Geological characteristics of witherite-barite deposit in Miao Zi, Wanyuan, Sichuan Province

Miao Zi witherite-barite deposit is located in Miao Zi Township, Dazhu District, 68km northeast of Wanyuan City, Sichuan Province. The mining area is located in the north of Daba Mountain, and the north and south Daba Mountain faults are adjacent to the Yangtze paraplatform. The exposed strata are mainly Dengying Formation of Upper Sinian and Lujiaping Formation of Lower Cambrian (Figure 3-9). Folds and faults are developed in this area, and the structural line direction is NE-SW. The mining area is located in the west section of Huangxihe compound anticline. No magmatic rocks are exposed in this area.

I. Mining strata

The exposed strata in the mining area are mainly Upper Sinian Dengying Formation (Zdn) and Lower Cambrian Lujiaping Formation 2.

(1) Upper Sinian Dengying Formation (Z2dn)

Dengying Formation is divided into upper lithologic member and lower lithologic member.

Figure 3-Geological Schematic Diagram of witherite-barite Mining Area in Miao Zi, 90,000 Yuan.

(According to Team 604 of Southwest Geological Exploration Bureau 1997)

1. Lower segment (Z2dn 1)

This section is dominated by black thick layered massive siliceous rocks, with thin layers of siliceous rocks or siliceous slate. The thick siliceous rock is cryptocrystalline texture. The thickness is about120m.

2. Upper segment (Z2dn2)

According to the characteristics of lithologic combination, it can be divided into three lithologic layers from bottom to top:

(1) A lithologic layer

It is mainly black medium-thick layered siliceous rocks with a small amount of thin carbonaceous siliceous slate. Siliceous rocks have cryptocrystalline texture, banded and massive structures. 36.5 meters thick.

(2) the second lithologic layer

The second lithologic member is mainly medium-thick layered siliceous rocks mixed with thin-layer siliceous rocks, and transits upward to thin-medium thick carbonaceous siliceous slate, with barium-mixed mineralized dolomite (dolomite limestone) or barium mineral lens, with a lens thickness of 0.5- 1.5m and a length less than 10m. This layer is 50 meters thick.

(3) Three lithologic layers

The third lithologic section is the main ore-bearing horizon in the mining area.

The lower part is barium deposit, and the lower part is mainly dark gray dense massive micrite limestone, followed by barium slate, with stable horizon but discontinuous along the strike; The upper layer is crystalline massive fine-coarse barium slate-witherite layer, with barium slate as the main layer and witherite as the secondary layer, and the horizon is stable.

The upper part is thin siliceous rock mixed with thin carbonaceous siliceous slate. Single-layer siliceous rocks with a thickness of 5 ~ 10 cm and single-layer carbonaceous siliceous slate with a thickness of 0.5 ~ 1 cm are both characterized by interbedding. This layer is the direct roof of coal seam, which contains many siliceous nodules and phosphorus nodules with a particle size of 0.5 ~ 15 cm. Barium minerals such as banded or veined barium slate with a width of 1 ~ 2 cm can be seen in the contact part with the seam. This layer is a prospecting indicator layer.

(2) Lower Cambrian Lujiaping Formation

This stratum is roughly divided into upper and lower sections.

1. Lower segment

The lower member is mainly black carbonaceous slate mixed with calcareous argillaceous slate. Slate at the bottom is thin, well bedded and contains collophanite nodules (particle size 2 ~ 12 cm). The foliation of slate in the middle and upper part is not well developed, and it is medium-thick layered, with less carbon content and more sand and argillaceous components. 80 meters thick.

2. The above paragraph

The upper member is mainly thin to medium-thick siltstone with a small amount of carbonaceous argillaceous slate. Siltstone is mainly composed of quartz silt, argillaceous and a small amount of pyrite and sericite.

