Abstract

Two styles of precious metal vein mineralization, epithermal and mesothermal, occur in the Okanagan Valley of southern British Columbia. The epithermal deposit (Dusty Mac) is composed of quartz stockwork mineralization in Eocene volcanic and volcaniclastic rocks. The mesothermal deposits (Fairview and Oro Fino) consist of thick (1-10 m) quartz veins in Paleozoic and Mesozoic metamorphic rocks. Fluid inclusion and stable isotope studies indicate that two distinct hydrothermal fluids were responsible for the mineralization events. At Dusty Mac, the epithermal fluid had a relatively low temperature (230 degrees -250 degrees C), extremely low salinity (<1 equiv wt % NaCl), and low delta 18 O (-7 to -9ppm) and delta D (-133ppm) values. At Fairview and Oro Fino, the mesothermal fluids had higher temperatures (280 degrees -330 degrees C), significant CO 2 contents, and higher salinities (3-6 equiv wt % NaCl). Stable isotope data show that the mesothermal fluids had low delta D (-121 to -148ppm) and delta 13 C (-8.5ppm) values, but high delta 18 O (+4 to +6ppm) values. The data indicate that the fluids involved in both styles of mineralization are 18 O-shifted meteoric water, with shallow circulation responsible for the epithermal deposits and deep circulation involved in the formation of the mesothermal deposits. Although both styles of mineralization occur in the same tectonic regime, it appears that they are not temporally or genetically related to each other.

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