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Open File Report 55

Mineralogy and geochemistry of the Lights of Israel Gold Mine, Davyhurst, Western Australia

Douglas, G.B., Robertson, I.D.M. and Butt, C.R.M.

The dispersion of gold and 32 other elements in the lateritic regolith has been studied at the Lights of Israel gold mine, Davyhurst. The Au mineralization occurs primarily within a westerly dipping biotite schist within tholeiitic metabasalts that have been metamorphosed to amphibolite facies. The mineralized sequence has been variably weathered and has been truncated to the upper saprolite, and is partially concealed beneath a thin (1 m) residual soil which has received minor input from surrounding granitoid terrain. Two hundred and sixty-one samples from near the surface, within the saprolite and from the fresh rock have been analyzed to examine the element distribution throughout the entire remaining weathering profile. The elements associated with Au mineralization appear to be S, W, As, Sb and Mo, but these have low mean concentrations i.e. S (0.3 %), W (2.9 ppm), As (5.5 ppm), Sb (0.6 ppm) and Mo (3.6 ppm) compared to other Au mineralization in the Yilgarn Block.

The Au distribution in the regolith is typical of the southern Yilgarn Block with a patchy dispersion within the regolith and a distinct geochemical anomaly associated within pedogenic carbonates. A zone of apparently secondary Au enrichment occurs approximately 30 m below the surface and is accompanied by minor enrichments in a number of other elements including rare earths (La, Ce, Y), and base and transition metals (Fe, Mn, Co, Cu, Zn, Ni). There is little evidence of the zone of leaching in the upper saprolite horizons that is commonly reported from other deposits. The unweathered metabasalts, saprolites, near surface samples, soils and, to a lesser extent, biotite schists can be discriminated geochemically using Zr-Ti-Cr plots.

There are several implications for exploration for Au and other commodities. In general, the data presented in this report support the contention that at local to subregional scales, Au is one of the best indicators of Au mineralization, despite (or perhaps because of) its chemical mobility during weathering. The principal proviso is that sampling must take into account the distribution of Au in the regolith, as exemplified by Lights of Israel and numerous other sites in the Yilgarn Block.

Last updated: Thursday, January 06, 2000 09:03 AM


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