An Overview of the Geology and Geochemistry of the Coso Geothermal Area, Inyo County, CA.
Alan E. Williams, 1991. "An Overview of the Geology and Geochemistry of the Coso Geothermal Area, Inyo County, CA.", The Diversity of Mineral and Energy Resources of Southern California, Michael A. McKibben
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The Coso Geothermal Project is a generation facility which produces 240 megawatts of electric power using turbine generators powered directly from geothermal steam. In this area, steam is provided by an active hydrothermal circulation system established in the fractured granitic basement rocks and extending upward into the overlying silicic volcanics and volcaniclastics. The geothermal reservoir has been tapped at depths of 1–2 km. and produces water and steam at temperatures of about 250–350°C. This active hydrothermal circulation may be quite analogous to fossil systems which have produced precious metal–bearing ore bodies in rhyolite-hosted environments. This paper will review the geologic setting of the Coso system and provide an overview of its reservoir chemistry.
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The Kramer borate deposit is located in the northwestern Mojave Desert, about 90 air miles northeast of Los Angeles and 3 miles north of the town of Boron (figure 1). The deposit derives its name from the mining district in which it lies. The Kramer deposit, presently being mined from the Boron open pit, has been a world-class source of sodium borates since mine startup in 1926 and continues to be the largest source of borates in the world.
The Kramer ore body is a roughly lenticular sedimentary sequence of borax (Na2B4O7 • 10H2O) and kernite (Na2B4O7 • 4H2O) containing interbedded claystone. This central crystalline facies is successively enveloped by facies consisting of ulexite (Na,CaB5O9 • 8H2O) -bearing claystone, colemanite (Ca2B6O11 • 5H2O) -bearing claystone, and barren claystone. Studies indicate the Kramer borates were deposited in a small structural, nonmarine basin, associated with thermal (volcanic) spring activity during Miocene time.
The Kramer deposit does not crop out. It was discovered accidentally in 1213 by Dr. John Suckow, a homesteader, who struck colemanite while drilling a water well (figure 2). Exploratory drilling and shaft sinking after World War I by Pacific Coast Borax Company, the predecessor of U.S. Borax, led to the discovery of borax and kernite in 1925. In 1926 PCB went into large-scale, underground sodium borate mining in the Baker mine, located nearly 2 miles east of Suckow's discovery well. The company soon closed all its calcium borate operations near Ryan in Death Valley in favor of the more easily processed sodium borates at Boron.
U.S. Borax ships mostly bulk, refined sodium borate products and boric acid to both domestic and world markets from Boron. Principal uses for these products are in the manufacturing of glass and fiberglass, herbicides, ceramics, soaps and detergents, fluxes, fertilizers, and fire retardants.