(2) Main geological characteristics of various lead-zinc deposits.

1. Lead-zinc deposits related to magmatic intrusion

This is a group of lead-zinc deposits closely related to the mineralization of intermediate and acidic intrusive rocks, especially small intrusive rocks. According to the metallogenic geological environment and metallogenic mode, lead-zinc deposits can be divided into three types: skarn type, porphyry type and hydrothermal vein type. Sometimes they occur independently, such as Taolin in Hunan and Fozichong in Guangxi, and sometimes they form a deposit (field) together, such as Shuikoushan-Kangjiawan in Hunan.

This kind of lead-zinc deposits are widely distributed in eastern China, with 24 large and medium-sized deposits/kloc-0, such as Shuikoushan-Kangjiawan, Huangshaping and Taolin in Hunan, Dachang, Mora and Fozichong in Guangxi, Dabaoshan in Guangdong, Lengshuikeng in Jiangxi, Baiyinnuo and Haobugao in Inner Mongolia, Cuihongshan in Heilongjiang, Caijiaying in Hebei, Niu Shan in Gansu, Gejiu and Dulong in Yunnan, etc. Their accumulated reserves are1013130,000 tons of lead and 23.35 million tons of zinc, accounting for 39.5% and 29.7% of the total reserves of large and medium-sized lead-zinc deposits in China, respectively, of which skarn type accounts for 12.7% and13. Its importance is second only to lead-zinc deposits related to hot (brine) water activities. The lead and zinc reserves of such deposits account for about 20% of the world's total lead and zinc reserves, of which skarn type accounts for 6% and hydrothermal type accounts for 14%. In contrast, they are more important to our country, and also reflect some uniqueness of mineralization in the coastal Pacific Ocean.

(1) skarn lead-zinc deposit

This kind of deposit refers to the lead-zinc deposit in which the ore body occurs in skarn or skarn marble in the contact zone between acid-intermediate acid intrusive rocks and carbonate rocks. The occurrence and shape of ore bodies are controlled by the occurrence and shape of skarn or skarn marble, which is generally complicated. Ore bodies are usually layered, lenticular, cystic, veined and irregular. A deposit consists of dozens to dozens or even hundreds of ore bodies of different sizes. A single ore body is generally several meters to tens of meters long, and the main ore body can reach hundreds to thousands of meters; The inclined depth is generally tens to hundreds of meters; The thickness is less than 1m to tens of meters. The scale of deposits is mainly small and medium, and there are also large deposits.

The complex composition of ore is a characteristic of this kind of deposit. The main ore minerals are sphalerite, galena, pyrite, chalcopyrite and pyrrhotite, followed by arsenopyrite, magnetite, cassiterite, scheelite, molybdenite, bismuthite, tetrahedrite, argentite, tetrahedrite and so on. Gangue minerals include garnet, diopside, tremolite-actinolite, pumice, manganese hedenbergite, calcium magnesium, manganese aluminum garnet, yingshi, calcite and fluorite. Ore structures are mainly disseminated, variegated and banded, followed by massive and reticulated veins. The ore structure is crystalline granular, interstitial and various metasomatic texture. The lead-zinc grade of ore is generally greater than 4%, and the lead-zinc ratio is generally less than 1, including iron, copper, tungsten and tin. According to the useful metal combination of the deposit, it can be divided into lead-zinc (copper, tin) groups, such as Baiyinnuo in Inner Mongolia (Figures 4-3 and 4-4); Copper, lead and zinc (tin and iron) buildings, such as Haobugao in Inner Mongolia and Fozichong in Guangxi; Tin-lead-zinc buildings, such as Gejiu and Dulong in Yunnan; Tungsten-lead-zinc-silver buildings, such as Li Jiao, Jiangxi; Iron (-lead)-zinc buildings, such as Chaobuleng and Huanggang in Inner Mongolia, Kendekeke in Qinghai and Sanyizhuang in Hebei. In the latter four structural deposits, lead and zinc often coexist with iron, tin or tungsten, and sometimes with copper.

