Danchi ore belt

Publish: 2021-05-22 23:31:09

Nandan Hechi tin polymetallic metallogenic area is a famous tin polymetallic metallogenic belt in China. It is mainly located in MANGCHANG Hechi Wuwei area of Nandan. It is located in the junction zone of Youjiang regenerated geosyncline and Guizhong depression in geotectonics. It is NW-SE trending and controlled by Ziyun Nanning Regional large fault zone. The main exposed strata are Devonian, Carboniferous, Permian and Triassic, and the main lithology is carbonate rock and clastic rock. Among them, a set of turbidite is developed in the middle and Lower Devonian, while reef limestone, siliceous rock, quartz and other exhalative rocks occur in the middle and Upper Devonian

There are NW trending basement faults and nearly Sn trending fault block structures in the area; The cover structure is dominated by the NW trending Danchi anticline and Nandan Kunlunguan fault. The fold shape is generally tight, narrow and long, arranged in echelon, with linear fold characteristics. Five short axis anticlines formed by the superposition of NE trending structures control the distribution of Mayang, MANGCHANG, Dachang, BEIXIANG and furongchang ore fields respectively

the magmatic rocks in the area are mainly Yanshanian intermediate acid hypabyssal rocks with Longxianggai rock body, and sporadically distributed in MANGCHANG area in the north as batholith, batholith, dyke and dike. Rock types include granite porphyry, quartz porphyry, diorite porphyry, quartz diorite, quartz andesite porphyry, etc. According to the gravity anomaly, there are concealed rock bodies in Wuwei area in the south. The rocks are distributed in beaded shape on both sides of the Danchi fault, or intrude into the axis of the Danchi anticline, MANGCHANG anticline and Dachang anticline

1:200000 stream sediment survey results show that tin, copper, lead, zinc, silver and other elements have good anomalies, and 6 comprehensive anomalies are delineated, including 3 known ore anomalies and 3 unknown ore anomalies. The anomalies are mainly distributed in Danchi large fault zone and Bama fault zone, and the strike of anomalies is basically consistent with the strike of faults, which is obviously controlled by faults. The anomalies distributed in Danchi large fault zone are closely related to tin polymetallic deposits, with long axis shape, obvious concentration center and outer, middle and inner concentration zoning. The content characteristics of each element abnormal concentration area: the content of tin is more than 70% × 10 - 6 , copper (57-166) × 10 - 6 , Pb > 220 × 10 - 6 , Zn > 469 × 10 - 6 , silver greater than 859 × 10^-9

There are many kinds of mineral resources in this metallogenic area. There are 11 large-scale deposits (Changpo Tongkeng and Bali Longtoushan tin polymetallic deposits reach super large scale), 7 medium-sized deposits and 9 small-sized deposits, which are mainly distributed in MANGCHANG, Dachang and Wuwei ore fields. The preliminary statistics show that the accumulated proven reserves of tin are 125 × 10 4 t, lead zinc 780 × 10 4 t, Sb 130 × 10 4 t, copper 33 × 10 4 t, tungsten 18 × 10 4 t, silver 8000t. The prospecting potential is huge

Dachang tin polymetallic deposit is one of the most important tin polymetallic deposits in the world, which is located in the south of Danchi ore concentration area in Northwest Guangxi. Due to its large scale, complex element combination and diversified occurrence characteristics, Dachang tin polymetallic deposit has been highly valued by the geological circles at home and abroad for a long time, and has been a hot spot in the study of deposit geology. Up to now, there are still different views on the genesis of Dachang tin deposit, which can be divided into three categories: 1. It is considered that the deposit was formed in Yanshanian, belonging to epigenetic metasomatic filling deposit, which is genetically related to granite (Chen Yuchuan, 1964, 1965; 2; Chen Yuchuan et al., 1985, 1993; Li Xilin et al., 1981; Zhang Ping, 1983; Ye Xusun, 1985, 1986; Liang Zhenting et al., 1985). Especially in the 1990s, Chen Yuchuan et al. (1993, 1996) and Wang denghong et al. (1996) systematically studied the genesis of Dachang tin deposit, clearly pointed out that the mineralization was mainly magmatic hydrothermal metasomatism along the strata, and systematically studied the metasomatism along the strata of 91 # orebody and 92 # orebody and lamellar granite in Lamo mining area, The metallogenic model was established and the metallogenic series were determined (Chen Yuchuan et al., 1985, 1993, 1996); ② It is considered that the deposit was formed in Devonian, belonging to syngenetic sedimentary exhalative deposit or marine volcanic origin, and has nothing to do with granite in Genesis (CAI Hongyuan et al., 1983; Han FA et al., 1997; Qin Dexian, 2002); ③ Sedimentary hydrothermal superimposed mineralization suggests that Pb, Zn and pyrite may be derived from strata and Sn from granite (Zeng Yunfu et al., 1982; Tu Guangchi, 1984, 1987; Chen Jun, 1988; Ding tiping, 1988)

one of the focuses of the above arguments is the age of mineralization. Early predecessors used RB Sr and K-Ar dating methods to determine the ages of fine-grained granite exposed in the mining area, potash feldspar altered rock in the early mineralization stage of Tongkeng mining area, and illite formed in the middle and late stage of ore crystal cavity (Xu Wenxin et al., 1986; Xu Wenxin et al; Chen Yuchuan et al., 1993), whose ages range from 91 Ma to 138.6 Ma, indicate that the mineralization occurred in the Yanshanian period and was basically contemporaneous with the Longxianggai granite, which indicates that there is an internal genetic relationship between the mineralization and the Yanshanian granite. In recent years, we have done a lot of work on geochronology and obtained a lot of new data:

