This belt is the eastward extension of Qinling-Dabie gold-silver polymetallic ore belt. The secondary structural units, structural types and magmatic series in this area have obvious temporal and spatial correspondence with mineralization, and the spatial distribution of deposits in this area has the laws of zonal distribution and cluster concentration respectively on the plane. The main ore deposits in Dabie Mountain uplift area are concentrated in Tongbai-Huoshan in the north and Suizhou-Zhangbaling in the south, showing the law of symmetrical distribution from the central uplift belt of orogenic belt to both sides, and the main ore belts are distributed in the relative depression area or the uplift-depression transition zone on both sides.
The Tongbai-Huoshan gold, silver, lead and zinc metallogenic sub-belt corresponds to the North Huaiyang structural belt in the northern Dabie orogenic belt, which is mainly composed of metamorphic basement from Mesoproterozoic to Early Paleozoic and volcanic-sedimentary rock series in Mesozoic. The belt should be in the back-arc basin environment of pre-Indosinian subduction stage, and fold, deformation and uplift occurred during Indosinian collision. The northern margin of the basin is superimposed with Yanshanian continental basins, and there are large-scale volcanic-intrusive activities, forming a set of high-potassium calc-alkaline and olivine andesite rock series, and its overall characteristics can be comparable to those of the lower Yangtze area. Gold, silver and polymetallic minerals are the main minerals in this area, followed by molybdenum, rare earth, rare earth and radioactive metals. The main mineralization types are: structural altered rock type gold deposit, continental volcanic rock type low-temperature hydrothermal gold, silver, polymetallic ore, stratabound skarn type lead-zinc ore and molybdenum, rare earth, rare metal and polymetallic ore (mineralization) related to granite and alkaline granite. Typical deposits are: Poshan silver mine, Yindongpo gold mine, Create gold mine, Huangchengshan silver mine, Baishipo silver polymetallic mine, Shuiyindongchong lead-zinc mine, Yinshuisi lead-zinc mine and Dongxi gold mine. Among them, the Laowan structural altered rock type gold deposit, which occurs in the metamorphic rocks of Guishan Formation, is the only large gold deposit in this area, and it is also the youngest known ore-forming age deposit in Dabie area, with a metallogenic age of 90 Ma.
Suizhou-Zhangbaling gold ore-forming sub-belt is the foreland fold thrust belt of Dabie orogenic belt. The exposed strata in this area represent the basement and sedimentary cover of the late Proterozoic passive continental margin on the northern margin of the Yangtze plate, and were involved in the foreland thrust belt during the continental collision. The mineralization types in this zone are mainly structural altered rock type and low-temperature hydrothermal gold mineralization. Typical deposits are: Heilongtan Gold Mine, Huaqiao Gold Mine, Xiaomiaoshan Gold Mine and Longwangjian Gold Mine. The metallogenic age of the metal deposits in the foreland thrust belt of the orogenic belt is mainly 130 ~ 145 Ma, and the time span is from late Jurassic to early Cretaceous, which reflects the existence of two superimposed magmatic activities.
(2) Jiangnan uplift metallogenic belt of tungsten, tin, gold, silver, lead, zinc, molybdenum and antimony.
This belt is adjacent to the metallogenic belt in the middle and lower reaches of the Yangtze River in the north, Zhejiang-Jiangxi metallogenic belt in the south and Hunan Province in the west. It is an important metallogenic belt in Jiangnan block, and the study area is divided into three secondary metallogenic sub-belts.
