Granite-related Nickel skarn modelling in Tasmania
Kenex has been undertaking exploration in Tasmania since 2006, when a new style of mineral deposit was introduced to explorers with the type deposit located at Avebury in Tasmania. The granite-related nickel skarn system was only recently recognised and is associated with remobilisation of nickel from ultramafic host rocks during granite intrusion. This style of nickel mineralisation is thought to have formed when Cambrian ultramafic rocks were intruded by Carboniferous granites. It is believed that during granite intrusion, associated fluids leached nickel from nearby mafic lithologies, which combined with sulphur in the granitic fluids to form nickel sulphides. The nickel sulphide deposits at Avebury are located along the margins of folded and faulted ultramafic bodies which are in contact with metamorphosed and altered sediments. At these locations, mobilised fluids trapped and concentrated nickel sulphides in the ultramafic hosts or in the adjacent metasedimentary units. The Avebury nickel deposit in western Tasmania is the type example of the granite-related nickel skarn style of mineralisation. It was mined by Allegiance Mining until 2008.
As the lithologies near Avebury are not unique, it is believed that similar deposits could exist elsewhere in Tasmania and further afield in Australia or New Zealand. The relationships between the geology and the mineralisation are easily recognised spatially and temporally and Kenex has generated a prospectivity model to locate areas in Tasmania where other deposit like the Avebury could be located.
A GIS based weights of evidence modelling technique provided an ideal tool for indentifying areas with similar geological conditions for future granite-related nickel skarn exploration. Using modern GIS modelling software and currently available digital data from geological surveys in Australia this modelling has allowed our clients to target areas previously unexplored which have highly favourable geological conditions for a granite-related nickel skarn deposit.
The weights of evidence spatial modelling technique required expert knowledge about the deposit mineral system and included geological mapping, geological structural interpretations, geochemistry and geophysics. The main geological features from the Avebury mineral system model were used to develop predictive themes representing all stages of the mineral systems model. Existing economic deposits were used as training data to weight the model themes, and these weighted themes were then combined to create a prospectivity map showing areas favourable for granite-related nickel deposits. The model highlighted the importance of geological and geochemical data sets as predictors of mineralisation and has identified several regions similar to the Avebury Deposit that have good potential to host nickel sulphide mineralisation. These targets were ranked and the most prospective were chosen for follow-up investigation, and several new exploration permits were acquired by our clients in Tasmania. As well as finding targets in Tasmania the model also identified areas elsewhere in Australia with similar geological conditions to Avebury; the map below shows how the granite-related nickel skarn model was used to target new exploration permits near Rockhampton in Queensland for Accord Mining Pty Ltd.