What Is Seafloor Spreading?

The development of human society is inseparable from the development and utilization of various resources. Today, with the gradual depletion of land resources, people have set their sights on the deep ocean. In addition to the well-known manganese nodules and deep-sea oil and gas, the underwater world also has hydrothermal deposits and the hottest natural gas hydrates. The reserves of natural gas hydrates are extremely large. It is estimated that the total amount of organic carbon in natural gas hydrates cannot be caught up with the total amount of organic carbon in natural gas hydrates, which has been used up by humans and has not yet been developed. If this estimate is good, it is undoubtedly the gospel of human beings, because it is likely to become a new energy source in the new century.

Subsea resources

The seafloor includes the international seafloor area and continental shelf areas under some national jurisdiction (including the legal continental shelf). The strategic position of the deep sea is rooted in its vast

Underwater World Space and abundant resources. Deep seabed resources include: (1) Polymetallic nodules that are distributed on the seafloor at a depth of 4,000 to 6,000 meters and rich in metals such as copper, nickel, cobalt, and manganese. (2) Cobalt-rich crusts distributed on the surface of the seabed and hydrothermal polymetallic sulfides distributed in the mid-ocean ridges and fault active zones. (3) The biological communities living in the deep-sea hydrothermal vent area and sea mountain area, due to their special environment, their protection and utilization have attracted great attention from the international community. (4) Natural gas hydrates mainly found on the continental margins today are converted into methane gas of about 1.8-2.1X1016m3, which is about twice the total reserves of coal, oil, and natural gas in the world. New energy with great potential for development in the 21st century. The deep sea will become a strategic development base for a variety of natural resources in the 21st century, and may form deep sea industrial clusters including deep sea mining, deep sea biotechnology, and deep sea technology equipment manufacturing. Over the past few decades, the rapid development of knowledge about deep seabed resources will not only significantly increase the world's resource base, but also may bring considerable economic benefits to the world in the future. Most of the newly discovered resources are international seabeds beyond national jurisdiction, some of which are more abundant than any land deposit. To this end, the International Seabed Authority, which organizes and manages exploration and development activities in the international seabed area, is working on the formulation of relevant regulations. The Authority has passed regulations for the exploration and exploration of polymetallic nodules in the international seabed area in 2000, and is currently developing a similar set of exploration and exploration regulations for polymetallic sulphides and cobalt-rich crusts.

Subsea Resources Traditional Mineral Resources

Traditional mineral resources refer to mineral resources that were found earlier in the deep sea, have been industrially mined or have industrial mining capabilities, such as deep-sea oil and gas, polymetallic nodule minerals, and so on. Oil and gas buried in the seabed will be included in the submarine oil resources regardless of whether the environment in which they are generated belongs to the marine environment.

Underwater World Over the past forty years of offshore oil exploration, it has been found that the seabed is rich in oil and gas resources. According to 1979 statistics, the proven recoverable oil reserves of the world's offshore seabed were 22 billion tons, and the natural gas reserves were 17 trillion cubic meters, accounting for 24% and 23% of the world's proven total recoverable oil and gas reserves.

There was oil on the ocean floor, which was not well understood in the past. Since the discovery of oil on the ocean floor at the end of the 19th century, scientists have studied the theory of oil production. In the Mesozoic and Cenozoic, the submarine floor plate and the continental plate squeezed to form many sedimentary basins, and thousands of kilometers of sediments were formed in these basins. These sediments are the remains of plankton in the ocean (they multiply in a specific favourable environment), and the organic matter that rivers bring from land. These sediments are buried in the seabed by tectonic movement, and tectonic movement deforms the basin rocks, forming fault blocks and anticlines. Magmatic activities occur with tectonic movements, generating a large amount of thermal energy, accelerating the conversion of organic matter into petroleum, and accumulating and preserving it in traps, becoming today's shelf oil fields.

The coast of China and the seafloor near the islands are rich in oil and gas resources. Some people abroad estimate that China's offshore oil reserves are about 1 to 2.5 million tons. China is undoubtedly one of the countries with rich marine oil and gas resources in the world. The Bohai Sea is China's first developed subsea oil field. The Bohai Sea shelf is the center of subsidence and accumulation in North China. Most of the Cenozoic sediments found were up to 4,000 meters thick and the thickest was 7000 meters. This is a very thick sea-land interaction layer. Among the surrounding land, a large amount of organic matter and sediment are deposited. The Bohai Sea is deposited in a high-temperature climate suitable for the reproduction of marine organisms in the Cenozoic Tertiary. advantageous. Due to the rifts associated with rifts, a series of anticline and tectonic belts are generated, forming various types of oil and gas reservoirs. The East China Sea continental shelf is wide, with a sedimentary thickness greater than 200 meters. Foreigners believe that the East China Sea is one of the regions with the best oil prospects in the world; the potential for natural gas reserves in the East China Sea may be greater than oil.

