Structural relations at the Hideout No. 1 uranium mine, Deer Flat area, San Juan County, Utah

Abstract

The Hideout No. 1 uranium-copper mine is in sec. 14, T. 36 S., R. 17 E., Salt Lake meridian, about 30 miles N. 86 degrees W. of Blanding, Utah.Consolidated sedimentary rocks exposed in the vicinity of the mine range in age from Permian to Triassic. The rock units, from oldest to youngest, are: the Cedar Mesa sandstone member, the Organ Rock tongue, and the Hoskinnini tongue of the Cutler formation of Permian age; the Moenkopi formation of Early and Middle (?) Triassic age; and the Shinarump member, the mudstone-sandstone unit, and the Moss Back member of the Chinle formation of Late Triassic age.The area is on the west flank of the Monument upwarp, and the beds dip 1 degrees to 3 degrees west-southwest. Local monoclines interrupt the regional dip. The prominent joint sets dip steeply and trend N 45 degrees to 55 degrees E, N 35 degrees to 70 degrees W, and N 10 degrees E to N 25 degrees W.The Hideout No. 1 uranium-copper deposit is in the Shinarump member of the Chinle formation where it fills a stream channel cut in the top of the Moenkopi formation. The apparent relation between the uranium-copper deposit and a low-amplitude monoclinal fold may be explained in the following ways:1. The beds may have been folded before the Shinarump member was deposited, as suggested by the apparent erosional thinning of the Moenkopi formation along the anticlinal bends; and the flexures may have altered the course and gradient of the Late Triassic streams and perhaps caused thick sediments to accumulate locally.2. Regardless of whether the beds were folded before or after deposition of the Shinarump member, the local flattening of dip at the Hideout No. 1 channel may have slowed and guided laterally migrating ore solutions into the channel sediments where ore deposits could form.3. Tension joints associated with the flexure in the Moenkopi formation may have been pathways that allowed ascending ore solutions to reach the channel sediments.Thus, the intersection of channels and flexures may be guides to favorable ground for uranium deposits in the Shinarump member of the Chinle formation.