Tonglushan copper deposit is located in the Yangtze platform fold belt under the Yangtze paraplatform, which is the western end of an arc fault depression belt protruding southward.
Second, the mining area geology
(1) stratum (Table 2-66)
Table 2-66 Scale of Ore-bearing Strata in Tonglushan Area
Ore bodies mainly occur in the contact zone between various lithologic sections of Daye Group and diorite porphyrite.
(2) Structure
The tectonic framework of the mining area is restricted by regional structure and ore field structure, and the structural characteristics of different directions, different periods and different scales are generally developed, especially fold deformation and fold superposition, and faults have the characteristics of multi-stage activity. The NW-trending structural traces formed during the Indosinian movement laid the structural framework in this area. The NE-trending structures since Yanshan Movement (NE-trending faults, folds and associated NEE and NW-trending faults) are superimposed on the early structures and intertwined with each other, forming a complex and regular typical Neocathaysian strain image of the mining area. The ore body of the deposit is mainly controlled by the NE-trending fault contact fracture zone.
1. Fold structure
The inverted anticline with the axial direction of N22°E is characterized by white marble in its axial part, dolomite marble in its two wings, and steep strata in its east wing. The fold is composed of Middle Triassic and Lower Triassic. Due to the strong destruction and cutting caused by the intrusion of intermediate-acid magma, there is a relatively complete relic only in the south of the mining area (I ore body is located in the axis of the anticline), leaving only a monoclinal structure in the north (that is, the east wing of the anticline).
2. Fault structure
Characteristics of fault structure in mining area:
(1) is mainly developed in the contact zone between magmatic rock and marble and the axis of anticline, followed by marble interlayer;
(2) The occurrence of fracture zone is consistent with that of contact zone, and only a few of them are oblique;
Figure 2- 1 10 Geological map of the bedrock of Tonglushan copper-iron deposit in daye city, Hubei Province (Figure 2-10 Geological map of Tongshan copper-iron deposit in Hubei Province (according to Xue Dikang, 1997) (after Xue Dikang,10)
1- andesite tuff breccia; 2- Lime dolomite marble; 3- marble; 4- dolomite marble; 5- sodium porphyry; 6- timely diorite porphyrite; 7- garnet diopside skarn; 8- phlogopite diopside skarn; 9- garnet skarn; 10- plagioclase; 1 1- structural fracture zone; 12- copper ore body; 13- iron ore body; 14- copper-iron ore body; 15-cobalt ore body; 16- Normal fault; 17- reverse fault; 18- plane reasoning layer; 19- failure of unknown nature; 20— Boundary and occurrence of stratum segmentation
(3) At the center of the fault, the fault is strong, gradually weakening towards both ends along the strike or dip, and sometimes it changes from broken breccia to strong fragmentation;
(4) The fault distance of the fracture zone is generally small, and the breccia is the breccia of nearby rocks or ores;
(5) In addition, the scale of the fracture zone seems to be related to the scale of marble blocks seen at present, that is, if the marble blocks remaining in the rock mass are large, the scale of the fracture zone is also large and there are large ore bodies.
Orebodies Ⅰ-ⅵ are controlled by n22°e-trending structural line, and orebodies ⅶ-ⅹ are controlled by n68°e-trending structural line (Figure 2-1/kloc-0). The fault structure in the mining area can be divided into three stages: pre-mineralization and post-mineralization. After mineralization, most of the structures inherited the early fault development, which caused the ore body to be broken, but the fault distance was small and the damage to the ore body was not great.
(3) intrusive rocks
The tonalite porphyrite in Tonglushan was formed in the third magmatic intrusion in the early Yanshan period (Rr-Sr isochron age 127Ma). It is an irregular short-axis ellipse with an exposed area of about 1 1km2. This is an odd mushroom-shaped rock strain, which overlaps to the south and leans to the east. It belongs to medium-shallow facies, and the erosion depth is very shallow. The rock mass is well differentiated and can be divided into three lithofacies zones from south to north: the upper zone (shallow facies) is amphibole porphyrite, the middle zone (middle shallow facies) is porphyritic amphibole diorite, and the lower zone (middle deep facies) is amphibole diorite. The iron-copper mineralization in Tonglushan mining area is closely related to the depth of rock mass: the contact between shallow rocks and carbonate rocks has extensive contact metasomatism, and with the transition to middle-deep rocks, metasomatism weakens and assimilation increases. All industrial ore bodies in Tonglushan mining area are confined to the middle and upper part of rock mass. It has a close spatial relationship with the shallow facies of diorite.
