Depositional Framework, Hydrostratigraphy, and Uranium Mineralization of the Oakville Sandstone (Miocene), Texas Coastal

RI0113. Depositional Framework, Hydrostratigraphy, and Uranium Mineralization of the Oakville Sandstone (Miocene), Texas Coastal Plain, by W. E. Galloway, C. D. Henry, and G. E. Smith. 51 p., 34 figs., 9 tables, 1982. ISSN: 0082-335X: Print.


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ABSTRACT
The Oakville Sandstone (Miocene) of the Texas Coastal Plain comprises a major sand-rich fluvial system composed of deposits of several major and minor rivers that originated within Texas and surrounding states. Broad bed-load fluvial axes, including the Hebbronville, George West, and New Davy trends, lie south of the San Marcos Arch and host significant reserves of uranium. To the north, the Moulton streamplain consists of deposits of numerous small, flashy to ephemeral streams that drained the inland margin of the Coastal Plain. The Burton/Penn mixed-load fluvial axes traverse the Coastal Plain in the area of the modern Colorado and Brazos Rivers.

Each fluvial axis consists of diagnostic facies deposited in channel, crevasse splay, and floodplain environments. Sand percentage, sand-body dimensions and lateral relationships, and vary systematically among the axes. Overall transmissivity of the Oakville Formation, which closely corresponds to the Jasper aquifer system in conventional hydrostratigraphic terminology, correlates directly with mapped facies composition and trend. Uranium deposit size relates directly to associated aquifer transmissivity.

Commercial uranium deposits lie within channel and interbedded sheet-splay sands in or along the margin of major fluvial belts, typically near shallow faults. Mineralization occurs along narrow, elongate fronts separating altered, but commonly resulfidized, host sand from epigenetically sulfidized reduced sand. Deposits show pronounced spatial zoning of trace metals and iron sulfide, carbonate, and locally, clay mineral phases across the mineralization front.

Keywords: deposition, hydrostratigraphy, uranium, mineralization, Oakville Formation, Miocene, Coastal Plain, Texas, Hebbronville, George West, New Davy, San Marcos Arch, Moulton streamplain, Texas


CONTENTS

Abstract

Introduction

Objectives and methodologies

The Gulf Coast artesian basin

Depositional framework of the Oakville aquifer

OAKVILLE DEPOSITIONAL SYSTEM

Hebbronville and George West fluvial axes

Conglomeratic bed-load channel-fill facies

Sandy bed-load channel-fill facies

Sheet-splay facies

Facies associations and distribution

New Davy fluvial axis

Conglomeratic bed-load channel- fill facies

Mixed-load channel-fill facies

Crevasse splay and sheet-splay facies

Facies associations and distribution

Moulton streamplain

Channel-fill facies

Sheet-splay and crevasse splay facies

Facies associations and distribution

Burton/Penn fluvial axes

Sinuous channel-fill facies

Crevasse splay and sheet-splay facies

Facies associations and distribution

Floodplain facies

Facies summary

MINERALOGIC COMPOSITION

Mudrock petrofacies

Sand petrofacies

SUMMARY OF GENETIC STRATIGRAPHY

Structural framework

FAULT DISTRIBUTION

IMPACTS ON HYDROGEOLOGY

Hydrostratigraphy

HYDROGEOLOGIC UNITS

AQUIFER TRANSMISSIVITY

Geology and geochemistry of Oakville uranium deposits

RAY POINT DISTRICT

Geochemical and mineralogical zonation

Ore paragenesis

GEORGE WEST DISTRICT

Geochemical and mineralogical

Ore paragenesis

Conclusions

Acknowledgments

References

Appendix A

Appendix B

Figures

1. Index map showing location of the study area, outcrop of the Oakville Sandstone, sample localities, and distribution of cross sections

2. Regional structural features of the Tertiary Gulf Coastal Plain and Edwards Plateau

3. Generalized offlapping stratigraphic sequence of the Texas Coastal Plain

4. Stratigraphic relationships of the Oakville Sandstone, Live Oak County

5. Net-sand isolith map of the Oakville Sandstone

6. Sand-percentage map of the Oakville Sandstone

7. Regional updip strike section illustrating facies of the Oakville fluvial system

8. Depositional elements of the Oakville fluvial system

9. Facies architecture of a composite sand belt of the George West fluvial axis

10. Line tracing showing a channel fill of the Ray Point fluvial axis

11. Line tracing illustrating structures and textures characteristic of the George West bed-load channel facies

12. Variation of the sandy bed-load channel-fill facies consisting of interstratified sand and mud-clast conglomerate

13. Schematic reconstruction of Oakville fluvialdepositional environments

14. Sheet-splay deposits of the George West axis exposed in the Smith uranium mine

15. Schematic facies architecture of a typical New Davy axis sand belt

16. Schematic facies architecture of a sand belt within the Moulton streamplain

17. Road cur displaying lateral accretion of a mixed-load channel of the Burton/Penn axes

18. Schematic facies architecture of a typical Burton/Penn axes sand belt

19. Compositional summary of Oakville sands

20. A. Euhedral sparry calcite porefill cement. B. Silica cement

21. Summary of genetic components and geometric and compositional characteristics of aquifer units within the Oakville depositional elements

22. Generalized distribution of faults and diapiric intrusions within or below the Oakville Sandstone

23. Stratigraphic dip sections comparing lithostratigraphic and hydrostratigraphic units

24. Geohydrologic data base used for pump test permeability data

25. Calculated permeabilities for major permeable facies belts

26. Regional transmissivity of the Oakville aquifer system

27. Schematic distribution of epigenetic zones within an oxidized aquifer

28. Geographic and geologic setting of the Ray Point district, Live Oak County

29. Cross section of the Oakville aquifer in the Ray Point district

30. Core transect of the Zamzow mineralization front

31. Paragenesis of the Zamzow mineralization front and associated geochemical zones

32. Cross section through the George West district

33. Geographic and geologic setting of the George West district, Live Oak County

34. Paragenesis of mineralization and associated zones along the southern alteration front, George West district

Tables

1. Clay mineralogyof representative fine-grained Oakville samples

2. Geochemical barriers capable of concentrating uranium and associated metals in ground-water flow systems

3. Summary of Oakville uranium-producing districts and areas

4. Compositional summary of Zamzow core cross section sample suite

5. Carbon isotope composition of selected Oakville samples

6. Compositional summary of George West district core sample suite

B-1. Analytical data for core samples, Zamzow mine site

B-2. Analytical data for core samples, George West deposit A

B-3. Analytical data for core samples, George West deposit B


Citation
Galloway, W. E., Henry, C. D., and Smith, G. E., 1982, Depositional Framework, Hydrostratigraphy, and Uranium Mineralization of the Oakville Sandstone (Miocene), Texas Coastal Plain: The University of Texas at Austin, Bureau of Economic Geology, Report of Investigations No. 113, 51 p.