Located in the western margin of Yangtze platform, this area is not only the accretion zone of ancient land block, but also the junction of ocean crust and continental crust, with strong geological tectonic activity and deep faults. The uplift zone and depression zone formed by long-term structural development are bounded by crustal faults or super-crustal faults. A series of deep faults not only control the development and evolution of regional geological history, but also directly control the occurrence and distribution of alkali-rich porphyry copper polymetallic deposits.
The geotectonic environment of alkali-rich porphyry copper polymetallic mineralization in this area can be divided into two types: one is the marginal environment of continental or intracontinental ancient plates (such as Yao 'an lead-silver-gold mine); The second is the continental margin accretion zone environment (such as Ninglang-Dali Cu-Mo-Au deposit), under which Himalayan alkali-rich porphyry copper polymetallic and precious metal deposits were formed, which is the main feature of mineralization in this area.
The deep faults in this area are bounded by the suture line of Jinsha River-Ailaoshan plate, and there are north-south faults in central Yunnan, northeast faults in Sanjiangkou-Qinghe and northwest faults in Lanping-Simao in the west, all of which belong to Tethys-Himalaya deep fault system.
Figure 6- 1 Schematic Diagram of Distribution of Copper Polymetallic Deposits in Porphyry Metallogenic Belt in Western Yunnan Figure 6- 1 Mineral Distribution Map of Copper Belt in Western Yunnan
The suture line of Jinsha River-Ailaoshan plate belongs to a super-crustal fault, extending along the Jinsha River valley and the west side of Ailaoshan, and generally showing NW-SE direction. Its structural characteristics are the composite characteristics of thrust nappe and ductile shear zone. The main active periods are Hercynian, Indosinian and Himalayan, and the late tectonic activities are characterized by the formation of large strike-slip ductile shear zones in the mainland, with isotopic ages of 40 ~20Ma. The copper polymetallic mineralization of alkali-rich porphyry mainly occurs in the accretion zone on both sides of Ailaoshan-Jinshajiang fault, which may be related to the intense compression of late tectonic activities and strike-slip shear tectonic activities.
Late tectonic activity of Jinshajiang-Ailaoshan fault zone and isotopic age of Himalayan porphyry copper deposits in eastern Tibet (33 ~49Ma) and the last extinction period of Tethys-the end of Eocene (38. 2Ma), indicating that the tectonic-magmatic-metallogenic time is consistent.
The north-south deep fault zone in central Yunnan is located on the northeast side of the suture line of Jinsha River-Ailaoshan plate. From east to west, there are Yuanmou-Lvzhijiang fault, Dukou-Chuxiong concealed deep fault, Chenghai-Binchuan fault and Jingzanhe fault. The north-south direction is parallel and slightly symmetrical. The fault combination is in the form of horst graben, which controls the Mesozoic platform margin rift in Yao 'an, the Paleozoic accretion fold belt in Ninglang-Dali and Zhongdian Island respectively.
The Sanjiangkou-Qinghe River north-east fault zone mainly includes Xiaojinhe-Sanjiangkou fault, Lijiang-Muli fault and Qinghe fault from north to south. This group of faults was formed in the early Paleozoic, with strong activity in Hercynian (Permian), accompanied by basic-ultrabasic magmatic intrusion. Paleozoic-Triassic may be a set of extended normal faults, which together with * * * form a trough. This NE-trending fault zone may have concealed faults in Dayao and Nanhua areas to the south, and may cross Jinsha River and Honghe fault to Lanping-Simao basin, which may be a cross-regional reflection of coastal Pacific structures. The alkali-rich porphyry belt in the western margin of the platform is mostly distributed in the northeast direction, which is related to this group of deep faults.
Two groups of deep faults, north-south and northeast, are important rock-controlling and ore-controlling structures in this area, which not only control the boundary of the terrane at the edge of the platform, but also obviously restrict the distribution of alkali-rich porphyries in Himalayan period and the division of metallogenic areas. Such as Beiya, Ma Changqing, Yao 'an and other copper, lead (silver) and gold polymetallic metallogenic areas are controlled by it, and become the most characteristic alkali-rich porphyry copper-lead polymetallic deposits in the western margin of the Yangtze platform.
The NW-trending fault zone in Lanping-Simao basin is mainly developed in the Late Paleozoic depression trough at the edge of the basin, parallel to and inclined to the plate suture line, and is a group of NW-trending and NW-trending deep faults. From east to west, there are mainly Fujiaohe fault, Amojiang fault, Weixi-Qiaohou fault and Yangla-Chezhulin fault.
