CRC LEME
Open File Report 19
ABSTRACT
Gold morphology and composition at Panglo, Eastern Goldfields,
WA
Scott, K.M. and Davis, J.J.
Samples of the generally thin soil were collected along two traverses
over the Beasley Creek Mine Site, prior to mining. The soil and
its components have been examined petrographically, mineralogically
and geochemically.
The coarse fraction (710-4000 µm) consists of black, goethite
and hematite rich nodules (some of which are magnetic), red to yellow
ferruginous clay granules, quartz fragments and scarce fragments
of calcrete, hardpan and cellular ironstone. The 710-4000 µm
fraction is petrographically indistinguishable from the fine lag
which was formed by deflation of the top layers of soil. The fragments
of cellular ironstone, which are probably gossanous, are slightly
more abundant near the subcrop of the ore.
The black, goethite- and hematite-rich fragments contain lithorelics
which have microscopic remnants of muscovite and pseudomorphs after
kaolinite, set in, and largely replaced by, massive, spongy or vesicular
goethite. The clay-rich granules consist largely of hematite- or
goethite-stained kaolinite and some include goethite-rich lithorelics.
The soil also contains a significant, quartz-rich, wind-blown component,
most abundant in the 75-710 µm fraction, which acts as a geochemical
diluent. These subrounded, sand to silt-sized particles, which include
a few grains of fresh microcline, are coated with red iron oxides.
The silty fraction (<75 µm) contains less quartz but more
iron oxides and day. The <4 µm fraction is very clay rich.
Sieving and clay sedimentation were used to separate the soil into
the 710-4000, the <75 and the <4 µm fractions. The complete
soil and its constituent size fractions were geochemically analysed
to assess their value as sampling media. The 75-710 µm fraction
has a significant component of aeolian sand and was discarded. The
distributions of As, Au, Cd, Cu, Sb, Se, W and Zn are related to
the occurrence of mineralisation, with anomalies centred over the
subcrop of the shales hosting the ore. Maxima in Ca, Mg, P and Sr
delineate the calcretes, the P peak being probably related to bone
fragments from burrows under the calcrete. The phyllitic ore host
rock is indicated by maxima in Ba and Mn and possibly by a decrease
in Y. The explanation for a maximum in S over the ore and its host
rock is problematical. The complete soil has clearly been diluted
by wind-blown sandy material and it is less effective than its fractions
as a sampling medium. The most effective medium is the ferruginous
710-4000 µm fraction, followed by the <4 µm clays.
The <75 µm silt fraction also contains a significant wind-blown
component and is the least effective size fraction.
Last updated: Tuesday, January 04, 2000 01:19 PM
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