Abstract
The discovery of new mineral deposits contributes to the sustainable mineral industrial development, which is essential to satisfy global resource demands. The exploration for new mineral resources is challenging in Canada since its vast lands are mostly covered by a thick layer of Quaternary sediments that obscure bedrock geology. In the course of the recent decades, indicator minerals recovered from till heavy mineral concentrates have been effectively used to prospect for a broad range of mineral deposits including diamond, gold, and base metals. However, these methods traditionally focus on (visual) investigation of the 0.25–2.0 mm grain-size fraction of unconsolidated sediments, whilst our observations emphasize on higher abundance, or sometimes unique occurrence of precious metal (Au, Ag, and platinum-group elements) minerals in the finer-grained fractions (<0.25 mm). This study aims to present the advantages of applying a mineral detection routine initially developed for gold grains counting and characterization, to platinum-group minerals in <50 µm till heavy mineral concentrates. This technique, which uses an automated scanning electron microscopy (SEM) equipped with an energy dispersive spectrometer, can provide quantitative mineralogical and semi-quantitative chemical data of heavy minerals of interest, simultaneously. This work presents the mineralogical and chemical characteristics, the grain size distribution, and the surface textures of 2664 discrete platinum-group mineral grains recovered from the processing of 5194 glacial sediment samples collected from different zones in the Canadian Shield (mostly Quebec and Ontario provinces). Fifty-eight different platinum-group mineral species have been identified to date, among which sperrylite (PtAs2) is by far the most abundant (n = 1488; 55.86%). Textural and mineral-chemical data suggest that detrital platinum-group minerals in the studied samples have been derived, at least in part, from Au-rich ore systems.
Highlights
Despite historically high mineral exploration spending over the past decades, there has been no corresponding increase in new discoveries [1]
A total of 2664 discrete platinum-group minerals (PGM) grains have been identified and analyzed in heavy mineral super-concentrates obtained from processing of till samples
The diversity and distribution of PGMs found in the studied samples are illustrated in Figures 3 and 4, and selected backscatter electron (BSE) images of relatively abundant platinum-group elements (PGE)-bearing minerals are displayed in Figures 5 and 6
Summary
Despite historically high mineral exploration spending over the past decades, there has been no corresponding increase in new discoveries [1]. The industry is facing a challenge in regard of resource renewal, and new exploration methods are needed, for targeting ore deposits buried under glacial sediment and areas of transported cover that does not respond properly to geophysics, such as in vast areas of the subarctic zone (e.g., Alaska, Canada, Scandinavia, Siberia) [2]. In such environment, the glacial sediments, perceived as a hindrance to exploration, led to development of methods capable of detecting the signal from the mineral deposits as they are eroded and dispersed in the sediments. This issue mostly relates to the difficulty of prospecting for this group of metals, notably due to their low abundance, mineralogical complexities, and lack of geophysical or geochemical signatures outside of nickel sulfide occurrences
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