Rock mass in the NW-trending tectonic-magmatic active zone of Santiaoling-Yixingzhai-Boqiang-Haoditang

This is a tectonic-magmatic active zone located in Wutai Mountain-Hengshan Platform Uplift in the west of Yanshan Platform Fold Belt. The intensity of volcanic activity in the Tanghe tectonic-magmatic active zone is obviously weakened, but the intrusions and subvolcanic rocks are more developed. These include intermediate-acid intrusions in the south of Yingxian County (Luojiatuo Shi Ying feldspar porphyry bed, Changchenggou granodiorite porphyry, Huangyangshu granite porphyry and Quegou Shi Ying adamellite dike, etc.). Sunzhuang complex rock mass in the north of fan shi and Yixingzhai sub-quartz porphyry (sub-volcanic neck) body group; Luguya complex rock mass, Boqiang granodiorite (porphyry) rock mass, Houyu adamellite rock mass, Gengzhuang complex rock mass and Chafang complex rock mass in southeast fan shi; Tiewa Hall in the northeast of Wutai County, Guhuayan and Guhuayan South, luoquan Bay, Shantangwan, Pandao, Guaijiu, Dadi-Heiya and luoquan Bay biotite granite bodies, etc. Wutai County Haoditang volcanic neck cryptoexplosive breccia tube group, etc. After this tectonic-magmatic activity extended to the southeast of Hebei Province, there were zhang jia zhuang and Malan rocks in Fuping County, Hebei Province. The whole tectonic-magmatic active belt runs in the direction of 31 ~ 33, and the length in Shanxi Province is about 75km. It is a tectonic-magmatic belt with the development of intermediate-acid-acid hypabyssal-ultrahypabyssal intrusions in the middle Yanshanian period in northeast Shanxi. However, most of these rocks belong to crust-source remelting type intermediate-acidic and acidic intrusive rocks, or the central phase of the rock mass is transitional remelting type, while the transitional phase or marginal phase belongs to crust-source remelting type. The representative rock masses related to polymetallic mineralization are described as follows.

(1) Sunzhuang composite rock mass

This composite rock mass is located 1.5km east of Sunzhuang, with an exposed area of about 4km2. The lithology is Shi Ying syenite diorite in the middle and early Yanshanian stage, granodiorite porphyry in the middle and late Yanshanian stage, and granite porphyry in the center. There are Shi Ying diorite porphyrite veins interspersed in the northern part of the rock mass (Figure 3-17).

Figure 3-17 Schematic diagram of the relationship between Sunzhuang complex and surrounding rock and porphyry

1-granodiorite; 2-Granite porphyry; 3-diorite

Shi Ying syenite diorite is gray and semi-self-shaped. The mineral composition is medium feldspar (2 ~ 5 mm, 5%), medium feldspar (2 ~ 3 mm, 2%), common amphibole (1 ~ 4 mm, 1% ~ 15%), biotite (1 ~ 3 mm, 3% ~ 5%) and Shi Ying (1 ~ 3 mm, ≥5%).

granodiorite porphyry is grayish white, with brownish yellow microstrip and porphyritic structure. The phenocrysts consist of medium feldspar (2 ~ 5 mm× 5 ~ 1 mm, 3% ~ 35%), potash feldspar (5 ~ 1 mm, 1% ~ 2%), amphibole (2 ~ 6 mm, .5%), biotite (1 ~ 5 mm, 3% ~ 5%) and Shi Ying. The matrix (.5～1 mm) has a fine-grained granite structure, and the mineral components are orthoclase (2% ~ 25%), Shi Ying (15%), plagioclase (15%) and muscovite (1%).

the granite porphyry is brownish yellow with porphyritic structure. The phenocrysts (2 mm×4 mm) consist of plagioclase (1%), Shi Ying (2% ~ 3%), a small amount of potash feldspar and biotite. The matrix (1 mm) consists of Shi Ying (≥2%), orthoclase (4% ~ 45%), plagioclase (15%) and muscovite. The accessory minerals are mainly magnetite and apatite. It is characterized by high mass fraction of pyrite and sphalerite (31×1-6 and 17×1-6 respectively).

the chemical composition of composite rock mass is listed in table 3 -15, characterized by high mass fraction of K2O＋Na2O and low mass fraction of CaO, MgO and Fe2O3.

