1. Analysis of genetic types and mineralization mechanisms of precious metal deposits
(1) Classification of genetic types of gold deposits
According to the mineralization and mineralization of mineral deposits The gold deposits and gold-related non-ferrous metal deposits in the Nanling area can be divided into 10 main genetic types based on their methods, material sources, ore-controlling conditions and deposit characteristics: ① gold deposits related to magmatic rocks; ② volcanic rock-type gold deposits; ③ Porphyry gold deposits; ④ Altered rock gold deposits in structural fracture zones; ⑤ Fine disseminated gold deposits; ⑥ Vein type gold deposits in metamorphic clastic rocks; ⑦ Gold deposits related to supergene processes; ⑧ Placer gold deposits; ⑨ Laterite type gold deposit; ⑩ Iron hat type gold deposit.
(2) Classification of genetic types of silver deposits
According to the classification principles of mineral deposit origin, mineralization and mineralization methods, material sources, ore-controlling conditions and mineral deposit characteristics, etc., Nanling Regional silver deposits and silver-related non-ferrous metal deposits can be divided into eight main genetic types: porphyry type, contact metasomatism type, high and medium temperature hydrothermal type, medium and low temperature hydrothermal type, volcanic hydrothermal type, syngenetic sedimentary type, Sedimentary transformation type, epigenetic type, etc.
(1) Porphyry deposits
This type of deposits are distributed in the rock back of the western slope of Wuyi Mountain in southern Jiangxi, Fenghuangdong, Lianhua Mountain in eastern Guangdong, Xiling, etc. The surrounding rocks are Jurassic volcanic rocks and Upper Paleozoic. The ore-forming rock body is early Yanshan granite porphyry, showing Sn, W-Cu, Pb, Zn-Ag mineralization combination. The ore body is produced in the contact zone between the inside and outside of the rock body. , like layered and lens-like, and the wall rock alteration includes potassium feldsparization, sericitization, chloritization and fluoritization. It often appears as associated and silver-bearing deposits, and the size of the deposits is mainly small.
(2) Contact metasomatic deposits
Mainly distributed in southern Jiangxi, southern Hunan, northern Guangdong, central Guangdong, western Guangxi, eastern Guangdong and southeastern Yunnan. Such as Jiaoli, Baoshan, Pingtouling, Jinzi'ao, Chuandu, Dongpo, Yaogangxian, Xianghualing, Dayishan, Dachanglamo and Fozichong. Generally distributed along the structural magma belt, the ore-bearing strata are mostly Upper Paleozoic D2-P1, and the surrounding rocks are mainly carbonate rocks or calcium-containing clastic rocks. The mineralization is related to the biotite granite from the third stage of the early Yanshan to the late Yanshan. Related to small intrusive bodies. Most of the mineral deposits are controlled by NE-trending folds and faults, and the composite parts of regional multiple sets of fault structures and different types of structures are often extremely beneficial to mineralization. Ore bodies are mostly formed in the contact zone between granite rock bodies and surrounding rocks. They are lens-shaped, layer-like, lentil-shaped, and some are vein-shaped. Main useful element combinations: W, Sn-Pb, Zn-Cu(Au)-Ag (associated), Ag-Pb, Zn-Cu, Sn-W-Bi-Be-Ag (containing Ag), W-Mo-Bi -Cu-Ag (containing Ag), Pb, Zn-Ag (primary or associated), etc. Silver in ores can form independent silver minerals or silver-containing minerals; the scale of silver reserves is mainly small and medium-sized, and some silver deposits can reach medium-sized scale, such as Lamo, Jiaoli, Baoshan, Fozichong, etc.
(3) High- to medium-temperature hydrothermal deposits
Mainly distributed in southern Jiangxi, southern Hunan, northern Guangdong, northern Guangxi, and southeastern Yunnan, and are mainly large vein types or thin veins Type tungsten-tin polymetallic deposits were collectively referred to as quartz vein types in the past. In recent years, it has been discovered that the silver content in these deposits or sections reaches the requirements for primary or even independent silver deposits. Most of them are distributed along the inner and outer zones of the structure-magma belt, and the ore-bearing surrounding rocks are Sinian-Devonian-Carboniferous-Permian. of clastic rocks and carbonate rocks. It is mainly related to the Caledonian-Yanshanian granite intrusive rocks. The mineralization is mainly from the first stage of the early Yanshan to the first stage of the late Yanshan. Among them, the main mineralization period of lead, zinc and silver is from the third stage of the early Yanshan to the late Yanshan. A few belong to the Xuefeng period and the Indosinian period. Such as Xihua Mountain, Piaotang, Maoping, Daji Mountain, Huangsha, Sawbankeng, Shirenzhang, Hongling, Meiziwo, Dongpo, Dayi Mountain, Yaogangxian, Coral, Mangchang Dashan, Wuming Liangjiang, Gejiu Kafang and other mineral deposits.
Silver is produced in various mineralization element combination deposits as primary ore, associated ore or other silver-containing minerals. The silver grade of some sections of the ore body can meet the requirements of independent silver mines. The size of silver reserves is generally medium.
