Assessment of Native Sulfur Potential of State-Owned Lands, Trans-Pecos Texas

A model of the requisite geologic and chemical conditions for native sulfur mineralization in evaporite rocks enables an objective first approximation of the regional sulfur potential in and surrounding the sulfur districts of Trans-Pecos Texas. From studies of Gulf Coast salt-dome cap-rock occurrences of native sulfur, it is known that sulfur mineralization in commercial quantities is dependent upon the coexistence of several factors: (1) anaerobic, sulfate-reducing bacteria, (2) hydrocarbons, (3) circulating meteoric groundwater, (4) shallow (< 2,500 ft of ground surface) and voluminous deposits of anhydrite and/or gypsum, (5) faults, joints, pervasive dissolution features, or some combination thereof in the evaporite deposit, and (6) structural traps. Bacteria, contained in a mixture of groundwater, hydrocarbons, and dissolved calcium sulfate, metabolize the dilute hydrocarbons to form hydrogen sulfide through the chemical reduction of sulfate ions. Oxygenated groundwater then oxidizes the hydrogen sulfide to elemental sulfur. Fracture systems allow the mixture of these ingredients and also permit their migration to traps, which provide sufficient residence time necessary for the formation of sulfur in commercial quantities. Definition and evaluation of these geologic aspects in the study areas form the basis of this assessment model.