1. Shitai-Taiping Ag-Pb-Zn polymetallic metallogenic sub-belt.
This sub-region corresponds to the so-called Jiangnan transition zone in Anhui Province. It is bounded by Gaotan-Zhou Wang fault in the north and connected with the metallogenic belt in the middle and lower reaches of the Yangtze River. East to the western Zhejiang block, west to the Xiushui transition zone north of Jiuling, Jiangxi. The exposed strata from Sinian to Triassic in this belt are relatively complete, and faults and fold structures are relatively developed. The Yanshanian magmatism can be divided into two stages, and the middle-deep intrusive rocks formed in the middle Yanshan period can be divided into two rock series: high-potassium calc-alkaline granodiorite and calc-alkaline granite. The sub-zone is bounded by Jiangnan fault and divided into two metallogenic areas, east and west. Dongzhi-Shitai metallogenic area, located in the west section, has a relatively complete outcrop of Nanhua-Triassic strata, a carbonate platform facies of Cambrian-Ordovician, and strong mineralization of gold, silver, lead, zinc and antimony. Typical deposits are Huangshanling stratabound skarn lead-zinc deposit in Guichi and Huashan hydrothermal gold-antimony deposit in Dongzhi. Taiping-Ningguo metallogenic area in the east is a large Silurian stratigraphic distribution area. From Cambrian to Silurian, this area is a deep-sea trough-basin facies and a set of muddy flysch formation in the early Paleozoic. Late Paleozoic strata only remained in a limited syncline basin, and the overall mineralization in the east was relatively weak. The main deposits (spots) and types are: Tongshan stratabound skarn copper deposit in Jingxian county, near the contact zone between Carboniferous and small rock masses, and around some large rock masses. In recent years, many hydrothermal (fissure filling) and porphyry gold-silver polymetallic mineralization are related to Yanshanian porphyries and dikes (Wuxi, Zijinshan, Jingxian, etc.). ) has been found in the Silurian strata distribution area in Jingxian-Ningguo area, which has certain industrial significance and prospecting prospects.
In addition, the low-temperature hydrothermal (stratabound transformation) silver-lead-zinc mineralization related to Sinian-Cambrian black shale in this metallogenic sub-zone has certain prospecting prospects.
2. Duchang-Qimen-Jixi tungsten-tin polymetallic metallogenic sub-belt.
This sub-zone is an important tungsten-tin metallogenic sub-zone in Jiangnan block. This belt is equivalent to Xiuwu-Yangzhanling ancient back-arc basin in Jinning period in geological structure unit, and its shape is anti-S-shaped, crossing northwest Jiangxi and southern Anhui, and its western end enters Liuyang in eastern Hunan. The middle section of the belt enters Anhui in a nearly east-west direction and then turns northeast, crossing Ningguo-Jixi fault and then turns northeast. A set of Mesozoic-Neoproterozoic argillaceous flysch sedimentary rock series which experienced low greenschist facies metamorphism is mainly exposed in this area, followed by early Paleozoic stratigraphic residual basins (Lantian basin and Jixi basin) along the south of this area, and the South China-Sinian shallow metamorphic rocks and early Paleozoic stratigraphic exposure areas are mainly in the north of Tianmu Mountain at the junction of Zhejiang and Anhui. It is worth mentioning that this zone is a transitional zone near the core of Jiuling-Jiangnan uplift. Its western section is called Jiangxi Xiuwu transition zone, and its eastern section is cut off by a NE-trending fault, which is connected with Zhexi Depression and Zhexi Depression respectively. Because the sub-zone is located in the compound part of structure-magma-mineralization, mineralization also has its own characteristics.
A series of Yanshanian granites related to mineralization developed in this metallogenic sub-zone, which can be divided into early and late stages. In the early stage, it was intermediate-acid porphyry with mixed source of crust and mantle (type I), mainly granodiorite porphyry, forming porphyry tungsten and molybdenum deposits (Yangchuling, Duchang, Xiwukou and Ningguo), and a series of large and medium-sized deposits related to Yanshanian magmatism, such as explosive breccia copper polymetallic deposit (Qimen Sanbao) and skarn tungsten deposit (Jixi Xiaoyao, Jixi Xia Ji and Ningguo Dawujian). The deposits related to (S-type) granite (light-colored potassium-rich feldspar granite) mainly include Pengshan tin mine in Jiangxi, lead-zinc (silver) ore field and Maopengdian tin mine. In recent years, great progress has been made in the exploration of Zengjialong tin mine and Zhangshiba lead-zinc (silver) mine centered on Pengshan dome in Jiangxi Province. A series of small and medium-sized W-Mo-Ag-Pb-Zn deposits have also been discovered around Fuling rock mass in Jixi, Anhui Province, and a number of new high-concentration geochemical anomalies of W, Mo, Ag, Pb and Zn have been delineated in the sediment survey of1:50,000 stream system.
