URANIUM-BEARING VEINS IN PLATEAU STRATA, KANE CREEK, UTAH.
Uranium deposits in the metallogenic province of the Colorado Plateau, with a few possible exceptions, are commonly peneconcordant, completely enclosed in sedimentary strata, and lack hydrothermal feeder dikes. Among the few exceptional vertical uranium-bearing structures penetrating Plateau strata are the deposits of Kane Springs Canyon, Utah, where evidence for upward migration of uranium ions may be critically examined. Here nearly vertical uranium-bearing mineralized fractures (age about 60 m.y.) penetrate older strata (age about 225 m.y.). Closely associated with the uranium minerals of the veins are clay minerals, chlorite, and a local development of micaceous foliation. While evidence in support of an original hydrothermal source for the uranium ions is strong, several links are missing in the interpretation of natural events which would tie the vertical fractures to deposits in overlying horizontal strata. Combined field and laboratory study indicate that two periods of fluid invasion caused mineral alteration along faults in the Cutler Formation at Kane Creek. Normally, red and purple strata exhibit massive areas of bleaching up to 50 feet thick which gradually taper away from the faults and disappear within a mile or more. This early bleaching is followed by a later, localized green-gray clay-mineral alteration which ranges from a few inches to 20 feet thick and closely follows steeply inclined fault planes. These fault planes are uranium-bearing, with uraninite (UO 2 ) being the principal ore mineral. The mineral assemblage of the veins provides evidence that moderate- to low-temperature thermal solutions prevailed during the formation of the ores.