Prepared in cooperation with the Bureau of Land Management 

Review of Samples of Water, Sediment, Tailings, 

and Biota at the Little Bonanza Mercury Mine, San 

Luis Obispo County, California 

By James J. Rytuba, Roger L. Hothem, Daniel N. Goldstein, Brianne E. Brussee, and Jason T. May 

Open-File Report 2011–1122

U.S. Department of the Interior 

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

KEN SALAZAR, Secretary 

U.S. Geological Survey 

Marcia K. McNutt, Director 

U.S. Geological Survey, Reston, Virginia 2010 

For more information on the USGS—the Federal source for science about the Earth, 

its natural and living resources, natural hazards, and the environment: 

World Wide Web: http://www.usgs.gov 

Telephone: 1-888-ASK-USGS 

Suggested citation: 

Rytuba, J.J., Hothem, R.L., Goldstein, D.N., Brussee, B.E., and May, J.T., 2011, Review of 

samples of water, sediment, tailings, and biota at the Little Bonanza mercury mine, San Luis 

Obispo County, California: U.S. Geological Survey Open-File Report 2011-1122, 46 p. 

[http://pubs.usgs.gov/of/2011/1122/].

Any use of trade, product, or firm names is for descriptive purposes only and does not imply 

endorsement by the U.S. Government. 

Although this report is in the public domain, permission must be secured from the individual 

copyright owners to reproduce any copyrighted material contained within this report. 
iii

Contents 

Conversion Factors................................................................................................................................................. vi

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

Background and Objectives......................................................................................................................................... 1

History and Geology........................................................................................................................................................ 2

Sample Sites and Methods ............................................................................................................................................. 2

Field Sampling Methods.................................................................................................................................................. 2

Dry and Wet Sediment and Tailings ............................................................................................................................ 2

Water ........................................................................................................................................................................... 3

Invertebrates................................................................................................................................................................ 3

Analytical Methods .......................................................................................................................................................... 4

Sediments and Tailings ............................................................................................................................................... 4

Water ........................................................................................................................................................................... 4

Biota............................................................................................................................................................................. 5

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

Tailings at the Little Bonanza Mine Areas ................................................................................................................... 6

Sediment in WF Las Tablas Creek near the Little Bonanza Mine ............................................................................... 7

Water Chemistry.......................................................................................................................................................... 7

Hg T and MMeHg in waters.......................................................................................................................................... 7

HgT and MMeHg in Biota ............................................................................................................................................. 8

Conclusions..................................................................................................................................................................... 8

Acknowledgments ......................................................................................................................................................... 10

References Cited........................................................................................................................................................... 10

Tables 

Table 1. Sample locations and physical and selected chemical parameters for waters from the Little Bonanza Mine 

on April 6, 2010. ............................................................................................................................................................ 12

Table 2. Mercury and associated major and minor elements in sediment, precipitates, and calcines from the Little 

Bonanza Mine. .............................................................................................................................................................. 13

Table 3. Mercury and monomethylmercury concentrations in waters and sediment................................................. 17

Table 4. Geochemistry of filtered samples from the Little Bonanza Mine, ICP-MS results (major elements, ICP-AES 

results)....... .................................................................................................................................................................. 18

Table 5. Geochemistry of unfiltered samples from the Little Bonanza Mine, ICP-MS results (major elements, ICPAES results). ................................................................................................................................................................. 20
iv

Table 6. Invertebrate samples collected from the Little Bonanza Mine and Trout Creek on April 6, 2010................ 22

Table 7. Sample sites and physical and selected chemical parameters for waters from the Little Bonanza Mine 

collected during a high-flow sampling event.................................................................................................................. 23

Table 8. Mercury and monomethylmercury concentrations in waters and sediment collected during a high-flow 

sampling event .............................................................................................................................................................. 24

Table 9. Concentrations of anions and selected cations in filtered water from the Little Bonanza Mine collected 

during a high-flow sampling event................................................................................................................................. 25

Table 10. Geochemistry of filtered samples from the Little Bonanza Mine collected during a high-flow sampling 

event, ICP-MS results (major elements, ICP-AES results) ........................................................................................... 26

Table 11. Geochemistry of unfiltered samples from the Little Bonanza Mine collected during a high-flow sampling 

event, ICP-MS results (major elements, ICP-AES results) ........................................................................................... 27

Figures 

Figure 1. General geology of the Little Bonanza Mine area (Yates and others, 1941). The workings at Little 

Bonanza explore a zone of fault breccia that trends northwest. The breccia consists of fragments of sandstone, 

greenstone, serpentine, and chert in a shale matrix. .................................................................................................... 28

Figure 2. Vertical projection of workings at the Little Bonanza Mine (Yates and others, 1941). ............................... 29

Figure 3. Cross-section of ore shoots at the Little Bonanza Mine (Yates and others, 1941). ................................... 30

Figure 4. Mine workings at the Little Bonanza Mine, with a cross section showing alteration and mercury ore zones 

(Yates and others, 1941)............................................................................................................................................... 31

Figure 5. Three-pipe retort at the Little Bonanza Mine that was used to process Hg ores. ...................................... 32

Figure 6. Mine processing area at the Little Bonanza Mine, showing remains of a three-pipe retort........................ 33

Figure 7. Calcines (mine tailings) adjacent to retort at the Little Bonanza Mine. ...................................................... 34
v

Figure 8. Sulfides that formed in three-pipe retort at the Little Bonanza Mine. ......................................................... 35

Figure 9. Calcines (mine tailings) at the Little Bonanza Mine exposed along bank of WF Las Tablas Creek. ......... 36

Figure 10. Little Bonanza Mine area, showing locations of all sample sites (Google Earth). Area in yellow box is 

shown in detail in figure 11............................................................................................................................................ 37

Figure 11. Closeup of figure 10, showing locations of sample sites in mine area (Google Earth). Yellow box 

delineates land managed by BLM. ................................................................................................................................ 38

Figure 12. Coarse-grained calcines (mine tailings) exposed in bank of WF Las Tablas Creek at the Little Bonanza 

Mine............ ................................................................................................................................................................ 39

Figure 13. Sample site 10LB1 in WF Las Tablas Creek at the Little Bonanza Mine................................................. 40

Figure 14. Sample site 10LB3 in creek that extends into area of dam, now failed, at the Little Bonanza Mine........ 41

Figure 15. Hg concentration in unfiltered versus filtered samples from the Rinconada and Little Bonanza Mines... 42

Figure 16. Hg versus MMeHg concentrations in unfiltered water samples from the Rinconada and Little Bonanza 

Mines.......... ................................................................................................................................................................. 43

Figure 17. Hg concentration versus %MMeHg in sediment samples from the Little Bonanza Mine......................... 44

Figure 18. MMeHg concentration versus %MMeHg in sediment samples from the Little Bonanza Mine................. 45

Figure 19. Comparison of HgT and dissolved Hg concentrations in waters sampled at the Little Bonanza Mine, 

beginning with the most upstream sample site, LB2, at the adit, and moving downstream to sample sites LB1, LB3, 

LB4 and LB5, respectively............................................................................................................................................. 46
vi

Abbreviations, Definitions, Datum Used, and 

Conversion Factors 

Vertical and horizontal coordinate information is referenced to the North American Datum of 1927 

DOC, dissolved organic carbon 

DOM, dissolved organic matter 

EE/CA, engineering evaluation/cost analysis for “non-time-critical removal actions,” as defined by the U.S. Environmental 

Protection Agency’s Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). 

Hg, elemental symbol for mercury; does not denote speciation. 

HgT, total mercury (inorganic plus organic). 

HgF, total mercury (inorganic plus organic) in a filtered sample (either 0.1 or 0.45 μm, as specified in the text).

MMeHg, monomethylmercury, methylmercury, and monomethylmercury ion (CH3Hg+) 

ng/g, nanogram per gram, equivalent to parts per trillion. 

ng/L, nanogram per liter, approximately equivalent to parts per trillion. 

ppm, parts per million, equivalent to mg/kg or μg/g. 

SC, specific (electrical) conductivity, reported in units of millisiemens per centimeter (mS/cm). 

Flask, 34.5 kg or 76 lb of Hg 

RPD, relative percent difference 

ANOVA, analysis of variance 

ASTM, American Society for Testing and Materials 

BLM, Bureau of Land Management 

CDFG, California Department of Fish and Game 

Cl‐

, chloride 

CVAFS, cold‐vapor atomic‐fluorescence spectroscopy 

CVAAS, cold‐vapor atomic‐absorbption spectroscopy 

CVRWQCB, Central Valley Regional Water Quality Control Board 

HCl, hydrochloric acid 

H2SO4, sulfuric acid 

ICP‐AES, inductively‐coupled plasma atomic‐emission spectroscopy 

ICP‐MS, inductively‐coupled plasma‐mass spectroscopy 

TMDL , total maximum daily load 

EPA, U.S. Environmental Protection Agency 

USGS, U.S. Geological Survey 

Conversion Factors 

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

acre 4,047 square meter (m2)

acre 0.4047 hectare (ha)

acre 0.004047 square kilometer (km2)

Volume

gallon (gal) 3.785 liter (L) 
vii

gallon (gal) 0.003785 cubic meter (m3) 

cubic inch (in3) 16.39 cubic centimeter (cm3) 

cubic inch (in3) 0.01639 liter (L)

cubic foot (ft3) 0.02832 cubic meter (m3) 

Flow rate

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

gallon per minute (gal/min) 0.06309 liter per second (L/s)

Mass

gram (g) 0.03527 ounce, avoirdupois (oz)

kilogram 2.205 pound, avoirdupois (lb)

microgram (μg) 0.0000000353 ounce, avoirdupois (oz)

milligram (mg) 0.0000353 ounce, avoirdupois (oz)

nanogram (ng) 0.0000000000353 ounce, avoirdupois (oz)

ounce, avoirdupois (oz) 28.35 gram (g) 

pound, avoirdupois (lb) 0.4536 kilogram (kg) 

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows: 

°F = (1.8×°C)+32 

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows: 

°C = (°F‐32)/1.8 

Specific conductance is given in microsiemens per centimeter (μS/cm) at 25 °C  

Concentrations of chemical constituents in water are given in milligrams per liter (mg/L, parts per million),  micrograms 

per liter (μg/L, parts per billion), or nanograms per liter (ng/L, parts per trillion). 

