Since 1990s, the research results of geophysics in the field of the earth's magnetic field (earth's magnetic field intensity, polarity reversal efficiency and true pole shift) reveal that the whole world is in a period of low magnetic field intensity of 200 ~1000 Ma, and 124 ~ 83ma and 170 ~ 16544 are in a low level. Morgan( 197 1) and Larson( 199 1) and others put forward mantle plume theory and super mantle plume model, Courtillot( 1988) and Maruyama S. et al. (1988). Sun Aiqun et al. (1997) considered that the lower part of Hehuai area is a typical mantle plume (equivalent to the secondary column of Maruyama S., 1994) according to the mantle plume model of Maruyama S. and the geological structure evolution characteristics of North China Platform. It is considered that several important gold and silver mineralization concentrated areas in North China (Jiaodong, Hebei, Qinling and Taihang) are located at the periphery of this sub-thermal column, which is the third-level unit of the further evolution of the mantle sub-thermal column, equivalent to the third-level column of Maruyama S.( 1994), and is called mantle branch structure (Niu et al., 1996). Deng et al. (1994) pointed out that when the eastern China landmass was finally assembled in the early Mesozoic (Indosinian period), the lithosphere had roots, and its depth exceeded 150 ~ 200 km. Since Cenozoic, the thickness of the lithosphere is only 60 ~ 80 km, indicating that the lithosphere has been thinned by at least 150~200 km since Yanshanian. Xiongershan-Xiaoqinling area is located in the southern margin of North China platform, and there was strong tectonic magmatism in Mesozoic. The metallogenic age of gold is 224 ~1000 ma, which is also the Mesozoic global mantle plume activity period. There are aegirine syenites (Rb-Sr age, 2 16 Ma, Qiu Jiaxiang,1993; 204 Ma, U-Pb, Ren Fugen et al., 1998), potash feldspar (type A) granite (Rb-Sr age, 207 Ma, Xu Qidong, 1998), igneous carbonate (206 Ma, Qiu Jiaxiang,1998). Mesozoic granitic magmatic rocks were formed in 175 ~ 100 Ma. The Archean medium-deep metamorphic rocks in this area are metamorphic core complexes (Shi Quanzeng et al., 1993), and the formation mechanism is crust thickening magma upwelling → crust necking → detachment extension (Zhang Jinjiang et al., 65438+). According to the theory of mantle plume activity, this area should be an active area in Mesozoic, and the result will inevitably lead to the mineralization of mantle fluid and ore-forming elements in the favorable part of shallow crustal structure.
The distribution characteristics of gold and non-ferrous minerals in Xiaoqinling-Xiongershan area are related to the strong material and energy exchange in the crust and the action of mantle fluid. This geological event is restricted by the deep mantle plume and the lithospheric settlement caused by it. The activity of mantle plume provides important metallogenic environment and conditions for mineralization. According to the research, the upwelling of the hot mantle plume to the lithosphere can produce a huge thermal halo (Maruyama, S. 1994), which can not only drive the hydrothermal convection cycle, but also cause large-scale long-distance migration of ore-forming fluids. In Xiaoqinling-Xiongershan area, mantle upwelling is accompanied by high heat flux anomaly and alkaline magma intrusion. In the early stage of craton continental rupture, the high grade metamorphism of ancient continental basement was mixed with migmatization, mixed granitization and rheological gneiss, which was closely related to mantle plume activity. Because the mantle plume carries huge energy in the rising process, the crust is baked and heated, which promotes the increase of the geothermal gradient of the continental crust and causes extensive crustal melting events. Therefore, large-scale crustal melting metamorphism can be used as a means to identify mantle plume (He Shijie et al., 2003). Li et al. (200 1) considered that the Proterozoic granite in South China was the result of mantle plume in South China at that time. According to the stable isotope characteristics, the w(3Ge)/w(4Ge) of the mantle plume is at least 50 times higher than that of the atmosphere, and the w(3Ge)/w(4Ge) ratio of the Xiaoqinling gold deposit is (0.4 ~ 2.6) × 10-6, with an average value of1.26. The high w(3Ge)/w(4Ge) ratio is usually considered as the result of insufficient mantle degassing process, which provides evidence that the mantle plume originated from the lower mantle (He Shijie et al., 2003).
The upwelling of the mantle will also shorten and vertically uplift the crust. With the formation and development of fault basins and strike-slip pull-apart basins, besides Au, it also provides important metallogenic conditions and environment for the migration, enrichment, precipitation and mineralization of other active elements (Pb, Zn, Ag, Gg, Sb, As, etc.). ).