About 40 percent of the uranium ore reserves in the United States, minable at $8 per pound of contained U308, are in roll-type deposits in the State of Wyoming. The host rocks are arkosic sandstones, deposited in intermontane basins under fluvial conditions, and derived from the granitic cores of mountain ranges that flank the basins. The host rocks are Eocene and possibly Paleocene in age and are, or were, overlain by a sequence of continental tuffaceous siltstones, sandstones, and conglomerates 400-700 meters thick.
Most of the ore is unoxidized and lies below the water table. It contains pyrite, uraninite, coffinite, marcasite, hematite, ferroselite, and native selenium(?). The ore bodies range in size from a few hundred to several hundred thousand tons of material containing 0.10-5 percent U308. As mined, the ore averages about 0.25 percent U308.
The ore bodies are genetically related to and lie at the margins of large tongues of altered sandstone. The character of the alteration and the distribution of several elements within and near the altered sandstone suggest that the ore-bearing fluid was ground water, neutral to slightly alkaline and oxidizing with respect to the elements being transporter.
Roll-type deposits in littoral and fluvial sandstones have recently been discovered in the Gulf Coastal Plain area of Texas. These deposits appear to be similar to the Wyoming deposits in form, distribution of elements, and genesis.
