Yangshan Gold Deposit in Wenxian County, Gansu Province

Yangshan Gold Mine in Wenxian County, Gansu Province is located at the junction of Sichuan, Shaanxi and Gansu, and its administrative division is under the jurisdiction of Wenxian County, Gansu Province. The ore belt is about 30 kilometers long from east to west and 4 kilometers wide from north to south. Its geographical coordinates are: east longitude 1 0430 ′ 00 ″ ~ north latitude10450 ′ 00 ″ ~ 3300 ′ 00 ″ (figure1).

Figure 1 Traffic Location Map of Yangshan Gold Mine

1- county; 2- Township; 3- provincial highway; 4- Country roads; 5- Mountain peak; 6- Study area

This work area is famous for its rich placer gold. Since the 1980s, with the efforts of various geological teams, major breakthroughs have been made in rock gold exploration in this area, and gold deposits such as Xinguan, Lianhecun and Guojiapo have been discovered successively, as well as a number of geochemical dispersed flow anomalies. 1994, the 12th gold detachment of the Armed Police stationed in this area. Through the verification of geochemical anomalies of1∶ 200,000, it was found that Guanyinba-Gaoloushan area has a good prospecting prospect. From 65438 to 0997, Yangshan gold mine was discovered after a breakthrough in prospecting. By 2008, the whole Yangshan gold belt has become a super-large gold deposit with a gold reserve of 308 t, including Yangshan, Gaoloushan, Anba, Getiaowan, Zhangjiashan, Nishan and Tangbugou, and the scale is still expanding, showing a good metallogenic prospect in this area.

1 regional metallogenic geological environment

1. 1 geotectonic unit

The deposit is located in the triangle zone to the north of Yangtze plate, to the south of China-Korea plate and to the east of Songpan-Ganzi fold system, and belongs to the South Asia belt in the west of Qinling fold belt.

1.2 regional stratum

The strata exposed in this area mainly include Bikou Group of Lower Paleozoic, Devonian of Paleozoic, Carboniferous, Permian, Triassic and Jurassic of Mesozoic. In addition, there are large areas of Paleogene aeolian loess and Quaternary alluvial and diluvial sediments in this area.

Bikou Group is a set of extremely thick shallow metamorphic volcanic-sedimentary rocks, with the exposed area accounting for about 70% of the exposed area of bedrock, and the maximum exposed thickness exceeding16000 m. It is mainly composed of basic volcanic rocks and acidic volcanic rocks, sandwiched with plywood, phyllite and dolomite, and neutral volcanic rocks are rarely exposed.

The Middle Devonian Sanhekou Formation is a set of clastic-argillaceous-carbonate sedimentary formations with extremely thick shallow-sea facies, which is divided into 6 lithologic sections. The first and second lithologic members form an incomplete transgression cycle, and the third, fourth and fifth lithologic members form a complete transgression-regression sedimentary cycle of clastic rock-argillaceous rock-carbonate rock. This layer is the main surrounding rock of Yangshan Gold Mine. Wang Xueming et al. (1999) studied the gold content of Sanhekou Group in this area (table 1). The results show that sandstone has the highest gold content (7.78× 10-9), followed by carbonaceous rock (4.52× 10-9).

Table 1 Gold content of various rocks of Sanhekou Group in Wenkang area

(According to Wang Xueming et al., 1999)

Carboniferous is mainly composed of carbonate rocks, with a small amount of clastic rocks and lenticular hematite at the bottom. The Permian consists of marine carbonate rocks and normal sedimentary clastic rocks. Triassic is mainly composed of terrigenous clastic rocks in coastal and shallow seas, containing a small amount of carbonate rocks, which are in overall contact with the underlying Permian. The Jurassic is dominated by red glutenite sedimentary formation, and the exposed thickness is > 300m m.

1.3 regional tectonic framework

The deposit is located in the southeast of anticlinorium, Bailong River. The main structure controlling this area is Wenxian arc structure, which consists of a series of faults and folds in the near east-west direction (Figure 2).

Fold structures are mainly related to Jiagou-Hejiaba anticline and Lujiaba-Lengbaozi anticline. The fault structures mainly include Baisong-Liping fault, Anchanghe-Guanyinba fault, Majiamo-Weijiaba fault and Baima-Linjiang fault.

