Cu Ratios in Acid Mine Water from Iron

Chapter 22

Seasonal Variations of Zn/Cu Ratios in Acid Mine Water from Iron Mountain, California Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on October 13, 2015 | http://pubs.acs.org Publication Date: December 20, 1993 | doi: 10.1021/bk-1994-0550.ch022

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Charles N. Alpers , D. Kirk Nordstrom , and J. Michael Thompson 1

Water Resources Division, U.S. Geological Survey, Federal Building, Room W-2233, 2800 Cottage Way, Sacramento, CA 95825 Water Resources Division, U.S. Geological Survey, 3215 Marine Street, Boulder, CO 80303 Geologic Division, U.S. Geological Survey, Branch of Volcanic and Geothermal Processes, MS-910, 345 Middlefield Road, Menlo Park, CA 94025 2

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Time-series data on Zn/Cu weight ratios from portal effluent compositions [(Zn/Cu) ] at Iron Mountain, California, show seasonal variations that can be related to the precipitation and dissolution of melanterite [(Fe ,Zn,Cu)SO •7H O]. Mine water and actively forming melanterite were collected from underground mine workings and chemically analyzed. The temperature-dependent solubility of Zn-Cu-bearing melanterite solid solutions was investigated by heating-cooling experiments using the mine water. Rapid kinetics of melanterite dissolution and precipitation facilitated reversed solubility experiments at 25°C. Non-reversed solubility data were obtained in the laboratory at 4° and 35°C and at ambient underground mine conditions (38° and 42°C). Copper is partitioned preferentially to zinc into melanterite solid solutions at all temperatures investigated. During the annual dry season, values of (Zn/Cu) in the Richmond portal effluent increase to values between 8 to 13, consistent with formation of melanterite during this period. During the annual wet season, the onset of high discharge from the mine portals is characterized by a significant decrease in (Zn/Cu) to values as low as 2. This phenomenon may be caused by dissolution of melanterite with values of (Zn/Cu) ranging from 1.5 to 3.5. water

II

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water

water

solid

The rapid oxidation rate of sulfide minerals in abandoned mines and associated waste materials results in the formation of metal-rich sulfuric acid solutions that pose a threat to human health and the environment Cycles of wetting and drying determined by local climate and hydrology can influence soil-water and ground-water composition (1). In particular, the progress of sulfide oxidation reactions and the composition of resulting acid mine drainage responds to wetting-drying cycles by transient storage of metals and acidity in the form of secondary sulfate minerals (2-5). Seasonal variations in the relative concentrations of metals, measured in certain mine waters, may be controlled in general by cycles of precipitation and dissolution of soluble secondary This chapter not subject to U.S. copyright Published 1994 American Chemical Society In Environmental Geochemistry of Sulfide Oxidation; Alpers, C., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1993.

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Variations of Zn/Cu Ratios in Acid Mine Water

ALPERS ET AL.

sulfate salts. Melanterite, a Zn-Cu-bearing hydrated ferrous-sulfate sait [(Fe ,Zn,Cu)S0 7H 0], may be a major contributor to this phenomenon, based on its propensity to incorporate Cu in preference to Zn in solid solution and the observation that it is generally the first mineral to form when Fe(II)-rich acid mine water is evaporated. The primary dissolved components of most acid mine drainage (AMD) are iron and sulfate, resulting from oxidation of the minerals pyrite (FeS^, marcasite (FeS^, and pyrrhotite (Fe^S). Massive sulfide deposits hosted in volcanic rocks are a principal contributor to AMD problems because of the high concentrations of sulfide minerals and the relative lack of neutralizing agents found in carbonate-hosted massive sulfide deposits (for example, Leadville, Colorado). Other base metals typically associated with iron in massive sulfide deposits include Cd, Cu, Pb, and Zn. These elements occur most commonly in the minerals chalcopyrite (CuFeS ), galena (PbS), and sphalerite [(ZnJFe,Cd)S)]. Lead concentrations in sulfate-rich water are low because of the limited solubility of anglesite (PbS0 ) (6,7). As a result, Cd, Cu, and Zn, are mostfrequendythe primary base metals of environmental concern in AMD from massive sulfide deposits. An improved knowledge of geochemical mechanisms controlling the composition of AMD is required to anticipate how metal concentrations in surface and ground waters would be affected by proposed remediation efforts at abandoned mine sites. Melanterite, a common efflorescent salt, is often the first mineral deposited from solutions at sites of pyrite oxidation (2,8,9). Melanterite has a crystal structure that can accommodate large proportions of Cu and Zn substituting for Fe in solid solution. A general formula for the melanterite solid solution can be expressed as (Fe _ . Zn Cu )S0 *7H 0. Maximum values of Zn and Cu molefractionsrecorded for natural samples are χ = 0.307 and y = 0.654, respectively (10-11). In this study, actively forming melanterite and associated mine water near to melanterite saturation were collectedfromunderground mine workings. These water samples were used in heating-cooling experiments to show that Zn/Cu partitioning into melanterite can explain cyclic seasonal variations in mine-water chemistry. Although numerous other sulfate salts of Cu, Fe, and Zn form in similar environments, melanterite is a common, moderately soluble mineral in mine workings and mine tailings containing abundant pyrite (12). Therefore, the formation and dissolution of melanterite can have a dominant effect on the chemistry of mine effluent, which responds to seasonal cycles of wetting and drying. n

Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on October 13, 2015 | http://pubs.acs.org Publication Date: December 20, 1993 | doi: 10.1021/bk-1994-0550.ch022

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Hydrogeologic Setting and Mining History at Iron Mountain, California Mine drainage from the pyritic massive sulfide deposits at Iron Mountain, California (Figure 1), is the most acidic and metal-rich reported anywhere in the world (4,14). The AMD leaving the Richmond adit (Figure 2) ranges in pH from 0.02 to 1.5, and contains more than 100,000 mg/L of total dissolved solids (4.13). Effluentfrommine workings mixes with metal-rich runoff and with seepsfromsulfidic waste-rock piles and flows into Boulder and Slickrock Creeks, which are tributaries to Spring Creek (Figure 1). The metal-rich water of Spring Creek (pH -3.0) is impounded in Spring Creek Reservoir behind the Spring Creek Debris Dam, built by the U.S. Bureau of Reclamation (USBR) in 1963 to prevent sediment buildup at the Spring Creek Powerplant. EffluentfromSpring Creek Reservoir is released into Keswick Reservoir,

In Environmental Geochemistry of Sulfide Oxidation; Alpers, C., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1993.

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ENVIRONMENTAL GEOCHEMISTRY OF SULFIDE OXIDATION

Figure 1. Location of Iron Mountain and plan view of mine workings on the 2600 level of the Richmond Mine. (Adapted from Alpers and others, 13)



East

ι 0

1

1

1

1

1

1000 FEET

250 METERS

Figure 2. Cross section through Iron Mountain showing location of Richmond and Hornet deposits, Richmond adit, and Lawson tunnel. (Adapted from Alpers and others, 13)

NOTE: Hornet Mine workings not shown


West


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where mixing occurs with relatively dilute water released from the Spring Creek Powerplant and from Shasta Dam. Releases from the Spring Creek Debris Dam, the Spring Creek Powerplant, and Shasta Dam are controlled by the USBR to ensure that dissolved metal concentrations at Keswick Dam meet criteria for Cu, Zn, and Cd designed to protect beneficial uses, including fish and wildlife habitats. The Iron Mountain area was placed on the National Priority List of the U.S. Environmental Protection Agency (EPA) for cleanup under the Superfund program in September 1983 (15). Renovation of underground workings in the Richmond Mine by the EPA in 1989-91 provided access to stopes, drifts, and raises that had been inaccessible for 35 years. Samples of mine water and efflorescent sulfate minerals were collected and analyzed by the U.S. Geological Survey (USGS) to document the storage of metals and acidity in the underground workings. Drip water was found to give extreme measurements of pH, including the first negative pH values ever documented from such a setting (4.14). Measured values of pH from mine-tunnel drips were found to range from -0.45 to -3.4, using methods described in a later section. The massive sulfide deposits at Iron Mountain (Figure 1) constitute a part of the West Shasta mining district. Host rocks are hydrothermally altered volcanic rocks of Devonian age, including the keratophyric Balaklala Rhyolite and the spilitized Copley Greenstone (16.17). A cross section through Iron Mountain (Figure 2) shows the presence of two sulfide deposits, the Richmond and Hornet deposits, that originally were a continuous lens of massive sulfide cut later by normal faults (16). The pyriterich Brick Flat deposit (not shown on Figure 2) was also originally connected to the Richmond deposit and offset by normal faulting (16). Gossan, the oxidized top part of a massive sulfide deposit consisting of oxidized iron minerals (goethite and hematite) and residual silica, is found on the top of Iron Mountain and also in the area of Boulder Creek near the Lawson portal (Figure 2). The gossan was mined for its silver content during the 1880's. The Hornet deposit was mined for its Cu content by underground methods from 1907 to 1926. The Richmond deposit was discovered about 1915 but was not mined for Cu and Zn on a large scale until the 1940's. The Brick Flat deposit was mined principally for its pyrite content by open-pit methods from 1950 to 1962. As part of a remedial action mandated by the EPA in 1985-86 (18), the Brick Rat pit was equipped with a liner and used as a disposal site for pyritic tailings. Future plans for site remediation include preparation of the Brick Flat pit for disposal of high-density sludgefromlime treatment of the AMD now flowing from the Richmond and Lawson portals (19). The total metal load from the combined effluent from the Richmond adit and the Lawson tunnel represents about 75% of the Cu and 90% of the Cd and Zn released to surface waters in the area (20). The massive sulfide deposits at Iron Mountain consist almost entirely (90 to 99 percent by volume) of pyrite, sphalerite, and chalcopyrite. Small amounts of bornite ( C u F e S ) , arsenopyrite (FeAsS), and tennantite-tetrahedrite ((Cu,AgJFe,Zn) (As,Sb) S ) have been reported (16). Trace amounts of gangue minerals, also present in the ore, include quartz, calcite, muscovite, and chlorite (16). The wall rock for the Richmond deposit is Balaklala Rhyolite, a dacitic unit which was affected by sea-floor metasomatism (keratophyrization; Γ7) and hydrothermal alteration. The wall rock consists mainly of albite, chlorite, epidote, quartz, and muscovite. The dissolution of these minerals contributes Al, Ca, K, Mg, and Si to the mine water in proportions determined by mass-balance calculations described by Alpers and others (13.21). 5