1) Wang denghong et al. (2004) studied the diorthosite in 91 # layered ore body of Tongkeng Changpo deposit in the west ore belt of Dachang orefield and 100 # layered ore body of Longtoushan deposit Conventional fast neutron activation and laser in situ 40 AR / 39 Ar dating of quartz show that the 40 AR / 39 ar plateau age of quartz in massive cassiterite sulfide ore of 91 # orebody is 94.52 ± 33 Ma, isochron age 95. 37 ± 45 Ma, with an inverse isochron age of 94. 89 ± The laser 40 AR / 39 ar isochron age of diorite is 91.4 ± 2.9Ma; The plateau age of quartz in 100 # orebody is 94.56 ± 45 Ma, isochron age 93. 5 ± 2 mA, the reverse isochron age was 93. 29 ± 0.16Ma;

Recently, Chen Yuchuan, Li Huaqin and Wang denghong have systematically studied the isotopic geochronology of quartz in cassiterite sulfide ores and granites related to mineralization in three metallogenic belts of Dachang tin polymetallic ore field, Guangxi Province (the methods used include 40 AR / 39 ar fast neutron activation method, 40 AR / 39 ar fast neutron activation method,

2) The 40 AR / 39 ar plateau ages of Cassiterite from dafuluu and Kangma cassiterite sulfide deposits in the eastern ore belt are 119 ± 21 Ma and 114. 7 ma ± 2Ma; The RB SR isochron age of quartz mineral fluid inclusion of ore bearing quartz vein in Lamo Cu Zn deposit of middle ore belt is 100.5 ± The RB SR isochron age of quartz fluid inclusion in chashanao w-sb deposit vein is 44.4 MA (95% confidence) ± The 40 AR / 39 ar plateau age of quartz is 54.7 ± 1.5Ma; The 40 AR / 39 ar plateau age of cassiterite in the middle section of Tongkeng 405 in the west ore belt is 127.8 ± 3Ma; The whole rock RB Sr and zircon U-Pb ages of the cage cover porphyry biotite granite exposed in the middle 530 section of Lamo mining area are 98.6 and 98.6, respectively ± 3mA (95% confidence) and 94 ± 4mA (95% confidence)

3) recently, Liang Ting, Wang denghong, Qu Wenjun and others, with the support of the crisis mine project, have further carried out the Re Os isochron and other new methods of metallic minerals such as pyrite, molybdenite, arsenopyrite, etc., and achieved new results

The samples used for isotopic geochronology were collected from the cassiterite pyrrhotite veins of dafuluu and Kangma deposits in the east ore belt of Dachang orefield; The porphyry biotite granite in Longxianggai biotite granite, quartz in ore bearing quartz vein of Lamo copper zinc deposit and ore bearing quartz vein of chashanao tungsten antimony deposit in Lamo mining area are exposed in the tunnel of 530 middle section of Lamo mining area in middle ore belt; Cassiterite in 91 # orebody occurs in the middle section of Tongkeng 405 in the west ore belt. According to the conventional mineral separation method, pure zircon is separated from granite, cassiterite and quartz are separated from ore, which can also be used for isotopic age determination. In addition, Liang Ting et al. Completed the age determination of arsenopyrite and pyrite in Tongkeng 92 # orebody, and the results show that the Re Os isochron age of arsenopyrite is 89 ± The Re Os isochron age of some pyrite data is 122 ma ± 44Ma

Analysis method

1) zircon U-Pb dating. Zircon samples were collected from the biotite granite in Longxianggai in the field, and zircon samples were separated from the granite in the laboratory. Then zircon samples with good crystal form were selected and pasted on the surface of epoxy resin with standard zircon (TEM) under binocular lens, polished and gilded. Before shrimp isotope analysis, transmission light and reflection light micrographs of zircon samples were taken. In situ U-Pb isotopic analysis of zircon was performed on shrimp-ii ion probe of Beijing ion probe center. The results were corrected for uranium content and age with reference materials

(2) Rb Sr isotopic dating of fluid inclusions in quartz. The RB SR isochron age of quartz minerals was determined by the analytical procere reported by Li Huaqin et al. (1993); RB and Sr isotopic analysis was performed on the MAT-261 adjustable multi receiver mass spectrometer in the Isotope Laboratory of Yichang Institute of Geology and mineral resources, Ministry of land and resources; In the process of analysis, nbs-987 was used to monitor the state, and nbs607 and gbw04411 were used to monitor the process. The above standard values were: nbs987, 87 Sr / 86 sR = 0.71026 ± 0.00006; NBS607，Rb/10^-6=523.22，Sr/10^-6=65.56，⁸⁷Sr/⁸⁶Sr=1.20035 ± 0.00009; GBW04411:Rb/10^-6=249.08，Sr/10^-6=158.39，⁸⁷Sr/⁸⁶Sr=0.76006 ± 0.00009; 87 Rb / 86 Sr and 87 Rb / 86 SR are better than 1.5% ～ 3% (quartz mineral) and 0.008% ～ 0.02%. All operations are carried out in the purification laboratory. The utensils used are made of fluoroplastics, quartz or platinum. After sub boiling distillation, the RB SR blank was 10 - 11 - 10 - 12 G / g. The high purity water was purified by milli-q water purification system, and the blank values of Rb and Sr were 10 - 12 G / g; The blank of the whole process was about 0.3ng. When the content of Rb and SR was less than 10 - 6 , the blank was corrected. RB SR isochron data were processed by isoplot program compiled by Ludwing (2001)

