Hongxiban fluorite deposit in Dean County, Jiangxi Province

1. Deposit name

Hongxiban fluorite deposit in De 'an County, Jiangxi Province.

2. Geographical location

Located in Shanwan Township, De 'an County. Geographical coordinates: east longitude115 39'18 ",north latitude 29 29'15".

3 deposit type, resource reserves, scale, grade, degree of exploration and development.

Hongxiban fluorite deposit belongs to low-temperature hydrothermal filling fluorite deposit.

The fluorite deposit was discovered in 1958. 1972 to 1974, Geological Brigade of Jiangxi Geological Bureau 9 16 made a detailed survey of the deposit and submitted a large fluorite deposit.

At present, the fluorite mine is being mined.

4. Grade III and IV metallogenic belts.

Hongxiban fluorite deposit is located in the Ⅲ metallogenic belt of Cu-Au-Fe-Pb-Zn-Sr-Mo-Sb-pyrite gypsum metallogenic belt in the middle and lower reaches of the Yangtze River and in the Mufushan-Jiuhuashan Pb-Zn-Sn-W M0 Nb-Ta fluorite metallogenic sub-belt.

Second, the geological characteristics of the deposit

Metallogenic and ore-controlling geological conditions of (1) deposit

1. Strata

The mining area is located at the turning point of the west wing of Pengshan short-axis anticline, and there are Ordovician and Silurian in the mining area.

The Lower Ordovician Shanlun Formation (O 1l) is gray-white thick-bedded dolomite, dolomitic limestone, gray-white thick-bedded limestone mixed with a small amount of dolomitic banded limestone, and dolomitic limestone mixed with dolomitic banded limestone. The middle Ordovician Tangshan Formation (O2t) has carbon-bearing banded limestone at the bottom, gray thick layered pure limestone in the middle, dolomite limestone, thin-medium thick layered carbon banded limestone and peat limestone at the top. The Upper Ordovician Tangtou Formation (O3t) is purplish red and blue gray thin-medium layered nodular limestone mixed with argillaceous striated limestone. Longmaxi Formation of Lower Silurian is grayish green thin-layer sandstone mixed with shale.

Industrial fluorite ore bodies occur in limestone and nodular limestone of Middle and Upper Ordovician, especially in pure limestone of Tangshan Formation of Middle Ordovician. No fluorite mineralization was found in dolomite limestone and dolomite of Lower Ordovician (Figure 8- 12).

Figure 8- 12 Geological Schematic Diagram of Hongxiban Fluorite Deposit in De 'an County

(According to Wu Ziqiang et al., 1989)

1- Lower Silurian Longmaxi Formation thin sandstone mixed with shale; 2- Tumorous limestone and striated limestone of the Upper Ordovician Tangtou Formation; Middle Ordovician Tangshan Formation 3 thick layered pure limestone; 4— Dolomitic limestone and dolomite of Shanlun Formation of Lower Ordovician; 5- silicified fracture zone; 6- lamprophyre; 7- fluorite ore body; 8- Mine (waste) stone pile

2. Structure

The folds in this mining area are not obvious, mainly fault structures. Faults are divided into three groups: northeast-southwest, north-south and northwest.

NE-SW fault is the main fault in the mining area, which is distributed in an arc and obliquely cuts Ordovician and Silurian. There are many parallel secondary faults in the Ordovician limestone in the footwall of the fault, forming a fault zone, in which silicification and fluorite mineralization can be seen, forming a large fluorite mineralization and silicified fracture zone. The fault is characterized by sinistral compression and torsion in the early stage and tension and torsion in the later stage. This group of faults is closely related to mineralization, which is not only a ore-guiding structure, but also a ore-hosting structure. Due to the repeated activities of faults, the mineralization is repeated, which is characterized by the mutual cutting of veins, and the early ore is wrapped by the later vein cutting.

3. Magmatic rocks

There is only one quartz diorite vein and several amphibole lamprophyres in the mining area, which has little to do with fluorite mineralization.

