I. Regional Geological Environment
Tectonic location: Daye intracontinental rift in southeastern Hubei fold belt.
Main ore-bearing strata: Middle Permian Maokou Formation and Qixia Formation; Lower Triassic Daye Formation; Jialingjiang Formation of Middle and Lower Triassic; Middle triassic puyin formation.
Ore-controlling intrusive rocks: syenite porphyry, granodiorite porphyry, syenite diorite and diorite porphyry.
Metallogenic age: 156 ~ 1 15 Ma.
Structural parts: Daye platform fold thrust valley and Jinniu continental margin rift.
The main ore-controlling structures: NWW fold fault in the near east-west direction and cross fold fault in the northeast direction; Complex contact area.
Ore-controlling sedimentary formations: shoal-tidal flat granular rock facies, Sabuha-tidal flat degummed microcrystalline limestone dolomite, dolomite facies and lagoon gypsum-bearing dolomite facies.
Wall rock alteration: skarnization and hornblende; The stronger the alteration, the better the mineralization, the wider the alteration zone and the wider the mineralization zone.
Petrochemical composition: silica: 5.8% ~ 68%; K2O+Na2O:7.6%~9.5%。
Rock mass scale: large rock mass.
Second, regional metallogenic geological characteristics
The metallogenic geological characteristics of several typical deposits in Daye Iron Mine are as follows.
(1) Tieshan iron (copper) deposit
Intrusive rocks: syenite diorite, porphyritic syenite porphyrite or biotite diopside diorite.
Surrounding Rock: Daye Formation and Jialingjiang Formation.
Metallogenic age: K-Ar age: phlogopite 132 ~ 149 Ma. The isotopic age of the rock mass is 148 ~ 165 Ma.
Structure: The contact zone with "S" shape or concave-convex bending has the best mineralization.
Wall rock alteration: skarnization and magnetite mineralization.
Temperature and pressure conditions: the diagenetic temperature of rock mass is 950 ~ 1030℃, and that of skarn is 580 ~ 640℃. The burst temperature of magnetite is divided into three groups: 700 ~ 800℃, 475 ~ 630℃ and 330 ~ 450℃. Diagenetic pressure (55 ~ 7 1) × 106 Pa.
Ore body shape: 6 large ore bodies and 26 small ore bodies. Six large ore bodies are irregular lenticular, layered and cystic.
Mineral assemblage: magnetite, hematite, siderite, pyrite, chalcopyrite, pyrrhotite, bornite and white iron ore.
(2) Tonglushan copper (iron) deposit
Intrusive rock: the shallow marginal facies is syenite diorite porphyrite; The middle-shallow transition phase is porphyritic syenite diorite; The middle-shallow central facies is anisometric syenite diorite.
Surrounding rock: Lower Triassic Daye Formation and Lower Triassic Jialingjiang Formation carbonate strata.
Metallogenic age: K-Ar age: 98 ~ 145 Ma for phlogopite and ore, and 143 ~ 150 Ma for biotite.
Ore-controlling structure: fold deformation and fold superposition are obvious, and faults have the characteristics of multi-stage activity; Fracture-contact fracture zone.
Metallogenic conditions: the diagenetic temperature of the rock mass is 956 ~1040℃; The homogenization temperature in skarn is 473 ~ 740℃, and the highest explosion temperature in magnetite is 506℃, mostly between 340 ~ 460℃.
Alteration: from rock mass to surrounding rock: (1) potash zone; (2) greenstone-like rock zone; (3) internal skarnization zone; (4) skarn belt; (5) Outer skarnized zone; (6) greenstone-like tectonic belt; (7) Muddy areas.
Minerals: limonite hematite, limonite (hematite) and magnetite.
(3) Lingxiang Iron Mine
Intrusive rock: diorite porphyrite.
Surrounding rock: Triassic carbonate strata.
Diagenetic age:195 ~137 5ma.
Ore-controlling structure: the developed part of fault structure, the vicinity of contact zone and the top edge of rock mass.
Ore body shape: lenticular, lentil and layered.
Ore: magnetite-hematite.
(4) Wang Baoshan Iron Mine
Intrusive rocks: diorite porphyrite and diorite porphyrite.
Metallogenic age: 673 ~1375 ma.
