GSV TR2006/3 - Nickel Prospectivity of Victoria

Category: Technical Records	Product Code: MP-R-33536
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Executive Summary This report provides an analysis of the potential for the occurrence of nickel mineralisation in Victoria. Detailed in this report are nickel deposit analogues relevant to Victoria’s geotectonic setting. Criteria common to these deposit styles are identified and their relationship to the regional geology and tectonic settings are reviewed. Results of previous exploration and research efforts have been used to support the investigation. The report identifies areas considered prospective for nickel mineralisation based on the occurrence of analogue criteria and relevant exploration results.

To date known nickel occurrences in mafic/ultramafic lithologies are used by explorers to define prospective areas. The generation of nickel sulphide and laterite deposit models provides necessary criteria for nickel mineralisation including tectonic setting, regional geology, type and age of mineralisation. This understanding will permit selection of appropriate analogues to better delineate prospective areas in Victoria.

As subduction and rifting are interpreted to have occurred during Victoria’s tectonic history, appropriate analogues for nickel sulphide mineralisation may include:

Ni-Cu sulphides in mafic-ultramafic intrusions (e.g. Thomson River copper mine at Coopers Creek in eastern Victoria) where mineralisation may be hosted by mafic rocks or may occur as stratabound mineralisation in gabbro/dolerite sills associated with ultramafic complexes.
Igneous rock hosted Ni-Cu mineralisation (e.g. Aguablanca, SW Spain) – this style of mineralisation is associated with rocks of calc-alkaline association intruded in an active continental margin (Casquet et al., 2001).
Remobilised hydrothermal nickel sulphides (e.g. Avebury, western Tasmania).
Laterite/saprolite Ni, Co, Fe (e.g. Goro, New Caledonia; Murrin Murrin, Western Australia).

Research has highlighted the geochemical affinities of the Jamieson-Licola Volcanics and the greenstones in the Grampians-Stavely region, with the Mount Read Volcanics (Crawford et al., 2003). The correlation is supported by the physical connection provided by the Selwyn Block – Neoproterozoic-Cambrian crust (Crawford, 1988; VandenBerg et al., 1995). The presence of older parts of the craton (Selwyn Block) beneath the Murray Basin has positive implications for potential nickel sulphide mineralisation. This continental basement may have provided magma from the upper mantle with a source of sulphur, enabling intrusions to potentially reach sulphur saturation and precipitate nickel sulphides.

Analysis of Victoria’s metallogenic provinces suggests potential for rift-related mineralisation and Avebury-style nickel sulphides in the undercover extensions of the Murray Basin to the north of the Glenelg zone. Rift-related mineralisation could occur as Ni-Cu-Co±PGE sulphides associated with basal contacts and feeder zones of S-saturated tholeiitic mafic-ultramafic intrusions, particularly where they intrude reduced sediment packages. There appears to be little potential for Noril’sk-type Ni-Cu-PGE deposits associated with voluminous continental flood basalt systems.

The potential for rift-related mineralisation could carry east into the Grampians-Stavely (and Stawell?) zone, where the potential for Avebury-style NiS mineralisation is also a possibility. Hydrothermal remobilisation of nickel sulphides by later plutons intruding Cambrian serpentinites could have occurred in the Heathcote and North Wilsons Promontory areas. Fractionation of potential host units could also play a role in the creation of a suitable setting for Ni-Cu-PGE mineralisation as seen at the Thomson River copper mine in eastern Victoria.

The potential for laterite nickel is somewhat more difficult to evaluate due to a lack of data. Whilst sufficient exploration and analysis for nickel laterite has been conducted in western Victoria, limited exploration in other parts of Victoria makes it impossible to evaluate the potential for such occurrences.

The need to further investigate the implications of the Selwyn Block – and compare those implications with those attributed to rift boundaries/Delamerian edge is highlighted by this report. Understanding Victoria’s tectonic setting is a challenge that is still being resolved as more data becomes available (e.g. recent seismic surveys across parts of central Victoria). Enhancing our understanding of the tectonic setting would allow us to better assess the relevance of arcs – with most known younger deposits associated with them. An enhanced understanding of the geotectonic setting would also establish links between New South Wales, South Australia, and Tasmania.

Bibliographic reference Seymon, A.R., 2006. Nickel prospectivity in Victoria. Geological Survey of Victoria Technical Record 2006/3. Geological Survey of Victoria.