Taihua rock group is the general name of Precambrian metamorphic basement in Henan and Shaanxi areas, which is mainly composed of metamorphic rock series undergoing amphibolite facies metamorphism, including two genetic rock types, one belongs to the supracrustal rock of stratigraphic system, and the other belongs to the ancient TTG plutonic intrusion undergoing metamorphism and deformation. The ratio of the area occupied by intrusions to supracrustal rocks is about 4: 1. Judging from the rock assemblage characteristics of the whole metamorphic basement, it belongs to granite-greenstone belt assemblage (Hu,1988; Li Junjian et al.,1992; Li Shimei et al., 1994). The Archean granite-greenstone belt in the area is distributed in a narrow-band shape in the east-west direction (Figure 4- 13). The metamorphic basement has obvious double-layer structure, and its lower layer is composed of TTG granite gneiss composed of mafic volcanic rocks of Taihua Group and Jindongcha Formation (also known as Lujiayu Formation), which is a set of plagioclase amphibolite with irregular and banded inclusions distributed in TTG gneiss. The upper layer is a set of metamorphic sedimentary rocks rich in magnesium and aluminum. The main rock types are biotite granulite, garnet-bearing siliceous granulite, graphite-bearing granulite, quartzite, granulite, marble and magnetite quartzite. Its original rocks are felsic volcanic rocks, pyroclastic rocks and sedimentary rocks, which have the characteristics of Kunzite series combination. The lower layer is located in the axis of Xiaoqinling, and the upper layer is distributed on the north and south sides of Xiaoqinling area. Gold deposits in this area, especially large-scale gold deposits, are mainly distributed in the Lower Taihua Group composed of amphibolite and gneiss. Oblique amphibolite is the main rock type of Taihua Group, which is layered, banded and lenticular, with a few irregular occurrences. Single layer is 0.5~30m thick and often occurs in Archean TTG gneiss or interbedded with granulite in the form of inclusions. The hemp direction of the slice is consistent with TTG. Its protolith is continental tholeiite (Shen Baofeng et al., 1994 b) with mantle-derived characteristics. TTG gneiss belongs to Archaean plutonic intrusive rocks (Li Shimei et al., 1996), and the rock types are biotite plagioclase gneiss, biotite plagioclase amphibole gneiss, amphibole biotite plagioclase gneiss and granite gneiss. Its original rocks are mainly augite, tonalite, granodiorite and a small amount of granite, and TTG magma comes from partial melting of tholeiite. The Taihua Group in Xiaoqinling was formed between 2500 and 2980 Ma, belonging to Neoarchean, and its metamorphic age was 235 1 103 Ma (Li Shimei et al., 1996).
The fault structures in this area are well developed and are the main ore-controlling structures in this area, including east-west, northeast, north-south, northeast and northwest faults. The east-west fault is mainly compressive and shear-compressive, and mylonite and fracture zone are developed in the fault, which is the main ore-controlling structure in this area. The ore bodies developed along this group of faults are vein-like, lenticular and goose-like. The NE-trending fault is mainly shear, with both tensile and/or compressive shear, and it is an interlayer sliding shear fault, in which the gold ore bodies are lenticular and veined. The N-S, N-E and N-W faults are tensile and shear, and the scale of faults is generally small, and the shape is often serrated, which is one of the main ore-controlling structures in the area.
