Geochemical anomalies in soils and uppermost siliciclastic units overlying the Phoenix uranium deposit, Athabasca Basin, Saskatchewan

Abstract

Many mineral deposits are concealed by younger rocks and unconsolidated glacial deposits, which make buried deposits difficult to explore using traditional exploration tools. Under the TGI4 program, this project is examining whether surficial geochemical anomalies exist for deeply buried uranium deposits. This study selected the Phoenix deposit on Denison Mines' Wheeler River Property, located in the southeastern Athabasca Basin, northern Saskatchewan. Discovered in 2008, the deposit currently has a National Instrument 43-101 indicated resource of approximately 40 million lbs U3O8. The uranium oxide minerals are localized within four pods termed the A, B, C and D ore zones. These pods are located mostly along the unconformity between the crystalline basement rocks and overlying Athabasca sandstone units, approximately 400 metres below the surface. The region is characterized by gently rolling hills comprising glacial till and moraines ranging in thickness from 30 to 50 m, with continuous permafrost. A total of 226 soil samples (humus, E-, B-, and C-horizon) were collected from 59 sites along 3 transects at approximately 10 metre intervals over the "A" and "B" ore zones. The extensive transects facilitated sampling of both "mineralized" and "background values" in the study area. Preliminary geochemical analyses of the samples revealed the presence of U, Mo, Co, Ag and W anomalies in humus, B-horizon soil and uppermost sandstone units overlying the ore zones and directly above the basement location of a nearby northeast-trending "WS Hanging Wall" shear zone. Concentrations in the surface media are up to 6 times background values for U, 5 times for Mo, 4 times for Co, 20 times for Ag and 18 times for W. The geochemical anomalies in the surface media and the uppermost sandstone units over the shear zone suggest that the fault has acted as a conduit for upward migration of fluids from the deposit. This preliminary study indicates that geochemical analysis of surface media is potentially an efficient and inexpensive exploration tool for detecting deep-seated uranium deposits.