The amphibole diorite porphyrite exposed near the mining area has a porphyritic structure. The phenocrysts are plagioclase and amphibole, and the matrix is syenite, orthoclase and a small amount of plagioclase. The plagioclase is mainly composed of intermediate feldspar (An32—An35), which is often banded, while orthoclase is mostly spotted with a particle size of 5 ~ 20 mm. ..
The chemical composition of diorite porphyrite is characterized by relatively rich potassium, high acidity and low iron and magnesium content. Trace element characteristics: Fe-loving element Mo is high, Co is close, and Ni is lower than Vickers average; Copper-loving elements Cu and Ag are on the high side, and the average content of copper is 67× 10-6, which is twice as high as Vickers value, while Pb and Zn are close to and lower than Vickers average value respectively. The contents of strontium, barium, titanium, vanadium and chromium in pro- MagmaElemental are lower than Vickers average. See Table 2-67 for the main petrochemical compositions in the mining area.
Table 2-67 Chemical Composition of Main Intrusive Rocks in Tonglushan Mining Area
Three. geology of ore deposits
The deposit consists of 12 ore bodies (groups) with different sizes (Figure 2- 1 10), and the spatial distribution of ore bodies is obviously three ore zones.
The NNE ore belt (main ore belt) extends along N22°E direction. It consists of seven ore bodies I, III, IV, V, VI, VII and I. The ore belt extends from Line 28 in the south to Line 59 in the north. The ore belt is about 2 100 m long and 300 ~ 350 m wide. The ore bodies in the main ore belt are a group of parallel veins with different exposure depths on the plane, which have the phenomena of pinch-out and recurrence. The single pulse is long and narrow and lenticular, and the waves are soothing; On the profile, most of the ore bodies (groups) are centered on the main ore body, and there are many parallel and obliquely arranged ore bodies on both sides (Figure 2-11). The ore bodies are inclined to SE with an inclination of 50 ~ 80. The ore bodies are not connected with each other on the surface, with the interval of several meters to 100 meters, below the elevation of-125m, and the III and IV ore bodies are connected. This ore belt is mainly rich in ore bodies, and its buried depth is relatively large. In the south, No.1 and No.2 ore bodies are located above -250 m above sea level, No.3 ore body is buried to -700 m above sea level, No.4 ore body is not quenched below -800 m, and No.6 and No.VII ore bodies are located above -250 m above sea level, forming a thick and large ore body group centered on No.3 ore body.
NEE ore belt is distributed along the direction of NE60 and consists of four ore bodies: X, VIII, VII and VII. The ore belt starts from Zhongshan in the west and passes through Dayinshan to Luositang, with a length of1850m and a width of100m ... The ore body is irregular and lenticular, inclined to the southeast with an inclination of 60 ~ 70. The ore bodies in this ore belt are small in scale, scattered and poor in continuity.
Fig. 2-11Daye Tonglushan copper-iron mine 12 and line 7 comprehensive profile (according to Xue.
1-dolomite marble; 2- marble; 3- dolomite marble; 4- marble with dolomite; 5— Thin marble with argillaceous bands; 6— Dolomitic marble; 7- timely diorite porphyrite; 8- plagioclase mineralized diorite porphyrite; 9— porphyritic sychronicdiorite; 10-syenite diorite; 11-albite porphyry; 12- plagioclase; 13— skarn; 14- iron ore body; 15- copper-iron ore body; 16- copper ore body; 17- molybdenum ore body; 18- structural breccia; 19- dissolved breccia; 20— Fault and Movement Direction
(1) ore body characteristics
In the ore body, no. I didn't. III and No IV is the largest, and its shape and occurrence are as follows:
Ore body 1 (Xianrenzuo): located between Line 26 and Line10 in the south of the mining area, the ore body mainly occurs in the fracture zone of contact fault structure. The roof of the ore body is mainly plagioclase syenite porphyrite, and the floor of the ore body is banded dolomite marble and medium-thick marble in the fifth and sixth lithologic members of Daye Formation of Lower Triassic. It consists of an upper ore body and a lower ore body. The upper ore body is the main body of 1 ore body. The No.1 ore body is 400 meters long, with a maximum extension of 320 meters, generally extending 32-270 meters downward and 40-60 meters thick ... It is gourd-shaped (in situ) on the plane and lenticular in the section. The ore body strikes NE25, inclines to SE, and the dip angle is 70 ~ 80. The width of each segment is inconsistent with the extension length, and it is obtuse. The ore type is mainly copper-iron ore, and the copper in the upper part of the ore body has been leached into rich iron ore, while the copper-iron ore in the lower part. Because of the different oxidation degree, all the lines from 22 to 16 are oxidized minerals, and the oxidation zone and mixed zone can be drawn between 14 and 16. The ore body is large in scale, and the proven copper reserves account for 24% of the whole deposit, with an average grade of Cu 2.3 1%. Iron ore reserves account for 25% of the deposit, with an average grade of 5 1.23%. The lower ore body is located in the lower part of the main ore body between the lines 12 and 14. It is a concealed ore body, layered, dominated by copper-iron ore, followed by copper ore. The ore body is small in scale.
