Spatial distribution law of regional mineralization

1. the position of large metallogenic belt in regional structure

The large-scale Yanshanian mineralization in southeastern China was directly attributed to the large-scale thinning of the lithosphere and the injection of new mantle materials, which led to three discontinuous Yanshanian reactivations of the lithosphere, becoming the center of tectonic-magmatic-metallogenic activities and an important ore-accumulating structure in this area. Previous studies have confirmed that these three lithospheric discontinuities are inherited and developed on the basis of different basement structural belts in the pre-Yanshanian period, and there are three depression belts dominated by volcanic-sedimentary activities, corresponding to three metallogenic belts and multiple copper, gold and iron (sulfur) ore-rich areas. Igneous rocks of mantle source and crust-mantle mixed source are developed in the three depression zones, and a large number of new mantle-derived materials are injected into the continental crust, which is a sign of discontinuous reactivation of lithosphere scale. However, in the uplift area, there is little or no volcanic-sedimentary activity, mainly some large-scale deep crust-derived granites and few mantle-derived rocks, which is little or no obvious difference from the copper deposits in the basin area, mainly exposed parts of metallogenic belts such as tungsten, tin, gold, silver, lead and zinc.

The division of metallogenic belt in southeastern China is consistent with the division of "uplift-depression" in Yanshan period. At the junction of Dabie orogenic belt and Yangtze and Cathaysian landmasses, corresponding to Lower Yangtze Depression, Jiangnan Uplift, Zhejiang-Jiangxi Depression, Wuyi Uplift and Yongmei Depression, a NE-trending metal metallogenic belt is formed, and a series of super-large and large metal deposits are distributed. The Lower Yangtze Depression is a large skarn copper-gold deposit and porphyry iron-sulfur deposit metallogenic belt. Jiangnan metallogenic belt is a famous tungsten-tin-gold polymetallic metallogenic belt, and Zhejiang-Jiangxi depression belt is characterized by syntectic porphyry copper-gold polymetallic mineralization. Wuyi-Yunkaishan-Huijishan metallogenic belt, distributed along the eastern front of South China Caledonian, is a tungsten, tin, tantalum, uranium, gold and silver metallogenic belt related to crustal remelting granite or volcanic rocks. There are super-large deposits such as Shizhuyuan tungsten polymetallic mine, Yichun tantalum-niobium mine, Xiangshan uranium mine and Lengshuikeng silver mine. Yongmeihui sag belt is a metallogenic belt dominated by volcanic-subvolcanic hydrothermal type, porphyry copper-gold type and low-temperature hydrothermal type silver-antimony ore.

The area is divided into five tectonic-magmatic-metallogenic belts: Lower Yangtze, East Jiangnan, Zhejiang-Jiangxi, Wugongshan-Beiwuyi and Yongmei, with obvious metallogenic characteristics. The mineralization of the metallogenic belt in the depression zone is controlled by tectonic-magmatism and characterized by deep mineralization, mainly sulfur-bearing copper polymetallic deposits; The metallogenic belt in the uplift area is related to remelting magmatic rocks from crust, the mineralization in the Jiangnan belt is related to middle-shallow granite, and the uplift belt in Wuyi and coastal basement is mainly related to subvolcanic rocks and porphyries, forming lithophile minerals such as tungsten, tin, silver and antimony.

The above uplift structure controls five ore belts distributed horizontally, and the metallogenic characteristics are subsection or subsection enrichment. The metallogenic belt in the middle and lower reaches of the Yangtze River can be divided into Daye iron-copper metallogenic section, Jiurui copper-gold metallogenic section, Tongling copper-gold metallogenic section, Luzong iron-sulfur copper-gold metallogenic section, Ningwu iron-sulfur metallogenic section and Ningzhen lead-zinc metallogenic section from west to east. Jiangnan metallogenic belt is famous for its W-Sb-Au metallogenic belt in the west and W-Sn-Au metallogenic belt in the east. The Zhejiang-Jiangxi metallogenic belt is dominated by copper and gold related to type I porphyry and subvolcanic rocks, and the southwest part of Hunan and Guangxi is dominated by lead, zinc and gold. Wuyi metallogenic belt is dominated by S-type plutonic granite metallogenic sub-series in the west of Ganjiang fault zone, and the mineralization related to S-type subvolcanic rocks and porphyries in the east is significantly enhanced. In Yongmeihui metallogenic belt, low-temperature hydrothermal Ag-Sb ore is dominant in the west, and in Shanghang area, it is a NE-trending and NW-trending tectonic-magmatic-metallogenic belt, forming a large copper-gold concentration area in Zijinshan.

