Leaching, Transport, and Methylation of Mercury 

in and around Abandoned Mercury Mines in the 

Humboldt River Basin and Surrounding Areas, Nevada 

U.S. Department of the Interior 

U.S. Geological Survey 

U.S. Geological Survey Bulletin 2210-C 

By John E. Gray 

Version 1.0 2003 
Leaching, Transport, and Methylation of Mecury 

in and around Abandoned Mercury Mines in the 

Humboldt River Basin and Surrounding Areas, Nevada 

By John E. Gray 

Chapter C of


Geoenvironmental Investigations of the Humboldt River Basin, Northern Nevada


Edited by Lisa L. Stillings 

U.S. Geological Survey Bulletin 2210-C 

U.S. Department of the Interior 

U.S. Geological Survey 
U.S. Department of the Interior 

Gale A. Norton, Secretary 

U.S. Geological Survey 

Charles G. Groat, Director 

Posted online September 2003, version 1.0 

This publication is only available online at: 

http://geology.cr.usgs.gov/pub/bulletins/b2210-c/ 

Any use of trade, product, or firm names in this publication 

is for descriptive purposes only and does not 

imply endorsement by the U.S. Government 
Preface 

Northern Nevada is one of the world’s foremost regions of gold production. The 

Humboldt River Basin (HRB) covers 43,500 km2 in northern Nevada (Crompton, 1995), 

and it is home to approximately 18 active gold and silver mines (Driesner and Coyner, 

2001) among at least 55 significant metallic mineral deposits (Long and others, 1998). 

Many of the gold mines are along the Carlin trend in the east-central portion of the HRB, 

and together they have produced 50 million ounces of gold from 1962 (when the Carlin 

mine first opened) through April 2002 (Nevada Mining Association, 2002). Mining is 

not new to the region, however. Beginning in 1849, mining has taken place in numerous 

districts that cover 39 percent of the land area in the HRB (Tingley, 1998). In addition to 

gold and silver, As, Ba, Cu, Fe, Hg, Li, Mn, Mo, Pb, S, Sb, V, W, Zn, and industrial commodities such as barite, limestone, fluorite, sand and gravel, gypsum, gemstones, pumice, 

zeolites, and building stone, have been extracted from the HRB (McFaul and others, 

2000). 

Due to the large amount of historical and recent mining in the HRB, the Bureau of 

Land Management (BLM) in Nevada asked the U.S. Geological Survey (USGS) Mineral 

Resources Program to conduct a series of mineral-deposit-related environmental studies in the HRB. BLM required data and geoenvironmental interpretations regarding (1) 

the chemical composition of water, soil, sediment, and mine waste in the HRB, (2) the 

natural background chemistry of these materials, and (3) how mining activities may have 

altered their chemistry. The paper that follows describes one of the studies conducted by 

the USGS Minerals Program to answer these and similar questions. 

All papers within this series of investigations can be found as lettered chapters of 

USGS Bulletin 2210, Geoenvironmental Investigations of the Humboldt River Basin, 

Northern Nevada. Each chapter is available separately online. 

References Cited 

Crompton, E.J., 1995, Potential hydrologic effects of mining in the Humboldt River Basin, northern 

Nevada: U.S. Geological Survey Water Resources Investigations Report 94-4233, 2 sheets. 

Driesner, D., and Coyner, A., 2001, Major mines of Nevada 2000: Mineral industries in Nevada’s 

economy: Nevada Bureau of Mines and Geology Special Publication P-12, 28 p. 

Long, K.R., DeYoung, J.H., Jr., and Ludington, S.D., 1998, Significant deposits of gold, silver, copper, 

lead, and zinc in the United States: U.S. Geological Survey Open-File Report 98-206A, 33 p. [USGS 

Open-File Report 98-206B contains one 3.5-inch diskette]. 

McFaul, E.J., Mason G.T., Jr., Ferguson, W.B., and Lipin, B.R., 2000, U.S. Geological Survey mineral 

databases—MRDS and MAS/MILS: U.S. Geological Survey Digital Data Series DDS-52, two CDROMs. 

Nevada Mining Association, 2002, Industry to celebrate 50 millionth ounce of gold: Nevada Mining 

Association News Release, April 11, 2002. 

Tingley, J.V., 1998, Mining districts of Nevada (2nd ed.): Nevada Bureau of Mines and Geology 

Report 47d, one CD-ROM. 
Contents 

Preface ..........................................................................................................................................................III


Abstract .......................................................................................................................................................... 1


Introduction ................................................................................................................................................... 1


Study Area Description................................................................................................................................ 3


Uses of Mercury and the Mercury Mining Process ............................................................................... 4


Methods ......................................................................................................................................................... 5


Field Studies and Sample Collection ................................................................................................ 5


Chemical Analysis ............................................................................................................................... 6


Results ............................................................................................................................................................ 6


Ore and Mine Wastes ......................................................................................................................... 6


Stream- and Lake-Sediment Samples............................................................................................ 10


Stream- and Lake-Water Samples.................................................................................................. 11


Water-Leach Studies......................................................................................................................... 11


Discussion.................................................................................................................................................... 12


Summary ...................................................................................................................................................... 14


References................................................................................................................................................... 14


Figures 

1. 	 Map showing location of mercury mines studied and sample locations 


from the Humboldt River, Rye Patch Reservoir, and Rock Creek.......................................... 2


2. Location map and plan-view sketch map of the Cahill mine................................................. 3


3. 	 Photographs of the Humboldt River basin and the Rye Patch Reservoir 


from the Eldorado mine, cinnabar in silicified sandstone from the 


Cahill mine, and the Cahill mine in the Poverty Peaks district.............................................. 4


4. 	 Graph of mercury versus methylmercury concentration in mine-waste 


calcine, mine-drainage sediments, and Humboldt River sediment samples ................... 10


5. 	 Graphs of mercury in sediments versus distance from mines for all 


mine drainages, the Eldorado mine, and the Mt. Tobin mine .............................................. 11


6. 	 Graph of mercury versus methylmercury concentration in unfiltered 


water samples collected downstream from the Eldorado and 


Mt. Tobin mines, and from the Humboldt River...................................................................... 12


7. 	 Graph of mercury concentration versus pH in filtered water samples of 


leachates from mine-waste calcine and filtered water samples collected 


from the Humboldt River, Rye Patch Reservoir, and mine drainages ................................ 12


IV

V


Tables 

1. Description and production of mercury mines studied.......................................................... 5


2. 	 Mercury data for mine-waste calcines and sediment samples collected from 


selected mercury mines, the Humboldt River, Rye Patch Reservoir, and Rock Creek...... 7


3. 	 Geochemical data for water samples collected from two mercury mines, 


the Humboldt River, Rye Patch Reservoir, and Rock Creek................................................... 9


4. 	 Geochemical data for filtered water leachates of mine-waste samples 


collected from several mercury mines ................................................................................... 13

Leaching, Transport, and Methylation of Mercury 

in and around Abandoned Mercury Mines in the 

Humboldt River Basin and Surrounding Areas, Nevada 

By John E. Gray1 

Abstract 

Mercury and methylmercury concentrations were measured in mine wastes, stream sediments, and stream waters 

collected both proximal and distal from abandoned mercury mines to evaluate mercury contamination and mercury 

methylation in the Humboldt River system. The climate in the 

study area is arid, and due to the lack of mine-water runoff, 

water-leaching laboratory experiments were used to evaluate 

the potential of mine wastes to release mercury. Mine-waste 

calcine contains mercury concentrations as high as 14,000 

μg/g. Stream-sediment samples collected within 1 km of the 

mercury mines studied contain mercury concentrations as high 

as 170 μg/g, but sediments collected from the Humboldt River 

and regional baseline sites have much lower mercury contents, 

less than 0.44 μg/g. Similarly, methylmercury concentrations in mine-waste calcine are locally as high as 96 ng/g, but 

methylmercury contents in stream sediments collected downstream from the mines and from the Humboldt River are lower 

(<0.05–0.95 ng/g). Stream-water samples collected below two 

mines studied contain mercury concentrations ranging from 6 

to 2,000 ng/L, whereas mercury contents in Humboldt River 

and Rye Patch Reservoir water were generally lower, ranging 

from 2.1 to 9.0 ng/L. Methylmercury concentrations in Humboldt River system water were the lowest in this study (<0.02– 

0.27 ng/L). Although mercury and methylmercury concentrations were elevated in some mine-waste calcine and mercury 

concentrations were locally high in mine-waste leachate 

samples, data show significant dilution of mercury and lower 

mercury methylation down gradient from the mines, especially 

in the sediments and water collected from the Humboldt River, 

which is more than 8 km from any mercury mines. Data show 

only minor, local transference of mercury and methylmercury 

from mine-waste calcine to stream sediment, and then onto the 

water column, and indicate little transference of mercury from 

the mine sites to the Humboldt River system. 

