Open File Report 122
Charters Towers - North Drummond Basin Field Excursion, Field
K. Scott, Li Shu, S. Fraser, I.D. Campbell, R.R. Anand and I.D.M.
The principal objective of the P417 Project is to improve substantially
geochemical methods of exploration for base metals and Au in areas
obscured by weathering or under younger cover. The research includes
geochemical dispersion studies, regolith mapping, regolith characterisation,
dating of profiles and investigation of regolith evolution. The
project has sites in both the Mt Isa Region and in the Charters
Towers-North Drummond Basin.
Essential to this project is translation of research findings into
practical exploration outcomes. Field excursions are an essential
link in this technology transfer. The last excursion was in July
1995 and covered the Eastern and Western Successions of the Mt Isa
Region, where research sites have deeply weathered profiles on Proterozoic
and Mesozoic bedrocks and are partly overlain by variable thickness
of recent sediments. This second excursion provides opportunities
to examine the weathering of younger Palaeozoic rocks and their
Tertiary cover sequences (Suttor, Southern Cross and Campaspe Formations)
and the geomorphology of the region, all of which are important
to geochemical exploration of the region.
The excursion includes visits to mineral deposits, prospects and
field sites. On the first day the excursion visits Red Falls, where
the Campaspe Formation can be demonstrated to overlie the Southern
Cross Formation, the Featherby Walls, where the sandstones of Southern
Cross Formation unconformably overlie the Ravenswood Granodiorite.
At both these sites, mottling and nodules are common. In the Waterloo
Area a ferruginous profile is developed in the top of the Campaspe
Formation. The Waterloo Deposit has been quoted as occurring below
60 m of Campaspe Formation, however, work done in this Project indicates
that the thickness of the cover has been overestimated in places
and a Pb mechanical dispersion train occurs at the base of the Campaspe
The second day covers Scott Lode, the Cindy Deposit and the Wahines
Prospect. Here, weathered profiles are developed on cover sequences
and on the basement. Weathered components of earlier sequences have
been included as detritus in later materials, implying a complex
and continued weathering history. Concentrations of Fe have developed
both at surface and at depth in the cover sequences, which have
adsorbed pathfinder elements related to mineralisation in the basement.
The Police Creek and Wirralie prospects and profiles through the
Suttor Formation are visited on the third day. Ferruginous duricrusts
and silcretes are developed on the Suttor Formation.
At the Police Creek Prospect, the transported cover is generally
less than 6 m thick and mottles have developed both in it and in
the underlying bedrock. There appears to be both hydromorphic and
mechanical dispersion in the cover. The < 75 µm fraction
of the soil has a more intense Au anomaly than the <180 µm
fraction. Although As and Sb occur in the fine fraction, these elements
are concentrated with Fe oxides of the coarse fraction with Mo.
At the Wirralie Deposit, the Au anomalies in the Suttor Formation
reflect mechanical transport from the basement. Arsenic and Sb contents
are generally low in the Suttor Formation, except where ferruginous