1. Overview

Limestone is the main rock type of carbonate rock. It is widely distributed in the earth's crust, accounting for about 20% of the total area of ??sedimentary rocks, and is found in the bottom layers of all eras. output. Many metal and non-metal mineral deposits and the output of oil and natural gas are related to carbonate rocks such as limestone. It has a wide range of uses in construction, metallurgy, chemical industry, light industry, food, petroleum, agriculture and many other fields, and is an important raw material for the cement industry.

2. Mineral properties

The chemical molecular formula of limestone is CaCO3, and its chemical composition is mainly CaO, generally 45% to 55%; followed by MgO, SiO2, Al2O3, Fe2O3, K2O, Na2O, etc., but the content is very small, and the loss on ignition can reach 35% to 50% in chemical analysis.

Limestone is insoluble in water and foams violently when exposed to dilute hydrochloric acid, releasing CO2. When limestone is calcined above 900°C, it decomposes and transforms into lime (CaO), releasing CO2. Quicklime deliquesces when exposed to water and immediately forms hydrated lime [Ca(OH)2]. The slurry can be adjusted after the hydrated lime dissolves in water, and it hardens easily in the air.

The mineral composition of limestone is mainly calcite, accompanied by dolomite, magnesite and other carbonate minerals. In addition, it also contains chalcedony, opal, clay minerals, pyrite, glauconite, and gypsum. , anhydrite, phosphate minerals, etc. Some types of limestone also contain organic matter such as coal, asphalt, alkali metal compounds, and compounds such as strontium, barium, manganese, titanium, and fluorine, but the content is very low. The color is colorless, white, gray, off-white, and turns to gray-yellow, light red or blue-green when containing impurities. The streaks are colorless and glassy. The fracture surface is uneven, the hardness is 3, and the density is 2.6~2.8g/cm3. Lime has excellent properties such as thermal conductivity, solidity, water absorption, air impermeability, sound insulation, polishability, good cementing properties, and processability.

3. Uses

Limestone is widely used in many industrial sectors such as building materials, metallurgy, chemical industry, and construction engineering. It can either directly utilize raw ore or be deeply processed.

1) Cement raw materials. Limestone is the main raw material for the production of Portland cement. Limestone, combined with clay raw materials, siliceous raw materials, iron powder, etc., can be calcined into cement clinker. Its dosage is about 80% of the general cement raw materials.

2) Make quicklime. Limestone is calcined to produce CaO, or quicklime, which is then hydrolyzed to produce Ca(OH)2, or hydrated lime, which is a hard cementitious material widely used in the construction industry.

3) Metallurgical flux. Mainly used as a flux for smelting pig iron, steel and non-ferrous metals.

4) Chemical industry. In the chemical industry, it is used to make alkali, calcium carbide, nitrogen fertilizer and phosphate fertilizer.

5) Pure limestone, after being crushed, can be widely used as filler in paints, plastics, papermaking, coatings, rubber, building sealants, etc.

6) Used in sugar, glass, ceramics, printing and other industrial fields.

7) Processed into stone for architectural decoration.

IV. Geological Characteristics

Calcite in magmatic rocks is the main mineral component of carbonate rocks, and calcite in hydrothermal veins is a common gangue mineral. Calcium carbonate deposition is mainly a biological and biochemical deposition process, which occurs in shallow sea environments at the edge of sea basins and clean waters under warm climate conditions.

Generally, limestone deposits are divided into the following types.

1) Chemical sedimentation deposits. It is the most important type of limestone deposit. According to its lithology, it can be divided into two types: micritic limestone deposits and oolitic limestone deposits. The mineralization age and distribution range of micritic limestone deposits are wide, and they are produced in almost all major ore-bearing strata. Typical deposits include cement limestone deposits such as Fengfeng in Handan, Hebei, Emeishan in Sichuan, and Umbrella Mountain in Tongling, Anhui. The shape of the ore body of this type of deposit is generally simple, layered or layer-like, extending up to several kilometers, with a thickness of several meters to tens of meters or even hundreds of meters. The scale of the deposits is mainly large and medium-sized. The ore is generally gray to dark gray, with a micrite structure and a massive structure. It has pure chemical composition and low impurity content. It is a calcareous raw material for high-quality cement. The formation of oolitic limestone is related to the action of wave currents, and often has large-scale cross-bedding. The ore body shape of this kind of deposit is mainly layered, the layers are relatively stable, the thickness is several meters to tens of meters, and the size of the deposit is mainly large and medium. The color of the ore ranges from light to dark, with a granular structure, mainly bright crystal cementation, and a massive structure.