Table 3-15 Chemical composition mass fraction WB/%of each rock mass in Yixingzhai

Note: Ⅰ. Sunzhuang composite rock mass: 1. Granite porphyry; 2. Granodiorite porphyry (4 samples); 3. Shi Ying syenite diorite (2 samples); Ⅱ. volcanic neck and other dikes in Yixingzhai: 4. Feldspar porphyry; 5. quartz porphyry; 6. Rhombic quartz porphyry (2 samples); 7. South Gate Mountain volcanic neck-quartz porphyry (4 samples); 8 Bay volcanic neck-Sub-quartz porphyry (4 samples).

(According to Wu Tieshan et al., 1983)

(II) Shi Ying Porphyry Body of volcanic neck Phase in Yixingzhai

There are four volcanic neck rock pipes in this area, such as Hewan, Nanmenshan, Tietangdong and Jinjiling, which are long and common with many quartz porphyry and Fei porphyry dikes in NW direction, a few in N-S direction and NE direction, and gold-bearing quartz veins in near N-S direction (Figure 3-18

The cryptoexplosive breccia tubes are all nearly round, and the volcanic neck in Hewan is the largest (5 m× 55 m). South Gate Mountain volcanic neck is 65 m long from east to west and 1～2 m； wide; Volcanic neck diameter of iron pond adit is 2m× 25m; Jinjiling volcanic neck is 17 m in diameter. In Tietangdong and Jinjiling volcanic neck, except for a small amount of cryptoexplosive breccia, most of them are filled by skarn, the first two volcanic neck are mainly filled by subvolcanic facies-like quartz porphyry, and dolomite collapse breccia of Gaoyuzhuang Formation of Great Wall system is also seen in volcanic neck of Nanmenshan.

all volcanic neck and Shi Ying porphyry dikes, porphyry dikes and gold-bearing structural altered rock belts (i.e. gold-bearing quartz veins) are obviously controlled by NW-trending fracture zones and their derived fractures. Therefore, it becomes a part of this tectonic-magmatic active belt. Volcanic neck facies quartz porphyry is earlier than pyroxene syenite diorite in Sunzhuang composite rock mass, which may be the product of the second stage of early Yanshanian.

quartz porphyry is light gray or off-white, with sparse patchy structure, matrix with micro-granular structure and massive structure, with obvious rhyolite structure at the edge. Porphyry crystals (1 ~ 2 mm) are composed of Shi Ying (5%), potash feldspar (1% ~ 2%) and plagioclase (2% ~ 3%). The matrix (.1～.4 mm) consists of orthoclase (4% ~ 45%), Shi Ying (3% ~ 35%) and plagioclase (5% ~ 15%). In addition to common magnetite, apatite and zircon, there are many accessory minerals such as limonite (23×1-6), pyrite (295×1-6), sphalerite (78.8×1-6), galena, chalcopyrite and natural gold.

Feifine porphyry dikes are generally light gray or yellow gray with sparse porphyritic structure, and the matrix is Feifine structure and rhyolite structure. The difference from quartz porphyry is that the volume fraction of plagioclase is more than that of orthoclase. The phenocrysts are orthoclase.

see table 3-14 for the chemical composition and mass fraction of quartz porphyry and porphyry.

(3) Chafang composite rock mass

is located at 1.5km north of Chafang Village, with a width of 35m from east to west and a length of 4 ~ 45 m from north to south. It is dominated by syenite diorite in the first stage in the middle Yanshanian period, and granodiorite porphyry in the second stage is interspersed with the main rock mass in the northwest direction. (Figure 3-19).

Figure 3-18 tectonic map of Yixingzhai gold ore field

1-loose sediments in modern riverbed; 2-Loess; 3— Gravel mixed with clay layer and bottom conglomerate layer (alluvial gold in ancient river bed); 4-Volcanic deposit of Jingangku Formation-ferrosilicon formation;

tonalite from May to Wutai; 6-diorite porphyrite; 7-diorite body; 8— Sunzhuang diorite complex; 9-quartz porphyry; 1— cryptoexplosive breccia tube;

11-gold-bearing structural altered rock belt and its number; 12— placer gold deposit; 13-rock gold deposit; 14— Transverse tensile fracture; 15— Brittle-ductile shear zone

Chafang rock mass is located at the intersection of NW-trending and nearly EW-trending faults, and its surrounding rocks are Wutai-stage adamellite-tonalite (namely Beitai rock mass) and Gaoyuzhuang Formation dolomite. There are skarn-type iron deposits on the east side of the rock mass, and there are many gold-bearing and polymetallic veins along the gneiss fracture of Beitai rock mass (metamorphic rock is biotite plagioclase gneiss) in Donggou area of Beidongzhai.