1

 U.S. Geological Survey, Box 25046, Federal Center, Mail Stop 973, Denver, 

CO 80225 USA; email: jgray@usgs.gov. 

Introduction 

This study is part of a larger project conducted by the 

U.S. Geological Survey (USGS) to evaluate the geology, mineral resources, and environmental geochemistry of the Humboldt River basin (HRB), which is the longest river system 

in Nevada and an important ecosystem (fig. 1). Nevada is 

one of the world’s largest regions of gold production, and 

the HRB—covering about 43,500 km2 in northern Nevada— 

contains at least 18 major gold and silver mines. At least 

1,400 t (50 million oz) of gold was produced between 1962 

and 2002 in the HRB, as well as significant As, Ba, Cu, F, 

Fe, Li, Mn, Pb, S, V, W, and Zn. Due to the large amount of 

metallic and nonmetallic mineral resources in the HRB, the 

U.S. Bureau of Land Management (BLM) asked the USGS 

Mineral Resources Program to conduct several environmental studies in the region; this report is one product of these 

investigations. The BLM was interested in obtaining data on 

the chemical composition of water, soil, sediment, and mine 

wastes in the HRB; the natural background chemistry of geologic materials in the region; and how mining activities may 

have altered the local and regional geochemistry. 

In addition to the large amount of precious-metal 

resources produced in Nevada, abundant mercury was also 

recovered in this region from the early 1900s until the early 

1990s. Historical production from mercury mines in western 

and central Nevada exceeds 10,000 t (Willden, 1964; Johnson, 

1977; Noble and others, 1988), making Nevada the second 

largest mercury-producing region in the United States, ranking only behind the California Coast Ranges (Peabody, 1993). 

Many of the mercury mines in this region are located in the 

HRB, and because of the toxic nature of mercury, the presence 

of these mercury mines is a potential hazard to residents and 

wildlife when drainage from the mines enters local streams 

and rivers, and potentially the HRB (fig. 2). Thus, this study 

was undertaken to determine if weathering of mercury mines 

in this region has resulted in any significant erosion and transport of mercury to surrounding ecosystems, specifically the 

HRB (fig. 3A). 

Mercury is a heavy metal of environmental concern 

1

2 Geoenvironmental Investigations of the Humboldt River Basin, Northern Nevada 

119 ̊ 118 ̊ 117 ̊

0 

0 

10 

10 

20 

20 MILES 

30 KILOMETERS 

SANTA ROSA RANGE

Quinn River 

Kings 

River 

BLACK ROCK RANGE 

Jackson Creek 

JACKSON MOUNTAINS 

SLUMBERING HILLS 

OSGOOD MTS

Little 

Humboldt 

River 

Evans Creek 

Denio 

Winnemucca Clear Creek 

TOBIN RANGE 

EAST RANGE 

Spring Creek

HUMBOLDT 

Lovelock 

Pershing 

SHOSHONE RANGE 

CORTEZ MOUNTAINS 

FISH CREEK MOUNTAINS 

Reese River Battle Mountain 

Carlin 

Rock Creek 

TUSCARORA 

MOUNTAINS 

Silver Cloud 

41 ̊ 

42 ̊ 

116 ̊ 

42 ̊ 

McDermitt 

Dutch Flat 

Cahill 

Goldbanks 

Eldorado 

RANGE 

Bottle Creek 

X

X

X

X X

X

X

X Juniper 

X

River

Humboldt

Humboldt River 

McDermitt 

HMB5 

RYP5 

RYP2 

RYP3 

Rye Patch 

Reservoir 

RYP4 

RYP1 

HMB4 

HMB3 

HMB1 

HMB2 

NEVADA 

study 

area 

X Red Devil 

HMB6 

HMB7 

HMB8 

HMB9 

X Cinnabar City 

HMB15 

X

Horton 

SONOMA RANGE 

HMB10 

HMB11 

HMB12 

HMB13 

HMB14 

X Butte 

X

Mt. Tobin 

RC01 

RC02 

X

EXPLANATION 

Mines studied 

Sample sites 

RYP6 

40 ̊ 

Figure 1. Location of mercury mines studied and sample locations from the Humboldt River, Rye Patch 

Reservoir, and Rock Creek. 

because it is toxic to all organisms, including humans. The 

most problematic forms are organic mercury compounds, 

which are the most toxic, water and lipid soluble, and can 

biomagnify with increasing trophic position in the food chain. 

Under certain conditions, some inorganic mercury (such as 

elemental mercury, Hg0) that remains in mine wastes may be 

converted to organic mercury (most commonly, methylmercury, CH3

Hg+). Mercury mine wastes are known to contain 

a number of mercury byproducts (Biester and others, 1999; 

Kim and others, 2000), and potentially the most problematic 

is Hg0 that can oxidize to Hg2+, which becomes available 

for microbial methylation, subsequently forming bioavailable 

compounds such as methylmercury. Mercury methylation 

is primarily a result of anaerobic microbial activity in sediments, which is typically enhanced in environments with 

high concentrations of organic matter (Compeau and Bartha, 

1985). 

To evaluate the distribution of mercury and mercury 

methylation in and around these mines, the concentration of 

mercury and (or) methylmercury was measured in samples 

of (1) ore, mine-waste calcine (roasted ore), stream sediment, 

and water collected near and downstream from several of the 

mines, and (2) stream sediment and water collected from the 

Humboldt River and in Rye Patch Reservoir. Sediment and 

water samples were also collected from two sites on Rock 

Creek, which is one of the larger watersheds in the region 

and one of the few where flowing water was observed in 

June 2000. The sample sites on Rock Creek were more than 

15 km below the Silver Cloud mine and, thus, are likely representative of the regional geochemical baseline. Due to the 

abundance of mines and associated downstream transport of 

mercury in this region, there are probably no true background 

sites (i.e., areas without anthropogenic mercury contributions). As a result of funding limitations, only a subset of the 

collected samples were analyzed for methylmercury, but these 

results are critical for evaluating mercury methylation near 

the mercury mines, as well as in the HRB. During this study, 

mine-water runoff was rarely observed (only two localities) 

due to the arid climate in this region. Therefore, laboratory 

water-leaching studies of mine-waste calcine were conducted 

to simulate mine-water runoff and to evaluate the capacity of 

the mine wastes to release mercury. 
Leaching, Transport, and Methylation of Mercury, near Abandoned Mercury Mines, Humboldt River Basin, Nevada 3 

117 ̊ 30' 117 ̊ 27' 30" 41 ̊ 22' 30" 

99CAHS1 

99CAHS2 

inset 

0 

0 

100 Feet 

30 Meters 

(Scale approximate) 

VN Sketch Map of Cahill Mine Site 

01CAH1rt 

old retort 

99CAH01ca 

01CAH03ca 

condenser 

furnace 

calcine 

pile 

crusher 

belt calcine 

shoot 

water tank 

road 

road 

v

dry tributary of

Little Humboldt River 

V

 dry tributary of

Little Humboldt River 

road 

0 

0 1 Kilometer 

1 Mile 

opalite ore pile 

41 ̊ 20' 

Figure 2. Location and plan-view sketch map of the Cahill mine, which outlines the sources of mercury in and around the mercury mines studied. Mercury remaining in ore, mine-waste calcine, and retorts and furnaces can be released down gradient from the mines into stream drainages. Location of samples for some of the data in table 2 is also shown. 

Study Area Description 

The mercury mines studied (fig. 1) are part of a mercury belt that consists of numerous deposits found in a broad 

region in western and central Nevada. This mercury belt was 

first suggested to extend from McDermitt to Beatty, Nev., by 

Bailey and Phoenix (1944), who also divided these deposits 

into eight different types based on geologic bedrock associations. These mercury deposits are found in a wide variety 

of lithologies including sandstone, limestone, chert, granitic 

rocks, diabase dikes, rhyolitic tuffs and flows, andesites, 

and metamorphic rocks such as schists and phyllite (Bailey 

and Phoenix, 1944; Willden, 1964; Johnson, 1977). Ore 

and gangue minerals are commonly found in highly silicified rocks, veins, and vein breccias. “Opalite” is a common 

host rock, which is typically volcanic rock that is altered 

to amorphous and cryptocrystalline quartz, including opal. 

