A Physical Property Evaluation Method of Disseminated Seafloor Polymetallic Sulfide Rocks Based on Time Domain Induced Polarization Relaxation Time Spectra

Seafloor polymetallic sulfides mainly occur in mid-ocean ridges are increasingly regarded as strategic and promising metal resources for the future. One of the most difficult to detect in situ is disseminated seafloor polymetallic sulfide. It is necessary and urgent to search effective exploration and evaluation technologies. Relaxation time spectra (RTS) originated from induced polarization logging in petroleum exploration, the recognition and research on RTS of metal ore especially seafloor polymetallic sulfide is obviously insufficient. In this study, the theory of intrinsic semiconductor polarization was introduced into the traditional RTS based on membrane polarization theory and a physical property evaluation method for disseminated seafloor polymetallic sulfide rock was proposed. Synthesized and rock physics experiment data were calculated and analyzed to verify the validity of this method. The result shows that this method can effectively evaluate the induced polarization characteristics of disseminated seafloor polymetallic sulfide rocks, including the evaluation of conventional physical properties such as the relaxation time constant and chargeability, as well as the identification of possible polarization sources inside the rock. This method also can be used to evaluate the volume content and grain size of sulfide particles. Based on the rock physics experiment, the RTS of seafloor polymetallic sulfide rocks was divided into four typical types, which can indicate the induced polarization characteristics of rocks containing metal sulfides with multiple distribution. Delay duration is an important factor that affects the evaluation of induced polarization characteristics. Slightly larger delay duration can cause the induced polarization effect of disseminated metal sulfides to be greatly underestimated. This method has a directive function for the induced polarization logging interpretation of seafloor polymetallic sulfide rocks.