What Is Coal Geology?
Coal geology is based on the geological theory, and studies the material composition, genesis, properties and distribution of coal, coal seams, coal-bearing rock series, coal basins, and other minerals (oil shale, coal gas, etc.) that are associated with coal Subject. Also called coalfield geology. It is an early branch discipline in geology. Coal geology is closely related to geotectonics, structural geology, sedimentology, mineralogy, geophysical prospecting, and petroleum geology.
Coal geology
1. The concept of coal: Coal is a solid combustible organic rock.
2. The concept of coal formation: from plant death and accumulation to conversion to coal, it has undergone a series of complex biochemical, physical chemistry, and geochemical changes. These effects are collectively referred to as coal formation.
3. Two stages of coal formation: the first stage is the sludge stage or the peat stage. At this stage, the remains of the plants are decomposed, combined, and accumulated by the microorganisms. The lower plants are transformed into saproli, and the higher plants are transformed into peat. The second stage is the stage of coalification. Due to crustal subsidence, peat or saprolite formed after the death of the plant is buried deep in the ground, and consolidation diagenesis and metamorphism occur under temperature and pressure conditions. The role that peat transforms into young lignite is diagenesis. The role that young lignite, old lignite, bituminous coal and anthracite undergo is called metamorphism.
1. The relationship between the evolution of plants and coal formation: Plants are the main raw materials for coal formation, so the evolution of plants directly affects the formation of coal. Bacteria and algae era. Archaic to Early Devonian. Early vascular plant era. From late Silurian to Middle Devonian, aquatic plants transitioned to terrestrial plants. Age of ferns and ancient gymnosperms. Late Devonian to Late Permian, the period of higher plant prosperity, typical plants are tall trees, coal accumulation is strong, Carboniferous-Permian is the first coal accumulation period. Age of gymnosperms. From the Late Permian to the Mesozoic, under the influence of Haixi and Indosinian tectonic movements, the land area expanded and the terrain height difference was obvious. Jurassic and Early Cretaceous were the second largest coal accumulation periods. Jurassic coal resources in western China are about 60% of the country's total coal resources. Angiosperm era. From the Early Cretaceous to the Paleogene and Neogene, the tectonic activity was strong and the climatic zone was obvious. It was the third largest coal accumulation period.
2. Plant composition
Plants are mainly composed of carbohydrates (cellulose, hemicellulose and pectin), lignin, proteins and lipids. Lower plants are mainly composed of proteins and carbohydrates and have higher lipid content. Higher plants are predominantly cellulose, hemicellulose and lignin.
Carbohydrates (cellulose, hemicellulose and pectin)
Cellulose is the main substance that forms the cell wall of plants, and is easy to hydrolyze.
Lignin
Lignin is also the main substance constituting the plant cell wall, which is more stable than cellulose and less prone to hydrolysis. Decomposed by microorganisms in swamp environment and participate in the formation of humus.
protein
Protein is the main substance of plant cytoplasm, which accounts for a small proportion in plants and is highly hydrophilic. N and S in coal are related to plant proteins.
Lipid compounds
Insoluble in water, soluble in organic solvents. Lipid compounds include fats, waxes, resins, cutin, sclerostin, and spores. Fat is relatively stable and decomposes to form fatty acids; waxy, resinous, keratinous, and sclerostinous properties are stable; spores and pollen properties are very stable; it can withstand certain temperatures and acid and alkali treatments, and is often stored in coal.
1.The concept of swamps
A swamp is a low-lying area where the surface soil is fully wet, seasonal or long-term water accumulation, and is crowded with wet plants. The marshes that form peat deposits are called peat bogs. It is neither real land nor water, but a transition state between the two.
2. Formation and accumulation of peat
After the plant dies, it is decomposed, synthesized, and accumulated through biochemical action. When the amount of organic matter exceeds the amount of decomposition, a peat layer is formed. The peat swamp vertical profile is divided into three layers: the surface layer (oxidized environment), the middle layer (transitional seascape), and the bottom layer (reduced environment).
3. Plant debris accumulation
It is mainly piled up in situ, and a few are piled up in different places. Most of the coal seams of industrial mining significance are piled up in situ.
Peat bog
1. Types of peat bogs
According to the surface morphology, water supply, nutrition and vegetation characteristics of peat bogs, it can be divided into three types:
Low peat swamp
The lower peat swamp has a higher diving level, sufficient water supply, rich nutrition, and lush vegetation. Easy to peat layer.
High Peat Swamp
The high-level peat swamp has a low diving level. The water supply is mainly dependent on precipitation and poor nutrition. Most of them are herbs and moss, which is not conducive to the formation of peat layers.
Median peat swamp
The state of the median peat bog is somewhere in between.
2.Development area of peat bog
The coastal plain. Has a low peat swamp development environment.
Inland rivers and lakes.
Mountainous and plateau areas.
3.The way peat bogs are formed
The waters are transformed into peat bogs, which include three modes:
The shallow shore lake is transformed into a peat swamp, and the plant growth type has a zoning phenomenon. During the formation of peat, the lake water continues to become shallow and the plant type changes accordingly.
The deep-water steep bank lake was transformed into a peat bog. After the phytoplankton died, it sank to the bottom of the lake and turned into peat.
The river is transformed into a peat bog, similar to a shallow-water slow-shore lake transformation model.
land swamp
Closed depressions on the ground may form swamps.
