Summary:
The Deposits are classified as sandstone hosted - uranium deposits. Sandstone-type uranium deposits typically occur in fine to coarse grained sediments deposited in a continental fluvial environment. The uranium may be derived from a weathered rock containing anomalously high concentrations of uranium, leached from the sandstone itself or an adjacent stratigraphic unit. It is then transported in oxygenated water until it is precipitated from solution under reducing conditions at an oxidation-reduction interface. The reducing conditions may be caused by such reducing agents in the sandstone as carbonaceous material, sulphides, hydrocarbons, hydrogen sulphide, or brines.
Uranium mineralization on the Property is hosted by favorable sandstone horizons in the lowermost portion of the Salt Wash Member of the Jurassic age Morrison Formation, where detrital organic debris is present. Mineralization primarily consists of coffinite, with minor uraninite, which usually occurs in close association with vanadium mineralization. Mineralization occurs as intergranular disseminations, as well as coatings and/or cement on and between sand grains and organic debris. Vanadium occurs as montroseite (hydrous vanadium oxide) and vanadium chlorite in primary mineralized zones located below the water table (i.e., the northernmost portion of the Tony M deposit).
The vanadium content of the Henry Mountains Basin deposits is relatively low compared to many other Salt Wash hosted deposits on the Colorado Plateau. Furthermore, the Henry Mountains Basin deposits occur in broad alluvial sand accumulations, rather than in major sandstone channels as is typical of the Uravan Mineral Belt deposits of western Colorado. The Henry Mountains Basin deposits do, however, have the same general characteristic geochemistry of the Uravan deposits, and are therefore classified as Salt Wash type deposits.
The Deposits occur within an arcuate zone over a north-south length of approximately 15,000 ft and a width ranging from 1,000 ft to 3,000 ft. Mineralization occurs in a series of three individual stratiform layers included within a 30 ft to 62 ft thick sandstone interval. Mineralization in the Tony M deposit occurs over three stratigraphic zones of the lower Salt Wash Member of the Morrison Formation, with a minor mineralized zone in the underlying Tidwell Member included in the lower zone.
The Deposits occur in the lowermost 35ft to 62ft of the Salt Wash Member sandstone. Mineralization within the UL unit is offset to the east as compared to mineralization in the LL unit.
Mineralization comprising the mineralized interval of the Deposits has an average thickness of three feet to six feet, depending on assumptions regarding GT cut-off and dilution. Inspection of logs by SLR, as RPA, in 2012, indicated that the thickness of uranium mineralization in individual drill holes only occasionallyexceeds 12 ft.
At the Tony M mine, the main mineralized horizons appear as laterally discontinuous, horizontal bands of dark material separated vertically by lighter zones lacking uranium but enriched in vanadium. On a small scale (inches to feet), the dark material often exhibits lithologic control, following cross-bed laminae or closely associated with, though not concentrated directly within, pockets of detrital organic debris.
The uranium-vanadium mineralization of the Henry Mountains Basin area is similar to the mineralization observed elsewhere in other parts of the Colorado Plateau. It occurs as intragranular disseminations within the fluvial sand facies of the Salt Wash Member, and forms coatings on sand grains and coatings and impregnations of organic associated masses. A significant portion of the uranium occurs in a very fine grained phase whose mineralogy is best defined with the aid of an electron microscope.
Extensive research by Northrop and Goldhaber (1990) and associates indicates that the Henry Mountains Basin deposits were formed at the interface of an underlying brine with overlying oxygenated flowing groundwaters carrying uranium and vanadium in solution. Reduction and subsequent deposition of the mineralization were enhanced where the interface occurred within sandstones containing carbonaceous debris. The multiple mineralized horizons developed at favorable intervals as the brine surface migrated upwards. Geochemical studies indicate the uranium and vanadium were leached either from the Salt Wash sandstone or the overlying Brushy Basin Member. Northrop and Goldhaber (1990) also established that the relationship between the uranium and vanadium mineralization in the Tony M and nearby Frank M deposits was not a simple one. Vanadium enrichment in the mineralized intervals occurred over a thicker interval than uranium. Northrop and Goldhaber (1990) found that while uranium and vanadium often reached their maximum concentration at the top of each uranium-bearing horizon, the vertical distribution of vanadium was frequently distinct from uranium.
Vanadium occurs as montroseite (hydrous vanadium oxide (V, Fe)O(OH)) and vanadium chlorite in primary mineralized zones located below the water table (i.e., the northern portion of the Tony M deposit). Montroseite is the only vanadium oxide mineral identified in this interval. An unusual vanadium bearing chlorite or interlayered vanadium bearing chlorite-smectite is the only authigenic clay mineral(s) recognized. The grain size and sorting characteristics of detrital quartz grains vary within the host rocks, while cross-bed lamainae with coarser grains and better sorting are invariably more highly mineralized (Wanty et al., 1990).
Above the water table to the south, vanadium chlorite is absent, while montroseite and a suite of secondary uranium-vanadium minerals are present. These include tyuyamunite (Ca(UO2)2V2O85-8H2O), metatyuyamunite (Ca(UO2)2V2O83H2O), rauvite (Ca(UO2)2V+510O28-16H2O), and carnotite (K2(UO2)2V2O8-3H2O) all of which have been identified in samples from the southern portion of the Tony M deposit. Carnotite is a secondary hydrous potassium-vanadium-uranium mineral, while the other three are similar minerals with calcium replacing potassium. The later minerals occur above the water table in the zone that has been subjected to near surface secondary oxidation. Approximately 40% of the southern portion of the Tony M deposit is located in this zone, with the remainder, together with the Southwest deposit, located in the reduced zone below the water table.
Other ore-stage minerals identified in the USGS study include pyrite (0% to 3.3%), quartz overgrowths (0% to 17%), dolomite, and calcite (Wanty et al., 1990). The quartz overgrowths are often visible to the naked eye within the Tony M mine. While dolomite is associated with the mineralized zones, the abundance of calcite decreases in highly mineralized zones. This is thought to occur because calcite postdates the deposition of vanadium bearing chlorite and other ore-stage minerals that preferentially fill the pores of the mineralized zone.
No significant differences between cores, or within cores, have been identified for the sandstone framework mineralogy. Significant mineralogic differences, however, exist in the authigenic pore- filling material. These vary in abundance and type vertically within cores, in association with mineralized intervals (Northrop and Goldhaber, 1990).