Placer gold deposits are widely distributed in this area, covering the entire Qilian metallogenic belt. According to statistics, there are 4 1 mineral deposits in China, including 3 medium-sized and 9 small-sized ones, such as Tianpenghe medium-sized placer gold mine, Chuancigou small-sized placer gold mine, Hatenghe small-sized placer gold mine, Hongshuiliang small-sized placer gold mine and many placer gold spots in the south of Danghe River. Types of alluvial and diluvial placer gold in this area. For example, the Tianpenghe placer gold deposit is located in the VI terrace with a gold grade of 0.044 ~ 10.74 g/m3. Chuancigou small placer gold (platinum) mine is located at the bottom of rivers, I-V terraces and alluvial fans. The gold grade is 0.065 ~ 0.984 g/m3, accompanied by placer gold and platinum. Hongshuiliang small placer gold (platinum) deposit is located in II-IV terrace (Yu Pusheng et al., 2000). The existence of placer gold deposits provides a favorable clue for finding primary gold deposits in this area. According to the distribution characteristics of placer gold deposits, many rock gold deposits in this area were discovered by tracing the source, so placer gold deposits can be used as an important symbol to find primary gold deposits.
There are 57 gold deposits in Oedolgae, including large 1, medium-sized 6 and small 2 1. As far as gold deposits in Oedolgae are concerned, they can be divided into two types, namely, structural altered rock type and hydrothermal type (including chronological vein type). According to the metallogenic tectonic environment, they can all be classified as orogenic types (including plate subduction orogeny, arc-continent collision orogeny and land-continent collision orogeny, etc.). ). In other words, they are the products of the compressive tectonic environment. Large and medium-sized gold deposits such as Hanshan, Yingzui Mountain, Heicigou, Qinglonggou, Tanjianshan, Wild Camel Spring and Hongliugou have been formed in this area. Hydrothermal gold deposits (including chronological type) are represented by Tongziba, Caojiakou, Qingfengling, Chelugou and Haoquangou.
I. Structural altered rock-type gold deposits
1. Hanshan Gold Mine
The deposit is located at the western end of the North Qilian orogenic belt, in the Changma-Lenglongling-Yongdeng Caledonian arc zone. The exposed stratum in the mining area is a set of volcanic sedimentary rock series formed in the island arc environment, which includes andesite-dacite tuff, andesite, pillow lava, sand (slate) rock, etc. Industrial ore bodies occur in flaky tuff, and the host rocks have high porosity (50%) and effective porosity, which is beneficial to hydrothermal migration. The regional gold background value is high (17.74× 10? 9) Strong chemical activity is beneficial to hydrothermal metasomatism and deposit formation (Xia et al., 200 1). In the south of the mining area, diorite intrudes into Ordovician, and its zircon U-Pb isotopic age is 370? Horse 25? Ma ~347. 1? Ma 6.4? The fault structure in Ma mining area is developed, which is composed of regional NW-trending structure and nearly EW-trending structure. The ore body is developed in the NWW brittle-ductile shear zone, with a length of 10km and a width of 200 ~ 600 m (Figure 3-50).
Figure 3-50 Geological Map of Hanshan Gold Mine
(quoted from Mao Jingwen et al., 1997)
1- four yuan; 2- Middle Ordovician Yaoshenshan limestone; 3- Lower Ordovician basaltic andesite volcanic rocks; 4- Lower Ordovician basaltic andesite lava; 5- Lower Ordovician sandstone slate; 6- Fault; 7- Translation error; 8— Ore body and number
Since the discovery of the deposit by 1994, 65 mineralized alteration zones and 3 1 ore bodies have been delineated in the mining area. The mineralized alteration zone is 100 ~ 10~30m long and 10~30m wide. The surface of this zone is khaki-gray jarosite or brown iron-dyed carbonate rock and limonite strong schist, in which ore bodies are produced, and the strongly silicified altered rocks and the timely sulfide vein gold filled in them mostly reach industrial grade. The ore bodies are generally distributed in the east-west direction and tend to the south. Most ore bodies are arranged in parallel or trapezoid, and they are imbricate in profile. Single ore bodies are mostly long lenticular and banded, with expansion and contraction, S-shaped bending and branching compound phenomena along the strike and dip. The types of ores are chrysotile sericite schist, chrysotile sericite schist and isochronous vein type. The primary ore minerals are mainly silver-gold, argentite, pyrite and arsenopyrite, followed by tetrahedrite, galena, sphalerite and chalcopyrite. Other metal minerals are magnetite, stibnite, molybdenite, anatase and ilmenite, and gangue minerals are mainly timely, sericite, ankerite and barite, followed by chlorite, muscovite, illite, kaolinite and zircon. The secondary ore minerals are mainly natural gold and silver-gold ore, which are distributed in the cleavage plane, micro-cracks and honeycomb of honeycomb sericite schist in the form of thin films, grains and filaments, and local secondary gold wires are formed. Others include limonite, chalcocite, chalcocite, light blue, skunk stone, galena, galena, jarosite and malachite. The average grade of gold is 5× 10-6. In the compound parts of faults in different directions, the ore body is large in scale and the gold grade of ore is often high.
