Jinchuan nickel-copper deposit is located in the south of Longshoushan uplift belt in the southwest of China-Korea Craton in early Precambrian (Tang Zhongli et al., 1987), adjacent to Caledonian fold belt in North Qilian Mountains.
Second, the mining area geology
(1) stratum
The exposed strata of Longshoushan Uplift mainly include Proterozoic, Neoproterozoic, Devonian, Carboniferous, Permian and Jurassic. Paleoproterozoic distributed in the northwest, consisting of Baijiazui Formation () and Tamagou Formation (). The former is mainly composed of migmatite, gneiss and serpentine marble. The latter is mainly composed of gneiss, schist and banded marble. The above two groups of rocks are unconformity or false conformity contact. The K-Ar isotopic age of the white pegmatite dike in Tamagou Formation is 17 19Ma. Neoproterozoic strata are also distributed along NWW direction, mainly composed of Dunzigou Formation and Hanmushan Group. The former is mainly composed of conglomerate, sandstone and crystalline limestone; The latter is mainly composed of sericite schist, calcareous schist and calcareous breccia, which is unconformity or fault contact.
(2) Structure
The Paleoproterozoic is composed of a monoclinic structure inclined to the southwest, which is covered by the Neoproterozoic that formed the anticlinorium. Synclinal folds were formed in Upper Paleozoic and Mesozoic.
Longshoushan uplift belt runs east-west, and turns west to northwest. The linear characteristics of the structure are very obvious. There are deep faults on both sides of the uplift belt. The fracture dip angle is 60 ~ 70 (Figure 2-2). The secondary faults parallel to the main fault are also well developed, and there is a gentle inference layer in NE direction in the uplift zone. This kind of fault is very common in Jinchuan intrusion, and the intrusion is cut.
(3) Magmatic rocks
Magmatic activities are developed in this area. The intrusive bodies in Lvliang period (1700Ma) are pegmatite granite and amphibole, which are often lenticular and often penetrated by Caledonian mafic dikes. The sulfide-bearing ultramafic rock mass was formed by many times of magma infiltration, and the formation age was Mesoproterozoic 1508 Ma 3 1Ma+0 Ma. Caledonian magmatism was extremely common. The main representative rocks are granitic intrusive rocks with different sizes, and a small amount of ultramafic rocks, basic gabbro, diorite and granodiorite can also be seen.
Figure 2- 1 Distribution Map of Magmatic Detached Copper Deposits in China Figure 2- 1 Distribution Map of Molten Copper Deposits in China.
Figure 2-2 Jinchuan Regional Geology Tu Tu 2-2 Jinchuan Regional Geological Map
1- four yuan; 2- Mesozoic-Tertiary; 3- Paleozoic; 4- Precambrian; 5- Longshoushan uplift belt; 6- granodiorite intrusion; 7- mafic-ultramafic intrusive rocks; 8- Fracture
1. Rock Geology
Jinchuan sulfide-bearing ultramafic plutonic body intruded into the metamorphic rocks of Proterozoic Baijiazui Formation at an angle of 100. The Nd-Sm isotopic age of the rock mass is 1508 Ma 3 1 Ma (Tang Zhongli et al., 1992). The rock mass is 6500 meters long and tens to 500 meters wide, and both ends are covered by Quaternary. The exposed length of the surface is about 4500m, the exposed area is 1.34km2, the strike is N50 W, and the dip angle is 50 ~ 80. It is irregularly veined and cut into four by E-NE shear fault.
The intrusion in No.3 mining area is more than 900 meters away from the intrusion in No.3 mining area. The mining area is located in the southwest of F2 fault and covered by Quaternary sediments with a thickness of 40 ~ 50m. The intrusion is more than 500 meters long, wide in the east and pointed in the west. The eastern part of the tip extends below 600 meters, and the western end is wedge-shaped, with a depth of about 200 meters. The rock mass tends to the south with an inclination angle of 60 ~ 70.
The exposed length of intrusive body in a mining area is about 1500m, which is wide in the west and narrow in the east. The west end is 320 meters wide and the east end is about 20 meters wide. It extends downward over 700 meters, with a steep dip (70 ~ 80) and tends to the southwest.