The red river-Qiaohou fault and Amujiang fault correspond to each other in spatial distribution, and a NW-trending banded rift zone was formed at the edge of the basin between the late Paleozoic and early Mesozoic and the Jinsha River-Ailaoshan fault. The Himalayan alkali-rich porphyry distributed intermittently along the rift zone, forming a rift structural porphyry zone. From south to north, there are Jinping-Lu Chun Porphyry Group, Weishan Porphyry Group, Laojunshan Porphyry Group in Jianchuan, Weixi Porphyry Group and Deqin Porphyry Group. Gold mineralization is also widespread, forming an important copper-gold mineralization belt in this area. This alkali-rich porphyry polymetallic metallogenic belt extends northward and is adjacent to Yulong ore belt in eastern Tibet.
The rock-controlling and ore-controlling mechanism of deep faults can be inferred as a deep penetrating structural system formed by the Jinshajiang-Ailaoshan fault zone and the north-south, northeast and northwest faults on both sides, which leads to the continuous rise of deep magma and ore-bearing hot water solution along this penetrating structural system and the formation of deposits in the secondary fault zone derived from late tectonic activities (such as compression and relative strike-slip shear activities), which shows the disharmony between regional structure and ore-controlling structure.
The rock-controlling and ore-controlling indicators of deep and large faults can be summarized as follows: the intersection and composite parts of multiple deep and large faults, the intense compression of late tectonic activities and the development of structural fractures are the most favorable metallogenic parts. For example, the Ma Changqing-Xiaolongtan metallogenic concentration area is located at the intersection of the northwest ductile shear structural belt of Ailao Mountain and the north-south deep fault of Binchuan. The porphyry belt is distributed in the northeast, and the ore-controlling structures are mostly east-west tensile faults.
Second, the magmatic rock sign.
The mark of magmatic rocks includes two meanings: one is the mark of multi-cycle volcanic-magmatic activity; Secondly, it is the symbol of alkali-rich porphyry mineralization series.
1. Ore-controlling indicator of multi-cycle volcanic magmatic activity
Porphyry copper deposits are mostly related to the widely developed calc-alkaline and alkaline calc-alkaline series of intermediate-acid volcanic magmatism, and most deposits are consistent with contemporary volcanic magmatic belts. Porphyry formation is the product of hypabyssal-ultrahypabyssal magma intrusion, which often forms a unified regional intrusive rock belt with regional plutonic formation. Therefore, the multi-cycle volcanic-magmatic composite rock mass indicator has maintained a long-term relationship with magma chamber, which is an important indicator of mineralization.
Magmatic activity in Yunnan is very strong, with the characteristics of multi-stage activity, wide distribution and complex types. Magmatic activities within the scope of this book are mainly Hercynian, Indosinian and Himalayan periods after the late Paleozoic, with volcanic rocks as the main ones.
Volcanic rocks are the main magmatic activities in Hercynian period and widely distributed in late Permian. Most of the rocks are basalt, and a few are alkaline basalt, dacite and rhyolite, which belong to marine and marine-continental eruptive rocks. The intrusive rocks in the same period are ultrabasic rocks, which are exposed on both sides of Ailaoshan fault and produce copper-nickel sulfide vanadium-titanium magnetite deposits.
The Indosinian magmatism was intense, mainly volcanic rocks, distributed in Lancang River, Jiangda-Lu Chun, Yidun and Ganzi Litang on the western margin of the Yangtze Platform. The volcanic rocks in Lancang River are intermediate-acidic and basic volcanic rocks in the Middle and Late Triassic, belonging to calc-alkaline series. The northern part of the Jiangda-Lvchun volcanic-magmatic belt is a middle-late Triassic intermediate-acid volcanic rock, and the southern part is a late Triassic calc-alkaline volcanic rock. Yidun belt is dominated by middle Triassic intermediate-acidic volcanic rocks, while Ganzi Litang belt is middle Triassic basic-ultrabasic rocks and intermediate-acidic volcanic rocks, all of which have copper anomalies, with the highest reaching (70 ~ 120) × 10-6. Indosinian intrusive rocks belong to intermediate-acid rocks, which are divided into diorite, quartz diorite assemblage and granodiorite and adamellite assemblage. Most of them are distributed in the banded bedrock along the north-south fault in Gezan, with copper, lead and zinc mineralization, forming porphyry and skarn copper and molybdenum polymetallic deposits, such as Xuejiping and Hongshan.