Wall rock alteration: chloritization, silicification and carbonation, followed by skarnization, epididymitization and pyritization.
Structural location: conglomerate at the bottom of Lingxiang Group.
Minerals: magnetite, hematite, pyrite and occasionally siderite.
Three. Geological characteristics of Tieshan iron (copper) deposit
Taking Tieshan Iron (Copper) Mine in Huangshi City, Hubei Province as a typical representative of Daye Iron Mine, this paper briefly introduces its geological characteristics.
General situation of (1) deposit
Tieshan iron (copper) deposit is a large-scale iron deposit, with an iron resource reserve of162910.6 million tons, with an average grade of TFe48.79%% and Cu0.629%%. Associated copper metal is 672,947 tons, and associated cobalt metal is 365,438+0,434 tons.
(2) Geology of mining area
The geological map of Tieshan Iron Mine is shown in Figure 6-2.
Figure 6-2 Geological Map of Tieshan Iron Mine
1. Strata
The strata related to mineralization are limestone and dolomite limestone of Daye Formation in Lower Triassic. The third lithologic member is mainly thin-layer microcrystalline limestone with argillaceous bands; The fourth lithologic member is thick layered limestone and dolomite, with gypsum pseudocrystals and oolitic limestone at the top; Gravelly dolomite with an included angle between thin dolomite and dolomitic limestone in the fifth lithologic member contains gypsum pseudocrystals; The sixth lithologic member is thin and thick limestone with argillaceous bands; Thick layer and thin layer of the seventh lithologic member, breccia dolomite and calcareous dolomite. Due to thermal metamorphism, the surrounding rocks near the mine become marble and dolomite marble, which are distributed in the south side of the ore body.
2. Structure
The mining area is located in the fold bundle of Daye depression in the fold belt of Yangtze depression under the Yangtze paraplatform. Geomechanically, it belongs to the west wing of the front arc of Huaiyang mountain structure.
Mineralization-related structures are a series of NWW- SE compressional structural belts with developed folds and faults. Tieshan pluton intrudes along the fault zone, a secondary fold structure in the northern wing of Tieshan anticline. The faults, contact structures or their composite structures before mineralization control the formation of ore bodies. The main ore bodies are all located in the contact zone between diorite and marble in the middle of the southern margin of Tieshan pluton. The leading edge and the lower edge of the tongue-shaped contact structure formed by the contact zone between marble and quartz diorite are the most favorable metallogenic sites.
3. Magmatic rocks
Tieshan pluton, a product of early Yanshanian, belongs to deep-seated syntectic intermediate-acid rock, and consists of granodiorite, quartz diorite, pyroxene diorite and syenite diorite. The K-Ar isotopic age of quartz diorite is 143 ~ 138 Ma. Tieshan pluton is mainly composed of diorite (internal phase) and quartz diorite (marginal phase). Due to the assimilation and contamination of calcium and magnesium, diopside diopside and biotite diopside diopside appear at the edge, Shi Ying diopside near the contact zone often has diopside and albitization, while biotite diopside diopside often has potash feldspar and andalusite.
(3) characteristics of ore bodies
The deposit is about 5 kilometers long, 500 meters wide and covers an area of 2.5 square kilometers. * * * There are six large ore bodies, which are Tiemenkan, Longdong, Jianlin Mountain, Elephant Trunk Mountain, Lion Mountain and Jianshan Mountain from west to east. All ore bodies occur in the contact zone between diorite and marble and are controlled by faults and contact zones (Figure 6-3). Except Jianlinshan ore body, other ore bodies are exposed to the surface.
Except Jianshan ore body occurs in the xenolith contact zone, all other ore bodies occur in the positive contact zone.
The shape and occurrence of ore bodies are controlled by contact zones, faults and their derived low-order transverse faults and marble tongue-shaped contact zones. The shape and occurrence of ore bodies in different sections are quite different. At the end of marble tongue, the ore bodies are thick and flat, mostly lenticular, such as Jianlinshan and Xiangbishan ore bodies. In the steep contact zone, the ore bodies are layered, and their occurrence is steep and extended, such as the middle section of Shizishan, Longdong and Tiemenkan ore bodies. In the contact zone oblique to the strike of strata, the shape and occurrence of ore bodies are more complicated. Most of them are cystic, with branching and compounding phenomena, such as Jianshan ore body.
