The deposit occurs in metamorphic rock series of early Cambrian. The rock series is composed of schist and gneiss rich in graphite and high in aluminum, and also composed of metamorphic rocks such as marble and quartzite, also known as khondalite series. The common characteristic minerals in rock series are graphite, apatite, sillimanite, hypersthene, clinopyroxene, feldspar, garnet and cordierite. The graphite deposits in regional metamorphic rock series at home and abroad occur in khondalite series and similar metamorphic sedimentary rock series without exception. The original rocks in khondalite series are high alumina claystone-semi claystone, sandstone, dolomitic marl and carbon-rich limestone. There are often round clastic particles of rutile and zircon in gneiss, which indicates that the original rock should be the product of terrigenous shallow sea deposition, and most of them were formed at the end of Neoarchean-Paleoproterozoic.
Graphite deposits are generally layered, quasi-layered, lenticular and multi-layered, which are in integral contact with host rocks and have stratabound characteristics, and can extend for several kilometers to dozens of kilometers along a certain horizon. The deformation of ore bodies is strong, which makes the shape and occurrence of ore bodies complicated, and sometimes they can be distributed in groups and belts. The ore body is mainly graphite schist or graphite gneiss, and the metamorphic degree generally reaches amphibolite facies and granulite facies. Due to migmatization, some granite pegmatite veins sometimes appear near the deposit.
The material composition and structure of the ore are the same as those of the surrounding rock near the mine. The common natural types of ores are graphite schist and graphite gneiss, followed by graphite diabase, and there are graphite granulite, graphite marble and graphite migmatite in a few deposits. This kind of ore is characterized by containing flaky graphite. In addition, there are plagioclase, quartz, biotite, garnet, potash feldspar, diopside, zircon, rutile and metal sulfides such as iron, copper and zinc. Minerals such as graphite are evenly distributed and directionally arranged in the ore, forming gneiss or flake structure, and the flake diameter is generally 0.5 ~ 65438 0.5 mm. Due to migmatization, the flake size can be increased, and the scales are locally concentrated to form variegated structure until some graphite veins are formed. The grade of ore is relatively stable, and the carbon content is generally 5% ~ 10%. The content of V2O5 in some ores is relatively high, ranging from 0.02% to 0.1%. The content of P2O5 is also high. When the ore body is destroyed by cracks, the graphite ore is slimed, and the quality of the ore decreases where the cracks pass.
The carbon isotope value of graphite in ore is quite different from that of calcite in marble, but similar to that of natural coke and crude oil (Table 3- 1), indicating that the carbon forming graphite comes from organic carbon, not inorganic carbon transformed from carbonate rocks by metamorphism.
Table 3- 1 Determination Table of Carbon Isotopic Composition of Graphite Deposits and Organic Compounds
Table 3- 1 shows that the graphite deposits in the early Precambrian crystalline schist belong to the regional metamorphic type. The appearance of natural graphite deposit in central Dali, khondalite series in the early Precambrian recorded the first large-scale biological activity on the earth, and it was speculated that the atmosphere at that time had changed from reduction to oxidation. The shallow sea sedimentary environment developed in kunzite is suitable for algae growth. A large number of propagated algae are buried in mud and sand sediments, and regional metamorphism forms graphite deposits.
This kind of deposit is generally large and medium-sized, with good graphite quality and stable grade, which is easy for mineral processing and open-pit mining. It is the most important type of graphite deposit and occupies a very important position in the world. 95% of the proven graphite reserves in China come from this type.
China's southwest villa in Laixi, Shandong, Liumao in Jixi, Heilongjiang, Boli Foling, Xinghe in Inner Mongolia, Jinxi in Jiangxi and other graphite deposits all belong to this type. In addition, it is also an important type of graphite deposit in Russia, North Korea, Madagascar, Norway and other countries.
