Silver Mineralogy and Modes of Occurrence at the Silver Hart Deposit, South East Yukon.

Abstract: The Silver Hart property is a high grade silver-lead-zinc deposit consisting of polymetallic vein style, manto (carbonate replacement) style, and skarn type mineralization. Host rock consists of calcareous and non-calcareous sediments of the Cassiar Platform, mainly biotite schists, limestone units, and the monzogranite unit of the Cassiar Batholith. Bulk geochemistry shows that silver concentrations are closely related to copper and antimony values, suggesting freibergite, a silver-rich endmember of tetrahedrite, is the dominant silver mineral. EPMA (microprobe) analyses identified 6 silver minerals present; silver-bearing anglesite, freibergite, diaphorite, stephanite, pyrargyrite, and silver substitution in galena. Sulfur isotope analyses of galena gave an average δ34S of 6.9‰ vs VCDT, indicating a mixed mineralizing fluid source. Metal zoning patterns indicates that there is a thermal gradient across the main vein from hottest in the south-west, above the monzogranite intrusion, to coolest in the north-east. Microprobe analyses of freibergite indicates initial ore-forming fluid temperatures were between 250°C - 350°C, with subsequent cooler mineralization fluids of 170°C - 200°C.