Brittle (ductile) fracture structure

For vein hydrothermal deposits, especially those with deep-seated fluids, large brittle faults and their subordinate secondary and more secondary fault structures are the necessary prerequisites for mineralization. Multi-stage tectonic magmatism in Jiaodong area formed a criss-crossing complex structural network. The basement structure in this area is a fault structure composed of Qixia anticlinorium and Precambrian strata, and its structural line direction is nearly east-west. Controlled by the regional tectonic stress field of collision orogeny and subduction, a fault structure system dominated by NE and NNE faults is superimposed on the basement structure. There are seven faults in the upper wall of the Tanlu fault, namely Sanshandao-Cangshang (Sanshandao fault), Xincheng-Jiaojia (Jiaojia fault), Zhaoyuan-Pingdu (Zhaoping fault), Qixia, Mu Ping-Jimo (Mouyi fault), Jinniu Mountain and Mishan, which are distributed in turn from west to east. The first four faults are in the west, and the overall trend is northeast; The latter two are located in the east of Jiaodong, and the overall trend is close to Sn. Mu Ping-Jimo fault is located in the boundary zone, and it is a boundary fault, generally trending northeast. These faults are all super-crustal faults developed in the region, and they are channels for deep magma to rise, which not only affect the spatial positioning of regional magmatic rocks, but also control the formation and distribution of precious metals and non-ferrous metals. The main fracture features are as follows:

(1) Tanlu fault zone

Located in the western edge of the study area, it is a deep fault in Jiaodong area. From west to east, it consists of four faults: Yishui-Tangtou, Tangqi-Gegou, Anqiu-Juxian and Changyi-Dadian, among which Anqiu-Juxian fault is the boundary fault between Jiaodong and Luxi. These four normal faults form the structural pattern of "two grabens and one floor" of the whole fault zone, namely Anqiu-Juxian graben, Mazhan-Sucun graben and Mercury mountain graben (Li Hongkui et al., 20 10). The overall strike of the fault zone is 10 ~ 20, which is more than 300 kilometers long and 20 ~ 60 kilometers wide in Shandong. The fault is characterized by long-term activity. There are both deep ductile structures and shallow brittle breccia in the fault zone, which gradually converges and narrows from north to south. This fault has frequent tectonic activities and plays an important role in controlling the tectonic framework in eastern China and Shandong (Ni Zhenping et al., 20 1 1). As a boundary fault, it has adjusted the whole tectonic stress field in eastern Chinese mainland since its formation, made a direct contribution to the uplift and fault depression of the eastern part (footwall) since Mesozoic, and directly led to large-scale tectonic magmatism and huge metal accumulation in this area.

(2) Discontinuities in the middle crust and three fault zones in the northwest of Jiaodong.

Sun Fengyue et al. (1995) pointed out that the west of Jiaodong is sandwiched between the Tanlu fault and the Taocun fault, and there are brittle fracture systems in the middle crust and brittle fracture systems in the upper crust. The former, together with the east-west basement fault, controls the spatial distribution of granite magma activity and gold mineralization.

Sanshandao-Cangshang fault zone is intermittently exposed in Sanshandao-Shibu area of Laizhou, extending to Bohai Sea at the northeast end, with land exposure > > 10km, 3km in the northern sea area and 200-400 m wide; On the plane, it is gentle and wavy, with a general trend of NE40 and a tendency of SE, with an inclination of 30 ~ 40; The upper part of the fault is superimposed on the contact zone between Jiaodong Group and Linglong and guojialing granites, and the lower part extends into guojialing granite in the northeast. The structural altered rocks in this fault zone are developed, which are characterized by anticlockwise compression and torsion and multi-stage composite superposition of more than two periods. On the fault zone, super-large and large Jiaojia-style gold deposits have been discovered in Sanshandao, Cangshang, Xiling, northern sea area and Xinli.

