Search CRC LEME :

powered by FreeFind

Publication Policy

Open File Report Series

OFRS Index


Regolith Maps

Annual Reports

Articles & Papers


Minerals Briefs

"Focus on Salt"

Other LEME Reports

Order Form

Open File Report 125

Regolith-landscape characteristics, evolution and regional synthesis of the Mt Isa Region, Progress Report

R.R. Anand, C. Phang, J. Wilford, J.E. Wildman, Li Shu, I.D.M. Robertson and T.J. Munday

The Little Eva Cu Prospect is located 12 km north of the Dugald River Zn-Pb orebody and is situated in scapolitic granofelses of the Corella Formation and is associated with feldspar porphyry and magnetite-rich rocks. Although, in the vicinity of the Little Eva shaft, these rocks are exposed or occur under a very thin soil, the prospective rocks to the south are masked by colluvium. This prospect had been investigated intensively by CRA Exploration Pty Ltd., (CRAE), using the geochemistry of samples drilled from bedrock.

The geomorphology and regolith units were investigated on a district and on a local scale. This was to provide the setting for an orientation survey to test the effectiveness of soil sampling in areas where there is a thin layer of transported cover. South of the Little Eva Cu Prospect, detritus, from low quartzite hills and quartz veins, has been shed onto pediments gently inclined, towards Cabbage Tree Creek, to form a thin colluvial mantle of acid red earths with a quartz- and quartzite-rich lag. Near Cabbage Tree Creek, erosion has been active, etching into and through the colluvium, exposing the basement. This is largely covered by a thin, carbonate-rich lithosol, characterised by a lag rich in quartz and magnetite clasts. The magnetite is primary, although it has been partly weathered at the surface or near-surface. To the north, the area is dominated by alluvium and colluvium on which black clay soils are developed. Part of the colluvium, south of the Prospect, has been almost completely dismantled, leaving an area of linear 'gilgai', occupied by dark brown, smectitic, cracking clay soils.

Soil sampling on an approximately triangular 200 m grid, shows that Cu and Au are the only indicator elements for Little Eva style mineralisation. Muted anomalies in both elements indicate the trend of the bedrock Cu anomaly, as determined by CRAE, even through the thin colluvium. The fine fraction (<75 µm) is more effective than the coarse (710-2000 µm) fraction. Iron, Co and V in the soil indicate concentrations of magnetite which may have some exploration significance.

Bioturbation by ants and termites and/or hydromorphic dispersion could have contributed to moving the Cu and Au geochemical signal in the fine fraction upward from the basement and through the colluvium. However, the low tenor of the anomalies requires that careful attention be paid to setting the correct thresholds and the use of appropriate display methods (e.g., logarithmic scales).


Cooperative Research Centres Australia

About Us | News & Events | Research
Publications | Education | Staff Only | Links

Contact Us | Disclaimer | Sitemap
© CRC LEME 2004

CRC LEME is established and supported under the Australian Government's Cooperative Research Centres Program. The CRC Program is an Australian Government initiative which brings together research groups with common interests.

CRC LEME Core Parties