The above-mentioned fault structures in this area are generally NEE-oriented, and some of them are east-west, but actually they still extend to the west, and the strike turns to the northwest, forming an arc structure protruding south (Figure 2). The above-mentioned faults are only in the central and eastern parts. In addition, there are some nearly north-south fault structures at the top of the arc structure.

1.4 regional magmatism

The exposed area of magmatic rocks in the area is small, which has the following characteristics on the whole: ① There are many types, including ultrabasic rocks, basic volcanic rocks, intermediate-acid volcanic rocks and intrusive rocks; ② Magmatic activity is controlled by regional tectonic evolution, and the structural mechanism inducing magma emplacement and eruption is mainly large-scale structural fracture zone, which is syntectonic magmatism; ③ Magmatic activities are multi-stage and can be divided into three tectonic magmatic events: Caledonian-Variscan, Indosinian and Yanshanian. ④ The spatial distribution is extensive and scattered; ⑤ The scale is generally small, and the intrusive rocks are mostly small stones or dikes, but they are closely related to gold mineralization. Some intrusions are directly involved in gold mineralization (such as Yangshan gold mine and Brazil gold mine), among which Yanshanian magmatism plays an extremely important role in gold and polymetallic mineralization.

Caledonian-Variscan tectonic magmatism has a long time span and many rock types, and the lithology is mainly metamorphic basalt and tuff. The volcanic activity in Indosinian was weak, limited to the late Indosinian structure, mainly a small amount of basic volcanic rocks developed in Triassic marine strata; Yanshanian magmatism was intense and widely distributed, with the characteristics of homology, simultaneity and heterogeneity. The main rock types are basalt, andesite and rhyolite dacite. The K-Ar isotopic age of Jurassic volcanic rocks is 19 1.57 Ma, and the Rb-Sr age of Cretaceous volcanic rocks is112 27ma. Yanshanian intrusions are widely distributed and scattered, and the distribution of rock masses is closely related to Mesozoic fault structures. Rock types are mainly intermediate-acid rocks and intermediate-acid rocks. Yanshanian magmatism is closely related to gold mineralization.

Fig. 2 Schematic diagram of Wenxian arc structure

(According to Qi Jinzhong 200 1)

T- Triassic system; C- carboniferous; D- Devonian system; Z- sinian system. 1- quartz diorite vein; 2- fracture; 3- Inverted oblique syncline; 4- Formation occurrence inversion; 5— Formation occurrence; 6- gold deposit

1.5 metallogenic unit

The tectonic position of the deposit is located in the south Asia belt of Qinling-Dabie metallogenic province in Qin-Qi-Kun metallogenic domain.

2 Geological characteristics of mining area

2. 1 mining stratum

The strata exposed in the mining area are mainly a set of phyllite, sandstone and limestone in the third and fourth lithologic members of Sanhekou Formation of Middle Devonian, and the ore bodies are mainly produced in phyllite in the fourth lithologic member (Figure 3). According to different lithology, the fourth lithologic section (D2s4) in the mining area is divided into five secondary lithologic sections, as follows:

Located at the southernmost tip of the mining area, the lithology is mainly gray medium-thick-thin-medium-thick limestone mixed with siliceous rocks (quartzite). There are two kinds of siliceous rocks, namely, gray-white siliceous rocks are relatively pure, accounting for more than 95% of the mineral composition, and containing a small amount of sericite. Gray-black siliceous rocks contain a certain amount of impurities in addition to aging. The occurrence of strata is steep, mainly N dip, and closed anticline folds can be seen.

Located in Getiaowan area, it is dominated by purple phyllite, locally mixed with gray-black phyllite and carbonaceous phyllite. The strata in the mining area have strong flexural deformation and are the main ore-bearing strata in Getiaowan mining area. Most of the strata are in fault contact with the underlying strata, and the exposed range is also unstable.

Located in the priceless mountain and its west side, it is mainly composed of thin-medium-thick limestone, with gray-black slate and phyllite, and locally with carbonaceous phyllite. The formation deformation of this group is also strong, and carbonate cemented breccia zone can be seen locally. This layer is mainly exposed at the fold core, and is in fault contact with the underlying strata.