No.Ⅲ (Sheshantou) orebody: It consists of two parts, the upper part is exposed to the surface, most of which has been eroded, and the lower part is a complete large concealed orebody, with a general distance of 35 ~ 64m. Ore bodies are mainly produced in marble residues and xenoliths in the fracture zone of contact fault structure. The surrounding rock of the roof and floor is altered plagioclase.
Upper Ⅲ ore body: from Line 2 in the south to Line 1 1 in the north, it is about 375m long and 4 ~ 54m wide. The whole ore body is located above the Om elevation, striking NE25 with an inclination of 50 ~ 600. The ore body is lenticular in plane and wedge-shaped in section, extending downward for 24 ~ 76m. It is composed of low-grade combined copper ore and copper oxide iron ore, and the ore body is small in scale.
No.3 lower ore body: located between 0 ~ 13 line in the middle of the mining area, it is a concealed ore body with a length of 350 ~ 400 meters, and the ore body strikes Ne 20 ~ 30, inclines to SE, and the dip angle is 60 ~ 70. It is lenticular and layered. The orebody in the section of Line 7 is the largest, with a vertical thickness of 1 10m in the center and a downward extension of 8 15m, and the tail boundary is not delineated. The ore type of line 5 ~ 13 is mainly copper-iron ore, and line 0 ~ 3 is disseminated copper ore. The lower part of No.III ore body is the largest ore body in the deposit, and the proven copper metal accounts for 39.37% of the copper reserves of the deposit, with an average grade of 1.75438+0%. Iron ore reserves account for 38.3 1% of the iron reserves in the deposit, and the average grade of TFEO is 39.78%.
Ore body Ⅳ (west of Sheshantou): it is located in the north of the mining area, starting from line 13 in the south and reaching line 39 in the north. The ore body consists of three parts, and the upper ore body is a concealed ore body, which occurs in the upper contact zone of marble xenoliths. The central ore body is exposed to the surface, mainly between the contact fault structural zone (the contact zone under marble xenolith) and marble; The lower ore body mainly occurs in the upper contact zone of deep marble xenoliths.
The central ore body is the main body of the IV ore body, and the 15 ~ 19 line segment is the main body of the ore body, with large thickness and deep downward extension. Strike NE 19, dip NE, dip angle 65 ~ 75. Copper iron ore is the main ore type. Generally, disseminated copper ore is found in copper-iron ore bodies, with copper-iron ore in the south of 19 line and copper ore in the north of 19 line. The oxidation degree of ore is deep, generally reaching the elevation of -5m, and the deepest reaches the elevation of-105m. Most of the copper in the shallow layer of the surface is lost and turned into iron ore. The scale of ore body Ⅳ is second only to that of ore body Ⅲ, which is equivalent to that of ore body Ⅰ. The proven copper reserves account for 24% of the copper reserves of this deposit, with an average grade of 1.5%. Iron ore reserves account for 24% of the iron reserves in the deposit, with an average grade of 36.46%.
(2) type of ore and mineral composition of ore
The ore types and mineral compositions of the deposit are complex, which can be divided into five industrial types, 10 natural types and 14 ore formations. There are more than 130 kinds of known minerals, among which 49 kinds can be used in industry, only 19 kinds are common, and 8 kinds are gangue minerals. In Tonglushan copper-iron mine, besides the main associated components of gold, silver and cobalt, sulfur, indium, tellurium and rhenium also have comprehensive utilization value. The average grade of gold is1.15×10-6; The average grade of silver is11.73x10-6; The average grade of cobalt is 0.0 1.54%.
