Figure 7.57 Guizhou Danzhai Mercury Mine-Maoerdong-Wugongqu Deposit
(According to Guizhou Mercury Bureau)
If the internal rotation is active, for example, due to the rotation of magma or the dislocation of faults when it is in place, elasticity holds that:
The tectonic stress field controls rocks and minerals.
So σ 1, σ3 and τmax are inversely proportional to the square of the radius from the torsion center (column or vortex). The intensity of structural deformation is strong inside and weak outside, and the closer it is to the pillar, the stronger the deformation is, which provides a good space for mineralization, increases the surface area of rocks and is conducive to the replacement of mineral liquid. From the point of view of stress-driven ore liquid, hydrothermal solution will move outward from ore pillar under stress.
Fig. 7.58 Magmatic deformation of the crust caused by deep rotation and torsional emplacement.
Fig. 7.59 Relative dislocation of two fault disks
If it is external rotation activity, the fault far from the center of rotation and torsion is dislocated. At this point:
The tectonic stress field controls rocks and minerals.
That is, σ 1, σ3 and τmax are all proportional to the radius p from the torsion center (column or vortex). The deformation intensity is strong outside and weak inside, and the ore-forming solution moves from the periphery to the center of rotation and torsion under the stress drive. Causing zoning of metallogenic elements. For example, the rotating structure of Kuangshan Village, Hanxing County, Hebei Province is surrounded by a series of folds, which are distributed like a turbine. The migration of ore-forming fluid is strictly controlled by the rotational response force field, so the main ore deposits and ore bodies are located in the folds and turning points of the cyclic structural anticline, which control the changes of magnetite and TiO2 content. The trend analysis of TiO2 _ 2 in magnetite shows that the ore liquid migrates from outside to inside (Figure 7.60).
Fig. 7.60 Ideal schematic diagram of mineral liquid migration form in ore field.
(According to Yang Kaiqing et al., 1982)
1-titanium dioxide content (%) and isoline in magnetite; 2— Ideal streamline and flow direction of mineral liquid
Due to tectonic stress transfer, magma crystallization is affected. Liquid or plastic flowing substances are controlled by tectonic stress field during crystallization. Crystalline substances (elements) move and gather regularly according to their own properties and transmissible stress properties, magnitude (strength) and direction (element distribution geochemistry), so that different lithofacies and mineral facies crystallize under a certain tectonic stress field pattern. This clarifies the relationship between tectonic stress field and geochemical field. This field theory unifies momentum, energy and mass. Dong Shuwen's research on brush tectonic stress field and geochemical field of Shaxi porphyry copper deposit in Anhui Province is a good example. Firstly, the coordinates of each twisted strip are processed to obtain the curve equation of each twisted strip. Shaxi broom structure is calculated according to the mechanical model of infinite plate concentrated couple. The stress field of broom structure is divided into intensity areas, namely, the strong internal rotation stress area, the middle stress area and the weak external rotation and torsion stress area.
1) The convergence direction of Larsen index (LDL) of ore-bearing rock mass is lower than that of diffusion direction, and the inner rotation region is lower than that of the outer rotation region, and the vortex is lower than that of each rotation region, indicating that the same rock mass is alkaline at the convergence position of broom structure, and the diffusion direction is acidic, and the alkalinity of inner rotation region is greater than that of outer rotation region. At the same time, the distribution of Larsen index shows that the ore-bearing magma evolved from the inner rotation zone to the outer rotation zone, from convergence to diffusion intrusion.
2) The distribution law of Si4+ in ore-bearing rock mass, the number of Si4+ atoms gradually increases from the convergent end to the divergent end of each twisted band, and from the inner twisted band to the outer twisted band.
3) Rotational and torsional stress fields act on the whole diagenetic and metallogenic process of porphyry, resulting in the enrichment of heavy elements (Ti, Fe, Mn, etc.). ) in the stress zone; Ca and Mg are enriched in the middle stress zone, while light elements K and Na are enriched in the weak stress zone, which correspondingly form three ore zones of Au, Cu-Mo and Pb-Zn, and form a material field under the action of tectonic stress.