Concentrations of chemical constituents in tissues are given in micrograms per gram (μg/g, parts per million). 

Concentrations of chemical constituents in sediment are given in micrograms per gram (μg/g, parts per million) or 

nanograms per gram (ng/g, parts per billion) 
Review of Samples of Water, Sediment, Tailings, 

and Biota at the Little Bonanza Mercury Mine, San 

Luis Obispo County, California 

By James J. Rytuba,1 Roger L. Hothem,2 Daniel N. Goldstein,1 Brianne E. Brussee,2 and Jason T. 

May3

Introduction 

Background and Objectives 

The Little Bonanza mercury (Hg) mine, located in San Luis Obispo County, California, is a 

relatively small mine with a historical total Hg production of about 1,000 flasks (fig. 1). The mine 

workings and tailings are located in the headwaters of the previously unnamed west fork of Las Tablas 

Creek (WF Las Tablas Creek), which flows into the Nacimiento Reservoir. Wasterock and tailings 

eroded from the Little Bonanza Hg Mine have contributed Hg-enriched mine wastes to the headwaters 

of WF Las Tablas Creek. The mine is located on Federal land managed by the U.S. Bureau of Land 

Management (BLM), which requested that the U.S. Geological Survey (USGS) measure and 

characterize Hg and other geochemical constituents in tailings, sediment, water, and biota at and 

downstream from the minesite. This report is in response that request, from the lead agency which is 

mandated to conduct a Comprehensive Environmental Response, Compensation, and Liability Act

(CERCLA) - Removal Site Investigation (RSI). The RSI applies to removal of Hg-contaminated mine 

waste from the Little Bonanza minesite as a means of reducing Hg transport to WF Las Tablas Creek. 

1

U.S. Geological Survey, Menlo Park, California. 

2

U.S. Geological Survey, Dixon, California 

3

U.S. Geological Survey, Sacramento, California 
2

This report summarizes data obtained from field sampling of mine tailings, wasterock, 

sediment, water, and biota at the Little Bonanza Mine that was completed on April 6, 2010. 

Conditions during sampling were dry and no rain had occurred in the watershed for several 

weeks. Our results permit a preliminary assessment of the mining sources of Hg and associated 

chemical constituents that could produce elevated levels of monomethyl mercury (MMeHg) in 

WF Las Tablas Creek and in biota. 

History and Geology 

The history of the Little Bonanza Hg mine is summarized here from Yates (1943) and 

other references as cited. The Little Bonanza Mine, located 20 mi west of Paso Robles, was 

discovered in 1862. Although production was minor until 1900, from 1900 to 1906, the mine 

produced about 1,000 flasks of Hg. Intermittent production continued into the 1940s but was 

relatively limited. Underground workings, now caved and inaccessible, include about 3,000 ft of 

drifts, crosscuts, and raises on three levels extending 260 ft downward (figs. 1, 2). 

The workings at the Little Bonanza Mine explore a zone of fault breccia, which trends 

northwest (fig. 1). The breccia is composed of fragments of sandstone, greenstone, serpentine, 

and chert in a shale matrix. The serpentine has been hydrothermally altered to silica-carbonate 

rock, and the Hg deposit is hosted within the zone of alteration. The veins are discontinuous and 

irregular, but form a steplike pattern along the fault zone (figs. 3, 4). The principal mineralization 

occurring in the veins is irregular, consisting of disseminated zones of cinnabar. Most of the 

veins in the mine area contain cinnabar. 

Sample Sites and Methods 

Samples were collected to assess the concentrations of Hg and biogeochemically relevant 

constituents in tailings and wasterock piles at the Little Bonanza Hg mine. Tailings are present 

adjacent to a three-pipe retort used to process the Hg ore (figs. 5, 6). The tailings occur in the 

upper 15 cm of the soil adjacent to the retort (fig. 7) and slag from the retort is present on the 

surface (fig. 8). An area of disturbed soil and rock uphill from the retort was likely formed 

during construction of a dam that provided water for mining activities. Wasterock in these piles 

was sampled (fig. 6). The largest amount of tailings is exposed to the west of the retort in the 

bank of WF Las Tablas Creek (fig. 9). Water, sediment, and biota were sampled from WF Las 

Tablas Creek, which flows through the mine area. Sample-site locations are shown in figures 10 

and 11 and listed in table 1. Samples were collected when streamflow was low and no 

precipitation had occurred. 

Field Sampling Methods 

Dry and Wet Sediment and Tailings 

Samples consisting of 100 to 500 g of mine tailings and wasterock were collected from 

piles at the Little Bonanza Hg mine, stored, and shipped in Ziploc® bags at ambient temperature. 

Wet sediment was collected in polycarbonate jars (100-mL capacity) and frozen with dry ice 

immediately after collection (freezing time, approx 20-30 minutes). Samples were kept frozen 
3

until shipped overnight on dry ice to the analytical laboratory (Brooks Rand, Seattle, WA), 

where they were kept frozen until analysis. The temperature of samples arriving at the laboratory 

ranged from 1°C to 4°C, within the limits specified in USEPA method 1631E.

Water 

Stream and adit drainage samples were collected with new 60-mL sterile polypropylene 

syringes. Bulk water samples were subsampled for analysis of metal(loid)s and anions. 

Subsamples for metal(loid) determinations were acidified to pH<2 with trace metal (Ultrex, J.T. 

Baker)-grade HNO3 and stored in acid-washed, high-density polyethylene (HDPE) bottles. 

Subsamples for anion and alkalinity measurements were filtered, stored in HDPE bottles, and 

chilled to approximately 4°C until analysis, in accordance with USGS protocols for trace metals 

(http://pubs.water.usgs.gov/twri9A). Water samples were filtered with disposable 25-mmdiameter sterile cellulose acetate filters (0.45-μm openings) in the field for analysis of anions and 

alkalinity, and for inductively coupled plasma mass spectrometry (ICP-MS) and inductively 

coupled plasma atomic-emission spectrometric (ICP-AES) analyses. 

Water variables, including pH, conductivity, and temperature, dissolved oxygen, and 

oxidation-reduction potential (ORP), were measured in the field, using a battery-powered Sonde 

hydrolab. Measurements were taken by placing the probe directly into the flowing streamwater. 

Samples for total Hg (HgT) and MMeHg analyses were collected in trace-metal-free 

certified 250 mL bottles (Nalgene ICHEM) with no headspace. The MMeHg bottles contained an 

HCl preservative provided by the analytical laboratory. Procedures for HgT analysis followed 

ultra clean sampling and handling protocols (Bloom, 1995, Gill and Fitzgerald, 1987) during the 

collection of field samples and subsequent analysis to avoid introduction of Hg. Samples were 

kept on ice until shipped. Samples were shipped on icepacks and arrived the next morning at the 

analytical facilities at temperatures ranging from 1 to 4o C, as specified by EPA method 1631E, 

to minimize biologically induced phase changes and MMeHg degradation. 

During every sampling event, a field blank was collected by processing deionized water 

and collecting the same subsamples (except for alkalinity), following the same procedures as 

used for the field samples. Laboratory blanks and acid blanks were processed periodically to 

determine whether our equipment, containers, reagents, and procedures introduced significant 

contamination. 

Invertebrates 

The target macroinvertebrates for this study were predatory insects, depending on their 

abundance and availability at each sample site. Taxa collected were larval dragonflies (order 

Odonata, families Aeshnidae and Gomphidae), adult water striders (order Hemiptera, family 

Gerridae), predaceous diving beetles (order Coleoptera, family Dytiscidae), and larval 

dobsonflies (order Megaloptera, family Corydalidae). 

Invertebrates were collected with dipnets and by hand and placed in Ziploc plastic bags 

with native water. Samples were kept in a cooler and allowed to depurate in native water on wet 

ice for 4-24 hours before being sorted at the end of the collection day. Individuals were sorted by 

family and placed in disposable plastic weighboats using Teflon-coated forceps or by hand while 

wearing disposable latex gloves. When possible, we collected replicate samples, multiple size 

classes within a taxon, or both to assess variations in concentration and to identify any relations 

of tissue concentrations to size. Organisms were thoroughly rinsed with deionized water and 

patted dry with a clean paper towel. Then, samples were sorted and composited by family with 
4

the goal of obtaining at least 1g of wet biomass per sample. Each sample consisted of 3 to 15 

individuals of the same family. Samples were weighed on an electronic balance (±0.01 g) and 

placed in chemically cleaned glass jars with Teflon-lined lids. The lids were sealed with 

Parafilm, and the samples were frozen until they could be shipped to the analytical laboratory on 

April 13, 2010, for analysis of HgT, MMeHg, and total solids. 

Analytical Methods 

Sediments and Tailings 

Multielement analyses of all dry-sediment and tailings samples were performed in the 

laboratories of ALS CHEMEX. Bulk samples were ground in a zirconia ring mill and subjected 

to a near-total four-acid digestion. Major element concentrations were determined by ICP-AES; 

minor–element concentrations, other than Hg, were determined by ICP–MS. Hg concentration 

was determined by cold-vapor atomic-absorption spectroscopy (CVAAS), following methods 

similar to those described by Crock (1996) and O’Leary and others (1996). 

Hg and MMeHg analyses of all wet-sediment samples were performed at Brooks Rand 

Laboratories in Seattle, WA. Dry-sediment samples analyzed by ALS CHEMEX were also 

analyzed by Brooks Rand for Hg. For these analyses, the sediment was leached with cold aqua 

regia, followed by stannous chloride (SnCl2) reduction, two-stage gold amalgamation, and coldvapor atomic-fluorescence spectroscopy (CVAFS) detection. Monomethylmercury was 

determined by acid bromide/methyl chloride extraction, followed by aqueous-phase ethylation, 

isothermal gas-chromatographic (GC) separation, and CVAFS detection (Horvat and others, 

1993). Results reported on both a wet- and dry-weight basis are listed in Table 2 for analyses 

provided by Brooks Rand, and on a dry-weight basis for the analyses completed by ALS 

CHEMEX (tables 3, 4). 

