Hongqiling basic-ultrabasic rock group is located in the southern margin of Zhangguangcailing geosyncline fold belt, adjacent to the northern margin of North China landmass. Some geologists (Fu Debin, 1994) believe that this area belongs to Caledonian back-arc basin and is controlled by the NW-trending secondary fault of Huifahe deep fault zone. From Hongqiling to Hulan Town, a series of basic-ultrabasic small rock mass groups are distributed in a NW-trending belt.

Second, the mining area geology

(1) mining stratum

The surrounding rocks of basic-ultrabasic rocks are amphibole, biotite plagioclase gneiss, schist and marble lens of Huangyingtun Formation (354Ma) of Hulan Group in Lower Paleozoic.

(2) Mining area structure

Folds and faults are developed in the mining area. The NE-trending tensional and torsional Huifahe fault is most closely related to the basic-ultrabasic rock mass, and the rock mass is directly controlled by the NW-trending secondary compressive and torsional fault of the main fault. The emplacement of basic-ultrabasic magma is characterized by multi-cycle and multi-stage pulsation. The K-Ar age of the ore-bearing rock mass is 39 1 ~ 350 ma, which belongs to the early Variscan period.

(3) Rock mass geology

The basic-ultrabasic rocks in Hongqiling are lenticular, spindle and veined. The emplacement period is from late Caledonian to early Variscan, and the ore-bearing rock mass is mainly the product of early Variscan. Rock types are complex, including gabbro, pyroxenite, peridotite, plagioclase pyroxenite, amphibole peridotite, etc., all of which belong to normal rock series. Large copper-nickel sulfide deposits occur in Hongqiling 1 and No.7 rock masses.

Now, taking Hongqiling No.7 and 1 ore-bearing rock masses as examples, the main characteristics are described (Table 2-7).

Table 2-7 Types and main characteristics of basic-ultrabasic rocks in Hongqiling.

1 .hongqiling No.7 ore-bearing rock mass

The rock mass is located in the southeast of the mining area, and the intrusion of NW-trending compression-torsion hierarchical faults is unconformity with the surrounding rock. The floor of the rock mass is biotite gneiss, and the roof is the interbedded zone of granite gneiss, amphibole and marble. The southern part of the rock mass is covered by tertiary glutenite, and the glutenite and biotite gneiss are in unconformity contact (Figure 2- 16). The rock mass strikes N30 ~ 60 W, with a total length of several hundred meters, a width of several tens of meters and a thickness of 10 ~ 170 m, and gradually becomes thinner from northwest to south. There are two small lenticular rocks in the northwest that are not connected with the main rock mass. On the profile, the rock mass is in the shape of a rock wall (Figure 2- 17), with an inclination of NE and an inclination of 75 ~ 80. In the middle of the rock mass (such as Line 4), the occurrence changes little, from steep to slow from top to bottom, and narrows at the corner. Near Line 4, a small concealed rock mass appears on the upper and lower walls of the rock mass, and its occurrence is basically the same as that of the main rock mass.

Lithofacies combination and rock characteristics of the rock mass: the main lithofacies of the rock mass is dense pyroxenite (locally strong hypoamphibolite is altered pyroxenite) and a small amount of syenite. The former is the main body of rock mass, accounting for 96% of the total volume of rock mass. Most syenites are located at the edge of rock mass and are in contact with surrounding rocks in a structural fracture. According to its petrochemical characteristics and occurrence in rock mass, it may be formed by the assimilation of pyroxenite to surrounding rock. The distribution of altered pyroxenite has no obvious law, mostly at the edge of rock mass or inside syenite.

In the middle part of the rock mass near the footwall, there are often pyroxenite veins, sometimes transiting to peridotite or olivine pyroxenite, but its composition is still dominated by pyroxenite. There are obvious contact boundaries with surrounding rocks (enstatite or altered pyroxene) on both sides, and the contact zones are often separated by small broken zones.

Refractory pyroxenite: dark green, medium fine grained, authigenic-semi-authigenic granular structure. The mineral composition is mainly enstatite (En9 1, with a content of 75% ~ 80%), with a small amount of brown amphibole, Labrador and clinopyroxene. Some rocks are strongly altered, mainly soap-petrification, sub-flash petrification, slip petrification and a small amount of sericitization. Generally, it contains a lot of metal sulfides, which often constitute spongy meteorite-like or disseminated ores. Sometimes irregular sulfides are filled between rock-forming minerals and metasilicate along cleavage.

