2014 Volume 63 Issue 3 Pages 244-249
Seafloor hydrothermal deposits have been found to be widespread in the waters off Okinawa Island. Since Japan currently depends heavily on foreign mineral resources, it is expected that such deposits will be developed in the near future. To assist with the design and manufacture of mining and crushing machinery and ore transportation equipment, in this study the mechanical properties of seafloor hydrothermal deposits were investigated. Tests were carried out on the strength, hardness and abrasiveness of boring cores and block samples of the deposits. The average uniaxial compressive strength was found to be between 20 and 60 MPa, the CERCHAR abrasiveness index was between 1 and 2, and the Mohs hardness was between 4 and 6. In uniaxial compression tests, in which a specimen was crushed up to 20% of its initial height, size of debris was a little smaller than tuff, andesite and sandstone. The specific energy calculated with the boring data was found to be closely related to the mechanical properties of the hydrothermal deposits, and its distribution beneath the seafloor was determined from some boring data. The results obtained in this study provide important guidelines for the development of mining techniques for seafloor hydrothermal deposits.