The South China Sea continental shelf is a very large sedimentary basin. The Cenozoic strata are about 2000-3000 meters long, and some are 6000-7000 meters long. They have good oil-generating and oil-bearing rock series. The oil-bearing rock formation is 1000-4000 meters thick, with proven oil reserves of 640 million tons and natural gas reserves of 980 billion cubic meters. It is the world's subsea oil-rich area. Therefore, some foreign oil experts believe that the South China Sea may become another Persian Gulf or North Sea oil field.

The development and utilization of offshore petroleum resources have broad prospects. However, because the conditions for finding and extracting oil at sea are different from those on land, technical means are more complicated than on land, construction investment is higher than on land, and risks are greater than on land. Therefore, today s world offshore oil development Activities, most countries have adopted international cooperation.

Underwater World In order to accelerate the development of offshore petroleum resources, China clearly stipulates that China has the ownership and jurisdiction of petroleum resources; the sea areas, resources and products of the cooperation zone are owned by China; the sea area and area of the cooperation zone, and the choice of cooperation targets are determined by China. A series of articles protecting China's sovereignty and interests. The rational use of foreign capital and technology has become an important way to accelerate the development of offshore petroleum resources. As we all know, with the rapid development of industry and economy in the world, the consumption of mineral resources has increased dramatically, and terrestrial mineral resources have become increasingly scarce and exhausted worldwide. People can only use the ocean, which accounts for more than 71% of the earth's surface area, as a future mineral source.

Subsea minerals In addition to the oil and natural gas we mentioned earlier, the seabed is also rich in metal and non-metallic minerals. So far, mineral resources such as polymetallic nodule deposits, phosphate deposits, precious metals and rare elemental sand deposits, and sulfide deposits found in the ocean floor have been found at 600 billion tons. If more than 16 billion tons of polymetallic nodule deposits in the bottom of the Pacific Ocean are mined, nickel can be used for 20,000 years worldwide; cobalt for 340,000 years; manganese for 180,000 years; and copper for 1,000 years. What's more interesting is that people find that manganese nodule ore (including manganese, iron, copper, cobalt, nickel, titanium, vanadium, zirconium, molybdenum and other metals) is still growing. It will never be caused by human exploitation. Disappear in the future. According to American scientist Meru's estimation, manganese nodules at the bottom of the Pacific Ocean continue to grow at a rate of about 10 million tons per year. If we only extract metals from newly grown manganese nodules at the bottom of the Pacific each year, copper can be used for three years worldwide; cobalt can be used for four years; nickel can be used for one year. Manganese nodules, the "jewel" deep in the ocean, is an inexhaustible and inexhaustible precious resource in the world and a common wealth of mankind.

However, it is not easy to adopt manganese nodules from the bottom of the ocean that is four or five kilometers deep. It must have advanced technology. At present, only a few developed countries can do this. China has also basically been equipped to develop ocean manganese nodules. By the 21st century, it is expected to achieve productive mining. The ocean provides extremely rich and precious resources for the survival of human beings. As long as we can develop and use them reasonably, it will be used endlessly by human beings, inexhaustible and inexhaustible. It is an important human resource in the next century. Place of supply.

Bohai Oilfield Ocean basins are a source of various mineral deposits. In addition to previously known mineral deposits, newly discovered marine mineral resources include polymetallic sulphides, in which the copper, zinc, silver and gold contents vary. Polymetallic sulphide deposits have accumulated over thousands of years near submarine hot springs, which are located around active volcanic mountains below the sea, which spread across all ocean basins around the world. Polymetallic sulphide deposits also form at locations adjacent to volcanic islands, such as the islands along the western Pacific border. Another type of newly discovered marine mineral resource is cobalt-rich crusts. This ore crust was deposited on the side of an underwater extinct volcano and formed over millions of years. Its minerals come from dissolved metals in seawater, which are provided by river water and submarine hot springs. The hot spring concentrates the deposition of polymetallic sulfides, and at the same time spreads various metals to the ocean, promoting the accumulation of cobalt-rich crusts. Not only that, the hot spring also provides chemical energy from the earth's interior, which is used by microorganisms to grow. These microorganisms are at the bottom of the food chain of the hot spring life form ecosystem, and basically do not need light energy, while the bottom plants of the terrestrial food chain need light energy to produce photosynthesis. These microorganisms are very important and are a new source of compounds with industrial and medical uses. These microbes also include primitive life forms that may help unravel the mysteries of the origin of life.

Submarine resources

It is no exaggeration to say that the ocean has almost all the resources available on land, and there are some resources that are not on land. At present people have discovered the following six categories.

