The mineralogy of the Golden Sunlight gold-silver telluride deposit, Whitehall, Montana, USA

The Golden Sunlight gold-silver telluride deposit, hosted primarily within the Mineral Hill breccia pipe (MHBP), is spatially related to a high-level, Late Cretaceous multiple intrusive, alkaline to subalkaline porphyry system. Base metal veins and manganese (rhodochrosite) mineralization occur up to 2km from the MHBP and form part of a regional mineral zonation pattern genetically related to a low-grade porphyry molybdenum system. Proterozoic rocks of the LaHood Formation and the informally named Bull Mountain Group host the MHBP and contain stratabound sulphides/ sulphosalts (up to 50% pyrite with minor to trace amounts of chalcopyrite, tennantite, pyrrhotite, sphalerite, galena, and molybdenite). Four periods of hypogene mineralization occur in the breccia pipe. Stages I and IV constitute approximate to 99% of the mineralization; native gold (4-11 wt.% Ag), calaverite, tetradymite, tellurobismuthite, Se-bearing Bi sulphosalts (aikinite, lindstromite, krupkaite, gladite, bismuthinite, and ?benjaminite), tennantite (Zn, Fe, Te, and Bi varieties), coloradoite, melonite, galena (up to 6.7 wt.% Bi and 6.4 wt.% Se), stannite, chalcocite, and the rare mineral buckhornite are included in stage Ib. Minor amounts of base metals are present in stage II. Gold-silver tellurides (krennerite, petzite, sylvanite, and possibly the rare ''x-phase'') developed in stage III whereas barite, fluorite, dolomite, magnesite, trace kaolinite, and sericite formed during stage IV. Utilizing the mineral assemblages in stage Ib, calculated values of log f Te-2 and log f S-2 range from -10.5 to -9.7, and -12.6 to -5.5, respectively. Ore forming components (e.g., Au, Ag, Te, Cu, Bi, Mo, and much of the S) were likely derived from the Late Cretaceous intrusive system with possible contributions from the Proterozoic host rocks.