Case Study of the Environmental Signature of a Recently Abandoned, Carbonate-Hosted Replacement Deposit: The Clayton Mine, Idaho

摘要

The Clayton mine (Fig. 1) is a silver-lead-zinc replacement deposit in the Bayhorse mining district in Custer County, Idaho. The mine was last operated by Clayton Silver Mines, Inc. through 1986. The modern mill at the mine site is along Kinnikinic Creek, which drains into the Salmon River at Clayton, about 1.5 miles (2.4 km) downstream from the mine. The mill produced a lead concentrate by selective flotation that contained 35 to 45 percent lead and 3,400 to 6,800 g/t silver (Hillman, 1986). Mill tailings were placed as terraces along steep slopes within the narrow stream valley, extending to the edge of creek. Prior to the most recent mining activity, a historic smelter, on the north bank of the Salmon River at the town of Clayton, processed ores from a number of mines in the district and dumped slag directly into the river. The smelter operated intermittently from the 1880s to 1902 (Wells, 1983). The U.S. Environmental Protection Agency (EPA) and the U.S. Bureau of Land Management (BLM) have been investigating environmental issues related to the abandoned mine site since the early 1990s (EPA, 2000a). In October, 2001, EPA completed a Time-Critical Removal Action to stabilize mine tailings to prevent erosion into Kinnikinic Creek, to control infiltration of water into tailings and seepage of water from tailings, and to minimize wind erosion (EPA 1999, 2001). USGS sampled solids and waters at the site in August, 1999 and repeated water sampling in August, 2000. Data for solids, surface waters, and leachates from composite mine waste and mill tailings are reported here, along with descriptive information from the literature, in the form of a geoenvironmental model for the deposit. Sample locations from global positioning system instruments (GPS) and laboratory numbers keyed to the National Geochemical Database (U.S. Geological Survey, 1997) are listed in Appendix A. Analytical methods and detection limits are given in the Appendix B.