On the basis of long-term field investigation and indoor research, the author found that there are seven ore-controlling structural types in Mesozoic Yanshan intracontinental orogenic belt, namely, intrusive ring structure, ancient volcanic ring structure, metamorphic core complex structure, broom structure, I-shaped structure, I-shaped structure and ductile shear zone. This section will analyze these seven Mesozoic ore-controlling structural types one by one.
I. Ore-controlling by ring structure
Through the structural interpretation of aerial photos and satellite photos, combined with field observation, it is found that a large number of ring structures developed in this area in Mesozoic. These ring structures can be divided into ring structures related to magmatic intrusion, ring structures related to ancient craters, ring structures related to concealed rock masses, spiral ring structures and ring structures with unknown genesis. The size of the ring structure varies greatly, ranging from several square kilometers to several hundred square kilometers (Figure 5-9). Its spatial distribution is controlled by Mesozoic deep faults and uplift zones.
In Mesozoic, a large number of gold, silver and polymetallic deposits were distributed in or around the ring structure, and the mineralization was obviously restricted by the ring structure (Figure 5-9). There are two main ore-controlling structures, namely, intrusive ring structure and ancient volcanic ring structure.
1. intrusive ring structure ore control
The annular structure of intrusive body includes the annular structure related to the exposed intrusive body on the surface and the annular structure related to the concealed rock mass. The former has ring structures such as Xiabarrack, Baizhangzi, Bajiazi, Shouwangfen, Xiaosigou and Caijiaying. This annular structure is related to intermediate-acid intrusive rocks and distributed in the interior or edge of giant complex. For example, Baizhangzi ring structure is distributed in the northwest edge of Yangzhangzi-Tangdaohe granodiorite complex. Shouwangfen ring structure is distributed in the south of acid complex in Shouwangfen. The latter, such as Xiaoyingpan, Arowana, Qifeng Tea, Majiazi, and the narrow ring structure-Laomigoumen. There are no corresponding intrusions exposed on the surface of this ring structure, only some intermediate-acid dikes are seen, and there are hidden rock masses under them.
The above-mentioned ring structures are all ore-controlling ring structures, such as Jinchangyu Gold Mine, Xiaoyingpan Gold Mine, Baizhangzi Gold Mine, Bajiazi Lead-zinc Mine, Shouwangfen Copper Mine, Xiaosigou Copper Mine and Qifengcha Gold Mine, which are all distributed in the corresponding ring structures in the mining area (Figure 5-9). Field observation shows that the annular images related to intrusions are all related to hydrothermal alteration or contact thermal metamorphism accompanied by intrusions, and the annular structure is a favorable part for mineral liquid activity and mineral migration and enrichment, which is a good prospecting indicator. The ring structure of skarn deposits such as Bajiazi lead-zinc mine, Shouwangfen copper mine and Xiaosigou copper mine mainly reflects the spatial distribution of skarn belt and marble belt, and the ore bodies are distributed in skarn belt (Figure 5- 10a). In hydrothermal deposits, such as Wazidian Gold Mine, Qifengcha Gold Mine, Jinchangyu Gold Mine and Baizhangzi Gold Mine, the ring structure of the mining area reflects the spatial distribution of chloritization, sericitization and silicification, and the ore bodies are distributed in the alteration zone. In addition, in the ring structure of intrusive body, folds and faults are more developed than those around it, such as Shouwangfen copper mine (Figure 5- 10a), which is beneficial to the migration of mineral liquid and mineral enrichment. It can be seen that intrusive ring structure ore-controlling is a common structural ore-controlling type.
Fig. 5-9 Schematic diagram of the relationship between the ring structure of Yanshan intracontinental orogenic belt and the distribution of gold deposits.
