The characteristics of the deposit, the structure of the strata, the difficulties in selection and mining. The mysterious veil of Lanping lead-zinc mine, the largest lead-zinc mine in Asia

Abstract: Jinding lead-zinc deposit in Yunnan is the largest lead-zinc deposit in China at present, and it is also one of the world-class super-large deposits with metal reserves of more than 10 million tons. This paper will make a deep bottom of the lead-zinc mine from the aspects of metallogenic background, deposit characteristics, strata, structure, orebody characteristics, ore minerals, ore-controlling factors, mining difficulties and so on, so as to show you the elegant demeanor of the largest lead-zinc deposit in Asia.

Core logic

Formation background: convergence and collision between the Himalayan Indian plate and the Eurasian plate

Ore-controlling structure: the main ore-controlling structures of the lead-zinc deposit are intersecting faults and domed salt dunes.

Metallogenic age: the metallogenic age is 57-23 Ma.

Genesis of ore deposits: the understanding of the genesis of ore deposits is dominated by epigenetic deposits.

Reasons for difficult selection and mining: its own conditions and geographical location lead to difficult selection and mining

Lanping Jinding lead-Zinc Mine, located 18 kilometers northwest of Lanping County, Lanping is located in the core area of the World Natural Heritage site of Nujiang River, Lancang River and Jinsha River in southwest China. The county is rich in lead-zinc deposits, so Lanping is also known as the "zinc capital of China".

Lanping Jinding lead-Zinc Mine is a mining asset in Yunnan Province, which is buried shallow and easy to open-pit mining. As the largest lead-zinc deposit in Asia, Jinding lead-zinc deposit was discovered by heavy sand survey team of Yunnan Provincial Geological Bureau in 1957, and detailed investigation and exploration were carried out by the third Geological Battalion of Yunnan Provincial Geological Bureau in 1965. Detailed investigation and exploration reports were submitted in 1984 and 1989 respectively. the cumulative controlled reserves are 15 million t, 1.2%, 6.08% and 11.7%, respectively. It is predicted that there are still 1 million tons of potential Pb and Zn metals in the deep part of the deposit, and nearly 6 million tons of Pb and Zn metals have been denuded at the top of the deposit. Therefore, in fact, in the process of mineralization, the total metal content of Jinding lead-zinc deposit is more than 22 million tons. It was once the largest proven lead-zinc deposit in China, and it is also the largest lead-zinc deposit in Asia, with a potential economic value of 100 billion yuan. Its characteristics and causes have always attracted the attention of earth scientists, and some scholars have done long-term and systematic research.

Metallogenic setting

The Jinding lead-zinc mining area is located at the northern end of the Lanping-Simao Meso-Cenozoic rift basin in the southern section of the Sanjiang fold system in southwest China. The mining area is 4.5 km, long and 2.5 km, wide. The exposed strata are composed of external system and in-situ system. The alien system is composed of Upper Triassic, Middle Jurassic and Lower Cretaceous. It is napped from east to west by horizontal nappe faults and overturned on the in-situ system. The in-situ system is composed of Upper Cretaceous and Paleogene. In the ore field, the two synchronous folds form a NNE-trending fornix structure, which is distributed on the west side of the Bijiang fault, and the east-west sides are cut by the north-south fault.

The formation and development of geological structure in Sanjiang area have experienced three times of opening and closing of the original Tethys (Pt3-Pz1), the Paleo-Tethys (D-T3) and the Middle Tethys (T3-E1). The two strong collision orogeny in Indosinian and Yanshanian-Himalayan period and the complex evolution of two kinds of transformation between basin and mountain (or oceanic land) and crust and mantle resulted in the large cycle, mixing and convergence of matter in each circle of the earth. It has created conditions for the formation of a unique metallogenic background in Sanjiang area. In particular, the convergence and collision between the Himalayan Indian plate and the Eurasian plate resulted in the formation of large nappe, thrust, strike-slip and regional metamorphism in this area, resulting in the convection of deep and shallow hot gas-liquid fluids along the fault system. This is an important thermal event, which has a great influence on the migration and enrichment of metals and ore-forming materials in the region. Jinding super-large lead-zinc deposit was formed under such regional geological background.