(4) Medium-low temperature hydrothermal deposits
This type of deposit is one of the most important types of silver deposits in the Nanling area. They are distributed throughout the region, such as: Lahu Lake, Liumukeng, Chikeng, Daxing Mountain, Changganling, Houpao, Yinshi, Tiandong, Baoshan, Huangshaping, Tongshanling, Xianghualing, Mangchang, Ma'anshan, Laochang, Phoenix Mountain, Jinshan, Zhongsu, Xiadong and Xiachang etc. Distributed in different structural units, mainly the late Paleozoic-Mesozoic depression area, followed by the uplift area.
The ore-bearing surrounding rocks range from Sinian to Triassic. The mineralization is mainly related to Yanshanian granite. Part of it is related to the granitoids of the Galli period or the Indosinian period. The ore-controlling structures are mainly EW-trending, NNE-trending and NW-trending faults. The ore bodies are mainly vein-shaped, and some are lens-shaped. The main mineralizing elements are Pb, Zn, Ag, Au, w, etc. Deposits dominated by Pb and Zn are associated with Ag, Cu, As, W, and Cd; independent silver deposits are often associated with Pb, Zn, Cu, Sn, and occasionally Au (such as Zhanggongling, Jinshan, Daxing Mountain, Changganling, etc.) ; Tungsten ore is a single scheelite (such as the 16 mining area, etc.).
(5) Volcanic hydrothermal deposits
This type of typical deposit is only found in eastern Guangdong. The bottom of the carbonaceous shale of the Jinji Formation of the Lower Jurassic System is andesite, and the ore-bearing surrounding rock of the silver antimony deposit is explosive breccia-dacite rhyolite tuff-dacite rhyolite-porphyry breccia lava (Zhong Qiuyang) and ignimbite-tuff breccia-rhyolitic tuff lava (Baoshan), etc. The main element combinations of mineralization are divided into Ag-Sb, Pb, Zn, Cu, Ag and Sn, Pb, Zn, Ag, etc. In the silver and antimony combination, the silver grade is rich, and other components are associated or contain silver. There are large, medium and small silver reserves.
(6) Syngenetic sedimentary deposits
This type of deposits is mainly distributed in the late Paleozoic carbonate platform sedimentary area in the depression area of ??northern Guangdong, such as Yangliutang, Tianziling and other lead deposits. Zinc and silver deposits. Controlled by the NE-trending ancient structural fault zone, a large number of syngenetic sedimentary structural features can be seen in the mining area. The ore-bearing horizon is Devonian-Carboniferous, and the ore body shapes include layered, layer-like, and lenticular. The ore structure often retains layered, disseminated and biological residual structures. The main elements are Pb, Zn, and Ag, accompanied by siderite, antimony, etc. It is a small and medium-sized organic (associated) silver deposit.
(7) Sedimentary transformation type deposits
This type of deposit is one of the most industrially valuable silver deposits. It is mainly distributed on the edge of the uplift area, that is, the transition zone between the depression area and the uplift area, and is mostly carbonate platform deposits. Such as Fankou, Manjiazhai and other lead-zinc-silver deposits or antimony and silver deposits. Another subcategory is the sedimentary-magmatic hydrothermal superposition modification type, such as the Bainiuchang silver, lead-zinc and Dabaoshan polymetallic deposits. In addition to retaining sedimentary characteristics, the formation of the deposits shows a large number of magmatic hydrothermal mineralization characteristics. The ore body shapes include layered, layer-like, lens-shaped, and a few vein-shaped. The main element combinations of the deposit are: Cu-Pb-Zn-Ag, Pb-Zn-Ag, Pb-Zn-Sb-Ag. The silver grade is rich and meets the requirements of independent and independent silver mines. Silver reserves are mainly large and medium-sized deposits. There are still different opinions on the origin of the Fankou silver, lead, zinc ore and Bainiuchang tin, lead, zinc, and silver ore in this type of deposit.
(8) Supergene deposits
Related silver deposits transformed and enriched by surface weathering. Primary ore deposits and supergene deposits are controlled by the same structure. The main element combinations of the deposit are W-Sn (Heshangtian), Mn-Pb, Zn (small zone), Mn-Ag (Phoenix Mountain oxidation zone), Sn-Pb, Zn -Ag (Xiaodong, Longshujiao), etc., the silver grade is rich and poor, and the scale of silver reserves is mostly medium and small.
