Gypsum and anhydrite can be produced under endogenous mineralization. For example, gypsum precipitation is seen near some craters and hot springs; There are anhydrite deposits formed by hydrothermal alteration in volcanic rocks in eastern China. Except anhydrite which causes alteration, no industrial deposits are found between endogenetic gypsum and anhydrite. A large number of gypsum and anhydrite deposits are formed under exogenous conditions, mainly by brine evaporation and lake basin deposition, and are one of the important minerals of salt deposits. In recent years, the viewpoint of the origin of mechanical precipitation has been put forward for some gypsum deposits, but it is still controversial.
1. sedimentary basin
The deposition of gypsum and anhydrite, like other salt deposits, needs a closed or semi-closed basin or depression. The views of "sandbar theory" and "desert theory" on salt-forming basins are narrow, but in fact, the environment in which salt deposits are formed can be varied. Russian scholar strakhov thinks that there are five types of salt-forming basins, namely, inland basins, lagoons, continental marginal seas (the edge of Guang Hai), bays and inland seas. In recent years, the study of Sabha found that Holocene gypsum, anhydrite, halite and dolomite were widely distributed in Sabha sediments in Arabian Gulf and Baja California. Some researchers have suggested that many ancient gypsum deposits were also formed in the Sabha environment.
Russian scholars put forward that the formation of basins is caused by the depression of the earth's crust, and divided them into three categories, namely platform syncline, marginal depression and intermountain basins. After summarizing the data of many famous gypsum-salt deposits at home and abroad, Yuan Jianqi pointed out that faults are the main factor controlling basins, and many basins that were once considered as piedmont depressions were also found to be related to faults. For example, there are a series of red bed basins in the "second subsidence zone" in eastern China. On both sides of the subsidence zone are the Taihang piedmont fault and the Tan-Lu fault zone, in which the north-south fault divides them into several sections, and the secondary fault divides each section into blocks, and the salt-forming basin is located in the fault block. Guo Jun Zhuang proposed that almost all large gypsum-forming basins in eastern China from Cretaceous to Paleogene were located in this "second subsidence zone". Similar examples abroad include the Rhine Graben and the Great Rift Valley in East Africa. As for the older gypsum-making basins, such as the Triassic Yangtze Sea area in China, it is also considered to be composed of more than 20 secondary fault basins. Gypsum and salt deposits often occur in these basins.
2. Paleoclimatic conditions
Like other evaporated salt deposits, the formation of gypsum and anhydrite deposits requires dry climatic conditions, and the water supply in the basin is less than evaporation, which leads to the increase of seawater concentration and the precipitation of gypsum and anhydrite. Modern arid climate zone is mainly distributed in south latitude 10 ~ 15 and north latitude 40 ~ 55, and most modern salt deposits are distributed in this climate zone. The distribution of ancient arid climate zone was also mainly controlled by latitude, but the position of equator changed in geological history, so the distribution of ancient gypsum and salt deposits was not consistent with modern times.
3. Water depth at the time of deposition
It is generally believed that gypsum and anhydrite are the products of the early stage of seawater evaporation and deposition, and the water will not be too shallow when depositing. However, the actual data show that many gypsum-bearing rock series have obvious signs of shallow water deposition. For example, in the interlayer of Triassic gypsum-bearing rock series in Jiangsu, Anhui, Sichuan and other places, shallow water traces such as cross bedding, oblique bedding and wave marks are very developed, and sometimes mud cracks and insect marks appear. Gypsum and anhydrite from Sabha can even be on water. Under the condition of strong evaporation, the brine in the cracks is quickly concentrated by the evaporation pump and rises along the capillary, which leads to the widespread deposition of gypsum on the salt flats. In addition, the layered gypsum with still water mark, turbidite composed of gypsum and anhydrite, and salt dome-like thick gypsum found during drilling at a depth of 4000 meters below the sea surface in the Gulf of Mexico all indicate that gypsum and anhydrite also have deep water origin. The available data show that most deposits belong to shallow water deposits.