2. Structural types of ore concentration areas or large deposits

Ore concentration areas or large-scale deposits are the result of a large number of ores accumulated in a limited range, so they are formed in a unique geological environment. The large-scale metallogenic belt in the southeast of China corresponds to the structural pattern of Chang 'ao sub-region, and the location of large-scale ore concentration areas is in some parts of the metallogenic belt where large-scale structural anomalies change or structures overlap and compound. Remarkably, the main ore concentration areas or large-scale deposits in the southeast of China are controlled by a large-scale "rhombic grid structure" system composed of the intersection of NE and NW structures, and the favorable place for mineralization is the intersection of Paleotethys tectonic system and Pacific tectonic system. For example, Tongling ore concentration area is located at the intersection of east-west basement structure and northwest structure-magmatic rock belt, while Zijinshan ore concentration area is the superposition of northwest Hangzhou-Xiao Yun volcanic rock belt in the northeast of the depression. The most striking thing is that the tungsten-tin metallogenic belt in Jiangnan uplift and the large copper-gold-silver-lead-zinc concentration area in northeast Jiangxi are controlled by large anti-S-shaped structures formed by the superposition of various structures. Ore-accumulating structures in large-scale ore-concentrated areas in northeast Jiangxi are detailed as follows.

The surface structures of large-scale ore concentration areas in northeast Jiangxi are mainly NE-trending, NE-trending and NE-trending. It is inferred from the distribution characteristics of the porphyry belt in the area that there are NW-trending and nearly EW-trending structures in the deep part. NW-trending and EW-trending (-NE-trending) structures belong to Tethys structural system, and NE-trending and NE-trending structures belong to Pacific coastal structural system. The late Pacific tectonic system was superimposed on the early Tethys tectonic system, forming a large anti-S structure that controlled rocks and minerals in the area. Because the late tectonic system accommodated the early structure or made it move again, it was further developed. Therefore, they are all important metallogenic structural systems in Yanshan period. Because of its specific structural combination and different structural planes, many types of rock-controlling and ore-controlling structures have been formed, and there are five typical ones.

1) NE-trending or NE-trending imbricate thrust fault type: Dexing Tongchang porphyry copper ore field is its typical representative. The NE-trending super-crust fault zone, Jiujiang-Dexing-Sanmenao extensional fault zone and Zhenjiang-yingtan-Anyuan NE fault zone jointly control the upper magma chamber. The footwall of the three ore-forming porphyry rocks is multi-peak along the Qiao Zhen-Haikou northeast imbricate thrust belt, and intrudes from northwest to southeast, forming a series of three NW-trending (295) porphyry copper deposits around the rocks.

2) The NE-trending imbricate nappe structure type: Guixi Lengshuikeng porphyry silver ore field is its representative. Metallogenic granite porphyry intrudes in a multi-peak shape along F2 wave-like thrust nappe. The large lenticular porphyry Ag-Pb-Zn ore body is controlled by a derivative fault zone gently dipping to the northwest. The deposit extends to the northwest with a controlled depth of 700 meters. It is possible to find concealed deposits in Madi, Northwest China.

3) NNE fold-fault combination: Dexing Yinshan ore field is its representative. The ore field is controlled by the back structure with an axial direction of 40 NNE and NNE and NNE-trending faults, and the folds take schistosity as the deformation surface, which tends to NNE and the dip angle is 60 ~ 80. At the intersection of the back axis and the NE-trending fault, a porphyritic rock tube is formed, and a copper-gold-lead-silver metallogenic belt is formed around the rock tube. With the downward extension of the rock pipe, the copper deposit has reached below 1500 m, and the structure controlling the ore body is three groups of faults and the unconformity surface at the bottom of the middle Jurassic volcanic rock series. The latter is common, and there are no industrial ore bodies in the mineralization range and the periphery of the ore field. Three groups of ore-bearing fault zones are common supporting faults in the NNE structure (Neocathaysia) in northeast Jiangxi and its adjacent areas. Among them, the NE-trending fracture zone is the most important, which is developed in the NE schistosity of Beishan and Area 9, and forms an arc ore body with the back nose, which has compression-shear characteristics and large mineralization depth. The other group is a NW-trending tensional and torsional ore-controlling fault zone, which is developed in Yinshan ore block. This group of faults is widely developed in this area, and Huwei gold vein and Raojiapai silver vein are controlled by this group of faults. The morphology changes greatly and the mineralization depth is small; A NE-trending ore-bearing fracture zone is also found in Yinshan ore block, which is characterized by sinistral compression and shear, and the Xiangaoshan pyrite vein in the area is also controlled by this fracture zone.