The main metal minerals are chalcopyrite, bornite, pyrite, magnetite, hematite and malachite. The secondary metal minerals are: chalcocite, molybdenite, white iron ore, sphalerite, cobalt-bearing pyrite, colloidal pyrite, limonite, azurite, chalcopyrite, siderite, native copper, pseudomalachite and maghemite. The main gangue minerals are calcite, dolomite, quartz, chalcedony, diopside, hypodiopside, almandine, almandine and phlogopite.
(3) Alteration and mineralization zoning of the deposit (inner layer-outer layer)
(1) K-silicified plagioclase mineralizes the diorite porphyrite-molybdenite mineralization zone;
(2) plagioclase-(molybdenite-pyrite) molybdenum belt;
(3) skarn plagioclase-(chalcopyrite, pyrite) copper belt;
(4) Gold-bearing mica diopside skarn-(chalcopyrite, porphyrite, magnetite) copper-iron ore belt. Copper accounts for 76.66% of the total, and iron accounts for 85. 17% of the total, which is the most important ore belt.
(5) Skarn marble-(chalcopyrite, bornite and chalcocite) copper belt.
(4) the structure of ore
The main ore structure is isomorphic to automorphic granular structure and metasomatic texture, followed by solid solution decomposition structure and colloidal recrystallization structure. The main ore structural features are as follows:
Dense massive structure: the metal content is more than 75%, mainly magnetite and copper-iron composite ore, with magnetite accounting for more than 75% and a small amount of hematite, pyrite, chalcopyrite, bornite, etc. Dense massive chalcopyrite and hematite can also be seen locally.
Disseminated structure: It is formed by metasomatism of various skarn, marble, plagioclase or early crystallized metal minerals as ore-bearing hydrothermal solution. Include sparse broadcast, moderate broadcast and dense broadcast.
Vein structure: Veins of metallic minerals indicate skarn, plagioclase, marble or early ore.
Bubble structure: the ore is broken into breccia, especially magnetite and copper-bearing magnetite ore breccia, and its cements are chalcedony, calcite and dolomite.
Silty structure: the former is mainly formed by the weathering of magnetite and hematite in the ore body oxidation zone-mixed zone. The latter was formed by intense crushing in the ore body.
(5) Contact metasomatism and surrounding rock alteration
Skarn zoning is obvious, which can be divided into two types according to the different properties of the original rocks of carbonate strata in contact with magmatic rocks: syenite diorite porphyrite contacts with limestone to form a zoning dominated by calcium skarn, and from the outside of the rock mass, it is syenite porphyrite-plagioclase-syenite porphyrite-plagioclase-garnet skarn. The contact between diorite porphyrite and dolomite forms a zoning dominated by magnesium skarn, and the zoning from the rock mass outward is: diorite porphyrite-plagioclase diagenesis diorite porphyrite-plagioclase-garnet diopside skarn-phlogopite skarn-diopside skarn-phlogopite diopside diopside.
The main relationship between hydrothermal alteration and mineralization is as follows: early iron mineralization was diopside, phlogopite, albite, sodium amphibole, epidote and serpentine; Early molybdenum mineralization was silicified and potassium feldspar; In the middle stage, the copper mineralization is potassium feldspar, silicification, siderization, anhydrite, barite, phlogopite and chloritization. The late copper mineralization is carbonation, silicification, kaolin and zeolite.
(VI) Geophysical and geochemical anomalies of the deposit (Figure 2-11)
1. Geophysical anomaly
Copper-iron ore bodies are characterized by high magnetism, high weight, high polarization and low resistance. Occurred in marble xenoliths and skarns, it has the characteristics of heavy weight, high resistance, weak magnetism and weak polarization. The ore-forming parent rock diorite porphyrite has the characteristics of medium-low density, medium magnetism, medium resistance and micro-polarization.
