Study and exploration of New Zealand, the underwater continent

Category Other
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Malahoff, Alexander
Holding Date 11 October 2008

With the expanded EEZ, 95% of New Zealand lies under water. The submarine geology of this country is widely diverse in geology and age having parted from Gondwanaland 80 million years ago. The basement geology of the large submarine plateaus, namely the Chatham Rise, the Campbell Plateau and the Challenger Plateau are underpinned by the metamorphic rocks of Gondwanda terrain and are located at an average water depth of 1000 metres.
The Challenger Plateau margin is covered by thick sequences of organic-rich sediment that have produced liquid and gas hydrocarbons.
The Campbell Plateau is equally overlain by thick sequences of sediment with good hydrocarbon prospects. Extending north of the North Island is the Kermadec subduction zone. The Kermadec Island Arc marks the latest site of active marine geology and geophysics research. Industry is attracted by the presence of submarine hydrothermal polymetallic sulphide deposits associated with submarine volcanoes.
In a multi-national, multi-institutional, multi-investigator expedition, six active Kermadec Arc submarine volcanoes located between 34°S and 36°30’S were mapped and sampled between April and July 2005, using submersibles. The purpose of the expedition was to study the relationship between hydrothermal activity, formation of hydrothermal mineral deposits, structure of the volcanoes, and the biodiversity of life associated with the hydrothermal vents. All volcanoes examined showed evidence of hydrothermal activity. Only two of the volcanoes, namely Brothers and Clark, showed chimneys and surficial polymetallic sulfide deposition. Hydrothermal venting at 300c at a water depth of approximately 1,650 meters near the base of the northwest caldera wall of Brothers volcano has produced a field of chimneys, up to seven meters high and discharging black smoker venting. Clark volcano at a water depth of 875 meters has a near-summit hydrothermal vent field with five-meter tall venting chimneys with water temperatures of 200°C.Analyses of the massive polymetallic sulfide samples show chimneys atBrothers are mainly sphalerite dominant with lesser amounts of chalcopyrite. Sulphides from Clark volcano are barite-rich with lesser sphalerite and pyrite/marcasite. Sulphides from Brothers volcano range in gold concentration between 0.2 and 1.9 ppm with silver concentrations up to 4,390 ppm . Only the deeper vent sites within the vlcano show massive sulfide deposition along the marginal faults near the caldera floor.
These results have prompted exploration companies to take out mineral licences along the Kermadec portion of the NZ EEZ. It is industry interests that have expanded the exploration of this newest mineral interest area in New Zealand and will enhance our knowledge of the geology of this vast largely unexplored ocean floor.