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Research about Montana

Source-linked reports with geographic coverage including Montana.

At least 1,027 records · Page 57Linked to original sources
USGS1954

Reconnaissance for uranium-bearing lignite in the Ekalaka Lignite Field, Carter County, Montana

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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USGS1953

Beaverhead formation, a Laramide deposit in Beaverhead County, Montana

The name Beaverhead formation is proposed for a thick sequence of conglomerate, sandstone, siltstone, and limestone that crops out over an area of at least 400 square miles in Beaverhead County, Montana, extends southward across the Montana-Idaho boundary, and may extend eastward into Madison County. These rocks are clearly sedimentary by-products of the Laramide orogeny and probably range from late Cretaceous to early Eocene. The Beaverhead formations consists predominantly of conglomerate. In part of the area, an upper and a lower conglomerate member are separated by a middle member of limestone. Where the limestone member is inconspicuous or absent, the upper and lower conglomerate members cannot be differentiated. The most nearly complete and best-exposed known section of the Beaverhead formation, designated the type section, is near the mouth of McKnight Canyon, 6 miles west of Dell, Montana. Here the formation can be divided into four mappable units; elsewhere no more than three units can be recognized. In the McKnight Canyon section, the top and bottom members are dominantly conglomerate, composed of pebbles, cobbles, and subordinate boulders set in a sandy matrix cemented by calcite; breccia beds occur locally. This coarse debris was derived from rocks of Precambrian, Paleozoic, and Mesozoic age and consists largely of limestone and quartzite. The intermediate member consists of two mappable units: a lower thick, massive limestone, locally concretionary, and an upper sequence of interbedded siltstone, sandstone, arkose, limestone, and subordinate conglomerate. At McKnight Canyon, where the base and the top of the formation have been faulted and eroded, the exposed thickness of the section is approximately 9700 feet. The Beaverhead formation rests unconformably on rocks as young as the Colorado group and as old as early Paleozoic, and it probably rests unconformably upon rocks as young as the Montana group and as old as Precambrian. It is unconformably overlain by vertebrate-bearing fluviatile or lacustrine tuffaceous beds of Eocene and Oligocene age. The coarse debris that composes the formation was eroded from nearby mountains that were uplifted in Late Cretaceous, Paleocene, and early Eocene time, and was deposited in basins adjacent to these mountains. The resulting rocks, a product of Laramide orogeny, were later folded and displaced by overthrusting and block faulting. In places, these rocks are overlain by thrust sheets of Paleozoic rocks. © 1953, The Geological Society of America, Inc.

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USGS1953

The geology and mineralogy of the W. Wilson mine near Clancey, Jefferson County, Montana

The W. Wilson mine, near Clancey, Mont., explores a siliceous vein in quartz monzonite of the Boulder batholith. The vein is a composite structure that consists of several closely spaced veinlets of quartz and chalcedony separated by silicified quartz monzonite. The vein has been recurrently brecciated and silicified. Typically, the quartz monzonite has been hydrothermally altered in zones of decreasing intensity outward from the vein. Pitchblende was deposited in and along the vein during one stage of the silicification that is characterized by fine-grained disseminated pyrite in black chalcedony. Subsequently most of the pitchblende was oxidized and hydrated to form a series of brightly colored secondary uranium minerals that exhibit a zonal relationship. Most of the known uranium minerals are localized in two small elongate ore bodies.

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USGS1953

Preliminary report on the Clancy Creek area, Jefferson City quadrangle, Jefferson County, Montana

Several radioactivity anomalies and secondary uranium minerals have been found in the Clancy Creek area near the northern margin of the Boulder batholith. These are principally associated with chalcedonic zones that consist of one or more discontinuous stringers and veins of cryptocrystalline silica and fine-grained quartz in silicified quartz monzonite and alaskite. Uranium ore has been produced at the W. Wilson mine from one of these vein zones, and exploration work is being done on another--the G. Washington-A. Lincoln. Some very fine-grained pyrite and minute quantities of other sulfides have been recognized in deposits of this type. At the Lone Eagle mine small amount of uranium ore has been developed along a siliceous vein that contains sooty pitchblende (?) in small irregular fractures; significant amounts of galena and sphalerite are distributed sporadically along the vein. In the Clancy Creek area, no anomalous radioactivity has been detected in the pre-batholithic volcanic rocks or in the post-batholithic dacite and andesite.

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