(3) Analysis of mineralization mechanism
1. Gold deposit structural system transformation and mineralization enrichment mechanism related to structural fracture zone (shear zone)
During the gold prospecting boom in the 1990s, there were many studies and related opinions on gold deposits related to structural fracture zones (shear zones). Based on the summary of field surveys, it is believed that gold deposits should be paid attention to in the investigation and evaluation of gold deposits in the area. Analysis of structural ore control, especially the structural fracture, fluid flow and mineral aggregation mechanism issues related to gold deposits (Wei Changshan et al., 1996), which involves issues such as mineral enrichment mechanism and ore prospecting direction. In Hetai gold mine in Guangdong, Tuanziping gold mine, Daping gold mine, Shenjiaya gold mine, Xianrenyan gold mine in Hunan, etc., early quartz vein ductile deformation is often found in thrust or low-gentle structural fracture zones and ductile shear zones. Superimposed enrichment mineralization, quartz vein re-crushing and mineralization, breccia groups that can be combined, vertical and gentle network vein combinations, etc. There are lenses formed at a later stage in the sides of many ore-bearing fracture zones, and their lateral direction indicates the main structure. The direction of belt movement and its structure-fluid-mineralization mechanism can be explained by the "fault valve-seismic pump" model.
In the Shuikou Mountain ore field, the fissures and quartz veins generated at different stages of development of the structural fracture zone (shear zone) have greatly different gold content. The relevant ore prospecting signs are the structural decompression zone and silicification related to the fault. Rock zone; in the Daping-Touziping gold deposit area, the gold ore body is produced in a lens-shaped shear zone that intersects with the regional schistosity. A large number of alteration zones outside the shear zone only have gold mineralization or no mineralization. ; The gold-bearing ore bodies are mainly silicified rocks caused by strong silicification of early structural rocks. The gold-rich gray-white silicified rocks often have ductile deformation phenomena. Pyrite fragmentation and pressure shadows can also be seen. The remaining quartz in the weak strain zone is similar to sugar. It is granular, and in the later stage there is a fissure network vein body, that is, milky white silicified rock superimposed (Cao Jinliang, 2000; Chen Mingyang, 1996), indicating that after the formation of silicified body, it has experienced brittle → ductile transition and ductile → brittle transition. Similar tectonodynamic mineralization is also seen in the Tinkuang antimony deposit.
2. Origin of “lateritic” gold deposits and epithermal gold deposits
“Laterite” gold deposits are epigenetic gold deposits, but they are not It is completely weathered from fine-grained disseminated gold ore. "Laterite-type" gold deposits are developed in the area, mainly in western Guangxi, southern Hunan, northern Guangdong, western Jiangxi and other places. This type of gold deposit has wide distribution, large scale, low grade, exposed surface, easy mining and dressing, and obvious ore prospecting signs. , quick results and other characteristics, it can not only become a mineral deposit itself, but also serve as an indicator for finding other types of metal deposits. The comprehensive prospecting method in the evaluation of mineral resources should be paid attention to.
The epithermal gold deposits in southern Hunan are represented by the Xianrenyan in the Shuikoushan ore field and the Dafang mining area in the Pingbao ore field. Their mineralization conditions can be summarized as: "gold-bearing ore layers, fractures The necessary conditions for mineralization are the trinity of "structure, magma and hot springs" (Liu Zhengtao, 2000). Among them, the gold-bearing deposits of ancient hot springs such as siliceous dolomite and microquartzite of the Hutian Group in the Middle and Upper Carboniferous were built, and the Lower Permian The gold-bearing formation layers such as hydrothermal sedimentary siliceous rocks and calcium-silicate argillaceous shale of the Tongdangchong Formation are more favorable for mineralization. Among them, the Shuikou Mountain area, Yangshi in the north of Guiyang, Xujiadong area, and Pingbao in Chen County are the most favorable for mineralization. Look for promising areas for this type of gold mine.
In the Xianrenyan gold deposit area, the main overthrust fault zone is characterized by strong silicification, forming a silicified breccia zone. The fault mud and breccia zone are weathered and leached to form gold-bearing black soil with breccia-type gold. Ore deposits, where fault intersections and inverted anticlines intersect with regional nappe detachment structures, often control the output of thick, gold-rich ore bodies. The hot spring "silicon cap" belts generally spread linearly in the NNE and SN directions, are not connected to each other, and are distributed in groups and bands, forming steep ridges and isolated hills. The shape of a single "silicon cap" is elliptical, round, or strip-shaped on the plane; in cross-section, it is mostly like an upward-branching cone, cylindrical, or irregular dendrite. "Silicon cap" belts can be roughly divided into two categories: silicified breccia bodies (belts), that is, silicified breccia bodies (belts) related to nappe structures in the early stage, and silicified breccia bodies (belts) formed by hot spring activities in the late period. Silicon Hat”. The black soil-type gold deposits and "silicon cap" zones formed in different periods have different mineral contents.
The laterite-type gold deposits in southern Hunan are controlled by basement faults and are distributed in a band. They have small weathering profile thickness, low maturity, strong dependence on the type of ore source body and Au content, and a single ore-bearing layer with a relatively thick thickness. Small features. The secondary enrichment of gold is closely related to the oxidation of pyrite and the adsorption of limonite (Zeng Zhifang et al., 2002).
Guangxi’s “laterite” gold deposits are divided into 7 categories, including carbonate rocks, volcanic rocks, altered structural rocks, fine clastic rocks, basic-ultrabasic rocks, silica In the past, three types of rock types, hydrothermal sedimentary rocks and ancient sandy conglomerates were more developed. The output of gold mines was controlled by the ore source body, the development degree of red weathering crust and the physical and chemical conditions of mineralization.
