Tetsuo Yamazaki

Characteristics of the Environment Around a Massive Sea-Floor Sulfide Area in the Okinawa Trough

It is necessary to carry out a proper environmental impact assessment for not only the sea-floor massive sulfide area where a special hydrothermal-vent chemosynthetic ecosystem is observed, but also its surrounding area. This paper shows provisional results of the environmental baseline survey conducted at the Izena Cauldron in 2009. Environmental conditions differed clearly between inside and outside of the Cauldron. In the inside area, a high turbidity layer was recognized at ca. 200 m above the sea-floor. In the bottom layer close to the hydrothermal active region, water temperature was slightly higher than the surrounding area with the lower pH, higher concentrations of both carbon dioxide and the dissolved Mn. Inside the Cauldron, the sulfur isotope ratio of the sediment close to a sea-floor massive sulfide was similar to that of the hydrothermal sulfate. In addition, heavy metal concentrations of the sediment were higher inside than outside of the Cauldron. Especially, concentrations of Cd, As and Hg were as high as poisonous levels. These results show the possibility that most of the chemical materials derived from hydrothermal vent remain in the Cauldron. Pelagic shrimps of the family Oplophoridae were widely distributed in the bottom layer inside the Cauldron. The biomass of benthic shrimps which belong to infraorder Caridea was higher inside than outside of the Cauldron. These higher biomass was likely caused by the abundant organic matter. This hypothesis was reinforced by the result of the mooring sediment trap (placed at ca. 50 m above the seafloor) experiment, which demonstrated that the settling particle in the Cauldron was supplied from not only the euphotic zone but also the hydrothermal-vent ecosystem.Copyright

Preliminary Economic Feasibility Analysis of Cobalt-Rich Manganese Crust Mining for Rare Metal Recovery

The importance of cobalt-rich manganese crusts on the Pacific seamounts for possible future rare metal sources has currently been recognized. The thin layer-type deposit characteristics affect not only the excavation efficiency but also the economy of mining venture. Considering the thin layer-type distribution and the utilization of some rare metals in cobalt-rich manganese crusts, a preliminary economic feasibility of the mining venture is evaluated. Under some preliminary technical assumptions, the possibility of cobalt-rich manganese crusts for future rare metal sources for Japan is examined. The important role of utilization of rare metals in the crusts is highlighted.Copyright

Fundamental Geotechnical Considerations for Design of Deep-Sea Mining Systems

The importance of manganese nodules, seafloor massive sulfides, and cobalt-rich manganese crusts as future metal sources has been well recognized. However, less geotechnical information of the resources is available to aid the design of mining system. The results of fundamental studies for geotechnical characteristics of the resources and sediments associated with the resources are presented in this chapter. Effects of the characteristics on the design of mining system are examined. Some additional engineering and economic considerations for the design are also discussed.

Waste Rejection on Seafloor by Hydrocyclone for Economic Seafloor Massive Sulfide Mining

Many seafloor massive sulfide (SMS) deposits have been discovered in Japan’s exclusive economic zones (EEZ). They have some useful metals and are expected to become future metal resources. In Japan, because of an expensive waste disposal cost, it seems to be difficult to realize the SMS mining. Adding a function of primary waste separation from metal-rich parts of SMS ore on seafloor by a hyrocyclone is proposed to overcome the problem. The water flow structure in a model hydrocyclone is observed in the study at first. Secondly, the performance of separation using differences in specific gravities of particles by the hydrocyclone is experimentally examined. Finally, the application of hydrocyclone in the actual sea area is examined. The result shows that 67% of larger specific gravity are collected and 67% of smaller one are rejected. From the separation efficiency, the hydrocyclone method is recognized to have a high possibility of application in the actual sea area.Copyright