The mineralization of skarn deposits can be divided into skarn stage and hydrothermal stage. The latter includes oxide-sulfide-isochron, sulfide-isochron and sulfide-carbonate stages, which evolved from medium-high temperature to low temperature stage. The mineralization of iron, tungsten, tin and zinc mostly occurred in the early stage, while the mineralization of lead and zinc (silver) mainly occurred in the middle and late stage. Therefore, with the evolution of mineralization, there are often clear alteration zoning and surrounding rock mineralization zoning, that is, rock mass shows calcium (magnesium) skarnization → manganese skarnization, silicification, chloritization and sericitization → marble and alteration zoning of Fe, W, Sn or Mo, Zn→Cu, Pb, Zn→Pb, Zn → this mineralization zoning in space.

The variation range of sulfur isotope composition of ore is small, mostly between-4 ‰ and+6 ‰, which has the characteristics of tower distribution and the peak value is close to zero. The lead isotopic composition of ore is mainly abnormal lead, which is often similar to feldspar in granite. All these indicate that the source of ore-forming materials is closely related to magmatic intrusion. The hydrogen and oxygen isotopic composition of fluid inclusions in ore minerals shows that the medium water of ore-forming fluid is the mixed water of atmospheric precipitation and magmatic water.

Figure 4-3 Geological Schematic Diagram of Baiyinnuo Mining Area

Figure 4-4 Schematic Diagram of Line 79 Section of Baiyinnuo Deposit

(2) Hydrothermal Pb-Zn deposit

Hydrothermal lead-zinc deposits occur in carbonate rocks or clastic rocks in the external contact zone of granite intrusion, and some occur directly in granite and are controlled by fault structures.

Due to the different properties of surrounding rocks, the metallogenic characteristics of the deposits are obviously different. The ore bodies occurring in carbonate fractures are layered, lenticular, veined, cystic, columnar and irregular, with complex occurrence and shape, and often compound and pinch out along strike and dip. In a deposit, there are dozens of ore bodies in groups and more than 300 ore bodies in Huangshaping, but only 1 ~ 5 ore bodies are of industrial significance. A single ore body is generally ten to tens of meters long, with a maximum length of 700 ~ 1000 meters, a dip depth of ten to tens of meters, and a maximum dip depth of more than 500 meters. It is tens of centimeters to several meters thick and hundreds of meters thick. Ore is rich in grade, Pb+Zn is generally greater than 4%, and the ratio of W (Pb)/W (Zn) is mostly (1.5 ~ 1) ~ 0.5. The scale of the deposit is mainly large and medium-sized, such as Dachang in Guangxi.

The shape and occurrence of ore bodies in clastic rocks, metamorphic clastic rocks and granite-like rock fractures are relatively simple, mainly veins. Veins are tens to hundreds of meters long, and some are thousands of meters long; The depth is several tens to several hundred meters, and the pulse width is several tens to five meters. Some veins are composed of veinlets. Along the strike and dip of the vein, branching compound, expansion and contraction and pinch-out often occur. Ore grade is generally low, Pb+Zn is generally less than 5%, and it is often accompanied by W, Sn and other components. The ratio of W (Pb)/W (Zn) is (2 ∶1) ~ (1∶1.5), and the scale is mainly small and medium-sized, but also large, such as Taolin, Hunan.

Figure 4-5 Ore Body Shape of 3 15 Exploration Line Profile of Caijiaying Deposit

The ore minerals of hydrothermal lead-zinc deposits are complex, including galena, sphalerite, pyrite, chalcopyrite, cassiterite, arsenopyrite, stibnite and argentite. Gangue minerals mainly include quartz, calcite, dolomite, barite and fluorite. Ores usually have massive, banded, breccia and veinlet structures, as well as various crystalline granular, metasomatic and crushed structures. According to the combination of main ore-forming elements, ores can be divided into Pb-Zn-Ag formations, such as Meng 'en Tolgoi in Inner Mongolia, Zhanggongling in Guangxi, Xinhua in Sichuan and Nonggeshan. Tungsten-tin-lead-zinc buildings, such as Shawankeng and Houpo 'ao in Guangdong, Dachang in Guangxi, Xianghualing and Xianghuapu in Hunan.