Submarine ore 1. Petroleum gas. It is estimated that the world's limit oil reserves are 1 trillion tons, and the recoverable reserves are 300 billion tons, of which 135 billion tons are subsea oil; the world's natural gas reserves are 25-28 billion cubic meters, and ocean reserves account for 14 billion cubic meters. At the end of the last century, the annual output of offshore oil reached 3 billion tons, accounting for 50% of the world's total oil output. China's oil and gas reserves in adjacent sea areas are about 4-5 billion tons. Due to the discovery of abundant marine oil and gas resources, China is likely to become one of the world's five largest oil producers.

2. Solid minerals such as coal and iron. Coal and iron deposits have been mined in many of the world's offshore seabeds. Subsea coal mining in Japan accounts for 30% of its total output; Chile, the United Kingdom, Canada, and Turkey also have mining. One of the world's largest iron mines was discovered near the sea floor in Kyushu, Japan. Many Asian countries have also found many submarine tin mines. More than 20 types of subsea solid minerals have been discovered. Copper, coal, sulfur, phosphorus, limestone and other ore are widely distributed in the shallow sea area of China's continental shelf.

3 Sandy beach. There are many precious minerals in seashore sediments, such as: rutile containing solid fuel titanium for launching rockets; monazite containing niobium for rockets, aircraft shells and tantalum for reactors and microcircuits; high temperature resistance for nuclear submarines and nuclear reactors And corrosion-resistant zircon, zircon; some sea areas also have gold, platinum and silver. In China's offshore waters, there are also sand ore with high economic value, such as gold, zircon, ilmenite, monazite, and chromium spinel.

4 Polymetallic nodules and cobalt-rich manganese crusts. Polymetallic nodules contain dozens of elements such as manganese, iron, nickel, cobalt, and copper. There are about 3 trillion tons of polymetallic nodules stored in the ocean floor at a depth of 3500 to 6000 meters. The output of manganese can be used for 18,000 years in the world, and nickel can be used for 25,000 years. China has surveyed an area of more than 2 million square kilometers in the Pacific Ocean, of which more than 300,000 square kilometers are prospective mining areas with mining value. The United Nations has approved the allocation of 150,000 square kilometers of these areas as development areas. Cobalt-rich manganese crusts are stored on the ocean floor at a depth of 300 to 4,000 meters and are easy to mine. Countries such as the United States and Japan have designed some mining systems.

Subsea petroleum samples 5. Hydrothermal deposits. It is a kind of sulfide containing a large amount of metal. It was formed by the cooling and deposition of high-temperature magma sprayed from the submarine rift, and more than 30 deposits have been found. The United States alone has 25 million tons of reserves in the Galapagos Rift Valley, with a mining value of $ 3.9 billion.

6. Combustible ice. It is a new type of mineral called natural gas hydrate. It is an ice solid substance composed of hydrocarbons and water molecules under low temperature and high pressure conditions. It has high energy density, few impurities, almost no pollution after combustion, thick ore layer, large scale, wide distribution and rich resources. It is estimated that global reserves of combustible ice are twice the existing oil and gas reserves. In the last century, Japan, the former Soviet Union, and the United States have all found large areas of combustible ice distribution. China has also found combustible ice in the South China Sea and East China Sea. According to estimates, China s combustible ice resources in the South China Sea alone amount to 70 billion tons of oil equivalent, which is about half of China s total onshore oil and gas resources. With the world's oil and gas resources gradually depleted, the discovery of combustible ice has brought new hope to humankind.

As humans have not sufficiently investigated the polar waters and the vast deep-sea areas, it is difficult to know how many seabed minerals remain in the ocean.

Subsea resources

It is the most important traditional marine mineral resource, which is called "blood of industry". With the sharp increase in demand, the energy crisis has intensified. Some people even suggested that "the wolf of the oil age is here!", But in fact the "wolf" did not come because the seabed oil and gas resources have great development potential. At present, subsea oil reserves account for 45% of the global total, and natural gas accounts for 50%. The total marine output accounts for about 1/3 of the global total. And now the water and well depths of subsea oil development are getting bigger and bigger.