4. Source of ore-forming materials
Shazhou believes that seawater is the only material source for the formation of salt deposits, but it is difficult to explain the formation of some extremely thick gypsum layers, such as the extremely thick gypsum deposits in Central Asia. According to the above statement, it is obviously impossible to deposit a quarter of calcium sulfate in all seawater on earth. H. Bochet pointed out that only gypsum with a thickness of 1000m can be deposited by evaporating seawater with a depth of 1m in the basin, but in fact, gypsum layers with a thickness of several hundred meters are common. Although the theories of basin separation, seepage backflow and synsedimentary subsidence can explain the deposition of a single huge gypsum, it is still difficult to explain the source of huge materials. As for the material source of continental gypsum salt deposition, it is generally considered to be the weathering product of continental rocks, including weathered salt, halide salt, redissolution salt and volcanic salt. Only these sources can not explain the formation of continental extremely thick deposits.
In the past half century, with the new geological discovery, the viewpoint of endogenous gypsum salt-forming substances has been put forward again. In 1960s, the existence of deep hot brine was discovered. For example, there is a deep hot brine pool 2000 meters below the surface of the Red Sea, with a salinity of 257.76 g/L, and its element content is 8 ~ 10 times higher than that of normal seawater. The sediments under hot brine can be divided into 7 mineral facies zones, including anhydrite facies zones. Another example is the discovery of hot brine at a depth of 1600 meters underground near the salton Tide in California, USA. Based on this, some scholars suggest that hot brine is one of the possible material sources of gypsum-salt deposits, and controlling deep faults in gypsum-salt basins may be the channel for hot brine to rise. Some scholars at home and abroad have also noticed the relationship between volcanism and gypsum deposits. Volcanic rocks often exist at the bottom of Cretaceous-Paleogene gypsum-bearing rock series in eastern China, and gypsum interlayer exists in volcanic rock series in southern Anhui, indicating that gypsum-forming materials may be related to volcanic eruption. Based on the above data, the ore-forming materials of gypsum and anhydrite deposits are: ① seawater; ② Weathering products of continental rocks; ③ Deep source.
Second, the main genetic types and geological characteristics of the deposit
According to mineralization and ore-bearing formation, gypsum and anhydrite deposits can be divided into the following genetic types:
1. Evaporative deposition type
(1) marine evaporative deposition type-carbonate strata and clastic strata
(2) The formation of lacustrine evaporative sedimentary red clastic rocks.
2. Mechanical deposition type
(1) fluvial alluvial clastic strata
(2) Gypsum sand deposition in aeolian sand dunes.
3. Weathering-secondary filling type
(1) Types of fracture filling in clastic rocks
(2) Carbonate karst cave filling type
4. Hydrothermal metasomatism type
Contact metasomatic type in (1) carbonate rocks
(2) hydrothermal metasomatism in volcanic rocks
(1) marine evaporation gypsum and anhydrite deposition
The deposits are distributed in ancient continental margin seas, bays, tidal flats and lagoons. Gypsum-bearing salt series include marine carbonate formation, coastal terrigenous clastic formation and their transitional types.
1. Gypsum and anhydrite deposits in the construction of marine carbonate rocks
Gypsum-bearing rock series is composed of limestone, dolomite and their transition rocks, including gypsum layer and syngenetic breccia, expansion breccia and collapse breccia. The lower part of the rock series is dominated by limestone, and the upper part of dolomite is increased. The gypsum layer is produced in the sedimentary sequence of the upper dolomite. Gypsum-bearing rock series is widely distributed in layers, with stable horizons and comparability, with a total thickness of several hundred meters to several thousand meters.
In the gypsum-bearing rock series of Middle Triassic in Sichuan and Middle Ordovician in Shanxi, the ore bodies are layered, with a single layer thickness of several meters to more than ten meters, several hundred meters in some cases, and a total thickness of more than tens of meters. The ore minerals are mainly anhydrite (calcium sulfate content is 60%, generally 80% ~ 90%), and gypsum content is less. Associated minerals include calcite, dolomite, celestite and clay minerals. The natural types of ores include massive breccia, banded and flaky anhydrite. Ore reserves are very large, generally tens of millions to hundreds of millions of tons, which is one of the main industrial types of mineral deposits.
Example of deposit: marine evaporated gypsum deposit in Taiyuan, Shanxi Province
The deposit is located in Qinshuitai sag of Shanxi platform anticline, and the Paleozoic and Mesozoic strata are exposed in the mining area. The Paleozoic strata formed a syncline structure which spread in the northeast and tilted to the south, and the dip angle of the strata in the syncline was generally around10.
Gypsum deposit occurs in the lower member of Fengfeng Formation (O2f) of Middle Ordovician, and its stratification is as follows:
carboniferous system
-False integration.
The upper member of Fengfeng Formation (O2F2) is 37.7m.