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Variations of Zn/Cu Ratios in Acid Mine Water329

The AMD at Iron Mountain is among the most acidic ever reported because the massive sulfide deposits have remained in the unsaturated zone since underground mining activity ceased in the 1950's. The Richmond adit and Lawson tunnel at elevations of about 2,600 and 2,200 feet above sea level (Figure 2), provide effective drains for the Richmond and Hornet deposits. A comparison of discharge rates from the Richmond and Lawson portals (mine openings), based on weekly monitoring data from 1983 to 1991 (13), shows a generally positive correlation, but differences between the hydrologie response of the two portals are significant. Minimum flow rates during dry-season conditions are about twice as high at the Lawson portal as at the Richmond portal (Figure 3, Table I), which indicates that the Lawson tunnel receives a greater proportion of steady ground-water inflow than does the Richmond Mine. Discharge rates at both portals increase during the wet season, generally from October through April (Figure 4). The total range in discharge (Table I) is much greater for the Richmond portal (0.5 to 50 l/s) than for the Lawson portal (0.8 to 15 l/s), indicating that flows from the Richmond Mine are affected more by rapidly infiltrating surface waters. Geochemistry of Acid Mine Drainage Effluent from the Richmond and Lawson portals has been monitored weekly during the wet seasons and monthly during the dry seasons since 1983 by the California Regional Water Quality Control Board, in cooperation with the EPA. In addition to discharge measurements, water samples were analyzed for pH and dissolved Cd, Cu, and Zn. A summary of the data for discharge, pH, Cu, and Zn for 1983 to 1991 is presented in Table I. Metal concentrations generally are about three times higher in the Richmond portal effluent than in the Lawson portal effluent, and the pH is about 1 unit lower. Table Π presents analytical data for major and trace elements in four water samples from the Richmond Mine. Samples 90WA103, 90WA108, and 90WA109 were collected at extreme low-flow conditions during September 1990, after 5 consecutive years of below-average precipitation. Sample 91WA111 was collected in June 1991. Sample 90WA103 isfromthe Richmond portal effluent, which represents the sum of all water leaving the Richmond Mine workings on the 2600 level (Figures 1 and 2). Samples 90WA108,90WA109, and 91WA111 represent drip water collected on the 2600 level either from timbers (108) or from melanterite stalactites (109 and 111). The dissolved metals in the Richmond portal effluent clearly are derived from oxidation of sulfide minerals in the Richmond Mine; however, it remained unclear whether the dissolved constituents in the Lawson portal effluent were also derived from the Richmond mine and not from the more proximal Hornet deposit (Figure 2). Mass-balance analysis using 11 dissolved constituents in water samples collected from the Richmond and Lawson portals during low-flow conditions of September 1990 showed that at least 94% of the dissolved metals in the Lawson portal effluent were derived from sulfide oxidation in the Hornet deposit (13). Thus, the Richmond and Lawson portal effluents represent two distinct hydrogeochemical reactors in the Richmond and Hornet deposits, respectively. The gravimetric concentration ratios of Zn to Cu from the two portal effluents


