3.2.2. 1 Geology of mining area
(1) mining stratum
There are mainly Proterozoic Fenzishan Group, Neoproterozoic Penglai Group and Mesozoic Qingshan Group (Figure 3.30). Among them, the strata related to mineralization are mainly limestone section and marl section of Xiangkuang Formation in Penglai Group, and the lithology is mainly marl, limestone mixed with thin slate and argillaceous limestone.
(2) Mining area structure
It is mainly a fault structure, mainly in NEE direction and NE direction. The former (F 1) is located in the middle of the mining area, almost parallel to the fault development at the edge of Zanggezhuang basin. The fault plane is inclined to SE, and the dip angle is 60 ~ 70; Pre-fracture and post-cutting basically control the intrusion and exposure range of porphyry in the later period; The latter, represented by Zaolin fault, strikes 10, inclines to SE, and the dip angle is 74; Controls the eastern boundary of the rock mass.
Fig. 3.30 Geological Schematic Diagram of Hunan Mining Area
(Modified according to the Third Exploration Team of Shandong Metallurgical Geological Exploration Company, 1980)
1-Quaternary sandy clay; 2- andesite porphyrite; 3- taupe dacite-rhyolite pyroclastic rocks and clastic lava; 4- submerged breccia dacite porphyry; 5— Thick limestone mixed with argillaceous limestone and slate; 6-marl and limestone interbedded with thin rock; 7— Calcareous slate and slate mixed with marl; 8- granodiorite porphyry; 9— skarn; 10- lead-zinc ore body; 1 1- compression-torsion fault; 12- tension-torsion fault; 13- failure of unknown nature; 14-Inferring the fault; 15- geological boundary; 16- Angle unconformity geological boundary; 17-rock occurrence; 18- Location of exploration line
(3) Intrusive rocks in mining area
It includes intermediate-acid porphyry in the late Yanshanian period of Mesozoic and volcanic rocks such as dacite porphyry and andesite porphyry. Among them, the granodiorite porphyry in the late Yanshanian is closely related to mineralization and is the parent rock of copper, lead and zinc (molybdenum) mineralization in this area. The fault along the southern margin of the volcanic basin (F 1) intrudes into the basement limestone in an east-west direction, and is controlled by the east-west and north-east faults, and is exposed sporadically in the form of rocks, branches and dikes, with an east-west length of about 8000m and a north-south width of about 2000m. Skarnized lead-zinc mineralization develops at the contact with thin argillaceous limestone of Hunan Formation, and porphyry lead-zinc bodies and copper (molybdenum) orebodies are formed in or at the edge of the rock mass (Figure 3.3 1).
Geology of 3.2.2.2 deposit
Mineralization in the mining area is controlled by limestone and porphyry of Hunan Formation in the late Yanshan period, mainly developed around the contact zone between them, and a small amount occurs in altered rocks around the contact zone. The mineralization of the whole mining area constitutes a three-dimensional mineralization space centered on porphyry (vein), which is about 1700mm long, about 600m wide and more than 700 m deep, with obvious vertical zoning of mineralization in the vertical direction. From shallow to deep, it is lead-zinc mineralization, copper ore body and copper-molybdenum mineralization, and the metallogenic element combination is PbZn-(Pb)ZnCu-CuMo (Figure 3.3 1) respectively. Among them, the four main ore bodies are Ⅰ and Ⅱ copper ore bodies and Ⅳ and Ⅴ lead-zinc ore bodies.
(1) ore body characteristics
Orebodies are distributed intermittently along the contact zone, and the occurrence is basically consistent with the contact zone. On the plane, it is an arc protruding to the south, and the west end is close to EW direction, inclined to S, with an inclination angle of 30 ~ 45; It gradually changes to NEE direction to the east, and looks obliquely, with an inclination angle of 45 ~ 60. On the profile, the main strike is lead-zinc ore body above, zinc-copper ore body in the middle and copper (molybdenum) ore body below.
Shallow lead-zinc belt: skarn ore body. Most of them are produced at the edge of contact zone, and a few are developed in veins in limestone cracks. The ore body is small in scale and long in strike, extending obliquely from ten meters to hundreds of meters; The shape is complex and the occurrence changes greatly. It is often lenticular, lentil, veined, cystic and layered, and the lower part is mostly a single zinc ore body. Gradually transition downward to copper-sulfur ore body.
Figure 3.3 1 Section of No.24 Exploration Line in Qixiaxiang Mine Area
(quoted by Ni Zhenping et al., 20 1 1)
Copper-sulfur ore belt: skarn-porphyry ore body. Mainly in the middle of the contact zone, between 200 meters and 500 meters underground. I The ore body (main ore body) is about 1054m long, with an inclined extension of 200~300m, the maximum extension of 700m, and the thickness of10 ~ 44m; It is layered and stable in occurrence, and its resources account for 80% of the total copper and sulfur in the whole region. In addition, there are a few small-scale layered and lenticular copper-sulfur ore bodies in skarn outside the contact zone and altered granodiorite porphyry inside the contact zone.
