This part mainly introduces other endogenous sedimentary rocks besides carbonate rocks, mainly composed of siliceous rock, aluminous rock, iron rock, manganese rock, phosphorous rock and evaporite ( Fang Yesen et al., 1987).
1. Siliceous rock
1. Basic characteristics of siliceous rock
Silicate rock refers to chemical, biological and biochemical processes as well as certain Silica-rich rocks formed by some volcanic processes (Figure 10-12). It also includes siliceous rocks that have been mechanically broken and redeposited in the basin, but does not include quartz sandstone and sedimentary quartz that were deposited by transporting terrigenous quartz clasts.
Figure 10-12 Siliceous rock under a cross-polarizing microscope
The mineral components of siliceous rock mainly include various types of opal, semi-crystalline chalcedony and authigenic quartz (Zeng Yunfu et al., 1996). In addition, other minerals can be mixed in, such as clay minerals, carbonate minerals and iron oxide. Some siliceous rocks may also contain glauconite, zeolite, pyrite, organic matter, etc.
The structure of siliceous rock can include amorphous colloidal structure, cryptocrystalline structure, particulate structure, biological structure and granular structure. Various metasomatic residual structures can also be seen. Siliceous rocks can be layered alone or sandwiched in other rocks (often carbonate rocks) into thin layers, lenses, strips, or nodules of various shapes.
Silicate rocks come in a variety of colors, often gray, gray-black, gray-white, and gray-green. The lithology is hard, brittle, chemically stable and not easily weathered. Siliceous rocks are widely distributed and rank fourth among sedimentary rocks.
2. The main types of siliceous rock
Diatomaceous earth is mainly composed of the remains of diatoms, mainly opal.
Sponge rock is composed of siliceous sponge spicules, mainly opal and sometimes chalcedony.
Radiolarite is composed of radiolarian shells, mainly opal.
Protein soil is mainly composed of opal.
The main components of flint are chalcedony and quartz, and layered flint and nodular flint are common.
3. The origin of siliceous rock
(1) The source of SiO2
It is generally believed that silica in nature mainly comes from the following aspects:
a. Volcanic eruptions can bring out a large amount of SiO2-containing volcanic hydrothermal fluid from the deep crust and inject it into water basins; in addition, the acidic volcanic lava and pyroclastic rocks formed by volcanism will be dissolved in the sea during the decomposition stage. When decomposed and transformed into clay minerals and montmorillonite, a large amount of SiO2 can also be released, so SiO2 precipitation can be formed in local seawater.
b. The long-term chemical weathering of rocks in terrestrial areas is an important source of SiO2. The parent rock derived from sediments undergoes chemical weathering under conditions rich in water, oxygen and carbonic acid. The silicate and aluminosilicate minerals in the parent rock undergo chemical decomposition, and the SiO2 produced is mostly in the form of true solution or colloidal solution. Migrate in water and can precipitate under certain conditions.
c. The shells of siliceous organisms such as diatom crusts, siliceous sponge spicules and radiolarians gradually decompose after burial and are also one of the important sources of SiO2.
d. Clay minerals can also release a certain amount of SiO2 during diagenetic transformation. For example, SiO2 can be released when smectite clay transforms into kaolinite or illite clay.
(2) Dissolution of SiO2
The solubility of silicon oxide is closely related to the pH value. When the pH value is in the range of 2 to 8.5, the solubility remains unchanged; the pH value increases further , the solubility increases sharply; it reaches an extremely high value (5000mg/g) when pH=11.
In addition to pH value, temperature can also affect the solubility of SiO2. As the temperature increases, the solubility of SiO2 also increases.
(3) Formation of siliceous rocks
Biogenic siliceous rocks are primary sediments; nodular chert is mainly a product of the diagenetic period.
As for the origin of layered chert, there are three types:
a. It is formed by primary precipitation of saturated SiO2 and is of chemical origin.
b. It is formed by enrichment of siliceous biological organisms. For example, some flints have a laminated structure, which is of biological origin.
c. Some cherts contain components such as ooids, intraclasts, and bioclasts, which are the products of mechanical deposition.
4. Geological distribution of siliceous rocks
Chert is the most common geological distribution of siliceous rocks in nature, and biogenic siliceous rocks appeared after the Cretaceous. Siliceous rocks are widely distributed in geological history. They were most abundant in the Precambrian period and then gradually decreased in quantity.
2. Evaporite
1. Basic concept of evaporite
The water body in the sea basin or lake basin continues to evaporate, the salinity of the water body increases, and salt minerals occur Precipitation, this chemically formed rock is called evaporite, also called "salt rock". It includes chloride rock, sulfate rock and borate rock, among which chloride rock and sulfate rock are widely distributed.
