Boron Isotopic Studies of Hydrothermal Fluids and AssociatedVein Mineralization

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The purpose of this SGER award is to initiate a collaborative investigation of B isotopic fractionation between well characterized samples of hydrothermal brines and associated vein mineralization at the Salton Sea, Coso, and Geysers geothermal fields. This study will serve to evaluate both B elemental and isotopic partitioning between several common alteration minerals and the fluids from which they precipitated. Empirical calibration of temperature effects on such partitioning is also possible using reservoir characteristics established for commercial geothermal wells in these fields. Essentially, it is planned to use the natural systems as a form of experimental calibration. This approach will provide an important survey of B concentrations in a variety of hydrothermal minerals(and of the feasibility of B isotopic analysis in each) that will focus subsequent detailed experimentation on those mineral species having the greatest potential for practical applications. Isotopic measurements will be carried out at the National Institute for Standards and Technology in collaboration with R. Vocke whose research group has recently developed an improved method for B isotopic mass spectrometry. It is proposed to first analyze selected fluid samples previously collected by M.A. McKibben to refine methods for isotopic analysis, then to visit representative wells from each of the geothermal fields for further sampling of fluids and vein mineralization (from core and cuttings).