The mining area is located in the northern wing of Shankou-Shuangchagou syncline in the bitter water syncline bundle of Jueluotag syncline in the eastern part of Beishan syncline in Tianshan geosyncline fold belt.
Second, the mining area geology
(1) stratum
The ore-bearing complex rock mass in the eastern part of Huangshan Mountain is located in the East Jiangxi Formation. There are three lithologic sections exposed in the mining area of Gandong Formation (Figure 2- 1 1): the upper section (C2g3) is distributed in the southwest corner of the mining area, composed of fine sandstone and siltstone, and has Shi Ying amphibole lens, with an exposed thickness of 498m, which is in integral contact with the middle section, and the middle section (C2g2) is distributed in the south of the mining area, belonging to phyllization of single lithology. The exposed thickness is141m. The lower member (C2g 1) is distributed in the middle and north of the mining area. The lithology of the upper part is siltstone, slate, limestone and clastic limestone, mixed with thin layers of fine sandstone, conglomerate and siliceous rocks, with an exposed thickness of 825m, and the lower part is dominated by coarse clastic rocks, consisting of conglomerate, glutenite, sandstone, calcareous siltstone and limestone. Ore-bearing basic-ultrabasic rocks intrude into this horizon. Rock mass and surrounding rock intersect obliquely, cut through surrounding rock layer, and assimilate and capture surrounding rock.
(2) Structure
The structure of the mining area is inclined. Ultrabasic rocks containing copper-nickel sulfide intrude into the syncline core in the east of Huangshan Mountain. The structure is mainly east-west, and the ore-bearing rock mass is controlled by high-angle reverse faults and their derived faults near east-west and northeast, and the surface morphology is rhombic (Figure 2- 1 1).
(3) Characteristics of basic-ultrabasic rocks
The basic-ultrabasic rock mass in the east of Huangshan is a compound rock mass with the same origin, the same period and different invasion stages (Table 2-4), in which basic rocks are dominant (the distribution area accounts for more than 85% of the area) and ultrabasic rocks are rare (the area accounts for 15%). Eight lithofacies can be drawn according to the lithology (Table 2-4). The intrusion age of rock mass is the first intrusion in the late Variscan period, which is located in the carbonaceous silty slate in the upper part of the lower lithologic member of Gandong Formation. The strike of rock mass is 72 ~ 252, which is strictly controlled by F9 fault and its secondary structure. The exposed area is 2.8km2, the surface is rhombic (Figure 2- 1 1) and the space is funnel-shaped (Figure 2- 12, Figure 2- 13). The surface uplift part (No.28 exploration line) is 1 190m wide and about 5250m long, and there are two pits in the deep part at No.5 and 16 exploration lines (Figure 2- 13). The included angle between the strike of rock mass and the strike of stratum is generally about 18, and the strike of local sections is consistent.
The emplacement process of the first intrusive body can be divided into three stages: emplacement differentiation of main gabbro magma (formation of Huangshandong rock mass) → ultrabasic magmatic activity (formation of ultrabasic rock mass) → residual magma activity (intrusion of coarse amphibole-pyroxene and pegmatite diorite veins).
The ultrabasic rock body 1 starts from the No.9 exploration line in the west and reaches the No.28 exploration line in the east, about 1.95km long, and is concealed under gabbro in the east. Its occurrence is rock branches steeply inclined to the south, and its surface is banded and branched. Ultra-basic rock mass ⅲ is located at the eastern end of complex rock mass, with a semi-ring belt-like surface, which is controlled by fault zone, and the deep part is broken and occurs in veins. Ultra-basic rock mass ⅳ is located on the north side of the western end of the complex, which is banded and steeply inclined to the south, and is compounded with ultra-basic rock mass ⅰ at the exploration line 16.