Water 

Alkalinity (as CaCO3) was determined in the laboratory by titration with H2SO4, using 

Gran’s technique (Orion Research, Inc., 1978), within 2-4 days after sample collection. Sulfate, 

chloride, nitrate, and fluoride concentrations were determined by ion chromatography (Fishman 

and Pyen, 1979). 

Cations were analyzed by ICP–AES and ICP–MS. Ion chromatographic and alkalinity 

analyses were performed in USGS laboratories under the direction of Paul Lamothe, and ICPAES analyses were determined in USGS laboratories under the direction of Paul Briggs. 

Duplicate water samples, blank samples, and USGS Water Resource Division standard reference 

waters were analyzed with the dataset. 

At Brooks Rand, samples were handled in a Class-100 clean-air station that was 

monitored routinely for low levels of total gaseous Hg. An ultraclean Hg trace-metal protocol 

was followed, including the use of rigorously cleaned and tested Teflon equipment and sample 

bottles and prescreened and purified reagents. Laboratory atmosphere and water supply were 

also routinely monitored for low levels of Hg. Primary standards used in the laboratory were 

NIST certified or traceable to NIST certified materials. Following USEPA Method 1631, 

MMeHg standards were made from pure powder, calibrated against NBS-3133, and crossverified by daily analysis of Certified Reference Material DORM-2 (National Research Council 
5

of Canada Institute for National Measurement Standards, 1999). HgT content was determined by 

bromine monochloride (BrCl) oxidation followed by SnCl2 reduction, two-stage gold 

amalgamation, and CVAFS detection (Bloom and others, 1988). Monomethylmercury was 

liberated from water using an all-Teflon distillation system. Distilled samples were analyzed 

using aqueous-phase ethylation with purging onto Carbotrap, isothermal GC separation, and 

CVAFS detection (Bloom, 1989). To address accuracy and precision, quality-assurance 

measures were used with the following minimum frequency: laboratory duplicates, 1 per 10 

samples; method blanks, three per analytical batch; filtration blanks, 1 per 10 samples; and spike 

recovery or standard reference material, 1 per 10 samples. 

Biota 

Samples were analyzed for HgT and MMeHg at Brooks Rand Laboratory, Seattle, WA. A 

solid sample was homogenized, and an aliquot measured into a preweighed vessel, dried in an 

oven overnight, and weighed again, and, then, the percentage of dried solid material was 

calculated. This standard operating procedure (SOP), BR-1501, is analogous to EPA standard 

method 2540 G (residue, total). 

Once thawed, the samples were homogenized by using precleaned commercial-grade 

homogenization equipment. A homogenization blank was collected after cleaning the equipment 

and before homogenizing the samples. The blank was digested as a tissue sample and analyzed 

along with the associated homogenates. The result for the homogenization blank was less than 10 

times the lowest sample result, indicating no significant contamination during homogenization 

(SOP BR-0106). 

HgT was determined as outlined in EPA method 1631 (SOP BR-0002). Samples were 

digested in nitric acid (HNO3) and sulfuric acid (H2SO4) and then further oxidized with bromine 

monochloride (BrCl). Samples were analyzed by stannous chloride (SnCl2) reduction, single 

gold amalgamation, and CVAFS detection using a BRL Model III CVAFS Mercury Analyzer. 

All sample results for low-level Hg analysis were blank corrected. 

For MMeHg analysis, samples were prepared by potassium hydroxide (KOH)-methanol 

(CH3OH) digestion. Samples were analyzed by aqueous-phase ethylation, Tenax trap collection, 

GC separation, isothermal decomposition and CVAFS detection, using a BRL Model III CVAFS 

Mercury Analyzer. All sample results for low-level Hg analysis were blank corrected, as outlined 

in the calculations section of Brooks Rand SOP BR-0011. 

Duplicate samples were analyzed at a rate of 5 percent, with at least one duplicate per 

matrix per analytical run to estimate the precision of the methods. The relative percent 

differences (RPD) for the HgT duplicates ranged from 0.8 to 23 percent; the RPDs for all results 

were within the acceptable criterion (RPD < 30 percent). The RPDs for invertebrate MMeHg 

duplicates ranged from 2 to 19 percent, all within the acceptable criterion of an RPD < 35 

percent. 

To assure the accuracy of the methods, procedural blanks, spiked samples, and Standard 

Reference Materials were analyzed. To assure that no analyte was added during the processing of 

the sample, procedural blanks were analyzed at a rate of 5 percent of the total samples, with at 

least one blank per matrix per analytical run. The averages for the HgT blanks ranged from 0.01 

to 0.03 ng/g, with method detection limits (MDL) of 0.04 ng/g. The averages for MMeHg blanks 

ranged from 0.1 to 0.2 ng/g, with an MDL of 1.0 ng/g. All blank results were less than the 

acceptable criterion of twice the MDL. 
6

Spiked samples were analyzed at a rate of 5 percent, with at least one spike per matrix per 

analytical run. Spikes were samples fortified with a known quantity of analyte and analyzed as 

part of the run. The Hg T recovery ranged from 78 to 120 percent, with RPDs ranging from 0.2 to 

13 percent; MMeHg recovery ranged from 67 to 130 percent. Although one sample had an 

unacceptable MMeHg recovery of 151 percent, reanalysis produced acceptable results. The 

MMeHg RPDs ranged from 0.1 to 20 percent. The results met the criterion of 70 to 130-percent 

recovery with an RPD<30 percent for HgT and 65 to 135 percent with an RPD<35 percent for 

MMeHg. 

Standard Reference Materials (DORM-3 2010) were analyzed at a rate of 5 percent to 

ensure that the method worked with naturally incorporated Hg. HgT recovery was 103 to 116 

percent, within the criterion of 75 to 125 percent; MMeHg recovery was 80 to 93 percent, within 

the criterion of 65 to 135 percent. 

Results 

Tailings at the Little Bonanza Mine Areas 

The Hg concentration in waste materials at the Little Bonanza Mine area varies in 

dependence on material type. Tailings (calcines) have the highest, and wasterock the lowest Hg 

concentrations. Ores processed in the three-pipe retort produced tailings that were disposed of in 

the flat area that extends from just west of the retort to WF Las Tablas Creek. The calcines, 

which are well exposed in the bank of WF Las Tablas Creek (fig. 9), consist of medium- to 

coarse–grained, well–stratified materials (fig. 12). Four samples of the calcines were collected in 

the exposure in WF Las Tablas Creek (fig. 11, samples 10LB9-10LB12). One grab sample that 

was taken at the uppermost exposure of the calcines (sample 10LB9) had an HgT concentration 

of 101 ppm. Channel samples of the calcines were taken from the lower (sample 10LB11), 

middle (sample 10LB10), and upper part (sample 10LB12) parts of the exposure (table 1). The 

HgT concentration in the calcines increases from 43.7 ppm in the lower part, to 66 ppm in the 

middle part, to 141 ppm in the upper part of the section (table 2). The highest HgT concentration 

is comparable to that in the grab sample taken from the top of the section. 

Calcines with an HgT concentration of 142 ppm are present adjacent to the retort and are 

irregularly distributed in the upper 25 cm of the soil. Calcines in the three-pipe retort have an 

HgT concentration of 27 ppm, and slag from the retort has a relatively low HgT concentration of 

1.79 ppm and high iron (Fe) and manganese (Mn) concentrations (table 2). 

The calcines have elevated concentrations of Co (87 ppm), Cr (4,270 ppm), and Ni (2,410 

ppm) that reflect the serpentinite host rock of the Hg mineralization (table 2). Exceptionally high Mg 

concentrations, up to 13.5 percent, are present in the calcines as a result of the presence of 

magnesite and serpentinite. No other trace elements are present in high concentrations. Gold was 

detected in six of the calcine samples, in concentrations ranging from 0.011 to 0.052 ppm. Trace 

metals that are moderately elevated and exceed the BLM Ecotoxicity screening criteria in 

calcines include As (13 ppm), Cu (48 ppm), Pb (109 ppm), and Zn (94 ppm, table 2); however, 

these elements do not exceed the BLM Camper screening criteria or the EPA preliminary 

remediation goals (PRGs). 

Calcines and wasterock are present in the bank deposits of WF Las Tablas Creek 

upstream from the mine workings located on BLM lands at sample site 10BL3C (fig. 11). The 
7

calcines have an HgT concentration of 108 ppm and high Co, Cr, and Ni concentrations, similar 

to concentrations in the calcines exposed farther downstream at sample site 10LB9-12C. 

Sediment in WF Las Tablas Creek near the Little Bonanza Mine 

The headwaters of WF Las Tablas Creek begin above the Little Bonanza Mine area near 

an adit located at sample site 10LB2 (fig. 11). Sediment at the partially collapsed adit has a high 

HgT concentration, 72 ppm (table 3). Farther downstream, at sample site 10BL1 (figs. 11, 13), 

the stream sediment has an exceptionally high Hg concentration, 346 ppm (table 2). This site is 

located just downstream from the calcines present in bank sediment at sample sites 10LB9 

through 10LB12C. Farther downstream in WF Las Tablas Creek, at sample site 10LB4 (fig. 10), 

the HgT concentration in sediment is still elevated, 44.9 ppm (table 3). The sediment in the small 

tributary that drains the area of the collapsed dam (figs. 11, 14) has a low Hg concentration, 

0.228 ppm, typical of background sediment concentrations (sample site 10LB3, table 3). 

The MMeHg concentration in sediment from WF Las Tablas Creek at all sample sites is 

relatively low, ranging from 0.042 ng/g to 0.304 at sample site 10LB1 (table 3). 