(3) ar fast neutron activation dating of cassiterite. It has been reported that cassiterite can be used to directly determine the age of ore deposits. B. The U-Pb and Pb isotopic dating of Cassiterite from the wuliyan tin deposit in Indonesia and the zaaiplaats deposit in South Africa by L. gulson and M. T. Jones (1992) shows that cassiterite, as an ore mineral, has more advantages than rutile and zircon in direct dating of ore deposits, but the 40 AR / 39 ar fast neutron activation dating of cassiterite has not been reported so far, In this paper, we tried to determine the age of cassiterite 40 AR / 39 AR, and achieved initial success. The cassiterite samples studied were heated by the fast neutron activation method of 40 AR / 39 ar. the analytical method used is reported by Liu Yimao et al. (2002). Ar ar isotopic analysis was performed on mm1200 noble gas mass spectrometer in Isotope Laboratory of Guilin Institute of mineral geology. The vacuum degree of the instrument is about 2 × 10 - 7 PA, 10 - 14 mol for 40 AR, 10 - 16 mol for 36 AR, 37 AR, 38 AR and 39 ar. The sample was cooled by fast neutron irradiation for about 120 days and then put into the all stainless steel ultra-high vacuum extraction purification system. The sample was heated together with the system at 250 ℃ and roasted to remove gas. After cooling, the vacuum degree reaches 10 - 8 - 10 - 9 PA. The samples were heated by electron bombardment furnace, and the gas was purified by sponge titanium, evaporated titanium and Zr al degassing pump. Finally, the Ar isotope peaks were determined by X-ray mass spectrometry. The interference Ar isotope inced by nuclear reaction is corrected by the Ar isotope proced by irradiation of pure potassium and calcium salts. The K-Ar age biotite reference material (132.5ma) was used to calculate the stage age and plateau age of the samples

(2) test results and interpretation

1. Metallogenic age determination results of the east ore belt

the cassiterite of cassiterite pyrrhotite vein in dafuluu and Kangma tin sulfide polymetallic deposits in the east ore belt of Dachang ore field was 40 AR / 39 ar. the results are shown in table 2-1, Figure 2-1, table 2-2 and figure 2-2. The plateau age spectra of cassiterite in dafuluu and Kangma tin deposits show normal flat type spectra, and the 39Ar precipitated at most stages of temperature rise are in line with the plateau forming conditions. The plateau age of 2-4 stages (750-1050 ℃) of the two samples is 119.7 ± 2mA and 114.7% ± The plateau age of the two is similar to that of the corresponding melting age (120 mA) ± 5mA and 115.4 ± 5mA) in the range of measurement error. This shows that the age data obtained from the heating up of 40 AR / 39 AR in the fast neutron activation stage are basically reliable, and it is inferred that the formation age of dafuluo and Kangma cassiterite sulfide polymetallic deposits in the east ore belt of Dachang ore field is early Cretaceous

Table 2-1 cassiterite 40 AR / 39 ar stage heating dating data of dafuluu cassiterite sulfide deposit in Dachang ore field

test: Dai Tongmo and Chen minyang of Guilin Institute of mineral geology, sample weight 0.3992g, j = 0.0040885, Ping age 119.7 ± 2mA, full melting age 120 ± 5Ma

Table 2-2 temperature rising dating data of cassiterite 40 AR / 39 AR in Kangma cassiterite sulfide deposit in Dachang orefield ± 2mA, full melting age = 115.4 ± 5Ma

Fig. 2-1 ar ar age spectrum of cassiterite in dafuluu cassiterite pyrrhotite vein of Dachang ore field

Fig. 2-2 ar age spectrum of cassiterite in Kangma cassiterite sulfide deposit of Dachang ore field

2. yes

The Dachang type tin polymetallic deposit in Guangxi is located in the Nandan Hechi fold belt of the South China fold system, Jiangxi Hunan Guangdong Guangxi fold belt. The exposed strata are mainly Devonian, Carboniferous and Permian, followed by Triassic. Devonian system is an important ore bearing stratum, and its lithology is a set of organic rich fine clastic rock siliceous rock limestone assemblage, and the development of reefs. Tin mainly occurs in limestone and siliceous rock, copper and zinc are mostly confined to shale with rich organic matter and marl, mercury is often found in carbonaceous limestone or dolomitized limestone

The second, third and fourth times of biotite granite, granite porphyry and granite are related to mineralization and control the distribution of ore fields and deposits. Large rock bodies are occult semi occult in the deep part of the ore field, and only dyke, sill or dike group can be seen on the surface. Tungsten, tin, molybdenum, lead, zinc and other ore-forming elements in the pluton are several to dozens of times higher than the average value of acid intrusive rocks in China, which belong to crust derived remelting type granite

The structure is mainly composed of NW trending Danchi fault and a series of tight long narrow linear folds arranged in echelon, supplemented by NE trending folds and faults. The composite superimposed position is the favorable position for diagenesis and mineralization. The deposit is closely distributed around the rock mass and occurs in the anticline axis of multiple structural superimposed uplifts. The ore body or ore belt is controlled by NW, NE, EW and Sn faults, collapse position of fold saddle, bedding fracture zone, bedding fracture zone and granite contact zone

There are Mayang, MANGCHANG, Dachang, BEIXIANG and Wuwei ore fields in the metallogenic belt from northwest to Southeast, which show obvious zoning around the late Yanshanian granite body: W-Mo deposit occurs directly in the rock body, Sn polymetallic deposit is adjacent to the rock body, while sb Hg as sulfide deposit is far away from the rock body

