A, mining strata
The exposed strata in the mining area are mainly Dengying Formation (Zdn) of Upper Sinian and Lujiaping Formation 2 of Lower Cambrian.
(1) Dengying Formation of Upper Sinian System (Z2dn)
Dengying Formation is divided into upper and lower lithologic sections.
Fig. 3-9 Geological Sketch of Wanyuan Miaozi witherite-barite Mining Area
(According to Team 604 of Southwest Geological Exploration Bureau, 1997)
1. Lower segment (Z2dn 1)
This section is dominated by black thick-bedded massive siliceous rocks, with thin-bedded siliceous rocks or siliceous slate. The thick siliceous rock is cryptocrystalline texture. About 120m thick.
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 structure, banded and massive structure. 36.5m thick.
(2) 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, which is mixed with barium mineralized dolomite (dolomite limestone) or barium mineral lens, with the lens thickness ranging from 0.5 ~1.5m and the length less than 10m. This layer is 50m thick.
(3) Three lithologic layers
The third lithologic section is the main ore-bearing horizon in the mining area.
The lower part is barium seam, and the lower part is mainly dark gray dense massive micrite, followed by barium slabstone, with stable horizon but discontinuous along the strike; The upper seam is crystalline massive fine-coarse barium slabstone-witherite layer, with barium slabstone as the main one, witherite as the secondary one and stable horizon.
The upper part is thin siliceous rock mixed with thin carbonaceous siliceous slate. 5 ~10 cm behind a single layer of siliceous rocks and 0.5 ~1cm in thickness of a single layer of carbonaceous siliceous slate, both of which are characterized by interbedding. This layer is the direct roof of the seam, which mostly contains siliceous nodules and phosphorus nodules with a particle size of 0.5 ~15 cm. Barium minerals such as1~ 2 cm wide banded or veined barium slabstone can be seen at the contact part with the seam. This layer is a prospecting indicator layer.
(2) Lower Cambrian Lujiaping Formation
This formation is roughly divided into upper and lower sections.
1. Lower segment
The lower member is mainly black carbonaceous slate with calcareous argillaceous slate. Slate at the bottom is thin-bedded, well-bedded, and contains collophanite nodules (particle size 2 ~12cm). Slate foliation in the middle and upper part is not well developed, and it is medium-thick layered, with less carbon and more sand and argillaceous components. 80m thick.
2. The above paragraph
The upper member is mainly thin-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 strata in this mining area are classified as Dengying Formation of Upper Sinian, but the mining area and Chongqing Bashan witherite deposit are both in the secondary fold of the northeast wing of Huangxihe compound anticline, while the ore-bearing strata of Bashan witherite deposit are classified as Lujiaping Formation of Lower Cambrian (see the second section of this chapter). Both witherite deposits (bodies) are stable in horizon, occurring in carbonaceous siliceous rocks or siliceous slate, and have roughly the same ore-bearing strata structure. The two deposits are located in the middle of the 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 of China (Editorial Committee of China Stratigraphic Code, 1999), Lujiaping Formation in Ziyang District, where Huangbaishuwan witherite deposit is located, contains some horizons of Dengying Formation of Sinian, while Dengying Formation in Chengkou District covers some horizons of Lujiaping Formation. And Ziyang Huangbaishuwan witherite deposit (body) occurs in the siliceous rocks in the lower part of Lujiaping Formation (see the first section of this chapter), so it is speculated that witherite deposits may occur in the same horizon in 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 the area are mainly synclinal anticline and syncline of NW-SE syncline, and the general anticline is closed and the syncline is open. The general tectonic line direction is nw315 ~ 320. The faults in this area are mainly NW-SE trending faults (Figure 3-9).
(1) Fold
The secondary folds related to the mining area are mainly Gaojiawan-Majiagou syncline anticline and Dongjiapo-Dongyuemiao syncline.
1. Gaojiawan-Majiagou syncline anticline
The anticline is centered on the thick-bedded massive siliceous rocks of Dengying Formation (and) of Sinian system, and the Lujiaping Formation of Cambrian system is flanked by two wings. The axis of the anticline is NW, the axial plane is inclined to SW225°, and the dip angle is 57 ~ 71,and gradually steepens from NW to SE. The anticline is cuneiform in Majiagou area in the southeast. The two wings of the anticline are locally staggered by strike faults F20 and F22, resulting in the local fracture of the ore bed along the strike.