Ultrabasic rocks Ⅰ, Ⅲ and Ⅳ are the products of the same stage, with the same rock types, including pyroxene amphibolite, altered peridotite and pyroxene. Rock has residual inclusion structure and scale metamorphic structure. The content of olivine is 40% ~ 50%, pyroxene is 20% ~ 25%, amphibole is 25% ~ 30%, and plagioclase is less. Rock alteration is strong, including serpentine, slip petrification, fiber flash petrification and chloritization. Coarse-grained amphibole-pyroxenite is distributed along the edge of ultrabasic rock mass and is a late product of rock mass.
No. II ultrabasic rock body is located in the north of the central part of the main gabbro (Figure 2- 1 1). Rock has a typical inclusion structure. The content of olivine is about 50%, the particle size is 0.5 ~ 1.5 mm, cracks are developed, and serpentine is seen at the edge of cracks. The content of bronze pyroxene is 5% ~ 15%, ordinary pyroxene is 5% ~ 15%, and amphibole is 5% ~ 10%, all of which are distributed in the gaps of olivine. Coarse pyroxene mineral crystals usually contain olivine particles. The content of plagioclase is 10% ~ 20% in general, and 30% in some cases.
Fig. 2-1/geological map of Huangshan copper-nickel deposit (according to Hao, Zhang Yongzhen, 1988. Same as Figure 2- 12 and Figure 2- 13) (after Hao Ganfuli and Zhang Yongzhen, 1988)
1- Lower member of Gandong Formation of Middle Carboniferous; 2- Middle Carboniferous Gandong Formation; 3- Upper member of Gandong Formation of Middle Carboniferous; 4 hornblende gabbro; 5- light gabbro; 6- amphibole olivine gabbro; 7- gabbro diorite; 8- diorite; 9— ultrabasic rocks in the second intrusive stage; 10-ultrabasic rocks in the third intrusive stage; 11-gabbro; 12- granite; 13-code of ultrabasic rock body; 14- fault structure and number; 15 heavy structure; 16- exploration line and number
Figure 2- 10 1
1- lean nickel sulfide ore and its quantity; 2- rich nickel sulfide ore (see Figure 2- 1 1 and Figure 2- 13 for other illustrations).
Table 2-4 Lithofacies Classification of the First Invasion of Basic-ultrabasic Complex in Late Variscan Table 2-4 Lithofacies Classification of Basic-ultrabasic Complex in the First Invasion Stage in Late Variscan
Figure 2-13 Section of 28 Exploration Line
1- lean nickel sulfide ore and its quantity; 2- rich nickel sulfide ore (see Figure 2- 1 1 for other illustrations)
The rock type is mainly plagioclase amphibolite.
Gabbro is the main component of composite rock mass. According to the interpenetration between rocks, it can be divided into the first intrusive stage dominated by amphibole gabbro and the second intrusive stage dominated by light gabbro and gabbro.
In the first intrusion stage, hornblende gabbro includes three lithofacies zones, all of which are in phase transition relationship, with hornblende gabbro as the main one, followed by hornblende olivine gabbro and gabbro, and diorite is a mixed zone at the edge of rock mass.
Hornblende gabbro is distributed between 2 ~ 28 exploration lines, and the rock has medium-grained gabbro mosaic structure. The main mineral components are: Labrador 65% ~ 70%, pyroxene 65,438+00% ~ 65,438+05%, amphibole 25% ~ 30%.
Hornblende olivine gabbro is distributed in hornblende gabbro in the northwest of complex rock mass, which is spherical. Mineral characteristics: plagioclase accounts for 65%, plate-shaped, with flaky twins; Amphibole 10% ~ 25%, with coarse crystal; 20% pyroxene and a little olivine.
Gabbro diorite is distributed in the southeast of complex rock mass and the west of ultrabasic rock mass ⅲ. The rocks near faults and "X"-shaped joints are broken, showing mylonite and cataclastic rocks, with plagioclase content of 55%, pyroxene and amphibole content of 35% ~ 40%, and a small amount is timely.
Diorite is distributed in the marginal zone of gabbro, which is a mixed rock formed by gabbro and surrounding rocks. It has a porphyritic structure and consists of feldspar, amphibole, quartz, biotite and pyroxene.
