The Kawerau hydrothermal system lies at the northern end of the Taupo Volcanic Zone, on the some 20 km south of the Bay of Plenty. The system, which is thought to have been active for at least 200,000 years, is situated over an area which has been volcanically active through time. Relatively recent local magmatism is found in the 800 m high, 3000-10,000 year old Mt. Edgecumbe dacite massif and the 200 m high Onepu Dome complex which lie adjacent to and within, respectively, the present day resistivity anomaly. Shallow reservoir fluids show evidence of steam heating as expressed by elevated bicarbonate and/or sulphate contents and mildly to strongly acidic pH, whereas the deep fluids are dominantly alkaline at their respective temperatures. The calculated base fluid composition is comprised of 2.5 wt% CO$/sb2$ and ca. 890 mg/kg Cl at 310$/sp/circ$C. Fluid inclusion studies show a largely stable, boiling point thermal regime through time, whereas oxygen stable isotope studies on hydrothermal carbonates prove the existence of one or more pulses of isotopically heavy fluids into the reservoir at some time(s) in the past. Hydrothermal alteration associated with these isotopic anomalies indicate strongly oxidising conditions relative to both alteration elsewhere in the reservoir and the present day reservoir redox conditions. Collectively, the data suggest a magmatic source for these transient, isotopically heavy fluids. The present day system is ore forming, as evident from both metal rich scales formed in the production silencers of the geothermal wells and open fracture reservoir mineralogy. Stockwork environments in the deep reservoir are host to both base and precious metals, and evidence indicates that boiling is the main depositional mechanism for these ore phases. / Subscription resource available via Digital Dissertations only.
| Identifer | oai:union.ndltd.org:ADTP/275915 |
| Date | January 1987 |
| Creators | Christenson, Bruce William |
| Publisher | ResearchSpace@Auckland |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Source | http://wwwlib.umi.com/dissertations/fullcit/8904865 |
| Rights | Subscription resource available via Digital Dissertations only. Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated., http://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm, Copyright: The author |
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