Abstract: Mineralogy of Uranium Deposits Northeast of Laguna District, Sandoval County, New Mexico

S. R. Hafenfeld, D. G. Brookins

In the Westwater Canyon Member of the Morrison Formation, northeast of the Laguna district, Sandoval County, New Mexico, both primary and secondary uranium mineralization is present. Petrographic and chemical analyses of core samples show that the host rock consists of fine- to medium-grained quartz sandstone with up to 10 percent feldspar, calcite (as a weak cementing agent), minor amounts (< 1 percent) of very fine-grained pyrite, clay galls, and kaolinite "nests," with occasional interbedded siltstones. Quartz overgrowths are also common in unaltered sediments, being most abundant in the finer grained fraction, and are sparse to absent in mineralized and altered ground. Organic matter exhibits a positive correlation with mineralization. In oxidized rock calcite and yrite are absent.

During and/or after the deposition of Westwater channel sands, the introduction of uranium-bearing solutions was followed by precipitation of coffinite(?) as a result of bacterial and/or chemical action (on the attendant organic material and iron sulfides) which provided a suitable geochemical environment. Later oxidizing ground waters destroyed calcite and pyrite, locally remobilizing the uranium which was redeposited as secondary or "stack" ore, leaving a residue of iron oxide staining (to varying degrees) throughout the host rock. This presumably was followed by kaolinization as a weak cementing agent.

AAPG Search and Discovery Article #90979©1975 AAPG – SEPM Rocky Mountain Sections Annual Meeting, Albuquerque, New Mexico