Geologic Occurrence and Regional Assessment of Evaporite-Hosted Native Sulfur, Trans-Pecos Texas

RI0184. Geologic Occurrence and Regional Assessment of Evaporite-Hosted Native Sulfur, Trans-Pecos Texas, by T. F. Hentz, J. G. Price, and G. N. Gutierrez. 70 p., 51 figs., 7 tables, 1 plate, 1989. ISSN: 0082335X: Print.


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ABSTRACT
In the western Delaware Basin and southern Central Basin Platform of Trans-Pecos Texas, Upper Permian (Ochoan) evaporite strata host locally voluminous but notoriously unpredictable, sporadic deposits of biogenic native sulfur. The two sulfur-bearing regions, the Rustler Springs (Culberson and Reeves Counties) and Fort Stockton (Pecos County) sulfur districts, encompass about 2,000 State-owned tracts that are widely distributed throughout the two districts. This study was initiated to provide the General Land Office of Texas (GLO) with a regional assessment of sulfur potential of the Trans-Pecos, thus enabling more effective land management. Specific goals were to (1) investigate the presumed geologic controls on sulfur occurrence by detailing the structural and stratigraphic context of sulfur within the sulfur districts, (2) provide details about biogenic sulfur formation, Ochoan evaporite lithology, radiation log expression, and geology of prominent mines---subjects either discussed in diverse sources or in industry sources not readily accessible to the public, (3) construct a computerized data base documenting formation tops and sulfur-bearing zones, and (4) provide a tract-by-tract sulfur assessment of State-owned lands.

Approximately 1,450 well logs from GLO files were the primary source of subsurface data. Stratigraphic correlation of Ochoan evaporites in the Rustler Springs sulfur district indicates that component formations (Castile, Salado, and Rustler) dip gently eastward toward the center of the Delaware Basin. However, strata are locally disrupted in the central and eastern parts of the district by small, uniformly northeast-trending graben systems and high-angle normal faults that probably formed during late-phase Basin and Range extension. Mineralization in two of the largest sulfur deposits in the district, the Pennzoil Culberson mine and the Texasgulf Phillips Ranch deposit, is restricted to dissolution-enhanced fault zones within the downfaulted blocks. Underexplored grabens detected on regional cross sections and structure-contour maps potentially contain commercial sulfur deposits. Photogeologic inspection of the Gypsum Plain in the western part of the Rustler Springs sulfur district reveals (1) a concentration of exposed northeast-trending grabens and normal faults representative of the subsurface structures and (2) east-trending, fracture-controlled dissolution troughs that are locally associated with commercial sulfur deposits. Computer-contoured isopach and structure maps of the districtwide sulfur-bearing zone reveal no distinct regional trends in orebody geometry but are invaluable in delineating areas of sulfur concentration.

In contrast, isopach and structure-contour maps of the Fort Stockton sulfur district define a trend of sulfur concentration in aligned culminations along the axis of a northwest-oriented anticline that locally affects bedding of Guadalupian and Ochoan evaporitic formations (Seven Rivers, Yates, Tansill, Salado, and Rustler) at the southern end of the Central Basin Platform. Associated faults, especially along the southwestern edge of the anticline, have high sulfur potential but have been poorly explored.

Summary maps of the two sulfur districts identify areas where significant sulfur potential exists, as determined by depth (shallowest sulfur occurrence), thickness (thickest sulfur-bearing zones), and concentration (densest surficial fractures and lineaments) limits. Areas where these criteria overlap define regions of highest sulfur potential.