Mineralization is multi-stage, which can usually be divided into oxide-sulfide stage, sulfide-time stage, sulfide-thioantimonate stage and sulfide-carbonate stage, reflecting the pulsation of mineralization, and evolving from moderate temperature to low temperature (400 ~ 100℃).

The surrounding rock is strongly altered, and the type of alteration is related to the lithology of surrounding rock. For carbonate rocks, silicification, sericitization, chloritization and carbonation are the main types, while for siliceous and aluminum rocks, silicification, sericitization, pyritization, fluorination and barite are the main types. The alteration zoning and mineralization zoning of surrounding rock are controlled by fault structure and distributed linearly. For example, in the horizontal direction, silicification and sericitization are dominant near granite, and the mineralization of tungsten and tin is enhanced, while sericitization, chloritization and carbonation far away from granite are dominant, and the mineralization of lead, zinc and silver is enhanced. In the vertical direction, the lower part is mainly silicified, sericitized and mineralized with tungsten and tin, while the upper part is mainly sericitized, chloritization, carbonated and mineralized with lead, zinc and silver. Some deposits have also formed "multilayer" alteration zoning and mineralization zoning.

The sulfur isotopic composition of the ore has little change, mostly ranging from 0 to+5 ‰, with a tower distribution and a peak value close to zero. Some deposits, such as Taolin, Hunan, have large negative sulfur isotope composition; The isotopic composition of lead in ores varies greatly, mainly radioactive lead, and some deposits are mainly normal lead. These may indicate that the sources of ore-forming materials are complex, including magmatic sources and stratigraphic sources. The hydrogen and oxygen isotopic composition of fluid inclusions in ore minerals shows that the medium water of ore-forming fluid is a mixture of magmatic water and atmospheric precipitation, and even atmospheric precipitation is the main one.

(3) Porphyry lead-zinc deposit

Porphyry lead-zinc deposits are little known at present, and occur in small rock masses such as hypabyssal-ultrahypabyssal granite porphyry, rhyolite porphyry and syenite porphyry and their contact zones. These hypabyssal-ultrahypabyssal small rock bodies are often closely related to acidic and alkaline volcanic activities in mainland China, and sometimes the ore-forming rock bodies are cryptoexplosive breccia tubes. The ore body is composed of veinlets disseminated, disseminated and veinlets network mineralized, which is layered, lenticular and veinlets, with the phenomena of branching, compounding and pinching along strike and dip. The strike of ore bodies is tens to hundreds of meters long, and some are more than one kilometer long; The tilt depth is tens to hundreds of meters, even thousands of meters; A few meters to dozens of meters thick. The ore grade is low, Pb+Zn is often less than 4%, and the ratio of W (Pb)/W (Zn) is (1.2:1) ~ (1:1.5). The scale of the deposit is mainly large and medium-sized, such as Lengshuikeng in Jiangxi.

The mineral composition of the ore is simple, mainly galena, sphalerite, pyrite, argentite and so on. Gangue minerals are mainly timely, sericite, chlorite and carbonate minerals. The ore is disseminated, veinlet disseminated, veined and reticulated, crystallized and metasomatic texture.

The wall rocks are strongly altered, mainly silicified, sericitized, chloritization, pyritized and carbonated, with plane development. From the center of the rock mass to the contact zone, alteration zoning and mineralization zoning often occur: chloritization → silicification, sericitization, pyritization → silicification, carbonation alteration zoning and corresponding (Cu)→Pb, Zn→Pb, Zn and Ag mineralization zoning.

The variation range of sulfur isotopic composition of ore is small, ranging from-2 ‰ to+4 ‰, with a tower distribution and a peak value close to zero. The lead isotopic composition of ore is relatively stable, with abnormal lead as the main component. This shows that the ore-forming metal substances mainly come from magma-hydrothermal system. The hydrogen and oxygen isotopic composition of fluid inclusions in ore minerals shows that the medium water of ore-forming fluid is mainly atmospheric precipitation, mixed with a small amount of magmatic water.

