CRC LEME
Open File Report 28
ABSTRACT
Laterite geochemistry in the CSIRO-AGE Database for the Albany-Fraser
Region (Collie, Dumbleyung, Mt Barker, Pemberton sheets)
Grunsky, E.C.
A multi-element geochemical study has been carried out on laterite
and associated ferruginous samples that cover parts of the granitoid-gneiss
terrain of the COLLIE, DUMBLEYUNG, MOUNT BARKER, and PEMBERTON 1:250
000 map sheets. The report presents a summary of the data and a
provisional interpretation of selected parts of the data. The data
used in this study are contained in the accompanying diskette (in
the back pocket).
The sampling arose as part of a combined research programme between
CSIRO and an experimental exploration programme (the AGE Joint Venture
Programme) during the period 1983 to 1986. The database which was
used for the study is composed of laterite and associated ferruginous
samples collected over predominantly gneissic and felsic intrusive
rocks that span the Archaean Yilgarn Block and the Proterozoic Albany-Fraser
Province. The data were split into two groups representing the distinctions
between the two geological provinces. Laterite is the most abundant
material. The laterites are predominantly composed of loose nodules
and pisoliths and number 543 samples in the Yilgarn block, and 456
samples in the Proterozoic province.
A total of 1026 samples were analyzed for 30 elements. Summary
statistics, histograms, and maps of the percentile classes are presented
for selected elements in laterites. Several numerically based procedures
were applied for the purposes of outlining regional trends and detecting
areas of relatively-high abundances of selected elements (anomalies).
Numerical techniques included the use of principal components analysis,
and ranking of individual elements, ranking of CHI-6*X, PEG-4, and
NUMCHI indices, and multivariate ranking of selected chalcophile
elements (chi-squared plots).
The resulting ranked scores of these techniques have been plotted
on maps and scatter plots. The most anomalous samples tend to occur
as outliers when these methods are applied. The results of these
applications confirm the presence of some broad regional geochemical
trends that are most probably related to lithological variation
within the granitoid-gneiss terrane.
There are significant geochemical distinctions between the laterites
developed over the Archaean terrain (Yilgarn) and the laterites
developed over the Albany-Fraser Orogenic belt based on the examination
of histograms, order statistics, and a discriminant function analysis.
Yilgarn laterite samples contain greater mean abundances for Ti,
Mn, V, Zn, Sn, W, Ga, Nb, Zr, and Ba. Albany-Fraser laterite samples
contain greater mean abundances for Cr, Ni, As, Sb, Bi, Mo, Se and
Au.
The essential geochemical features of the area are:
Yilgarn Laterites
- Gold occurs as individual Au anomalies as well as multi-element
associations with Sb, W, Mo, Pb, and As in Whistlers, Darling
Hill, Muradup, Boscabel, north of Trollup Hill, Peringillup, and
Cranbrook areas.
- Areas with the greatest Sn, W, Nb, Ta potential occur in the
Whistlers, Darling Hill, Darkan, Quindanning, Boscabel, north
of Trollup Hill and Peringillup areas.
- Molybdenum occurs with Sn and As in the Whistlers, Darling Hill,
Darkan, Boscabel and north of Trollup Hill areas.
- Tungsten is associated with As, Mo, Sb, Pb, and Au and as isolated
anomalies. Tungsten anomalies occur in the Whistlers, Darling
Hill, Darkan, Quindanning, and Boscabel areas.
- Silver appears to have a very limited multi-element association
with the exception of a slight association with Pb and Ga. Elevated
Ag occurs in the Whistlers, Darling Hill, Darkan, and Boscabel
areas.
Albany-Fraser Laterites
- Elevated multi-element abundances of Au occur with Sn, Sb,
W, and Sn. The areas which contain these multi-element associations
include the Carbarup Hill, Mt Barker, Denbarker, Lake Katherine,
and Lake Muir areas.
- Tin and Nb occur as single and multi-element associations southeast
and southwest of Denbarker, north of Mt Barker, and the Lake Muir
areas. Tin is also associated with Nb, Mn, Zr, Au, Mo, Sb, and
Se in the Denbarker to Lake Katherine and Lake Muir areas.
- Molybdenum occurs as single and multi-element associations with
As, Rb, Pb; As, Ni, Zn, and Cr; Ni, Sb, and Co in the Carbarup
Hill, Denbarker to Lake Katherine, north of Lake Muir, and Mt
Barker areas.
- Tungsten occurs with little or no multi-element signature. Elevated
abundances of W occur in the Denbarker and Lake Muir areas.
- Silver occurs with virtually no multi-element signature. Elevated
abundances of Ag occur south of Denbarker, west of Lake Katherine,
and the Lake Muir areas.
- Other elements are difficult to assess individually. Since most
economic commodities being sought have multi-element geochemical
signatures, it makes sense to employ methods that make use of
these multi-element characteristics. The results of the principal
components analysis, the CHI-6*X, PEG-4, and NUMCHI indices, and
Mahalanobis distance methods all show zones that have multi-element
enrichment and indicate that the areas mentioned above may warrant
additional follow-up investigation. Exploration for Au and associated
precious metal deposits may be assisted by the use of several
of these multi-element methods.
The data and results presented in this report, plus additional
geophysical lithological, lithogeochemical, and structural data,
may provide sufficient information for a selective and cost efficient
exploration programme.
Last updated: Tuesday, January 04, 2000 03:46 PM
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