(3) Time description of ore-bearing strata

The ore-bearing stratum in this mining area belongs to Dengying Formation of Upper Sinian, but both the mining area and Chongqing Bashan witherite deposit are located in the second fold of the northeast wing of Huangxihe compound anticline, while the ore-bearing stratum of Bashan witherite deposit belongs to Lujiaping Formation of Lower Cambrian (see the second section of this chapter). The horizon of the two witherite deposits (bodies) is stable, occurring in carbonaceous siliceous rocks or siliceous slate, and the ore-bearing strata structure is roughly the same. These two deposits are located in the middle of Dabashan witherite metallogenic belt, and the ore-bearing strata of other witherite deposits in this metallogenic belt are all the Lower Cambrian Lujiaping Formation, and the ore beds (bodies) are also produced in siliceous rocks. According to the study of CAMBRIAN stratigraphic code in China (edited by stratigraphic code, China, 1999), Lujiaping Formation in Ziyang area where Huangbaishuwan witherite deposit is located contains some horizons of Sinian Dengying Formation, and Dengying Formation in Chengkou area covers some horizons of Lujiaping Formation. The witherite deposit (body) in Huangbaishuwan, Ziyang occurs in the siliceous rocks in the lower part of Lujiaping Formation (see the first section of this chapter), so it is speculated that the witherite deposit may occur in the same horizon of the regional Dabashan witherite metallogenic belt. Because stratigraphic division and correlation are not the focus of this book, I won't go into details here.

Second, the mining structure

The mining area is located in the northwest secondary fold of the northeast wing of Huangxihe compound anticline. The secondary folds in this area are mainly synclines, anticlines and synclines of NW-SE syncline. Generally, the anticlines are closed and synclines are open. The general structural line direction is NW 3 15 ~ 320. Faults in this area are mainly NW-SE faults (Figure 3-9).

(1) folding

The secondary folds related to the mining area are mainly Gaojiawan-Majiagou syncline and Dongjiapo-Dongyuemiao syncline.

1. Gaojiawan-Majiagou syncline anticline

The anticline takes the Sinian Dengying Formation (and) thick massive siliceous rocks as the core, and the Cambrian Lujiaping Formation as the two wings. The axis of the anticline strikes NW, the axial plane is inclined to SW225, and the dip angle is 57 ~ 7 1, which gradually steepens from NW to SE. Majiagou area in the southeast of anticline is wedge-shaped. The two wings of the anticline are partially staggered by strike faults F20 and F22, resulting in local fracture of the ore bed along the strike.

2. Dongjiapo-Dongyue Temple syncline

Syncline is located in the south wing of Gaojiawan-Majiagou anticline, and it is arranged in a close echelon with it. The axis of syncline is Lujiaping Formation, and the two wings are Shangdengying Formation. The axial plane is inclined to SW, with an inclination angle of about 88.

(2) Failure

The faults in the mining area are mainly NW-SE faults, which are distributed in the contact area between Dengying Formation and Lujiaping Formation on the wing of the fold. The fault strike is basically consistent with the stratum. This group of faults has a certain destructive effect on folds and ore bodies (Table 3-6). In addition, there are NE-trending faults, which are scattered on the strike fault zone in the mining area. This group of faults is small in scale and the ore body has no influence.

Table 3-6 Characteristics of Strike Faults

Three. Ore body (layer) geology

Miaozibei mining area can be roughly divided into five ore bodies, each with the same coal seam structure. Taking No.2 ore body (layer) as an example, this paper discusses its characteristics.

(1) characteristics of ore body (layer)

The distribution of No.2 ore body is controlled by Gaojiawan-Majiagou syncline anticline, which is distributed on the two wings of the inclined part of the anticline. Due to the destruction of strike faults F2 and F20, it is further divided into four sub-orebodies: 2- 1, 2-2 (northeast wing) and 2-3, 2-4 (southwest wing).

1.2- 1 ore body

The ore body is located in the northwest section of the northeast wing of the anticline, with an outcrop of 970 meters long. The ore body is layered and quasi-layered, which is consistent with the occurrence of surrounding rock. The general strike is SE 135, with dip angle of 52 ~ 85, and the strata are reversed (Figure 3- 10). The thickness of coal seam is 0.30 ~ 1.58 m, with an average thickness of 0.59m；; The grade of BaCO3 is 29.78% ~ 94.02%, with an average of 58.06%. The ore body is rich in witherite, followed by barium anatase and witherite mixed ore.

The roof and floor of the ore body are all thin-bedded siliceous rocks and carbonaceous siliceous slate. The siliceous slate often contains barite, the content of which is generally less than 10%, and only hits 34.54% locally. The exposed elevation of ore body is 732 ~1121m.

