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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 65 (1981)

Issue: 5. (May)

First Page: 916

Last Page: 916

Title: Mineralogy and Petrology of Texaco's Hobson Uranium Deposit, Karnes County, Texas: ABSTRACT

Author(s): Harry M. Dahl, Harold A. Palmer, Christie A. Callender

Article Type: Meeting abstract


Texaco's Hobson uranium deposit is located in Karnes County, Texas, along the prominent south Texas uranium trend. The uranium mineralization occurs in the Deweesville Sandstone of the Whitsett Formation of the Eocene Jackson Group. The host rock is a friable, fine-grained, well-sorted, highly porous and permeable sand interpreted to be a beach deposit. The sand contains significant volcanic constituents and ranges in composition from arkosic to tuffaceous. Locally, the host sand contains hard, dense opal-cemented sandstone beds. Bentonitic shales underlie and overlie the mineralized sand unit.

Geometrically, the Hobson uranium-bearing zone resembles an elongated roll-front type deposit. Chemical uranium values compared with gamma ray equivalent uranium values indicate that the uranium has been dissolved from the updip side and precipitated on the downdip side of the roll-front.

Details of the uranium mineralization were studied using thin section microscopy, autoradiography, X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy techniques. The uranium mineralization occurs in the pores of the sand, as sand-grain coatings and as replacements of sand-size and smaller grains. The uranium mineralization is commonly associated with pyrite and other opaque grains. Favored hosts for uranium, other than pore openings, appear to be clay aggregates, altered rock and glass fragments, and carbonaceous plant debris. Aggregates of coffinite were identified by XRD and SEM-EDS analyses. Some uranium mineralization also appears to be dispersed, and is postulated to be absorbed on the clay and carbonaceous matter.

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