Evaporite has a wide range of uses in industry. Salt rock is an indispensable salt in people's daily lives. It is also an important raw material in the chemical industry. There is also a close relationship between oil and gas layers and evaporites. Existing data also show that in many large oil fields known in the world (containing more than 7.95×107m3 of recoverable oil) and many large gas fields (containing more than 9.9×106m3 of recoverable natural gas), there is an important relationship between oil and gas layers and salt formations. The proportion of related large oil fields and gas fields is very high.
2. Compositional characteristics of evaporite
The main mineral components of evaporite are chlorides, sulfates and carbonates of potassium, sodium, calcium and magnesium, especially gypsum (CaSO4·2H2O), anhydrite (CaSO4) and halite (NaCl) are the most important. In addition to common marine and non-marine salt minerals, evaporites can also contain terrestrial clastic minerals (such as quartz, feldspar, mica) and other authigenic minerals (such as dolomite, magnesite, celestite, barite, etc.).
3. Structure and structural characteristics of evaporite
The structure of evaporite mainly includes the crystalline granular structure formed by chemical precipitation, the granular structure caused by mechanical sedimentation, and the granular structure formed during the diagenetic stage. Spotted crystal structure, metasomatic structure, etc.
The structures of evaporite include dense massive structures, laminated or striped structures, uneven layered structures, nodule-like structures, cross bedding, grain sequence bedding, ripple marks, etc. . Spot structures, deformation structures, brecciated structures, etc. can be formed during the diagenetic process.
4. The main rock types of evaporite
According to different mineral compositions, evaporite can be divided into gypsum-anhydrite rock, salt rock and potash-magnesium salt rock.
(1) Gypsum-anhydrite rock
Gypsum and anhydrite mainly form monomineral rocks (Figure 10-13, Figure 10-14), sometimes forming gypsum-anhydrite or Anhydrite-gypsum mixed rock, common associated authigenic minerals include dolomite, halite, pyrite, opal, chalcedony, quartz, etc. There are often sandy-silty and clayey mixtures in continental gypsum.
Gypsum crystals are usually white, gray or brown translucent, and the aggregates are in the form of blocks, fibers or clusters. Anhydrite crystals are colorless and transparent, sometimes white, brown or sky blue. When clay admixtures are present, anhydrite is often gray or dark gray, translucent, with a glassy to weak grease sheen.
Figure 10-13 Anhydrite Rock
Figure 10-14 Gypsum Rock
(2) Salt Rock
The main mineral composition is Rock salt contains small amounts of other chlorides, sulfates and clay. It is generally a massive and coarse crystalline structure, and a granular structure can be formed due to mechanical redeposition. Laminar structures and the interbedded gypsum and anhydrite that originate from rock salt are often seen in rock salt.
(3) Potash salt rock
The main mineral components are potassium halite, carnallite, etc., which often occur with halite rocks. According to the composition characteristics, potash rock can be subdivided into the following types:
Kash rock is composed of potassium salt and rock salt as well as a small amount of anhydrite, clay and other mixed substances. It is mostly milky white and Reddish brown, often with obvious layering. Potash rock is the main potash deposit, such as the Saskatchewan mine in Canada.
Carnallite rock is composed of carnallite and rock salt as well as a small amount of anhydrite and clay.
Potassium sulfate rock is mainly composed of potassium magnesium and polyhalite. The primary minerals are halite, anhydrite, etc.
5. Geological distribution of evaporites
Since the beginning of the Paleozoic era, evaporites have been deposited in every geological period. The main salt-forming periods are the Cambrian and Silurian periods. , Devonian, Permian, Triassic, Paleogene-Neogene. The main salt-forming periods in my country are the Triassic, Cretaceous, Paleogene-Neogene, followed by the Ordovician.
3. Aluminous rock
1. Compositional characteristics of aluminous rock
Aluminous rock is a kind of chemical composition rich in Al2O3, mainly composed of Endogenous sedimentary rocks composed of aluminum minerals (aluminum hydroxides). The characteristic of the chemical composition of aluminous rock is that the content of Al2O3 is greater than the content of SiO2 (С.Φ.Малявкин, 1937). If Al2O3＞40% and Al2O3:SiO2≥2:1 in aluminous rock, the aluminous rock is Become bauxite.
(1) Chemical composition of aluminous rock
The chemical composition of aluminous rock is mainly Al2O3, SiO2, Fe2O3, FeO, TiO2 and H2O, and the minor components are CaO and MgO , Na2O, K2O, P2O5, etc., and also contains various trace elements such as U, V, Cr, Ni, etc.
