Summary:
The Christensen Ranch Project Area targets mineralization in the Eocene-aged Wasatch Formation of the Powder River Basin.
Mineralization in the Christensen Ranch Project Area occurs in fluvial sandstones of the lower parts of the Wasatch Formation. Most of the upper Wasatch Formation has been eroded away. The sandstones are arkosic, fine- to coarse-grained with local calcareous lenses. The sandstones contain minor amounts of organic carbon that occurs as dispersed bits or as stringers. Unaltered sandstones are generally gray, while altered sandstones are tan or pink due to hematite, or show yellowish coloring due to limonite.
Pyrite occurs in several forms within the host sandstones. In unaltered sandstones, pyrite occurs as small to large single euhedral crystals associated with magnetite, ilmenite and other dark detrital minerals. In altered sandstone, pyrite is typically absent, but locally occurs as tarnished, very fine-grained euhedral crystals. In areas of intense or heavy mineralization, pyrite locally occurs as massive, tarnished crystal aggregates.
The Christensen Ranch Project Area contains portions of four alteration systems, all within fluvial sands of the Wasatch Formation. These fluvial host systems are identified as K1, K2, K3 and K4 sands and are in descending order. These sands vary in thickness from 0 feet to 100 feet within the Christensen Ranch Project Area. They coalesce within portions of the Christensen Ranch Project Area and form massive sand sequences of roughly 250 feet (80 m) in thickness. These sands in turn host the K1, K2, K3 and K4 uranium roll-front systems, each of which is composed of multiple stacked individual roll-front deposits.
Uranium mineralization at the Christensen Ranch Project Area is typical of Wyoming roll-front sandstone deposits. The formation of roll-front deposits is largely a groundwater process that occurs when uranium-rich, oxygenated groundwater interacts with a reducing environment in the subsurface and precipitates uranium. The most favorable host rocks for roll-fronts are permeable sandstones with large aquifer systems. Interbedded mudstone, claystone and siltstone are often present and aid in the formation process by focusing groundwater flux. The geometry of mineralization is dominated by the classic roll-front “C” shape or crescent configuration at the redox interface. The highest-grade portion of the front occurs in a zone termed the “nose” within reduced ground just ahead of the alteration front. Ahead of the nose, at the leading edge of the solution front, mineral quality gradually diminishes to barren within the “seepage” zone. Trailing behind the nose, in oxidized (altered) ground, are weak remnants of mineralization referred to as “tails” which have resisted re-mobilization to the nose due to association with shale, carbonaceous material or other lithologies of lower permeability. Tails are generally not amenable to ISR because the uranium is typically found within strongly reduced or impermeable strata, therefore making it difficult to leach.