Use of stream sediment elemental enrichment factors in geochemical exploration for carbonatite and uranium, Arkansas, U.S.A.

Abstract

Three hundred and thirty-five stream sediment samples (<75×10−3 mm diameter) from 3275 km2 in central Arkansas, U.S.A. were utilized to evaluate geochemistry as an exploration method for carbonatite and U in this geologically diverse area. Approximately one-half of the area is located in the Ouachita Mountains and the other half is located in the Gulf Coastal Plain. Alkalic igneous intrusions are located in both regions; however, shale, sandstone, novaculite and unconsolidated sediments are the major lithologies. The areas was divided into four geochemical regions based on similarities in geology and geochemistry. Neutron activation analysis was used to analyze for rare earth elements (REE), Ti, F, U, and 17 other elements. A REE+Ti+ F map based on an enrichment index and a U concentration map delineate two anomalous areas. One of these anomalous areas is near the Magnet Cove intrusion which contains carbonatite, and the other is near lignite deposits that contain U and unusually high concentrations of REE. R-mode cluster analysis indicates that these two areas are distinctly different geochemical environments. Less anomalous samples are associated with syenite intrusions and shale. Anomalous samples associated with the carbonatite are enriched in light REE relative to anomalies associated with syenite intrusions and are enriched in light REE and Ti compared to anomalies associated with sedimentary rocks and lignite.