1887
ASEG2007 - 19th Geophysical Conference
  • ISSN: 2202-0586
  • E-ISSN:

Abstract

Summary

Geophysical data from the southern Coromandel Volcanic Zone provide information critical to the investigation of epithermal mineral deposits and their regional structural setting. Regional gravity data show steep linear gradients that coincide with major faults bounding the Hauraki Rift to the west and the Waihi caldera to the east. Regional magnetic data are dominated by a large bi-polar anomaly coincident with the Waihi caldera, which may result from a sub-caldera intrusion, and otherwise by high-amplitude shorter wavelength magnetic anomalies associated with the volcanic rocks.

High-resolution aeromagnetic and radiometric data reveal distinct signatures associated with epithermal deposits. Extensive magnetically quiet areas clearly delineate the location and extent of hydrothermal alteration zones around the deposits, whereas more localised zones of high K/Th ratios in these magnetically quiet areas delineate areas of intense potassium metasomatism. Epithermal deposits exhibit gravity signatures with two contrasting modalities: i) small negative anomalies (e.g. ≤30 gu at Golden Cross and Scotia) and ii) small positive anomalies (e.g. 40-50 gu at Karangahake and Waihi-Favona). Near-surface, low-density clay-altered andesite and/or enhanced fracture volume can account for small negative anomalies. However, positive gravity signatures show that significant mass anomalies must occur at greater depths; these may be either dense intrusions and/or zones of concentrated sulphide mineralisation.