The intrusive body length of the No.2 mining area is more than 3,000 meters, which is covered by Quaternary in the east and gradually widens to the west. The maximum width is 530 meters near F 17, and then narrows to the west. The intrusion strike is about N50 W, the dip angle is 50 ~ 60, the dip angle is SW, and the dip angle in the east becomes slow.
The invasion position of No.4 mining area is located at the easternmost end of the whole mining area, with a length of1300m. Except that the western end is located under migmatite, the rest are covered by Quaternary, with a covering thickness of 50 ~ 140m. The intrusive body is strongly deflected, with a dip angle of 50 ~ 60 and a tendency of SW. The intrusive body is irregular lenticular in shape, and the eastern part bifurcates downward and pinches out. The maximum width is more than 230m, and it extends down to 400-600m. To sum up, the shape of Jinchuan rock mass is controlled by the nature of faults around it. In the area where the shear fault is obviously controlled, the intrusive body extends down deeply and is flat (Figure 2-3b). In the area where extensional faults are developed, the intrusive body does not extend deeply downward, and the profile is funnel-shaped (Figure 2-3c). In the shear zone, magma differentiation is not obvious; However, in areas where extensional faults are developed, magmatic differentiation is very obvious and various lithofacies are well developed.
Figure 2-3 Plan (a) and Section (b, c) of Jinchuan Rock Mass Geological Map.
1- four yuan; 2-Yuangu language; 3- lherzolite; 4- plagioclase lherzolite; 5- olivine diabase; 6—era dite； 7- disseminated ore; 8- reticular rich ore; 9- oxidized ore; 10-metasomatic ore; 1 1- massive sulfide ore; 12- suspended disseminated ore; 13- contact boundary of magmatic rocks; 14 —— Lithofacies contact interface in different stages; 15- Fault
2. Invasion stage and rock type of intrusive body
Jinchuan copper-nickel sulfide rock mass is a compound rock mass, which can be divided into three intrusion periods.
The first stage is fine-medium grained peridotite and olivine lherzolite, which mainly occur in the middle and upper part (southwest side) of intrusions in I and III mining areas, and gradually narrow to the southeast until F 16. In the second stage, medium-coarse ultramafic rocks are distributed in the middle and lower parts of intrusions in mining areas I and III, and gradually widen to the southeast, becoming the main lithofacies of intrusions in mining areas II and IV. The third stage is medium-grained dunite, which mainly occurs in the lower part of intrusions in I and II mining areas.
At each stage, the basic part of rock mass appears in the center of lithofacies, and the basic degree outward gradually decreases (Figure 2-3). The contact boundary between rocks in the same period is gradually transitional, while the contact boundary between different periods is abrupt. Early intrusions have been altered or severely broken, and some contact zones are often filled by late dikes.
The main rock-forming minerals of various rocks in Jinchuan are olivine, clinopyroxene, orthopyroxene and plagioclase. Olivine is generally a semi-self-shaped-self-shaped short column, but it is round when it is wrapped by other mineral particles. Generally, the FO is 77% ~ 90%, and a very small part of the FO is 9 1% ~ 94%. Oblique orthopyroxene mainly appears in the form of heteromorphic crystals, and semi-automorphic crystals are rare, containing 80% ~ 87.3% En, and its composition is similar to that of bronze pyroxene. Among the pyroxenes, orthopyroxene is hypersthene, and its nitrogen content is 76.5%, which is lower than that of clinopyroxene.
All rocks have been altered, olivine is generally altered into serpentine and chrysotile, and altered minerals are generally distributed along faults and replaced by diorite in strongly altered areas. Bronze pyroxene often erodes into sericite. Clinopyroxene is generally transformed into amphibole and tremolite, appearing as clinopyroxene illusion, but when it is transformed into chlorite, its original clinopyroxene structure becomes blurred. Plagioclase is generally replaced by prehnite. Magnesite, calcite and chlorite occur in places with strong alteration in dunite.
