Radiometric results and areal distribution for granitic samples from the Granite Mountains, Wyoming

Abstract

Analyses of surface samples from the Granite Mountains, Wyoming, generally agree with the findings from drilling at two different localities. The dominant Precambrian granitic rock type is the biotitic phase of the granite of Lankin Dome. This rock type is characterized by high potassium and anomalously high thorium concentrations, and is the most favorable granitic source for the uranium deposits in the surrounding area. Areal distribution patterns for radioelement concentrations show that the most favorable source regions are located closest to known uranium deposits. Most of the granitic rocks in the Granite Mountains region are characterized by high thorium-uranium ratios. These high ratios are interpreted to be the result of uranium loss. Non-gaussian distribution of radioelement contents and poor correlation between radioelement pairs are interpreted to be the result of some redistribution of radioelements during the last phase of granite crystallization and to recent uranium loss. A good correlation between thorium and iron is attributed to the mobilization of thorium into microcrystalline iron oxides during a late portion of the magmatic history. A comparison of sulfur data for surface and shallow drill-hole samples suggests that sulfur has been removed from the granite to at least a depth of 20 m. The loss of uranium and sulfur from these samples suggests that other trace elements found in association with uranium deposits might have been removed from the granite.