Sandstone-type uranium deposits typically occur in fine to coarse grained sediments deposited in a continental fluvial environment. The uranium is either derived from a weathered rock containing anomalously high concentrations of uranium or 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 front. The reducing conditions may be caused by such reducing agents in the sandstone as carbonaceous material, sulphides, hydrocarbons, hydrogen sulphide, or brines.

The vanadium content of the Henry Mountains Basin deposits is relatively low compared to many Uravan deposits. Furthermore, the Henry Mountains Basin deposits occur in broad alluvial sand accumulations, rather than in major sandstone channels as is typical of the Uravan deposits of Colorado. The Henry Mountains Basin deposits do, however, have the characteristic geochemistry of the Uravan deposits and are therefore classified as Salt Wash type deposits.

Extensive research by Northrop and Goldhaber (1990) and associates shows that the Henry Mountains Basin deposits were formed at the interface of an underlying brine with overlying oxygenated flowing waters carrying uranium and vanadium in solution. Reduction and deposition of the mineralization were enhanced where the interface occurred within sandstones containing carbonaceous debris. The multiple mineralized horizons developed at favourable 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.

Uranium mineralization in the Henry Mountains Complex property is hosted by favourable sandstone horizons containing detrital organic debris. 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. The stratabound primary mineralization routinely occurs as thin layers related to the stratigraphic units that are present over a wide area of the Tony M– Southwest and Copper Bench–Indian Bench deposits.

The vanadium:uranium weight ratios in Salt Wash-type deposits range from about 1:1 to 20:1. The deposits are, therefore, technically classified as vanadium deposits with accessory uranium. Because of the relative economic importance of the uranium, less emphasis is placed on the vanadium.

The Henry Mountains Complex vanadium-uranium deposits consist of two extensive elongate, tabular zones containing a large concentration of mineralization. The Tony M–Southwest deposit extends for a distance of approximately 2.5 miles along a north-south trend and has a maximum width of about 3,000 ft. The larger Copper Bench-Indian Bench deposit extends approximately 3.5 miles along a northwesterly trend to the northeast of the Tony M–Southwest deposit.

The Tony M–Southwest deposit occurs within an arcuate zone over a north-south length of about 15,000 ft. and a width ranging from 1,000 ft. to 3,000 ft. The Copper Bench-Indian Bench deposit extends northwesterly over a length of approximately 15,000 ft. and a width of 1,000 ft. to 2,500 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 Salt Wash Member of the Morrison Formation, when a minor zone in the Tidwell is included in the lower zone.

The Tony M-Southwest deposit occurs in the lowermost 35 ft. to 62 ft. of the Salt Wash Member sandstone. Mineralization within the Upper Lower unit is offset to the east as compared to mineralization in the Lower Lower unit. Mineralization forming the Copper Bench Indian Bench deposit occurs between 60 ft. and 100 ft. above the base of the Salt Wash Member.

Mineralization making up the mineral resources of the Tony M-Southwest and the Copper Bench Indian Bench has average thicknesses of three feet to six feet, depending on assumptions regarding GT cut-off and dilution. Inspection of logs by RPA indicates that the thickness of uranium mineralization in individual drill holes only occasionally exceeds 12 ft.

The weighted average grade of the Indicated Resource blocks for the Copper Bench-Indian Bench deposit is 0.325% eU3O8, while the average grade of the individual blocks range from 0.2% eU3O8 to 2.193% eU3O8. The indicated resource blocks have an average thickness of 5.2 ft and range from 2.0 ft. to 14.5 ft. thick. About 25% of these intercepts have a thickness of 7.0 ft. or greater and represent about one third of the tons and pounds of the total Indicated Resource.

Therefore, while 25% of the indicated resource blocks can be mined at a full mining height of 8 ft. or greater, a majority of the zones are less than 7 ft. in thickness. In the thinner zones the mining technique of split shooting, or resuing is typically used to mine Salt Wash hosted ores of the Uravan District. Resuing is a method of stoping wherein the wall rock on one side of the ore zone is removed before the ore is broken. It is employed on ore beds with a thickness of as little as 30 in. or less, and yields cleaner ore than when wall rock and ore are broken together. Split shooting is a standard practice for mining the thin ore beds of the Uravan Mineral Belt.

The White Mesa Mill is located six miles south of Blanding in southeastern Utah. Its construction by EFNI was based on the anticipated reopening of many small low-grade mines on the Colorado Plateau, and the mill was designed to treat 2,000 tons of ore per day. The mill has operated at rates in excess of the 2,000 tons per day design rate. The mill has been modified to treat higher grade ores from the Arizona Strip, as well as the common Colorado Plateau ores. Processing of Arizona Strip ores is typically at a lower rate of throughput than for the Colorado Plateau ores. The basic mill process is a sulphuric acid leach with solvent extraction recovery of uranium and vanadium.

Run-of-mine ore is reduced to minus 28 mesh in a six-foot by 18-ft. diameter semiautogenous grinding (SAG) mill. Leaching of the ore is accomplished in two stages: a pre-leach and a hot acid leach. The first, or pre-leach, circuit, consisting of two mechanically agitated tanks, utilizes pregnant (high-grade) strong acid solution from the countercurrent decantation (CCD) circuit which serves both to initiate the leaching process and to neutralize excess acid. The pre-leach circuit discharges to a 125-ft. thickener where the underflow solids are pumped to the second stage leach and the overflow solution is pumped to clarification, filtration, and solvent extraction circuits.

A hot strong acid leach is used in the second stage leach unit, which consists of seven mechanically agitated tanks having a retention time of 24 hours. Free acid is controlled at 70 grams per litre and the temperature is maintained at 75o C. Leached pulp is washed and thickened in the CCD circuit, which consists of eight highcapacity thickeners. Underflow from the final thickener at 50% solids is discharged to the tailings area. Overflow from the first thickener (pregnant solution) is returned to the pre-leach tanks.

The solvent extraction (SX) circuit consists of four extraction stages in which uranium in pregnant solution is transferred to the organic phase, a mixture consisting of 2.5% amine, 2.5% isodeconal, and 95% kerosene. Loaded organic is pumped to six stages of stripping by a 1.5 molar sodium chloride solution, and thence to a continuous ammonia precipitation circuit. Precipitated uranium is settled, thickened, centrifuged, and dried at 1,200o F. The final product at about 95% U3O8 is packed into 55 gallon drums for shipment.