Oxygen Isotope Investigation of the Fossil Hydrothermal System in the Comstock Lode Mining District, Nevada

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I propose to make a detailed study of oxygen isotope relations in volcanic rocks in the Comstock lode mining district, Nevada, where a relatively small (75 km2) zone was affected by intense circulation of meteoric-hydrothermal fluid, resulting in regional propylitization and in the formation of important epithermal Au-Ag deposits. Oxygen isotope data will be used to map the circulation pattern, to identify infiltration-related isotopic disequilibrium effects, and to characterize the fluid sources and the temperature distribution in the ancient hydrothermal system. Data from surface samples will be augmented with data on samples from mine workings in order to construct the first detailed 3-dimensional image of a hydrothermal system in an important mining district. I anticipate that the research will disclose critical relationships between circulation patterns and geologic factors that will advance understanding of these systems and that may be invaluable guides to ore deposits. The study will also advance knowledge about the regional geologic framework of our continent, and will provide fundamental data about the geologic environments and processes in which convective systems participate.