DIATOMITE
Diatomite is one of the biogenic siliceous sedimentary rocks. It consists dominantly of remains of ancient diatoms with subordinate clay minerals and minor amounts of quartz, feldspar, biotite, organic material and salts. Diatomite is characterized by a special structure and a density, a high absorption capability, and a large specific surface area, relatively high corrosion-resistance and high chemical stability. It can be used in many fields. It is mostly used as filter-aids to filter and clean liquids. It can also be used as a filler and extender in paints and coatings, paper-making, rubber, plastics and so on.
It is used as thermo-insulation materials, carriers of agricultural chemicals and catalysts, fixing agent of chromatogram, lustering abrasives and so on. Diatomite in China was firstly found in Shengxian County, Zhejiang in 1929, and in 1935 a deposit of superior diatomite was found in the vicinity of Shanwang Village of Linqu County, Shandong. The production of diatomite started in the 1940s, but the large-scale development and utilization of it began after 1949. A number of diatomite mines in Shandong, Zhejiang, Jilin etc were successively put into production in the 1950s to 1960s. Since the 1980s diatomite mines in Sichuan, Yunnan, Hebei and so on have been exploited. Up to now three diatomite producing bases in Jilin, Zhejiang and Yunnan respectively have been set up.
4.21.1 Resources
4.21.1.1 Reserves and Resources
The resources of diatomite in China are comparably rich with an estimated volume of over 2 billion tons. By the end of 1997, 36 diatomite occurrences with retained reserves (6 large, 15 medium-sized and 15 small) were explored with the total retained diatomite ore reserves of categories B+C+D of 389.98 million tons, standing in the forefront of the world.
Among the retained diatomite ore reserves, categories B+C reserves account for 28% of the total. Exploration or detailed reconnaisance has been carried out in most exploiting mines. Of the occurrences with retained reserves, 15 (3 large, 6 medium-sized, 6 small) have carried out mining operations with a total of retained ore reserves of 0.16 million tons, which account for 42% of the total retained reserves and can meet the needs for diatomite industrial production to 2020 and for a long period of time afterward. 18 occurrences can be selected to be developed in the near future, which have a retained ore reserves of more than 0.21 billion tons, accounting for 55% of the national total retained diatomite ore reserves. 3 occurrences are difficult to develop in the near future. There retained ore reserves are more than 10 million tons, accounting for 3% of the national total retained diatomite ore reserves.
4.21.1.2 Characteristics
The distribution of diatomite occurrences in China has a certain regional character. The diatomite occurrences and the retained reserves are relatively concentrated in the eastern and southwestern areas of China. They are less in the northwestern areas. The diatomite occurrences are distributed in Jilin, Yunnan, Zhejiang, Hebei, Sichuan, Inner Mongolia, Fujian, Guangdong, Jiangxi and Shandong. There are 21 large and medium-sized occurrences with retained reserves ( see Fig. 4.21.1).
Jilin Province is the most important diatomite area in China with retained ore reserves of 211.1 million tons, which account for 54% of the national total retained reserves. Most of the reserves are distributed in Changbai County, where the Xidapo Mine has retained ore reserves of over 0.16 billion tons. The reserves are less commonly in Linjiang, Dunhua, Wusong, Huadian, Meihekou, Yongji and so on. 10 medium-sized and small deposits have been mined, and they are the major supply bases of raw materials for diatomite filter-aids in China.
Yunnan Province has retained diatomite ore reserves of 88.24 million tons, which account for 21% of the national total retained ore reserves. They are mainly distributed in the Songshudi Mine Field, Xianfeng Lignite Mine Area, Xundian County. The size of the diatomite deposit, in which diatomite is associated with coal, is exceedingly large. It has been mined. Less important are medium-sized and small deposits in Tengchong County which can be developed and exploited.
There are 42.86 million tons of retained diatomite ore reserves in Zhejiang Province, which account for 11% of the national total retained ore reserves and are distributed in large and medium-sized deposits in Sheng County. The Puyi large mine in Sheng County has already been mined and is the major producing area of diatomite ore for refractories in China.
Additionally, there is one large deposit separately in Zhangbei County and Shengyi County of Hebei Province. Some medium-sized diatomite deposits are distributed in Miyi County, Sichuan and Shengdu County, Inner Mongolia. A number of small diatomite deposits are distributed in Huade County of Inner Mongolia, Zhangpu County of Fujian, Leizhou City of Guangdong, Guangchang County of Jiangxi, and Linqu County of Shandong. Part of them have been mined. Some of them can be selected to be developed.
The diatomite deposits in China are of lacustrine type. There are 3 types of minerogenetic lake basins; they are volcanic basins (such as those in Changbai of Jilin, Linqu of Shandong and Sheng County of Zhejiang ), fault basins (for instance that in Kunming of Yunnan) and intermontane basins (such as that in Miyi County of Sichuan). Diatomite-bearing strata belong to biochemical sedimentary type of fresh water lakes. They are characterized by the presence of considerable animal and plant fossils and their association with carbonaceous clastic siltstone layers, silty clay layers and diatomaceous clay layers. The bedding of diatomite-bearing strata are well developed. There are no significant changes in lithology and lithofacies. The orebodies occur as beds and lences. The strata dip gently from the peripheries to the center of the basin. The diatoms are of fresh water type, such as Melosira and Sinomicrochara.
In accordance with the sources of SiO2, the diatomite deposits in China can be divided into two subtypes: volcanogenic diatomite deposits and terrigenous diatomite deposits. In the first subtype, diatoms were formed in lake basins in the intermittency periods between basaltic eruptions. SiO2 came from volcanoes. The diatomite-bearing strata are intercalated with basalt layers. Examples are a number of deposits in Changbai and Dunhua of Jilin, Linqu of Shandong and Shengxian County of Zhejiang in eastern China. In the subtype of diatomite deposits, there are no basalt layers in diatomite-bearing rock series. Nevertheless, there exist often basalts of earlier ages in the surrounding areas, which are the source rocks of diatomite. For example, the deposits occurring in Xundian of Yunnan and Miyi of Sichuan are attributed to this subtype.
