HYDROTHERMAL ALTERATION IN THE YELLOW PINE DEPOSIT, STIBNITE GOLD PROJECT, IDAHO; VEIN CROSS CUTTING, VIR-NIR-SWIR SPECTROSCOPY AND MULTI-ELEMENT GEOCHEMISTRY

The Yellow Pine-Stibnite mining district in central Idaho hosts several world class gold deposits and has been mined intermittently since the 1920s for gold, tungsten and antimony. The Yellow Pine deposit is the largest known in the district with substantial gold and antimony mineral reserves. VIS-NIR-SWIR spectroscopy, vein crosscutting relations and ICP-AES geochemistry of Midas Gold Inc. drill core samples provide insight into hydrothermal alteration zonation within the deposit. Illite-chlorite assemblages are predominant outside the bounding structures of the deposit and may represent an alteration halo. Within the deposit, gold mineralization is associated with illite and ammonium-illite assemblages and extensive potassic alteration. Illite-calcite or illite-iron carbonate assemblages occur adjacent to the ore-grade zones and are associated with moderate potassic alteration. Variations in illite spectral maturity generally correlate with host rock lithology, rather than alteration zonation. Some regions of the deposit are characterized by smectite assemblages which are interpreted as a lower temperature, retrograde alteration event associated with tungsten-antimony-silica alteration subsequent to gold deposition. Geochemical plots, alteration indices and multivariate statistical analyses were utilized for characterization of lithology and alteration styles in the full Yellow Pine drill-data set from ICP-AES geochemical data. Drillhole data was modeled in 3D using geostatistical methods for support of ongoing geometallurgy, waste rock characterization and mine planning studies for the Stibnite Gold Project.