Fig. 5-9 Spatial relationship between ring structure and deposit in Yanshan intracontinental orogenic belt
1 ring structure; 2 ~ 7 are different minerals: 2- gold deposit; 3- silver ore; 4- Polymetallic ore; 5- Lead-zinc mine; 6-Molybdenum ore; 7- copper mine; 8 ~ 9 indicates the scale of the deposit (taking gold mine as an example): 8— large and medium-sized gold mines; 9- Small Gold Mine
2. The ring structure of ancient volcano controls ore.
The annular structure of the ancient volcano is composed of annular and radial faults and related annular images around the ancient crater. Such as Hongshilao, Nailingou and Erdaogou in western Liaoning, Sanyizhuang and Dazhuangke in northwest Hebei. This annular structure is well developed in silicification and sericitization, and is a favorable place for volcanic gold, silver and polymetallic mineralization. Volcanic gold deposits such as Hongshilai gold deposit, Erdaogou gold deposit and Nailingou gold deposit are all distributed in the ancient volcanic ring structure, which is related to volcanic activity in the early Cretaceous. Among them, the veins of Nailingou Gold Mine are distributed in a ring shape, which is restricted by ring faults (Figure 5- 10b). The ring structure of Hongshilai gold mining area is composed of radial and ring faults, and some faults develop gold mineralization and copper mineralization. The ring structure of Dazhuangke molybdenum deposit and Sanyizhuang lead-zinc polymetallic deposit is related to Yanshanian cryptoexplosive breccia tube, in which large porphyry molybdenum mineralization and lead-zinc polymetallic mineralization are developed respectively. Therefore, the ring structure of Mesozoic paleovolcano is another important structural ore-controlling type.
3. Ore-controlling structure of metamorphic core complex
In recent years, the author and other members of Yanshan Project Team of Institute of Geomechanics have discovered a large metamorphic core complex in the field-Yiwulvshan metamorphic core complex. The center of metamorphic core complex is Yanshanian Beizhen granite, followed by Archean Jianping Group middle-deep metamorphic rock series, Mesoproterozoic carbonate-clastic rock series and Jurassic-Cretaceous volcanic-sedimentary rock series. Metamorphic rocks around granite have experienced strong solid plastic flow and ductile shear deformation (Figure 5- 1 1). A large number of structural types such as recumbent folds and rootless closed folds have been formed in the plastic rheological zone. Eyeball mylonite is widely distributed in ductile shear zone, and there are structural types such as stone sausage, structural lens and hook asymmetric fold. Mylonite schistosity is distributed annularly with Beizhen granite as the center, and the schistosity tendency and shear sliding direction all point to the periphery with rock mass as the center. In the surrounding Mesoproterozoic carbonate-clastic rock series, strong fold deformation developed, forming complex fold structure and a small number of ductile shear zones developed. The formation and evolution of this annular ductile shear zone and its associated solid-plastic rheological structure are related to the thermal power of Beizhen granite in Yanshan period and the sliding and thinning of the overlying strata caused by magmatic emplacement. There are still Yunmengshan metamorphic core complex and Fangshan metamorphic core complex in the south of Yanshan orogenic belt, and their basic characteristics are similar to those of Yiwulvshan metamorphic core complex. It is worth pointing out that there are still different understandings of the above-mentioned "metamorphic core complex".
Fig. 5- 10 Ore-controlling examples of ring structure in Shouwangfen (a) and Nailingou (b) mining areas.
Figure 5- 10 Example of Ore Body Distribution Controlled by Circular Structure
A— Shouwangfen copper mine: 1— Jurassic glutenite; 2- Yanshanian granite; 3- Yanshanian granodiorite; 4- Main thrust fault; 5-general fracture; 6- copper ore body; 7— The appearance of stream surface; Pt2g—- Mesoproterozoic B- Nailingou gold deposit:1-intermediate acid volcanic rocks; 2- Volcanic breccia; 3- gold vein
These metamorphic core complexes are favorable structural sites for gold mineralization, especially the Yiwulvshan metamorphic core complex and Yunmengshan metamorphic core complex have obvious control over the distribution of gold deposits. Some large and medium-sized gold deposits have been discovered in the ductile shear zone and its periphery. For example, Paishanlou gold deposit, a large ductile shear type gold deposit, was discovered in the north of Yiwulu Mountain metamorphic core complex, and several small and medium-sized compound vein gold deposits such as Qifengcha were discovered in the east of Yunmengshan metamorphic core complex.
