Day 1: Mesquite Mining District, Southeastern California
R.M. Tosdal, G.F. Willis, S.L. Manske, D. Lang, M. Lusk, 1991. "Day 1: Mesquite Mining District, Southeastern California", The Diversity of Mineral and Energy Resources of Southern California, Michael A. McKibben
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The Mesquite Mining District lies on the southern piedmont flanks of the Chocolate Mountains in southeastemmost California, some 60 km east of the Salton Sea and about 50 km northwest of Yuma, Arizona (Fig. 1). This range is part of the eastern margin of the Salton Trough, the locus of active faulting along the modem San Andreas fault system (Crowell, 1979) and the locale for this field trip (Fig. 1). Inactive strands of the Neogene San Andreas fault system cut the Chocolate Mountains (Dillon, 1976; Crowell, 1979).
Production from the Mesquite Mining district began in 1985 and is now one of the largest producers of gold in California (B umett, 1990). Announced economic reserves (Gold Fields Operating Co., 1990) are 93.7 million short tons at an average grade of 0.033 troy ounces per short ton. The Oligocene gold orebodies that constitute the mining district formed in an epithermal environment and are hosted by gneiss and granite of Mesozoic age (see below). This part of the field trip examines the setting of epithermal gold mineralization in the mining district. The structural control on the orebodies is the primary focus of the field trip and we will examine some of the evidence supporting the interpretation of a dextral strike-slip control on the mineralization (Willis and others, 1987, 1989; Manske and Einaudi, 1989). Another structural model links the formation of the gold orebodies to Tertiary extensional deformation and related detachment faulting (Drobeck and)
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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.