Kear, D.; Schofield, J.C. 1973 Waikato coalfields : Maramarua Coalfield. Scale 1:15,840. Wellington: Department of Scientific and Industrial Research. Miscellaneous series map / New Zealand Geological Survey 2; Miscellaneous series map / New Zealand Geological Survey 3 2 fold. maps + 1 booklet
Abstract: The Maramarua Coalfield, 50 miles SE of Auckland, has yielded just over 6, 000,000 tons of coal since it was discovered about 1869. Its best known mine, Kopuku Opencast, has alone produced over 90% of this total since 1948, with an annual production averaging nearly 400,000 tons during the last 10 years. Shortly after the Second World War, a large number of drillholes, put down by Glen Afton Collieries Ltd, and several local farmers, indicated considerable reserves of underground and opencast coal. Detailed drilling in 1952-7, supervised jointly by Mines Department and N.Z. Geological Survey on behalf of the then State Hydro-electric Department and Glen Afton, showed 25, 000, 000 tons of opencast and 53,000,000 tons of underground recoverable coal, sufficient to supply a power station at Meremere on the Waikato River, 6 miles from Kopuku. The only parts of the coalfield that remain poorly prospected are the Puketoka and Mangatangi sectors, where significant additional coal reserves might be located. Only the Kupakupa Seam is present. Its thickness ranges up to 70 ft (20 m), but averages 25 ft (8 m) over wide areas. The sulphur (0.2-0.6%) and ash (3- 10%) contents are low, the volatile matter content appears to increase eastwards (48-53% on a dry ash-free basis), the bed-moisture is close to 26% the calorific value (air-dried coal) averages 9,400 Btu/lb, and shows the coal to be at the top of the Sub-bituminous C rank of the A.S.T.M. classification. The coalfield is bounded to the west by the large Maungaroa Fault. Foote Fault, with south-eastern downthrow of 1,000 ft, cuts across the field, and has a 45 degree hade. The regional dip of the coal is 10 degrees to 20 degrees NW.