2. Lead-zinc deposits related to volcanic activity

This kind of lead-zinc deposits are distributed in the areas where volcanic rocks are developed in China. They are formed by volcanic eruption and shallow-ultra-shallow volcanic activities, and occur in volcanic rocks or volcanic sedimentary rocks. Because of the different geological and tectonic environments of volcanic activity, it can be divided into two types: continental volcanic rock type and marine volcanic rock type. Continental volcanic lead-zinc deposits are mainly distributed in eastern China, where Mesozoic volcanic rocks are developed. Marine volcanic lead-zinc deposits are mainly distributed in volcanic sedimentary rock series in the best geosyncline area of China. Generally speaking, volcanic lead-zinc deposits in China are widely distributed and large in number, but they are mainly small and ore occurrences. There are only 15 large and medium-sized deposits (excluding Ashele, Cocotale, Timit and Abagong in Xinjiang, and not listed in the reserve table 1998), such as Wubao and Dalingkou in Zhejiang, Yinshan in Jiangxi, Yinkeng in Putian in Fujian and Xiacun in Sichuan. Their accumulated reserves are Pb 2257 1 10,000 tons and Zn10.2505 million tons, accounting for 8.8% and 1.5% of the total lead and zinc reserves of large and medium-sized deposits in China, respectively. The continental volcanic lead-zinc deposits account for 2.5% and 3.8% respectively, and the marine volcanic lead-zinc deposits account for 6.3% and 12. 1% respectively (zinc reserves in pyrite-bearing copper deposits). According to перваго (1975), the reserves of pyrite-type lead-zinc deposits (excluding zinc reserves in pyrite-type copper deposits) account for 3 1% of the world's total lead-zinc reserves, including 9% in Precambrian and 20% in Paleozoic. He regarded the continental volcanic lead-zinc deposit as a medium-low temperature hydrothermal deposit and classified it as a hydrothermal deposit. In contrast, the importance of volcanic lead-zinc deposits in China is also obvious.

(1) continental volcanic lead-zinc deposit

This kind of lead-zinc deposit occurs in the crater edge of continental volcanic sedimentary basin. It is veined and lenticular in acidic and intermediate acidic volcanic cracks, such as Yinshan in Jiangxi and Wubao in Zhejiang. It also occurs in the transition zone of pyroclastic rocks or volcanic sedimentary rocks with different particle sizes. It is controlled by interlayer fracture and is layered and lenticular. Some people classify the former as a continental volcanic hydrothermal deposit and the latter as a continental volcanic sedimentary deposit. For continental volcanic lead-zinc deposits, although their occurrence characteristics are different, their genesis is similar. A single ore body is tens to hundreds of meters long, and some are thousands of meters long; The tilt depth is tens to hundreds of meters, and the maximum tilt depth exceeds kilometers; The thickness is tens of centimeters to several meters, and the maximum thickness is about 50 meters. There are branching, recombination and expansion and contraction phenomena along the strike and dip of ore bodies. Vein ore bodies are rich in grade, with lead and zinc mostly around 4%, and the ratio of w(Pb)/w(Zn) is (2 ∶1) ~ (1∶ 2). The layered ore body is poor in ore, Pb+Zn is less than 4%, and the ratio of w(Pb)/w(Zn) is 1.5 ~ 0.8. The scale of deposits is mainly small, and a few are large (such as one-fifth in Zhejiang; Figure 4-6).

Figure 4-6 Schematic Diagram of Geological Profile of 5 1 Exploration Line in Wubao Lead-zinc Mine, Zhejiang Province

Ore minerals are simple, mainly galena, sphalerite, pyrite and chalcopyrite, and gangue minerals are mainly timely, sericite, siderite and manganese-containing calcite. The ore structures are mainly massive, massive, veinlets, disseminated and breccia, and the structures are mainly crystalline granular and metasomatic. Mineralization is multi-stage, which can usually be divided into sulfide-isochronous stage, sulfide-antimony sulfide stage and sulfide-carbonate stage, and evolved from moderate temperature to low temperature (300 ~ 100℃).