The west of Xincheng-Jiaojia fault zone is 14km away from Sanshandao fault. It starts from Fenghuang Mountain in Longkou in the northeast, passes through Huangshan Pavilion in Longkou, Laizhou New City and Zhaoyuan Jiaojia in the southwest, and extends to Pinglidian in Laizhou, with a total exposed length of 27km at both ends. It extends in waves, with a strike of 20 ~ 40, NW dip and an inclination of 30 ~ 45. The fault zone cuts Malianzhuang Formation and exquisite granite, and controls Shangzhuang Unit of guojialing Superunit. The structural rock alteration zoning in the fault is obvious, the mineralization is disseminated and reticulate, and the ore body is tabular or lenticular and parallel to the footwall of the main fracture surface. The multi-stage activity is obvious, which is compressive and torsional before mineralization, tensile and torsional during mineralization and compressive and torsional after mineralization. Jiaojia fault is a first-class ore-controlling fault in this area, which controls large and super-large gold deposits such as Jiaojia, Xincheng, Sizhuang, Matangshen, Chen Nan and Shaling. Secondary structures such as Shangzhuang-Wangershan fault and Lingshan-Beijie fault control the gold deposits in Wangershan, Lingshangou and Beijie.

Zhaoyuan-Pingdu fault zone starts from Pingdu in the south, crosses Zhaoyuan in the north and enters Bohai Sea in the east of Penglai, with a total length of nearly 200km. It is a large-scale fault in the west of Jiaodong, bounded by Xiadian, and it is left translated into two S-shapes in the north and south by the Guo Qian-Malianzhuang fault near Dayingzhuang, extending to the northeast for nearly 100 kilometers. The northern and southern parts of the fault show different occurrences and shapes. The overall distribution direction of the fault zone is Ne 30 ~ 40, and it deflects locally from east to west. The dip angle of the northern section and the middle section is gentle, ranging from 30 to 45, while the dip angle of the southern section is steep, generally ranging from 45 to 60, and the width of the fault zone is 80 to 300 m. Generally speaking, the granitoids are in the west of the fault and the metamorphic rocks of Jiaodong Group are in the east of the fault. There are a series of secondary faults in Zhaoping fault zone, such as Toutouqing fault, Fushan fault and Linglong fault. The main fault and the secondary fault zone jointly control the production of many gold mines, such as Taishang Gold Mine, Dayinggezhuang Gold Mine and Xiadian Gold Mine.

The above three regional fault zones are all fracture zones with similar properties and huge scale, with developed tectonic rocks, which may all be branches of the Tan-Lu fault (Yu Xiaofei, 2003), and these fault zones form strong negative pressure gradients, which make ore fluids converge in the fault zones (Sun Fengyue et al., 20 10, internal data). The three fault zones belong to the same level, and the two adjacent faults have opposite tendencies in profile, and have the characteristics of * * * yoke in profile, forming undulating discontinuities in the middle crust (Sun Fengyue et al., 1995), and the fluctuation range is 10 ~ 18 km, which controls the gold mineralization and the distribution of Mesozoic granitic rocks. The combination of the three faults leads to the accumulation and mineralization of a large amount of mineral liquid in two adjacent regional faults with opposite dip, while there is no ore on the upper wall of the two faults with opposite dip (Figure 2. 1 1, Sun Fengyue et al., 1995). The deposit production of Qixia fault zone is also controlled by regional fault structure. A series of small and medium-sized gold deposits have been developed because of shallow erosion and the discontinuity of crustal fluctuation has not been exposed to the surface. There are no large-scale deposits in the granite in the first two belts. However, gravity data show that there is a large area of granitic rocks in the deep part of the belt (Yang Lixin et al., 1998). There are probably large and super-large gold deposits in the first two metallogenic belts of Qixia-Penglai fault zone hundreds of meters below the surface, and there are huge prospecting prospects in the deep part (Sun Fengyue et al., 1995). The discovery of Hushan Gold Mine, a large gold mine in Qixia area, initially confirmed this statement.

Fig. 2. 1 1 Schematic diagram of the * * * yoke fracture in the east-west section of the rubber.

