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Broadlands (Ohaaki), Taupo District, Waikato Region, North Island, New Zealand

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Latitude & Longitude (WGS84): 38° 30' 48'' South , 176° 18' 46'' East
Latitude & Longitude (decimal): -38.51345,176.31300
GeoHash:G#: rcjkuhg4y
Köppen climate type:Cfb : Temperate oceanic climate


Geothermal area. Ohaaki is sometimes spelled Ohaki in the references, however, Mindat's main title refers to the official topographical map name.

Located 25 kilometres north-north-east of Taupo.

In 1989 the Ohaaki geothermal power station opened on the field. Despite test drilling since 1965 and voluminous geological reports, there appears little understanding on how extraction of heated water out of the system would affect surface geothermal features and the future viability of the power station. This has parallels to the present gas fracking debates occurring in various parts of the world, and how the process will alter water resources.

Prior to the power station, there was a small natural geothermal area called Broadlands on the east side of the Waikato River, consisting of patches of steaming ground, and a few warm springs with vigorous gas discharges. Three kilometres to the north-west was the larger Ohaaki geothermal area, consisting of the main Ohaaki Pool, edged by white sinter deposits, and several small springs nearby. The pool has cultural significance to the local Maori tribe. Some references call the area Broadlands or Ohaaki as a whole.

No environmental report was produced until after the test drilling, and after water levels had fallen as a possible result, in the Ohaaki Pool. The report did not address at all any effects the power station may have on the existing natural geothermal features.

After the power station was erected, and wells sunk, all the small springs dried up, water levels fell further in Ohaaki Pool, while the white sinter deposit partially collapsed, became a dirty grey colour, and has plants growing through it. Power generation has reduced from 108 megawatts in 1989, to 45 megawatts at the time of writing, due to the ingress of cool marginal groundwater into the geothermal area.

The geothermal field occupies a subsiding basin on the eastern margins of the Taupo Volcanic Zone. The basement is greywacke sandstone, then above this the Waikora Formation of greywacke conglomerate with interbedded Ohakuri group volcanics; Rangitaiki Ignimbrite; then 800-1000 metres of variable deposits of lacustrine sediments, lava domes of rhyolite and dacite, and breccia. At least four faults displaced the basement greywacke, however none show on the surface.

Surface deposits consist of pumice sand, rhyolite gravels, with some cemented by silica, kaolin, and sulphur. Kaolinite is widespread, while some steaming ground may contain crystalline yellow sulphur.

Hydrothermal waters have deposited ore grade levels of Au and Ag, and erratically distributed sulphides, mainly pyrite, with lesser galena, sphalerite and chalcopyrite, and rare pyrrhotite. The base metal sulphides may also be associated with rare cobaltite, an un-named silver telluride, arsenopyrite, and glaucodot.

Quartz, plagioclase, biotite, hornblende, pyroxene, magnetite, and glass, may be fully or partially hydrothermally altered to quartz, albite, adularia, calcite, chlorite, illite, montmorillonite, kaolinite, siderite, mordenite, wairakite, epidote, sphene, leucoxene, pyrite and pyrrhotite. The alteration minerals along with base metal sulphides sphalerite, galena, and chalcopyrite occur in veins and lining vugs. High levels of Co2, restricts the development of wairakite and epidote and favours the deposition of calcite. The clays, chlorite, quartz, albite, adularia are noted as common.

Showing how dynamic some of these areas are, some minerals rapidly formed in abandoned drill wells. Teschemacherite, normally associated with guano deposits, formed as a precipitate. In one case, gas pressures forced a 0.5-metre section of the mineral out of an opened well, popping out like a champagne cork. It formed from a reaction of Co2, and Nh3. Sinter spherules, some metal-rich, and pale orange-yellow aragonite have also precipitated from the wells.

Select Mineral List Type

Standard Detailed Strunz Dana Chemical Elements

Mineral List


16 valid minerals.

