CRC LEME
Open File Report 127
ABSTRACT
Soil, bedrock and profile geochemistry at Police Creek, Drummond
Basin, Queensland
K. M. Scott
Anomalies within residual soils along the 20300E traverse at Police
Creek are defined by both the +2 mm and -75 µm fractions.
Although Au, As and Sb are anomalous in both soil fractions, Au
is preferentially concentrated in the fine fraction and As and Sb
in the coarse fraction. Significant Mo may also be present, especially
in the coarse fraction in anomalous areas. Gold >40 ppb in the
fine fraction and As >100 ppm in the coarse fraction define an
anomaly at least 1 km x 600 m (southern anomaly) in alluvium and
residual soil. As in the previous survey at 20050E, a second anomaly
was found to the north of the major geochemical anomaly and again
identified by anomalous Au, As and Sb contents in both soil fractions.
Arsenic >100 ppm defines the 400x150 m northern anomaly in residual
soil. Comparison of results from residual soils and adjacent outcrop
reveals that the fine fraction of the soils concentrate Au with
respect to the rock. These features indicate that the soils at Police
Creek are a good sample medium whether they are transported or residual.
The effect of weathering on three distinctive profiles have been
observed. Highly mineralized samples with illite, adularia and kaolinite
associated with arsenical pyrite (up to 7.3% As, 2.3% Sb and 0.4%
Hg) weather to illite, kaolinite, jarosite and Fe oxides. In less
mineralized samples, chlorite and calcite occur with adularia and
illite, with the latter two minerals retained in outcrop with neoformed
kaolinite. Areas of argillic alteration contain dickite and pyrophyllite,
with the former being retained in outcrop. Such mineralogical and
consequent geochemical variation in the feldspar and phyllosilicate
stabilities/abundances could be defined by PIMA and radiometric
survey of outcrop (or shallow drill spoil) to provide vectors to
the most altered areas during exploration.
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