Authors / CoAuthors
Mann, A. | de Caritat, P. | Lilly, R. | Sylvester, G.
Abstract
Multi-element soil geochemical surveys are a common feature of continental, regional, and prospect-scale exploration and environmental programs. They contain a wealth of useful lithogeochemical information, often under-utilised in favour of subjectively selected single-element investigations and contoured maps. In part this may be due to the problem of providing an illustrative, concise statistical outcome when up to 50 elements are analysed. The aim of the Degree of Geochemical Similarity (DOGS) methodology is to provide a simple, objective and comparative analysis of samples in any geochemical database. The methodology comprises six steps: (1) Transformation of the elemental concentrations (ppm) to log10 units and ordering of the elements in alphabetical order; (2) Removal of those elements with (say) >40% of censored data (below the lower limit of detection or above the upper limit of detection); (3) Selection of a key reference sample of known or sought provenance against which to compare other samples in the database; (4) Plotting bar diagrams of the fingerprint of the reference sample and of the difference between any sample and the reference; (5) Calculation of a correlation factor which quantifies the affinity of any sample with the chosen reference sample; and (6) Mapping this correlation factor as the DOGS of all samples to the reference sample, using percentile-based exploratory data analysis (EDA) symbols. Application of the DOGS methodology to the 1190 sample National Geochemical Survey of Australia (NGSA) Mobile Metal Ion (MMI) database, using the Pearson least squares correlation coefficient at step (5) above, shows the following. The geochemical data (42 elements remaining after step (2) above) contains elemental information suggesting high affinity between some samples in the Proterozoic Albany Fraser belt and the Archaean Yilgarn Craton granitoid (Beverley granite reference). A high DOGS is also apparent on an EDA map for some Albany Fraser belt catchment outlet sediments (soils) with a Yilgarn Craton sample from a mafic rock dominated catchment (the Kalgoorlie greenstone reference). Soil samples collected over marine carbonates are distinguished from those containing abundant secondary carbonate (calcrete) by their geochemical signatures after application of DOGS methodology using a reference soil sample on the Nullarbor limestone. The choice of a catchment outlet sediment reference sample north of Mt Isa/Cloncurry provides a means of highlighting on an EDA map other areas in Australia potentially prospective for similar mineral endowment. Application of the methodology to a separate 48 sample prospect-scale MMI survey in northern Queensland illustrates its potential to identify and map mineral-hosting lithologies from background lithologies. Substitution of other correlation techniques (e.g. Spearman Rank correlation) at step (5) above produces very similar results, demonstrating the robustness of the methodology, but more importantly the inherent diagnostic capability of multi-element soil geochemistry to delineate underlying lithology.
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nonGeographicDataset
eCat Id
89847
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Cnr Jerrabomberra Ave and Hindmarsh Dr GPO Box 378
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- External Publication
- Australian and New Zealand Standard Research Classification (ANZSRC)
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- Earth Sciences
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- Published_Internal
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2015-01-01T00:00:00
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geoscientificInformation
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[-44.0, -10.0, 112.0, 154.0]
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