Geophysical anomalies can be divided into two types according to the different tectonic positions of ore deposits:
(1) occurs in marble xenoliths in rock mass (Figure 2-11), characterized by aeromagnetic anomalies, and its shape is more than 500nT, which is consistent with the metallogenic tectonic belt; The magnetic anomaly string is superimposed on the background of low magnetic field or negative magnetic field caused by buried marble in Northeast China. The shape of a single anomaly is regular, the intensity is generally greater than 2000 mt, and the gradient is steep. When surface ore and concealed oblique ore are superimposed, secondary anomalies appear next to high-value peak anomalies; The gravity anomaly is a gradient belt in the northeast, and the ore body is closed or tongue-shaped, with high gravity. The relative amplitude (0.2 ~1.0) ×10-5m/S2 is consistent with the magnetic anomaly. There are regular IP anomalies with intensity greater than 10%, and the ratio of maximum value to background value is greater than 2; The electric sounding curve is H-shaped or KH-shaped in the ore body, A-shaped in the ore-free rock mass, and a low-resistance depression with a medium-high value background or a relatively high-resistance uplift in the profile. Orebodies often occur in low-middle resistance depressions and high-low resistance transition zones.
(2) It occurs in the contact zone of the northern edge of the rock mass. The aeromagnetic anomaly of this kind of deposit rises locally under the background of negative magnetic field, with a relative amplitude of more than 50nT and regular shape, which is consistent with the composite structural belt of ore-controlling fault contact zone. Anomaly of shallow ore body is superimposed on gradient zone, and strong magnetic anomaly and local gravity anomaly are closed, with regular shape, magnetic field intensity greater than 2000 mt, steep gradient, marble in external contact zone with obvious negative pole minimum, and relative gravity amplitude is 0.6× 10-5m/S2. The deep ore body shows low and gentle gravity and magnetic anomalies on the gradient zone, and the magnetic isoline protrudes outward to the north side of the rock mass, with the intensity greater than 100nT, and the gravity isoline is twisted locally or is tongue-shaped with high gravity, and the profile is stepped. When the buried depth of ore body exceeds 500 meters, the ore anomaly will be covered up, and if the anomaly is strengthened by polarization treatment, weak anomaly will appear. The gradient zone is a relatively low-resistivity anomaly, with H-shaped curve and low-resistivity sag in the profile, and most ore bodies are located in the low-resistivity sag zone, and the profile curve is a low-resistivity orthogonal point and a low-resistivity anomaly.
2. Remote sensing characteristics of ore deposits
The image characteristics show that this type of deposit is located at the intersection of three groups of linear structures, namely, NNE and NW-nearly EW-and NE-and it is also controlled by large-scale inclusion ring structures, that is, there are many small-scale ring structures in the big ring. Most ore bodies are distributed in the inner part of the big ring or the center of the small ring, which belongs to the "three-group intersection" structure. In color aerial photos, the ore body is located in the center of the inner ring.
3. Geochemical anomalies
The mineral deposits are composed of copper, gold, silver, iron, zinc, cobalt, nickel, bismuth, molybdenum, lead, arsenic, boron, manganese, fluorine, chlorine, tungsten, tin, strontium and barium. , forming geochemical anomalies with different scales and intensities, with high contrast and original contrast. The original contrast of copper, gold, silver and bismuth can be as high as more than 20 times, arsenic, fluorine, cobalt, zinc and molybdenum are 5 ~ 15 times, and other elements are 1 ~ 3 times. Copper grass is prosperous on the surface.
The geochemical anomalies of bedrock are directional, distributed in belts on different deposits, or distributed in NNE, NNE or NW directions, all of which are related to the fault-xenolith composite structural belt. At the intersection of multiple groups of ore-controlling faults, anomalies are distributed in a plane. Centralized classification is obvious, with high intensity and large scale. Generally speaking, the anomalies of copper inner zone and molybdenum, silver and zinc indicate the occurrence position of ore bodies. The indicator elements of ore deposits have obvious horizontal zoning, that is, from rock mass to contact zone (ore body) and then to marble. The zoning of elements is Mo, W, Co, Bi, Sn, Mn, Zn→Cu, Ag, Au→B, As, F, Pb and Ba. Characteristics of borehole primary halo: the abnormal field of the deposit weakens to both sides around the ore-controlling structure and ore body, showing concentric oval distribution and obvious concentration gradient. Among them, copper, silver, gold and molybdenum halos are concentrated in the ore body, and there are middle and outer belt anomalies above and below the ore occurrence. Zinc, manganese, bismuth, cobalt and tin halos are closely related to the ore body, with a slightly larger range and surrounding the ore body. Arsenic, barium, fluorine and chlorine (lead) halos are mainly distributed in the ore front and head, which are closely related to ore-controlling structures. The range of F and Cl halos is larger than that of As and Ba(Pb) halos. The vertical zoning order of primary halo of the deposit is (from top to bottom): F-As-Au-Cu-Mn-Zn-Co-W (Mo).