The middle phase of Chafang composite rock mass is medium-coarse grained syenite with Shi Ying, and the marginal phase is syenite with pyroxene. Medium-coarse grained syenite diorite containing Shi Ying is flesh red, with authigenic grain structure and massive structure. Mineral compositions include plagioclase (2 ~ 5 mm, 5% ~ 55%), orthoclase (2 ~ 4 mm, 2% ~ 25%), biotite (.1～.5 mm, < .5%) and Shi Ying (1 ~ 2 mm, ≥5%).

syenite diorite containing pyroxene is dark in color, with authigenic grain structure and massive structure. Mineral compositions include plagioclase (1 mm, 5% ~ 55%), orthoclase (1 mm, 15%), amphibole (.5 ~ 2 mm, 1% ~ 15%), augite (1 mm, 5% ~ 1%), biotite (.1 ~ .5～2 mm, 3.

Figure 3-19 Geological Profile of Chafang Composite Rock Mass

① Wutai Ordovician Granite-tonalite; ② The Great Wall system is higher than the dolomite of Zhuang Formation; ③ syenite diorite containing pyroxene;

④ Shi Ying syenite diorite; ⑤ Granodiorite porphyry; ⑥ skarn and contact metasomatic iron ore body

granodiorite porphyry are generally light brown-gray, with porphyritic texture and fine-grained granite matrix. The phenocrysts (2 ~ 5 mm) consist of plagioclase (5% ~ 1%), potash feldspar (3% ~ 5%) and Shi Ying (3%). The mineral components of the matrix (< ＜1 mm) are plagioclase (4%), orthoclase (2%), Shi Ying (15% ~ 2%) and biotite (1% ~ 2%).

in the accessory mineral composition of Shi Ying syenite diorite and pyroxene syenite diorite, the mass fraction of magnetite is high ((159 ~ 17868) × 1-6), and pyrite and particulate galena are also found. The accessory minerals of granodiorite porphyry are relatively poor, but the mass fraction of barite is high (189×1-6). Among trace elements, Cu is highly abundant ((5 ~ 7) × 1-6).

the chemical composition of the composite rock mass is listed in table 3-16. It can be seen that the content of SiO2 _ 2 in syenite diorite is low, but the content of (K2O＋Na2O) is high, with w (Na2O) > w (K2O) and Rietmann index δ = 4, which belongs to calc-alkaline.

table 3-16 chemical composition mass fraction wB/%

note: 1. silicified granodiorite porphyry; 2. Granodiorite porphyry; 3. Shi Ying syenite diorite; 4. syenite diorite containing pyroxene.

There is a cryptoexplosive breccia body near the east of Chafang Village, with an exposed area of only 1 m2, which is a part of the subvolcanic rock active area in Boqiang area.

(4) Boqiang granodiorite porphyry body

This rock body is exposed in NE-SW direction, with a length of more than 6 m and a width of 3～45 m, and its surrounding rocks are Wutai-stage adamellite-tonalite and dolomite of Gaoyuzhuang Formation of Great Wall System. The rock mass is typical "mushroom-shaped", and the roof part extends 5～6 m westward along the bedding of the lower part of Gaoyuzhuang Formation, and is cut by the Houyu Yangshugou adamellite. This rock mass is commonly known as the shallow porphyry rock mass, and a series of rocks, such as granodiorite, Shi Ying syenite and feldspar quartz porphyry, are produced due to differential phase transformation. This rock mass is the largest known metallogenic porphyry in northeast Shanxi. There are also cryptoexplosive breccia on the west side of the rock mass.

granodiorite porphyry is light red and grayish red, with medium-grained granite structure and porphyritic structure, massive and rhyolitic structure. The mineral composition includes feldspar (2 ~ 4 mm, 4% ~ 45%), orthoclase (1 ~ 3 mm, 25%), Shi Ying (1 ~ 2 mm, 2% ~ 25%) and common amphibole (1 ~ 3 mm, 5%). In addition to more magnetite, there are pyrite, galena, limonite and molybdenite. The chemical composition of rocks is listed in Table 3 -17. Compared with China granodiorite, the mass fraction of SiO2 and K2O is higher.

