Geology

The West Coast Coal Region

The West Coast coal region is situated on the West Coast of the South Island. It comprises coalfields formed during the Late Cretaceous and Early Tertiary period within a narrow, elongate, fault-bound basin (the Paparoa trough), which extends from Ross in the south to Seddonville in the north. Rapid fault activity during this deposition resulted in abrupt facies variations within the coal measures and in irregular lensoidal geometry through the coal seams.

A marine incursion from the Eocene to Oligocene period resulted in up to 2,500m of marine sediments being deposited into the trough over the coal-bearing sediments, which were later, uplifted by a major change of tectonic activity, reducing cover across the region.

Buller

The Buller History is located adjacent to the western coast of the South Island, approximately parallel to the coastline and centred close to the coastal town of Westport.

The coalfield is on a tilted basement block, bounded on the west by about 2,000m of vertical uplift along the Kongahu fault, which resulted in the formation of the Papahaua Range and erosion of the tertiary marine sediments overlying the coal measures. This tectonic activity also caused the formation (through basin eversion) of a pattern of northeast trending normal and reverse faults, which are characteristic of the coalfield.

The Brunner coal measures, formed in the Buller, have a lithological sequence of basal pebble-conglomerate, quartzose sandstone, mudstones and coal seams. Shallow marine sediments overlay the measures.

Most of the coal resources within the Buller History occur within a single, thick base seam traditionally named the Mangatini seam. A notable characteristic of this seam is the relatively high sulphur levels in the roof and floor plies, with very low ash and sulphur levels within the middle plies.

Stockton Opencast Mine

Within the Stockton coal mining licence there is generally a single seam present, the Mangatini seam, which ranges in thickness from 5m to 10m. The seam dips 5 to 10 degrees to the northeast with local variations around faults. Depth-of-cover ranges from 10m to 30m. Quartzose sandstone units form erosion-resistant caps, aiding high wall stability.

Terrace Underground Mine

The basal No. 4 Seam at Terrace Mine Reefton is worked by drill/blast with hydraulic transportation of the coal. The seam is an average 8m in thickness with a range from 6m to 25m. Depth of cover is up to 170m and seam dip is 20 degrees.

Greymouth

The Greymouth History is located near the town of Runanga, about 100km south of Westport. Most of the coal resource is contained within the Paparoa coal measures, a terrestrial unit of Late Mesozoic to Early Cainozoic, overlain on a basement of Palaeozoic metasediment. These coal measures comprise four coal-bearing units each separated by a lacustrine mudstone. Unconformably overlying these coal measures are the Brunner coal measures.

The coal-bearing units have been upwardly named the Jay, Morgan, Rewanui and Dunollie formations. Late Tertiary tectonism produced eversion of the Paparoa trough and subsequent erosion has removed large areas of the overlying Tertiary marine sediments.

The coalfield is dissected by a number of northeast trending normal and reverse faults. Regional dip is to the southeast with moderate to steep angles, with the whole field plunging south. Cover ranges from outcrop and shallow sub crop in the north to over 600m in the southwest.

Spring Creek

Most of the coal resource is contained within the Rewanui formation. Four mineable seams are present - E, D, C and Kimbell. Seam thickness ranges from 4m to 6m with localised areas up to 15m thick. Cover within the coal mining licence ranges from outcrop or shallow sub crop to vertical as the seams plunge south. The coal mining licence is broken into blocks by a series of north/north-east trending faults. Hydraulic mining extraction methods are used.

Waikato Coal Region
The West Coast Coal Region
Southland Coal Region