Geochemical characteristics of the Church Rock 1 and 1 East uranium deposits, Grants uranium region, New Mexico

Abstract

In the Church Rock 1 and 1 East mines, Grants uranium region (GUR), New Mexico, uranium orebodies occur within three sandstone units in the upper part of the Westwater Canyon Member of the late Jurassic Morrison Formation. Geochemical analyses reveal that organic carbon contents in ore samples from all three sand units are uniformly low (most are less than 0.01 percent). Vanadium (ranging from 0.0002 to 0.19 percent) and sulfur (ranging from <0.01 to 0.74 percent) typically show positive correlations with uranium; however, vanadium contents rarely exceed those of uranium in ore samples. Although no systematic relationship of either selenium or molybdenum to uranium is evident, some ore samples contain anomalously high concentrations of either of these elements. Geochemically, the ore deposits of the Church Rock area contrast greatly with primary (tabular) uranium orebodies in the GUR which contain abundant organic carbon and greater amounts of vanadium and sulfur. These differences and radiometric age determinations strongly suggest that the Church Rock ores formed as a result of the redistribution of uranium from preexisting uranium deposits within the last 1 m.y. However, the Church Rock deposits differ geochemically from redistributed orebodies in the Westwater Canyon Member elsewhere in the GUR. Specifically, redistributed orebodies in the Ambrosia Lake district, which are comparable in contents of uranium and organic carbon with the Church Rock deposits, are characterized by vanadium contents typically higher than those of uranium. Similarly, sulfur contents in the redistributed deposits of the Ambrosia Lake district are greater than those found in the Church Rock ores. In addition, anomalously high concentrations of molybdenum have rarely been found in other redistributed orebodies of the GUR.