3. Chemical composition of intrusive rocks
The average chemical composition of Jinchuan intrusive rocks is similar to that of lherzolite (Table 2- 1), in which the contents of Mg, Fe, Ni and Cr and the value of w(Mg)/w(Fe) (3.02 ~ 2.2) decrease regularly with the decrease of rock alkalinity. The contents of Fe2+ and Fe3+ are inversely proportional, and Fe3+ is related to alteration strength. The contents of silicon, calcium, aluminum, sodium and potassium are inversely proportional to the contents of magnesium and iron. The content of Na2O is generally less than 0.5%, but it is more than 1% in some rocks containing plagioclase or amphibole containing olivine, and w (K2O) is less than w (Na2O). About 2% of the samples contain more than 0.3% K2O. In a few samples, its content is > 65438 0%. The Cr content in ultramafic rocks containing nickel sulfide is lower than that of similar rocks without ore, which reflects the affinity of Cr3+ for clinopyroxene. The low Cr content may be related to the replacement of Cr in chrome spinel by Fe in the late stage of rock alteration to form magnetite.
Table 2- 1 Rock Composition of Jinchuan Rock Mass (WB/%) Table 2- 1 Rock Composition of Jinchuan Rock Mass (WB/%)
Note: loss on ignition; M/f=Mg2+ number of atoms /[(Fe3+Fe2++Mn2+) number of atoms]
Three. Geological characteristics of the deposit
(1) orebody and ore type
Jinchuan deposit is known to have three main ore bodies (No.24, 1 and No.2), and its copper and nickel metal reserves account for more than 90% of the whole deposit, while the rest ore bodies are less than 10%.
The ore of Jinchuan deposit can be divided into three types, and the corresponding mineralization is magma, gas hydrothermal solution and hydrothermal solution. Magmatic ore can be divided into three types according to its detachment (immiscible sulfide separation) position and emplacement order: in-situ detachment, deep detachment penetration and late penetration. Gas production-hydrothermal mineralization mainly forms contact metasomatic ore. Pure hydrothermal ore is mainly superimposed on deep detached-penetrating ore bodies, and individual ore bodies are superimposed on in-situ detached ore bodies.
1. In-situ magma melted the ore (mainly disseminated sulfide ore)
This kind of ore ranks second in Jinchuan deposit and is a kind of ore with economic value. Lenticular, distributed in each phase zone of the intrusive body, hundreds of meters long and tens of meters thick1m. There is branching compound phenomenon along the strike and dip of ore body, and branching phenomenon is more obvious along the dip of ore body. Larger ore bodies generally occur in peridotite-rich lherzolite, which is located in the middle and lower part of the rock mass.
The ore is mainly disseminated sulfide. The sulfide in the middle of the ore body is the most abundant, and it gradually decreases from the ore body to the surrounding rock. The main sulfide minerals are pyrrhotite, nickel pyrite and chalcopyrite with a ratio of 5.9: 5.6: 1. Other sulfide minerals are chalcopyrite, Marquino ore and chalcopyrite. The sulfide minerals are irregular pudding-shaped, with a general particle size of about 1 ~ 3 mm, and are evenly filled in the gaps of silicate minerals such as olivine and pyroxene. Porphyry minerals formed by late hydrothermal process can be seen at the lower edge of the ore body. These ore minerals are characterized by a large change in aggregate fragmentation (0. 1 ~ 10 cm). Most of the nickel pyrite and pyrrhotite in the upper part of the ore body have been eroded into purple-nickel pyrite, white iron ore and pyrite, but the residual structure still exists.
Figure 2-4 Schematic diagram of longitudinal section of main ore body of Jinchuan deposit Figure 2-4 Schematic diagram of longitudinal section of main ore body of Jinchuan deposit
1- migmatite; 2- marble; 3- plagioclase amphibolite; 4- lherzolite; 5- plagioclase lherzolite; 6- olivine diabase; 7- star ore: 8- sponge iron ore; 9- massive ore; 10- lithofacies boundary; 1 1- main ore body number
2. Deep magma melts and penetrates into ore (mainly forming reticular sulfide ore).
This kind of ore is the most important, and its ore body is large in scale, with a thickness of tens to hundreds of meters and a length of hundreds to thousands of meters, mainly occurring in the deep or bottom of intrusive bodies (Figure 2-4). Several ore bodies are located on the upper wall of the rock mass, while one or two ore bodies pass through the lower wall of the intrusive body. The shape of ore bodies is usually flat and lenticular, but some of them are veined, and the ore bodies suddenly become thinner or thicker, and branches are common.