Water Chemistry 

All the waters in WF Las Tablas Creek in the mine area are alkaline as a result of the 

serpentinite that underlies most of the watershed and the presence of carbonate alteration in the 

mine area (table 1). The sulfate concentration in WF Las Tablas Creek waters is anomalous, 

ranging from 19 to 78 ppm. The highest sulfate concentration, 146 ppm, occurs in the waters 

being released from the adit at sample site 10LB2. High Mg and Ca concentrations are present in 

all waters, with the highest concentrations associated with mine drainage from the adit (tables 4, 

5). Dissolved organic carbon (DOC) concentration ranges from 2.6 to 6.6 ppm, comparable to 

those measured downstream from the Rinconada Hg mine (figs. 15, 16). 

Hg T and MMeHg in waters 

Under low flow conditions, the Hg T concentrations in water samples collected from WF 

Las Tablas Creek in the mine area are elevated, with the highest concentration, 96.2 ng/L at 

sample site 10LB1, located just below the exposure of calcines. At 2.5 km downstream from the 

mine area, at sample site 10LB4, HgT concentration decreases considerably to 5.58-5.91 ng/L 

(table 3). The water emanating from the adit above the mine processing area has a relatively high 

HgT concentration, 46.7 ng/L, and the water that drains the breached dam in the mine area has a 

considerably lower but anomalous HgT concentration, 17.4 ng/L. The HgT concentration in the 

filtered fraction varies, ranging from 13.5 ng/L in water from the adit to 67.6 ng/L at sample site 

10LB1 (fig. 15). MMeHg concentrations in water from WF Las Tablas Creek and from the adit 

are all very low, ranging from 0.02 ng/L at the adit to 0.058 ng/L at sample site 10 LB1. 

Although the waters have high HgT concentrations, MMeHg concentrations are very low, 

constituting less than 1 percent of the total Hg present in the water column (fig. 16). 

Under high-flow conditions, Hg concentrations in unfiltered and filtered waters are 

considerably higher at all sample sites than under low-flow conditions (fig. 19; table 8). 

Downstream from the adit, at sample site 11LB2, the HgT concentrations in unfiltered and 

filtered waters are 190 and 51.8 ng/L, respectively. Farther downstream, at sample site 11LB1, 

located in the mine processing area, the HgT concentrations increase to 206 ng/L in unfiltered 

waters and decrease slightly in filtered water to 51.8 ng/L. The HgT concentrations in unfiltered 
8

waters decrease downstream from the mine area. At sample site 11LB4, located 1.25 km 

downstream from the mine area, the HgT concentration is about two-thirds that in the mine area. 

At sample site 11LB5, located 2.5 km downstream from the mine area, the HgT concentration 

decreases to about a third of that in the mine area (fig. 19). Hg concentrations in filtered waters 

decrease downstream from the mine area but account for an increasing amount of the total Hg 

present at each site. MMeHg concentrations are considerably higher under high-flow conditions 

than under low-flow conditions, ranging from 0.163 to 0.236 ng/L; however, no systematic 

variation in MMeHg concentrations was observed. 

HgT and MMeHg in Biota 

We collected composite samples of aquatic invertebrates (table 6), for analyses of HgT

and MMeHg from one sample site (LBUP) at the Little Bonanza Mine and another downstream 

(LBBR) on April 6, 2010. 

The highest HgT concentration (0.446 μg/g wet weight (ww)) was measured in a 

composite sample of six dobsonfly larvae (family Corydalidae) collected from Little Bonanza 

upstream (LBUP); the lowest HgT concentration was measured in a sample of six dragonfly 

larvae (Aeshnidae) from the downstream site, Little Bonanza at the bridge (LBBR) (0.118 μg/g 

ww). The highest MMeHg concentration (0.148 μg/g ww) was measured in dragonfly larvae 

(Gomphidae) collected from LBBR; the lowest MMeHg concentration was measured in a sample 

of three dobsonfly larvae from LBUP (0.057 μg/g ww). 

MMeHg in the two dobsonfly samples collected from LBUP averaged 18.1 percent, 

whereas that in the same taxa at LBBR was 42.0 percent. MMeHg in other taxa collected from 

LBBR ranged from 66.5 percent in Gerridae to 77.5 percent in Aeshnidae. 

The only taxon collected at both sites was dobsonflies. The average HgT and MMeHg 

concentrations at LBUP were 0.0795 and 0.439 μg/g, respectively. The comparable 

concentrations in dobsonflies from LBBR were 0.057 and 0.136 μg/g, lower by 28 and 69 

percent, respectively, than at LBUP. 

Conclusions

Past mining and mine wastes at the Little Bonanza Hg mine have contaminated sediment 

in WF Las Tablas Creek with high HgT concentrations. A significant amount of calcines still 

remains at the Little Bonanza Hg mine and continues to contribute Hg-enriched sediment to the 

creek. The calcines are well exposed in the bank of WF Las Tablas Creek, and the flat area 

extending eastward from the exposures in the creek toward the remains of the retort is likely 

underlain by calcines. Test pits in this area would be necessary to determine the extent and 

volume of the calcines that may be present in the area. 

Although the calcines have only moderately high HgT concentrations, 43 to 141 ppm, the 

HgT concentration in the sediment of WF Las Tablas Creek in the mine area is extremely high 

(max. 304 ppm at sample site 10LB1). HgT concentrations higher than 100 ppm in sediment are 

rare downstream from Hg mines in the Coast Ranges. Only one tributary that drains the Petray 

Mine in the Cache Creek Watershed, Colusa County, California, is reported to have similarly 

high HgT concentrations in stream sediments (Slowey and Rytuba, 2008). At sample site 10LB4, 

located about 2.5 km downstream from the mine area, the HgT concentration in sediment is still 

very high, 44.9 ppm. The HgT concentration in calcines is not sufficiently high to account for the 

high HgT concentrations in sediment. An unmined Hg mineralized zone is likely being eroded 
9

and contributing Hg-enriched sediment to the creek. The calcines also have very high Mg 

concentrations and elevated Co, Cr, and Ni concentrations that reflect the serpentinite host rock. 

Other trace metals in the calcines are absent in concentrations of significant environmental 

concern. 

The HgT concentrations in water samples collected from WF Las Tablas Creek in and 

downstream from the mine area are extremely high under both low- and high-flow conditions. 

The high-flow HgT concentrations are comparable to those measured downstream from some of 

the larger Hg mines in the Coast Ranges, including the Rinconada Hg mine (fig. 15). The 

calcines present in bank deposits contribute to the high HgT and Total Suspended Solids (TSS) 

concentrations. Effluent from the adit also contributes Hg to the creek, but most Hg from the adit 

is in the filtered fraction and consists of colloidal and dissolved Hg phases. The HgT

concentration in waters in the mine area does not meet the 50-ng/L EPA criterion (EPA, 1999) 

and is above the water-quality objective of 12 ng/L under both high- and low-flow conditions. 

However, under low-flow conditions, the MMeHg concentrations in the waters of WF Las 

Tablas Creek are very low, lower than in all waters sampled downstream from the Rinconada Hg 

mine under all flow conditions (fig. 16). Under high-flow conditions, MMeHg concentrations are 

considerably higher, comparable to those measured downstream from the Rinconada Hg mine. 

The percentages of Hg present as MMeHg in the stream-sediment samples are all very 

low, ranging from 0.0001 to 0.01 (fig. 17). The percentage of MMeHg (%MMeHg) in sediment 

(fig. 18, table 3) can be used as an indicator for net production of MMeHg when MMeHg is 

normalized to HgT (Drott and others, 2008). The %MMeHg is calculated by dividing the 

measured MMeHg concentrations in sediment by the HgT concentration present in the same 

sample: 

%MMeHg = (MMeHg, in ng/g in sediment)/(HgT, in ng/g in sediment) 

The very low %MMeHg in stream sediment in WF Las Tablas Creek (table 3, fig. 18) 

indicates that methylation of Hg is not favorable in the mine area. Because there are adequate 

concentrations of SO4 and DOC in the water for sulfate reducing bacteria to methylate Hg, the 

low MMeHg concentrations may result from the Hg phase in the creek sediment not being 

bioaccessible, as would be the case if cinnabar were the primary phase in the sediment. 

Invertebrates collected from the mine area at sample site 10LB1 had elevated HgT

concentrations, but MMeHg concentrations were similar to those observed at the downstream 

sample site (10LB4) and in a nearby Hg-mine impacted stream (Rinconada Creek). The 

%MMeHg at sample site 10LB1 averaged about 18 percent, consistent with the low observed 

%MMeHg in sediment at that site. Although the MMeHg concentrations in the invertebrates 

collected from the downstream site were similar to those from sample site 10LB1, the %MMeHg 

in invertebrates from the lower site was nearly 4 times greater, relating to the lower HgT

concentration in sediment at the lower site. MMeHg concentrations in water were similar at the 

two sites, but HgT concentration in the water at the minesite was 17 times greater than at the 

lower site. Overall, the MMeHg concentrations in invertebrates from the Little Bonanza sites 

were 2.5 to 6 times higher than in similar taxa collected from a nearby stream not impacted by 

Hg mining (Trout Creek). Transport of Hg in creek waters depends on flow conditions; the 

highest concentrations and greatest transport of Hg occur under high-flow conditions. The high 

HgT concentrations in sediment in WF Las Tablas Creek in the mine area and the elevated HgT

concentrations under low-flow conditions sampled during this study indicate that very high Hg 
10

concentrations are potentially transported from the mine area during high-flow events. Thus, 

although the Little Bonanza Mine has a small volume of calcines, it may release a significant 

amount of Hg to downstream environments during high-flow events. We recommend that at least 

one high-flow sampling be done during a winter storm to assess the magnitude of Hg release 

from the mine area. 

Acknowledgments

We appreciate the guidance and assistance provided by Kent Varvel of the Bakersfield 

Field Office of the BLM. 

References Cited 

Bloom, N.S., 1989, Determination of picogram levels of methylmercury by 

aqueous phase ethylation, followed by cryogenic gas chromatography with 

cold vapour atomic fluorescence detection: Canadian Journal of Fisheries 

and Aquatic Sciences, v. 46, p. 1131-1140. 

