Hunan antimony gold deposits are concentrated in Xuefeng arc uplift belt and its southeast side in the metallogenic domain of northwest Hunan, which is the so-called "Xuefeng (antimony gold) ore concentration area" There are not only large and super-large antimony gold deposits such as Xikuangshan and Woxi, but also many antimony gold deposits (spots) such as Liaojiaping, Fuzhuxi, Longshan and Mo Bin. The understanding of the genesis of antimony-gold deposits in this ore concentration area is still controversial. Three main viewpoints on the genesis of antimony-gold deposits in Xuefeng ore concentration area are put forward:
(1) The earliest theory of magmatic genesis holds that magmatic hydrothermal process provides the main ore source and thermodynamic power source for mineralization (Zhang Zhenru et al.,1978; Yang Shunquan, 1986).
(2) The popular theory of sedimentary-metamorphic genesis in 1980s holds that the ore-forming materials mainly come from the host rocks, and the mineralization is the result of the activation, migration and enrichment of metal elements in the host rocks during metamorphism (Tu Guangchi et al.,1984; Luo Xianlin et al., 1996), this process of element migration and ore enrichment is closely related to large-scale fluid activities in the crust (Ma Dongsheng, 1997).
(3) Metallogenic theory of submarine hot brine jet (or hot spring) (Zhang Ligang, 1985).
After the theory of magmatic genesis was put forward, it was quickly questioned and denied, mainly because magmatic rocks were not found in many deposits, and the direct relationship between magmatic rocks and known ore bodies could not be found for a while. Such as Woxi, Mo Bin and Longshan deposits. However, the "magma negation theory" (completely denying the contribution of magmatism to antimony gold mineralization) is inconsistent with many newly discovered geological facts in recent years. Under the guidance of the academic thought of "re-mineralization" (Tu Guangchi et al., 1984), the understanding of the genesis of sedimentation-metamorphism has been generally accepted and popular, but the huge accumulation of metallic antimony such as tin ore (more than 2 million tons) is formed by the migration and re-enrichment of metallic elements in the strata, which is not only unverifiable at present, but also challenged by a large number of latest isotopic dating data. Similarly, viewpoint (3) is difficult to agree with a large number of isotope dating results (Lingshui City, 1999).
Metallogenic characteristics: Antimony gold mineralization in this area occurs not only in Precambrian shallow metamorphic rock series, such as Mesoproterozoic Lengjiaxi Group, Neoproterozoic Banxi Group Madiyi Formation, Wuqiangxi Formation, and Sinian Jiangkou Formation (such as a large number of typical antimony gold deposits in xi 'an, Woxi, Mo Bin and Longshan). ) and widely distributed in different strata of Phanerozoic. Such as the main ore body of Xikuangshan super-large antimony deposit. Another example is the Banbanxi Sb-Au deposit (occurrence) in Anhua, which occurs in the shallow metamorphic rocks of the Ordovician Ningguo Formation (Bao, 1993). Chenxi Changtianwan antimony deposit occurs in Carboniferous limestone. There are many rock series strata in Anhua Taiping Gold Mine, from Neoproterozoic Banxi Group to Paleozoic Silurian, but the main antimony gold mineralization is not controlled by Precambrian metamorphic rock series, but developed in Paleozoic Ordovician silty rock series (Zhang Ning, 1999). In addition, fine disseminated gold mineralization has also been found in the Cretaceous red beds on the northwest side of Xuefeng Uplift. It can be seen that the regional antimony gold mineralization is not limited to a certain horizon, but has very obvious regional cross-layer metallogenic characteristics.
