South Texas Coastal Plain - Panna Maria, Lamprecht, Felder, Benavides, Kingsville, Vasquez

Texas, USA

Main commodities: U
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More than 100 roll front style uranium occurrences, prospects and significant exploited deposits are distributed over an arcuate, north-south to north-east trending, 450 x 20 to 35 km belt on the coastal plain of southern Texas, USA, approximately 150 km inland from and parallel to the Gulf of Mexico coast. The southern limit of the belt is the Mexican border. Significant operations include the Conquista, Burns, O'Hern and Ray Point in situ leach operation, and the Panna Maria, Lamprecht - Hahn - Zamzaw - Felder - McLean, Kingsville Dome, Vasquez, Alta Mesa, La Palangana  and Benavides mines.

The Laramide Orogeny that produced mountain building in western North America, also uplifted the central, south-western and western border regions of Texas leading to the end of marine deposition. At the boundary between the uplifting plateau and the subsiding Gulf Coast area, a series of normal (extensional) faults formed. Large, south-east flowing rivers draining the Rocky Mountains to the west buried the older marine deposits on the Gulf of Mexico coast producing major deltas which prograded the early Cenozoic coastline more than 150 km seaward into the gulf. Among the effects of this major increase in sediment volume moving into the Gulf of Mexico was renewed upward migration of thick Mesozoic marine salt and the formation of salt domes in the coastal plain in South Texas. In addition, rapid deposition of deltaic sands over older marine muds resulted in a mechanically unstable sediment column, leading to displacement of the sediments by growth faults. Linear zones of these growth faults of various ages extend from north-eastern Mexico through Texas into Louisiana and produced traps for large oil and gas fields. At the boundary between this uplifting plateau and the subsiding Gulf Coast area, a series of normal (extensional) faults formed farther inland than did the extensive growth faults.

Eocene to Miocene (47 to 17 Ma) volcanic activity and accompanying regional deformation produced around fourteen volcanic calderas and associated thick lava and ash-flow tuff accumulations. The transition from the Laramide compressional regime to an extensional environment took place at about 30 Ma and led to the development of a series of elongate, north and north-west trending, fault-bounded basins separated by intervening highlands. During the middle to late Tertiary, large volumes of sand and gravel were transported from the west and accumulated in large alluvial fans deposited on older Palaeozoic and Mesozoic rocks. Vast amounts of fine-grained, wind-blown sediments were also deposited along with the alluvial material. Between 2 and 1 Ma, the fans in Texas were cut off from their Rocky Mountain source, and the eastern edge of the alluvial sheet began to retreat westward as rivers draining into the Gulf of Mexico caused headward erosion.

Uranium mineralisation is developed within fluvial-lacustrine coastal plain sediments, comprising gently south-east dipping tuffacous-sandstones and sandstones of the Whitsett Formation of the Eocene Jackson Group, Oligocene-Miocene Catahoula Tuff, Miocene Oakville Sandstone and the Miocene-Pliocene Goliad Sand.

The sandstones of the Whitsett Formation contain significant carbonised plant debris or lignite which has influenced the development and concentration of uranium ore, while those of the Catahoula Tuff and the Oakville Sandstone do not. North-west trending faults are typically close and parallel to elongate orebodies. Oil and gas fields in the region are also elongate in the same direction and controlled by the same fault system and are often found below the uranium accumulations. It has been interpreted that the deposits within the sediments without carbonised plan debris or lignite are the result of sour (H2S rich) natural gas leakage up the adjacent faults to produce an alternative reducing environment.

The host sandstones to uranium mineralisation is normally grey, reflecting their reduced character, with abundant pyrite and marcasite occurring down dip of the uranium mineralisation. Up-dip, limiting the mineralisation, the host sandstones are usually light reddish to yellow and oxidised.

Many of the deposits of the belt are small. An example of the larger accumulations is the combined Felder-Lamprecht deposit which is around 5 km long and sinuous in plan. Many of the orebodies occur as 'C' shaped rolls, with their concave side against oxidised host on the up-dip side. However, many deposits depart from the idealised mode, including:  i). irregularly shaped accumulations distributed at random along the oxidation front;  ii). 'C' shaped deposits entirely within reduced hosts;  iii). accumulations along the margins of fluvial channels entirely within reduced, pyritic clayey sand to sandy mud without a 'C' shaped roll form.

Un-weathered primary uranium occurs as coffinite and uraninite, but where oxidised is present as meta-autunite and meta-tyuyamunite.