Silicified veins, and siliceous-sinter deposits formed by the 

surface deposition of hot-spring fluids, are also common host 

rocks of mercury ore. The dominant ore mineral is cinnabar 

(HgS, hexagonal) (fig. 3B), but minor metacinnabar (HgS, 

cubic, dimorphous with cinnabar), native mercury (Hgo

), 

calomel (Hg2Cl2), and mercury oxychlorides (e.g., Hg2ClO 

and Hg4Cl2O) are found in some deposits; pyrite (FeS2), marcasite (FeS2

), sphalerite ((Zn, Fe)S), and stibnite (Sb2S3) are 

rare (Bailey and Phoenix, 1944). Gangue is most commonly 

quartz and calcite, with subordinate barite, muscovite, alunite, 

jarosite, and clay minerals (Bailey and Phoenix, 1944). The 

mercury deposits in Nevada are generally of Miocene age, 

but some are possibly younger, and their formation has been 

interpreted to be related to extensional tectonics and related 

magmatism (Bailey and Phoenix, 1944; Noble and others, 

1988). 

Mercury mines in Nevada operated between about 1907 

and 1991, when the McDermitt mine closed. Mercury mines 

throughout the United States are not presently operating 
4 Geoenvironmental Investigations of the Humboldt River Basin, Northern Nevada 

A

B

Alluvial pediment Eldorado Canyon

Rye Patch Reservoir 

C

Calcine 

Condenser Furnace 

because of low prices and low demand, although some minor 

byproduct mercury is recovered from a few precious-metal 

mines. As previously mentioned, mercury production in 

Nevada exceeds 10,000 t (approximately 300,000 flasks; 

1 flask = 76 lb), about 90 percent of which came from the 

McDermitt mine (Willden, 1964; Johnson, 1977; Noble and 

others, 1988). Geologic characteristics and mercury production of the districts studied are shown in table 1. 

Figure 3 (facing column). A, View of the Humboldt River basin and 

the Rye Patch Reservoir from the Eldorado mercury mine in the Humboldt Range. This photograph shows that sediment or water runoff 

from the mines is transported and diluted through a large volume of 

alluvial pediment before it reaches Rye Patch Reservoir, which is part 

of the Humboldt River system. The Eldorado mine is one of the closest 

mines to the Humboldt River system and is located about 8 km from 

Rye Patch Reservoir. B, Cinnabar (red mineral) in silicified sandstone 

from the Cahill mine. C, Photograph of the Cahill mine in the Poverty 

Peaks district. A calcine pile (left foreground) is representative of 

the majority of mercury-bearing waste rock at the mines studied in 

Nevada. The rotary furnace and condensation unit (far right) is where 

mercury ore was burned, generating elemental mercury that was 

condensed and collected. 

Uses of Mercury and the 

Mercury Mining Process 

Mercury has many diverse properties and has been used 

historically in many products. Mercury is a liquid at room 

temperature that responds to changes in temperature, which 

has resulted in its well-known use in thermometers. Mercury 

also is used in navigational instruments to measure changes 

in temperature and pressure. Mercury is a good metallic conductor with a low electrical resistivity, and it has been used in 

electrical products including electrical wiring and switches, 

fluorescent lamps, mercury batteries, and thermostats (Eisler, 

1987). In the medical field, mercury is used as a component 

in dental fillings and as a preservative in many pharmaceutical 

products. Mercury has been used in industrial and agricultural 

applications such as in the production of chlorine and caustic 

soda, in nuclear reactors, in plastic production, as a fungicide 

in seeds and bulbs, and as an antifouling agent in paper, paper 

pulp, and paint (Eisler, 1987). Mercury fulminate is used in 

munitions, such as blasting-cap detonators. Liquid mercury 

has the unique property of combining or amalgamating with 

precious metals, and therefore, it has been used for centuries 

for the extraction of gold and silver during mining (Lacerda 

and Salomons, 1998). 

The recovery of mercury from its ore is a relatively simple 

process and is generally inexpensive, and as a result, mercury 

mining has been conducted for several centuries (Bailey and 

Phoenix, 1944; Lacerda and Salomons, 1998). As a result of its 

simple and inexpensive recovery, mercury was typically produced at the site of mining. Cinnabar is the most common mercury ore mineral worldwide, and cinnabar-bearing ore is simply 

crushed and burned at a temperature of 600°–700°C, which 

exceeds the stability of cinnabar, releasing mercury as vapor. 

The mercury vapor is then condensed by air- or water-cooling 

to form liquid mercury (also known as quicksilver). Lime 

(CaO) is typically added prior to ore roasting to remove sulfur 

gas (SO2

), which is also released during the heating process. 

The ore is typically burned in either a retort (a small, externally 
Leaching, Transport, and Methylation of Mercury, near Abandoned Mercury Mines, Humboldt River Basin, Nevada 5 

Table 1. Description and production of mercury mines studied. 

District Mines studied Geology Approximate mercury 

production (flasks/district) 

Dutch Flat ....................Dutch Flat..........................................Veins in Paleozoic schist and..................................................... 90 1, 2 

phyllite cut by Tertiary granodiorite 

Beowawe......................Red Devil (Beowawe).......................Veins in Paleozoic(?) limestone............................................... 150 1 

conglomerate overlain by Tertiary andesite 

Spring Valley...............Cinnabar City ....................................Veins in Triassic limestone and .............................................. 500 3 

Quaternary volcanic tuff and basalt 

Sonoma ........................Horton ...............................................Veins in altered Paleozoic greenstone ..................................... 500 3 

Poverty Peaks...............Cahill.................................................Veins in Paleozoic and Triassic limestone ........................... 1,000 2 

and sandstone, and Tertiary opalite 

Imlay ............................Eldorado (Blackjack)........................Veins in Triassic limestone and shale................................... 1,000 1 

Mt. Tobin .....................Mt. Tobin...........................................Silicified Tertiary rhyolite and tuff and ................................ 1,500 1, 3 

pre-Tertiary conglomerate and shale 

Ivanhoe.........................Silver Cloud, Butte............................Opalite altered Tertiary volcanic tuff..................................>2,000 1 

Goldbanks....................Goldbanks .........................................Opalite altered Tertiary volcanic tuff ................................... 2,700 3 

and breccia 

Bottle Creek.................White Peaks (Bottle Creek) ..............Veins in Paleozoic and Triassic tuffs and............................. 4,500 1 

sandstone and Tertiary diabase dikes 

Antelope Springs .........Pershing, Juniper ..............................Veins in Triassic limestone, dolomite................................. 12,500 3 

conglomerate, and shale 

Opalite..........................McDermitt.........................................Opalite altered Tertiary volcanic tuffs..............................270,000 4 

1Bailey and Phoenix (1944), 2Willden (1964), 3Johnson (1977), 4Noble and others (1988). 

heated, oven-like furnace) or in a large rotary furnace (fig. 3C) 

in which ore is heated internally and continuously rotated. In 

Nevada, retorts generally processed as much as a few tons of 

ore daily and were generally used at smaller mines, whereas 

rotary furnaces processed larger volumes of ore, as much as 100 

t of ore daily (Bailey and Phoenix, 1944). At the larger mines in 

Nevada, both retorts and rotary furnaces are found, and retorts 

were often used to recover mercury from smaller volumes of 

high-grade ore or from mercury-rich soot that typically collected in condensers (Bailey and Phoenix, 1944). This method 

of heating ore to vaporize mercury is a type of calcination 

process, and thus, resultant mercury mine wastes are termed 

calcine or mine-waste calcine. 

Mercury mine-waste calcine is typically red-brown in 

color (fig. 3), which results from the burning and oxidation of 

iron-sulfide minerals typically contained in the ore. Following 

ore roasting, mine wastes are discarded on the ground, generally at the mine site. However, the roasting process to remove 

mercury at mines worldwide is not totally efficient and is often 

incomplete, and thus, mine-waste calcine contains elemental 

Hg, elemental mercury sorbed onto particulates, cinnabar, 

metacinnabar, and several water-soluble mercury compounds 

such as sulfates, chlorides, and oxychlorides, which are present even after many years following cessation of mining (Biester and others, 1999; Kim and others, 2000). Due to the presence of elemental mercury and soluble mercury compounds, 

mine-waste calcine is not an appropriate construction material, 

especially for public roads. Furthermore, studies have shown 

elevated mercury gas emissions from mercury mines in 

Nevada and California (Gustin and others, 2000), indicating 

that extended human exposure to mercury mine calcine is not 

advisable (i.e., building houses on abandoned mercury mine 

sites should be avoided). 

Methods 

Field Studies and Sample Collection 

The 14 mercury mines studied are located in 12 districts 

(fig. 1) and represent a range in deposit size (mercury production) and geological characteristics (table 1). Most of the sites 

studied were within the HRB including the Eldorado, Dutch 

Flat, Cahill, Cinnabar City, Goldbanks, Silver Cloud, Butte, 

Mt. Tobin, Red Devil, and Horton mines, which were studied 

to evaluate any adverse influence of mercury to the HRB. In 

addition, localities outside of the HRB such as the McDermitt, 

Bottle Creek, Juniper, and Pershing mines were studied as 

analogs for mercury-transport processes within the HRB. The 

most important mine studied outside of the Humboldt River 

basin was McDermitt, the largest mercury mine in Nevada. 