The ore body position can be roughly estimated by using two combined indexes of 50w(Cu)/w(Fe) and 103w(Ag)/w(Cu). 50w(Cu)/w(Fe) value: above 3 in the mine, 1 ~ 3 in the mine and below 1 in the mine; 103w(Ag)/w(Cu) value: above 0.75 in the mine, 0.75 ~ 0.50 in the mine and below 0.50 in the mine.
Four. minerogenetic condition
(1) stable isotope
The variation range of sulfide δ34S in ore bodies is -4.9 ‰ ~+ 12.8 ‰, with an average value of +2.42 ‰. The frequency chart is tower-shaped, and its average value is close to the sulfur isotope composition of meteorites. At the same time, its δ34S variation characteristics are similar to those of typical porphyry copper mines abroad and contact metasomatic copper-iron mines in China, but obviously different from those of sedimentary copper mines and sedimentary metamorphic copper mines, with large variation range and wavy frequency distribution. All these fully show that Tonglushan copper-iron deposit has the same sulfur source as porphyry copper deposits and contact metasomatic copper-iron deposits in China, and they should mainly come from magmatic separation, suggesting that ore-forming materials come from the lower crust or upper mantle, and ore-forming fluids assimilate and mix with water-bearing upper crust components during upward migration.
According to the measured values of stable mineral isotopes δ 18O and δ 13C, the calculation results of mineral water balance formula (Table 2-68) show that the mineralized aqueous solution of Tonglushan deposit mainly comes from migmatite magma, and some rainwater is added in the later stage of mineralization.
Table 2-68 Calculation Results of Isotopic Fractionation Balance of Mineral Water in Tonglushan Copper-iron Deposit Table 2-68 Calculation Results of Isotopic Fractionation Balance of Mineral Water
(2) Composition of inclusions
According to the mineral inclusion composition and mineral analysis data formed after metasomatism, the gas-liquid composition of Tonglushan copper-iron deposit is mainly alkali metal (Na+K) oxide and CO2 aqueous solution. In addition to H2O, H+ and OH, the main components are Cl-, Na+, K+ and CO2, followed by F-, B-, H2S and Ca2+. The ore-forming solution is essentially chlorine-rich brine.
(3) Analysis of metallogenic conditions
According to the mineral genetic relationship and mineral inclusion data, it shows that the deposit was formed under the conditions of long-term and large-scale temperature change and multiple gasification-hydrothermal activities. Diagenesis and mineralization are complex and characterized by multi-stage and multi-stage. The metallogenic process can be divided into three metallogenic periods and five metallogenic stages.
1. skarn stage
(1) skarn stage: early skarn mineral garnet (740 ~ 590℃), diopside-hypodiopside (695 ~ 502℃) and contact zone plagioclase (7 17 ~ 5 15℃) were formed. With the decrease of temperature, high-temperature ore-bearing gases and liquids near the contact zone gather in large quantities, followed by phlogopite (450 ~ 426℃), actinolite (470℃), magnesium-rich amphibole, pumice stone and andalusite. All of them are formed, accompanied by a small amount of magnetite, phlogopite and diopside, in a * * * shape, forming a sponge meteorite structure locally.
(2) High temperature oxide-magnetite stage gasification: garnet and diopside are crystallized in the early anhydrous silicate stage of skarn, and phlogopite, actinolite and magnesium-sodium-rich hornblende are crystallized in the late hydrous silicate stage. K and Na participate in the mineral lattice, indicating that the environment is gradually changing from weak acid-weak alkali medium to weak alkali medium. At this time, a large amount of iron exists in the high-temperature gas-liquid aggregate in the form of Fe2+ and Fe3+ complexes, and gradually enriches with the slow cooling of ore-bearing gas-liquid, and permeates and migrates to Fe-Mg-Ca medium-coarse skarn with strong iron affinity. When the temperature drops below the critical point of magnetite, high-temperature iron-rich gas and liquid will occupy diopside, phlogopite and garnet on a large scale. With the enhancement of oxidation, hematite crystallizes and magnetite is constantly replaced, forming magnetite-hematite (420 ~ 360℃) ore. In the process of metasomatism and precipitation of magnetite, a large amount of sodium is accompanied by serpentine. The crystallization of albite and sodium amphibole accelerates the precipitation and replacement of iron complex anions and complexes in alkaline oxidation medium, indicating that epidotization of crystallization under alkaline conditions is closely related to magnetite. The above shows that magnetite is formed by the continuous and slow large-scale replacement of skarn (mainly diopside) in alkaline oxidation medium after the formation of skarn. The oxidation-magnetite stage belongs to the inherited mineralization of Na-Fe series iron.
