The metallogenic regularity of gold indicates that endogenous gold deposits are closely related to fault structure. Some faults are ore-conducting structures, and some faults are ore-bearing structures. Some faults are both ore-conducting structures and ore-bearing structures, while others are neither orbital nor mineral-bearing, and even destroy gold deposits. In the following process, the gold mineralization process, the relationship between the tectonic decompression expansion mechanism and metallogenesis during the ore-forming period, and the control effect of different stress fields on the ore body shape, ore type and grade are discussed.
1 The change of tectonic stress causes the activation, migration and deposition of gold. During the slow accumulation of tectonic stress, the pressure on the rock is gradually increased. Before the stress reaches the rigid deformation of the rock, it is gold and its associated metal elements and silicon. The process of activation of alkali and alkaline earth metal elements such as potassium and sodium and migration by infiltration. With the formation of rigid deformation of the rock, the formation of the fracture structure, the stress in the system is released, and the stress environment is abrupt. The pressure dip system is open and the gold-bearing fluid collects into the pressure release zone. This violent physical-chemical environment causes the volatiles to escape, causing the gold and its associated metal elements such as copper , lead , zinc , and silver , which migrated in the form of complexes, to lose their coordination with anions, potassium and sodium plasma radii. Large alkali and alkaline earth metals are retained in the rocks on both sides of the fracture to form an alkaline alteration, which leads to the decomposition of gold complexes and the deposition of gold and its associated metal elements. The actual output of various gold mines in Jiaodong is a good evidence for the above. For example, the Jiaojia-type gold deposit (altered rock type) is produced in the brittle-tough structure composite section of the main ore-controlling structure; the Lingshan-type gold deposit (belt-shaped fine vein type) is produced in the ore-controlling structural composite section or associated secondary Within the fissure zone; the Linglong gold deposit ( quartz vein type) is produced in the lower plate associated with the ore-controlling tectonic belt, and the low-order and low-order faults are derived; the Shangzhuang gold deposit (saccular micro-fine vein impregnation type) is under control. The main structure of the ore structure is in the micro-fracture zone near the bottom plate. The output parts of various gold mines are the space for the reduction of tectonic stress.
The ore-controlling structures of various types of gold deposits in Ludong and Jidong have the common characteristics of multi-stage and multi-stage activities, and each period and sub-sedimentary activities have hydrothermal activities and mineralizations of varying strengths. Mineral action. This proves that the change of tectonic stress is intrinsically related to the activation, migration and deposition of gold and its associated metal elements. The change of stress is one of the main reasons for mineralization.
2 Controlling the ore body shape during the same ore-forming period
Stress is the dominant factor of tectonic activity. The physical properties of rock determine the difference of structural traces. The energy of the fracture site is released and the tectonic decompression zone is formed. Different structural traces correspond to different physical-chemical conditions and tectonic stress fields, thus controlling different mineralization types and ore body morphology. In the micro-fractures such as rock fissures and cleavage, the ore-forming mineralization is dominant, and irregular ore bodies composed of vein-like and disseminated ore are formed; the cross-section with good smooth cross-section formed at the location of torsional stress concentration In the torsional structure, the filling ore-forming is mainly used to form the vein-like ore body; in the soothing wave-like compression-torsion fracture, the cystic, columnar and lenticular ore bodies appearing at equal intervals in the direction and inclination are formed, such as The output of several types of gold mines in the above Jiaodong area.
