2000 GSA Annual Meeting -- Reno, Nevada
2000 GSA Annual Meeting -- Reno, Nevada
Author(s): TEMPEL, Regina N., Dept. of Geological Sciences, Univ. of NV, Reno, Reno, NV 89557, gina@mines.unr.edu; BALISTRIERI, Laurie S., USGS, Univ. of WA, Box 357940, Seattle, WA 98195; STILLINGS, Lisa L., USGS, Univ. of NV, Reno, Reno, NV 89557
Keywords: pit-lake, mining, Nevada, modeling,environmental
Dexter pit lake, located near the townsite of Tuscarora, Nevada, has been the focus of a 2-year study to identify the processes affecting water quality in a mine pit lake. The initial geochemical modeling phase of our work is focused on developing methods to quantitatively evaluate the relative importance of hydrological, limnological, and geochemical processes that control major ion chemistry in the pit lake system. Processes that are being evaluated include: (1) extent of wall rock dissolution; (2) mineral precipitation; (3) dilution of epilimnion waters by inflowing surface waters; (4) mixing of groundwaters with pit lake waters in the hypolimnion waters; (5) evaporative concentration of the epilimnion; and (6) turnover of the entire water column. Continuing modeling work will evaluate the effects of diagenesis, benthic fluxes, and adsorption on concentrations of dissolved oxygen, Mn, Fe, nutrients, and As in the water column. Initial results indicate that wall rock reaction is essentially negligible because reactive mineral phases, such as carbonate and sulfide minerals, are present in trace amounts. Concentrations of major ions as well as minor elements, including Al, Fe, Mn, and Si, are controlled by kaolinite, goethite, hausmannite, and amorphous silica, respectively, in thermodynamic calculations. These minerals have either been observed in bottom sediments or were selected based on their stability within the geochemical conditions of the pit lake. Although goethite and hausmannite have been selected based on Eh-pH conditions in the lake, these minerals have not been conclusively observed due to their poorly crystalline form, and modeled Fe concentrations constrained by goethite do not match observed Fe concentrations well. Other Fe-phases, such as ferrihydrite and hematite, do not produce better results. Differences may be due to reaction kinetics and quality of Fe-mineral thermodynamic data.
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