As a part of the Qinling orogenic belt, the western Qinling metallogenic belt has experienced a complex history of tectonic magma development and formed a complex gold deposit. There are many disputes about the classification of gold deposits. The main understanding of the classification of gold deposits in West Qinling is that Chen Yuchuan (1999) classified all gold deposits as hydrothermal deposits, and divided them into hot water type (Ba Li), ductile shear zone type (Ma Qiao 'an), sodalite carbonate breccia type (Wang Shuang), hot water leaching type (Luerba, Dashui) and tectonic hydrothermal transformation type (frying). Chen Jiming (1992) is dominated by ore-bearing rock series, which can be divided into gold deposits occurring in Phanerozoic mafic and ultramafic rocks, metamorphic clastic rock-type gold deposits, gold deposits occurring in sedimentary rock series, volcanic rock-type gold deposits and gold deposits related to intrusive rocks. China Geological Survey (2002) "Study on Key Selected Areas of Mineral Resources Investigation and Evaluation in Major Metallogenic Prospecting Areas in China (IX)" divides the gold deposits in West Qinling into epithermal (micro-disseminated type) (Ba Li, Manaoke and Pangjiahe), ductile shear zone (Ma Qiao 'an and Pangjiahe) and sodalite-breccia gold deposit (also micro-disseminated type) (Wang Shuang). Shao (1999) divided the gold deposits in West Qinling into four types according to the characteristics of host rocks and ores: shallow metamorphic fine clastic rock type, Carlin type, albite breccia type and chronological vein type. Lu (200 1) thinks that most of the gold deposits in North Qinling are related to ductile shear zone, most of the gold deposits in Middle Qinling belong to structural altered rock type, and most of the gold deposits in South Qinling have structural hydrothermal metasomatism characteristics. Wang Pingan (1998) thinks that the gold deposits in the west Qinling area are mainly magmatic hydrothermal; Zhao Yiming (2004) thinks that the west Qinling area is dominated by volcanic rocks, fine clastic carbonate rocks, carbon-bearing shallow metamorphic clastic rocks and intermediate-acid intrusive rocks. Mao Jingwen (200 1) thinks that the gold deposits in Paleozoic basins in Minxian-Taibai area belong to orogenic gold deposits.
The types of gold deposits in West Qinling can be summarized as follows: ① Carlin-Carlin-like type or fine disseminated type (Liu Miao,1994; Li,1994; Zhang Fuxing, 1996,1998; Zhao Huiqing,1999; Wei Yinglong,1999; Zhu Huaping,1999; Tan Yunjin et al., 2000; Guo Jian,1998; Sun Shuhao, 2005; Wang Keyong, 20065438+0; Qi Jinzhong, 2006); (2) ductile shear zone type (Kui,1999; Zhong Jianhua,1997); ③ Magmatic hydrothermal type (Zhang, 2000; Feng Jianzhong et al., 2002; Wang Pingan et al.,1998); ④ Hot water sedimentary type (Wang Hengdeng,1996); ⑤ Carbonaceous siliceous mudstone type (Wang Ju,1994); ⑥ Tectonic altered rock type (Shi Li,1998; Sun Ming,1998; Gao Quanzhen,1999; Li Jianzhong,1999); ⑦ Orogenic type (0,2001) ⑧ Sedimentary-hydrothermal type (Chen et al., 2004)⑨ Sedimentary-magmatic reformation type (Fang Chunjia, 2005).
The gold deposits in the central and eastern part of the western Qinling metallogenic belt are similar to Carlin-type gold deposits at home and abroad (Yang, 2007) (Table 6. 1), mainly showing that the host rocks are all a set of upper Paleozoic-lower Paleozoic and Mesozoic shallow metamorphic sedimentary rocks, and the host rocks are mainly fine clastic rocks-carbonate rocks; The output of ore bodies is strictly controlled by structures, especially large thrust faults and their secondary faults. The mineral assemblage and characteristic element assemblage of the ore are similar to those of typical fine disseminated gold deposits. All ores contain a certain amount of organic carbon; Wall rock alteration includes silicification, sericitization, carbonation, pyritization, arsenopyrite, stibnite mineralization, cinnabarinization and clayey. The difference is that the gold deposits in the central and eastern part of the western Qinling metallogenic belt contain some aragonite Shi Ying veins (such as Yangshan, Xiaogouli and Sihe). ), which is different from the typical Carlin-type gold deposit. The ore bodies are closely related to the intermediate-acid intrusions in the area in time and space. Ore-forming fluids are derived from meteoric water and magmatic fluids, and both magma and strata contribute to the source of ore-forming materials. Carlin-type gold deposits in the United States are mainly produced in basins and ridge provinces within the mainland, Carlin-type gold deposits in China, Yunnan, Guizhou and Guangxi are mainly produced in rifts or rift troughs on the edge of land blocks, and gold deposits in the central and eastern parts of the western Qinling metallogenic belt are mainly produced in the continental-continental collision orogenic belt. The chronological vein-like ore bodies with a small amount of visible natural gold developed in Yangshan Gold Mine and Xiaogouli Gold Mine are characterized by orogenic gold deposits (Table 6.2), which do not conform to the metallogenic criteria and ore-forming fluid characteristics of typical Carlin type gold deposits. Therefore, the classification of genetic types of gold deposits in the western Qinling metallogenic belt needs further detailed and systematic research.
