Figure l.Location map for Makushin Geothermal Area. Figure 2.Geologic map of the Makushin Geothermal Area. Figure 3.Webre mini-cyclone separator in use at well ST-1,Makushin Geothermal Area. Figure 4.CO.-H5S-N5 compositions of well ST-1 andfumarolicgasesfromMakushinGeothermalArea. Figure 5.No/Ar vs Ho/Ar plot for well ST-1 gases,Makushin Geothermal Area. Figure 6.Quartz solubility curve and values for well ST-1,Makushin Geothermal Area . Figure 7.Calcite saturation curve and values for well ST-1,Makushin Geothermal Area. Figure 8.Anhydrite saturation curve and values for well ST-1,Makushin Geothermal Area. Figure 9.Stable isotope analyses of well ST-1,thermal 'springs,;-and meteoric waters from the Makushin Geothermal Area. ; Figure 10.Tritium analyses of well ST-1,thermal springs,and ground water streams in the Makushin Geothermal Area.The three values at right give 1980 data from Anchorage for comparison. Figure ll.13¢compositions of CO.in gases from wellST-1,fumaroles,and hot springs in the Makushin Geothermal Area. Figure 12.He isotope analyses from well ST-1, fumaroles,and hot springs in the Makushin Geothermal Area compared with values from various tectonic settings. Figure 13.Comparison of geothermometry of well ST-1, Makushin Geothermal Area. Figure 14.Lithologic log and temperature profile of geothermal gradient hole D-1,Makushin Geothermal Area. Figure 15.Lithologic log and temperature profile of geothermal gradient hole E-1,Makushin Geothermal Area. Figure Figure 16.Lithologic log and temperature profile of geothermal gradient hole I-1,Makushin Geothermal Area. 17.Lithologic log and temperature profile of _geothermal well ST-1,Makushin Geothermal Area. Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure 18.Lithologic log and temperature profile of geothermal gradient hole A-1,Makushin Geothermal Area. 19.Paragenetic chart of Makushin alteration minerals. 20.Fluid inclusions in quartz from the Makushin Geothermal Area. 21.Fluid inclusions showing daughter minerals. 22.Histogram of fluid inclusions last ice melting. 23.Temperatures of fluid inclusion homogenization. 24.Chemical potential diagram for the system 25.Makushin reservoir waters plotted on the activity diagram for the system Ca0-A150,-Si05-H502 . 26.Makushin reservoir waters plotted on the activity diagram for the system Ca0-K,0 -Al1,03-Si05-H.O at 200 deg.C. 27.Makushin reservoir waters plotted on the activity diagram for the system CaO-Na.0-Al.03-SiO0,-H20 at 200 deg.C. 28.Fugacity of oxygen vs pH diagram for the system Fe-S-H,0 at 250 deg.C (after Crerar andBarnes,1970). 29.Boundaries and generalized results of E-scan electrical resistivity survey of the Makushin Geothermal Area performed by Premier Geophysics, Inc.of Vancouver,Canada (taken from appendix E of RGI final report to APA,1985 ). 30.Model of resistivity section through E-1 and ST-1 by Premier Geophysics,Inc.of Vancouver, Canada (taken from appendix E of RGI final report to APA,1985 ). Figure 31.Generalized model of a geothermal system typical of active island-arc andesite volcanoes ( reproduced from Henley and Ellis,1983). Figure 32.Cross-section of Makushin Geothermal systen. Location of section AA'is shown on figure 2. Isotherms are based on locations of fumaroles and hot springs and on temperature data from thermal gradient holes and well ST-1.Geology is from Nye and others,1984.. LY NORTHERN UNALASKA 'ISLAND | \Wide Bay Cone Table Top Mt.©'Fumarole .e Cl Thermal spring Pt.Kadin ©Sugarloaf Cone Dutch . Vents an arbor *HCO3-SO4 Thermal spring ST-1 GRY alaska (Not all indicated): :©Drill hole. Makushin - »Geothermal Area | aA ST-1 Makushin Volcaro .,"eoOW, Pakushin Cone +r .Composite volcano *&Satellite cones &vents Anchorage'a Alaska Peninsula 0 5 10 mi .UNALASKA IS. |L -¥ 0|||a.e .Pa e e Location Map ny a farSata nA <1 .cutee ayy evra Ae pa "4aeweyiNAJiH Tu wn ? % ; ? ev . 2<+--___. AREA GEOLOGICAL MAP OF THE MAKUSHIN GEOTHERMAL ea Tu " 4 dag ><" Seya2 vant gacen Tu Map utter Nye and orners (1984) 1 oO 1 LS Mies Ksiometers EXPLANATION OF MAP SYMBOLS_ Alluvium Ga Tolluvium Qc Pyroclastic Debris Op Glacial Till Qt vere ...J . .vr?wHomogeneousVolcanicseee ove ee r>ased .>a t4InhomogeneousVolcanicsworeelad"<ws | Unalaska Formation Tu ++eo 4 © . bananane Contact MetamorphosedGabbronoriteteeeeUnalaskaFormation+t oo 4 $+ee Fumarole A Contact oe 7 Warm Ground a Fault {o) HC03-S0,Thermal Springs bs Test Well > Cl-Thermal Springs g Therma!Gradiant Well © Hy | Gas Samples Fumaroles &springs Oo NaOH sample A Regular sample ST-1 o NaOH sample HoS X 10 20 CO,/10 80 Makushin Geothermal Area a N2/ArMakushin Geothermal Area ST-1 2GB oO dis air 688 O H2/Ar Quartz Solubility 700 600 - 500 + 400 3500 -Si02,mg/kg200 - 100- --Computed Values 120 Lf ' 160 T,deg C. + |'| 200 240 ST-1 Samples 280 The pressure required to sustain such high temperatures at saturation boiling point conditions is about 40 bars which is equivalent to a hydrostatic head of over 400 meters.To produce such high pressures the system must have either been self-sealed or some other mechanism of pressure loading most have been in effect.We reject the hypothesis of lithostatic self-sealed pressurization because of the high pressures involved and because of the highly fractured nature of the host gabbronorite as evidenced by the numerous fumaroles and hot-springs that presently exist throughout the area. Instead we prefer to invoke ice-loading of the hydrothermal system during a neo-glacial advance to explain the anomalously high temperatures recorded by the fluid in- clusions.Ice-thicknesses af 400 -500 m are commonly found in present-day valley type glaciers in Alaska and it is reasonable to assume such ice-thicknesses existed in Makushin and Glacier Valleys in neo-glacial times.The in- creased hydrostatic pressure exerted by the ice would be sufficient to produce the elevated temperatures recorded by the fluid inclusions.Such interactions between ice loading and hydrothermal systems exist today in Iceland, particularly in the Vatnajokul]Grimsvotn caldera area (Bijornsson,1975)and are also thought to have occurred during glacier advances and retreats in the Yellowstone weNational Park geothermal areas (Muffler and others,1971; R.Fournier,USGS,pers.comm.) The thermal fields at Makushin lie at the heads of valleys on the flanks of a volcano which still maintains a sizeable ice-cap and a system of valley glaciers.At least two neoglacial advances that reached tide water have been dacumented elsewhere in the Aleutians (Black,1983)and it is reasonable to assume that correlative glacial advances occurred at Makushin.There are in fact abundant neoglacial moraines,outwash deposits,and glacial scours in Glacier,Makushin,and Driftwood Bay Valleys.The most recent advance and retreat in the Aleutians is estimated by Black (1983)to have occurred about 3,000-4,000 years b-p. At the Vatnajokull in Iceland,meltwater generated by sub- glacial geothermal heating becomes entrapped in large,hy- drostatically sealed subglacial chambers.The seals on these subglacial meltwater reservoirs are periodically broken resulting in catastrophic release of the entrapped water known as jokulhlaups (Bjornsson,1975).Similar pres--- sure release phenomena probably occurred at the Makushin geothermal area during neoglacial times and could have caused the breccias found in the ST-1 and D-1 drill cores. Subsequent deglaciation would decrease the hydrostatic pres- sure causing boiling to increase in the upper part of the eemanhydrothermal system.A net loss of water caused by the boiling and from the decrease in recharging glacier mel- tuater would in turn result in a decline of the system's water table.As discussed previously,rapid boiling could explain the curious co-precipitated mineral assemblage of guartz-calcite-anhydrite-magnetite that is found in the up- per parts of ST-1 and E-1. If our hypothesis is correct,the drop in temperature in the upper part of the hydrothermal system may reflect an episode of intense boiling and water loss rather than overall cooling of the system.The sulfate-water oxygen isotope geothermometer does predict a reservoir temperature of.-250°C which is similar to fluid inclusion temperatures found in the upper part of the system.As discussed under geothermometry,re-equilibration of the sulfate-water oxy- gen isotope geothermometer at lower temperatures is much slower than the other geothermometers and thus the 250°C tem- .perature may reflect deep reservoir conditions. DISCUSSION OF PREMIER GEOPHYSICS ELECTRICAL RESISTIVITY STUDY At the recommendation of OGGS scientists,an electrical resistivity survey of upper Makushin Valley was incor- porated into the geothermal exploration program for the sum- mer of 1984.The rationale for the survey was that data on reservoir fluid conductance and drill hole data was now available to guide the survey and that the survey could potentially delimit the lateral boundaries of the subsur- face hydrothermal resource.Economic feasibility of developing the resource would be greatly enhanced if the resource could be shown to exist further down Makushin Val- ley or at the head of Driftwood Valley.The electrical resistivity survey would also help test the proposed hypothesis that the geothermal system is offset east- southeast of Makushin Volcano as suggested by the regional alignment of fumarole fields and thermal springs. The electrical resistivity survey was conducted by Premier Geophysics of Vancouver,Canada.The outcome of the elec- trical resistivity survey is discussed in detail by G. Shore of Premier Geophysics in Appendix E of RGI's final report of 1985.The surveyed area,reproduced in figure 29, covered all of upper Makushin Valley and the plateau at the head of Driftwood Valley.The survey penetrated to depths of 2000 m.-A brief summary of Shore's more pertinent fin- dings are reviewed here: 1)The survey defined the north and east boundaries of a main resistivity anomaly which was taken to be indicative of the main hydrothermal reservoir.These boundaries,shown Meee.on figure 29,are located in Fox Canyon on the north and east of ST-1.The conductive zone extends west and south for at least two kilometers and is then beyond the range of the survey. 2)A sloping lower boundary separates the conductive'reser- voir rocks from an underlying higher resistivity regime as depicted in figure 30. 3)No resource is thought to underlie the part of Fox Canyon covered by the survey. 4)No other parts of the survey coverage area,including Sugarloaf,yielded results comparable to those of the known reservoir area. 3)A major near-vertical discontinuity in resistivity oc- curs in a zone extending south from Sugarloaf.The discon- tinuity is infered by Shore to be a fault zone.An alter- nate explanation for the discontinuity is a change in bedrock mineralization. We now attempt to resolve the conclusions of the resistivity survey with data from geologic mapping and geochemistry.No known geological boundary correlates with the change in resistivity demarcating the eastern edge of the main resistivity anomaly.The northern boundary is on strike with the block fault found to the southeast and per- haps is an extension of this fault.An alternate explana- tion for the discontinuity is that the canyon is the approx- imate boundary between the gabbroic intrusive and the horns- felsic metamorphosed Unalaska Formation border zone.| Pyritization was found to occur mostly along the horns- felsic border zone and thus the resistivity change could reflect sulfide mineralization. We believe the sloping contact between low and high resistivity zones found by the survey in the vicinity of E-1 and ST-1 is the large open fracture at bottom of ST-1. The surface location of the dipping horizon is constrained to +50 m of the position shown in figure 30.However,the uncertainty in the slope of the boundary increases with depth and the boundary could be very well be placed at the bottom of ST-1. lt is possible that the fracture and the dipping horizon are related to the fault mapped through the canyon adjacent to fumarole field 2.The fault dips steeply to the north- northwest and its projection passes through the vicinity of fumarole field 1.The fault,which is also the contact between Unalaska Formation rocks to the south and horns- felsic rocks to the north,could be acting as a conduit for thermal fluids that are feeding the fumaroles and hot springs. eet.No surface expression could be found of any major fault through the Sugarloaf region as suggested by the resistivity data.We prefer Shore's alternate explanation for the resistivity contrast,that of a steeply.dipping con- tact between rock types.The nature of the subsurface con- tact between the two different Unalaska Formation rock types is concealed by the thick sequence of Holocene lavas that fill upper Driftwood Valley.The eastern valley wall consists mainly of Unalaska Formation lava flows while the west side is mostly pyroclastic flows.The pyroclastic flows were found to be much more altered and pyritized then the lava flows.Thus the change in resistivity could be cae es feo athe due to a change in mineralization. Although drill hole A-1 encountered temperatures as high as 180°C at a depth of -580 m,electrical resistivity survey found no indication of a hydrothermal resource in this .area.Thus the ST-1 site and the region upvalley from it appear to offer the best potential for future resource development. The results of the resistivity survey have strong implica- tions regarding the source of the geothermal fluids.The resistivity models indicate the the hydrothermal system ex- tends in a wedge shape towards the south and west of ST-1 and E-1.The boundaries on the main resistivity anomaly es- eesentially rule out any major hydrothermal system offset from the volcano.Instead ,the resistivity data support a model in which thermal fluids ascend from a reservoir over- lying a centrally located heat source beneath the volcano. The fluids migrate upward then spread laterally as they ap- proach the surface with fractures and faults acting as con- duits which feed fumaroles and ST-1. oeheedMODEL OF MAKUSHIN GEOTHERMAL SYSTEM In preparation REFERENCES CITED Arnorsson,Stefan,1983,Chemical equilibria in Islandic geothermal systems -implications for chemicalgeothermometryinvestigations:Geothermics,v.12,no.2/3,p.119-128. Arnorsson,Stefan,Gunnlaugsson,Einar,and Svavarsson,Hordur, 1983,The chemistry of geothermal waters in Iceland.III. Chemical geothermometry in geothermal investigations: Geochimica et Cosmochimica Acta,v.47,no.3,p.567-578. Bargar,K.E.and Beeson,M.H.,1984a,Hydrothermal Alteration in Research Drill Hole Y-6,Upper Firehole River,Yellowstone National Park,Wyoming:U.S.Geological survey ProfessionalPaper1054-B,24 p. 