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G )ok to the Geology of Northwest Colorado,1955 <br /> .% . a . — 1 9.5 b — 1 . A . P. . G <br /> URAltlI160 & DEPOSITS IN THE SKULL CREEK AND URANIUM PEAK <br /> DISTRICTS, NORTHWEST COLORADO <br /> By Y. WILLIAM ISACHSEN <br /> U. S. Atomic Energy Commission, Grand Junction, Colorado <br /> INTRODUCTION Stratigraphy <br /> Production of radioactive minerals in northwestern Rocks exposed in the area range from the Pennsyl- <br /> Colorado reportedly began in 1903 when a property vanian Weber sandstone to the Mancos shale of Cre- <br /> near Skull Creek, Colorado yielded several tons of ore taceous age. Uranium deposits have only been. found <br /> which were shipped to France for radium extractions. in the Curtis and Weber formations in the area, and <br /> The most significant production of radioactive minerals- the Weber.deposit has not been studied. The Chinle <br /> from northwestern Colorado, however, has come from (Shinarump ?) and-Morrison formations, which- are <br /> the Uranium Peak area near Meeker. The economic major uranium producing units on the Colorado Plateau, <br /> geology of deposits in these two areas is herein stun- have not yet proven to be economically important in <br /> marized. the Skull Creek area. <br /> Stratigraphic relationships relating to the Blue <br /> SKULL CREEK. DISTRICT Mountain Group Mine are described by McDougald (in <br /> Location and History of Deposits press). The Curtis host rock overlies massive Entrada <br /> sandstone, and is a water-laid, ripple marked, thinly <br /> Uranium ore has been mined from two areas in the ode, sandstone ranging in thickness from six inches <br /> Skull Creek District. The oldest and -most extensive to 3 feet This unit"grades upward into marine sand- <br /> workings are on the southern flank of Skull Creek anti- stone containing pelecypods,thus marking the transition <br /> cline in-the NV2NEV4, sec. 35, T. 4 N., R. 101 W.; from terrestrial to marine environment. <br /> where copper-uranium-vanadium ore occurs in a basal <br /> sand_stone of the Curtis (?) formation. A second min- <br /> Economic Geology <br /> ing property resulted when a small uranium orebody <br /> was discovered in the Weber sandstone immediately Ore minerals in the Blue Mountain Group mine are <br /> north of the Skull Creek anticline in 1954. This deposit all oxidized,. and include azurite, malachite( carnotite, <br /> was largely mined out shortly after discovery. caIdo-volborthite, and black vanadium minerals. These <br /> occur disseminated in the host sandstone,.with concen- <br /> The Curtis deposit is reached by travelling west from trations along zones containing.carbonized plant frag- . <br /> Skull Greek, Colorado, for one mile; thence north on ments. Ore is. confined to the thin-bedded sandstone <br /> an unimproved dirt road for 1V2 miles. unit between the eolian. Entrada .sandstone and the <br /> This deposit was mined for radium in 1903 and overlying fossiliferous sandstone. .Immediately below, <br /> thereafter lay idle until the 1920's when a small amount the ore-bearing unit, the, Entrada is limonite-stained, <br /> of ore was mined for vanadium content. The.property thus facilitating recognition of the contact during <br /> again became inactive until 1953,-when claims were drilling. <br /> relocated as the Blue Mountain Group, and develop- Known orebodies are elongated parallel to strike <br /> merit drifting for uranium was initiated (McDougald, of host beds but no ore trends are known. The produc- <br /> in press). tion potential of the basal Curtis is regarded as poor <br /> (Isachsen, et al., 1955). <br /> Structure <br /> Skull Creek.anticline trends east-west, and is located URANIUM PEAK DISTRICT <br /> north of Skull Creek,Colorado. Dips are greatest along Location and History of Deposits <br /> the southern flank, site of the Curtis deposit, where Mines in the Uranium Peak District are located <br /> they measure up to 45 degrees. Flanks of the upwarp northeast of Meeker, Colorado, in T. 2 N., R. 91 W. <br /> are characterized by broad warps plunging down dip, and R. 92 W. The area may be reached by traveling <br /> and widespread fracturing which includes longitudinal, 3 miles northeast from Meeker on State Highway 13 <br /> transverse, and diagonal joints. Locally displacements to County Highway 320, thence 11 miles to the Forest <br /> of a few inches occur parallel to or along longitudinal Service road which leads east from Yeilowjacket Pass <br /> joints. into the mining area. <br /> CJ 2010 Rocky Mountain Association of Geologists <br />