The Panna Maria deposit is hosted by the Whitsett Formation, the upper-most unit of the Upper-Eocene Jackson Group. The Whitsett Formation is composed of alternating fine grained, commonly tuffaceous sandstone, tuffaceous sandstone and lignite deposited in beach, distributary-channel, deltaic and lagoonal environments. The immediate host, the Tordilla Sandstone Member is a strike-oriented coastal barrier bounded above by lagoonal lignitic beds and below by tuffaceous and clayey silt and sand of the non-marine Dubose Clay Member.  The main orebody is approximately 5 km long, trends at 60° (parallel to the regional strike of the hosts) and is buried 23 to 60 m below the surface. The host dips at around 1°SE. In cross-section the ore has a 'C' shaped roll form, concave on its up-dip side to the NW where the host has been altered to a light-orange to pale-red colour. The NE striking ore zone parallels the fault trends and the elongation of the nearby oil and gas fields from which various hydrocarbons, including sour gas have been produced.

The sinuous Felder - Lamprecht string of deposits in the Ray Point District are distributed over a length of around 5 km long and a width of up to 750 m and are hosted by fluvial channel fill sandstones the Miocene Oakville Sandstone in which organic carbon is essentially absent. All of the mineralisation is developed parallel to and within 1.5 km up-dip from the Oakville Fault, which in the south-western section of the deposit string has a normal displacement of 33 m. Studies indicate that migrating aqueous sulphide emanating from the fault has invaded and reduced the host sandstone intermittently since deposition of the sandstone.  The uranium mineralisation within these deposits is largely developed within the basal sandstone of the Oakville Formation, immediately overlying the Catahoula Formation claystone. The host sands were laid down as a point bar deposit and range from 12 to 23 m in thickness. Mineralisation is developed over a stratigraphic thickness of 4.6 m within the downthrown sandstone host, up-dip from the Oakville Fault and is found over a vertical interval of 27.4 m, with oxidation only evident in the upper 2.4 m, which represents the part of the deposit above the water table.   In areas studies, the highest concentration of ore occurs along the Oakville Fault, decreasing rapidly outwards to a more uniform, but lower grade.  In the mine area the Oakville Sandstone is a uniform textured, medium grained (1.3 mm), well sorted sand composed of detrital quartz, feldspar and rock fragments (dominantly silicic volcanics). Adjacent to the fault it is a calcite-cemented indurated rock, which when strongly mineralised is friable. The dominant uranium mineral is a botryoidal pitchblende occurring as a coating on detrital grains or replacing calcite.   The similar Benavides deposit, 170 km to the SW, is hosted by sandstones of the Oligocene-Miocene Catahoula Tuff, which also has no observable carbonised organic debris, but is developed adjacent to a fault zone.

Historic production from the South Texas Coastal Plain between 1954 and 1982 totalled 24 250 t of U
3O8 at an average grade of 0.12% U3O8 (Shawe, et al., 1991).

In 1984 uranium resources were estimated at 282 000 t U
3O8, of which 45 500 t were measured and 68 300 t were inferred resources.

Uranium production had stopped by 1999, but restarted in 2004. By 2006, three mines were active: Kingsville Dome in Kleberg County, the Vasquez mine in Duval County, and the Alta Mesa mine in Brooks County. An application was in train to commence mining at the La Palangana deposit in Duval County in 2008.

The most recent source geological information used to prepare this summary was dated: 2007.    
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.

  References & Additional Information
   Selected References:
Bomber B J, Ledger E B, Tieh T T  1986 - Ore petrography of a sedimentary Uranium deposit, Live Oak County, Texas: in    Econ. Geol.   v81 pp 131-142
Goldhaber M B, Reynolds R L, Rye R O  1983 - Role of fluid mixing and fault-related Sulfide in the origin of the Ray Point Uranium District, South Texas: in    Econ. Geol.   v78 pp 1043-1063
Ludwig K R, Goldhaber MB, Reynolds R L, Simmons K R  1982 - Uranium-lead isochron age and preliminary sulfur isotope systematics of the Felder uranium deposit, south Texas: in    Econ. Geol.   v77 pp 557-563
Reynolds R L, Goldhaber M B  1983 - Iron Disulfide minerals and the genesis of roll-type Uranium deposits: in    Econ. Geol.   v78 pp 105-120
Reynolds R L, Goldhaber M B, Carpenter D J  1982 - Biogenic and nonbiogenic ore-forming processes in the South Texas Uranium district: evidence from the Panna Maria deposit: in    Econ. Geol.   v77 pp 541-556

Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge.   It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published.   While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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