(2) Geological characteristics of the deposit

1. Ore body characteristics

Hongxiban fluorite deposit in De 'an County is divided into four ore sections, I, II, III and IV, from west to east. I, II and III ore blocks are located in Hongxiban, and IV ore block is located in Jinjiadong (9 16 Brigade of Jiangxi Geological Bureau,1971; Jiangxi Bureau of Geology and Mineral Resources 9 16 Brigade, 1990). Fluorite ore bodies mainly occur in Tangshan Formation of Middle Ordovician and cracks in surrounding rocks. Hongxiban I, II and III ore blocks are divided into three ore bodies and nine ore blocks, and Jinjiadong IV ore block is divided into four ore bodies.

The spatial distribution of fluorite ore bodies is roughly divided into three parts. ① It occurs in SILURIAN silicified sandstone and shale fractures. ② It occurs in the nodular limestone and argillaceous banded limestone of Tangshan Formation of Middle Ordovician or at the junction with Tangshan Formation limestone. ③ It occurs in pure limestone of Tangshan Formation. ④ It occurs in the limestone fracture zone of Tangshan Formation.

The ore bodies in limestone are mostly layered and lentil-shaped, with stable thickness in strike and dip. The ore bodies are mainly banded, followed by disseminated. The ore bodies in the fracture zone are vein-like and lenticular, and some ore bodies are branched and compound and lean ore bodies alternate along the strike and dip. The length of a single ore body is 50 ~ 100 m, the maximum thickness is 24.03 m, and the ore body strikes northwest with an inclination of 20 ~ 65 degrees. The ore body grade is 15.34% ~ 76.40% (Figure 8- 13, Figure 8- 14).

Fig. 8- 13 Line 24 Section of Hongxiban Fluorite Deposit in De 'an County

(According to Wu Ziqiang et al., 1989)

1- Lower Silurian Longmaxi Formation thin sandstone mixed with shale; 2- Tumorous limestone and striated limestone of the Upper Ordovician Tangtou Formation; Middle Ordovician Tangshan Formation 3 thick layered pure limestone; 4— Dolomitic limestone and dolomite of Shanlun Formation of Lower Ordovician; 5- silicified fracture zone; 6- fluorite ore body

2. Ore characteristics

(1) Ore type

Mainly fluorite, quartz-fluorite, silicified limestone-fluorite, and a small amount of calcite-fluorite and calcite-quartz-fluorite.

Fig. 8- 14 Line 2 Section of Hongxiban Fluorite Deposit in De 'an County

(According to Wu Ziqiang et al., 1989)

1- Lower Silurian Longmaxi Formation thin sandstone mixed with shale; 2- Tumorous limestone and striated limestone of the Upper Ordovician Tangtou Formation; Middle Ordovician Tangshan Formation 3 thick layered pure limestone; 4— Dolomitic limestone and dolomite of Shanlun Formation of Lower Ordovician; 5- fluorite ore body

(2) Natural types of ore

Fluorite minerals are mainly banded, disseminated and massive, followed by crusty, breccia and reticular fluorite minerals.

The banded fluorite deposits can be divided into three subtypes, that is, fluorite and limestone alternate belts, fluorite, isochron and limestone alternate belts, and fluorite and isochron alternate belts. The former fluorite is fine aggregate embedded in limestone in strips.

The fluorite of disseminated fluorite ore is distributed in the surrounding rock in the form of fine particles or granular aggregates, and there are also fine fluorite particles scattered along the particles in limestone, which are banded.

The massive fluorite ore is mostly giant fluorite vein or vein fluorite. Fluorite particles are coarse and the boundaries between particles are not obvious. In order to fill fluorite, it is mostly distributed in the middle of ore-rich nests.

(3) Structural structure

The ore structure mainly includes granular structure, coarse-grained structure and giant crystal structure.

Ore structures are mainly banded, disseminated and massive structures, followed by shell-like, breccia-like and reticulated vein structures.