Bloom, N.S., 1995, Mercury as a case study of ultra-clean sample handling and 

storage in aquatic trace metal research: Environmental Laboratory, v. 3-4, p. 

20-25. 

Bloom, N.S., Crecelius, E.A., and Fitzgerald, W.F., 1988, Determination of 

volatile mercury species at the picogram level by low temperature gas 

chromatography with cold vapor atomic fluorescence detection: Analytica 

Chimica Acta, v. 208, p. 151-161. 

Crock, J.G., 1996, Mercury, Chapter 29 of Sparks, D.L., ed., Chemical methods, 

pt. 3 of Methods of soil analysis: Soil Science Society of America Book 

Series, no. 5, p. 769-791. 

Drott, A., Lambertsson, L., Björn, E., and Skyllberg, U., 2008, Do potential 

methylation rates reflect accumulated methyl mercury in contaminated 

sediments?: Environmental Science & Technology, v. 42, p. 153-158. 

Fishman, M.J. and Pyen, G., 1979, Determination of selected anions in water by 

ion chromatography: U.S. Geological Survey Techniques of Water 

Resources Investigations 79-101, 30 p. 

Gill, G.A., and Fitzgerald, W.F., 1987, Picomolar mercury measurements in 

seawater and other materials using stannous chloride reduction and twostage gold amalgamation with gas phase detection: Marine Chemistry, v. 20, 

p. 227-243. 
11

Horvat, M., Bloom, N.S., and Liang, L., 1993, Comparison of distillation with 

other current isolation methods for the determination of methyl mercury 

compounds in low level environmental samples. Part 1, Sediments: 

Analytica Chimica Acta, v. 281, p. 135-152. 

National Research Council of Canada, Institute for National Measurement 

Standards, 1999, DORM-2, DOLT-2, Dogfish muscle and liver certified 

reference materials for trace metals: Certified Reference Materials Data 

Sheet, 4 p. [http://www.ems.nrc.ca/ems1.htm, accessed January 28, 2009]. 

O'Leary, R.M., Hageman, P.L., and Crock, J.G., 1996, Determination of mercury 

in water, geologic, and plant materials by continuous flow-cold vaporatomic absorption spectrophotometry, in Arbogast, B.F., ed., Quality 

assurance manual for the branch of geochemistry; United States Geological 

Survey: U.S. Geological Survey Open-File Report 96-525, p. 42-55. 

Orion Research, Inc., 1978, Analytical methods guide (9th ed.): Cambridge, 

Mass., 48 p. 

Slowey, A.J., and Rytuba, J.J., 2008, Mercury release from the Rathburn Mine, 

Petray Mine, and Bear Valley saline springs, Colusa County, California, 

2004-2006: U.S. Geological Survey Open-File Report 2008-1179, 49 p. 

[http://pubs.usgs.gov/of/2008 /1179/]. 

Yates, R.G., Eckel, E.B. and Granger, A.E., 1941, Quicksilver deposits in San 

Luis Obispo County and southwestern Monterey County, California: U.S. 

Geological Survey Bulletin 922-R, p. 564-565.
12

Table 1. Sample locations and physical and selected chemical parameters for waters from the Little Bonanza Mine o

Site Site Conductivity 

Water and 

sediments Biota Latitude Longitude Sample Site Description micro Siemens p

WF Las Tablas Creek

10LB1A LBUP 35.58414 -120.91121 Little Bonanza Creek 772 7.7

10LB4A LBBR 35.59845 -120.91093 WF Las Tablas Creek 461 7.7

Mine Drainage from Adit

10LB2A 35.583 -120.91109 Mine adit drainage 1,142 7.9

Reservoir Creek

10LB3A 35.58424 -120.90997 Reservoir drainage 318 7.6

Little Bonanza calcines and waste rock

10LB3C 35.58393 -120.91101 Calcines in creek bank near pipe down 

from adit

10LB4C 35.58355 -120.91033 Waste rock and some calcines

10LB5C 35.58397 -120.91080 Slag from retort

10LB6C 35.58397 -120.91080 Roasted ore from retort

10LB7C 35.58397 -120.91080 Calcines adjacent to retort about 25 cm 

thick

10LB8C 35.58382 -120.91068 Waste rock on disturbed slope above retort

10LB9C 35.5838 -120.91103 Calcines exposed in bank of creek west of 

retort

10LB10C 35.58393 -120.91101 Calcines in bank of creek west of retort, 

middle 0.75 m

10LB11C 35.58393 -120.91101 Calcines in bank of creek west of retort, 

bottom 0.5 m

10LB12C 35.58393 -120.91101 Calcines in bank of creek west of retort, 

top 0.5 m

Trout Creek Reference site

TRCR 35.38875 -120.58167 Trout Creek reference site 120.58167 120.5816
13

Table 2. Mercury and associated major and minor elements in sediment, precipitates, and calcines from the Little Bonanza Mine.

Field 

Number Latitude Longitude Date Sample Site Description

Hg

ppm

Ag

ppm

Al

%

WF Las Tablas Creek

10LB1A 35.58414 -120.91121 4/6/10 Little Bonanza Creek 346 0.04 6.78

10LB4A 35.59845 -120.91093 4/6/10 WF Las Tablas Creek 3.79 0.08 7.2

Mine Drainage from Adit

10LB2A 35.583 -120.91109 4/6/10 Mine adit drainage 292 0.05 7.4

Reservoir Creek

10LB3A 35.58424 -120.90997 4/6/10 Reservoir drainage 0.25 0.05 7.39

Little Bonanza calcines and waste rock

10LB3C 35.58393 -120.91101 Calcines in creek bank near pipe down from adit 108.5 0.07 3.53

10LB4C 35.58355 -120.91033 Waste rock and some calcines 30.3 0.03 1.2

10LB5C 35.58397 -120.91080 Slag from retort 1.79 0.16 0.12

10LB6C 35.58397 -120.91080 Roasted ore from retort 27.2 0.05 0.48

10LB7C 35.58397 -120.91080 Calcines adjacent to retort about 25 cm thick 142.5 0.12 2.31

10LB8C 35.58382 -120.91068 Waste rock on disturbed slope above retort 0.29 0.07 5.09

10LB9C 35.5838 -120.91103 Calcines exposed in bank of creek west of retort 101 0.08 5.2

10LB10C 35.58393 -120.91101 Calcine in bank of creek west of retort, middle 0.75 m 66.2 0.02 1.08

10LB11C 35.58393 -120.91101 Calcine in bank of creek west of retort, bottom 0.5 m 43.7 0.03 1.39

10LB12C 35.58393 -120.91101 Calcine in bank of creek west of retort, top 0.5 m 141 0.03 1.36
14

Table 2 (cont’d)

Field Number

As

ppm

Ba

ppm

Be

ppm

Bi

ppm

Ca

%

Cd

ppm

Ce

ppm

Co

ppm

Cr

ppm

Cs

ppm

Cu

ppm

Fe

%

Ga

ppm

Ge

ppm

Hf

ppm

In

ppm

WF Las Tablas Creek

10LB1A 10.4 680 0.97 0.21 1.11 0.17 32.6 52.9 1,490 5.58 55.5 6.11 16.2 0.1 2.3 0.065

10LB4A 11.7 460 1.16 0.25 1.32 0.16 39.7 37.7 280 5.13 47.9 5.32 17.35 0.15 2.4 0.066

Mine Drainage from Adit

10LB2A 9.5 400 0.99 0.19 0.7 0.08 32.3 40.2 663 13.55 56.5 5.41 18 0.16 2 0.072

Reservoir Creek

10LB3A 12.1 590 1.23 0.3 1.1 0.11 38.7 34.1 464 5.72 44.9 4.92 18.3 0.15 2.4 0.063

Little Bonanza calcines and waste rock

10LB3C 13.2 190 0.68 0.09 0.84 0.05 8.07 123 2,910 5.76 22.1 7.25 9.97 0.19 1.2 0.03

10LB4C 11 320 0.4 0.03 1.14 0.03 5.13 86.4 2,910 2.26 13.5 4.56 3.18 0.08 0.3 0.01

10LB5C 5.3 10 0.05 0.01 0.08 0.02 1.08 27 70 0.07 78.9 >50 7.62 1.97 0.1 0.005

10LB6C 8.3 80 0.3 0.03 2.36 0.04 1.91 87.1 2,050 1.28 9.2 4.69 1.9 0.1 0.1 0.006

10LB7C 11 360 0.48 0.18 7.13 0.24 10.35 69.7 4,270 3.61 39.6 6.34 5.82 0.12 0.8 0.029

10LB8C 4 330 0.64 0.11 2.37 0.09 20.1 40.3 659 3.46 44.4 4.92 12.25 0.11 1.6 0.044

10LB9C 12.6 340 0.74 0.1 1.5 0.1 25 48.9 788 5.15 48.1 5.74 11.1 0.13 1.7 0.052

10LB10C 3.7 120 0.37 0.02 0.95 0.02 4.62 77.9 2,480 1.58 16.1 4.45 2.97 0.1 0.3 0.011

10LB11C 4.1 130 0.4 0.03 1.38 0.04 6.02 71.7 2,080 1.84 15.9 4.2 3.68 0.12 0.4 0.013

10LB12C 3.5 100 0.36 0.03 0.88 0.04 6.54 71.6 1,820 1.88 13.8 4.31 3.3 0.1 0.4 0.015
15

Table 2 (cont’d)