Detailed Mineral List:

Albite
Formula: Na(AlSi3O8)
Reference: Simmons, S.F. Browne, P.L. (1997) Saline fluid inclusions in sphalerite from the Broadlands-Ohaaki geothermal system; a coincidental trapping of fluids being boiled toward drynes. Economic Geology, 92:4, 485-489.
Aragonite
Formula: CaCO3
Reference: Railton, G.T., Watters, W.A. (1990) Minerals of New Zealand. New Zealand Geological Survey Bulletin 104, 89 pages.
Arsenopyrite
Formula: FeAsS
Reference: Railton, G.T., Watters, W.A. (1990) Minerals of New Zealand. New Zealand Geological Survey Bulletin 104, 89 pages. Simmons, S.F. Browne, P.L. (1997) Saline fluid inclusions in sphalerite from the Broadlands-Ohaaki geothermal system; a coincidental trapping of fluids being boiled toward drynes. Economic Geology, 92:4, 485-489.
Calcite
Formula: CaCO3
Reference: Simmons, S.F. Browne, P.L. (1997) Saline fluid inclusions in sphalerite from the Broadlands-Ohaaki geothermal system; a coincidental trapping of fluids being boiled toward drynes. Economic Geology, 92:4, 485-489.
Chalcopyrite
Formula: CuFeS2
Reference: Simmons, S.F. Browne, P.L. (1997) Saline fluid inclusions in sphalerite from the Broadlands-Ohaaki geothermal system; a coincidental trapping of fluids being boiled toward drynes. Economic Geology, 92:4, 485-489.
'Chlorite Group'
Reference: Simmons, S.F. Browne, P.L. (1997) Saline fluid inclusions in sphalerite from the Broadlands-Ohaaki geothermal system; a coincidental trapping of fluids being boiled toward drynes. Economic Geology, 92:4, 485-489.
Cobaltite
Formula: CoAsS
Reference: Railton, G.T., Watters, W.A. (1990) Minerals of New Zealand. New Zealand Geological Survey Bulletin 104, 89 pages. Simmons, S.F. Browne, P.L. (1997) Saline fluid inclusions in sphalerite from the Broadlands-Ohaaki geothermal system; a coincidental trapping of fluids being boiled toward drynes. Economic Geology, 92:4, 485-489.
Epidote
Formula: {Ca2}{Al2Fe3+}(Si2O7)(SiO4)O(OH)
Reference: Simmons, S.F. Browne, P.L. (1997) Saline fluid inclusions in sphalerite from the Broadlands-Ohaaki geothermal system; a coincidental trapping of fluids being boiled toward drynes. Economic Geology, 92:4, 485-489. Bird, D.K., Schiffman, P., Elders, W.A., Williams, A.E., McDowell, S.D. (1984) Calc-silicate mineralization in active geothermal systems. Economic Geology 79:4, 671-695
Galena
Formula: PbS
Reference: Simmons, S.F. Browne, P.L. (1997) Saline fluid inclusions in sphalerite from the Broadlands-Ohaaki geothermal system; a coincidental trapping of fluids being boiled toward drynes. Economic Geology, 92:4, 485-489.
Glaucodot
Formula: (Co0.50Fe0.50)AsS
Reference: Simmons, S.F. Browne, P.L. (1997) Saline fluid inclusions in sphalerite from the Broadlands-Ohaaki geothermal system; a coincidental trapping of fluids being boiled toward drynes. Economic Geology, 92:4, 485-489.
'Heulandite subgroup'
Reference: Bird, D.K., Schiffman, P., Elders, W.A., Williams, A.E., McDowell, S.D. (1984) Calc-silicate mineralization in active geothermal systems. Economic Geology 79:4, 671-695.
'K Feldspar'
Reference: Econ Geol (1997) 92:485-489
'K Feldspar var: Adularia'
Formula: KAlSi3O8
Reference: Simmons, S.F. Browne, P.L. (1997) Saline fluid inclusions in sphalerite from the Broadlands-Ohaaki geothermal system; a coincidental trapping of fluids being boiled toward drynes. Economic Geology, 92:4, 485-489.
Muscovite
Formula: KAl2(AlSi3O10)(OH)2
Reference: Econ Geol (1997) 92:485-489
Muscovite var: Illite
Formula: K0.65Al2.0[Al0.65Si3.35O10](OH)2
Reference: Simmons, S.F. Browne, P.L. (1997) Saline fluid inclusions in sphalerite from the Broadlands-Ohaaki geothermal system; a coincidental trapping of fluids being boiled toward drynes. Economic Geology, 92:4, 485-489.
Pyrrhotite
Formula: Fe7S8
Reference: Simmons, S.F. Browne, P.L. (1997) Saline fluid inclusions in sphalerite from the Broadlands-Ohaaki geothermal system; a coincidental trapping of fluids being boiled toward drynes. Economic Geology, 92:4, 485-489.
Quartz
Formula: SiO2
Reference: Simmons, S.F. Browne, P.L. (1997) Saline fluid inclusions in sphalerite from the Broadlands-Ohaaki geothermal system; a coincidental trapping of fluids being boiled toward drynes. Economic Geology, 92:4, 485-489.
Siderite
Formula: FeCO3
Reference: Simmons, S.F. Browne, P.L. (1997) Saline fluid inclusions in sphalerite from the Broadlands-Ohaaki geothermal system; a coincidental trapping of fluids being boiled toward drynes. Economic Geology, 92:4, 485-489.
Sphalerite
Formula: ZnS
Reference: Econ Geol (1997) 92:485-489
Teschemacherite
Formula: (NH4)HCO3
Reference: Browne, P.R.L (1972) Occurrence of Teschemacherite in a Geothermal Well at Broadlands, New Zealand. American Mineralogist, 57:7-8, 1304-1305.
Wairakite
Formula: Ca(Al2Si4O12) · 2H2O
Reference: Bird, D.K., Schiffman, P., Elders, W.A., Williams, A.E., McDowell, S.D. (1984) Calc-silicate mineralization in active geothermal systems. Economic Geology 79:4, 671-695. Simmons, S.F. Browne, P.L. (1997) Saline fluid inclusions in sphalerite from the Broadlands-Ohaaki geothermal system; a coincidental trapping of fluids being boiled toward drynes. Economic Geology, 92:4, 485-489.