Second, the broom structure controls the ore.
The Mesozoic brush-like structures in this area are well developed, such as the brush-like structure of Shouwangfen (Figure 5- 10a), the brush-like structure of sharp point, the brush-like structure of Liugou in Pingquan, and the brush-like structure of Zhaogezhuang in Luanxian. They may be related to the left-lateral translation activities of the main faults of Neocathaysia, and belong to derivative and associated faults, such as Liugou and Zhaogezhuang broom structures. Or it is related to Mesozoic rock intrusion, such as Shouwangfen and Huajian broom structure. Brush-like structures related to intrusions are of great control significance to Mesozoic mineralization, and the ore bodies of Shouwangfen copper mine and Huajian gold mine are all restricted by this brush-like structure (Figure 5- 10 and Figure 5- 12).
Fig. 5- Structural Distribution Map of Yiwulu Mountain Metamorphic Core Complex +0 1
Fig. 5- 1 1 Schematic diagram of Yiwulu Mountain metamorphic core complex
1- Early Cretaceous clastic rocks; 2- Mesoproterozoic; 3- Archean-Proterozoic metamorphic rocks; 4- Yanshanian granite; 5- solid plastic rheological-ductile shear zone; 6- Normal fault; 7- Gold deposits and occurrences
Broom-like structure related to intrusive body has two remarkable characteristics: first, it is closely related to ring-like structure in space and is a part of ring-like structure, both of which are related to intrusion activities, and broom-like structure is distributed around rock mass; Second, there is intense thermal fluid activity in this brush-like structure, including strong alteration such as chloritization, sericitization and silicification, such as Huajian Gold Mine, or marble and skarnization, such as Shouwangfen Copper Mine (Figure 5- 10). Mineralization or distribution in the convergence end of broom structure, such as Shouwangfen copper mine area (Figure 5-10); Or distributed in brush fractures, such as Huajian Gold Mine (Figure 5- 12).
Three. "Ru" structure controls ore.
The "middle" structure is composed of main faults and secondary associated and derived faults, which intersect at an acute angle to form a "middle" structure, which can be divided into two types: plane "middle" structure and section "middle" structure. These two types of structures are important ore-controlling structures. Generally speaking, the main fault is the ore-guiding structure and the secondary fault is the ore-hosting structure. Some ore bodies also occur in major faults in some mining areas.
Two ore-controlling examples of plane Ru-shaped structure are Zheshanzi Gold Mine (Figure 5- 13) and Sanjia Gold Mine (Figure 5- 14). The ore bodies of Sanjia Gold Mine are mainly distributed in the secondary compressive and torsional main faults. The main structures in the area are Neocathaysian secondary and tertiary faults, which are ore-bearing structures. The ore-hosting fault is a derivative structure produced by the left-lateral translation of the main fault (Figure 5- 14). The orebodies of Zheshushanzi gold deposit are distributed in the main and secondary faults of "in" structure. The main fault is an east-west tension-torsion fault zone, which belongs to the tertiary fault structure zone in Weichang-Chifeng belt fault on the northern margin of Yanshan Mountain. Among them, gold mineralization is mainly altered rock type; The NW-trending secondary derived fault is a tensional fault, and the mineralization is mainly time-dependent gold mineralization (Figure 5- 13).