Table 6. 1 comparison of geological and geochemical characteristics of gold deposits in central and eastern west Qinling with Carlin-type gold deposits in the United States and Yunnan, Guizhou and Guangxi.
sequential
(According to Yang, 2007, slightly modified)
Table 6.2 Main characteristics of orogenic gold deposits
(According to Yang, 2007)
Regardless of the genesis, the main types of gold deposits in the west Qinling area are structural altered rock type, chronological vein type, structural altered rock type+chronological vein type, skarn type, silica mortar type and greenschist type.
1) skarn type: the deposit is generally small in scale and occurs in skarn formed by intermediate-acid rock mass and carbonate rock. For example, in Xiaojinchang Gold Mine, the ore bodies are strictly controlled by skarn and associated with copper ore bodies, which are mostly lenticular, irregular and cystic. Metal minerals include chalcopyrite, pyrrhotite and pyrite. With metasomatic residual structure, massive and vein structure, natural gold is embedded in pyrite and chalcopyrite fractures.
2) Tectonic altered rock type: it can be divided into two types: structural altered rock type and structural altered rock type in outer contact zone. The structural alteration rock types in the outer contact zone are mainly produced outside the intermediate-acid rocks in the northern sub-zone of South Qinling, and are controlled by thermal erosion halo in the outer contact zone, the structural fractured rock zone and the structural fractured alteration zone, mainly including gold deposits outside the Zhongchuan rock mass such as Ba Li. The ore bodies of structural altered rock type gold deposits are all produced in structural fractured rock belts and structural fractured altered rocks, and the ore-bearing strata are mainly Devonian and Triassic. The ore type belongs to fine refractory gold ore containing sulfur, arsenic and carbon. The occurrence of gold is mainly intergranular gold, followed by fracture gold and inclusion gold. The surrounding rocks have been eroded into silicification, arsenopyrite, carbonation, sericitization and kaolinite. The deposit is large, super-large and super-large.
3) Time-dependent pulse type: mainly distributed in the contact zone inside and outside the rock mass of Xicheng Basin and the greenschist in the metallogenic sub-zone of North Qinling, including Chaijiazhuang Gold Mine, Xiaogouli, Sanhuazui and Sanyeba. Gold deposits are mainly composed of chronological veins, followed by altered rocks beside the veins. All areas with high gold grade have timely veins. There are also a large number of time-related veins in the altered rocks beside the time-related veins with high gold content. The gold content of the time-dependent pulse is generally higher than that of the surrounding rock beside the pulse. The gold mineralization intensity of surrounding rock is directly proportional to the gold content of the corresponding pulse itself; The gold content of surrounding rock is inversely proportional to its distance from the corresponding vein, so the gold content decreases from the surrounding rock near the mine to the surrounding rock far away. Gold minerals are silver gold and natural gold, mainly light gold, with complex and diverse forms, mainly fissure gold and intergranular gold, and some of them exist in the form of inclusion gold. The main metal minerals are pyrite and coarse-grained arsenopyrite, followed by galena, sphalerite, chalcopyrite and tetrahedrite. The main surrounding rocks are silicified, carbonized and sericitized, followed by albitization, chloritization, kaolinite and electrochemical petrifaction.
4) Tectonic altered rock+chronological pulse type: mainly distributed in greenschist, including Li Ziyuan gold deposit and silicon alloy deposit. The ore body is composed of gold-bearing chronological sulfide veins and lateral altered rocks, which are veined and lenticular. The ore is mainly of time-related vein type, followed by altered rock type; In ore bodies, lamprophyre veins and diorite veins are usually filled and superimposed, and the grade is also obviously improved. The wall rock alteration mainly includes silicification, pyritization, chalcopyrite mineralization, sericitization and carbonation, and the surface oxidation has limonite mineralization and malachite fossilization. Alteration is positively related to the intensity of gold mineralization, that is, the stronger the alteration, the better the mineralization.
5) Silica gypsum rock type: mainly distributed in the anticlinorium axis of Bailong River, occurring in black rock series. As a representative of Larma large-scale gold deposit, gold mineralization occurs in cataclastic rocks and breccia of carbonaceous siliceous clastic rock series from Taiyangding Group of Upper Sinian to Duer Formation of Lower Cambrian, and is controlled by secondary faults in the east-west direction. The shape of ore body is complex, which is strip-shaped, layered, lenticular, strip-shaped, cystic and vein-shaped. Common metal minerals are stibnite, pyrite, cinnabar, realgar and orpiment. Gold is mainly composed of fissure gold and encapsulated gold, embedded in vein-like quartz, barite or encapsulated in micro-particles of mercury selenite. The ore types are porphyry-breccia silicified siliceous rock type, veinlet-fractured silicified carbonaceous slate type, veinlet silicified silty slate type and reticulate veinlet-fractured carbonaceous slate type.
6) Green schist type: This type of deposit mainly occurs in the southern pyroclastic strata, mainly in Huachanggou gold deposit, and occurs in tuffaceous sericite phyllite in the first lithologic member of Sanhekou Formation of Lower Devonian, and the ore-bearing rock is altered spilite. Gold mineralization is distributed in NW-trending reverse faults; The ore types are mainly altered spilite type, followed by chronological vein type and limonite type. Gold minerals are mainly natural gold, mainly produced in pyrite.