Fig. 3 Geological schematic diagram of Yangshan gold mining area in Gansu Province

-Middle and Lower Jurassic; -Lower Permian; -The fourth, third, second and first lithologic members of Sanhekou Formation of Middle Devonian; -Bikou Group is in Yuanguyu; γ π plagioclase granite porphyry. 1-unconformity surface;

2- failure; 3- presumption of fault; 4— Gold ore body and number

Widely exposed, the rock is mainly a set of grayish black-grayish white phyllite, with limestone, carbonaceous phyllite and red quartz (silicified) sandstone interlayer locally, with strong rock fragmentation and strong limonitization locally. Among them, the distribution of silicified sandstone is also unstable and often lenticular.

Located in the south of Sidouping, the rock is a set of interbedded gray-black phyllite and purple (silicified) chronological sandstone. The chronological sandstone tends to thicken northward, showing a medium-thick layer, interspersed with chronological veinlets and fine mesh veins, but metal mineralization is rare and the rock is dense. The mineral composition is mainly seasonal, with a small amount of carbonate minerals.

2.2 magmatic rocks in mining area

Small rock clusters and dikes in the mining area are developed along the structural fracture zone, and their lithology is mainly hypabyssal granite, including plagioclase granite porphyry, granite fine-grained rock and felsic porphyry.

2.2. 1 plagioclase granite porphyry vein

Veins in the mining area are mainly plagioclase granite porphyry, and the rocks are grayish white to light red, which varies according to the intensity of oxidation alteration. Generally, it is 300~500m long and 1 ~ 5m wide. The occurrence along bedding is mostly in or near the fault zone, and multiple veins often form a compound vein belt together (for example, the vein of Getiaowan 402 is a compound vein belt composed of multiple plagioclase granite porphyry veins). Oblique granite porphyry veins are closely related to ore bodies, and ore bodies formed by alteration of veins themselves are common. In Getiaowan, Anba, Gaoloushan and Yangshan ore sections, the ore bodies are all oblique granite porphyry veins or the surrounding rocks of veins. There are many plagioclase granite porphyries with weak deformation and alteration in the mining area, which do not constitute ore bodies.

In the mining area, due to the influence of the intrusion depth and scale of plagioclase granite porphyry veins, the veins have a certain phase transition. Among them, there are medium-coarse plagioclase granite porphyry veins in Xinguan mine outside the mining area, and there are plagioclase granite porphyry veins with aphanitic matrix in Tangbugou area, but their mineral compositions are basically the same.

2.2.2 Granite fine-grained dikes

In addition to plagioclase granite porphyry, there are a few fine-grained granite veins in the mining area. The rocks are grayish white and exposed in Tangbugou and Getiaowan, but the scale is small, generally less than 200 m long and 2 m wide. They are usually accompanied by plagioclase granite porphyry veins and run through them. Obviously, they were formed later than plagioclase granite porphyry veins. Similarly, fine-grained granite veins are mostly found in or near the fault zone, which is basically consistent with the occurrence of strata. Granite fine-grained dikes are also closely related to ore bodies. Fine-grained granite veins are broken and altered in Getiaowan ore section to form ore bodies (locally called white ore).

The content of SiO2 _ 2 in rocks is 69.85% ~ 80.77%, with an average of 73.88%, and Rietmann index (δ) is generally 0.3 ~ 0.4, which belongs to calc-alkaline series. On the Q-A-P triangle diagram, the chemical composition of rocks has the characteristics of continuous change. Among them, plagioclase granite porphyry veins are most often exposed in mining areas and have the closest relationship with gold ore bodies.

2.3 Mining Area Structure

The mining area is located on the Anchanghe-Guanyinba fault zone, with strong rock deformation and extremely complicated structural deformation.

Large-scale fold structures include Getiaowan-Caopingliang anticlinorium and priceless mountain syncline. There are also a large number of small folds, including slow-producing open folds with two wings, steep-producing closed folds with two wings, and small inverted anticlines and recumbent folds, among which closed folds are more common.