Volcanic-subvolcanic magmatism was widespread in Himalayan period, and basic-ultrabasic volcanic rocks erupted on land in Jianchuan, Dali and Mojiang. The intrusive rocks are mainly intermediate-acid hypabyssal intrusive rocks, which are distributed along both sides of Ailaoshan-Jinshajiang fault. The rock types are mainly syenite porphyry, adamellite porphyry and granite porphyry. At the same time, there are a few branches of basic, intermediate and acidic dikes, forming a large alkali-rich porphyry belt, and the rock types in the belt are slightly zoned. The Yan Yulong belt in the northern section is calc-alkaline adamellite, mainly copper mineralization; The southern section is alkaline granite, syenite intrusive rock, alkaline and acidic rock mass, and contains copper, molybdenum, lead, zinc and silver polymetallic mineralization.
As we all know, the mineralization of large-scale porphyry copper deposits in China is related to multi-cycle volcanic-magmatic activities. For example, the volcanic magmatism of the Yulong Himalayan porphyry copper deposit in eastern Tibet can be divided into four stages: the first stage is intermediate-acid volcanic lava and tuff, the second stage is granodiorite and quartz diorite, the third stage is biotite monzogranite porphyry (ore-bearing rock mass), and the fourth stage is monzogranite porphyry, albite porphyry and granodiorite porphyry.
Composite rock mass (or composite rock mass) reflects the multi-stage activity and high evolution of magma, and is an important symbol of prospecting prediction.
2. Metallogenic indicators of alkali-rich porphyry series
Himalayan magmatism was intense, developed in the collision zone between Indian plate and Eurasian plate, belonging to shallow-ultra-shallow intermediate-acidic and alkaline rocks, distributed in groups along the Ailaoshan-Jinshajiang suture line, forming an alkali-rich porphyry intrusive rock zone, with faults on the mainland and its edge.
The types of alkali-rich porphyries in the western margin of the Yangtze platform are mainly syenite, quartz monzonite, syenite granite and monzogranite, and the rock mass is in the form of branches, tubes, dikes and dykes, and the exposed area is generally less than 65438±0k m2. According to 75 chemical analysis calculations, Rietmann index (δ value) ranges from 2 to 7, indicating that most of them are alkaline series, and some are alkaline calcium and overbased. The isotopic age of alkali-rich intrusive rocks ranges from 49 to 33 Ma, which is equivalent to the product of the early and middle Himalayan period. The alkaline granite (49 ~40Ma) is slightly earlier than the alkaline syenite (37 ~ 33 Ma), and the magmatic differentiation evolves from acidic to neutral and then to alkaline from north to south (for example, Yulong is biotite monzoporphyry, Ma Changqing is porphyry granite and syenite, and Tongchang Changan is porphyry syenite. The mineralization in the northern section is mainly molybdenum and copper, the mineralization in the middle section is copper, molybdenum, lead, zinc, silver and gold, and the mineralization in the southern section is copper, molybdenum and gold, forming a copper polymetallic-precious metal metallogenic belt related to alkali-rich porphyry.
The Ailaoshan-Jinshajiang alkali-rich porphyry belt stretches over 800 kilometers in Yunnan and can be divided into five rock areas. The east side of the suture line is Yao 'an, Dali and Jianchuan areas, and the west side is Yongping and Jinping areas. Each rock area is controlled by structural zoning, showing different tectonic magmatic environment and geological background. The diagenetic time in Dali area is earlier (67 ~36. 3Ma) and last for a long time. Rock mass has high acidity (silica 57. 87%-70.54%) and low alkalinity (delta value is 3. Average 74). Mineralization is dominated by copper and gold, which is the most important porphyry metallogenic area in the western margin of Yangtze platform. Jianchuan district is similar to Dali district, but it was formed relatively late (33 ~ 4 1. 8ma), with low acidity and mineralization of copper, molybdenum, gold and silver. Yongping district has the strongest alkalinity (SiO2 46. 78% ~ 6 1.34%), with the highest alkalinity (δ value 7. 95) and high rare earth content (σ REE 74. 6× 10-6), copper-bearing and gold mineralization. Some characteristics of rocks in Jinping area and Yao 'an area are similar, and the formation age is 35. 3 ~ 34 Ma, silica 64. 4 1% ~ 62.5 1%, and the δ value is 5. 4 1 ~ 5. 17, high rare earth content (σ REE (605
Judging from the rock series of the above five rock areas, Dali area and Jianchuan area have low alkalinity, belonging to intermediate-acid calc-alkaline series, mainly alkaline granite; Jinping and Yao 'an areas are very alkaline and belong to alkaline rock series. Yongping district is a series of saline-alkali land. Copper polymetallic deposits related to alkali-rich porphyry are mostly distributed in Dali area and Jinping-Yao 'an area, which is an important sign of mineralization.