In China, the Nanshu graphite deposit in Shandong Province is the most typical one of this type of deposits, and its characteristics are as follows: the deposit is located in the upper part of the Paleoproterozoic Jingshan Group at the southwest end of the Jiaoliao block in the China-Korea craton (Figure 3-2), and the rock combination constitutes the graphite formation, which can be divided into three rock combinations from bottom to top.
1. Combination of marble, amphibole plagioclase gneiss and graphite gneiss
The main interlayer is serpentine olivine marble and amphibole plagioclase gneiss, with graphite gneiss, garnet plagioclase gneiss and a small amount of amphibole, diopside and quartzite, with the maximum thickness of 420m, 1 graphite layer.
2. amphibole plagioclase gneiss is combined with marble and graphite gneiss.
It is mainly amphibolite plagioclase gneiss, with phlogopite, periclase marble and graphite gneiss, and a small amount of biotite granulite and amphibole, with a maximum thickness of 950m, 1 graphite layer.
3. Marble amphibole plagioclase gneiss assemblage
It is composed of dolomite marble, serpentine olive marble and amphibole plagioclase gneiss, with a small amount of graphite-bearing rocks, generally without industrial graphite layer, and the maximum thickness is about 5 10m.
In the whole ore-bearing formation, the most important rock type is amphibole plagioclase gneiss, whose thickness accounts for more than 60% of the section; Secondly, the dolomite marble is dominated by olive marble, accounting for about 25% of the thickness; Graphite gneiss accounts for about 7% ~ 8%; The rest rocks only account for 6% ~ 7%. Therefore, the ore-bearing formations are carbon-bearing amphibole plagioclase gneiss-graphite biotite gneiss-magnesium marble and amphibole plagioclase gneiss, and their original rocks are carbon-bearing sandstone-claystone-magnesium carbonate formations in shallow sea or lagoon facies, in which rich organic matter provides a material basis for the formation of graphite deposits in the future.
Nanshu graphite mine includes Hou Yuan ore body, Liujiazhuang ore body and Yueshi ore body, which extends intermittently from east to west for about 4 kilometers. ① The ore body behind the courtyard is lenticular, 600 meters long from east to west and about 80 meters thick. The direct surrounding rocks of the ore body are diabase, dolomite marble, etc. ② Liujiazhuang orebody is located 80m north of Hou Yuan orebody, and several layers of graphite deposits with different thicknesses are superimposed together to form a complex ore group. The graphite deposit extends about 2 kilometers from Liujiazhuang to the west with a thickness of 4 ~ 53 meters. The surrounding rocks are mainly garnet plagioclase gneiss and dolomite marble, and diopside or feldspar diopside is often distributed near the rock mass. ③ Yueshi ore bodies are mainly distributed in the west bank of Xiaoguhe River, with a length of more than 1km in the east and a total thickness of 100 ~ 200m. The rocks are mainly garnet plagioclase gneiss, in addition to diopside and quartzite. The ore body inclines to the south, and the surrounding rocks of the footwall are biotite garnet plagioclase gneiss, serpentine marble, feldspar diopside and diopside.
Figure 3-2 Geological Schematic Diagram of Graphite Deposit in Lunatone
(According to the exploration report of Nanshu graphite mine, 1965)
BM- artificial deposition; Q- four yuan; Mfhg-migmatized garnet plagioclase gneiss;
BG mica gneiss; AHg—- amphibole plagioclase gneiss; SMB-serpentine marble;
HD- feldspar diorite; G- graphite gneiss; F- fracture zone
The scale diameter of Nanshu graphite mine is 0.0 1 ~ 6 mm, with 0. 1 ~ 0.4 mm as the most, and the proportion of coarse scales is relatively high. The grade of various ores is generally 5% ~ 10%. The content of sulfur and iron is high, Fe2O3 is 5% ~ 12%, and S is 1% ~ 5%, which mainly comes from pyrite distributed in veinlets and thin slices. Many graphite gneiss ores contain rutile, especially those rich in felsic minerals. Generally, the rutile content per ton of raw ore is 1 ~ 3 kg, which can be comprehensively recovered. The composition of sulfide veins and felsic minerals are related to migmatization.