The main fault in the mining area is Anchanghe-Guanyinba fault, which is generally distributed in NWW direction and consists of a series of secondary faults and strong deformation zones. From the distribution direction, there are mainly secondary faults in NEE and NWW directions in the mining area, which are mainly developed in the two wings of the anticline.

NEE-trending fault zone is the main fault structure in the mining area, among which the larger one develops in the south of the mining area along Yangshuxia-Sanjiaodi-Caopingliang, and there is a structural lens with multiple branches or hard strata. This fault zone is the main part of Guanyinba fault zone in Anchanghe River, and it is also an important ore-bearing fault in Getiaowan mining area, numbered 40 1, 402, 403 and 404.

NWW-trending faults exist in all ore sections of Yangshan gold belt, but they are more frequent in Getiaowan ore section, mainly occurring in the north wing of anticlinorium, Caopingliang, Getiaowan, which is basically consistent with the stratigraphic occurrence. It is a group of bedding faults and a group of ore-bearing faults.

2.4 surrounding rock alteration

The wall rock alteration of the deposit mainly includes silicification, sericitization, argillization, carbonation, pyritization, arsenopyrite and limonite. It is characterized by epithermal alteration, in which sericitization, argillization and carbonation are widely developed in this area.

There is a certain alteration zoning phenomenon from ore body to surrounding rock, which is characterized by strong silicification and pyritization near ore body and clay and carbonation in the distance. However, due to the influence of structural fragmentation and surrounding rock composition, alteration zoning is not obvious.

3 Geological characteristics of ore deposits (bodies)

3. 1 ore body characteristics

Yangshan gold belt starts from Guzhen in the east and ends at Baoziba in the west, with a total length of 12km. It is divided into Yangshan, Gaolou Mountain, Anba and Getiaowan. A total of 49 gold veins have been discovered, of which the largest veins No.305, No.365 and No.438+04 are located in Anba ore section (Figure 3). Vein 305 is located in the fractured zone in the south wing of Anba anticline, and consists of cataclastic phyllite, pyritized phyllite and plagioclase granite porphyry. The veins are gentle, the plane is wavy and the profile is veined. The general strike is NEE, the dip is N, and the dip angle is 45 ~ 70. Only 1 ore body is delineated, with the length of 1800m, and the dip depth is controlled. The 3 14 vein is parallel to the 305 vein and located on its upper wall. The delineated 1 ore body has a length of 2100m, a controlled dip angle of 330m, an average thickness of 5.6 1 m and an average grade of 5.52× 10-6. The calculated amount of gold resources is 27570 kg.

3.2 Ore composition

According to the degree of oxidation, the ore in the mining area can be divided into primary ore and oxidized ore, with primary ore as the main one. According to the original rock types, the ore can be divided into altered sandstone type, altered phyllite type, altered gray rock type and altered vein rock type, among which pyritized altered phyllite type and pyritized altered plagioclase granite porphyry type are the main types.

Mineral composition characteristics of ores. There are many kinds of metal minerals in the ore, mainly natural gold, silver-gold ore, arsenopyrite, pyrite and stibnite, followed by ilmenite, vanadium-titanium magnetite, magnetite, pyrrhotite, sphalerite, galena, white iron ore, jamesonite, pyrolusite, hard manganese ore and limonite. In < 2mm, fine-grained pyrite and arsenopyrite are dominant, and the content of arsenopyrite is slightly higher than pyrite.

The statistical results under the microscope show that the gold minerals in the ore are mainly natural gold, followed by silver-gold ore. Gold minerals mainly occur in arsenopyrite, limonite, stibnite and clay minerals, and there are three modes of occurrence: ① they occur in arsenopyrite, limonite and clay minerals in the form of inclusions, accounting for 75.46% of microscopic statistics; ② Broken gold occurs in micro-cracks of pyrite and limonite, accounting for11.82% of the statistics; ③ Intergranular gold occurs in clay minerals (12.72%), and the disseminated particle size of gold minerals is fine. The largest gold ore particles seen under the microscope are only 5 ~ 6 microns, and most of them are between 2 ~ 3 microns or smaller.

The main nonmetallic minerals in the ore are timely, sericite, calcite, dolomite and feldspar, followed by kaolin, chlorite, pyrophyllite, epidote, barite, realgar and garnet. Trace minerals include zircon, tourmaline, diopside, Scorpio and fluorite.