The wall rocks closely related to mineralization are changed into silicification, pyritization, sericitization, odorization and carbonation. The ore structure is disseminated, fine reticulate vein, massive, powdery and honeycomb. According to the symbiotic combination of structure and minerals, its mineralization is mainly divided into three stages: the first stage of mineralization is characterized by large-scale microcrystalline sericitization with a small amount of sulfide; The second stage is medium-fine sericite rich in sulfide, with high sulfide content and many kinds; The third stage is coarse spar quartz carbonate minerals.
The results of stable isotopes and rare earth elements show that the ore-forming material comes from the host volcanic rocks, and the ore-forming fluid is a low temperature, low salt and low density solution, and the ore-forming fluid is a mixed hydrothermal solution mainly composed of atmospheric precipitation and magmatic fluid. The multi-stage intrusive magmatic activities in the area provide a heat source for mineralization, and the ductile-brittle shear zone is its ore-hosting space. Mineralization is controlled by the fault system during (and after) collision orogeny, especially the brittle shear fault (strong foliation zone) superimposed on ductile shear zone. It is preliminarily considered that the deposit is a structurally fractured altered rock type gold deposit, and its metallogenic age is 395 Ma 46 Ma ~ 303 Ma1000 Ma (Xia et al., 200 1).
In addition, Yingzuishan Gold Mine, which is adjacent to Hanshan Gold Mine, is also a structural altered rock deposit. The metallogenic tectonic environment of the deposit is a subduction complex belt at the boundary of plate collision. The exposed strata in this area are volcanic sedimentary rock series (Heicigou Formation) formed in the continental rift environment of Middle Cambrian. The intrusive rocks are mainly Caledonian vein ultramafic rocks, and the structure is mainly NWW brittle-ductile shear zone. Mineralization in this mining area is mainly distributed along NWW-trending faults, and the enclosed 1 1 ore body is generally 50-600 meters long and 0.5-4.7 meters thick. The ore body is controlled by the contact fracture zone between ultramafic rocks and surrounding silty slate and the NW-trending fracture. The mineralization type is altered rock type, with a small amount of time-dependent veins interspersed, and the ore minerals are complex, mainly pyrite. Gold mainly exists as a single mineral, attached to the grains of Yingshi and pyrite, followed by silver-gold deposits. Wall rock alteration development, including silicification, serpentine, slip petrochemical, carbonation and so on. , with obvious zoning. Geological and geochemical studies of the deposit show that the ore-forming materials come directly from ultramafic rocks (Xia et al., 200 1). The gold grade is1.5×10-6 ~ 9.6×10-6, and the contents of lead, zinc, copper and silver in the ore body are above the cut-off grade.
It is preliminarily considered that the mineralization (endogenetic ore) of Yingzuishan gold deposit can be divided into two stages. The first stage is microcrystalline quartzitization, forming dense massive quartzite with a width of several meters to more than ten meters; The second stage is the pulse-like chronosulfide stage, which is superimposed on the quartzite in the first stage, showing medium-coarse Shi Ying vein or sulfide chronosulfide vein. The Rb-Sr isochron age of gold-bearing silicified altered rocks in this deposit is 465,438 0.3 Ma 5 Ma, and the metallogenic age is Late Silurian. The ore-forming fluid is mainly composed of deep ascending fluid (magmatic water) mixed with a small amount of shallow precipitation, and the ore-forming temperature is below 200℃. It is preliminarily considered to be a low-temperature hydrothermal structural altered rock type gold deposit related to ultramafic rocks.