Field Number

K

%

La

ppm

Li

ppm

Mg

%

Mn

ppm

Mo

ppm

Na

%

Nb

ppm

Ni

ppm

P

ppm

Pb

ppm

Rb

ppm

Re

ppm

S

%

Sb

ppm

Se

ppm

WF Las Tablas Creek

10LB1A 1.08 13.9 61.2 4.08 1250 0.93 1.12 7.4 429 510 12.8 56.1 <0.002 0.04 1.1 2

10LB4A 1.43 19.1 52.3 3.07 1010 0.94 1.47 9.3 268 540 15.6 75.5 <0.002 0.01 1.49 2

Mine Drainage from Adit

10LB2A 1.17 15.5 113.5 1.21 773 1.06 0.8 7.8 592 550 9.9 75.8 <0.002 0.03 1.03 2

Reservoir Creek

10LB3A 1.57 19.1 50.3 3.27 878 0.86 1.38 9.3 248 540 16 82.5 <0.002 0.01 1.58 2

Little Bonanza calcines and waste rock

10LB3C 0.59 4.2 64 4.73 1030 0.67 0.06 2 2,410 190 4.4 42 <0.002 0.08 0.73 1

10LB4C 0.19 2.5 36.1 11.05 643 0.25 0.1 1.1 1,790 110 2.9 11.6 <0.002 0.13 0.49 1

10LB5C 0.02 0.5 0.7 0.07 3690 4.11 0.02 1.1 29.3 310 6.2 1.1 0.004 0.07 0.4 1

10LB6C 0.06 0.9 34 12.6 769 0.91 0.04 0.4 1,695 90 100.5 3.3 <0.002 0.1 4.43 1

10LB7C 0.32 5 33.7 8.51 918 2.19 0.35 3.1 1,150 330 109 18.5 <0.002 0.08 5.13 1

10LB8C 0.58 9.3 59 9.46 843 0.38 0.22 5.1 626 460 6.3 27.6 <0.002 0.01 0.5 1

10LB9C 0.75 10.9 65.4 4.49 1060 0.85 0.65 5.1 612 450 9.5 41 <0.002 0.04 1.22 1

10LB10C 0.15 2 37 13.55 616 0.29 0.17 1 1,530 100 3 9 <0.002 0.11 0.41 1

10LB11C 0.19 2.7 34.3 11.25 637 0.36 0.16 1.3 1,415 120 2.6 11.4 <0.002 0.08 0.39 1

10LB12C 0.21 2.9 37.7 13.4 668 0.27 0.16 1.3 1,440 140 3.1 11.6 <0.002 0.12 0.41 1
16

Table 2 (cont’d)

Field Number

Sn

ppm

Sr

ppm

Ta

ppm

Te

ppm

Th

ppm

Ti

%

Tl

ppm

U

ppm

V

ppm

W

ppm

Y

ppm

Zn

ppm

Zr

ppm

Au

ppm

WF Las Tablas Creek

10LB1A 1.6 129 0.44 <0.05 4.7 0.457 0.39 1.4 143 1.1 21.8 108 79.9 0.009

10LB4A 1.9 127 0.59 0.05 7.2 0.456 0.48 2.2 131 1.4 21.1 101 77.5 0.005

Mine Drainage from Adit

10LB2A 1.5 248 0.47 0.05 5 0.497 0.53 1.3 151 1.1 21.7 88 64.9 0.008

Reservoir Creek

10LB3A 2.1 107 0.61 <0.05 7.9 0.432 0.51 2.3 125 1.7 21.1 97 79.2 0.004

Little Bonanza calcines and waste rock

10LB3C 0.8 105.5 0.13 <0.05 1.6 0.125 0.53 0.6 88 0.6 9.4 75 41.8 0.001

10LB4C 0.3 117.5 0.07 <0.05 0.8 0.064 0.2 0.4 39 0.3 3.3 50 12.5 0.001

10LB5C 3.1 5.9 <0.05 0.17 0.2 0.007 <0.02 0.7 62 6.2 0.5 <2 2.7 <0.001

10LB6C 0.4 135.5 <0.05 <0.05 0.2 0.021 0.21 0.2 29 0.7 1.5 45 4.5 <0.001

10LB7C 1.4 320 0.18 0.05 1.3 0.163 0.34 4.5 78 9.7 8.2 94 30.1 0.001

10LB8C 0.9 384 0.33 0.05 3.4 0.3 0.15 1.1 97 0.7 16 79 58.3 <0.001

10LB9C 1 156 0.34 0.06 3.3 0.365 0.32 1.1 117 0.8 16.6 88 58.8 <0.001

10LB10C 0.2 97.7 0.06 <0.05 0.6 0.062 0.15 0.4 42 0.2 2.8 49 11.6 0.001

10LB11C 0.3 115.5 0.08 <0.05 0.9 0.076 0.17 0.5 40 0.3 3.9 47 16.3 0.001

10LB12C 0.3 102 0.08 <0.05 0.9 0.08 0.16 0.4 44 0.3 3.9 49 15.5 <0.001
17

Table 3. Mercury and monomethylmercury concentrations in waters and sediment. 

Sample Date

Water

Hg Total

 ng/L

Water

Hg Filtered 

 ng/L

Water

Total MMeHg

 ng/L

Sediment

Hg 

ng/g

D.O.C.

mg/L

Sediment

MMeHg

ng/g

% MMeHg

(MMeHg/Hg)

in sediment

WF Las Tablas Creek

10LB1A 4/6/10 96.2 67.6 0.058 304,000 2.7 0.304 0.000001

10LB4A 4/6/10 5.58 0.055 44,900 2.6 0.096 2.13808E-06

10LB4A2 4/6/10 5.91

Mine Drainage from Adit

10LB2A 4/6/10 46.7 13.5 0.02 72,400 0.151 2.08564E-06

Reservoir Creek

10LB3A 4/6/10 17.4 0.101 228 6.6 0.042 1.84211E-04

10LB3A2 4/6/10 17
18

Table 4. Geochemistry of filtered samples from the Little Bonanza Mine, ICP-MS results (major elements, ICP-AES results).

Sample Latitude Longitude

Ag

μg/L

Al

μg/L

As

μg/L

B

μg/L

Ba

μg/L

Be

μg/L

Bi

μg/L

Ca

mg/L

Cd

μg/L

Ce

μg/L

Co

μg/L

Cr

μg/L

Cs

μg/L

Cu

μg/L

WF Las Tablas Creek

10LB1B 35.58414 -120.91121 1 5 1 123 124 0.05 0.2 35.2 0.02 0.03 0.02 1.6 0.02 1

10LB4B 35.59845 -120.91093 1 11.2 1 66.8 93.5 0.9 0.2 47.1 0.02 0.04 0.02 1 0.02 0.83

Mine Drainage from Adit

10LB2B 35.583 -120.91109 1 2.3 1 249 119 0.05 0.2 30.1 0.02 0.01 4.78 1.4 1.58 1.5

Reservoir Creek

10LB3B 35.58424 -120.90997 1 44.9 1 43.2 76.2 0.05 0.2 28.9 0.02 0.15 0.06 1.3 0.02 1.6

Sample Latitude Longitude

Dy

μg/L

Er

μg/L

Eu

μg/L

Fe

μg/L

Ga

μg/L

Gd

μg/L

Ge

μg/L

Ho

μg/L

K

mg/L

La

μg/L

Li

μg/L

Lu

μg/L

Mg

mg/L

Mn

μg/L

WF Las Tablas Creek

10LB1B 35.58414 -120.91121 0.005 0.005 0.01 50 0.05 0.007 0.05 0.005 1.16 0.02 16.2 0.1 70.7 0.3

10LB4B 35.59845 -120.91093 0.02 0.005 0.005 50 0.05 0.02 0.05 0.005 0.7 0.05 2.8 0.1 20.1 1

Mine Drainage from Adit

10LB2B 35.583 -120.91109 0.005 0.005 0.009 50 0.05 0.005 0.1 0.005 1.94 0.01 48.5 0.1 129 2.4

Reservoir Creek

10LB3B 35.58424 -120.90997 0.05 0.03 0.02 86 0.05 0.06 0.05 0.01 0.82 0.13 0.9 0.1 14.7 2

Sample Latitude Longitude

Mo

μg/L

Na

mg/L

Nb

μg/L

Nd

μg/L

Ni

μg/L

P

mg/L

Pb

μg/L

Pr

μg/L

Rb

μg/L

Sb

μg/L

Sc

μg/L

Se

μg/L

SiO2

mg/L

Sm

μg/L

WF Las Tablas Creek

10LB1B 35.58414 -120.91121 2 15 0.2 0.03 5 0.01 0.05 0.01 0.41 0.3 0.8 1 9.5 0.01

10LB4B 35.59845 -120.91093 3.1 12.4 0.2 0.07 0.4 0.01 0.05 0.02 0.17 0.3 0.9 1 9.5 0.01

Mine Drainage from Adit

10LB2B 35.583 -120.91109 2 17.8 0.2 0.01 476 0.01 0.05 0.01 3.49 0.44 0.7 1 7.8 0.01

Reservoir Creek

10LB3B 35.58424 -120.90997 2 8.9 0.2 0.18 1.4 0.01 0.05 0.04 0.13 0.3 0.9 1 10.1 0.04
19

Table 4 (cont’d)

Sample Latitude Longitude

SO4

mg/L

Sr

μg/L

Ta

μg/L

Tb

μg/L

Th

μg/L

Ti

μg/L

Tl

μg/L

Tm

μg/L

U

μg/L

V

μg/L

W

μg/L

Y

μg/L

Yb

μg/L

Zn

μg/L

WF Las Tablas Creek

10LB1B 35.58414 -120.91121 28 274 0.05 0.005 0.2 0.6 0.1 0.005 0.16 0.6 0.5 0.08 0.006 1.7

10LB4B 35.59845 -120.91093 43 298 0.02 0.005 0.2 3.4 0.1 0.005 0.37 0.5 0.5 0.09 0.006 0.7

Mine Drainage from Adit

10LB2B 35.583 -120.91109 130 460 0.05 0.005 0.2 2 0.1 0.005 0.14 0.6 0.5 0.03 0.005 1.7

Reservoir Creek

10LB3B 35.58424 -120.90997 17 209 0.05 0.008 0.2 10 0.1 0.005 0.14 0.8 0.5 0.28 0.03 0.5

Sample Latitude Longitude

Zr

μg/L

WF Las Tablas Creek

10LB1B 35.58414 -120.91121 0.2

10LB4B 35.59845 -120.91093 0.2

Mine Drainage from Adit

10LB2B 35.583 -120.91109 0.2

Reservoir Creek

10LB3B 35.58424 -120.90997 0.2
20

Table 5. Geochemistry of unfiltered samples from the Little Bonanza Mine, ICP-MS results (major elements, ICP-AES results).