2.2-2 orebody

The ore body is located at the eastern end of the northeast wing of the anticline, with a length of 1 10m. The ore bodies are layered and quasi-layered. Because it is located in the dip angle of anticline, affected by faults, the coal seam is twisted and developed, and the local strike changes greatly. The overall occurrence is 205 ∠ 68 (Figure 3 10). Coal seam thickness is 0.53 ~ 0.84 m, with an average of 0.64 m; The grade of BaCO3 is 3 1.7 1% ~ 77.83%, with an average of 56.03%. The ore belongs to barium anatase-witherite type, with an average mineral content of 34.63% witherite and 32.26% barium anatase.

The roof and floor of the ore body are thin-bedded siliceous rocks and carbonaceous siliceous slate, and the siliceous slate often contains barite with a content of 6. 18% ~ 16.62%. The exposed elevation of the ore body is 938 ~ 990 meters.

3.2-3 Ore Body

The ore body is located in the northwest section of the southwest wing of the anticline, with an outcrop length of more than 700m m. The ore body is layered and quasi-layered, and some sections are strongly distorted, with an overall strike of 135 ~ 140, a dip of SW and an inclination of 50 (Figure 3- 10). Coal seam thickness is 0.39 ~1.11m, with an average of 0.64 m; The grade of BaCO3 is 30.43% ~ 69.25%, with an average of 44.07%. The ore is basically barium anatase-witherite type, with an average mineral content of witherite of 23.37% and barium anatase of 3 1.85%.

Barite is often produced in carbonaceous siliceous slate on the roof and floor of ore bodies, and its content ranges from 0.41%to 26.18%, with an average of 9.66%. The exposed elevation of the ore body is 938 ~ 990 meters.

4.2-4 Ore Body

The ore body is located in the northwest section of the southwest wing of the anticline, with an outcrop of 500 meters long. The ore bodies are layered and quasi-layered. Affected by faults, the coal seam is twisted and developed, with general strike 136, dip SW and dip angle of 62 (Figure 3- 10). Coal seam thickness is 0.30 ~ 1.72 m, with an average of 0.92 m; The grade of BaCO3 is 3 1.84% ~ 92.36%, with an average of 56.82%. The ore is basically barium anatase-witherite type, with an average mineral content of witherite of 23.37% and barium anatase of 3 1.85%.

Barite is often produced in carbonaceous siliceous slate on the roof and floor of ore bodies, and its content ranges from 0.41%to 26.18%, with an average of 9.66%. The exposed elevation of ore body is 894 ~1121m.

(2) Ore characteristics

1. Mineral composition of ore

(1) ore minerals

The ore minerals in this area are mainly witherite, followed by barite, and a small amount of barite, aluminum-silicon-barium and rhombohedral alkaline earth minerals. It belongs to a mixed barium deposit dominated by barium carbonate.

1) witherite: it is mostly light gray-dark gray muddy aggregate with particle size less than 0.0 1mm, accompanied by timely, carbonaceous and granular barite, directionally distributed, with micro-bedding structure, which should be formed in quasi-contemporaneous period. The content of witherite in ore is generally 40%, and the highest can reach 80% ~ 85%.

Figure 3- 10 Exploration Line Profile of Miao Zi Barite Mining Area

1- Lower Cambrian Lujiaping Formation; 2— The third lithologic layer of the upper sub-group of Dengying Formation in Sinian system; 3— The second lithologic layer of the upper sub-group of Dengying Formation in Sinian system; 4— The first lithologic layer of the upper sub-group of Dengying Formation in Sinian system; 5 thick to medium thick siliceous rocks; 6 thick siliceous rocks; 7— Barium mineralized dolomitic rocks; 8— Slate; 9— Silty slate; 10-carbonaceous slate; 1 1- carbonaceous siliceous slate; 12-barium carbonate ore; 13- Fault and number; 14- adit and its number; 15-exploration slot location and number; 16- orebody and serial number

2) Barium cleavage stone: gray, mostly granular-tabular, with a particle size of 0.02 ~ 2.0 mm and calcite cleavage. Because the carbon is gray-dark gray, witherite, barite and dolomite are often explained, and the illusion of witherite or barite is often wrapped, reflecting the cause of subsequent explanation. The content of barite in minerals is generally 0 ~ 95%, which often forms a single barite ore.

