Regional Perspective and Assessment of Native Sulfur Resources, Trans-Pecos Texas

Tucker F. Hentz, J. G. Price, G. N. Gutierrez

A model of the requisite physiochemical conditions for sulfur mineralization in bedded evaporites enables an objective first approximation of resource potential in Trans-Pecos Texas. Mineralization in commercial quantities is dependent on the coexistence of (1) anaerobic, sulfate-reducing bacteria, (2) hydrocarbons, (3) circulating meteoric ground water, (4) shallow (< 2,500 ft) and voluminous deposits of anhydrite and/or gypsum, (5) fractures, and (6) structural traps. Evaluation of critical geologic aspects forms the basis of this assessment study.

Structural and stratigraphic conditions of ore distribution in the Rustler Springs (Culberson and Reeves Counties) and Fort Stockton (Pecos County) sulfur districts were investigated using 1,450 sulfur exploration well logs (gamma-ray and neutron). The gentle eastward dip of Upper Permian (Ochoan) strata in the western Delaware basin (Rustler Springs sulfur district) is locally disrupted by small northeast-trending late Tertiary(?) grabens and high-angle normal faults. Commercial-scale deposits are restricted to the downfaulted blocks. Photogeologic inspection of the sulfur district reveals concentrations of northeast-trending fractures and lineaments and east-trending, fracture-controlled dissolution troughs. Isopach and structure-contour maps of the sulfur-bearing zone show no regional trends in orebody geometry but delineate areas of sulfur concentration. Orebodies in the Fort Stockton sulfur district occur along a northwest-oriented anticline that locally affects bedding of Guadalupian and Ochoan evaporitic formations on the southern Central Basin platform. Associated faults represent relatively poorly explored areas of high sulfur potential.

Areas of high, moderate, and low sulfur potential are defined by (1) the degree of geologic favorability, (2) the existence of past and/or present production, and (3) the presence of reserves or known resources. Regional variability of sulfur potential is based on individual favorability criteria, such as depth (shallowest sulfur occurrence), thickness (thickest sulfur-bearing zones), and concentration (densest surficial fractures) limits. Areas of greatest overlap of these criteria define regions of highest sulfur potential.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.