Sheet QM282 Coromandel : geological resource map of New Zealand 1:250 000

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Christie, A.B.; Wadsworth, D.; Williams, A.L.; Petty, D.R.; Brathwaite, R.L.; Skinner, D.N.B.; Brown, L.J.; Ogilvie, M.J. 1994 Sheet QM282 Coromandel : geological resource map of New Zealand 1:250 000. Lower Hutt: Institute of Geological & Nuclear Sciences Institute of Geological & Nuclear Sciences science report 94/12 130 p.

Abstract: The Coromandel Sheet area includes most of the Hauraki Goldfield which comprises a large number of epithermal vein gold-silver-lead-zinc-copper deposits, a few epithermal pyrite and mercury deposits, and several occurrences of porphyry copper style mineralisation, all related to late Cenozoic volcanism. Mining of the epithermal deposits between the 1850s and 1975 produced approximately 300 000 kg of gold and one million kg of silver. Lead, zinc, and copper were mined at Tui for export, between 1967 and 1974. The pyrite-marcasite deposits in the Kauaeranga valley and at Waihi Monument have been prospected as a potential source of sulphur, and the occurrences of porphyry copper mineralisation have been prospected for copper, gold, and molybdenum. New gold mines at Waihi and Golden Cross commenced production in 1988 and 1991 respectively, and have a combined annual production of about 5000 kg of gold and 22 000 kg of silver. Andesite is the most commonly quarried rock for use as aggregate; however greywacke, dacite, and rhyolite are also extracted. Selection of rock for good quality aggregate is limited to areas unaffected by the widespread hydrothermal alteration associated with late Cenozoic geothermal activity and mineralisation, and by inherent deleterious rock properties (including reactive minerals and clays) and weathering. During the 1970s, green andesite at Maratoto and Komata was mined and crushed for use as a coating on roof tiles, and rhodochrosite was mined from Maratoto for use as a toothpaste additive. Some local greywacke, andesite, dacite, jasper, ignimbrite, and rhyolite have potential for use as dimension stone. Sand has been extracted from alluvial, coastal, and offshore deposits. Limestone is present in the Amodeo Bay area and is extracted for local use as road aggregate and agricultural lime. Small quantities of kaolitic clay, tonned by hydrothermal alteration of rhyohte, were mined in the Hahei area. Several other small deposits are present locally and similar deposits associated with alteration in andesites are known at Black Jack, Pumpkin Hill, and Waihi Monument. Perlite was quarried from rhyolite domes at Hikuai and Paku Island. Semi-precious gemstones including quartz, chalcedony, agate, jasper, semi-opal, and silicified wood, each of variable quality and quantity, are prospected for by rock collectors. Two shallow wildcat holes drilled on Great Barrier Island failed to find significant hydrocarbons. The potential for hydrocarbon production and accumulation in the sheet area is severely limited by the thin development and probable inadequate depth of burial of the Cenozoic sedimentary sequence. Hot springs occur on the Coromandel Peninsula within the Hahei-Hot Water Beach area and several hot, and mineralised cold, springs occur on the eastern margin of the Hauraki Plains, including the Te Aroha springs, and Puriri and Paeroa soda springs. In the Bay of Plenty, hot springs occur near Katikati and on Mayor (Tuhua) Island. The Hot Water Beach, Katikati, and Te Aroha springs, and drillholes at Whitianga, supply hot water for public bathing pools. Waters from Puriri and Paeroa soda springs have been bottled commercially. Groundwater resources are important on the Hauraki Plains and the western Bay of Plenty. (auths)