Abstract

Temple Mountain, Utah, is an erosional remnant capped by resistant dolomtic alteration of the Triassic Wingate and Chinle Formations. Carbonate, Fe-oxide, phyllosilicate, sulfate, and other mineral alterations are related to a collapse structure. Elemental zoning (Cr, Cu, Co, Ni, As) of the ore district is unlike that found in other uranium districts hosted by the Chinle Formation. A major uranium ore belt in the Chinle Formation partially encircles the collapse structure ∼500 m away.

Two theories on the genesis of the Temple Mountain district have been proposed. Both suggest a relationship between alteration, ore mineralization, and formation of the collapse structures but differ substantially as to the intrinsic parameters of the alteration/ore mineralizing fluids. One theory suggests hydrothermal solutions up to 350 °C, whereas the other proposes cool solutions rich in CO2. Fluid-inclusion data collected from alteration dolomite and sphalerite and geochemical modeling of a CO2-rich system support aspects of the latter theory. Median homogenization temperatures for fluid inclusions in dolomite, calcite, quartz, and sphalerite are 67, 59, 74, and 73 °C, respectively. Fluid salinity measured in inclusions in sphalerite is 7.8 to 9.7 eq. wt % NaCl. Alunite, spatially associated with uranium mineralization and the collapse structure alteration, has been dated at ∼13 Ma by K-Ar methods. Acid solutions containing carbon and sulfur derived from natural gas dissolved carbonate, caused collapse, and transported and fixed uranium as oxidation states varied.

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