2. Tanjianshan Gold Mine
Tanjianshan Gold Mine is located in the Jinlonggou area of Tanjianshan, about 75km southwest of Dachaidan (Figure 3-5 1), in the Saishitengshan-Xitieshan rift zone. The exposed strata in this area are mainly Mesoproterozoic Wandonggou Group, which belongs to a set of carbonaceous argillaceous clastic rocks and magnesium-rich carbonate rocks that have been subjected to regional metamorphism and dynamic metamorphism. There are strong tectonic activities in the mining area, including faults and folds, and different types of structures are intertwined in different periods, forming a complex structural pattern. In the NW-trending shear zone of Wandonggou Group, the fracture zone along the axis and wings of the NNE-NNS secondary fold is the ore-controlling structure in this area. The magmatic rocks in the mining area are mainly intrusive rocks, mainly acidic, followed by neutral rocks. Rock types include plagioclase granite porphyry, granite porphyry, granite fine grained rock, plagioclase fine grained rock, diorite porphyry, diorite fine grained rock and chrysolite. According to the recent work of Institute of Mineral Resources of Chinese Academy of Geological Sciences and Qinghai Geological Exploration Bureau, the K-Ar isotopic age of plagioclase granite porphyry is 294.7? Ma 3.8? Ma ~309.87? Ma 4.77? Ma, Rb-Sr isotopic age is 330.03? Ma, the K-Ar isotopic age of the whole granite fine-grained rock is 308.8? Horse 5.4? Ma, the diagenetic age is mainly in the middle of Variscan, while the age of altered granite-porphyry gold deposit is 268.94? Ma 4.3 1? Ma (K-Ar), the Huangyan age of fine vein cloud of vein gold ore body is 288.9Ma(K-Ar), which indicates that the metallogenic age is later than the diagenetic age, mainly occurring in the middle and late Variscan. According to the petrochemical characteristics of intrusive rocks, the diagenetic environment is judged. The intermediate-acid rock mass in this mining area was formed in collision orogenic environment, in which the syncollision orogenic environment is the main one. Metallogenic geological environment and polymetallic mineral prediction in the northern margin of Qaidam basin. 2000。
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Figure 3-5 1 Geological Schematic Diagram of Tanjianshan Gold Mine Area
(Quoted from Zhang Dequan, 2000)
1- four yuan; 2- Carbonaceous phyllite and schist; 3- marble; 4- plagioclase granite porphyry; 5- dike; 6- ore body; 7— Geological boundary and occurrence; 8- Fault; 9— back axle; 10-radial axis; 1 1- exploration line
Figure 3-52 C-D Section of Jinlonggou in Tanjianshan Mining Area
(Quoted from Zhang Dequan et al., 2000)
1- four yuan; 2- carbonaceous sericite phyllite and spotted carbonaceous sericite phyllite; 3- dolomite marble; 4- granite porphyry; 5- gold ore body; 6. Inferring gold ore bodies; 7-Drilling and numbering; 8— Pulse Punching and Numbering
All ore bodies occur in carbonaceous phyllite and schist sections of Wandonggou Group, and are strictly controlled by fracture zones (brittle faults) and interlayer strike-slip faults in NNE and NW foliation zones. The main industrial ore bodies (accounting for more than 90% of the reserves) are all located in the NNE-NNS fracture zone on the axis and wings of the fold, and a few ore bodies are distributed in the NW direction. The ore bodies are mostly vein-like, branched vein-like and lenticular, with the phenomena of branching compound and pinch-out reappearing along strike and dip, and have no obvious boundary with altered surrounding rocks, showing a gradual transition relationship. The main ore body is inclined to SE with steep dip angle (60 ~ 70). The ore body is 20 ~ 430m long and 0.6 ~ 62.38m wide, with great changes, and the maximum dip angle is controlled at100m (Figure 3-52).