Polymetallic nodules Submarine oil and gas distribution New Zealand has a BSR distribution area with an area of more than 4 × 104 km2 in the offshore sea depth of 1-3 km on the east coast of the North Island. In recent years, Australia has found a BSR distribution area of 8 × 104km2 on the Lord Howe's submarine plateau in the east. Pakistan has also conducted water surveys in the Gulf of Oman and has made progress. About 180 billion oil equivalents of natural gas hydrate resources were found in the mid-ridge slopes of the Juan-Desaica Ocean on the west side of Canada. In short, the areas where natural gas hydrates have been found and delineated are mainly distributed in the Bering Sea, Okhotsk Sea, Thousand Island Trench, Okinawa Trough, Sea of Japan, Shikoku Trough, South Sea Trough, Sulawesi Sea , North Island of New Zealand; Central American Trough in the Eastern Pacific Ocean, Northern California-Oregon Coast, Peru Trough; Atlantic Ocean in the U.S. East Coast, Black Sea Terrace, Gulf of Mexico, Caribbean Sea, South American East Coast Outer Margin, West Africa The west coast waters; the Gulf of Oman in the Indian Ocean; the Barents and Beaufort Seas in the Arctic; the Ross and Weddell Seas in the Antarctic; and the Black and Caspian Seas. At present, natural gas hydrates have been found directly or indirectly in 88 of these seas in the world. Among them, natural gas hydrates have been seen in 26 cores, and BSR-like reflections (BSR) with natural gas hydrate seismic signs have been seen in many places. Biological and carbonate crusting signs. According to estimates from experts, in the marginal seas, deep-sea troughs and ocean basins of the world, the amount of methane in natural gas hydrometeors in sediments within a depth of 3000m has been found to be 2.1 × 1016m3 (2.1 trillion trillion m3). . The total carbon content of methane in hydrates is twice the total amount of coal, oil and natural gas known worldwide. It can meet the needs of mankind for 1,000 years. Its large reserves and wide distribution area are rare energy for humanity in the future. The above reserves estimation does not include the free gas under the natural gas hydrate layer.

Cobalt-rich crust The status of research and investigation on submarine oil and gas in China. In recent years, Chinese state leaders and leaders of the Ministry of Land and Resources, China's Ministry of Science and Technology, China's Ministry of Finance, China's State Planning Commission and other ministries and commissions have attached great importance to the investigation and research of gas hydrates. The first is the analysis of a large number of seismic survey data over the years under the jurisdiction of China. In the slopes of the Okinawa Trough, the northern slopes of the South China Sea, the Xisha Trough, and the southern slopes of the Xisha Islands, the existence of submarine-like gas hydrates was found. Seismic reflection layer (BSR) sign. In addition, a systematic study has been conducted on the genesis, geochemistry, geophysical characteristics, north-south collection, data processing and interpretation, borehole sampling, well logging analysis, resource evaluation, and geological hazards of the seabed. Rich information and a lot of data.

Since 1984, the Chinese geological community has systematically compiled data on the status of hydromass surveys abroad and their huge resource potential. Scientific and technical personnel of the Guangzhou Marine Geological Survey conducted a review of more than 20,000 kilometers of seismic data completed in the northern slope of the South China Sea in the early and mid-1980s, and a BSR-like display was found in the northern slope of the South China Sea. According to the arrangements of the China Geological Survey of the Ministry of Land and Resources, the Guangzhou Marine Geological Survey first conducted a preliminary experimental survey of marine gas hydrates in the Xisha Trough area in the northern South China Sea in October 1999. A total of 543.3km of three high resolution seismic lines were completed. From September to November 2000, the "Treasure Explorer" and "Ocean IV" survey vessels of the Guangzhou Marine Geological Survey continued their investigation of natural gas water content in the Xisha Trough. A total of 1589.39 km of high-resolution multi-seismic earthquakes, 703.5 km of multi-beam seafloor topography, 20 geochemical samples, 18 pore water samples, and 33 samples of gaseous hydrocarbon sensors for rapid determination were completed. Make breakthrough progress. The data show that there are obvious submarine-like reflection interfaces (BSR) and amplitude blanks on the seismic profile. "BSR" interface is generally located below the sea floor

Subsea resources 300-700m, the shallowest is about 180m. The amplitude blank band or weak amplitude band is about 80-600m thick, and the distribution area of "BSR" is about 2400km '. A multidisciplinary comprehensive survey mainly based on earthquakes shows that natural gas hydrates in sea areas are mainly found in deep-water slope areas of active continental margins and inactive continental margins, especially active continental margin subduction zones, accretionary wedge regions, inactive continental margins, and continental uplifts. Water content in the platform fold zone is very developed. According to the ODP184 voyage 1144 drilling data, in the southeast area of the Dongsha Islands in the South China Sea, the sedimentation rate has been between 400-1200 m per million years, and the sedimentary velocity in the Yinggehai Basin has been very high since the Miocene. The data indicate that the sedimentation rates in the northern and western slopes of the South China Sea are similar to those in the Black Sea area off the east coast of the United States where rich natural gas hydrate resources have been found. The favorable locations where water content in the South China Sea may be located are: the northern continental slope area, the western strike-slip shear zone, the eastern edge of the plate convergence, and the southern platform trough area. This area has four types of hydrate seismic marker BSR configurations: accretionary wedge-type double BSR, slot-edge slope BSR, platform-type BSR, and basin-edge slope BSR. Geochemical studies have found that there is often anomalous satellite thermal infrared warming before the earthquake on the northern slopes of the South China Sea and the Nansha waters. The temperature is 5-6 ° C higher than the surrounding seas, especially in the northern slopes of the South China Sea. Through the Dongsha Islands, up to the southwest of Taiwan, repeated temperature anomalies repeatedly occurred, which may be related to natural gas hydrates and oil and gas on the sea floor. Comprehensive data shows that there should be rich natural gas hydrate deposits in the land slopes and Lulong areas of the South China Sea. It is estimated that their total resources amount to 643.5-77.22 billion tons of oil equivalent, which is equivalent to about 1/2 of China s onshore and offshore oil and gas resources. .