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Motyka,R.J.,Moorman,M.A.,and Poreda,Robert,1983,Progress report -thermal fluid investigations of the Makushingeothermalarea:Alaska Division of GeologicalandGeophysicalSurveysReportofInvestigations83-15,48 p. Muffler,L.J.P.,White,D.E.,and Truesdell,A.H.,1971, Hydrothermal explosin craters,Yellowstone National Park: Geological Society of America Bulletin,v.82,p.723-740 Nehring,N.L.,Truesdell,A.H.,and Janik,Cc.J.,1982, Procedure for collecting and analyzing gas samples from geothermal and volcanic systems:U.S.Geological SurveyOpen-file Report (in preparation). Nye,C.J.,Queen,L.D.,and Motyka,R.J.,1984,Geologic map of the Makushin geothermal area,Unalaska Island,Alaska: -Alaska Division of Geological and Geophysical Surveys Report of Investigations 84-3,2 sheets,1:24,000. Nye,C.J.,Swanson,S.E.,and Reeder,J.W.,1985,Petrology and geochemistry of Quaternary volcanic rocks from Makushin Volcano,Central Aleutian Arc,(in preparation ). Okko,V.,1955,Glacial drift in Iceland.Its origin and morphology:Comm.Geol.de Finlande Bull.,no.170,133 p. O'Neil,J.R.,Clayton,R.N.,and Mayeda,T.,1969,Oxygenisotopefractionationindivalentmetalcarbonates:Journal of Chemical Physics,v.51,p.902-909. Panichi,C.,and Gonfiantini,R.,1978,Environmental isotopes in geothermal studies:Geothermics,v.6,p.143-161. Perfit,M.R.,and Lawrence,J.R.,1979,Oxygen isotope evidence for meteoric water interaction with the Captains Bay pluton, Aleutian Islands:Earth and Planetary Science Letters,v. 45,p.16-22. Parmentier,P.P.,Reeder,J.W.,and Henning,M.W.,1983,Geology and hydrothermal resources of Makushin geothermal area, Unalaska Island,Alaska:Geothermal Resource Council Transactions,v.7,p.181-185. Poreda,R.J.,1983,Helium,neon,water and carbon in volcanic rocks and gases:University of California,San Diego,Ph.D.thesis,215 p. towPotter,II,R.W.,Clynne,M.A.,and Brown,D.L.,1978,Freezing point depression of aqueous sodium chloride solutions: Economic Geology,v.73,p.284-285. Presser,T.S.,and Barnes,Ivan,1974,Special techniques for determining chemical properties of geothermal waters,U.S. Geological Survey Water-Resources Investigation Report 22- 74,1llp. Queen,L.D.,1984,Lithologic log and hydrothermal alteration of core from the Makushin Geothermal area,Unalaska,Alaska: Alaska Division of Geological and Geophysical Surveys Report of Investigations 84-23,1 sheet. Reeder,J.W.,1982,Hydrothermal resources of the northern part of Unalaska Island,Alaska:Alaska Division of Geological and Geophysical Surveys Open File Report AOF-163,17 p. Republic Geothermal Inc.,1983,The Unalaska Geothermal Exploration Project,Phase 1B,Final Report,prepared for the Alaska Power Authority. Republic Geothermal Inc.,1984,The Unalaska Geothermal Exploration Project,Phase II Final Report,prepared fortheAlaskaPowerAuthority. Republic Geothermal Inc.,1985,The Unalaska Geothermal Exploration Project,Phase III Final Report,prepared for the Alaska Power Authority. Roedder,E.,1984,Fliud Inclusions:Reviews in Mineralogy,v. 12,Mineralogical Soviety of America,664 p. Shore,R.A.,1985,Resistivity survey and interpretation,in Republic Geothermal Inc.,The Unalaska Geothermal Exploration Project,Phase III Final Report,prepared for Alaska Power Authority,Appendix E. Taguchi,S.,1983,Study on Geothermal Geology of the Kirishima Volcanic Region:Ph.D.dissertation,Kyusha University,131 Pp. Taguchi,S.,Okaguchi,M.,and Yamasaki,T.,1980,Reduction in the lengths of fussion tracks by geothermal heating and its application to thermal history:Rept.Res.Inst.Industrial Sci.,Kyushu Univ.,No.72,p.21-26 (in Japanese;English abstr.). Torgersen,T.,Lupton,J.E.,Sheppard,D.S.,and Giggenbach,W. F.,1982,Helium isotope variations in the thermal areas of New Zealand:Journal of Volcanology and Geothermal Research, v.12,p.283-298. Torgersen,T.,and Jenkins,W.J.,1982,Helium isotopes in geothermal systers:Iceland,The Geysers,Raft River,and Steamboat Springs:Geochimica et Cosmochima Acta,v.46,p. 739-48. Truesdell,A.H.,and Singers,Wendy,1973,Computer calculation of downhole chemistry in geothermal areas:New Zealand Deptartment of Science and Industry,Research Chemistry Division Report CD2136,145 p. Truesdell,A.H.,1976,Geochemical techniques in exploration: United Nations Symposium on the Development and Use of Geothermal Resources,2nd,San Francisco,1975,Proceedings, v.1,p.liii-lxxix. Truesdell,A.H.,and Fournier,R.0O.,1977,Procedure for estimating the temperature of a hot-water component in a mixed water by using a plot of dissolved silica versus enthalpy:Journal of Research,U.S.Geological Survey,v. 5,no.l,p.49-52. Truesdell,A.H.,and Hulston,J.R.,1980,Isotopic evidence onenvironmentsofgeothermalsystems,in Handbook of Environmental Isotope Geochemistry:Elsevier,p.1979-2019. Welhan,J.A.,1981,Carbon and Hydrogen Gases in HydrothermalSystems:the Search foraMantle Source:University ofCalifornia,San Diego,Ph.D.thesis,182 p. oeoeTABLES Table 1.Fraction of Steam Separated from Flashed Well Fluids! Sample #9 Collection Collection 4 Steam DGGS USGS Date Time Pressure,Bars Temperature,°C Fraction 71 ]8-27-83 (+1.5 hr)2.00 120 0.144 74 2A 9-1-83 17:30 3.17 135.5 0.116 75 3B 9-2-83 10:10 3.03 134 0.119 76 4B +9-2-83 16:20 4.48 147.5 0.093 77 5A .9-3-83 19:50 4655 147.5 0.092 84-1 -8-4-84 15:00 2.65 129.5 0.127 84-2 -8-7-84 13:00 2.79 131 0.124 1.Fluids collected using Webre type mini-cyclone separator, 2.Parenthetical value for 71 is the time elapsed after initial discharge from fracture zone at 1946'depth. Well was then shut-off until 9-1-83.Well was re-opened at 14:40,9-1-83 and was run continuously until about 22:00,9-3-83.Well was re-opened again on 7-4-84 and run nearly continuously until 8-8-84. 3.At the separator.These are absolute values calculated from gauge pressure plus atmosphere pressure which was assumed to be 0.96 bars., 4.Determined from the collection pressure assuming liquid-vapor equilibrium (Keenan et al.,1969). 5.Steam fraction calculated using a BHT=193°C and reservoir enthalpy value of 821 kJ/kg (Keenan et al.,1969). Table 2.Chemical analyses of waters collected from Makushin Valley test well ST-1,1983°, (Concentrations in mg/1 unless otherwise specified). From Webre-neparator'Off End of Exhaust 71 74 75 76 7 64 Te 75 76 iCations™ Na 2120 2020 2010 1900 2010 -2840 2400 2470 2420 2460 K 270 280 270 250 250 .360 180 310 300 310 Ca 150 139 140 128 L44 216 175 175 175 181 Mg 0.2 0.21 0.1 0.1 0.1 0.3 0.2 0.2 0.2 0.2 Li 11 il ll 10 10 14 13 13 13 13 Sr 2.4 2.3 2.8 2.5 2.6 3.1 3.2 3.3 3.3 3.1 Cs 1.4 1.4 1.4 1.4 1.4 1.6 nd nd nd nd NH,nd nd nd nd 41 nd nd nd nd nd Total®108.5 103.5 103.0 97.0 102.6 145.6 119.6 126.0 123.7 125.7 Anions ° RCO,<5 <5 <5 <5 <1.0 <5 nd nd nd nd so 91 86 85 77 80 190 nd nd nd ndf1.2 1.2 1.2 1.0 1.0 1.6 nd nd nd nd cl 3670 3540 3500 3230 3370 4870 4160 4240 4200 4220 Br 14 13 12 12 13 19 nd nd nd ndTotal®105.7 101.8 100.6 93.0 96.9 141.8 117.3 119.7 118.5 119.1 Balance%2.6 1.7 2.4 4.2 5.7 2.7 1.9 5.2 4.3 5.4 $10 343 335 340 306 323 450 393 395 402 3954,8 nd 2.7 1.5 ud x9 nd nd nd nd nd B 68 64 65 59 6 86 74 76 77 78 Al nd nd nd nd 0.02 nd nd nd nd nd As 12 °11 13 12 12 16 14 15 1S 15 Fe nd nd nd nd 0.13 nd nd nd nd nd tos!6760 6500 6450 5990 6280 9070 ----o----------pil,field®8.1 8.0 7.8 7.6 7.9 7.8 nd nd nd nd Date Sampled 8/27/83 9/1/83 9/2/83 9/2/83 9/3/83 8/24/83 9/1/83 9/2/83 9/2/83 9/3/83 a)Alaska Division of Geologica}and Geophysical Surveys,Fairbanks,M.A.Moorman and R..J.Motyka,analysts.b)Sampling conditions and steam fraction given in Table }. c)Cation and anion totals in milllequivalents/liter. d)Calculated.; e)Semple 64 measured at T=50°C;all others measured after cooling to 15°C. nd=not determined Table 3.Chemical analyses of waters collected from Makushin ValleytestwellST-1,1984."(Concentrations in mg/l unless otherwise specified). From Webre-separator™Off end of exhaustTW2HIE2E Cations "Na 1910 1930 2290 2290 K 260 250 300 310 Ca 129 133 155 149 Mg 0.2 0.2 1.3 0.6 Li *10 10 12 11.5 Sr 2.7 2.7 3.2 3.2 Cs 1.4 1.3 1.6 1.5 NH,gl <1 nd nd Total®97.6 98.5 116.9 116.7 Anions HCO,26 12 nd nd So 95 97 115 112#1.2 1.2 1.4 1.4 Cl 3480 3500 4180 4170 Br 12 12 14 14 Total®100.9 101.3 120.5 120.2 Balance'-3.3 -2.8 -3.1 -3.0 sio --328 397 384H,8 <1 1 nd nd B --67 78 79 Al nd 0.004 nd nd As 12 il 15 14 Fe 0.26 0.20 0.32 0.24 TDs?e nd 6360 7560 7540 pH,field 7.7 7.6 nd nd Date Sampled 8/4/84 8/7/84 8/4/84 8/7/84 a)Alaska Division of Geological and Geophysical Surveys,Fairbanks,R.J.Motyka and M.A.Moorman,analysts. b)Sampling conditions and steam fraction given in Table l. c)Cation and anion totals in milliequivalents/liter. d)Calculated. e)pH measured after waters cooled to 15°C. nd=not determined Table 4.Chemical analyses of 1983 waters from Makushin Valley test well ST-1,corrected to reservoir conditions. (€oncentrations in mg/1 unless otherwise specified). 71 74°75 76 77 Average Cations Na 1820 1780 1780 1730 1820 1790 K 230 250 240 230 230 240 Ca 128 123 124 116 131 124 Mg 0.2 0.1 0.1 0.1 0.1 °0.1 Li 9 9 10 9 9 9 Sr 2.1 2.0 2.5 2.3 2.4 2.3 Cs 1.2 1.2 1.2 1.3 1.3 1.2 NH,nd nd nd nd 1.0 1.0 Anions HCO,<5 £5 <5 <5 <1.0 <5 so 78 76 75 70 73 747)1.0 1.1 1.1 1.1 0.9 1.0 Cl 3140 3130 3080 2930 3060 3070 Br 12 il 11 ll 12 11 sio 294 296 300 278 293 292H,8 nd 2.4 1.3 nd nd 1.9 B 58 57 no 57.54 56 56 Trace Al nd nd nd nd 0.02 0.02 As 1l 10 11 ll 11 10.5 Fe nd nd nd nd 0.12 0.12 TDS 5790 5750 5680 5430 5700 5670 Date Sampled 8/27/83 9/1/83 9/2/83 9/2/83 9/3/83 nd =not determined Table 5. Cations Na K Ca Mg Li Sr Cs NH, Anions sO TDS Date Sampled Chemical analyses of 1984 waters collected from the Makushin Valley test well ST-1,corrected to reservoir conditions. (Concentrations in mg/l unless otherwise specified). 8/4/84 nd=not determined l. 59. 0.004 10. 0.18 5570. 8/7/84 Table 6.Chemical analyses of exhaust pipe waters from Makushin Valley test well sT5lcorrectedforreservoirconditionsassuming60deg”C end point flash temperature. (Concentrations in mg/l unless otherwise specified). Cations Anions Steam Sample #Date Na K Ca Mg Li Sr Cs Hcof so}F cl Br siof.B As Fe TDS Fraction RM83-64 8-24-83 2120 270 160 0.2 il 2.3 1.2 nd¥140 1.2 3650 14 337¥64 12 nd 6780 0.252 RM83-74 9-01-83 1800 130 130 0.1 9.4 2.4 nd nd nd nd 3110 nd 294 55 il nd 5540 0.252 RM83-75 9-02-83 1850 230 130 0.2 9.6 2.5 nd nd nd nd 3170 nd 296 57 ll nd 5760 0.252 RM83-76 9-02-83 1810 230 130 0.1 9.7 25 nd nd nd nd ==3149 nd 301 58 et nd 5690 0.252 RM83-77 9-03-83 1840 230 140 0.1 9.7 2.3 nd nd nd nd 3160 nd 296 58 il nd 5740 0.252 RM84-01 8-04-84 1710 *220 120 1.0 8.8 2.4 1.2 nd 86 1.0 3130 10 297 58 11 0.24 5660 0.252 0.5 8.5 2.4 1.1 nd -84 1.0 3120 10 287 59 10 0.18 5640 0.252RM84-02 8-07-84 1710 .230 110 a)Alaska Division of Geological and Geophysical Surveys,Fairbanks,Alaska,HLA.Moorman,analyst. 7 Unt Table 2.Makushin test well,air corrected gas analyses,mole Z, S le Cod Date S$led RO X co HZS H cng NH N A NZ/A c/sampleCodeateSampledRbg4_it t 4 ft r WT r l MVTW-1 DS/CJ 8-27-83 0.00 0.070 87.74 1.80 0.28 0.006 0.76 9.24 0.18 50.4 48.9 MVTW-2A DS/CJ 9-01-83 0.00 0.098 89.61 2.71 0.46 0.007 0.18 6.92 0.10 67.3 33.0 MVTW-3B DS/CJ 9-02-83 0.00 0.081 92.54 2.27 0.17 0.006 0.25 4.68 0.07 66.8 40.7 MVTW-4B DS/CJ 9-02-83 0.00 0.109 91.61 3.15 0.12 0.007 0.20 4.84 0.08 63.8 29.1 MVTW-5A DS/CJ 9-03-83 0.00 0.105 92.73 2.28 0.10 0.006 0.18 4.63 0.07 63.2 40.7 MVTW-1G-C RM/CJ 8-04-84 0.27 0.089 86.26 2.52 0.04 tr 0.46 10.57 0.15 70.5 2 MVTW-2G-A RM/CJ 8-07-84 0.50 0.056 85.94 |2.52 0.06 tr 0.67 10.69 0.12 89.6 34.1 MVTW-2G-B RM/CJ 8-07-84 0.14 0.064 93.81 i 2.02 0.02 tr 0.30 3.77 0.07 51.7 46.3 '.¥aDapnettact|Scout fee pS Fo dveltad for de A DS/CJ =D.Sheppard,DSTR;New Zealand,and C.Janik,US6S,Menlo Park,analysts.-=),Cadeytind AttRM/CJ =R.Motyka,ADGGS,Fairbanks,and C.Janik.USGS,analysts.