Ore Precipitation in Epithermal Systems

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A combined field and laboratory study is proposed for epithermal ore deposits of the Champion Mine, Bohemia district, in the western Cascades, Oregon. Veins in this deposit record multiple episodes of fluid flow and precipitation. Field relations have been mapped by a PhD student involved in the project. They will be studied in detail (fluid inclusion measurements, microprobe analysis of ore, gangue, and alteration minerals, and Ar-Ar geochronology of igneous and mineralization episodes). Observational data will be interpreted in terms of theoretical models of ore formation involving cooling, boiling, mixing, and redox histories of ore forming brines. Numerical simulations will be used to model (a) mechanisms of sulfide and gold precipitation, and (b) the role of heat transfer to and from wall rocks. These studies will be of application to understanding many epithermal ore deposits.