What we have
The West Coast is composed of a variety of rock types of variable age. The old resistant granites and gneisses form the bulk of the mountainous terrain to the north of Greymouth. Younger schists and greywackes form the alpine sequences to the east. Outcrops of granite occur at isolated locations further south and west of the Alpine Fault.
Sedimentary rocks throughout the region comprise sandstones, siltstones, limestones and mudstones. These form scenic attractions including the Pancake Rocks, limestone caves, and karst landscapes.
Slope stability problems occur on a wide variety of formations throughout the region. Failures, sometimes catastrophic, may be induced by intense rainfalls or earthquakes or a combination of both.
Mineralisation is associated with many older rocks in the region where they have come into contact with adjacent granitic rocks. The Reefton goldfield, where the second largest gold mine in the country operated for over half a century, is the most significant example of this.
Detrital gold, which remains as a lag deposit in outwash gravels after glacial retreat, is an important resource which has sustained mining in the region for over a century.
Extensive bituminous and sub-bituminous coal-fields exist north of Greymouth. Currently extraction accounts for a significant amount of the national coal production. The low ash and low sulphur bituminous coal deposits offer future long term export opportunities.
Reserves of ilmenite are spread throughout the region in coastal beach sands. Potentially commercially viable deposits are concentrated near Barrytown and around Cape Foulwind. The mineral originates from widely dispersed plutonic and metamorphic rocks within the region.
Greenstone or pounamu is found east of the Alpine Fault, principally in the catchments that lie between the Taramakau and Arahura rivers, but also in the region’s far south. It has traditionally featured as a tradeable commodity. Pounamu is considered by Poutini Ngai Tahu to be a taonga or treasure protected by the taniwha Poutini. It is prominent in their oral tradition and lore. Regional pounamu resources contribute significantly to the mana of Poutini Ngai Tahu.
A number of industrial minerals are found throughout the region. These include rock, gravel and sand for road and railway formation and the construction industry. Limestone is used for cement and clay for pottery and ceramics.