Summary:
The Project’s uranium-vanadium deposits in the Jurassic Salt Wash Member of the Morrison Formation are sandstone-type deposits that fit into the U.S. Department of Energy’s (DOE) classification as defined by Austin and D’Andrea (Mickle and Mathews, 1978) Class 240-sandstone; Subclass 244-nonchannelcontrolled peneconcordant. Any future deep drilling to explore for deposits in the Triassic basal Chinle Formation (Moss Back Member) would fit the DOE classification as Class 240-sandstone; Subclass 243- channel-controlled peneconcordant. These classes are very similar to those of Dahlkamp (1993) Type 4- sandstone; Subtype 4.1-tabular/peneconcordant; Class 4.1.2 (a) Vanadium—Uranium (Salt Wash type) and Class 4.1.3-basal-channel (Chinle type).
The La Sal Trend uranium-vanadium deposits are a similar type to those elsewhere in the Uravan Mineral Belt. The Uravan Mineral Belt was defined by Fisher and Hilpert (1952) as a curved, elongated area in southwestern Colorado where the uranium-vanadium deposits in the Salt Wash Member of the Morrison Formation generally have closer spacing, larger size, and higher grade than those in adjacent areas and the region as a whole. The location and shape of mineralized deposits are largely controlled by the permeability of the host sandstone. Most mineralization is in trends where Top Rim sandstones are thick, usually 40 ft or greater.
The La Sal Trend is a large channel of Top Rim sandstone that trends due east, possibly as a major trunk channel to tributaries that fanned-out to the east to make a portion of the Uravan Mineral Belt. The Energy Queen deposit appears to be at the location of the junction of a tributary channel that joins the main channel from the southwest. The Rattlesnake open pit is located upstream of this tributary channel (U.S. Atomic Energy Commission, 1959). The deposit in Section 36 (ML-49313) is in the western extension of the main channel. The channel remains relatively straight, and the uranium deposits get larger as it continues eastward through the Redd Block IV and Beaver Shaft deposits. East of the Beaver Shaft, the channel appears to widen and contain large meanders as it continues through the Mike claims of the La Sal Decline and the Snowball and Pandora Mines to the east.
Most of the La Sal Trend and the Uravan Mineral Belt consist of oxidized sediments of the Morrison Formation, exhibiting red, hematite-rich rocks. Individual deposits are localized in areas of reduced, gray sandstone and gray or green mudstone (Thamm et al., 1981). The Morrison sediments accumulated as oxidized detritus in a fluvial environment; however, there were isolated environments where reduced conditions existed, such as oxbow lakes and carbon-rich point bars. During early burial and diagenesis, the through-flowing ground water within the large, saturated pile of Salt Wash and Brushy Basin material remained oxidized, thereby transporting uranium in solution. When the uranium-rich waters encountered the zones of trapped reduced water, the uranium precipitated. Vanadium may have been leached from the iron-titanium mineral grains and subsequently deposited along with, or prior to uranium.
The habits of the deposits in the La Sal Trend have been reported to be typical of the Uravan Mineral Belt deposits. Where the sandstone has thin, flat beds, the mineralization is usually tabular. In massive sections, it “rolls” across the bedding, reflecting the mixing interface of the two waters. This accounts for several horizons within the Top Rim that are mineralized. Very thin clay layers on cross-beds appear to have retarded ground water flow, which enhanced uranium precipitation. The beds immediately above mineralized horizons sometimes contain abundant carbonized plant material and green or gray clay galls. The mudstone beds adjacent to mineralized sandstone are reduced but can grade to oxidized within a few feet. Lithology logs by Union Carbide of core from historical drilling along the La Sal Trend record these same characteristics, as do interpretations of electric bore hole logs and logging of cuttings in rotary drill holes by Denison and EFR geologists. There are no significant differences between mineral depositional habits in the Top Rim and those in lower Salt Wash sands. EFR drilling (2007 to 2008) near the Energy Queen Mine indicated mineralization occurring at the tops of carbonaceous trash zones in drill holes EQ07-1, EQ-07-16, and EQ-08-18.
Mineralization
The uranium and vanadium bearing minerals tend to occur as fine-grained coatings on the detrital sand grains. Minerals fill the pore spaces between the sand grains, and they replace some carbonaceous material and detrital quartz and feldspar grains.
The primary uranium mineral is uraninite (pitchblende – UO2) with minor amounts of coffinite (USiO4OH). Montroseite (VOOH) is the primary vanadium mineral, along with vanadium clays and hydromica. Traces of metallic sulfides occur. In outcrops and shallow oxidized areas of older mines in the surrounding areas, the minerals now exposed are the calcium and potassium uranyl vanadates, tyuyamunite, and carnotite. The remnant deposits in the ribs and pillars of older workings show a variety of oxidized minerals common along the La Sal Trend. These brightly colored minerals result from the moist-air oxidation of the primary minerals. Minerals from several oxidation stages can be seen, including corvusite, rauvite, and pascoite. Undoubtedly, the excess vanadium forms other vanadium oxides depending on the availability of other cations and the pH of the oxidizing environment (Weeks et al., 1959). The Energy Queen Mine has been full of standing water since 1990, so no direct observations have been made of the mine’s workings by the SLR QP.
Some stoping areas in the mine workings are well over 1,000 ft long and several hundred feet wide. Individual mineralized beds vary in thickness from several inches to over six feet. There are three horizons in the Top Rim of the Salt Wash that host mineralization in the La Sal Trend, which are 25 ft to 40 ft apart.