CRC LEME
Open File Report 118
ABSTRACT
Regional regolith mapping around Alice Springs, Northern Territory
Fraser, S.J., Skwarnecki, M.S. and Robertson, I.D.M.
This report is part of the final documentation of a collaborative
research initiative between Gutnick Resources N.L. and CRC LEME.
The CRC provided geochemical and regolith research into a major
exploration program being undertaken by Gutnick Resources N.L. for
Witwatersrand-style gold mineralization in the sediments of the
Ngalia and Amadeus Basins.
As part of this initiative, the CRC produced a rapid, first-pass
assessment of the regional landform and regolith over an area of
twenty-five 1:250 000 map sheets. The specific objectives were to:
-
- Establish broad spatial relationships between landforms, regolith
and lithology;
- Propose effective geochemical exploration strategies for different
regolith-landform settings.
Two maps were produced: -
- A Landform Interpretation Map (1:1 000 000 scale) showing the
distribution of various landform units. These units were based
on i) a re-assessment of previous land system mapping (1:1 000
000 scale; Perry, 1961), ii) interpretation of landforms from
Landsat MSS imagery, and iii) five weeks of limited fieldwork.
Because of inaccuracies in the land system mapping, it is not
recommended that the final maps be viewed at scales greater than
1:1 000 000.
- A Regolith-Landform Status Map (1:1 000 000 scale) grouping
the landform units into three broad terrain categories: Relict,
Erosional and Depositional.
The relict terrains group is tentative, subjective and relatively
small. In the erosional terrains, there has been little preservation
of deeply weathered profiles on lithologies of the Arunta Province.
Rates of erosion have kept pace with, or exceeded, those of chemical
weathering. Rocks of the Amadeus Basin are either not deeply weathered
or weathering is difficult to recognize; saprock is common.
Depositional terrains dominate the area. Two types can be identified;
i) flat, low, regional plains; ii) 'perched' deposits that occur
above the regional plains.
The regional plains are low and flat, formed by filling of a deeply
eroded basement topography with proximal and distal sediments, now
largely overlain by a veneer of wind-blown sand. Hidden beneath
some of these are Tertiary basins up to 200 m deep. 'Perched' depositional
deposits are small and are dominated by locally derived materials.
They include fans, river terraces or valleyfills, which are being
reworked. All these comprise a significant barrier to exploration.
Drilling or use of techniques, that can 'see through' the cover
will be needed to prospect them adequately.
Lateritic, ferruginous materials should be sampled within relict
terrains. Within the erosional terrains, stream sediment, soil,
lag and rock-chip sampling should be adequate but small anomalies
are likely, unless iron-rich mottles and nodules can be located.
Where detritus in the streams reflects local lithologies, significant
stream sediment dispersion trains in all fractions are expected
but, where the detritus is dominated by distal material, weak dispersions
are likely only in the finest fraction (<75 um).
Low, regional plains are a significant barrier to exploration.
They will need sub-surface sampling. Although substantial occurrences
of calcrete were observed, initial indications are that at least
some are of the groundwater type and so are unsuitable for Au search.
Consideration should be given to groundwater geochemistry. The groundwaters
are of low salinity, anomalies are expected to be weak but distinct.
Last updated: Friday, January 25, 2002 3:56 PM
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