In addition, there are still deposits related to sedimentation in the remaining early Paleozoic sedimentary basins in this zone, mainly including silver polymetallic deposits (Xikeng in Yixian County) deposited in the black shale of Lantian Formation in Sinian system and vanadium and phosphate deposits in the black shale at the bottom of Tanghe Formation in Cambrian system.
3. Lianhuashan-Zhanggongshan gold, tungsten, tin and polymetallic metallogenic sub-belt.
This subregion is located in the core of Jiangnan uplift (Bazinao-Zhanggongshan). Judging from the natural connection between the Late Paleozoic-Middle Triassic strata distributed in the northeast and Pingxiang-Leping sub-depression, it is speculated that the sub-zone is a strong uplift zone of Yanshanian EW-trending structure-magmatism on the basis of the early northeast structure, which shows a composite zone of near EW-trending fold uplift, structure-magmatism and NE-NNE-trending fault structure, and the rocks in the area have experienced the superposition of near EW-trending structure-magmatism.
In this sub-belt, the early Cretaceous biotite granite and biotite adamellite rock belts along the core of the near east-west composite fold are closely related to the discovered gold, tungsten, tin and polymetallic deposits in this area. The tectonic altered rock-type gold deposits (Jinjiawu and Dabeiwu) and Zangwan placer gold deposits around the crust source (S-type) of early Cretaceous biotite adamellite in Ehu, Jiangxi Province have reached medium and large scale. Only Xiaoliankou gold deposit (small) was found in Qimenwangcun-Banqiao area on the northern slope of Zhanggongshan Mountain in Anhui Province, but the large-area and high-concentration anomalies of gold, tungsten and tin in this area have not been proved. In addition, tin ore (qimenyoulong), molybdenum ore (qimenlidongkeng) and Li Guangshan hydrothermal antimony ore related to Yanshanian porphyry are also found in the area.
With poor natural conditions and low geological work, this sub-region is one of the important areas where Anhui and Jiangxi provinces are expected to make breakthroughs in gold, tungsten and tin prospecting.
(3) Wuyishan Au-Cu-Pb-Zn-Sn-Ta metallogenic belt
This zone is mainly controlled by the basement structure of the ancient Cathaysian block (Figure 4-2), and can be divided into five metallogenic sub-zones around and inside it. Its main features are as follows:
Figure 4-2 Division Map of Wuyi-Taiwan Province Corridor Metallogenic Belt
1. Wugongshan-Beiwuyi Ag-U-W (Au) metallogenic belt.
It is controlled by the tectonic-granite uplift belt developed on the basis of the pre-Caledonian fold thrust belt in South China, and has no obvious boundary with the Dongxiang-Yanshan ore belt. The mineralization in Wugongshan-Yuhuashan area in the west is related to Yanshanian crust-derived S-type granite, including Yichun Ta-Nb ore field and large tungsten deposits such as Hukeng, Xiatongling and Xushan. The mineralization in this area is mainly related to Yanshanian crust-derived S-type volcanoes and subvolcanic porphyries, including the super-large Lengshuikeng Ag-Pb-Zn ore field and Xiangshan uranium ore field. At the same time, a number of small and medium-sized silver deposits and occurrences such as Tanjiashan have been newly discovered. In addition, there is tungsten-tin mineralization related to S granite. Whether the newly discovered A-type granite has Ta-Nb-Pb-Zn mineralization needs further verification.
2. Zixi-Guangchang Pb-Zn-Ag-Au metallogenic belt
Located in the hinterland of Wuyishan Mountains adjacent to Fujian and Jiangxi provinces. The outcropped Mayuan Group is the oldest stratum in this area. Therefore, this belt should be the oldest continental core of Wuyi Uplift. The migmatization in metamorphic rocks is strong, and various shear zone structures are developed at the same time. There was a large area of granitoid intrusion in Caledonian and Yanshanian, indicating that this area belongs to the long-term active thermal dome center. Porphyries are densely distributed along the yingtan-Anyuan fault zone. There are no other Paleozoic strata in this area except Cambrian strata on both sides of Wuyishan vein, which indicates that it was in a state of compression uplift for a long time in Paleozoic.