4) The distribution law of main characteristic elements in ore-bearing rock mass is divided into three groups according to atomic weight and element density, with heavy elements (atomic weight 47-55, density 4.5-7.86 g/cm3) and h = σ (Ti4++Fe3++Fe2++Mn2+); Intermediate element (atomic weight 24 ~ 40, density 1.54 ~ 1.74g/cm3), m = σ (Ca2++Mg2+); Light element (atomic weight 22 ~ 39, density 0.86 ~ 0.97 g/cm3), L = σ (K++Na+). Elements are regularly distributed in the broom structure according to atomic weight and density. Heavy elements are mostly concentrated in convergence direction or internal rotation and torsion zone; Light elements are mostly concentrated at the end of loose elements or in the external torsion zone;
5) The middle element is centered. The characteristic values of elements also reflect the radius of elements: RH = 0.064 ~ 0.09 1 nm, RM = 0.078 ~ 0. 106 nm, RL = 0.098 ~ 0. 133 nm. The elements with large ionic radius are mostly concentrated in the spreading direction. The distribution law of δ34S in ore-bearing rock mass includes high stress area and low stress area. The δ34S value of the same twisted band changes from high to low from convergent end to divergent direction, and vortex > inner twisted band > outer twisted band.
The above facts show that stress plays a controlling role in magma crystallization. It is proved that the torsional and compressive stress can be transmitted in magma, and this transmission presents a certain gradient. The appearance of stress gradient leads to the adjustment of substances in magma to reach balance. When the stress gradient is constant, the adjustment of materials mainly depends on elements, physical properties and chemical properties. The corresponding relationship between stress gradient and substance quality and quantity proves that tectonism not only controls the distribution of substances, but also controls the formation of substances to a certain extent.
Zhang Zhitao studied the Weiya rock mass in the southeast of Hami, Xinjiang, and pointed out that the rock mass has obvious characteristics of rotation and torsion. The core is circular, and the monzonite is distributed in rings. The shapes of each ring are consistent with the cyclotron structure, indicating that the rock mass experienced clockwise cyclotron motion before consolidation. It is considered that diagenesis is controlled by the torsional stress field, that is, the magma remains molten for a period of time after emplacement and rotates clockwise, and the specific gravity of each component of the multi-component magma melt is different (including the specific gravity difference between various ions, complex ions and molecules, and the specific gravity difference between early crystallized minerals and the molten slurry that has not yet crystallized). Generally speaking, those rich in Ti, Fe and Mg are heavier and those rich in Si and O are lighter. In the rotating motion, heavy matter is subjected to greater centrifugal force. When the kinetic energy of particles is equal, the motion speed of heavy matter is less than that of light matter. Therefore, the heavy matter moves outward and makes opposite relative motion with the cyclone, which leads to the gradual increase of the proportion of heavy matter at the edge of rock mass. Because the center of gyration is in the northwest direction of the geometric center of rock mass, this eccentric gyration causes the melt to have different speeds on each side. The northwest side is close to the center of gyration, and the speed is faster, while the northeast side is far away and the speed is slower, which makes the heavy materials gradually gather to the northeast and the speed is slower. In particular, magnetite, pyroxene and anorthite crystallized in the early stage become alkaline complexes after condensation; Where the flow rate is fast, the kinetic energy is high, the cooling is slow and the flow rate is slow, the opposite is true. Therefore, the early condensed monzonite is narrow in the west and wide in the east; The newly condensed monzonite still has certain plasticity. Due to the continuous rotation of the molten magma in the center, the northwest of the monzonite ring is subjected to greater lateral pressure, which makes the monzonite shell creep from southeast to northeast, and it is oval under the influence of regional stress field.
