1) background and significance of microbial mineralization research.
As one of the most active geological forces on the earth's surface, biological action can directly form combustible organic minerals. A series of achievements have been made in the biomineralization research of some nonmetallic minerals such as sulfur and phosphorus, and the biomineralization research of metal deposits is also being carried out in depth. Microorganisms can participate in many stages, such as sedimentation, diagenesis, structure and metamorphism, mineralization and weathering. However, in different stages of mineralization, the importance and manifestations of microbial mineralization are completely different. Specific to a certain mineralization stage of a particular deposit, some biological actions may be dominant. Modern biological research and various experimental results (such As biomineralization test and industrial wastewater microbial treatment test) show that microorganisms and their organic matter can separate many rare dispersed elements such as P, Fe, Mn, Mg, Cu, Pb, Zn, V, U, Cr, Ni, Mo, Co, Au, Ag, Pt, Hg, S, As, Se, Sb and I. To sum up, there are several ways for microorganisms to participate in the formation of ore deposits (Zhu Shixing, 1993):
(1) The function of microorganisms to directly aggregate ore-forming elements: microorganisms have the function of directly absorbing and adsorbing various elements or minerals due to physiological needs. Microorganisms have amazing ability to enrich a variety of metal elements. Under different environmental conditions, their enrichment coefficients vary greatly and there is selective enrichment. For example, in marine biota mainly composed of algae and bacteria, the concentration of many elements can be hundreds to hundreds of thousands of times higher than that of seawater. Some experimental studies in the United States and Canada have proved that algae, especially Chlorella, have strong gold adsorption ability, and many microorganisms have amazing gold accumulation ability. For example, the seaweed mat in Lake figueroa, California contains 65,438+08 kg/ton of gold. At present, besides iron and manganese, gold, silver, copper and lead are the most widely studied metal elements in microbial aggregation. There are only two mechanisms of microbial immobilization of metals in microbial mineralization: one is through the medium; The other is that cells interact directly with metals. Many metal elements are very toxic to organisms, but organisms are very resistant to toxicity in some environments. Biologists have found that organisms can eliminate these unfavorable factors in many ways and have strong absorption ability for some highly toxic metals. These anti-toxicity mechanisms of microorganisms provide the possibility for organisms to participate in mineralization, because in some unfavorable environments (such as high metal concentration), the anti-toxicity function of organisms will upset the balance between solid and liquid phases, thus leading to the enrichment of metals in the solid phase.
(2) Biochemical sedimentation of microorganisms: microorganisms are of universal significance to mineralization in changing the physical and chemical parameters of the environment. Its metabolism can not only cause the transformation of the binding relationship of related elements and the formation of new minerals, but also change the pH value and redox potential of the surrounding solution, thus creating a microenvironment conducive to the precipitation of some new minerals. For example, sulfide bacteria can oxidize sulfur to form sulfate radicals, thus forming sulfate minerals; Anaerobic respiratory anti-sulfide bacteria can reduce sulfate to generate hydrogen sulfide, which will react with metals to generate various metal sulfides and form reduced metal minerals. Microorganisms not only form a local reduction environment under oxidation conditions, but also have an interface to change chemical conditions.
(3) Biophysical sedimentation of microorganisms: Modern stromatolite research shows that filamentous stromatolite microorganisms with mucilage sheaths have a strong binding and capturing effect on mineral particles or ore-bearing cuttings in seawater due to their dynamic action (vibration and smoothness). Stromatolite columns formed by microorganisms and their bioreefs suddenly change (reduce) hydrodynamic conditions, so that transported minerals or ore-bearing debris are physically deposited and enriched between stromatolite columns or before and after their bioreefs.
(4) Organic substances produced by microorganisms participate in mineralization: after the death of microorganisms, they can be metabolized or decomposed to produce various organic substances, such as organic acids, organic bases, organic colloids and carbonaceous substances. These organic matters have low thermal stability and play an important role in the activation, migration, precipitation and enrichment of ore-forming elements. Some of these organic substances form complexes-chelates with metals and enter sediments, releasing metals or being replaced to form more stable complexes during diagenesis; Some (organic colloids and particles) can enrich a large number of metal ions through physical adsorption. Some (such as organic carbon) are reducing agents, which reduce soluble high-valent ions to insoluble low-valent ions, thus precipitating and enriching. For example, in Japan, when sludge containing humic acid is used to treat heavy metal wastewater, the removal rate of mercury, cadmium, copper, nickel and zinc plasma is over 98%. In China, the experiment of treating industrial wastewater containing mercury, lead, cadmium, copper, zinc, chromium, nickel and cobalt plasma with humic acid coal and humic acid resin has also achieved ideal results. In recent years, the study of organic matter in fluid inclusions of ore deposits further shows that organic matter is one of the evidences that microorganisms participate in mineralization.
2) The research content of microbial mineralization.
