Identification of geochemical signatures associated with seafloor massive sulfide mineralization at the Iheya North Knoll, middle Okinawa Trough

The geochemical signatures associated with seafloor massive sulfide mineralization recorded in pumiceous sediments in the Iheya North Knoll, middle Okinawa Trough, are examined. The key purpose of this research is to establish a method for the geochemical exploration of massive sub-seafloor volcanogenic sulfide deposits. Presently, the discovery of sub-seafloor mineralized zones is strongly method-oriented, including direct sampling and observation of ores. The utilizing of conventional method is even more complicated in the case of buried ore bodies. The well-characterized sub-seafloor hydrothermal systems of the Iheya North Knoll, containing delineated recharge-discharge zones, provide an opportunity to both verify and develop geochemical exploration methods. In this study, whole-rock geochemical data are obtained from samples taken from recharge and discharge zones, and from migration zones between these two regions. The resulting geochemical signatures are difficult to interpret due to variations in mineralization as well as magmatic effects. Normalization of the compositions of samples obtained from the discharge and migration zones relative to the composition of the recharge zone reveals the relationship between the average normalized values of rare-earth and ore-related elements. This method successfully distinguishes enrichment due to magmatic differentiation and mineralization. The approach described herein also allows the location of the discharge zone to be inferred, even in the case of a thin covering of sediment above the seafloor. This technique could allow surveying via systematic or grid sampling using dredging and/or piston-coring methods, both of which are simpler and less expensive than conventional methods.