The ores in this area are mainly structural altered rocks, which can be divided into altered carbonaceous phyllite schist type and altered vein rock type according to the different original rocks of altered rocks. Altered phyllite schist ore is a kind of "punctate" carbonaceous phyllite and carbonaceous schist, which has undergone structural fragmentation, alteration and gold mineralization. Altered vein type gold deposits are granite fine-grained rocks (or plagioclase fine-grained rocks), diorite porphyrite, huangyan and granite porphyry that have been cut by faults or folded synchronously with strata and mineralized by hydrothermal alteration. Ore minerals mainly include natural gold, silver-gold ore, pyrite, arsenopyrite, arsenic-bearing pyrite and a small amount of gold-silver ore, antimony-copper-silver ore, Yin Hui-bearing arsenic-nickel ore, sphalerite, chalcopyrite, anorthite, galena, magnetite, hematite, cassiterite, sky blue, bornite, cobalt-rich arsenopyrite, nickel arsenopyrite, pyrrhotite, natural bismuth and limonite. Gangue minerals mainly include quartz, sericite, graphite, amorphous carbon, chlorite, epidote and dolomite. The ore structure is mainly pyrite autotype to semi-autotype granular structure, ring-edge ring structure, sieve structure and so on. Ore structures mainly include disseminated structure, eyeball structure, massive structure and veinlet-reticular vein structure. The average grade of gold is 3.9×10-6 ~13.4×10-9.
Wall rock alteration mainly includes pyritization, silicification, sericitization and a small amount of carbonation. The metallogenic age is the middle and late Variscan.
The comprehensive study of stable isotopes of ore in the mining area shows that the water in ore-forming fluid is a mixture of metamorphic water and variegated magma, the sulfur in ore is mainly magmatic sulfur, the carbon in ore and calcite is mainly magmatic carbon, and the lead in ore is a mixture of magmatic lead and metamorphic strata lead, which proves that the ore-forming materials of the deposit are partly derived from variegated magma. The metallogenic temperature is 232 ~ 278℃, which belongs to moderate temperature mineralization.
Figure 3-53 Abnormal Map of Geological Soil Investigation in Hongliugou Gold Mine Area
(Quoted from Zhang Dequan, 2000)
1- four yuan; 2- Neogene; 3- Lower Jurassic; 4- Lower Carboniferous; 5- Upper Devonian Yakeshan Formation; 6- Qinjian Mountain Group; 7- Late Wallis plagiogranite; 8- Caledonian diorite; 9— Granite porphyry; 10- timely pulse; 1 1- actually measured geological boundary; 12- reverse fault; 13- failure of unknown nature; 14- stratum occurrence; 15- gold ore body; 16—1:10,000 soil anomaly (from the outermost circle, 2,4,8,16,32,64,128,256×10.
3. Hongliugou Gold Mine
Hongliugou Gold Mine is located in Hongliugou area south of Gao Quan Coal Mine in the northern margin of Qaidam Basin. It is located in the Saishiteng mountain fire sedimentary basin in the central and western part of the Saishiteng-Xitieshan Caledonian rift zone. The exposed strata in the mining area include Tanjianshan Formation (O2ST), Upper Devonian Yakeshan Formation (D3m), Lower Jurassic (J 1), Tertiary and Quaternary. This structure is mainly a fault structure (Figure 3-53), which is a large NW-trending ductile shear zone developed in Qinjianshan Group, and the fold structure is not obvious. Magmatic activities are intense, including Caledonian diorite, Variscan plagiogranite and plagioclase granite porphyry. There are three main types of quartz veins: copper-bearing quartz veins, ivory quartz veins and calcite quartz veins. The discovered gold bodies are all distributed along the structural fracture alteration zone controlled by the nearly north-south ductile-brittle shear zone group (F5 and F6) next to the northwest large ductile shear zone (see Figure 3-53). The host rocks are sericite quartz schist, sericite schist and altered andesite of Tanjianshan Group. The shape of the ore body is veined and lenticular, with obvious characteristics of branching and compounding, expansion and contraction and pinching out.
