Gold exploration in the callion area, eastern goldfields, western Australia

Abstract

Abstract The Callion gold-quartz veins are hosted by metabasalts, interflow sediments and acid metatuffs within the Archaean Norseman-Wiluna greenstone belt. The area has been subjected to deep lateritic weathering. Gold prospecting using soil geochemistry led to the discovery of a laterite Au deposit (geological reserves of 103,000 t with 1.86 g/t Au at 0.7 g/t cut-off) and subsequently to the discovery of the underlying quartz vein mineralization (geological reserves of 104,000 t with 7.9 g/t Au at 2 g/t cut-off). The quartz vein mineralization is blind, beneath 2–10 m of laterite cover. The vein, which can be traced along strike for 1 km, is mineralized over a strike length of 300 m. Weathering around the vein extends to a depth of 70 m below surface. Ore microscopy shows that the Au in the weathered vein was partially mobilized and deposited contemporaneously with Fe-hydroxides. Mining of the laterite and the top of the quartz vein enabled a detailed reconstruction to be made of the Au-grade distribution from the top of the laterite down to the saprolite. The grade distribution is mushroom-shaped, widening at the top of the mottled zone or base of the pisolithic zone. From the vein in the saprolite, the “mushroom”, defined by the 2.5 ppm Au contour, widens to 40 m, at least 5 times the original width. This zone represents the transition to the overlying wide soil anomaly which has peak Au values of 2 ppm, which are about 50% of those in the laterite in the vicinity of the vein. Magnetic methods were also used during the course of exploration and led to the discovery of another small mineralized vein.