3 Influence of structural decompression and expansion on ore grade during the same metallogenic period
The internal stress causes the rock to deform and displace, which leads to the change of the internal structure of the rock. The different forms of structural decompression and expansion have different control on the enrichment degree of gold and its related elements. [next]
3.1 Tectonic decompression caused by metasomatism The change of rock fabric caused by the replacement of rock by the mineral fluid leads to the decrease of rock strength and the formation of low stress zone, which is an indirect structural decompression method. It is a recessive decompression caused by the change of rock fabric, and there is no spatial change in the visual sense. The decompression zone can be distributed in a line shape or in a planar shape. The pressure gradient changes relatively small, and basically does not show the expansion space. The ore liquid is generally dominated by percolation and metasomatism, and alkali and alkaline earth metals are used. The element occludes the original rock, and gold and its associated metal elements are deposited in the metamorphic altered rock. Most gold-containing altered granites fall into this category. The ore grade of this type of ore body is generally low, but the mineralized area is large, and the ore body continuity is good. The gold is mainly distributed in the metal sulfides which are scattered in the altered rock.
3.2 The accumulation of internal stress caused by the fracture and fracture zone causes the local integrity of the rock to be destroyed, but there is no obvious relative displacement, which only causes the rock to break, forming a fracture zone, and the ground stress is released and a band-like distribution is formed. The structure of the decompression belt. The ore fluid is mainly diffused and metasomatized, immersed in the fractured rock and its fissures to form altered fractured rocks, and silicon and gold and other associated metal elements are deposited in the fracture zone. Broken altered rock type gold deposits belong to this category, such as Jiaojia Gold Mine. The ore content of such ore bodies is generally low, but the size of the ore body is relatively large, and it is distributed along the fracture zone, with silicification and cloudying in the fracture zone. Rock formation is the main feature.
3.3 The structural decompression expansion caused by the sliding displacement of the fault block is broken and displaced under the internal stress of the ground, forming a through fault, and the ground stress is fully released. The structural decompression expansion is characterized by the stress drop perpendicular to the fault distribution direction and along the fault. Space expansion in the direction of the spread. The ore liquid migrates from the high stress zone to the decompression zone, filling the fault to form a quartz vein, and the gold is retained in the quartz vein or crystallized together with the polymetallic sulfide. The ore content of this type of ore body is generally higher, such as the Linglong gold mine.
3.4 Structure decompression expansion caused by the staggered trap space The two-disc type of the torsional wave-shaped torsional fault creates a local extension space caused by a relatively long distance relative motion, forming a trapped structural decompression zone. The stress release is the most complete, the stress contrast is maximum before and after the shift, and the physical-chemical environment changes the most, and the mineral pool is also the most fully filled and deposited. More vesicular, columnar, lenticular ore-rich bodies are formed. The ore content of ore is generally high, and the local amount can reach tens to hundreds of grams. However, the scale of the ore body is generally small, and the space is mostly represented by the isometric of the ore body. Or near isometric arrangement, such as the Yuerya gold mine.
4 Conclusion 4.1 The structure of fracture structure decompression and expansion affects the sedimentation form, alteration type and mineralization of gold-bearing ore. Studies have shown that certain elements in the earth's crust have a stable state under the high pressure to reduce their volume to adapt to the high pressure environment. For example, potassium, sodium and other elements have relatively large ion compression, and are less active under high pressure; while silicon, aluminum , iron , magnesium , calcium and other elements have relatively small ion compression and are highly active under high pressure. This characteristic of the element indicates that different stresses in different stages of stress and different tectonic stress areas result in different depositions of different elements in the ore due to different stress states and different ways of structural decompression expansion. . The active elements under high pressure are easily stabilized in a sudden pressure (decompression) environment to form a new mineral combination.
4.2 Loss of energy is one of the main reasons for the formation of ore bodies. The formation of gold ore bodies is a transition from equilibrium to non-equilibrium to new equilibrium, and internal structure from order to disorder to new order. In this process, the conversion of the system and the external energy plays an important role. In the initial stage of mineralization, the ground stress gradually increases, the energy aggregates, the activation and migration of gold and its ore-bearing medium, and the late stage shows the structural decompression expansion, energy. Lost, gold and its associated metal elements deposit mineralization.
4.3 Analysis and study of the genesis and mechanical properties of fault structures are of great significance for the search for blind ore bodies and their exploration and location.
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