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Kawerau Geothermal field, Kawerau District, Bay of Plenty Region (Te Moana-a-Toi), North Island, New Zealand

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Latitude & Longitude (WGS84): 38° 3' 32'' South , 176° 43' 15'' East
Latitude & Longitude (decimal): -38.05889,176.72111
GeoHash:G#: rcjxmrs6u
Köppen climate type:Cfb : Temperate oceanic climate

The Kawerau geothermal field is located immediately east of Kawerau township. Most of the surface thermal features are believed to have been in a natural state of decline prior to development, which arose from the energy requirements of the large Tasman pulp and paper processing plant built in the 1950s. Until the commissioning of the Ohaaki power station at Broadlands-Ohaaki, Kawerau was the second largest producing field in New Zealand and its steam supply for industrial use equates to half of the world's total steam supply for industrial applications.

The town of Kawerau was established in the early 1950's to service the Tasman pulp and paper mill, and its associated geothermal power station. All the Onepu hot springs ceased flowing between 1952 to 1988. Unlike Rotorua, there is little geothermal activity to see on the surface, with the mill constructed next to the spring, and sludge from it, destroying what was left. Most of the voluminous writings about the geothermal field focus on the rock units, and aspects relating to power generation. Specimens like wairakite occur from hydrothermal alteration of the basement greywacke several hundred metres underground. Specimens seen for the location may have come from the numerous drill cores in the area, but is uncertain.

Mount Edgecumbe (Putauaki) (821) is a prominent 5000 year old dacite-andesite multi vent volcano immediately east of the town. The last substantial eruption was in 300 BCE, with no activity since 1850, although there was a major earthquake in the area in 1987.

The geothermal field lies near the north-west axis, and at the southern end of the Whakatane complex regional graben. This has been infilled with various rock units including rhyolites, andesite lava, ignimbrite, and more recent sediments. The area is a series of stepped blocks created by north-east trending faults, and cross-cutting north-west faults. The faults are not often observable on the surface due to alluvium. The Kawerau geothermal field sits on the eastern edge of the Taupo Volcanic Zone, and unlike other fields in the area is not part of a caldera.

The units from the surface are:
1) Recent alluvium- peat, sand, gravel, pyroclastics (10-50 metres thick).
2) Hydrothermal eruption breccia (up to 10 metres thick).
3) Unconsolidated pyroclastics- unwelded pumiceous pyroclastic flows and airfall tuffs (up to 10 metres thick).
4) Onepu Formation- twin surficial domes of rhyodacite with plagioclase and minor quartz, amphibolite, pyroxene, biotite, and magnetite (up to 200 metres thick).
5) Matachina Formation- ignimbrite, partly welded, grey, and vitric tuff, with obsidian, plagioclase, quartz, hornblende, pyroxene (up to 410 metres thick).
6) Tahuna Formation- crystal rich fine sandstone, siltstone, muddy breccia, and unwelded pumice rhyolite lapilli tuff (up to 360 metres thick).
7) Coxton Formation- buried domes of spherulitic and banded rhyolite and intrusive, with quartz, plagioclase, biotite, apatite, and amphibolite (up to 450 metres thick).
8) Karaponga Formation- partly welded crystal lithic tuffs (up to 180 metres thick).
9) Onerahi Formation- tuffaceous to muddy breccias and coarse tuffaceous sandstone (up to 85 metres thick).
10) Kawerau Andesite- augite and plagioclase andesite flows, breccias and tuff (up to 300 metres thick).
11) Raepaphu Formation- partly welded crystal lithic tuffs (up to 165 metres thick).
12) Tasman Formation- muddy breccia, sandstone, and siltstone (up to 25 metres thick).
13) Te Teko Formation- partly welded grey crystal vitric tuffs, with quartz, plagioclase, minor biotite and ferromagnesian minerals (up to 225 metres thick).
14) Rotoroa Formation- tuffaceous sandstone, poorly sorted crystal and lithic siltstone (up to 200 metres thick).
15) Waikora Formation- greywacke pebble conglomerate, and minor intercalated tuff and siltstone (up to 450 metres thick).
16) Basal greywacke.