\e"e J ¢7onaXg=Ratio,moles gas to moles steam inf.prank Ro Ratio,oxygen in sample to oxygen in air. G pyro Table 13.Mass f gas content of total discharge,using of,corrected gas analyses. Sample #/o Steam Fraction Mass %gas Mass %gas :in Steam Total Discharge MVTW-1 DS/CJ 0.144 0.163 0.023 MVTW-2A DS/CJ 0.116 0.231 0.027 MVTW-3B DS/CJ 0.119 0.192 0.023 MVTW-4B DS/CJ 0.093 0.260 0.024 MVIW-5A DS/CJ 0.092 0.252 0.023 MVTW-1G-C RM/CJ 0.127 0.208 0.026 MVTW-2G-A RM/CJ 0.124 0.132 0.016 MVTW-2G-B RM/CJ 0.124 0.154 0.019 Table 9.Concentrations of chemical species in mmoles/i000 gm REO forreservoirwatersat193degeees ecisaae °C Sample pH Li Na K Cs Mg Ca MVTR-1 5.9 1.4 76.6 5.9 0.009 0.004 2.9 MVTR-28 5.9 1.4 75.3 6.3 0.009 0.002 2.8 HVTR-3B 5.7 1.4 74.7 6.0 0.009 0.002 2.9 MVTH-4B 5.4 1.3 72.7 5.7 0.010 06.002 2.7 MVTH-5a 5.7 1.3 77.0 5.7 0,010 0.002 3.0 MVTH-1K 5.4 1.3 70.2 5.7 0.009 0.004 2.7 MVTR2G-a 5.9 1.3 71.2 5.5 0.009 0.004 2.7 MVTH2G-B 5.3 1.3 71.2 5.5 0.009 0.004 2.7 Sample Fe Al F EF cl Nacl KCl MVTH-1 nd nd 0.052 0.002 86.7 2.41 0.077 MVTH-2A nd nd 0.053 0.003 86.3 2.36 0.083 MVTH-3B nd nd 0.051 0.005 25.4 2.32 0.079 HVTR-4B nd née 0.ust 0.006 80.8 2.17 0.072 MVTR-5A 0.002 0.001 0.O45 0.003 84.3 2.36 0.074 MVTR-1K 0.004 nd 0.040 0.015 $3.9 2.17 0.075 MVTR2G-A 0.003 <0.001 0.053 0.003 S4.7 2.21 0.073 MVTR2G-E 0.003 <0,001 0.052 0.003 84.7 2.21 0.073 Sample Er so}HSO NaSoO KSO Kgsod caso MVTR-1 0.15 0.22 0.002 0.44 0.021 0.003 0.13 MVTH-2A 0.14 0.22 0,003 0.43 0.022 0.002 0.12 MVIR-3B c.13 0.21 0.204 0.42 0.021 0.002 0.12 MVTH-4B 0.74 0.20 0.006 0.39 0.019 0.002 0.11 MVTR-5A 0.15 0.20 0,003 0.41 0.019 0.002 0.12 MVTH-1K 0.13 0.24 0.017 0.45 0.023 0.003 0.13 MVTR2G-A 0.13 0.25 0.002 0.48 0.023 6.603 0.14 MVTH2G-B 0.12 0.25 0.003 0.48 0.023 0.003 0.14 Table 9.Continued MVTR-1 5.4 0.007 4.9 4.9 0.009 0.14 MVTH-24 5.3 0.005 5.0 5.0 0.007 0.13 MVTH-3B 5.3 0,004 5.0 5.0 0.005 0.15 MVTH-4B 5.0 0.002 4.6 4.6 0.002 0.15 MVTH-SA 5.2 0.004 4.9 4.9 0.006 0.15 MVTH-1H nd nd 4.8 4.8 6.001 0.14 MVTH2G-&5.5 0.006 4.8 4.8 0.008 0.13 MVTR2G-B 5.5 0.005 4.8 4.8 0.006 0.13 Sample H¢cog HCOp Caco}caucod HES HS MVTH-1 4.3 0.38 06.0010 0.20 0.09 0.009 MVTR-28 5.2 0.34 0.0007 0.17 0.23 0.017 MVTH 3B 4.6 0.22 0.0003 0.11 0.15 0.008 MVTR-4B 5.0 0.13 6.0001 0.06 0.18 0.005 MVTH-5SA 4.7 0.25 0.0043 0.14 0.14 0.009 MVTH-1R 5.3 0.06 0.0002 0.03 G.16 0.002 MVTR2G-A 3.1 0.25 0.0006 0.12 0.11 0.010 MVTR2G-B 4.0 0.25 0.0005 0.12 0.11 0.008 Table 10.Partial pressure of cof and HPS in solution,reservoir conditions. millimole fraction Partial pressure in total fluid bars Sample co HPS cof HES MVTW-1 0.0882 0.0018 0.55 0.0036 MVTW-2A 0.1026 0.0031 0.64 0.0062 MVTH-3B 0.0893 -6.0022 0.56 0.0043 MVTH-4B 0.0943 0.0033 0.60 0.0065 MVTH-5A 0.0909 0.0023 0.57 0.0045 MVTH-1W 0.0979 0.0029 0.62 0.0057 MYTW2G-A 0.0601 0.0018 0.38 0.0035 MVTW2G-B 0.0749 0.0016 0.47 0.0032 l\.aeTable47.180 Afo in anhydrite obtained from test well core.” Aho {fo -CaS04,T °C,equil'. Depth,m(ft)WRT SMOW (c)(d) 148 (486)-2.98 351 249 592.5 (1944)-1.87 319 226 593.1 (1946)-0.91 295 208 a) b) c) d) Vb.Gtdested Fo teryAnalyzedatUS€S5,Menlo Park.T °C,equil.=equilibration fractionation temperature assuming {$o/1%oforHOis-10.,the current reservoir water value (USGS analysis).Temperature computed using Lloyd (1968)fractionation equation: 1000 In&=3.88 (10°)/T?-2.90,T=°K. Temperature computed using fractionation equation of Chiba and others (1981): 1000 Ine =3.21 (10°)/T?-4.72,T=°K. FSJX& Table 7.Makushin Valley test well ST-1,Oxygen and deuterium isotope analyses -steam and water. (Parts per mil with respect to SMOW). Sample #Water Steam DGGS USGS Date p/u (stu)89/18 csmuy -80/!®0 (uses)psn csuuy 180/180 csmvy 807 !®0 (uses) 71 1 8/27/83 -79 -9.7 -9.2 -97 -13.9 13.45 74 2 9/1/83 -77 -10.05 9.5 -90 -13.2 13.05 75 3 9/2/83 -77.5 -9.95 -9.6 -90 -13.2 -13.05 76 4.9/2/83 -77.5 -8.4 91.6 87.3 -13.15 12.85 77 5 9/3/83 -77.6 -9.8 -9.6 -88.3 -13.1 -13.0 84-1 8/4/84 -66 10.25 -1 -86 -11.25 - 84-2 8/7/84 -81.5 -9.95 --90 -12.3 - SMU =Southern Methodist University,Stable Isotope Laboratory,R.Harmon and J.Borthwick,analysts. USGS =U.S.Geological Survey,Menlo Park,C.Janik,analyst. mean temperature of homogenization of all the samples is at or exceeds the hydrostatic boiling curve indicating boiling should have taken place.The fluid inclusion data does not "rule out boiling at the time of the inclusion trapping,but if boiling were taking place the homogenization temperatures could not exceed that of the boiling curve.The boiling curve must have,therefore,been shifted toward higher temperatures for a given present depth in the early geothermal system. A shift of the boiling curve can be effected by an increase in salinity or an increase in pressure.For the Makushin geothermal system the increase in salinity can be ruled out based on the fluid inclusion freezing data.This means the sur. shift in the boiling curve must have been due to increased pressure in the past.Additional pressure can be supplied if the system is self-sealed so that lithostatic pressures rather than hydrostatic apply.The lithostatic pressures are,however,still to small too prevent boiling in all but deepest the samples.Self-sealed geothermal systems can over-pressure,however the over-pressure can not exceed the lithostatic pressure by more than approximately 30 per cent(Muffler and others,1971).In the case of the Makushin system the-over-pressure required to prevent boiling in the upper samples exceeds the lithostatic pressure by a factor of 3. 55 We must therefore invoke a mechanism to increase the hydrostatic and/or the lithostatic pressure.This can only be done by increasing the overburden on the system.In many fossil systems the overburden is assumed to be rock.If we assume that the Makushin system was solely under hydrostatic pressure then the amount of rock that has been eroded must exceed 300 meters.A lithostatic load would require 100 meters of rock. This is probably an unreasonable amount of material to erode during the expected lifetime of this geothermal system. Rates of erosion by two large glaciers in Iceland were calculated to be 6.4em and 55cem/100 yr respectively(Okko, 1955).Assuming these values to be a upper and lower limit to the erosion rate in the Makushin area we can estimate the amount of time require to erode the 100 to 300 m of rock over-burden.The result is it would require between approximately 20,000 to 500,000 years.While these numbers are reasonable given the amount of time the geothermal system could exist the surface alteration suggest that this is not what occurred. If the additional pressure were supplied by rock now eroded away one would expect to find evidence of the liquid dominated system at the surface.The evidence would be in the form of veins and liquid-dominated type alteration.As was discussed earlier the surface alteration is confined to 56 Mammovapor-dominated type alteration.Thus it does not seem likely that rock is the source of the additional pressure. Instead,as we will discuss in a subsequent section,we propose that the additional pressure was supplied by glacial loading. Alteration Equilibrium in the Makushin System Having established the likely temperatures and pressures of the paleogeothermal system it is now possible to apply thermodynamic data.to the.alteration mineral assemblages and check for consistency. The authigenic minerals of a hydrothermal system are the end result of the interaction among several physical-chemical factors.Browne(1978)grouped these factors under six major headings:(1)temperature (2)pressure (3)rock type (4) fluid composition (5)permeability and (6)duration of activity.These factors vary form fieldto field and in most cases vary greatly even with an individual field.Most of these factors can be more or less directly measured to determine the present conditions.Chemical thermodyamics allows use to predict the results of some of the factors. 57 The model created by the chemical thermodynamic data can then be compared to what is actually seen. Figure 25 is a chemical potential diagram for the system Ca0-Al203-SiO02-H20.The phases shown are all found in the Makushin system.Good thermodynamic data is unavailable for some of the phases.This precludes their being shown on a standard activity diagram.One can,however,obtain information about the system from the shape of their fields and their location on chemical potential diagrams.There are some restrictions which can be applied to the chemical potential diagram shown. Wairakite is known to form only at or above quartz saturation.This means that for a given temperature all the phases to the right of wairakite form at silica activities above quartz saturation.Margarite is also known to form only at silica activities below quartz saturation.Thus one would not expect to find zeolites and margarite together. Indeed this is the case.Zeolites are present in the Makushin system while margarite and gibbsite are absent. Prehnite is also absent in the system.This could indicate that Ca activity is limited by some mechanism. The zoning of zeolites on the diagram reflect the zoning of zeolites with temperature shown in the system.Similar zoning patterns are seen in other systems.The mechanism 58 Memeofor this zoning appears to be related to the change in the silica activity buffer with temperature.At temperatures above 180°C,water is usually saturated with respect to "quartz;at lewer temperatures,however,the stable silica Phase becomes chalcedony or opal(Arnorsson,1975).This allows the higher silica zeolites to form at the lower temperatures and thus creates the zoning pattern(Browne, 1978;Henley and Ellis,1983). Figure 25 is the activity diagram for the Ca-Al203-Si02-H20 system at 200°C.As one can see the Makushin water plots in the Kaolinite stability field.Kaolinite is not an abundant mineral in the cores,however.This might be due to one of three things:(1)The actual temperature of the water is 195°C and thus the diagram is at an inappropriate temperature.(2)Kaolinite is present but in such small amount it was overlooked.(3)The water does rot plot correctly.This last problem appears to be the case.The difference in temperature between the actual temperature of the fluid and the diagram is not enough'to change the relative position of the point in the fields.If kaolinite is present in small quantities that have been overlooked then it would indicate a non-silicate mineral represents the bulk of the calcium bearing alteration.This is possible but would be unusual for most geothermal systems.The water is saturated with respect to quartz at about 207°C.While the change from 207°C to 195°C would allow the silica 59 activity to rise it is not sufficient to allow the depostion of wairakite.It would be enough to allow for the depostion of laumontite.Laumontite is close to it's upper thermal boundary at 200°C but in the Makushin system it does appear to be stable. Laumontite might well be the stable zeolite in the Makushin system under the present conditions.The wairakite may have formed shortly after the formation of the magnetite assemblage while the system was cooling.If this was accomplished in a rapid fashion (i.e.boiling)then the Silica activity would be allowed to rise considerably above the quartz saturation limit.This would in turn allow the formation of.wairnakite..Thus the wairakite may be more indicative of the past conditions than of the present. Figures 26 and 27 are activity diagrams for the systems K20- Al203-CaO-H20 and Na20-Al203-Ca-H20 respectively.The Makushin waters in these diagrams fall in the white mica fields.Although white mica is not shown in the alteration charts it is present in the cores.The plagioclase around some of the recent veins always has some white mica alteration.The amounts are small but significant.White mica has also been reported as the most recent mineral from vein material recovered from the bottom fracture of ST-1. In this case it does seem likely that the active diagrams do reflect the equilibrium in the present system. 60 A final phase diagram has been drown to help explain the 'unusual magnetite assemblage from the ST-1 breccias.All the available evidence indicates the magnetite breccias formed during or shortly after the end of the high temperature stage of the Makushin hydrothermal system. Figure 28 is a f0O2-ph diagram for the system Fe-O-S at 250 °C.Also shown are the calcite and anhydrite insoluble lines.From the homogenization temperatures,250°C is a reasonable Suess at the temperature of the high temperature stage, The original.fluid.must-have had a pH and f02 such that calcite and anhydrite were soluble.Furthermore the f02 cannot have been lower than the pyrite-pyrrhotite line, since pyrrhotite is not present in the Makushin system.For geothermal systems at 250-300°C,Ellis and Mahon(1977)have proposed f0z2 values of between 10°*°and 10°77°°.These are our assumed conditions of the origin system.Clearly under these conditions anhydrite,calcite and magnetite could not formed. Deposition could be accomplished by changing the f02 values but changes in oxidation are difficult and slow at these conditions.Instead it much easier to change the pH.One simply allows the fluids to boil.The pH change in the 61 present Makushin waters due to boiling is over 2.0 pH units. Since fluid inclusion data indicates that the composition of the paleofluids were similar to the present fluids,it is reasonable to assume similar change in pH if the early Makushin system rapidly boiled.Such a change could result in the deposition of anhydrite,magnetite,calcite and quartz. 62 PeerGLACIER UNLOADING:CAUSE OF RECENT CHANGE IN THE GEOTHERMAL SYSTEM We have accumulated compelling evidence indicating that a rapid decline in the water table and a cooling of the upper part of the Makushin hydrothermal system occurred in the geologically recent past .The current depth to the pres- surized hydrothermal system as determined from drill holes, lies at 230-240 m below the the surface in upper Makushin Valley.A vapor-dominated zone presently extends from this depth to the surface.By inference a shallow vapor- dominated zone of similar magnitude is thought to exist at the head of Glacier Valley in the vicinity of fumarole field 3.Yet halite was found coating hydrothermally cemen-. ted rocks in neoglacial moraines and scutwash deposits in the upper part of Glacier Valley (Motyka and others,1983). These salt deposits are thought to be relicts of fossil chloride-rich thermal springs and indicate a hot-water system reached the surface in recent times in a region that is now dominated by fumarole activity and HCO3;-SOQ.thermal a springs. The hydrothermal alteration mineral assemblages found in the upper parts of holes E-1 and ST-1 (which include quartz,calcite,anhydrite,wairakite,and montmorillonite) could only have been formed under hot-water neutral to slightly alkaline conditions and not the acid-steam condi- tions that presently exist in this zone.Furthermore, trace-element enrichment and depletion studies of core from the Makushin geothermal area also indicate neutral pH hot- water rather than acid-steam conditions in the upper parts of the drill holes (Isselhardt and others,1983).The ap- perent lack of steam-dominated mineral assembleges and trace-element geochemistry in these zones indicates the hy- drothermal system water level dropped fairly recently. The evidence from our fluid inclusion studies indicates that the temperature of the hot-water hydrothermal system at the time the fluid inclusions were entrapped in vein -deposited quartz in the upper parts of the system were sub- stantially hotter than present-day temperatures.Examina- tion of figure 23 shows that paleotemperatures at depths as shallow as 100 m below the present day surface were as high as 250°C.The studies also indicate that the waters fram which the quartz was precipitated had a salinity nearly the same as the present-day system.If the paleo-fluid is as- sumed to have had a &**O composition similar to the present day reservoir waters we can then apply the equilibrium frac- tionation equation of Chiba and others (1981)to anhydrite found in a vein at a depth of 149 m (cf.table 11).The result gives a temperature of formation of -250°C which is similar to the temperatures of formation of fluid inclu- sions in the associated quartz. SF 07.0( FLUID GEOCHEMISTRY AND FLUID-MINERAL EQUILIBRIA IN TEST WELLS AND THERMAL GRADIENT HOLES AT THE MAKUSHIN GEOTHERMAL AREA,UNALASKA ISLAND,ALASKA July,1985 Final report submitted to the Alaska Power Authority,under RSA # RSO8-8227,Unalaska Geothermal Drilling. by R.J.Motyka'!,L.D.Queen',C.J.Janik?,D.S.Sheppard', R.J.Poreda'.and S.A."Liss!""