Deposit type

According to the geological characteristics and genesis of barite deposits, the deposits can be divided into the following five types, namely, sedimentary (hot water) type, sedimentary transformation type, volcanic-sedimentary type, post-magmatic hydrothermal type (hydrothermal type for short) and eluvial type.

I. Sedimentary (hydrothermal) barite deposits

Most of the known large and super-large barite deposits in China belong to hydrothermal sedimentary type. The ore-bearing strata are mainly the bottom of Lower Cambrian, followed by Upper Devonian, and some are early, middle Ordovician and Cretaceous. The ore-bearing rock series is a black rock series composed of carbonaceous and siliceous fine clastic rocks, which usually coexist with phosphorite, phosphorite nodules and stony coal seams. Fine clastic rocks and siliceous rocks in rock series are rich in uranium, vanadium, nickel, molybdenum, silver and rare earth elements. The temporal and spatial conditions of sedimentation are near the continental rift or the syngenetic fault zone in aulacogen. The deposit has a certain horizon, which is layered and quasi-layered, with a thickness of several meters. The floor is composed of siliceous rocks, and the roof is often carbonaceous rocks or black mudstone mixed with fine sandstone. Trace elements and rare earth elements in siliceous rocks are close to those in modern ocean hot water sediments, indicating that barite was deposited in seawater. Layered barite rocks and their surrounding rocks are rich in organic matter and mainly evolved from lower plankton, indicating that the ore-bearing rock series in sedimentary basins are generally deep and in a stagnant and reducing environment. This type of barite deposit has a wide distribution area and large reserves, and the ore grade is as high as 80%. Barite from Guizhou, Hunan and Guangxi is the most famous in China, and it is also distributed in Gansu, Shaanxi, Shandong, Sichuan, Fuzhou and Hubei provinces. Mineral reserves account for more than 60% of the total barite reserves in China.

The Gongsa-Gangchuan barite deposit in Xinhuang County, Hunan Province is a typical barite deposit.

1. ore-bearing rock series

The main ore-bearing rock series is the lower member of Niutitang Formation of Lower Cambrian, and the secondary ore-bearing stratum is the top of Upper Sinian (Figure 8-3).

Figure 8-3 Comprehensive Histogram of Ore-bearing Strata in Gong Xi-Okawa Barite Ore Field

(According to Li Wenyan et al., 1990)

2. The appearance of seams

Barite ore bodies are layered and quasi-layered, and the ore-bearing strata extend from several kilometers to several tens of kilometers, for example, the barite ore-bearing strata in Gong Xi-Okawa reach 29 kilometers. The length of the ore body is generally 1000 ~ 5000 m (Gongxi Mine), the dip angle is over 300m (such as Gongxi Mine and Liulin Mine), the thickness is mainly several meters, ranging from tens of centimeters to 10.2m, and most of the ore beds have been folded and deformed (Figure 8-4). The surrounding rock of coal seam floor is thin siliceous rock mixed with phosphorite, and the surrounding rock of roof is black carbonaceous shale mixed with phosphorite nodules.

Fig. 8-4 Profile of Gong Xi-Okawa Barite Ore Field

(According to Li Wenyan et al., 1990)

1-Lower Sinian; 2-Upper Sinian; 3- Lower Cambrian; 4- Middle Cambrian; 5- Upper Cambrian; 6- Integrating stratigraphic boundaries; 7- Unconformity stratum boundary; 8- Reverse fault; 9- drilling; 10- barite seam

3. Ore and its structure and structure

The ore is gray-black-dark gray, with fine-grained structure, banded, massive and bean-like structure. There are often vertical zoning, impure barite composition in the lower part, coarse grains, obvious band width, and often siliceous lens interlayer; The barite in the middle is pure, with fine stripes and fine and uniform particles, and can be sandwiched with thin layers of black shale; The upper part recovered the obvious banded structure; There are barite nodules in the roof siliceous shale or shale. There are basically two types of ore structures: one is barite radial pellets with a diameter of several millimeters, which are composed of slender needle-like and plate-like barite and converge towards the center. The length of single crystal is 0.2 ~ 0.5 mm, and sometimes fine barite remains in the center of pellets, which reveals that barite was originally fine and recrystallized into radial pellets during early diagenesis; The other is fine-grained structure, which is the most common structure type. Single crystals include microcrystals (particle size 0.01~ 0.5 mm), medium-fine crystals (particle size 0.01~ 0.5 mm) and coarse crystals (particle size above 0.5 mm). Generally, microcrystals and fine crystals are dominant, showing an equigranular-unequal granular structure. Microcrystallines are formed by chemical precipitation and become thicker by recrystallization.

taste

The grade of massive ore is generally above 80%, and it can contain a small amount of calcite and calcite. Striped ores are widely distributed and consist of barite, argillaceous and siliceous, with a grade of about 60% ~ 80%. Bean-shaped (or oolitic) ore is composed of barite beans, mud and silicon matrix. The beans are unevenly distributed and the grade is generally lower than 60%. In addition, there are nodule-like ores with nodule diameter of 4 ~ 40 cm. The grade of barite in nodules can reach 85.32% ~ 93.90%, and it also contains SiO _ 2 <1%,and the rest impurities V and Ni < 0.5% ~ 0.00 1%, containing trace elements Sr, etc. In the range of several meters above the top boundary of coal seam in Dachuan, V2O5 is 0.5% ~ 1.44%, and Ag is 10 ~ 33g/t, which has reached the industrial requirements.