Figure 4- 13 Geological Schematic Diagram of Gold Deposits in Xiaoqinling Area
1- Mesoproterozoic; 2- Middle marble-calcium silicate assemblage in khondalite series, Upper Taihua Group; Middle Moyan plagioclase gneiss-granulite assemblage in khondalite series, Upper Taihua Group; 4- Granitic gneiss with basic xenoliths; 5-Middle quartzite-graphite siliceous biotite gneiss assemblage in khondalite series, Upper Taihua Group; Lower Taihuaya Group 6- plagioclase amphibolite-gneiss assemblage; 7- granite; 8- pegmatite granite; 9- biotite (amphibole) adamellite; 10- gold deposit
Magmatic activities in this area are long-term and multi-stage, and the formation time span is very large. It can be roughly divided into: ①TTG gneiss, an ancient plutonic intrusive body that has undergone metamorphism and deformation, mainly formed in Neoarchean (Zhang et al.,1996; Kroner et al., 1988), the age of Wulipu adamellite in Dengfeng is 2604±4Ma, and the age of Yingyun gneiss in Lushan Mountain is 2906±7Ma to 284 1 6Ma, which is equivalent to the isochron age of Sm-Nd amphibolite in Taihua Group. Lu Songnian et al. (1997) determined the U-Pb age of biotite granite in Jindongcha mining area, Lingbao Gold Mine, Henan Province by single zircon U-Pb method, indicating that there was TTG magmatism in Paleoproterozoic. ② pegmatite granite (granite pegmatite vein) is widely distributed in this area, and it is injected into TTG gneiss in vein or irregular shape, in which zircon U-Pb age is1806 3ma (Lu Songnian et al., 1997), which is another early thermal tectonic event after TTG magma intrusion and is a secondary metamorphism in this area. (3) Diabase occurs in veins and is widely distributed, with a length of more than 200 meters, up to several kilometers and a thickness of about 2 meters. The surface age of zircon U-Pb is 498.7±7.5ma, and the intrusion time is Caledonian. ④ Yanshanian adamellite mainly refers to rocks distributed in Huashan, Wenyu and Niangniangshan. The age range was 100 ~ 130Ma(K-Ar method) and 72.5 ~ 179.6 Ma (Rb-Sr method). (5) Veins, mainly syenite porphyry, adamellite porphyry, quartz porphyry, diabase vein, lamprophyre vein and chronological vein. , formed in Neoarchean-Mesozoic.
Magmatic activity is of great significance to the formation of gold deposits. Early magmatism promoted the initial crustal activation and transformation, enriched the ore-forming elements in the Precambrian metamorphic basement and even formed gold deposits. In the later period, especially during the Yanshanian granite intrusion and the formation of metamorphic core complex, gold was re-enriched.
Gold deposits in the southern margin of North China landmass are mainly distributed in Xiaoqinling area. Up to now, more than 200 gold-bearing quartz veins 1200 have been found, mainly distributed along the back fold axis in Yangzhaiyu-Wenyu ore belt, followed by Dahuyu-Linghu ore belt, and a small amount in Jinqugou area in the middle of the mining area. Judging from the occurrence and spatial relationship of ore bodies, the occurrence of ore bodies has the following characteristics: ① The distribution of gold-bearing quartz veins in ore fields is extremely uneven, mainly in groups or belts. Gold-bearing quartz veins vary in size, ranging in length from tens of meters to thousands of meters, with a thickness of 0.3 ~ 2m, the thickest reaching 7.7 1m, the depth ranging from 100 ~ 500m and the deepest reaching 8 10m. ② Gold-bearing quartz veins mainly occur as single veins, with some phenomena of expansion, contraction, branching and compounding. The ore bodies are vein-shaped, lenticular, thin-plate and pod-shaped. ③ The occurrence of gold-bearing quartz veins is strictly controlled by ductile shear zones, closely related to mylonite, and their spatial distribution is basically parallel.
Gold-bearing quartz veins are concentrated in the amphibole-gneiss assemblage of the metamorphic basement structure in the lower layer of Taihua Group, and are the main ore-bearing strata of gold deposits. There are few gold veins in the metamorphic basement of Upper khondalite series. There are two types of gold-bearing quartz veins, pyrite-type quartz veins and polymetallic sulfide quartz veins, and the former is dominant. The gold minerals in the ore are mainly natural gold, silver gold ore and a small amount of tellurium gold ore. Metal minerals are mainly metal sulfides, accompanied by a small amount of metal oxides and tellurides, of which pyrite has the highest content, followed by galena, chalcopyrite and sphalerite. Gangue minerals are mainly chronological, with a small amount of calcite, dolomite and ankerite. Ore structures mainly include self-shaped, semi-self-shaped and special-shaped structures, metasomatic structures and filling structures. Ore structures are mainly banded, massive, veinlets, disseminated, variegated, breccia, crystal cave and honeycomb. There are four metallogenic stages: pyrite-isochronous stage, isochronous-pyrite stage, isochronous-polymetallic sulfide stage and isochronous-pyrite-carbonate stage.
