METHODS

Mineral identifications were made from examination of 98 polished thin sections. Quantitative analyses of sulfide minerals were performed using a Cameca Camebax SX50 electron microprobe in the Department of Geology and Geophysics at Texas A&M University. Operating conditions were 15 kV with a beam current of 30 nA, a counting time of 30 s, and a 1-µm focused beam. Natural sulfide standards from Chuck Taylor (FeS₂, ZnS, PbS, GaAs, and Sb₂Te₃) were used for calibration of Fe, S, Zn, Pb, As, and Sb, respectively, and routinely analyzed as unknowns to check for drift. Pure Cu wire (also analyzed as a drift standard), Ni, Co, and Au were used as calibration standards.