2. Dongjiapo-Dongyue Temple syncline
The syncline is located in the south wing of Gaojiawan-Majiagou anticline, which is arranged in a close echelon with it. The axis of syncline is Lujiaping Formation, and the two wings are upper Dengying Formation. The axial plane is inclined to SW, with an inclination angle of about 88.
(2) Faults
The faults in the mining area are mainly NW-SE strike 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 have certain destructive effects on folds and ore bodies (Table 3-6). In addition, there are NE-trending faults, which are scattered in the strike fault zone of the mining area. The scale of this group of faults is small and the ore body has no influence.
Table 3-6 Characteristics of Strike Faults
Iii. Geology of ore bodies (layers)
Miaozibei mining area can be roughly divided into five ore bodies, each of which has the same seam structure. Taking No.2 ore body (layer) as an example, this paper discusses its characteristics.
(1) Characteristics of ore bodies (layers)
The distribution of No.2 ore body is controlled by Gaojiawan-Majiagou syncline anticline, which is distributed on the two wings of the dipping part of the anticline. It is further divided into four sub-ore bodies, 2- 1, 2-2 (northeast wing) and 2-3, 2-4 (southwest wing), which are damaged by strike faults F2 and F20.
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 970m long. The ore body is layered and quasi-layered, which is consistent with the occurrence of surrounding rocks. The overall strike is Se135, and the dip angle is 52 ~ 85 with the strata inversion (Figure 3- 10). The seam thickness is 0.30 ~1.58m, with an average thickness of 0.59m；; BaCO3 grade is 29.78% ~ 94.02%, with an average of 58.06%. The ore body is rich in witherite, followed by the mixed ore of barium anatase and witherite.
The roof and floor of the ore body are 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 34.54% is hit 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 body is layered and quasi-layered. Because it is located in the dip part of the anticline and affected by faults, the seam twists and develops, and the local strike changes greatly, with an overall occurrence of 205 ∠ 68 (Figure 3 10). The seam thickness is 0.53 ~ 0.84 m, with an average of 0.64 m; BaCO3 grade is 31.71%~ 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 both 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 ore body is 938～990m.
3.2-3 Ore Body
The ore body is located in the northwest section of the southwest wing of the anticline, and its outcrop is longer than 700m m. The ore body is layered and quasi-layered, with strong bending in some sections. The overall strike is135 ~140, with SW dip and dip angle of 50 (Figure 3- 10). The seam thickness is 0.39 ~1.1m, with an average of 0.64 m; BaCO3 grade 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 found in carbonaceous siliceous slate on the roof and floor of ore bodies, with a content of 0.41%~ 26.18%, with an average of 9.66%. The exposed elevation of ore body is 938～990m.
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 500m long. The ore body is layered and quasi-layered. Affected by faults, the seam twists and develops, with an overall strike of136, a dip of SW and an inclination of 62 (Figure 3- 10). The seam thickness is 0.30 ~1.72m, with an average of 0.92m；; BaCO3 grade is 31.84% ~ 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 found in carbonaceous siliceous slate on the roof and floor of ore bodies, with a content of 0.41%~ 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, with a small amount of barite, alumino-silicobarium 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 mud-grained aggregate, with the particle size less than 0.0 1mm, associated with Shi Ying, carbonaceous and granular barite, directionally distributed, showing micro-bedding structure, which should be generated in quasi-contemporaneous stage. The content of witherite in ore is generally 40%, and the highest content can reach 80% ~ 85%.
Figure 3- 10 Exploration Line Profile of Miaozi Barite Mining Area
1-Lower Cambrian Lujiaping Formation; 2— The third lithologic layer of the upper sub-group of Dengying Formation of Sinian system; 3— The second lithologic layer of the upper sub-group of Dengying Formation of Sinian system; 4— The first lithologic layer of the upper sub-group of Dengying Formation of 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; 11-carbonaceous siliceous slate; 12-barium carbonate ore; 13-Fault and its number; 14-adit and its number; 15 —— Trench and its number; 16-ore body and its number
2) Barium cleavage stone: gray, mostly granular-tabular, with a particle size of 0.02 ~ 2.0 mm, with calcite-like cleavage. It is gray-dark gray because it contains carbon, and witherite, barite and dolomite are often confessed, and the illusion of witherite or barite is often wrapped, reflecting the causes of subsequent metasomatism. 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 0.01~ 0.03 mm, and the crystals often contain carbon. 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 Al-Si-Ba-Shi and rhombic alkaline earth minerals.
