Mesozoic and Cenozoic volcanic rocks and related intrusive rocks and their relationship with gold deposits

Mesozoic-Cenozoic magmatism and magmatic geothermal activity are closely related to the gold mineralization process in eastern and southwestern China, at least in the following aspects: ① The main metallogenic stage of gold deposits and nonferrous metals in eastern China is Yanshanian, which is synchronous with the Yanshanian magmatism and magmatic geothermal (hydrothermal) activity later in the same period; The metallogenic stages of gold deposits and nonferrous metals in southwest China are synchronized with Indosinian-Yanshan-Himalayan magmatism and magmatic geothermal activity. ② The spatial distribution of Mesozoic and Cenozoic gold deposits and related nonferrous metal deposits is closely related to related tectonic-magmatic activities. ③ The material and energy movement form of gold mineralization is inherited from the series combination of volcanic rocks, subvolcanic rocks and related intrusive rocks, as well as the structure and composition of crust and mantle. ④ According to the related conditions of volcanic rocks, volcanic sedimentary rocks, subvolcanic rocks and related intrusive rocks, the location conditions of gold mineralization can be roughly judged. ⑤ Combining the regional structure controlling the metallogenic belt, ore field structure and volcanic structure is beneficial to comprehensively determine the location and space of gold mineralization and predict the deep concealed ore. Therefore, the temporal and spatial distribution, series combination, volcanic structure and volcanic facies of Mesozoic and Cenozoic volcanic rocks, subvolcanic rocks and related intrusive rocks, as well as the tectonic background and deep geology of magmatism, are the important geological background and ore-controlling conditions for gold mineralization in eastern and southwestern China.

The Mesozoic and Cenozoic magmatic activities in China are basically synchronized with the tectonic activities. Volcanism and intrusion are mainly divided into four stages: Indosinian, early Yanshan, late Yanshan and Himalayan.

Temporal and spatial distribution of (1) Indosinian igneous rocks

The Indosinian igneous rocks (Table 1- 1) developed on the background of the Variscan fold belt, obviously inherited the magmatic activities in the late Variscan period, and mainly distributed in the east-west direction (NEE, EW or NWW), which is basically consistent with the structural line direction of the Variscan fold belt. Igneous rocks are mainly distributed in Yunnan, Tibet and Northeast China, but only sporadically in other places.

Table 1- 1 isotopic age of Indosinian igneous rocks (Ma)

Marine volcanic rocks are mainly distributed in Songpan-Ganzi, Yarlung Zangbo River and Nadanha Daling in Heilongjiang Province. In the early Triassic, there were intermediate-acid volcanic rocks in Wulanchajia and Longyangxia. Intermediate-acid and basic volcanic rocks are developed in Baise-Longan and Pingxiang-Dongmen in western Guangxi, respectively. Ophiolite occurs in Anima Qing area in the northern margin of Songpan-Ganzi, while Yidun-Zhongdian calc-alkaline volcanic rocks occur in the southern margin. Middle Triassic marine volcanic rocks are distributed in Pingxiang-Dongmen area of western Guangxi, which are intermediate-acid volcanic rocks. The coast of Lancang River in western Yunnan is dominated by acidic volcanic rocks. Queshan Temple in southern Tibet is a calc-alkaline volcanic rock. Late Triassic marine volcanic rocks are confined to Songpan-Ganzi area, and there are a large number of andesite in Yidun-Zhongdian on the east side of Jinsha River. The andesite in the Jiangda area on both sides extends northwest to the Tuohe area in Qinghai, and is connected with the intermediate-alkaline volcanic rocks in Deqin area in northwest Yunnan to the southeast. Triassic volcanic rocks in the east are relatively concentrated in the northeast, namely Nadanha Daling (Wandashan) area and Zhangguangcailing, with isotopic age of 2 15 ~ 180Ma.