2. Time-sulfide period
(1) Middle-high temperature stress-sulfide stage: After magnetite mineralization, the temperature continued to drop, SiO2 _ 2 crystallized in a large amount of stress (chalcedony) and sulfide precipitated on a large scale. After magnetite precipitation, the ore-bearing gas-liquid becomes acidic, and the residual iron and sulfur in the ore-bearing hydrothermal solution combine to form high-temperature nickel-bearing pyrite, pyrrhotite and pyrite (explosion temperature is 350 ~ 360℃). With the precipitation of potassium in ore-bearing gas and liquid, molybdenite crystallizes. Subsequently, some iron combined with copper, zinc and sulfur to form (cubic) chalcopyrite-marmatite (the temperature measured by chalcopyrite explosion method is 290 ~ 260℃), and pyrite and chalcopyrite crystals (250 ~ 240℃) appeared in the last two generations. Copper mineralization is mainly in the form of veinlet-disseminated and lump-massive metasomatism, which is filled along the cracks of iron ore body and magnetite particles formed in the early stage, forming a copper-iron composite ore body superimposed on iron ore, and metasomatism acts on skarn marble and plagioclase cracks on both sides of iron ore body to form a veinlet-disseminated single copper body. Second only to chalcopyrite, bornite, chalcocite, chalcocite and siderite. Crystallization in turn, the mineralization process is accompanied by extensive hydrothermal alteration such as potash feldspar, silicification, chloritization and carbonation. In a word, the isochron-sulfide stage is produced under the condition of weak acid-acid reduction, and copper mineralization is later than magnetite and superimposed on magnetite.
(2) Middle-low temperature carbonate sulfate stage: after sulfide mineralization, the temperature drops, and the unused sulfur in gas and liquid combines with Ca2+, Mg2+, Ba2+ and Sr2+ to form anhydrite, barite and celestite; F- combines with Ca2+ to form fluorite, and with Ca2+, Mg2+ and Fe2+ to form dolomite, calcite, ankerite and siderite, accompanied by timely (chalcedony) crystallization. At this stage, only a small amount of pyrite crystallizes into stars.
3. Supergene action
(1) oxidation leaching secondary enrichment stage: long-term oxidation leaching of shallow ore bodies, oxidation of magnetite into hematite or limonite, decomposition of sulfide into copper sulfate and copper carbonate, and common natural copper, chalcopyrite, chalcocite and chalcocite in the secondary enrichment zone.
K-Ar and Rb-Sr isotopic ages show that different occurrences of phlogopite have different isotopic ages. The age value of massive phlogopite near the iron ore body is151ma (determined by k-ar method). The phlogopite in iron-copper ore bodies is 142Ma, 13 1Ma(Rb-Sr method); Late vein phlogopite is 1 15 Ma (measured by rubidium strontium method) and 1 17 Ma (measured by potassium argon method). It can be seen that the age of skarnization and metal mineralization is very close to Yangxin amphibolite diorite (127 ~ 150 Ma), which proves that mineralization is related to the intrusion of intermediate-acid intrusive rocks in this area, reflecting multi-stage and long-term mineralization.
To sum up, geological age, spatial relationship between rock mass and mineralization, abundance of rock mass and ore-forming elements, and stable isotopes (S, O, C) all indicate that the tonalite porphyrite in Tonglushan is closely related to the Tonglushan iron and copper deposit. Ore bodies mainly occur in the contact zone, and the formation of ore deposits is the product of specific environment in a certain stage of alteration and replacement. The ore has a typical metasomatic texture, and the material composition and chemical composition of the ore have a certain inheritance relationship. The chemical composition and trace typomorphic elements of ores are different from other genetic types, but they have the characteristics of contact metasomatic deposits. Therefore, the genetic type of the deposit is post-magmatic gasification-high temperature hydrothermal contact metasomatic copper-iron deposit, which is a typical narrow sense skarn copper-iron deposit.
