Recent geophysical exploration of the Kawerau geothermal field, North Island, New Zealand

Macdonald, W. J. P.; Muffler, L. J. Patrick

doi:10.1080/00288306.1972.10422334

Cited by 18 publications

(6 citation statements)

References 9 publications

(5 reference statements)

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“…The low resistivities in the geothermal areas result from high temperatures and increased salinity in the ground water. Macdonald & Muffler (1972) report bulk resistivities below 5 !2m for fractured andesite of average porosity 15 per cent, containing saline water at 250°C, in such a geothermal field. Such hot, saline water in fractured rocks of similar porosity could produce the resistivities observed beneath the Main Ranges.…”

Section: Magnetotelluric Soundings In Conada 261mentioning

confidence: 99%

Magnetotelluric soundings in the Canadian Rocky Mountains

Hutton

Gough

Dawes

et al. 1987

Geophysical Journal International

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Magnetotelluric soundings have been made at 25 stations in the Rocky Mountain Trench (RMT) and Main Ranges near 53"N, close to the centre of a major conductivity anomaly which had been mapped in a magnetovariation array study. Most stations covered the frequency range 0.01-500 Hz and three stations 0.0002-500 Hz. The resistivity tensor shows low to moderate anisotropy in the RMT, but is strongly 2-D or 3-D in the Rocky Mountains. Apparent resistivities as a function of frequency are displayed in pseudosections along the Trench and along a transverse profile across the RMT and into the Main Ranges. In preparation for 2-D modelling, 1-D inversions have been used to construct resistivity-depth sections satisfying both magnitudes and phases of the MT responses. These show very low resistivities, in the range 1-10S2m, in the upper crust under the RMT and even lower values under the Main Ranges. The latter values give strong confirmation of the Northern Rockies conductor reported by Bingham, Gough & Ingham and are in agreement with models of the conductors fitted to long-period magnetovariation fields by Ingham, Gough & Parkinson. The MT results here reported add some essential depth and resistivity information. It is suggested-that the conductors beneath the Rocky Mountains Main Ranges and Trench constitute a thickening at the edge of the Canadian Cordilleran Regional (CCR) conductor. Gough has argued that a wide variety of geophysical and geological parameters indicate high temperatures and partial melting in the mantle under the CCR conductor. At the upper crustal depths penetrated in this magnetotelluric study, it is considered more probable that the high conductivity is caused by hot, saline water of mantle origin rather than silicate melt. The CCR in general may have two layers of fluid producing its high conductivity, silicate melt below and saline hot water above. 246K R. S. Hutton et al.

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Section: Magnetotelluric Soundings In Conada 261mentioning

confidence: 99%

Magnetotelluric soundings in the Canadian Rocky Mountains

Hutton

Gough

Dawes

et al. 1987

Geophysical Journal International

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“…Schlumberger and Wenner methods were used for most of the early resistivity surveys, especially in New Zealand (Banwell and Macdonald, t965;Hatherton et al, 1966;Macdonald and Muffler, 1972), but have also been used in some recent surveys (e.g. Meidav and Furgerson, 1972;Zohdy et al, 1973;Stanley ez" at., 1976;Trippet al, 1978;Razo et at., 1980).…”

Section: The Electrical Methodsmentioning

confidence: 99%

Electromagnetic studies in geothermal regions

Berktold¹

1983

Geophysical Surveys

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Abstract. During the past 25 yr, nearly all available electromagnetic and geoelectric techniques have been tested for their usefulness in geothermal exploration and exploitation. Dipole-dipole profiling, audiomagnetotellurics and controlled source electromagnetic methods are examples of those which have proven to be rather efficient for geothermal exploration. From the hundreds of field surveys which have been performed in many geothermal regions of the world, a large variety of geothermal regions and local geothermal systems, with different geological, hydrological and heat transfer characteristics, has been found to exist. Depending on the combination of these different characteristics each geothermal region or system presents a new problem which may need a different field technique or group of field techniques for optimal exploration. Despite these problems, new geothermal regions have been detected and structures and processes in geothermal systems are now much better understood. For example, advances have been made in the study of (a) the characteristics of porous/permeable hot water/vapor reservoirs and of fractioned zones for hot water/vapor circulation and production (b) the distribution and movement of cold meteoric and of hot water (c) the thermal insulation of reservoirs by cap-rocks (d) convective and/or conductive heat transfer and (e) the thermal influence of magma intrusions to high crustal levels.New exploration techniques, data analysis procedures and model calculations have been developed in the course of research in geothermal areas. They include the controlled source electromagnetic methods, the remote reference field technique and the development of better and faster algorithms for direct and inverse model calculations. Problems for the future are (a) the development and improvement of equipment and field techniques for more precise delineation and resolution of the conductivity distribution in geothermal areas especially those with productive zones of high porosity/permeability and fracturing, (b) the improvement of computerised data analysis in the field to optimise progress during the field measurements and (c) the development of more efficient interpretation procedures for the rather inhomogeneous conductivity distribution which exists in most geothermal areas.