Indosinian intrusive rocks are widely distributed in the west, and a variety of rocks are developed. Ultramafic rocks occur in the northern section of Wulan-Yushu fault, Zhapu-Chasang-Lancang River, Jinsha River, Batang-Derong, Litang-Wu Kang and other areas. In Yushu area, basic rock walls are also well developed. Intermediate-acid intrusive rocks are distributed in Tanyatong and Jiangda-Mangkang areas in northern Tibet, mainly biotite granite and granodiorite. The eastern Tibet-western Yunnan region is distributed along the nearly north-south fault zone, with diorite and granodiorite in the Jinsha River area in the north and biotite adamellite in the Ailaoshan rock belt in the south. Three calc-alkaline granite belts are developed in Kunlun, Qaidam margin and Qinling area. The isotopic age of Indosinian intrusive rocks in the east is 230 ~ 200 Ma, which is relatively concentrated in Zhangguangcailing, Xiaoxing 'anling, central Daxing 'anling and the northern margin of North China, and is mainly composed of calc-alkaline to weakly alkaline intermediate-acid rocks. Granite is also distributed in Guangxi, Hunan, Guangdong and Jiangxi. Alkaline and overbased intrusive rocks are only exposed sporadically. In Yongning River, Panxi, Sichuan, Fu Gui-Lincang, Yunnan and Fengcheng, Liaoning, the isotopic age of Yongning River alkaline complex can span Permian and Triassic (263 ~ 202 Ma).

Indosinian igneous rocks are mostly the result of continuous development in the background of Variscan fold belt, so the distribution of volcanic rocks and intrusive rocks is basically consistent with the direction of Variscan fold belt, especially the intrusive rocks in the early Triassic are often the continuation of magmatism in the late Permian. It is often related to "delayed" magmatism after collision orogeny.

(2) Temporal and spatial distribution of Yanshanian volcanic rocks and intrusive rocks.

Yanshanian is the most important period of magmatic activity in China (Table 1-2), mainly distributed in the east and southwest. Due to the different order of collision and splicing between different blocks, the northeast and north China are earlier and the south China is later, but they are the strongest from late Jurassic to early Cretaceous.

Table 1-2 isotopic age of Yanshanian igneous rocks (Ma)

The northeast of China is centered on Songliao Basin (the basement is an unconsolidated middle block of Proterozoic), and Yanshan volcanic rocks are divided into two zones: east and west. Volcanic rocks in the western region are mainly distributed in Ergon, Daxing 'anling and Xiaoxing 'anling, with a northeast-northeast distribution. The general trend is that volcanic rocks are basic in the early stage, intermediate in the middle stage and bimodal in the late stage. Yanshanian volcanic rocks are distributed in eastern Kyrgyzstan and , with moderate acidity in the lower part and moderate alkalinity in the upper part. The eastern and western intrusive rock belts correspond to volcanic rocks in lithologic combination.

The Yanshanian magmatism in Tarim area is weak, and only small rocks (120.7Ma) are distributed in the Mesozoic graben in the southern margin of Altun Mountain. Magmatic activities in North China are relatively developed, with activities from early Jurassic to late Cretaceous, and the peak period is from late Jurassic to early Cretaceous, which can be divided into five zones, two of which are near east-west and three are north-northeast The Liao Yan tectonic magmatic belt in the northern margin of North China is nearly east-west, with basic volcanic rocks in the early Jurassic, neutral volcanic rocks in the middle Jurassic and intermediate-acid volcanic rocks in the late Jurassic. The alkalinity of calc-alkaline volcanic rocks tends to change from old to new. Basic and neutral intrusive rocks dominated in early and middle Jurassic, and intermediate-acid intrusive rocks with a small amount of alkaline rocks in late Jurassic to early Cretaceous. The Henan-Shaanxi-Huaihe region in the southern margin of North China landmass is a neutral and acidic intrusive rock belt from late Jurassic to early Cretaceous, with a small amount of alkaline to alkaline syenite.

