Fluid generation and movement are key components of basin evolution, with important implications for hydrocarbon and mineral exploration. Unlike high-temperature hydrothermal systems, the low-temperature basinal brines associated with diagenesis and hydrocarbon maturation often leave subtle physical or chemical evidence, making their passage difficult to recognize in the rock record. Exceptional outcrops in the Paradox Basin display bleaching and Fe-Mn, Cu, and U-V accumulations that provide a unique opportunity for detailed investigation into paleofluid flow. This study examines bleaching and Cu mineralization in the Jurassic Wingate Sandstone on the southwestern flank of the Paradox Valley salt anticline near the Cashin mine. Bleaching within the Wingate Sandstone extends for more than 12 km along the southwestern flank of the Paradox anticline and is centered around minor subvertical normal faults orthogonal to the anticlinal crest. Bleaching affects the full thickness of the Wingate Sandstone along the Paradox salt anticline and pinches out down-dip and laterally toward the top contact of the eolian sandstone with the overlying Kayenta Formation. Petrographic studies of the Wingate Sandstone show that bleaching involved the dissolution of Fe-oxides and reprecipitation of most of the Fe as pyrite as well as alteration of quartz, feldspar, and Fe-Ti grains, precipitation of kaolinite and barite, dissolution of dolomite cements, and introduction of hydrocarbons. The bleached zones appear to represent an exhumed paleohydrocarbon reservoir. A second fluid flow event transmitted Cu-bearing saline brines along the Cashin fault creating the Cashin Cu deposit in highly receptive pyrite- and hydrocarbon-bearing bleached rocks.

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