Geology and lignite resources of the East Southland Group, New Zealand

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Isaac, M.J.; Lindqvist, J.K.; Pocknall, D.T. 1990 Geology and lignite resources of the East Southland Group, New Zealand. Lower Hutt: DSIR Geology and Geophysics. New Zealand Geological Survey bulletin 101 202 p.

Abstract: Between 1976 and 1985, the lignite resources of Eastern Southland were explored by several government-funded programmes involving drilling, geophysical logging, seismic surveys, mapping, and lithofacies analysis. Investigations covered the Maitland Basin north of Gore, and that area of Eastern Southland between the Oreti and Mataura rivers, from Gore south to Foveaux Strait, a total of about 2800 km2. Over most of this area, extensive Pleistocene-Holocene terrace gravels are underlain by Late Oligocene-? Middle Miocene marine and nonmarine clastic sediments of the East Southland Group (new name), a paralic regressive unit comprising basal or near basal estuarine (Pomahaka Formation) and marine (Chatton Formation) beds, succeeded by (and probably intercalated with), the fluvio-deltaic Gore Lignite Measures. In the NW, the Early Miocene Forest Hill Formation is laterally equivalent to East Southland Group lithofacies indicate deposition in a range of shallow marine shelf, coastal margin, delta plain, and fluvial plain environments. The Gore Lignite Measures comprise a lower, sandstone-dominated unit with only minor lignite, a lignite-bearing interval commonly including multiple, laterally persistent seams, and an upper unit of conglomerates and sandstones, with thick intervening mudstones, and little or no coal. At Mataura, the outcrop or subcrop beneath the younger gravels, as a result of faulting, folding, and gentle tilting. At least mine areas have sufficient lignite at shallow enough depth to be of future interest. The total resource at less than 200 m of cover is estimated to be 6760 million tonnes of Indicated, and 1570 million tonnes of Inferred coal-in-ground. Mining feasibility studies concluded that the Morton Mains, Waimatua and Kapuka (Ashers-Waituna) coafields have sufficient lignite to sustain a 450 million tonne opencast at overburden to coal ratios of better than 4:1 Kapuka (Ashers-Waituna) was favoured for any such development. (auths)