- *Alaska Division of Geological &Geophysical Surveys,Fair- banks,Alaska. 27U.S.Geological Survey,Menlo Park,California. *Departmaent of Science and Industrial Research,Welling- ton,New Zealand. *Scripps Institute of Oceanography,University of Califor- nia,La Jolla,California. CONTENTS Introduction Geologic Setting Drilling History Fluid Geochemistry Sampling procedures Methods of analyses Water chemistry Gas chemistry Reservoir fluid composition Fluid saturation Isotope Analyses Oxygen 18 and deuterium Tritium Carbon 13 Helium 3 Geothermometry Hydrothermal Alteration Methods Surface alteration ttee Authigenic minerals in the core Paragenesis and alteration assemblages Fluid Inclusions Methods Fluid salinity Homogenization temperatures Alteration Equilibrium Glacier Unloading:Cause of Recent Change in the Geothermal System : Discussion of Premier Geophysics Electrical Resistivity Study Model of Makushin Geothermal System References Tables Figures Appendix A:Fluid Geochemistry Data Tables for Fumaroles and hot springs INTRODUCTION The Makushin geothermal area is located on northern Unalaska Island in the east-central Aleutian Chain (fig. 1).The explored portion of the geothermal field lies on the east and southeast flanks of Makushin volcano,about 20 km west of the villages of Unalaska and Dutch Harbor.Sur- face manifestations of the hydrothermal system include numerous fumaroles,bicarbonate-sulfate thermal springs, and zones of intense alteration at the heads of Makushin and Glacier valleys (fig.2).Additional fumaroles occur on the north and south flanks of the volcano and areas of warm ground are found..near Sugarloaf and at the head of Nateekin Valley.Resuits of reconnaissance investigations indicated these thermal areas are underlain by a boiling hot-water reservoir capped by a shallow vapor-dominated zone (Motyka and others,1981;Motyka and others,1983). A state-funded exploration drilling program was initiated in 1982 by Republic Geothermal,Inc.(RG1)of Santa Fe Springs,California under contract to the Alaska Power Authority CAPA)(RGI report,1983).In late August,1983 a test-well located near the head of Makushin Valley (ST-1, fig-2)intersected a large fracture at a depth of 1946 ft from which hot waters were successfully produced at the well-head.The well was briefly tested over a five day period then shut down until early July of 1984,then re- opened and allowed to flow for period of 45 days.The Flowing bottom hole temperature (BHT)in both cases measured 193 °C.Aithough fluid enthalpy is fairly lou, results of the reservoir engineering tests indicated the productivity of the fracture was sufficient for at least two production wells which could each drive 5 MW generators CRGI report,1985). Through the cooperation of RGI and APA,the authors were aLle to obtain samples of ST-1 fluids at the well-head during the initial testing of the well in 1983 and again in August of 1984 after the well had flowed for approximately 40 days.Rock cores extracted-from a thermal gradient hole (TGH)drilled near Sugarloaf in 1984 (A-1,fig.2)were shipped to Fairbanks,examined for mineral alteration,and campared te well-logs for ST-!and TGH E-1,D-1,and I-i which were previously examined by Queen,1984.This report presents the findings of our geothermal fluid,mineral al- teration,and fluid-mineral investigations of well ST-1 and the thermal gradient holes.Appendix A of this report also includes updated geochemical data on fumaroles,thermal springs,and cold waters in the Makushin geothermal area that were first discussed in Motyka and others,1983. Objectives of our investigations included: 1)Determination of reservoir fluid geochemistry. 2)Provision of pre-develapment geochemical data base. 3)Study of fluid-mineral equilibria. 4)Information on deeper reservoir characteristics and on the origin chemical constituents in the reservoir fluids. 3)Geothermometry. 6)Mixing relationships. 7)Determination of potential scaling and environmental problems. 8)Comparison of isotopic and chemical composition of ST-1 fluids to neighboring fumaroles and springs. 9)History of the hydrothermal system. The Makushin geothermal system is the first in the Aleutian arc of active volcanism to have been successfully drilled and produce fluids at temperatures above atmospheric boiling.As such,the Makushin program has provided us with a unique opportunity to study arc-related hydrothermal systems and the dynamic interactions between volcanism, glaciation,and hydrothermal systems. The findings of our studies,discussed below,combined with our previous observations,and with results of volcanic in- vestigations by Nye and others (1985),with measurements and tests made by RGI on the thermal gradient holes and test well (RGI reports,1983,1984,and 1985),and the results of an electrical resistivity survey conducted in 1984 by Shore (1985)have led us to the following model for the Makushin geothermal system: 1)The heat source driving the hydrothermal system is presumed to be a shallow-lying body of magma as suggested by the caldera at the summit of Makushin volcano.The mag- ma chamber is thought to be related to the post-glacial outpouring of homogeneous lavas on the northeast flank of Makushin volcano and the pyroclastic flows at the head of Makushin Valley. 2)The main hydrothermal reservior has a temperature of 250°C and is located over the heat source.Hot waters from the reservoir ascend through the core region of the volcano then cool as they spread laterally.Steam and gases that evolve from the boiling of the outflowing plume of hot water as it nears the surface feed the fumaroles and bicarbonate-sulfate thermal springs that abound at mid- elevations on the south and east flanks of the volcano. 3)The reservoir is charged by meteoric waters that infil- trate into the system along fractures located at mid-to lower elevations of the valcano.The reservoir waters ob- tain their chemical composition partially from release of volatile gases from the underlying magma system but mainly from interaction with the reservoir rock.ST-1 waters are moderately rich in sodium and chloride and have relatively high concentrations of calcium.The latter is attributed to the interaction of hot waters with the gabbronoritic in- trusive that appears to be acting as the host rock for at least a portion of the reservior waters. 4)Fluids being produced from ST-1 are out of equilibrium with the measured flowing BHT.Geothermometry indicates the waters were hotter and must have cooled upan ascent. Results of tritium studies rule out mixing of meteoric waters as the cause of the cooling.Fluids at the bottom of ST-1 are below the pressure boiling point.The remaining alternative is that the waters cooled conduc- tively upon ascent and passage through bedrock. >)Results of electrical resistivity surveys,conducted by Premier Geophysics of Vancouver,British Columbia,indicate that the hydrothermal system at the head of Makushin Valley is bounded by faults and fractures and that the hydrother=- mal system extends west and south of ST-1 and E-1.The elec-- trical resistivity survey showed no evidence for any hy- drothermal system east of fumarole field 1 nor for any linear hydrothermal system offset to the east from the main volcano.These findings indicate that of any future production wells should be sited at or up-valley of ST-l. 6)A wealth of evidence derived from mineral alteration and fluid inclusion studies indicates that the Cl-rich hot- water system extended to the surface at the heads of Makushin and Glacier Valleys in the recent past and that Peeranthe near-surface system temperature reached 250 °C.The change in hydrostatic pressure caused by the advance and retreat of Holocene glaciers is proposed as the cause of these changes in the near-surface regime of the hydrother- mal system. GEOLOGIC SETTING The Makushin area is one of over 70 major volcanic centers that comprise the Aleutian arc of active volcanism.The Aleutian Chain lies immediately north of the Aleutian Trench,a convergent boundary between the North American and the Pacific lithospheric plates.The eruption of Aleu- tian magmas appears to be intimately tied to the subduction of the Pacific plate beneath the North American plate. Makushin Volcano (2,000 m)is a large composite,poly- genitic volcanic center that dominates northwestern Unalaska Island.The broad domed-shaped summit is capped by a -5 km diameter ice-filled caldera and has glaciers that descend the larger valleys to elevationsas Tow as 300 m.Four satellitic late-Pleistocene to Holocene volcanic cones also occur in the area and are aligned in a nor- theasterly trend,roughly subparallel to the strike of this portion of the Aleutian arc. Geology of the Makushin study area,generalized from Nye and others (1984),is shown in figure 2.The oldest unit exposed in the study area is the Unalaska Formation which consists of Miocene to early Pliocene volcanoclastic rocks, dikes,sills,lava flows,and minor sedimentary rocks.The upper part of the formation consists primarily of pyroclastic rocks while lava flows dominate the lower sec- tion.The formation has been metamorphosed to grades as high as the pyroxene hornfels facies near contacts with an unzoned gabbronoritic stock that is extensively exposed at the heads of Makushin and Glacier Valleys.The intrusive is medium-grained,equigranular to porphyritic,and con- sists primarily of plagioclase (50 to 75 modal percent, Anso to Anyo)with subequal amounts of clinopyroxene and or- thopyroxene (Nye and others,1984).THe gabbronorite is thought to be roughly correlative with other intrusives ex- posed on the island and which have been dated at 10 -13 MeyebePpe Fumaroles and hot springs at the heads of.Makushin and Glacier Valleys emanate almost exclusively from the gab- bronorite and hornsfelsic border zone.The gabbronorite was encountered in all five holes drilled at the Makushin geothermal area and appears to be acting as the primary reservoir rock at least in the explored portions of the field.Interdigitation of the Unalaska Formation with the gabbronorite is common,suggesting that only the roof of the stock has been exposed. The volcanic rocks which comprise Makushin Volcano and the satellitic vents are discussed in detail by Nye and others (1985).Makushin Volcano is a polygenetic composite stratovolcano that is primarily composed of basalt ahd an- desite flows,lahars,and pyroclastic flows.Available K-Ar ages on the Makushin lavas are less than 1 m-y.in- dicating that the Makushin volcanics in the study area are exclusively Quaternary. The satellitic cones are post-Wisconsinan monogenic vents consisting primarily of chemically homogeneous basaltic toa andesitic flows and pyroclastic flous and cinders.A thick series of chemically homogeneous valley-filling,post- Wisconsinan andesite flows also issued from the east flank of Makushin Volcano,envoloping Sugarloaf and filling Driftwood Valley.This large outpouring of post- Wisconsinan lavas and pyroclastic rocks suggests a Holocene magmatic pulse of exceptional volume.However,trace ele- ment geochemical studies (Nye and others,1985)indicate that the satellitic cones had source regions and plumbing systems separate from the ones supplying Makushin Volcano. The huge amount of lavas represented in the east flank Holocene Makushin eruption suggests that a large volume of residual magma may have lodged in the subcrustal region of the volcano and may be acting as the heat source for the present-day hydrothermal system. DRILLING HISTORY ST-1 Test well ST-1 is located near the head of Makushin Valley (fig.2).The wellhead sits upon the upper edge of an apron of pyroclastic debris that fills the bottom of upper Makushin Valley.Details of the procedures followed in the drilling of test well ST-1 Cand TGH A-1)can be found in RGI's 1984 report to the Alaska Power Authority.The site chosen for ST-1 was based on the following factors:1)prox- imity to E-1,which was the hottest of the thermal gradient holes drilled in 19823;2)proximity to fumarole fields 1 and 2 and to a fault which runs up-canyon from ST-13;and 3) convenient logistical staging area for drilling.The upper part of ST-1 was drilled to a diameter of about 15 cm to a depth of about 215 m .Hole diameter below 215 m down to well bottom is approximately 7-6 cm.Except for the top 10 m which are composed of pyroclastics,ST-1 penetrates the gabbronorite to a depth of 593 m (Queen,1984). The drillers encountered a pressurized steam-filled frac- ture at a depth of 210 m.Well-head pressures after shut- in indicated steam temperatures of 140 to 150 °C.Samples' of gases and steam evolving from the fracture were obtained from a well-head release valve.Subsequent drilling and downhole pressure measurements showed the pressurized hy- drothermal system water table to lie at a depth of -30m below this fracture.Thus