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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 65 (1981)

Issue: 5. (May)

First Page: 952

Last Page: 952

Title: Geology and Uranium Deposits of Tallahassee Creek District, Fremont County, Colorado: ABSTRACT

Author(s): Bruce A. MacPherson

Article Type: Meeting abstract


Following discoveries of commercial uranium deposits near Tallahassee Creek in 1955 and 1956, field studies were undertaken to investigate the general geology of the area and its relation to uranium occurrences. The Tallahassee Creek district may serve as a type locality upon which to further evaluate uranium potential in adjacent areas with similar geology.

Rocks of the Tallahassee Creek district are Precambrian, Tertiary, and Quaternary in age. The Precambrian is composed of the Pikes Peak granite and metamorphic rocks of the Idaho Springs Formation which have complicated structural relations and form the basement to the study area. Approximately 100 to 300 ft (30 to 91 m) of relief existed on the Precambrian surface before deposition of the Tertiary sediments. The basal unit of the Eocene consists of residual arkoses which are restricted to the lows of the buried Precambrian topography. Sanidine rhyolites and augite andesites overlie the arkoses and also overstep the Precambrian relief. After an erosional period, Oligocene and Miocene volcanic conglomerates with interbedded lavas and tuffs were deposited unconformably over the Eocene a gite andesites and the Precambrian basement. Overlying the conglomerates, thick deposits of volcanic rock, chiefly brecciated andesite flows, pyroclastics, and rhyolites, are considered to be Oligocene-Miocene in age by superposition only. A series of parallel, northwest-trending faults, apparently reflects pre-existing zones of weakness in the Precambrian basement. Movement occurred during early Oligocene-Miocene time and again in the late Miocene or Pliocene.

Two uranium deposits occur in the volcanic conglomerates, and a third in the arkosic sediments at the base of the Tertiary. Generally, the ore deposits are lenticular bodies in paleostream channels or basins. Physical and chemical characteristics of the enclosing sediments are believed to have influenced the localization of uranium. All ore bodies are related to faults, or linear features which reflect probable faults at depth. It is believed that the uranium originated in hypogene solutions which ascended along the fault zones.

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