Mississippi Valley-Type Sulfides in Lower Permian Dolomites, Delaware Basin, Texas: Implications for Basin Evolution

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Mississippi Valley-type Pb-Zn mineralization occurs in Lower Permian (Leonardian) shelf-margin dolomites rimming an inner-shelf, carbonate-evaporite province on the southern Central Basin platform. The sulfide-hosting dolomites pass abruptly along a bounding fault system into basinal facies of the coeval Bone Spring formation. Zoned sphalerite and lesser amounts of galena and pyrite are the major sulfides present in this occurrence. Sulfur isotopes and fluid inclusions, in conjunction with considerations of the burial history of the area, suggest that Pb-Zn precipitation occurred during the late Mesozoic to Tertiary, in contact with mineralizing fluids heated to 96°-122°C (205°-252°F). These fluids were likely discharged along the Central Basin platfor from basin aquifers that are part of a regional, eastward, gravity-driven flow system that has been operative since at least the Tertiary. Sulfide precipitation appears to have resulted from mixing of basinal brines and ambient host fluids that were charged with sulfur derived from laterally contiguous shelf evaporites. Burial paragenesis of the shelf-margin host involved several episodes of eogenetic and mesogenetic dolomitization and partial dissolution (ground preparation) prior to and partly concurrent with sulfide emplacement. The occlusion of some pores by coarse-crystalline, luminescent-banded dolomite and calcite cements subsequent to mineralization is the last diagenetic event recognized in the host carbonates.