⑥ Gray-black dense limestone (upper limestone O2F2-2)17.20m.
⑤ Yellow-gray-pink dolomite, limestone and yellow-green shale (O2F2- 1)
Lower member of Fengfeng Formation (O2f 1)
④ The upper part is gypsum and clay gypsum layer, the lower part is dolomite limestone and gypsum interlayer, with a thin layer in the middle.
Glauber's salt (gypsum belt O2F 1-3)
③ Gray-dark gray dense limestone and dolomite limestone (middle limestone O2F 1-2)
② Clayey gypsum, breccia clayey gypsum and dolomitic limestone mixed with thin dolomitic gypsum layer and gypsum vein.
(Lower gypsum belt O2F 1- 1)
Shangmajiagou Formation (O2s)
① Gray-dark gray limestone, dolomite limestone and interbedded dolomite and marl (lower limestone)
The deposit consists of two gypsum belts separated by limestone. The Upper Gypsum Zone is divided into three ore groups: ① The ore group consists of six layers of high-grade gypsum, anhydrite and clay gypsum, with a thickness of13.65m and a length of 500m ... ② The ore group consists of two layers of medium-grade dolomite gypsum, with a thickness of 7.3m and a length of 500m, and the top and bottom plates are dolomite (containing gypsum veins). ③ The upper part of the ore group is mainly dolomitic gypsum layer, and the lower part is mainly clayey gypsum and breccia clayey gypsum layer. The ore group is19.04m thick and about 300m long. The lower gypsum layer consists of clayey gypsum, breccia clayey gypsum, medium-grade dolomite gypsum and dolomite limestone. ④ Ore group, 30m thick and 300m long.
The ore bodies are layered and quasi-layered, interbedded with clay gypsum, dolomite and dolomite limestone. There are fiber gypsum veinlets or reticular veinlets in the footwall and surrounding rock of the ore body, which are parallel to or cut into the surrounding rock. The vein thickness is not large, about10 ~ 60 mm. The ore is mainly composed of gypsum, anhydrite, mirabilite, dolomite, clay, pyrite and calcite, and sometimes there is a small amount of celestite. The ore has granular, snowflake-like, porphyritic, fibrous, breccia-like and vein-like structure. The content of gypsum in various ores is above 25%.
There are many gypsum layers in the upper gypsum mine belt, which has industrial significance. The gypsum layer in the lower gypsum zone is thin and muddy, which has little industrial value. After weathering, primary gypsum is leached into cracks or holes in surrounding rock to form fiber gypsum and transparent gypsum, which has no industrial value.
2. Gypsum and anhydrite deposits in clastic rock construction
Gypsum-bearing salt system consists of sandstone, siltstone, mudstone, thin limestone and dolomite, and gypsum layer is sandwiched between mudstone or dolomite. The total thickness of gypsum-bearing rock series is several hundred meters, and the ore body is layered and lenticular. Generally, the thickness of a single layer is tens of centimeters to 2 ~ 3 meters, and the total thickness is10 ~ 20m ~ 20m. Along the strike and dip, the coal seam is several hundred meters to several thousand meters long. The ores are mainly massive anhydrite and mud gypsum, and some are secondary hornblende gypsum and fiber gypsum, with the highest calcium sulfate content of 55% ~ 75%. Ore reserves are not large, and individual huge ones can reach tens of millions of tons.
Gypsum-bearing rock series of such deposits in China often show shallow-water sedimentary characteristics. For example, in the Triassic gypsum-bearing rock series in Sichuan, the tidal flat sedimentary characteristics of carbonate rocks are very obvious, and shallow water marks such as debris, wave marks, small plate-like staggered layers and scouring surfaces in the lower part of the subtidal high energy band and intertidal zone are clearly visible, and common biological sinkholes, flexural structures, quasi-syngenetic dolomite and nodular gypsum are found in the intertidal zone and the upper part of the intertidal zone. The shallow water sedimentary characteristics of Triassic gypsum deposits in Hubei and Jiangsu are also obvious, indicating that Triassic Yangtze sea area belongs to shallow water evaporation sedimentary environment.