(2) Gangue minerals
Mainly Shi Ying, with the content of1%~ 30%, mainly Shi Ying residue in siliceous rocks or siliceous slate, with a general particle size of 0.01mm; A small amount of carbon, the content of which is generally1%~ 3%, is mostly distributed in the form of finely 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 0.01~ 0.03 mm, which are closely arranged. Mainly found in dense massive ores.
2) Fine-coarse crystal structure: minerals are well crystallized with different sizes, with a particle size of 0.1~ 2.0mm.. It is mainly found in barium anatase ore and barium anatase-witherite ore.
3) Medium-coarse crystalline structure: the minerals are well crystallized, with uniform size, and the crystals with particle size of 0.1~1mm are set in teeth. It is mainly found in ores dominated by barium slabstone, and is developed in 2-3 and 2-4 ore bodies.
4) Bundle-radial structure: the tabular minerals (such as barium anatase) crystals form a bundle-like and radial aggregate.
(2) Structure
1) striated structure: micrite-microcrystal minerals are directionally arranged, forming striations with a thickness of1~ 2mm, and there are more mud and carbon distributed between striations, showing a "algae laminated" structure, showing the primary sedimentary structure. Common in witherite ore.
2) Dense massive structure: it is composed of fine or different-sized minerals arranged in disorder, and sometimes it can be seen that the minerals are not obviously oriented. The formation of this structure is related to metasomatism. Common in witherite and mixed ores.
3) Crystalline massive structure: It is composed of minerals with different crystal sizes or similar particle sizes, with crystals generally larger than 0. 1mm, and minerals often undergo recrystallization and metasomatism. Widely distributed in all kinds of ores.
3. Chemical composition of ore
The chemical components of ore in the mining area are mainly BaO and CO2, followed by CaO and SiO2, and other small amounts (Table 3-7).
Table 3-7 Table of Ore Chemical Composition in Miaozi Barium Mining Area
4. Ore type
The industrial type is carbonate barium ore. According to the different contents of minerals, it can be divided into three natural types: witherite ore, barium anatase ore and barium anatase-witherite ore.
(1) Barite-witherite ore
Gray-gray-black, micrite, fine-coarse grain structure and metasomatic texture, dense massive structure, and sometimes residual microlayer structure. Witherite and barite are the main materials, with a little barite, containing impurities such as Shi Ying, calcite, carbon and sporadic pyrite. The content of witherite is slightly higher than that of barium anatase, and the content of BaCO3 is generally 40% ~ 70%, with the highest of 89.37%.
This type of ore is the main ore type in the area.
(2) micrite witherite ore
Gray-dark gray, micrite-microcrystal structure, dense massive structure. It is dominated by witherite, with a small amount of barite and barite, accompanied by a small amount of impurities such as Shi Ying and carbon. The ore quality is good, with the highest BaCO3 content of 94.02%, generally more than 80%. It is mainly distributed at the bottom or lower part of the seam, and most of them are lens-like distribution from several meters to tens 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 grain structure, medium-coarse grain metamorphic structure, metasomatic and metasomatic residual structure. The massive structure is dominated by barium anatase, followed by witherite, and a small amount of other barium minerals. Barium pyrophyllite is well crystallized, mostly in granular or bundle-like aggregates, and witherite and barite are commonly explained. Part of barium calcite and Shi Ying occur in veinlets. The highest content of BaCO3 in this kind of ore is 50% ~ 70%, which is a secondary ore type.
IV. Genesis of the deposit
In this deposit, witherite constitutes the main body of barium ore. Primary sedimentary structures such as massive structure and striated structure ("algae stack") developed in ores; The micrite-microcrystal structure, fine-medium coarse-grained structure and various metasomatic texture fabric characteristics reflect the sedimentary origin of the deposit.