Abstract

Sedimentologic studies in south-central Utah indicate a close association between uranium-bearing sandstone beds and thin gray carbon-bearing mudstone beds that were deposited in small lakes or ponds and are referred to as favorable gray mudstone beds. Favorable mudstone strata may occur directly above or below ore-bearing sandstone beds, or the ore-bearing part of a sandstone bed may occur a short distance laterally from the nearest favorable mudstone bed.

The distribution of favorable gray lacustrine mudstone strata apparently was influenced by the relationships among stream energy or transport capacity, stream flow pathways, and contemporaneous tectonic movements. The lake beds occur in the distal part of an alluvial-plain facies that was deposited largely by low-energy braided streams, as suggested by high stratification ratios in fluvial sandstones. Facies relationships and variations in thickness of the main ore-bearing depositional sequence suggest that contemporaneous tectonism produced folds that trended more or less perpendicular to the general direction of stream flow. The growing folds evidently acted as barriers to sediment distribution and allowed small lakes or ponds to form in the most sheltered parts of the growing synclines. The consistent association of favorable mudstone beds with uraniferous sandstone suggests an exploration strategy based on searching for the favorable mudstone beds and then for the closely associated ore deposits.