In China, most of these deposits occur in Triassic and older strata. Cambrian gypsum deposits are distributed in northeastern China, southern North China and some southwestern provinces. The Ordovician gypsum deposits are concentrated in the North China Platform. Carboniferous gypsum deposits are mainly distributed in Xinjiang, Qinghai, Gansu, Ningxia, Inner Mongolia, Guangxi, Guizhou and Yunnan. Triassic gypsum deposits are distributed in Yangtze platform. From Cambrian to Triassic, the distribution position of gypsum deposits moved from north to south, and the distribution area became wider and wider. The main producing areas are Quxian in Sichuan, Nanjing in Jiangsu, Taiyuan in Shanxi, Tianzhu in Gansu, Liaoyang in Liaoning and Xixiang in Shaanxi.
(2) the deposition of gypsum and anhydrite by lake evaporation.
The deposit occurs in inland lake basin and is obviously controlled by faults. Gypsum-bearing rock series is a set of continental red or variegated strata, which consists of conglomerate, sandstone, siltstone, mudstone, dolomite and dolomite limestone. Among them, it can be divided into clastic rock formation, carbonate-gypsum formation, anhydrite formation and the transitional types between them. The reserves of mineral deposits are very large, often from several million tons to several hundred million tons. Gypsum and anhydrite deposits in red clastic rocks are layered and layered, with a length of several hundred meters to several thousand meters. Gypsum layers are often produced in multiple layers, and the thickness of a single layer is tens of centimeters to several meters and dozens of meters. The natural types of minerals mainly include mud gypsum, fiber gypsum, alabaster and anhydrite, with calcium sulfate content of 55% ~ 80% and fiber gypsum of 98%. Associated minerals include clay minerals, calcite, dolomite, quartz, feldspar and mirabilite.
Such deposits are widely distributed in China, accounting for two-thirds of the total gypsum reserves in China. The metallogenic age is from Cretaceous to Paleogene, which is mainly distributed in three structural zones: ① Tancheng fault zone (gypsum-bearing basins of Paleogene such as Hengyang, Shaodong, Liuyang, Dingyuan, Zaozhuang and Dawenkou); ② Daxinganling-Taihang-Xuefeng deep fault zone (Paleogene gypsum-bearing basins such as Sanmenxia, Biyang, Xichuan, Xunxian, Fangxian and Zaoyang); ③ Yinkun fault zone (Paleogene gypsum-bearing basins such as Hangjinqi in Inner Mongolia, Tongqin in Ningxia, Mile in Yunnan and Honghe Basin). In addition, some gypsum-bearing basins are controlled by east-west fault depression, such as Jingmen, Yunmeng, Yingcheng and Sanshui. The lower part of this kind of gypsum basin in China is mostly volcanic rock. For example, there are 14 layers of Yanshanian basalt in Yunying basin, with a total thickness of more than 200 meters. The occurrence of basalt is consistent with the surrounding rock, and the changes of main chemical components and trace elements are also closely related, indicating that volcanic fire may be an important source of ore-forming materials for this type of gypsum deposit. The main producing areas are Yingcheng in Hubei, Yunmeng, Jingmen, Shaodong in Hunan, Dawenkou in Shandong and Yisa in Honghe, Yunnan.
Example of deposit: Yingcheng gypsum deposit in Hubei Province
The deposit belongs to lacustrine sedimentary deposit, which is located in Panjiaji secondary sag in the western margin of Yunying sag. The ore-bearing rock series in Yunying Depression is Paleogene Eocene lacustrine clastic rock, which is composed of mudstone, siltstone, gypsum, glauberite and halite, with a thickness of 394 ~1628 m ... from bottom to top, it is as follows: the lower gypsum section is 72 ~ 223 m thick, with more than 400 layers of fiber gypsum, with a single layer thickness of 1 ~ 25 cm. The lower section contains glauberite with a thickness of 57 ~ 285 m, and the lower section contains more than 70 layers of fiber gypsum13 m, with a single thickness of1~13 m. There are three recoverable gypsum groups. The thickness of salt-bearing rock section is 230 ~ 910m; The upper section of glauberite is 7 ~ 81m thick; The upper gypsum-bearing section is 28 ~ 129 m thick, and there are dozens of layers of fiber gypsum (Figure 13- 1).