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“…For an array spacing of 500 m these measured resistivities can be regarded as weighted averages of the resistivity within the top 300 m depth (600 m depth for the 1000 m array; Bibby et al, 1995). Early surveys in the area (1969 -1970) were shallow penetrating, and indicated a resource area of 10 km 2 at ~250 m depth, centred on the site of the Tasman mill (Macdonald et al, 1970;Macdonald and Muffler, 1972). Surveys, from 1969 -70 andextended in 1989, undertaken to greater depths have revealed that the geothermal resource is present over a greater area (Allis et al, 1995).…”

Section: Subsurface Extent Of the Field: Geophysical Evidencementioning

confidence: 99%

“…This conclusion is supported by measurements of anomalous temperatures, and chloride and boron concentrations in groundwater wells situated 5 to 10 km north of the field (Allis et al, 1993(Allis et al, , 1995Allis, 1997;Bignall, 2005). Summaries of geophysical surveys at Kawerau can be found in Studt (1952), Macdonald and Muffler (1970) and Macdonald et al (1972).…”

Section: Subsurface Extent Of the Field: Geophysical Evidencementioning

confidence: 99%

“…Across much of the Kawerau Field, there is a distinctive unit of intermediate composition, the Kawerau Andesite, which is inferred from textural evidence and the presence of marginal breccias to represent a composite pile of lava flows (Bogie, 1981). The source is inferred to be in the northwest part of the field, which magnetic surveys (MacDonald and Muffler, 1972) ascribe to an andesitic volcanic centre, although no inferred feeder structures have been intercepted in the geothermal drillholes (cf. rhyolites of the Caxton and Onepu formations, below).…”

Section: Karaponga Formationmentioning

confidence: 99%

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Aspects of the Chronology, Structure and Thermal History of the Kawerau Geothermal Field

Milicich¹

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<p>The development and management of high-temperature geothermal resources for electrical power generation requires accurate knowledge of the local geological conditions, particularly where they impact on the hydrology of the resource. This study is an integrated programme of work designed to develop new perspectives on the geological and structural framework of the Kawerau geothermal resource as a sound basis for field management. Although the geological approaches and techniques utilised in this study have previously been used, their application to an integrated study of a geothermal system in New Zealand has not been previously undertaken. Correlating volcanic and sedimentary stratigraphy in geothermal areas in New Zealand can be challenging due to similarities in lithology and the destruction of distinctive chemical, mineralogical and textural characteristic by hydrothermal alteration. A means to overcoming these issues is to utilise dating to correlate the stratigraphy. Zircons are resistant to the effects of typical hydrothermal conditions and were dated using SIMS techniques (SHRIMP-RG) to retrieve U–Pb ages on zircons. These age data were then used to correlate units across the field, in part aided by correlations to material that had previously been dated from fresh rock by ⁴⁰Ar/³⁹Ar techniques, and used to redefine the stratigraphic framework for the area. [...] Although previously inferred to be a long–lived system, the modern Kawerau Geothermal Field is a Holocene entity reflecting the rejuvenation of magmatic heat flux associated with Putauaki volcano superimposed on an area of multiple reactivated fault structures, sporadic magmatism and variable rates of subsidence. This study documents past patterns of fluid flow, temperatures and chemistry, and inferred permeability within the field. Using textural relationships in selected samples, the relative timing and patterns of hydrothermal alteration, and fluid flows can be established. These textural relationships are then calibrated against fluid inclusion palaeotemperature measurements and isotope data and related to temperatures and compositions of past fluids. Short–lived heat sources beneath the field resulted from local magma intrusions, and are responsible for the 0.36 Ma and 0.138 Ma rhyolites and Holocene eruptive activity of Putauaki andesite–dacite volcano. The Putauaki activity is inferred to be responsible for the thermal and alteration characteristics of the modern system.</p>

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Recent geophysical exploration of the Kawerau geothermal field, North Island, New Zealand

Cited by 18 publications

References 9 publications

Magnetotelluric soundings in the Canadian Rocky Mountains

Magnetotelluric soundings in the Canadian Rocky Mountains

Electromagnetic studies in geothermal regions

Aspects of the Chronology, Structure and Thermal History of the Kawerau Geothermal Field

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