Role of fluid mixing and fault-related sulfide in the origin of the Ray Point uranium district, South Texas

Abstract

The Lamprecht and Felder deposits are two of many roll-type uranium deposits hosted by the Miocene Oakville Sandstone in the Ray Point (south Texas) uranium district. The deposits in this district are aligned parallel to or are intersected by the Oakville fault which suggests control by the faults on their origin and/or preservation. The Lamprecht and Felder deposits show fundamentally similar patterns of geochemical zonation and of distribution of authigenic iron disulfide (FeS/sub 2/) minerals. Distribution of U, Mo, and Se are typical of roll-type deposits that result from invasion of geochemically reduced rock by oxygenated uranium-bearing solutions. Sulfur content of these deposits is high (as much as 9%), with almost all sulfur occurring as FeS/sub 2/ minerals. Organic carbon is virtually absent. Four distinct stages of FeS/sub 2/ mineral formation are recognized: (1) a generation of isotopically light (delta/sup 34/S 0%o), and (4) a yet later generation of marcasite with isotopically light sulfur close to the values of stages 1 and 2. The alteredmore » tongue in these deposits is anomalous in that it contains FeS/sub 2/ minerals in contrast to other Texas and Wyoming roll-type deposits which typically have an oxidized (ferric iron-bearing) altered tongue. The dominant FeS/sub 2/ mineral in the altered tongue is isotopically heavy pyrite (stage 3) with subordinate amounts of late marcasite (stage 4).« less