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 18

Report on laterite geochemistry in the CSIRO-AGE Database for the Northern Murchison Region (Cue, Belele, Glengarry, Sandstone sheets)

Grunsky, E.C., Smith, R.E. and Perdrix, J.L.

A multi-element geochemical study has been carried out upon laterite and ferricrete samples that cover parts of the main greenstone belts of the CUE, BELELE, GLENGARRY, and SANDSTONE 1:250,000 map sheets. This report presents a summary of the data, and a provisional interpretation of selected parts of the data. The data used in the study are contained in the accompanying diskette (in the back pocket).

The sampling arose as part of a combined research programme at CSIRO and an experimental exploration programme (the AGE Joint Venture Programme) during the period 1983 to 1986.

In the region covered by the present report a total of 1065 samples were analyzed for 30 elements. Summary statistics, histograms, and maps of the percentile classes, are presented for selected elements in laterites and some very Fe-rich materials from partly eroded profiles which have been referred to as ferricretes.

The database that was used for the study is dominated by two major sample types, laterites and ferricretes. The two sample media have different geochemical characteristics, and thus have been treated separately. Lateritic sample media are abundant in the southwestern parts of the area and ferricrete sample media are more abundant in the northern and eastern parts of the area. The study also provides knowledge of the element abundance levels and variation of laterite and ferricrete geochemistry that complement information arising from orientation studies about mineral deposits.

The geochemical characteristics of the area have been studied using four techniques:

  1. Exploratory data analysis techniques were employed to rank the data for each element. Samples that rank in the upper percentiles for selected elements (chalcophile) have been considered as significant for further exploration follow-up.
  2. Principal components analysis of the multi-element data was used for the purpose of isolating significant linear combinations of elements that are associated with dispersion haloes within potentially mineralized zones. The results of the analysis also confirm the presence of some broad regional geochemical trends that are related to bedrock lithologies and regional alteration processes.
  3. Chalcophile and pegmatophile indices were computed for the purposes of isolating areas that are enriched in elements that are commonly associated with several types of mineral deposits. These indices are based on the cumulative concentrations of selected elements and outline regions where further exploration follow-up may be warranted.
  4. Chi-square plots provide a means of isolating multi-element outliers from the background population of samples. These outliers may be related to multi-element dispersion haloes that surround many types of mineral deposits and may warrant further exploration follow-up.

Application of the above methods of data analysis have outlined the following dominant geochemical features:

  1. district-scale (10 to 30 km in length) patterns in the distribution of Cu + Zn + Ni + Co ± Cr; V + Sn; and Zr + Nb; each pattern appearing to relate to the dominant characteristics of varying bedrock associations;
  2. an As + Sb + Mo + Sn + Be + W + Au association in the Weld Range - Meekatharra -Gnaweeda greenstone belts trending northeasterly which infers the presence of a chalcophile corridor;
  3. an association of Au and W within selected laterite samples in the Dalgaranga greenstone area;
  4. an association of Au and Sb within selected ferricrete sample in the Weld Range - Meekatharra -Gnaweeda greenstone areas; and,
  5. several anomalies at the 1 km scale that require follow-up sampling in order to assess their continuity and significance. These anomalies have been determined by a variety of methods. The most anomalous samples tend to occur as outliers when these methods are applied.

Sporadic Au anomalies also occur. However, the general sample spacing of 3 km with fill-in sampling at 1 km is too wide for reliable interpretation of Au patterns in laterites. Laterite and ferricrete geochemistry at these low sample densities generally requires the use of intermediate zonal targets, such as anomalous chalcophile envelopes, which can occur about individual deposits.

Last updated: Tuesday, January 04, 2000 12:56 PM


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