Dendrochemistry and soil clay geochemistry applied to exploration for deep U mineralization at the Halliday Lake Prospect, Athabasca Basin, Canada

Abstract

Drilling at the c. 750 m deep Halliday Lake prospect in the Athabasca Basin has identified features favourable for unconformity-related U mineralization such as sandstone enrichments in pathfinder elements, graphitic metapelite gneiss, sandstone and basement hosted faulting, hydrothermal alteration and sub-economic U mineralization. Soils, jack pine ( Pinus banksiana ) and black spruce ( Picea mariana ) tree cores were collected on a 250 m sampling grid to assess their effectiveness as exploration geochemical media for concealed mineralization. The <2 µm soil clay-size fractions comprise mixtures of quartz, chlorite, illite, kaolinite, and plagioclase with the plagioclase reflecting basement boulders transported in the Quaternary cover. Basement rocks in the till impart a geochemical signature enriched in K, Ba, Bi, Co, Cr, Cs, Cu, Li, Mn and Ni, complicating the interpretation of some pathfinder elements in the <2 µm soil clay-size fraction. Tree cores have Mo, Co, Cu and S enrichments in areas of thin overburden also associated with sandstone hosted hydrothermal alteration and pathfinder element enrichment. Radiogenic Pb isotope ratios in the <2 µm soil clay-size fraction are associated with drill holes hosting sub-economic U mineralization whereas barren drill holes are spatially associated with common Pb isotope ratios. Radiogenic tree core Pb isotope ratios are supportive of the <2 µm soil clay-size fraction Pb isotope ratios.