Whole rock geochemistry and hyperspectral mineralogy of Western Australian LCT pegmatites

CSIRO Mineral Resources evaluates geochemical and optical sensing technologies for cost-effective exploration and ore body characterisation of a wide range of critical metals deposits, such as pegmatite-hosted Li-deposits. This paper presents varieties of ore and gangue mineral assemblages of five drill cores from the Greenbushes, King Col and Londonderry LCT pegmatites, located in the Yilgarn and Pilbara Cratons of Western Australia, respectively. The mineralogical drill core data were collected by the Geological Survey of Western Australia (GSWA) using a hyperspectral drill core scanner, HyLogger3, which is part of AuScope's National Virtual Core Library research infrastructure program. The HyLogger3 data are publicly available through the AuScope portal (http://portal.auscope.org.au/) and GSWA's GeoView portal (GeoVIEW.WA). The thermal infrared hyperspectral data collected by HyLogger3 allow cost-effective mapping of Li-host minerals, such as spodumene, petalite, holmquistite and amblygonite. Spodumene represents the main Li-host at Greenbushes, whereas considerable amounts of petalite can be found at King Col in addition to spodumene. Holmquistite and amblygonite are minor Li-host minerals. A range of spectral signatures of spodumene and petalite can be observed in both mineral deposits and are potentially due to variations of chemical composition of the Li-host minerals, including Fe:Al and Li:Na ratios. Feldspars are common gangue minerals in both deposits and show different Na:Ca ratios down hole, indicating zoning of the ore body. The HyLogger3 data were used to identify 101 samples from Greenbushes drill core C3DD024 for FTIR and geochemical analysis, which allowed calibration of the HyLogger3 data and Partial Least Squares-modelling based prediction of Li, Na and other key geochemical elements across the five drill cores. Our case study demonstrates the potential for advanced but cost-effective Li-resource characterisation by means of reflectance spectroscopy, helping to assess the economic value of different ore bodies quickly.