Wall rock alteration mainly includes silicification, sericitization, chloritization, pyrite, siderite, manganese-containing calcite and fluorite. Alteration zoning and mineralization zoning are generally not obvious. In some deposits (such as Yinshan, Jiangxi Province), from subvolcanic rocks outward, from deep to shallow, it shows pyritization, silicification, sericitization → chloritization, siderization alteration zoning and corresponding Cu → Cu-Pb-Zn → Pb-Zn-Ag mineralization zoning.

The sulfur isotopic composition of the ore varies from -5% to +5%, showing a tower distribution with a peak value close to zero. The lead isotopic composition of ore has little change, mainly radioactive lead. This shows that the ore-forming materials come from deep magma. Hydrogen and oxygen isotopes of fluid inclusions in ore minerals show that the medium water of ore-forming fluid is mainly meteoric migmatite slurry water.

(2) Marine volcanic lead-zinc deposits

These deposits are distributed in geosyncline orogenic belt and occur in volcanic sedimentary rock series formed by spilite porphyry or rhyolite-basalt. The host rocks are amphibole tuff, rhyolite tuff, spilite, pyroclastic rock or marble in the contact zone between chlorite schist and marble. Such deposits are often formed in different geological environments. As far as marine volcanic copper polymetallic deposits in Qilian, northern China are concerned, they can be divided into copper-iron type (Honggou type), copper-zinc type (ophiolite type) and copper-lead-zinc type (Baiyinchang type) (Xia et al., 19 1. Sun Haitian et al., 1993). Copper-iron deposit is formed in arc or back-arc basin environment, and the host rock is spilite; The Cu-Zn deposit was formed in a marine extensional environment, and the ore-bearing rocks are located in the transition layer between pillow spilite and metamorphic tuff, carbonaceous slate and schist in the upper part of ophiolite suite. The Cu-Pb-Zn deposit was formed in the rift island arc environment in the early stage of geosyncline development, which was related to the eruption of intermediate-acid volcano in the middle. The ore-bearing rock is amphibole tuff. The ore bodies are layered and lenticular, and they are produced in groups. The occurrence of ore body is consistent with that of surrounding rock. A single ore body is tens to thousands of meters long, tens to hundreds of meters deep and several to tens of meters thick. The ore is moderately rich in grade, often accompanied by Cu*** and rich in gold and silver. The ratio of W (Pb)/W (Zn) (for lead-zinc deposits) is (1:1.5) ~ (1:3), and the scale is large and medium.

Ore minerals are mainly pyrite, chalcopyrite, sphalerite and galena, and gangue minerals are mainly timely, sericite, chlorite, barite and calcite, with massive, disseminated, banded, veinlets and breccia structures, crystalline granules and metasomatic texture. According to the combination characteristics of metal elements in the ore, it can be divided into copper formation, copper-zinc formation (such as Hongtoushan in Liaoning and Ashele in Xinjiang), copper-lead-zinc formation (such as Xiaotieshan in Gansu and Xiacun in Sichuan) and lead-zinc formation (such as Xitieshan in Qinghai, Figure 4-7 and Keketale in Xinjiang). They often occur in a ore field or a metallogenic belt, forming a complete metallogenic series.

The wall rocks are strongly altered, including silicification, sericitization, chloritization and barite. In some deposits, alteration zoning and mineralization zoning are not obvious, but the copper content tends to increase in the vertical direction of the ore body. Some deposits have tubular silicified and sericitized alteration zones in the lower part, accompanied by vein and veinlet disseminated mineralization, and layered silicified, barite and calcite altered zones in the upper part, accompanied by layered and lenticular massive sulfide ore bodies.

The sulfur isotopic composition of the ore is about 0 ~+8 ‰, with a tower distribution and a peak value of 4 ‰ ~ 5 ‰. The isotopic composition of lead in ore changes slightly, mainly normal lead and radioactive lead. This may indicate that the ore-forming metal substances mainly come from submarine volcanic rocks. The hydrogen and oxygen isotopic composition of fluid inclusions in ore minerals shows that the medium water of ore-forming fluid is mainly seawater migmatite slurry water.

