Tectonic evolution and mineralization in Yanshan-Himalayan period

After the Indosinian Movement, the geological structure pattern of China changed greatly. Taking Helanshan-Kangdian Uplift as the boundary, China can be divided into two distinct parts. In the eastern region, the interaction between the East Asian continent and the western Pacific plate has been strengthened, resulting in strong volcanic-intrusive activities in the coastal Pacific tectonic belt (Ren Jishun, 1998), while various sedimentary basins have developed in the mainland. In the western part of the mainland, the Qinghai-Tibet blocks separated from Gondwana moved northward one after another, and finally collided with the northern mainland of China to form a whole.

In Mesozoic, inland fault basins such as Ordos Basin and Sichuan Basin developed in the western belt of the eastern structural domain of China, which were rich in coal seams, oil and natural gas. There are offshore basins such as Songliao, North China and Jianghan in the central and eastern part of the mainland, among which Songliao basin is dominated by Cretaceous deep-water lacustrine deposits, forming Daqing, Liaohe and other oil fields.

The eastern zone of the eastern structural domain of China is characterized by the development of a large number of volcanic rocks, accompanied by abundant porphyry, skarn and epithermal deposits, and the three volcanic rocks are arranged in a NNE-SW-SW pattern. Its northwest belt is alkali-rich volcanic rock belt in Daxinganling, accompanied by gold-lead-zinc-tin-iron ore metallogenic system; The intermediate zone is a basic andesite volcanic rock extending along the Tanlu fault. It extends from the eastern part of Jiaodong through Shandong and northern Jiangsu to the lower reaches of the Yangtze River. Yanshanian granitoids, including sylvite, are widely exposed in this belt, which is characterized by the development of copper, iron, gold and sulfur deposits, such as the famous metallogenic belt in the middle and lower reaches of the Yangtze River. The volcanic belt along the continental margin of Fujian and Zhejiang in the southeast and the south of the Korean Peninsula in the north, dominated by andesite and rhyolite, has widely formed medium-low temperature hydrothermal Pb-Zn-Ag-Cu-Au deposits, with Zijinshan gold-copper deposit as the representative and Proterozoic shallow metamorphic basement Cu-Au-Ag deposits concentrated in the northwest.

In eastern China, due to the obvious differences in evolution history and material composition between North China Block and Yangtze Block, different regional geochemical blocks and metallogenic belts were formed after Indosinian period. In North China, it is characterized by large-scale gold-molybdenum mineralization at the edge of the North China block, such as Yangjiazhangzi and Laiyuan molybdenum mines at the northern edge of the block and Hebei gold mines (Dongping and Jinchangyu), Xiaoqinling gold mines, molybdenum mines (Wenyu and Jinduicheng) and Jiaodong gold mines at the southern edge of the block. However, in South China, due to the double pushing of India plate and Western Pacific plate, strong tectonic thermal events developed in the pre-Caledonian accretion fold belt of South China, and the asthenosphere and deep source materials of the lower crust upwelling, and the middle-deep siliceous and aluminous crust partially melted, forming large-scale remelted granite, which was widely distributed along deep faults and thermal domes, accompanied by a series of important W, Sn, Bi and rare earth deposits, such as Shizhuyuan and Xihuashan deposits.

As far as copper deposits are concerned, there are large deposits in North China and Yangtze massif, but relatively few in Qinling area.

The gold deposits in China were mainly formed in Yanshanian period, mostly distributed in Precambrian granite-greenstone belt. Metabasic volcanic rocks in Archean and Proterozoic strata are gold-bearing strata, which have undergone many transformations and enrichment, mainly due to the influence of Yanshanian granite magmatism, and are highly enriched, which is obviously different from the concentration of gold mineralization in other ancient metamorphic rocks in the world in Precambrian.

The huge basin-mountain system in the west of China consists of fault-block mountain ranges and large intermountain basins alternately, and is divided into Tarim-Tianshan area in the northwest and Kunlun-Qilian area in the southeast by Altun giant strike-slip fault. Among them, the Tarim Basin has experienced a complex history, and there are abundant oil and natural gas resources on the edge and inside of the basin. Qaidam basin is rich in petroleum, halite, potassium, lithium and boron resources.

During the Himalayan movement, about 60 ~ 65 Ma, the Indian plate and the Eurasian plate began to collide and dock, and most parts of Qinghai-Tibet uplift. There are chromite deposits in the Himalayan fold belt and ophiolite suite (such as Luobusa); In the Gangdise structural belt, a huge porphyry copper-molybdenum-gold metallogenic belt has been developed, and several large copper mines such as Qulong have been discovered, with a metal reserve of nearly 10 million tons. Porphyry copper belts related to calc-alkaline granite (such as Yulong copper mine), gold belts related to structural melange belts (such as Laowangzhai gold mine) and lead-zinc deposits in clastic rocks of continental rift basin (such as Lanping Jinding mine) are developed in the docking subduction zone in Sanjiang area. In the northern part of Taiwan Province Province, China, there is a famous epithermal gold deposit (Jinguashi deposit) in volcanic rock series directly influenced by the subduction zone of the western Pacific plate.

