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Mineralogy, alteration zonation, and genesis of the Waterpump Creek carbonate-replacement deposit, Alaska

Glenn, Justin
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Monecke, Thomas
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Date
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2024
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Keywords
Alaska
 carbonate-replacement deposit
 diaphorite exsolution
 Galena
 UV manganoan calcite
 visible alteration
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2024 - Mines Theses & Dissertations
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https://hdl.handle.net/11124/179231
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Abstract
The Waterpump Creek Pb-Zn-Ag deposit in the Illinois Creek mining district, western Central Alaska is a carbonate-replacement deposit consisting of flat-lying mantos and steeply dipping chimneys of massive and semi-massive sulfides hosted in dolostone. This study examines the geological setting, metal and visible carbonate alteration zonation, and ore mineralogy of the Waterpump Creek deposit through drill core logging, sulfide and carbonate petrography, cathodoluminescence microscopy, fluid inclusion analysis, and geochemical analysis of sulfides. The research shows that the visible alteration halo surrounding mineralization at Waterpump Creek is characterized by widespread recrystallization, sanding, bleaching, and silicification. Proximal increased carbonate compositional changes, strong recrystallization, and the presence of UV-active manganoan calcite provide vectors to mineralization. Silver-enrichment is primarily related to the presence of Ag- and Ag-Pb-Sb-sulfosalts hosted as small (≤1 µm) inclusions in galena with a small amount of Ag (0.1 – 0.3 wt%) being incorporated into the crystal structure of this sulfide. Diaphorite is the most abundant Ag-mineral inclusion hosted in galena. Textural evidence indicates that Ag-minerals exsolved from the initially higher-temperature Ag-enriched galena after deposit formation, presumably during cooling and uplift. Diffusion-limited growth sphalerite dendrites, zebra texture, recrystallization, open-space growth, dissolution, and replacement textures reflect highly reactive, self-organized, far-from-equilibrium processes. Based on the research, a deposit model for Waterpump Creek is proposed. It is hypothesized that mineral assemblage zoning is likely related to the degree of host-rock buffering of high-temperature (>250°C) magmatic-hydrothermal fluids derived from a deeper-seated intrusion. A set of exploration vectors toward higher-temperature fluid pathways is developed.
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