To sum up, this deposit is the only super-large barite deposit in the world with outstanding sedimentary genetic characteristics and huge scale.

Two. Sedimentary transformation (stratabound) barite deposit

The tectonic position of the deposit belongs to the category of South China block, which is distributed in central Guangxi and northern Guangdong. The main pay zone is Devonian, followed by Jurassic (South Guangdong South China Sea) and Sinian Cambrian (Northeast Guangxi).

The deposits in Devonian sedimentary basin are located on the carbonate side of clastic rock and carbonate rock phase transition zone. Favorable metallogenic sedimentary facies zones are all controlled by synsedimentary fault zones. Barite ore bodies are mostly vein-like, reticulate vein-like, lenticular, etc., which are distributed in specific horizons and appear in groups, obviously controlled by secondary fault zones, fracture zones and interlayer fractures. The thickness of a single ore body is 1~20m ~ 20m, extending for hundreds of meters. The alteration of surrounding rock is mainly silicification and carbonization. In addition to barite, timely and carbonate, pyrite, galena, sphalerite, chalcopyrite and other sulfides are also found in the ore. Ore types can be divided into massive, breccia and disseminated. Generally, it can be divided into three mineralization stages: early silicification, middle barite deposition and late weak barite, often accompanied by metal sulfide. The ore body has the enrichment law of "thick on top and thin on bottom, rich on top and poor on bottom".

In addition, barite deposits in southwestern Hubei, southeastern Sichuan and central Guizhou also have certain horizons in the Hubei-Guizhou fold belt of the Yangtze platform, mainly distributed in the Upper Cambrian-Lower Ordovician. The lower Ordovician Hongyuan formation, the host rock is carbonate rock, often mixed with gypsum and salt layer; The overlying interlayer is mainly mudstone, showing stratabound characteristics.

The abundance of barium in the ore-controlling strata or underlying surrounding rocks of this kind of deposits is generally 1 ~ 3 orders of magnitude higher than that of similar rocks, and most of them are sandwiched with gypsum and salt beds, which provide sulfur sources for mineralization. The sulfur isotope of this kind of deposit is heavy sulfur, δ 34s =+35.56 ‰ ~+ 16.3 ‰, belonging to evaporite (Zhang, 1985). The isotopic compositions of hydrogen and oxygen in the ore are δ 18O =+5.9 1‰, δ18oh2o =-19.77 ‰ ~-5.25 ‰, and δ dh2o =-89.5 ‰. This is consistent with the hydrogen isotope composition of the Jurassic-Cretaceous precipitation in China (Zhang Ligang, 1986). Therefore, it is speculated that the ore-forming medium is mixed with atmospheric precipitation.

According to the above speculation, the ore-forming hydrothermal solution of barium extracted from deep surrounding rocks or ore source beds rises along structural fractures, and when it is mixed with permeable shallow seawater, barite precipitates and minerals are precipitated. Therefore, this type of deposit belongs to stratabound deposit, which is not only related to barium deposited in different periods in space, but also obviously controlled by structural faults. In addition, it also needs a suitable ore-hosting environment, that is, fragile carbonate rock layer and poor permeability interlayer, which leads to ore liquid convergence.

The scale of such deposits is generally large and medium-sized, and the famous ones are Xiangzhou in Guangxi, Yidu in Hubei and Shibing in Guizhou. The following describes the metallogenic characteristics of Pancun deposit in Xiangzhou, Guangxi (Figure 8-5).

1. Ore-producing strata

It is mainly composed of four rows of Lower Devonian, with limestone and marl mixed with mudstone as the main lithology, and mudstone mixed with limestone as the lower part, with a thickness of 370m m.

The deposits are mainly distributed in the rocks of the lower member of Sipai Formation, with prominent stratabound characteristics.

2. Metallogenic structure

There are mainly two groups of faults, one is strike 3 13 ~ 355, dip ne, dip angle 52 ~ 85; The other group has a strike of 350 ~ 360, an inclination of E and an inclination of 70 ~ 80. There are more than 80 barite veins in the mining area, and their occurrences are basically consistent with faults (Figure 8-5).

3. Occurrence and scale of ore bodies

Barite deposits are vein-shaped, about 30 ~ 1700 m long, and generally100 ~ 500 m; The thickness is mostly 1 ~ 10m, generally 2 ~ 4m, and the extension depth is generally 50 ~ 60m, with the maximum exceeding 170m. Ore bodies mainly occur in limestone, argillaceous limestone and mudstone. The surrounding rocks are silicified, barite, calcite, brecciated and faded. Barite is closely related to silicification, and barite often coexists with time.

Figure 8-5 Geological map of Pancun ore section in Pancun barite mining area, Xiangzhou County, Guangxi.