Summarizing the metallogenic geological characteristics of some typical antimony-gold deposits in Precambrian shallow metamorphic rocks in this area shows that calcareous sandstone or sandy slate, siltstone or silty slate and tuff are favorable ore-forming/ore-controlling surrounding rocks for antimony-gold deposits. However, in recent years, many antimony and gold deposits discovered in central Hunan, such as Taiping, Liaojiaping, Gaojiaao, Baiyunpu and Xiamaqiao, mostly occur in different horizons such as Lower Ordovician and Middle Devonian. The main ore-controlling surrounding rocks are argillaceous siltstone, seasonal complex sandstone and silty mudstone (Chen Qiangchun, 1998). In addition, the host rock of Maxiong antimony deposit in Guangxi is carbonaceous and argillaceous siltstone of Lower Devonian. The Muli antimony deposit in Yunnan occurs in limestone, siliceous rocks and shale of the Lower Devonian (Hua Renmin, 1994). Olimpiada Sb-Au (W) deposits in other parts of the world, such as Siberia, occur in clastic sedimentary rocks interbedded with (Mesoproterozoic) limestone and metamorphic slate (Afanasjeva et al.,1995); Ixtahuacan antimony-gold (tungsten) deposit in South America occurs in black shale composed of carbonaceous shale, sandstone and limestone interlayer. The host rocks of many antimony gold deposits in Bolivia, USA are Devonian and Silurian siltstone, slate and interbedded carbonaceous slate. Antimony-gold deposits in Central Europe, Czech Republic and Slovakia mainly occur in the slightly metamorphic argillaceous sandstone series (Dill, 1998) such as graphite schist, green phyllite and metamorphic sandstone, which are rich in intermediate-acid pyroclastic rocks. Compared with similar deposits in neighboring provinces and other parts of the world, Hunan antimony gold deposit has similar (same) host/ore-controlling surrounding rock lithology. In addition, terrigenous clastic melange series rich in carbon, calcium and tuff may be the most favorable ore-forming/ore-controlling surrounding rock for this kind of deposit. Therefore, antimony gold mineralization in this area is not limited to one or several horizons, but is enriched in favorable surrounding rocks with the same (similar) lithology through strata of different times. That is, lithology controls ore rather than "stratum controls ore".
Characteristics of Antimony and Gold Content in Ore-bearing Surrounding Rock madong Sheng et al. (1998) systematically studied the content characteristics of antimony, gold and other mineralized elements in Precambrian metamorphic rocks in this area, and measured the antimony content in ore-bearing surrounding rock at1.6×10-6 ~ 2.6×/kloc-0-. The gold content is 2.4×10-9 ~ 3.6×10-9, and the enrichment degree is between 1.3 ~ 2. However, at present, there is little systematic analysis and research on the content of mineralized elements in other ore-bearing rock series in Phanerozoic. The analysis results of Liu Jishun (1996) show that the gold content in Yu Xiansheng ranges from 1.7× 10-9 to 4.4× 10-9, and the antimony content ranges from 7.5× 10-6 to/kloc. However, the antimony content of Devonian in this area ranges from 0.68×10-6 to 2.26×10-6. Different researchers get different analysis results, but after comparison, it is found that Yu Xiansheng and Precambrian rocks have similar gold-bearing characteristics: the gold content is low, which is close to the crustal abundance value (1.8× 10-9). At the same time, compared with Precambrian, although the Sb content in Phanerozoic may be higher, the Sb content in Devonian strata and Precambrian strata is almost the same, which is close to its crustal abundance value (0.2× 10-6). Although antimony gold deposits have obvious cross-layer metallogenic characteristics in the region, the scale and intensity of antimony gold mineralization in different horizons are obviously different.
Statistical analysis shows that 53% of the gold deposits (spots) in Hunan Province are distributed in Precambrian rocks, and Precambrian metamorphic rocks contain more than 55% of the gold reserves in the province. Phanerozoic Devonian has the largest antimony deposit in the world-Xikuangshan antimony deposit. The significant difference in the scale and intensity of antimony and gold mineralization in different horizons is in sharp contrast with the characteristics of antimony and gold content in ore-bearing strata. It seems that the characteristics of antimony and gold content in a certain part or profile of ore-bearing strata are not the key factors to determine the intensity and degree of antimony and gold mineralization. In addition, a large number of analysis results show that the distribution of antimony and gold in host rocks is extremely uneven. Antimony gold mineralization is a special uneven distribution of antimony and gold in strata. Therefore, to explore the metallogenic mechanism of antimony and gold is to explore the mechanism of uneven distribution of antimony and gold to a great extent.
