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Geology of the Shinarump No. 1 Uranium Mine, Seven Mile Canyon Area, Grand County, Utah

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Geology of the Shinarump No. 1 Uranium Mine, Seven Mile Canyon Area, Grand County, Utah GEOLOGICAL SURVEY CIRCULAR 336 GEOLOGY OF THE SHINARUMP NO. 1 URANIUM MINE, SEVEN MILE CANYON AREA, GRAND COUNTY, UTAH This report concerns work done on behalf of the U. S. Atomic Energy Commission and is published with the permission of the Commission. UNITED STATES DEPARTMENT OF THE INTERIOR Douglas McKay, Secretary GEOLOGICAL SURVEY W. E. Wrather, Director GEOLOGICAL SURVEY CIRCULAR 336 GEOLOGY OF THE SHINARUMP NO. 1 URANIUM MINE, SEVEN MILE CANYON AREA, GRAND COUNTY, UTAH By W. L Pinch This report concerns work done on behalf of the U. S. Atomic Energy Commission and is published with the permission of the Commission. __________Washington, D. C., 1954 Free on application to the Geological Survey, Washington 25, D. C. , B E A V E R * 'IRON .-'I GAR WASHINGTON L K«n«b'p U A.R I EXPLANATION Uranium deposit or group of deposits in the Shinarump conglomerate Uranium deposit or group of deposits in the Chfnle formation 25 0 I i i i i I Figure 1. Map of part of the Colorado Plateau showing the location of the Shinarump No. 1 mine and the distribu­ tion of uranium deposits in the Shinarump and Chinle formations. GEOLOGY OF THE SHINARUMP NO. 1 URANIUM MINE, SEVEN MILE CANYON AREA, GRAND COUNTY, UTAH By W. I. Finch CONTENTS Page Page Abstract..................................... 1 History and production........................ 4 Introduction.................................. 2 Ore deposits................................. 4 General geology............................... 2 Mineralogy.................................. 5 Stratigraphy............................. 2 Petrology.................................... 6 Stratigraphic section................ 2 Habits of ore bodies .......................... 9 Cutler formation.................... 3 Spectrographic study.......................... 10 Moenkopi formation................. 3 Age determinations of uraninite................ 12 Shinarump conglomerate Origin of deposit............. ................ 12 and Chinle formation.............. 3 Conclusions........ ........... .............. 13 Wingate sandstone................... 4 Literature cited.............................. 13 Jurassic rocks..................... 4 Unpublished reports .......................... 14 Structure................................ 4 Group number classification................... 14 ILLUSTRATIONS [Plates are in pocket] Page Plate 1. Geologic maps and sections of the Seven Mile Canyon and Shinarump No. 1 mine areas, Grand County, Utah. 2. Selected maps of mine walls from the Shinarump No. 1 mine. Figure 1. Map of part of the Colorado Plateau showing the location of the Shinarump No. 1 mine and the distribution of uranium deposits in the Shinarump and Chinle formations................ ii 2. Paragenesis of uraninite and sulfide minerals, Shinarump No. 1 mine............................. 6 3. Photomicrographs of polished and thin sections from the Shinarump No. 1 mine .................. 7 4. Cumulative curves of grain size of samples from the Seven Mile Canyon area.................... 9 5. Frequency curves of grain size of samples from the Seven Mile Canyon area .................... 9 6. Curves of grain size of ore-bearing and barren siltstone from Shinarump No. 1 mine............. 10 7. Geologic map and sections of the Shinarump No. 1 mine........................................ 11 TABLES Page Table 1. Samples from Seven Mile Canyon area..................................................... .. 8 2. Geometric mean values (in percent) of elements contained in barren and uranium-bearing rock from the Shinarump No. 1 mine, copper-bearing rock from nearby copper deposits, and uranium-bearing rock from a nearby deposit in the Morrison formation................... 12 ABSTRACT are found in three zones in the lower 25 feet of the Chinle formation of Late Triassic age. The Shinarump No. 1 The geology of the Shinarump No. 1 uranium mine, mine, which is in the lowermost zone, is located on the located about 12 miles northwest of Moab, Utah, in the west flank of the Moab anticline near the Moab fault. Seven Mile Canyon area, Grand County, Utah, was studied to determine the habits, ore controls, and The Shinarump No. 1 uranium deposit consists of possible origin of the deposit. discontinuous lenticular layers of mineralized rock, ir­ regular in outline, that, in general, follow the bedding. Rocks of Permian, Triassic, and Jurassic age Ore minerals, mainly uraninite, impregnate the rock, crop out in the area mapped, and uranium deposits High-grade ore seams of uraninite and chalcocite occur along bedding planes. Uraninite formed later than, or area is given by McKnight (1940). Below is a brief simultaneous