Hydrothermal alteration in the Mesozoic greywackes has produced three assemblages 1) wairakite-prehnite, 2)calcite 3) quartz-calcite-adularia-calc silicates with illite, abundant epidote and clinozoisite, and some laumonite. The earliest hydrothermal activity produced (1), followed by high gas pressure via a hydraulic fracturing event precipitating (2), and finally more recent hydrothermal activity (3).

Calcite is said to be common near the top of the greywacke, while wairakite is locally abundant. (Tulloch) states calcite comes in uncommon platy forms, as well as prismatic and scalenohedron, associated with sulphides pyrrhotite, with trace sphalerite, galena, chalcopyrite, and covellite. (Bignall et. al., 2012) states alteration minerals are quartz, adularia, albite, clay, calcite, chlorite, titanite, pyrite, and epidote. (Milicich, 2013) adds alunite, halloysite, cristobalite, smectite, kaolinite, tridymite, pyrophyllite, chalcedony, diaspore, dickite, anhydrite, sericite, rutile, and apatite, depending on acidity, temperature, and salinity of the fluids.

Mineral List

14 valid minerals.

Regional Geology

This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.

Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org

0 - 2.588 Ma

ID: 3187411
Cenozoic volcanic rocks

Age: Pleistocene (0 - 2.588 Ma)

Lithology: Ignimbrite(s); felsic volcanic rocks; rhyolite

Reference: Chorlton, L.B. Generalized geology of the world: bedrock domains and major faults in GIS format: a small-scale world geology map with an extended geological attribute database. doi: 10.4095/223767. Geological Survey of Canada, Open File 5529. [154]

0 - 2.588 Ma

ID: 1313740
Late Quaternary ignimbrite

Age: Pleistocene (0 - 2.588 Ma)

Stratigraphic Name: Pakihi Supergroup

Description: Non-welded, rhyolite ignimbrite and minor fall deposits; includes minor reworked deposits and dacite pumice on Macauley Island.

Comments: Zealandia Megasequence Extrusive and Intrusive Rocks (Neogene)

Lithology: Pyroclastic material, ash, rhyolite, dacite

Reference: Edbrooke, S.W., Heron, D.W., Forsyth, P.J., Jongens, R. (compilers). Geology Map of New Zealand 1:1 000 000. GNS Science Geological Map 2. [12]

Late Pleistocene
0.0117 - 0.126 Ma

ID: 1348962
Rotoiti Formation (Okataina Group) ignimbrite mantled by thick Mangaone Subgroup fall deposits of Okataina Volcanic Centre

Age: Pleistocene (0.0117 - 0.126 Ma)

Stratigraphic Name: Rotoiti Formation

Description: Non-welded rhyolite ignimbrite; minor fall deposits.overlain by rhyolite fall deposits.

Comments: Late Pleistocene igneous rocks. Age based on mixed

Lithology: Major:: {ignimbrite},Minor:: {pumice, lapilli, ash}

Reference: Heron, D.W. . Geology Map of New Zealand 1:250 000. GNS Science Geological Map 1. [13]

Data and map coding provided by Macrostrat.org, used under Creative Commons Attribution 4.0 License

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Wood, C.P., Brathwaite, R.L. (1999) The basement at Kawerau geothermal field. Proceedings of the 21st New Zealand Geothermal Workshop, pp. 101-106: Geothermal Institute, University of Auckland.
Tulloch, A.J. Mineralogical observations on carbonate scaling in geothermal wells at Kawerau and Broadlands, New Zealand Geological Survey.
Macdonald, W.J.P., Muffler, L.J.P. (1972) Recent geophysical exploration of the Kawerau Geothermal Field, North Island, New Zealand. New Zealand Journal of Geology and Geophysics, 15:3, 303-317.
Absar, A., Blattner, P. (1985) Successive hydrothermal events as indicated by oxygen isotope composition and petrography of greywacke basement rocks Kawerau geothermal field New Zealand, Proceedings of the 7th New Zealand Geothermal Workshop.
Bignall, G., Milicich, S.D. (2012) Kawerau geothermal field geological framework, GNS Science Report 2012/33.
Milicich, S.D. (2013) Aspects of the Chronology, Structure and Thermal History of the Kawerau Geothermal Field. (unpublished thesis, PhD in Geology), Victoria University of Wellington.

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