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Open File Report 27

Laterite geochemistry in the CSIRO-AGE Database for the Wiluna Region (Duketon, Kingston, Sir Samuel, Wiluna sheets)

Grunsky, E.C.

A multi-element geochemical study has been carried out on laterite and ferricrete samples that cover parts of the greenstone belts and portions of the granitoid-gneiss terrain of the DUKETON, KINGSTON, SIR SAMUEL, and WILUNA 1:250 000 map sheets. The report presents a summary of the data and a provisional interpretation of selected parts of the data. The data used in this study are contained in the accompanying diskette (in the back pocket).

The sampling arose as part of a combined research programme between CSIRO and an experimental exploration programme (the AGE Joint Venture Programme) during the period 1983 to 1986. The database which was used for the study is composed of predominantly supracrustal metavolcanic and metasedimentary rocks over four supracrustal sequences; the Duketon, Dingo Range, Lake Violet-Milrose-Yandal, and Wiluna-Mt Keith-Perseverance-Agnew greenstone belts.

Laterite and ferricrete are both abundant materials in this area. The laterites are predominantly composed of loose nodules and mottled zone scree and number 272 samples. The ferricrete materials are mostly massive and fragments of ferricrete, numbering 174 samples. Fifty samples of lateritized rock are also included in the database but were not included in the interpretation.

A total of 496 samples were analyzed for 30 elements. Summary statistics, histograms, and maps of the percentile classes are presented for selected elements in laterites. Several numerically-based procedures were applied for the purposes of outlining regional trends and detecting areas of relatively-high abundances of selected elements (anomalies). Numerical techniques included the use of principal components analysis, ranking of individual elements, ranking of CHI-6*X, PEG-4, and NUMCHI indices, and multivariate ranking of selected chalcophile elements (chi-squared plots).

The resulting ranked scores of these techniques have been plotted on maps and scatter plots. The most anomalous samples tend to occur as outliers when these methods are applied. The results of these applications confirm the presence of some broad regional geochemical trends which are related to bedrock lithologies and possible regional alteration processes.

The dominant geochemical features are:

  • Several multi-element associations with Au have been noted in the Rose Hills, Milrose, and several localities in the Duketon greenstone belt.
  • Several Au anomalies occur in the Rose Hills, Milrose, southeast corner of the WILUNA sheet, and in the southern part of the Duketon greenstone belt on the DUKETON sheet.
  • Several individual elements (Bi, Mo, Sn, W, Ag, Nb, Se) indicate that the Rose Hills, Milrose, and Biddy Well areas are the most favourable areas for exploration on the WILUNA sheet and the Quongdong Well, Urarey Well, Christmas Well (Erlistoun), and Swanson Hill areas are the most favourable on the DUKETON sheet.
  • Regional, geochemical features that are characteristic of the greenstone belts are defined by higher relative abundances of Cr, Mn, V, Zn, Ni, Co, and Fe2O3. Geochemical features, characteristic of the marginal granitoid-gneiss terrain, are defined by higher relative abundances of Nb, Ga, Mo, and Pb.

The data and results presented in this report may provide sufficient information for a selective and cost efficient exploration programme.

Last updated: Tuesday, January 04, 2000 03:32 PM


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