The light gabbro has a phase change relationship with the gabbro in the second intrusion stage, with gabbro as the main one and light gabbro as the second. Mainly distributed in the west of composite rock mass. Light gabbro is distributed at the top of gabbro, which is the product of crystal differentiation. The rock mass is a monoclinic branch with steep dip to the south, and it intruded into contact with Nagaiwama in the first intrusion stage. Gabbro-syenite has a medium-coarse grain mosaic structure, and its mineral composition is: feldspar-Labrador 45% ~ 50%, hypersthene 15% ~ 20%, augite 5% ~ 8%, amphibole 20%. Light-colored gabbro is medium-grained gabbro structure, with mineral composition: plagioclase 65% ~ 70%, pyroxene 25% ~ 30%, and amphibole less.
According to the K-Ar isotopic age of (262.99 ~ 266.33) Ma 5.69 Ma, the petrochemical composition of rocks has changed regularly, which not only reproduces the evolution law of magmatic composition in the diagenesis of magmatic deposits, but also provides metallogenic information. The content changes of main rock-forming oxides, such as SiO2 _ 2, Al _ 2O _ 3, CaO, Na2O, K2O and TiO2 _ 2, decrease with the increase of rock alkalinity, while MgO, FeO and Al _ 2O _ 3 are the opposite. The negative correlation between calcium and magnesium shows the typical characteristics of the crystallization differentiation process of basic-ultrabasic magma. In addition, CaO and al2o 3 increase with the decrease of alkalinity, and the common feature of composite rock mass is that alkali metal oxides are generally high.
According to the contents of rock-forming oxides CaO, Al2O3, TiO2 _ 2 and alkali metals, and the characteristics of plagioclase in ultrabasic rocks, this ultrabasic rock body belongs to type B, and its occurrence is closely related to basic rocks. The content of MgO < 30%, CaO 6.43%, K2O 0.2 1%, Na2O 1.5%, Al2O3 10.37%, TiO20.59%, rich in platinum group elements, less in chromium and strong in copper-nickel sulfide, which is differentiated from Binus basaltic magma.
According to the changes of numerical characteristics such as Mg-Fe ratio and Mg-Si ratio, the petrochemical conditions of Huangshan complex are favorable for the formation of Cu-Ni deposits. The petrochemical conditions of gabbro and ultrabasic rocks I-IV are more prominent.
To sum up, according to the differentiation degree of the complex, the change of mineral composition, the average petrochemical composition and the standard mineral molecular content (plagioclase 27%, clinopyroxene 15%, orthopyroxene 3 1%, olivine 17%), the original magma of the complex is basic magma containing olivine, with tholeiite.
Three. geology of ore deposits
(1) ore body characteristics
According to the occurrence, ore type, shape and occurrence, ore bodies can be divided into suspended ore bodies in the middle and lower parts of ultrabasic rocks, ore bodies in the contact zone between the bottom of ultrabasic rocks and basic rocks, ore bodies in ultrabasic rocks IV and ore bodies in gabbro.
The suspended ore body (Figure 2- 13) occurs in the middle and lower part of No.3 ore body. The II ultrabasic rock is layered and controlled by the shape of ultrabasic rock body, with an inclination of about 30. The ore grade is low, but the grade changes uniformly, generally it is off-balance sheet nickel sulfide (Ni content < 0.3%). The thickness of the ore body is small, several meters, and the thickness changes stably along the strike (Figure 2- 12), as shown inNo.. 15 and no 16 ore bodies. The ore body extends about 800 meters along the strike and about 200 meters along the dip, and is mainly composed of disseminated star-shaped ore. The boundary between ore body and surrounding rock is unclear and the rock alteration is weak.