Related factors and characteristics

Characteristics and distribution of ore deposits

Glutenite-type lead-zinc deposits occur in marine or continental sandstone, feldspar sandstone and conglomerate. The composition of the ore is simple, the grade of lead and zinc is high, the alteration of surrounding rock is weak, and the metallogenic temperature is low. Although these deposits are not widely distributed in China, most of them are large and super large deposits, which are of great economic value for development. The typical deposit is the Lanping Jinding lead-zinc deposit in Yunnan, which is located in the strike-slip pull-apart basin of the Sanjiang orogenic belt. After the closure of the Neo-Tethys Ocean, the collision between the Indian continent and the Eurasian continent is related to the collision between the Indian continent and the Eurasian continent, with a total reserves of more than 1500 million tons of lead and zinc, and contains silver, cadmium, TI, sulfur and other useful elements. The center of the fornix structure in the mining area is denuded and the strata of the Hutousi formation are exposed. Around the center of the fornix are Beichang, Jiayashan, Fengzi Mountain, West Slope, South Factory, White Lawn, Happy Valley and other mining sections.

Stratum

The strata in the mining area can be divided into two parts: external system and in-situ system.

The alien system strata are inverted above the in-situ system strata, which are composed of the Upper Triassic, Jurassic and a small part of the Lower Cretaceous, and the in-situ system is composed of the Upper Cretaceous and the Paleogene Yunlong formation. There is a structural nappe surface contact between the two sets of strata systems. In the alien system, the upper part of the Lower Cretaceous Jingxing formation (K1j) is gray thick layer fine quartz sandstone, and the lower part is gray gravel (calcareous breccia) fine sandstone with siltstone. This formation is the main ore-bearing layer in the mining area. The upper part of the salt-bearing strata (E1yb) of the Paleogene Yunlong formation (E1y) in the in-situ system is gray with purplish red gravel limestone and gravel-bearing fine-medium sandstone, which is also the main ore-bearing layer.

Structure

The main ore-controlling structures of Jinding lead-zinc deposit are intersecting faults and domed salt dunes. Located at the intersection of the SN Bijiang fault and the NE hidden fault, the mineralization is controlled by the two major faults, and the mineralization is the strongest in the intersection zone of the two faults, and the mineralization tends to weaken gradually along the fault to the outside.

The Jinding super-large lead-zinc deposit is distributed in a vault structure with a length of 3 km and a width of 2km. A series of radial faults seem to develop along the edge of the fornix structure. There is a harmonious relationship between the shape and scale of the salt mound and the vault structure of the mining area. A series of radial faults developed along the edge of the fornix structure indicate that the fornix structure may be caused by the inversion of the density of the salt-bearing strata under the action of regional tectonic stress, resulting in the formation of the salt mound and the formation of the fornix structure in the Jinding mining area. The ore body thickness changes with the control of the fornix, which is embodied in the following aspects: in the process of vault fold, under the action of lateral pressure, sliding occurs with the wing strata, and the gentle area is the extension zone, so the orebody becomes rich and thick; The steep dip section is the compression section, so the orebody becomes thinner and poorer.