the steam in the fracture probably evalved from boiling of the water table. The steam fracture was sealed and drilling continued.No additional open fractures were encountered until 585 m below the surface.The well was shut and pressure allowed to build.Upon opening of the well hot waters spurted in- termittently from the well-head exhaust but continuous flow was was not sustainable.Field measurements of chloride concentrations in the flashed waters ranged from ee ee ce 5,000 to 7,000 ppm. Drilling was continued to a depth of 593 m where upon the drill string dropped an estimated 1 m indicating a major cpen fracture had been intersected.The well was im- mediately shut and the well-head pressure allowed to in- crease until it stabilized at approximately three bars. The well was then opened on August 27,1983 and the resul- tant fluid-flow up the borehole became self-sustaining. The well was briefly flowed and exhaust-end water samples collected for chemical analyses to determine whether any ad- verse environmental effects would occur upon discharge of the well waters into a local stream.After approval for discharging the waters was obtained from the appropriate agencies the well was re-opened on August 29 for a five-day flow test which included downhole pressure and temperature measurements by RGI staff scientists.During this period the authors collected five separate suites of water and gas samples. The well was then shut down and well-head pressure monitored through the winter months.Static down-hole pres- sure and temperature measurements were made on July 5,1984 and the well was re-opened on July 7.The well was flowed almost continuously over a 45-day period until shut-down on August 10,1984.Samples of the well fluids were obtained by the authors on August 7 and again on August 9,1984. Original plans for 1984 called for a deepening of ST-1 after the flow test.The APA decided against the deepening in order to maintain the well?for demonstration purposes. Flowing bottom hole temperatures measured 193 °C in both 1983 and 1984 (RGI report,1985).The static hole tempera- ture measurements made by RGI on July 5,1984 gave a max- imum down-hole temperature of -198 °C at a depth of -460 me Static bottom hole temperature measured -195°C. FLUID GEOCHEMISTRY Sampling Procedures Samples of fluids produced from the test-well were collec- ted both in 1983 and 1984.The majority of the samples are of fluids from the major production zone at 593 m depth. These samples were obtained between August 27,1983 and Sept.3,1983 and between August 1,1984 and August 7, 1984.The test-well was shut from Sept.3,1983 until July 4,1984,then run continuously until shut-down on August 8, 1984. Samples of gases and waters from ST-1 were collected using a Webre type mini-cyclone separator.Design and use of the separator are described in Nehring and Truesdell,1982. Figure 3 shows the separator as used at ST-1.The separator was attached to the side of the exhaust manifold at a point about 5 m from the wellhead and 2 m before the throttling orifice.Separator pressure was monitored with a high pres- sure gauge located before the separator's water exhaust val- ve.Fluid collection pressures and temperatures toagether with sampling dates and steam fractions are given in table 1. The separator was first adjusted for collection of the water fraction.Fluids emerging from the water exhaust port of the separator were routed through a condensing coil im- mersed in an ice bath,then collected and filtered through 0.45 micron filters.The sample suite normally consisted of 1 liter filtered untreated,1 liter filtered acidified (HCI),1 liter filtered and treated with formaldehyde for 6'*0-SO.determinations,100 ml of water at a dilution of 1:10 and 1:5 for silica determinations,i liter of un- treated water for tritium determinations,and 30 ml of water for stable isotope determinations.In addition,raw untreated samples were callected for in-field determination of HCOs;,pH,H2S,and NHs-In two cases (samples 77 and 02),waters were filtered through O.1 micron filters and treated in the field for Al analysis following methads described by Presser and Barnes,1974. As an additional check on water chemistry,water samples were collected from the end of the exhaust manifold.This was done by placing a large paolyethelene beaker beneath the pipe-end and allowing the flashed water to flow into the container. Steam and gas samples were collected after first adjusting the separator for pure steam phase flow.The steam and gases were routed through the condensing coil then collec- ted in sodium hydroxide charged evacuated flasks.Ad- ditional samples were collected in uncharged evacuated flasks for 7He/*He analyses.A 500 ml sample of the steam condensate was collected for Cl analyses as a check against water phase contamination.Thirty ml samples of the con- desate were also collected for stable isotope analyses. Methods of Analyses Water HCO;,PH,H2S,and NHs were determined in the field fol- lowing methods described in Presser and Barnes (1974).The remaining constituents were analzed at the DGGS water laboratory in Fairbanks.Major and minor cation concentra- tions were determined using a Perkin-Elmer atomic absorp- tion spectrometer and following standard procedures.Sul- fate and bromide were determined on a Dionex ion chromatograph.Fluoride vas determined using specific ion electrode methods.Chlorides were analyzed by Mohr titra- tion and boron by carminic acid spectroscopy.Silica con- centrations were determined by the molybedinate biue method. Stable isotopes (*°0/1*O and D/H)were analyzed at Southern Methodist University,Dallas,Texas and at U.S.Geolsgical Survey,Menlo Park,California.Tritium concentrations were determined-at the Tritium Laboratory,University of Miami,Miami,Florida. Gases Residual gases,i.e.,gases not absorbed in the sodium hy- droxide solution (He,Hz,Ar,O2,N2,and CHa)were analy- zed on a dual-column gas chromatograph with both argon and helium carrier gases at the U.S.Geological Survey,Menlo Park,California.Moles of residual gas were calculated from measured gas pressures and head space volumes.COz and H2S concentrations in the sodium hydroxide solutons were determined by titration and by ion chromatography respectively.Concentrations of these gases were also checked by gravimetric methods using SrClz2 and BaCiz to precipitate SrCO3z;and BaSQ,.The SrCOzs precipitate was then reacted with phosphoric acid to determine COz2 yield. The evolved gas was saved and analyzed for '*7C/*?C.Steam content of the gases was determined by weight difference before and after sampling.Ammonia was analyzed by specific ion electrode method. Adjustments were made for head space gases dissolved in the solution using Henry's Law.Moles of each constituent col- lected were then determined and the mole percent of each constituent was calculated.A correction was made for air contamination by using the ratio sf oxygen in the sample to oxygen in air.The gas concentrations in mole percent were then recalculated on an air-free basis. Helium isotope ratios (*He/*He)were determined at the Scripps Institute of Oceanography,La Jolla,California. SenterolCarbon isotope ratios in CO2 ('4C/'?C)were analyzed at the U.S.Geological Survey,Menlo Park,California. Water Chemistry Results of geochemical analyses of ST-1 waters obtained from the Webre mini-cyclone separator and fram the end of the exhaust pipe are given in tables 2 and 3.Total discharge water chemistries,given in tables 4 and 5,were calculated using separator water and steam fractions given in table 1.The latter were based on separator pressure and a discharge enthalpy of 821 kJ/kg which corresponds to the measured flowing bottom-hole temperature of 193 °C. End-of-exhaust water analyses give total discharge concen- trations of constituents 10 to 15 percent higher than separator values if the exhaust water fraction is cal- culated on the assumpticon of atmospheric pressure-boiling point conditions.However,flashing at the exhaust end ap- parently occurs at pressures well below atmospheric (OD. Michaels,pers.comm.,RGI,1984).Supporting evidence for the latter comes from a temperature measurement of the cen- ter of fluid flow from the exhaust .made by P.Parmentier (RGI).The temperature measured was 60°C indicating that low-pressure effects that are not well understood are causing increased flashing of the exhaust fluid.Using the 60°C temperature results in an exhaust-end water fraction of 0.75.Applying this water fraction to exhaust analyses gives total discharge chemistries that are in close harmony with those obtained from the separator method (table 6.). Additional support for basing total discharge chemistry on the separator water analyses comes from RGI's reported analyses of 1983 ST-1 water samples.Two of their samples were obtained under high-pressures using an entirely dif- ferent technique than the mini-cyclone separator method (RGI Final Report,1984,pg.XII).These samples yielded total discharge chemistries nearly identical to our separator samples. The ST-1 waters are moderately saline and low in bicar- bonate.Comparison of 1983 to 1984 chemistries show the waters to be nearly identical 3;the 1984 waters are slightly less saline and slightly richer in HCOz3.The ST-1 waters are high in arsenic which could pose a potential water pollution problem for salmon spawning areas if ex- haust waters are discharged directly into.Makushin Valley streams.Compared to waters in other geothermal systems, ST-1 waters are relatively rich in calcium.The source of calcium is probably alteration of plagioclase in the gab- bronoritic host reservoir rock.The plagioclase has a com- position of Anso-Anzo so more calcium than sodium should be dissolved by the waters.Much of the dissolved calcium must therefore be removed from the reservoir waters through reactions involving preciptation of anhydrite,calcite,and formation of zeolites. Gas Chemistry Air corrected analyses of gases collected from test-well ST-1 in mole-percent are given in table 7.Gas content in total discharge is given table 8.Of the 1984 samples, MVTW-2G-B is the least air-contaminated and its analysis is considered the most reliable and representative of the August,1984 geothermal system. Gas concentrations in total discharge are extremely low,- 0.02 percent,with a slight decline in total gases occur- ring between 1983 and 1984.Hydrogen content in particular seems to have dropped significantly,nearly an order of mag- nitude since the well was first opened.Methane concentra-- tions appear to have also declined and was present in only trace amounts in the 1984 samples.Hydrogen sulfide,al- though 2 -2.5 percent of the total non-steam gases,is in such low concentration in the total discharge it should not pose any significant health or polluticn problems. The COz2-H2S-Ne composition of ST-1 gases are plotted ona tri-lateral diagram which also shows compositions of fumarolic gases in the Makushin geothermal area (fig.4). Gases from the superheated fumarole (3sh,150°C)show the highest relative concentrations of Hz2S.Gases from other fumaroles and from ST-1 follow a trend towards increasingly greater proportion of Ne indicating that the H2S in these discharges is being selectively removed by oxidation with air or air dissolved in water. The ratio of Nz to Ar is plotted against He to Ar in figure 5S»The Ne/Ar ratios in the atmosphere and for air dissol- ved in water at 25°C are also shown for comparison.Except for 688,all ST-1i samples fall between these two values in- dicating air is the primary source of N2 dissolved in the reservoir waters.We note also that the trend of decreasing He with time is shown on this graph.The trend may indicate a preferential outgassing of the lighter gases from the reservoir fluids early in the well-test.An alter- native passibility is that fluids from the 593 m fracture flowing up the borehole are being contaminated with gases leaking from the steam fracture at 210 m with the amount of contamination decreasing with time. Reservoir Fluid Composition Concentrations of chemical species dissoived in the aquifer waters feeding ST-1 at the 593 m fracture were calculated using ENTHALP,a program originally developed by Truesdell] and Singers (1973)and recently updated by Singers and Hen- ley (pers.comm.,1984).Results of the computor calcula- Meeetions in molal units are given in table $.The pH of the ST-1 waters at the reported flowing down-hole temperature is -,5.8,which is slightly alkaline compared to neutral pH of 5.65 for waters at this temperature. The partial pressures of COz2 and H2S in the aquifer waters are given in table 10.The average PCOz in 1983 was 0.58 bars compared to 0.47 bars for 2G-B in 1984.PH2S also declined from 0.005 bars in 1983 to 0.003 bars in 1984. Again these declines in pressures could reflect a general outgassing of the aquifer fluids or,alternatively,con- tamination from the 210 m steam fracture which has decreased with time. The oxygen partial pressures,PO2,of the ST-1 fluids can be estimated from the relationship between temperature and PO2 determined by D*Amore and Panichi (1980), log PO2 =8.20 -(23643/T)(1) where T is the fluid temperature in °K.For 193 °C,the PO2 of the ST-1 fluids is on the order of 10°43 atm.A check can be made on POz using the equation log PO2 =12.5 -26888/T -9/7 log (PH2 S/PCOz ) +6/7 log PCO2 (2) CD'Amore and Panichi,1980).Inserting values from table 10 into equation (2)gives results nearly identical to those derived using equation (1). Fluid Saturation Three hydrothermally deposited minerals were found layered aon the gabbronorite wallrock retrieved from the open frac- ture at the bottom of ST-1.The innermost layer was com- posed primarily of quartz;the second layer was mostly cal- cite;while the outermost layer consisted primarily of anhy- drite.The degrees of saturation of SiO2,CaCOQz2,and CaSO. were examined to determine whether any of these minerals are presently being deposited in the system. The solid curve