The alteration of surrounding rock, viewed from the transverse vein, changes from strong to weak from ore body to surrounding rock, and there is often obvious zoning phenomenon, which can be divided into strong alteration zone, medium intensity alteration zone and weak alteration zone. Pyrite sericitization mainly occurs in the strong alteration zone, including pyritization, silicification, chalcopyrite and carbonation. The moderate alteration zone is represented by blue rocks and sericitization, while the weak alteration zone only has blue rocks.
The metallogenic age of Xiaoqinling gold deposit has always been controversial. From the analysis of the main characteristics of gold deposit formation, firstly, it occurs in the ductile shear zone in the granite-greenstone belt without exception, and the gold-bearing quartz vein is often closely produced with the Lvliang granite pegmatite vein belt. Secondly, the hydrogen and oxygen isotopic composition of the timely xenolith water in the gold-bearing quartz vein shows that its ore-forming fluid is between metamorphic water and magmatic water, and the gold deposits in the area are all distributed outside the Yanshanian Niangniangshan granite body. The ore-controlling ductile shear zone of metamorphic basement in this area was formed in1768 25.3 Ma (K-Ar method, Li Shimei et al., 1996), and the isotopic ages of Niangniangshan granite, Wenyu granite and Huashan granite in Yanshanian period were130 ~100 Ma (. The previous period was about 65.438+0.8 billion years. During the formation of ductile shear zone, ore-forming hydrothermal solution migrated along ductile shear zone. In the favorable part of the structure, due to the changes of physical and chemical conditions such as redox, the stability of gold chloride complex is destroyed and the ore is enriched. In the late Yanshanian Mesozoic, due to collision orogeny, the granite-greenstone belt was remelted in the deep crust to form Yanshanian Wenyu rock and Niangniangshan rock. After collision orogeny, metamorphic core complexes and gold deposits were formed under the extensional system. Late mineralization may be the superposition and enrichment of early mineralization.
Taking Wenyu, Yangzhaiyu and Dongchuan gold deposits as representatives, the characteristics of gold metallogenic areas (belts) in the southern margin of North China are further analyzed.
1. Wenyu Gold Mine
Wenyu gold deposit is a large gold deposit in the southern margin of North China block (with a reserve of 32.7 19t), which is mainly distributed in amphibolite-gneiss in the metamorphic basement of Lower Taihua Group (Figure 4- 14). TTG granite is widely distributed in this area. As a supracrustal rock series, amphibole exists in TTG granite as inclusions with different sizes.
Figure 4- 14 vein distribution map of Wenyu Gold Mine
1-TTG gneiss; 2- gold vein and its number
The fold structure in the mining area is mainly Laoyacha anticline located in the north, with an axial direction of 270 west and 300 east, a dip angle of 30-60 in the north wing, 50-70 in the south wing and 80 in the local area. This anticline controls the distribution of gold-bearing quartz veins in the mining area. The fault structures in this area are divided into three groups according to strike: ① The near east-west compression-torsion fault structure belt, with strike of 270 ~ 3 10, bends with the axial change, inclines to the south, with dip angle of 37 ~ 55, and is mostly filled by time pulse, which is generally large in scale and extends for thousands of meters. It is the main ore-controlling structure in this area, such as veins 505, 565 and 438+02. ② The NE-trending tension-shear fault zone tends to the west, such as vein 5 19. (3) NNE and NNW faults, mainly shear faults, are generated by * * * yoke. Its dip angle is steep, mostly above 60 degrees, extending about 500 meters, and its thickness is 0.2 ~ 0.5 meters. Most of them are filled with diabase, and some of them are filled with time pulse.
Magmatic rocks are mainly dike rocks, strictly controlled by faults, widely distributed and varied. Mainly basic dikes, mainly diabase, followed by pegmatite, a small amount of alkaline granite porphyry and syenite porphyry.