The main ore bodies of the deposit strike nearly north-south, nearly vertical or steep eastward. The scale of ore bodies is generally small, the thickness of a single ore body varies greatly, with an average of 0.32 ~ 6.09 m, and the controlled length of ore bodies is 62 ~196 m. The gold deposits in this deposit can be divided into time-dependent pulse type and altered rock type. Time-pulse type gold deposits can often form independent gold bodies, while time-pulse type gold deposits consist of pyrite (1% ~ 5%), chalcopyrite (1% ~ 2%), sky blue (1%), natural gold (trace), limonite (small amount) and malachite (small amount) The ore structure is mainly vein, vein and lenticular, followed by sparse disseminated structure and mylonite structure; Ore structures include cataclastic structures and metasomatic penetrating structures. Altered rock type gold deposits consist of pyrite (1% ~ 2%), chalcopyrite (1% ~ 2%), limonite formed by oxidation of natural gold (trace) and pyrite, quartz (30% ~ 50%), sericite (10% ~ 30%). There is little difference between the two ores except that the content of metal minerals is high and the gangue minerals are mainly timely. The mylonite structure and millstone structure are developed in the ore, and the scale granular metamorphic structure and metasomatic texture characteristics are obvious. The wall rock alteration of the deposit is mainly silicification (timely), sericitization, chloritization, epidotization and carbonation, followed by supergene pyrite, chalcopyrite and limonite.
In a word, Hongliugou gold deposit occurs in the stratum of Tanjianshan Group, and the mining area is located in the outer contact zone on the southeast side of Tuanyushan rock mass. The early Caledonian regional orogeny formed the NNW schistosity zone, and the late Caledonian magmatic intrusion formed the Tuanyushan rock mass. During the Variscan period, with the intense tectonic magmatic activity, the Hongliugou gold mine area formed some small intrusions and dikes, such as near-north-south compressive-torsional fracture structure, ductile-brittle fracture zone, plagiogranite and granite porphyry. The initial magmatic hydrothermal solution is mainly composed of siliceous components, and the milky white time pulse without obvious mineralization is formed along the early near-north-south extensional fault. The further evolution of magmatic hydrothermal solution increases the composition of ore-forming materials and water, and under the action of stress, it permeates along the ductile-brittle fracture zone in the later period, forming a time-dependent gold ore body. At the same time, ore-forming fluid infiltrates into the fractured surrounding rock, causing it to undergo alteration and gold mineralization, forming fractured alteration zone and altered rock type gold ore body. Therefore, the deposit was formed in the Variscan period and is a gold-bearing quartz vein altered rock type gold deposit formed by tectonic magmatism.
2. Hydrothermal gold deposits (including chronological pulse type)
Hydrothermal gold deposits in this area (including the chronological vein type) are mainly formed in the intracontinental orogenic stage, which can form a single deposit or a composite deposit with other types. Only hydrothermal deposits are dissected here.
1. Qingfengling Gold Mine
Qingfengling Gold Mine is located in Tianzhu County, Gansu Province. It was discovered and explored by the sixth geological team of Gansu Province on 1985. Gold deposits occur in Ordovician intermediate-acid volcanic rocks, carbonaceous siliceous slate and Variscan amphibole monzonite, which are controlled by NW-trending faults and NE-trending extensional faults and formed by the superposition of multi-stage hydrothermal solutions. The deposit is located in the north wing of Qingfengling syncline, a secondary fold of Nanshan-Lenglongling anticlinorium in the middle part of Caledonian Island arc belt in North Qilian.
The exposed strata in the area are Ordovician, Devonian, Carboniferous, Permian, Triassic and Quaternary. The Ordovician system extends in northwest direction, forming Qingfengling syncline structure, which is divided into upper and lower groups. The lower formation is a set of shallow-sea clastic rocks, and the upper formation is a marine volcanic rock-clastic rock composed of multi-stage volcanic eruption-sedimentary cycles, which is the ore-bearing stratum of Qingfengling Gold Mine. Devonian is composed of red clastic rocks, Carboniferous is composed of coal-bearing clastic rocks with alternating land and sea, Permian is composed of lacustrine clastic rocks, and Triassic is composed of fluvial clastic rocks and organic sand shale.
Magmatic activities are frequent, mainly Caledonian quartz diorite, granodiorite and plagiogranite, followed by Variscan amphibolite monzonite (308 ~ 290 Ma). Variscan amphibole monzonite is only distributed in Qingfengling area, and intrudes into Ordovician in the form of rock branches along the axis and wings of syncline, which is closely related to gold deposits.