Figure 13- 1 Tao Weiping et al. (1994) Gypsum-bearing Rock Series Profile in Yunying Basin
The ore-bearing rock series of Panjiaji gypsum mine in Yingcheng lacks gypsum-bearing section and glauberite-bearing section, and is covered by Quaternary system, with a thickness of 8 ~ 23m. Gypsum layer is distributed along the edge of the depression basin and inclines into the basin with an inclination angle of 7. Generally, fiber gypsum and argillaceous gypsum are dominant within 2km from the basin edge, and anhydrite (including some fiber gypsum) is dominant within 2 ~ 4 km from the basin edge. Fiber gypsum with industrial value is produced in the blue-gray stratum with bedding fractures. The single layer thickness is 4 ~ 8 cm, the maximum thickness is 25.5cm, the thickness of recoverable gypsum group is 1.7 ~ 2.5m, the ore content is14% ~19.13%, and the strike extension can be achieved. Fiber gypsum is pure and has excellent texture, and the ore grade (CaSO4 2H2O) is generally 98%. It is the main product of Yingcheng gypsum mine and the main producing area of high-quality gypsum in China. The thickness of argillaceous gypsum is 5 ~ 28 cm, and the ore grade is 60%, which can be mixed with fiber gypsum. There is also anhydrite, with a single layer thickness of 2 ~ 8m, strike extension 1.9 ~ 3.5km, dip extension 1km or more, and ore grade of 55% ~ 75%. Several large, medium and small gypsum mines have been proved in Yingcheng and Yunmeng areas, with proven reserves exceeding 654.38 billion t.
Gypsum deposition model in lacustrine sedimentary rocks of continental basin
Based on the study of China Huxiang gypsum deposit, Wang Erli and others put forward the gypsum deposit model in Huxiang sedimentary rocks in inland basin (Figure 13-2).
Figure 13-2 Model diagram of gypsum deposit in Huxiang sedimentary rocks in continental basin (according to Wang Shuli, 1995).
Brief description of the model and main metallogenic mechanism: concentrated brine from the preparatory basin flows into the closed and semi-closed secondary tectonic depression (metallogenic basin). In the dry climate, the brine in the salt lake is continuously evaporated and concentrated, and a large amount of gypsum is first precipitated with the increase of salinity. Then, when the salinity of brine increases or the composition of solution changes (such as chloride increases), a small amount of anhydrite is directly precipitated. Most of the primary precipitated gypsum and anhydrite were preserved in the diagenetic stage at a proper temperature and depth, and gypsum deposits and anhydrite deposits were formed by consolidation. Due to the change of temperature and pressure, part of gypsum is dehydrated into secondary hard gypsum, and the primary gypsum is metasomatic, forming metasomatic anhydrite mine. After the gypsum deposit was formed, the mineralization occurred in the epigenetic stage when the ore-forming brine flowed in again. If the ore-forming brine is filled along the cracks of gypsum deposits, overlapping gypsum deposits will be formed; Vein gypsum mine will be formed if it is filled along mudstone cracks.
The main ore-controlling factors are as follows: ① Like most salt-forming basins in the world, China is a basin system formed in a large subsidence area controlled by deep faults; Secondary faults divide the basin system into several secondary basins. Due to the activity of the basin and the migration and separation of water in it, a series of salt deposits have been caused. Therefore, fault activity determines the occurrence and development of gypsum-forming basin and salt-forming basin. ② According to stratigraphic profile, paleontology and sporopollen analysis, gypsum deposition is closely related to paleoclimate. For example, the sporopollen assemblage of extremely thick gypsum strata is mainly drought-loving ephedra plants, while the sporopollen assemblage of upper and lower marls and oil shale strata is mainly Taxodium distichum, single bundle and double bundle. This shows that climate controls gypsum deposition. ③ Weathered salt, deep water and short-lived seawater brought by land surface water are the material basis of gypsum salt deposition, which directly affect the scale, grade and distribution of the deposit.
The prospecting indicators mainly include: ① shallow water indicators such as mudstone, marl and cracks under coal seams; ② The sporopollen assemblage of strata is mainly drought-tolerant ephedra.
Main deposit examples: Shandong Dawenkou gypsum mine, Hebei Shuangbei gypsum mine, Hubei Yunying gypsum mine, Guangdong Sanshui gypsum mine and Yunnan Honghe Yisa gypsum mine.
(3) Gypsum deposit in river alluvial clastic rock construction.
