About This Item

Share This Item

The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 55 (1971)

Issue: 2. (February)

First Page: 358

Last Page: 358

Title: Sedimentary Environmental Control of Sandstone-Type Uranium Deposits: ABSTRACT

Author(s): Ruffin I. Racklay

Article Type: Meeting abstract

Abstract:

Uranium deposits of the Rocky Mountain area are present in fluvial sandstones that were derived from granitic highland source areas and deposited in adjacent intermontane basins. The sandstones are arkosic to arkose in composition and contain a small percentage of carbonized plant debris and pyrite, medium grained to conglomeratic in size, subrounded to angular in shape, and are poorly to moderately sorted. The sandstones intertongue and are interbedded with green mudstone.

The host sandstone sequence represents a change in tectonic and/or climatic conditions. A local or regional unconformity is present at the base of the sequence and the character of the rocks is commonly substantially different. The climate was temperate and humid, and the groundwater level was very near the surface. The oxidation-reduction potential was low, which caused the carbonization of woody debris and the formation of pyrite, a condition also favorable for the precipitation of uranium and the other commonly associated metals. The depositional pattern of the aggrading streams was influenced by both tectonic and topographic elements of the area being buried.

Following deposition and burial further tectonic events induced changes in the hydrodynamic system which caused an invasion of the reduced sediments by an oxidizing cell that obtained much of its energy from the oxidation of the pyrite. The oxidizing cell mobilized the uranium and other susceptible elements and swept them ahead. Where the cell encountered resistance from variations in thickness of the sandstone units its progress was impeded, therefore areas of pinchouts or intertonguing of sandstone and mudstone tend to be favorable areas for the localization of uranium mineralization.

End_of_Article - Last_Page 358------------

Copyright 1997 American Association of Petroleum Geologists