The "red soil type" gold deposits in western Jiangxi are mainly distributed in the Yuanshui Depression and have the characteristics of "3 favorable ore-bearing horizons, 3 favorable ore-bearing lithologies and 3 favorable element combinations" (Chen Dajing , 2001). Among them, the laterite area in the Pingle Depression, which is formed due to the weathering of the parent rock of fine-grained disseminated gold deposits, is the most favorable area for searching for "laterite" gold deposits.
3. Output characteristics of silver mines related to structural alteration and fracture zones
Silver mines related to structural alteration and fracture zones are mainly produced in western Guangdong and northwest Guangdong, such as Liannan Bikeng Silver Mine, Yun'an Gaoji Silver Mine and Gaoming Dieping Silver Mine, etc. This type of silver ore often occurs with metal sulfides such as pyrite, sphalerite (galena), chalcopyrite, etc.
The surrounding rock of Gaoji Silver Mine is altered granite, and the ore body is obviously controlled by the nearly EW-trending fault structural zone. The occurrence of the structural zone is 170°∠71°, and a breccia zone about 15cm wide develops close to the roof. , the breccia is silicified rock, which contains fine-powdered pyrite. The breccia has a smooth shape and its long axis is parallel to the structural plane. The zone is dominated by silicification, sericitization, pyritization and limonization, with irregular cross-sections. The main ore minerals include pyrite, galena, sphalerite, rhodochrosite, and rhodochrosite. Galena is produced in the form of colloidal lumps. Alteration mineralization in the mining area can be roughly divided into three stages: ① Silicification pyrite stage; ② Carbonation stage, mainly rhodochrosite mineralization; ③ Silicification and pyrite (produced in the form of veinlets) Lead and zinc mineralization stage. Among them, the early ① stage pyrite is euhedral, in the shape of massive and agglomerated rocks; the ② stage is the rhodochrosite stage, with disseminated pyrite distributed within it; and the ③ stage is quartz veinlets (sulfide-containing stage). Drill core observations show that lead-zinc mineralization in the deep structural zone is enhanced and rhodochrosite is significantly reduced. The silver ore body extends into the Cretaceous conglomerate and still shows mineralization, with grades of Ag270g/t, Pb0.056%, and Zn0.052%, reflecting the late Yanshanian or early Himalayan mineralization.
The Liannan Bikeng Silver Mine is a NE-trending anomaly zone close to the SN-trending ore-bearing silicification fracture zone. The ore (chemical) zone is mostly produced along the interlayer fracture zone. The metal mineral of the V2 ore body is pyrite. , chalcopyrite, and bornite are the main components. The V5 ore body rock ore identification found weak mineralization of chalcopyrite and blue copper ore, showing that its primary ore is characterized by copper-silver mineralization. The ore rare earth normalized partitioning curve of North American shale has negative Ce anomalies and negative Eu anomalies. Combined with the trace element content, it is inferred that there may be submarine volcanism in the early stage and magmatic hydrothermal superposition in the later stage.
4. The geological characteristics and alteration types of fine-grained disseminated gold deposits (Carlin type) in neighboring Yunnan, Guizhou and Guangxi areas
The fine-grained disseminated type (Carlin type) is a A type of mineral deposit with unique origin, huge reserves and economic significance. The adjacent areas of Yunnan, Guizhou and Guangxi, as well as the northwest edge of the Central Hunan Depression and the Central Guangdong Depression, are rich in reserves of this type of mineral deposits.
Fine-grained disseminated gold deposits have a set of low-temperature hydrothermal mineral combinations, including pyrite, barite, stibnite, realgar, orpiment, arsenopyrite, cinnabar and a small amount of heavy metal sulfides such as Zinc ore, galena, twillite, chalcopyrite, marcasite, etc.
Combined with a large number of previous geochemical research results, it can be believed that the fine-grained disseminated gold deposit ore-forming fluid medium is mostly derived from atmospheric precipitation. The medium water passes through the strata in the basin and mixes with the construction water to circulate, dissolving Filter out the minerals. The migration of ore-forming fluids is obviously related to the process of large-scale tectonic-thermal events (magmatic events) in the basin, and mineralization has experienced the mixing, cooling, and oxidation of fluids.