The dip angle of the ore body is sometimes steeper than that of the intrusive body, and sometimes slower than that of the intrusive body, in which the lithofacies that formed the intrusive body first is interspersed. The distribution of ore bodies is not controlled by the distribution of early differential facies.
The size and location of ore bodies have nothing to do with the differentiation degree and scale of intrusions. The sulfide-bearing rock is dunite. From the middle of the rock mass to the edge, the content of pyroxene increases. The size of sulfide aggregate is about 1 ~ 6 mm, which is filled in the gaps of silicate minerals to form reticular ore, and its content can account for 12% ~ 15% of dunite. Local dynamics and hydrothermal processes make sulfides gneiss, fluff and nebula-like. The structure and mineral assemblage of this kind of ore are basically the same as those of in-situ magmatic molten ore bodies, and opaque, flame-like, lattice-like, image-like and thin-layered structures are well developed, all of which are molten products. The reticular structure and girdle structure formed by metasomatism are common. The main metal minerals are pyrrhotite, nickel pyrite and chalcopyrite, and the ratio is 4.8∶2.6∶ 1. In some ore zones, platinum, palladium, gold and silver are relatively rich, and the content is greater than 1× 10-6. The thickness of the ore belt can reach tens of meters, the length can reach hundreds of meters, and it extends down to 100 meters.
The main characteristics of the ore-rich belt are: the structural fractures are relatively developed, and the ore structure, structure and mineral combination change greatly; The ore structure can be seen as reticular structure, metasomatic reticular structure (the mineralized material is foliate) and gneiss, nebula or cloud structure; Sulfide is generally characterized by metasomatic erosion structure and residual structure; Silicate minerals are generally strongly eroded into serpentine, carbonate and talc, forming chrysotile-talc-magnesite aggregate.
Copper minerals, especially chalcopyrite, have increased significantly in the ore-rich zone, even reaching more than half of the total sulfide. As shown in Figure 2-4, these ore-rich zones are rich in platinum, palladium, gold, silver, selenium and other elements, including copper, which mainly exist in the main minerals in the form of arsenic compounds, natural elements, metal mixtures, tellurides, bismuth compounds and antimonides. Co mainly exists in nickel minerals in the form of solid solution, and the value of w(Ni)/w(Co) is 465,438+0. Nickel-cobalt ore and iron-nickel-cobalt ore are rare. Selenium often replaces sulfur in sulfides.
3. Late penetrating ore (mainly massive sulfide ore)
This kind of ore is located in the deepest part of intrusive rock, where it melts and penetrates into the bottom of ore body or the contact zone with surrounding rock. Ore bodies usually appear in the form of irregular lenses or vein groups, with a length of several meters to several hundred meters and a thickness of several tens of centimeters to 20 meters, which narrows and expands abruptly. This kind of ore is dominated by massive sulfide, and sometimes sub-massive and breccia-like ores appear at the edge or end of the ore body. The composition of breccia includes primary reticular ore, diabase and other surrounding rocks. The gangue mineral content of massive sulfide ore is less than 2%, mainly chlorite aggregate. The metal minerals in the ore are pyrrhotite, pyrite, chalcopyrite, nickel pyrite and a small amount of magnetite, hematite and pyrite-copper-potassium ore. The content ratio of pyrrhotite, nickel sulfide and chalcopyrite is 4.3∶ 1∶ 1. The content of nickel sulfide in this type of ore is lower than that in other types of ore. They were formed in the low temperature environment in the late magmatic period.
