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

Abstract

Between 1976 and 1985, the lignite resources of Eastern Southland were explored by 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 km{sup 2}. 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) which includes the fluvio-deltaic Gore Lignite Measures. These 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 lignite-bearing interval is typically thick. At least nine 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) coalfields 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. The bulletin has a pocket containing a 1:100,000 lignite resource map of Eastern Southland.