(According to Tang et al., 1983)

4. Ore and its grade

According to the different ratio of barite to synchrony, the veins can be divided into barite veins, synchrony-barite veins and barite-synchrony veins. Calcite is also a common biological mineral. The grade of surface ore is relatively stable, most of which are rich, and the grade decreases towards the deep. For example, the average grade of some veins is 83.58% in the surface layer and 64. 12% in the deep layer. The thickness also tends to decrease from the surface to the depth.

According to the different proportions of barite, timely and calcite, the ores can be divided into two types: rich minerals are barite single mineral minerals with milky white and coarse crystals, which can reach several tens of centimeters, barite content is 85% ~ 95%, and others are timely and calcite; Lean ore belongs to the timely-barite ore type, with barite content ranging from 30% to 85%, mostly concentrated in 50% to 60%. Deep ore is closely related to symbiosis, so it is difficult to beneficiate.

The chemical composition of ore is simple, mainly BaSO4, followed by SiO2, Fe2O3, Al2O3 and water-soluble salts. Sometimes it also contains elements such as Sr (up to 1%). Copper-lead-zinc sulfide can be seen in some ores, which can reach industrial grade in some places, but the content is obviously reduced.

The deposit has a reserve of over 500× 105t, which is a super-large deposit.

Three. sedimentary volcanogenic mineral deposit,volca nosedimentary deposit

This deposit is directly related to volcanism, that is, the ore-forming materials come from volcanoes and are deposited near the crater or in the basin at a certain distance. This kind of deposit is rare, represented by Huashugou (Jingtieshan) iron-barite deposit in Sunan County, Gansu Province.

The genesis of Jingtieshan deposit has always been controversial. Some people think it is sedimentary, others think it is volcanic. The deposit is located in Neoproterozoic volcanic rock series in Caledonian fold belt of Qilian Mountain. The ore-bearing rock series are black phyllite and gray-green phyllite, and the upper and lower parts and periphery of the rock series are volcanic rocks. The seam is located in the transitional zone between Qianer and Manger, with a thickness of10 ~150m. The thick layered seam is consistent with the occurrence of surrounding rocks, with obvious boundaries, and the longest ore body is over 2000m.

The ore composition is composed of siderite, specularite, jasper, barite and ankerite, with occasional pyrite and chalcopyrite, mainly in granular structure and banded structure, with banded width of 2 ~ 12 mm and individual100 mm; ; Followed by huge, scattered and broken structures. Barite and iron ore exist in three forms: ① Barite lens is sandwiched in iron ore deposit; (2) Barite zone in iron ore is the main occurrence form of barite; ③ Fine barite is mixed in siderite or specularite.

Because most ores have low grade and limited scale, their economic value is limited to comprehensive utilization and recovery like iron ore mining.

Fourthly, hydrothermal deposits.

The temporal and spatial distribution of this kind of deposits is closely related to acid intrusive rocks, which are distributed around the intrusive bodies, and some of them are obviously zonal, that is, skarn-type metal deposits → mesothermal lead-zinc polymetallic deposits → lead-bearing barite deposits, such as the Songguantuan deposit in Anqiu, Shandong Province. The deposits are controlled by NE and NW secondary faults beside the deep fault zone (NNE), such as Anqiu and Mulin deposits in Shandong Province. The age and lithology of ore-bearing surrounding rocks range from Archean to Cretaceous, from ancient gneiss to various sedimentary rocks, volcanic rocks and pyroclastic rocks. Wall rock alteration is common, mainly silicification, followed by barite, sericitization, pyritization and fading. The ore bodies are veined, lenticular and dendritic, and the thickness is between 1 and10m. The main biological minerals in the ore are barite, galena and Yingshi, followed by chalcopyrite, sphalerite, pyrite and calcite. Barite content is 52% ~ 87%. The timely temperature of the ore in Songguantuan barite deposit in Shandong Province is 165℃ (homogenization method), galena δ34S=-4.92‰, barite δ34S=+ 19.44‰, all of which belong to the sulfur isotope category of granite. It can be seen from the above characteristics that the deposit belongs to low-temperature magmatic hydrothermal deposit.

Such deposits are generally medium-sized and small in scale.

V residual slope barite deposit

This kind of deposit occurs in Quaternary eluvial deposits, and the output of ore bodies is limited by primary deposits, which can be distributed in strips or areas. There is no surrounding rock at the top, so it is easy to mine. Generally, primary deposits often develop near it, but the scale varies greatly. There are residual diluvial heavy crystal deposits in Sizun, Xiangzhou, Ling Bing, Danxian, Hanshan and Tizishan in Guangxi. Ore reserves can reach one million tons. For example:

The distribution area of Xiangzhou Sicun deposit is 0.3 ~ 1km2, and the accumulation thickness is 3 ~ 5m. The ore is accumulated by detrital, and the size of detrital is granular, gravelly and boulder-like, and the larger fragmentation can reach 4.3m3, which basically retains the structure and structure of primary ore. The grade of ore is generally higher than that of primary ore, generally above 95%, and the highest is about 99%.