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Table I. Characteristics of Portal Effluents, 1983-91 (--, no data) Richmond portal effluent Mean

Range

Lawson portal effluent Mean

Range


Overall Discharge (liters/second)

4.4

0.5 - 50

2.5

0.8 - 15

pH (units)

0.8

0.02 - 1.5

1.6

0.6 - 2.8

1,600

Zinc (mg/l) Copper (mg/l) Zinc/copper (weight ratio)

250

700 - 2,600

540

280 - 840

120 - 650

90

50 - 150

7.5

6.2

2 - 13

2-10

Wet season Discharge (liters/second) Zinc/copper (weight ratio)

6 - 12+

--

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2-6

--

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~ 1.3

< 1.9

8-13

-

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Dry season Discharge (liters/second) Zinc/copper (weight ratio)

~ 0.9

DISCHARGE (liters/second)

Figure 3. Gravimetric concentration ratios of Zn to Cu as a function of discharge rate, Richmond and Lawson portal effluents, 1983-91. (AdaptedfromAlpers and ; others, 13)


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Variations of Zn/Cu Ratios in Acid Mine Water 331

ALPERS ET AL. 15.0

?

io.o Γ-

Ι

5.0 h

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(L/s LU 10.0 CD OC

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melanterite

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90WA108

38°C 38°C 4°C 90WA109

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J

28°C 28°C 91WA111

Figure 6. Gravimetric concentration ratios of Zn to Cu in melanterite and coexisting mine water from Richmond Mine. Filled symbols indicate melanterite, open symbols indicate mine water; open symbols with dots indicate water samples with melanterite present. Squares represent samples collected in situ at temperature indicated; triangles represent products from heating-cooling experiments using mine water samples at 4° and 25°C. Ranges of values of concentration ratio of Zn to Cu for Richmond and Lawson portal effluents during wet and dry seasons shown for comparison. lower than values of (Zn/Cu) for coexisting mine water (open squares with dots). Raw water samples 90WA109-F and 90WA109-X4 were saturated with melanterite solid solution at the time of collection; melanterite formed on cooling to 25° and 4°C. The compositions of the residual water and the melanterite formed on cooling are given in Tables IV and V, and the Zn/Cu ratios are plotted in Figures 5 and 6. As the temperature decreased in experimental runs 90WA109-F and 90WA109-X4, the (Zn/Cu) ratio of the precipitates decreased (in 90WA109-F) from an initial values between about 1.8 and 2.0 at 38°C to a value of 1.5 at 4°C (Table V); the values of (Zn/Cu) increased from an initial value of 3.3 at 38°C (in 90WA109) to a value of 7.9 in the residual water (of 90WA109-F) at 4°C (Table IV). The Zn/Cu ratios of coexisting water and melanterite are shown in Figure 6. At the lower temperatures, more extreme differences in Zn/Cu between water and solid were observed. Because each experiment was a closed system, except for the subsamples collected for analysis (1 ml for each analysis from 125 ml total volume), Cu was depleted to a great degree in the water as the solid melanterite crystallized on cooling (Figure 5C). These results indicate that Zn/Cu partitioning favors Cu into the solid phase at all temperatures, and that this tendency is accentuated at lower temperatures. The compositional data for Fe(II), Zn, and Cu in the experimental solutions are plotted in Figures 5(A-D) as a function of temperature. Dots in open symbols in Figure 5 indicate the presence of solid melanterite. Vertical triangles indicate that the temperature was reached by heating and inverted triangles indicate cooling. Reversed solubility data (temperature approached from both directions) were obtained only at 25°C. Figure 5A indicates the strong temperature dependence of melanterite solubility, as documented by Reardon and Beckie (28). Figures 5B and 5C show a relatively water