(2) Mineral composition of aluminous rock
The main mineral composition of aluminous rock is aluminum hydroxide, such as gibbsite (Al(OH)3), Boehmite (γ-AlO(OH)), diaspore (α-AlO(OH)), followed by various clay minerals, quartz, chalcedony and a small amount of heavy minerals, in addition, there are authigenic minerals Such as siderite, calcite and iron hydroxide, etc.
2. Structure of aluminous rock
The structure of aluminous rock can be divided into structures of mechanical origin, chemical origin and secondary origin.
(1) Mechanically-derived structure
The mechanically-derived structure of aluminous rock is a debris structure, which is mainly composed of debris and interstitial materials. The debris includes the inner parts of aluminous rock. Crumbs, encapsulated grains (bean grains, ooid grains), agglomerates (pellets) and agglomerates, etc. The interstitial material is mainly a micrite matrix, and its composition is usually the same as the particles.
(2) Chemically derived structure
The chemically derived structure of aluminous rock is formed during the process of chemical deposition, and mainly includes colloidal structure and microcrystalline structure.
(3) Structure of secondary origin
Due to the influence of secondary leaching in the supergene zone, aluminous rocks form a secondary leaching structure.
3. Rock types of aluminous rocks
Aluminous rocks can be divided into two main types: laterite aluminous rocks and sedimentary aluminous rocks (Zeng Yunfu et al., 1996 ).
(1) Laterite-type aluminous rock
Laterite-type aluminous rock is often red, brown or yellow, with a loose texture. The main mineral component is gibbsite. In addition, there is Diaspore, iron-containing minerals (such as goethite, hematite), clay minerals (such as kaolinite) and residual minerals quartz, etc. The chemical composition of laterite-type aluminous rock is mainly Al2O3, SiO2, Fe2O3, and TiO2. Laterite-type aluminous rocks are distributed in Zhangpu, Fujian, my country.
(2) Sedimentary aluminous rock
The bauxite material formed by laterization is transported to the edges of sea and lake basins in the form of debris or colloidal solution under the action of flowing water. Aluminous rocks that are deposited and consolidated into rocks are sedimentary aluminous rocks. According to different depositional environments, sedimentary aluminous rocks can be divided into two types: marine deposition and continental deposition.
Marine aluminous rocks are mainly deposited in coastal and lagoon environments at the edges of ocean basins. The rock mass is layered, and the minerals are mainly diaspore and boehmite. The associated minerals include goethite and lepidite, with oolitic or bean grain structures. For example, the bauxite deposits from the Carboniferous Permian in Guizhou, my country, belong to this type.
Continental aluminous rocks are related to the depositional environment of lakes and swamps. The rock mass is lenticular or layered.
Many carboniferous and Permian bauxite deposits in northern my country belong to this type, such as the bauxite deposits in the Upper Permian coal-bearing strata in Zibo, Shandong Province.
4. Geological distribution of aluminous rocks
Laterite-type aluminous rocks (bauxite) are widely distributed in my country and are mainly produced in the weathering crust of Quaternary basalt. Sedimentary aluminous rocks (bauxite) are more widely distributed and are mainly produced in Carboniferous and Permian strata.
4. Ferruginous rock
People customarily call sedimentary rocks with an iron content greater than 15% as ferruginous rocks (H.J. Janes, 1966). If the grade of iron reaches the requirements for industrial mining (such as hematite ore > 30%, siderite ore > 25%), it becomes iron ore.
1. Chemical composition of iron rock
The chemical composition of iron rock (В.А.Г.лаэковски, 1954) is mainly Fe, in addition to Mn, Al , Si, Mg, Ca, V, Ni, Co, Cr, O, S, etc.
2. Mineral composition of iron rock
Oxides include magnetite (Fe3O4), hematite (Fe2O3) (Figure 10-15), goethite FeO (OH), limonite (Fe2O3·nH2O), etc.
Sulfides include pyrite (FeS2), marcasite (FeS2), hydropyrite (FeS·nH2O), etc.
Figure 10-15 Oolitic hematite
Carbonates include siderite (FeCO3), ankerite [Ca (Fe2+, Mg, Mn) (CO3) 2 ]wait.
Silicate types include oolitic chlorite [(Fe2+, Mg, Fe3+) 5Al (Si, Al) 4O10 (OH, O) 8], black hard chlorite [K (Fe2+, Fe3+ , Mg) 8 (Si, Al) 12 (O, OH) 27], glauconite [(K, Na) (Fe3+, Al, Mg) 2 (Si, Al) 4O10 (OH) 2], etc.