The fine-grained disseminated gold deposits in Yunnan, Guizhou and Guangxi are concentrated in the Youjiang Rift Basin, located in the section sandwiched between the NE-trending Panjiang Fault Zone and the NW-trending Youjiang Fault Zone. Slightly triangular in shape, it is structurally located at the junction of the southwestern edge of the Yangtze Massif and the Youjiang Indosinian fold belt of the South China fold system. Cambrian and Devonian strata are scattered in the area, and Carboniferous, Permian, and Triassic strata are widespread. distributed. The northwest part of the Nanpanjiang fault is a platform facies area, which is mainly distributed with Permian-Triassic strata. Except for the Emeishan basalt exposed between the lower and upper Permian on the northern edge, the lower part of the upper Permian is composed of marine and continental coal. Outside of the Triassic strata, carbonate rocks are distributed over a large area; the southeastern part of the Nanpanjiang Fault is the trough clastic lithofacies area, and the Triassic strata are dominated by clastic lithofacies with carbonate rocks intercalated. The rhythm of clastic sedimentation is developed, and turbidity current sedimentary structures such as Bouma sequence, trough mold, syngenetic slip-slump accumulation, and enveloping bedding can be observed. It is the main gold-bearing rock series in the region. A series of fine-grained disseminated gold deposits have been discovered in the area. In addition to large gold mines such as Zimutang, Getang and Lannigou in Guizhou and Jinya and Gaolong in Guangxi, gold deposits have also been discovered in Funing Gedang and Luoping Lubuge in Yunnan. Similar to gold deposits, it shows that the Yunnan, Guizhou and Guangxi regions are important fine-grained disseminated gold mineralization areas and prospecting areas in China.
An important factor affecting the gold mineralization in the area is the Permian Emeishan basalt widely distributed in the north of the area, and the Triassic deep-water and semi-deep-water basin turbidity current deposits developed in the area. .
There is no magmatic rock in the area, but according to regional gravity data, it is believed that there are two hidden granite belts in the depths of the area, one is the Xingren-Nandan hidden granite belt, and the other is the Longlin-Bama hidden granite belt. However, their genetic connection with the fine-grained disseminated gold deposits in the area remains to be studied.
The alteration effect of fine-grained disseminated gold deposits in this area is not very strong, the zoning is not obvious, and metasomatic dissolution is not developed. Therefore, it is difficult to distinguish the surrounding rock, mineralized surrounding rock, and mineral deposits from a macro perspective. the exact boundaries between bodies. However, the basic types of wall rock alteration can be determined, including decarbonation, silicification, mudification, sulfideation and carbonation.
At least three stages of silicification can be distinguished, that is, silicification in the early stage of mineralization, forming cryptogranular and particulate quartz, which is prominent in Banqi and Getang gold deposits; silicification in the main mineralization stage, mostly forming fine particles. Reticular quartz, the outstanding feature of this period of quartz is clean surface and good transparency, often accompanied by dolomite, arsenopyrite, and pyrite; silicification in the late stage of mineralization forms thick and clean quartz veins or comb-shaped quartz, many of which are Contains coarse-grained euhedral pyrite, chalcopyrite, sphalerite, marcasite, and dolomite-quartz veins.
Mudification is one of the important alterations in gold mineralization. It mainly forms illite and dikaite, which are commonly developed in all deposits. From the analysis results, it can be seen that the stronger the mudification, the more clay minerals. The higher the content, the higher the gold content, indicating a positive correlation between the two. Carbonation occurs in the late mineralization stage, forming mainly calcite and a small amount of dolomite.
The formation of fine-grained disseminated gold deposits in the Yunnan, Guizhou and Guangxi regions can generally be divided into four mineralization stages, namely the pyrite-quartz stage and the arsenopyrite-pyrite-illite-quartz stage. , the polymetallic-dikaisite or polymetallic sulfide-quartz stage, the late stage of mineralization, and the mineralization period is generally divided into two stages: the hydrothermal stage and the epigenetic stage.
5. The formation mechanism of gold and silver deposits related to medium-acidic granite (porphyry) bodies
Mainly found in the middle and lower reaches of the Yangtze River, the ore bodies were produced in the Yanshanian granodiorite In the contact zone between porphyry bodies and Triassic carbonate rocks, the mineralization is mostly related to the Yanshanian intermediate-acidic granite (porphyry) rock bodies, and its formation age is consistent with the intermediate-acidic granite (porphyry) bodies (140±5Ma ), representative deposits include: Jilongshan, Fengsandong, Lijiawan, Jiguanzui and other large to medium-sized copper-gold polymetallic deposits, which constitute an important part of the polymetallic mineralization belt in the middle and lower reaches of the Yangtze River.
2. The mineralization relationship between precious metals and non-ferrous metals
Tungsten and tin deposits are a type of deposits with strong mineralization specificity and are closely related to granite magma activity. Tungsten, tin, niobium, and tantalum deposits are closely related to the formation of early Yanshan crust-source granite, while copper (iron), lead, zinc and other deposits are closely related to the formation of crust-mantle mixed-source granite and are controlled by fault zones. of epigenetic granites. Cheng Yuqi, Chen Yuchuan et al. (1979) proposed "a mineralization series type of lead, zinc, and sulfur (silver, copper, mercury, antimony) deposits related to crust-mantle mixed source granodiorite and a mineralization series type related to crust-source biotite granite. Relevant mineralization series types of rare, rare earth, tungsten, tin, copper, lead, zinc, antimony, mercury, silver (molybdenum, uranium) deposits." The types of mineralization are different in various regions of Nanling. Generally speaking, the southern Gansu region is dominated by tungsten mineralization. The western Nandanhechi area of ??northern Guangxi is dominated by tin, lead, zinc, and antimony mineralization, while the eastern region is dominated by lead and zinc. Tungsten, tin, lead, and zinc are all important in southern Hunan and northern Guangdong, while tin is dominant in eastern Guangdong and southeastern Yunnan, and lead and zinc are dominant in southeastern Yunnan. The relationship between silver and tungsten, tin, (lead, zinc) ores also varies with regions and mineralization times. This heterogeneity of spatial distribution is determined by the spatiotemporal evolution of structure-magma-mineralization, and is related to the heterogeneity of element distribution to a certain extent.
