Conglomeratic sandstone strata at the base of the Brushy Basin member of the Morrison formation as related to uranium-vanadium deposits, southwestern Colorado and southeastern Utah

Abstract

In southwestern Colorado and southeastern Utah strata of conglomeratic sandstone are localized at the base of the Brush Basin shale member of the Morrison formation of Jurassic age. These strata are discrete lithologic units that contain sedimentary structures oriented in a prevailing easterly direction, they locally rest upon sandstone in the Salt Wash that is ore bearing, and they are believed to cover about one-third of the underlying Salt Wash sandstone member in southwestern Colorado and southeastern Utah. Easterly trending planar cross-stratification and trough cross-stratification-type bedding and a general westward coarsening of sediments in the strata suggest they are the products of stream aggradation from westerly source areas. Uranium-vanadium deposits in the uppermost, almost continuous, layer of sandstone of the Salt Wash member have been classified according to their association with the conglomerate strata. Of the 364 deposits that have been studied in the uppermost sandstone layer of the Salt Wash, 29 percent of the total are directly below a conglomeratic sandstone stratum, 61 percent are below their projected trend, 6 percent are beyond the safe limits of projection, and 4 percent are lateral to their margins. Locally, a conglomeratic sandstone stratum may be mineralized. Where this happens, it is usually near clusters of deposits in the uppermost sandstone of the underlying Salt Wash member. Late Jurassic Morrison ground-water conditions can be postulated to localize uranium-vanadium rich ground water below the conglomerate strata.