Subsea resources The Xisha Trough is located in the Cenozoic passive continental marginal sedimentary basin in the northern slope of the South China Sea. The Cenozoic has a maximum sedimentary thickness of more than 7000 m and is active in faults. Water depth is greater than 400m. Based on the application of the National 863 Research Project "Deepwater Multichannel High Resolution Seismic Technology", reliable seismic signs of natural gas hydrate existence were obtained: 1) A strong BSR display was found on the northern slope of the Xisha Trough Basin and the platform depth of 200-700m in the south. Obvious oblique intersection between BSR and stratum can be seen in some survey lines. 2) The amplitude is abnormal. Weak amplitude or blank bands appear above the BSR, which are distributed in layers and blocks, with a thickness of 80-450m. 3) Compared with the reflected wave on the sea floor, the BSR waveform has obvious reverse polarity. 4) The amplitude blank band above the BSR has a clear tendency of increasing velocity. Data show that the area of natural gas hydrate in the Xisha Trough in the northern South China Sea is large, and it is a favorable natural gas hydrate remote area.

In 2001, with the support of the Chinese Ministry of Finance, the China Geological Survey of China continued the investigation and research of natural gas hydrate resources in the northern waters of the South China Sea, and plans to conduct a high-resolution multi-channel seismic survey of 3500km in the waters near the Dongsha Islands. In the Xisha Trough area, sediment sampling and supporting geochemical anomaly detection at 35 stations and other multi-beam submarine topographic detection, submarine television cameras, and shallow profile measurements were performed. In addition, according to the data of the National Taiwan University's Oceanographic Research Institute and the China National Petroleum Corporation of Taiwan, BSR is widely distributed in southwestern Taiwan with water depth of 500-2000m, and its area is 2 × 104km2. In addition, a large area of white gas hydrate reservoirs was found on the southeast Taiwan seabed.

Polymetallic nodules

In 1873, the British Challenger conducted the first global ocean survey and collected a black ball in the Atlantic Ocean. Because its main components are manganese and iron, it is called "manganese ore balls". Later, it was discovered that the ore ball had a core and a continuous growing layer, so it was renamed "manganese nodules". Recently, more than 60 metal components such as copper, cobalt, nickel, lead, zinc, aluminum, and rare earth elements have been analyzed from it, so it is also called "polymetallic nodules". Tuberculosis varies in shape and size, but it is mostly brown-black and round in shape, with diameters ranging from less than 1 mm to several tens of centimeters, and a few more than 1 meter.

Polymetallic nodules are mostly distributed on the surface of the ocean floor at a depth of 4-6 kilometers. It is estimated that its reserves are about 3 trillion tons and its recoverable potential is about 75 billion tons. The total reserves of manganese contained in it are 779 times that of land, 36 times that of copper, 5250 times of cobalt, 405 times of nickel, 4.3 times of iron, 75 times of aluminum, and 33 times of lead. Based on world consumption in the 1980s, it can be used by humans for thousands to hundreds of thousands of years. Because nodules are formed by inexhaustible seawater gelation, they are a growing resource. 10 million tons of new reserves are added each year, and its growth rate is faster than human consumption! Therefore, this type of minerals alone is enough to give mankind a strong motivation to march to the ocean.

Cobalt-rich crust

Cobalt-rich crusts are produced on sea-hill slopes with flat top surfaces and steep two wings, with a water depth of 1 to 3.5 kilometers. The color is black like coal, light and brittle, and the surface is like a flower bud-like shell, and the thickness is generally a few millimeters to a dozen centimeters. The cobalt content of the cobalt-rich crusts can be as high as 2%, which is 20 times that of terrestrial cobalt-bearing deposits; the platinum content of precious metals is also equivalent to 80 times that of platinum on land. The potential resources of cobalt-rich crust deposits amount to 1 billion tons, with a total value of more than 100 billion US dollars. Therefore, the development of marine mineral resources has been a hot spot since the 1980s. China also kicked off the formal investigation of cobalt-rich crusts in the mid-1990s.