The Dachang ore field is located in the middle of the Danchi metallogenic belt. The Danchi fault and the main anticline pass through the middle of the ore field, which divides the ore field into three ore belts: West, middle and East. The West deposit has tin polymetallic deposits such as Tongkeng, Changpo, Bali and Longtoushan; The middlings include Lamo Cu Zn deposit and chashanao W Sb deposit; There are tin polymetallic deposits such as dafuluu and kengma in the east ore deposit. Tin polymetallic deposits in the west ore belt occur in Upper Devonian siliceous rocks, banded limestones and lenticular limestones. From top to bottom, there are large vein type, veinlet belt type, stratoid veinlet type and stratoid stockwork type orebodies, among which the stratoid stockwork type orebodies are large in scale; The Lamo Cu Zn deposit in the middle zone belongs to skarn type. It occurs in the outer contact zone of the Longxianggai biotite granite in a stratoid form and is superimposed with wolframite stibnite quartz fluorite vein deposits; The tin polymetallic deposits in the eastern ore belt occur in the middle and Upper Devonian strata in the form of veins and veinlets

There are three mineralization types in Dachang ore field, namely Cu Zn, Sn polymetallic and W Sb mineralization, corresponding to skarn type Cu Zn ore, cassiterite polymetallic sulfide (sulfide) ore and W Sb ore. Among them, cassiterite polymetallic sulfide ore is the main type in Dachang mining area. Except cassiterite, marmatite, pyrrhotite, pyrite, chalrite, arsenopyrite and galena, metallic minerals are characterized by antimony lead sulfide minerals rich in Ag, Cu and Sn. The ore field association shows a certain zonation, that is, the sulfide of lead and antimony appears as galena and stibnite single metal sulfide in the upper part of the deposit, and occurs as lead and antimony sulfide in the lower part

The wall rock alteration is skarnization and marble developed in the contact zone of the rock mass, and the cassiterite polymetallic sulfide mineralization period is characterized by electrification, potassic feldsparization, muscovitization, silicification, sericitization and siderite mineralization

(3) metallogenic model the formation of Dachang type tin polymetallic deposit in Danchi metallogenic belt is closely related to the crust remelting type biotite granite of late Yanshanian in time, space and genesis. The strong Yanshanian movement caused the intrusion of granite. With the differentiation evolution and crystallization of magma, the post magmatic hydrothermal solution rich in minerals and volatile components was formed. Under the coordination of tectonism, the ore bearing hydrothermal solution migrated along the fissures of surrounding rock. Due to the change of physicochemical conditions, the balance of ore bearing hydrothermal system was destroyed, resulting in the rapid precipitation of minerals, Therefore, a series of ordered tin polymetallic deposit assemblages from high temperature to low temperature are formed around the granite body: greisen type tungsten molybdenum deposit skarn type copper zinc deposit high and medium temperature hydrothermal tin polymetallic deposit medium and low temperature silver polymetallic, tungsten antimony, mercury antimony deposit (Fig. 3-1)

(4) comprehensive information indicators (model)

1) geological indicators: anticline axis of multiple structural superimposed uplift in the depression belt; Sn rich late Yanshanian crust derived remelting granites are developed in the anticline axis; There are fine clastic rock siliceous rock carbonate rock assemblages with organic matter in the middle and Upper Devonian; Many groups of faults and fissures are developed; The wall rocks developed silicification, sericitization, chloritization, pyritization and skarnization alteration; The mineralization of the Wai series rock body has obvious zoning

(2) geophysical indicators: NW local gravity is low at the turning part of the large gravity gradient variation zone of the Bouguer gravity anomaly, and the aeromagnetic △ t local magnetic field is high and the magnetic field is low at the positive magnetic anomaly area of the variation zone

3) geochemical indicators: there are obvious W, Sn, MKO, Bi and Ag, Pb, Zn comprehensive anomalies with large scale and good correspondence with the mining area. The anomalies of single element Sn, W, Pb, Zn and Ag are also obvious

(4) remote sensing signs: remote sensing images show that there are groups of small circular structures distributed in NW trending linear structures, and there are secondary NE trending linear faults intersecting with NW trending structures

The Dabaoshan copper polymetallic deposit in Qujiang, Guangdong Province is located in the South China fold system, the Jiangxi Hunan Guangdong Guangxi fold belt, the basin edge of the late paleo depression in northern Guangdong, and the intersection area of faults and structures

The strata are Cambrian, Sinian basement and Devonian source beds rich in W, Sn, Pb, Zn, Cu, Ag and Au. The deposit occurs in the first transgressive cycle of Hercynian period and the transition from clastic rock to carbonate rock intercalated with clastic rock formation. They are calcareous and dolomitic fine clastic rocks intercalated with quartz fine sandstone at the bottom of the Middle Devonian QIZIQIAO FORMATION AND limestone of the upper Devonian Tianziling formation, which are brittle, porous and active in chemical properties

(2) structure: the deposit is located in the transitional zone between the depression and uplift. Under the action of long-term active EW, NE and NW fault fold belts, the ore body location is controlled by EW faults and interlayer faults along the strata and different lithologic interfaces, and the later folds lead to the thickening and enrichment of ore bodies

(3) magmatic rocks: related to intermediate acid granodiorite and sub dacite porphyry of Yanshanian hypabyssal ultrahypabyssal crust mantle mixed source

Fig. 3-1 metallogenic model of cassiterite sulfide related to Yanshanian biotite granite in Danchi metallogenic belt