The precious metal deposits in the Nanling area have a very obvious affinity with the tungsten, tin, lead-zinc deposits, which are mainly reflected in:
1. The relationship between gold deposits and tungsten-tin deposits
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With the continuous improvement of the level of work and research, a number of primary gold deposits (spots) have been discovered in southern Jiangxi. Up to now, more than 50 rock gold deposits (sites) have been discovered in the study area, distributed in Xingguo-Ruijin, Shangyou-Xinfeng, Sannan (Dingnan, Longnan and Quannan)-Xunwu and other areas. Concentrated in the tungsten-tin ore concentration area or the periphery of the tungsten-tin ore deposit.
This study shows that the gold deposits in southern Jiangxi have the following characteristics: ① 95% of the gold deposits are distributed in the Precambrian strata, and the ore-bearing surrounding rock strata have high gold abundance, which is generally rich in the crust. 2 to 3 times the degree of gold deposits (Wang Dingsheng, 2001); ② Gold deposits are closely related to magmatic rocks, and the abundance of gold in magmatic rocks near almost all gold deposits (points) is relatively high; ③ Structure has obvious control over gold deposits, and almost all gold deposits have a relatively high abundance. The spatial distribution of gold and silver deposits is directly controlled by the fault structure; ④ Gold and silver deposits are mainly distributed in tungsten-tin ore concentration areas or on the periphery of tungsten-tin ore deposits, and tungsten-tin ore deposits have obvious mineralization zoning phenomena.
Although some researchers realize that there may be some genetic connections between gold deposits and tungsten-tin deposits in this area, they have not conducted in-depth research on tungsten-tin deposits and gold deposits as a mineralization system. The following main issues require further study. :
1) The issue of the metallogenic age of gold deposits. Although gold deposits and tungsten-tin deposits exist spatially, are they synchronized in mineralization time? Are they formed by the superposition of mineralization in different eras or are they the product of different evolution stages of the ore-forming magma at the same time?
2) Issues related to magmatic rocks related to gold mineralization. That is, the diagenetic age, lithological characteristics, geochemical characteristics of magmatic rocks related to gold mineralization and the structural background of their production need to be systematically divided and classified, and their rules should be summarized. Conduct comparative analysis of magmatic rocks to clarify the differences and connections between the two;
3) The metallogenic mechanism and metallogenic model of gold deposits in this area.
2. The temporal relationship between silver mineralization and tungsten, tin, lead and zinc mineralization
The mineralization age of tungsten and tin (lead and zinc) in the study area can be divided into pre-Gali There are five mineralization stages including the Eastern, Caledonian, Variscan, Indosinian and Yanshanian stages. Among them, the Yanshanian stage can be divided into the second and third stages of the early Yanshanian stage and the early stage of the late Yanshanian stage. The Yanshan period is the most important mineralization period in the area. Different mineralization stages have different combinations of deposit types. Silver ore is produced with the production of different phases and types of tungsten, tin, lead-zinc ore, and also has its own mineralization characteristics.
The southern Jiangxi area is dominated by tungsten and (tin) mineralization, which was formed between 170 and 104 Ma. It is closely related to the intrusive activities of granitoids in the second and third stages of the early Yanshanian period and the early stage of the late Yanshanian period. The entire mineralization can be divided into 5 to 7 stages. Silver mineralization starts from the early tungsten mineralization and ends before the final carbonation stage, but it is mainly in the III or V stage, forming the genetic type and A series of deposits with different combinations of mineralized elements, including contact metasomatic silver-tungsten deposits, silver-bearing quartz vein-type tungsten and (tin) deposits, mesothermal hydrothermal silver-tungsten deposits and silver deposits. This series of tungsten, (tin), and silver deposits is a series of products under different temperature and pressure mineralization conditions under the same magma-hydrothermal evolution. Silver and tungsten are enriched at different mineralization stages in the same deposit. The peak enrichment period of silver is later than that of tungsten. Therefore, when the tungsten content is high in space, the silver content is not high. When the silver content increases in the high-medium to medium-low temperature stages, the concentration of tungsten increases. The content has been reduced.
Tungsten, tin, lead, and zinc deposits are intensively produced in Xiangnan District, and their genetic types range from contact metasomatism to medium- and low-temperature hydrothermal types. The mineralization is closely related to the emplacement of Yanshanian granite. Most of the known mineral deposits are located in the contact zone of highly emplaced small rock bodies or in the surrounding rocks. The mineralization of tungsten ore is mostly limited to the high-temperature hydrothermal stage. The mineralization time of tin is slightly later than that of tungsten, and the mineralization is mainly based on high- and medium-temperature hydrothermal fluids. The mineralization time of lead, zinc and silver is relatively late, mainly in the medium-low temperature hydrothermal stage. When tin mineralization begins, silver enrichment is enhanced, but by the time lead and zinc are massively enriched, tin has been exhausted and silver enrichment intensity increases. Generally speaking, the time sequence of mineralization is tungsten → tin (copper, silver) → lead, zinc, silver.