Tertiary (Paleogene and Neogene) intracontinental rift basalts developed in northeast and north China of China, accompanied by corundum (sapphire) and other minerals.

1. Yanshanian structure and metallogenic characteristics

The Yanshanian mineralization in Chinese mainland, especially in the eastern part of China, is widely developed and has great mineralization intensity, which is the main formation age of most metal minerals in China. Characterized in that:

1) There are many kinds of deposits. Metal minerals include gold, silver, copper, iron, tungsten, tin, molybdenum, bismuth, lead, zinc, mercury, antimony, beryllium, niobium, tantalum and so on. Non-metallic minerals include fluorite, alunite, pyrophyllite, barite, crystal and asbestos. Energy sources include oil, natural gas, coal and uranium.

2) There are many types of ore deposits. There are altered granite type, greisen type, skarn type, porphyry type, hydrothermal vein type, epithermal type, altered shear zone type, subvolcanic magma infiltration type, sedimentation and biological sedimentation type.

3) The metallogenic environment is controlled by intraplate tectonic activation zones, including tectonic-magmatic zone, volcanic-subvolcanic zone, intracontinental fault fold zone, subduction zone, continental margin shear zone, intracontinental depression zone, intracontinental deep fault zone and intracontinental fault basin.

4) Metallogenic belts are mainly concentrated in the eastern tectonic domain of China, including the following metallogenic belts:

① Daxinganling-Taihang Mountain Fe-Cu-Mo-Au-Pb-Zn metallogenic belt; ② Cu-Au-Diamond metallogenic belt of Tanlu fault; ③ Iron-rare earth-lead-zinc-gold-silver-copper metallogenic belt in the northern margin of North China block; ④ Xiaoqinling gold metallogenic belt; ⑤ Au-Mo-W-Fe-Cu-Sb metallogenic belt in western Henan; ⑥ Fe-Cu-Au-S metallogenic belt in the middle and lower reaches of the Yangtze River; ⑦ Lead-zinc-gold-silver metallogenic belt of volcanic rocks along the southeast coast; ⑧ The central Hunan W-Sn-Pb-Zn metallogenic belt; Nanling tungsten-tin-bismuth-niobium-tantalum rare earth metallogenic belt; Participated in the mercury-antimony-arsenic-gold metallogenic belt in the southwest margin of the Yangtze block.

The Yanshanian metallogenic belt is either developed in the Precambrian metamorphic crystalline basement, or superimposed on the Paleozoic structural layer, or superimposed on the early Mesozoic-Triassic strata, which is generally controlled by magma, fluid and basin sedimentation caused by the strong disturbance of lithosphere-asthenosphere in eastern Chinese mainland.

2. Himalayan structure and metallogenic characteristics

Himalayan tectonic movement is mainly developed in southwest China. Due to the Indian plate pushing the Himalayan-Tethys terrane, there are many tectonic-magmatic-metallogenic belts in the Qinghai-Tibet Plateau and Sanjiang area, which are rich in mineral resources and have great potential. In addition, Himalayan magmatism and metal deposits have also been discovered in western Sichuan in recent years.

Himalayan mineralization is mainly characterized by the crust-mantle metallogenic system:

1) The deposit types are gold, copper, lead, zinc, silver and chromium, and there are olivine, ruby and sapphire in Himalayan alkaline basalt.

2) There are porphyry copper-molybdenum deposits, skarn iron-copper deposits, magmatic chromium deposits, shear zone gold deposits, volcanic-subvolcanic gold deposits and hot spring gold deposits, as well as widely distributed laterite weathering crust deposits and various river and sea placers.

3) Metallogenic environment includes orogenic belt, rift, graben and rift basin, inland lake basin and coastal zone.

The main metallogenic areas in Himalayan period are:

① The Yarlung Zangbo ultramafic chromite metallogenic belt; ② Cu-Mo-Au metallogenic belt of Gangdise intermediate-acid rocks; ③ Sanjiang Tethys Cu-Au-W-Sn polymetallic metallogenic belt; ④ Western Sichuan tectonic-magmatic copper polymetallic metallogenic belt; ⑤ Northeast-North China alkaline basalt gem metallogenic belt; ⑥ Jinguashi gold-copper belt in Taiwan Province Province.

In the past, there was not enough research on Himalayan mineralization. In recent years, many discoveries about Himalayan deposits show that Himalayan mineralization in China may have great intensity, especially in the southwest, northwest and southeast coastal areas, which should be paid attention to. It is of great significance to comprehensively study the regional geomorphological landscape and rock erosion degree for finding Himalayan deposits.