The ore-controlling examples of the Ru-shaped structure on the profile include Rujiawanzi Gold Mine, Baimiaozi Gold Mine, Xiaomaping Gold Mine, Guzigou-Dongshan Ag-Pb-Zn Belt, Liangjiagou Silver Mine and so on. Their common feature is that part or all of the ore bodies occur in bedding fractures of Mesoproterozoic clastic rocks and carbonate rocks. Bedding fractures are tensile and tensile fractures, mainly from dry compression and torsion fractures, and are the main ore-hosting structures; The main fault belongs to the second and third grade northeast fault or belt fault of Neocathaysia, and it is the main ore-controlling structure. In some mining areas, such as Rujiawanzi Gold Mine and Xiaomaping Gold Mine, gold-bearing quartz veins are also developed in the main faults (Figure 5- 15). When the Ru-shaped structure on the profile controls ore, if the surrounding rocks are mainly sandstone, conglomerate, shale and quartzite, the mineralization in bedding fractures is mainly gold mineralization, such as gold deposits in Rujiawanzi, Baimiaozi and Xiaomaping. If the surrounding rock is dolomite mixed with shale, the mineralization in bedding fractures is mainly silver, lead and zinc mineralization, such as Guzigou-Dongshan silver-lead-zinc belt and Liangjiagou silver-lead-zinc ore body (Figure 5- 16).
Figure 5- 12 Geological Schematic Diagram of Huajian Gold Mine (reduced according to mine geological map)
Figure 5- 12 Geological Map of Huajian Gold Mine
1- Yanshanian granite (); 2- Gold vein. Ar- taiguyu
Figure 5- 13 Geological Sketch of Zi Shan Gold Mine (modified according to geological map of mining area)
Figure 5- 13 Geological Map of Zuanshanzi Gold Mine
1-granite (); 2— diorite (); 3- Tensile and torsional fracture; 4- gold vein; P- Permian limestone and sandstone shale
Figure 5- 14 Geological Sketch of Sanjia Gold Mine Area (reduced according to the geological data of Team 522)
Figure 5- 14 Geological Map of Shanjia Gold Mine
1- Trunk compression and torsion fracture; 2- gold vein; Ar- Archean medium-deep metamorphic rock series
Fig. 5- 15 Cross-section of private mining roadway in Danjiawanzi Gold Mine
Figure 5- 15 Profile of Danjiawanzi Gold Deposit
1- great wall group quartzite; 2- gold vein; 3- fracture
Fig. 5- 16 profile of liangjiagou silver polymetallic deposit (quoted from yang xibin et al., 1990)
Figure 5- 16 Profile of Liangjiagou Silver Deposit
1-dolomite of Gaoyuzhuang Formation; 2-Shale higher than Zhuang Formation; 3- metamorphic rocks; 4-compression and torsion fracture of trunk; 5— Ore body
Four, "multi" structure ore control
The "two-shaped" structure is composed of a series of nearly parallel structural zones, which are distributed in a wild goose.
"Duo" structure is one of the main ore-controlling structural types of ore bodies, which is mainly composed of secondary faults derived from regional secondary and tertiary faults, such as Yuerya Gold Mine, Jinchanggouliang Gold Mine, Banbishan-Miaozhangzi Gold Mine, Gao Chang Gold Mine, Dongwujiazi Gold Mine and Wazidian Gold Mine. A type of ore-controlling "multi"-shaped structure is NE-trending and consists of associated faults in the Neocathaysian system, such as Yuerya Gold Mine, Wazidian Gold Mine and Banbishan-Miaozhangzi Gold Mine. The ore-controlling "multi"-shaped structure in Yuerya Gold Mine is generally distributed in an "S" shape, which is composed of a series of NE-NE compressional and compressive-torsional faults (Figure 5- 17). These ore-bearing faults are related to the regional Neocathaysian Yuerya-Tangdaohe fault zone. Among them, the mineralization in compression fracture is mainly altered rock type, and the mineralization in torsion-compression-torsion fracture is mainly time-dependent pulse type.
Another type of ore-controlling "multi"-shaped structure is NW-trending and consists of NW-trending tensile and torsional faults originating from Neocathaysia, such as Jinchanggouliang Gold Mine (Figure 5- 18), Honghuagou Gold Mine and Gao Chang Gold Mine. Individual mining areas are east-west extensional fault zones, such as Shuiquan Gold Mine. The ore bodies controlled by this kind of structure are often chicken-nest-shaped and lenticular, distributed in tension-torsion fractures, and the surrounding rock tension breccia is common in the ore.