in figure 6 is the solubility of quartz in water at the vapor pressure of the solution from Fournier and Potter,1982.All the samples obtained from ST-1 are slightly supersaturated with respect to the measured bottom hole temperature of 193°C.The quartz -silica equilibrium temperature for the ST-1 waters is 207°C which suggests that the waters have cooled before entering the borehole. The solid curve in figure 7 is the calcite saturation curve and the crosses are the values for ST-1 waters as deter- mined by ENTHALP.The ST-1 waters are all undersaturated at 193°C.However,calcite was found deposited on an instru- ment cable that was left in the borehole for several days in mid-July,1984.The ST-1 waters apparently became super- saturated with respect to calcite as they boiled upon ascen- ding the borehole.The potential for calcite scaling of production well boreholes therefore exists and must be reckoned with in future development. An estimate of the temperature of deposition of the calcite was obtained by determining the degree of fractionation of '80 between the water and the calcite.The 6*0O of the cal- cite sinter was analyzed by the stable Isotope Laboratory at Southern Methodist University and determined to be +0.6 with respect to standard mean ocean water (SMOW).Using a value of -10.2 for 6'*0 of the water (cf.table 13)and the fractionation equation of O*'Neil and others (1969),gives a temperatue of deposition of -177°C. The state of anhydrite saturation in ST-1 waters is shown by crosses in figure 8 The anhydrite equilibrium solublity curve (solid)is taken from Helgeson (1969),with the activity product of anhydrite as defined by Helgeson plotted on the Y-axis.Activity coefficientsandmolal con- centrations for:Ca and S04 innic species were determined using ENTHALP.As can be seen from the figure,the waters would have to be considerably warmer for anhydrite deposi- tion to occur at ST-1. An estimate of the temperature at which the anhydrite deposition occurred was obtained by determining the degree of fractionation of **0O between the anhydrite and the reser- voir waters (table 11).Using the fractionation equation of Chiba and athers (1981)and assuming a 6**0O of 10.2 for the reservoir waters gives a temperature of deposition of - 208°C for anhydrite found at the bottom hole fracture.In contrast,using the same technique,anhydrite found in a vein at 592.5 m depth has an estimated temperature of depositon of 226°C while anhydite found in a vein at 148 m depth has an estimated temperature of depostion af 249°C. )"ISOTOPE "ANALYSES Oxygen 18 and Deuterium Results of oxygen and deuterium isotope analyses of water and steam samples that were collected using the mini- cyclone separator at the ST-1 welli-head are given in table 12.The corresponding pre-flash isotopic compositions of ST-1 waters are given in table 13 and plotted in figure 9. Because of suspected sampling and analyses problems,sam- ples 76 and 84-1 are not included on figure 9.Also plot- ted on figure 9 are isotopic compositions of locally derived meteoric waters (LDMW),Tow Cl,high HCO; SOQ,ther- mal spring waters,Cl rich thermal spring waters,the oemeteoric water line defined by Craig (1961),and the Adak precipitation line (Motyka,1982). The majority of meteoric and low chloride thermal spring water samples plot to the left of both meteoric water lines While the chloride thermal spring and ST-1 waters plot to the right of the lines.Meteoric stream waters whose source regions lie at mid-to lower elevations on the volcano have heavier isotopic compositions than meteoric stream waters whose source regions are at higher elevations.The range of isotopic compositions for low chloride thermal spring waters directly overlaps the mid-range for meteoric waters indicating the thermal waters are locally derived meteoric a:a ann waters at mid-elevations. On the basis of similarities in deuterium composition of meteoric and thermal waters,reservoir waters in the majority of explored hydrothermal systems are thought to be derived mostly from meteoric sources (Craig,1963).The Makushin system is no exception.The deuterium values of the ST-1 waters correlate with the mid-to upper range for meteoric waters which suggests that the waters charging the reservoir feeding ST-1 originated as precipitation on the mid-to lower flanks of the volcano.These meteoric waters probably infiltrate into the reservoir system through frac- tures on the periphery of the hydrothermal system. The ST-1 waters show a positive shift of 1 mil in 6**0 with respect to the two meteoric water lines and a shift of about 1.5 mils with respect to Makushin meteoric waters. Such shifts are commonly observed in geothermal systems and are caused by high-temperature oxygen isotope exchange between the thermal waters and the reservoir rock.Similar shifts are not seen for deuterium because of the lack of hy- drogen bearing minerals.The magnitude of an oxygen isotope shift is a function of water temperature,duration of contact,and the magnitude of the difference in the water vs.rock isotopic compositions.The gabbronorite reservoir rock at Makushin was found to have a 6**®O composi- tion ranging from -4.0 for highly altered rocks to +2.8 for slightly altered rocks (table 14).The difference in unal- tered vs altered composition indicates isotope exchange has occurred in the Makushin hydrothermal system and thus the 6**0 shift observed for the ST-1 waters is probably due to high temperature exchange. Tritium Results of tritium analyses for waters collected from ST-1 and from various springs and streams are given in table 15 and plotted in figure 10.Panichi and Gonfiantini (1978) have reviewed the use of tritium as an indicator of age and mixing of waters in geothermal systems.Tritium was in- troduced into the atmosphere in large quantities during the years of thermo-nuclear weapons testing following 1952. Since the test ban treaty of 1963,tritium in the at- mosphere has steadily declined,but still remains at levels much greater than pre-1952.Because of its relatively short half-life (12.3 yrs),tritium provides a good marker for waters of recent age-To provide a comparison for Makushin waters,the tritium levels in 1980 precipitation at Anchorage (the nearest station and most recent year for which data is available)are also plotted on figure 10. The weighted-average tritium content of precipitation in An- chorage in 1980 was 29 Tritium Units (T.U.),with a seasonal variation ranging from a winter minimum of 16 T.U. to a late-spring maximum of 51 T.U. A water sample collected from a coid spring fed by snow melt has tritium level of 11 T.U.,which is consistent with winter precipitation.Tritium concentrations in lTouw-Cl HCO;-SOQ,thermal springs ranged from 16 to 36 T.U.which in- dicates these waters are very young and probably originated as local precipitation.The two samples collected from Ci-rich thermal springs,although lower in tritium (6 and 10 T.U.)than any of the other spring waters sampled,are still high enoughin tritiumto indicate that thermal waters are probably mixing with meteoric waters near the surface before emerging as springs. In contrast,two water samples collected from ST-1 gave tritium concentrations of 0.3 and 0.5 T.U.Concentrations this low indicate the waters are at least 25 years in age and probably alder (Panichi and Gonfiantini,1978).Fur- thermore,the low level of tritium in the ST-1 waters strongly argues against any substantial cold-water mixing at ST-1.Tritium concentrations in waters older than 60 yrs would be expected to be <O.1 T.U.(Truesdell?and Hulston,1980).If we assume this value as the limit for deep thermal waters at Makushin and use 29 T.U.for a cold water end member than the cold water fraction in any mixing would be at most 1.4 percent. Carbon 13 in Carbon Dioxide Results of analyses of 6&*7C composition of COz2 gas collected from ST-1 are given in table 16 and plotted in figure 11. Also plotted are 6**C compositions of COz2 gas collected from various fumaroles and hot springs.Mantle-derived COz is thought to have 6**C compositions ranging from -4 to -8 per- mil (Craig,1953;Welhan,1981),while COz from organic- sedimentary sources have 6*7C values <-11 permil.The highest 6'7C compositions at the Makushin geothermal area were found for the samples from the summit and from the superheated fumarole in field 3.The majority of the sam- pled gases including those from ST-1 in 1983 fall in the narrow range of --11.5 to -13-5 permil which lies at the up- per end of values for organic- sedimentary COz2.'For reasons demoedyet unknown the 6'7C-COz2 in 1984 ST-1 fluids was found to be -15 permil,1-5 mils less than the 1983 values. The 6**C-CO2 compositions at Makushin suggest that the COQ is in part being generated from thermogenic breakdown of organic-sedimentary material underlying the volcano with a magmatic intrusion acting as the heat source.These ther- mogenic gases then mix with COz outgassing from the magma body itself and migrate into the hydrothermal reservoir. Helium Isotopes Samples of gases obtained from ST-1 were analyzed for helium isotope compositions.Enrichments in 7He with respect to atmospheric levels have been correlated wih mag- matic activity on a worldwide basis with the excess *He thought to be derived from the mantle (Craig and Lupton, 1981).Samples of gases for *He/*He testing were collected in 50-cc glass flasks (Corning 1720)fitted with high- vacuum stopcocks.The procedures followed for gas extrac- tion,measurement of absolute helium amounts,mass spec trometer measurement of ?He/*He ratios,and application of He/Ne correction for air contamination are described in Lup- ton and Craig (1975),Torgersen and athers (1982),and Poreda (1983). Table 17 presents helium isotope data for ST-1 and for gases collected from fumaroles and hot springs in the Makushin geothermal area-The R/Ra value (*He/*He ratios of sample vs air)of 7.8 obtained for the summit fumaroles falls within the range of values of 5 to &found at other volcanic vents in the Aleutian Arc and from convergent mar gin volcanic arc settings elsewhere in the world (fig.12) (Craig and others,1978;Poreda,1983).R/R.a values for gases from the flanks of Makushin are all lower than that from the summit,with the lowest values occurring at fumarole field 3 and for ST-1. Variations in R/R.have been found at other volcanically related geathermal systems(Craig and others,1978;Welhan, 1981;Torgersen and others,19823 Torgerson and Jenkins, 1982).A high value for R/Rz in gases from geothermal systems suggests a more direct connection to magmatic sour- ces with Tittle or no crustal contamination --although it may also result from leaching of young volcanic rock (Trues- dell and Hulston,1980).Lower values indicate a greater crustal influence of radiogenic "He. If the summit value of R/Rz is taken to represent the *He/*He ratio of the parent cooling magma,then the R/R, values for sites on the flanks of the volcano represent varying degrees of mixing with a crustal *He component. One effective method for increasing the amount of 'He present in the gases is by hot-water interaction with and Coaneleaching of reservoir wall rock.At Makushin the hast reservoir rock is a gabbronoritic pluton.Calculations by Torgersen and Jenkins (1982)indicate that the R/R.ratio in an intrusive would fall to <O.1 through radiogenic decay of U and Th for emplacement ages >1.0 mey.&mixing of 55 percent crustal He and 45 percent magmatic He would produce an R/R.value of 3.7 with 7.8 for the magmatic component and 0.1 for the crustal component. GEOTHERMOMETRY The results of applying water,isotope,and gas geother- mometers to ST-1 thermal fluid geochemistry are given in tables 18,19,and 20 and compared in figure 13.Only two of the geothermometers,the chalcedony geothermometer of Fournier (1981)and the Na/Li geothermometer of Foullic and Michard (1981),give temperatures in agreement with the Flowing bottom hole temperature of 193°C reported by RGI. Free quartz is found in the gabbronorite and for tempera- tures greater than 180°C quartz is the silica phase most likely to control dissolved silica (Fournier,1981).Thus for ST-1 the quartz temperatures which average about 207°C are the more appropriate estimates to use. The Na/K geathermometer of Arnorsson (1983)for basaltic rocks is chosen as the most appropriate for ST-1 since the host reservoir rock is a gabbronorite.The average tempera- ture of 225°C given by this geothermometer is in close agree- ment with the average temperature of 226°C given by the Na-K- Ca geothermometer of Fournier and Truesdell (1973).The water-sulfate oxygen isotope geothermometer of McKenzie and Truesdell}(1977)predicts even higher temperatures (table 19.).Using the isotopic composition of ST-1 waters (cf. table 13)this geothermometer gives reservoir temperatures of 247°C. Results of applying three different gas geothermometers to ST-1 fluids are given in table 20.The gas geothermometer of D'Amore and Panichi (1980)is based on an empirical rela- tionship between ratios of H2S,Hz,and CH.to COz and the partial pressure of COz in the reservoir.For analyses in which CHs was present in only trace amounts a value of 0.001 mole percent was used in the computations.The H2S geathermometer of D*'Amore and Truesdell (1983)is based on equilibria between constituents affecting H2S concen- trations.The COz2 geothermometer of Arnorsson and others (1983)is based on an empirical relationship between tem- perature and PCO.observed in geothermal waters from drill- holes in Iceland. Discounting the 250°C temperature given by the D'Amore- Panichi geothermometer for MVTW-2A,the average tempera- tures given by the gas geothermometers are 211,216,and eetsosd219°C,respectively.These temperatures fall between the temperatures predicted by the quartz and cation geother- mometers. Almost al]the geothermometers that were applied to ST-1 predict temperatures substantially higher than the reported flowing bottom hole tempertature of 193°C,which indicates the fluid chemistry is out of equilibrium with the measured temperature.Such differences in geothermometer tempera- tures ,particularly between the quartz,cation,and sulfate-water axygen isotope geothermometers,have been ob- served at numerous other high-temperature hot-water systems and have been commonly attributed to the combination of cooling of the thermal fluids upon ascent and the differen- ces in the re-equalibration times of the various geother- mometers (Fournier,1981).For example,quartz equilibrates fairly rapidly,on the order of days to weeks at T -200°C,while the cation geathermometers equilibrate on the order of weeks to months for T -200°C.