More than 70 large and small veins have been discovered in Wenyu mining area, among which 7 veins strike more than 1000 m, 9 veins strike 500 ~ 1000 m, 33 veins strike 100 ~ 300 m, and 30 veins strike less than 100 m.. The compressive shear layer parallel to the axis of anticline controls the most NW-trending veins, which have many industrial values, such as 505, 5 12 and 5 19 veins. Veins controlled by NNE and NNW extensional faults are few in number and small in scale, but high in grade, such as vein 509.
Generally speaking, the distribution of veins has the following characteristics: ① veins are distributed in the TTG granite-dominated zone in the north. ② Most veins are located in the south wing of Laoyacha anticline, 20 ~ 1200m away from the axis of the anticline. Outside this area, there are many gold-bearing quartz veins with no industrial value. ③ Gold-bearing quartz veins are strictly controlled by NW-trending and SW-trending compressive and torsional faults. (4) According to the distribution characteristics of gold-bearing quartz veins in the mining area, there are fewer in the east and more in the west, and they retreat to the east and converge to the west. ⑤ From north to south, mineralization changed from polymetallic mineralization to pyritization.
No.505 vein is the largest and most important vein in Wenyu mining area, in which gold reserves account for more than 70% of the whole mining area, and the exposed length of the surface is 4,200m, starting from Daxiyugou west in the west and extending eastward to Dongchuang mining area, in which the length of industrial ore body is 3170m, and the largest ore body is 360m. The maximum extension depth of the ore body is 900 meters, and the vertical depth is 84 1 meter. The mineralization type is mainly polymetallic mineralization, and the gold grade of ore body is high, with an average grade of12.85 ~16.78 g/t.
The metal minerals in the ore are mainly galena and pyrite, followed by chalcopyrite and sphalerite, and the trace minerals are magnetite, siderite, pyrrhotite, wolframite, scheelite and natural gold. Gangue minerals are mainly timely, with a small amount of calcite, ankerite, barite and sericite. Supergene minerals include limonite, malachite, sky blue, lead and vanadium, jarosite and so on. , but the latter is not developed. Ore structure: The ore structure mainly includes authigenic-heteromorphic granular structure, metasomatic texture and crumpled structure, in addition, there are emulsion-drop structure, net structure, broken block structure, variegated structure and lattice structure. Ore structures mainly include massive structure, reticulate vein and cloud structure, banded structure, symmetrical banded structure and disseminated structure. In addition, there are cave filling structures, dendritic structures and honeycomb structures in some areas, among which block structures are the most common, followed by reticulated veins and cloud structures. There are four types of ore: pyrite type ore, polymetallic sulfide type ore, mineralized country rock type ore and oxidized ore (undeveloped in this area). There are three metallogenic stages: pyrite-isochron stage, isochron-pyrite stage and polymetallic sulfide stage.
The surrounding rock near the mine is strongly altered, and three alteration zones can be divided outward from the ore body, and the alteration width is 0.5 ~ 2m m. The types of wall rock alteration include sericitization, pyritization, silicification, carbonization, biotite, potash feldspar and chloritization.
2. Yangzhaiyu Gold Mine
Yangzhaiyu gold deposit is a large gold deposit with a gold reserve of 34.311t. It is distributed in the metamorphic basement of Taihua Group and consists of two kinds of rocks, one is the supracrustal rock dominated by amphibole, and the other is the deformed TTG plutonic intrusion. The former exists in the latter as inclusions with different sizes and shapes.
There are east-west folds and fault groups with different directions and properties in the mining area.
Fold structure: Laoyacha anticline in the east-west direction runs through the whole area, with the axis of the anticline inclined to the north, the dip angle of the north wing is 20 ~ 30, and the dip angle of the south wing stratum is 30 ~ 70, which constitutes an asymmetric anticline with gentle north and steep south. The anticline controls the spatial distribution of the main gold veins in the area.
Fault structure: there are many groups of faults in the area, such as near east-west, north-south and northeast.
There are 27 east-west faults along the axis of the anticline, with strike of 265 ~ 305, trending NNE or SW-SW, north dip angle 10 ~ 25, and south dip angle of 45. This group of faults is generally large in scale and extends far, and is the main ore-controlling fault. Other groups of faults have experienced multiple composite superposition, including mineralization and basic dike filling.