The gold deposit is located in the axis of Qingfengling syncline, and the ore body is controlled by Ordovician marine volcanic rocks, carbonaceous black rock series, amphibole monzonite and NW, NW and ne faults, especially at the intersection of faults. Gold ore bodies mainly occur in altered amphibole monzonite and its peripheral zone, and are strictly controlled by compressive fracture zone, mainly in time-dependent vein type, followed by fractured altered rock type. The mining area is divided into north and south zones. The northern belt is located in the nearly NW-trending compressive structural belt in the altered amphibole diorite, mainly of altered rock type, with an intermittent length of 1 100 m and a width of 20-95 m. There are 17 vein-like and lenticular ore bodies with a length of 25- 155 m. The southern ore belt occurs in time-dependent veins, altered rocks and some surrounding rocks, and is controlled by the NW-trending compressive shear zone in the rock mass, with time-dependent veins as the main type, accompanied by altered rocks. The ore belt extends intermittently, with a length of more than 660m and a width of 30 ~ 65438+50 ~150m. There are 32 ore bodies, which are veined and layered, inclined to the northeast or southwest, with an inclination of 60 ~ 68, lying in the northwest, with a length of15 ~ 31. The ore types are quartz vein type gold deposit and structural altered rock type gold deposit. The mineral composition of the ore includes natural gold, pyrite, chalcopyrite, galena, pyrrhotite and trace magnetite, goethite, ilmenite, tetrahedrite, sphalerite, arsenopyrite, malachite and celestite. Gangue minerals include quartz, barite, calcite, sericite, dolomite and chlorite. The time-dependent vein type gold deposit structure is irregular granular, granular, veinlet-like structure and star-shaped sparse disseminated broken structure; Tectonic altered rock type gold deposits are characterized by authigenic, semi-authigenic, irregular granular structure and massive-sparse disseminated structure. The timely vein gold deposit is rich in gold, with an average grade of 2 1.46× 10-6, the highest is 36×10-6 ~183.3×10-6, and the silver content is 0.5×/6. There are many copper and lead minerals in gold-rich areas, with copper content of 0.0 1% ~ 0.03%, lead content of 0.02% ~ 0.06% and zinc content of 0.00% ~ 0.02%. Generally speaking, the timely vein is rich on both sides, poor in the middle, rich in branch parts of vein body and poor in expansion parts. The gold grade of structural altered rock type gold deposit is/kloc-0 /×10-6 ~ 7.87×10-6, the highest gold grade is 1 1.8× 10-6, and the silver grade is 0.0.
Wall rock alteration is mainly sericitization, carbonation (dolomite and ankerite), pyritization, limonite, kaolin, silicification, partial chloritization and epidote, and gold mineralization is related to silicification, sericitization and carbonation.
The ore-forming materials of the deposit are derived from Ordovician intermediate-basic volcanic rocks and their clastic rocks (the average gold content of intermediate-basic volcanic rocks is 14.8× 10-9, and the local gold content is as high as179.3×10-9 ~ 660×10-9. Variscan magmatic intrusion provided heat, power and some gold sources for the formation of gold deposits (the gold content of amphibole monzonite is 0.3× 10-9 ~ 47× 10-9, and part of it is173./kloc-0 /×10. Therefore, the mineralization of the deposit can be divided into regional metamorphic period and hydrothermal metallogenic period, the latter being the main metallogenic period.
2. Haoquangou Gold Mine
Haoquangou Gold Mine is located in the north of Baiyin City, in the east section of Caledonian in the northern Qilian Mountains. The mining area is located in the northeast of the NW-trending Shiqingdong-Sujiawan regional deep fault (that is, the fault on the southern edge of the northern Qilian Mountains) and the southern edge of the Heishishan volcanic dome. The exposed strata are mainly Cambrian marine acidic-basic volcanic rocks, and the acidic intrusive rock Eryun plagiogranite intrudes into the acidic volcanic rocks as beads. The structure in this area is dominated by faults, mainly east-west compressive faults, followed by north-south compressive faults, which are X-shaped in plane (Figure 3-54).