The Dachang ore field (ore deposit) is composed of cassiterite-sulfide polymetallic and silver materials related to the late Yanshan epigenetic granite (Rb-Sr age is 99±6Ma～115±3Ma. Chen Yuchuan et al., 1993) , antimony, arsenic, and mercury mineralization sub-series, and its mineralization can be divided into five stages. Silver ore is mainly formed in the second mineralization stage of tin, silver, sulfide-sulfate-carbonate mineralization.
Tungsten, tin, lead, zinc, and silver deposits in southeastern Yunnan are all distributed near three small rock bodies that protrude from the Yanshanian granite base. Due to the development of a series of sulfur-philic tin deposits in this area, lead, zinc, and silver mainly precipitate and form minerals in the sulfide stage. The ore-forming temperatures range from 260 to 350°C in Gejiu and 108 to 31°C in Bainiuchang (Yu Chongwen, 1987). Generally speaking, silver has the same mineralization age as tungsten and tin, but its mineralization time is later than tungsten, slightly later than tin, slightly earlier than lead-zinc, and ends before the carbonate stage.
Tungsten and tin-based mineralization, if it develops in multiple stages from high temperature to low temperature, the associated silver mineralization will be obvious, while if it develops in a single stage, the silver mineralization will be poor or non-existent.
3. Spatial relationship between silver mineralization and tungsten and tin deposits
Silver mineralization and tungsten and tin deposits in the Nanling area are often "inseparable" in space and are produced together, and It often shows the characteristics of evolution from high temperature to medium and low temperature deposits with the Yanshanian granite body as the center and outwards.
For example, the Gejiu metallogenic area in southeastern Yunnan is centered on the Yanshanian granite body, and outwards appear in sequence: W, Mo, Bi→Cu, Sn→Sn, Zn, Ag→Pb, Zn, Ag graded deposit series; Dachang Mine in western Guangxi The field is also centered on the cage lid granite body, and appears outwards in order: Co, Zn, Ag (skarn mineralization period) → Sn, Zn, Pb, Ag, Sb (cassiterite-sulfide polymetallic mineralization period) →Zoning phenomenon of W and Sb (tungsten and antimony mineralization period). Large independent silver deposits are often associated with or contain tin in the deep parts. For example, the Houpao silver, tin, lead, and zinc mine in Chaozhou City is a large-scale silver deposit, and tin, lead, and zinc are both medium-sized; the tin associated with silver in the deep parts of the Bainiuchang silver deposit is also of industrial grade. This reflects the thermal effect of temperature gradient and the specificity of mineral deposit zoning, which is a common phenomenon in the Nanling area.
Regional mineralization geological environment and specific deposit positioning mechanisms both restrict and depend on each other and vary from place to place. Therefore, there are multiple forms of deposit combinations, multiple types and Different scales. For example, tungsten and silver deposits in eastern Guangdong are spatially distributed in the Yongmeihui Depression, especially concentrated in the Meixian Depression in the north. They are produced in the Caledonian fold fault-magma belt and are controlled by the Yanshan Phase 3 complex granite body. Tin and silver deposits are controlled by the Lianhuashan and Chaozhou-Puning Haifeng deep faults. Lead, zinc, and silver deposits are relatively concentrated in and near the Lianhuashan fault-magma zone. The spatial distribution of copper, lead, zinc, silver, silver, antimony, gold, and silver deposits is mainly controlled by volcanic basins and EW-trending faults. Another example is the gold and silver deposits along the edge of the Yunkai uplift in southeastern Guangxi, from Lianjiang Pangxi Cave-Jinshan-Zhongsu-Wangtian Cave, Shike-Xiaying-Longshui-Zhanggongling, etc., which are obviously affected by the Bobai-Cenxi Deep Control of granite magma activity by faulting and deep source synmelting.