In Yue's orebody, the ore is dominated by gneiss structure, graphite scales are roughly evenly distributed and directionally arranged, and some of them are parallel fine stripes according to different minerals, reflecting the original micro-bedding.
The ore structure of Hou Yuan orebody is mainly porphyritic structure and gneiss structure. The graphite scales of porphyritic minerals are larger than those of pockmarked minerals, and often concentrate into small aggregates, which are distributed among feldspar, quartz and other mineral particles, and become thicker due to recrystallization, so the arrangement of chips has no certain directionality.
The carbon isotope analysis data of graphite in Nanshu graphite deposit and carbonate in surrounding rock marble show that they are not homologous, graphite carbon comes from organic matter, while carbonate carbon in marble is inorganic (Figure 3- 1).
Various characteristics show that the Nanshu deposit was formed by sedimentary metamorphism, and the ore body was partially transformed by hydrothermal solution in the process of migmatization.
The quality of the graphite ore in Xishu, Laixi, Shandong Province is good, and the proven reserves are 390× 105t, which is close to large-scale deposits. It is the oldest mine producing graphite in China and occupies an important position in domestic graphite production.
Two. Contact metamorphic graphite deposit
Cryptomeric soil graphite produced in metamorphic coal measures strata is the second largest graphite deposit type after regional metamorphic layered graphite deposits. This kind of deposit is formed by contact thermal metamorphism caused by the intrusion of intermediate-acid magma into coal seam, which determines a series of geological characteristics. China mainly has Lutang graphite mine in Chen County, Hunan Province and Yantongshan graphite mine in panshi city, Jilin Province.
The coal-bearing series consists of clastic rocks and biological rocks, namely argillaceous rocks, argillaceous siltstones, sandstones, coal seams (rocks) and oil shale. Except contact metamorphic coal seam becomes graphite ore, other rocks are invaded by magma, and various hornfels are formed due to contact thermal metamorphism. Although the distance from the intrusive body is different and the intensity of thermal metamorphism is different, there are zones of thermal metamorphic facies, especially argillaceous rocks are more sensitive. From high temperature to low temperature, metamorphic minerals characterized by garnet, sillimanite, tourmaline, cordierite and andalusite appear. From the contact zone, the whole rock stratum is strongly keratinized to slightly keratinized until the original rock does not deteriorate. However, the coal seam gradually transits from crystalline fine flake graphite to aphanitic graphite, graphitized anthracite and anthracite.
Because there are often multiple layers of coal in coal-bearing rock series, there are often multiple layers of graphite. The ore body is layered or lenticular, with a thickness of tens of meters and an extension of hundreds of meters or kilometers.
The ore is mainly composed of aphanitic graphite, the degree of graphite crystallization is extremely low, the particle size is less than 1μm, and the aggregate is soil-like, in which the impurity minerals are timely, clay minerals, rutile, carbonate and pyrite. The grade of ore is high, generally 60% ~ 80%, and some are above 90%, but the floatability of ore is poor. In most cases, the finished products are obtained by hand selection and fine grinding and classification. Generally, the selected concentrates and tailings can be sold as products with different quality.
This kind of deposit is one of the main types of graphite deposits with large scale and high graphite content, and occupies an important economic position in the world. Because the ore is earthy, it is not widely used like flake graphite.
In China, such graphite deposits are widely distributed in Carboniferous, Permian and Jurassic coal measures. The main graphite deposits are Panshi in Jilin, Lutang in Hunan, Gaoshan in Zhangping in Fujian and Mei Dong in Li Anping, Guangdong. The main countries producing aphanitic graphite abroad are North Korea, Austria, Mexico and Russia.