Liu Xun et al. (1998) studied the migration of mineral liquid in the tension-torsion structure, and pointed out that the expansion area of the tension-torsion structure is mainly distributed in the faults that make up the rotation-torsion structure. At the beginning of the fault, the expansion area is narrow, while the expansion area at the convergence end is wide and interconnected, generally in the form of a turbine rotating in the same direction as the fault. The outer side of each arc fracture is the compression zone (Figure 7. 1). The migration and expansion area of mineral liquid in the compression-torsion-torsion structure is not distributed along each component fault of the torsion structure, but between two adjacent faults. That is to say, the crack endpoint areas extending from the part with large curvature of the crack to the inner side of the crack in the radial direction to the convergent end side of the adjacent crack are distributed in a belt shape. Its combined form is usually turbine-like, and its rotation direction is opposite to the fracture direction (Figure 7.62). Most of these parts are tensile fracture development areas that match the compression-torsion arc fracture.
The ore-controlling effect of tensional and torsional structures can be taken as an example of Erdaodianzi Gold Mine in Jilin Province (Liu Xun et al., 1998). The ore-controlling structure is Erdaodianzi tension-torsion broom structure, which consists of Erdaodianzi arc structural belt, southwest bifurcation arc structural belt and dome arc structural belt. All three arc-shaped structural zones protrude to the southwest and sag to the northeast; Converging to the southeast end and spreading to the northwest end; During the metallogenic period, the outer layer twisted relative to the inner layer. Orebodies are mainly distributed in the main faults in the arc structural belt (Figure 7.63). The innermost Erdaodianzi arc structural belt has the best mineralization, which is the main metallogenic structural belt. The outward mineralization becomes worse, and only the outermost Dixiaozi arc structural belt can see mineralization. The convergence end of broom structure has the best mineralization, while the divergence end becomes worse. This rule is consistent with the extension area of tension-torsion torsion structure obtained by experiment.
Fig. 7.6 1 regional distribution of torsional rotation structure δ > 0
(According to Liu Xun et al., 1998)
Fig. 7.62 Distribution of δ > 0 and δ < 0 regions of compression-torsion structure.
(According to Liu Xun et al., 1998)
Fig. 7.63 schematic diagram of ore-controlling structure and ore body distribution of Erdaodianzi Gold Mine.
(According to Liu Xun et al., 1998)
1- tensile and torsional fracture; 2- fracture; 3- Paleozoic strata; 4- Cenozoic basalt; 5- Hercynian granite; 6- Yanshanian granite; 7- gold ore body
The turbine-like structure in Kuangcun, Hanxing District, Hebei Province is an example of stress field control of compression-torsion turbine-like structure (Figure 7.64). There is a turbine-like spiral structure around Kuangshancun rock mass, and its revolving surface is composed of a series of arc folds around Majiaao, which is a compression-torsion turbine-like structure. The external force at the boundary acts in the way that the outer ring twists counterclockwise and the strut twists clockwise. This turbine-like tectonic stress field not only controls the activity of magma, but also controls the migration of ore liquid and the distribution of iron ore bodies. Based on the determination of magma streamline and the calculation of TiO2 _ 2 geological thermometer in magnetite, the iron mine team of Tianjin Institute of Geology and Mineral Resources determined that the direction of mineral liquid migration is from the outer ring direction, along the spiral direction of the rotary surface, to the inner ring convergence, and then to the direction around the pillar. There are two areas where iron ore bodies are enriched, that is, the areas where ore liquid is concentrated: one is around the spiral pillar, such as Majiaao ore body and Shibanpo ore body; Second, the extension area of anticline core in the middle of arc fold or fold belt is relatively large, which is equivalent to the area of revolution surface 1/3 ~ 2/3, that is, the part between turbine constructional column and outer ring, but there is no obvious ore body in the extension direction of outer ring.
Fig. 7.64 Schematic Diagram of Mine Field Structure in Mine Village
(According to Tianjin Institute of Geology and Mineral Resources)
1- Permian; 2- Carboniferous; 3- Middle Ordovician; 4- diorite-monzonite; 5- iron ore body; 6- anticline; 7- syncline; 8- compression-torsion fault; 9— Unknown nature or presumed fault; 10- streamline of rock mass