(4) Mineral composition

The mineral composition of the ore is simple, mainly fluorite, calcite and calcite, accompanied by a small amount of metal sulfide locally.

(5) Chemical composition

The chemical composition of ore is mainly CaF2, followed by SiO2, CaCO3, Al2O3, Fe, etc.

3. Wall rock alteration

The wall rock alteration in this area is mainly characterized by silicification, marble, tremolite, dolomite, chloritization, carbonation and sericitization. Silicification is an important alteration in this area, mainly distributed in the main fault zone and its surrounding rocks, forming a strong silicified fracture zone.

Three. Genesis of ore deposit

Metallogenic and ore-controlling factors of (1) deposit

1. Stratigraphic control of fluorite deposits

As mentioned above, the strata in the mining area are Ordovician and Lower Silurian. No fluorite was found in sandstone and shale of Lower Silurian, and only a few timely fluorite veins were filled in the fractures near the fault zone. There is no fluorite mineralization in lower Ordovician dolomite, limestone and dolomite. Fluorite only occurs in limestone and nodular limestone of middle and upper Ordovician, and industrial fluorite ore bodies occur in pure limestone of middle Ordovician. Similar to Bamianshan fluorite deposit in Changshan County, Zhejiang Province, the formation of fluorite deposit is related to limestone strata.

2. The control of faults on fluorite deposits.

Faults have obvious control over fluorite deposits, and some fluorite bodies in this area occur in the fracture zone and cracks of surrounding rocks. In the mining area, NE-SW faults are dominant, and Ordovician and Silurian are obliquely cut. Fluorite ore bodies are often formed in the fracture zone formed by cutting Ordovician limestone.

The contact thickness between the main fault zone and the convex part of "S" type flexural fold in this mining area is large and the grade is high. Small ore-rich nests are usually formed at the intersection of two sets of faults. In Jinjiadong ore block, the output of fluorite ore body is controlled by the main fault, and the output of ore body is basically consistent with the fault structure.

Comprehensive analysis shows that Hongxiban fluorite deposit in Dean County, Jiangxi Province belongs to hydrothermal filling fluorite deposit.

(2) Metallogenic period and age

The fluorite deposits in this area are controlled by faults, and the main faults cut Ordovician and Silurian, which were formed after Silurian, and the fluorite deposits should be formed after Silurian. The mineralization stage is the first stage, and Hu (1997) thinks it belongs to the late Yanshan period.

(3) Mineralization

Regarding the genesis of the Hongxiban fluorite deposit in De 'an County, Jiangxi Geological Bureau Team 9 16 (1974) divided the fluorite deposit into two types: hydrothermal metasomatism type and hydrothermal filling type. It is considered that fluorite produced in fractured zones and fractures of surrounding rocks belongs to hydrothermal filling type, and fluorite produced in thick layered limestone of Tangshan Formation of Middle Ordovician and nodular limestone of Tangtou Formation of Upper Ordovician is formed by fluorine-containing hydrothermal metasomatism, which belongs to hydrothermal metasomatism type. Hu (1997) thinks that the ore in Jinjiadong ore block of Hongxiban fluorite deposit in De 'an County, Jiangxi Province has metasomatic texture and metasomatic residual structure, which belongs to the post-magmatic low-temperature hydrothermal filling metasomatic type. No photos, sketches or detailed descriptions of metasomatic texture of carbonate rocks were replaced by fluorite.

The author thinks that Hongxiban fluorite deposit in De 'an County belongs to hydrothermal filling metasomatism type and should be classified as hydrothermal filling type.

Magmatic intrusion in the late Yanshan period led to the formation of Pengshan magmatic arch (anticline) structure, which also provided a good geological and structural environment for mineralization in Pengshan area.

Due to magmatic activity, fluorine-containing hydrothermal solution migrated upward along the fault. During the migration process, calcium was precipitated from the limestone of the Middle-Upper Ordovician and precipitated in the fracture zone, forming a low-temperature hydrothermal filling fluorite deposit.