Keywords: Central Basin Platform, Delaware Basin, evaporites, Fort Stockton sulfur district, Ochoan, resource assessment, Rustler Springs sulfur district, sulfur, Trans-Pecos Texas

CONTENTS

Abstract

Introduction

Objectives

Methods of Analysis

Subsurface Methods

Surficial Methods

Computerized Methods

Geophysical Methods

History of Sulfur Exploration

Mode of Sulfur Mineralization

Biochemical Conditions of Mineralization

Physical Conditions of Mineralization

Secondary Calcite

Geology of Sulfur-Bearing Strata of the Delaware Basin and Central Basin Platform

Geologic Setting

Stratigraphy of Ochoan Rocks

Rustler Springs Sulfur District

Castile Formation

Salado Formation

Rustler Formation

Dewey Lake Redbeds

Cox Sandstone and Undifferentiated Surficial Deposits

Fort Stockton Sulfur District

Seven Rivers Formation

Yates Formation

Tansill Formation

Salado Formation

Rustler Formation

Dewey Lake Redbeds

Undifferentiated Surficial Deposits

Structure of Ochoan Rocks

Regional Structure

Rustler Springs Sulfur District

Faults

Geometry

Dissolution Features

Solution-Subsidence Troughs and Depressions

Dissolution and Collapse Breccias

Breccia Pipes

Fort Stockton Sulfur District

Flexure Faults

Geologic Occurrence of Sulfur

Structure of Orebodies

Near-Surface Deposits

Local Geology of Mines

Culberson Mine

Phillips Ranch Deposit

Pokorny Deposit

Fort Stockton Mine

Regional Geometry of Sulfur Occurrences

Rustler Springs Sulfur District

Fort Stockton Sulfur District

Ore Fabrics

Assessment of Sulfur Potential

Definition of Geologically Favorable Areas

Segregation of Areas with High, Moderate, and Low Potential

Construction of Data Base

Summary

Acknowledgments

References

Figures

1. Location map of Rustler Springs and Fort Stockton sulfur districts, Trans-Pecos Texas

2. Distribution of sulfur-exploration drilling activity on State-owned tracts in the Rustler Springs sulfur district, 1967 to 1970

3. Distribution of sulfur-exploration drilling activity on State-owned tracts in the Fort Stockton sulfur district, 1967 to 1970

4. Cross-section lines superimposed on structure-contour map of top of the Bell Canyon Formation, Rustler Springs sulfur district

5. Cross-section lines superimposed on structure-contour map of top of the Rustler Formation, Fort Stockton sulfur district

6. Location of sulfur districts in relation to structural subdivisions of the Permian Basin of West Texas and southeastern New Mexico

7. Upper Permian stratigraphy in the Rustler Springs (Delaware Basin) and Fort Stockton (Central Basin Platform) sulfur districts

8. Geologic map of the Rustler Springs sulfur district and vicinity

9. Regional dip-oriented cross section A-A' of the northern area of well coverage, Rustler Springs sulfur district

10. Regional dip-oriented cross section B-B' of the central area of well coverage, Rustler Springs sulfur district

11. Regional dip-oriented cross section C-C' of the southern area of well coverage, Rustler Springs sulfur district

12. Regional strike-oriented cross section 1-1' of the central area of well coverage, Rustler Springs sulfur district

13. Subsurface limits of halite marker beds within the Castile and Salado

14. Representative radiation log and lithology of the Castile Formation, Rustler Springs sulfur district

15. Representative radiation log and lithology of the Salado and Rustler Formations and part of the Castile and Dewey Lake Formations, Rustler Springs sulfur district

16. Regional strike-oriented cross section 2-2' of the eastern area of well coverage, Rustler Springs sulfur district

17. Regional strike-oriented cross section 3-3' of the western area of well coverage, Rustler Springs sulfur district

18. Regional cross section A-A' coinciding approximately with the anticlinal axis of the western part of the Fort Stockton High, Fort Stockton sulfur district

19. Regional cross section B-B' oriented perpendicular to the anticlinal axis in the northwestern Fort Stockton sulfur district

20. Regional cross section C-C' oriented perpendicular to the anticlinal axis in the southeastern Fort Stockton sulfur district

21. Representative radiation log and lithology of the Yates, Tansill, Salado, and Rustler Formations and part of the Seven Rivers and Dewey Lake Formations, southeastern Fort Stockton sulfur district