The scale and grade of ore bodies vary greatly. The strike of a single ore body extends 360~872 m, the dip angle is 20 ~ 550 m, and the thickness is10 ~180 m. The iron ore grade of Tiemenkan ore body is the highest, and that of Jianlinshan ore body is the lowest. Longdong ore body has the highest grade of copper ore, while Shizishan ore body has the lowest grade.
When the ore body is in contact with marble or quartz diorite, the boundary is clear. When the ore body comes into contact with skarn, diopside skarn is banded and banded, and gradually transforms into banded magnetite ore body. Ore bodies are disseminated when they contact with dolomite marble, and mixed lean ore bodies with different thicknesses containing siderite and hematite often appear in the contact zone.
(4) Ore characteristics
Magnetite is the main ore, followed by hematite. There are mainly pseudomorphic hematite, hematite, copper-bearing limonite, malachite, chalcopyrite and chalcopyrite in the oxidation zone, followed by magnetite, chalcopyrite, cerclase, cerclase and pyrolusite. Magnetite, chalcopyrite and pyrite are the main minerals in the primary zone, followed by hematite, siderite, white iron ore, porphyrite and pyrrhotite. Gangue minerals include chlorite, diopside, phlogopite, calcite, kaolinite, opal and gypsum.
The associated component copper exists as a single mineral, including chalcopyrite, bornite, malachite and chalcopyrite; Co exists in pyrite as isomorphism; Gold mainly occurs in pyrite, chalcopyrite and other metal sulfides, and exists in the form of encapsulated gold and fractured gold.
The natural types of iron ore are magnetite, hematite and mixed ore. According to mineral composition and chemical composition, ores can be divided into six industrial types: high copper and low sulfur oxide ores, high copper and high sulfur oxide ores, low copper and high sulfur oxide ores, high copper magnetite ores, low copper magnetite ores and copper-bearing lean iron ores.
Iron ore is mainly irregular granular structure, followed by metasomatic residual skeleton crystal structure, and semi-autogenous-autogenous granular, lattice and graphic texture structures are rare. Blocky and variegated structures are dominant, followed by honeycomb and soil structures, and breccia, variegated and banded structures are rare. Associated chalcopyrite and pyrite are distributed in massive magnetite in banded or disseminated form.
Iron ore is rich in iron, high in sulfur and low in phosphorus, accompanied by beneficial elements such as copper, cobalt and gold. It is an iron-copper deposit with high economic value.
(5) Wall rock alteration
Skarnization, phlogopite, epidote, chloritization, carbonation and kaolin are developed on both sides of the contact zone between rock mass and carbonate rock. The alteration zoning from diorite to marble is: slightly altered albite diorite → fine albite diorite → andalusite albite diorite → diopside (hypodiopside) skarn → diopside silicified marble → marble and dolomite marble; Or slight K (Na) feldspar petrochemical biotite pyroxene diorite → reticulated garnet-andalusite biotite pyroxene diorite → garnet-andalusite-K (Na) feldspar petrochemical skarn → iron-bearing phlogopite diopside (hypodiopside) skarn → marble.
Figure 6-3 16 Tieshan Iron Mine Section
Four. Genesis and metallogenic model of ore deposits
1. Metallogenic stage
According to the relationship between iron-copper mineralization and magmatic rocks, the distribution of mineralization and alteration intensity and the spatial distribution of ore bodies, the metallogenic stages and stages of Tieshan iron-copper deposit can be divided into:
(1) skarn stage
Skarn in this stage is composed of diopside, garnet, andalusite, wollastonite, albite and other minerals, which are generally distributed in strips along the contact zone, obviously controlled by the shape and occurrence of the contact surface, and also related to the early fault structure. At this stage, skarn shows that the inner belt on one side of rock mass is relatively developed, and the outer belt on one side of marble is relatively weak. The skarns in the inner zone are mostly reticulate and saccular, which are saccular diopside skarns → reticulate and saccular (wollastonite) garnet diopside skarns → reticulate garnet andalusite diopside skarns → sparse reticulate and veined albite diopside andalusite skarns. It is mainly distributed in the east of Jianshan ore body, the middle of Shizishan ore body, the east of Longdong ore body and the east and middle of Tiemenkan ore body.