The Cu Pb Zn ore bodies are stratoid, lenticular and folded synchronously with the strata, and are enriched in the synclinal trough with multiple layers. The ore mineral assemblage is complex, mainly including siderite and pyrite assemblage, pyrite, galena and sphalerite (silver) assemblage from top to bottom; Pyrrhotite, chalrite (gold) assemblage and peripheral scheelite, wolframite, molybdenite assemblage. Wall rock alteration mainly includes silicification, sericitization, chlorite pyritization, carbonatization and skarnization of peripheral contact metasomatic deposits

(3) metallogenic model: the deposit is located at the dip end of compound anticline and the margin of dome; It is distributed in the transitional layer between the middle and Upper Devonian limestone with fine sandstone and the middle and Lower Devonian clastic rock; High angle faults and medium amplitude folds are developed; The Yanshanian hypabyssal ultrahypabyssal intermediate acid crust mantle mixed source (syntectic) magmatic rocks are exposed (Fig. 3-2)

Fig. 3-2 metallogenic model of stratabound Cu Pb Zn deposits in northern Guangdong Province; The wall rocks are silicified, sericitized, Chloritized or skarn

(2) geophysical indicators: it is located in the northeast or southwest twist position of the isoline of the northwest step belt of the Bouguer gravity anomaly; Aeromagnetic △ t anomaly is a large-scale and irregular concave convex part of positive magnetic anomaly with high and low local magnetic force

Geochemical indicators: there are geochemical anomalies corresponding to the deposit, with complex components, well nested, obvious concentration center and concentration zoning. The main components are Cu, Mo, Pb, Zn and Ag, followed by as, Bi, Hg, Ni, Co, V, CD, Mn and ba. The anomaly trend is NW and consistent with the ore body extension

(4) remote sensing marks: there are diamond structure images in EW direction composed of NWW and NE linear structures and ring images displayed by structures or magmatic rocks

The Yanbei tin deposit in Jiangxi Province is located in the Paleozoic fold belt of Wuyishan uplift area and belongs to the tectonic magmatic activity area of West Fujian southeast Jiangxi Province. Since Mesozoic, it has been characterized by strong faulting, extensional subsidence and magmatic activity, with large-scale volcanic eruption and emplacement of hypabyssal intermediate acid granite along deep faults. The deposit occurs in an acidic intermediate acidic volcanic basin controlled by the NNE trending Shicheng Xunwu deep fault

(2) the Yanbei deposit is located in the southeast of the caldera pass of mikeng mountain, and tin mineralization occurs in EW, NNE and NW fault composite section. The mineralization is related to the activity of subvolcanic granite porphyry with the characteristics of ultra hypabyssal and cryptoexplosion. The ore body occurs in the inner contact zone of rhyolitic tuff lava and granite porphyry in jilongzhang formation (J 3 J), in which the inner contact zone accounts for two thirds. The overall strike of the ore body is NNE, the dip is n, and the dip angle is 18 ° The main ore body is irregular ellipse in plane, 450m long and 250m wide, with the thickest of 89m. In the longitudinal section, the orebody is lenticular and stratoid. The main ore minerals are cassiterite and chalrite, followed by sphalerite, magnetite, pyrite, galena, wolframite and argentite; The main nonmetallic minerals are quartz, topaz, chlorite, sericite, fluorite, etc. The ore structure is mainly disseminated and veinlet disseminated structure, and some breccia structure, with metasomatic structure, crystalline structure and solid solution separation structure. The alteration of the deposit is well developed and distributed in a plane type. Tin mineralization is closely related to the quartzitization of topaz, chlorite Topaz and quartzitization

(3) metallogenic model

the tin bearing granite body closely related to the mineralization of Yanbei deposit is not a subvolcanic rock body, but another tectonic magmatic metallogenic multi-stage intrusive granite series after the eruption of mikengshan volcano. The ore-forming parent rock is a highly emplaced fine-grained porphyry like granite body. The ore-forming bodies are different from the subvolcanic bodies in porphyry tin deposits (Fig. 3-3)

Fig. 3-3 metallogenic model of Yanbei tin deposit. RB, re and Nb TA mineralization occurred in the magmatic stage of tin bearing granite; The W and Sn bearing Topaz quartzite belt formed in the contact zone of the rock mass ring the gasification high temperature hydrothermal period; Cassiterite and sphalerite deposits are formed near the contact zone ring the high-temperature low-temperature hydrothermal period, and silver deposits are fractured far away from the contact zone

the ore-forming fluid mainly comes from magmatic hydrothermal solution with the addition of surface water. The ore-forming materials such as Sn, Fe, Cu and s are mainly derived from deep syntectic intermediate acid volcanic intrusive rocks. After the formation of magmatic stage, the ore bearing hot gas fluid rose along the large fault and paleovolcanic channel

The formation of Dachang deposit is obviously controlled by structure. The structure not only controls the distribution of ore deposits, but also controls the shape and change of ore bodies, that is, the structural conditions provide favorable space for the accumulation of ore-forming materials. It is reflected in the following aspects:

1. The structure controls the distribution of magmatic rocks and ore deposits in the mining area

Danchi basin is a secondary rift basin on the edge of Youjiang rift basin, belonging to the ancient Tethys tectonic domain, and the nature, evolution and development of the basin are controlled by the ancient Tethys ocean. During the Tangding stage of Early Devonian, along with the cracking of the Paleo Tethys ocean, NW trending basement faults proced tension activities, forming the NW trending Danchi depression belt and incing NE trending strike slip faults. The two groups of faults jointly controlled the Devonian and Carboniferous deposits in Danchi basin. Under the strong compression of Indosinian movement, NW trending folds and faults (such as Dachang anticline and Dachang fault) were formed, which laid the structural framework of the Danchi metallogenic belt. In the late Yanshanian period, e to the compression of the Pacific plate from the SE-NW direction, the NW and NE groups of faults experienced strike slip extension again. At the intersection of the two groups of faults, the tin bearing granite magma ascended and emplaced to form ore deposits. At the same time, e to the equidistant development of NE trending faults, the ore deposits were roughly equidistant. Therefore, in the Danchi metallogenic belt, there are Mayang, MANGCHANG, Dachang, BEIXIANG, Wuwei and other tin polymetallic deposits (fields) successively from north to south. In the Dachang ore field, the distribution of Longxianggai granite ore bodies is zonal, with dafuluu, maopingchong, kengma and other deposits in the East, Changpo Tongkeng, Paris, Longtoushan deposits in the west, and Lamo zinc (copper) ore bodies in the middle

The structure controls the occurrence, location and scale of ore body. The occurrence of ore bodies is not only affected by the properties of surrounding rocks, but also controlled by the structural properties. It is mainly reflected in the following aspects: 1) Dachang anticline is one of the main structural types in Dachang mining area. The turning end of anticline is the stress concentration position, which is easy to proce transverse joints and collapse space, which is concive to ore fluid filling. Therefore, the dip end of Dachang inverted anticline is a favorable place for the occurrence of large vein like orebodies. With the anticline dipping to se, the large vein like orebodies graally decrease or disappear, The scale of this kind of ore body is small, the continuity of the vein is good and stable, and the grade of the ore body is rich at the top and poor at the bottom; ② Under the action of stress, the shear fold in the strata, the interlayer slippage structure of different lithology and the fracture structure in the strata are the main types of ore hosting structures in the area, which control the layered and stockwork ore bodies in the area, and the scale of such ore bodies is large (such as No. 75, No. 77, No. 79, No. 91, No. 92 ore bodies); ③ In the late stage, the NE, NW and Sn trending faults with both extensional and shear properties are favorable for the formation of vein like orebodies; ④ The turning ends of some secondary folds often form collapse positions, which is concive to the formation of small and rich ore packets; ⑤ The occurrence of layered and veined Zn Cu ore bodies (such as Lamo Zn Cu ore) is favorable to the occurrence of outburst, contact zone and fault structure in the contact area between rock mass and surrounding rock; ⑥ The occurrence of No. 100 orebody is also obviously controlled by the structure. At the top of the reef uplift at the axis of the anticline, e to the strong compression, there are different degrees of interlayer stripping and fragmentation. At the intersection of faults and fissures, some rich ore packets and pillars are proced in a certain range; In the West Wing of the unsymmetrical uplift of the reef, some Sn trending transverse faults and interlaminar dislocations often occur, resulting in some steeply dipping orebodies and layered orebodies; In the axial part of the reef, controlled by two compression torsion thrust faults and the special lithology of the reef, a large "collapse space" is formed in the deep part where the stress is concentrated and the compression is strong, which provides a favorable field for the filling of ore fluid and the formation of No. 100 super large orebody

As a matter of fact, the formation of ore bodies is the combination of various favorable structural features proced by faults, folds and intrusion of rock mass. The distribution of ore bodies is also determined by the direction of the dominant ore controlling structures, and the main ore hosting structures of the deposit are secondary faults derived from the main faults, such as NE trending faults

1、 Deep structure and metallogenic enrichment mechanism "Changpo Tongkeng deposit deep area" and "Heishuigou dashujiao area" are the two deep prospecting areas of the Dachang Mine replacement resource exploration project. Among them, the deep area of Changpo Tongkeng deposit refers to the footwall area of Dachang fault (F1). Tin polymetallic mineralization in the area is mainly controlled by a group of NW trending imbricate thrust faults and secondary folds; Heishuigou dashujiao area is located in the eastern part of LAOCHANGPO deposit, with a distance of 300-500m. The zinc polymetallic mineralization in the area is mainly controlled by NE, NW trending faults and NE trending flexure structures

The characteristics of imbricate structure in the deep part of Changpo deposit and its control on mineralization (1) imbricate structure the NW trending fault structure is developed in Changpo mining area, and the surface is represented by Dachang fault (F1), which occurs near the axis of the West Wing of Dachang inverted anticline. Deep drilling revealed that there are a series of parallel thrust faults (f1-1, F3, F5, etc.) in the footwall of F1. The hanging wall of these faults thrusts upward in turn and overlaps upward and downward on the profile, forming imbricate structure (Fig. 5-15)

The NW trending faults have the same characteristics and strike nw330 °～ three hundred and forty °， Inclination ne, dip 25 °～ eighty °， The fault plane is steep in the upper part and gentle in the lower part, and occurs in the shape of plough. The faults developed on the basis of Devonian synsedimentary faults. Geophysical data show that NW trending faults are still clearly reflected on the Mohs depth map, indicating that their influence depth reaches the middle and lower crust or upper mantle. Since Mesozoic, the faults have experienced thrust movement in Indosinian and extensional and torsional reactivation in Yanshanian (CAI Minghai et al., 2004)

Fig. 5-15 profile of 125 exploration line in deep area of Changpo deposit

Taking F 1 , f 3 and f 5 as the natural boundary, the deep part of Changpo deposit is divided into three imbricate structural zones from top to bottom (Fig. 5-15)