4) Compression-shear fault zone: This is the most common ore-controlling structure of Yanshanian dynamic thermal metamorphic gold-silver deposits in this area. Developed in shallow metamorphic rock series, it often succumbs to foliation development, forming a compressive fracture zone or structural foliation zone, with ductile-brittle deformation characteristics dominated by brittle deformation. The most common one is near east-west or north-east, and the main part belongs to the inheritance and development of Tethys structural system (Dabeiwu, Hujiajian and Changshouyuan), followed by northeast (toad stone), while Jinjiawu is a brush-like compression-torsion structure with near east-west schistosity, converging to the northwest, expanding to the east and slightly bending to the south. The internal rotation twists clockwise, and the mineralization in the middle is the most abundant. It is preliminarily observed that their ductile deformation degree is related to the distance of magma heat source. Dabeiwu and Hujiajian are close to intrusions, and their ductile deformation is slightly stronger. Jinjiawu is farthest from the intrusive body, and its ductile deformation is not obvious.

5) Goose-flying type: The early Tethys tectonic system was represented by Dexing Jinshan gold ore field. The gold-bearing ductile shear system runs from northeast to nearly east-west and gently inclines to northwest. During Yanshanian period, the ductile shear zone was distorted by NE-NNE strike-slip ductile-brittle faults on both sides, and gold mineralization was generally enriched at the superposition of loops.

3. Metallogenic model of intracontinental subduction orogeny in Yanshan period —— Taking northeast Jiangxi as an example.

Northeast Jiangxi is located in the eastern part of Zhejiang-Jiangxi depression. Jinning period is the combination zone of subduction and collision between Cathaysian and Yangtze landmasses, and it experienced Caledonian intense orogeny, Hercynian rift movement and Indosinian-Yanshan intracontinental movement, among which Yanshan intracontinental orogeny is most closely related to mineralization, which is of typical significance in southeastern China. See Figure 5-5 for the rock-controlling and ore-controlling model of the intracontinental orogenic belt.

Figure 5-5 Yanshanian intracontinental subduction orogeny diagenetic and metallogenic model in northeastern Jiangxi metallogenic area

1), there are three super-crust thrust fault zones developed from ancient suture zones, namely Yanshan intracontinental subduction zone, and its front uplift-granite zone, namely Yanshan intracontinental orogenic belt.

2) Along the three intracontinental subduction zones, three copper, gold and silver polymetallic ore zones related to deep type I intermediate-acid subvolcanic rocks and porphyries were formed.

3) These intracontinental subduction zones were ancient plate subduction zones in the early stage, and they were also important ductile, ductile-brittle shear zones and compression zones, so they often formed dynamic thermal metamorphic gold-silver ore zones or gold-silver mineralization zones.

4) Mineralization of granite uplift zone is mainly related to S-type plutonic granite or S-type subvolcanic porphyry, among which tungsten-tin ore is closely related to light-colored granite in orogenic belt. There are I-type granite and porphyrite in this zone, but the mineralization is still dominated by tungsten and molybdenum.

5) The Lingshan-Damaoshan Ta-Nb-W-Sn ore belt related to A-type granite is formed in the extension zone at the rear edge of the intracontinental subduction zone. As for the Ta-Nb mineralization of A-type granite formed in the extension stage of uplift-granite belt, it needs to be further ascertained.

The metallogenic zoning formed by the above-mentioned intracontinental subduction orogeny is very similar to the subduction zone B of the Andean continental margin, that is, copper and gold are in the inner zone and tungsten and tin are in the outer zone. Therefore, it is not difficult to see that the intracontinental subduction orogeny and mineralization in northeastern Jiangxi Province have important typical significance.