List of minerals arranged by Strunz 10th Edition classification

Group 2 - Sulphides and Sulfosalts
'Arsenopyrite'2.EB.20FeAsS
'Chalcopyrite'2.CB.10aCuFeS2
'Cobaltite'2.EB.25CoAsS
'Galena'2.CD.10PbS
'Glaucodot'2.EB.10c(Co0.50Fe0.50)AsS
Pyrrhotite2.CC.10Fe7S8
Sphalerite2.CB.05aZnS
Group 4 - Oxides and Hydroxides
Quartz4.DA.05SiO2
Group 5 - Nitrates and Carbonates
'Aragonite'5.AB.15CaCO3
'Calcite'5.AB.05CaCO3
Siderite5.AB.05FeCO3
Teschemacherite5.AA.25(NH4)HCO3
Group 9 - Silicates
'Albite'9.FA.35Na(AlSi3O8)
'Epidote'9.BG.05a{Ca2}{Al2Fe3+}(Si2O7)(SiO4)O(OH)
Muscovite9.EC.15KAl2(AlSi3O10)(OH)2
var: Illite9.EC.15K0.65Al2.0[Al0.65Si3.35O10](OH)2
Wairakite9.GB.05Ca(Al2Si4O12) · 2H2O
Unclassified Minerals, Rocks, etc.
'Chlorite Group'-
'Heulandite subgroup'-
K Feldspar-
'var: Adularia'-KAlSi3O8

List of minerals arranged by Dana 8th Edition classification

Group 2 - SULFIDES
AmXp, with m:p = 1:1
Galena2.8.1.1PbS
Pyrrhotite2.8.10.1Fe7S8
Sphalerite2.8.2.1ZnS
AmBnXp, with (m+n):p = 1:1
Chalcopyrite2.9.1.1CuFeS2
AmBnXp, with (m+n):p = 1:2
Arsenopyrite2.12.4.1FeAsS
Cobaltite2.12.3.1CoAsS
Glaucodot2.12.6.1(Co0.50Fe0.50)AsS
Group 13 - ACID CARBONATES
Miscellaneous
Teschemacherite13.1.3.1(NH4)HCO3
Group 14 - ANHYDROUS NORMAL CARBONATES
A(XO3)
Calcite14.1.1.1CaCO3
Siderite14.1.1.3FeCO3
Group 58 - SOROSILICATES Insular, Mixed, Single, and Larger Tetrahedral Groups
Insular, Mixed, Single, and Larger Tetrahedral Groups with cations in [6] and higher coordination; single and double groups (n = 1, 2)
Epidote58.2.1a.7{Ca2}{Al2Fe3+}(Si2O7)(SiO4)O(OH)
Group 71 - PHYLLOSILICATES Sheets of Six-Membered Rings
Sheets of 6-membered rings with 2:1 layers
Muscovite71.2.2a.1KAl2(AlSi3O10)(OH)2
var: Illite71.2.2d.2K0.65Al2.0[Al0.65Si3.35O10](OH)2
Group 75 - TECTOSILICATES Si Tetrahedral Frameworks
Si Tetrahedral Frameworks - SiO2 with [4] coordinated Si
Quartz75.1.3.1SiO2
Group 76 - TECTOSILICATES Al-Si Framework
Al-Si Framework with Al-Si frameworks
Albite76.1.3.1Na(AlSi3O8)
Group 77 - TECTOSILICATES Zeolites
Zeolite group - True zeolites
Wairakite77.1.1.3Ca(Al2Si4O12) · 2H2O
Unclassified Minerals, Rocks, etc.
Aragonite-CaCO3
'Chlorite Group'-
'Heulandite subgroup'-
'K Feldspar'-
'var: Adularia'-KAlSi3O8