Copper (molybdenum) ore belt: it is a typical porphyry ore body. It occurs in deep altered granodiorite porphyry, with a buried depth of over 500m and a large thickness, exceeding100m locally. Vein and lenticular distribution, mainly copper mineralization and molybdenum mineralization. Ore mineralization is relatively uniform, with copper grade of 0. 1% ~ 0.3% and molybdenum grade of 0.002% ~ 0.005%.
(2) Ore characteristics
Including skarn type and sericite porphyry type; According to the composition of metal minerals, they can be roughly divided into lead-zinc mine, copper mine and copper-molybdenum mine. Ore structures include semi-self-shaped-shaped granular structure, emulsion drop structure, inclusion structure, reaction edge structure, ring structure, metasomatic residual structure and so on. , mainly disseminated, veinlets disseminated, massive and banded structures. Among them, corresponding to the different types and intensities of hydrothermal alteration, different types of ore structures are obviously different, showing that lead-zinc mine, copper mine and copper (molybdenum) mine have massive, disseminated and veinlet-disseminated structural characteristics respectively.
Mineral composition: mainly galena, sphalerite, pyrite, chalcopyrite, garnet, diopside, feldspar, timely, calcite, etc. Among them, the content of metal minerals varies with different ore types, and the upper lead-zinc mine is mainly galena and sphalerite; The copper mines in the central part are mainly pyrite and chalcopyrite, with a small amount of galena and sphalerite; The lower copper-molybdenum mineralization zone is dominated by pyrite and chalcopyrite, with a small amount of pyrrhotite and molybdenite. The ore is rich in deep elements such as selenium, tellurium and indium, indicating that mineralization is related to mantle-derived materials.
(3) Surrounding rock and surrounding rock alteration
The deposit occurs in the contact metamorphic zone between granodiorite porphyry and limestone. The alteration of surrounding rock has obvious zonation (Figure 3.32), and the alteration types from the inside to the outside of rock mass are: silicification, sericitization, alkalization → skarnization → chloritization, epidotization, sericitization and carbonation. Among them, skarnization, alkalization and silicification are closely related to metal mineralization.
Fig. 3.32 Schematic diagram of alteration zoning of surrounding rock of Hunan copper-lead-zinc deposit.
(According to Kong Qingyou and others, 2007; Wang Kuifeng, 2008)
1- granodiorite porphyry; 2- skarn; 3— limestone of Xiangkuang Formation; 4- Lead-zinc ore body; 5- copper ore body; 6- Carbonated sericitization zone; 7- weak chloritization epidote belt; 8- skarnized zone; 9- weak potassium and strong silicified sericite carbonization zone; 10- lead-zinc mineralization; 1 1- copper-molybdenum mineralization
(4) Metallogenic stage and mineral generation sequence.
The mineralization in this area is mainly divided into three stages: ⅰ. In the stage of skarnization-pyritization, a large area of skarnization was formed. During this period, the mineralization was weak, mainly forming early pyrite, and the nonmetallic minerals were skarn minerals such as garnet, diopside and chlorite. Ⅱ. In the timely copper-molybdenum mineralization stage, copper-molybdenum mineralization was mainly formed in rock mass. Metal minerals include chalcopyrite, molybdenite, pyrrhotite and pyrite. Non-metallic minerals mainly include quartz, sericite, biotite and potash feldspar. Ⅲ. In the timely polymetallic lead-zinc mineralization stage, the main metal minerals formed are chalcopyrite, sphalerite, galena and pyrite. Non-metallic minerals include timely and sericite. Ⅳ During the carbonation stage, a small amount of pyrite and galena are generated, and the nonmetallic minerals are mainly calcite, chlorite, sericite, timely and barite.
Characteristics of ore-forming fluids in 3.2.2.3
Because the mine has been shut down for many years, only one calcite vein in the late lead-zinc mineralization was obtained for inclusion testing, and the research work was carried out in the Geological Fluid Laboratory of Jilin University. Combined with the previous work (No.3 Exploration Team of Shandong Metallurgical Geological Exploration Company, 1980), the properties of ore-forming fluids in this area are briefly analyzed.
Study on fluid inclusions (Kong Qingyou et al., 2007; The book shows that the fluid inclusions in the studied samples are mainly divided into four types: three-phase inclusions containing CO2, three-phase inclusions containing daughter minerals, gas-liquid two-phase inclusions and pure liquid-phase inclusions. The temperature of ore-forming fluid is obviously divided into three groups (Figure 3.33), that is, the range of 287 ~ 430℃, which represents the temperature of (wet) skarnization stage and timely copper-molybdenum mineralization stage; 192 ~ 270℃ represents the mid-term temperature of copper, lead and zinc mineralization, and 120 ~ 180℃ represents the late temperature of timely carbonation. Another temperature value of 587℃ may represent the temperature of early skarn stage.