Stream-sediment samples consisted of channel-bed 
6 Geoenvironmental Investigations of the Humboldt River Basin, Northern Nevada 

alluvium. Lake-sediment samples were collected along the 

shoreline below the waterline of Rye Patch Reservoir. Sediment samples were composited by collecting and mixing representative material from several localities at each site. Minewaste calcine was collected as grab samples. Sediment and 

mine-waste samples were air-dried and ground prior to analysis. Unfiltered water samples for mercury and methylmercury 

analysis were collected in precleaned Teflon bottles and were 

shipped within 48 hours to a commercial laboratory for analysis; at the laboratory, samples were acidified with ultrapure 

hydrochloric acid. An additional set of filtered and unfiltered 

water samples were collected at each locality for mercury 

analysis; these samples were collected to compare suspended 

(unfiltered) and dissolved (filtered) mercury concentrations in 

water. This set of water samples was collected in precleaned 

glass bottles and preserved with ultrapure nitric acid saturated 

with sodium dichromate; samples were subsequently analyzed 

by the USGS. All filtered water samples were passed through a 

0.45-μm sterile membrane. Stream-water characteristics such 

as pH, conductivity, alkalinity, turbidity, temperature, Fe2+, and 

dissolved oxygen were measured in the field at each sample 

site. 

Laboratory water-leaching studies were conducted on 

samples of mine-waste calcine using a modified version of 

the U.S. Environmental Protection Agency (EPA) 1312 synthetic precipitation leaching procedure (U.S. Environmental 

Protection Agency, 1986). Twenty-two mine-waste samples 

were air-dried and sieved to minus 9.5 mm prior to laboratory 

water-leaching studies. Following the EPA-1312 method, 2 L 

of deionized water acidified to pH 4.2 was added to 100 g of 

sample; these samples were leached as they were rotated at 

28 rpm for 18 hours. The only modification to the EPA-1312 

method was that the leachate was extracted and filtered at 0.45 

μm, rather than with a 0.7-μm filter. This procedural modification was made so that the same filtration method was used for 

both leachates and surface-water samples collected in the field. 

Conductivity, pH, Fe2+, and alkalinity were also measured in 

leachates. 

Chemical Analysis 

Measurement of mercury followed EPA method 1631, 

and EPA method 1630 for analysis of methylmercury (Bloom 

1989). The concentration of mercury was determined in the 

mine-waste, sediment, water, and leachate samples using 

cold-vapor atomic absorption spectrophotometry (CVAAS) 

methods modified from Kennedy and Crock (1987), or by a 

cold-vapor atomic fluorescence spectrometry (CVAFS) technique developed by Bloom and Fitzgerald (1988). Methylmercury was determined in samples using CVAFS (Bloom, 1989). 

During methylmercury analysis, sediment and mine-waste 

samples were extracted into methylene chloride during digestion to avoid possible methylation artifact effects (Bloom and 

others, 1997). Quality control for mercury and methylmercury 

analysis was addressed with field blanks, method blanks, blank 

spikes, matrix spikes, certified reference materials, and sample 

duplicates. Recoveries on blank and matrix spikes were 

80–120 percent, and the relative standard deviation was <15 

percent on reference standards. Method blanks were below the 

limits of determination. Sample duplicates are shown in tables 

2 and 3. The sediment and water samples were analyzed for 

additional major and trace elements using several methods, but 

these results are not discussed in this paper. These additional 

geochemical data are available in Gray and others (1999). 

Results 

Ore and Mine Wastes 

Significant mine stockpiles of unprocessed ore were not 

found, and only minor fragments of mineralized rock containing cinnabar were observed near shafts or adits, indicating that 

ore was efficiently mined and processed at the sites studied. 

At the Silver Cloud, Cahill, Butte, Goldbanks, and McDermitt mines, finely disseminated cinnabar was found in bedded 

opalite in open cuts and rock fragments. In addition, metacinnabar was observed in opalite ore from the Silver Cloud mine, 

and a probable mercury oxychloride (a bright-yellow mineral 

that darkened upon exposure to sunlight) was found along 

with vein cinnabar at the Cahill mine. Mercury concentrations in grab samples of ore varied widely from a low of 20 

μg/g (Dutch Flat mine) to cinnabar-rich samples containing 

as much as 6.9 percent (McDermitt mine) (Gray and others, 

1999). The mean mercury concentration of ores collected in 

this study was about 1.4 percent, which is similar to the average content of mercury ore mined throughout Nevada (Bailey 

and Phoenix, 1944; Willden, 1964; Johnson, 1977). 

Mine-waste calcine observed at most of the mines studied 

in Nevada is similar to calcine found worldwide, which is typically red-brown due to the presence of fine-grained iron oxide 

and minor cinnabar. However, where opalite was the dominant 

host rock of ore (e.g., the Silver Cloud mine), mine wastes 

are bleached white or light pink, which is consistent with the 

silica-rich nature of opalite at such sites. Mercury concentrations are highly variable in samples of mine-waste calcine 

collected from various mines. For example, calcine collected 

from the Eldorado mine contains mercury concentrations varying from 25 to 1,300 μg/g, whereas calcine from the Silver 

Cloud mine contains mercury ranging from 3.0 to 180 μg/g 

(table 2). Methylmercury concentrations in mine-waste calcine collected from the mines studied also vary widely—from 

<0.05 to 96 ng/g (table 2, fig. 4). 

In addition to measuring the concentration of mercury 

in the mine-waste calcine, the volume of calcine at the sites 

studied was also estimated in the field using compass and tape 

mapping. The amount of calcine remaining at these mercury 

mines is variable but is consistent with the general size and 

mercury production as shown in table 1. Calcine was estimated 
Leaching, Transport, and Methylation of Mercury, near Abandoned Mercury Mines, Humboldt River Basin, Nevada 7 

Table 2. Mercury data for mine-waste calcines and sediment samples collected from selected mercury mines, the Humboldt 

River, Rye Patch Reservoir, and Rock Creek. 

[Sample-number prefixes indicate collection date, e.g., 99 = 1999. a, replicate analyses; n.a., not analyzed] 

Sample number Location/description Hg (Pg/g) Methyl-Hg (ng/g) 

99DFL1ca 

99DFL2ca 

99DFL1ca 

00RD1ca 

00RD1ca 

00RD1ca 

00RD1s 

00RD2s 

00RD3s 

00CC1ca 

00CC2ca 

00CC3ca 

00CC1s 

00CC2s 

00CC3s 

00HN03ca 

01HN1ca 

01HN2ca 

00HN01s 

00HN02s 

00HN03s 

99CAH01ca 

01CAH1rt 

01CAH03ca 

99CAH1s 

99CAH2s 

00BJK01ca 

00BJK02ca 

01BJK01ca 

00BJK01s 

00BJK02s 

00BJK03s 

01TB01ca 

01TB02ca 

01TB03ca 

00TB01s 

00TB02s 

00TB03s 

00TB04s 

00TB05s 

99SLV1ca 

99SLV2ca 

99SLV1rt 

99SLV01s 

99SLV01s 

00BU01ca 

00BU02ca 

00BU03ca 

Dutch Flat mine-waste calcines


Dutch Flat mine-waste calcines


Dutch Flat mine-waste calcines inside small retort 


Red Devil mine-waste calcines


Red Devil mine-waste calcines


Red Devil mine-waste calcines


Red Devil mine, stream sediment 300 m below mine 


Red Devil mine, stream sediment 500 m below mine 


Red Devil mine, stream sediment 1,000 m below mine 


Cinnabar City mine-waste calcines 


Cinnabar City mine-waste calcines 


Cinnabar City mine-waste calcines 


Cinnabar City mine, stream sediment 100 m below mine 


Cinnabar City mine, stream sediment 300 m below mine 


Cinnabar City mine, stream sediment 1,500 m below mine 


Horton mine-waste calcines


Horton mine-waste calcines


Horton mine-waste calcines


Horton mine, stream sediment 300 m below mine 


Horton mine, stream sediment 800 m below mine 


Horton mine, stream sediment 5,000 m below mine 


Cahill mine-waste calcines


Cahill mine-waste calcines inside small retort


Cahill mine-waste calcines


Cahill mine, stream sediment 500 m below mine 


Cahill mine, stream sediment 800 m below mine 


Eldorado mine-waste calcines


Eldorado mine-waste calcines


Eldorado mine-waste calcines


Eldorado mine, stream sediment 100 m below mine 


Eldorado mine, stream sediment 500 m below mine 


Eldorado mine, stream sediment 2000 m below mine 


Mt. Tobin mine-waste calcines


Mt. Tobin mine-waste calcines


Mt. Tobin mine-waste calcines


Mt. Tobin mine, stream sediment 50 m below mine 


Mt. Tobin mine, stream sediment 400 m below mine 


Mt. Tobin mine, stream sediment 1,500 m below mine 


Mt. Tobin mine, stream sediment 6,000 m below mine 


Mt. Tobin mine, stream sediment 8,000 m below mine 


Silver Cloud mine-waste calcines 


Silver Cloud mine-waste calcines 


Silver Cloud mine-waste calcines inside small retort 


Silver Cloud mine, stream sediment 150 m below mine 


Silver Cloud mine, stream sediment 2,000 m below mine 


Butte mine-waste calcines


Butte mine-waste calcines


Butte mine-waste calcines


320 n.a. 

