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Appendix C Metal Distribution and Potential for Mobilization 199
200 THE POTENTIAL IMPACTS OF GOLD MINING IN VIRGINIA TABLE C-1â Distribution of Some Metals in Virginia Gold Deposits and Potential for Mobilization in Waters Antimony Distribution Antimony can be a trace to minor constituent in sulfides, like pyrite (USGS, 2017). Tetrahedrite ((Cu,Fe)12Sb4S13) is reported in massive sulfides in Virginia and the Eldridge deposit (Mangan et al., 1984). Mobilization Pyrite and other sulfides, including tetrahedrite, are unstable in the oxidized, weathering environment, and any antimony hosted in these phases would likely be released during mining, processing, and long-term storage of waste and could potentially make its way into the local groundwater/surface water system. Arsenic Distribution Distribution in deposit: The main arsenic-bearing mineral phase associated with gold deposits is arsenopyrite (FeAsS). Pardee and Park (1948) report that arsenopyrite is rare in most gold deposits in Virginia. Park (1936), in referring to deposits in the gold-pyrite belt, notes that âarsenopyrite has previously been reported as occurring in the ores but has not been observed in the recent work.â Rimstidt et al. (1994) report that arsenopyrite is among the most reactive of all sulfide minerals studied, indicating that any arsenopyrite in the ores would be oxidized relatively quickly. Arsenic also occurs as a trace to minor component in pyrite, and arsenian pyrite is common in many gold deposits. Arsenic contents of gold ores in the gold-pyrite belt are expected to be in concentrations of a few hundred to perhaps a few thousand parts per million, with essentially all of the arsenic hosted in trace arsenopyrite and as a trace element inÂ pyrite. Mobilization Both pyrite and arsenopyrite are unstable in the oxidized, weathering environment, and any arsenic hosted in these phases would likely be released during mining, processing, and long-term storage of waste and could potentially make its way into the local groundwater/ surface water system. Cadmium Distribution Minerals in which cadmium is a major component, including the cadmium sulfide phase greenockite (CdS), are not reported in any gold deposits in Virginia. Most cadmium that occurs in the gold deposits of Virginia is thought to occur as a trace element in sphalerite (ZnS) and, to a lesser extent, in other sulfide minerals. Schwartz (2000) reports concentrations of cadmium in sphalerite ranging up to 5 wt.% with chalcopyrite (600â1,200 mg/kg), galena (10â500 mg/kg), and pyrite (1â200 mg/kg) also serving as potential hosts for cadmium. Hammarstrom et al. (2006) report cadmium concentrations in pyrite from the Valzinco Mine of 0.18 wt.% (1,800 mg/kg). Mobilization During mining, processing, and long-term storage of waste rock and tailings, all (or most) cadmium contained in sphalerite and other sulfide phases could be released into the local environment and potentially make its way into the local groundwater/surface water system. Copper Distribution Chalcopyrite (CuFeS2) is a common trace sulfide phase in many gold deposits in the gold- pyrite belt, and in the Virgilina district the main copper-bearing phase is bornite (Cu5FeS4). Other copper-bearing phases that have been reported include native copper, chalcocite (Cu2S), cuprite (Cu2O), malachite [CuCO3 â¢ Cu(OH)2], and azurite [2CuCO3 â¢ Cu(OH)2]. Mobilization Copper in chalcopyrite and bornite are likely to break down during exposure to humid, oxidizing conditions and release copper to the local environment, but Rimstidt et al. (1994) note that the rate of oxidation of chalcopyrite is about 30 times slower than that of pyrite under similar conditions. Copper hosted in native copper, chalcocite, cuprite, malachite, and azurite are more stable at near surface conditions. Copper contained in these mineral phases may remain sequestered and not release into the environment. Lead Distribution Trace to minor amounts of galena (PbS) are reported in most mines in the gold-pyrite belt. Mobilization Galena reacts (oxidizes) about 300 times faster than sphalerite at pH 2 (but still slower than pyrite) (Rimstidt et al., 1994). Products of weathering of lead-bearing sulfides, including pyromorphite [Pb5(PO4)3Cl], vanadinite [Pb5(VO4)3Cl], and cerrusite (PbCO3), have also been reported at some locations in the gold-pyrite belt. While the overall lead content of the ores is low, it is expected that all or most of the lead in a given deposit could be mobilized as a result of mining activities.
APPENDIX C 201 TABLE C-1âContinued Selenium Distribution No minerals in which selenium is a major component have been reported in any deposits from the gold-pyrite belt. Stillings (2017) reports that while selenium-bearing minerals are common, in hydrothermal sulfide ore deposits most of the selenium occurs as a trace element in sulfides such as bornite (Cu5FeS4), chalcocite (Cu2S), chalcopyrite (CuFeS2), galena (PbS), and pyrite (FeS2), all of which have been reported in gold deposits in the gold-pyrite belt. In the Virgilina district, the main ore in the copper deposits is bornite. Babedi et al. (2022) report selenium concentrations in pyrite from orogenic gold deposits ranging from below detection to 200 mg/kg, with a mean value of 25 mg/kg, and report values ranging from 1,500 to 1,900 mg/kg in pyrites from low-sulfidation gold deposits. Chinnasamy et al. (2021) report selenium contents of pyrites from different stages in the Jonnagiri shear-zone hosted gold deposit in India that range from below detection to 80 mg/kg. Mobilization While the concentrations of selenium appear to be low in ores from the gold-pyrite belt, if most of the selenium is contained as a trace component in pyrite (and other sulfide minerals), the selenium would be released during mining, processing, and long-term storage of waste. Thallium Distribution Thallium minerals are rare, and none have been reported in the gold deposits of the gold-pyrite belt. In hydrothermal sulfide ores, thallium dominantly occurs as a trace component in pyrite, galena, and sphalerite. Bojakowska and Paulo (2013) report average thallium concentrations of 52.1 mg/kg in lead-zinc ores from ore deposits in Poland, and 1.4 mg/kg thallium in copper ores. Maximum values reported are 17.9 mg/kg for copper ores and 547 mg/kg for zinc-lead ores, with most of the thallium in lead-zinc ores contained in sphalerite. Chinnasamy et al. (2021) analyzed numerous pyrites from different stages in the Jonnagiri shear-zone hosted gold deposit in India and reported thallium concentrations ranging from below detection to 0.388 mg/kg. Majumdar et al. (2019) studied pyrites from shear-zone hosted gold occurrences in the South Purulia shear zone, India, and report thallium values ranging from below detection to 0.75 mg/kg. These workers also report 0.64 and 1.25 mg/kg thallium in chalcopyrite from these same deposits. Babedi et al. (2022) report thallium concentrations in pyrite from orogenic gold deposits ranging from below detection to 4,244 mg/kg, with a mean value of 98 mg/kg, and report values ranging from 10 to 2,700 mg/kg in pyrites from low-sulfidation gold deposits, with a mean value of 262 mg/kg. Mobilization Most or all of the thallium in gold deposits in the gold-pyrite belt is likely hosted in pyrite and other sulfide phases and would be released during mining, processing, and long-term storage of waste. Zinc Distribution Trace to minor amounts of sphalerite (ZnS) are reported in most mines in the gold-pyrite belt, and trace amounts of the alteration product smithsonite (ZnCO3) have been rarely reported. Mobilization Most zinc in sphalerite will likely be released to the environment as a result of alteration and decomposition during mining activities. The insignificant amount of zinc hosted by smithsonite will remain sequestered in the mineral, which is stable at surface conditions.