Recognition of geochemical footprints of mineral systems in the regolith at regional to continental scales

Abstract

Understanding the character of Australia's extensive regolith cover is crucial to the continuing success of mineral exploration. We hypothesise that the regolith contains geochemical fingerprints of processes related to the development and preservation of mineral systems at a range of scales. We test this hypothesis by analysing the composition of surface sediments within greenfield regionalscale (southern Thomson Orogen) and continental-scale (Australia) study areas. In the southern Thomson Orogen area, the first principal component (PC1) derived in our study [Ca, Sr, Cu, Mg, Au and Mo at one end; rare earth elements (REEs) and Th at the other] is very similar to the empirical vector used by a local company (enrichment in Sr, Ca and Au concomitant with depletion in REEs) to successfully site exploration drill holes for Cu-Au mineralisation. Mapping of the spatial distribution of PC1 in the region reveals several areas of elevated values and possible mineralisation potential. One of the strongest targets in the PC1 map is located between Brewarrina and Bourke in northern New South Wales. Here, exploration drilling has intersected porphyry Cu-Au mineralisation with up to 1 wt% Cu, 0.1 g/t Au, and 717 ppm Zn. The analysis of a comparable geochemical dataset at the continental scale yields a compositionally similar PC1 (Ca, Sr, Mg, Cu, Au and Mo at one end; REEs and Th at the other) to that of the regional study. Mapping PC1 at the continental scale shows patterns that (1) are spatially compatible with the regional study and (2) reveal several geological regions of elevated values, possibly suggesting an enhanced potential for porphyry Cu-Au mineralisation. These include well-endowed mineral provinces such as the Curnamona and Capricorn regions, but also some greenfield regions such as the Albany-Fraser/western Eucla, western Murray and Eromanga geological regions. We conclude that the geochemical composition of Australia's regolith may hold critical information pertaining to mineralisation within/beneath it.

Using Machine Learning to Map Western Australian Landscapes

“…These datasets can assist in characterising landscape features and their distribution at regional scales [e.g. [22][23][24], which directly impacts many disciplines, including mineral exploration, geomorphology, environmental studies and geoarchaeology, amongst others [e.g. [8][9][10]25].…”

An improved method for assessing the degree of geochemical similarity (DOGS2) between samples from multi-element geochemical datasets

“…They form a relatively coherent grouping in South Australia, which extends across the Gawler and Curnamona regions into western New South Wales and the SE of the Northern Territory; it coincides with much of the area shown on Figure 9 with known Cu mineralization likely to be of the IOCG type. One 'outlier' is from the southern Thomson region of New South Wales, an area which was studied by MMI as a pilot project to the NGSA (Mann et al 2009) and also the subject of a PCA study of the MMI NGSA data (Caritat et al 2017), whilst two samples further north in the Eromanga region of central Queensland are probably 'false positives'. There is one sample from the Cu mineralized Mt Isa/ Cloncurry district of this type, and two samples from the coastal Pilbara of Western Australia which overlap samples of the Mt Isa type; the latter are from outlet sediments of the Sherlock and De Grey Rivers, catchments which host VMS style Cu-Zn-Pb deposits.…”

Exploratory Analysis of Geochemical Data and Inference of Soil Minerals at Sites Across Canada

“…Principal component analysis (PCA) is a prominent exploratory data technique that can reduce the number of variables (in this case, chemical composition) in a data set (Grunsky 2010). These principal components may reveal element associations (i.e., mineral stoichiometry) that reflect geological origins and, as such, may be used to infer soil minerals (de Caritat et al 2017).…”