3) Barite: mostly in granular, short columnar and plate shape, with a particle size of 0.0 1 ~ 0.03 mm, and often contains carbon in the crystal. Generally, it is distributed in the surrounding rock of the roof and floor, and occurs in micro-layered and banded form, with the highest content of 26. 18%.

A small amount of aluminosilicate and rhombic alkaline earth minerals.

(2) Gangue minerals

It is mainly seasonal, with the content of 1% ~ 30%, mainly seasonal residues in siliceous rocks or siliceous slate, with a general particle size of 0.01mm; ; A small amount of carbon, the content of which is generally 1% ~ 3%, is mostly distributed in the form of fine dispersed dust spots. Others include a small amount of dolomite, calcite and collophanite.

2. Ore structure

(1) structure

1) micrite-microcrystal structure: the ore consists of minerals less than 0.0 1 ~ 0.03 mm, which are closely arranged. It mainly exists in dense massive ores.

2) Fine-coarse crystal structure: minerals are well crystallized with different sizes, and the particle size is 0. 1 ~ 2.0 mm ... which mainly exists in barium anatase and barium anatase-witherite ores.

3) Medium-coarse crystal structure: the mineral crystals are well crystallized and uniform in size, and the crystals with particle size of 0. 1 ~ 1 mm are embedded between teeth. It is mainly found in barium slate-dominated ores and developed in 2-3 and 2-4 ore bodies.

4) Beam-like radial structure: plate-like minerals (such as anatase barium) crystals form beam-like radial aggregates.

(2) Structure

1) layered structure: micrite-microcrystal minerals are directionally arranged to form 1 ~ 2mm thick striations. There are more peat distributed between laminae, showing a "algal laminae" structure, showing the primary sedimentary structure. Common in witherite ore.

2) Dense massive structure: It is formed by disordered arrangement of fine or unequal minerals, and sometimes it can be seen that the mineral orientation is not obvious. The formation of this structure is related to metasomatism. Common in witherite and mixed ore.

3) Crystalline massive structure: It is composed of minerals with different crystal sizes or similar particle sizes, and the crystals are generally larger than 0. 1mm, and minerals often undergo recrystallization and metasomatism. Widely distributed in various ores.

3. Chemical composition of ore

The chemical composition of ore in the mining area is mainly BaO and CO2, followed by CaO and SiO2, and there are a few other chemical compositions (Table 3-7).

Table 3-7 Table of Chemical Composition of Ore in Miao Zi Barium Mining Area

4. Ore type

The industrial type is barium carbonate ore. According to the different mineral content, it can be divided into three natural types: witherite, barium anatase and barium anatase-witherite.

(1) barium anatase-witherite ore

Gray-gray-black, micrite limestone, fine-coarse grained structure, metasomatic texture, dense massive structure, and sometimes residual microlayer structure. The main substances are witherite and barite, with a small amount of barite, impurities such as calcite, carbon and sporadic pyrite. The content of witherite is slightly higher than that of anatase barium, and the content of BaCO3 is generally 40% ~ 70%, with the highest of 89.37%.

This kind of ore is the main ore type in this area.

(2) micrite witherite ore

Gray-dark gray, micrite-microcrystal structure, dense massive structure. It is dominated by witherite, containing a small amount of barite and barite, accompanied by a small amount of impurities such as timeliness and carbon. The ore quality is good, and the highest content of BaCO3 is 94.02%, generally above 80%. It is mainly distributed at the bottom or lower part of coal seam, and it is lenticular from several meters to dozens of meters along the strike.

This type is a secondary ore type, mainly distributed in 2- 1 and 2-4 ore bodies.

(3) Barium calcite ore

Dark gray, fine-coarse grained texture, medium-coarse grained metamorphic texture, metasomatism and metasomatism residual structure. The massive structure is dominated by barium anatase, followed by witherite and a small amount of other barium minerals. Pyrophyllite barium is well crystallized, mostly in granular or fascicular aggregates, and witherite and barite are common explanations. Some barium calcite and calcite are veinlets. The highest content of BaCO3 in this kind of ore is 50% ~ 70%, which belongs to the secondary ore type.

Four. Genesis of ore deposit

Witherite is the main body of barium ore in this deposit. Primary sedimentary structures developed in ores, such as massive structures and striated structures ("algal piles"); The micrite-microcrystal structure, fine-medium coarse-grained structure and various metasomatic texture fabric characteristics reflect the sedimentary origin of the deposit.