4. Contact metasomatic ore
Some of these ores occur in the upper wall of intrusive body or xenolith of surrounding rock, but mainly in the lower wall of intrusive body. Large ore bodies are about several hundred meters long and several to several tens of meters thick, which are layered, lenticular or cystic, close to sulfide-bearing intrusions or integrated with surrounding rocks. Ore bodies are mainly composed of sparse disseminated-dense disseminated and reticulated ores. The nickel content is the highest near the intrusion, and gradually decreases away from the intrusion. The opposite is true for copper and nickel. The main sulfide minerals in the ore are pyrrhotite (+pyrite), nickel pyrite (+chalcopyrite) and chalcopyrite (+chalcopyrite and chalcopyrite), and their content ratio is 1.2:0.7∶ 1. Magnetite and hematite are less than 1%, and Marquino ore rarely appears. Sulfide minerals are semi-automorphic or heteromorphic, with rare banded metasomatic texture, metasomatic pseudostructure and exsolution structure. After metasomatism, the surrounding rocks can also form ore bodies. These surrounding rocks include marble, gneiss and amphibolite. Marble is often eroded into diopside, diopside and chlorite schist containing calcium-aluminum garnet. Alteration is mainly distributed in the periphery of ore bodies.
(2) Ore composition
1. Mineral composition of ore
The main metal minerals are pyrrhotite, nickel pyrite, chalcopyrite, chalcopyrite, Marquino mine, chalcopyrite and purple pyrite. , as well as natural gold, silver, natural platinum and their alloys, various telluride, bismuth, antimony, arsenic minerals and chromium spinel minerals. Gangue minerals mainly include olivine, bronze pyroxene, enstatite, diopside, serpentine and Labrador stone.
2. Chemical composition of ore
In Jinchuan deposit, the ore body accounts for 43% of the total volume of the whole intrusive body. The whole rock mass contains nickel 0.42%, copper 0.23% and sulfur 1.74% on average.
The w(Ni)/w(Cu) values of various ores in Jinchuan deposit are 0.6 1 ~ 2.97, with an average value of 1.29. The value of w(Ni)/w(Cu) in massive ore is the highest. The lowest ratio of hydrothermal ore is 0.6 1.
The average content of platinum group elements in Jinchuan mining area is high. The average content of platinum in each mining area is (0.05 ~ 0.64) × 10-6, and the content of platinum and palladium is higher than that of osmium, iridium, ruthenium and rhodium, with a ratio of 2.0 ~ 7.45. In porphyry ores, the platinum content of individual samples is as high as 8 1.67× 10-6 (Li, 2000).
(3) Ore texture and structure
Jinchuan copper-nickel mine has various ore structures. Magma melts away from the ore body in situ, and the ore structure is mainly semi-authigenic to irregular granular structure, followed by metasomatic texture and metasomatic residual structure; The ore is dominated by sparse disseminated structure. The minerals in the deep magma detachment-penetration ore body are semi-authigenic, irregular granular texture, opacified texture, lattice structure, metasomatic texture and blade structure. The ore is dominated by sponge crystal rank structure, with local nebula and cloud structure. The ore structure of late penetrating ore body is mainly semi-authigenic granular structure. The common structure of ore is massive structure. Other types of ores have been described before and are not redundant.
(IV) Alteration characteristics of surrounding rock
The ore bodies formed in magmatic period are mainly influenced by late autometamorphism and hydrothermal process, and often occur serpentinization, carbonation and decollement. Sika mineralization and chloritization occur locally in contact metasomatism and hydrothermal superimposed ore bodies. When the surrounding rock is marble, eclogite, diopside and tremolite are common.
(5) Characteristics of geophysical and geochemical anomalies
On the tectonic magmatic belt where Jinchuan rock mass is located, there is an obvious gravity gradient dense belt with a gravity gradient value of 25mg/km. The magnetic field intensity (△T) of this magmatic belt is generally 200 ~ 400 nt, and the maximum value is 700nT. The IP anomaly in copper-nickel ore body is obvious, and the ηs value is generally greater than 5%, and the highest value can reach 12%.
The geochemical anomalies of soil on the surface of ore-bearing rock mass are obvious, with obvious inner, middle and outer zones, mainly Cu, Ni and Cr, accompanied by anomalies of elements such as Co and Sr.
Four. minerogenetic condition
(1) isotopic characteristics
The sulfur isotope δ34S of various ores in different stages of the deposit is 1.06 ‰ ~ 2.53 ‰, which is close to meteorite sulfur. Sulfur may come from the upper mantle.