Combustible ice molecular composition Formation and distribution of cobalt-rich iron-manganese crust oxidized deposits throughout the world's oceans, concentrated on the slopes and tops of seamounts, ridges and platforms. For millions of years, ocean floor currents have cleared these ocean floor sediments. Some of these seamounts are as large as the mountains on land. There are about 50,000 seamounts in the Pacific Ocean, and their cobalt-rich crusts have the most abundant reserves, but few seamounts have been surveyed and sampled. There are far fewer seamounts in the Atlantic and Indian Oceans. The minerals in the crust are likely to be assisted by bacterial activity to precipitate from the surrounding cold sea water to the rock surface. The crust forms a paved layer up to 25 cm thick with an area of many square kilometers. It is estimated that approximately 6.35 million square kilometers of the ocean floor (1.7% of the ocean floor area) is covered by cobalt-rich crusts. Based on this calculation, the total amount of cobalt is about 1 billion tons. Crusts cannot form where the surface of the rock is covered by sediment. Crusts are distributed on the ocean floor at a depth of about 400-4, 000 meters, and polymetallic nodules are distributed on the ocean floor at a depth of 4,000-5,000 meters. The thickest crusts have the most abundant cobalt content, formed on the outer terraces of the seamounts at 800-2,500 meters deep and the wide saddles on the top.

Crusts generally grow at a rate of one molecular layer every 1 to 3 months (that is, 1 to 6 millimeters per 1 million years), which is one of the slowest natural processes on the planet. Therefore, it can take up to 60 million years to form a thick crust layer. Some crusts have shown that the crust has experienced two formation periods in the past 20 million years, and the ferromanganese accretion process was interrupted by a layer of Phosphate and Calcareous soil formed 8 million to 9 million years ago. This layer's separation between new and old material can provide clues for finding older, richer deposits. The abundance of ore deposits in the lowest oxygen-containing layers has led investigators to attribute part of the enrichment of cobalt to the low oxygen content of seawater. According to conditions such as grade, reserves and oceanography, the crust sites with the most potential for mining are located in the Central Pacific near the equator, especially around Johnston Island and the U.S. Hawaiian Islands, Marshall Islands, and the Federated States of Micronesia. Economic Zone, and the Central Pacific International Seabed Area. In addition, the crust has the highest proportion of mineral content in shallow water depths, which is an important factor in mining.

Features and Compositions In addition to cobalt, crusts are an important potential source of many other metals and rare earth elements, such as titanium, cerium, nickel, platinum, manganese, phosphorus, hafnium, tellurium, zirconium, tungsten, bismuth and molybdenum. The crust is composed of hydroxanthite (manganese oxide) and hydrofiberite (iron oxide). Thicker crusts have a certain amount of carbon apatite, and most crusts contain a small amount of quartz and feldspar. The crust cobalt content is very high, which can be as high as 1.7%; on a large area of some seamounts, the crust cobalt content can be as high as 1%. The content of these cobalt is much higher than 0.1% to 0.2% of land-based cobalt ore. After cobalt, the most valuable minerals in the crust are titanium, cerium, nickel, and zirconium. Another important consideration is the contrast in physical properties between the crust and the bedrock to which it is attached. Crusts are formed on various types of rocks, so it is difficult to distinguish crusts from their bedrock using ordinary remote sensing techniques. However, crusts differ from bedrock in that they emit much higher gamma rays. Therefore, thin crusts overlying sediments and surveying crust thickness on seamounts

Hydrothermal fluid Remote sensing with gamma rays may be a useful tool. When looking for crusts that can be mined in the future, miners are likely to pay attention to the following characteristics. Including: the sea mountain with a water depth of not more than 1,000-1,500 meters and an age of more than 20 million years. There is no large atoll or reef on the top. It is a mature hypoxic zone, away from rivers and wind-laden debris that are injected into the ocean. In addition, the sea floor they are looking for should be undulating, located on a mountaintop terrace, saddle-like zone, or pass, with a gentle slope and no local volcanic activity. The average cobalt content shall be at least 0.8% and the average crust thickness shall not be less than 4 cm.

Industrial applications The metals contained in cobalt-rich crusts (mainly cobalt, manganese, and nickel) are used in steel to increase special properties such as hardness, strength, and corrosion resistance. In industrialized countries, about one-quarter to one-half of cobalt consumption is used in the aerospace industry to produce superalloys. These metals are also used in the chemical and high-tech industries to produce photovoltaic and solar cells, superconductors, advanced laser systems, catalysts, fuel cells and powerful magnets, as well as cutting tools.

The survey conducted to date was the first systematic survey of crusts in the Central Pacific in 1981. Early work was carried out by research teams in Germany, the United States, the former Soviet Union (later the Russian Federation), Japan, France, the United Kingdom, China and South Korea. The United States, Germany, the United Kingdom and France have completed field investigations. The most detailed investigations are deposits in the equatorial Pacific, mainly in the exclusive economic zones of many island nations. About 42 research voyages (1981-2001) surveyed cobalt-rich crusts and other deep-sea deposits in Pacific waters, with field and research costs totaling $ 70 million to $ 100 million. Since 1985, Japan has conducted many of these surveys for developing island nations in the South Pacific Applied Geoscience Commission (SOPAC) under a 15-year project.