There are mainly two types of mineralization in this zone, namely regional metamorphism, deep geological structure mineralization and porphyry mineralization.
3. Shicheng-Huichang copper-tin ore-forming sub-zone.
There are many Yanshanian porphyry deposits concentrated in the west of the southern section of yingtan-Anyuan fault, and the typical deposits are Shicheng Songling tin-tungsten deposit and Yanbei tin deposit.
4. Shaowu-Taining Gold (Silver) Metallogenic Subzone
This belt is located in the ancient aulacogen in the west of Bao Si period. The volcanic sedimentary formation represented by Jiaoxi Formation is a typical product of aulacogen, and its protolith is amphibole intermediate-acid volcanic rock. The marine strata of Lintian Formation were deposited in Cambrian and then uplifted for a long time. In the early Jurassic, influenced by the early Yanshan movement, the Chong 'an-Shicheng fault further developed, forming a series of long trough-shaped fault basins along the fault zone. The continental strata of the Lishan Formation in the early Jurassic were deposited on the metamorphic basement, and then the fault zone continued to move repeatedly, forming the red basin accumulation of the late Cretaceous Mingshi Group. Granite intrusion occurred in both Caledonian and Yanshan periods.
Only gold deposits have been found in this area, all of which belong to the structural altered rock type of Hebaoshan metamorphic rock. It is worth discussing that although the Chong 'an-Shicheng fault running through this zone belongs to the same large-scale regional fault as the aforementioned yingtan-Anyuan fault, there are not many porphyry bodies and porphyry deposits in the latter. Shaowu-Taining area in this belt is a gold metallogenic area. In addition, it has been found that there are clues to find silver in the early Jurassic strata in this area.
There are Hebaoshan Gold Mine, Meiqiao Gold Mine, Changxing Gold Mine and Wu Liting Gold Mine at the southern end of Shaowu-Taining Gold Mine, and Jinkeng Gold Mine at the northern end. They all belong to metamorphic structural altered rock type, but the gold deposits in the south occur in the metamorphic rocks of the Mesoproterozoic Jiaoxi Formation, and the gold deposits in the north occur in the Cambrian shallow metamorphic rocks.
5. Zhenghe-Youxi Au-Pb-Zn-Cu metallogenic belt
This belt is located at the eastern edge of Wuyi Uplift, starting from Zhenghe in the north and extending to Youxi in the south until near Dehua. It is characterized by the development of a rift-like volcanic sedimentary formation of Mamianshan Group in the rift. There are ultramafic extrusive rocks in dongyan formation, which indicates that the rift has reached the mantle layer. Due to the thinning of the crust and the uplift of the mantle, more ore-forming materials are brought to the crust, so this belt has rich ore-source conditions. There was another inherited rift in Sinian, and there was a small-scale eruption of intermediate-basic volcanic rocks on the eastern margin of the rift. Since then, the belt has been uplifted for a long time, only in the southwest edge near Yongmei sag. Due to the transgression of Variscan, some Carboniferous and Permian strata have been formed. The Yanshanian movement in the early Jurassic further developed and formed the Zhenghe-Dabu fault in the belt. A large-scale tensile fault occurred in Zhenghe area on the east side of the rift valley, forming a graben-type long-trough fault basin and depositing the Lishan Formation. A large-scale continental volcanic activity occurred in the late Jurassic, and its initial eruption location was probably the fault eruption zone marked by porphyry lava belt on the east side of this zone, and then it spread to both sides and spread to this metallogenic belt. Caledonian and Yanshanian granitoids invaded many places in this area and played a positive role in mineralization. Because of its superior metallogenic geological conditions, this belt has become a concentrated production area of several important deposits in the study area. The main regional mineralization and its metallogenic types and deposit types are: Shuiji metamorphic basic volcanic rock stratabound lead-zinc-silver deposit formed by marine volcanism, and Shuangqishan metamorphic rock shear zone gold deposit formed by regional metamorphism and plutonic geological structure. In addition, there are Dongyan spilite porphyry copper deposit and Longfengchang layered skarn lead-zinc deposit. However, it is also necessary to discuss why Zhenghe-Dabu fault is a large-scale regional fault, but there are few porphyry bodies and porphyry deposits like yingtan-Anyuan fault, which need further study.
