Kermode, L.O.; Meshesha, M.Y.; Christie, A.B.; Brathwaite, R.L.; Brown, L.J. 1992 Sheet QM281 Manukau : geological resource map of New Zealand 1:250 000. Lower Hutt: Institute of Geological & Nuclear Sciences. Institute of Geological & Nuclear Sciences science report 92/15. 95 p.
Abstract: The area covered by Manukau Sheet has substantial resources of aggregate, coal, limestone, ironsand, and groundwater, all of which are being currently exploited. Quarried aggregate resources include basalt, andesite, greywacke, and conglomerate, but access to some high quality resources in the Auckland area is limited by urbanisation. The greywacke terrain along the eastern coast has good prospects for shingle (gravel) resources. Sand for use in mortar and concrete aggregate occurs mainly along the Waikato River, in west coast dune sands, and in offshore deposits of the Hauraki Gulf and Kaipara Harbour. More than 40 million tonnes (Mt) of sub-bituminous coal have been extracted from coal deposits within the sheet, and production during 1990 totaled 0.75 Mt. Remaining coal-in-ground resources are more than 1500 Mt. Resources of argillaceous limestone are present in the northern part of the sheet and are extracted for use in road aggregate, cement manufacture, and agriculture. Crystalline limestone occurs south of Auckland, particularly in the Raglan area, but the potential of much of the resource is limited by overburden and poor accessibility. Ironsand resources of the western coastal area are extensive. About 1.4 Mt of concentrate (57% Fe and 0.4% V2O5) is extracted annually from Waikato North Head and used for iron and steel making at the Glenbrook mill. Current resources in nine onshore deposits, including Waikato North Head, are about 140 Mt indicated and 83 Mt inferred. Groundwater resources are plentiful in the Waikato valley and Manukau lowland. Coldwater springs have been an important source of major local water supplies in the Manukau Sheet but few are used at present. Hot springs at Waiwera, Parakai, and Miranda supply hot water for public swimming baths and heating. Resources of clay, silica sand, pumice, diatomite, dimension stone, and serpentite are also present. During the 1800s, gold-silver bullion was mined from Great Barrier Island and northern Coromandel Peninsula, copper was mined from Kawau Island, and manganese from Kawau Island and Waiheke Island. The gold-silver mining continued into the early 1900s, and manganese was mined from three deposits in the Otau-Bombay area between 1937 and 1960. Known resources of these metals are small. Other important historical mining includes the digging for kauri gum in many of the lowlands, between 1850 and 1900.