In February 2024, enCore Energy Corp. entered a joint venture with Boss Energy, Ltd. to develop and advance the Project. enCore retains ownership of 70% of the project and Boss Energy holds 30%.
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Summary:
The Mestena Grande Project lies within the southern part of the South Texas Uranium Province.
In Jim Hogg County and across the Project area, the Eocene Jackson Group, the Miocene Catahoula and Frio Formations, the Pliocene Goliad Formation and Quaternary windblown deposits outcrop at the surface. In most of the county these units subcrop beneath a blanket of Holocene sediments brought inland by easterly and southeasterly winds. The Miocene age Oakville Formation and Lagarto Clays do not outcrop in this area.
The deposits are roll-fronts, typical to others found in the South Texas Uranium Province. The ore bodies are isolated within several sand units, which occur within the middle portion of the Goliad Formation.
Genesis of the ore deposits are related to the presence of chemical reductants trapped in the various host formations (Goliad, Oakville, and Catahoula).
The Alta Mesa Dome is a deep-seated, non-piercement shale diapir structure associated with the Vicksburg Flexure. Deformation of the subsurface strata is considerable at depth but at the Goliad level, maximum uplift is on the order of only 100 to 125 feet. The location of the ore deposit closely coincides with the top of the dome at the Goliad stratigraphic level. Domal uplift is believed to have been active but subdued during deposition of the Goliad Formation. The rate of uplift was insufficient to divert fluvial deposition but did limit its extent.
As a result, strata thin over the dome and thicken off the dome. Clay interbeds are more abundant and more continuous over the dome. At the Goliad stratigraphic level, symmetry of the dome is broken on the western and northwestern flanks by a pair of subparallel, normal faults. These appear to be zones of structural failure associated with sporadic reactivation of domal uplift. The throw of these faults is opposite to each other, creating an intervening graben structure. Surface expression of faulting did not occur until after the ore mineralization phase.
Mineralization
Uranium mineralization occurs primarily as uraninite with some coffinite and like other deposits within the South Texas Uranium Province, is stratabound in clay-bounded sandstone packages. Mineralization occurs as roll front type deposits with “C” shaped configurations in cross section and elongated sinuous ribbons in plan-view. Deposits are diagenetic and/or epigenetic forming because of a geochemical process whereby oxidized surface water leaches uranium from source rocks (Finch, 1996). Source rocks of the south Texas deposits are generally agreed to be Miocene and Oligocene age volcanic ash from west Texas and/or Mexico (Galloway et al, 1977 and Aguirre-Diaz and Renne, 2008).
The deposits at Mesteña Grande are characterized by vertically stacked roll-fronts controlled by stratigraphic heterogeneity, host lithology, permeability, reductant type and concentration, and groundwater geochemistry. Individual known roll-fronts are a few tens of feet wide, 2 to 10 feet thick, and often thousands of feet long. Collectively, roll-fronts are inferred to result in an overall deposit that is up to a few hundred feet wide, 50 to 75 feet thick and continuous for miles in length.
Depth of known mineralization occurs at various depths, from 400 to over 1,200 feet.