Section 4 The main composition and properties of peat
1. Chemical composition of peat
In addition to a large amount of water, peat also includes organic matter and minerals.
Organic matter. Including plant debris and humus.
Peat organic matter content refers to the percentage of organic matter in the total dry matter of peat. China's peat is dominated by herbaceous peat, with an organic matter content of about 60%.
Organic matter: C: 55%, O: 35%, H: 6%, N: 2%, S: 0.3%
In peat organic matter, the substance extracted with dilute alkali solution is called humic acid, which is a characteristic component of peat. Humic acid is not a single compound but a mixture of hydroxyaromatic carboxylic acids with different molecular sizes and different structures.
Minerals
The minerals in the peat are mainly derived from the minerals in the wind and water currents, which are converted into peat components through sedimentation. Common minerals are quartz and secondary clay minerals. The element is mainly silicon, followed by iron, aluminum, calcium, and magnesium. Another source of minerals is the plant itself.
2. Physical and chemical properties of peat
Degree of decomposition: refers to the relative content of plant residues that have lost cellular structure due to decay, or the percentage of amorphous humus in organic matter in peat
water content
There are two ways to express humidity and water holding capacity. Peat humidity refers to the percentage of moisture in peat to the total weight of peat. Water holding capacity refers to the percentage of moisture in peat dry matter weight.
Specific gravity and bulk density of peat
The specific gravity of peat is generally around 1.4, moss peat is lighter, woody peat and herbaceous peat are heavier. Dimensionless.
The bulk density of peat in the natural state is called the wet bulk density, and the dry bulk density is called the dry bulk density. The unit is g / cm
Structure and color
The peat structure is loose and porous with poor mechanical stability. Moss peat is spongy, herbaceous peat is fibrous, and woody peat is fragmented.
The color of peat is related to the plants, the degree of decomposition and the minerals. For example, moss peat is yellow, decomposed and transformed into humus is black, pyrite-containing blue is blue, and siderite-containing light green.
Flammability of peat
Peat is flammable and is expressed as heat. China's peat heat is mostly 10-12MJ / Kg.
3. Type of peat
According to the composition of plants, peat is divided into herbaceous peat, woody peat and moss peat.
Peat type | Ash content | Resolution ability | PH | Water content | colour | elasticity |
Herbal peat | Higher | Stronger | Slightly acidic | less | dark | Worse |
Woody peat | Lower | Weaker |
| less | Reddish brown | difference |
Moss peat | low | weak | Acidic | high | light | Strong |
Chapter 2 Section 1 Peatification
1. The biochemical changes of peatization can be divided into two stages: biochemical decomposition and biochemical synthesis.
Organic compounds in plant debris are converted into simple chemically active compounds through oxidative decomposition and hydrolysis.
Stable organic compounds such as humic acid and asphaltene are synthesized between the decomposition products. The process or effect of forming humic acid is called humification, which is not a biological effect, but a chemical effect in an oxidizing environment.
2.Gelling
After the plant undergoes humification during peatization, it will then undergo gelation; gelation means that the main components of the plant undergo biochemical and physical chemical changes during the peatization process to form humic acid. Process of colloidal substances with asphaltene as main component. Because the lignin and cellulose of the plant belong to the gel in terms of physicochemical properties, they have strong water absorption ability and gradually decompose in the reducing environment. The cell wall first absorbs water and expands, the cell cavity shrinks, and finally loses the cell structure completely, forming unstructured colloid. Or further converted into a sol; when electricity, acidity, alkalinity, and temperature change, colloidal chemical changes occur, and the above substances form a gel state. Because this process has both anaerobic and colloidal chemistry, it is also called "biochemical gelation".
3. Silk charring
When the surface of the swamp is relatively dry and the oxygen supply is sufficient, the lignin and cellulose in the plant cell wall are dehydrogenated and dehydrated with the participation of microorganisms, and the carbon content increases. After the oxidation reaches a certain stage, the plant remains quickly turn into a weakly oxidized or reduced environment. Oxidation is interrupted after being covered with mud or sand, a process called silk charring.
If the process of silk charring continues, it may lead to the complete decomposition of plant remains.
When the oxidative and reducing environment of plant remains changes alternately, silk charring and gelation may alternate. It should be noted that after the silk carbonization has fully formed the silk char material, the gelation will also end.
Section 2 Residualization
Residualization is a special case of peatization. When the peat bog water is flowing smoothly, under the condition of sufficient long-term oxygen supply, the unstable components are fully decomposed and taken away by the flowing water to stabilize the enrichment of the components. Another case is that when the swamp diving surface is lowered, the plant remains are not covered by water and are strongly oxidized, resulting in the enrichment of stable components.
Residualization products are formed by coalification.
Section III Septicification
In water bodies such as lakes, marsh waters, bays, and shallow seas, lower plant algae and planktonic remains, with the participation of anaerobic microorganisms in the reducing environment, undergo complex biochemical changes to form organic sludge rich in moisture. This process is called saproliation.
Lower plants are decomposed, condensed, and polymerized to form water-rich cotton floc colloids, which are dehydrated and compacted to form saprox. The color of sludge is generally yellow, dark brown, and dark gray.
Section 4 Influencing factors of different peat composition and properties
1. Plant community
Woody plants are rich in cellulose and lignin, which easily form gelatinous substances. The coals formed are characterized by bright coals; herbaceous plants contain more cellulose and protein, unstable components decompose, and stable components are enriched and formed. Coal rich in stable components (chitin group) has high hydrogen content and tar yield; bryophytes can secrete preservatives, so moss peat often retains more unstable components.