Orebodies occurring in the contact zone between the bottom of ultrabasic rocks I, II and III and gabbro, such as orebodies 1 No.,17 and No.20 (Figure 2- 12), are layered, and the occurrence of orebodies is consistent with the bottom boundary of rock mass. The ore body is large in scale, with a thickness of several meters to ten meters, a length of several kilometers and a width of several hundred meters. The dip angle of the ore body is 40 ~ 50, and the ore body changes complicated along the strike, with expansion and contraction (Figure 2- 12). The ore is mainly poor in nickel sulfide, but also rich in nickel sulfide. The grade of ore varies unevenly, and the grade is related to the output position and the thickness of ore body. The sections with large thickness and high grade are generally mainly in the parts where the bottom boundary of rock mass changes greatly and the occurrence of rock mass changes from steep to slow and relatively flat. It is composed of sparse disseminated-dense disseminated-massive-like ore, and the boundary between massive-like ore and sparse disseminated ore is clear. The wall rock alteration of ore body is not strong.
Ore bodies (Figure 2- 12) hosted in ultrabasic rock mass IV, such as1~14, are layered or convex mirror-shaped, and their shapes are controlled by the shape of rock mass. It occurs in the upper and lower parts of rock mass and contact zone, and locally it is whole rock mineralization. The ore body is small in scale, with a thickness of several meters to tens of meters, a length of about 250m, a width of about 150m, and an inclination angle of 500. The ore is poor in nickel sulfide, enriched in some areas, and the grade changes evenly. It consists of sparse disseminated ore. Dense disseminated ore has clear boundaries. The ore-bearing parent rock is strongly altered.
Ore bodies occurring in gabbro are all suspended ore bodies, such as No.3 ~ 10 ore body (Figure 2- 12), which are basically plate-like or convex-mirror-like, with oblique lines from shallow to deep. It is 200 ~ 500m long,150m wide and10-10m thick. The dip angle of ore body is about 700. Mainly poor nickel sulfide ore, rich ore can be seen in the ore body with large buried depth or thickness, and the boundary with poor ore is clear. The ore grade changes uniformly, mainly in sparse disseminated-dense disseminated and massive breccia-like nickel sulfide ores.
(2) Mineral composition of ore
The main metal minerals are pyrite, pyrrhotite, nickel pyrite, chalcopyrite, chalcocite, chalcopyrite, manganese cobalt ore, silver nickel yellow, arsenopyrite, iron ore, manganese iron ore and manganese iron ore. Non-metallic minerals have the same composition as basic and ultrabasic rocks, and there are other altered minerals, such as serpentine, talc, amphibole and chlorite.
(3) Ore texture and structure
The ore structure has a melt-dense disseminated structure, which represents the ore structure formed by crystallization of metal sulfide melt in the gap between rock-forming silicate minerals.
The bead structure reflects the structure formed by the metal sulfide melt before it sinks and accumulates due to the decrease of solubility, or the metal sulfide is melted and precipitated relatively late.
Breccia structure is a kind of ore structure formed by melting and infiltration. It is the result of the infiltration of metal sulfide along the cracks in the parent rock. Due to different fracture properties, the shape of breccia is also different.
Block-like structure represents a structure with rich metal sulfide and clear boundary between ore body and parent rock.
Vein-like structure and veinlet network structure represent ore structures formed by hydrothermal filling metasomatism. It is formed by gas-liquid replacement and filling of ore-bearing volatiles after magmatic period.
Dendritic and gneissic leaf structures are ore structures formed by dynamic action, and are structural forms formed by plastic flow of metal sulfides with greater plasticity under thermal action.
The ore structure includes autogenous, heteromorphic and crystalline sponge meteorite structure.
Blade-like, flame-like and knot-like structures are formed by solid solution separation.
The metasomatism formed corrosion structure and reaction side structure.
Tectonic stress forms a shriveled and broken structure.
(4) Chemical composition of ore
Beneficial elements is mainly copper and nickel, followed by cobalt, gold, silver and platinum group elements. The average content of beneficial elements is shown in Table 2-5.
