CRC LEME
Open File Report 137
ABSTRACT
A regional overview of the Charters Towers - North Drummond Basin
Region: Geomorphic Landform Provinces
S. J. Fraser
A regional-scale map (1:250,000 scale) of interpreted geomorphic
provinces has been produced over the Charters Towers - North Drummond
Basin area. The area has substantial mineral potential, but Tertiary
sediments conceal prospective lithologies.For explorationists, the
map is intended as a guide, to assist in area-selection and in formulating
exploration strategies. For regolith mappers and researchers, the
map provides a framework for more detailed studies. A digital version
of the mapped polygons is available upon request.
The landscape evolution and weathering history of the region since
the Mesozoic is complex. Erosional processes currently dominate;
however, the landscape retains evidence of a complex history of
at least two cycles of deposition, weathering and erosion.
The area has been subdivided on the basis of landform into seventeen
geomorphic provinces, each of which contains particular regolith
characteristics. These geomorphic-regolith provinces were delineated
using photoform, drainage and other textural features identified
on processed Landsat TM imagery. The resulting interpretation is
a broadscale regional subdivision of the landscape. For planning
geochemical surveys at tenement or prospect scales, a more detailed
subdivision of the landscape would be required than that presented
here.
Because the nature of the land's surface is critical in determining
an appropriate geochemical exploration strategy, the mapped geomorphic-regolith
provinces were grouped into regolith-terrain classes, which broadly
convey information regarding the nature of the surface, and the
state of preservation of weathering profile material. Three terrain
types have been identified: Duricrust Dominated Terrain, Saprolite
Dominated Terram and Alluvium and Colluvium Dominated Terrain.
In provinces belonging to the Duricrust Dominated Terrains, ferruginous
weathering products could be useful geochemical sampling media because
Au and other pathfinder elements such as As, Cu and Bi are generally
trapped in secondary iron oxides, which are in turn, the main components
of ferruginous materials. Such samples should be most informative
in those areas with duricrust preservation on basement lithologies,
however, extensive areas of duricrust development on basement have
not been recognised. Areas of duricrust are commonly found on outcrops
of Tertiary sediments, which belong to the Southern Cross (Suttor)
and Campaspe Formations. Despite these sediments being predominately
fluviatile, their associated secondary ferruginous weathering materials
could contain trace-element concentrations indicative of underlying
minetalization. Both elastic (mechanical) and hydromorphic geochemical
dispersal mechanisms have possibly operated. Of particular sigmficance
for mineral exploration is the development of a widespread, though
not continuous layer of weakly cemented ferruginous nodules towards
the top of weathering profiles associated with the Campaspe Formation
(unit UFP) on the western side of the study area. The possibility
that these ferruginous nodules may contain subtle geochemical anomalies
indicative of basement minetalization needs to be investigated further.
In those provinces belonging to the Saprolite Dominated Terrains,
secondary ferruginous materials, if available, should be sampled
wherever possible. However, these will need to be supplemented with
more traditional, geochemical samples, such as stream sediment,
rock chip, and soil samples, in areas where saprolite has been removed.
For those provinces in the Alluvium and Colluvium Dominated Terrains,
there are two geochemical strategies. In areas of colluvium, traditional
geochemical sampling methods should be appropriate. Areas with a
high contribution of alluvial material probably will require drilling
and subsurface sampling. And if buried weathering profiles are intersected
during drilling, ferruginous materials if available, should be preferentially
sampled.
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