2. Nutrition Supply
According to the nutritional supply of plant growth, it can be divided into three types: eutrophic, mesotrophic, and lean.
Low peat swamps often form eutrophic peat, high peat swamps often form poor nutrition peat, and middle peat swamps often form mesotrophic peat.
3. Acidity of the medium
High acidity is not conducive to bacterial survival, and neutral or weak alkaline is conducive to bacterial reproduction.
In the calcium-rich marshes, most of which are based on limestone, aerobic bacteria are active, and aquatic plants are the main components. The high S and N content in the coal formed may be related to the strong activity of sulfur bacteria.
In the high peat swamp, the acidity is high, and the moss can secrete preservatives (phenols), which is not conducive to the survival of bacteria, so the cell structure of the plant can be preserved.
4.Redox conditions
The surface layer of peat is in an oxidizing environment and is easily oxidized to form silk peat. The bottom layer of peat is in a reducing environment and is easy to form vitreous coal.
Coal is classified into three types according to the raw materials and the accumulation environment of coal:
Humus: Humus coal, residual plant coal. Higher plants form in swamp environments.
Humus saprophytes: Humus saprophytic. The lower and higher plants mix and form in lake and swamp environments.
Saprolite: saprophytic coal. Lower plants and a small number of animals form in the deep waters of lakes and swamps.
Chapter III Coalification and Types of Coal Metamorphism
Section 1 Stages and characteristics of coalification
1. Two stages of coalification
Diagenesis of coal
After the formation of peat, due to the subsidence of the basin, it was buried in the ground under the cover of overlying sediments. After compaction, dehydration, and carburization, it gradually consolidated. After physical and chemical action, it turned into young brown coal, called coal diagenesis. . During the diagenesis process, lignin and cellulose continue to participate in the formation of humic acid, and the formed humus forms a gelling component.
Coal metamorphism
Under the action of higher temperature, pressure and longer time, the young brown coal undergoes further physical and chemical changes, and becomes a process of becoming old brown coal, bituminous coal, anthracite, and anthracite. In this process, the humic substances continue to undergo polymerization reactions, the side chains of the fused ring aromatic system are reduced, the degree of aromatization is increased, and the molecular arrangement is more regular.
2. Characteristics of coalification
Carbonization trend. The volatile content is reduced, and the relative carbon content is increased.
Simplified structure. The peat phase contains a variety of functional groups. In the anthracite phase, it contains only condensed aromatic nuclei, and finally evolves into graphite.
The trend of homogenization of microscopic components.
It is irreversible.
Non-linearity of development.
Dense structure and directional arrangement.
Section 2 Factors of Coalification
1. Temperature: affected by the geothermal gradient.
2. Time: It is also an important factor.
3. Pressure: Pressure does not produce a chemical reaction, but it can change the physical structure of coal. For example, the porosity and moisture content decrease, the density increases, the organic macromolecules are aligned, and the light reflectance increases.
Section 3 Index of Coalification Degree
Coalification degree index, also called coalification index, coal-level index. The commonly used indicators of the degree of coalification are as follows:
moisture. In general, the moisture content decreases from low to medium coal.
Volatile matter. In the bituminous coal phase, as the degree of coalification increases, the volatile content decreases.
vitrin group reflectance. As the degree of coalification increases, the reflectance of the vitreous group increases.
Carbon content. As the degree of coalification increases, the relative content of C in organic matter increases.
Hydrogen content. From anthracite to anthracite stage, the hydrogen content decreases significantly.
Calories. The calorific value is related to the water content and is an indicator of the degree of coalification in the low coalification stage.
The chitin group is fluorescent. Chitin group fluorescence and reflectivity are mutually increasing and decreasing, which are indicators of low coalification degree.
X-ray diffraction. As the degree of coalification increases, the diffraction curve becomes steeper and the intensity increases.
Section 4 Types of Coal Metamorphism
1. According to the type of heat source, the metamorphism of coal can be divided into three types:
Deep into metamorphism. Mainly caused by geothermal, also known as regional metamorphism.
magmatic metamorphism. Thermal metamorphism caused by magma intrusion.
Dynamic metamorphism. Metamorphic effects caused by tectonic movement. The dynamic pressure generated by the tectonic movement does not directly produce a chemical reaction, and the frictional heat generation can accelerate the coal metamorphism.
2.Hill's law
The German scholar Hilter proposed according to the geological laws of western European coalfields that, with the formation being roughly horizontal, the volatile content of coal decreases by 2.3% for every 100 meters of depth increase.
1. Some basic concepts in the industrial classification of coal
The concept of base: benchmark, prerequisite. For example, d, ad, daf, dmmf, ar respectively represent a dry base, an air-dry base, a dry ash-free base, a dry mineral-free base, and a receiving base.
Cohesiveness of coal. It refers to the ability of coal particles (d <0.2mm) to bind themselves or inert materials to form blocks after being isolated from the air and heated.
Coking of coal. It refers to the property of coal particles that can produce high quality coke after being heated by air.
The total moisture of coal. It is the sum of the external moisture (surface water) and internal moisture of the coal. External water is the moisture that is lost in the air and the rest is internal water.