22. Representative radiation log and lithology of a sandstone-rich Yates Formation characteristic of the northwestern Fort Stockton sulfur district

23. Regional cross section D-D' oriented perpendicular to the anticlinal axis in the central Fort Stockton sulfur district

24. Photomosaic of western edge of Gypsum Plain illustrating grabens and high-angle normal faults in outcrops of the uppermost Bell Canyon and lowermost Castile Formations

25. Structure-contour map of top of the Bell Canyon Formation. Rustler Springs sulfur district

26. Structure-contour map of top of the Castile Formation, Rustler Springs sulfur district

27. Structure-contour map of top of the Salado Formation, Rustler Springs sulfur district

28. Permian and pre-Permian oil fields of northeastern Culberson and northwestern Reeves Counties

29. Photomosaic of east-trending solution-subsidence troughs, the dominant linear geomorphic features of the western and central Gypsum Plain

30. Circular dissolution sinks containing vertically localized breccia cores in outcrops of the Rustler Formation

31. Structure-contour map of top of the Salado Formation, Fort Stockton sulfur district

32. Structure-contour map of top of the Rustler Formation, Fort Stockton sulfur district

33. Permian and pre-Permian oil fields of northern Pecos County

34. Areal perspective of sulfur mineralization within the Culberson mine

35. Cross section of the Pennzoil Culberson mine oriented perpendicular to the axis of the sulfur-bearing graben

36. Oblique cross section through the sulfur-bearing graben of the Phillips Ranch deposit

37. Cross sections of the Texasgulf Fort Stockton sulfur mine

38. Contour map of the shallowest occurrences of sulfur within each 1-mi² section of the Rustler Springs sulfur district

39. Contour map of the deepest occurrences of sulfur within each 1-mi² section of the Rustler Springs sulfur district

40. lsopach map of net thickness of sulfur, Rustler Springs sulfur district

41. lsopach map of gross thickness of sulfur, Rustler Springs sulfur district

42. lsopach map of net thickness of high-grade (greater than 5 percent) sulfur, Rustler Springs sulfur district

43. lsopach map of gross thickness of high-grade (greater than 5 percent) sulfur, Rustler Springs sulfur district

44. Contour map of shallowest occurrences of sulfur within each 1-mi² section of the Fort Stockton sulfur district

45. Contour map of deepest occurrences of sulfur within each 1-mi² section of the Fort Stockton sulfur district

46. lsopach map of net thickness of sulfur, Fort Stockton sulfur district

47. lsopach map of gross thickness of sulfur, Fort Stockton sulfur district

48. Maps of Rustler Springs sulfur district illustrating areas of sulfur favorability

49. Maps of Fort Stockton sulfur district illustrating areas of sulfur favorability

50. Final assessment map of Rustler Springs sulfur district showing where areas of favorability overlap

51. Final assessment map of Fort Stockton sulfur district showing where areas of favorability overlap

Tables

1. Survey of mineral commodities in Trans-Pecos sulfur districts

2. Data provided for each sulfur exploration well from the sulfur districts

3. Values used to construct computer-generated contour maps

4. Classification of native sulfur

5. Subsurface stratigraphy of the Rustler Formation in the Rustler Springs sulfur district

6. Depth and thickness limits used to delineate most geologically favorable areas of sulfur mineralization in the sulfur districts

7. Numerical scale used to evaluate State-owned tracts for sulfur and other geologic commodities

Plate (in inside back pocket of book)

Fractures and lineaments, Rustler Springs sulfur district


Citation
Hentz, T, F., Price, J. G., and Gutierrez, G. N., 1989, Geologic Occurrence and Regional Assessment of Evaporite-Hosted Native Sulfur, Trans-Pecos Texas: The University of Texas at Austin, Bureau of Economic Geology, Report of Investigations No. 184, 70 p.