Economic Seafloor Massive Sulfide Mining by Japan’s Model

Because of the higher Au, Ag, and Cu contents, seafloor massive sulfides (SMS) have received much attention as future commercial mining targets by private companies and nations. One of them, Solwara 1 Project in Papua New Guinea (PNG), is scheduled to start the commercial mining operation from 2018. Because the mining site is inter-island area and almost no cost is necessary for the waste disposal in PNG, the economy of the mining is expected very well. In contrast with this, because all the SMS distribution sites in Japan locate outer ocean areas and the waste disposal cost on land in Japan is very expensive, the economy of SMS mining in Japan is quite negative. In order to overcome the problems, a self-standing riser with flexible link to the sea surface platform and a primary ore separation on the seafloor prior to the ore lift-up are proposed. The improved SMS mining concept named Japan’s model is examined.Copyright

Effect of Micro-Bubbling on Settling Behavior of Fine Particles for Deep-Sea Mining

A preliminary tank experiment for clarifying the effect of micro-bubbles on settling behavior of fine particles was conducted. The behavior of the particles was continuously photographed by a still camera and the images were analyzed by the gray scale intensity. From the results the authors found a suspension effect of micro-bubbles for the settling of fine particles. The effect should be studied in detail for preventing some serious environmental impacts during deep-sea mining.Copyright

New Platform to Monitor the Environmental Impacts of Seafloor Mining

Various unconventional natural resources (e.g. seafloor massive sulfide, methane hydrate and manganese nodules) existing on and under the seafloor will possibly be mined in the near future. When mining these deep sea resources, it is necessary to monitor the environmental impacts of seafloor mining. Environmental impacts have been usually monitored by mooring systems or stations put on the seafloor. Mooring systems consist of floats, sinker and sensors. Their heights rang e from one hundred meters to several kilometers. In order not to entangle in the mining machine and the support cable, it is impossible to put the mooring systems within the distance of their heights from points of the operation safety. The stations consist of a frame and sensors. Their heights are about a few meters. Therefore, we are able to put the stations near the mining point, but we can’t observe the upper water layer. In this study, we have developed a new platform to observe the environmental condition near the mining point and the upper layers of the seafloor. The developed platform consists of frame, sinker, releaser, winch, battery and sensor assembly. Because the size of this is 2 × 2 × 2 m, we can put this near the mining point. The sensor assembly is moved from the seafloor up to 150 m by the winch. This platform can automatically observe the environmental condition for several months without external power supply by using the internal battery. Therefore, we can automatically observe the environmental condition near the mining point and the upper layer by using this new developed platform. The platform is also effective for environmental monitoring near deep-sea petroleum exploitation points.Copyright

Preliminary Economic Examination of Seafloor Massive Mining Venture Under Japan’s Conditions

In Papua New Guinea (PNG), a seafloor massive sulfide (SMS) mining venture has been proposed to start in 2013 and the expected high profitability was presented. However, the geophysical and social conditions are quite different from Japan’s ones. The technologies and model used for the PNG mining are difficult to apply under Japan’s conditions. The economy of SMS mining has no reality in Japan, because the tailing waste disposal is very expensive. Based on a preliminary economic evaluation of seafloor massive sulfide mining venture under Japan’s conditions, some modifications in the mining system and material flow are proposed for the improvement of the economy.Copyright

Seafloor Primary Ore Dressing System for Economic Sulfide Mining

Because of the higher Au, Ag, and Cu contents, seafloor massive sulfides (SMS) have received much attention as immediate commercial mining targets by private companies and nations. One of them is scheduled to start the commercial mining program in the end of 2013 and the expected profitability is presented. However, the geophysical and social conditions are quite different from Japans ones. The material flow selected for the mining program, for example, has no economy under Japans social condition. One of the key technologies necessary for improving the economy in Japan, a primary ore dressing of excavated SMS ores on the seafloor, is introduced in this issue.

Conceptual Design of TMR-Less Manganese Nodule Mining System and the Economy Examination

Manganese nodules on deep ocean floors have been interested in as future metal resources these forty years. The Total Materials Requirement (TMR) of the conventional proposed mining method, however, is very high because of the much lifted water with the nodules from the seafloor to the sea surface and the longer transportation from the mining site to the smelting plant. An innovative conceptual design of the TMR-less mining system is presented. The economy is examined and compared with the one of the conventional method.Copyright