Volatile matter. The mass of air-dried coal samples reduced from water and carbon dioxide after heating in air for 7 minutes at 900 ° C. It is usually expressed as dry ash-free volatile matter. Vdaf /%
Ash content: The mass of the residue after the air-dried coal sample is heated to 815 ° C and completely burned.
Shotguns generate heat. It refers to the heat emitted when unit mass of coal is burned in a cartridge filled with excess oxygen, and the final product is 25 carbon dioxide, oxygen, nitrogen, nitric acid, sulfuric acid , liquid water and solid ash.
High heat. It refers to the heat emitted when unit mass of coal is burned in a cartridge filled with excess oxygen, and the final product is 25 carbon dioxide, oxygen, nitrogen, sulfur dioxide , liquid water and solid ash. Its value is equal to the calorific value of the cartridge minus the formation heat of nitric acid and sulfuric acid.
Low heat. It refers to the heat emitted when unit mass of coal is burned in a cartridge filled with excess oxygen, and the final product is 25 carbon dioxide, oxygen, nitrogen, sulfur dioxide, gaseous water and solid ash. Its value is equal to the high calorific value minus the heat of vaporization of water.
2.Use of coal
Thermal power 31%, industrial boiler 31%, civilian 20%, coking 8%, steam engine 4%, coal chemical 3%, export 3%
3. Basis of industrial classification of coal
According to the index of coalification degree (volatile matter, etc.) and the properties of thermal processing technology (adhesion, heat generation, etc.).
4.China coal classification table and description
Description of the numerical code of coal: the ten-digit number indicates the size of the dry ash-free volatile matter, and the single-digit number indicates its cohesiveness. Large digits indicate high volatile content; large single digits indicate high adhesion.
Anthracite classification: 3 numbers.
category | Numbering |
| Vdaf /% | Hdaf /% |
Anthracite | 01 | Old anthracite | 0-3.5 | 0-2 |
Anthracite II | 02 | Typical anthracite | 3.5-6.5 | 2-3 |
Anthracite III | 03 | New anthracite | 6.5-10 | 3-4 |
Bituminous coal classification: 24 numbers
The volatiles are 10-20%, 20-28%, 28-37%, and 37% or more, which are low, medium, medium high, and high volatiles, respectively.
The adhesion index G 0-5, 5-20, 20-50, 50-65, 65 and above are respectively non-sticky, weakly sticky, medium and low sticky, medium and high sticky and strong sticky.
Lignite classification: 2 numbers
category | Numbering |
| Vdaf /% | Visual colorimetric transmittance PM |
Lignite No. 1 | 51 | New lignite | 37 or more | 30 |
Lignite No. 2 | 52 | Old lignite | 37 or more | 30-50 |
Classification of Chinese coal
14 categories: lignite, long-flame coal, non-sticky coal, weakly sticky coal, 1/2 medium-clay coal, gas coal, gas-rich coal, 1/3 coking coal, fat coal, coking coal, lean coal, lean lean coal, poor Coal and anthracite.
17 small categories
5. Coal selectivity and evaluation method
The concept of coal preparation
The process of removing mineral impurities and improving the quality specifications of coal by taking advantage of the differences in physical and chemical properties of coal and mineral impurities.
Coal preparation method
It is mainly gravity coal separation. It uses jigging coal separation or heavy medium washing to make use of the difference between the density of coal and mineral impurities.
Coal optionality
It is easy to separate mineral impurities from coal to meet the requirements of industrial coal. Expressed as ± 0.1 near density.
Evaluation method
Screening test and floatation test.
Coal petrology
Section 1 Macro coal and rock composition and physical properties of coal
1. Macroscopic coal and rock composition: the basic unit of coal that can be distinguished by the naked eye.
Mirror coal. The color is dark black, the strongest luster, the shell-shaped fracture, the development of endogenous fissures, band-like or lenticular, formed by the gelation of the wood fiber tissue of the plant, is a simple macroscopic coal rock composition.
silk charcoal. The color is gray and black, fibrous structure, silk silk luster, loose and porous, hard and dense after filling with minerals, large specific gravity, formed by the carbonization of wood fiber tissue of plants, and it is also a simple macro-coalstone composition.
bright coal. Bright coal is a complex macroscopic coal and rock component, formed by the gelation of the lignocellulosic tissue of plants, and mixed with some mineral impurities brought by wind or water. Gloss and brightness are second only to mirror coal, and its cross section is flat. Endogenous cracks are not as well developed as mirror coal, often in thicker layers, and are the most common macroscopic coal and rock components.
Dark coal. Dark coal is a complex macroscopic coal and rock component, rich in crustaceous group, inertia group or minerals, with dim luster, gray-black, dense and hard, high specific gravity, high toughness, not easy to break, rough section, and generally does not develop endogenous cracks. . More common.
2. Macro coal and rock types
According to the composition of macroscopic coal and rock composition and the average gloss intensity reflected by it, it is divided into four types of macroscopic coal and rock.
Bright coal. It is mainly composed of mirror coal and bright coal (greater than 80%).
Semi-bright coal. Bright coal and mirror coal account for the majority (50-80%).
Semi-dark coal. Bright coal and specular coal account for 20-50%, and their hardness, toughness and specific gravity are relatively large.
Faint coal. Mirror coal and bright coal are less than 20%, with high hardness, toughness and specific gravity.
Second, the physical properties of coal
1.Optical properties
Color: Table color, pink, body color, reflection color, reflection fluorescence color
Surface color refers to the color reflected on the coal surface under ordinary white light.