(1) Evidence and signs of biomineralization. In order to carry out this work, we must first have sufficient evidence and signs of biomineralization. Therefore, three aspects need to be studied: ① Paleontology and its biological sedimentary structures (such as stromatolites, crystal nuclei, beads, clots, etc. ) and put forward the direct evidence of biomineralization; ② Study on biomineral crystallography, trace elements, stable isotopes and organic geochemistry of ore-bearing rock series, ore-bearing beds and interlayers, respectively, to determine the indirect signs of biomineralization and the types and characteristics of their markers; ③ By comparing the ore-bearing rock series with non-ore-bearing rock series and other ore-bearing rock series, the characteristics and exclusive relationship of paleontological and biogeochemical indicators related to the deposit are determined.
(2) The model and mechanism of biomineralization. (1) Combine the above paleontological and biogeochemical data with the geological background, lithofacies palaeogeography, ore structure and structural data of the deposit formation, and put forward the inference opinions on the biomineralization model and mechanism; (2) Carry out simulation experiments, combine with other experimental results (such as a large number of experimental data of industrial wastewater treatment) to enrich and improve the above reasoning, and finally put forward scientific opinions on the model and mechanism of biomineralization.
(3) The relationship between mineral zonation and biological facies zonation. In order to explore new prospecting criteria, the following work should be done: ① study the mineral zoning in the deposit and understand its specific temporal and spatial distribution law; (2) study the zoning of paleontological facies and sedimentary facies in the deposit and clarify its relationship with mineral facies zoning; ③ Study and determine the biogeochemical and biomarker characteristics of different ore zones (Zhu Shixing, 1993).
Through the above research, the distribution law and prospecting direction of different deposits are finally summarized with new data and viewpoints. It not only has scientific metallogenic theory, but also points out practical prospecting criteria. In the above research, we should mainly study the evidence and signs of biomineralization, because they are the starting point and the most basic foothold for forming conclusions.
3) New progress in microbial mineralization.
The minerals that have been studied more about microbial mineralization mainly include iron, manganese, gold, copper, sulfur and phosphorus. (Yin Hongfu et al., 1994).
For iron ore, microbial mineralization is certain. Biogas iron ore, lake iron ore and ocean iron ore were once considered as the origin of bacteria. More and more microfossils have been found in Precambrian banded iron-bearing formations, such as iron deposits related to microbial action in China, Australia and Canada. However, there is not much direct evidence of biomineralization, which still depends on the "biogenetic structure" existing in the sedimentary environment. In recent years, a class of magnetotactic bacteria that can synthesize magnetite in their cells has been discovered, which provides direct evidence for bacteria to participate in mineralization, which is a great progress in the study of iron biomineralization. Japanese and China scholars reported that there are many similarities in structure between modern biological banded iron ore and ancient microbial iron ore (Long Xuan type).
There are many researches on biomineralization of manganese deposits, such as Nikopol in Ukraine, Tannengebirge in Austria, Chiatura in Georgia, Groote Eylandt in Australia and Xiangtan manganese deposits in China, but most of them are inferred as biomineralization according to biogenetic structure. Clear sedimentary and isotopic geochemical evidence was found in the Sinian manganese carbonate deposit in southern China, indicating that organic matter actively participated in the mineralization process. In recent years, a series of manganese oxide bacteria have been isolated from manganese nodules on the seabed, and it has been further found that many manganese nodules are manganese stromatolites. This discovery opens up a new research direction of manganese biomineralization-the relationship between ultrastromatolite and manganese ore. In recent years, manganese minerals in polymetallic nodules have been found to be biogenic in the Clarion-Clipperton basin in the eastern Pacific Ocean, and the crust of nodules is biostromatolite. It is found for the first time that coccidia Pacific and actinomycetes China only exist in the biological structure of stromatolites, indicating that they are biogenic nodules, and it is considered that iron, manganese and other ore-forming elements in nodules are the products left after the seabed nano-organisms are absorbed into the body from seawater solution and die. China scholars also put forward microbiological evidence of iron and manganese differentiation.
Gold is usually an inactive element, but it is very active in living things. Gold has remarkable biological characteristics, and many organisms can accumulate gold. The Witwatersrand glutenite-type gold-uranium deposit in South Africa has been widely studied, and many fibrous particles show biological structure. There are also many researches on the biochemical causes of placer gold, such as those in Alaska and China, which are considered to be related to bacterial action. The microbial structure of gold mineralization was discovered in Alaska placer gold mine. After gold is completely dissolved, a spore similar to soil microorganism can be seen, which is the most significant progress in the study of microbial mineralization of gold. At the 30th International Geological Congress, there were many papers on the genetic relationship between microorganisms and gold deposits. In recent years, important progress has been made at home and abroad, such as the discovery of the structure of bacteria and microorganisms in lump gold, and it is also reported that some kinds of algae have obvious ability to enrich gold. Bacteria and molds isolated from Longgou Gold Mine in Baikonggou, Sichuan, China have strong gold accumulation ability. They have dual functions, adsorbing and accumulating gold in the early and middle stages of growth, and reducing gold in the later stage of growth.
