SECONDARY FE-OXIDES AND METAL MOBILITY: LAKE GEORGE ANTIMONY MINE TAILINGS, LAKE GEORGE, NEW BRUNSWICK, CANADA

The Lake George Antimony Mine is located 39 km southwest of Fredericton, New Brunswick, Canada. Stibnite (Sb₂S₃) and native antimony (Sb) were the main sources of antimony during the history of the mine (1880-1996). Other sulfides include arsenopyrite (FeAsS), chalcopyrite (CuFeS₂), gudmundite (FeSbS), pyrite (FeS₂), sphalerite ((Zn,Fe)S), and tetrahedrite ((Cu, Fe)₁₂Sb₄S₁₃). Major gangue minerals are calcite and quartz, with minor plagioclase and muscovite. Sulfide oxidation and associated reactions have created elevated SO₄, Fe, As, Ca, Na, K, Al, and Si concentrations in the tailings pore water. Relatively low Sb concentrations occur in the near-surface pore-water compared to pore-water at depth. SEM studies reveal that the pyrite grains are weathered in the near-surface tailings, suggesting that pyrite oxidation contributes to the elevated Fe concentrations. Analyses of Fe-oxyhydroxide rims on weathered pyrite using SEM-EDS reveal that the coatings are mainly composed of Fe and O with minor As, Si, Sb and Ca. A TEM-EDS study of the coatings confirmed the presence of Fe, O, Sb, As, Si, and Ca, and demonstrated that the coatings are compositionally layered. TEM-EDS analyses indicate that S concentrations are low in the coating, consistent with the occurrence of elevated SO_4­ in the pore-water. The As and Ca concentrations in the coating increase with distance from the pyrite surface, whereas the Si concentration is generally highest at the pyrite surface. Concentrations of Sb in the coating are variable, but generally increase with distance from the pyrite surface. The occurrence of Sb in the Fe-oxyhydroxide coating on pyrite suggests that adsorption and/or co precipitation could account for the relatively low aqueous Sb concentrations in the near-surface tailings. The data suggest that adsorption and/or co-precipitation processes involving Fe oxyhydroxides provide mechanisms for attenuation of Sb, As, Ca, and Si concentrations in the tailings pore water.