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Trace Element And Stable Isotope Geochemistry of Environmental Minerals and Acid Rock Drainage,Patagonia Mountains, Arizona

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SHANKS, W.C. III and LICHTE F. E., U S Geological Survey, MS 973 Denver Federal Center, Denver, CO 80225

As a first phase study of the abandoned mines in the Patagonia Mountains. mine drainage water, secondary salts, and mineralized samples from mine dumps were analyzed chemically and for sulfur isotope values. Water flows from many of the mine adits year round whereas leaching from the mine dumps occurs primarily during the high rainfall seasons.

Primary and secondary minerals containing Fe, Cu, Zn, Pb, & Mo were analyzed by laser ablation ICP-MS. Arsenic in sphalerite and pyrite ranges up to 8 wt.%, and Se and Te in galena are as high us 800 ppm. Waters from the mine adits range from 15-80 ppm Cu; 10-200 ppm Fe; 1-40 ppm Zn; 40-250 ppm Ca; 0.l-l2 ppb Pb; 10-120 ppb Cd; 0.2 7 ppb As; and l0-l140 ppm Mn suggesting potentially significant contributions of ionic elements to regional groundwater systems.

Sulfur isotope values of primary sulfide mineralization from Cu-F-Ag-Au deposits range from --5.4 to 0.4 permil. Sulfur isotope studies at the 3R Mine indicate that sulfate in mine drainage (-3.7) and in secondary salts on tailings (-2.8, - 3.2) have identical sulfur isotope values to primary pyrite (-3.9 to -1.2). Similarly, sulfate in 4 Metals mine drainage (-1.1) is identical to primary pyrite (-0.8 to -1.3). The lack of sulfur isotope fractionation during sulfide mineral oxidation makes this technique a particularly useful tracer for source of sulfate in acid drainage.

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