List of minerals for each chemical element

HHydrogen
H Epidote{Ca2}{Al2Fe3+}(Si2O7)(SiO4)O(OH)
H Muscovite (var: Illite)K0.65Al2.0[Al0.65Si3.35O10](OH)2
H MuscoviteKAl2(AlSi3O10)(OH)2
H Teschemacherite(NH4)HCO3
H WairakiteCa(Al2Si4O12) · 2H2O
CCarbon
C AragoniteCaCO3
C CalciteCaCO3
C SideriteFeCO3
C Teschemacherite(NH4)HCO3
NNitrogen
N Teschemacherite(NH4)HCO3
OOxygen
O K Feldspar (var: Adularia)KAlSi3O8
O AlbiteNa(AlSi3O8)
O AragoniteCaCO3
O CalciteCaCO3
O Epidote{Ca2}{Al2Fe3+}(Si2O7)(SiO4)O(OH)
O Muscovite (var: Illite)K0.65Al2.0[Al0.65Si3.35O10](OH)2
O MuscoviteKAl2(AlSi3O10)(OH)2
O QuartzSiO2
O SideriteFeCO3
O Teschemacherite(NH4)HCO3
O WairakiteCa(Al2Si4O12) · 2H2O
NaSodium
Na AlbiteNa(AlSi3O8)
AlAluminium
Al K Feldspar (var: Adularia)KAlSi3O8
Al AlbiteNa(AlSi3O8)
Al Epidote{Ca2}{Al2Fe3+}(Si2O7)(SiO4)O(OH)
Al Muscovite (var: Illite)K0.65Al2.0[Al0.65Si3.35O10](OH)2
Al MuscoviteKAl2(AlSi3O10)(OH)2
Al WairakiteCa(Al2Si4O12) · 2H2O
SiSilicon
Si K Feldspar (var: Adularia)KAlSi3O8
Si AlbiteNa(AlSi3O8)
Si Epidote{Ca2}{Al2Fe3+}(Si2O7)(SiO4)O(OH)
Si Muscovite (var: Illite)K0.65Al2.0[Al0.65Si3.35O10](OH)2
Si MuscoviteKAl2(AlSi3O10)(OH)2
Si QuartzSiO2
Si WairakiteCa(Al2Si4O12) · 2H2O
SSulfur
S ArsenopyriteFeAsS
S ChalcopyriteCuFeS2
S CobaltiteCoAsS
S GalenaPbS
S Glaucodot(Co0.50Fe0.50)AsS
S PyrrhotiteFe7S8
S SphaleriteZnS
KPotassium
K K Feldspar (var: Adularia)KAlSi3O8
K Muscovite (var: Illite)K0.65Al2.0[Al0.65Si3.35O10](OH)2
K MuscoviteKAl2(AlSi3O10)(OH)2
CaCalcium
Ca AragoniteCaCO3
Ca CalciteCaCO3
Ca Epidote{Ca2}{Al2Fe3+}(Si2O7)(SiO4)O(OH)
Ca WairakiteCa(Al2Si4O12) · 2H2O
FeIron
Fe ArsenopyriteFeAsS
Fe ChalcopyriteCuFeS2
Fe Epidote{Ca2}{Al2Fe3+}(Si2O7)(SiO4)O(OH)
Fe Glaucodot(Co0.50Fe0.50)AsS
Fe PyrrhotiteFe7S8
Fe SideriteFeCO3
CoCobalt
Co CobaltiteCoAsS
Co Glaucodot(Co0.50Fe0.50)AsS
CuCopper
Cu ChalcopyriteCuFeS2
ZnZinc
Zn SphaleriteZnS
AsArsenic
As ArsenopyriteFeAsS
As CobaltiteCoAsS
As Glaucodot(Co0.50Fe0.50)AsS
PbLead
Pb GalenaPbS

