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ARTICLE : Seabed Operations
Wednesday, 13 June 2012 11:21


Seabed Operations

Over the past decade a new phase of deep-sea mining has begun in the world. Two factors are responsible – one is rising demand for precious metal and the other is food. Growing world population needs more food and phosphor-based artificial fertilizers have significant importance for world food production. Phosphorus nodule mining at the seafloor is the best source for artificial fertilizer.

Deep sea mining is a relatively new mineral retrieval process that takes place on the floor of the ocean. Ocean mining sites are usually around large areas of polymetallic nodules or active and extinct hydrothermal vents. They are at about 1400-3700 meters below the ocean’s surface. The vents create sulfide deposits, which contain precious metals such as silver, gold, copper, manganese, cobalt, and zinc. These raw materials are found in various forms on the seabed, usually in higher concentrations than terrestrial mines.

The deposits are mined using either hydraulic pumps or bucket systems that take ore to the surface to be processed. Polymetallic nodules which contain nickel, copper, cobalt and manganese are found at depth of 4000 – 6000 meter. Manganese crusts are available at 800-2400 meter. Mainly cobalt, some vanadium, molybdenum and platinum are found in it. Sulfide deposits are found at an average depth of 1400-3700 which contains copper, lead, zinc, some gold and silver. Diamonds are also mined from the seabed.

The International Seabed Authority has entered into a 15-year contract with India in the year 2002 for pursuing exploration activity for deep sea mineral resources in the Indian Ocean on lines similar to its contracts with other countries including China. In pursuance of this agreement, the Ministry of Earth Sciences has undertaken exploration activity for which a total area of 75000 sq. km. in the Central Indian Ocean Basins is available to it. India will be amongst the few countries of the world which would be able to explore for deep sea mineral resources in  the years ahead.

History

A book titled ‘Mineral Resources in the Sea’ published in 1960 floated the idea of limitless supply of minerals at the floor of the ocean.  J L Mero also stated in his book that apart from nickel and cobalt manganese nodules are also occurs in these deposits. The regulation on deep sea mining came into force in 1994 and conventions followed in 1973 and 1994 which resulted in setting up of the International Seabed Authority (ISA). It regulates deep sea operations of each country outside their respective Exclusive Economic Zone. EEZ is a 200-nautical mile, i.e. 370 km area surrounding coastal nations. Each country explores two equal mining sites and turns one over to the ISA. The mining technology was also to be transferred to ISA for period of 10 -20 years along with the site. Initially nations agreed to this but later on they refused to do so as the operation was not enough profitable. Some industrialized countries refused to sign the treaty.

At present, Solwara 1 Project in the waters of Papua New Guinea, in the Bismarck sea, New Ireland Province, has high grade copper-gold resource and the world’s first sea floor Massive Sulphide (SMS) resources. The relatively shallow water depth of 1050 of these locations in Central and Eastern Manus Basin promises of excellent mining. The first production is expected in the year 2013.( Eastern and Central Manus Basin around Papua New Guinea and the crater of Conical Seamount to the east are locations-check maps etc,)

Extraction Method

At present Remotely Operated Vehicles (ROVs) are used to collect mineral samples from mine sites. Using drills and other cutting tools, the ROVs gather samples to be analyzed for precious materials. Once the site is located, a mining ship or station is set up to mine the area. Two systems are being used for extraction namely continuous-line bucket system (CLB) and the hydraulic suction system (HS). CLB system is very convenient for collection of nodules. It operates like a conveyor belt. It runs from the sea floor to the surface of the ocean where a ship or mining platform extracts the desired material and returns the rest of the material, i.e. tailing to the ocean. In the Hydraulic suction system, two separate pipes are used, one for collecting nodules and the other for returning trailing. A pipe is lowered to the seafloor which transfers nodules along with other material up to the mining ship. The nodules are separated and trailing are sent back to the seafloor by another pipe.

Environmental Concerns

All mining operations raise questions about environmental damages to the surrounding areas. Here in water also the concern is about disturbance to the living organisms in that area, change in sediment or rocky layer of sea floor, change in toxicity of the water column and foodweb.

Removal of parts of the sea floor will disturb the benthic layer. The type of mining and location will cause permanent disturbance to the habitat of benthic organisms. Besides this direct impact of mining the area, leakages, spills and corrosion would alter the chemical make-up of this area.

It is feared that sediment plumes will have the greatest impact. Plumes are caused when the tailings from mining are dumped back into the ocean. These fine particles create a cloud of particles floating in the water. Two types of plumes occur: near bottom plumes and surface plumes. When the tailings are pumped  back into the mining site, the floating particles increase the turbidity or cloudiness of the water. This clogs filter-feeding apparatuses used by benthic organisms.

Surface plumes cause a more serious problem. Depending on the size of the particles and water currents the plumes could spread over vast area. These plumes could impact zooplanktons and light penetration. This affects the food web of the area.