3.3 Ore fabric and metallogenic stage division

There are many structures in the ores in this area. The ore structure mainly includes authigenic granular, heteromorphic, banded, circumferential, radial, inclusion, colloidal, metasomatic, strawberry and polycrystalline. The ore structure is mainly vein, disseminated, massive, loose powder and broken.

Generally speaking, the mineralization has gone through the primary deposit formation period-hydrothermal mineralization period and the secondary enrichment integration period-supergene oxidation mineralization period (Table 2).

Table 2 Characteristics of Yangshan Gold Belt in Different Metallogenic Stages

Hydrothermal metallogenic period can be divided into four metallogenic stages according to the relationship between vein penetration and mineral assemblage: ① Pyrite-isochronous stage (ⅰ): This stage is characterized by the formation and silicification of authigenic mesopyrite, and pyrite is often sparsely disseminated in phyllite, limestone and plagioclase granite porphyry. ② Phase (Ⅱ) of Yanshi-arsenopyrite: characterized by strong silicification, pyritization and arsenopyrite in fracture zone and cleavage zone. Pyrite and arsenopyrite are mostly disseminated or veined in Yanshi or altered phyllite and limestone. The quartz-pyrite veinlets with a pulse width of 2 ~ 3 mm can be seen in the cleavage zone, which is the main mineralization stage in this area and widely distributed. ③ Yingshi-stibnite stage (Ⅲ): Mineralization in this stage occurs in veins with a thickness of several centimeters to more than ten centimeters, indicating that it obviously cuts through the ore bed formed in the early Yingshi-arsenopyrite-pyrite stage, and the mineralization in this stage is only locally developed. ④ Synchronism-calcite stage (Ⅳ): Mineralization in this stage occurs in the form of calcite veinlets, in which a small amount of synchronism has a pulse width of several millimeters to several centimeters and a length of several centimeters to several tens of centimeters, and contains a very small amount of pyrite, which is widely distributed but has low mineralization intensity.

The second and third stages are the main metallogenic stages in this area.

3.4 Weathering characteristics of ore

After the formation of the deposit, due to Himalayan movement, the crust uplifted further, and most of the ore was exposed to the surface, with strong oxidation, mainly manifested in hematitization and limonite mineralization, some formed iron hat or hematite-limonite belt, and yellow, potassium, iron and vanadium developed. At present, the deepest mining depth is 220 meters, all of which are oxide ores.

4 genetic analysis of the deposit

4. 1 Characteristics of fluid inclusions

62 fluid inclusions in 19 sample were analyzed by microscopic temperature measurement. The results show that the homogeneous temperature range of fluid inclusions is 105 ~ 3 10℃, mainly concentrated in 150 ~ 250℃. The salinity of fluid inclusions ranges from 1.6%- 10.4%, mainly between 1.6%-6.5%. The results of fluid inclusion composition analysis show that H2O and CO2 are the main gas components of the fluid, with a small amount of CH4 and H2. The contents of cations in the liquid phase components are Na+, K+, Ca2+, Mg2 ++ and Li+ from high to low, while anions are characterized by being rich in Cl- and poor in F-, and their contents change greatly.

4.2 Isotopic geochemical markers

4.2. 1 sulfur isotope

The test results of sulfur isotopic composition of pyrite and stibnite show that the sulfur in the ore is relatively enriched for 34S, and the δ34S value is -3.47 ‰ ~ 13.23 ‰. It is generally believed that this sulfur isotope composition is dispersed, and there may be many sulfur sources in the process of mineralization. The δ34S value of pyrite-quartz veinlets in this area is close to mineralized phyllite, and the δ34S value of stibnite is close to rebalanced magmatic hydrothermal deposits (-2 ‰ ~ 3 ‰), indicating that both stratigraphic sulfur and magmatic sulfur participated in mineralization.

Hydrogen and oxygen isotopes

The hydrogen and oxygen isotope analysis of fine pyrite in ore shows that the time-dependent value of δ 18O is 3.23 ‰ ~ 0.4 1 ‰, and the δD value is -92.4 ‰ ~ 62.9 ‰. According to Clayton formula, the calculated value is-12. 13 ‰ ~. On the map, the projection point of hydrogen and oxygen isotope composition of ore in the mining area is near the atmospheric precipitation line, and the δD value is close to that of magmatic water around the world (-85 ‰ ~-50 ‰), indicating that the ore-forming hydrothermal solution is mainly atmospheric precipitation, and magmatic water also participates in mineralization to some extent.