(According to Sun Fengyue et al., 1995)

1-Jiaodong Group; 2- Linglong or guojialing granitic rocks; 3- Luanjiahe granite; 4- Fault structure; 5— Migration route of mineral liquid; ① Sanshandao fault; ② Jiaojia fault; ③ Zhaoping fault

(3) Qixia fault zone

It starts from the bathhouse on the northern edge of Laiyang Mesozoic basin in the south, passes through Chu Yang and Qixia City in Qixia, reaches Yujiakuang in Penglai, reaches Jiesongying in the north and goes straight into the Yellow Sea, with a total length of about 800km. On the southern edge of Zangjiazhuang Basin, the north and south sections are staggered. The southern segment is mainly Qixia Chu Yang fault, and the northern segment is Yujiakuang fault. The fault width is 30 ~170m, strike 10 ~ 25, dip SW and dip angle is 40 ~ 65. Hydrothermal alteration generally occurs in the zone, and the alteration zone is dominated by sericitization, followed by pyritization, chloritization and carbonation. The fracture is gentle and wavy, with sliding mirror and scratches, and the extrusion characteristics are obvious, which is left-handed compression and torsion. This fault and secondary faults control the output of large and medium-sized gold deposits such as Heilangou, Majiayao, Shancheng and Houkuang. There are many small gold mines in this belt. The gold deposit in the northern section is of the time-pulse type+fractured zone altered rock type, and the southern section is of the time-pulse type. It is considered that Qixia fault zone is essentially an upper secondary fault, and the discontinuity of the middle crust is exposed in this area.

(4) Mu Ping-Jimo fault zone.

It is the largest fault in the region, starting from Laishan in Yantai in the north, passing through Taocun area, leaving the region to the south of Guo Cheng and Haiyang in the south, and connecting with Wulian-Rongcheng fault, with an overall strike of 40 ~ 50, a length of about 300km and a width of 20 ~ 60 km. It consists of four main faults: Taocun-Dongdoushan (Taocun fault), Guo Cheng, Zhuwu-Duck (Duck fault) and Yuli-Haiyang (Yuli fault), which are arranged from west to east with a distance of about 10 ~ 15 km. Among them, Taocun-Dongdoushan fault is the boundary fault between the east and the west of Jiaodong. Guo Cheng fault is a fault in the eastern margin of the basin, which tends to NW, while other faults tend to SE. The whole fault zone converges to the southwest and tends to converge (Yu Xiaofei, 2003). The width of a single fault varies from tens of meters to hundreds of meters, with strike of 35 ~ 45 and dip angle of 48 ~ 80. The area through which the fault passes includes Mesozoic sediments in the middle and south sections and Proterozoic and Mesozoic granites in the north section. In this area, the rocks are strongly broken, the tectonic rocks are developed, the composition is complex, and the alteration is strong, and the nearly parallel veins (groups) such as lamprophyre veins, diorite veins and isochronous veins are developed. The fault cut the basin and Weideshan granite (Yashan, Yuangezhuang, Haiyang and other rock masses) in the late Yanshanian period of Mesozoic, making them move to the left. It is speculated that it may have formed in the basin-forming period of Jiaolai basin and experienced many activities in the later period. This group of faults cut the basin, which may be the channel of volcanic activity in Qingshan period. The developed secondary faults are closely related to gold, lead, zinc and silver mineralization.

