Abstract

Stable isotope and chemical relations have been determined in a typical epithermal Au-Ag deposit located in the Bodie mining district of California. Analyses were made of altered host rocks, vein minerals, alteration clays, fluid inclusions, modern spring waters, and unaltered rocks of the area.The results indicate that a hydrothermal convection system was set up by the interaction of a cooling shallow intrusion and local meteoric water. The water traveled to depth where it picked up ore constituents and SiO 2 , K, and Rb, without significant shifts in the stable isotope ratios of the water. The altered rocks have equilibrated to various degrees with an ore fluid of constant K/Rb, O 18 /O 16 and D/H ratios. Deposition of ore took place over the approximate temperature range 215 degrees -245 degrees . From C 13 /C 12 ratios of minor calcite, a volcanic source of CO 2 is postulated. The chemical and isotope composition of the ore fluid is strikingly similar to that of modern spring waters in the area.All ore deposition at Bodie took place from essentially isotopically unaltered ground water with delta O 18 = -13ppm and delta D = -98ppm.

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