No.1 imbricate structural belt: composed of F 1 fault and a series of secondary folds and faults on its hanging wall, it is the occurrence position of 91 and 92 layered orebodies and vein orebodies in Changpo Tongkeng mining area

The second imbricate structural belt is distributed between the f 1 and f 3 faults in the West Wing of Dachang inverted anticline, which is composed of the first secondary fold and several secondary faults in the West Wing of Dachang inverted anticline. The f 1-1 fault further complicates the east wing of the secondary syncline. No. 115, 77, 77-1 and 77-2 ore bodies are all hosted in the fold fault zone

No.3 imbricate structural belt: it is distributed between F 3 and f 5 faults on the West Wing of Dachang inverted anticline, and is composed of the second secondary anticline and several secondary faults on the West Wing of Dachang inverted anticline. No.116 and No.117 orebodies are found in the southern part of the structural belt

(2) mineralization characteristics in imbricate structure belt

in NW imbricate structure, there are many cassiterite sulfide orebodies, which occur as stratoid and fissure veins. The relationship between main orebodies and imbricate structure is as follows:

Changpo Tongkeng Tin polymetallic deposit includes large vein type, veinlet type and 91 and 92 orebodies, It occurs in the No. 1 imbricate structural belt in the east wing of Dachang anticline, which is strictly controlled by the axial fracture zone of Dachang anticline and the secondary fold, bedding sliding fault and NE trending fracture structure in the northeast wing. The occurrence form of ore bodies has obvious zonal characteristics, The order from top to bottom is: fractured vein and veinlet zone orebody → interlayer stripping stratoid orebody → stratoid veinlet zone type 91 orebody → stratoid veinlet zone type 92 orebody

LAOCHANGPO silver zinc deposit is located in the West Wing of Dachang anticline in the No.2 imbricate structural belt, in the south of the deep area of Changpo Tongkeng deposit. There are No.111, 112, 113, 114, 115 and 16 orebodies, among which no.111-114 orebodies are steep inclined fissure vein orebodies, and NO.115 and No.16 orebodies are gently inclined stratoid orebodies

The tin polymetallic deposit in the deep part of Changpo Tongkeng deposit is a newly discovered deposit in recent years. It occurs in the No.2 imbricate structural belt in the West Wing of Dachang inverted anticline. It is between F 1 and f 3 and there are many layered and fractured vein like orebodies. There are 115, 77, 77-1, 77-2, 75-1 and 79-1 stratoid orebodies, and 200 NW and NE trending mineralized fracture veins in fracture vein orebodies

In addition, there is no instrial ore body in the area between F 3 and f 5 , that is, in the No. 3 imbricate structural belt, e to the low degree of engineering control

(3) structural ore controlling regularities the ore controlling regularities in the deep area of Changpo Tongkeng deposit are as follows: ① the occurrence of strata on the profile changes from gentle to steep, and the thickness and strength of ore veins increase, which shows that the late Yanshanian extensional and torsional tectonic activities controlled the mineralization; ② It is easy to proce interlayer fracture zone and interlayer sliding near rigid and plastic rock interface, which is a good metallogenic space; ③ The ore bodies (veins) tend to be enriched in mineralization in the middle, coexisted with Sn and Zn, and become poor at both ends. The ore-forming elements become mainly Sn or Zn instead of Sn and Zn; ④ The dip extension of fissured veins is often greater than strike extension

In recent years, Heishuigou dashujiao area is an effective exploration area for deep geological prospecting in the periphery of the old mining area. Through deep drilling in 2005-2006, rich and thick orebody 96 was found in the lower part of orebody 95, and four orebodies in the six boreholes were more than 10m thick, The maximum thickness is more than 30 meters, which breaks through the previous view that No. 96 ore body is smaller and poorer to the north, opens up a new idea for the prospecting of this area, expands the scale of the deposit, increases the amount of zinc and copper resources by (333) 980000 tons, and the deposit boundary is not controlled, showing a good prospecting prospect

The Heishuigou dashujiao deposit is located at the junction of the west ore belt and the middle ore belt of the Dachang ore field, adjacent to the Changpo Tongkeng superlarge tin polymetallic deposit in the west, the Bali Longtoushan superlarge tin polymetallic deposit in the south, and the Longxianggai large skarn zinc copper deposit in the North (Fig. 5-16)

(1) structural characteristics of Heishuigou dashujiao area

Heishuigou dashujiao area is located in the northeast wing (flat wing) of Dachang inverted anticline. In the deep part, there is a NE trending flexure structure with a length of 2500m, a width of 500-700m and an axial direction of 30 m °， The orebodies are mainly distributed along the northwest wing of the bend. The fault structures in the area are relatively developed, mainly including Dachang fault in NW direction and Heishuigou fault in NE direction (Fig. 5-16)

Dachang fault. Dachang fault runs through the axis of Dachang anticline, and its length is more than 8km. The dip angle of the north section (north of Pali) is 15 °～ thirty °， The fault distance is 150-250m and the extension depth is more than 800m; The shallow part of the middle section (Bali Longtoushan) is mainly in the form of fracture zone, with fracture bandwidth of tens of meters, and the deep part is a group of fracture zones; The dip angle of the southern section (south of Longtoushan) is 40 °～ forty-five ° The fault is exposed on the surface of the west side of the mining area, and the lower part cuts into the deep part of the mining area, which is the ore guiding structure in this area

2) Heishuigou fault. It is a normal fault, about 4km long, strike 37 °， The dip angle is 60 °～ seventy ° The fault cuts across the mining area and intersects with Dachang fault in the West. The ore bodies in the area are mainly distributed along the fault and its two sides, which indicates that the fault plays an important role in controlling mineralization and is the ore matching structure in the area

