CRC LEME
Open File Report 150
Preface and Executive Summary
Regolith Studies at Edoldeh Tank (ET) Gold Prospect, Gawler Craton,
South Australia
M. J. Lintern, I. J. Tapley, M. J. Sheard, M. A. Craig, G. Gouthas
and A. J. Cornelius
Compiled by M. J. Lintern and M. A. Craig
The Edoldeh Tank (ET) Regolith Project is part of the broader
“South Australia Regolith Project” of CRC LEME, the
principal aim of which is “to develop technically efficient
procedures for mineral exploration in the major cratons of South
Australia through a comprehensive understanding of the processes
of regolith development and landscape evolution and their effects
on the surface expression of concealed mineralisation”.
This project is a follow-on to an initial study of regolith geology
and geochemistry in the Gawler Craton, sponsored by CRC LEME, PIRSA
and Gawler Joint Venture exploration tenement holders completed
in 2002. It was developed after extensive consultation with industry
geologists, and an excursion to various sites. The principal problems
identified relate to verification of the thickness of transported
overburden and to procedures for exploration in terrains where transported
overburden is present.
The principal objective of the ET Regolith Project was to evaluate
the use of components of transported overburden for detecting buried
Au deposits in the western Gawler Craton. Five prospects (ET, Monsoon,
South Hilga, Golf Bore and Jumbuck) were initially investigated.
The objective was to determine the most suitable site for a detailed
study. A single traverse, several hundred metres in length, was
selected across each prospect that had mineralisation, transported
overburden and adequate drill spoil. The regolith stratigraphy was
described at each site and drill spoil collected for multi-element
analysis. An existing company geochemical database for each prospect
was also used. The results of the five prospect survey are reported
in Lintern et al, 2002. The initial studies (Lintern et al, 2002)
indicated that ET has the following properties:
- two hundred drill holes spread over the prospect with cuttings
in good condition;
- a large Au in calcrete anomaly that had not been linked to a
primary source, leaving potential for additional areas of investigation
and possible drill targets;
- indications that mineralisation might be expressed in the transported
overburden;
- a greater spread and thickness of transported overburden compared
with other sites; and
- sand dunes, typical of the western Gawler Craton, and a hindrance
to exploration in this region so there are few, if any, previous
studies in this type of terrain.
Regolith mapping at ET was based on the identification and detailed
representation of the distribution of surficial material and the
broader surface regolith units. The map was not only based on datasets
commonly used in regolith map construction e.g., Landsat TM, aerial
photography and DEM, but also processed AIRSAR, and HyMapTM data
sets played an important role in determining the final regolithlandform
relationships. Regolith stratigraphy was determined using field
observations, collection and analysis of drill cuttings from chip
trays, and PIMA analysis. These data determined relationships between
materials, weathering, landform history and the geochemical data.
Drill cuttings, calcrete, soil and vegetation were collected to
determine the distribution of Au and other elements, which was visualised
in 3D and 2D.
The principal results indicate that:
- In in situ regolith, Au was found to be concentrated in calcrete
near the surface and above an interpreted leached zone of low
Au concentration (leached zone?) that can extend down several
tens of metres into the weathered regolith. The surficial Au anomaly
extends from the ridge into transported regolith and, in places
with thin (<5 m) sand cover, appears to be locally enhanced,
possibly due to Au additions to the surface from underlying buried
mineralisation in the transported overburden. Calcrete appears
to be the best sample medium for Au exploration over soil, vegetation
and silcrete. Gold appears to be the best target element although
As may also provide information on the location of mineralisation.
- Data sets obtained by remote sensing were particular useful
in discriminating regolith units and in determining surface mineralogies.
They were important in assisting in the construction of the regolith-landform
map.
- Landsat TM was most useful in mapping at the 1:5000 scale required
for this study. A DEM was generated from aerial photographs and
was useful in distinguishing landforms. Ground-truthing was important
in delineating features, such as the extent and type of lag deposits,
and in the final construction of the map. iv
- The complimentary use of PIMA and visual logging of chip trays
enabled determination of selected clay mineralogy, colour and
lithology of the regolith including the boundary between transported
and in situ regolith. 3D and 2D visualisations of the data assisted
in determining the regolith stratigraphy and were able to integrate
the information from PIMA, geochemistry and other data sets.
The study has led to a better understanding of Au dispersion in
sand dunes, improved interpretation of calcrete-hosted Au anomalies,
and indicated potential new drilling targets.
M. J. Lintern and I. J. Tapley
Project Leaders April 2003
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