110 n.a. 

680 n.a. 

26 n.a. 

320 n.a. 

2.4 n.a. 

0.21 n.a. 

0.80 n.a. 

0.23 n.a. 

12 n.a. 

1.3 n.a. 

6.2 n.a. 

7.8 n.a. 

3.5 n.a. 

0.8 n.a. 

610 n.a. 

380 0.80 

220 0.99 

0.90 n.a. 

0.90 n.a. 

0.17 n.a. 

680 n.a. 

27, 28 a 0.87 

64, 62 a 0.31 

170 n.a. 

2.0 n.a. 

1,000 7.7 

25 < 0.05 

1,300, 1,200 a 3.5, 4.2 a 

1.7 0.95 

1.4 0.26 

0.87 0.23 

520, 540 a 0.073 

290 < 0.05 

1,200 2.9 

40 0.18 

60 0.21 

22 0.12 

0.16 n.a. 

0.23 n.a. 

3.0 n.a. 

17 n.a. 

180 n.a. 

18 n.a. 

8.8 n.a. 

79 0.07 

14 < 0.05 

45 n.a. 
8 Geoenvironmental Investigations of the Humboldt River Basin, Northern Nevada 

Table 2. Mercury data for mine-waste calcines and sediment samples collected from selected mercury mines, the Humboldt 

River, Rye Patch Reservoir, and Rock Creek—Continued. 

Sample number Location/description Hg (Pg/g) Methyl-Hg (ng/g) 

99GLB1ca Goldbanks mine-waste calcines 2.5 n.a. 

99GLB2ca Goldbanks mine-waste calcines 10 n.a. 

99GLB1s Goldbanks mine, stream sediment 300 m below mine 2.6 n.a. 

99GLB2s Goldbanks mine, stream sediment 1,000 m below mine 2.2 n.a. 

99GLB3s Goldbanks mine, stream sediment 4,000 m below mine 0.24 n.a. 

99GLB4s Goldbanks mine, stream sediment 5,000 m below mine 0.60 n.a. 

99BCK1ca Bottle Creek mine-waste calcines 7.8 n.a. 

99BCK2ca Bottle Creek mine-waste calcines 5.4 n.a. 

99BCK3ca Bottle Creek mine-waste calcines 210 n.a. 

99PER1ca Pershing mine-waste calcines 11 n.a. 

99PER2ca Pershing mine-waste calcines 9.3 n.a. 

99PER3ca Pershing mine-waste calcines 13 n.a. 

99PER1rt Pershing mine-waste calcines 310 n.a. 

99ANT1ca Juniper mine-waste calcines 3.6 n.a. 

99ANT2ca Juniper mine-waste calcines 43 n.a. 

99ANT2ca Juniper mine-waste calcines 100 n.a. 

00McD1ca McDermitt mine-waste calcines 1,200 88, 92, 96 a 

00McD2ca McDermitt mine-waste calcines 40 6.8, 6.0 a 

00McD3ca McDermitt mine-waste calcines 1,400 0.58 

01McD1ca McDermitt mine-waste calcines 1,400 19 

01McD2ca McDermitt mine-waste calcines 200 0.88 

01McD3ca McDermitt mine-waste calcines 330 0.19 

01McD4rt McDermitt mine-waste calcines inside small retort 14,000 4.3 

01HMB1 Humboldt River, stream sediment 0.008 0.072 

01HMB2 Humboldt River, stream sediment 0.05 n.a. 

01HMB3 Humboldt River, stream sediment 0.05 n.a. 

01HMB4 Humboldt River, stream sediment 0.01 n.a. 

01HMB5 Humboldt River, stream sediment 0.01 n.a. 

00HMB6 Humboldt River, stream sediment 0.017 < 0.05 

00HMB7 Humboldt River, stream sediment 0.014 < 0.05 

00HMB8 Humboldt River, stream sediment 0.016 0.077 

00HMB9 Humboldt River, stream sediment 0.080 n.a. 

00HMB10 Humboldt River, stream sediment 0.010 < 0.05 

00HMB11 Humboldt River, stream sediment 0.017 < 0.05 

00HMB12 Humboldt River, stream sediment 0.019 < 0.05, < 0.05 a 

01HMB13 Humboldt River, stream sediment 0.10 n.a. 

00HMB14 Humboldt River, stream sediment 0.28 n.a. 

00HMB15 Humboldt River, stream sediment 0.021 < 0.05 

99RYP1 Rye Patch Reservoir, lake sediment 0.15 n.a. 

99RYP2 Rye Patch Reservoir, lake sediment 0.05 n.a. 

99RYP3 Rye Patch Reservoir, lake sediment 0.07 n.a. 

99RYP4 Rye Patch Reservoir, lake sediment 0.09 n.a. 

99RYP5 Rye Patch Reservoir, lake sediment 0.09 n.a. 

01RYP6 Rye Patch Reservoir, lake sediment 0.004 0.090 

00RC01 Rock Creek, baseline stream sediment 0.44 n.a. 

00RC02 Rock Creek, baseline stream sediment 0.27 n.a. 
Leaching, Transport, and Methylation of Mercury, near Abandoned Mercury Mines, Humboldt River Basin, Nevada 9 

Table 3. Geochemical data for water samples collected from two mercury mines, the Humboldt River, Rye Patch Reservoir, and Rock Creek. 

[Sample-number prefixes indicate collection date, e.g., 99 = 1999. NTU, nephelometric turbidity units; n.a., not analyzed; a, replicate analyses] 

Sample number Location/description Hg Methyl-Hg pH Conductivity Turbidity 

(ng/L) (ng/L) (PS/cm) (NTU) 

99BJK1 Eldorado mine, unfiltered stream water 100 m below mine 8.0 n.a. 8.6 350 5 

99BJK2 Eldorado mine, unfiltered stream water 500 m below mine 6.0 n.a. 8.7 330 8 

01BJK1 Eldorado mine, unfiltered stream water above mine 3.1 0.039 8.3 350 10 

01BJK2 Eldorado mine, unfiltered stream water 100 m below mine 13 0.11 8.6 350 10 

01BJK3 Eldorado mine, unfiltered stream water 500 m below mine 8.7 0.89 8.7 380 10 

99BJK1 Eldorado mine, filtered stream water 100 m below mine < 5.0 n.a. 8.6 n.a. n.a. 

99BJK2 Eldorado mine, filtered stream water 500 m below mine < 5.0 n.a. 8.7 n.a. n.a. 

00TB01 Mt. Tobin mine, unfiltered stream water 50 m below mine 80 n.a. 8.5 440 2 

00TB02 Mt. Tobin mine, unfiltered stream water 400 m below mine 130 n.a. 8.4 485 5 

00TB03 Mt. Tobin mine, unfiltered stream water 1,500 m below mine 120 n.a. 8.6 510 7 

01TB01 Mt. Tobin mine, unfiltered stream water 50 m below mine 55 0.20 8.5 440 2 

01TB02 Mt. Tobin mine, unfiltered stream water 400 m below mine 388 0.49 8.4 450 5 

01TB03 Mt. Tobin mine, unfiltered stream water 1,500 m below mine 330, 305 a 0.60 8.6 450 10 

01TB04 Mt. Tobin mine, unfiltered stream water 6,000 m below mine 2,000 0.92, 0.89 a 8.2 470 20 

00TB01 Mt. Tobin mine, filtered stream water 50 m below mine < 5.0 n.a. 8.5 n.a. n.a. 

00TB02 Mt. Tobin mine, filtered stream water 50 m below mine < 5.0 n.a. 8.4 n.a. n.a. 

00TB03 Mt. Tobin mine, filtered stream water 50 m below mine < 5.0 n.a. 8.6 n.a. n.a. 