Fig. 2- 16 geological map of hongqiling No.7 plot (according to team 607, 1972) (after team 607, 1972)

1-biotite gneiss: 2-amphibole schist; 3- marble; 4— Gravel; 5- enstatite; 6- altered pyroxenite; 7- syenite; 8— Edge fracture zone; 9— Projection boundary of rock mass; 10- lithofacies boundary

Syenite: it is distributed in the contact zone between enstatite and surrounding rock, and has a gradual relationship with the former. Dark gray-gray-green, fragmented structure, gabbro structure. The main minerals are plagioclase, orthopyroxene, brown amphibole and a small amount of ordinary pyroxene. Generally, rocks are strongly altered, characterized by slip petrification, secondary flash petrification and Labrador sericitization of orthopyroxene. The content of metal sulfide is low (less than 3%), and it is mostly disseminated and punctate, with occasional veinlets. Sulfide metasomatism silicate phenomenon is very common.

Pyrite (dike rock): black, medium-grained semi-authigenic granular structure, inclusion structure. The main mineral is olivine (70%), followed by enstatite and brown amphibole. Metal sulfides are evenly distributed, with the content of about 15% and 70% locally. Serpentine is strongly mineralized.

2. hongqiling 1 ore-bearing rock mass

The rock mass 1 is spindle-shaped in the plane (Figure 2- 18), and strikes NW46, with a length of 980m and a width of150 ~ 280m, with a maximum controlled depth of 560m and an exposed area of 0.2km2. In the longitudinal section (Figure 2-/kloc-)

Wu Dianying's research in 1987 further shows that 1 rock mass is a compound rock mass formed by three intrusions of nickel-bearing basic-basic magma. The author divides it into gabbro, pyroxene-pyroxene peridotite and olivine pyroxene. All lithofacies are intrusive contact. This negates the previous understanding of a single rock mass.

Lithofacies features are as follows:

Gabbro facies: its volume accounts for about 65438 0% of the rock mass, mainly distributed near the upper surface of the rock mass, and obviously appears in the form of xenoliths of pyroxene peridotite facies. It contains a small amount of emulsified copper-nickel sulfide, which has not yet constituted mineralization.

Pyrite-pyroxene peridotite facies: it accounts for about 95% of the rock mass and is the main lithofacies of the rock mass. The upper part is pyroxene phase and the lower part is pyroxene peridotite. Their volume ratio is 6.3∶93.7. At the bottom of lithofacies, sulfide is rich in porphyry ore, but its reserves can be ignored.

Olivine pyroxenite facies: exposed at the eastern edge of surface rock mass and located at the bottom edge of underground rock mass. This lithofacies only accounts for 4% of the volume of the rock mass, but it is the main ore-bearing lithofacies of the rock mass. It is composed of olivine (Fo 87% ~ 20%), orthopyroxene (mainly bronze pyroxene, with a content of 40% ~ 70%) and plagioclase (An 58 ~ 60, with a content of 5% ~ 10%).

The average sulfide content of this lithofacies is about 35%, and it tends to increase gradually from top to bottom. The corresponding ore structure ranges from dense disseminated to spongy meteorites and then to breccia.

There is a flowing structure in the ore body at the bottom of the lithofacies, and the occurrence of the flowing layer is consistent with the occurrence of the contact zone of the rock or the underlying surrounding rock, indicating that the dynamic factor is the main factor for the formation of the lithofacies rich ore body, followed by the gravity factor.

Through the calculation of petrochemical analysis data of more than 30 samples collected from different lithofacies (Wang Hengsheng, Bai Wenji, etc. , 1975), indicating that the ore-bearing rock mass belongs to the normal basic-ultrabasic rock mass series (Figure 2-20). The m/f of basic rocks is 0.5 ~ 2, which belongs to iron basic rocks; The m/f of ultrabasic rocks is 2 ~ 5.66, which belongs to iron ultrabasic rocks. M/f = 2 ~ 4 has good ore-bearing property, and m/f = 3 ~ 4 has the best ore-bearing property.