Spatio-temporal coupling between antimony gold mineralization and Indosinian-Yanshan magmatism ① Indosinian-Yanshan magmatism is a major geological event sweeping the whole region. Although no magmatic rocks have been found in some deposits such as Woxi, Longshan and Mo Bin, the large-scale regional faults in Taojiang-baimashan-Chengbu and the rocks or complex rocks distributed on both sides such as Chengbu, Wawutang, baimashan, Furong, Guandi Temple and Weishan are Indosinian-Yanshan intrusions or Indosinian-Yanshan intrusions, and these rocks or dikes have formed a spectacular scale in space. (2) A series of dike swarms have been formed in Furong compound granite, and 65,438+060 intermediate acid dike swarms have been found in the inner and outer contact zone of Weishan granite, and many basic dike swarms such as lamprophyre have also been found in the west of Wawutang-Chongyang Ping-Zhonghuashan granite, especially in Wei Zi, Kuixiping-Dongdiping and other places. ③ Various antimony-bearing gold veins are developed in and/or around a large number of antimony-bearing gold deposits such as Taiping, Fuzhuxi, Liaojiaping, Shenjiaya, Woxi, Mojiaping and Xikuangshan in the northwest of regional faults and Xuefeng Uplift (and its south); ④ On the southeast side of the regional fault, magmatic activity is relatively strong, such as Shuikoushan, Guandi Temple (Indosinian period) and a large number of lamprophyres around it (there are more than 100 lamprophyres in Qingshuitang and Matoushan alone).
In recent years, a large number of Indosinian-Yanshanian basic and ultrabasic rocks and intermediate-acid felsic veins (bodies) have been discovered in a large number of antimony-gold deposits such as Xikuangshan, Liaojiaping, Fuzhuxi, Banxi, Tianzhuang and Taiping. At the same time, antimony gold deposits/spots (congruence, 1998) have been found in and/or around granite bodies such as baimashan, Zhonghuashan, Huang Mao Garden, Dachengshan and Furong. In particular, some dikes have high gold and antimony contents, making them industrial ore bodies, which shows the contribution of magmatic activity to gold mineralization in this area. For example, the gold content of granite porphyry veins developed in the Liaojiaping gold deposit in Anhua can be as high as 6. 1× 10-6, mostly above 0.5× 10-6 (Luo,1994); Lamprophyre-type gold mineralization was discovered in Jiangnan town, Anhua (Huang, 1996). However, the analysis results of Sb and Au contents of some Indosinian-Yanshan intermediate acid rocks (Table 7- 1) further illustrate the possible relationship between magmatic activity and antimony-gold mineralization in this area.
As far as gold is concerned, the gold content of other known rock bodies is obviously higher than its crustal abundance value, except the gold content of Xian 'e Baodan rock body is close to its crustal abundance value, and it has a high degree of enrichment. Moreover, the gold content of basic rocks and ultrabasic rocks in different ages tends to increase with age. The gold content of acid rocks tends to increase with age, and the gold content of Yanshanian type ⅰ granite is the highest (Yang Shunquan,1986; Wang Furen,1993; Li Hengxin, 1995). For antimony, the enrichment of Sb in Yanshanian granite (rock mass or dike) is also obvious. For example, the Sb content of stibnite in Shuikoushan granodiorite is 30×10-9; The antimony content of stibnite in Lishu 'ao granodiorite porphyry group in Xinshao reaches 265,438+00× 65,438+00-9 ~ 350× 65,438+00-9. However, sphalerite in some Yanshanian rock deposits also contains high antimony. For example, sphalerite in Yagongtang mining area contains more than 1000× 10-6 Sb (Fu-ren wang, 1993).
All these indicate that there is an obvious time-space relationship between Indosinian-Yanshan magmatic rocks and antimony-gold deposits in this area, and the Indosinian-Yanshan magmatism and antimony-gold mineralization in this area are related to the source of ore-forming materials and ore-forming fluids.
