Abstract
Pyrite in magmatic-hydrothermal settings contains significant concentrations of trace elements of economic and environmental importance, including Ag, As, Au, Bi, Cd, Co, Cu, Hg, Ni, Pb, Sb, Se, Te, Tl and Zn, which reflect the availability (solubility) of these elements in their parent hydrothermal solution. A review of our own and published analyses (including EMPA, SIMS, LA-ICP-MS, PIXE and HRTEM) of pyrite from Carlin-type, epithermal, and orogenic gold deposits reveals positive correlations for Sb-Pb-Bi, Au-Ag-Te, and Cu-Ag-Sb in all samples. Element-element ratios for most analyzed pyrites are: Au/Ag - 0.8-1.1, Au/Te - 0.8 to 1.0, Au/Sb - 0.7 to 1.1, Te/Pb - <1.1, Sb/Pb - 0.9-1.1, Sb/Cu - <1.0, Ag/Pb - 0.8-1.1, Bi/Pb - 1.0-0.7, and Bi/Sb - 0.7-1.1 in all types of deposits. Silver is enriched with respect to Te in low-T deposits, which have relatively high Ag/Te ratios of 1.0-1.2. Previous work has shown that As facilitates the incorporation of Au into pyrite via structural distortion and charge imbalance and that the Au content of pyrite is related to its As content such that the maximum Au content is C (sub Au) = 0.02C (sub As) + 4.10 (super -5) . Pyrite with Au-As contents above this maximum contain nano-inclusions of Au. These relations apply to epithermal and Carlin-type deposits, which form at relatively low temperatures. Au-As relations in pyrites from orogenic gold and skarn deposits, which form at higher temperatures, show similar relations but with smaller amounts of Au for any specific As content, suggesting that the solubility of Au in pyrite (as a function of As) decreases with increasing temperature. Arsenic also appears to facilitate incorporation of Ag, Te, Sb, Bi and Hg into the pyrite structure in the same mode as for gold, although analyses are not sufficient to establish specific solubility limits. Samples with contents of these elements that exceed the apparent solubility limits contain nanoparticulate sulfides and sulfosalts in distorted, polycrystalline areas of pyrite.