Geochemical and stable isotope studies of the No. 4 lode, Kalgoorlie, Western Australia

Norseman-Wiluna greenstone belt, Archean gold-telluride mineralization. Wallrock alteration is characterized by an increase in the K ₂ O/Na ₂ O ratio and the introduction of CO ₂ and S. Ankerites in the lode zone have delta ¹⁸ O values from 11.5 per mil to 13.8 per mil with a mean of 12.4 + or - 0.5 per mil. Ambient temperatures of mineralization are estimated to have been 250 degrees + or - 50 degrees C. The calculated delta ₁₈ O of the hydrothermal solution is 4.5 + or - 2 per mil, consistent with fluids of metamorphic derivation. The delta ¹³ C values of ankerites have a mean value of -3.6 + or - 0.4 per mil; calculated delta ¹³ C of the mineralizing fluids is -3 + or - 1 per mil. Sulfur and carbon isotopic data are consistent with a moderately reduced near-neutral (pH approximately 6) fluid which has incorporated magmatic sulfur and carbon. Gold was precipitated by a decrease in the activity of reduced sulfur by formation of pyritic wall-rock assemblages.--Modified journal abstract.