Middle Tertiary Unconformity, North Boulder and Jefferson Basins, Southwestern Montana

Kuenzi, W. David; Richard, Benjamin H.

doi:10.1130/0016-7606(1969)80[315:mtunba]2.0.co;2

Cited by 3 publications

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“…As presently understood, these basins share a common geologic history. That history has been well documented by Robinson (1961Robinson ( , 1963Robinson ( , 1967 in the Toston, Townsend, Clarkston, and Three Forks areas; Kuenzi (1966), Kuenzi andFields (1968b, 1971), and Kuenzi and Richard (1969) The origins of the basins are somewhat obscure. Tectonic, erosional, and regional climatic factors were certainly important in their original delineation and development.…”

Section: Regional Geologymentioning

confidence: 91%

Summary geologic report on the Missoula/Bitterroot Drilling Project, Missoula/Bitterroot Basins, Montana

Abramiuk

1980

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The objective of _the drilling project was to obtain information to assess the favorability of the Tertiary sedimentary unfts in the Missoula and Bitterroot Valleys for uranium potential. The group of•Montana Tertiary basins, including the Missoula and Bitterroot Basins, has been assigned a speculative uranium potential of 46,557 tons of U308 at $100/lb by the 1980 National Uranium Resource Evaluation report. The seven drill holes, two in the Missoula Valley• and five in the Bitterroot Valley, verified observations made during surface studies and provided additional information about the subsurface that was previously unknown. No uranium was found, although of the two localities the Bitterroot Valley is the more favorable. Thr~e stratigraphic units were tentatively identified on the basis of lithology: pre-Renova elastic unit~, Renova Formation equivalents, and Sixmile Creek Formation equivalents. Of the three, the Renova Formation equivalents in the Bitterroot Valley appear to be the most favorable for possible uranium occurrences and the pre-Renova elastic units the least favorable.

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Section: Regional Geologymentioning

confidence: 91%

Summary geologic report on the Missoula/Bitterroot Drilling Project, Missoula/Bitterroot Basins, Montana

Abramiuk

1980

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“…The Tertiary sedimentary basins cover approximately a third of the Dillon Quadrangle and represent a geologic environment that at least locally may be favorable for uranium deposition. Plate 10 shows the location of the basins, the recently active faults along their boundaries, and the approximate boundary between Eocene-lower Miocene and lower Miocene-Pliocene sediments after Anderson (1956Anderson ( , 1957Anderson ( , 1959, Kuenzi and Richard (1969), Rasmussen (1973), andWopat andothers (1977). Geologic factors most important in evaluating the favorability of the basins for uranium deposition are probably an adequate source rock for the uranium, both permeable and impermeable strata, and reducing conditions.…”

Section: Samplesmentioning

confidence: 99%

Dillon quadrangle, Montana and Idaho

Wodzicki¹,

Krason²

1981

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All geologic conditions in the Dillon Quadrangle (Montana and Idaho) have been thoroughly examined, and, using National Uranium Resource Evaluation criteria, environments are favorable for uranium deposits along fractured zones of Precambrian Y metasediments, in the McGowan Creek Formation, and in some Tertiary sedimentary basins.A 9-m-wide quartz-bearing fractured zone in Precambrian Y quartzites near Gibbonsville contains 175 ppm uranium, probably derived from formerly overlying Challis Volcanics by supergene processes.The Mississippian McGowan Creek Formation consists of uraniferous, black, siliceous mudstone and chert. In the Melrose district it has been fractured by a low-angle fault, and uranium has been further concentrated by circulating ground water in the 2-to 6-m-thick brecciated zones that in outcrop contain 90 to 170 ppm uranium.The Wise River, northern Divide Creek, Jefferson River, Salmon River, Horse Prairie, Beaverhead River, and upper Ruby River Basins are considered favorable for uranium deposits in sandstone. Present are suitable uraniferous source rocks such as the Boulder batholith, rhyolitic flow breccia, laharic deposits, or strongly welded tuffs; permeable sediments, including most sandstones and conglomerates, providing they do not contain devitrified glass; suitable reductants such as lignite, pyrite, or low-Eh geothermal water; and uranium occurrences. 9 probably flowed out into the Horse Prairie, Grasshopper Creek, Jefferson River, and upper Ruby River Tertiary basins. Plutonic Rocks. Four major Laramide batholiths crop out within the Dillon Quadrangle. They are the Boulder batholith, the Idaho batholith, the Pioneer batholith, and the Tobacco Root batholith. All are dominantly quartz monzonitic composition and hypidiomorphic-granular texture. Minor Tertiary intrusions are present, mainly in Idaho.The southern part of the Boulder batholith lies within the quadrangle and consists mainly of quartz monzonite, but also contains gabbro, quartz diorite, granodiorite, granite, and the late-stage differentiates, alaskite, aplite, and pegmatite. The batholith dates 78 to 72 m.y., overlapping the age of the Elkhorn Mountain Volcanics (Robinson and others, 1968). The batholith intrudes pre-Belt gneisses, Belt Supergroup metasediments, Paleozoic-Mesozoic sediments, and Elkhorn Mountain Volcanics. Two radically different models have been proposed for the emplacement of the batholith.

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Phanerozoic stratigraphy of the northern Rocky Mountain region

Peterson¹

Sedimentary Cover—North American Craton

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Middle Tertiary Unconformity, North Boulder and Jefferson Basins, Southwestern Montana

Cited by 3 publications

References 0 publications

Summary geologic report on the Missoula/Bitterroot Drilling Project, Missoula/Bitterroot Basins, Montana

Summary geologic report on the Missoula/Bitterroot Drilling Project, Missoula/Bitterroot Basins, Montana

Dillon quadrangle, Montana and Idaho

Phanerozoic stratigraphy of the northern Rocky Mountain region

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