3. Structure of iron rock
The structure of iron rock can be divided into mechanical, chemical and biological structural types according to its origin.
(1) Mechanically originated structure
The mechanically originated structure is a clastic structure, which is mainly composed of clasts and interstitial materials. The clasts include intraclasts of iron rocks. , ooid grains, etc., the interstitial material is mainly micrite matrix, and its composition is also iron minerals.
(2) Chemically derived structure
The chemically derived structure of iron rock is formed during the process of chemical deposition, and mainly includes colloidal structure and microcrystalline structure.
(3) Biogenic structure
The ferruginous rock structure formed by biological processes is mainly formed by the action of blue-green algae, such as ferruginous cryptoalgal debris structure, iron Mud cryptoalgae structure, etc.
4. Rock types of iron rocks
According to the composition of iron-containing minerals, iron rocks can be divided into iron sulfide rocks, iron oxide rocks, and iron carbonate rocks. and four types of iron silicate rocks.
(1) Ferric sulfide rock
The main iron minerals of ferric sulfide rock are marcasite and pyrite, and they are both formed during the diagenetic stage. Usually they are only associated components in rocks, and sometimes they can become important components of black slate and black limestone.
(2) Oxidized iron rock
Old iron rock is the most important type of iron rock, and the most common ones have an oolitic structure. Oolitic limonite rocks are mainly distributed in the Mesozoic and Paleogene-Neogene. Oolitic hematite rocks are mainly distributed in Paleozoic or older strata, such as the iron deposits in the lower part of the Changcheng System in my country.
(3) Carbonate iron rock
The main iron-containing mineral in carbonate iron rock is siderite. Siderite often combines with chert to form chert carbonate iron rock. There are also carbonate iron rocks produced in the form of nodules in clastic rocks, limestones and claystones.
(4) Iron silicate rock
The main iron-containing mineral in iron silicate rock is oolitic chlorite. Oolitic chlorite iron rock is a very important iron rock type after the Cambrian, and it often transitions or forms interbeds with oolitic hematite rocks.
5. Geological distribution of iron rocks
Sedimentary iron deposits in my country are found in the Precambrian, Paleozoic, Mesozoic and Cenozoic strata, and are widely distributed (Zeng Yunfu et al., 1996). Most of the Pre-Sinian jasper ferrosite or iron-bearing quartzite are giant deposits in the world, such as Superior (Upper Lake) in the United States, Kursk in the Soviet Union, and Anshan in China. Most of the oolitic hematite deposits can form large-scale industrial deposits, such as the Jurassic Laurentian deposits in Western Europe, the Silurian Clinton deposits in North America, and the Xuanlong iron deposits in my country. Their main mineralization eras are the Paleozoic, Late Proterozoic, and Middle Mesozoic Era.
5. Manganese rocks
Manganese rocks are sedimentary rocks with manganese compounds as important rock-forming minerals. When the manganese content reaches industrial requirements (such as manganese oxide ore > 20 %, manganese carbonate ore >10%) constitutes manganese ore (Zeng Yunfu et al., 1996).
1. Chemical composition of manganese rock
The chemical composition of manganese rock varies greatly depending on the rock type. Usually, in addition to manganese, there is more Al2O3 , SiO2, CaO, MgO, etc., generally contain more Fe. In addition, there are small amounts of Ti, Co, V, Ni, Cu, etc.
2. Mineral composition of manganese rocks
The minerals containing manganese in manganese rocks mainly include manganese oxides and hydroxides, manganese carbonates, and a small amount of Manganese phosphates, sulfides, borates, etc. The oxides and hydroxides of manganese mainly include pyrolusite (MnO2), hydromanganite (Mn2O3·H2O), duromanganite (mMnO2·nH2O), metamanganite (MnO2·nH2O), etc. The main carbonates of manganese include rhodochrosite (MnCO3), manganese calcite [(Ca, Mn)CO3], etc. The main borate of manganese is manganese borate (Mn3B7O13Cl).
3. Structural characteristics of manganese rock
The structural characteristics of manganese rock can be roughly compared to carbonate rock, and its structural classification is a new and very meaningful structure. The classification of causes mainly includes particle structure of mechanical origin, chemical origin structure and biological origin structure.
4. Rock types of manganese rocks
According to the different types of manganese-containing rocks, manganese rocks can be divided into manganese clay rocks, manganese carbonate rocks, and manganese rocks. Clastic rocks and manganese siliceous rocks.
(1) Manganese claystone
Manganese claystone is mainly manganese black shale, silty shale, siliceous shale and calcareous shale.