The typical deposit of this type is Lutang graphite deposit in Chenzhou, Hunan Province, which has the following characteristics:
The strata in the mining area include: Upper Permian Douling Formation (P2ι) coal-bearing clastic rock series with a thickness of 390 m; Lower Permian Dangchong Formation (P 1d) carbonaceous shale intercalated with limestone and ferromanganese silicalite, with a thickness of 25m；; Qixia Formation (P 1q) is composed of crystalline limestone and marl, with a thickness of 75m, which constitutes an oblique structure. Douling Formation is mainly distributed in syncline, and its lower member (P2ι 1) is mainly argillaceous rock and siltstone. The upper member (P2ι2) contains four layers of coal except argillaceous rock, siltstone and sandstone, which is a graphite-bearing layer.
During Indosinian period (158 ~ 233 Ma), Qitianling granite invaded Permian along the east wing of syncline structure. The rock mass is oval with an area of about 70km2. Its long axis is parallel to the fold axis, and there is a long contact zone (6500m long and 800m wide). It is white porphyritic fine-grained biotite granite. The invasion resulted in contact metamorphism of coal-bearing measures in Douling Formation, keratinization of clastic rocks, andalusite and cordierite amphibole, and coal seam metamorphism into anthracite and graphite.
The graphite deposit mainly occurs in the upper member of Douling Formation, and the coal seam is equivalent to the coal seam, which shows the changing relationship between anthracite graphitized anthracite and graphite ore in the coal seam. The contact zone with granite is generally flaky crystalline graphite within 500m, and the closer to the rock mass, the larger the scale; Fine flake to aphanitic graphite within 500 ~ 800 meters from the contact zone; All the contact zone is aphanitic soil graphite within 800 ~ 1200m; Graphitized anthracite is outside 1200m. This zoning is roughly parallel to granite. The ore body is layered, with four layers of ore along the coal seam (Figure 3-3a). The average thickness of each coal seam is Ⅰ (0.59m), Ⅱ (1.42m), Ⅲ (0.57) and Ⅳ (1.14m), in which Ⅱ and Ⅲ are the main coal seams. The distance between each coal seam is 45m between Ⅰ and Ⅱ, 56m between Ⅱ and Ⅲ, and 57m between Ⅲ and Ⅳ. The graphite crack is controlled to be 800 ~ 1000m long, with an average thickness of 1.42 ~ 1.5m and a depth of more than 200 ~ 400m m. Due to extrusion, the seam undergoes severe plastic deformation along the inclined direction, and complex soft folds appear, which are dentate, fasciculate, rhizomatous and fasciculate branches (Figure 3-3b), and the layered deposit loses stability. The ore is earthy, dense, massive or flaky, but the original bedding structure can still be seen. The ore is mainly composed of graphite (70% ~ 80%), Yingshi (5% ~ 7%), illite and kaolinite (5% ~ 10%) and a small amount of pyrite. Graphite is mostly aphanitic and microcrystalline aggregates, mainly aphanitic, with a small amount of fine-grained scales. The aphanitic graphite is in the shape of amorphous petals and layered, in which the impurities are semi-self-self-self-form hexagonal flake, and the flake is generally 0.2 μ m. The fine-grained flake is found in the cracks or holes of the aphanitic block, with a diameter of 65,438 0 ~ 2 μ m, and is arranged in a feather or bundle. The ore grade is 68% ~ 80%, reaching 94% locally, and the sulfur content is 0.07% ~ 1.60%. There are usually several meters to more than ten meters of oxidation zone marked by low-carbon sulfur near the surface of graphite deposits, in which the fixed carbon content is 55% ~ 65%, and some ores lose industrial value. At present, the proven reserves are 664.5× 105t, which is the largest contact metamorphic graphite deposit in China.