In Table 2-5, different types of ore bodies have different contents of beneficial components. In the ore body in the contact zone between ultrabasic rocks and gabbro bottom, the content of Ni is high, and the correlation coefficient between Ni and S is above 0.93. The contents of copper and cobalt are related to the basicity of ore-forming parent rocks and nickel content. The copper content of ore bodies in basic rocks is high and the cobalt content is low, while ultrabasic rocks are the opposite. The content of main ore-forming elements is closely related to the spatial position, ore-forming position, ore type and thickness of ore bodies.
The contents of gold, silver and platinum group elements in ore bodies are low, but they are closely related to copper, iridium and silver. Rock mass is rich in trace elements Cr, Ni, Cu, Co and Ti, in which Cr is (n102 ~ n103) ×10-6 and Cu is (n10 ~ n102). The content of uranium and thorium is low, less than 1× 10-6.
Four. minerogenetic condition
The sulfur content of ore is generally dozens of times higher than that of ore-bearing parent rock. Although the mineral types, mineralization types, occurrence sites and ore-storing rocks are different, the sulfur isotope composition is the same. 32S/34S is 22.238 ~ 22. 179, with a difference of 0.057. The variation range of δ34S is -0.79 ‰ ~ 2.775 ‰, the arithmetic mean value is 0.82‰, and the overall standard error is 0.68‰, which shows a tower distribution and is close to the sulfur isotope composition of meteorites. At the same time, the logarithmic ratio of sulfur to nickel [lgw(S)/lgw(Ni)] is close to the constant 1, reflecting that sulfur comes from the upper mantle and is homologous to the original magma of the complex. Rb-Sr isotopes of ore-bearing rocks show that the ratio of w(Rb)/w(Sr) is 0.0384 ~ 0.6942, the value of 87Rb/87Sr is 0.067 ~ 0. 1.567, and the value of 87Sr/86Sr is 0.70366 ~ 0.70585, indicating that the rock mass originated from. The occurrence position, ore type, fabric, mineral assemblage and distribution law of beneficial elements all reflect the existence of various mineralization in Huangshan East copper-nickel deposit.
Table 2-5 Average content of beneficial elements in various types of ore bodies.
The Donghuangshan copper-nickel deposit is dominated by detachment mineralization, supplemented by detachment-infiltration and hydrothermal metasomatism. Generally speaking, copper-poor nickel sulfide ore is formed by melting, and rich ore body is formed by melting-infiltration mineralization, and hydrothermal process has superposition effect.
The molten pulp formed in the process of magma chamber differentiation is in place with magma intrusion, forming a low-grade, uniform and small-thickness suspended ore body. Due to gravity and tectonic stress, part of the pulp infiltrated into the inner and outer contact zones, forming a molten penetrating ore body. This kind of ore body is rich in grade, thick and complex in ore composition.
During the emplacement of gabbro, due to the rapid change of physical and chemical conditions, the pulp was sealed in the gaps between rock-forming minerals and crystallized to form ore bodies. The ore bodies are arranged in an oblique order from top to bottom, from poor to rich and from small to large. Due to tectonic stress, the ore-rich slurry that has not yet crystallized is fractured and infiltrated along the crystallized ore body and surrounding rock, forming breccia-like ore.
Hydrothermal mineralization is a ore-bearing hydrothermal solution after magmatic period, which migrates along the primary cracks of rock mass, and metal sulfide precipitates and mineralizes in the cracks of rock mass, forming vein-like and reticular ores, causing the surrounding rock alteration near the mine.
To sum up, the main body of the deposit belongs to detachment-penetration copper sulfide deposit.
The prospecting criteria of this deposit are obvious. Through geological and geophysical methods to find basic ultrabasic rock bodies, compare and optimize well differentiated and poorly differentiated rock bodies, and determine ore-bearing rock bodies. Rock mass with high Cu, Cr, Ni, Co and S is selected for large-scale geophysical exploration, and drilling verification is mainly carried out in overlapping areas with high gravity, strong magnetic field, good conductivity and high polarization, and hidden Cu-Ni sulfide deposits may be found.