In addition, in the Luofu formation, e to the compression tectonic stress in the early stage, the different lithologic combinations of marl, calcareous mudstone and shale are easy to proce interlayer sliding, forming interlayer detachment and interlayer fracture zone structure, and in the late stage, the interlayer folding structure, interlayer detachment zone and small folds near EW direction are formed e to the tectonic extension and shear deformation, No. 95 and No. 96 orebodies occur in this kind of structure

(2) mineralization characteristics

the orebodies in the area are mainly distributed in the northeast wing of Dachang anticline, and occur in the marl and calcareous mudstone in the middle and lower part of Luofu formation of Middle Devonian in a stratoid manner. The occurrence is basically the same as that of the stratum. Due to the influence of the NE trending flexure structure in the deep part of the area, the orebodies are inclined from northwest to northeast, and mainly distributed along the northwest wing of the flexure, tending to NW, At the tip of the tree (the foot of the big tree), it turns to NNE. The plane shape of the ore body is simple and tongue shaped, spreading from SW to ne (Fig. 5-16). The tin polymetallic sulfide ore body is located in the south-west end, and the zinc copper ore body is located in the north-east end. A number of instrial ore bodies have been found in the area, of which No. 95 and No. 96 are the two main ore bodies. They are nearly parallel, with a vertical distance of 70-130m. No. 95 overlies No. 96 ore body (Fig. 5-17)

No. 95 orebody. It occurs in the middle part of Luofu formation with strike of 25 °， Dip NW, dip 21 ° Left and right, northeastward and laterally. The ore body is controlled to be 2600m long and 60-800m wide with good continuity. Taking line 39 as the boundary, the South ore section (Bali wayaoshan) is mainly tin polymetallic sulfide ore body, and the North ore section (Heishuigou dashujiao) is mainly zinc copper ore body

No. 96 orebody. It occurs in the lower part of Luofu formation, strike 58 °， Dip NW, dip 28 °， The extension length is 2550m and the control area is 1.15km 2 . Line 9 of ore body inclines to n with dip angle of 15 ° The ore bodies are stratoid, discontinuous, and the thickness varies greatly. The ore body is characterized by expansion, contraction and branching. There are tin polymetallic ore bodies in the south of line 39 and zinc copper ore bodies in the north. The tin polymetallic sulfide ore block is controlled to be 340m in length, 160-240m in width and 10.30m in average thickness; The control length of zinc copper ore section is 1850m, the width is 100-500m, and the average thickness is 9.50M. The thickness is unstable, and the thickness variation coefficient is 129%

Fig. 5-16 geological sketch of Tongkeng Heishuigou dashujiao zinc copper deposit C 2 H 2 - dolomitic limestone of Middle Carboniferous Huanglong Formation; C 2 H 1 - chert banded limestone of Middle Carboniferous Huanglong Formation; C 1 C - quartz sandstone of Lower Carboniferous Simen formation; D 3 T 3 - limestone and shale of Upper Devonian tongchejiang formation; D 3 W 2 - lenticular and banded limestone of Upper Devonian Wushan formation; D 3 L 1 - siliceous rocks of the upper Devonian Liujiang formation; D 2 L 2 - marl and mudstone of Middle Devonian Luofu formation; D 2 L 1 - reef limestone of Middle Devonian Luofu formation; δμ 3B 5 - diorite porphyrite; γ 3C 5 - granite porphyry; 1 - stratigraphic boundary; 2 - unconformity stratigraphic boundary; 3 - anticline axis; 4-reversed anticline axis; 5 - syncline axis; 6-normal fault; 7 - reverse fault; 8 - ore body and number; 9-placer tin deposit

(3) the characteristics and laws of structural ore control

the control of structure on mineralization is shown as follows: NW trending structure (Dachang anticline, Dachang fault) and NE trending structure (Heishuigou fault, concealed deflection) superimposed section and concealed rock uplift jointly control the deposit location in this area. In the southern part of the deposit, e to the mainstay action of reef limestone in the core of Dachang anticline, the local stress field changes, which makes the overlying Luofu formation form interlayer stripping and interlayer crushing structure, controlling cassiterite sulfide orebody. The northern part of the deposit is affected by late tectonic extension and shear deformation, resulting in intrastratal folding structure and interlayer detachment zone, controlling skarn type zinc copper orebody. The NE trending flexure structure is developed in the deep part of the area, and it is inclined from southwest to northeast. The dip end is shown in Fig. 5-47 Tongkeng Longxianggai section of Dachang mining area (revised according to the data of No. 215 geological team of Guangxi Huaxi Group). II. The deep prospecting results are shown in Dachang Mine of Guangxi

bus line: No.310 → Metro Line 2 → Metro Line 1, the whole journey is about 36.7 km

1. Walk about 640 meters from Sichuan Institute of media to tuanjiezhen station

2. Take No.310, pass 13 stops, reach Tianfu Road South Station

3. Walk about 280 meters, reach Xipu station

4. Take Metro Line 2, pass 14 stops, reach Tianfu Square Station

5 Take Metro Line 1, pass 10 stops to Jincheng Square Station

6, walk about 250 meters to Sichuan Shuhui law firm

7. Take subway line 1 and get off century city

Take No.14 or No.7 bus at Shilidian station, get off at Hongxingqiao station, take Metro Line 3 at the next Hongxingqiao station, get off at provincial Stadium station, transfer to Metro Line 1, get off at Jincheng square station, exit a, northwest is

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