Gravity, magnetic and resistivity investigations of the Okauia Low Temperature Geothermal System in alluvial sediments of the Hauraki Depression, New Zealand. Issue 3 (1st September 2017)

• Record Type: Journal Article
• Authors: Soengkono, Supri; Reeves, Robert
• Is Part Of: Exploration geophysics. Volume 48:Issue 3(2017)
• Page Start: 316
• Page End: 331
• Publication Date: 2017-09-01
• Subjects: alluvial, geophysical modelling, gravity, low temperature geothermal system, magnetic, resistivity, TDEM.; Geophysics -- Periodicals; Prospecting -- Geophysical methods -- Periodicals; 622.15
• DOI: 10.1071/EG15052
• Languages: English
• ISSNs: 0812-3985

Abstract

Abstract : Gravity, ground magnetics, DC resistivity traversing, and time domain electromagnetic soundings (fixed-loop and in-loop) were conducted to investigate the Okauia Low Temperature Geothermal System near the eastern boundary of the Hauraki Depression in North Island of New Zealand. The gravity study revealed a hidden extension of the Tertiary-age Waiteariki Ignimbrite, underlying plio-Pleistocene alluvium deposits of the Hinuera Formation, which locally host an aquifer of warm geothermal fluids. A 3D magnetic model derived from the ground magnetic measurements helped identify probable paleo-channels within the sedimentary sequence of the Hinuera Formation. These paleo-channels could represent higher permeability at shallow (<50 m) depth, although the exact relationship between the locations of the surface thermal manifestations and identified paleo-channels is still unclear. The results of the resistivity surveys suggest that values less than 25 Ωm are indicative of the presence of warm waters at Okauia. Most warm water occurrences at Okauia take place near the Okauia Fault, particularly at 0 m RL (sea level) elevation. The near-surface extent of the Okauia Low Temperature Geothermal System can be approximated from the results of this study. Abstract : Gravity, ground magnetics, DC resistivity and TDEM measurements are used to delineate the near-surface extent of the Okauia Low Temperature Geothermal System, New Zealand. Potential permeable pathways mapped by the geophysical surveys are consistent with the geological environment.