CRC LEME
Open File Report 107
ABSTRACT
Selective and partial extraction analyses of transported overburden
for exploration in the Yilgarn Craton and its margins
Gray, D.J., Wildman, J.E. and Longman, G.D.
Seven sites from across the Yilgarn Craton and the northern Proterozoic
margin were selected to test the utility of partial extractions
for exploration for buried mineralization. The techniques used were
selective extractions for carbonates, Mn oxides and amorphous Fe,
varying HCl treatments, the CSIRO iodide extraction for Au, mobile
metal ions (MMI) and enzyme leach. The selective extractions work
consistently and give good correlations with the HCl digests. The
MMI method involves two separate extractions: the first, for Cd,
Cu. Pb and Zn, gave results that are similar, in terms of comparison
between samples at each site, to HCl and selective extractions;
whereas the second extraction, for Ag, Au, Co, Ni and Pd. commonly
dissolves all of the extractable Au and Ag (commonly 70-80% of the
total Au, and closely correlated with total, iodide and HCl soluble
extractions). Therefore, the MMI extraction does not appear to be
giving any additional information for Au or Ag than can not be obtained
using standard analyses. The enzyme leach reagent is targeted at
an 'amorphous' Mn phase, though the proportion of the Mn dissolved
(< 0.5 to 20%) varies dramatically between sites. The enzyme
leach method also appears to give unique results, not correlated
with other methods, and gives a much larger range of elements than
MMI. However, Cs, Fe, Ga, Hf. La, Li, Nb, rare earth elements, Pb,
Sc, Sn, Th, Ti and Zr show very close linear correlations, suggesting
either a highly specific interaction between these elements and
Fe or an analytical interference from Fe
The extraction results for the soil traverses indicate that soil
is a successful exploration medium only where the transported overburden
in thin (<10 m), as at Safari and in restricted areas at Baxter
and Fender, and that Au, for a number of methods, is by far the
best target element. Use of partial extractions gave a number of
strong false positives and/or very poor ability for the extraction
methods to shows buried mineralization, except where total extractions
would work anyway. Even at those sites where Au successfully delineates
mineralization, partial extraction methods for the other elements
are unsuccessful.
Last updated: Sunday, August 05, 2001 14:02:36
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