Table 3-17 Chemical Composition Mass Fraction WB/%of Boqiang and Yangshugou Rocks

Note: Boqiang Rocks: 1. Granodiorite (2 samples); 2. Quartz diorite; 3. Shi Ying syenite (2 samples); 4. Granite; Yangshugou rock mass: 5. adamellite.

In 195s, Geological Team 218 conducted geological exploration on molybdenum and copper related to Boqiang rock mass, and at the end of 2th century, Geological Team 211 conducted general survey and evaluation on Chaishuling gold related to this rock mass. On the south side of this rock mass, there are many gold-bearing quartz veins and banded gold-bearing structural altered rocks in NW direction and near North-South direction. These different types of mineralization belong to the same metallogenic series.

(5) Yangshugou adamellite rock mass

This rock mass is located in the northwest of Houyu Village, fan shi, and is in the shape of a nearly circular rock mass, with a diameter of about 3m and an exposed area of .1km2 The surrounding rock is dolomite of Gaoyuzhuang Formation and shale of Lower Cambrian mixed with thin limestone and marl. The contact zone has been keratinized and marbled, and skarn-type high-grade copper, lead and zinc polymetallic mineralization can be seen on the north and west sides, but the ore body scale is very small.

adamellite is light gray, with porphyritic medium-fine grained granite structure and massive structure. Porphyry minerals are composed of potash feldspar (5 ~ 8 mm, 5%), orthoclase (1 ~ 15 mm, 1% ~ 15%) and Shi Ying (3 ~ 5 mm, 5%). The matrix minerals consist of plagioclase (2 ~ 3mm, 25%), orthoclase (2 ~ 3mm, 2% ~ 15%), Shi Ying (2 ~ 3mm, 2% ~ 25%), muscovite (.5～2 mm, 1% ~ 2%) and biotite (.5 ~ 2%). There are more pyrite (9287×1-6) in the accessory minerals, and others are apatite, chalcopyrite, molybdenite and limonite. W(Cu) is (5 ~ 1) × 1-6 and w(Pb) is (1 ~ 3) × 1-6 in trace elements. See Table 3-16 for the mass fraction of petrochemicals.

Wu Tieshan et al. (year) classified it as early Yanshanian according to its isotopic age value (186.3Ma), its occurrence and formation depth, which preceded the formation of Boqiang rock mass. However, according to the drilling data in Yangshugou, Yangshugou rock mass passes through the top cover of Qiebeqiang rock mass, and extends westward along the lower horizon of Gaoyuzhuang Formation to the feldspar quartz porphyry bedrock. Therefore, the sequence of formation of this kind of rock mass should be carefully judged.

(6) Gengzhuang composite rock mass

This rock mass is located in the west of Boqiang rock mass and south of Gengzhuang village. Obviously controlled by the NW-trending Hongmenyan fault system (Figure 3-2). The long axis of the rock mass is nearly north-south, with an exposed length of 85 m and a width of 4 m. The main body of the composite rock mass is volcanic neck phase angle conglomerate, and the hypabyssal-ultrahypabyssal granite porphyry and late subvolcanic rocks are closely accompanied by cryptoexplosive breccia. Because these rocks were shattered by volcanic eruption, and were later altered by hydrothermal solution and interspersed with subvolcanic rocks, the composition and generation sequence of composite rock masses are not very clear. Wu Tieshan et al. (1983), based on some petrological and petrochemical data, successively listed the formation sequence of various rocks in the composite rock mass as follows:

Figure 3-2 Geological structure of Gengzhuang gold-silver ore body (I) and geological map of mining area (II)

1—Composite cryptoexplosive breccia; 2-clayey rock breccia; 3-limestone breccia, and other breccia components include carbonaceous shale, granite and gneiss; 4-Potash granite porphyry; 5-K-Na granite; 6-Beitai rock mass; 7-Polymetallic ore bodies; 8— Exploration lines and drilling holes; 9-cryptoexplosive breccia tube; 1— Transverse tension fault; 11— Torsional fault; 12-secondary fracture; 13-Fault < P > There are many Mesozoic magmatic hydrothermal types in northeastern Shanxi.