(4) Ag, Pb, Zn, Mo, Sn and Cu (Au) metallogenic belts in Zhejiang, Fujian and Guangdong.
This belt corresponds to the Mesozoic volcanic fault depression area in Zhejiang, Fujian and Guangdong, and is actually a uplift area in structural geomorphology, so it is described as a metallogenic unit in the uplift area. This belt is located in the east of Zhenghe-Dabu fault, adjacent to Wuyi Uplift and Yongmei Depression in the west, and is covered by volcanic eruption. It is divided into two sub-belts of copper, gold and silver mineralization in western Fujian-eastern Guangdong and silver, lead and zinc mineralization in coastal volcanic basement.
1. Minxi-Yuedong metallogenic belt
There are three secondary metallogenic units in the Mesozoic volcanic eruption zone along the coast of Fujian and Guangdong: Putian-Fuqing Pb-Zn-Ag metallogenic area, Pinghe-Nanjing Cu-Pb-Zn metallogenic area and Chaoan-Huilai Pb-Zn-Ag-Cu metallogenic area.
Putian-Fuqing Pb-Zn-Ag metallogenic area: Located in the south of Lianjiang-Yongding fault zone and Yunshan early Cretaceous volcanic basin, there are upper Jurassic volcanic strata and small-scale early Cretaceous granite intrusions. There are two small and medium-sized deposits in the community, namely, Yinkeng in Putian and Xiaxidi in Fuqing, both of which are related to continental volcanic mineralization.
Pinghe-Nanjing Cu-Pb-Zn metallogenic area: located on both sides of Shanghang-Xiao Yun fault, mainly distributed in late Jurassic continental volcanic rocks, with porphyritic lava exposed near Meilin in the north and small volcanic basins in Pinghe-Xiao Yun area in the south. In addition, the Permian basement strata are exposed in the northwest of Nanjing, and the upper Triassic-lower Jurassic basement strata are exposed in a large area along the Nanjing-Pinghe line, indicating that the erosion in this area is deep and the volcanic cover will not be preserved too thick. Late Jurassic and early Cretaceous granitoids invaded in this area successively, forming volcanic-intrusive complex. There are two small deposits in the community: Pinghe Zhongteng Heping and Dawangshan. The former belongs to porphyry-subvolcanic hydrothermal Cu-Mo deposit, while the latter belongs to magmatic hydrothermal and structural filling Ag-Pb-Zn deposit.
Chaoan-Huilai Pb-Zn-Ag-Cu metallogenic area: Located on the Xingning-Chaoan fault zone, the volcanic basement of Upper Triassic-Lower Jurassic exposed in a large area has become the main surrounding rock of the deposit. There are large-super-large tin polymetallic deposits in Houpo sag in the community, and there are a series of mineralization anomalies around them, which together constitute the Houpo sag ore field.
2. Metallogenic sub-zone of volcanic basement in Zhejiang and Fujian.
The coastal volcanic basement metallogenic belt includes Shouning-Changtai gold-lead-zinc-silver-copper metallogenic belt and Fuding lead-zinc-silver metallogenic belt.
1) Changtai gold-lead-zinc-silver-copper metallogenic area: this zone is located between Fuan-Nanjing fault zone and Pingnan-Youxi Mesozoic porphyry lava zone. The volcanic basement exposed in the north of Minjiang River is pre-Sinian metamorphic rock, while the upper Paleozoic-Mesozoic sedimentary rocks gradually appear in the south of Minjiang River, indicating that the properties of the basement in the north and south are different. According to the geophysical data such as gravity and aeromagnetism, the buried depth of the top surface of the basement layer shows two convexities and two concavities. The buried depth of Shouning-Pingnan area in the north is shallow, generally 200 ~ 400 m, while Pingnan-Gutian suddenly deepens to1.700 ~1.800 m. The basement between Gutian and Dehua is uplifted, and the buried depth is less than 400 m. Dehua is a deep depression with a buried depth of 2000 m to the south. This change may be related to the northwest Songxi-Ningde and Yong 'an-Quanzhou fault zones. All the basement strata fall into the stepped fault depression on the south side of the fault zone. Judging from the known skylight exposed in the basement, most of them are distributed in the relatively protruding area of the basement. The metallogenic types of deposits in this belt are mainly layered skarn type and continental volcanic tectonic altered rock type. However, from the analysis of metallogenic geological conditions, the types of porphyry can not be ignored.