Figure 3-3a Geological Profile of Lutang Graphite Mine
(According to He Changzhu et al. 1987)
1— Changxing Formation (P2C); 2— Upper member of Douling Formation (P2 ι 2); 3— Lower member of Douling Formation (p2 ι1); γ-Qitianling granite; Ⅰ-Ⅳ graphite layer; F failure
Figure 3-3b Schematic Diagram of Lutang Graphite Ore Body Morphology
(According to He Changzhu et al. 1987)
1-timely sandstone; 2- carbonaceous slate; 3 angular claystone; 4— Graphite ore body
Three. Hydrothermal vein graphite deposit
This kind of graphite deposit occurs in the cracks between crystalline schist and marble, which often constitutes a huge ore belt. The belt has pegmatite dikes and granite dikes. The veins in the ore belt are single vein, dendritic or reticulate, and some are plate-shaped ore bodies, which are consistent with the foliation of surrounding rocks, and the dip angle of veins is generally steep. The pulse thickness varies from a few centimeters to dozens of centimeters, and the extension can reach more than tens of meters. The graphite content in most veins is extremely high, and some can reach 75% ~ 98%. * * * Biogenic minerals are mainly high-temperature gas-generated minerals such as topaz, tourmaline and apatite, and sulfides such as feldspar, pyroxene, rutile, magnetite, Yingshi, calcite, pyrite and molybdenite. Graphite is columnar, tabular, fibrous and other slender crystals, which grow perpendicular to the vein wall. The length of crystals is generally several centimeters, and some of them can reach1m. At present, there is not enough research on the formation of this type of deposit. It is speculated that it may be related to the action of metamorphic hydrothermal solution or migmatized hydrothermal solution, which promotes the activation and migration of carbon in rocks and enriches the ore in structural fractures. It is worth noting that gold mineralization is often distributed near this vein.
This kind of deposit has good quality and certain economic value, but it is not widely distributed. The total reserves of Sri Lanka's (large vein) graphite deposits are 2000× 105t, and there are also such deposits in the United States and Mexico.
Four. Skarn graphite deposit
These deposits occur in diopside and garnet skarn in the contact zone between intrusive rocks and limestone. The ore body is lenticular and nested, and flake graphite is embedded in skarn. The ore body is more than ten meters thick, and the length is100 ~150m. The graphite grade is generally 10% ~ 20%, and the highest is 60% ~ 80%. This kind of deposit has good graphite quality and large reserves. It is an important deposit type abroad, but it is rarely distributed. At present, only Ontario and Quebec in Canada are the most famous deposits, and there are also such deposits in Andludak in the United States.
Verb (abbreviation of verb) magmatic graphite deposit
The deposit occurs in nepheline syenite and mixed granite. Orebodies are plant-like, nest-like, lenticular and veinlets with different sizes, and can appear in groups. Although the scale of a single ore body is small, it is only a few meters to tens of meters long.
In nepheline syenite, graphite is a fine scale-like aggregate with mixed distribution, and the graphite content is high, generally reaching 60% ~ 85%. The deposit is small in scale and not widely distributed. The genesis of the deposit belongs to magmatic deposit. After syenite invaded the surrounding rock, limestone was captured in it. After being assimilated by magma, the magma is rich in CO2. During its crystallization, CO2 is reduced and crystallized into graphite. Represented by the Potogor deposit in Irkutsk, Russia.
Graphite in mixed granite is a crystalline scale-like aggregate, which is spherical, pea-like, variegated and disseminated. Rock mass contains graphite, and the relationship between ore body and surrounding rock is gradually transitional. Graphite ore contains copper sulfide and rare rare earth minerals, which can be comprehensively utilized. The fixed carbon content in ore is generally 4% ~ 6%, and the associated elements are Cu, Ti, Zr, Hf, Y, Yb, Ge, Be, Ta, Nb and other elements. The deposit may be crystallized from granite residual liquid rich in volatile components (CO2). There are a lot of carbonaceous shale breccia in the ore body, so it is speculated that at least part of the carbon in the residual slurry comes from the organic carbon in the surrounding rock. This kind of deposit is very small.