Magmatic mineral deposits of nickel, copper and the platinum-group elements (Ni-Cu-PGE) form by the immiscible separation and concentration of Ni-Cu-PGE-rich sulfide liquids from magmas of mantle origin. An important sub-type of these deposits is the tholeiitic intrusion-hosted Ni-Cu-PGE sulfide deposit class, typified by the giant Noril'sk (Russia), Voisey's Bay (Canada) and Jinchuan (China) deposits. These contribute significant proportions of the world's production of Ni and PGEs, and represent some of the most valuable mineral deposits on Earth. However, there are very few known tholeiitic intrusion-hosted Ni-Cu-PGE sulfide deposits in Australia, and these are mostly uneconomic due to small size, low grade and/or remoteness.
This continental-scale study of the potential for tholeiitic intrusion-hosted Ni-Cu-PGE sulfide deposits in Australia addresses the problem of whether the apparent under-representation of resources of this type in Australia is due to lack of geological endowment or is a consequence of concealment of mineral deposits by sediments, basins and regolith (cover) which has hindered exploration success.
This study is the first continental-scale assessment of Ni-Cu-PGE mineral potential of Australia to apply a knowledge-driven GIS-based prospectivity analysis method. A mineral systems approach is used to identify new mineral provinces as well as extensions to known provinces with potential to host giant or major Ni-Cu-PGE sulfide deposits.
Major Ni-Cu-PGE sulfide deposits are consequences of lithospheric-scale earth processes, and form where there was a coincidence of ore-forming processes in space and time. Ore formation required four components of the mineral systems to have operated efficiently, namely: (1) energy sources or drivers of the ore-forming system; (2) crustal and mantle lithospheric architecture; (3) sources of ore metals (i.e., Ni, Cu, PGE in this study); and (4) gradients in ore depositional physico-chemical parameters. Conceptual criteria were developed that represent essential geological processes involved in each of the four components of the mineral system. These were translated into practical, mappable, criteria for which proxy geoscientific datasets were developed. Maps of favourability were constructed for each of the four system components. These were created using overlays of input rasters that were weighted (using a fuzzy logic-based method) according to the perceived importance, applicability and confidence level of each input dataset in the mineral system analysis. The results for the four maps were allowed to contribute equally to the final mineral potential map so that the areas of highest potential represent targets where all four mineral system components combine most favourably.
The assessment predicts high potential for tholeiitic intrusion-hosted Ni-Cu-PGE sulfide deposits in a wide range of geological regions of Australia, including those of known prospectivity and several with previously unrecognised potential. Importantly, the districts hosting the few known major intrusion-hosted Ni-Cu-PGE sulfide deposits were successfully predicted with high potential, despite non-inclusion of these deposits as inputs in the modelling (to avoid biasing the results).
In addition to the Geoscience Australia Record, the results of the study are available as a series of Geodatabase digital maps (rasters). The Python programming script used in the GIS analysis is also available online (Coghlan, 2015. Finally, the primary digital data used to create the input datasets for the modelling are available on-line for users' own purposes.
