Examination of core from drillhole OKM3 on the western bank of Orakei Korako geothermal field

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dc.contributor.author Purnomo, MJ en
dc.contributor.author Lynne, Bridget en
dc.contributor.author Zarrouk, Sadiq en
dc.contributor.author Boseley, C en
dc.coverage.spatial Rotorua, New Zealand en
dc.date.accessioned 2017-11-06T23:09:38Z en
dc.date.issued 2013 en
dc.identifier.citation 35th New Zealand Geothermal Workshop (NZGW), Rotorua, New Zealand, 17 Nov 2013 - 20 Nov 2013. en
dc.identifier.uri http://hdl.handle.net/2292/36336 en
dc.description.abstract The present-day surface activity at Orakei Korako dominantly occurs on the eastern side of the Lake Ohakuri with only minor surface activity on the western bank. A 30m deep drill hole (OKM3) was drilled on the western bank to monitor the shallow groundwater level. Continuous core was recovered providing the first core from the western side of Lake Ohakuri, as previously reported cored drillholes are located on the eastern side of Lake Ohakuri. Examination of OKM3 core involved identifying the lithology and stratigraphy which consists of pyroclastic rocks of Taupo Pumice alluvium and Akatarewa breccias. At 22 m depth a thin (~10 cm) siliceous sinter horizon is present, indicating historic surface discharge of alkali chloride thermal water. X-Ray Diffraction (XRD), petrographic microscopy, Scanning Electron Microscopy (SEM) and Energy-Dispersive X-Ray Spectroscopy (EDS) were used to examine hydrothermal alteration within the core. Hydrothermal alteration minerals identified include zeolites (mordenite and clinoptilolite). These zeolites are common alteration products of pyroclastic rocks and infer low temperature alteration (<~100 °C). Zeolite is a late stage alteration product and indicates near-neutral water which may be of meteoric or mixed groundwater and thermal origin. Early stage relict, neutral pH, high temperature, alkali chloride water alteration was identified in the core. Illite-chlorite indicating a series of medium temperature (190-220°C) alteration was identified at 9 to 10 m depth. Illite indicating high temperature (>~220°C) alteration, was identified at 27-28 m depth. The location of the drill site is on an uplifted block of the Emerald fault and this relict alteration indicates temperatures >220 °C where at depth at some stage in the past. These findings reveal low temperature hydrothermal alteration has taken place in the shallow environment (<30 m depth) on the western side of Lake Ohakuri. However, historically, high temperature geothermal fluid occurred at depth in this area. Presently, no thermal activity occurs at the surface. The identification of relict high temperature zone and a previously unknown siliceous sinter horizon at 22 m depth indicates historic flow of alkali chloride fluids at surface and high temperature fluid at depth was more widespread than that of today. en
dc.publisher University of Auckland en
dc.relation.ispartof 35th New Zealand Geothermal Workshop (NZGW) en
dc.relation.ispartofseries 35th New Zealand Geothermal Workshop: 2013 Proceedings en
dc.rights Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated. Previously published items are made available in accordance with the copyright policy of the publisher. en
dc.rights.uri https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm en
dc.title Examination of core from drillhole OKM3 on the western bank of Orakei Korako geothermal field en
dc.type Conference Item en
dc.rights.holder Copyright: University of Auckland en
pubs.author-url https://www.geothermal-energy.org/pdf/IGAstandard/NZGW/2013/Lynne_Final.pdf en
pubs.finish-date 2013-11-20 en
pubs.start-date 2013-11-17 en
dc.rights.accessrights http://purl.org/eprint/accessRights/RestrictedAccess en
pubs.subtype Proceedings en
pubs.elements-id 544682 en
pubs.org-id Engineering en
pubs.org-id Engineering Science en
pubs.record-created-at-source-date 2016-11-05 en

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