Three, the surrounding rock alteration and mineral element combination marks
1. Alteration zoning mark
The alteration zoning directly related to porphyry copper polymetallic mineralization is generally outward from porphyry body, mainly from timely potash feldspar (Mo, Cu, Au) → timely sericitization (Cu, Mo) → Shi Shui muscovite or bluestone (Pb, Zn, Ag, Au) in Yili, and the wall rock alteration is mainly skarnization (carbonate rock) and hornblende (clastic rock).
The scale, zonation and superposition of alteration play an important role in controlling mineralization. The appearance of alteration zone is related to the infiltration, diffusion and convection circulation of ore-bearing hydrothermal solution rising along a certain channel. The alteration range is large, reflecting the sufficient heat source and the development of structural fractures, which is a sign of large-scale deposit mineralization.
The alteration zone of Ma Changqing porphyry in Xiangyun is strongly silicified zone-medium potassium silicified zone-weak potassium feldspar silicified zone. Copper occurs in the second zone, and there is a wide contact metamorphic zone (100 ~600m m wide) outside the rock mass, which is plagioclase-diopside felsic hornfelsic → biotite chronological hornblende from the inside out. The study of hydrogen and oxygen isotopes shows that the accumulation place of metal sulfide is the mixed zone of magmatic water and groundwater. In the early stage of alteration, the hydrothermal solution of K-feldspar mineralization was mainly magmatic water, in the middle stage it was timely sericitization, and in the late stage it was muscovite in Shi Shui, Yili, mainly natural water.
2. Prospecting mineralogy and trace element markers
The metasomatic alteration of porphyry reduces the grade of plagioclase, and the potash feldspar changes from feldspar-like to banded feldspar and some microcline feldspar. The order degree of potash feldspar increases, and the stronger the alteration, the higher the order degree value.
Volatile components are of great significance to improve the migration ability of ore-forming elements. Mineralization element combination of each alteration zone: the K-feldspar zone is Cl-S-Fe; The timely sericitization zone is chlorine-fluorine-sulfur-arsenic-antimony-selenium; The water dolomite mother zone is carbon dioxide-arsenic-antimony-selenium.
Accessory mineral assemblage: unmodified porphyrite includes magnetite, apatite, zircon and sphene. After alteration, magnetite and apatite decreased, while pyrite and rutile appeared in large quantities. The ore-bearing porphyry is characterized by iron-rich biotite. Rutile and biotite in porphyrite are rich in copper. Magnetite and metal sulfide minerals generally contain platinum group elements, among which chalcopyrite has the highest content. Pyrite in some deposits contains Ag and Au, chalcopyrite contains Au, and molybdenite contains Re and Au.
During hydrothermal alteration, rare earth elements changed obviously, and the loss of europium was closely related to mineralization. After porphyry alteration, σ REE increased, σ Ce/σ Y decreased, and the loss of europium was obvious, and δEu was 0. 49 to 0. 52. Among them, the σ REE of potassium-bearing zone increased by 0. 64 times, while it increased by 0 in sericitized zone. 18 times, but σ REE in the surrounding rock decreases after alteration, indicating that the changes of rare earth elements in porphyry and surrounding rock are complementary.
Four. Metallogenic series and zoning marks of ore deposits
In the porphyry copper polymetallic metallogenic belt, deposits often form porphyry polymetallic metallogenic series related to the combination of porphyry type, subvolcanic hydrothermal vein type and skarn type in the same metallogenic era, which are related to intermediate-acid calcium-alkali series hypabyssal or ultrahypabyssal intrusive rocks respectively, and are the products of genetic connection, different depths and different geological conditions.
Yunnan porphyry copper deposits can be divided into Indosinian island arc type and Himalayan continental margin fault type.