Additionally, a diatomite deposit of brackish water type was found on the Leizhou Peninsula of Guangdong. It reveals that there are also deposits of swamp facies and deep-lake facies besides the above-mentioned deposits of fresh water lake facies.
The minerogenetic age of diatomite deposits in China is very limited. Principal diatomite deposits are mostly of Miocene to Pleistocene age with Miocene deposits predominating. For example, large deposits in Changbai of Jilin and Xundian of Yunnan are Miocene deposits. The distribution of lacustrine diatomite deposits of continental facies in China was controlled by Cenozoic basins. In the Cenozoic rifting and uplift and subsidence in eastern China gave rise to a series of down-faulted basins, in which the lakes prepared good places for the subsistence of diatoms and accumulation of remains. The widely developed basic rocks and appropriate Paleogeographical environment provided the long-term stable sources and subsistent con-ditions for the growth and proliferation of diatoms. The diatomite occurrences in western
Fig. 4.21.1 Map of distribution of diatomite occurrences in China
1. Xiejiafang, Shandu County, Inner Mongolia; 2. Shimengou, Shangyi County, Hebei; 3. Yangpo, Zhangbei County, Hebei; 4. Xinsheng, Dunhua City, Jilin; 5. Gaosongshushenchang, Dunhua City, Jilin; 6. Xixiaoshan, Linjiang City, Jilin; 7. Liudaogou West Ore Section, Linjiang City, Jilin; 8. Liudaogou East Ore Section, Linjiang City, Jilin; 9. Cuocaodingzhi South Hill, Linjiang City, Jilin; 10. Ma'anshan No.˘ňOre Section, Changbai County, Jilin; 11. Xidapo Ore Section, Ma'anshan Mine, Changbai County, Jilin; 12. Xidapo detailed reconnaissance area, Changbai County, Jilin; 13. Detailed reconnaissance area in the surrounding area of Xidapo, Changbai County, Jilin; 14. Manpa, Tengchong County, Yunnan; 15. Huihangou, Miyi County, Sichuan; 16. Xinmincun,Miyi County, Sichan; 17. Zhonglianzhi, Miyi County, Sichuan; 18. Lianzhidian, Miyi County, Sichuan; 19.Songshudi Mine Field, Xianfeng Lignite Mine Area, Xundian County, Yunnan; 20. Puyi, Sheng County, Zhejiang; 21. Pugiao, Sheng County, Zhejiang.
China, for instance in Yunnan Province, were not related to volcanic activities. The soluble siliceous substances were provided by the rocks surrounding weathered and decomposed basins. So the areas in eastern China, where the NE- and NNE-trending faults are developed and accompanied by Cenozoic volcanic activities and the areas of lignite deposition in the ENE-trending structural basins formed by the Himalayan orogenic movement in southwes-tern China are the favorable minerogenetic areas, where new diatomite occurrences are expected to be found. Additionally, in areas in Tertiary shallow-sea basins accompanied by Cenozoic volcanic activity along the southeast coast, marine diatomite deposits are possible to be found.
The types of diatomite ores in China are dominated by clay-containing diatomite and clayey. They are of intermediate quality with few products of I and II grades. The ores are mostly Melosira suitable for the catalysts, and Coscinodisus suitable for the filter-aids are less. The average grade of ores ( content of SiO2) in 36 occurrences with retained reserves is between 45.33% and 86.13%; among them, the average content of SiO2 in 7 occurrences is higher than 80%. The total retained ore reserves of these occurrences are 0.17 billion tons, accounting for 45% of the total national retained ore reserves, and are distributed in Maan-shan and Xidapo of Changbai County, Jilin and in the Xingtang Mine of Tengchong County, Yunnan. Their average content of SiO2 in 23 occurrences is between 80% and 60%. The retained ore reserves amount to more than 0.1 billion tons, accounting for 27% of the total national retained ore reserves and are distributed in Linjiang and Dunhua of Jilin, Shengxian County of Zhejiang, Miyi of Sichuan, Linqu of Shandong, Huade and Shangdu of Inner Mongolia, Leizhou of Guangzhou and so on. The average content of SiO2 in 6 occurrences is less than 60%. The retained ore reserves amount to more than 0.1 billion tons, accounting for 28% of the total national retained ore reserves and are distributed in Xundian of Yunnan, Zhangbei and Shangyi of Hebei, Guangchang of Jiangxi, Zhangpu of Fujian and so on. The average content of the harmful constituents Al2O3 and Fe2O3 in diatomite ores are generally lower than the standard limit. Nevertheless, the average content of Al2O3 in ores of some deposits is higher than 18%, and that of Fe2O3 is higher than 7%.
Diatomite is usually associated with clay. The latter may occur as separate layers or mix with diatomite, forming clayey diatomite or diatomaceous clay. Generally speaking, clay is a harmful constituent, but it is useful in some applications. The typical example of association of diatomite ore with lignite and peat layers is the Xianfeng Ore District in Yunnan Province. The orebody is thick. The size of the deposit is superlarge. The content of SiO2 in original ores is rather low. Nevertheless its quality is better remarkably and the ore is easy to concentrate after calcination.
Generally, the minerogenetic age of diatomite deposits is younger. Most of the ore is not deeply buried. Most diatomite deposits are suitable to be excavated by the open-pit mining method, and only a part of them need to be mined with the underground method. Some of diatomite deposits are excavated from under water and pumped out in the form of mineral slurry.
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