solid

water



342


minor decrease in Zn concentrations and a strong decrease in Cu concentrations, respectively, with decreasing temperature in the residual mine water as melanterite crystallized on cooling. The significant increase in the Zn/Cu ratio in the residual water at the lower temperatures (Figure 5D) indicates that Cu is partitioned into the melanterite solid solution preferentially to Zn. Rapid kinetics of melanterite dissolution and crystallization facilitated collection of reversed solubility data at 25°C. It is assumed that equilibrium was reached between the aqueous phase and the surface of the melanterite. The homogeneity of the melanterite was not tested because poor polishing properties and its tendency to dehydrate under vacuum made this material not suitable for electron microprobe analysis. Therefore, it is not known whether or not the melanterite crystals came to homogeneous equilibrium with the aqueous phase at each temperature. Also shown in Figure 6 are the ranges in values of (Zn/Cu) for effluent mine water from the Richmond and Lawson portals. The lower values of (Zn/Cu) for mine effluent in the wet season are similar to the values of the melanterite crystals. The higher values of (Zn/Cu) during the dry season for both portals are similar to the values of the residual waters after melanterite precipitation. These similarities indicate that cyclic precipitation and dissolution of Zn-Cu-bearing melanterite solid solutions during the annual wetting-drying cycles may be at least partly responsible for the observed annual cycles in the Zn/Cu ratios in mine effluents. water

water

water

Conclusions Acid mine water issuing from the Richmond and Lawson portals of Iron Mountain show significant and systematic variations in Zn/Cu weight ratios related to seasonal patterns of climate. High discharges during the wet seasonresultin low Zxi/Ca ratios (values of 2 to 6 in both portal effluents) whereas Zn/Cu ratios obtained during the dry season are consistently higher (values of 8 to 13 in the Richmond portal effluent and 4 to 10 in the Lawson portal effluent). The underground mine workings contain abundant masses of highly soluble, efflorescent salts. Melanterite, a common efflorescent mineral and usually the first to form during evaporation of Fe(H)-rich mine water, is a good candidate to affect changing patterns of Zn and Cu concentrations in this AMD because of its large compositional range. An experimental study, designed to investigate the temperature-dependent solubility of melanterite precipitated from actual mine water samples of low pH (-0.7 to 3.0), demonstrated strong preferential partitioning of dissolved Cu into the melanterite solid solution. This partitioning provides a mechanism to explain the correlation of Zn/Cu variations in the portal effluent with climatic fluctuations. The Zn/Cu ratios in the melanterite are relatively low (2 to 4) due to the enrichment in Cu. When melanterite dissolves during high flow conditions, the effluent mine water ratios decrease to similar low values. The dry season conditions promote formation of melanterite, causing a decrease in Cu concentration of the residual mine water and a marked increase in Zn/Cu ratios in the AMD to values above 4 (Lawson portal) and above 8 (Richmond portal). Additional work is needed to establish the thermodynamic properties of both melanterite solid solutions and the concentrated acid-sulfate brines from which they precipitate. The specific ion interaction approach of Pitzer (25) is the most appropriate method by which to compute the non-ideal behavior of the most concentrated AMD


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ALPERS ET AL.

343 Variations of Zn/Cu Ratios in Acid Mine Water

(e.g. 28). When thermodynamic data become available for the interactions of Zn and Cu with the Fe(n)-S0 -HS0 -H 0 system, it will be possible to derive mixing parameters for melanterite solid solutions of the general formula (Fe . . Zn CupS047H 0. Until then, the empirical data presented here will be useful in defining the solubility relations in the ZnS0 -CuS0 -Fe(n)S0 -H S0 -H 0 system. 4

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Acknowledgments The authors thank Rick Sugarek of the U.S. Environmental Protection Agency for providing financial support and access to the underground workings at Iron Mountain. We also thank the following individuals for assistance with underground sampling: Dale Smith (CH2M Hill), Larry Salhaney (formerly of Engineering International), Cathy Maenz (McGill University), and Nick Waber (NAGRA, Switzerland). Our interpretation of hydrology and geochemistry at Iron Mountain benefitted from discussions with Rick Sugarek (EPA); Daryl Greenway, Dick Coon, Jim Mavis, and Pete Lawson (CH2M Hill); and Jo Burchard (USGS). The manuscript was improved by thoughtful reviews by R. Fujii (USGS), J. Hem (USGS), E. Reardon (Univ. of Waterloo), and an anonymous reviewer. A portion of this work was done while CNA was a National Research Council/Resident Research Associate at the U.S. Geological Survey in Menlo Park, CA. Funding was also obtained from the National Science and Engineering Research Council (NSERC) of Canada and from the Fonds pour la Formation de Chercheurs et L'Aide à la Recherche (FCAR) of Québec, while C.N. Alpers was an Assistant Professor at McGill University. Literature Cited 1. 2.

