大洋富钴结壳资源调查与研究进展

摘要

Cobalt-rich crusts constitute another deep-sea sedimentary solid mineral resource discovered after oceanic polymetallic nodule. Cobalt-rich crusts are distributed on the seafloor of the Pacific Ocean, the Atlantic Ocean and the Indian Ocean. It is estimated that the amount of dry crust resources in the three oceans is (1081.1661~2162.3322)×108 t. Survey of the cobalt-rich crust by various countries in the world began in the early 1980s. So far, 4 countries, i.e., Japan, China, Russia and Brazil, have signed a cobalt-rich crust exploration contract with the International Seabed Authority. The application of cobalt-rich crusts mining area submitted by South Korea was also approved by International Seabed Authority in 2016. Cobalt-rich crusts can be divided into plate curst, gravel-like crust and nodule-like crust according to their shapes. Cobalt-rich crusts are usually three-layer structure in the macro. Upper layer is called bright coal seam layer, intermediate layer is called loose layer, and bottom layer is called relatively loose layer. Microscopically, cobalt-rich crusts are mainly characterized by such structures as columnar structure, callenia structure, plaque structure, and laminar structure. The minerals of cobalt-rich crusts are mainly authigenic iron and manganese minerals, which include vemadite, todorokite, amakinite, akaganeite, feroxyhyte, goethite, and so on. Cobalt-rich crusts are rich in Mn, Fe, Co, Ni, Cu, Pb, Zn as well as REEs and PGEs. The content of Co of cobalt-rich crusts is particularly significant. The average content of Co in cobalt-rich crusts from the Pacific Ocean is the highest in the three large oceans in the world. Formation process of cobalt-rich crusts is extremely slow. Only several millimeters of crust can be formed in one million years. Studies show that cobalt-rich crusts from the West Pacific Ocean were formed as early as Eocene to early Miocene. It's generally accepted that the cobalt-rich crust is hydatogenic. Co, Fe, Mn and other metal elements in crusts originate from sea water. In addition, studies have shown that microorganisms play a very important role in the formation of cobalt-rich crusts. The distribution and characteristics of cobalt-rich crust are affected by such factors as topography, water depth, substrate rocks type, hydrochemical characteristics of seawater, latitude and longitude. Cobalt-rich crusts are formed on the slope of seamount and island and submarine highland above the depth of carbonate compensation and below oxygen minimum zone, with the water depth of 800~2500m. West and Central Pacific seamounts are considered to be the main production area of cobalt-rich crusts in the world.%富钴结壳是继多金属结核资源之后被发现的又一深海沉积固体矿产资源,在太平洋、大西洋和印度洋的海底均有分布.据估算,全球三大洋海山富钴结壳干结壳资源量为(1081.1661~2162.3322)×108 t.世界各国对富钴结壳的调查始于20世纪80年代初,截至目前,已有日本、中国、俄罗斯和巴西等4个国家与国际海底管理局签订了富钴结壳勘探合同,而韩国的矿区申请也于2016年获得核准.富钴结壳按形态可分为板状结壳,砾状结壳和钴结核3种类型.富钴结壳内部结构构造在宏观上通常表现为三层构造,即底部亮煤层、中部疏松层和顶部较致密层;在微观下主要表现为柱状构造、叠层构造、斑块状构造、纹层状构造等多种类型.富钴结壳的矿物成分主要为自生的铁锰矿物,包括水羟锰矿、钡镁锰矿、羟铁矿、四方纤铁矿、六方纤铁矿、针铁矿等.富钴结壳富含Mn、Fe、Co、Ni、Cu、Pb、Zn等金属元素以及稀土元素和铂族元素,其中Co含量尤为显著.三大洋中,以太平洋富钴结壳的Co平均含量最高.富钴结壳的生长过程极其缓慢,平均仅几毫米每百万年.研究表明,西太平洋富钴结壳最早于始新世-早中新世开始生长.目前通常认为富钴结壳为水成成因,即Co、Fe、Mn等金属元素来源于海水.此外,有研究表明微生物在富钴结壳的形成过程中也起着非常重要的作用.富钴结壳的分布及特征受地形、水深、基岩类型、海水水文化学特征、经纬度等多种因素的影响,其主要分布于碳酸盐补偿深度以上、最低含氧带以下、水深800~2500 m的海山、岛屿斜坡和海底高地上,西、中太平洋海山区被认为是全球富钴结壳的最主要产出区.