Magmatic activities are frequent in this area, and magmatic rocks of different ages, scales and shapes are distributed. According to their formation, there are mixed pegmatite, biotite granite, pegmatite, gabbro, gabbro porphyrite, diabase, granite fine-grained rock, chronological vein, Yunhuangyan and so on.
Gold-bearing quartz veins are mainly distributed intermittently along the near-east-west compressive-torsional fault structural belt. The largest pulse is No.60, followed by No.212, No.213, No.201,No.202, No.203, No.301. The strike length of No.60 gold vein is more than 4,200m, the thickness is about 7m, and the thickest part reaches 20 m. * * * is composed of 15 ore body, and its gold reserves account for 84.438+0% of the whole mining area. There are six large-scale ore bodies, among which the No.3 ore body is 740m long, with a maximum dip angle of 528m, an average thickness of1.26m and an average grade of15g/ton, making it the largest ore body in the whole region. The west section 1 orebody is 6 10m long, with a maximum dip angle of 339m, an average thickness of 1.87m and an average grade of 12.68g/t, making it the second largest orebody in the mining area.
The ore bodies are irregular, lenticular and banded, and the shape of individual ore bodies is complex. The distribution trend of ore bodies is high in the west and low in the east, inclined to the south and east, and inclined to the south and west along the dip, with an inclination of 37 ~ 50.
There are more than 30 kinds of metal minerals in the ore, the main metal mineral is pyrite, followed by chalcopyrite, scheelite, galena and sphalerite. Besides natural gold, trace minerals include natural silver, argentite and more than ten kinds of tellurium minerals. The secondary minerals are limonite, sky blue, malachite, lead and vanadium, but the content is very small. It is the main nonmetallic mineral, followed by calcite, dolomite and barite. The ore structure includes medium-coarse autogenous-semi-autogenous granular structure, medium-fine autogenous-semi-autogenous granular structure, fine autogenous granular structure, filling structure, inclusion structure, broken structure, porphyritic structure and staggered residual structure. Ore structures include banded structure, massive structure, disseminated structure, star structure, variegated structure, veinlets structure and honeycomb structure. The deposit can be divided into three metallogenic stages: pyrite-isochronous stage, isochronous-pyrite stage and carbonate isochronous stage. Ores can be divided into primary ore and oxidized ore according to their genesis, among which primary ore can be divided into pyrite ore, polymetallic sulfide ore and gold-bearing structural rock (mineralized surrounding rock type) ore. The number of oxide ores is small, accounting for only 2% of the total.
Natural gold is the main gold mineral in the deposit, and its forms are equigranular, thin-film, banded and veinlets. The maximum particle size is 1mm, and the minimum particle size is 0.000 1mm, mainly fine gold. Natural gold is filled in the cracks and intergranular spaces of pyrite, or embedded in the timely manner in granular and irregular forms. The purity of natural gold is very high, ranging from 860 to 960.
Wall rock alteration is generally silicification, sericitization, pyritization, carbonation and their combinations, with epidote, chloritization, potash feldspar and albitization in some areas, and the most typical and closely related to mineralization is pyrite sericitization.
3. Dongchuang Gold Mine
Dongchuang gold deposit is located in the middle of Xiaoqinling gold belt. Nanchuangou is adjacent to Wenyu Gold Mine in the west and Laoyacha Gold Mine in the east of Chang 'ancha. The area is about 5km2. The deposit is large in scale with a reserve of 27.642t (Gold Command of Chinese People's Armed Police Force, 1997).
The strata exposed in the mining area are mainly Archean Taihua Group medium-deep metamorphic rock series, which is a set of metamorphic volcanic-sedimentary rock series and invaded by TTG rock series. Its rock assemblage is similar to Wenyu and Yangzhaiyu gold deposits, so I won't go into details here.
