Mineral resource assessment of the Thames-Coromandel and Hauraki districts, New Zealand

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Christie, A.B.; Brathwaite, R.L.; Barker, R.G.; Skinner, D.N.B. 2008 Mineral resource assessment of the Thames-Coromandel and Hauraki districts, New Zealand. Lower Hutt, N.Z.: GNS Science. GNS Science report 2008/14 119 p. + 1 CD

Abstract: The Coromandel area comprising the Thames-Coromandel and Hauraki districts, is one of the most mineral-rich areas of New Zealand. It includes most of the Hauraki Goldfield, which comprises a large number of mineral deposits. Known mineral deposits include more than 50 epithermal gold-silver-lead-zinc-copper deposits, five epithermal pyrite and mercury deposits and five occurrences of porphyry copper style mineralisation, all related to late Cenozoic volcanism. The epithermal deposits have produced more than 350,000 kg of gold and 1.2 million kg of silver worth $13,775 million and $957 million, respectively, at current prices for gold (NZ$1225/oz) and silver (NS$24.80/oz). Gold and silver are currently produced from the Martha Hill open pit mine (approximately 1,600 Au and 10,000 kg Ag annually, down from a typical previous production of 2,700 kg Au and 20,000 kg Ag annually in the late 1990s and early 2000s) and Favona underground mine (3,400 kg Au and 8,800 kg Ag annually). In addition to these metals, the area also produces rock aggregate (mostly andesite), sand and peat. Limestone, clay, perlite, lead, zinc, copper and mercury have been produced in the past. Resources of aggregate have not been quantified, but are estimated to be large and sufficient to meet foreseeable local demand. The value of potential resources estimated for 12 metallic and 6 non-metallic mineral deposit models for the Coromandel area totals NZ$54 billion, mostly in gold, silver and peat. These estimates were made mainly using a three step process involving mineral deposit models, a geographic information system (GIS) of spatial data sets, and a counting method of assessment. Current total mineral production in the Coromandel area has a value of about $225 million per year using March 2009 international prices of gold and silver. Cessation of gold-silver mining (which accounts for about 97% of the current value) would reduce this to about $6.5 million. A scenario of increased aggregate production, new gold and silver production to levels higher than present, continuation of peat mining at current levels, and mining of new commodities could increase production to almost $300 million. This scenario would be possible over a 15 year time-frame, provided that: there is a sufficient level of exploration to define the new resources and new discoveries can be developed. (auth)