For sulfide deposits such as copper, lead and zinc, firstly, organisms and their organic matter can reduce or metabolize organic sulfides to provide S2-; Secondly, many microorganisms, such as spores and hyphae of fungi, can absorb a considerable amount of copper, lead and zinc. The research of biomineralization mainly focuses on the stratabound copper deposits containing stromatolites in Proterozoic, copper deposits in copper-bearing shale, lead-zinc deposits in Mississippi valley and contemporaneous exhalation lead-zinc deposits. This microbial mineralization can be seen near the hot spring vents on the mid-ocean ridge in modern times, where microorganisms such as bacteria that ingest copper, lead and zinc from the vents live.
There are also many studies on microbial mineralization of sulfur, phosphorus and other minerals. In addition, some achievements have been made in the study of microbial mineralization of uranium, tungsten, silver and bauxite.
4) The key research direction of microbial mineralization.
The theoretical research of microbial mineralization is carried out late, and there are many fields to be studied. We can focus on the following aspects (Yin Hongfu, 1994):
(1) "Biological-Organic-Fluid" metallogenic system. At present, although the research on biomineralization has obtained many evidences that microorganisms participate in mineralization, there is still a lack of systematic research on biomineralization, and it is difficult to make a big breakthrough in isolated biomineralization research. It is necessary to study the evolution of biomineralization from the perspective of development. Therefore, it is particularly important to study the "biological-organic-fluid" metallogenic system. This is to study the evolution of biomineralization from the viewpoint of the development and connection of metallogenic system, that is, to systematically study the biomineralization (such as preconcentration), biomineralization of various organic substances (such as dissolution and enrichment), and then mineralization of organic fluids.
There is a "biological-organic-fluid" metallogenic system in the basin-orogenic belt. As early as the early 1970s, people have noticed the possible causes and spatial relationship between oil and gas deposits and some metal deposits. For example, a large lead-zinc mine in Pinepat was discovered near Albert Oilfield in northwest Canada, and a Colorado Plateau-type K-V-U deposit was discovered in the oil-bearing area of Somalia. In recent years, not only some metal deposits have been discovered in oil and gas areas, but also it has been further discovered that oil and gas fields may be related to some active metal deposits. At present, the research has developed to the stage of discussing the relative positions and survey marks of metal deposits in oil-gas-bearing basins, involving mercury, antimony, uranium, molybdenum, gold, copper, lead, zinc and other deposits. The study of inclusions in metal deposits associated with oil and gas deposits shows that the ore-forming fluid of metal deposits is similar to oilfield brine, and the organic matter in the ore-forming fluid also has similar properties. The study of "biological-organic-fluid" metallogenic system reveals the essential relationship between the two types of deposits: when the original basin was deposited, a large number of organisms laid a material foundation for the formation of oil and gas, and at the same time pre-enriched metal-forming substances, which provided a material basis for the formation of metal deposits; In the process of diagenesis, organisms are transformed into organic matter and organic thermal fluid, which can dissolve, extract and enrich integrated metal substances; During the orogenic activity in the primitive basin, the organic thermal fluid migrated to the orogenic belt, and the fluid carried a lot of ore-forming materials, which made the metal ore-forming materials migrate. The circulation and confluence of different fluids (such as organic fluids in oil and gas basins and fluids rich in metals in orogenic belts) will eventually lead to the formation of metal deposits. The study of the metallogenic system can not only improve and deepen the above-mentioned theories of biological mineralization and fluid mineralization, but also guide the prospecting work.
(2) The mechanism and conditions of biomineralization in modern and ancient times are comprehensively compared and studied. Discussion from the past is now an important principle in the field of earth science. Many understandings of biomineralization also come from the direct observation and research of modern biomineralization, such as biomineralization in the hot spring spout area of the mid-ocean ridge, bacterial genesis of manganese nodules in the ocean, bacterial or biochemical genesis of placer gold mines, and the discovery of magnetotactic bacteria for synthetic magnetite. The study of modern biomineralization is helpful for us to understand the mechanism of biomineralization, such as the ways of biological enrichment and metal precipitation, as well as the biophysical and morphological characteristics involved in mineralization. Only by solving these problems can we convincingly study the biomineralization of ancient typical deposits, understand the changes and functions of paleontology in different stages of rock deposition, diagenesis and metamorphism, understand the paleontological mineralization process, and avoid discussing biomineralization only from morphological characteristics. Therefore, it is a very important research direction of biomineralization theory to study biomineralization in modern geological history, that is, to study the deposits formed by biomineralization.
(3) Comprehensive study on microbial mineralization from the perspective of other related branches of biogeography: biomineralization is an interdisciplinary subject between biology and sedimentary science. Its research must be combined with relevant disciplines of biogeography, such as biomineralization and biogeochemistry. For example, some bacteria will reduce gold ions and grow into crystals after adsorption, and the gold crystals will fall off from the bacteria when they grow up. Therefore, it is necessary to study the gold crystallization caused by these bacteria in detail from the perspective of biomineralization, so as to distinguish the organic and inorganic causes of these minerals, provide evidence for biomineralization and develop biomineralization theory.
In a word, we must study and develop the theory of biomineralization from two aspects: one is to study the internal factors of organisms, such as the mechanism and process of biomineralization, and the other is to study the external conditions, such as sedimentary environment. In a word, it is the key to develop biomineralization theory to study the evolution of biomineralization systematically, comprehensively and systematically.