3. Lead-zinc deposits related to hot (brine) water activities

This kind of deposit is called stratabound deposit, and some people call it sedimentary or sedimentary reformed deposit. Guo et al. (1987) regarded it as a generalized hydrothermal deposit and called it stratabound (layered)-hydrothermal deposit. This kind of deposit has both syngenetic and epigenetic characteristics, and is controlled by comprehensive factors such as certain horizon, specific lithofacies, lithology and structure, and is not closely related to magmatic activity. It is a multi-source and multi-genetic ore-forming deposit.

This deposit is one of the main sources of lead and zinc in the world. Because of the different understanding of its meaning, the lead-zinc mine reserves counted by different researchers are quite different. According to statistics of Ulf 1976, 55% of the world's total lead-zinc reserves are concentrated in such deposits. According to ваберваг 10868+0975, 35% of the world's total lead-zinc reserves are concentrated in such deposits. In China, there are 50 large and medium-sized lead-zinc deposits, such as Tianbaoshan and Daliangzi in Sichuan, Jinding in Yunnan, Qixia Mountain in Jiangsu, Dongjiahe, Baiyunpu and Houjiang Bridge in Hunan, Fankou in Guangdong, Beishan in Guangxi, Qingchengzi in Liaoning, Changba, Bijiashan, Lijiagou and Dengjiashan in Gansu. Their accumulated reserves are Pb11180,000 tons and Zn 3396.7 million tons, respectively, accounting for 47.3% and 466.5438+0% of the total reserves of large and medium-sized deposits in China. Among them, 3.4% and 2. 1% are pre-Sinian lead-zinc deposits, 8.1.0% and 8. 1% are early Paleozoic lead-zinc deposits, 22.4% and 2 1.0% are late Paleozoic lead-zinc deposits, and Mesozoic-Cenozoic lead-zinc deposits.

Figure 4-7 Geological Profile of S5 Exploration Line of Xitieshan Deposit

According to the properties of host rocks, this kind of lead-zinc deposits in China can be divided into three types: carbonate rock type, fine clastic rock type and glutenite type.

(1) carbonate lead-zinc deposit

The deposit is located in the depression belt on the edge of ancient uplift or Phanerozoic depression on the platform. The ore-bearing lithology is shallow-sea carbonate rocks, especially bionic limestone and dolomite rich in organic matter and argillaceous, which can sometimes be divided into dolomite type and limestone type, and controlled by contemporaneous ancient faults, regional folds, faults and interlayer dislocation. The ore bodies are layered, quasi-layered and lenticular, with a large number. They occur in multiple layers and overlap each other, which is often consistent with the occurrence of strata. A few ore bodies are vein-like and saccate, cutting strata. The boundary between ore body and surrounding rock is clear, and the phenomena of branch recombination and pinch-out reappear along the strike and dip. A single ore body is tens of meters to thousands of meters long, some thousands of meters deep and several tens of meters thick. Ore grades vary greatly, from rich and poor (such as Dongjiahe, Hunan) with Pb+Zn around 2% to rich (such as Fankou, Guangdong) with Pb+Zn above 10%. The ratio of w(Pb)/w(Zn) is generally (1∶ 2) ~ (1∶ 5).

(2) Fine clastic lead-zinc deposit

The deposit is located in the depression zone on the edge of the ancient uplift, and the ore-bearing strata are a set of shallow metamorphic rock series with shallow marine facies clastic-clay-carbonate facies, which are mainly interbedded zones composed of carbonaceous slate, carbonaceous phyllite, limestone, quartzite and biotite quartz schist, and sometimes metamorphic volcanic rocks (calcareous chlorite schist and plagioclase amphibole). Orebodies are mainly produced in the interbedded zone of carbonaceous slate and limestone, which are layered, layered and lenticular with multiple layers. Branching compound and pinch-out often occur along the strike, which is consistent with the occurrence of surrounding rock. A single ore body is tens to thousands of meters long, tens to hundreds of meters deep and tens to tens of meters thick. This kind of ore is of medium grade and usually coexists with copper. Pb+Zn is about 5%, and the ratio of W (Pb)/W (Zn) is (1:1.5) ~ (1:5).

