Blevin, Phillip1; Downes, Peter1; Fitzherbert, Joel1; Ford, Arianne2; Peters, Katie2; Greenfield, John1
1Geological Survey of New South Wales, Department of Regional NSW, Maitland, Australia, 2Kenex Ltd, Wellington, New Zealand
The Geological Survey of New South Wales (GSNSW) has completed a four-year mineral potential mapping project across the major metallogenic provinces of NSW. These include the New England, eastern and central Lachlan and Delamerian orogens as well as the Curnamona Province. Mineral system models, specific to each province/event, were prepared for orogenic Au and Au–Sb, polymetallic volcanic associated massive sulfide, Broken Hill Pb–Zn–Ag, Cobar Pb‒Zn and Cu-Au, Macquarie Arc porphyry Cu–Au and intrusion-related Au and Sn–W systems. Modelling of the skarn potential of the eastern Lachlan Orogen was also undertaken to test the intersection between granite fertility with structural and reactive rock data to potentially model fluid flow and traps using essentially 2D data.
In excess of 10 million drillhole assays, 152,000 attributed faults, 31,190 mineral occurrences, 197,754 field observations and 883,967 surface geochemical assays were used in addition to the NSW Seamless Geology, and statewide geophysical and metamorphic datasets.
Where possible, a weights-of-evidence approach was used. Typically, over 100 valid predictive maps were generated for each mineral system to model source, transport, trap and depositional characteristics. Spatial relationships were tested with between 8 to 28 training points. Between 8 to 18 predictive maps were selected for each final model. The efficiency of classification for most models was better than 95%, with the prospective areas covering 3% to 16% of the relevant province and the highly prospective areas being significantly smaller.
Importantly, measures of data confidence were captured, and all polygons have attached metadata indicating the predictive layers used in their construction. There was interactive feedback at all stages between the Kenex spatial analysts and GSNSW mineral system specialists. The final reports, primary datasets, spatial data tables and data, including thousands of intrinsically useful predictive maps, are freely available for download from DIGS, with key spatial layers also accessible on the MinView platform. The prepared data outputs provide an ideal opportunity for testing revised and new mineral system models, or to add new data and explore alternate methodologies.
In areas under cover, geophysical mapping of secondary structures and intrusions was key in compensating for a lower data density. The associations of many mineral systems with gravity and magnetic worms at various depths is also intriguing, although the reason for this association is not yet clear. The correlation and understanding of these linkages through the crust will be a focus for future mineral potential mapping studies in areas devoid of relevant surface data.
A key learning from the project is the need to ensure that all datasets are in usable formats and fit-for-purpose prior to spatial modelling. This includes the standardisation of geological drill logs, stratigraphic unit descriptions and attributes in mineral occurrence and petrological databases. In the future, rock reactivity and permeability values, petrophysical data and magmatic fertility parameters combined with seamless geology, and fully attributed fault and metamorphic layers willallow for the construction of on-demand mineral potential maps viewable on MinView and permit the data to be exported into machine learning packages for real-time modelling on online platforms.
Phil Blevin (BSc – UNE, PhD – JCUNQ) specialises in understanding controls on the fertility of felsic magmas as well as related Sn(-W), W-Mo-Bi, granite related Au and porphyry Cu-Au mineral systems. He currently leads the mineral system (MinSys) team at GSNSW, including HyLogger operations.