(2) Manganese carbonate rock
Manganese carbonate includes manganese limestone, manganese siliceous rock, and manganese dolomite.
(3) Manganese clastic rocks
Manganese clastic rocks are mainly manganese siltstone and some are manganese sandstone.
(4) Manganese siliceous rock
The main mineral components of manganese siliceous rock are chalcedony and opal.
5. Geological distribution of manganese rocks
The sources of manganese rocks are mainly products of continental weathering and submarine volcanic activity. Its mineralization environment is mainly marine facies, followed by lake and swamp facies. my country is rich in manganese ore resources, and the most important one is marine sedimentary manganese ore. The mineralization ages of manganese deposits include the Sinian, Devonian, Ordovician, Carboniferous, Permian and Triassic periods.
6. Phosphate Rock
Phosphate rock refers to endogenous sedimentary rock containing phosphorus. According to the phosphorus content, phosphorus rocks can be divided into phosphorus-containing sedimentary rocks (P2O5<8%), phosphorus rocks (P2O5=8%-18%) and phosphorus block rocks (P2O5>18%) (Zeng Yunfu et al., 1996).
The most common minerals in phosphate rocks are carbon fluoroapatite and phosphate apatite. Non-phosphate components in phosphoric rocks include SiO2, clay minerals, calcite, dolomite, glauconite, etc.
1. Structure of phosphoric rock
The structural characteristics of phosphoric rock are very similar to those of carbonate rock. According to the genetic characteristics, the structural types of phosphoric rock can be divided into mechanical Genetic, chemical, biogenic and diagenetic structures.
(1) Structure of mechanical origin
The structure of mechanical origin has the characteristics of clastic structure. According to the content of micrite (grain size less than 0.0039mm) in the rock, it is divided into clastic structure ( Micrite content is less than 50%), grain debris-micrite structure (micrite content is 90% to 50%), micrite structure (micrite content is greater than 90%). There are five common types of pellet debris: intraclasts, encapsulated pellets, pellets (pellets), agglomerates and bioclasts.
(2) Structure caused by chemical deposition
There are two types of structures caused by chemical deposition: microcrystalline structure and colloidal structure.
(3) Biogenic structures
Biogenic structures include bone structure, cryptoalgae structure and struvite.
(4) Structures caused by diagenesis
The structures caused by diagenesis include metasomatic structure and recrystallization structure.
2. Rock types of phosphoric rocks
According to the structural and genetic characteristics of phosphoric rocks, phosphoric rocks can be divided into mechanical, chemical, biological, recrystallized and metasomatic phosphoric rocks. Four categories.
(1) Phosphate rock of mechanical origin
Phosphate rock of mechanical origin is composed of various phosphate particles (such as intraclasts, inclusions, aggregates, bone fragments, agglomerates) and phosphate block rocks composed of micrite matrix.
According to the ratio of granular debris and micrite, it can be divided into granular phosphate rock, granular micrite phosphate rock, and micritic phosphate rock. Grainy phosphate rock can be divided into grain-supported type (micrite content less than 15%) and miscellaneous matrix-supported type (micrite content between 15% and 50%). The former is called bright crystalline phosphate rock, and the latter It is called micrite phosphorite.
(2) Chemical phosphate rock
Chemical phosphate rock is a type of phosphate rock formed by chemical reactions. It has the characteristics of in-situ phosphate colloid chemical deposition. The rock is composed of colloids. It is composed of apatite (or collophosphate) with spherical or ultrafine grains, mostly light brown and brown.
(3) Biological phosphate rock
Biological phosphate rock is mainly algal reef phosphate rock, which can be divided into two types: nodular algae and Synechote algae.
(4) Secondary and recrystallized phosphate rock
Secondary and recrystallized phosphate rock refers to dispersed phosphates that have been enriched, recrystallized or metasomatized by weathering and leaching Crystalline phosphorite formed from other rocks. In addition, granular carbonate can also be metasomatized by phosphate to form phosphoric rock, which often has various residual structures.
3. Geological distribution of phosphate rock
The geological distribution of phosphate rock has certain regularity. Its important mineralization periods include:
a. From the late Sinian to the early Cambrian, the main phosphorus accumulation areas were Asia and Australia.
b. During the phosphorus-forming period of the Permian, the main phosphorus accumulation areas were central North America.
c. During the Cretaceous-Neogene phosphorus-forming period, the main phosphorus accumulation centers were Europe, North Africa and North America.
Phosphoric rocks are mainly distributed in limited shallow seas, intertidal zones, coastal zones, subtidal near-land margins or ancient sea islands with "topographic highlands" on the seafloor, and have a relatively stable geotectonic environment.