Recent Developments In Offshore Mining

Abstract

Abstract Offshore mining continues to provide a major share of the world's limonite, retile, zircon, and tin supplies. A better understanding of shore processes, more detailed offshore bathymetry, and more complete information on pale geographic history are being used to locate and evaluate marine placer deposits. The author reviews the status of beach and offshore mining in Australia, Brazil, England, India, Japan, Malaysia, New Zealand, South Africa, and the United States of America. Prospecting activity has recently taken place on the Bering Sea floor adjacent to the Seward peninsula, Alaska; the Celtic Sea floor adjacent to the Cornwall peninsula; and the Gulf of Carpentaria floor west of the Cape York peninsula, Australia. Information which has been made public concerning these investigations will be summarized. Other ocean mining activities, which include extraction of sulphur from sub-sea floor salt domes in the Gulf area, the dredging of sand and gravel for construction materials, and the mining of oyster shell for a variety of industrial purposes, will be briefly reviewed to complete this status report on mining in the sea. Introductory Notes The term "offshore mining" has been used in the past to include a variety of marine activities, including the extraction of salt, the recovery of petroleum and natural gas from reservoirs beneath the sea floor, and the production of magnesium and bromine by treatment of sea water. For the purpose of this paper, "offshore mining" is restricted to the recovery of mineral materials now found at the edge of the sea, on the bottom of the sea, or below the floor of the sea. Petroleum and natural gas will be excluded, and chemical treatment of sea water for whatever purpose (such as desalination or recovery of materials dissolved in sea water) will also be omitted. Marine placer deposits, in the author's opinion, are among the most promising of all ocean resources, and will receive special attention in this paper. "Marine placers" are defined as any accumulation of valuable detritus minerals which owes its development to a near shore marine environment. High-value minerals most frequently found in marine placers are listed in Table 1. The combined sorting and winnowing effects of ocean waves, offshore currents, tidal forces, and wind action makes possible a concentration of valuable minerals into a "marine placer". This placer may now be on the beach, in shallow water offshore, or buried under more recent sediments on the sea floor. There is much confusion in the technical press concerning marine resources. Reports of mineral discoveries are intermixed with production data, so that the reader is not sure whether actual mining is taking place, or whether only a prospecting venture has been conducted. Since the technology of mining in the sea is, on the one hand, an old established procedure called "dredging" and, on the other hand, a comparatively untested mixture of innovative techniques; the mere discovery of a marine mineral resource does not guarantee that it can be exploited "at a profit". Since mining investment has long hinged on the adequate size of a newly discovered ore body, the discovery of huge quantities of mineral materials on the sea floor seems to justify enthusiasm, since mining equipment has nearly always been equal to any mining task. But mining in the ocean can provide technical challenges which are well beyond the present limits of the state of mining art, and while technology can answer the challenge, the cost to the investor will be substantial. Thus, the financial requirements for offshore mining have been a deterrent, and are l