01HMB1 Humboldt River, unfiltered stream water 6.0 0.19, 0.21 a 8.7 550 40 

99HMB2 Humboldt River, unfiltered stream water < 5.0 n.a. 8.2 600 90 

99HMB3 Humboldt River, unfiltered stream water 8.0 n.a. 8.4 630 150 

99HMB4 Humboldt River, unfiltered stream water 9.0 n.a. 8.3 660 150 

99HMB5 Humboldt River, unfiltered stream water < 5.0 n.a. 8.6 840 50 

01HMB6 Humboldt River, unfiltered stream water 5.0 < 0.02 8.5 400 40 

00HMB7 Humboldt River, unfiltered stream water < 5.0 n.a. 8.5 400 50 

01HMB8 Humboldt River, unfiltered stream water 2.2, 2.3 a 0.19 8.6 480 40 

00HMB9 Humboldt River, unfiltered stream water < 5.0 n.a. 8.5 420 70 

01HMB10 Humboldt River, unfiltered stream water 6.9 < 0.02, 0.02 a 8.6 1000 150 

00HMB11 Humboldt River, unfiltered stream water < 5.0 n.a. 8.5 810 150 

00HMB12 Humboldt River, unfiltered stream water 6.0 n.a. 8.5 800 120 

00HMB13 Humboldt River, unfiltered stream water < 5.0 n.a. 8.6 770 140 

00HMB14 Humboldt River, unfiltered stream water < 5.0 n.a. 8.5 860 150 

00HMB15 Humboldt River, unfiltered stream water < 5.0 n.a. 8.4 490 100 

01HMB1 Humboldt River, filtered stream water < 5.0 n.a. 8.7 n.a. n.a. 

99HMB2 Humboldt River, filtered stream water < 5.0 n.a. 8.2 n.a. n.a. 

99HMB3 Humboldt River, filtered stream water < 5.0 n.a. 8.4 n.a. n.a. 

99HMB4 Humboldt River, filtered stream water < 5.0 n.a. 8.3 n.a. n.a. 

99HMB5 Humboldt River, filtered stream water < 5.0 n.a. 8.6 n.a. n.a. 

00HMB6 Humboldt River, filtered stream water < 5.0 n.a. 8.5 n.a. n.a. 

00HMB7 Humboldt River, filtered stream water < 5.0 n.a. 8.5 n.a. n.a. 

00HMB8 Humboldt River, filtered stream water < 5.0 n.a. 8.6 n.a. n.a. 

00HMB9 Humboldt River, filtered stream water < 5.0 n.a. 8.5 n.a. n.a. 

00HMB10 Humboldt River, filtered stream water < 5.0 n.a. 8.6 n.a. n.a. 

00HMB11 Humboldt River, filtered stream water < 5.0 n.a. 8.5 n.a. n.a. 

00HMB12 Humboldt River, filtered stream water < 5.0 n.a. 8.5 n.a. n.a. 

00HMB13 Humboldt River, filtered stream water < 5.0 n.a. 8.6 n.a. n.a. 

00HMB14 Humboldt River, filtered stream water < 5.0 n.a. 8.5 n.a. n.a. 

00HMB15 Humboldt River, filtered stream water < 5.0 n.a. 8.4 n.a. n.a. 

99RYP1 Rye Patch Reservoir, unfiltered lake water 8.0 n.a. 8.5 730 140 

99RYP2 Rye Patch Reservoir, unfiltered lake water 8.0 n.a. 8.5 730 140 

99RYP3 Rye Patch Reservoir, unfiltered lake water 5.0 n.a. 8.6 740 80 

99RYP4 Rye Patch Reservoir, unfiltered lake water < 5.0 n.a. 8.6 780 40 

99RYP5 Rye Patch Reservoir, unfiltered lake water < 5.0 n.a. 8.6 820 50 

00RYP6 Rye Patch Reservoir, unfiltered lake water 5.5 < 0.02 8.6 800 100 
10 Geoenvironmental Investigations of the Humboldt River Basin, Northern Nevada 

Table 3. Geochemical data for water samples collected from two mercury mines, the Humboldt River, Rye Patch Reservoir, and Rock Creek— 

Continued. 

Sample number Location/description Hg Methyl-Hg pH Conductivity Turbidity 

(ng/L) (ng/L) (PS/cm) (NTU) 

01RYP6 Rye Patch Reservoir, unfiltered lake water 2.1 0.27 8.6 780 80 

99RYP1 Rye Patch Reservoir, filtered lake water 5.0 n.a. 8.5 n.a. n.a. 

99RYP2 Rye Patch Reservoir, filtered lake water < 5.0 n.a. 8.5 n.a. n.a. 

99RYP3 Rye Patch Reservoir, filtered lake water < 5.0 n.a. 8.6 n.a. n.a. 

99RYP4 Rye Patch Reservoir, filtered lake water < 5.0 n.a. 8.6 n.a. n.a. 

99RYP5 Rye Patch Reservoir, filtered lake water < 5.0 n.a. 8.6 n.a. n.a. 

00RC01 Rock Creek baseline, unfiltered stream water < 5.0 n.a. 9.4 350 5 

00RC02 Rock Creek baseline, unfiltered stream water < 5.0 n.a. 9.8 360 5 

to vary from approximately 300 m3 (at Dutch Flat, the smallest 

mine studied) to greater than 1,000,000 m3 (at McDermitt, the 

largest mine studied). Using these volumes and the mercury 

concentrations determined in samples of calcine collected 

from the mines, there is about 1 t of mercury remaining in the 

calcine at the Dutch Flat mine, and greater than 1,000 t of mercury in calcine at the McDermitt mine. Thus, there is a large 

amount of mercury remaining in the mine-waste piles that is 

potentially available for leaching, downstream transport, and 

possible conversion to other forms of mercury. 

Mine-waste calcines Mine drainages 

Humboldt River sediments 

100,000 

1000 

10 

0.1 

0.001 

0.001 0.01 0.1 1 10 100 1,000 

Alaska mine drainages 

Methylmercury (ng/g) 

Figure 4. Mercury versus methylmercury concentration in minewaste calcine, mine-drainage sediments, and Humboldt River 

sediment samples. The range of data for mine-drainage sediments 

collected from mercury mines in Alaska (Gray and others, 2000) are 

shown for reference. 

H

g (

μg/g) 

Stream- and Lake-Sediment Samples 

Stream-sediment samples collected within 1 km of the 

mines studied contain mercury concentrations as high as 170 

μg/g (Cahill mine, table 2). Such samples are highly elevated 

in mercury when compared to stream sediments collected 

distant from the mines (several kilometers), such as the Rock 

Creek regional geochemical baseline site and the Humboldt 

River, both of which have mercury concentrations of less than 

0.44 μg/g (table 2, fig. 5A). Few structures were observed to 

keep on-site mine-waste materials from eroding down gradient, and as a result, calcine and ore-bearing detritus were 

visible in streambeds below most mines. However, the concentration of mercury in stream sediments collected below the 

mines is generally lower than that in calcine material from the 

corresponding mine. For example, although calcine material 

from the Eldorado mine contains as much as 1,300 μg/g mercury, stream sediment collected about 100 m downstream from 

the mine contains only 1.7 μg/g mercury, and sediment collected about 2 km below the mine contains 0.87 μg/g mercury 

(table 2, fig. 5B). The Eldorado mine is located about midway 

along Eldorado Creek, which is a large drainage basin with 

a stream length of about 10 km. Thus, sediment transported 

downstream from the Eldorado mine is significantly diluted by 

barren (unmineralized) detritus in this large drainage basin, as 

evidenced by the mercury data for stream-sediment samples 

collected from Eldorado Creek. Stream-sediment samples collected downstream from the Mt. Tobin mine show a similar 

pattern (fig. 5C). Perhaps most importantly, sediment samples 

collected from the Humboldt River and Rye Patch Reservoir 

contain mercury concentrations of less than 0.28 μg/g (table 

2). These results are not overly surprising because the mercury 

mines are located more than 8 km from the Humboldt River 

and Rye Patch Reservoir, and as a result, mercury is dispersed 

and significantly diluted before it reaches the Humboldt River 

system. 