The 87Sr/86Sr of the rock mass is relatively high, ranging from 0.702547 to 0.711761,and part of it falls on the evolution line of continental crust, indicating that the magma may be polluted by strontium in the crust. 143Nd/ 144Nd is (0.51180010) ~ (0.51206412), which is close to or larger than pellets.
Sm-Nd isochron age of Jinchuan rock mass is 1508 Ma 3 1 Ma.
(2) Physical and chemical conditions of mineralization
According to the theoretical estimation of rock-forming minerals, the melting test of rock-forming minerals and the determination of melt inclusions, the liquidus temperature and solidus temperature of olivine are 1400℃ and1200℃. Pyroxene and plagioclase began to crystallize at 1 100℃. The emplacement depth of magma is 10 ~ 15 km, and the depth of magma chamber is below 30km. The initial melting temperature of sulfide is 1400 ~ 1500℃, and the crystallization temperature of sulfide as a monosulfide solid solution is 1000℃. Solid solution decomposition occurs when the temperature is lower than 600℃, and hydrothermal superposition occurs around 4 14 ~ 488℃.
Verb (abbreviation of verb) genetic model of ore deposit
(1) metallogenic stage
The rise and infiltration of sulfide-bearing magma can be divided into four continuous stages, namely: silicate magma stage; Sulfide-bearing magmatic stage; Sulfide-rich magma stage and sulfide melting stage. Each stage has the following characteristics:
In the first stage, silicate magma only formed a few ore bodies composed of sparse disseminated sulfides, which were small hanging convex mirrors located in the middle and upper part of the western segment of the intrusive body (Figure 2-3b).
In the second stage, the sulfide-bearing magma formed a thick layered and lenticular ore body composed of sparse disseminated sulfide, which was located in the middle and lower part of the intrusive body (Figure 2-3c), and its nickel and copper reserves accounted for 65,438+00% of the ore block reserves.
After the intrusion of sulfide-rich magma in the third stage, a reticular ore body is formed, which is located at the lower side of the intrusion in the form of a large convex mirror (Figure 2-3b and Figure 2-3c), and its nickel and copper reserves account for 85% of the reserves of the ore section.
In the fourth stage, sulfide melt mainly seeps into the bottom or bottommost cracks of the ore body, showing a network structure (Figure 2-3c). Only in a few cases can sulfide melt penetrate into its top, upper wall or lower wall. This kind of ore body is vein-shaped, lenticular and cystic, and consists of massive sulfide, and its nickel and copper reserves account for 1% of the total reserves of the ore section.
In addition, contact metasomatic ore bodies can be seen in the surrounding rocks near the contact zone at the bottom and upper part of the intrusive body, and in the xenoliths around the intrusive body, accounting for 1% ~ 2% of the nickel and copper reserves in the ore block. Hydrothermal superimposed ore bodies can also be seen, which occur in primary reticular ore bodies, especially sparse disseminated ore bodies, and are generally characterized by rich Cu, Pt, Pa, Au, Ag and se.
See Table 2-2 for the w(Cu)/w(Cu+Ni) and w(Pt)/w(Pt+Pd) values of various ore bodies.
Table 2-2 Content Ratio of Related Elements of Jinchuan Ore Type Table 2-2 List of Content Ratio of Some Elements in Jinchuan Ore Deposit
(B) Integrated model
According to the geochemical characteristics of Jinchuan deposit obtained at present, the following genetic models are put forward:
Iron-bearing ultrabasic magma originated from the mantle and intruded into the crust 10km above magma chamber (Figure 2-5a). The volume of primitive magma is at least three times larger than that of the present intrusive body.
Figure 2-5 Genetic model of Jinchuan nickel-copper deposit Figure 2-5 Metallurgical model of Jinchuan nickel-copper deposit
1- silicate magma; Magma containing sulfide; 3- sulfide-rich magma; 4- sulfide melt; 5- contact metasomatism mineralization; 6- hydrothermal superimposed mineralization
After the mantle magma rises to the magma chamber in the crust, the immiscible fluid melts separate and olivine crystals differentiate within the range of 1700 ~ 1400℃ (Figure 2-5b). After melting, sulfide melts gather and sink to the bottom of magma chamber under the action of gravity, and a large amount of olivine also crystallizes. Then it precipitates on the sulfide melt, and the sulfide melt separated from the subsequent magma precipitates between olivine crystals, forming a network structure ore bed. Later, some sulfide droplets separated, so they stopped and suspended in the upper part of the magma. Thus, a layered model of ore-free magma-sulfide-bearing magma-sulfide-rich magma-sulfide melt (decreasing series) was formed in magma chamber.