Sample Latitude Longitude

Ag

μg/L

Al

μg/L

As

μg/L

B

μg/L

Ba

μg/L

Be

μg/L

Bi

μg/L

Ca

mg/L

Cd

μg/L

Ce

μg/L

Co

μg/L

Cr

μg/L

Cs

μg/L

Cu

μg/L

WF Las Tablas Creek

10LB1B 35.58414 -120.91121 1 22.7 1 127 127 0.05 0.2 36.9 0.02 0.04 0.02 2.2 0.02 1.1

10LB4B 35.59845 -120.91093 1 107 1 67.7 72.7 0.05 0.2 47.2 0.02 0.1 0.04 1 0.02 1.2

Mine Drainage from Adit

10LB2B 35.583 -120.91109 1 5.9 1 246 116 0.05 0.2 29.3 0.02 0.01 4.67 1.1 1.53 1.5

Reservoir Creek

10LB3B 35.58424 -120.90997 1 794 1 45.5 88.6 0.05 0.2 30.3 0.02 0.84 0.7 5.9 0.04 2.7

Sample Latitude Longitude

Dy

μg/L

Er

μg/L

Eu

μg/L

Fe

μg/L

Ga

μg/L

Gd

μg/L

Ge

μg/L

Ho

μg/L

K

mg/L

La

μg/L

Li

μg/L

Lu

μg/L

Mg

mg/L

Mn

μg/L

WF Las Tablas Creek

10LB1B 35.58414 -120.91121 0.01 0.007 0.01 50 0.05 0.008 0.05 0.005 1.19 0.02 14.7 0.1 71.9 0.8

10LB4B 35.59845 -120.91093 0.02 0.01 0.007 112 0.05 0.03 0.05 0.005 0.85 0.06 8.9 0.1 20.2 3.2

Mine Drainage from Adit

10LB2B 35.583 -120.91109 0.005 0.005 0.008 50 0.05 0.005 0.1 0.005 1.96 0.01 45.1 0.1 128 2.5

Reservoir Creek

10LB3B 35.58424 -120.90997 0.099 0.061 0.03 912 0.26 0.13 0.05 0.02 0.91 0.35 3.6 0.1 15.5 21.7

Sample Latitude Longitude

Mo

μg/L

Na

mg/L

Nb

μg/L

Nd

μg/L

Ni

μg/L

P

mg/L

Pb

μg/L

Pr

μg/L

Rb

μg/L

Sb

μg/L

Sc

μg/L

Se

μg/L

SiO2

mg/L

Sm

μg/L

WF Las Tablas Creek

10LB1B 35.58414 -120.91121 2 15.2 0.2 0.03 5.4 0.01 0.05 0.01 0.42 0.3 0.9 1 10.1 0.01

10LB4B 35.59845 -120.91093 2 17.6 0.2 0.08 0.4 0.01 0.08 0.02 0.24 0.3 1.4 1 16 0.01

Mine Drainage from Adit

10LB2B 35.583 -120.91109 2 18.6 0.2 0.01 457 0.01 0.05 0.01 3.27 0.44 0.7 1 7.8 0.01

Reservoir Creek

10LB3B 35.58424 -120.90997 2 9.16 0.2 0.44 9.6 0.01 0.3 0.1 0.54 0.3 1.4 1 14 0.1
21

Table 5 (cont’d)

Sample Latitude Longitude

SO4

mg/L

Sr

μg/L

Ta

μg/L

Tb

μg/L

Th

μg/L

Ti

μg/L

Tl

μg/L

Tm

μg/L

U

μg/L

V

μg/L

W

μg/L

Y

μg/L

Yb

μg/L

Zn

μg/L

WF Las Tablas Creek

10LB1B 35.58414 -120.91121 31.9 278 0.07 0.005 0.2 1 0.1 0.005 0.17 0.8 0.5 0.08 0.005 2.3

10LB4B 35.59845 -120.91093 78.6 317 0.06 0.005 0.2 7.1 0.1 0.005 0.36 0.7 0.5 0.12 0.006 85.1

Mine Drainage from Adit

10LB2B 35.583 -120.91109 146.3 434 0.06 0.005 0.2 2 0.1 0.005 0.13 0.5 0.5 0.03 0.005 1.3

Reservoir Creek

10LB3B 35.58424 -120.90997 21 220 0.07 0.02 0.2 31.3 0.1 0.007 0.16 2.5 0.5 0.55 0.05 2.5

Sample Latitude Longitude

Zr

μg/L

WF Las Tablas Creek

10LB1B 35.58414 -120.91121 0.2

10LB4B 35.59845 -120.91093 0.2

Mine Drainage from Adit

10LB2B 35.583 -120.91109 0.2

Reservoir Creek

10LB3B 35.58424 -120.90997 0.4
22

Table 6. Invertebrate samples collected from the Little Bonanza Mine and Trout Creek on April 6, 2010.

Sample code Site Location Order Family No. Mass (g) Ave. Mass (g) % Solids

Hg T 

(μg/g ww)

MeHg 

(μg/g ww) % MeHg

CR-LBUP040610-001LBUP Little Bonanza 

Upstream

Megaloptera Corydalidae 3 1.47 0.490 20.54 0.432 0.085 19.61

CR-LBUP040610-002LBUP Little Bonanza 

Upstream

Megaloptera Corydalidae 6 0.53 0.088 NA 0.446 0.074 16.61

CR-LBBR040610-001LBBR Little Bonanza 

at Bridge

Megaloptera Corydalidae 3 1.08 0.360 NA 0.136 0.057 41.99

CR-LBBR040610-003LBBR Little Bonanza 

at Bridge

Odonata Aeshnidae 6 1.34 0.223 22.74 0.118 0.092 77.54

CR-LBBR040610-002LBBR Little Bonanza 

at Bridge

Odonata Gomphidae 5 1.03 0.206 29.58 0.198 0.148 74.75

CR-LBBR040610-004LBBR Little Bonanza 

at Bridge

Coleoptera Dytiscidae 7 0.53 0.076 NA 0.129 0.090 69.61

CR-LBBR040610-005LBBR Little Bonanza 

at Bridge

Hemiptera Gerridae 15 0.91 0.061 37.71 0.127 0.084 66.46

CR-TRCR040610-002TRCR Trout Creek Odonata Aeshnidae 3 1.59 0.530 15.03 0.042 0.037 86.52

CR-TRCR040610-003TRCR Trout Creek Odonata Libellulidae 10 2.12 0.212 18.43 0.039 0.035 90.18

CR-TRCR040610-004TRCR Trout Creek Odonata Libellulidae 10 2.04 0.204 17.64 0.040 0.039 96.51

CR-TRCR040610-006TRCR Trout Creek Odonata Coenagrionidae 20 1.10 0.055 25.09 0.016 0.013 86.45

CR-TRCR040610-001TRCR Trout Creek Coleoptera Dytiscidae 13 0.79 0.061 35.85 0.037 0.034 93.19

CR-TRCR040610-005TRCR Trout Creek Hemiptera Gerridae 14 0.67 0.048 NA 0.016 0.014 89.10

NA = not analyzed
23

Table 7. Sample sites and physical and selected chemical parameters for waters from the Little Bonanza Mine collected during a high-flow sampling event.

Field Sampling Conductivity Temperature Dissolved O2

Number Latitude Longitude Date Sample Site Description micro Siemens pH oC ppm

WF Las Tablas Creek

11LB1A 35.58414 -120.91121 2/21/11 Little Bonanza Creek 189 7.27 11.5 5

11LB4A 35.59845 -120.91093 2/21/11 Tablas Creek, 1.25 km downstream from mine 150.3 7.52 12.55 4.6

11LB5A 35.59845 -120.91093 2/21/11 Tablas Creek, 2.25 km downstream from mine 151 7.2 12.55 4.57

11LB2A 35.583 -120.91109 2/21/11 Downstream from mine adit drainage 101 7.16 12.4 4.7

Reservoir Creek

11LB3A 35.58424 -120.90997 2/21/11 Reservoir drainage 199 7.39 12.55 5.03
24

Table 8. Mercury and monomethylmercury concentrations in waters and sediment collected during a 

high-flow sampling event

Water Water Water Water Total Suspended

DOC Hg Total Hg Filtered Total MMeHg Sediment (TSS)

Sample mg/L ng/L ng/L ng/L mg/L

WF Las Tablas Creek

11LB1A 6.28 206 51.8 0.208 14.6

11LB4A 7.04 135 24.7 0.164 56.1

11LB5A 7.32 68.3 27.8 0.163 65.0

11LB2A 9.38 190 55 0.165 22.5

Reservoir Creek

11LB3A 6.09 49.1 36 0.236 40.5
25

Table 9. Concentrations of anions and selected cations in filtered water from the Little Bonanza Mine collected 

during a high-flow sampling event

Sample Cl F NO3 SO4 CaCO3 Ca Fe K Li Mg Na

ppm ppm ppm ppm ppm mg/L μg/L mg/L μg/L mg/L mg/L

WF Las Tablas Creek

11LB1B 10.1 341 1.1 < 0.1 15.1 4.33

11LB2B 7.79 700 0.92 < 0.1 4.46 4.2

11LB4B 10.6 378 0.98 0.1 7.14 5.59

11LB5B 11.5 260 0.87 0.3 7.04 5.95

Reservoir Creek

11LB3B 10.2 285 1.2 1.1 14.9 4.49
26

Table 10. Geochemistry of filtered samples from the Little Bonanza Mine collected during a high-flow sampling event, ICP-MS results (major elements,

ICP-AES results)

Sample Al B Ba Ca Ce Co Cr Cs Cu Dy Er Eu Fe Ga Gd/P Ho K La Li

μg/L μg/L μg/L mg/L μg/L μg/L μg/L μg/L μg/L μg/L μg/L μg/L μg/L μg/L μg/L μg/L mg/L μg/L μg/L