Three Eryun plagioclase granite bodies are exposed in the mining area, and their distribution direction is nearly east-west, which is consistent with the main fault structures in the area. The rock mass generally contains gold, with an average content of 0. 179× 106, which is 36 times higher than that of vickers acid rock. Faults are developed in the rock mass, in which the north-south faults are large in scale and extend stably, and are filled with loose fault breccia, altered rocks and time veins, generally 0.4 ~ 1.0m wide. This group of faults not only controls ore but also accommodates ore, and the main ore body occurs in this group of faults. Generally, the width of the east-west fault is less than 0.25m, which is mainly filled by the time pulse, and the gold mineralization is unstable. Only a few faults contain gold ore bodies, and other NE and NW faults are post-mineralization faults, which are small in scale and destroy gold ore bodies. Ore-bearing rocks experienced late magmatic autometamorphism and hydrothermal alteration. The former is mainly silicification, muscovization and microcline alteration of rocks, and has nothing to do with gold mineralization. The development degree of hydrothermal alteration is one of the main signs of gold mineralization and mineralization intensity, which is mainly manifested in silicification, muscovite-sericitization (potassium), chloritization, carbonation and pyritization of near-ore rocks, with alteration zoning.
Figure 3-54 Geological Schematic Diagram of Haoquangou Gold Mine
(According to Wang Guangning 1999)
1- Quaternary loess slope deposit; 2- Triassic glutenite; 3- Shi Ying's corner spot; 4- Quartz keratophyre without quartz porphyry; 5 hornblende porphyry with breccia; 6- spilite porphyrite; 7- phyllite; 8- siliceous phyllite; 9- metamorphic sandstone; 10-Eryun plagiogranite; 1 1- granite porphyry; 12- failure; 13- number of ore-bearing rock mass
Orebodies mainly occur in north-south faults and some east-west faults in rock mass, and some gold bodies extend into surrounding rocks. The ore body is strictly controlled by the fault with large dip angle, and it is veined and lenticular, with local expansion and contraction, pinchout and reappearance, with obvious branching phenomenon. About 50 ore bodies in the mining area have been delineated. The length of a single ore body is 45 ~ 125m, the thickness varies greatly, generally 0.2 ~ 3m, the depth is 50 ~ 100m, and the gold grade is generally 3× 10-6 ~ 7× 10-6, the highest. The distribution is extremely uneven, the local grade changes dramatically, and thick and rich ore bodies are often formed at the intersection of faults. The ore type is mainly gold-bearing polymetallic sulfide time-pulse type, which is distributed in the upper part of rock mass; The second type is gold-bearing altered rock type, which is distributed on both sides of the time pulse of gold-bearing polymetallic sulfide and in the fracture alteration zone in the deep part of rock mass. Ore minerals include natural gold, silver-gold ore, pyrite, chalcopyrite, galena, sphalerite, tetrahedrite and so on. Most of gold exists in the form of independent minerals, mainly embedded in the grain boundaries or mineral cracks of metal sulfides, and some of it coexists with galena, sphalerite and chalcopyrite. Sometimes it is produced by polymerization; Gangue minerals include quartz, muscovite, sericite, biotite, chlorite and calcite. In addition to gold and silver, metal elements are accompanied by beneficial components such as copper, lead and zinc, which can be comprehensively recovered. The research shows that the deposit is a epithermal gold deposit, and the ore-forming material comes from rock mass (Wang Guangning, 1999).
3. Danghe South Mountain Gold Mine
Dangheshan gold deposit is located in the Caledonian intracontinental rift zone of Dangheshan in Qilian Mountains. Since 1990s, a number of gold deposits, occurrences and mineralization points have been discovered in this area, such as Heicigou, Jiagongtai, Zhenxingliang and Langchagou. It is characterized by altered rock-type gold deposits related to early Paleozoic Ordovician and Silurian stratigraphic clastic rocks or pyroclastic rocks and chronological vein-type gold deposits occurring inside and outside intermediate-acid intrusive rocks, represented by Heicigou and Jiagongtai gold deposits respectively (Peng Deqi, 1999). See table 3- 15 for their respective metallogenic characteristics.
Three. Metallogenic geological characteristics
According to the above discussion on the metallogenic characteristics of typical structural altered rock-type gold deposits and hydrothermal gold deposits (including chronological vein type), combined with the metallogenic characteristics of other similar gold deposits in the region, it can be seen that for orogenic gold deposits, although the metallogenic geological background, metallogenic age and material source of gold may be different, most of them have experienced strong orogeny and the influence and transformation of tectonic-magmatic activities related to orogeny, so it can be said that the basic conditions for gold mineralization are as follows.