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

Holocene
0 - 0.0117 Ma



ID: 1339504
OIS1 (Holocene) river deposits (Taupo Pumice Alluvium)

Age: Anthropocene (0 - 0.0117 Ma)

Stratigraphic Name: Taupo Pumice Alluvium

Description: Predominantly pumice sand, silt and gravel alluvium with charcoal fragments; derived from Taupo Pumice Formation.

Comments: Holocene river deposits. Age based on provenance

Lithology: Major:: {pumice},Minor:: {sand, silt, gravel}

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

Quaternary
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]

Quaternary
0 - 2.588 Ma



ID: 1309964
Late Quaternary alluvium and colluvium

Age: Pleistocene (0 - 2.588 Ma)

Stratigraphic Name: Pakihi Supergroup

Description: Unconsolidated to poorly consolidated mud, sand, gravel and peat.

Comments: Zealandia Megasequence Terrestrial and Shallow Marine Sedimentary Rocks (Neogene)

Lithology: Mud, sand, gravel, peat

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]

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

References

Sort by

Year (asc) Year (desc) Author (A-Z) Author (Z-A)
Browne, P.R.L. (1969) Sulfide mineralization in a Broadlands geothermal drill hole, Taupo Volcanic Zone, New Zealand. Economic Geology, 64:2, 156-159.
Browne, P.R.L., Ellis, A.J. (1970) The Ohaki-Broadlands hydrothermal area New Zealand: mineralogy and related geochemistry. American Journal of Science, Vol. 269, 297-331.
Browne, P.R.L (1972) Occurrence of Teschemacherite in a Geothermal Well at Broadlands, New Zealand. American Mineralogist, 57:7&8, 1304-1305.
Browne, P.R.L. (1973) Aragonite deposited from Broadlands geothermal drillhole water. New Zealand Journal of Geology and Geophysics, 16:4, 927-933.
Browne, P.R.L. (1973) The Geology, Mineralogy and Geothermometry of the Broadlands Geothermal Field, Taupo Volcanic Zone, New Zealand. (unpublished thesis, PhD), Victoria University of Wellington.
Browne, P.R.L., Lovering, J.F. (1973) Composition of Sphalerites from the Broadlands Geothermal Field and Their Significance to Sphalerite Geothermometry and Geobarometry. Economic Geology, Vol. 68:3, 381-387.
Railton, G.T., Watters, W.A. (1990) Minerals of New Zealand. New Zealand Geological Survey Bulletin 104, 89 pages.
Simmons, S.F. Browne, P.L. (1997) Saline fluid inclusions in sphalerite from the Broadlands-Ohaaki geothermal system; a coincidental trapping of fluids being boiled toward drynes. Economic Geology, 92:4, 485-489.
Browne, P.R.L. (2000) Hydrothermal minerals and precious metals in the Broadlands-Ohaaki geothermal system: implications for understanding low sulfidation epithermal environments, Economic Geology, 95:5, 971-999.
Lee, S., Bacon, L. (2000) Operational history of the Ohaaki geothermal field New Zealand, Contact Energy Ltd Taupo New Zealand, Proceedings World Geothermal Conference 2000 Kyushu-Tohoku Japan, May 28-June 10 2000.
Hunt, T. (2000) Five lectures on environmental effects of geothermal utilization, The United Nations University, Geothermal Training Programmes, Reports 2000, #1, Institute of Geological and Nuclear Sciences Taupo New Zealand, pub Reykjavick Iceland June 2001.
Stokes, E. (2003) Ohaaki - a power station on Maori land, Te Matahauariki Institute, University of Waikato.

External Links



This page contains all mineral locality references listed on mindat.org. This does not claim to be a complete list. If you know of more minerals from this site, please register so you can add to our database. This locality information is for reference purposes only. You should never attempt to visit any sites listed in mindat.org without first ensuring that you have the permission of the land and/or mineral rights holders for access and that you are aware of all safety precautions necessary.
 
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