There are three igneous belts in North China landmass: ① belts in eastern Jilin, eastern Liaoning and eastern Shandong, which are mainly distributed on both sides of the Tan-Lu fault, and their volcanic rocks and intrusive rocks are well developed. In the Middle Jurassic, only a small amount of neutral volcanic rocks were distributed in Guo Song Basin, Jilin Province. From the Late Jurassic to the Early Cretaceous, neutral and moderately acidic and alkaline volcanic rocks were dominant, and neutral volcanic rocks were alkaline in some areas in the Late Cretaceous. Basic, neutral and intermediate-acid intrusive rocks dominated in the early Yanshan period, intermediate-acid and acidic intrusive rocks dominated in the late Jurassic to early Cretaceous, and a small amount of alkaline-weakly alkaline neutral intrusive rocks. ② Taihang Mountain Rock Belt, whose northern section starts from Fuping in the south and connects to the southern section of Daxing 'anling in the north, overlaps with Liaoyan Rock Belt. The late Jurassic is dominated by neutral and intermediate-acid intrusive rocks, and the early Cretaceous is intermediate-acid and acidic intrusive rocks. The southern segment is distributed in the eastern foot of the southern Taihang Mountain, which is a basic and intermediate-basic intrusive body and consists of calc-alkaline to alkaline rocks. (3) The Luhuai rock belt is dominated by neutral and small intrusive rocks, which are scattered in NNE direction, and the intrusion age is from Late Jurassic to Early Cretaceous.

(3) Temporal and spatial distribution of volcanic rocks and intrusive rocks in Himalayan period.

Cenozoic volcanic rocks in China are mainly distributed in the East Pacific (Table 1-3), followed by Tibet and western Yunnan. The former is dominated by rift basalt in extensional tectonic background, while the latter is collision orogenic belt and post-collision intermediate-acid volcanic rocks and intrusive rocks. Cenozoic basalts in eastern China developed from Paleogene to Quaternary. It can be divided into three zones: ① Northeast-North China continental rift basalt zone, in which Paleogene basin rift basalt is distributed in Fushun, Lower Liaohe-Bohai, Subei-South Yellow Sea, Huanghua, Jizhong, Jiyang and Jianghan basins; Neogene graben rift basalt is mainly distributed in the Tanlu fault zone and its two sides, as well as some sections of Fushun-Mishan and Yilan-Yitong graben extending northward. Miocene flood basalt is mainly distributed in Zhangjiakou, Zhangbei, Chongli, Jining, Zuoyun, Weichang and Chifeng. Pliocene and Quaternary basalts are mainly distributed in the Northeast-North China Rift System. In addition to alkaline basalt, there may be a small amount of alkaline trachyte and alkaline rhyolite. ② Rift trough basalt belts in the southeast continental margin are mainly distributed in Zhejiang, Fujian, Guangdong, Hainan and offshore continental shelf areas. Besides basalt, there may be a small amount of trachyte and alkaline rhyolite in Paleogene volcanic rocks. Miocene and Pliocene are alkaline and tholeiitic basalts, which are distributed in Shengzhou, Xinchang, Tiantai, Ninghai and Dongyang in Zhejiang, Changting-Songling, Yongding-Fuding, Dongshan-Xiamen in Fujian, Guangdong and Lei Qiong in Hainan. ③ There are three sets of Cenozoic volcanic rocks in Taiwan Province Province, with Miocene basalt in the intraplate rift zone in the west, ophiolite suite in the east and Quaternary calc-alkaline andesite series in the north.

Table 1-3 Isotopic Age of Himalayan Volcanic Rocks in Eastern China (Ma)

Cenozoic volcanic rocks in the Qinghai-Tibet Plateau and its surrounding areas are not as developed as those in eastern China, but they are also distributed in many areas. ① The Gangdise volcanic belt dominated by Paleogene is calc-alkaline neutral and acidic volcanic rocks, and the southern Xinjiang and northern Tibet dominated by Paleogene are high-potassium calc-alkaline neutral volcanic rocks with isotopic age of 65.5 ~ 38.2Ma, with isotopic age of 60 ~ 20ma. ③ Hengduanshan-Sanjiang area is dominated by Neogene, which is calc-alkaline-high-potassium calc-alkaline intermediate rock with isotopic age of 39 ~ 28 Ma. ④ The Tengchong area is dominated by Neogene and Quaternary, with calc-alkaline-calc-alkaline intermediate and neutral volcanic rocks, with isotopic age of 17.8 ~ 0. 13 Ma. ⑤ The Karakorum and Central Kunlun areas dominated by Quaternary are calc-alkaline intermediate-acid volcanic rocks and pyroclastic rocks, with isotopic ages ranging from 2.8 to 0.12ma.