2) Mechanical clastic sedimentary deposits. It is mainly distributed in the Upper Cambrian and Lower Ordovician in northern China, and is also produced in the Upper Devonian and Lower Triassic in the south. Generally, mineralization occurs in the supratidal zone or intertidal zone as a result of repeated erosion, transport, and deposition of carbonate sediments by tidal waves under conditions of frequent advance and retreat of seawater, strong oscillation, and frequent changes in the depositional environment. The lithology is mainly gravel, sand, and silty limestone, often intercalated with micrite limestone and oolitic limestone. Cement limestone deposits such as Qifeng Mountain in Datong, Shanxi, Mingzu Mountain in Qingzhou, Shandong, and Laobao Mountain in Liujiang, Guangxi all belong to this type. The shape of the ore body is layered, layer-like, several meters to more than ten meters thick, and the size of the deposit ranges from small to large.

The ore is light gray, gray-brown or gray-yellow, with a granular structure and a thin-layered structure. It is cemented with micrite or bright crystals and has high mud and iron content. Common biological detritus such as brachiopods, trilobites, ostracods, etc. Insects, echinoderms, etc. have large changes in chemical composition, and the CaO content is generally low. Due to the strong evaporation in the depositional environment, high magnesium brine is easily formed, causing dolomitization of the limestone, and the MgO content is often high.

3) Biochemical sedimentary deposits. Often marked by rich bioclasts, they are distributed in both the south and the north, especially in the upper Paleozoic in the south. For example, the Huanglong Limestone of the Middle Carboniferous System in Zhejiang, Jiangsu, Anhui, Jiangxi and other places is a bioclastic limestone mainly composed of fossils and crinoid fossils. The Upper Carboniferous Chuanshan Limestone above it is composed of nucleoids and Other bioclastic limestones dominated by bioclasts; Middle and Upper Devonian phycococcococcal limestone in Guangxi, Guizhou, Yunnan and other places and Permian bioclastic limestone in Shaanxi, Sichuan, Yunnan and other places; Precambrian in Liaoning , Hebei Jixian County - Neoproterozoic laminated limestone and algal limestone, etc., are composed of cement limestone deposits all belong to this type. Ore bodies are often produced in layers, with relatively stable shapes and thicknesses ranging from several meters to tens of meters or even hundreds of meters. The size of the deposits is mainly large and medium. The ore is grey-black, with a powdery structure and a massive structure. It contains many types of biological debris, such as foraminifera, ostracods, brachiopods, gastropods, stromatoporoids, etc., often mixed with micrite and powder. Crystalline limestone. In bioclastic limestone ores formed by accumulation of biological skeletons, the CaO content is generally above 50% and the MgO content is low, making it an excellent cement limestone raw material.

4) Recrystallization deposits. It is formed after the recrystallization of limestone due to magma intrusion and regional metamorphism. Cement marble deposits in Heilongjiang, Xinjiang, Liaoning, Inner Mongolia and other places belong to this type, for example, Heilongjiang Acheng Xinming, Xinjiang and Jingrehu cement marble deposits. Limestone becomes crystalline limestone or marble after recrystallization. The ore is dense and hard. The morphology of ore bodies is generally complex, including layered, layer-like, lenticular, nested, etc. The size of the deposits is mainly medium and small. The chemical composition of marble is relatively stable, with CaO content generally greater than 52% and low MgO content. This type of deposit often affects the quality of the ore due to silicification, and at the same time, the development of rock veins affects mining and utilization.

5. Distribution of Mineral Deposits

my country is one of the countries rich in limestone mineral resources. The limestone resources are widely distributed, large in reserves and of high quality. The prospective reserves of surface limestone are very huge. Limestone minerals have been deposited in every geological era and distributed in various stages of geological structural development, but limestone deposits with good quality and large scale often exist in certain layers.

Paleoproterozoic limestone is mainly distributed in Inner Mongolia, Heilongjiang, central Jilin, and Xinyang and Nanyang in Henan, and is dominated by marble.

Mesoproterozoic limestone resources are mainly distributed in Liaodong Peninsula, Tianjin, Beijing, northern Jiangsu, Gansu, Qinghai, Fujian and other places. The main lithology is siliceous limestone, chert limestone, etc.

