Sheet QM359 Greymouth : geological resource map of New Zealand 1:250 000

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McPherson, R.I.; Roser, B.P.; Suggate, R.P.; Christie, A.B.; Nathan, S.; Deely, J.M.; Mackwell, J.A.; Leslie, M.G.; Brooker, M.; Doole, M.H.; Brown, L.J.; Brathwaite, R.L. 1994 Sheet QM359 Greymouth : geological resource map of New Zealand 1:250 000. Lower Hutt: Institute of Geological & Nuclear Sciences Institute of Geological & Nuclear Sciences science report 94/13 91 p.

Abstract: The Greymouth Sheet is endowed with a wide variety of geological resources as a result of a complex geological history from early Paleozoic to Recent. Gold, coal, aggregate, limestone, and rip rap are the most important resources currently extracted. Additional commodities mined at present and in the past include antimony, clay, dimension stone, mica, greenstone, silica sand, and silver. A permit to mine ilmenite at Barrytown is currently being sought. Other commodities of potential interest include feldspar, fluorite, garnet, petroleum, serpentinite, tungsten, and zirconium, whereas occurrences of antimony, asbestos, barite, beryllium, chromium, copper, lead, molybdenum, nickel, talc, tin, uranium, and zinc are at present only of curiosity value. Gold production began with the gold rushes of the 1860s. Approximately 240 000 kg of gold have been mined from fluvioglacial and beach placer deposits, predominantly of Pleistocene age, and about 94 000 kg have been produced from auriferous quartz veins in Ordovician greywacke. Current mining of the placer deposits produces more than 500 kg of gold annually from the Grey River dredge and more than 40 small operations. The Greymouth Sheet includes the southwest part of the Buller Coalfield, and the Charleston, Punakaiki, Pike River, Greymouth, and Aratika coalfields, and Garden Gully and Fox River coal deposits, although not all of these areas have been mined. Coal mining began in 1862 (Greymouth Coalfield) and production has been continuous to the present, amounting to more than 40 million tonnes (Mt) from Paparoa (Late Cretaceous-Paleocene) and Brunner (Late Eocene) coal measures. Buller and Greymouth coalfields produce all of New Zealand's bituminous coal, whereas production from other areas within the sheet is of sub-bituminous coal. Current annual production is around 100 000 t and estimated recoverable coal resources are more than 200 Mt. Aggregate sources are abundant and most of the 80 000 t annual production is from pits working greywacke and granite gravels in Quaternary fluvioglacial deposits and modern river channels. A few hard rock quarries work greywacke, granite or limestone. Large deposits of limestone are present including Waitakere, Cobden, Potikohua, and Kowhitirangi limestones. Current annual production is about 0.7 Mt: 0.6 Mt for cement making, 40 000 t for rip rap, and 28 000 t for agricultural lime. Extensive deposits of Holocene ilmenite-rich sand are present along the coast with resources of 175 Mt estimated for the Barrytown-Twelve Mile, Nine Mile, and Carters deposits. Accessory minerals include garnet, gold, zircon, monazite, rutile, and cassiterite. Barrytown is the most intensively explored deposit and has resources of 50 Mt of sand at an average grade of 13.8% ilmenite (6.9 Mt), 0.2% zircon, 100 mg/mi gold, and less than 0.1% each of monazite and rutile. Investigations are being carried out into the potential use of ilmenite from Westport (a mineable resource of perhaps 10 -20 Mt) for pigment manufacture in Japan and Europe. Kaolinitic clay, for production of fire bricks and building bricks, has been worked from deposits in coal measures, deeply weathered basement rocks, and Tertiary mudstone units (e.g. Blue Bottom Group). Sandstone with a high silica content (ganister) is present in coal measures of the Buller, Charleston, and Greymouth coalfields, and silica sand occurs at Little Totara River and Ross. Granitoid intrusive rocks and their contact zones in the metasedimentary country rock contain mineral occurrences of fluorite, scheelite, barite, chalcopyrite, galena, molybdenite, cassiterite, and sphalerite; pegmatite dikes at Charleston contain beryl, feldspar and mica; and ultrarnafic rocks have asbestos, greenstone, nickel, serpentinite, and talc. Oil and gas seeps at Kotuku and in the Greymouth Coalfield have led to continuing petroleum exploration interest. Two deep offshore wells and about 15 deep onshore wells have been drilled, many producing oil and gas shows, but no deposit of economic significance has been discovered. A few hot springs are present in valleys immediately east of the Alpine Fault, in the southeast of the sheet, and are used for recreational bathing. There is little demand for groundwater because of a high rainfall and most water used for domestic consumption within the sheet area is obtained from rivers, streams and rainfall. There is potential to export water because of its high purity. (auth)