Himalayan alkali-rich porphyry distributed in the western margin of Yangtze platform belongs to continental margin fault type, distributed along both sides of Ailaoshan-Jinshajiang strike-slip ductile shear zone, all controlled by deep faults, and can be divided into three sub-zones: Yaoan porphyry zone in the east is controlled by Dukou-Chuxiong north-south concealed fault; The central Ninglang-Dali porphyry belt is controlled by the northwest Jinsha River-Honghe fault and the north-south Chenghai fault. The Jinping-Yuanyang-Weishan porphyry belt in the west is controlled by the NW-trending Armin River fault and Weixi-Qiaohou fault. Shallow porphyry belts appear along these faults and their derived secondary faults, with isotopic ages ranging from 32 to 62 Ma. The metal minerals related to alkali-rich porphyry are copper, molybdenum, lead, zinc, gold, silver and iron, which constitute the Himalayan alkali-rich porphyry metallogenic series. The ore-forming rocks are mainly granite porphyry, syenite porphyry and syenite porphyry.
The Ma Changqing rock mass (mainly granite porphyry) in the middle of the ore belt consists of 67. 7% silica, 8. 17% K2O+Na2O and 2. 75 δ, belonging to the calc-alkaline series. Yaoan rock mass in the east (mainly Shiying syenite porphyry) contains 63.46% ~ 70.06% SiO _ 2, 9. 24% K2O+Na2O and 4. 23 δ, belonging to alkaline series. Xitongchang rock mass (mainly Shiying syenite porphyry) consists of 66% SiO2 and 9. 18% K2O+Na2O, belonging to alkaline calcium series. Magmatic differentiation is alkaline-intermediate acid-alkaline-calcium in the ore belt from east to west, and accordingly, lead-zinc-gold-silver metallogenic sub-series related to syenite porphyry assemblage (represented by Yao 'an) and copper-molybdenum-gold metallogenic sub-series related to granite porphyry assemblage (represented by Ma Changqing) are formed.
For example, the zoning of metal elements in Ma Changqing Cu-Mo-Au deposit is centered on molybdenum, and copper and gold (lead and zinc) are irregularly distributed in a ring. The zoning of metallic minerals is chalcopyrite → chalcopyrite, pyrite → pyrite, chalcopyrite → pyrite, arsenopyrite, galena, sphalerite and natural gold. Metal elements are divided into molybdenum copper, molybdenum copper gold lead, zinc, gold, arsenic lead, zinc and silver.
The main mineralization types in Ma Changqing are veinlet-disseminated molybdenum ore in rocks, copper-bearing magnetite ore in contact zone skarn, copper-molybdenum ore in calc-skarn and veinlet-disseminated copper ore in amphibole, fractured altered rock type gold ore and peripheral hydrothermal vein type gold ore.
The zoning of metal minerals and metal elements and the distribution of mineralization types show the metallogenic changes from high temperature to medium and low temperature.
The traditional metallogenic model of porphyry copper deposits is composed of disseminated pyrite, chalcopyrite and porphyry, fissure-filled veins and timely veinlets. The zoning features are as follows: ① The intrusion center is weakly mineralized or not mineralized, containing a small amount of chalcopyrite, molybdenite and pyrite, with the content less than 2%; (2) The surrounding ring-shaped mineralized crusts are rich in molybdenite and chalcopyrite, and the content of metal minerals is 10% ~ 15%, with pyrite increasing outward; ③ The gold and silver-bearing metal veinlets are distributed in the radial fracture zone around pyrite halo.
Porphyry polymetallic deposits have horizontal and vertical alteration zones from the center to both sides from bottom to top. Zoning of metal minerals and metal elements is an important sign for finding blind ore bodies and judging the denudation degree and burial depth of ore bodies.
Verb (abbreviation of verb) the control sign of volcanic mechanism
The intersection of two or more sets of faults is often the center of volcanic magmatic activity, and ore-controlling structures are mostly related to the relatively uplifted volcanic mechanism, such as volcanic neck structure, volcanic dome, annular fault, radial fault and other associated volcanic structures in anticline areas. The existence of breccia volcanic lava and subvolcanic lava shows that the deep tectonic stress is strong, which is one of the signs for finding porphyry polymetallic deposits. For example, Yao 'an Pb-Ag-Au deposit is controlled by the caldera and lateral caldera of Huoshan fault basin during the contraction of continental rift, and the volcanic rocks include trachyte, leucite alkaline basalt, tuff and volcanic breccia.
