A GRAVITY CORING TECHNIQUE APPLIED TO COBALT-RICH MANGANESE DEPOSITS IN THE PACIFIC-OCEAN

Cobalt-rich manganese deposits on Pacific seamounts have become a foca l point as one of the marine mineral resources with the most potential for the twenty-first century. Extent and distribution of the deposits have not yet been well determined. Conventional survey techniques hav e estimated the distribution of the deposits by the surface coverage o f nodules and crusts based only on visual observations. In order to de termine more clearly the distribution characteristics of the deposits, a large-diameter gravity coring system was developed and used during survey cruises of the research vessel R/V Hakurei-maru No. 2 in 1991 a nd 1992. Samples and photos obtained using the system have provided si gnificant data and information for investigation of the economic poten tial and processes of formation of these deposits. Analysis of the cor es provided important new findings on crust thickness, buried deposits , and debris flow-like deposition. Based on the initial experience wit h the large-diameter corer, some corer design improvements are present ed.