Cambrian limestone resources are distributed in Shanxi, Beijing, Hebei, Shandong, Anhui, Jiangsu, Zhejiang, Henan, Hubei, Guizhou, Yunnan, Xinjiang, Qinghai, Ningxia, Inner Mongolia, Liaoning, Jilin, Heilongjiang, etc. The ground is dominated by oolitic limestone, pure limestone, bamboo leaf limestone, and thin-layer dolomitic limestone.

Ordovician limestone resources are distributed in Heilongjiang, Inner Mongolia, Jilin, Liaoning, Beijing, Hebei, Shanxi, Henan, Shaanxi, Gansu, Qinghai, Xinjiang, Sichuan, Guizhou, Hubei, Anhui, Jiangsu, Jiangxi, etc. The main lithology is thin layer, thick layer pure limestone, dolomitic limestone, porphyry limestone, gravelly limestone, etc.

Silurian limestone is mainly distributed in Toksun, Xinjiang, Golmud, Qinghai, Gansu, Inner Mongolia and other places. The main lithology is argillaceous limestone, siliceous limestone, crystalline limestone, etc.

Devonian limestone resources are mainly distributed in Guangxi, Hunan, Guizhou, Yunnan, Guangdong, Heilongjiang, Xinjiang, Shaanxi, Sichuan and other places. The main lithology is thick pure limestone, dolomitic limestone, Crystalline limestone, thin-bed limestone, argillaceous limestone, etc.

Carboniferous limestone resources are mainly distributed in Jiangsu, Zhejiang, Anhui, Jiangxi, Fujian, Guangxi, Guangdong, Sichuan, Hubei, Henan, Hunan, Shaanxi, Xinjiang, Gansu, Qinghai, Yunnan, Guizhou, Inner Mongolia, In Jilin, Heilongjiang and other places, the main lithology is thick pure limestone, thick limestone intercalated with sandy shale, dolomitic limestone, marble, crystalline limestone, etc.

Permian limestone resources are mainly distributed in Sichuan, Yunnan, Guangxi, Guangdong, Fujian, Zhejiang, Jiangxi, Anhui, Jiangsu, Hubei, Hunan, Shaanxi, Gansu, Qinghai, Inner Mongolia, Heilongjiang, Jilin and other places , the main lithology is thick limestone, chert limestone, siliceous limestone, dolomitized limestone, marble, etc.

Triassic limestone resources are mainly distributed in Guangxi, Yunnan, Guizhou, Sichuan, Guangdong, Jiangxi, Fujian, Gansu, Qinghai, Zhejiang, Jiangsu, Anhui, Hunan, Hubei, Shaanxi and other places. The main lithology They are argillaceous limestone, thick-bed limestone, thin-bed limestone, etc.

Jurassic limestone resources are mainly distributed in the Zigong area of ??Sichuan, and are dominated by inland lacustrine sedimentary limestone.

Paleogene-Neogene limestone resources are mainly distributed in Xinxiang and Zhengzhou areas of Henan Province, and are dominated by marl and loose calcium carbonate.

6. Available resources

my country’s limestone can be divided into cement limestone, metallurgical limestone, limestone, chemical limestone, construction limestone and decorative limestone according to its uses. wait. By the end of 2005, my country had identified 2,050 limestone mineral deposits, including 1,554 limestone deposits for cement, 65 limestone deposits for construction and decoration, and 431 other mineral deposits. The identified resource reserves of limestone for construction are 13116×104m3, the identified resource reserves of limestone for facing are 11040.77×104m3, and the identified resource reserves of other minerals are 914.62×108t.

The distribution of identified resource reserves of major limestone mineral sites in my country is shown in Table 2-52-1, Table 2-52-2 and Table 2-52-3.

Table 2-52-1 Identified resource reserves of major limestone mineral sites in China

(According to the "National Mineral Resources and Reserves Report" of the Ministry of Land and Resources, 2005)

Table 2-52-2 Distribution of main mineral reserves of limestone for construction in China

(According to the "National Mineral Resources Reserve Report" of the Ministry of Land and Resources, 2005)

Table 2 -52-3 Distribution of main mineral reserves of limestone for facing in China

(According to the "National Mineral Resources and Reserves Report" of the Ministry of Land and Resources, 2005)