Fig. 3.33 Uniform temperature distribution of fluid inclusions in lead-zinc ore of Hunan Mine.
(According to this book, Kong Qingyou and others (2007))
The salinity of fluid inclusions first decreased and then increased from high temperature to low temperature from morning till night, and the average salinity of fluid in early skarn period (NaCleq) was 12.9%. In the middle stage of Yanshi-Cu-Mo mineralization, the average is 8.59%, in the middle and late stage, it is 4.48% (Kong Qingyou et al., 2007), and in the Yanshi-Carbonization stage, it is 7.35%. After calculation, the density of ore-forming fluid in the later stage is 0.94 ~ 0.99 g/cm3, which is a low-density fluid.
In this study, only five groups of data of gas-liquid two-phase inclusions with freezing temperature were obtained (Table 3. 14). On the basis of comprehensive consideration of the geological characteristics of the mining area and the inclusion system studied, the P-T-D diagram of NaCl-H2O system proposed by Roedder( 1979) is adopted for mapping (Figure 3.34). The pressure values of ore-forming fluids in Hunan mining area are roughly concentrated in two ranges: 75 ~ 95 MPa and 180 ~ 195 MPa. Combined with the metallogenic characteristics in this area, it is considered that the former is reasonable and the latter may be caused by high fluid salinity. Combined with the metallogenic characteristics of porphyry deposits in the mining area, the relationship between metallogenic pressure and metallogenic depth under rock static pressure is directly used to calculate that the metallogenic depth of the deposit is about 2.78~3.52km, which is more in line with the metallogenic reality of porphyry copper (molybdenum) deposits and skarn lead-zinc deposits.
Table 3. 14 Test Results of Fluid Inclusions in Calcite Veins in Hunan Mining Area
sequential
Fig. 3.34 P-T-D diagram of NaCl-H2 O system in Hunan mining area
(According to Roedder's basemap, 1979)
Characteristics of stable isotopes in 3.2.2.4
Characteristics of hydrogen and oxygen isotopes: The chronotropic analysis in lead-zinc ores shows that the δ 18OSMOW values of four chronotropic inclusion samples range from+5.8 ‰ to+9.0 ‰, with an average of 7.48 ‰; δ dsmow =-55.6 ‰ ~-74.2 ‰, with an average of -65. 1‰. The projections on the δD-δ 18O diagram (Figure 3.35) all fall within the range of magmatic water, indicating that the ore-forming fluid comes from magmatic hydrothermal solution.
Sulfur isotope characteristics: In this study, three sphalerite and two galena samples were selected from skarn-type and dense massive lead-zinc deposits (Table 3. 15). It can be seen that the variation range of sulfur isotope composition in lead-zinc mine area of Hunan Mine is small, and δ34S is between-1.4 ‰ ~1.1‰, which is close to the range of meteorite sulfur and all fall into the range of granite (Figure 3.36). Therefore, it is considered that S is also deep-source sulfur, which is consistent with the test results made by predecessors (Kong Qingyou et al.
Fig. 3.35 schematic diagram of timely δD-δ 18O of Hunan copper-lead-zinc mine.
(According to Wang Kuifeng, 2008)
Fig. 3.36 Distribution Map of Sulfur Isotope Composition in Hunan Mining Area
(Except the inverted triangle number, other data are based on Kong Qingyou et al., 2007).
Table 3. 15 Sulfur Isotope Analysis Results of Copper, Lead and Zinc Minerals in Hunan Mine
Genesis and metallogenic age of 3.2.2.5 deposit
From the above analysis, it can be seen that the facies copper-lead-zinc deposit is mainly controlled by the contact zone between granodiorite porphyry in late Yanshanian and limestone of Penglai Group facies group, and mainly occurs in the internal and external contact metamorphic zone and inside the porphyry. The upper part is skarn-type lead-zinc (copper) mineralization, and the lower part is porphyry-type copper (molybdenum) mineralization, which is a typical porphyry-skarn deposit. Ore-forming materials and ore-forming fluids come from the same source as rock mass. The formation process of the deposit is roughly as follows: in the late Yanshanian period of Mesozoic, the Jiaodong area was subsidence, and the interaction between crust and mantle was enhanced. Deep crust-mantle mixed lava flows up along the fault, forming a hydrothermal solution rich in ore-forming materials, and metasomatism occurs with the top of surrounding rock or rock mass at an appropriate place, and minerals precipitate to enrich ore. In limestone area, skarnization occurs, forming skarn mineralization. The metallogenic model of lead-zinc deposits in Hunan Mine is shown in Figure 3.37. K-Ar dating results of biotite and muscovite in the ore-forming parent rock granodiorite porphyry are 120.6Ma and 127.6Ma (Wangshan, 1984) respectively. Due to the low sealing stability of mica K-Ar isotope system, it is easy to be influenced by hot liquid in the later stage, so the author thinks it may be 127.6.