Combining geochemistry and geochronology of transported regolith to reveal bedrock-hosted mineralization in the arid east Wongatha area of south central Western Australia

Abstract

Metal anomalies in transported regolith that overlie bedrock-hosted mineralization indicate that a component of mineralization (the exogenic component) can migrate through regolith. In the east Wongatha area of Western Australia, the exogenic component in the fine fraction of sandplain deposits is spatially linked to known and/or inferred bedrock-hosted Au mineralization. In three regolith profiles, the concentration of Au in aqua regia and deionized water Au are correlated, and in two of the profiles Au varies in concentration independent of changes in regolith composition. In one profile, the Au concentration in chemically-mature regolith dominated by quartz sand decreases from 31 ppb at c. 180 cm depth to 7.3 ppb at 15 cm. Optically stimulated luminescence (OSL) ages of stratigraphically-controlled regolith samples ranging from 166.9 ± 46.6 ka to 5.4 ± 1.1 ka show a strong correlation with depth (r 2 = 0.99) over a three-metre interval, indicating a sandplain accumulation rate of c. 17 mm/1000 years. The decrease in Au concentration in east Wongatha regolith can be related to the migration rate of the exogenic component and the rate of sandplain accumulation. Supplementary material: Screening and analytical data for the < 50-µm fraction of regolith from three profile sites in the east Wongatha area are available at https://doi.org/10.6084/m9.figshare.c.4074413