Verb (abbreviation of verb) metallogenic model and prospecting criteria
(1) metallogenic model
Tonglushan deposit is located in the middle of southeastern Hubei Province. The regional metallogenic model of southeastern Hubei shows (Figure 2- 1 12) that there is diorite magma melting zone in the lower crust at a depth of 20 ~ 25 km, and there is intermediate-acid magma chamber in the upper crust 10 ~ 15 km. Due to the deep fault activity in NWW direction and NE or NNE direction in Yanshan period, a large amount of magma invaded the shallow crust and contacted with Ordovician-Triassic, which led to contact metasomatism and mineralization, forming various skarn-type deposits.
Fig. 2- 1 12 sub-series metallogenic model of iron-copper-gold-phosphorus-molybdenum deposits in southeastern and central Hubei. Southeast Hubei (according to Xue Dikang 1997) (after Xue Dikang 1997)
1- iron ore; 2- copper-iron ore; 3- copper (tungsten molybdenum) ore; 4- cobalt ore; 5- lead-zinc-silver ore; 6- gold mine; 7— Medium-fine grained diorite; 8- quartz diorite; 9- adamellite; 10-fine-grained amphibolite; 11-medium-grained diorite; 12- diorite porphyrite; 13- diorite porphyrite; 14— granodiorite; 15- granodiorite porphyry; 16- cryptoexplosive breccia; ① Zhangfushan Iron Mine; ② Liujiafan Iron Mine; ③ Tonglushan copper-iron mine; ④ Jiguanzui copper-gold deposit; ⑤ Yehua Township Copper Mine; ⑥ Tongshankou copper (cobalt) mine; ⑦ Baiyunshan copper deposit; (8) Longjiao Mountain-Fujiashan Cu-W (Mo) deposit; 9 Jinjingzui porphyry gold deposit; Attending Chenzishan Gold Mine; (1 1) Wang Baoshan iron mine; (12) Houtoushan copper mine; (13) Yinshan Ag-Pb-Zn deposit. K 1l—— Lingxiang Formation; T2p—- Puyin Group; T2l—— Lushuihe Formation; TL- Daye Formation; P- Permian; C- carboniferous; Silurian system; ∑-O. Cambrian-Ordovician; PT2-3- Mesoproterozoic. ~ ~. Structural detachment surface =. Direction of magma migration; Fracture; ..................................................................................................................................................................................
(2) Prospecting signs
1. Geological signs
The ore body occurs in the secondary fault-contact zone composite structure composed of diorite porphyrite xenoliths and carbonate rocks of Lower Triassic Daye Group (T1Dy1-T1Dy7), and passes through the NE anticline and the upper wall of the synclinal fault structure superimposed on it. The ore-controlling structures are NNE fault contact zone and interlayer fracture zone. Wall rock alteration is developed, and zoning is obvious, accompanied by mineralization zoning. The mineral assemblage of ore is complex. The composition of the deposit is mainly copper and iron ore, accompanied by many useful components such as gold, molybdenum, cobalt, selenium, tellurium, indium, gallium, sulfur and silver. The oxidation zone of the deposit is developed. Under the iron cap of the surface leaching zone, the secondary enrichment zone often has copper oxide enrichment section.
2. Geophysical signs
Table 2-69 Comprehensive prospecting criteria for Tonglushan copper-iron ore Table 2-69 Comprehensive prospecting criteria for Tonglushan copper-iron ore
The deposit corresponds to aeromagnetic anomalies with regular shape and wide range. The gravity and magnetic anomalies are in the NNE gradient zone, which reflects the extension range of ore bodies. There are high gravity and magnetic anomalies above the steep ore body, accompanied by obvious negative magnetic anomalies and charging anomalies. On the profile, the point sounding curve is H-shaped or KH-shaped, and the ore-free section is A-shaped. Ore bodies are mostly located in low-resistance depression zone and high-low resistance transition zone.
3. Geochemical signs
Various geochemical anomalies of ore bodies (stream sediments, soil, rocks, etc.). ) large scale, regular shape, obvious concentration zoning, and wide-band distribution of ore-controlling faults along NE direction. The anomalies in the inner zone of copper, gold and silver indicate the occurrence position of ore bodies.
See Table 2-69 for comprehensive prospecting indicators of this deposit.