CRC LEME
Open File Report 109
ABSTRACT
Eastern Goldfields Field Excursion Field Guide
Butt, C.R.M., Smith, R.E., Dell, M., Anand, R.R.,Lintern, M.J.,
Gray, D.J., Vinar, J., Bristow, A.P.J., Churchward, H.M., Varga,
Z.S. and Wildman J.E.
AMIRA Project 409, Geochemical exploration in areas of transported
overburden, Yilgarn Craton and environs, has, as its principal objective,
the development of geochemical exploration methods for areas having
a substantial cover of surficial sediments, through investigations
of the processes of geochemical dispersion from concealed mineralization.
An important aspect of the project is to translate research findings
into practical outcomes. Field excursions have a significant role
in this process, for they permit geologists and geochemists from
the research group and the supporting companies to examine key sites
together. This interaction promotes a much freer exchange of ideas
than is possible during, for example, the formal atmosphere of seminars.
The project has several important research sites and districts across
the Yilgarn Craton. It is impractical to visit all of these in one
excursion. The excursion in August 1995 examined sites in the Murchison
and adjacent areas, including Mt Gibson, Mt Magnet, Baxter and Fender,
having a variety of different types of transported overburden. Each
is characterized by the development of red-brown hardpan in the
surface horizons but, except at Mt Gibson, Pedogenic carbonates
are rare or absent. This second excursion is to the Eastern Goldfields
region and again provides an opportunity to examine a range of different
overburden types and offers a comparison between areas having a
strong development of pedogenic carbonates, south of the Menzies
line, and those having red-brown hardpans, to the north.
The first visit is to the Kanowna Belle gold mine. This has not,
in fact, been studied during this project, but it was an important
site for AMIRA Project 240A, Yilgarn Lateritic Environments. It
serves as an excellent introduction to many of the important features
of the regolith of the Kalgoorlie region and to the usefulness of
surface soil sampling in areas of shallow transported cover, including
the use of pedogenic carbonates as sample media. The excursion then
visits two areas within which the effectiveness of surface sampling
has been investigated where mineralization concealed by deeper sediments,
in both cases associated with palaeochannels. Steinway and Greenback
have supergene mineralization within and beneath 15-25 m of oxidizing
sediments. There is a surface anomaly at Steinway, whereas there
is none at Greenback, although mineralization is shallower and has
been mined. The anomaly at Steinway is now considered possibly coincidental,
a result of natural contamination - a common and potentially misleading
feature of the region. Argo and Apollo are concealed beneath reducing
lake sediments and channel sediments. Although Au is again concentrated
in the calcareous horizons of the soils, there is no surface anomaly.
Partial extraction analyses appear to be ineffective in defining
anomalies in either the Steinway or Argo-Apollo areas.
On the second day, the excursion visits the Safari prospect at
Mt Celia, and Golden Delicious, on or north of the Menzies line.
Carbonates are present at both sites, though commonly deeper in
the regolith (below 2-5 m) than the pedogenic carbonates further
south. Selective sampling of carbonates appears to give a good response
at Mt Celia, where the cover is shallow (mostly <10 m) and, for
the most part, overlies truncated profiles. At Golden Delicious,
about 17 m of sediments overlie residual profiles truncated to approximately
the mottled zone. There is no geochemical expression of the mineralization
in the sediments, but dispersion along the unconformity gives a
widespread anomaly, particularly associated with ferruginous nodules
and mottles.
Near Laverton, the South Lancefield, Telegraph and Beasley Creek
pits have Permian boulder clays exposed in the walls. These have
not been examined for their geochemical response, although some
results from the dispersion study at Beasley Creek, carried out
during AMIRA Projects 240 (Laterite Geochemistry) and 241 (Weathering
Processes) are given in this guide. The excursion then travels to
Bronzewing, to examine sites where essentially complete profiles
are preserved, with lateritic residuum close to the surface (Laterite
pit) or buried beneath alluvium and colluvium that includes lateritic
debris (Central pit). A similar situation is present at North Pit,
Lawlers, the last stop, where lateritic duricrust is buried by 20
m of sediments.
The authors of the articles in the guide wish to thank Colin Steel
and Angelo Vartesi for drafting the diagrams, and Gill Ashton for
preparing and compiling the final manuscript. Gill Ashton also assisted
with much of the organization of the excursion. We are also grateful
to Kanowna Belle Gold Mines, Newcrest, St Ives Gold Mines, RGC Exploration,
Acacia Resources Ltd., Metex Resources Ltd., Great Central Mines
and Plutonic Resources for permitting access to their mines and
exploration properties.
Last updated: Sunday, August 05, 2001 14:06:32
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