Methylmercury contents in sediment samples show a 

pattern similar to that of mercury in sediments. The only 
Leaching, Transport, and Methylation of Mercury, near Abandoned Mercury Mines, Humboldt River Basin, Nevada 11 

mine-drainage sediments analyzed for methylmercury were 

those collected from the Eldorado and Mt. Tobin mines, but 

methylmercury content in these samples are generally lower 

Mine-drainage sediments Rock Creek baseline 

Humboldt River sediments Rye Patch Reservoir 

1,000	

A

(0.12 to 0.95 ng/g) than that found in the upstream mine-waste 

calcine (<0.05–7.7 ng/g). Sediment samples collected from the 100 Humboldt River and Rye Patch Reservoir generally contain 

10 the lowest methylmercury contents (<0.05–0.090 ng/g) of the 

sediments collected in this study. 1 

0.1 Stream- and Lake-Water Samples 

0.01 

Stream water was found flowing at only the Eldorado 0.001 

20,000 40,000 60,000 80,000 100,000 and Mt. Tobin mine sites. During fieldwork in the summers 0 

Distance from mines (m) of 1999–2001, Eldorado Creek was dry about 1 km below the 

mine, whereas water flowed for about 6 km downstream from 

the Mt. Tobin mine. Mercury concentrations in unfiltered water 

Eldorado mine calcines Mine-drainage sediments 

Humboldt River sediments Rye Patch Reservoir 

collected downstream from these mines range from 6.0 to 

2,000 ng/L; all filtered mine-water samples have mercury con10,000 

B

tents of ≤5.0 ng/L (table 3). These results suggest transport of 

1,000 mercury primarily as finely suspended matter (probably finely 

particulate cinnabar or mercury adsorbed to suspended matter) 100 

downstream from these mines for short distances until the water 

10 flow dissipates. Mercury contents actually increase in unfiltered 

1 water collected downstream from the Mt. Tobin mine, which 

0.1 is probably due to abundant domestic animal activity (grazing livestock) in this area, resulting in significant disruption of 0.01 the stream bed, more suspended organic particulates, and an 

0.001 increase in downstream water turbidity. Mercury concentra0 10,000 20,000 30,000 40,000 tions in all of the unfiltered stream- and lake-water samples col- Distance from Eldorado mine (m)	 lected from the Humboldt River system were generally lower 

(≤5.0 to 9.0 ng/L) than those in the mine waters (fig. 6); all filtered water samples collected from the Humboldt River system 

had mercury concentrations of less than 5.0 ng/L. Unfiltered 

water samples collected from the Rock Creek baseline sites had 

Mt. Tobin mine calcines Mine-drainage sediments 

Humboldt River sediments Rye Patch Reservoir 

10,000 

mercury contents of less than 5.0 ng/L (table 3). 

1,000 C

Methylmercury concentrations in unfiltered water col100 lected downstream from the Eldorado and Mt. Tobin mines 

10 varied from 0.11 to 0.92 ng/L (table 3, fig. 6). Methylmercury 

concentrations in unfiltered water samples collected from the 

1 Humboldt River and Rye Patch Reservoir ranged from <0.02 

0.1 to 0.27 ng/L; these concentrations are generally lower than 

0.01 those observed in water collected downstream from the mercury mines studied. 0.001 

0 50,000 100,000 150,000 

Distance from Mt. Tobin mine (m) Water-Leach Studies 

Highly variable and elevated concentrations of mercury Figure 5. Mercury in sediments versus distance from mines for A, all were found in some of the leachates obtained from the mine- mine drainages; B, the Eldorado mine; and C, the Mt. Tobin mine. The 

distance plotted in A for samples collected from the Humboldt River waste calcine samples (fig. 7). For example, three leachates 

and Rye Patch Reservoir is that to the nearest upstream mercury of calcine samples obtained from the Silver Cloud mine conmine. These data document dilution of mercury below the mercury tained from 0.2 to 1,500 μg/L mercury—this represents leachmines in this study. ates with the highest and one of the lowest mercury concentrations determined in this study (table 4). Leachates obtained 

from three calcine samples collected from the McDermitt mine 

Hg (μg/g) 

H

g (μg/g)

Hg (μg/g) 
12 Geoenvironmental Investigations of the Humboldt River Basin, Northern Nevada 

Calcine leachates Humboldt River 

Rye Patch Reservoir Mine drainages 

Humboldt River system Eldorado mine Mt. Tobin mine 

10,000 

1,000 

100 

10 

1 

0.1 

0.01 

0.001 

0.001 0.01 0.1 1 10 

2,000 ng/L drinking water standard 

12 ng/L EPA standard 

Alaska mine waters 

Methylmercury (ng/L) 

Figure 6. Mercury versus methylmercury concentration in unfiltered 

water samples collected downstream from the Eldorado and Mt. Tobin 

mines, and from the Humboldt River and Rye Patch Reservoir. The 

range of data for unfiltered water samples collected from mercury 

mines in Alaska (Gray and others, 2000), the State of Nevada drinkingwater standard, and the EPA criterion continuous-concentration 

standard established to protect against chronic effects of mercury to 

aquatic wildlife are shown for reference. 

contained somewhat lower mercury concentrations (0.2–21 

μg/L). The concentration of mercury in these leachates is 

highly elevated when compared to that found in the natural 

surface waters examined in this study. There is no consistent 

correlation between leachate mercury concentrations and mercury contents in the corresponding calcine leached, or between 

leachate mercury concentrations and the type of ore processed 

from the various mines (Gray and others, 2002). Leaching 

of soluble mercury from these mine-waste calcines is most 

likely due to the presence of soluble mercury salts, which were 

reported in previous studies that identified mercury chlorides 

and oxychlorides at several mines in this region (Bailey and 

Phoenix, 1944). 

Conductivity (25–3,800 μS/cm) and pH (3.2–9.9) measured in the leachates also varied widely (table 4). Although 

the two leachates with the highest conductivities, 3,800 and 

3,400 μS/cm, also contain high mercury concentrations (1,500 

and 81 μg/L, respectively) the overall correlation between 

high conductivity and mercury concentration is weak (table 

4). There is also a poor correlation between leachate mercury 

concentration and pH (fig. 7), indicating that mercury concentration is not solely controlled by the capacity of the calcine 

samples to generate acid. 

Discussion 

The primary environmental concerns regarding mercury 

mines in Nevada are downstream transport of mercury and conversion of mercury to water soluble, bioavailable forms such as Hg (ng/L) 

10,000


1,000


100


10


1


0.1


0.01


0.001


Near neutral, 

low metal 

Near neutral,

extreme metal 

Acid, 

high metal 

High acid, 

extreme metal 

Near neutral, 

high metal 

0 2 4 6 8 10 12 14 

pH 

Figure 7. Mercury concentration versus pH in filtered water samples 

of leachates from mine-waste calcine and filtered water samples col�

lected from the Humboldt River, Rye Patch Reservoir, and mine drainages. Mercury concentrations in the leachates are highly variable; 

some plot in the near-neutral, extreme-metal field. All natural surfacewater samples collected plot in the near-neutral, low-metal field. 

methylmercury. At the mines studied, there is minor cinnabar 

visible in the area of the open-pit cuts, adits, trenches, in a few 

outcrops, and in mine-waste calcine. Fine-grained and encapsulated cinnabar observed in many of the calcine piles, and the 

high variability of mercury within samples of calcine from individual mines, probably indicates that retorting was not totally or 

uniformly efficient and that mercury byproduct compounds are 

present in calcine. Detrital cinnabar and mine-waste calcine are 

clearly visible in stream drainages below the mines, indicating 

that mercury is eroding downstream from the mines. Mercury 

concentrations in stream-sediment samples were significantly 

lower than those in mine-waste calcine collected from the corresponding mine, and thus, sediments show substantial dispersion of mercury downstream from the mines. Although mercury 

contents in mine-waste calcine (as much as 14,000 μg/g) and 

stream-sediment samples (as much as 170 μg/g) collected at 

or near the mines are highly elevated, the dominant form of 

the mercury is cinnabar (HgS), which is generally resistant to 

chemical and physical weathering (Gray and others, 2000). In 

addition, acid-water-generating sulfide minerals, such as pyrite, 

are rare in the mercury ores and mine wastes. Thus, the potential for acid-water generation near these mines is minimal even 

during high-flow runoff, which is important because cinnabar 

is more soluble in acidic conditions (Gray and others, 2003). 

During this study, elemental mercury, which is more chemically reactive than cinnabar, was not observed around retorts or 

rotary furnaces at any of the mines studied. The absence of elemental mercury at these sites may be related to the hot, arid climate and relative age of these mines (i.e., most of these mines 

have been inactive for several decades), and thus, elemental 

mercury may have evaporated over time. Hg (μ

g/L) 
Leaching, Transport, and Methylation of Mercury, near Abandoned Mercury Mines, Humboldt River Basin, Nevada 13 

Table 4. Geochemical data for filtered water leachates of mine-waste samples collected from several mercury mines. 