When the magma chamber temperature is between 1400℃ and 1200℃, only olivine continues to crystallize, and the sulfide remains in a molten state. Driven by fluctuating tectonic stress, ore-free magma-sulfide-rich magma-sulfide melt rises in turn (Figure 2-5c) and invades the crust 10 to 10. Magma intruded into one or more places in the upper part of magma chamber in the lower crust. Then, the above-mentioned ore-free magma-sulfide-containing magma-sulfide-rich magma and sulfide melt intruded into the position of uncured intrusion in a vein. Every pulsating upwelling is carried out along the lower side of the earlier formed rock mass, because this position represents a weak zone, which is conducive to magma upwelling.
Ore-free magma and sulfide-bearing magma continue to crystallize in situ at a temperature below 1200℃ (Kudo and Weil,1970; Huckley and Wright,1967; Institute of Geochemistry, Chinese Academy of Sciences, 198 1), bronze pyroxene, enstatite, Labrador stone, sparse sulfide droplets from deep zone and sulfide droplets formed by in-situ melting between olivine or late crystalline minerals are formed in turn, and sparse disseminated minerals are formed in suspended plate-like ore bodies.
After the four melts are in place, with the decrease of temperature and intermittent crystallization, the volatiles in them increase, and finally the volatiles gather, leading to self-metamorphism. Primary olivine and pyroxene are altered to form altered mineral aggregates, including serpentine, amphibole and chlorite. Sulfide intrudes into the surrounding rocks and xenoliths near the contact zone through osmotic diffusion and metasomatism (Figure 2-5d). The affected surrounding rocks (mainly carbonate rocks) are mixed and metasomatized to form skarns, including tremolite, chlorite, a small amount of almandine, silicomagnesite and other contact metasomatic minerals. The above contact replacement can be carried out at the temperature of 600 ~ 480℃. Because the composition of ore comes from sulfide in intrusive rocks, there is no difference between magmatic ore and sulfide mineral aggregate in contact metasomatic ore, but the proportion of copper mineral in the latter is higher. With the further accumulation of volatile components, the proportion of ore-forming components in volatile fluids has increased. Driven by tectonic stress, this highly volatile fluid infiltrates into the local structural weak zones in reticular ore bodies and disseminated ore bodies (Figure 2-5c), forming ore bodies with hydrothermal superposition characteristics. This hydrothermal mineralization can turn primary reticular ore into felt-like and nebula-like ore, and also can turn sparse disseminated ore into porphyry ore. It also makes silicate minerals undergo strong serpentine. The proportion of copper minerals, especially chalcopyrite, increased by about half compared with the total sulfide minerals, and the relative abundance of Pt, Pd, Au, Ag and Se in these ore bodies also increased significantly. Among them, Pt and Pd are produced in the form of arsenide, bismuth telluride and telluride, while Au and Ag exist in the form of microscopic fine particles (0.076mm) of natural gold and silver-gold solid solution. Selenium mainly appears as a substitute for sulfur in sulfide. In a word, the metallogenic stage is characterized by hydrothermal superposition, which is mainly manifested by the obvious enrichment of Cu, Pt, Pd, Au, Ag and Se in magmatic sulfide ores. The equilibrium temperature of pyrrhotite and chalcopyrite at this stage is 189 ~ 339℃.
The emplacement age of ore-bearing intrusive body is 65438±0500ma. After mineralization, the area experienced a long and complicated geological evolution process, showing obvious crustal uplift and erosion. By the Quaternary, most known sulfide-bearing intrusions were exposed to the surface. The western intrusive body is shallow, and the exposed part is oxidized, forming an oxidation zone on the nickel-copper sulfide deposit, while the eastern intrusive body has never been exposed, with a maximum burial depth of 300 meters.