with, most sulfides, and the chalcocite discussion of the stratigraphy and structure of the may be of two ages, with some being later than uran- Shinarump No. 1 mine area. inite. Uraninite and chalcocite are concentrated in the more poorly sorted parts of siltstones. In the Seven Mile Canyon area guides to ore inferred from the study Stratigraphy of the Shinarump No. 1 deposit are the presence of bleached siltstone, carbonaceous matter, and copper Stratigraphic section sulfides. Results of spectrographic analysis indicate that the mineralizing solutions contained important In the Shinarump No. 1 mine area, the Cutler, amounts of barium, vanadium, uranium, and copper, Moenkopi, Shinarump, Chinle, and Wingate formations as well as lesser amounts of strontium, chromium, form an escarpment along the west side of the Moab boron, yttrium, lead, and zinc. fault. The Upper Jurassic Morrison formation on the east side of the fault has been faulted against the The origin of the Shinarump No. 1 deposit Permian Cutler formation. Thus, in the area mapped, is thought to be hydrothermal. Jurassic rocks between the Wingate (Triassic) and Morrison formations are not exposed. A measured INTRODUCTION section of the rocks near the mine follows. The Shinarump No. 1 uranium mine is located Shinarump no. 1 claim section, measured about about 12 miles northwest of Moab, Utah, in the Seven 1. 500 feet south of Corral Canyon. Grand County. Mile Canyon area, Grand County, Utah (fig. 1). A Utah. Line of section S. 65 W.. sec. 27. T. 24 S.. road about a quarter of a mile long connects the mine R. 20 E.. Salt Lake meridian area with U. S. Highway 160. The mineralized zones crop out along a northwest-trending escarpment paral­ [Measured December 1952] leling Highway 160. Vegetation in the area is sparse. The United States Geological Survey studied the Wingate sandstone (incomplete): geology of the Shinarump No. 1 mine on behalf of the Top of section, not top of exposure. Atomic Energy Commission in order to determine the Sandstone, yellowish-gray (5Y8/1) 1 ; habits, ore controls, and possible origin of the deposit. weathers pale red (1OR6/2); fine-grained Vance Thorriburg, owner of the claims, was most co­ to very fine grained; bedding not distinct; operative and helpful throughout the investigation. only basal 5 ft examined; estimated height of cliff face 220 ft. Chinle formation and Field study began in January 19 52 and was carried Wingate sandstone contact placed at sharp on intermittently until April 1953. The Shinarump No. 1 change from cliff-forming sandstone of mine workings were mapped in detail by tape and open- Wingate to slope-forming shale and sand­ sight alidade early in 1952. Later a planetable map was stone of Chinle. Mudcracks at base of made of the area surrounding the mine to relate the mine Wingate; light-green alteration of upper few geology to the stratigraphic and structural features. A inches of Chinle and of mudcrack fillings. total of 31 samples of ore-bearing and barren rock were (Unit not measured.) taken in the area and analyzed chemically and spectro- Unconformity (local?). graphically. Stratigraphic sections were measured near the mine and in Little Canyon south of Seven Mile Canyon. Chinle formation: Shale and interbedded sandstone and con­ Previous work in the area includes a study of the glomerate, pale-red (1OR6/2); sandstone, geology of the area between the Green and Colorado fine-grained; conglomerate contains mostly Rivers by McKnight (1940) and recent studies of the clastic limestone concretions. Sandstone Seven Mile Canyon area in connection with exploration and conglomerate beds mostly 1 ft or less by the Atomic Energy Commission by Droullard (1951) in thickness. For most part unit forms and Droullard and Jones (1952). steep rubble-covered slope................... 73 Sandstone, light-red (5R6/6), fine-grained; quartzitic; thin horizontal bedding with some GENERAL GEOLOGY low-angle crossbedding; forms ledge; channels into lower unit..................... 7 Rocks of Permian, Triassic, and Jurassic Sandstone and mudstone, moderate-red age crop out in the area mapped. Uranium-bearing (5R5/4), fine-grained; irregular bedding; rock occurs in lower beds of the Upper Triassic forms ledge ............................... 12 rocks. Copper-bearing rock occurs in a large Sandstone and conglomerate, pale-red (5R6/2) talus block that may be Dakota sandstone of and light greenish-gray (5GY8/1), fine-grained. Cretaceous age and in the Moab fault gouge zone. Conglomerate consists mainly of clastic lime­ Outside the Shinarump No. 1 mine area, uranium- stone concretions. Abundant hematitic con­ bearing rock also occurs in the Morrison forma­ cretions scattered mainly in sandstone beds, tion of Late Jurassic age (pi. 1). Copper-bearing some silicified wood, some white calcite fill­ rock occurs along the Moab fault northwest of ing cavities
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