Pink refers to the color of the coal ground into powder or scratches formed on the surface of the coal with a steel needle. Also known as streak color.
Body color refers to polishing the coal surface and observing the color of the reflected light under a microscope.
Reflective fluorescent color: The color after polishing the coal surface and exciting it with blue or ultraviolet light.
Coal | Color | Pink | Body color | Reflection color | Reflected fluorescent color |
lignite | brown | brown | The higher the coal grade, the worse the light transmission | The higher the coal grade, the lighter the reflection color | The higher the coal grade, the weaker the fluorescent color |
Low rank bituminous coal | black | Dark brown |
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High-grade bituminous coal | black | black |
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anthracite | black | Dark black |
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gloss. Reflective power of fresh sections of coal. It is related to coal genesis, coal rock composition, coalification degree and weathering degree. Mirror coal bright coal dark coal silk charcoal, the luster is weakened. As the coal grade increases, the gloss increases.
Reflectivity, refractive index and absorption
The reflectivity of coal is the ratio of the intensity of reflected light to the intensity of incident light on the polished surface of the coal rock component under vertical lighting conditions.
The refractive index of coal is the sine ratio of the angle of incidence and the angle of refraction when light enters the interface of the coal.
The absorption rate of coal is the ratio of absorbed light energy to incident light energy.
2.Mechanical properties
Hardness. The ability to resist the intrusion of hard objects into the surface is divided into scoring hardness, indentation hardness and abrasion hardness.
Scoring hardness refers to the relative hardness obtained by scoring coal with standard minerals.
Indentation hardness refers to the microhardness of coal as measured by a special instrument.
Abrasion hardness refers to the hardness represented by the amount of abrasion resistance on the polished surface of coal.
Brittleness. The nature of an object's fragmentation after an external force. Large brittleness and poor toughness are not directly related to hardness. Coking coal is the most brittle.
Abradability. Ease of grinding. The grindability coefficient of coal refers to the energy ratio of grinding the same weight of standard coal samples and test coal samples from the same particle size to the same fineness in the air-dried state.
Compressibility. Percent change in volume of coal under constant temperature and pressure.
Fracture. Section broken after the coal is stressed.
Specific gravity and density.
Specific surface area. Total surface area per gram of coal. M2 / g
Wet method, BET method, Langmuir isothermal adsorption method, gas chromatography can be used. Lignite and anthracite have the largest specific surface area.
Porosity. The ratio of the total volume of pores and cracks in coal to the total volume of coal is also called porosity.
Conductivity. Usually expressed in resistivity. It is related to the degree of coalification, water, minerals, porosity and weathering.
Magnetic. Coal is a diamagnetic substance.
Thermal conductivity. The specific heat of coal is between water and minerals. The specific heat of water is large and the specific heat of minerals is small.
Cracks in coal
1. Endogenous fissures: Gels that are uniformly contracted under the action of temperature and pressure generate fissures formed by internal tension. Two groups develop perpendicularly to the bedding plane.
2. Exogenous fissures: products of tectonic stress in the later period, which intersect at different angles with the bedding plane, and there are coal debris in the fissures.
Fourth, the structure and structure of coal
1. The structure of coal is divided into primary structure and secondary structure. Primary structure refers to the coal structure formed without tectonic movement during coalification. Secondary structure refers to the structure of coal seam after tectonic movement, including fragmentation, fragmentation, and ridge structure.
2. Coal structure
As a kind of sedimentary rock, coal has sedimentary structure, including bedding, wave marks, etc .; some do not have bedding features and have a block structure. After the tectonic movement, the primary structure produces secondary structures, such as sliding mirrors, scale-like structures, and crumpled structures.
Section 2 Microstructure of Coal
I. Organic microscopic components of coal
1. Visor quality group. It is formed by the lignocellulosic tissue of plants under gelatinization under reducing conditions. The vitrin components are structural vitrin, unstructured vitrin and debris vitrin. Preserved plant cell structures are called structural vitrins, and those without plant cell structures are called unstructured vitrins, and those with a detritus-like distribution are called detrital vitrins.
2. Inert group. Also known as silk group, it is formed by the charcoalization of silk fiber tissue under oxidizing environment. High C content, high degree of aromatization, harder, high reflectivity, low volatile content, non-adhesive.
3. Chitin group. Also called stable group, lipid group. The chitin group also has a large number of fatty components, high hydrogen content, and generates a large amount of tar and gas when heated. Poor or non-adhesive, and fluorescent.
Second, the inorganic microscopic components of coal
1. Source of minerals in coal
Primary minerals. Minerals absorbed by plants through their roots.
Syngenetic minerals. Wind and water carry minerals that are deposited simultaneously with peat.
epigenetic minerals. After the coal seam is formed, the minerals formed in the coal body due to the intrusion of water or magma.
2. Types of minerals in coal
Clay ores, carbonate ores, oxides, sulfides, hydroxides, etc.
Section 3 Application of Coal Petrology
1. The history of coal seam deposition can be inferred from the coal seam profile, biological fossils, and coal cores.
2. The deposition history can be inferred from the coal seam formation curve.
3. The history of tectonic movement can be inferred by using different metamorphic degrees of the same depth.
Section 4 Research Methods of Coal Petrology
I. Macro research methods
Observe the cross section of the coal seam with the naked eye, draw a histogram of the coal rock, and describe the layer name, thickness, structure, structure, minerals, etc.