Orebody characteristics

There are two ore belts in the mining area, the upper ore belt is composed of quartz sandstone at the bottom of the Lower Cretaceous Jingxing formation, and the lower ore belt is composed of breccia sandstone and limestone breccia in the upper member of the Paleogene Yunlong formation. The orebody is obviously controlled by the lithology of the surrounding rock, and its occurrence is basically consistent with that of the surrounding rock. A total of 446 lead-zinc orebodies have been circled in the region, and more than 95% of the reserves in the mining area are distributed in four sections: Beichang, Jiayashan, Fengzishan and Happy Valley. The ore bodies associated with lead-zinc deposits include 76 pyrite ore bodies, 100 celestite ore bodies and 59 gypsum ore bodies. The orebodies of each section are distributed irregularly around the core of the fornix. According to space and horizon, lead-zinc orebodies are mainly developed in two sets of strata: Jingxing formation (upper ore-bearing belt) and upper member of Yunlong formation (lower ore-bearing zone). The upper ore-bearing zone is located in the calcareous cemented gray fine quartz sandstone, the mineralization is uniform and stable, almost the whole layer is mineralized, and most of the metal minerals are in the shape of disseminated spots. The orebody is layered and quasi-layered, extending for several hundred meters, nearly EW strike, inclined to N, with an inclination of about 30 °. The ore-bearing rocks in the lower ore-bearing zone are a set of ointment-bearing continental clastic rocks, the orebodies are lenticular, veined and irregular, and the metal minerals are filled and metasomatism along joints and fissures. In addition to lead and zinc, the orebody often contains pyrite, white iron ore, celestite and gypsum. They can sometimes form separate industrial orebodies.

Ore mineral

The primary metal minerals are sphalerite, galena, pyrite, white iron ore, a small amount of hematite, and occasionally trace amounts of chalcopyrite, natural silver, silver tetrahedrite, pyroxene and so on. Transparent minerals are mainly calcite, quartz (mostly clastic), Ba lapis lazuli, Sr barite,

Anhydrite, dolomite and various clastic minerals. The main oxidized minerals are smithsonite, wurtzite, heteropolite, galena, TI-bearing lead alum, limonite, siderite, Ba-free lapis lazuli, powdered barite, calcite and a small amount of cadmium sulphide. According to lithology, ore types can be divided into two categories: sandstone type and limestone breccia type. The sandstone-type ores mainly occur in the upper ore-bearing strata and the lower ore-bearing strata to the west of Beichang Line 17, and are distributed in Beichang, Fengzishan, Xipo, Jiayashan, Bailao and other ore sections. Limestone breccia type ore is found in the lower ore-bearing section, distributed in Jiayashan, Nanchang, Pamaping and other ore sections east of Beichang Line 17. The structure of sandstone type ore is relatively simple, which is mainly composed of cemented sand chips of metal minerals, followed by dissolution metasomatic structure and oolitic structure, and the ore structure is mainly disseminated spotted, followed by massive. On the other hand, the structure of limestone breccia type ore is more complex, mainly metasomatic dissolution structure, colloidal concentric zone structure, emulsion drop structure and similar image structure. The common structures are reticulated vein, breccia and strip structures, which have obvious characteristics of late filling metasomatism. The alteration of surrounding rocks often occurs in yellow (white) iron mineralization, calcination, hemlock iron mineralization, silicification, dolomitization, recrystallization, azure petrifaction and discoloration. In addition, the plastic deformation and vein-like intercalation of gypsum are also developed, and the alteration of limestone breccia type ore near the replenishment system is stronger than that of the upper sandstone type ore, especially in the breccia type ore. Closely related to lead-zinc mineralization are yellow (white) iron mineralization, calcination, hemlock iron mineralization, recrystallization and azure.

Ore controlling factors

The Bijiang fault zone distributed near the north-south direction along the edge of the central Cenozoic basin in Lanping basin is an important ore-conducting structure, sand and breccia are the main ore storage lithology, nappe structure, (gold roof) vault structure and fault structure control the distribution of orebodies. The Jinding orebody mainly occurs in the clastic rocks of Jingxing formation (K1j) and Yunlong formation (E1yb) in the nappe structure (F2) and its upper and lower vicinity, and the nappe structure is one of the ore-bearing structures. The ore-bearing rock series is mainly quartz sandstone and breccia, which has the characteristics of high porosity and high permeability. From the comprehensive analysis of reservoir thickness, reservoir type, sedimentary facies characteristics and effective porosity, it is a favorable reservoir space for ore-forming fluids. The nappe fault F2 and the main orebody form a vault structure with the in-situ system as the core in the mining area, and the nappe slip surface is also involved in the vault, reflecting that the nappe structure was formed in front of the vault structure. The fornix appears in isolation, and the orebody is distributed around the core of the fornix. The closer the thickness of the orebody is to the top of the fornix, the thicker the orebody is, and the gold roof vault is an important ore-bearing structure.