Judging from the volcanic mechanism metallogenic system, the top of the volcanic metallogenic system is composed of blasting breccia tube, breccia tuff and homologous layered volcanic cone, and large pyrite and lead-zinc-silver veinlets are often developed. Porphyry pillars and altered mineralization halos constitute the middle and upper part of the volcanic metallogenic system, which is characterized by the development of copper-molybdenum veinlets and reticulated vein fractures. Isogranular porphyry granite base related to porphyry column constitutes the bottom or lower part of volcanic system and is disseminated copper mineralization. Therefore, the study of volcanic mechanism and metallogenic system is also an important symbol of prospecting.
Six, strata ore-controlling signs
The sulfur and lead isotopes of alkali-rich porphyry indicate that the source of ore-forming elements is consistent with that of magma, which may come from the deep crust and upper mantle. Due to the rapid intrusion of magma, the rock mass is hypabyssal or ultrahypabyssal, so it condenses quickly. Therefore, it is considered that the surrounding rock has little influence on mineralization, and it is unlikely that the ore-forming elements mainly come from the surrounding rock, but the nature and structural development of the surrounding rock control the combination of deposit types and the enrichment of mineralization. The surrounding rocks are carbonate rocks, which form skarn, porphyry or hydrothermal composite deposits under relatively open conditions. If the surrounding rock is aluminosilicate, a single porphyry veinlet disseminated mineralization will be formed. At the same time, the surrounding rocks with high content of polymetallic elements can also provide some material sources. The higher the ore-forming elements of source rocks, the greater the magma concentration. During the metallogenic period, the infiltration and leaching of magmatic hydrothermal solution and groundwater can absorb ore-forming elements from surrounding rocks and form ore deposits.
The occurrence strata of alkali-rich porphyry copper polymetallic deposits in the western margin of Yangtze platform are mainly Ordovician, Middle-Lower Permian, Middle-Upper Triassic and Jurassic-Cretaceous.
1) Early Ordovician flysch formation and sandy argillaceous carbonate formation in shallow sea: The rocks of the Lower Ordovician Xiangyang Formation in Binchuan area of Dali are sandstone and shale mixed with limestone lentils, and the bottom is black argillaceous siltstone, which is in contact with medium-shallow porphyry, with keratinization and skarnization. It is the ore-bearing stratum of Ma Changqing Cu-Mo-Au deposit, and the black argillaceous siltstone contains Au 56. 5× 65438+. The southern part of Jinping Copper Factory area is dominated by Ordovician and Middle Silurian. The host rock is the lower Ordovician feldspar sandstone interlayer, and the limestone is composed of rhythmic layers. The content of Cu is (30 ~ 50) × 10-6, a few are (120 ~ 450) × 10-6, and Mo is 8 ×.
2) Platform-type shallow sea-coastal carbonate rock formation and basic volcanic rock formation of Middle and Lower Permian: copper deposits in Huaping-Ninglang area in the north occur in basalt with carbonate basaltic conglomerate, carbonaceous shale and marl, and the ore bodies are veinlets and layered.
3) Middle-Upper Triassic carbonate-clastic rock flysch formation and basic-intermediate acid volcanic rock formation: Indosinian porphyry skarn copper-molybdenum deposit in Zhongdian occurs in upper Triassic sandstone, limestone, marl and volcanic rock. The Beiya Pb-Zn-Au deposit in Heqing County occurs in limestone and sandstone shale of Middle Triassic, and the ore-forming elements in altered limestone are abundant, with Cu being (100 ~ 200) × 10-6, Pb being (500 ~ 600) × 10-6 and Zn being. Ag is (1 ~ 3) × 10-6, and Mo is (1 ~ 4) × 10-6. Xiaolongtan copper deposit occurs in upper Triassic timely sandstone and argillaceous siltstone, and Yuanyang Hubble polymetallic deposit occurs in middle and upper Triassic carbonate rocks, coal-bearing shale and volcanic rocks.
4) Jurassic-Cretaceous fluvial-littoral red formation, copper-bearing formation and gypsum-salt formation: it belongs to intracontinental rift basin deposition. Yao 'an lead-silver gold deposit and copper deposit are located in sandstone, glutenite and sandy limestone mudstone. Copper-bearing sandstone copper deposits are widely distributed in Mesozoic and Cenozoic red beds, with abundant copper sources.