Future exploration and mining In order to determine the location of potentially more productive areas, prospective miners will first need to draw detailed crust deposits and small-scale integrated sea-mountain landforms, including seismic profiles. Once the sampling stations are identified, trawls, core samplers, and sonar and video cameras can be deployed to identify the types and distribution of crusts, rocks, and sediments. To this end, a large, fully-equipped research vessel is needed to operate submarine sonic beacons and towing equipment, and to process a large number of samples. Manned submersibles or remotely operated systems (ROV) are required at a later stage. For environmental assessments, anchorage equipment and biological sampling equipment need to be deployed. The technical difficulty of mining crusts is much higher than that of polymetallic nodules. Collecting nodules is easier because nodules are formed on the base of loose sediments, while crusts are loosely or tightly attached to bedrock. In order to successfully mine crusts, it is necessary to avoid collecting too much bedrock when crusts are recovered, otherwise the ore quality will be greatly reduced. One possible crust recovery method is to use a submarine crawler mining machine with a hydraulic riser system and connection cables to the surface vessel. The articulated cutter on the mining machine will crack the crust while minimizing the amount of bedrock collected. Some innovative systems that have been proposed include: separating crusts from bedrock with hydrojets; in situ chemical leaching of crusts on seamounts to separate crusts with acoustic waves. Except for Japan, research and development on crust mining technology is limited. Despite various ideas, research and development of this technology is still in its early stages.

The seamount environment requires more research on the nature of seamount biomes in order to accumulate reliable evidence and make recommendations on environmental issues caused by crust exploration and mining. Except for their complex and changing characteristics, little is known about these communities; two seamounts located at the same depth may have completely different biological compositions. The composition and characteristics of seamount biological communities are determined by factors such as flow patterns, landforms, seafloor sediments and rock types and coverage areas, seamount sizes, water depth, and seawater oxygen content. It is also important to understand the currents around the seamounts in order to develop appropriate mining equipment and technology, and to determine the diffusion pathways of disturbed sediment particles and waste. Seamounts block the flow of ocean currents, producing a variety of stronger eddies and upwellings, thereby increasing the primary productivity of organisms. The effects of these currents are most intense on the outer edge around the top of the seamount, and it is in these places that the thickest crusts are found.

Economic factors In addition to the cobalt content higher than that of deep-water manganese nodules, the exploitation of crusts is considered to be beneficial because high-quality crusts are stored in the exclusive economic zone of island countries, with shallow water depths and waters close to coastal facilities. . In the late 1970s, especially in 1978, when the civil war broke out in the mining area of the world s first cobalt-producing country, Zaire (now the Democratic Republic of the Congo), cobalt prices soared, and people had a deep understanding of the economic potential of crust . As production in the Democratic Republic of the Congo continues to decline, by 2000, the total output of Zambia, Canada and the Russian Federation accounted for more than half of the global total (29,500 tons) (see chart).

Cobalt, like many other base metals, has continued to fall in spot market prices over the past 30 months, from more than $ 20 per pound in May 1999 to less than $ 10 per pound. Historically, cobalt prices have fluctuated significantly. During the unrest in Zaire's Sabah pre-1979, cobalt prices tripled in a matter of weeks. At that time, Zaire accounted for about half of global supply. Cobalt production is now much less geographically concentrated than before. However, in the short and medium term, demand still tends to lack price elasticity. As long as supply issues are considered to be possible, prices can still multiply rapidly.

One reason for the uncertain supply of cobalt is that it is a by-product of the copper mining industry in the two major producers, Zaire and Zambia. Therefore, the supply of cobalt depends on the demand for copper. The same is true for the supply of tellurium. This uncertainty has prompted companies to look for alternatives, so the market has only grown slightly. If other important sources can be developed for these metals, this will provide a stronger incentive to reuse them in products and increase consumption. The demand for one or more crusts other than cobalt that are rich in metals may ultimately be the driving force behind crust mining.

Despite the aforementioned economic and technical uncertainties, at least three companies have expressed interest in mining crusts. Some new situations (for example, land use priorities, freshwater issues, and environmental concerns in terrestrial mining areas) may change the economic environment and promote marine mining activities. Increasingly, it is now recognized that cobalt-rich crusts are an important potential resource. Therefore, research, exploration and technological development must be used to fill the information gaps in all aspects of crust mining.

Seabed resources combustible ice

Combustible ice composed of submarine natural gas hydrate is an ice-like solid substance synthesized from gas and water under low temperature (-10 + 100C) and high pressure (1 9Ma) conditions. It has a strong ability to store gas. A unit volume of natural gas hydrate can store 100 to 200 times the gas storage capacity of this volume. The useful component of natural gas hydrate is mainly methane, in addition it also contains a small amount of H2S, CO2, N2 and other hydrocarbon gases.