4.2.3 Whole Rock Carbon and Oxygen Isotopes

The results of carbon isotope analysis of the whole rock show that the δ 13CPDB value of mineralization time pulse is -8.36 ‰ ~-2. 19 ‰, which is relatively discrete. According to the data of Jinsheng et al. (1997), the upper limit of δ 13CPDB value of magmatic carbon is -4‰, > -4. In addition, the whole-rock PDB value of mineralization time pulse is-13.54 ‰ ~-9.06 ‰, which is close to the whole-rock PDB value of plagioclase granite porphyry vein (-9.77 ‰ ~-9.75 ‰), indicating that mineralization is related to magmatic activity.

4.3 Geochemical Characteristics of Rare Earth Elements

The analysis results of rare earth elements show that the contents of rare earth elements in different rocks and ores are quite different, and σσREE values range from16.1×10-6 to 202.2×10-6. The σ REE content of phyllite is the highest, with an average σ REE of 152× 10-6. The average σσREE of plagioclase granite porphyry is 84.04×10-6; The σ REE content of the time pulse is the lowest, and the average σ REE is only 25.45× 10-6.

The partition pattern of rare earth elements shows a steep curve inclined to the right, but its smoothness is poor, showing a shallow "V" shape (Figure 4), and δEu is 0.08 ~ 0.83, showing a weak-moderate negative anomaly of Eu. σ lree/σ hree value is 4.57 ~ 17.96, indicating that light rare earths are relatively enriched. Generally speaking, the distribution pattern of rare earth elements in ore or mineralization-related veinlets is similar to that of phyllite and plagioclase granite porphyry veinlets, which reflects that the ore inherits the material composition of surrounding rocks (strata) to some extent.

Fig. 4 distribution pattern of rare earth elements in Yangshan gold deposit

(According to Qi Jinzhong et al., 2003)

1-phyllite; 2- altered phyllite; 3- plagiogranite; 4- altered granite porphyry; 5- Gaolou Mountain Mine; 6- Anba mine; 7- Getiaowan Mine

4.4 diagenetic and metallogenic age

According to the K-Ar isotopic age of the whole rock of Yangshan plagioclase granite porphyry, the K-Ar age of the whole rock of the plagioclase granite porphyry vein in the mining area is 17 1 ~ 209 Ma, with an average age of 189.4 Ma, indicating that the age of the plagioclase granite porphyry vein should be from the end of Triassic to the beginning of Jurassic. Du Zitu et al. (1998) made a statistical study on the isotopic age of magmatic rocks in the west Qinling Mountains. The results show that there are mainly two magmatic isotopic peaks, namely, 180 ~ 220 Ma and 100 ~ 180~220 Ma, reflecting that this area was in the late Triassic to the early Jurassic.

Yang Guicai et al. (2007) determined the argon isotopic age of the timely veinlets in the mining area (Figure 5). The results show that the chronological age of the chronological pyrite veinlets is 195.438+0 0.86 Ma, which indicates that its metallogenic age is Jurassic.

Fig. 5 Isotopic test results of Yingshan Gold Mine from 39Ar-40Ar.

(According to Yang Guicai et al., 2007)

Ding Zhenju et al. (1999) determined the argon isotopic age of the Bikou Group copper deposit at the time of mineralization pulse. The results show that its age is 211.31.1ma, indicating that the copper deposit was formed at the end of Triassic.

4.5 Discussion on the genesis of the deposit

1) More than 90% ore bodies in Yangshan Gold Mine occur in Devonian silty phyllite. The analysis results of Wang Xueming et al. also show that the gold content in Devonian sandy (silty) rocks is the highest (7.78× 10-9), while the gold content in carbonaceous rocks, argillaceous rocks and carbonate rocks is relatively low, being 4.52× 104 respectively. 2.6 1× 10-9, sandy and silty rocks with high gold content provide favorable material basis for the formation of gold deposits.