(5) Jinniushan fault zone

It consists of four nearly parallel faults, namely Qinghushan-Tangjiagou fault (Tangjiagou fault), Shigou-Wu Shan fault (Jinniushan fault), Jiangjunshi-Quhezhuang fault (Jiangjunshi fault) and Majiazhuang-Gekou fault (Gekou fault), which are distributed at a distance of 4 ~ 5 km and exposed in the granite of Kunyushan. The fault zone is nearly north-south, 33 kilometers long and 2-25 kilometers wide; The overall strike is 0 ~ 15, obliquely, with the middle section inclined to the west with an inclination angle of 60 ~ 85. The fault plane is gentle and wavy, with sliding mirrors and scratches. Cataclastic rocks, breccia, fault gouge and extruded lens are developed in this zone. Lamprophyre veins and chronological veins are common, crushed by compression, and interspersed with lamprophyre veins in the later stage, indicating that they have the characteristics of multi-stage activity. It shows the characteristics of expansion and contraction in plane and vertical direction, and is the main ore body (An Yang et al., 20 1 1). Major faults control major gold deposits in the region, such as nearly 100 large, medium and small deposits and occurrences, such as Denggezhuang, Jinqingding, Lazigou, Heiniutai, Tangjiagou, Yinggezhuang, Sanjia, Tongxishan, Xidenggezhuang, Chikan, Li Shan, Shicheng, Shitouquan, Chahe, Jinniushan and Wushan.

(6) Mishan fault zone.

Also known as the Laomuhe fault, it is located in the area from the back of Wendeng Xishan to Hukouyao, along the Mishan Reservoir-Laomuhe, running north and south, and extending into the Yellow Sea. The overall strike of the fault zone is north-south, inclined to the east, with an inclination angle of 58 ~ 76; It is 27 kilometers long and tens to hundreds of meters wide. The northern part is located at the junction of Linglong Superunit and Weideshan Superunit, the central part controls the western edge of volcanic basin, and the southern part runs through Rongcheng Superunit. The rocks in this zone are strongly fractured, mainly granitic cataclastic rocks. Sericite and pyrite sericite are developed in the middle part, and some of them are filled with wide time veins. The timely vein is fractured and shows weak limonitization, and the small timely vein can be seen to penetrate along the fracture in the later stage. Fault gouge, scratches, steps, etc. Develop on fault plane; On both sides of the fault, a series of timely veins extending along the extensional fault can be seen. The fault has the characteristics of multi-stage and multi-stage activity. According to the research (Wang Wenan et al., 1995), the early faults developed along the SN- trending mylonite belt, which was extensive, with a large scale of filling in the time pulse, and the time pulse contained a lot of mylonite breccia; In the middle stage, it is dextral tension and torsion, and small thrust faults are seen in the fault zone, with the occurrence of 66 ∠ 42 and scratches; In the later stage, it is left-handed compression and torsion, forming an extruded physical and chemical lens body in the belt. Pre-structural breccia cut by sliding mirror image is seen locally, with mirror image scratch occurrence 170 ∠ 30. The fault zone is composed of mylonite, cataclastic rock, structural breccia, and chronological veins. It is generally changed by silicification, sericitization, chloritization and limonitization. The regional Bouguer gravity anomaly shows that there are closed anomalies on both sides of the fault, with low gravity on the west side and high gravity on the east side, which is the boundary between the two local anomalies. Aeromagnetic shows a north-south linear low magnetic anomaly zone, which cuts the north-east linear high magnetic anomaly zone, which has obvious linear influence on aerial photographs. 1:50000 structural geochemical exploration shows that the gold distribution in this belt is abnormal (Wang Wenan et al., 1995). This fault is a super-crustal fault (Ling Xianchang et al., 1995), which controls the formation and distribution of gold and polymetallic deposits in this area (Xu Shunshan,1997; Li Guohua et al., 20 13), have found more than 20 gold and polymetallic deposits (spots) in secondary faults on both sides.

In addition, it should be emphasized that the subduction in Mesozoic caused the lateral inhomogeneity of the upper mantle, resulting in mantle uplift and mantle depression. Basins of different scales evolved on the mantle uplift, and metamorphic core complex structures and large-scale super-crustal basin-edge faults formed at the basin edge, which affected the magmatic activity and mineralization in this area. Including Queshan metamorphic core complex (Jiaolai basin), Xilin-Yabi fault (Zangjiazhuang basin), Wuyangquan fault (Zhongqiao-Zangjiazhuang basin) and Lidao fault (Lidao basin).