The spatial relationship between the mineralization of tungsten, tin and silver in this area has an overlapping and transitional relationship between "syngenetic bodies" and "syngenetic bodies". For example, the Yaogangxian tungsten-silver deposit consists of multiple phases of overlapping mineralization. Each phase of magmatic activity has experienced gas-generated high-temperature hydrothermal fluids to medium-low-temperature hydrothermal fluids, forming various types of tungsten, tin, copper, molybdenum, lead, Many minerals such as zinc produce "allogeneic" silver deposits with tungsten and tin. But generally speaking, from the outside of the rock mass or from deep to shallow, the deposits containing silver, tungsten, and tin transition to the deposits of silver, lead, and zinc. For example, the elevation of Yaogangxian No. 501 vein increased from 950m to 820m to 110m, and the average silver grade increased from 57.6g/t to 118.5g/t to 180g/t, reflecting the change in silver ore output type from associated silver deposits to ***generated silver. Mineral deposit → evolution law of independent silver deposit. In tungsten-silver deposits in southern Jiangxi and southern Hunan, there are two types of mineralization elements: zoning and non-zoning: ① Tungsten (tin) and silver-generated deposits all have tungsten and silver zoning, among which, silver-containing quartz veins Type tungsten ores and mesothermal hydrothermal tungsten-silver deposits generally show reverse vertical zoning, with tungsten concentrated in the middle and upper parts, and silver in the lower part; skarn-type silver-tungsten deposits generally show forward zoning, with the tungsten ore body at the bottom. The silver ore body is above. This kind of zoning sometimes also appears in the horizontal direction, with parallel or row-like zoning of tungsten ore bodies and silver ore bodies. ② Ore deposits produced by lead and silver generally do not have zoning or the zoning phenomenon is not obvious. The vertical zoning of silver, tungsten, and tin ores in eastern Guangdong also has obvious regularity: generally, tungsten and tin mineralization have the characteristics of multi-stage reverse zoning, and tungsten and tin mineralization are mostly concentrated in ore bodies. In the upper part, the polymetallic sulfides gradually increase downward, that is, the upper part of the general ore body is tungsten and tin ore, and the lower part gradually becomes lead, zinc, copper, and silver ore bodies. For example, the Houpoao mining area in Chaozhou shows a zoning phenomenon of tin in the upper part and lead, zinc and silver in the lower part; tungsten and (tin) in the upper part and copper and silver in the lower part of the Guangkeng mining area.
4. The correlation between silver mineralization and tungsten-tin mineralization and the relationship with the types of ore-forming granites
1) Silver deposits related to syn-melting granitoids, silver is mostly related to Gold and polymetallic ores are associated or produced, and have no obvious correlation with tungsten and tin ores. The geochemical characteristics of its deposit are high content of Ni, Co, Cu, Mo, Ag and other elements, which are basically consistent or similar to the trace element characteristics of isotope granite. For example, in Pangxidong, Jinshan, Zhanggongling and other deposits, the vertical zoning of the primary halo: the front element is Sr-Mn-Ni-Co, the element in the mine is Cu-Ag-Pb-As-Zn-Au, and the tail element is Sb -Mo. This type of deep-source syn-melting granite mostly intrudes along the Bobai-Cenxi fault zone and the Lianhuashan fault zone. The rock mass generally contains high Ag content and can form independent (or independent) silver deposits.
The mineralization in southern Hunan and eastern Guangdong is related to synfusion-type granitoids. It is mainly found in depression areas and their edges. The mineralization of intermediate-acidic granites in the second stage of the Yanshanian period is mainly responsible for the formation of lead, zinc, and silver deposits. Mainly, it is often accompanied by the mineralization of copper, tin and tungsten.
2) The mineralization related to continental crust remelting granitoids is manifested in the uplift area, mainly the mineralization of the first stage of granite in the early Yanshan period, forming a mineralization concentration dominated by tungsten deposits. district. For example, early Yanshan biotite granite or biotite K-feldspar granite in the southern Jiangxi uplift area formed silver-bearing quartz vein type tungsten and (tin) deposits, contact metasomatic silver and tungsten deposits, mesothermal hydrothermal type silver and tungsten deposits and silver deposits ( Including gold and silver deposits containing W and Sn). The uplift and Ao edges form a mineralization area (belt) dominated by tungsten and tin, accompanied by copper, lead, zinc, and silver deposits. The Chenzhou area is on the edge of the uplift and the Ao. The activity of granite magma lasted from the early Yanshanian period to the late Yanshanian period. The mineralization process went through the mineralization stages of mainly tungsten → mainly tungsten and tin → mainly lead, zinc and silver. The mineralization peaks overlap, forming many large deposits such as Shizhuyuan, Hongqiling, Yaogangxian, Darjeeling, and Dongpo mines.
3) Multiple intrusions of granite magma and multiple mineralizations are also another feature of Nanling mineralization. For example, the Yaogangxian complex granite body has four intrusions and four mineralizations. The size of the rock mass changes from early to late, from large to small. The first three mineralizations are the main ones, and each intrusion is accompanied by metal mineralization. The first to third metal sulfides gradually strengthened and invaded from south east to north west, forming tungsten-silver mineralization → lead, zinc and silver mineralization zones. Another example is the Gejiu mine. In the western area where Indosinian-Yanshanian granites are exposed, there are Jiasha gabbro-monzonite body, Longchahe porphyritic biotite granite, Baiyunshan alkaline syenite and Changling gangnepheline syenite. There are many silver-lead and tin-lead mineral spots around the outer edge of the Longchahe complex. The eastern area is a hidden complex biotite granite base with a burial depth of 200-1000m. Only small areas are exposed in Baishachong, North Fort, Baishapo, etc. There are industries in the upper protruding parts of the hidden rock mass (Masong and Laoka areas). Tin, lead, zinc, silver mineralization.