GIS Modelling of Gold Prospectivity in New Zealand

Gold production in New Zealand has been significant since the mid 1800s, totalling 900 t (29 Moz) to 2005. In addition, there is potential for a further 1230 t (39.5 Moz) of gold in known and undiscovered deposits. Most of the gold has originated from epithermal and mesothermal (orogenic) hydrothermal systems. Epithermal gold occurs in the Northland, Coromandel and Taupo volcanic zones in quartz veins formed by shallow hydrothermal systems. All past production has been from the Coromandel region. Mesothermal gold occurs in Marlborough, West Coast and Otago in low-medium metamorphic grade sedimentary and schist host rocks, typically within quartz veins or shear zones that were formed during deformation. Placer gold mining has occurred downstream of mesothermal gold deposits in Otago and the West Coast of the South Island, and on some West Coast beaches. Considerable data are available in digital formats to assist exploration for new gold deposits using Geographic Information Systems (GIS) software. These data include modern geological mapping, geochemistry, geophysics, mineral occurrences, topographic data and cultural data, as well as derivative themes such as geophysical interpretation, metamorphic grade and structural trends. Key data components of epithermal and mesothermal Au mineral deposit models were extracted from these data sets, including host rocks, proximity to structures, lithofacies, quartz veins, alteration, metamorphic grade, geochemistry and volcanic features. The spatial relationships between these data and known gold deposits have been statistically quantified using the weights of evidence technique within GIS software. Stronger correlating data have been combined to create map models that quantify prospectivity. Many areas of elevated prospectivity with little previous mineral exploration have been identified suggesting that there is considerable potential for future gold discoveries in New Zealand.