The locations where combustible ice is distributed to develop natural gas hydrates are mainly distributed in the northern hemisphere, with the Pacific Ocean marginal waters the most, followed by the western Atlantic coast. From the perspective of the tectonic environment, they are mainly distributed on the continental margins: one is the continental slopes and slope feet distributed on the passive continental margins, and the other is the accretionary wedge development area on the active margins. At present, there are 57 natural gas hydrate locations discovered through drilling and inferred from the BSR (Submarine Simulated Reflective Layer), including 25 in the Pacific Ocean, 1 in the Indian Ocean, 6 poles in the Arctic Sea, 6 in the Southern Ocean, 17 in the Atlantic Ocean, and lakes and marsh areas Black Sea, Baikal). However, little is known about the distribution of natural gas hydrates in deep ocean basins, which account for most of the ocean. The reason for this is that the area under investigation for gas hydrates has not yet entered the ocean basin.

The necessary conditions for the formation of flammable ice to form natural gas hydrates include: interstitial water is filled in organic-rich sediments, hydrodynamics in deep waters are in a state of stagnation, there are biogenic gases, or there are pyrolysis causes entering from underlying formations Gases with specific pressure and temperature conditions. There are two possible modes of formation of natural gas hydrates: natural gas hydrates are part of the existing natural gas reservoirs, and then consolidate to gas hydrates in situ due to favorable temperature or pore pressure; microbial genesis gas or pyrolysis The formation of gas from the lower gas to the gas hydrate stability zone.

Resource potential and environmental problems Compared with the reserves of conventional natural gas fields, the potential natural gas resources in subsea gas hydrates are extremely large. According to the preliminary statistics of the International Gas Potential Commission, the total amount of natural gas hydrates in the world's oceans converted into methane gas is about 1.8-2.1x1016m3, which is equivalent to about twice the total reserves of coal, oil and natural gas in the world. It is considered as a new energy source with great potential for development in the 21st century. On the other hand, submarine gas hydrates have attracted great attention from the scientific community as a potential geological disaster and an unstable factor in global climate change.

Deep sea hydrothermal fluid

"Hydrothermal sulfide" mainly appears on the mid-ocean ridge and fault active zone at a depth of 2000 meters, and is an important mineral resource containing copper, zinc, lead, gold, silver and other elements. Regarding its formation, marine scientists believe that "hydrothermal sulfides" are seawater that invades seafloor cracks, is heated by heat sources deep in the crust, dissolves a variety of metal compounds in the crust, and then emits smoke from the ocean floor. The condensed eruption is called "black chimney". These black chimneys that grew billions of years ago can not only spray gold and spit silver, form submarine mineral deposits, and have a good prospect for development. And it is probably related to the origin of life and has great biomedical value.

The "black chimney" is a sulphide deposit standing on the bottom of the ocean. It has a thin, thick, cylindrical shape, and is called a "black chimney" by scientists because it looks like a chimney. Their diameters range from a few centimeters to 2 meters and their heights range from a few centimeters to 50 meters. The "black chimney" accumulation group and its deposits located on the sea floor are a bit like complex spires of church or temple buildings. Large-scale deposits can reach more than one million tons of gym size. Experts believe that the formation process of the "black chimney" on the sea floor is very complicated, and it is related to the differences between the composition and temperature of the mineral liquid and seawater. Due to the high temperature of the crust of the neo-oceanic ocean or the rift crust of the sea floor, seawater penetrates down the cracks up to several kilometers. After heating and heating in the deep crust, it leaches and dissolves many metal elements in the rocks, and rises along the convection of the cracks And erupted on the sea floor. When they were sprayed, they were clear solutions. After mixing with the surrounding seawater, they quickly turned into "black smoke" and accumulated into sulfides on the sea floor and in shallow passages. At present, scientists have found "black chimney" areas in more than 150 places in various oceans, which are mainly concentrated on the crust of the neo-ocean ocean, such as the location of the mid-ocean ridge and the post-arc basin expansion center. In 2003, "Ocean One" conducted China's first special investigation of hydrothermal sulfides in the ocean floor, which kicked off the entry into the field of oceanic polymetallic sulfides. After long-term unremitting "tracking", the complete "black chimney" of the ancient ocean floor was finally found, and their geological age was initially judged to be 1.43 billion "years". Previously, this not only further understood the distribution and resource status of hydrothermal polymetallic sulfides in the ocean floor in the deep ocean, but also paved the way for a new qualitative leap in the theory of earth sciences.

Hydrothermal distribution Scientists have now found many hydrothermal eruptions on the mid-ocean ridges. Hydrothermal deposits associated with hydrothermal activity can occur not only in the middle of the mid-ocean ridge, but also on both sides, even in marginal seas such as the Okinawa Trough. In addition, in the hydrothermal area, various special hot water biological populations live around the black chimney, which is stunned!