Microscopic research methods
1. Quantification of microscopic coal and rock components
Coal particle d1mm, average d = 0.8mm
2cm number of particles is about 25 × 25 = 625
2cm
When the measurement step is 0.6mm, the number of measurement points is 33 × 33 = 1089. Statistic principle: Count the components under the intersection of the crosspieces of the eyepieces. There is no statistics of the microscopic components under the intersections of the crosspieces. Judgment principle: If the intersection of the crosshairs falls on the component boundary, participate in the statistics according to the component filled with a certain quadrant.
2. Quantification of microscopic coal rock types
The eyepiece is inserted into a grid micro ruler, the number of grids is 20, the grid size is 0.5mm × 0.5mm, and the measurement step is 0.6mm. Statistical principle: Participate in statistics when the number of grids and coal particles crosses more than 10. Principles for judging data points: When the number of mineral points is less than 20% and there is no sulfide, the data point is determined as micro coal rock; When the number of mineral points is greater than 50% or the number of sulfide points is greater than 15%, the point is determined as mineral Other data points are determined as micro-mineral coal.
3. Comprehensive analysis of micro-components and micro-coal types
Insert a grid micro ruler into the eyepiece, and use a certain point of the grid micro ruler as the crosshair, and perform statistics and analysis based on the previous statistics and judgment basis.
Third, the reflectance of coal
Microphotometer
Fourth, equipment
1.Automatic microphotometer
Calculate the reflectivity according to the gray value, and judge the degree of coalification, microscopic composition or coal type.
2. Scanning electron microscope: used to study the surface morphology of solids.
3. Nuclear magnetic resonance: A specific atomic nucleus absorbs only a specific frequency of radio frequency energy in a specific external magnetic field. Used to study the chemical structure of coal molecules. A change in the aroma level is equivalent to a change in the applied magnetic field, and the absorbed RF frequency also changes.
4.Electronic paramagnetic resonance
Chapter 5 Coal-bearing Sedimentary System
1. Concept of coal-bearing rock series
It refers to the sedimentary population with a symbiotic relationship filled with coal seams in the basin. The color of coal-bearing rock series is mainly composed of gray, gray-green, and black. Rock types include sand, mudstone, carbonaceous mudstone, limestone, coal, and so on.
2. Conditions for coal seam formation
The predecessor of the coal seam is the peat layer. The formation and preservation of the peat layer are closely related to the water level in the swamp. According to the comparison of the accumulation speed of the plant remains and the rising speed of the marsh water surface, it can be divided into three cases, also known as three compensation methods: Over compensation, equalization compensation and under compensation.
3. Coal seam structure
Coal seams include coal strata and rock interlayers. Those without coal rock layers in the coal seam are called simple coal seams, and those with coal rock layers in the seam are called complex coal seams.
4. Floor and roof of coal seam
Mudstone and clay rock are the most common floor of coal seams, rich in plant rhizome fossils, commonly known as root soil rocks; if the floor is conglomerate or limestone, the plant remains are deposited in different places. Root clay contains gray illite, montmorillonite, kaolinite and other clay minerals.
There are many types of rocks on the roof of coal seams. The most common are mudstone, sandstone and limestone, which are related to the sedimentary environment. For example, the Taiyuan Formation of the Carboniferous coal-bearing rock series of the Carboniferous in North China in China is a marine-type filling sequence, and the coal-forming environment is mainly a lagoon-barrier island system with limestone roofs. The Shanxi Formation in North China is a regressive filling sequence. The coal-forming environment is mainly delta and river systems. The roof of the coal seam is lacustrine mudstone and impact sandstone.
5. Nodules, inclusions and fossils in the coal seam
The roof is a coal seam of marine sediments, pyrite nodules are common in the middle and top of the coal seam, and siliceous nodules are common in the lower half of the seam.
Peat is mixed into the peat to form inclusions.
Fossils of animals and plants are sometimes seen in coal seams.
6. Coal seam thickness, morphology and its controlling factors
Total coal seam thickness, beneficial thickness, recoverable thickness, recoverable coal seam, thickness level
Control factors of coal seam morphology: peat swamp basement shape, sedimentary environment (alluvial fans, rivers, lakes, deltas, lagoons-barrier islands), simultaneous tectonic changes (river or lake-phase clastic sediments invading coal seams, coal seam bifurcation, basement occurrence Faults, folds), late tectonic changes (folds, faults, magmatic intrusions, karst collapse columns)
7.Coal-containing sedimentary system
Coal-forming characteristics of sedimentary system in mountain alluvial fan zone: coal seams can be formed in inter-fan, intra-fan or fan-front basins with poor lateral continuity
Coal-forming characteristics of river sedimentary system: post-shore marshes and abandoned river channels are favorable for coal seam formation
Coal-forming characteristics of lake sedimentary system: During the lake silting process, the sedimentary grain size is fine and coarse.
Coal-forming characteristics of the delta sedimentary system: in the upper delta plain, near the river bank, coal seam bifurcation and ash increase occur due to the breaching fan deposition, forming low-sulfur coal; the lower delta plain is significantly affected by seawater and tides, and the roof of the coal seam is mostly sea Phase deposition, high sulfur content.
Coal-forming characteristics of the lagoon-barrier island sedimentary system: the lagoon is formed by shallow swamps, forming coal seams, with large thickness changes and high sulfur content in the coal seams.