Sample number Location/description Hg pH Conductivity 

(Pg/L) (PS/cm) 

99DFL1ca Dutch Flat mine-waste calcines, leachate 175 7.4 270 

99DFL1rt Dutch Flat mine-waste calcines inside small retort, leachate 0.10 3.2 1,500 

99CAH1ca Cahill mine-waste calcines, leachate 0.10 9.7 160 

99CAH3ca Cahill mine-waste calcines, leachate 0.30 9.4 100 

99CAH1rt Cahill mine-waste calcines inside small retort, leachate 2.0 9.3 1,700 

99BJK1ca Eldorado mine-waste calcines, leachate 5.0 9.2 130 

99BJK2ca Eldorado mine-waste calcines, leachate 0.10 8.9 70 

99BJK1rt Eldorado mine-waste calcines inside small retort, leachate 0.30 9.2 390 

99SLV1ca Silver Cloud mine-waste calcines, leachate 0.20 5.4 25 

99SLV2ca Silver Cloud mine-waste calcines, leachate 0.80 9.3 40 

99SLV1rt Silver Cloud mine-waste calcines inside small retort, leachate 1,500 7.9 3,800 

99GLB1ca Goldbanks mine-waste calcines, leachate 0.20 9.5 85 

99GLB2ca Goldbanks mine-waste calcines, leachate 0.10 8.0 80 

99BCK1ca Bottle Creek mine-waste calcines, leachate 7.0 7.8 95 

99BCK3ca Bottle Creek mine-waste calcines, leachate 290 9.2 80 

99PER1ca Pershing mine-waste calcines, leachate 0.20 9.8 290 

99PER1rt Pershing mine-waste calcines inside small retort, leachate 81 9.0 3,400 

99ANT1ca Juniper mine-waste calcines, leachate 1.1 9.9 940 

99ANT3ca Juniper mine-waste calcines, leachate 22 6.4 2,100 

99MCD1ca McDermitt mine-waste calcines, leachate 21 8.8 65 

99MCD2ca McDermitt mine-waste calcines, leachate 0.20 4.3 190 

99MCD3ca McDermitt mine-waste calcines, leachate 0.20 3.2 1,700 

Methylmercury concentrations in mine waste, water, 

and sediment collected from in and around the mines are 

more environmentally important than total mercury contents 

because methylmercury is highly toxic to organisms (National 

Academy of Sciences, 1978; Eisler, 1987; U.S. Environmental 

Protection Agency, 2001). Similar to the results for mercury, 

methylmercury contents in stream sediments collected downstream from mines are generally lower than methylmercury 

in corresponding mine-waste calcine (table 2). More importantly, methylmercury contents in sediments collected from 

the Humboldt River were the lowest found in the study (fig. 

4). Methylmercury results for mine-drainage sediment and the 

Humboldt River indicate significantly lower mercury methylation in stream environments both proximal and distal from the 

mercury mines when compared to methylmercury in minewaste calcine. 

Mercury concentrations in unfiltered water samples collected from the Humboldt River and Rye Patch Reservoir 

(2.1–9.0 ng/L) are below several important environmental and 

health standards including (1) the 2,000-ng/L State of Nevada 

drinking-water standard for mercury (Nevada Division of Environmental Protection, 2001), (2) the 2,400-ng/L mercury standard recommended by the EPA to protect against acute effects 

to aquatic wildlife, and (3) the 12-ng/L mercury standard 

recommended by the EPA to protect against chronic effects 

to aquatic wildlife (U.S. Environmental Protection Agency, 

1992) (fig. 6). The concentration of mercury in water samples 

collected downstream from the Eldorado and Mt. Tobin mercury mines is generally higher than that in the Humboldt River 

(fig. 6). Mercury concentrations in the mine-water samples 

was equal to or less than the State of Nevada drinking-water 

standard and less than the EPA acute aquatic-life standard for 

mercury. However, mercury concentrations in several of the 

mine-water samples exceed the 12-ng/L EPA mercury standard 

to protect against chronic effects to aquatic wildlife, especially 

stream water collected from the Mt. Tobin mine (fig. 6). Similarly, leachates obtained from calcine samples contained variable and some highly elevated mercury concentrations (fig. 7), 

and some of these concentrations are significantly higher than 

the 2,000 ng/L State of Nevada drinking-water standard for 
14 Geoenvironmental Investigations of the Humboldt River Basin, Northern Nevada 

mercury. The leachate data indicate that there are water-soluble 

forms of mercury in some mine-waste calcine samples or that 

finely particulate mercury-bearing material passed through the 

0.45-μm filter during leachate filtration. Leachates produced in 

this study probably represent the maximum mercury concentrations that can be obtained by water leaching of the mine-waste 

calcine because the EPA-1312 method is a rigorous leaching 

technique that includes rotation and agitation and a 20:1 waterto-sample ratio. 

Methylmercury concentrations in unfiltered water samples 

collected from the Humboldt River and Rye Patch Reservoir 

generally had the lowest methylmercury contents in this study 

(fig. 6). Conversely, results for the sediment and water samples 

indicate significant local methylation at mine sites. However, 

downstream transport of methylmercury in this arid region is 

limited by the lack of mine-water runoff. Of all the mines studied, stream water was observed only at the Eldorado and Mt. 

Tobin mines, and both of these streams were ephemeral and 

dry within a few kilometers of these mines. Thus, mine-water 

runoff is hydrologically disconnected from the Humboldt River 

system because such water does not flow directly into the Humboldt River. Surface-water runoff from all mercury mines in this 

region is rapidly diluted and infiltrates into broad areas of desert 

pediment before reaching the Humboldt River (fig. 3A). This 

is true even during periods of high precipitation, such as storm 

events or spring runoff, because the mines are distant from the 

Humboldt River (fig. 1). In addition, stream water below the 

mines studied and that from the Humboldt River is alkaline (pH 

8.2–8.7), and under such conditions, cinnabar generally has a 

low solubility. Proximal to most cinnabar-dominant mercury 

mines, mercury transport is mostly as finely suspended particulate cinnabar (Gray and others, 2000; Gray and others, 2002). 

The concentrations of mercury and methylmercury in 

mine-waste calcine and mine-drainage sediments collected in 

this study are similar to those found in other mercury mines 

in the United States, for example in Alaska (Gray and others, 

2000), although the methylmercury concentrations in calcine 

from the McDermitt mine are as much as several times those 

observed in samples from Alaska. The climatic settings of 

Nevada and Alaska are clearly different (arid versus subarctic), 

but the mercury mines in both regions are mineralogically 

similar because they both are hot-springs mineral deposits 

where ore is dominantly cinnabar (Gray and others, 1997). 

High local methylmercury concentrations in mercury-bearing 

mine wastes in Nevada suggest higher methylation in this 

climate where annual temperatures are higher, with possibly 

more microbial activity, resulting in greater methylation. Concentrations of mercury and methylmercury in mine water collected in this study are also comparable to those found in mine 

waters from Alaska. In Alaska, several of the mercury mines 

are located proximal to aquatic ecosystems that support freshwater fish and salmon, and in some instances, fish collected 

from such streams contain elevated concentrations of mercury 

(>0.5 μg/g, Gray and others, 2000). However, in Nevada, 

streams proximal to the mercury mines studied are small and 

ephemeral and do not contain fish. Thus, in this region of 

Nevada, the transference of significant methylmercury from 

mine-waste calcine to stream sediments, to stream water, and 

then to biota such as fish, is unlikely. Presently, there are no 

advisories for elevated mercury in fish on any water body in 

the Humboldt River system. Data presented here, which generally show low mercury and methylmercury contents in samples collected from the Humboldt River are consistent with the 

lack of advisories on the Humboldt River. 

Summary 

Results in this study indicate minimal adverse environmental effects to the Humboldt River ecosystem from mercury 

mines in Nevada because 

•	 The primary mercury ore mineral is cinnabar, which is 

resistant to physical and chemical weathering. Elemental mercury, which is more reactive than cinnabar, was 

not observed at any of the mines studied. 

•	 The climate in the study area is arid, and there is rarely 

runoff from the mines. Mine drainage was found at 

only 2 of the 14 mines studied, and drainage from 

these mines dissipated a few kilometers downstream. 

• 	 Samples of mine-waste calcine contain locally high 

concentrations of mercury and methylmercury, but 

stream-sediment samples collected downstream from 

the mines had generally lower mercury and methylmercury contents; these results indicate only minor, 

local downstream transference of mercury and methylmercury. Sediments collected from the Humboldt River 

and Rye Patch Reservoir had the lowest mercury and 

methylmercury contents in this study. 

• 	 Leachates from calcine collected from several of the 

mines generated variable, but in some instances significant, mercury concentrations (as much as 1,500 μg/L) 

during water-leaching experiments. However, natural 

runoff from the mercury mines has little influence on 

the major watersheds because mercury concentrations 

in water samples from the Humboldt River are much 

lower (<9.0 ng/L). 

• 	 The mines are distant from the Humboldt River, and 

mine runoff does not flow directly into the Humboldt 

River. In addition, mercury in water and sediment is 

transported and diluted through a significant volume of 

pediment before it reaches the Humboldt River. 

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Manuscript approved for publication June 23, 2003

Published in the Central Region, Denver, Colorado

Editing, page layout, photocomposition—Richard W. Scott, Jr.

Graphics by the author