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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 65 (1981)

Issue: 3. (March)

First Page: 565

Last Page: 565

Title: Environment Favorable for Deposition of Uranium, Jefferson River Basin, Southwestern Montana: ABSTRACT

Author(s): Linda K. McClain, Geoffrey W. Mathews

Article Type: Meeting abstract


Evaluation of 2° quadrangles for the U.S. Department of Energy's National Uranium Resource Evaluation (NURE) has shown that numerous Tertiary basins in southwestern Montana are potentially favorable for uranium deposits. However, only a few criteria essential for uranium deposition have been substantiated in each favorable basin. These criteria include one or more of the following: demonstrable source rock, evidence that uranium has been leached from the source and transported in surface or ground water, favorable host lithologies, potential reductants, and permeability contrasts. A small area of the Jefferson River basin adjacent to the northern end of the Rader Creek pluton of the Boulder batholith is of particular interest because it meets most of these criteria.

As much as 65% of the uranium has been leached from higher parts of the Rader Creek granodiorite during unroofing. This is indicated by trend surface analysis of modal data and major oxides from the pluton, and by significant correlations between elevation and U3O8, Th/U, and other selected geochemical variables within the pluton.

Surface drainage and near-surface ground water within the Rader Creek pluton carry leached uranium eastward into the Jefferson River basin. Streams draining the pluton contain up to 25 ppb uranium, whereas ground water from wells in the Tertiary basin sediments just adjacent to the pluton contains up to 50 ppb uranium. These fluvial and lacustrine Tertiary sediments were derived mainly from the Boulder batholith. Permeability contrasts in these sediments provide suitable sites for uranium concentrations. Traces of carbonaceous material and reduced sulfur-bearing hot springs are indications of adequate reductants for uranium.

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