Summary:
The Project is located along the northeast margin of the Date Creek Basin of the Basin and Range Province of the western United States. The Date Creek Basin is one of hundreds of Paleogene basins throughout western Arizona, southeastern California, Nevada and western Utah. Paleogene lacustrine and fluvial sediments, and Quaternary gravels have filled these basins to depths of several thousand meters (Urangesellschaft, 1979a).
Three major faults cross the Project: the East Boundary Fault System; Fault 1878; and the West Boundary Fault System (MinEx, 1978b). Faults trend predominantly N30ºW to N55ºW and dip steeply (approximately 80º) to the southwest.
Another set of faults trending more westerly (N65ºW) are present in the south-central portion of the Project. A fault set trending northeast-southwest has been speculated by Urangesellschaft and others, but has not been observed in the field (MinEx, 1978b). Many of the north-westerly surface water drainage tributaries are developed partially along fault traces
Minor faults and shear zones occur throughout the Project. These probably represent fractures with slight offset of strata during differential compaction of the underlying sediments or local adjustment to major faulting.
The largest fold in the area is a broad, gentle, northwest-trending syncline in the south-eastern quarter of Section 9, T11N, R10W. Dips reach a maximum of 13º, except where modified by shearing. Many smaller folds with amplitudes of several feet are present in the lacustrine strata (MinEx, 1978b).
Fault displacements range from a few centimetres to more than 100 m. Fault movement is generally of normal displacement resulting in stair-stepped fault blocks. Local faults also have a tendency to hinge. Minor faulting across the mineralized area is often difficult to discern from variations in sedimentary dips. The lacustrine sediments dip south to south-westerly from 2º to 5º, to a maximum of 15º (Urangesellschaft, 1979a). Much of this dip is attributed to recurrent faulting during deposition.
Stratigraphy
Uranium mineralization at the Project occurs exclusively in the sequence of Miocene-age lacustrine lakebed sediments. The lacustrine sediments unconformably overlie the andesitic volcanic unit over most of the Project. However, to the east of the Project, they overlie the felsic to intermediate volcanic unit.
Evidence suggests that deposition of the lacustrine sediments occurred in a restricted basin less than 5 km wide by 10 to 12 km long on the northern edge of an old Paleogene lake (Chapman, Wood & Griswold Inc., 1977). Moving southward, these sediments inter-tongue with siltstones and sandstones. The lakebed sediments represent time-transgressive facies deposited within a narrow, probably shallow, basinal feature. This type of depositional environment exhibits complex relationships between individual facies, lensing out, vertical and horizontal gradation, and interfingering (MinEx, 1978, b-c).
The lake sediments include green siltstones and mudstones, white calcareous siltstones, and silty limestone or calcareous tuffaceous material. Much of this material is silicified to varying extents and was derived in part from volcanic ashes and tuffs common throughout the lakebeds. Also present in the lacustrine sequence are zones of carbonaceous siltstone and lignitic material. Along the boundary between the former MinEx and Urangesellschaft properties, drill holes encounter the basal arkosic sandstone. To the south and southwest, lakebeds interfinger with and eventually are replaced by a thick, medium to coarse-grained arkosic sandstone unit (MinEx, 1978, b-c).
Mineralization
Uranium mineralization in outcrops and the pit floor at the old Anderson mine was reported by the US Bureau of Mines in Salt Lake City as tyuyamunite (Ca(UO2)2(VO4)2·5-8H2O). Carnotite (K(UO2)2(VO4)2·3H2O) and a rarer silicate mineral, weeksite (K2(UO2)2(Si2O5)3·4H2O), were also reported in outcrop samples. Carnotite mineralization occurs as fine coatings and coarse fibrous fillings along fractures and bedding planes, and has been noted in shallow drill holes and surface exposures.
The uranium mineralization found at depth on the former Urangesellschaft property was reported by Hazen Research, Inc. of Golden, Colorado, (Hazen Research) to be poorly crystallized, very fine-grained, amorphous uranium with silica. This could be in the form of either coffinite (U(SiO4)1-x(OH)4x) or uraninite (UO2) in a primary or unoxidized state (Hertzke, 1997). Mineralogical studies performed by Hazen Research (1978a, 1978b, 1978c and 1979) on Urangesellschaft core found that mineralization was associated, for the most part, with organic-rich fractions of the samples. Specifically, the uraniferous material occurs as stringers, irregular masses and disseminations in carbonaceous veinlets with uranium up to 54% as measured by microprobe analysis. X-ray diffraction identified the mineral as coffinite. It is possible that an amorphous, ill-defined uranium silicate with a variable U:Si ratio is precipitated and, under favorable conditions, develops into an identifiable crystalline form (coffinite).
Of special note is the detection of high-grade, low-reflecting uraniferous material occurring with carbonaceous material in the siltstone. Similar assemblages in unoxidized mineralization have also been reported for the former MinEx property (Hertzke, 1997).
Urangesellschaft (1979a) distinguished seven mineralized zones, identified as Horizons A, B, C, D, E, F and G, with the youngest (uppermost) being Horizon A and the oldest (deepest) being Horizon G. The majority of uranium occurs in Horizons A, B and C within the property. A conglomeratic sandstone unit interbeds with these units, but does not contain uranium mineralization; it is referred to as the Barren Sandstone Unit and it lies between Horizon C and Horizon D. Consequently, Horizons A through C have been called the Upper Lakebed Sequence and Horizons D through G have been called the Lower Lakebed Sequence.
Grades of mineralization range from 0.025% U3O8 to normal highs of 0.3% to 0.5% U3O8 with intercepts on occasion of 1.0% to 2.0% U3O8. Secondary enrichment of the syngenetic mineralization is observed along faults and at outcrops (Hertzke, 1997).
Uranium mineralization hosted by the basal San Miguel Formation of the UPC is interpreted to represent a variety of the roll-front-type mineralization by the early workers of Anschutz. Sandstone-type deposits are characteristically sedimentary formations of clastic-detrital origin, containing reducing environments. These deposits are usually tabular in shape and may occur in continental sandstones, deltaic or shallow marine environments. Typically, roll-front-type uranium deposits have, in the direction of the flow of mineralizing solutions, a barren (oxidized) interior zone surrounded by a (reduced) mineralized zone. Between the barren zone and the mineralized zone is an altered zone. The overall shape of the roll-front is similar to a crescent with extended tails at each end, which also outlines the barren interior zone, and uranium is deposited at the interface between the oxidized zone and the reduced zone. Ground water flow direction is usually a good guide in detecting roll-front-type deposits in sandstones.
The style of mineralization within the sandstones at the Project includes some characteristics of the roll-front-type mineralization, as in the Powder River Basin of Wyoming in the United States. It is likely that the style of mineralization is a variety of the roll-front-type uranium mineralization (Wilson, 2008).