CRC LEME
Open File Report 133
ABSTRACT
The significance of Campaspe-dominated terrains in exploration
within the Mt Windsor Sub-province, N.E. Queensland
K. M. Scott
Weathered altered volcanics associated with mineralisation within
the Mt Windsor Sub-province are characterised by very kaolinitic
assemblages (sometimes with alunite-jarosite minerals and barite)
derived from alteration of the feldspars. The younger Campaspe Formation
is generally characterised by feldspar-bearing assemblages and is
not strongly kaolinitic. Thus, the units are easily distinguished
on the basis of their kaolinite and feldspar contents. However,
where the volcanics are unaltered, feldspars are retained and other
criteria must be used to distinguish them from the overlying Campaspe
Formation sediments. If the volcanics are intermediate to basic
in composition, their lower Si, Cl and higher Al and Ti/Zr relative
to the Campaspe Formation can be used to discriminate. Unfortunately,
if the volcanics are felsic (as at Thalanga) the geochemical parameters,
e.g. Ti/Zr do not discriminate between the two units. In these cases,
although the unconformity between the two units is commonly associated
with Fe oxide enrichment in both units, to accurately define the
boundary, the degree of rounding of the quartz grains may be the
only reliable parameter for discrimination.
Chalcophile elements (Ba, Cu. Pb and Zn) may be dispersed by mechanical
means into the basal 10 m of the Campaspe Formation at Waterloo
and Thalanga East. The distribution of Cu. Pb and Zn within thick
sequences of the Campaspe Formation at Waterloo reveals that the
dispersion of Zn (and Cu) is more restricted (600 m x 300 m) than
that of Pb. The usually mobile elements (viz. Zn and Cu) may be
stabilised by being associated with dolomite (i.e. an alkaline environment).
At Brittania, quartz -rich "sand" occurs directly over
mineralised volcanics. Despite its location there is no dispersion
observed in this unit, probably because there is no suitable host
to immobilise chalcophile elements.
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