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Carbonate veins cutting pre-Cambrian metamorphic rocks in Golden Gate Canyon contain pitchblende and base-metal sulfides. The veins occupy extensive faults of Laramide age but normally contain pitchblende only where the cut hornblende gneiss. At the Union Pacific prospect, which was studied in detail, pitchblende, hermatite, and some ankerite formed in advance of sulfides, except possibly for minor pyrite. Base-metal sulfides and the bulk of ankerite-calcite vein-filling were deposited after the pitchblende. Chemical analyses show a high ferrous iron content in the hornblende gneiss in contrast to low ferrous iron in the adjacent biotite gneiss. It is hypothesized that ferrous iron released by alteration of hornblende was partly oxidized to hematite by the ore-bearing solutions and, contemporaneously, uranium was reduced and deposited as pitchblende. In other veins, biotite or iron sulfides may have been similarly effective in precipitating pitchblende. Apparently both the ferrous ion and the sulfide ion can serve as reducing agents and control pitchblende deposition. It is suggested that conditions particularly favorable for uranium deposition are present where uranium-bearing solutions had access to rocks rich in ferrous iron or pre-existing sulfides.
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Thirteen core holes, totaling 2,023 feet, were drilled during the fall of 1953 to explore the grade and extent of uranium-bearing beds of carbonaceous shale and lignite in the east-central part of the Goose Creek district, Cassia County, Idaho. The beds tested are interbedded with volcanic ash, bentonite, greenish-gray shale, sandstone, and conglomerate in two fairly well defined zones in the lower part of the Salt Lake formation of lower Pliocene age. Nine holes penetrated carbonaceous shale beds in the Barrett zone, and one hole penetrated carbonaceous shale and lignite beds in zone B, 160 feet stratigraphically below the Barrett zone. The highest concentration of uranium found by drilling is 0.10 percent in the upper part of a 4-foot bed of carbonaceous shale and lignite in zone B. The grade of carbonaceous shale beds in the Barrett zone ranges from 0.044 percent to less than 0.003 percent uranium. Inferred reserves in the district are estimated to be 790,000 tons in beds 1 foot or more thick containing an average of 0.014 percent or 120 tons of uranium.
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The Red Cliffs area comprises 296 square miles of canyon and plateau country in southwestern San Juan County, Utah. The rocks that crop out in the area are mostly deposits of terrestrial environment and are of Permian, Triassic, Jurassic, and Quaternary ages. The aggregate thickness of these rock is about 3,500 feet.
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Uranium-bearing lignite beds 1.5 to 8 feet thick occur in the Fort Union formation of the southern part of the Ekalaka Hills, Carter County, Mont. Data from surface outcrops indicate that an area of about 1,400 acres is underlain by 16,500,000 tons of uranium-bearing lignite containing 700 tons of uranium. The uranium content of the lignite beds ranges from 0.001 to 0.034 percent. Ironstone concretions in the massive coarse-grained sandstones in the upper part of the Fort Union formation contain 0.005 percent uranium in the northern and eastern parts of the area. These sandstones are good potential host rocks for uranium mineralization and are lithologically similar to the massive coarse-grained uranium-bearing sandstones of the Wasatch formation in the Pumpkin Buttes area of the Powder River Basin.
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Core drilling for data on uranium-bearing lignite in the Mendenhall area, Harding County, S. Dak. , was conducted by the U. S. Bureau of Mines during the period October 1952 to July 1953. Forty-two core holes totaling 9, 683 feet drilled in an area of about six square miles indicate a reserve of about 127/000,000 tons of lignite of which about 49,000,000 tons contain an average of 0.005 percent uranium or more. The Mendenhall area is near the center of the Slim Buttes, which are about 30 miles long from north to south. The uranium-bearing lignite averages, 5. 4 feet in thickness and occurs in the Ludlow member of the Fort Union formation of Paleocene age. Fuel analyses of about 130 samples indicate that the lignite contains about 15 percent ash, 36.7 percent moisture, 24r percent fixed carbon, 23.9 percent volatile matter, and 1.5 percent sulfur and has heating values of about 5,800 btu (as received). Uranium analyses of about 700 samples of lignite core indicate that about 2, 790 tons of uranium are present in the Mendenhall area. Inferred uranium reserves of 2,335 and .1. 050 tons are indicated by grade cutoffs of 0. 005 and 0. 01 percent uranium in the lignites, and 2, 065 and l s 35Stons are indicated by grade cutoffs of 0.03 and 0.05 percent uranium in the lignite ash. The above grade cutoffs have been incorporated on maps showing areal distribution: and thickness of mineralized beds.
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