Geology, alteration, and mineralization in the pyroclastic and sedimentary deposits of the Bretz-Aurora Basin, McDermitt Caldera, Nevada-Oregon
AuthorRonkos, Charles Joseph
Geological Sciences and Engineering
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Miocene to Pliocene age sediments in the Bretz-Aurora basin, 16 miles west of McDermitt, Nevada, form as a series of blanketing phreatomagmatic and plinian, ash and lapilli, subaerial and subaqueous deposits. Epithermal mercury associated with uranium, forms the center of an irregular zonational pattern in the lower 24.4m (80 ft.) of the stratigraphic section. A zonational sequence; mercury/silica-dioctahedral smectite (aluminum-rich) - pyrite-uranium/calcium carbonate-amorphous silica/minor uranium, progresses away from the center of the mineralizing system. The minerals and their distribution suggest a highly alkaline mineralizing solution with a pH greater than 9. A gradual decrease in pH and differences in solubility of each component created the zonational pattern.
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