WF Las Tablas Creek

11LB1B 274 38.7 36.1 10.1 0.27 0.71 3.3 0.04 1.7 0.063 0.03 0.02 341 0.1 0.062 0.01 1.1 0.14 < 0.1

11LB2B 630 25.7 33.9 7.79 1.3 1.5 4.8 0.05 2.4 0.17 0.098 0.052 700 0.23 0.22 0.04 0.92 0.59 < 0.1

11LB4B 348 35.9 29.9 10.6 0.53 2.4 3 0.03 1.6 0.1 0.053 0.01 378 0.1 0.11 0.01 0.98 0.27 0.1

11LB5B

244 34.2 29.4 11.5 0.44 0.44 2.2 < 

0.02

1.5 0.083 0.053 0.03 260 0.08 0.1 0.02 0.87 0.28 0.3

Reservoir Creek

11LB3B 248 39.4 35.7 10.2 0.26 1 3 0.04 1.4 0.058 0.04 0.02 285 0.07 0.056 0.01 1.2 0.14 1.1

Sample Mg Mn Na Nd Ni P Pb Pr Rb Sc SiO2 Sm SO4 Sr Tb/P Ti Tm V

mg/L μg/L mg/L μg/L μg/L mg/L μg/L μg/L μg/L μg/L mg/L μg/L mg/L μg/L μg/L μg/L μg/L μg/L

WF Las Tablas Creek

11LB1B 15.1 9.6 4.33 0.23 8 0.02 0.16 0.05 0.46 1 7.11 0.05 8.8 73.1 0.01 2.9 0.006 1.2

11LB2B 4.46 19 4.2 0.84 10.6 0.02 0.35 0.2 0.63 1.5 9.52 0.2 9.1 61.3 0.04 18.1 0.02 1.9

11LB4B 7.14 12.2 5.59 0.37 6 0.03 0.16 0.08 0.44 1.3 9.16 0.08 15 89 0.01 14.5 0.007 1.5

11LB5B 7.04 5.9 5.95 0.43 5.1 0.02 0.12 0.1 0.27 1.2 9.51 0.08 16 90.9 0.02 6.8 0.005 1

Reservoir Creek

11LB3B 14.9 8.5 4.49 0.21 7.4 0.01 0.1 0.05 0.37 1 7.03 0.05 8.4 74.7 0.009 1.5 0.005 1

Sample Y Yb Y Yb Zn

μg/L μg/L μg/L μg/L μg/L

WF Las Tablas Creek

11LB1B 0.32 0.03 0.08 0.006 1.7

11LB2B 0.94 0.08 0.03 < 0.005 1.7

11LB4B 0.45 0.04 0.09 0.006 0.7

11LB5B 0.46 0.04

Reservoir Creek

11LB3B 0.29 0.02 0.28 0.03 0.5

Not detected: Ag <1 μg/L, As <1 μg/L, Be <0.05 μg/L, Bi <0.2 μg/L, Cd <0.02 μg/L, Mo <2 μg/L,

Nb <0.2 μg/L, Sb <0.3 μg/L, Se <1 μg/L, Ta <0.02 μg/L, Th <0.2 μg/L, Tl <0.1 μg/L, U <0.1 μg/L, W <0.5 μg/L, Zn <3 μg/L, Zr <0.2 μg/L
27

Table 11. Geochemistry of unfiltered samples from the Little Bonanza Mine collected during a high-flow sampling event, ICP-MS results 

(major elements, ICP-AES results)

Sample Al B Ba Bi Ca Cd Ce Co Cr Cs Cu Dy Er Eu Fe Ga Gd/P Ho

μg/L μg/L μg/L μg/L mg/L μg/L μg/L μg/L μg/L μg/L μg/L μg/L μg/L μg/L μg/L μg/L μg/L μg/L

WF Las Tablas Creek

11LB1A 1,660 40.6 49 0.4 10.8 0.02 0.93 1.8 12.1 0.11 3.3 0.15 0.076 0.05 1,870 0.53 0.16 0.03

11LB2A 1,850 27.2 48 < 0.2 7.93 <0.02 3 1.6 12 0.14 3.8 0.3 0.14 0.072 2,200 0.67 0.33 0.06

11LB4A 2,090 35.7 48.8 < 0.2 11.3 <0.02 2.1 2.4 13.6 0.11 4.2 0.23 0.13 0.063 2,790 0.7 0.27 0.05

11LB5A 1,610 35.8 44.5 < 0.2 12.5 0.02 2.6 1.6 10 0.09 3.5 0.21 0.1 0.072 2,030 0.57 0.26 0.05

Reservoir Creek

11LB3A 1,410 40.7 49.2 < 0.2 10.8 <0.02 0.86 1.6 10.5 0.07 3.1 0.15 0.07 0.04 1,620 0.46 0.15 0.03

Sample K La Li Mg Mn Na Nb Nd Ni P Pb Pr Rb Sc SiO2 Sm SO4 Sr

mg/L μg/L μg/L μg/L μg/L mg/L μg/L μg/L μg/L mg/L μg/L μg/L μg/L μg/L mg/L μg/L mg/L μg/L

WF Las Tablas Creek

11LB1A 1.3 0.43 2.9 17.3 50.7 4.46 0.54 0.58 24.3 0.02 0.46 0.13 1.1 2 12.4 0.14 8.2 75.9

11LB2A 1.1 1 1.1 5.64 51.7 3.96 0.38 1.4 22 0.04 0.96 0.32 1.7 2.4 14.3 0.31 8 61.6

11LB4A 1.1 0.81 2.4 9.33 78.2 5.46 < 0.2 1.1 25.5 0.05 0.86 0.26 1.3 2.6 16.4 0.26 14 88.1

11LB5A 1 0.77 1.9 9.04 62.9 6.09 < 0.2 0.99 18.8 0.04 0.74 0.22 1.1 2.2 15 0.25 16 93.8

Reservoir Creek

11LB3A 1.3 0.4 2.2 17.4 47.8 4.51 < 0.2 0.53 23.3 0.02 0.42 0.11 0.91 1.8 11.2 0.15 8.7 79

Sample Ta Tb/P Ti Tl Tm U V Y Yb Zn Y Yb Zn Zr

μg/L μg/L μg/L μg/L μg/L μg/L μg/L μg/L μg/L μg/L μg/L μg/L μg/L μg/L

WF Las Tablas Creek

11LB1A 0.07 0.02 25.3 0.21 0.01 < 0.1 4.4 0.81 0.08 5.4 0.08 0.005 2.3 < 0.2

11LB2A 0.09 0.05 53.3 <0.1 0.02 < 0.1 4.8 1.4 0.13 6.2 0.03 < 0.005 1.3 < 0.2

11LB4A 0.05 0.04 56.4 <0.1 0.02 < 0.1 6 1.2 0.11 7.7 0.12 0.006 85.1 < 0.2

11LB5A 0.05 0.03 39 <0.1 0.01 0.1 4.4 1 0.07 5.8

Reservoir Creek

11LB3A 0.05 0.02 11.7 <0.1 0.01 < 0.1 3.7 0.74 0.05 5.2 0.55 0.05 2.5 0.4

Not detected: Ag <1 μg/L, As <1 μg /L, Be <0.05 μg /L, Mo <2 μg /L, Sb <0.3 μg /L, Se <1 μg /L, Th <0.2 μg /L, W <0.5 μg /L
28

 120°55’

Figure 1. General geology of the Little Bonanza Mine area (Yates and others, 1941). The workings at Little Bonanza explore a zone of fault breccia 

that trends northwest. The breccia consists of fragments of sandstone, greenstone, serpentine, and chert in a shale matrix. 

35°35’
29

Figure 2. Vertical projection of workings at the Little Bonanza Mine (Yates and others, 1941). 
30

Figure 3. Cross-section of ore shoots at the Little Bonanza Mine (Yates and others, 1941). 
31

Figure 4. Mine workings at the Little Bonanza Mine, with a cross section showing alteration and mercury ore zones (Yates and others, 1941). 
32

Figure 5. Three-pipe retort at the Little Bonanza Mine that was used to process Hg ores. 
33

Figure 6. Mine processing area at the Little Bonanza Mine, showing remains of a three-pipe retort. 
34

Figure 7. Calcines (mine tailings) adjacent to retort at the Little Bonanza Mine. 
35

Figure 8. Sulfides that formed in three-pipe retort at the Little Bonanza Mine. 
36

Figure 9. Calcines (mine tailings) at the Little Bonanza Mine exposed along bank of WF Las Tablas Creek.
37

Figure 10. Little Bonanza Mine area, showing locations of all sample sites (Google Earth). Area in yellow box is 

shown in detail in figure 11.
38

Figure 11. Closeup of figure 10, showing locations of sample sites in mine area (Google Earth). 

Yellow box delineates land managed by BLM.
39

Figure 12. Coarse-grained calcines (mine tailings) exposed in bank of WF Las Tablas Creek at the Little Bonanza Mine. 
40

Figure 13. Sample site 10LB1 in WF Las Tablas Creek at the Little Bonanza Mine. 
41

Figure 14. Sample site 10LB3 in creek that extends into area of dam, now failed, at the Little Bonanza Mine. 
42

Figure 15. Hg concentration in unfiltered versus filtered samples from the Rinconada and Little Bonanza Mines. 
43

Figure 16. Hg versus MMeHg concentrations in unfiltered water samples from the Rinconada and Little Bonanza Mines. 
44

Figure 17. Hg concentration versus %MMeHg in sediment samples from the Little Bonanza Mine. 
45

Figure 18. MMeHg concentration versus %MMeHg in sediment samples from the Little Bonanza Mine. 
46

Figure 19. Comparison of HgT and dissolved Hg concentrations in waters sampled at the Little Bonanza Mine, beginning with the most upstream 

sample site, LB2, at the adit, and moving downstream to sample sites LB1, LB3, LB4 and LB5, respectively.