The temperature measurement of garnet and diopside in skarn shows that the formation temperature of this stage is relatively high, ranging from 580℃ to 680℃.
(2) Magnetite stage
This stage is characterized by the abundant development of magnetite and the existence of water-bearing skarn minerals. It is mainly composed of magnetite, diopside, phlogopite, actinolite, epidote, apatite, tremolite, albite, garnet, serpentine and other minerals as well as specularite, anhydrite, siderite and pyrite. Most ores are disseminated, banded, massive and veined. The particle size of diopside in this stage is larger than that in the previous stage, and the degree of automorphism is high. Diopside, actinolite and magnetite in this stage are associated with early iron ore or cemented with early magnetite breccia in Shizishan ore body. In Tiemenkan ore body and Longdong ore body, skarn composed of garnet, diopside, epidote and other minerals is veined in the rock mass, with crystal cave structure developed in the vein, and hexagonal columnar apatite and octahedral magnetite are produced in the crystal cave. Massive magnetite is more common in skarn capsules. In Tiemenkan and Longdong ore bodies, coarse-grained diopside and actinolite crystal clusters are also embedded in massive coarse-grained magnetite.
According to the temperature measurement data, the formation temperature of minerals at this stage is between 320 ~ 560℃, and the formation temperature range is large. This shows that this stage lasts for a long time and the process is complicated.
(3) Timely sulfide stage.
This stage is characterized by complex mineral assemblage, high chalcopyrite content and no directional arrangement. The main mineral components are pyrite, chalcopyrite, white iron ore, pyrrhotite, bornite, sphalerite, Yingshi, fluorite and chlorite. They are often superimposed on the above stages in the form of veinlets and lumps. At this stage, sulfides are widely distributed in all ore bodies, especially in skarn development areas and deep parts. Often accompanied by membranous chloritization phenomenon. When sulfide and magmatic rocks form veins, there is potassium feldspar alteration on the vein side.
At this stage, the formation temperature of minerals is not high, and the temperature measurement results of pyrite and chalcopyrite are between 200 ~ 245℃.
(4) Carbonate stage
At this stage, carbonate minerals are mainly calcite, ankerite and siderite. , and most of them are cemented and broken into fine veins or reticulated veins by magnetite, or extend along the cracks of magnetite, and sometimes penetrate into diorite and marble. Crystal cave structure is developed in this vein, and calcite often grows on the wall of the cave as a complete autogenous crystal. In addition, there are timely, opal, chalcedony, goethite, pyrite and so on. It is regarded as a crystal cluster superimposed on calcite.
The temperature measurement results of inclusions in ankerite and Yingshizhong are 174 ~ 194℃ and 164 ~ 17 1℃, respectively, and the formation temperature is lower than the above periods.
2. Genesis and metallogenic model of the deposit
Daye type iron ore is skarn type iron ore. The metallogenic model can be summarized as shown in Figure 6-4.
1) Intermediate-acid magma from the deep intrudes into the surrounding rocks of Triassic Daye limestone and other carbonate rocks, and the high-temperature hydrothermal solution formed by magma metasomatism with surrounding rocks and rock masses forms various skarns and their zoning. The early skarn is composed of anhydrous skarn minerals such as garnet and diopside, which is called dry skarn stage; Subsequently, with the increase of gas and liquid and the decrease of temperature, dry skarn minerals are replaced by minerals such as tremolite, actinolite and epidote containing water, which is called wet skarn stage.
2) After the skarn is formed, the fluid is oxidized, and a large amount of iron in the hydrothermal solution precipitates to form magnetite. This stage is called oxidation stage, also known as magnetite stage, and it is the most important stage for the formation of skarn iron ore. Iron deposits such as Tieshan, Guangmiannao, Tiezishan, Yinongqing, Liudaishan, Tongkeng, Xiangzikou, Zhangfushan, Licun, Wang Baoshan and Xinwuxia are formed in the skarn in the contact zone between intrusive body and surrounding rock.
3) With the further reduction of hydrothermal temperature, the environment becomes reduced, and a large number of sulfides and timely precipitation are called the timely sulfide stage.
4) As the mineralization draws to a close, the hydrothermal temperature decreases, and a small number of fine carbonate network veins are formed, which is called carbonate stage.
Figure 6-4 Metallogenic Model of Daye Iron Mine