Natural Versus Mining-Related Water Quality Degradation to Tributaries Draining Mount Moly, Silverton, Colorado

Yager, Douglas B. ; Mast, M. Alisa ; Verplanck, Philip L. ; Bove, Dana J. ; Wright, Winfield G. ; Hageman, Philip L.
Organization: Society for Mining, Metallurgy & Exploration
Pages: 14
Publication Date: Jan 1, 2000
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Geological, hydrological, and geochemical information synthesized in a Geographical Information System (GIS) for water and rock surrounding South and Middle Forks of Mineral Creek, northwest of Silverton Colorado, was analyzed to distinguish between the natural and the mining-related sources of metals to dace waters in the watershed An important natural source of metals to surface water emanates from a porphyry molybdenum deposit south and upslope from the Middle Fork of Mineral Creek. Interaction of surface and ground water with fractured, altered rocks and permeable, Quatemay-age surficial deposits produces downstream water quality that does not meet current State of Colorado water quality standards for metals and pH. GIS site characterization and three-dimensional modeling distinguish surficial deposits as volumetrically substantial, significant sources of naturally occurring metals that strongly influence water quality and complicate ongoing mine-site mitigation efforts. Our findings indicate that regional hydrologic and geologic information needs to be evaluated before realistic water quality guidelines are established and mitigation recommendations are confidently implemented.
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