(3) Gravel lead-zinc deposit

The deposit occurs in fluvial strata of continental fault basin and is controlled by interlayer faults, such as Jinding, Yunnan (Figure 4-8). It also occurs in the littoral facies or marine-continental strata at the edge of the basin, and on the unconformity surface at the bottom of regional transgression, such as Baoan, Hunan. Therefore, they can be divided into two categories: one is continental glutenite, which is similar to continental sandstone copper deposits; The other type is coastal glutenite, which is usually dominated by lead. The ore bodies are layered, layered and lenticular, and occur in groups, which is consistent with the occurrence of surrounding rock strata. A single ore body is tens to thousands of meters long, tens to thousands of meters deep and 1 to tens of meters thick. The ore grade is moderately rich, with Pb+Zn above 4% and the ratio of W (Pb)/W (Zn) between (1:1.2) ~ (1:2). The Baoan deposit is dominated by medium-grade lead, and the ratio of W (Pb)/W (Zn) is between (1.5: 1) and (4: 1).

Figure 4-8 North Field Profile of Jinding Deposit 12 Exploration Line Profile

The mineral composition of this kind of lead-zinc deposits is simple, mainly galena, sphalerite and pyrite. Fine clastic rocks are usually chalcopyrite and pyrrhotite. The main gangue minerals are timely, dolomite, calcite, barite, and sometimes sericite, chlorite, celestite and asphalt. Ores have banded, striped, layered, massive, disseminated, nodular, veined and breccia structures, such as strawberry, granular, banded, gelatinous, crystalline granular, metasomatic and fractured structures, which are characterized by simultaneous and late transformation or reconstruction. The stronger the later transformation, the more complicated the ore structure and structure.

The surrounding rocks have been weakened by erosion. Carbonate rocks include dolomite, calcite and pyritization, while clastic rocks include silicification, sericitization, carbonation, chloritization, and sometimes celestite, barite and gypsum. Alteration zoning and mineralization zoning of surrounding rock are not obvious. Some deposits, such as Fankou, Guangdong, are vertically rich in lead and zinc in the upper part and pyrite in the lower part; In the horizontal direction, the strike lead-zinc ore body transits to pyrite ore body.

The sulfur isotopic composition of ores varies greatly. Lead-zinc deposits of dolomite type, fine clastic rock type and shallow-sea glutenite type are mainly positive values, ranging from+5 ‰ to+30 ‰; The continental glutenite type lead-zinc deposits are mainly negative, ranging from-1‰ to-30 ‰; Limestone lead-zinc deposits vary greatly, ranging from -26 ‰ to +26 ‰. The lead isotopic composition of ore is relatively stable, with normal lead as the main component and abnormal lead as well. This shows that the source of ore-forming materials of this kind of deposit is complex, including both the lower strata and seawater, and the mineralization is multi-stage. The hydrogen and oxygen isotopic composition of fluid inclusions in ore minerals shows that the medium water of ore-forming fluids mainly comes from atmospheric precipitation or circulating seawater.

4. Lead-zinc deposits related to sedimentary metamorphism

Sedimentary metamorphic lead-zinc deposit refers to a deposit in which mineralization is dominated by sedimentation, including volcanic jet (stream) sedimentation or hot water sedimentation, and later suffered regional metamorphism. The geological and tectonic environment of mineralization is mostly rift valley. The host rocks include metamorphic sandstone, metamorphic conglomerate, quartzite, phyllite, slate, schist, dolomite and marble. The degree of metamorphism is roughly equivalent to greenschist facies or low amphibolite facies. The ore body is layered, layered or lenticular, which is completely consistent with the occurrence of surrounding rock and folds synchronously. The ore minerals are mainly pyrite, galena, sphalerite, chalcopyrite and pyrrhotite, followed by magnetite, chalcopyrite and arsenopyrite. Gangue minerals mainly include quartz, calcite, dolomite and sericite. The ore structure is mainly dense and massive, but there are also banded, layered and disseminated shapes.

