GU Report 20 - Compilation of open-file surface geochemical data from the Bendigo 1:250 000 map sheet and adjacent areas, Victoria
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Product description:Executive summary Geochemical data for 73 812 samples from the entire Bendigo 1:250 000 map sheet, and from adjacent areas of the Swan Hill, St Arnaud and Deniliquin 1:250 000 map sheets, were extracted from the GeoScience Victoria surface geochemistry database. Information on sample type (rock chip, stream sediment, soil) and soil horizon was combined into a single database field to facilitate data levelling. Metadata for the analytical methods used were re-classified and simplified to indicate the digestion methods used for the analyses so that the data could be levelled and compared. Data were extracted for Au, Ag, As, Sb, Hg, W, Al, Ca, Fe and Mn. Coverage of the study area for all elements other than Au is poor; most samples were originally analysed for only one or a few elements. The few available multi-element data sets were used to assess associations between elements and to infer the occurrence of scavenging of key pathfinder elements by secondary Fe and Mn oxides, or in calcrete. In general, the base metals Cu and Zn showed a positive association with Fe, and there was a weak association between As and Fe. The elements Au, Sb and Pb showed no association with Fe, Mn or Ca. There was insufficient Fe and Mn data to allow correction for the possible effects of scavenging by secondary Fe and Mn oxides. The raw data from partial extraction techniques, such as Mobile Metal Ion (MMI) or Enzyme Leach methods, were excluded in order to produce plots of raw element distributions. The data were also levelled for sample type, soil horizon and digestion method, in order to produce levelled element distribution maps. Levelled element maps must be used with caution, as the data are biased toward samples from individual prospects located near known Au deposits that have often been analysed by a particular method. Levelling for analytical method therefore minimises element enrichments around known goldfields, but is necessary if data obtained by different digestion methods are to be plotted together. It is therefore recommended that raw and levelled data maps be viewed together. Few samples contained data from two or more of the pathfinder elements for central Victorian Au deposits, the most important of which are Au, As, Sb and Pb. These data have been combined to produce a series of RGB multivariate anomaly maps that highlight samples that have elevated concentrations of two or more elements. The results of RGB analysis for Au, As and Sb highlight all known goldfields, whereas RGB analysis of Au, As and Pb highlight known deposits in the Costerfield mineralogical domain. In both cases, anomalous samples not associated with known Au deposits were also identified; these locations merit follow-up investigation. Download The downloadable version of this report is supplied in PDF format. Appendices in MS Excel format are also supplied (ZIP). Bibliographic reference Arne D.C., 2009. Compilation of open-file surface geochemical data from the Bendigo 1:250 000 map sheet and adjacent areas, Victoria. GeoScience Victoria Gold Undercover Report 20. Department of Primary Industries. Related products:
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