Geochemical exploration for buried sandstone-hosted uranium mineralization using mobile U and Pb isotopes: case study of the REB deposit, Great Divide Basin, Wyoming

Abstract

Mobile radiogenic lead isotopes (206Pb, 207Pb, 208Pb and 210Pb) represent products of radioactive decay of their parental uranium and thorium isotopes (238U, 235U, 232Th), and are considered potential geochemical pathfinders of buried sandstone-type uranium deposits. Soil samples collected along a geochemical traverse intersecting buried uranium roll front mineralization at the REB deposit in the Great Divide Basin, Wyoming, USA were studied. Mineralization of this deposit is hosted in weakly lithified arkosic sands, at a depth of 120–200 m, without a strong surficial expression of its presence at depth, which makes discovery of this deposit type difficult, slow and expensive. All soil samples have been analysed for ratios of the mobile long-lived Pb isotopes and their parental U and Th isotopes, determined from partial leach products obtained using a weak acid leaching technique. The samples were also analysed for trace elements, assayed both in the partial leach products and using conventional whole-soil sample assays. Ratios of the mobile radiogenic Pb isotopes to their parental U and Th isotopes (206Pb/238U, 207Pb/235U and 208Pb/232Th) determined in the partial leach products exhibit anomalous contents in the soil samples collected above the uranium rolls. The anomalous values are several times greater than background values, to lateral distances of 350–400 m outside of the roll fronts. Notably, conventional whole-soil assays have failed to detect the anomalies that were detected using mobile Pb isotopes. Supplementary material: Minor and trace elements assays of the geochemical samples are available at https://doi.org/10.6084/m9.figshare.c.5610980