These deposits are mainly distributed in the metamorphic clastic rocks of Proterozoic Zaertai Group in Alashan Tailong on the northern margin of North China Platform and Langshan-Zaertai area in inner mongolian axis. Examples of ore deposits are Huogeqi, Tanyaokou, Dongshengmiao and Jiashengpan in Inner Mongolia, all of which are large in scale, and the Mesoproterozoic Gaobanhe lead-zinc deposit in northern Hebei also belongs to this category. In addition to Proterozoic, there are Caledonian (such as Wu Li in Sichuan and Shuiji in Fujian) and Hercynian (Yindongzi in Shaanxi) metallogenic ages. Their accumulated reserves are 6.5438+0.963 million tons of lead and 8.488 million tons of zinc, accounting for 3.9% and 7.9% of the total lead and zinc reserves in China, respectively.

The sulfur isotopic composition (δ34S) of ores is mostly positive, with a wide range of variation, ranging from+3.6 ‰ to+38.5 ‰, indicating that sulfur mainly comes from seawater sulfate during the sedimentary period. The lead isotope data point is located on the lead isotope tectonic environment map of B.R.Doe, near the mantle evolution line, indicating that the ore-forming element lead may belong to the mantle source area. The temperature measurement results of fluid inclusions in ore minerals are about 450℃ in Dongshengmiao, 300℃ in Tanyaokou, 65,438+050 ~ 325℃ in Huogeqi and 65,438+030 ~ 245℃ in uplifting, which is presumed to be caused by the distance difference between different ore deposits and submarine volcanic activity centers.

5. Lead-zinc deposits related to supergene oxidation

This kind of deposit is a supergene deposit formed by the enrichment of primary lead-zinc deposits or lead-zinc mineralized rocks by supergene weathering and leaching, and it also includes tailings, slag and waste piles when the ancients mined and smelted lead-zinc deposits with industrial significance. Mainly distributed in South China and Southwest China, it is related to subtropical warm and humid climate and local cutting topography. Most of them are eluvial and diluvial sediments, and a few are alluvial sediments. The geological characteristics of eluvial lead-zinc deposits are different, and most of them are weathered leaching deposits (oxide caps), ancient tailings and slag piles, and karst funnel accumulation (such as Jiao Na system in Sichuan). Alluvial deposits are usually placer lead deposits. Most of these deposits are small-scale occurrences, of which only five are medium-sized. They are Sichuan Jiao Na System, Guizhou Zhazi Factory, Yunnan Lancang Old Factory, Gejiu and Mining Factory. The accumulated reserves are Pb 12.82 tons and Zn 314,500 tons, accounting for 0.5% and 0.4% of the total reserves of large and medium-sized lead-zinc mines in China respectively.

This kind of deposit occurs at the bottom of Quaternary floating soil and above the bedrock surface. Generally, the upper part is red soil layer, the middle part is brown soil layer, and the lower part is black soil layer (i.e. ore layer). There may or may not be primary lead-zinc ore bodies in the lower part of the seam. The ore bodies are layered, layered, planar or funnel-shaped distributed in karst caves. The occurrence of ore bodies is controlled by the shape of bedrock surface or karst cave. The ore body is tens to thousands of meters long and wide, and 1m to tens of meters thick. Ore minerals are simple, mainly galena, lead alum, smithsonite, hemimorphite and so on. Gangue minerals include carbonate minerals and clay. The ore is soil-like, loose, nodular, massive and gravel-like. They are usually rich in lead and poor in zinc, and their grades vary greatly. The lead content is between 1%-40%, sometimes accompanied by tungsten and tin placer. Some mineral deposits, such as Jiao Na in Sichuan, are dominated by zinc, and the variation of zinc is between 1%-30%.