CRC LEME
Open File Report 55
ABSTRACT
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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