University of Tasmania
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Geology, geochemistry and gold mineralisation in the Sunset Well area, Eastern Goldfields Province, Western Australia

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posted on 2023-05-26, 20:05 authored by Grey, K A
The Sunset Well study area, 10 kilometres east of Leonora in the Archaean Eastern Goldfields Province of Western Australia, forms part of a group of gold exploration tenements held by RGC Exploration Pty Ltd. Geological mapping and a variety of geochemical techniques have outlined alteration within a shear zone and mineralisation at the Prospero prospect. Geological mapping has delineated three lithostratigraphic sequences separated by NNW trending faults. The western succession is comprised of andesite-derived volcaniclastic sediments (sandstone, breccia) with minor fine grained clastic sediment (shale) which are interpreted to represent a stack of subaqueous debris flows derived from a subaqueous andesite-dominated volcanic complex. The central succession is dominated by massive tholeiitic and high-Mg basalts with minor sediments. Fine grained clastic sediments make up the majority of the eastern succession. All sequences have been intruded by dolerite/gabbro sills and the western and central successions are intruded by several granodioritic porphyry stocks. Deep lateritic weathering and subsequent partial erosion has exposed saprolitic subcrops over much of the area with remnants of lateritic duricrust. Surface geochemical anomalism related to the mineralisation within the Prospero shear is outlined in residual lateritic material with a Au-W association (380 ppb Au and 12 ppm W). Sampling of saprolite from surface soil and drilling samples displays a spatial but non-coincident Au-As-W-Pb-Sb-Cu-Zn association. Analysis of K and Na in saprolite and saprock material outlines the sericitic and albitic alteration zones with maximum values centred on the mineralised Prospero shear zone. Mineralisation at Prospero is located within a broad east-dipping shear zone between andesitic volcaniclastics and high-Mg basalt. Supergene saprolitic mineralisation is well developed in broad subhorizontal sheets in the middle saprolite with a smaller accumulation near the saprolite-saprock boundary. Bedrock mineralisation is associated with intense zonal metasomatic alteration comprising an outer chlorite-sericite-quartz-calcite, middle sericite-quartz and inner quartz-albite-sericite-dolomite/ankerite-fuchsite alteration zone. Sulphide mineralogy is dominated by pyrite with minor galena, chalcopyrite, arsenopyrite, sphalerite, chalcocite and covellite. Gold grades are generally 0.2-0.6 ppm in the sericite zone and 0.5-3.0 ppm in the inner silicified zone. Thin quartz veins contain higher grade (5.0-30.0 ppm) mineralisation, with gold occuring as fine (-5 micron) free grains. The primary mineralised zone has a Au-As-W-Cu-Sb-Sr-V-Si-K-Na association. Mineralisation is interpreted to have formed during D1 shear zone formation and synchronous with zonal alteration.


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Copyright 1994 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s). Thesis (M.Ec.Geol.)--University of Tasmania, 1995. 7 folded maps in pocket at back of vol

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