Mineral Potential Mapping of the Lachlan Fold Belt, New South Wales
The Lachlan Fold Belt is a structural unit that forms the dominant part of the Tasmanides in New South Wales and Victoria, Australia, and also extends into Queensland and Tasmania. It is a Middle Paleozoic accretionary orogen and hosts one of the world's major gold provinces. The first major discovery of gold was in 1851 at the Ophir Gold Diggings. Later discoveries used geophysical surveys and deep drilling methods such as those at the Cobar and Cadia East mine sites.
Kenex generated GIS and mineral potential maps for porphyry, skarn, orogenic, and VMS mineralisation styles for gold within the LFB in New South Wales.
Predictive maps have been developed that map source, transport, trap, and metal deposition mechanisms for the four types of mineralisation. The spatial analysis used geophysical data, geochemistry analyses of rock, drill hole, and stream sediment samples, and detailed lithological and structural descriptions. For each mineralisation style, different geological parameters were identified as important for predicting gold mineralisation, including:
- Porphyry: proximity to felsic to intermediate intrusive and extrusive lithologies; anomalous Au, Ag, and Cu assays in drill holes and rock chips; proximity to high magnetic gradient.
- Skarn: proximity to Paleozoic calcareous lithology; N-S trending faults; proximity to areas of high competency contrast.
- Orogenic: proximity to Paleozoic clastic sediments; correlation with fault splays and intersections; proximity to magnetic lows.
- VMS: correlation with density of faults; proximity to syn-volcanic lithologies; anomalous Ag, As, Bi, Cu, Zn geochemistry in host rocks.
Using weights of evidence techniques, predictive maps that represent all stages of the relevant mineral system model were developed. Based on these, mineral potential maps were produced that assess the probability of finding each type of mineralisation.
The mineral potential maps and exploration GIS are a valuable tool for companies to accelerate exploration if they already hold tenements, or to get ahead of competitors if the aim is to identify potential opportunities in NSW's most productive goldfield. Moreover, models can be tailored to individual company needs using prospect scale exploration data to prioritise targets within an existing tenement portfolio.