2) Fuding Pb-Zn-Ag metallogenic area: Located in the northeast corner of the study area, there is a triangular skylight in Mesozoic continental volcanic rocks around Nanxi, Fuding, in which a small piece of Carboniferous-Permian strata is exposed. Although the area is only 7km2, there are different opinions on its tectonic significance. On this basis, some people think that there is a Hualixi geosyncline on the east coast of Fujian, some people think that there is an ancient strait connected with the Yongmei Depression, and recently some people suggest that it belongs to another Fuding-Ningbo Olla Trough. All the above viewpoints have one thing in common, that is, they are all considered to be in-situ basin deposits rather than foreign tectonic terranes. There is a silver cave type lead-zinc-silver deposit in this area.
Fuding Yindong Pb-Zn-Ag deposit occurs in the middle Carboniferous skarnized calcium silicalite. Skarns are layered, massive and veined, and their mineral components are diopside and garnet. Ore bodies are controlled by interlayer structure in skarn, and generally occur in bedding integration, and some of them are filled into veins along the fracture zone (Figure 4-3). The formation of ore bodies is also related to diorite porphyrite veins (once considered as marine neutral volcanic rocks) and breccia granite porphyry bodies. These dikes are themselves mineralized, and silicification tends to be enriched inside and outside the breccia granite porphyry. The composition of metal minerals is simple, mainly sphalerite, followed by galena and pyrite.
Figure 4-3 Longitudinal section of Yindong lead-zinc mine area in Fuding, Fujian (modified by He Yueji, etc.). )
The lead isotopic composition of galena includes normal lead and deep source lead, as well as abnormal lead with high uranium and thorium. The sulfur isotope δ 34S is 0.8 ‰ ~ 7.28 ‰, and the δ 18OH2O of water is -5. 14 ‰ ~ 8.73 ‰, all of which show multi-source characteristics. The deposit belongs to a typical layered skarn type. According to the analysis that the granite porphyry itself was also mineralized, the mineralization stage lasted until Yanshan period.
This deposit is of medium scale. There may be hidden basement strata and such deposits under the volcanic cover around the deposit.
3) Mesozoic volcanic fault depression area in Zhejiang, Fujian and Guangdong: The deposits formed are mainly related to Yanshanian continental volcanism-intrusion. During the Yanshanian period, strong faults and magmatic activities formed volcanic eruption centers at NW, NE-EW faults and their intersections with NE-trending main faults, and accompanied by magmatism, a series of metal mineralization such as silver, lead, zinc, molybdenum, tin and copper were formed, such as the Yinkeng lead-zinc deposit in Putian, and mineralization enrichment appeared in the volcanic cover. It is worth noting that mineralization is also developed in the metamorphic rocks of volcanic basement in the coastal volcanic fault uplift area, and the Ag-Pb-Zn metallogenic belt formed in the exposed area of volcanic basement ("skylight") is also a part of the Ag-Pb-Zn metallogenic series related to Yanshanian acid volcano-intrusion, such as Fuding Yindong Pb-Zn-Ag deposit, which occurs in the middle Carboniferous skarnized calcium silicalite layer in the volcanic basement (Figure 4-4). Therefore, the mineralization in this area has the characteristics of "double-layer" structure, and the future prospecting work should be paid attention to.
Figure 4-4 Profile of Yinkeng Lead-zinc Mine Area in Putian, Fujian Province
(5) Gold and copper metallogenic belt in eastern Taiwan Province Province.