Seven. Geophysical sign
Moho surface calculated by Bouguer gravity anomaly is nearly east-west distribution, and the stratum thickness tends to be thin in the south and thick in the north. Moho surface has the characteristics of fault block and wave deflection. The areas where Moho surface bends to the south are Jingdong-Mojiang-Jinping and Deqin-Lanping lines, which are areas where the crust suddenly thickens, that is, Moho surface sag. The parts of Moho that protrude northward are Shuangjiang-Jinghong and Yuanjiang-Hekou areas.
The residual gravity anomaly well reflects the characteristics of the tectonic-metallogenic belt in this area, with Lanping-Simao negative anomaly (-5 ~- 10 mgal) in the west, Sanjiangkou-Zhongdian negative anomaly (-10 ~- 15 mgal) in the east and Cangshan-Ailaoshan positive anomaly (. All of them are arranged in the northwest direction, and the change lines with alternating positive and negative anomalies, that is, near the zero isoline of the remaining anomalies, are consistent with the Honghe fault, Jinsha River fault, Qiaohou fault and Lancang River fault respectively. Most of the known alkali-rich porphyry copper polymetallic metallogenic series deposits in this area are located near the residual abnormal zero line, such as Jinping Copper Factory, Yao 'an, Ma Changqing and Beiya deposits, that is, the marginal zone of basement uplift and trough. Therefore, the obvious change zones of two geophysical fields, gravity field and aeromagnetic field, are regional geophysical indicators of the distribution of porphyry copper belts. Geophysical signs in the mining area show that large porphyry copper deposits are generally accompanied by large magnetic anomalies, induced polarization anomalies and self-electricity anomalies. Self-electricity anomaly is an indication anomaly near the mine, which is roughly consistent with the distribution range of ore bodies. IP anomalies and magnetic anomalies can indicate or delineate the range of alteration and mineralization.
Eight, geochemical markers
According to regional geochemical data, the main characteristics of trace elements distribution in Yunnan are: obvious zoning, different zoning with different characteristic element combinations and rich times. The study area can be divided into five geochemical divisions: Dayao District (copper, lead and arsenic), Ninglang-Dali District (copper polymetallic), Zhongdian District (copper, lead, antimony and arsenic), Jinping-Mojiang District (gold, arsenic, antimony, tungsten, nickel, cobalt and copper) and Lanping-copper.
Generally speaking, the contents of zinc, copper, tungsten, tin, chromium, iron, antimony, arsenic, gold and silver in the study area are relatively high. In terms of time evolution, Yuanguyu is rich in Fe and Cu, Pb and Zn in Paleozoic, Sb, Hg and As in Mesozoic, and some elements have obvious inheritance.
Signs of geochemical anomalies in mining areas or ore fields: the geochemical anomalies of the formed deposits are large in scale, and the combination zoning of geochemical anomalies is closely related to the alteration zone of surrounding rocks in mining areas. Generally, the surface of shallow denudation area is dominated by vertical zoning of lead, zinc and silver, while the deep denudation area is horizontally zonal with annular distribution, and there are concentric shell-shaped geochemical halos of Mo, Cu, Ag, Pb and Zn from the inside out. Geochemical primary halo anomaly can be used as a direct prospecting indicator.
Nine, remote sensing signs
In China, the known large-scale porphyry copper deposits all have well-developed annular images, and the mining areas are located inside or at the edge of the annular images. In addition to annular structural images, it is often accompanied by radial and tangential structural images. Through the comparative analysis of the favorable conditions of known mineralization and geochemical field mineralization in remote sensing images of known mining areas, the following understandings are put forward:
1) linear structural high-density zone reflects the weak zone of the earth's crust, and it is a dense area where faults, joints and cracks develop. Its distribution position and direction are generally close to the regional tectonic framework, and most of the known deposits (points) and geochemical anomalies are located at the intersection of linear structural density zones.
2) The main ore deposits (points) are mostly distributed at the edge of annular structure or its overlapping parts, especially at the intersection of annular structure and linear structure.
3) The circular image of the distribution area of alkali-rich porphyry in the western margin of the Yangtze platform shows a strip shape in the northwest and a cluster shape in the northeast, which is concentrated at the intersection of the three main structures in the northeast, south and north, reflecting the distribution law of alkali-rich porphyry polymetallic mineralization concentration areas.