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2007-12-01
2026-01-19

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References

  1. Allis, R. G., 1990, Geophysical anomalies over epithermal systems, Journal of Geochemical Research, 36, 339-374.
  2. Brathwaite, R.L. and Christie, A. B. 1996, Geology of the Waihi area 1:50 000. Wellington NZ. Institute of Geological and Nuclear Sciences.
  3. Brathwaite, R. L. Christie, A. B. and Skinner, D. N. B., 1989, The Hauraki Goldfield – Regional setting, mineralisation and recent exploration, in Mineral deposits of New Zealand, Monograph 13 (ed: D. Kear) pp 45-56, The Australasian Institute of Mining and Metallurgy, Melbourne.
  4. Briggs, R. M. and Fulton, B. W. J., 1990, Volcanism, structure and petrology of the Whiritoa-Whangamata coastal section, Coromandel Volcanic Zone, New Zealand: Facies model evidence for the Tunaiti caldera. NZ Journal Geology and Geophysics, 33, 623-633.
  5. Carter, L., Shane, P., Alloway, B., Hall, I. R., Harris, S. E. and Westgate, J. A., 2003, Demise of one volcanic zone and birth of another – A 12 m.y. marine record of major rhyolitic eruptions from New Zealand, Geology, 31(6), 493-496.
  6. Chiozzi, P., Pasquale, V., and Verdoya, M., 2007, Radiometric survey for exploration of hydrothermal alteration in a volcanic area: Journal of Geochemical Exploration, v. 93, p. 13-20.
  7. Christie, A. B., Brathwaite, R. L., Mauk, J. L. and Simpson, M. P., 2006, Hauraki Goldfield – Regional exploration databases and prospectivity studies, in Geology and Exploration of New Zealand Mineral Deposits Monograph 25, (eds: A. B. Christie and R. L. Brathwaite) pp 73-84, Australasian Institute of Mining and Metallurgy, Melbourne.
  8. Christie, A. B., Simpson, M. P., Brathwaite, R. L., Mauk, J. L., and Simmons, S. F., 2007, Epithermal Au-Ag and Related Deposits of the Hauraki Goldfield, Coromandel Volcanic Zone, New Zealand, Economic Geology, IN PRESS.
  9. Couper P. G. and Lawton D. C., 1978, Final report on exploration licence 33-051, Ministry of Economic Development NZ, Unpublished Mineral report MR350, Amoco Minerals Ltd.
  10. Couper, P. G. and O’Leary, G. P., 1980, Final report on exploration licence 33-067, Ministry of Economic Development NZ, Unpublished Mineral report MR379, Amoco Minerals Ltd.
  11. Davidge, S. C., 1982, A geophysical study of the south Hauraki lowlands, unpublished MSc thesis, The University of Auckland.
  12. Edbrooke, S. W. (compiler), 2001, Geology of the Auckland area, Institute of Geological and Nuclear Sciences 1:250000 Geological Map 3.
  13. Harris, M. C., 2006, Geophysical characteristics of epithermal deposits in the southern portion of the Waitekauri corridor, NZ, unpublished MSc thesis, The University of Auckland.
  14. Harris, M. C., Cassidy, J., Locke, C. A. and Mauk, J. L., 2005, Geophysical characteristics of the Karangahake epithermal deposit, Hauraki Goldfield, New Zealand, in Proceedings 2005 NZ Minerals Conference, pp 115-124, Crown Minerals, Ministry of Economic Development, The Australasian Institute of Mining and Metallurgy, New Zealand Branch.
  15. Hochstein, M. P. and Nixon, I. M., 1979, Geophysical study of the Hauraki Depression, North Island, New Zealand, NZ Journal Geology and Geophysics, 22, 1-19.
  16. Hochstein, M. P., and Balance, P. F., 1993, Hauraki Rift: A young, active, intra-continental rift in a back-arc setting: in: South Pacific sedimentary basins, Sedimentary Basins of the World 2, Elsevier, Amsterdam, p. 295-305.
  17. Houghton, B. F. and Cuthbertson, A. S., 1989, Sheet T14BDKaimai. Geological map of NZ 1:50 000 Wellington, NZ. Department of Scientific and Industrial Research.
  18. Irvine, R. J. and Smith, M. J., 1990, Geophysical exploration for epithermal gold deposits, Journal of Geochemical Exploration, 36, 375-412.
  19. Locke, C. A. and de Ronde, C. E. J., 1987, Delineation of gold-bearing hydrothermally altered rocks using gravity data – a New Zealand example, Geoexploration, 24, 471-481.
  20. Malengreau, B., Skinner, D. N. B., Bromley, C. J. and Black, P. M., 2000, Geophysical characterisation of large silicic volcanic structures in the Coromandel Peninsula, New Zealand, NZ Journal Geology and Geophysics, 43, 171-186.
  21. Mauk, J. L. and Simpson, M. P., 2007, Geochemistry and stable isotopic composition of wall rock alteration at the Golden Cross epithermal Au-Ag deposit, New Zealand: Economic Geology, IN PRESS.
  22. Morrell, A. E., 2004, Geophysical characteristics of lowsulfidation epithermal gold-silver deposits in the Waihi-Waitekauri region, New Zealand, unpublished MSc thesis, The University of Auckland.
  23. Morrell, A. E., Locke, C. A., Cassidy, J. and Mauk, J. L., 2003, Magnetic, gravity and radiometric surveys of the Waihi-Waitekauri region, New Zealand, in Proceedings of the 36th Annual Conference of the NZ Branch of the Australasian Institute of Mining and Metallurgy, pp 241-249.
  24. Rabone, S. D. C., 1991, Residual total force magnetic anomaly map Coromandel region, 1:100 000, New Zealand Geological Survey Report, M183.
  25. Simpson, M. P., Mauk, J. L. and Simmons, S. F., 2001, Hydrothermal alteration and hydrologic evolution of the Golden Cross epithermal Au-Ag deposit, New Zealand, Economic Geology, 93, 773-796.
  26. Skinner, D. N. B., 1986, Neogene volcanism in the Hauraki Volcanic Region, in Late Cenozoic volcanism in New Zealand (ed: I. E. M. Smith) Royal Society of NZ Bulletin, 23, 20-47.
  27. Skinner, D. N. B., 1993, Geology of the Coromandel Harbour area, Sheet S11BD & T11AC, Institute of Geological and Nuclear Sciences 1:50 000 Geological Map 4.
  28. Skinner, D. N. B., 1995, Geology of the Mercury Bay area, Sheet T11BD and part U11, Institute of Geological and Nuclear Sciences 1:50 000 Geological Map 17.
  29. Smith, N., Cassidy, J., Locke, C. A., Mauk, J. L. and Christie, A. B., 2006, The role of regional-scale faults in controlling a trap-door caldera, Coromandel Peninsula, NZ, Journal of Volcanology and Geothermal Research, 149, 312-328.
  30. Sporli, K. B., Begbie, M. J., Irwin, M. R. and Rowland, J. V., 2006, Structural processes and tectonic controls on the epithermal Au-Ag deposits of the Hauraki Goldfield, in Geology and Exploration of NZ Mineral Deposits Monograph 25, (eds: A. B. Christie and R. L. Brathwaite) pp 85-94, Australasian Institute of Mining and Metallurgy, Melbourne.
  31. Stagpoole, V. M., Christie, A. B., Henrys, S. A. and Woodward, D. J., 2001, Aeromagnetic map of the Coromandel region: total force anomalies 1:100 000, Institute of Geological and Nuclear Sciences Geophysical Map 14.
  32. Stuart, A. G. J., Simpson, M. P., Mauk, J. L. and Stevens, M, 2005, Geology and alteration mineralogy of the Karangahake adularia-sericite epithermal deposit, Coromandel Peninsula, New Zealand, in Proceedings 2005 NZ Minerals Conference, pp 405-415, Crown Minerals, Ministry of Economic Development, The Australasian Institute of Mining and Metallurgy, New Zealand Branch.
  33. Woodward, D. J., 1971, Sheet 3 Auckland, Gravity map of NZ 1:250 000, Wellington, NZ. Department of Scientific and Industrial Research.
  34. Woodward, D. J. and Ferry, M., 1973, Sheet 5 Rotorua, Gravity map of NZ 1:250 000, Wellington, NZ. Department of Scientific and Industrial Research.
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  • Article Type: Research Article
Keyword(s): aeromagnetic; Coromandel; epithermal; gravity; radiometric

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