HomeMy WebLinkAboutArea Soil Chemistry Hg-As - Amanda Kolker UAFNaknek – King Salmon Area Soil Mercury (Hg) and Arsenic (As): Phase 1 Results
Prepared by: Amanda Kolker, University of Alaska Fairbanks 10/26/2006
Background
In the absence of geothermal expressions (e.g., hot springs, fumaroles), and in the
absence of clear geologic structures such as faults, we decided to undertake soil sampling
for geothermal “tracers” or indicator elements.
Mercury (Hg) content in soils is probably the most commonly used geothermal resource
indicator. Mercury is a highly volatile and mobile element that occurs naturally in rocks
in very small concentrations. Geothermal heat volatilizes the Hg in rocks and carries it
upward and outward from the geothermal source, usually in association with CO2.
Soil arsenic (As) is another geothermal resource indicator. It is carried by geothermal
fluids, not gasses, so it is commonly used as a complement to Hg in geothermal
exploration studies.
Hg concentrations in soils can be influenced by human activity (buried waste, etc.) and/or
microbial activity.
Sampling and analytical methods
Samples were collected by the author, Ralph Mankuso, and Mike McClain on 9/10/2006.
Samples were collected approximately every 2 miles along three lines that parallelled the
King Salmon river. Samples were taken from 2-3 feet depth. Organic matter was avoided
except where noted. Some samples were frozen. The samples were collected in ziplock
plastic bags, and sent to ALS Chemex for preparation and analysis.
Results
The table below gives Hg and As values in ppm. Frozen samples are marked with an
asterisk (*) and samples that could have organic contamination are marked with an O.
METHOD
ME-
ICP41 Hg-CV41 METHOD
ME-
ICP41 Hg-CV41 METHOD
ME-
ICP41 Hg-CV41
SAMPLE As, ppm Hg, ppm SAMPLE As, ppm Hg, ppm SAMPLE As, ppm Hg, ppm
A1A-T2 4 0.02 B6A 2 0.05 C2A* 12 0.14
A1B-T2 2 0.01 B7A <2 0.01 C2B* 10 0.11
A2A 9 0.11 B7B 2 0.06 C3A 30 0.14
A2B 6 0.09 B8A 2 0.01 C3B 7 0.08
A3A 6 0.01 B8B 2 0.02 C4A 3 0.01
A3B 5 0.02 C4B 4 0.04
A4A 3 0.01 C6A-T5 2 0.01
A4B 3 0.03 C6B-T5 4 0.01
A5A 3 0.05 C7A 9 0.05
A5B <2 0.09 C7B 7 0.03
A6A-T3 6 0.04 C8A-T4 5 0.06
A6B-T3 5 0.05 C8B-T4 5 0.07
A7A 5 0.06 C8C-T4 4 0.04
A7B (O) 14 0.06
Concentrations of Hg, As and of identified geothermal areas are given below.
Roosevelt,
UT (max.)
Okinobe,
Japan (ave.)
Makushin
(median)
Makushin
(max)
Meager Ck
(mean)
Copper
R. basin
(ave.)
Hg (ppm) 5.5 0.05 60 31480 44-77 31
As (ppm) 858 7.8 ~5-9
Sources:
Roosevelt: Moore et al, 1983.
Okinobe: Shikawa, M. 1983.
Makushin: Matlick & Parmentier, 1981.
Meager Creek: Openshaw, 1983.
The following plots of Hg and As concentration show that there are “spikes” at the West
end of the sample area, though the range of values is not dramatic.
1 2 3 4 5 6 7
Ca
Cb
Ba
Bb
Aa
Ab
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
Sample #
Hg
1 2 3 4 5 6 7
Ca
Cb
Ba
Bb
Aa
Ab
0
5
10
15
20
25
30
Sample #
As
Preliminary Interpretation
Sample C3A has the highest concentrations of As and Hg. The sampling site was also
associated with a sulfur smell but the sample was free of permafrost and organics. Based
on these data alone, I would recommend targeting this site for future exploration. Another
soil survey should be conducted in the vicinity