The projection points of each lithofacies in Figure 5 are concentrated in the upper, middle and lower isolated areas, which reflects that the three lithofacies are the products of three magmatic intrusions, rather than the relationship of crystal differentiation. The upper part is gabbro, the middle part is olivine-bearing pyroxene, and the lower part is pyroxene peridotite. The projection vector of middle and lower ore-bearing lithofacies on sfm plane is short and steep, while the projection vector on sacm plane is long and slow, indicating the petrochemical characteristics of dark component rich in iron and poor in calcium and light component poor in calcium respectively. Practice shows that lithologic characteristics can be used as one of the evaluation criteria of ore-bearing rock mass.

Figure 2- 17 Geological Profile of No.7 Rock Mass in Hongqi Ridge (Figure 2- 17 Geological Profile of No.4 Exploration Line of No.7 Block in Hongqi Ridge (according to Team 607, 1972) (after Team 607. 1972).

1-topsoil and alluvium; 2- marble; 3 amphibole schist; 4- biotite gneiss; 5- enstatite; 6- altered pyroxenite; 7- syenite; 8— Broken zone; 9- Ore body oxidation zone

Three. geology of ore deposits

(I) Characteristics of No.7 Rock Mine

There are three types of ore bodies in rock mass: plate ore bodies, vein ore bodies and pure sulfide vein ore bodies.

Plate-shaped ore bodies: metal sulfides are widely distributed in No.7 rock body, and most of them constitute industrial ore bodies. Therefore, the shape and occurrence of the ore body are basically consistent with the rock mass. The ore-bearing rocks are mainly pyroxene or altered pyroxene with a small amount of syenite. Most of the ores are fine spongy texture, a little disseminated texture, and some are massive texture. The metal mineral assemblage of the ore is mainly pyrrhotite, nickel pyrite (containing a small amount of purple-sulfur-nickel ore) and chalcopyrite, with relative percentages of 54, 33 and 13 respectively. The value of w(Ni)/w(Cu) in ore is about 3.3.

Vein ore body: It mainly occurs in olivine vein, and its occurrence is basically the same as vein, and it is composed of sponge meteorite and porphyry ore. Its main metal mineral assemblages are also pyrrhotite, nickel pyrite and chalcopyrite, with relative percentages of 56, 39 and 5 respectively. The grade of nickel is higher than that of plate orebody, and the value of w(Ni)/w(Cu) is 5.2.

Pure sulfide vein ore body: it occurs in the contact fracture zone between enstatite and pyroxene vein, and the boundary between them is clear and abrupt. The ore bodies are all composed of dense massive ores, and the main metal minerals are pyrrhotite (58%), nickel pyrite (35%) and chalcopyrite (7%). Sometimes small amounts of olivine, pyroxene and brown amphibole can be seen. This kind of ore body has little change along strike and dip, and is a stable vein, extending more than depth.

There are three ore bodies in No.7 rock mass, of which the main ore body 1 is 750m long,14.5m thick and buried150m deep. Ores can be divided into three types.

The disseminated type in plagioclase pyroxenite: the ore structure is mainly disseminated and locally dense and massive; Semi-automorphic-heteromorphic granular structure; The ratio of pyrrhotite: nickel pyrite: chalcopyrite is 4.2 ∶ 2.5 ∶1; Sulfide content is about 9%; The average content of nickel is1.71%; The average content of copper is 0.52%.

Figure 2- 18 Geological map of copper-bearing nickel ore body. Geological map of Hongqiling 1 Figure 2- 18 Hongqiling 1

1-biotite gneiss; 2- amphibole schist; 3- gabbro; 4- plagioclase pyroxenite; 5- pyroxene peridotite; 6- olivine pyroxenite; 7- timely flying spot dike; 8- plagioclase vein; 9— Industrial ore bodies; 10- overthrust fault; 1 1- fracture zone; 12- failure of unknown nature; 13- phase transition boundary

Fig. 2- 19 schematic diagram of longitudinal section of copper-nickel bearing rock mass. Hongqiling 1 (Figure 2- 19 Hongqiling block containing copper and nickel/longitudinal sectionNo. kloc-0/) (the legend is the same as Figure 2-1 8).

Filamentous disseminated type in peridotite: the ore structure is sponge-meteorite-like and point-like; The ore structure is coarse grained; The ratio of pyrrhotite: nickel pyrite: chalcopyrite is1.2: 7.8:1; The sulfide content reaches 20%; The average content of nickel is 3.43%; The average content of copper is 0.6 6%.