Deposits are often distributed in the front of the fast-rising area with relatively flat terrain. Gypsum-bearing rock series belongs to Quaternary alluvium, which is formed by rapid accumulation of ancient gypsum debris transported by surface runoff in areas where runoff is blocked or flow velocity is slowed down. For example, the gypsum mine in Wu Jiayu, Lixian County, Hunan Province is located in the transition area from the western alpine region to the eastern quasi-plain region. The Triassic gypsum-bearing layer in the upper reaches of the mining area was eroded and transported by the ancient Lishui River and deposited in the gentle zone in the lower reaches. The ore body is horizontally layered, and the roof and floor are clay and chalk. The maximum thickness of the seam is 85 meters, and the thinnest is 2.5 meters, generally 20 ~ 50 meters. The ore is mainly composed of gypsum and clay minerals, with occasional chalk, celestite, sand and gravel. The ore types are granular and crystalline gypsum, followed by alabaster and translucent gypsum. The content of calcium sulfate is about 80%, and its reserves are about tens of millions of tons. There are two views on the origin of this kind of deposits: mechanical deposition and evaporative deposition.
(4) Gypsum sand deposition in aeolian sand dunes.
This kind of deposit is formed by physical weathering of primary gypsum layer to form gypsum sand, which is transported by wind and accumulated into sand dunes. The "White Sand" gypsum sand dune in Tularosa Desert, New Mexico, USA, is 10 meter high and covers an area of about 648 square kilometers. Dunes are composed of 97% ~ 99% gypsum sand, with a geological reserve of 6 billion tons. This gypsum dune has not been found in China.
(5) Weathering-secondary filling gypsum deposit
Gypsum, anhydrite deposits, gypsum-bearing rock series or other rocks generated in the early stage are chemically weathered to form groundwater solutions rich in Ca2+ and so24- 4, which enter cracks or caves in surrounding rocks after short-distance migration, and then precipitate to form secondary gypsum deposits. Including the following two types: ① Fracture-filled gypsum deposits in clastic rocks. Most ore bodies are plate-shaped and occur along rock strata or fractures. Veins often appear in groups, and the thickness of a single vein is several centimeters to several tens of centimeters. The minerals are mostly transparent gypsum and fiber gypsum, followed by clay and anhydrite. This deposit is small in scale and can be mined in situ. ② Karst cave gypsum deposits in carbonate rocks. Ore bodies are generally irregular, and often distributed along the bottom of the cave in the form of blocks, nests and sacs. Sometimes they are mixed in the gravel layer at the bottom of the cave in the form of shells or scattered, or stalagmites hanging on the top and wall of the cave. Sometimes gypsum is produced in karst caves in the form of well-developed crystals, the length of which can reach several tens of centimeters. This kind of deposit is generally of no industrial value.
(6) hydrothermal metasomatism of gypsum and anhydrite deposits
Hydrothermal solution rich in sulfuric acid metasomatism calcareous rocks to generate anhydrite, which constitutes a deposit when its content reaches industrial grade and has a certain scale. Including: ① hydrothermal metasomatism in volcanic rocks. The deposit occurs in neutral extrusive rocks such as andesite, and the ore body is lenticular or layered. The natural types of ores are anhydrite, kaolinite anhydrite containing pyrite or alunite and gypsum. Associated minerals in the ore include pyrite, alunite, kaolinite, Yingshi, barite, magnetite, natural sulfur and hematite. This deposit is very small in scale. ② Contact metasomatic type in carbonate rocks. The deposit occurs in the contact zone between neutral magmatic rocks and limestone, and the ore bodies are lenticular, with a strike length of tens to hundreds of meters and a thickness of several meters to tens of meters, and often produce multiple ore bodies. The ore types are anhydrite, dolomitic anhydrite and gypsum. Associated minerals include dolomite, calcite, magnetite, pyrite and chlorite. The scale of the deposit is small and medium-sized, and it often coexists with internal pig iron and copper ore.
Three. Resource distribution and metallogenic regularity
(A) the allocation of resources
China is rich in gypsum resources, and there are 23 provinces (autonomous regions) producing gypsum mines. There are 199 gypsum mines with proven reserves in China, and the proven resource reserves are about 644,438+0.6 million t. From the perspective of regional distribution, Shandong gypsum mine is the largest, accounting for 60% of the national resource reserves. Followed by Inner Mongolia, Qinghai, Hunan, Hubei, Ningxia, Guangxi, Anhui and Jiangsu provinces (autonomous regions), accounting for 32% of the total gypsum mine resources in China. The main gypsum mines are Etuoke Banner in Inner Mongolia, Yingcheng in Hubei, Hunjiang in Jilin, Nanjing in Jiangsu, Dawenkou in Shandong, Qinzhou in Guangxi, Taiyuan in Shanxi and Zhongwei in Ningxia.