Chapter 6 Coal-accumulating Basins and Coal-accumulating Rules
1. According to the formation conditions of coal-accumulating basins, it can be divided into depression-type coal accumulating basins, fault-depression coal accumulating basins, and tectonic erosion coal accumulating basins.
The Carboniferous Permian coal-accumulating basin in North China is a typical corrugated depression coal-accumulating basin. The Qinling-Dabieshan structural belt is on the south side of the basin, and the Yinshan tectonic belt is on the north side of the basin. Generally, it is a dustpan basin with a gentle slope from northwest to southeast, showing a pattern of "east-west subzonation and north-south migration".
Depression-type coal accumulation basin. It is formed by the action of fault and block subsidence.
Erosive coal-accumulating basin. The base is a concave land with an ablated surface.
2. Evolution of coal-fired basins
The evolution of the Jumei Basin is affected by paleontology, paleoclimate, paleogeography and paleostructure.
There is uneven settlement in the basin.
Under the influence of tectonic movement, seawater advance and retreat, and climate, the coal-accumulated basin has a lateral migration phenomenon.
Involved vocabulary: transgression, transgression, transgression and overturning, overlap, accretion (when retreating), regression (when retreating), sedimentary datum
3. Coal accumulation law
Under the influence of ancient plants, paleoclimate, paleogeography and paleostructure, coal accumulation always occurred in certain parts of the basin, showing a certain regularity in space and time.
Coal-rich belt. Refers to the well-developed and relatively enriched block of coal seam, which has the characteristics of band distribution in space.
Rich coal center. The part with thick coal seam in the coal-rich zone.
Generally, large coal-rich belts in large basins are circular or elliptical in shape and spread along the direction of structural lines when controlled by geological structures.
4. Research on coal formation
Coal affected by seawater has high sulfur content and high pyrite content, and is rich in minerals such as mica, dolomite, calcite and apatite.
The coal seam with a marine roof has dark coal due to its deep water environment.
Chapter VII Coal-Associated Mineral Resources
Section 1 oil shale
The organic matter in the oil shale is almost completely composed of algae remains, and the formation environment of the oil shale is mainly a hydrostatic sedimentary reduction environment.
Section 2 Coalbed Methane
1 The concept of coal resources
Coal reservoirs with mining value are called coal resources.
2 Classification of coal resources
According to the degree of understanding and mastery, it is divided into 2 levels: reserved reserves and predicted reserves. According to 1997 statistics, the reserves are 1 trillion tons, the predicted reserves below 1,000 meters are 1.8 trillion tons, and the total coal resources below 1,000 meters are 2.8 trillion tons; the predicted reserves below 2000 meters are 4.6 trillion The total resources of 2,000 meters and less are 5.6 trillion tons.
3 Division of coal resources
According to the geographical location, it is divided into 4 areas: North China, Northwest, Northeast and South China.
North China: Coal resources rank first, accounting for 50% of the country's total. Provinces covered: Central Plains north of the Yangtze River, north to Inner Mongolia. The coal-bearing strata are mainly Jurassic and Carboniferous Permian strata, and the coal ranks are mainly long-flame coal, gas coal, fat coal, coking coal and lean coal.
Northwest China: Coal resources rank second, accounting for 35% of the country's total. Provinces covered: Xinjiang, Gansu, and Ningxia. Coal-bearing strata are dominated by Jurassic strata, and coal strata are dominated by long-flame coal.
Northeast China: Coal resources rank third, accounting for 7% of the country's total. Provinces covered: Three provinces in Northeast China. The coal-bearing strata are dominated by Cretaceous strata, and the coal ranks are dominated by lignite.
South China: Coal resources rank fourth, accounting for 6.8% of the country's total. Provinces covered: Provinces south of the Yangtze River, mainly Yunnan, Guizhou, Sichuan, Jiangxi, and Hunan. The coal-bearing strata are dominated by Permian strata, and the coal ranks are dominated by gas coal, fat coal, coking coal and lean coal.
4 Ranking by province: Xinjiang 1.9 trillion tons, Inner Mongolia 1.4 trillion tons, Shanxi 0.6 trillion tons, Shaanxi 0.3 trillion tons, Guizhou 0.2 trillion tons.
The concept of coalbed methane resources
Coalbed methane reservoirs with economic development value are called coalbed methane resources.
Classification of coalbed methane resources
Paleogeographic structure and coal accumulation period
The Early Paleozoic inherited the paleotectonics of the Neoproterozoic. The Early Paleozoic experienced the Caledonian tectonic movement, forming a northeast to Caledonian trough in the southeast of China, and produced early Paleozoic saprolite peat coal in southeastern China; the Qinling and Yinshan areas uplifted and formed a Carboniferous Permian coal basin in North China. A good base condition was formed. At the end of the Early Paleozoic, the Caledonian Wuyi cloud folds formed in southeast China, and the Yangtze block proliferated.
Most of the Late Paleozoic inherited the structural contours of the Early Paleozoic, and the North China area is still in a state of uplift and erosion. The Devonian began transgression. By the late Carboniferous, seawater flooded the North China land mass, forming a coastal coal-bearing structure, and southern China was constructed of carbonate rocks. During the Permian, the Inner Mongolia-Daxinganling Trough was closed and uplifted, and North China became a transitional and continental facies coal-bearing sedimentary system. South China was still built for carbonate rocks in Guanghai. The Late Paleozoic Haixi Movement, China s Tianshan, Qilian Mountains, Qinling and Daxinganling troughs fold back, forming a huge mountain system from east to west, and a large area north of Qinling-Kunlun rises and transforms into the inland environment; the southeast coastal continent proliferates; forms the South China Sea "Hokuriku" paleogeographical appearance.