Metallogenic age

Most of the ore-bearing strata of Jinding type lead-zinc polymetallic deposits belong to the Lower Cretaceous, Paleocene and Jurassic. The metallogenic age should be later than that of the main rock. The Re-Os isotopic isochron age of microcrystalline pyrite in Jinding ore is 67 Ma,. The Ar-Ar age of silicified quartz in Baiyangping deposit is 62 Ma, which is consistent with the starting time of Himalayan mantle-crust alkaline magmatism (68 Ma). It is inferred that the metallogenic age is 57-23 Ma.

Regional metallogenic model

The genesis of Jinding deposit has been controversial. To sum up, there are mainly four views on the causes:

Syngenetic sedimentary-late transformation deposit;

Epigenetic hydrothermal or epigenetic hydrothermal-stratabound deposits;

Syngenetic sedimentary (jet deposition, that is, Sedex) deposit;

Special type of deposit.

In recent years, the understanding of the genesis of ore deposits is dominated by epigenetic deposits.

The understanding is as follows: on the basis of the Paleo-Tethys, the Jinding area successively accepted the residual sea and the discontinuous continental clastic deposits (including gypsum salt) in the depression basin, and the strike-slip tectonic activity near SN in the Cenozoic (Bijiang River, etc.). The salt-bearing clastic deposits appeared in the Paleogene pull-apart basin. Since the end of the Paleocene, the thrust structure from east to west has napped a large number of Mesozoic over the Paleogene. At the end of or after the nappe structure in the Jinding mining area, a local vault occurred, and the gold roof nappe structure was involved in the doming process. The fluid accumulation in the Jinding Dome basin is prone to the reduction of SO2-4 to H2S by bacteria in groundwater or oil and gas accumulated in the vault, which may form H _ 2S gas reservoir. The formation of ore deposits is the mixed mechanism of ore-bearing hot brine and groundwater. The ore-bearing hot brine brings heavy metal elements, groundwater plays a role in changing the metallogenic temperature, bringing organic matter, bacteria and sulfur, and changing the sulfur, oxygen fugacity, pH value and salinity of the ore-forming solution. The ore-bearing fluid is injected into the gold roof vault through the Bijiang fault in the eastern part of the mining area and migrated westward. The lead and zinc ions (clusters) react rapidly with H _ 2S in the gas reservoir and precipitate in the gold roof vault to form a lead-zinc deposit. The continuous replenishment of rich ore-bearing hot brine along the structure, good ore-bearing space and impermeable water layer are the most important factors for the formation of Jinding giant deposit. Further doming leads to the destruction of oil and gas reservoirs and the discontinuity of sulphide orebodies.

Technical difficulties in mining and separation

The mine has the advantages of high degree of geological exploration, large reserves of resources, thick and concentrated orebodies, open-pit mining, large ratio of zinc to lead, etc., but the mine is a rare mixed ore of oxygen and sulfur in the world, which is difficult to separate and stay in the world. The average grade is low, the development investment is large, and the processing cost is high. In addition, the mine is located in the high altitude mountain areas of southwest China and the poor areas of ethnic minorities. The transportation is inconvenient, and it is far away from the state power grid, coal char producing areas and railway lines. The investment environment and external conditions of development and construction are very poor.

References:

Zeng Rong, Xue Chunji, Liu Shuwen, et al. Analysis of metallogenic conditions of Jinding super-large lead-zinc deposit [J]. Journal of Geosciences and the Environment, 2005, 27 (2): 21-25.

Li Zhiming, Liao Zongting, Liu Jiajun, et al. Discussion on metallogenic age of Jinding super-large lead-zinc deposit in Lanping Basin [J]. Geological Prospecting Theory Cluster, 2006,21 (1): 23-27.

Zhang Changqing, Rui Zongyao, Chen Yuchuan, Wang Denghong, Chen Zhenghui, Lou Debo, etc. Potential and main strategic succession areas of lead-zinc ore resources in China. [J]. Volume 40, No. 1, February 2013