Dongchuang mining area is located in the south of Laoyacha anticline, which is a part of Laoyacha anticline. There is a "syncline" with steep occurrence of two wings in the south of the mining area, with an overall strike of nearly 300, with a dip angle of 45-60 in the north wing and 60-80 in the south wing. The dip angle of strata near the wellbore is about 100m, which is greater than 80, and the surface of the wellbore is nearly vertical and slightly inclined to the north. The axial direction of the secondary fold is NWW, which is consistent with the regional stratigraphic foliation trend. In addition, due to the replacement of foliation, a large number of rootless small folds are common in gneiss.
The fault structure in the mining area is developed and divided into two types: pre-mineralization and post-mineralization. According to the occurrence, the pre-metallogenic structures can be divided into three groups: NWW, NNW and NNE. Among them, NWW faults are divided into early brittle faults and late shear zone faults, which are important ore-controlling faults in the mining area. After mineralization, the fault activity is generally weak, and the fault after mineralization has no obvious damage to the ore body.
The magmatic activity in Dongchuan mining area is relatively strong, including the intrusion of Taihua Group granite and TTG magma, which constitute the crystalline basement of this area, and the intrusion of various dikes in the later period. Magmatic thermal events play a very important role in the activation and enrichment of gold.
Dongchuang Gold Mine consists of more than 20 veins, mainly 507 veins, of which 507, 504, 503, 505, 50 1, 502 and 540 veins are of industrial significance. Veins are strictly controlled by ore faults, and nearly east-west veins account for more than 95% of the total number of veins, and some of them are NNW veins.
The vein (vein No.507) of the near east-west formation is 5000m long and 200m short, generally1000 ~ 2000m ... The maximum thickness of the vein is 13. 14m, and the minimum is only a few centimeters, generally tens of centimeters to 2m. The vein of NNW Formation is a 5 17 vein, with strike length of 520m and thickness of 0.16 ~ 0.33m, generally 0.25m. For the east-west vein, it is characterized by gentle wave-like and wave-like bending along strike and dip, vein branch compounding, expansion and contraction, and pinchout reappearance. The vein strike is 260 ~ 280, and it tends to the south. Some small veins tend to the north with an inclination of 30 ~ 60. The NW-trending veins are thin-plate and lentil-shaped, and occur intermittently in mylonite and cataclastic rocks on the upper wall of diabase. The veins are gentle, wavy and swollen obviously. The NNW pulse (5 17 pulse) runs 330 ~ 350, generally 345, and tends to the northeast, with an inclination of more than 70, mostly around 78.
There are more than 30 kinds of minerals in the mining area: natural gold, silver-gold mine, gold-silver mine, tellurite mine, tellurite mine and tetrahedrite; Lead minerals include galena, galena, galena, lead and vanadium; Iron minerals include pyrite, pyrrhotite, white iron ore, magnetite, siderite and limonite; Copper minerals include chalcopyrite, chalcocite, bornite, tetrahedrite, malachite and sky blue; There are scheelite, wolframite and sphalerite. Gangue minerals include quartz, chlorite, biotite, sericite, potash feldspar, calcite, dolomite and ankerite. The total amount of metal minerals in ore accounts for 25% ~ 30% of the total amount of ore minerals, among which metal sulfides are the main ones. The ore structure includes autogenous-semi-autogenous granular, semi-autogenous-abnormal granular, crushing-crushing, metasomatic residue, inclusion, emulsion drop, filling and ring structure. The structure is irregular block, strip, reticulate vein, disseminated and breccia. The ore types include pyrite-bearing gold ore, polymetallic-bearing gold-lead ore, bearing gold-lead ore, altered rock-bearing gold-lead ore, mylonite-bearing gold-lead ore and so on. * * * is divided into four metallogenic stages: coarse pyrite-isochronous stage, fine pyrite-isochronous stage, polymetallic sulfide-isochronous stage and carbonate-isochronous stage.
The fineness of natural gold varies greatly, generally between 360 and 980. The occurrence state of natural gold is intergranular gold, fissure gold and inclusion gold. Intergranular gold accounts for 53. 1%, fracture gold and inclusion gold account for 3 1.7% and 15.2% respectively.
The types of wall rock alteration are potash, sericitization, chloritization, silicification, carbonization, magnetite, hematitization, pyrite, biotite, epidote and sodium zoisite.