In addition, the latest isotopic determination of metallogenic age (Table 7-2) shows that antimony gold mineralization in this area mainly occurred in Indosinian-Yanshan period. Secondly, Wu et al. (2000) measured the metallogenic age of tin deposits as156.29 4.63 Ma (SM-ND method); The lead isotope model age of Jinkengchong ore is 145 ~ 244 Ma (Luo Xianlin et al., 1996). Rb-Sr isochron ages of the fluid inclusions in Woxi and Longshan are144.81.7ma and175 27ma (Ma Dongsheng, 1999), respectively. These latest data of metallogenic age, which are widely quoted, initially reveal the obvious coupling relationship between antimony gold mineralization and Indosinian-Yanshanian large-scale magmatism in time. Although some researchers think that the dike scale in this area is small, it does not have the ability to provide a large number of minerals (gold and antimony) (Peng Jiantang et al., 1999). However, the existence of regional large-scale magmatism cannot be denied because of the small scale of dikes. On the contrary, the extensive exposure of many small-scale Indosinian-Yanshan dikes further proves the objective existence of large-scale magmatism in Indosinian-Yanshan period. As a special kind of rock, ore deposit is also the product of the stratification process of the earth. The obvious coupling relationship between Indosinian-Yanshan antimony gold mineralization and large-scale magmatism in time and space indicates that there may be genetic relationship between regional antimony gold mineralization and Indosinian-Yanshan magmatism.
Table 7- 1 Sb and Au contents of some Indosinian-Yanshanian rocks (veins)
Table 7-2 Isotopic Dating Results of Some Rocks (Veins)
Discussion on Mechanism The geochemical study of Sb shows that the enrichment or accumulation of huge metal Sb is a long-term and continuous process. During the geosphere process, Sb mainly migrates from the deep mantle and crustal sediments to the magma source area (Milleretal,1994; Poke? Ehrenbrinketal， 1994； JochumandHofmann, 1997), and then aggregate to form ore-bearing fluid reservoirs. Due to the incompatibility of Sb, the subduction zone environment is very favorable for Sb to migrate abnormally or accumulate in the crust in large quantities through subduction (Jochum and Hofmann, 1997). Gold and antimony have different tectonic geochemical properties, which can be migrated by non-magmatic water-bearing fluids or directly into the shallow crust by upwelling magma. Therefore, the two can be enriched and integrated at the same time, and can be mineralized separately, which is not related to each other.
At the end of Mesoproterozoic, the South China plate and the Yangtze block began to collide, forming a continental collision orogenic belt (Deng Jiarui et al., 1998). Xuefeng Sb-Au concentration area evolved and developed under this structural background. During Mesozoic Indosinian-Yanshan period, the fundamental transformation of the tectonic framework in South China (east-west extrusion extending to NNE) laid a geological background for the large-scale antimony gold mineralization explosion. During the collision between the South China Plate and the Yangtze Plate, the South China Plate subducted to the Yangtze Plate, and Sb-Au migrated to the plate convergence zone through the non-magmatic process of water-containing fluid. This process may have started at the end of Proterozoic and lasted until Caledonian. At the same time, in the process of plate subduction, due to the thermal uplift of the upper mantle, plate detachment occurred, which triggered the partial melting of the continental crust and formed the magma source or magma reservoir at the plate edge. Non-magmatic migration of antimony-gold ore-bearing fluid enters the plate-edge magmatic source region, forming antimony-gold ore-bearing fluid reservoir. This leads to the extreme accumulation of matter and energy in the magma source or magma reservoir at the edge of the plate. Influenced by deep geological processes such as lithospheric thinning in eastern China, a large-scale and sudden tectonic dynamic transformation occurred in eastern China during Mesozoic Indosinian-Yanshan period. The fundamental transformation of tectonic framework triggered faulting and increased the permeability of the crust. The abrupt change of tectonic stress and the rapid expansion of permeable structures provide a force source and create a space condition for the rapid release of materials and energy abnormally accumulated in magma source areas or magma reservoirs at the plate edge, which leads to the explosion of ore-bearing fluid reservoirs of antimony-gold deposits, the explosion of antimony-gold mineralization and the emplacement of magma. The widely developed antimony-gold deposits and various magmatic rocks and dikes in this area may be different manifestations of this ore-forming explosion.