Pure sulfide vein type: the ore structure is dense and massive; The ore structure is semi-authigenic granular; The ratio of pyrrhotite: nickel pyrite: chalcopyrite is 8.7: 5:1; The average content of nickel is 9.76%; The grade of copper is 0.63%.

(II) Characteristics of 1

Mineralization characteristics of different intrusive lithofacies are different (Fu Debin, 1982).

(1) The "layered" ore bodies in olivine pyroxenite occur at the bottom and edge of the rock mass, and their shapes and occurrences are consistent with those of the rock. The ore bodies are of flowing structure, and the marginal ore bodies tend to become larger upwards (Figure 2- 19). In particular, the ore body at the southeast end is exposed to the ground, with a thickness of 70m, extending downwards along the strike by 800m, with an average vertical depth of 250m, and gradually tapering downwards. These facts are difficult to be explained by the theory of crystallization gravity differentiation. The main ore minerals in the ore body are pyrrhotite, nickel pyrite and chalcopyrite, with contents of 60%, 30% and 5% respectively. In addition, there are a small amount of pyrite, porphyrite and arsenic-nickel ore. The ratio of tungsten (nickel) to tungsten (copper) in the ore is 5.1:1. According to the stable isotope of sulfur in sulfide "mineral pair" and the temperature measurement results of inclusions, the ore formation temperature is between 382 ~ 400℃. The formation temperature of ore-bearing lithofacies calculated by geological thermometer based on single pyroxene method is 65438 0265℃. If the spongy meteorite structure of the ore can explain that the sulfide was melted away before the silicate crystallized, then the sulfide in this ore-bearing rock phase is immiscible with silicate when it is higher than 1265℃ (the silicate has not crystallized), and after melting away, it penetrates into the crust together with silicate molten slurry or separately to form rocks and mineralization. Obviously, sulfide crystallized and mineralized after silicate crystallized for a long time (when the melt was in the form of crystal porridge), and the temperature dropped to about 400℃.

(2) "Suspended lenticular" and "layered" ore bodies in pyroxene peridotite. The former is produced in the upper part of lithofacies, with irregular shape, mainly lenticular, and mineral strips, lentils and thin layers also appear from time to time, generally with small scale, thin thickness, short extension and poor continuity. Most ores are sparsely disseminated, with low grade, great variation, poor beneficiation and little industrial significance. The latter is located at the bottom of lithofacies and above the interface of olivine pyroxenite. The boundary between ore and host rock facies is unclear, which is a gradual transition relationship. The ore is characterized by dense disseminated ore, with sponge meteorite-like structure occasionally seen in the rich and rare palindrome-like structure locally. The research shows that the ore minerals of the upper and lower ore bodies are similar, mainly pyrrhotite, nickel pyrite and chalcopyrite. According to statistics, the contents of the three minerals in the hanging ore body are 60%, 35% and 5% respectively, and the ratio of the three minerals is 12: 7: 1. The mineral granularity is 1 ~ 2mm, and the near-ore alteration is very slight. The sulfide content of lithofacies is 3% ~ 6%, the average nickel content is 0.22% ~ 0.30%, the copper content is 0.05%, and w (nickel) ∶ w (copper) = 6 ∶ 1. However, the chalcopyrite in the bottom ore body increased, with w(Ni)∶w(Cu)=2.3∶ 1. The diagenetic and metallogenic temperatures of this lithofacies are about 65438 0500℃ and 500℃ respectively. It is not difficult to see from the above that the ore body in pyroxene peridotite is obviously formed by in-situ crystallization and melting, which is different from the ore body at the bottom of olivine pyroxene. In other words, silicate melt or magma formed by deep liquid melting of molten slurry contains residual sulfide that has not been melted away. Under the influence of temperature drop and other factors, crystal melting occurs. Due to the action of gravity, a part of the sulfide that was initially melted settled to the bottom of lithofacies, forming a "bottom ore body", while another part of sulfide later melted and condensed before sinking, forming a "hanging ore body". This mineralization contains almost no mineralizer and has a high formation temperature.

Figure 2-20 Numerical Characteristics of Petrochemistry of Copper-nickel-bearing Rocks in Hongqiling Area 1 No.7; Numerical Characteristics of Rock Mass in Hongqiling 1 No.3 in Tu Tu (according to Wang Hengsheng and Bai Wenji, 1975) (later Wang Heng et al. 1975).