(2) Metallogenic regularity
There are many types of gypsum deposits in China, with a wide range of formation age and distribution. Gypsum is produced in almost every geological period, and its main metallogenic periods are Early-Middle Cambrian, Middle Ordovician, Early Carboniferous, Early-Middle Triassic and Cretaceous-Paleogene. These five metallogenic periods formed the most important gypsum deposit-sedimentary deposit in China, and it has obvious metallogenic regularity and distribution law: marine sedimentary deposits were formed in the early-middle Triassic and before, while lacustrine sedimentary deposits were mainly formed from Jurassic to Quaternary.
From CAMBRIAN to Triassic, with the gradual expansion of Chinese mainland and the southward movement of continental margin sea, the distribution position of marine gypsum deposits gradually moved from north to south, the distribution range became larger and larger, and the continuity of metallogenic belt became better and better. Early and Middle Cambrian gypsum deposits are mainly distributed in eastern Liaoning and southern Jilin, eastern Tibet, southeastern Sichuan and northeastern Yunnan, with sporadic mineralization in Guizhou, Hubei, Hunan, Shandong and Xinjiang. It belongs to gypsum and anhydrite deposits built by coastal carbonate clastic rocks and is the product of bays or lagoons. The deposit is of small thickness, poor continuity and low grade, but this mineralization period is of great significance to the northeast region lacking gypsum.
Middle Ordovician gypsum deposits are mainly distributed in western Shanxi and southern Hebei, and also found in Henan, Shaanxi and Shandong. They belong to marine carbonate gypsum and anhydrite deposits, with thick coal seams, good continuity and good quality, and are the main mining targets in North China.
Gypsum and anhydrite deposits were built in the northern part of gypsum mine in Early Carboniferous, which are coastal carbonate clastic rocks, mainly distributed in Xinjiang, Qinghai, Gansu, Ningxia and Inner Mongolia. Gypsum-bearing rock series is strip-shaped, with large thickness and good quality, which is the main mining object in northwest China. Gypsum and anhydrite deposits deposited in the early Carboniferous in southern China are marine carbonate rocks, mainly distributed in western Jiangxi, Hunan, Guizhou, northern Guangxi and eastern Yunnan.
The early and middle Triassic is an important metallogenic period. Gypsum deposit was formed in the marginal sea of North China continent at that time. Marine carbonate rocks are continuously distributed in Jiangsu, Anhui, Hubei, Hunan, Guizhou, Sichuan, Yunnan and Tibet. There are many deposits, thick seams and good quality, but they are on the edge of continental marginal seas, such as western Qinghai, southern Sichuan, western Yunnan, western Hubei and Hunan.
Cretaceous-Paleogene is also an important metallogenic period, and lacustrine gypsum deposits are widely distributed. Almost all gypsum-producing provinces have deposits formed in this period, but they are concentrated in the eastern and northwestern regions of China. Gypsum minerals are located in small inland lake basins, belonging to lacustrine clastic rock-forming gypsum and anhydrite deposits. Most of the gypsum-bearing fault basins are controlled by three deep fault zones, Tanlu, Taihang Xuefeng and Yinkun in Daxing 'anling, which are distributed in the northeast. There are gypsum-bearing basins such as Dawenkou, Zaozhuang, Dingyuan, Liuyang, Shaodong and Hengyang on the west side of the Tanlu fault zone. There are a series of gypsum-bearing basins such as Sanmenxia, Biyang, Xichuan, Xunxian, Fangxian, Zaoyang, Qing Yu and Ping Huang in the Xuefeng fault zone of Taihang Mountain in Daxing 'anling. There are gypsum-bearing basins in Yin Kun fault zone, such as Jin Hang, Tongxin, Dayi, Qionglai, Meishan, Tianquan, Xinjin, Xide, Mile and Honghe. These gypsum-bearing basins are all located in or near the fault zone. There are basically volcanic rocks in the lower part of gypsum-bearing rock series, but there is no gypsum in large basins far from the fault zone. In addition, some gypsum-bearing basins are piedmont fault basins or fault basins controlled by fold belts, such as Jingmen, Yingcheng Yunmeng and Sanshui, where gypsum is scattered. The metallogenic characteristics of Cretaceous-Paleogene gypsum are as follows: the scale of deposits is very different, the ore types are complex, the quality changes greatly, and the thickness of ore beds is small. Because the ore body is not deeply buried, it is the main mining object in the central and eastern regions of China.