- In contrast,the sulfate-water oxygen isotope geother- mometer takes much longer to equilibrate at lower tem- peratures.Experimental studies by Chiba and Sakai (1985) on the,fractionation of *®O between H20 and SOs.showed the equilibration time to be weakly dependent on pH and strongly dependent on temperature-e For a pH of 6 (similar to ST-1 waters)and a temperature of 250°C,the equilibra- tion half-time,ti,2,is on the order of several weeks while for a temperature of 200°C,ti,2 is on the order of 10 -20 years.Thus the sulfate-water oxygen isotope geother- mometer is a good indicator of deep reservoir temperatures. The correlation of lower calculated temperatures with shor- ter equilibration times for the geothermometers applied to ST-1 fluids indicates the thermal waters have slowly cooled upon ascent,before entering the ST-1 borehole.As seen from the results of the tritium analyses any cooling at- tributable to mixing with cold meteoric waters appears minimal.Temperature-pressure conditions preclude boiling at the bottom of ST-1 thus leaving conduction as the most likely process by which the ST-1 waters have cooled. HYDROTHERMAL ALTERATION Methods The description of the lithology and minerals is based largely on hand-samples.As a control,selected samples were chosen for additional study by x-ray diffraction and optical petrography.The location of the samples taken from the cores are shown on the core logs (figs.14,15,16,17, 18).Alteration minerals that could not be immediately identified by physical properties due either to their fine- frained nature (clays)or their rarity (zeolites)were 'identified using x-ray diffraction.Once positively identified it was possibleto find these minerals elsewhere in the core by their physical properties.Thin sections of representative samples from both the core and similar rocks from the surface were used to assist in the description of the lithology.The lithologic units used in this paper are those of Nye and others(1984). Surface Alteration Alteration minerals related to the active hydrothermal system in the Makushin area occur both at the surface and at depth.The alteration minerals at the surface reflect the 34 vapor-dominated nature of the upper portion of the Makushin hydrothermal system.Since surface alteration may not reflect the conditions of the deep production zones this study focused mainly on the subsurface alteration.The distribution and mineral assemblages of the surface alteration are discussed in Parmentier and others(1983).A brief discussion of the surface alteration follows. At the surface hydrothermal alteration is restricted to areas around fumarole fields both active and fossil. Alteraticn minerals also occur to a lesser degree near active and fossil hot springs.Both active and fossil fumarole fields exhibit the same alteration assemblage. Kaolinite is the dominate.mineral in the fumarole fields with lesser amounts of pyrite,iron oxides,and amorphous silica.Sulfur ane pickeringite have been identified from the fumarole encrustations.Pyrophyllite is also locally present.Outside the area of the main vents montmorillonite becomes the major clay mineral.This assemblage is interpreted to be a result of acid alteration caused by the shallow vapor-dominated zone(Parmentier and others,1983; Reeder,1982). The active hot-springs in the area are low chloride bicarbonate,sulfate springs.Active formation of authigenic minerals around these springs appears to be restricted to travertine.However,in Glacier Valley there 35 dened+are several altered.zones,interpreted to be fossil hot spring deposits,in Recent morainal deposits which contain significant amounts of halite.Motyka and others (1983) "suggest that this is evidence that in the recent past chloride-rich hot-springs did exist in the area. Alteration Minerals in the Core Quartz is common in all the alteration groups.Its habit varies from grey cryptocrystalline veins to clear,doubly terminated,1-2 cm long crystals in an anhydrite matrix. The most common occurrence is as veins ranging in size from 0.5 mm to 2.0 ecmin width.The quartz in the veins is often an opaque milky-white.The grains of quartz in the veins are anhedral to euhedral and range in size from 'eryptocrystalline to 1 cm in length.The finer grained material typically contains numerous fluid and clay inclusions while the larger euhedral crystals contain only a few scattered fluid inclusions.The quartz veins occasionally show fracturing and resealing by second generation quartz,but more frequently the quartz veins are cut by calcite and anhydrite veins. Calcite occurs in veins,as fine-grained mixtures with clay alteration,and as euhedral crystals in open-space quartz and calcite veins.Most of the calcite veins are thin(1-2 mm)and have fine-grained(<0.5 mm),anhedral calcite.The 36 calcite crystals in open-space veins are principally scalenohedral,but in the upper parts of well A-1 bladed calcite crystals also occur.At the bottom of well D-1 calcite is present in the brecciated hornfels as a sparry breccia filling with pyrite.The sparry calcite is transluscent and is relatively free of inclusions.These calcite grains are anhedral and are about 2mm in diameter. Anhydrite is present in two distinct habits.The more common habit is as a fine-grained vein filling.These anhydrite veins also contain calcite,quartz,pyrite,and occasional zeolites.Some of the veins are vuggy and are lined with terminated anhydrite crystals.The fine grain anhydrite veins are 1-20mmwide and are composed of subhedral anhydrite blades 0.5-1.0 mm wide and 1-3 mm long. The alteration around these anhydrite veins is about equal to the thickness of the veins.Plagioclase in the alteration envelope is typically altered to montmorillonite. The mafic minerals are altered to either chlorite or pyrite. The second habit of anhydrite is as sparry,coarsely erystalline (to 3 mm wide and 15 mm long)vein and breccia fillings.The sparry anhydrite occurs with quartz,calcite, and magnetite.Vugs containing euhedral crystals of anhydrite,quartz and calcite are common in the breccia zone of ST-1.The veins and breccia clasts commonly exhibit an 37 Iecoadalteration envelope.of chlorite rather than montmorillonite. The fine-grain anhydrite veins are younger than the sparry anhydrite veins. Epidote occurs both in veins and as disseminated anhedral grains in the gabbro.When present ina vein it is never the dominate mineral.Epidote is absent from the fine- grained anhydrite veins and is uncommon in the other vein types.The epidote bearing quartz and calcite veins are among the oldest veins in the core and many show multiple stage fracturing and deposition.Epidote occurs as euhedral erystals in irregularly shaped miarolitic,albite-epidote-. quartz veins.It can make up to 10 percent of the mode in the albite-quartz-epidoteveins.In the disseminated form epidote occurs as 0.5-1.0 mm diameter anhedral grains scattered throughout altered zones,especially those near the contacts between hornfels and gabbro. Albite and K-feldspar are among the oldest alteration minerals.The albite occurs as white subhedral to euhedral erystals(0.5-14 mm)in short(1 cm)pegmatitic veins found scattered throughout the gabbro.K-feldspar occurs with the albite in these veins.The K-feldspar grains are typically larger(3-4 mm)than those of 'the albite and are a pinkish grey.It is always anhedral. 38 Chlorite and actinolite were logged together because of their intimate association in some assemblages and the general difficulty in distinguishing them in the hand samples.They are pale green and appear fibrous in hand sample.They occur in veins and as disseminated replacement of pyroxenes.The veins are generally short(0.5-1.5 cm), thin(<2 mm)and monomineralic.They lack alteration envelopes.The disseminated alteration is is more common than the veins.Pyroxenes in much of the pluton have been completely altered to chlorite-actinolite.The alteration of pyroxenes is the only alteration present in some parts of the core. The alteration of_pyroxenes,particularly orthopyroxenes,to anthophyllite-cummingtonite is probably the most wide spread alteration in the core.It is difficult to see in hand specimen but in thin section it is readily apparent that most of the orthopyroxene has been altered to anthophyllite- cummingtonite and much clinopyroxene shows some degree of alteration.Like the chlorite-actinolite alteration,it appears to be unrelated to hydrothermal vein alteration. The anthophyllite-cummingtonite is thought to be the oldest alteration in the area. Sphene is locally present in the alteration envelopes around anhydrite veins and less commonly in the veins themselves. It is most abundant in the altered rock of the hydrothermal 39 2temo.breccia found in ST-1.It commonly occurs as irregularly shaped aggregates of grains,although some subhedral crystals have been found in the veins. Tllite is found at a single occurrence,a clay zone in I-1 at a depth of 358 m.The clay is greenish grey and contains a@ mixture of montmorillonite,illite,chlorite and calcite. Montmorillonite is the most abundant clay mineral in the Makushin Geothermal Area.It is the dominate mineral in the clay zones which occur throughout the upper portions of the cores,Generally the clay zones do not occur much deeper than 40 m below surface but in well I-1 montmorillonite clay zones occurto a depth of 450 m below surface.The clay zones are 2 to 20 cm wide fractures filled with a friable, fine-grained mixture of clay,chlorite and calcite.The Clay mixture is grey-green to grey to blue-green. Montmorillonite also replaces plagioclase in the alteration envelopes around the anhydrite veins.The.montmorillonite forms soft,white pseudomorphs after plagioclase laths. Kaolinite is rare in the core samples from Makushin,even though it is abundant in the fumarole fields in the area. It has been identified in some of the clay samples from the upper portions of wells ST-1 and E-1. 40 persLaumontite is the most common zeolite from the core.It eccurs as white,euhedral crystals in open space calcite veins.The crystals are typically 2-3 mm in length and may locally form clusters. Mordenite occurs as white acicular erystals in an open-space calcite-quartz vein in well I-1.The crystals are 6-7 mm in length. Yugawaralite is restricted to two occurrences in well E-1. The yugawaralite occurs as tiny 0.5 mm euhedral crystals in an altered gabbro honey-combed with small vugs. Wairakite has been identified in two samples from ST-1 and one from E-1.The sample from E-1 occurs at 426 Mm.The wairakite in this sample occurs as white,euhedral crystals on calcite crystals which in turn are on a quartz vein.The wairakite from ST-1,at 158 m and 202 m,forms massive, white alteration zones in the gabbro.In thin-section euhedral erystals of wairakite can be seen.The alteration zones are about 15-20 cm wide.The 202 m occurrence is associated with a steam producing fracture. Stilbite is restricted to a single occurrence at 65 min well ST-1.The stilbite forms numerous small1(0.5mm) euhedral crystals on the faces of quartz crystals in a vuggy qQuartz-clay vein. 41 Hematite is present as stains,small crystals lining fractures and rarely as replacement of magnetite.The "hematite crystals are <0.5mm euhedral and metallic red.The occurrences seem to be restricted to the upper-cooler portions of the system. \ Pyrite is ubiquitous throughout the core.The most common habit is as an-anhedral replacement of the primary magnetite and pyroxenes.Pyrite also replaces some of the authigenic magnetite. Pyrite may occur in veins as an accessory mineral.In the veins it occurs as small euhedral cubes(0.5-1.0 mm). Euhedral pyrite is also a common phase in the vein alteration envelopes. Authigenic magnetite is present in all the wells except for E-1.The authigenic magnetite occurs as large sooty anhedral grains associated with sparry anhydrite.The magnetite grains commonly appear somewhat rounded.In polished section they are homogeneous and quite distinct from the illmanite bearing primary magnetite.Rarely large frains of magnetite will occur in the gabbro seemingly removed from other alteration. 