Drever, J.L.; Smith, C.L. Amer. Jour. Sci., 1978, 278, 1448-1454. Nordstrom, D.K.; Dagenhart, T.V., Jr. Geological Society of America, Abstracts with Programs, 1978, 10, 464. 3. Dagenhart, T.V., Jr., M.Sc. Thesis, Univ. Virginia, Charlottesville, VA, 1980 4. Alpers, C.N.; Nordstrom, D.K. In Proceedings, Second International Conference on the Abatement of Acidic Drainage; Ottawa: MEND (Mine Environment Neutral Drainage); 1991, 2, 321-342. 5. Cravotta, C.A., ΙΠ. In this volume. 6. Dubrovsky, N.L. Ph.D. Thesis, Univ. of Waterloo, Waterloo, Ontario, 1986, 373 P7. Blowes, D.W.; Reardon, E.J.; Jambor, J.L.; Cherry, J.A. Geochimica et Cosmochimica Acta, 1991, 55, 965-978. 8. Buurman, P. Geologie en Mijnbouw, 1975, 54, 101-105. 9. Nordstrom, D.K., In Acid Sulfate Weathering; Kittrick, J.A.; Fanning, D.S.; Hossner, L.R., Eds.; Soil Science Soc. of Amer.: Madison, WI; Spec. Pub. 10, 1982, pp. 37-55. 10. Palache, C.; Berman, H.; Frondel, C. Dana's System of Mineralogy; J. Wiley & Sons: New York, 1951. 11. Glynn, P.D., In Chemical Modeling in Aqueous Systems II; Melchior, D.C. and



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Bassett, R.L., Eds.; ACS Symposium Series, No. 416; American Chemical Society: Washington, DC, 1990; 74-86. 12. Blowes, D.W.; Jambor, J.L. Applied Geochemistry, 1990, 5, 327-346. 13. Alpers, C.N.; Nordstrom, D.K.; Burchard, J.M. U.S. Geol. Survey Water-Resources Investigations Report 91-4160, 1992, 173 p. 14. Nordstrom, D.K.; Alpers, C.N.; Ball, J.W. Geological Society of America, Abstracts with Programs, 1991, 23, (3), A383. 15. Biggs, F.R. U.S. Bureau of Mines Information Circular 9289, 1991, 15 p. 16. Kinkel, A.R., Jr.; Hall, W.E.; Albers, J.P. U.S. Geol. Survey Professional Paper 285, 1956, 156 p. 17. Reed, M.H. Economic Geology, 1984, 79, 1299-1318. 18. U.S. Environmental Protection Agency. Final remedial investigation report, Iron Mountain mine, near Redding, California, Prepared by CH2M Hill: Redding, CA; EPA WA No. 48.9L17.0, 1985. 19. U.S. Environmental Protection Agency. Public Comment Remedial Investigation Report, Boulder Creek Operable Unit, Iron Mountain Mine, Redding, California; Prepared by CH2M Hill, Redding, CA; EPA WA No. 31-01-9N17, 1992. 20. U.S. Environmental Protection Agency. Public Comment Feasibility Study, Boulder Creek Operable Unit, Iron Mountain Mine, Redding, California; Prepared by CH2M Hill, Redding, CA; EPA WA No. 31-01-9N17, 1992. 21. Alpers, C.N.; Nordstrom, D.K. In Acid Mine Drainage - Designing for Closure; Gadsby, J.W.; Mallick, J.A.; Day, S.J., Eds.; Bi-Tech Publishers Ltd.: Vancouver, BC, 1990, 23-33. 22. Nordstrom, D.K. Selected papers in the Hydrologic Sciences 1985, U.S. Geological Survey Water-Supply Paper 2270, 1985, 113-119. 23. Suzuki, I.M., Takenuchi, . In this volume 24. Alpers, C.N.; Maenz,C.;Nordstrom, D.K.; Erd, R.C.; Thompson, J.M. Geol. Soc. Amer. Abstracts with Programs 1991, 23, (5), A382. 25. Pitzer, K.S.; Roy, R.N.; Silvester, L.F. Jour. Amer. Chem. Soc., 1977, 99, 49304936. 26. Plummer, L.N., Parkhurst, D.L.; Fleming, G.W.; Dunkle, S.A. U.S. Geol. Survey Water-Resources Investigations Report 88-4153, 1988. 27. Lide, D.R., Ed., CRC Handbook of Chemistry and Physics, 73rd edition; CRC Press: Ann Arbor, MI; 1992, p. 15-17. 28. Reardon, E.J.; Beckie, R.D. Geochimica et Cosmochimica Acta, 1987, 51, 23552368. RECEIVED September 23,

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Cu Ratios in Acid Mine Water from Iron

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