The Late Triassic Indosinian movement from the end of the Late Paleozoic to the early Mesozoic era changed the situation of China's "Southern Sea and Northland". All the northwestern "Snow Mountain Troughs" were folds and bulges. The land grew southwest, and the seawater retreated to Tibet in southwest China. Most of the middle and lower reaches of the Yangtze River and South China changed from shallow water to land, and China's north-south land was integrated.
After the Indosinian movement, a huge north-northeast uplift and depression belt formed in eastern China, bounded by the Greater Xing'an Mountains, Taihang Mountains, and Wuling Mountains. In the west, large Triassic and early-middle Jurassic large coal-accumulating basins developed, and inland lacustrine deposits Northeast China has developed early and middle Jurassic small sag coal basins, South China has developed Late Triassic Narrow Bay coal-forming environment, and Northeast China has developed Late Jurassic and Early Cretaceous fault depressions and sag coal basins.
After the Yanshanian movement during the Jurassic and Cretaceous periods, the Yanshan folds near Beijing were uplifted, and the inland basins west of the Daxingan Mountains, Taihang Mountains, and Xuefeng Mountains were relatively stable. Such basins as Ordos, Sichuan, Junggar, and Tarim were continuously accepted during the Mesozoic. River and lake facies deposits, the periphery of the basin are Paleozoic troughs. To the east of the above line, the tectonic activity is strong, and a large number of northeastward fold faults and small fault depressions are developed, accompanied by magmatic intrusion and volcanic movement along the southeast coast.
The orogenic movement since the Cenozoic is a Tertiary Himalayan tectonic movement. Under the squeeze of the Indian plate, southwestern China has a strong fold and uplift.
Early Paleozoic coal was formed in the coastal-shallow sea environment, and it was a saprolite coal transformed by bacteria and algae. The late Paleozoic was dominated by the coastal environment, and the Mesozoic and Cenozoic were dominated by inland basins.
Palaeoclimate of the main coal accumulation period:
1. Late Paleozoic coal accumulation period
Permian plants have distinct divisions. Most of China has a subtropical humid climate zone and develops Huaxia flora; a temperate and semi-humid Angara flora develops in the northeast and northwest; a temperate and cold-temperate semi-humid Gondwana flora develops in southern Tibet; and a subtropical and semi-humid climate in northern China; During the Late Permian, the southern part of North China had a warm and humid climate with coal seams and purple mudstones, and the northwest and most of North China had a dry climate.
2.Mesozoic coal accumulation period
During the Triassic, the northwest and north China had temperate and semi-humid climates.
During the Early and Middle Jurassic period, the ancient Mediterranean ocean air mass moved eastward, and the northwestern climate was humid and the rainfall increased. It was an important coal-bearing basin;
From the late Jurassic to early Cretaceous, the south had a tropical and subtropical arid climate with red deposits; the north of Yinshan was a temperate climate; the northeast was affected by the Pacific Ocean, humid and rainy, with lush vegetation and a rifted coal basin.
3. Cenozoic coal accumulation period
Since the Cenozoic, China has been warm temperate, subtropical, and tropical in order from north to south. With the uplift of the Qinghai-Tibet Plateau, the interior of Eurasia is dry; affected by the Pacific Ocean and the Indian Ocean, Tertiary coal-accumulating basins have developed in the Northeast and Southwest.
Buried Geological Conditions of Chinese Coal
1.Northeast District
Coal-bearing strata are mainly Late Jurassic-Early Cretaceous, and the formation of coal-bearing basins is mostly related to large-scale rifting in eastern China, which makes the basins appear semi-stratigraphic or geomorphic structures. These rift basins are developed on the basis of uplifts and often occur in groups.
2. North China
After the Middle Ordovician, after a long period of denudation in North China, the transgression of the platform in the stable period occurred widely, and the Late Paleozoic offshore coal measures spread throughout the region. The Upper Carboniferous-Lower Permian is the main coal-bearing interval; the accumulated thickness of the Upper Permian is nearly several kilometers. Only the Upper Shihezi Formation in Huainan still contains mineable coal seams. In the Mesozoic and Cenozoic, with the disintegration of the platform, the movement of internal block faults strengthened, and the east and west structures were clearly differentiated. The sedimentary basins and coal-accumulating areas became smaller from west to east.
3.Northwest District
After the Indosinian period, that is, after the Triassic, an early-middle Jurassic mountain coal-accumulating basin formed in the northwest. The Yanshan and Xishan movements increased the depth of coal seams.
4.Southern District
Yunguichuan has preserved a large amount of Paleozoic coal.
Yang Qi (1919-2010), graduated from Southwest United University in 1943. Graduated from Peking University in 1946. Academician of the Chinese Academy of Sciences, professor of China University of Geosciences, editor of "China Coal Field Geology", "Coal Field Geology" and other teaching materials, founded China's first coal field geology major [2] .
Dexin Han (1918-2009), graduated from Southwest United University in 1942, and researched at Peking University Institute from 1943 to 1945. He graduated from the University of Michigan Institute in 1950. Professor of China University of Mining and Technology, academician of Chinese Academy of Engineering, chief editor of "China Coal Field Geology", "China Coal Petrology" and other monographs and teaching materials [3]