Since Miocene and Pliocene, the Philippine plate has been subducted northward along the Sulphur Trench, forming the longitudinal valley continental collision orogenic belt in Taiwan Province Province, which has a large-scale lithospheric scale discontinuity, and the mineralization in it shows the characteristics of plate structure. The belt can be divided into three metallogenic units: Keelung gold-copper belt, Central Mountain gold-copper belt and Coastal Mountain copper belt, which are mainly distributed in Himalayan ocean-continent collision zone and volcanic latent zone. The main primary metal deposits in this zone are distributed in the coastal mountainous metallogenic belt, while the famous Jinguashi super-large gold deposit is located in the Keelung metallogenic area on the continental side of the ocean-continent collision zone, and its mineralization can be described as "a late bloomer".
The regional mineralization in the eastern part of Taiwan Province Province is mainly related to subvolcanic porphyry and regional metamorphism, thus forming a set of metallogenic series and metallogenic types with relatively new metallogenic age characteristics, as shown in Table 4-3.
Table 4-3 Brief Table of Mineralization, Metallogenic Series and Metallogenic Types of Tectonic Magmatic Belt in Eastern Taiwan Province Province
According to the distribution and geological structural units of gold and copper deposits in the area, they are divided into four metallogenic belts, and there are no metallogenic units in the belts. Only gold mines can be reached, and the rest are still ore occurrences (Figure 4-5).
Figure 4-5 Distribution Map of Point Mineralization Outcrop of Chimei Copper Mine in Hualien, Taiwan (based on data of Gao Zhenmin and Li Chaoyang)
1. Da 'nan 'ao Uplift Metallogenic Subzone (Ⅳ1)
The uplift is located on the eastern slope of the central mountain range, and its main body consists of the (Carboniferous)-Permian metamorphic basement in the Taroko belt, with ophiolite melange. The west is separated from the tertiary depression belt of Jiliangshan-Xueshan by faults, and the eastern coastal mountains are fractured, and the longitudinal valley of Taidong is connected with the coastal mountains. A set of ophiolite melange composed of schist and oceanic ophiolite suite is developed near the longitudinal valley of Taitung, which is considered to be the product of Cretaceous plate acting on suture line.
There are many copper mines in greenschists in this belt, such as Tongmen in Hualien and Dabaishan in Yilan, among which Tongmen in Hualien is the representative.
The ore body of Tongmen copper mine in Hualien is lenticular, integrated in greenschist and sericite schist, closely related to greenschist and diabase, and the metallogenic type belongs to metamorphic basic volcanic rock stratabound type. The composition of the ore is copper-bearing pyrite with a copper grade of 0.5% ~ 2.8%, which is disseminated and coexists with galena.
In addition, there is a similar occurrence in Tongshan, Yilan County, where the grade of copper can reach 3% ~ 4%.
2. Metallogenic sub-zone of Jiliangshan sag (Ⅳ 2)
Located in the west of the central mountain range, it is composed of slightly metamorphic tertiary strata. Deep metamorphism is mainly slate and phyllite in the eastern mountainous area, and shallow metamorphism is mainly argillaceous slate in the western snowy mountain area. This zone is separated from the Late Tertiary-Quaternary subsidence zone in western Taiwan by the Quchi-Chaozhou fault in the west, and is in fault contact with the Taroko fault uplift zone in the east.
There are many gold deposits in the shallow metamorphic rocks in this zone, such as Taibai Mountain in Yilan and Hehuan Mountain in Nantou. Gold-bearing quartz veins occur in argillaceous slate, phyllite and metamorphic sandstone. Some of its occurrences are consistent with surrounding rocks, showing synchronous folds, and some are through bedding. Thick veins can reach 1 m, and thin veins are only a few centimeters. Metal minerals include natural gold, galena and sphalerite, with grades ranging from 10× 10-6 to 1000× 10-6. Natural gold occurs in the uplift, bifurcation or morphological change of the timely vein. Wall rock alteration includes pyritization, chloritization, kaolinite and calcite. The metallogenic type belongs to metamorphic rock structure-altered rock type.
3. Metallogenic sub-zones in coastal mountainous areas (Ⅳ 3)
Located in the coastal zone on the eastern edge of Taiwan Province Island, the west is connected with the longitudinal valley of Taitung through coastal mountain faults. This terrane is a tectonic mosaic terrane, which is considered to be the product of the collision between Luzon Island Arc at the front of Philippine Sea Plate and Eurasia Plate in the early Cenozoic. The Miocene Chimei andesite igneous complex (with an exposed area of 22km2) and Miocene Duluanshan Formation andesite marine pyroclastic rocks originally belonged to Luzon volcanic arc, and the Pliocene-Miocene Dagangkou Formation sedimentary clastic rocks (including a small amount of pyroclastic rocks) on it belonged to flysch deposits in the pre-arc basin.
