Abstract
Various geophysical explorations have been recently conducted in the hydrothermal field of the middle Okinawa trough for exploration of seafloor massive sulfide. The sub-seafloor distribution of physical properties such as electric conductivity, density can be obtained by geophysical explorations, however, the implications of geological structure based on the physical information are restricted. For this reason, currently, a number of seafloor drillings are required to decide the prospect of mineral deposit in detail and to evaluate the quality, while the high drilling costs and low recovery rate of rock cores prevent the application. Therefore, it is necessary to extract the geological information appropriately on substances from the various physical properties obtained by the geophysical exploration, and a new technological development is required. In this study, we obtained rock samples from several seafloor areas in the Okinawa trough where the germination of seafloor massive sulfide is predicted. We measured the various physical properties, mineral composition and element concentration at laboratory, and investigated their relationship. We constructed a rock physics model to estimate the electrical conductivity from the other physical properties such as porosity. As a result of applying our rock physics model to the measurement data, we succeeded in reproducing the electric conduction characteristics of samples showing the high electrical conductivity, which could not be explained by the previous rock models. Furthermore, a clear positive correlation was found between an estimated parameter of the physics model and the volumetric content of conductive sulfide minerals in rock samples. This result indicates that the electrical conductivity of rock samples obtained from the seafloor hydrothermal areas can be explained by new rock physics model proposed in this paper.