Ⅰ-1rock mass; 1 ~ 4- gabbro; 5 ~13-pyroxenite containing olivine; 14 ~ 24- peridotite containing augite; Ⅱ-1rock F 1 footwall sample of fault: 25 ~ 3 1- peridotite contains augite; Ⅲ-7 rock mass; 32 ~ 35— Mixed-dyed syenite; 34,36—plagioclase pyroxenite

(3) Vein ore bodies are superimposed after diagenesis. After the main diagenesis and mineralization of rock mass is completed, there are still some late vein rocks and sulfide veins superimposed on the above two contemporaneous ore bodies along the structural cracks, which makes the mineralization more abundant. This phenomenon strongly proves the characteristics of multi-stage pulp mineralization. There are two main ore bodies in the 1 rock mass. The main ore body is 835 meters long, 9.5 ~ 65 meters wide, 30 ~ 50 meters thick and 0 ~ 440 meters buried. The main ore body is poor in nickel and copper, with an average grade of 0. 12%.

(3) Discussion on the genesis of the deposit.

(1) According to the traditional theory of in-situ crystallization and dissolution mineralization, the size of the ore body is directly proportional to the size of the parent rock mass. Based on this theory, J.H.L.Vogt( 1893) thinks that there is no large ore in small rock mass. Sulfide in the above rock mass accounts for 1/3, especially No.7 rock mass, and almost 100% of the whole rock mass is mineral. This fact cannot be explained by traditional genetic theory. So much nickel can not be explained by the average content of nickel in basic-ultrabasic rocks or the solubility of sulfide in them, but only by the infiltration and mineralization of sulfide-rich pulp formed by deep liquid melting of ore-bearing magma.

(2) The ore bodies in the Hongqiling 1 rock mass are layered and occur in surrounding rocks and adjacent surrounding rocks, especially the ore-bearing lithofacies (olivine facies) and ore bodies all have the same occurrence as the bottom contact zone, indicating that the dynamic action is the main factor in the diagenesis and mineralization process, supplemented by gravity differentiation. In particular, the No.7 rock mass is a rock wall and the rock mass is an ore body. There is no gravity differentiation phenomenon, which is purely a typical deep liquid detachment and penetration (Wu Dianying, 1987).

(3) The ore-bearing lithofacies is located in the middle of the rock mass, not in the lowest part, but in the lowest part, which shows that 1 The ore-bearing olivine pyroxene in the lower part of the rock mass and the ore in it are not the product of crystallization gravity differentiation, but formed by the infiltration of sulfide-bearing pulp separated by a single deep liquid.

(4) The ore-bearing olivine-pyroxene phase has a coarse grain size (generally 2 ~ 3 mm, up to 7 ~ 8 mm) and is rich in metal sulfides (generally containing 15% ~ 50%, up to 70%), and there is hydrothermal alteration near the sulfides. The water content of lithofacies is 5% ~ 6% (the highest is 8%). It can be seen that the volatile matter of pulp plays an important role in the formation and migration, which is one of the remarkable characteristics of pulp mineralization.

(5) According to the data, a typomorphic structure that can be used as ore pulp mineralization-the * * knot structure between olivine and sulfide, and the * * knot structure between spinel and silicate in chromite can be regarded as a sign of mineral crystallization from ore pulp (A.F. Koster,1967; д. b .пoд； φepoB， 1979)。

(6) The variation of δ34S in rock mass is+1.2 ‰ ~+2.8 ‰, and the δ34S values of different types of ores are very close, similar to the sulfur isotope values in meteorites. Moreover, the tower effect of frequency histogram is obvious, indicating that the diagenetic and metallogenic materials of ore-bearing rock mass come from the upper mantle.

To sum up, the Hongqiling copper-nickel sulfide deposit is a "slurry infiltration genesis" deposit formed by the sulfide-rich slurry melted from the primary ore-bearing magma in the upper mantle and separated into the upper crust by deep liquid. The mineralization can be summarized in Table 2-8. Table 2-8 shows that the original magma is the parent, magma and pulp are twin brothers (at the same level), and minerals and rocks are their descendants. Pulps can be divided into liquid molten pulp, crystalline molten pulp and late residual pulp. The pulp formed in different evolution stages of molten magma has different mineralization modes and ore body size.

Table 2-8 Mineralization of Hongqiyan Copper-Nickel Deposit Table 2-8 Mineralization of Hongqiling Copper-Nickel Deposit