Summary:
The Cebolleta deposits are classified as sandstone-hosted uranium deposits. The Project area lies on the eastern end of the prolific, northwest-southeast oriented Grants Mineral Belt.
Significant Mineralized Zones
The uranium mineralization at the Cebolleta Project is primarily hosted within the Jackpile Sandstone Member of the Upper Jurassic Morrison Formation. The mineralization is stratabound and tabular in nature, typically occurring in the lower half of the Jackpile unit. It is concentrated within medium- to coarse-grained fluvial sandstones that are rich in humate, carbonaceous material, and other reductants. The mineralized zones have been intercepted at depths ranging from approximately 200 feet in the shallowest parts of the deposit, such as St. Anthony, to over 700 feet in the deeper down-dip zones like Areas II and III. The thickness of the mineralized intervals typically ranges from 6 to 12 feet, although local zones are thicker and can exhibit grades exceeding 0.20% eU3O8.
The primary mineralized areas at the Project include the Sohio Area (comprising Areas I through V), the St. Anthony Mine Complex (North and South pits), and the Willie P Zone. The Sohio Area hosts the deepest and most extensive mineralized bodies, often ranging from 400 to 700 feet in depth. These deposits are interpreted to follow channelized sand bodies and are laterally extensive. The St. Anthony area, which includes both open pit and underground workings, is among the shallowest zones, with mineralization encountered around 200 feet below surface. The Willie P Zone is located southeast of St. Anthony and contains deeper underground resources, with mineralized intercepts commonly in the range of 500 to 600 feet in depth. Mineralization across these zones is consistent with typical Colorado Plateau Uranium Province sandstone-hosted deposits, and recent confirmation drilling has validated both the grade and continuity of historical mineralized zones.
These deposits are part of a broad and extensive area of uranium mineralization, including the Jackpile-Paguate deposit located 0.6 mi (one kilometre) south of the Project property, which was one of the largest concentrations of uranium mineralization in the United States (Moran and Daviess 2014). The Sohio occurrence area, formerly known as L-Bar, contains five distinct deposits, including Areas I, II, III, IV, and V. The historical JJ#1 Mine is situated in the northwest corner of the Area II and Area V deposit areas. The entrance to the JJ#1 Mine lies 50 m to the west of the Project boundary; however, most of the underground workings fall within the Project boundary. The Area I deposit, located in the southern part of the Sohio complex, extends south into the St. Anthony area adjacent to the St. Anthony open pits and the Willie P. underground mine (McLemore and Chenoweth 1991; McLemore 2000).
The common geological characteristics of the uranium deposits at Cebolleta are summarized from Carter (2008; 2011) and Moran and Daviess (2014), as follows:
• The majority of the potentially economic significant uranium mineralization is hosted by the Jackpile Sandstone, although minor amounts of mineralization is hosted in sandstones of the Brushy Basin Member of the Morrison Formation and the Dakota Sandstone in the St. Anthony area;
• Most of the mineralization is hosted in medium to coarse-grained sandstones that exhibit a high degree of large-scale tabular cross-stratification (Baird et al. 1980);
• Near the margins of the deposits the mineralization thins appreciably, although halos of low grade mineralization surround the deposits;
• Higher grade mineralization usually occurs in the centers of the mineralized zones;
• Strong mineralization appears to be concentrated in the lower half portions of the Jackpile Sandstone, although anomalous concentrations of uranium are present throughout the vertical extent of the unit (Jacobsen 1980);
• Most of the mineralization appears to be "reduced" with only isolated small pods, especially in the St. Anthony underground area, of discontinuous mineralization exhibiting oxidation (Baird et al. 1980). Mineralization in the St. Anthony South pit appears to be a "remnant" deposit, which has been partially depleted of uranium that was redeposited in the nearby (down-dip) North pit;
• Extensive chemical and radiometric analyses on core holes by Sohio demonstrated that the mineralization is generally within equilibrium (Geo-Management 1972; Olsen and Kopp 1982, Moran and Daviess 2014).
• Individual deposits do not show an overall preferred orientation or trend, and do not fully reflect the orientation of the main Jackpile Sandstone channel trend. Previous resource modeling efforts have demonstrated a north-northwest to south-southeast trending orientation to the better grade-thickness product (GT) mineralization;
• Nearly all of the deposits show some spatial relationship with carbonaceous material, although the mineralized zones exposed in the highwalls of the two open pits do not exhibit such a relationship;
• The deposits range in depth from approximately 200 ft (61 m) in the St. Anthony area, to nearly 700 ft (213 m) in the vicinity of the Area II and Area III deposits in the central and northern (down-dip) parts of the Project area;
• Grades greater than 0.10% eU3O8 are commonly seen in the sections, with numerous intercepts of 0.20% eU3O8 or better. This mineralization with thicknesses of several feet to tens of feet (six feet to 12 ft (1.8 m to 3.7 m)) occur throughout the Jackpile Sandstone unit which is 80 ft to 100 ft (24 m to 30.5 m) thick in the Cebolleta area;
• The upper and lower boundaries of these mineralized bodies are generally abrupt. Individual deposits are observed to develop into clusters. Locally, these clusters may be related to the coalescence of separate channel sandstone bodies. In this instance, mineralization is often thicker and higher grade than adjoining areas;
• Robertson and Associates (1978) reported that the uranium minerals at Cebolleta include Coffinite [U(SiO4)-x(OH4x)], Uraninite [UO2], organo-uranium complexes, and unidentified oxidized uranium complexes.
Controls on Mineralization
The key controls of uranium mineralization at Cebolleta are: (1) primary sedimentary structures including channel fills, bars, and crossbedding in the Jackpile Sandstone, and (2) the concentration of carbonaceous material to precipitate uranium (Jacobsen 1980; Baird et al. 1980). Carbonaceous material, including humate and/or carbonaceous plant debris, serve as reductants to precipitate uranium from circulating groundwater. The distribution of carbonaceous material tends to be localized as observed in the former JJ#1 Mine and in the pit walls of the two St. Anthony open pits. Jacobsen (1980) reports that there are no significant accumulations of uranium without carbonaceous material, however, this relationship is not well developed in low grade mineralized areas (0.03% to 0.06% U3O8) (Moran and Daviess 2014).
In the Willie P Mine, medium to coarse grained sandstones that exhibit large-scale tabular crossbedding is associated with substantial zones of uranium mineralization (Baird et al. 1980). This relationship between sedimentary features and uranium mineralization is also evident in the St. Anthony pit. In the St. Anthony area, there is an apparent northwest trend of the mineralization that may have resulted from the erosional retreat of the Jackpile Sandstone outcrop as well as the subsequent oxidation and redistribution of uranium mineralization closer to the outcrop (Baird et al. 1980; Jacobsen 1980).