Five, ductile shear zone ore control
There are many ductile shear zones in this area, mainly formed in Archean-Proterozoic and late Variscan-early Indosinian. The main ductile shear zones from late Variscan to early Indosinian are banded ductile shear zones and ne ductile shear zones. The former is mainly distributed in the east-west structural belt of Chongli-Chicheng-Damiao-Fuxin, such as Damiao ductile shear belt, Dalianjian-Longhua ductile shear belt, Tabenzalan-Xiafu ductile shear belt and Paishanlou ductile shear belt. The latter are Paishanlou-Jinzhou NE ductile shear zone and Jinchangyu NE ductile shear zone.
The work results in recent years show that the late Variscan-early Indosinian ductile shear zone in this area is one of the important ore-controlling structures of gold deposits. There are two basic types of ore control in ductile shear zone: direct ore control and indirect ore control.
The direct ore control of ductile shear zone is the direct ore control of ductile shear type gold deposits, such as Paishanlou Gold Mine and Xiaosanchakou Gold Mine. The main mineralization of Paishanlou gold deposit is characterized by veinlets and disseminated gold-bearing sulfides, which are distributed along the schistosity in the middle of the east-west ductile shear zone. There is no coarse-grained gold-bearing sulfide-time pulse, and the relationship between ore body and surrounding rock is gradual transition (Figure 5-5c). The ore grade is low, but the ore body is wide and stably distributed in the middle of ductile shear zone. The deposit is large in scale and is expected to reach super-large scale. The mineralization of Xiaosanchakou gold deposit is characterized by disseminated gold-bearing sulfide distributed in chlorite and sericite quartz schist, gold-bearing sulfide-quartz vein and carbonate vein distributed along the east-west ductile shear zone, and the latter distributed in the middle of the ductile shear zone in the form of lentils and veins. The main mineralization of the above ductile shear type gold deposits is distributed in the high strain zone in the center of ductile shear zone.
Figure 5- 17 Geological Schematic Diagram of Yuerya Gold Mine (reduced according to geological data of the mine)
Figure 5- 17 Geological Map of Yuerya Gold Mine
1- Yanshanian granite; 2- gold ore body; Pt2—-Dolomite and Shale of Gaoyuzhuang Formation
Figure 5- 18 Geological Schematic Diagram of Jinchanggouliang Gold Mine (according to the data of the Third Geological Brigade of Inner Mongolia Bureau of Geology and Minerals and the mining area)
Figure 5- 18 Geological Map of Jinchanggouliang Gold Deposit
1- intermediate acid volcanic rocks; 2- granite; 3- Compression and torsion fracture; 4- gold vein; Ar- Archean medium-deep metamorphic rock series
The ductile shear zone indirectly controls the ore, indicating that the ductile shear from late Variscan to early Indosinian led to the initial enrichment of gold, which provided good metallogenic structure and material conditions for Yanshanian gold mineralization, such as Jinchangyu and Hougou gold mining areas. The ductile shear zone of Jinchangyu Gold Mine is mainly composed of felsic mylonite, chlorite-sericite schist and albite schist, accompanied by gold-bearing iron mineralization, forming low-grade (≤2g/t) gold deposits, which constitutes the first phase of gold mineralization in the mining area. Sulfide-bearing mylonite and chlorite schist before the main metallogenic period were discovered in Hougou Gold Mine, Jinchanggouliang Gold Mine and Honghuagou Gold Mine. These ductile shear zones before the main metallogenic period provide a good metallogenic geological background and favorable metallogenic structural conditions for Yanshanian hydrothermal gold mineralization in the mining area.
In addition, there are often two or more structural ore-controlling types in the same mining area, such as Jinchangyu Gold Mine. There are three types of ore control: indirect ore control in ductile shear zone, ore control in annular structure and ore control in polygonal structure. The ductile shear zone controls the early albite-isochron-pyritization, and the serrated ring structure and polygonal fault structure control the main metallogenic period (i.e. sulfide-isochron pulse period). The distribution of ore bodies in Shouwangfen copper mine and Huajian gold mine is not only related to ring structure, but also controlled by broom structure related to intrusion.