Use of Lead Isotopes as Natural Tracers of Metal Contamination—A Case Study of the Penn Mine and Camanche Reservoir, California
S.E. Church, C.N. Alpers, R.B. Vaughn, P.H. Briggs, D.G. Slotton, 1997. "Use of Lead Isotopes as Natural Tracers of Metal Contamination—A Case Study of the Penn Mine and Camanche Reservoir, California", The Environmental Geochemistry of Mineral Deposits: Part A: Processes, Techniques, and Health Issues Part B: Case Studies and Research Topics, G.S. Plumlee, M.J. Logsdon, L.F. Filipek
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Lead isotopes have been used as tracers of geologic processes in both ore-genesis and petrogenesis studies. Recently, they have found increased application in contamination studies. There are two requirements for their application in contamination studies: (1) that the isotopic signature of the contaminant is different from the rock lead in the area, and (2) that the signature of the source is known or can be determined. In this study, we examined lead isotope data for sediments from Camanche Reservoir near Stockton, California. We identified two sources of contamination in the sediments and soils of the area: one from acid-mine drainage from the Penn Mine within the drainage basin, and a second exotic lead, probably from airborne deposition from combustion of leaded gasoline in the early 1970s, found in soils.
Lead isotope data for sediments from the drowned channel of the Mokelumne River in Camanche Reservoir plot on a mixing line between the lead isotope signature of massive sulfide Cu-Zn- Pb ores from the Penn Mine and unaffected sediments derived from tributaries draining into Camanche Reservoir. The contribution of lead from the source of these metals, the Penn Mine, is diluted by sediments supplied by these tributaries. Distribution profiles for copper and zinc mimic the behavior of lead. Geochemical and lead isotope data for a sediment sample recovered from the fish hatchery at Camanche Dam following the 1989 fish kill indicate that the sediment was from the deep portion of Camanche Reservoir. The water intake from the hatchery was subsequently moved to reduce the probability of intake of sulfidic, anoxic waters and associated metal-rich sediments from deep in the reservoir. Since 1994, the water level of the reservoir has been maintained at 180 feet or more as recommended by Slotton et al. (1994) on the basis of their sediment resuspension studies. Installation of a hypolimnetic aeration system has resulted in no subsequent fish kills in the fish hatchery at Camanche Dam.
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The Environmental Geochemistry of Mineral Deposits: Part A: Processes, Techniques, and Health Issues Part B: Case Studies and Research Topics
Environmental issues have become important, if not critical, factors in the success of proposed mining projects worldwide. In an ongoing and intense public debate about mining and its perceived environmental impacts, the mining industry points out that there are many examples of environmentally responsible mining currently being carried out (e.g., Todd and Struhsacker, 1997). The industry also emphasizes that the majority of mining-environmental problems facing society today are legacies from the past when environmental consequences of mining were poorly understood, not regulated, or viewed as secondary in importance to societal needs for the resources being extracted. On the other hand, environmental organizations (e.g., Mineral Policy Center, 1999) point to recent environmental problems, such as those stemming from open-pit gold mining at Summitville, Colorado, in the late 1980s (see Summitville summaries in Posey et al., 1995; Danielson and Alms, 1995; Williams, 1995; Plumlee, 1999), or those associated with a 1998 tailings dam collapse in Spain (van Geen and Chase, 1998), as an indication that environmental problems (whether accidental or resulting from inappropriate practices) can still occur in modern mining. Recent legislation imposing a moratorium on new mining in Wisconsin, and banning new mining in Montana using cyanide heap-leach extraction methods further underscore the seriousness of the debate and its implications for mineral resource extraction.
In this debate, one certainty exists: there will always be a need for mineral resources in developed and developing societies. Although recycling and substitution will help meet some of the worlds resource needs, mining will always be relied upon to meet the remaining needs. The challenge will be to continue to improve the ways in which mining is done so as to minimize its environmental effects.
The earth, engineering, and life sciences (which we group here under the term “earth-system sciences,” or ESS for short) provide an ample toolkit that can be drawn upon in the quest for environmentally friendly mineral resource development. The papers in this two-part volume provide many details on tools in the scientific toolkit, and how these tools can be used to better understand, anticipate, prevent, mitigate, and remediate the environmental effects of mining and mineral processing.
As with any toolkit, it is the professional’s responsibility to choose the tool(s) best suited to a specific job. By describing the tools now available, we do not mean to imply that all of these tools need even be considered at any given site, nor that