Summary:
Mineralization
The uranium mineralization found in the Mine area is contained within five sandstone units of the Westwater Canyon Member. Zones of mineralization vary from approximately one foot to 30 ft thick, 100 ft to 600 ft wide, and 200 ft to 3,000 ft in length in elongated pods. Uranium mineralization in the Mine area west to east, and northwest to southeast depending on general area within the Mine area, consistent with trends of the fluvial sedimentary structures of the Westwater Canyon Member, and the general trend of mineralization across the Ambrosia Lake subdistrict.
Core recovery from the 2007 drilling program indicates that uranium occurs in sandstones with large amounts of organic/high carbon material. Non-mineralized host rock is much lighter (light brown to light grey,) and it has background to slightly elevated radiometric readings.
Uranium mineralization in the Mine area is believed to be predominantly primary ("trend") mineralization, with some secondary mineralization due to oxidation and mobilization of uranium near permeable geologic structures. Uranium mineralization consists of dark organic-uranium oxide complexes. The uranium in the Mine area is dark grey to black in color and is found between depths of approximately 1,380 ft to 2,600 ft below the surface. Although coffinite and uraninite have been identified in the Grants uranium district, their abundance is not sufficient to account for the total uranium content in a mineralized sample. Admixed and associated with the uranium are enriched amounts of vanadium, molybdenum, copper, selenium, and arsenic, in order of decreasing abundance.
The primary mineralization pre-dates the formation of the Laramide aged structures in the Mine area, with a small amount of vertical offset of mineralization present across the local faults. There is a possibility of some redistribution and stack ore along faults, however, it appears that most of the Roca Honda mineralization is primary. Redistributed, post-fault, or stack mineralization occurs in the Ambrosia Lake subdistrict of the Grants uranium district, but is not apparent in the Roca Honda area.
Mineralization Controls
Mineralization is generally confined to the fluvial sandstones of the Westwater Canyon Member and the Poison Canyon Sandstone of the Brushy Basin Member, though there may be some localized seepage into the under/overlying shales and mudstones, as well as some minor extension (less than 10 ft) of mineralization into the underlying Recapture Member. Within the Mine area, the Westwater Canyon Member contains as many as seven individual sandstones, which the uranium mineralization is spread across. In Sections 9 and 16, the mineralization is typically found in the upper sandstones (A, B1, and B2). In the north-central portion of the Mine area (Section 10 and 11), the mineralization is concentrated in the lower sandstone units (C and D) due to a pinching out of the upper sands and a thickening of the Brushy Basin Member. In the far western area of the project (Section 17), the uranium mineralization is generally in the upper two to three sandstones (A, B1 and B2), with very few mineralized occurrences in the lower half of the Westwater Canyon Member. To the east of the Mine area, the mineralization is spread across all of the sandstone units (including the Poison Canyon Sandstone); this area also appears to be in a region of overall mineral convergence at multiple horizons within the Westwater Canyon Member and observed within the Mount Taylor Mine (Riese, 1977).
Deposit Types
The Grants uranium district is one of the largest uranium provinces in the world. The Grants uranium district extends from east of Laguna to west of Gallup in the San Juan Basin of New Mexico. Three types of sandstone uranium deposits are recognized: tabular, redistributed (roll-front, fault-related), and remnant-primary. The tabular deposits formed during the Jurassic Westwater Canyon time period. Subsequently, oxidizing solutions moved down dip, modifying tabular deposits into redistributed roll-front and fault-related deposits. Evidence, including age dates and geochemistry of the uranium deposits, suggests that redistributed deposits could have been formed shortly after deposition in the early Cretaceous Period and from a second oxidation front during the mid-Tertiary Period (McLemore, 2010).
Primary mineralization deposits are generally irregular, tabular, flat-lying bodies elongated along an east to southeast direction, ranging from thin pods a few feet in thickness and length to bodies several tens or hundreds of feet long. The deposits are roughly parallel to the enclosing beds but may form rolls (tabular lenses) that cut across bedding. The deposits may occur in more than one layer, form distinct trends, commonly parallel to depositional trends, and occur in clusters. Primary mineralization in the Ambrosia Lake subdistrict consists mostly of uranium-enriched humic matter that coats sand grains and impregnates the sandstone, imparting a dark color to the rock. The uranium mineralization consists largely of unidentifiable organic-uranium oxide complexes that are light grey-brown to black. A direct correlation exists between uranium content and organic-carbon content by weight percent in the "ores" (Squyres, 1970; Kendall, 1972).