Chimei copper deposit is located in Chimei igneous complex in this area, and Dulanshan copper deposit is located in volcanic-intrusive rock of Duluanshan Formation.
(1) Chimei copper mine
Chimei igneous complex is a medium-basic eruption-intrusion complex composed of basaltic andesite, porphyritic andesite, basalt, diorite and various dikes. Mineralization is related to diorite porphyry. Among them, pyroxene diorite is an early intrusive rock with a K-Ar age of 22.5Ma±3.5Ma, porphyritic pyroxene diorite with an alteration age of 65438±0.7Ma±2.5Ma Ma. Andesite is relatively late, with zircon age of 15.4 ~ 16.4Ma. The age of the mineralized altered diorite measured by He He 1969 is 9.0Ma±0.7Ma, which is considered as the metallogenic age. Five mineralized outcrops were found, all of which are porphyrite, chalcocite, sky blue, vitrinite, staghorn, copper-bearing limonite and patina. Alteration types include clay mineralization (montmorillonite, illite), green rock formation (epidote, chlorite, pyrite, calcite) and anhydrite formation. Among them, the third mineralized area consisting of outcrops No.3 and No.4 is 650 meters long from north to south and 400 meters wide from east to west. After drilling, if calculated by Cu > 0.3%, there are 7.33 million tons of ore reserves. > 0.5% is 6.5438+0.86 million tons (gold content is 0.4 ~ 0.5g/t), and the metallogenic type belongs to porphyry type. See Figure 4-5.
(2) Dulanshan Copper Mine
Miocene Duluanshan Formation is pyroclastic rocks such as andesite lump, tuff and tuffaceous sandstone, among which there are limestone lenses. Andesite porphyrite is a subvolcanic rock body, which is invaded by rocks, bedrock and tongue. The ore bodies are formed in the contact zone of andesite porphyry, with 6 outcrops, all of which are controlled by structural faults. The ore is composed of pyrite and chalcopyrite, with a small amount of chalcocite and celestite. Because of chalcedony symbiosis, locals call it Luanshan gem. Mineralization is disseminated or massive, and the surrounding rock is bluestone and argillaceous alteration. Among the six outcrops, the largest outcrop No.4 is a breccia tube with a diameter of 10 ~ 15cm, which is sub-circular and consists of clayey andesite, and andesite dikes often run through it, so it is presumed to be the center of volcanic eruption. The ore contains copper 0. 1% ~ 6.3%, with an average of 0.4%, gold 4.6× 10-6 and silver 15× 10-6. The metallogenic type is tentatively classified as subvolcanic hydrothermal type, and it is speculated that there may be porphyry copper deposits under the breccia tube.
4. Keelung Volcanic Arc Metallogenic Area (Ⅳ 4)
There are two volcanic groups in the north of Taiwan Province Province, Datun Mountain and Keelung, which are composed of Pleistocene basic-neutral volcanoes and subvolcanic rocks. The former has an area of 290km 2 and an isotopic age of 0.37 Ma 0.04 Ma ~ 2.56 Ma 0.5 Ma. The latter has an area of 12.3km2 and an isotopic age of1.1~1.7ma. In the past, it was generally believed that these volcanic groups were the western extension of the Ryukyu volcanic arc, but recently, according to the comparison of Sr and nd isotopes, they are different. Therefore, it is suggested that the Keelung Volcano Group is not the Ryukyu Volcano Arc, but the product of the extension environment after the Luzon Island Arc collided with the edge of Eurasia 2 Ma ago. Among them, Benshan rock body intruded along the axis ridge of sedimentary anticline at 1.7 ~ 1.4 Ma. The rest rocks were formed in 65438±0.0～0.9Ma Ma. The famous Jinguashi gold-copper ore field is located in the volcanic arc metallogenic area of Keelung.