Uranium series disequilibrium dating of black smoker chimneys

Within New Zealand's Exclusive Economic Zone there exists a vast submarine hydrothermal mineral resource associated with the Kermadec Ridge. Along this ridge twenty-six submarine volcanoes have been explored by GNS lead-researchers, and at least another nine await investigation. Of these, fifteen are known to be hydrothermally active, and each is almost certainly a site of active seafloor mineralisation. Determination of whether this mineralisation is economically viable in terms of grade and tonnage requires detailed seafloor exploration using manned submersibles and/or remotely operated vehicles capable of high-precision imagery and discrete rock and fluid sampling. A key aspect of these investigations is determining the age of the mineralisation, which will have a direct bearing on its mode of formation, time elapsed to amass an economic deposit and, ultimately, its capacity for sustainable extraction. An intact barite-rich 'black-smoker' chimney recovered from Brothers volcano, along with other hydrothermal deposits provide evidence of active mineralisation along the arc. The age range of such massive sulphide deposits can be determined from the disequilibrium between isotopes within the thorium or uranium decay chains. (author). 1 ref., 5 figs., 1 tab