42 Marcasite has been found in several of the open-space quartz veins.The marcasite is tarnished and has cockscomb habit. Paragenesis and Alteration Assemblages. The paragenetic sequence for the authigenic minerals was determined from the depositional sequence of vein minerals, cross-cutting relationships between veins,and replacement textures.Figure 19 is a paragenetic chart for all the authigenic minerals found in the drill core.Co-deposition of minerals as shown on this chart does not imply equilibrium among the phase being deposited.Local equilibriumis the.rule in near-surface hydrothermal. systems.Conditions can very greatly over short distances. Minerals which cannot coexist can thus form at the same time in different parts of the system.The paragenetic chart, therefore,tells very little about equilibrium in the system. The utility of the paragenetic chart is that allows one to see major changes in the Makushin hydrothermal area with time.For example,minerals such as biotite,hornblende and albite were deposited early on while the zeolites were deposited more recently.From the paragenetic chart and information about mineral stabilities,two major alteration events can be identified.The early alteration event is the 43 result of deuteric alteration of the pluton and is unrelated to the active hydrothermal system.The late alteration is the work of the Makushin hydrothermal system. The deuteric alteration comprises two assemblages:an albite +biotite +hornblende +actinolite +epidote +quartz assemblage found in comagmatic breccias and aplite dikes, which occur.randomly throughout the pluton,and an anthophyllite +cummingtonite +actinolite +magnetite + Pyrite assemblage which replaces mafic phases,in particular the orthopyroxenes,in the gabbronorite and hornfels.The deuteric alteration occurs throughout the pluton so that it is difficult to find unaltered orthopyroxenes. Perfit and others(1979)found that the rocks of the Captains Bay pluton showed depleted **0/'*O values with respect to normal igneous rocks.They interpreted this to be a result of the interaction of circulating meteoric water with the cooling pluton.Samples of the Makushin gabbro were analyzed for oxygen isotopes.The results.are shown in table 14.Like those of the Captains Bay pluton they show depleted *%0/'*0 values compared to normal igneous rocks. It is therefore likely that the Makushin pluton also interacted with circulating méteoric water as it cooled.The greenschist metamorphism of the Unalaska Formation is also believed to be related to hydrothermal systems set up by the cooling plutons (Perfit and others,1979). HY The alteration related to the Makushin geothermal system is divided into two periods of deposition;an early and late period.The early period authigenic minerals seem to be a single assemblage of anhydrite +magnetite +calcite + pyrite +chlorite +epidote +sphene.This will be referred to as the "magnetite"assemblage.The authigenic minerals of the late period form two distinct assemblages;a montmorillonite +chlorite +calcite +pyrite assemblage, the "argillic"assemblage,and anhydrite +calcite +quartz +zeolite +epidote +pyrite +sphalerite +sphene assemblage,the "zeolite”assemblage. The magnetite assemblage occurs principally in the hydrothermal breccias which are abundant in the upper 220 m of ST-1.The breccias occur less frequently in the other wells,The breccias consist of clasts of gabbro surrounded by a matrix of sparry anhydrite,anhedral magnetite, euhedral quartz crystals and rarely calcite crystals.The clasts are angular,0.5-4%ecm in diameter,and almost always have a chloritic alteration rind.In well D-1 the breccias are slightly different consisting of hornfels clasts in a matrix of sparry calcite and anhedral pyrite.The clasts are approximately the same size and shape and have chloritic alteration rinds. 45 The sparry anhydrite,as opposed to the finer @rain anhydrite of the zeolite assemblage,and the magnetite serve to distinguish this assemblage.The anhydrite and magnetite appear to have formed together.This is most unusual for a geothermal system.While anhydrite is common in explored geothermal areas,authigenic magnetite has only been reported from two other geothermal areas:Tongonan, Philippines and Tatun,Taiwan (Browne,1978:;Lan and others,1980).The Tongonan system has temperatures of above 300°C,much higher than those so far encountered in the Makushin system. The Makushin hydrothermal system clearly cannot have formed the magnetite assemblage under the present conditions.The breccias found in ST-1 are above the water table and the magnetite assemblage must have formed in a liquid dominated system.It also does not appear possible to deposit anhydrite and magnetite together at the present temperatures.Despite this,the magnetite assemblage does appear to be related to the Makushin system.No evidence of any early hydrothermal systems can be found in the Makushin area.Extensive exploration of the pluton at surface indicated only the deuteric alteration and the alteration around the fumaroles and hot springs.An unpublished geochemical study of the Makushin well drill chips by R. Bamford for Republic Geothermal,Ince.indicated no other hydrothermal active other than the present system.Finally 46 salinity data from the fluid inclusions(discussed later in this report)indicates the fluids that formed the magnetite assemblage are similar to the present fluids.Taken "together this is good evidence that the magnetite assemblage was formed by the Makushin system at an earlier stage. The zeolite and argillic assemblages are much easier to relate to the present system.The argillic assemblage is fairly typically of the vapor-dominated and cooler liquid- dominated portions of other geothermal systems (Ellis, 1979).It is basically confined to areas above the known water table to or liquid-dominated zones with temperature below 100°C. The zeolite assemblage is representative of the liquid dominated portions of the active system.The assemblage occurs in every core and is the most common of the hydrothermal assemblages.There is a rough temperature zoning for the zeolites.Mordenite was only found in I-1 and is assumed to be stable below 100°C.Laumontite is by far the most common zeolite in the Makushin system.It has been found at temperatures as low as 70°C.However,this may be a relict of the early stage.More reasonable is the occurrence in A-1 which starts at about 125°C.The upper temperature limit is probably around 190°C.Wairakite,like the laumontite,is found at temperatures that are too low to be reasonable for formation.In other systems wairakite u7 first appears around 175°C and disappears at about 250°C. Yugawaralite is rare in the Makushin core but probably has stabilities similar to that of wairakite. The only other zoning seen in the Makushin system is the zoning between bladed and scalenohedral calcite.In well I-17 bladed calcite occurs from 100 meters to about 340 m,below which point the calcite is scalenohedral. As mentioned there are occurrences of the zeolite assemblage that are,like the magnetite assemblage,outside the stability limits for the assemblage.In ST-1 wairakite occurs at 137 m and at 190 m.Both of the zones are above the present water table and are at temperatures well below those reasonable for wairakite formation.The 190 m occurrence is gabbro altered to wairakite surrounding a steam producing fracture.In order for wairakite to forn, the fluids must be supersaturated with respect to quartz. This impossible in a vapor-dominated system.Wairakite has been found in vapor dominated systems,but these occurrences are rare and always are at temperatures close to 200°C.The wairakite in ST-1 must have formed during an earlier period when the water table was higher than at present and the temperatures near the surface must have also been higher. The evidence from the authigenic minerals,therefore, indicates that a change in the Makushin hydrothermal system 48 has taken place.This change certainly involved a drop in the water table and a lowering of the temperature in the upper parts of the system. FLUID INCLUSIONS Methods The fluid inclusion samples were prepared according to procedures outlined in Roedder(1984).Special care was taken to avoid heating the samples above 80°C during preparation.The melting and homogenization measurements _were done on a Linkam 600 heating-cooling stage.To determine fluid salinitiesthe sample was cooled to -40°C, then heated at a rate of 10°C/min until the sample temperature reached -5°C.The sample was allowed to equilibrate at this temperature for one minute.Heating was then continued at 1.0°C/min until the last ice melted. After the last ice melted,heating was continued at the same rate to +12°C in order to check for clathrates. To measure homogenization temperatures the sample was heated at 20°C/min until the sample temperature reached 180°C.The sample was allowed to remain at 180°C for one minute.The rate of heating was then reduced to 5°C/min and heating continued until homogenization was achieved.Multiple homogenization runs were made on selected inclusions to 49 determine the repeatability of the results.Homogenization temperatures measured at heating rates of 1°C/min were within +1°C of homogenization temperatures measured at heating rates of 5°C/min. The fluid inclusion study was undertaken to determine the temperature and salinity of the fluids which formed the early hydrothermal minerals.Three samples from E-1,three samples from ST-1,and one sample from I-1 were selected for the homogenization and salinity investigation.The samples were selected on the basis of four criteria:(1)the samples had to contain quartz;(2)the quartz grains had to be larger than2 mm in diameter;(3)the veins the quartz came from had to be of hydrothermal origin and (4)the sample depths had to be varied to allow a paleogeothermal gradient to be determined.Description of the samples are given in Table 21. Although anhydrite and calcite also contain fluid inclusions and are abundant in the core,they were not used in the fluid inclusion study.They were judged unsuitable for the study for two major reasons.The first is grains of anhydrite and calcite large enough to have usable inclusions are not as abundant as large grains of quartz.The second reason is that anhydrite and calcite are thought to be more 50 susceptible to possible re-equilibration during retrograde events than is quartz. "The inclusions used in the study ranged from .01 mm to .5 mm in diameter.Most of the inclusions were primary but some psuedo secondary and secondary inclusions were also used. The vapor fillings were between 5 and 10 percent.The vapor bubbles were slightly darker than one would expect for pure H20 vapor.Typical inclusions are shown in figure 20. About half the inclusions contained thin,transparent, daughter minerals(fig 21).The daughter mineral did not show any visible dissolution even at 400°C.This may indicate that the,mineralsare accidental inclusions and not true daughters. Fluid Salinity Figure 22 shows the temperature of last ice melting for 80 inclusions from five samples(ST-1:277,ST-1:295,E-1:791,E- 1:141755,E-1:1396).The variation shown by the melting temperatures is within the error limits for the cooling stage.Thus it is reasonable to assume that the compositions of the fluid inclusions is constant. Using the equation given by Potter and others(1978)to determine the inclusion salinity in NaCl molar equivalents 51 from the temperature of last ice melting,one obtains for the mean temperature a salinity of 0.106 M NaCl or 6194 ppm. The measured salinity of the ST-1 waters is 0.098 M NaCl or 5868 ppm.Even ignoring the difficulty in measuring the salinity of low salinity inclusions,the agreement between present system salinities and the fluid inclusion salinites is remarkable. After the last ice melted the samples were checked for clathrates.Although the dark vapor bubble indicated the presence of some COz2,no clathrates were observed.The active hydrothermal system has COz partial pressures of 0.5 bars which are much too low to allow clathrate formation. Thus for the compositional information that can be obtained from freezing the inclusions the paleofluid and the present fluids appear the same.This seems to rule out any major changes in composition during the life of the Makushin hydrothermal system.Although it would be desirable to obtain quantitative chemical analysis of the fluid inclusion,this seems unlikely at the present due to the dilute nature of the fluid inclusions. Homogenization Temperatures Figures 23a,b,and c show the fluid inclusion homogenization temperatures at the appropriate sample depth 52 in each well.Also shown are the measured thermal Zradients(MTG)and the hydrostatic reference boiling curve(RBC). The degree of vapor filling in the inclusions at 40°C was essentially constant,being between 5 and 10 percent by volume.All of the inclusions homogenized to a high density fluid(i.e.the vapor bubble shrank).These observations are generally taken to indicate that the fluid inclusions were formed in a liquid-dominated environment and that the liquid was not boiling.However,experience in other geothermal fields indicates that similar inclusions can form from fluids which are boiling (Roedder,1984).Therefore one can not say that boiling has not occurred,but only that there is no evidence for boiling. The lack of evidence of boiling prevents the determination of the pressure correction to be applied to the homogenization temperatures to get the true temperature of trapping.However,in many explored geothermal system the pressure is close to hydrostatic.Since the Makushin samples came from fairly shallow depths the pressure correction should be small.Never the less the homogenization temperatures should be regarded as minimum temperature of trapping. 53 The most striking feature of the homogenizgation temperatures is that they are all above the measured well-temperatures for the sample depth.In some samples the highest homogenization temperatures are >100°C above the maximum bottom-hole temperature so far measured in the Makushin system.Despite this the inclusions do probably represent the conditions of the early Makushin Geothermal System.As discussed earlier in this report the evidence strongly suggests that all the hydrothermal alteration in the wells is related to one hydrothermal system. Fluid inclusion homogenization temperatures are often significantly greater than the present measured temperatures for a well (Bargar and others,1984a;Bargar and others, 1984b;Keith and others,1984;Huang,1984;Taguchi and others,1980;Taguchi,1983).The lower homogenization temperatures are,however,in most fields within +5°C of the preproduction measured temperature curve.The higher homogenization temperatures are,therefore,usually interpreted as evidence that the geothermal system has cooled.Thus the fluid inclusion homogenization temperatures suggest that the Makushin geothermal field has cooled as much as 100°C in places. The difficulty with this interpretation lies in that most of the homogenization temperatures lie above the hydrostatic boiling curve.As can be seen in figures 23a,b,and ec the 54