3D Anatomy of a 60-year-old siliceous hot spring deposit at Hipaua-Waihi-Tokaanu geothermal field, Taupo Volcanic Zone, New Zealand

A twenty day microearthquake survey of the Ngawha geothermal field, New Zealand, was undertaken in order to establish the level of preproduction seismicity and to test the usefulness of such surveys in geothermal exploration. The Ngawha geothermal field, in the far northwest of the North Island (Northland) is associated with a region of Quaternary basaltic volcanism. It is not a part of the much more extensive Taupo volcanic zone in the central North Island, site of the well‐known Wairakei geothermal field, among others. Although surface thermal activity at Ngawha is limited to a few relatively small hot springs, resistivity surveys have outlined a [Formula: see text] area of hot water at the 1-km depth level (Macdonald et al. , 1977). Test bores to that depth have encountered temperatures of up to 250 °C within Mesozoic graywacke. Overlying the graywacke is about 500 m of Cenozoic claystone and siltstone which forms an impermeable cap.

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Field-Based Tests of Geochemical Modeling Codes: New Zealand Hydrothermal Systems

MRS Proceedings ◽

10.1557/proc-333-617 ◽

1993 ◽

Vol 333 ◽

Cited By ~ 1

Author(s):

Carol J. Bruton ◽

William E. Glassley ◽

William L. Bourcier

Keyword(s):

New Zealand ◽

Nuclear Waste ◽

Kinetic Data ◽

Geochemical Modeling ◽

Geothermal Field ◽

Hydrothermal Systems ◽

Taupo Volcanic Zone ◽

Volcanic Zone ◽

Mineral Assemblages ◽

Modeling Code

ABSTRACTHydrothermal systems in the Taupo Volcanic Zone, North Island, New Zealand are being used as field-based modeling exercises for the EQ3/6 geochemical modeling code package. Comparisons of the observed state and evolution of the hydrothermal systems with predictions of fluid-solid equilibria made using geochemical modeling codes will determine how the codes can be used to predict the chemical and mineralogical response of the environment to nuclear waste emplacement. Field-based exercises allow us to test the models on time scales unattainable in the laboratory.Preliminary predictions of mineral assemblages in equilibrium with fluids sampled from wells in the Wairakei and Kawerau geothermal field suggest that affinity-temperature diagrams must be used in conjunction with EQ6 to minimize the effect of uncertainties in thermodynamic and kinetic data on code predictions.

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Taxonomic fidelity of silicified filamentous microbes from hot-spring systems in the Taupo Volcanic Zone, North Island, New Zealand

Transactions of the Royal Society of Edinburgh Earth Sciences ◽

10.1017/s0263593300000821 ◽

2003 ◽

Vol 94 (4) ◽

pp. 475-483 ◽

Cited By ~ 16

Author(s):

Brian Jones ◽

Robin W. Renaut ◽

Michael R. Rosen

Keyword(s):

New Zealand ◽

Hot Springs ◽

Hot Spring ◽

Morphological Characteristics ◽

Colony Morphology ◽

Taupo Volcanic Zone ◽

Volcanic Zone ◽

The North ◽

Preservation Potential ◽

Physical Changes

ABSTRACTModern, silica-precipitating hot springs, like those found in the Taupo Volcanic Zone (TVZ) on the North Island of New Zealand, are natural laboratories for assessing microbial silicification. Many of the silicified microbes found in the siliceous sinters of these spring systems seem to be life-like replicas of the original microbes. Such preservation reflects the fact that many of the microbes are replaced and encrusted by opal-A before they are destroyed by desiccation and decay. The taxonomic fidelity of these silicified microbes depends on the preservation potential of those features which are needed to identify them. For example, identification of extant cyanobacteria, relies on as many as 37 different features, most of which are not preserved by silicification.In the hot-spring systems of the TVZ, characterisation of cyanobacteria which have been replaced and encrusted by opal-A is typically restricted to colony morphology, the length, diameter and morphology of the filament, and the presence/absence of septa, branching or a sheath. In many cases, description is limited to a subset of these parameters. Such a limited set of morphological characteristics severely impedes identifications in terms of extant taxa. The physical changes which accompany the stepwise diagenetic progression from opal-A to opal-CT ± opal-C to microcrystalline quartz may lead to further degradation of the silicified microbes and the loss of more taxonomically important features. Clearly, considerable care must be taken when trying to name silicified microorganisms and make palaeoenvironmental inferences.

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Diagenetic transformations (opal-A to quartz) of low- and mid-temperature microbial textures in siliceous hot-spring deposits, Taupo Volcanic Zone, New Zealand

Canadian Journal of Earth Sciences ◽

10.1139/e03-064 ◽

2003 ◽

Vol 40 (11) ◽

pp. 1679-1696 ◽

Cited By ~ 51

Author(s):

Bridget Y Lynne ◽

Kathleen A Campbell

Keyword(s):

New Zealand ◽

Low Temperature ◽

Hot Spring ◽

Morphological Changes ◽

Taupo Volcanic Zone ◽

Volcanic Zone ◽

Alkali Chloride ◽

Silica Phase ◽

Outflow Channels ◽

Geologic Record

Silica sinter is a subaerial hot-spring deposit formed upon cooling (<100 °C) of discharging alkali-chloride waters. Silica deposition traps and fossilizes living microbes in low-temperature (<35 °C) to mid-temperature (~3559 °C) apronterrace outflow channels and pools, which record distinctive macrotextures and microtextures along a thermal gradient. Sinters from four geothermal fields, Orakei Korako, northern Waiotapu, Te Kopia, and Umukuri, within the Taupo Volcanic Zone, New Zealand, were sampled from two common microbe-rich microfacies (low-temperature palisade, mid-temperature bubble mat) through a range of ages (modern to ~40 000 years BP). We observed morphologic changes in microbial silicification and stepwise transitions in silica phase mineralogy throughout diagenesis (opal-A to quartz). X-ray powder diffractometry analysis of Taupo Volcanic Zone sinter samples revealed that mode of microbial fossilization is controlled by silica phase mineralogy, which also determines the preservation potential of environmentally significant and measurable filament parameters. Typical low-temperature palisade microfacies display thick sheaths (>3 µm diameter) and coarse tubular filament moulds >5 µm in diameter, whereas mid-temperature bubble mat microfacies characteristically consist of thin sheaths (~1 µm diameter) with fine moulds < 3 µm in diameter. Upon diagenesis and silica phase transformation to opal-CT, the two subenvironments cannot be distinguished based on filament diameter alone. This study of recurring microfacies in sinters of different ages allowed us to systematically track the transformation of mineralogical and morphological changes in bioticabiotic depositional elements during diagenesis of silica sinter, and therefore enhance the paleoenvironmental, paleobiological, and paleohydrologic utility of hydrothermal deposits in the geologic record.

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