2) Pyrite in ore can be divided into sedimentary origin and hydrothermal origin. The former is layered or striated, and deforms with the formation folds. Its shape is generally autogenous fine particles or semi-autogenous cubes, which often form strawberry-like aggregates. This kind of pyrite does not constitute an ore body, but it is obviously enriched in Au (the Au content in banded pyritized phyllite is 0. 1× 10-6 ~ 0.3). Pyrites of hydrothermal origin are often veined and reticulated, coexisting with arsenopyrite, natural gold and other minerals, and are the main gold-bearing minerals.

3) The overall distribution of ore belt is controlled by Anchanghe-Guanyinba fault zone. The measurement of sediments in1∶ 50,000 drainage system shows that gold anomalies are distributed in a beaded shape along the fault zone with roughly equal intervals. In addition, the veins in the ore belt are also consistent with the fault strike, while the ore body occurs in the secondary fracture zone or bedding shear zone in the fault zone.

4) Yangshan gold deposit is closely related to early Jurassic magmatic activity. In time, the KAr age of plagioclase granite porphyry vein is171~ 209 Ma (five samples), and the age of 39Ar-40Ar plateau with gold-bearing chronological vein is 195.40 1.05 Ma. In space, ore bodies generally occur near the contact zone between phyllite and plagioclase granite porphyry vein.

5) The geochemical study of the deposit shows that the ore-forming fluid is epithermal, mainly atmospheric precipitation and magmatic water. Sulfur isotope analysis shows that both stratigraphic sulfur and magmatic sulfur participated in mineralization; The results of carbon and oxygen isotope analysis also show that mineralization is related to sedimentary rocks and magmatic rocks.

To sum up, Yangshan gold deposit is a gold deposit controlled by structure and related to sedimentation and magmatic activity, that is, a set of carbon-silicon argillaceous layers with high gold content was deposited in this area during Devonian. In the process of sedimentary diagenesis and subsequent regional shallow metamorphism, Au was initially enriched, and the ore-forming hydrothermal solution related to the early Yanshanian magmatism was superimposed on it, further enriching Au, thus forming the Yangshan gold deposit, which was neither a deposit formed by a single metamorphic ore-forming fluid nor a deposit formed by a single non-metamorphic ore-forming fluid, but a polygenetic compound gold deposit formed by various mineralization.

refer to

Guo Junhua, Qi Jinzhong, Bin Sun et al. 2002. Geological characteristics and genesis of Yangshan superlarge gold deposit in Gansu Province. Gold Geology, 8 (2): 15 ~ 19.

Li Zhihong, Yang Yin. 2007. Metallogenic characteristics of Yangshan super-large hydrothermal gold deposit in Gansu Province. Structure and mineralogy, 3 1 (1): 63 ~ 76.

Luo, Qi Jinzhong, Yuan, et al. 2004. Geochemistry of trace elements and stable isotopes in Yangshan gold deposit, Gansu Province. Modern Geology, 18 (2): 203 ~ 209.

Qi Jinzhong, Yuan, Li Li et al. 2003. Geological and geochemical study of Yangshan gold deposit in Wenxian County, Gansu Province. Geology of mineral deposits, 22 (1): 24 ~ 3 1.

Qi Jinzhong, Yuan, Li Li et al. 2003. Geological characteristics and ore-controlling factors of Yangshan super-large gold deposit in Wenxian County, Gansu Province. Geological Review, 49 (1): 85 ~ 92.

Qi Jinzhong, Li Li and Yuan et al. 2005. SHRIMP U-Pb chronology of zircon from Yangshan gold deposit, Gansu province. Geology of mineral deposits, 24 (2):141~150.

Yang Guicai, Qi Jinzhong, Dong et al. 2007. Geological and isotopic characteristics of Yangshan gold deposit in Wenxian County, Gansu Province. Geology and exploration, 43 (3): 37 ~ 4 1.

, Li,. 1997. Isotopic geochemistry of China. Beijing: Science Press.

Yuan. 2007. Study on mineralization of Yangshan superlarge gold deposit in Wenxian County, Gansu Province. Minerals and Geology, 2 1 (4): 404 ~ 409.

(Author Li Wenliang)