Table 3- 15 Comparison Table of Gold Deposit Types and Metallogenic Geological Characteristics in Danghe South Mountain
Note: According to Yin Xianming et al. (2000) and Chang 'an University. Study on metallogenic regularity, ore-controlling factors and optimization of prospecting target area of Danghebei slope gold-copper deposit in Qilian, Longnan. 2000。
(2000) and other relevant materials.
Provenance: Gold mostly comes from ore-bearing strata (including volcanic rocks) or early formed rock masses. The ore-bearing strata are diverse in lithology and different in ages, including Proterozoic (such as Tanjianshan gold deposit) and Paleozoic, but mainly in early Paleozoic (such as Middle Cambrian, Lower Ordovician and Upper Ordovician volcanic rocks). The rock mass is dominated by basic ultrabasic rocks with high gold background value, forming deposits related to basic ultrabasic rocks, such as Yingzuishan and Longkong gold deposits.
Heat source: Most of the heat sources and power that contribute to the activation, migration and re-enrichment of gold-bearing mineral components are closely related to the tectonic dynamic thermal metamorphism, magmatic intrusion and associated hydrothermal activities caused by the formation of post orogenesis in ore-bearing formations. For hydrothermal gold deposits, intermediate-acid rocks invaded by Caledonian plate subduction orogeny and some Variscan-Indosinian intrusive rocks caused by late intracontinental orogeny (such as the northern margin of Qaidam) are closely related to gold mineralization. According to statistics, more than half of the gold deposits and occurrences in the northern Qilian area occur in the internal and external contact zones between these intrusive rocks and surrounding rocks (Yu Pusheng et al., 2000). Therefore, for rock gold deposits in the whole region, the contribution of intrusive rocks to gold mineralization not only provides a heat source for mineralization, but also provides a mineral source, such as Xi 'an Institute of Geology and Mineral Resources of Ba Laha Tu Gold Mine in Menyuan County and the Second Geological Team of Qinghai Province. Preliminary investigation report on gold deposits in Ba Laha-Tu area, Menyuan county, Qinghai province. 1999。
That is, the ore-forming materials of some gold deposits come directly from magmatic intrusions (such as Jiagongtai Gold Mine). This is the reason why gold deposits or gold bodies are associated with intermediate-acid rock bodies in space.
Space: structural ore control is the most obvious feature of gold deposits in this area. All discovered gold deposits and occurrences are closely related to fault structures (including ductile shear zones, brittle deformation zones and their superimposed ductile-brittle and brittle-ductile structural deformation zones), and deposits are often located at the intersection of NW-trending and NE-trending and N-S-trending structures. Most ore bodies and mineralized bodies occur in the structural fracture alteration zone. These structural zones are not only the channels of circulating convection caused by infiltration of atmospheric precipitation and mixing of deep magmatic hydrothermal solution, but also a good space for upward migration of ore-bearing solution and precipitation and accumulation of gold minerals. Rich ore bodies often exist at the intersection of several groups of faults or fractures.
Due to the above characteristics and conditions of gold mineralization in the metallogenic belt, it is determined that: ① the surrounding rocks of gold in this area are not exclusive, and any strata, rocks and Proterozoic metamorphic marine volcanic rocks can become ore-hosting places. (2) The alteration of surrounding rocks varies with lithology, but the alteration closely related to gold deposits is mainly silicification, sericitization, (iron, magnesium) carbonation and pyritization, followed by arsenopyrite, jarosite and chloritization. (3) Pyrite is the main metal mineral, followed by copper, lead, zinc and other sulfides, and the metal mineral assemblage of some structural altered rock-type gold deposits related to volcanic rocks is relatively complex; The deposit occurs on the side of deep fault or large ductile shear zone and its intersection with NE and NS faults. (4) Mineralization is often multi-stage, so in a mining area, the types of ore deposits are often complex and diverse, often showing that one is dominant and the other is superimposed on it, or both structural altered rock type and hydrothermal type, but hydrothermal type is often later than structural altered rock type. ⑤ The practice of gold prospecting proves that geochemical anomalies generally exist in gold deposits and near ore occurrences, and the abnormal element combinations are generally gold, arsenic, antimony, copper, lead and zinc. , and placer gold is still distributed in the downstream valley.