Alteration mapping on drill cores using a HySpex SWIR-320m hyperspectral camera: Application to the exploration of an unconformity-related uranium deposit (Saskatchewan, Canada)

International audienceIn mineral exploration, the search for geophysical, geochemical, and mineralogical pathfinders is of critical importance,and many techniques have been used to detect the presence of mineralization and related host-rockalteration. In the case of unconformity-type uranium deposits that are spatially-linked to unconformities betweensedimentary basin and underlying basement rocks, hydrothermal fluid-rock interactions produced extendedalteration envelopes which are used to target mineralization and are therefore important guides foruranium exploration.The purpose of this study is to evaluate the utility of hyperspectral mapping of alteration minerals in drill coresamples using the HySpex SWIR-320m hyperspectral camera that covers the 1300–2500 nm (SWIR) spectralrange. A series of representative samples, including pegmatite, pelitic gneiss, and sandstone, from the areaaround the Cigar Lake uraniumdeposit (Athabasca Basin, Saskatchewan, Canada) were analyzed by SWIR reflectancespectroscopy and opticalmicroscopy. An algorithmwas developed and implemented in the IDL language todetermine both the positions and depth of diagnostic absorption bands of variousminerals, and to calculate semiquantitativeestimates of mineral content. Subsequent petrographic analysis using optical microscopy validatedthe hyperspectral mapping methodology.Selected alteration minerals present in the core samples, such as clay minerals and carbonates, weremapped. The“pseudo-modal” mineralogical composition for each sample was determined. The mineral maps highlight themineralogy and the main petrographic textures such as foliation, bedding, veins, and the geometry of pervasivealteration.This study offers new perspectives for the use of this method in mineralogical analysis of drill core samples andthe characterization of hydrothermal alteration. The proposed mineralogical semi-quantification methodologymay be used in other geological contexts and should improve the understanding of the mineralogical alterationdistribution around hydrothermal metal deposits