BENTONITE

Bentonite, also known as amargosite, is defined as claystone-montmorillonitic claystone composed dominantly of the montmorillonite-group minerals. There are a complete range of bentonite varieties in China, including Ca-base, Na-base, NH4-base, Al-base and Na-Ca-base bentonites, as well as unclassified bentonite.

Bentonite has many important properties, such as water absorption, swelling, cation-exchange capacity, thixotropy, binding, water adsorption, thickening, lubrication, stability and decoloring. It is widely used in founding, energy industry, drilling and papermaking, and also in the manufacture of chemicals, building materials, drugs and textiles. Bentonite is mainly used in the making of iron concentrate pellets, drilling muds, foundry sand binders and decontaminants for animal and plant oil decoloriaing.

The use of bentonite in China began in the 1940s, when farmers at Yuyao County, Zhejiang Province, mined it on a small scale. China's modern bentonite industry emerged at the beginning of the 1950s, when the annual production of the whole country was only 800 tons. The earliest mines were the Qiushan mine at Yuyau, Zhejiang, the Heishan mine in Liaoning and the Jiutai mine in Sankuang. With the expansion of the application scope and increase in the demands, bentonite mines were built successively at Lin'an of Zhejiang, Xinyang of Henan, Weifang of Shandong, Xuanhua of Hebei, Shuangyang of Jilin, Shuangcheng of Fujian and Jiuquan of Gansu. By the end of the fifties outstanding progress had been made in the development of bentonite deposits in China.

4.23.1 Resources

4.23.1.1 Reserves and Resources

Bentonite resources are abundant in China. It is estimated that the resources are more than 7.0 billion tons. By the end of 1997, retained reserves of 87 occurrences (of which 12 were large, 32 medium-sized and 43 small) were obtained.

The categories B+C+D retained bentonite reserves were 2.434 billion tons, ranking first in the world.Categories B+C retained bentonite reserves account for 27% of the total. Detailed reconnaissance or exploration has been conducted in 75% of the 87 occurrences including major productive mines. Among the occurrences with retained reserves, 46 occurrences (including 9 large ones, 16 medium-sized ones and 21 small ones) have been mined and their retained bentonite reserves total 1.98 billion tons, accounting for 81% of the total, which can meet the demands of the bentonite production till 2010 and later; 38 occurrences (including 3 large ones, 16 medium-sized ones and 19 small ones) can be selectively mined in the near future and their retained bentonite reserves amount to 450 million tons, making up 18% of the total; 3 occurrences are small ones which are difficult to exploit in the near future and their retained bentonite reserves total over 3 million tons, constituting less than 1% of the total.

4.23.1.2 Characteristics of Resoruces

China's bentonite deposits are widely distributed in 23 provinces (autonomous regions). The retained reserves are mainly concentrated in some provinces (autonomous regions) in eastern China, where the retained reserves account for 62% of the total. The reserves in southern China are larger than those in northern China. The distribution of 44 large and medium-sized bentonite occurrences with retained reserves is shown in Fig. 4.23.1.

Retained bentonite reserves in the south-central region account for 35% of the total. The retained bentonite reserves in Guangxi are largest among all the provinces (autonomous regions) of China. They are mainly distributed in Ningming County, where the Ningming bentonite deposit is of superlarge size, with retained reserves of more than 600 million tons, and has been mined; the medium-sized and small deposits at Tiandong, Tiandong County, and Chenling, Binyang County, are also minable. There are three small deposits at Ezhou City, Hubei Province, of which the Litiepu deposit has been mined; the large and medium-sized deposits at Shangxiong, Jiangxia District, Wuhan City, can be selectively mined. In Henan, Guangdong, Hunan and Hainan provinces, the retained bentonite reserves are not many, but small and medium-sized deposits (in which bentonite is associated with pearlite or zeolite) at Xinyang County and Luoshan County, Henan, have been mined for many years. These areas are main bentonite producers of China. In Guangdong Province, the small Luocun deposit at Nanhai City and the small Fengcun deposit at Gaozhou City have also been mined. Small and medium-sized deposits (in which bentonite is associated with gypsum or other useful minerals) at Dashaba, Meixian County, and Shangling, Heping County, Guangdong Province, as well as the Wujiayu gypsum mine, Lixian County, Hunan Province, can be selectively mined. Only small deposits in Hainan Province are difficult to exploit in the near future.

The retained bentonite reserves in East China constitute 23% of the total. There are more retained reserves in Jiangsu, Shandong and Anhui provinces. Three large deposits at Jiashan, Jurong County, Jiangsu Province, Xintan, Huanshan City, Anhui Province, and Quanzhuang, Weifang City, Shandong Province, as well as medium-sized and small deposits at Xuyi and Dantu, Jiangsu Province, Weifang, Laizhou, Anqiu and Gaomi, Shandong Province, and Xiuning, Liu'an, Xiuning and Xuanzhou, Anhui Province, have been mostly mined on a small scale. Retained reserves in Zhejiang Province are not many, but large and medium-sized deposits and some small deposits at Lin'an, Yuyao and Anji have all been mined. The area is one of the main bentonite producers in China. The Pingshan deposit at Lin'an and the Qiushan at Yuhang have been mined for many years. Na-base bentonite produced in the Pingshan mine may be used in the manufacture of iron ore pellets; the Qiushan mine is China's first base for producing degreasing activated clay. Fujian and Jiangxi provinces have not many reserves, and there a few individual small deposits have been mined and some medium-sized and small deposits are minable.

The retained bentonite reserves in Northwest China account for 18% of the national total. Large and medium-sized deposits at Hoboksar County and Toksun County, Xinjiang, and Hongquan, Jinchang City, Gansu, have been mined. These areas are main bentonite producers in western China. In addition, large and medium-sized deposits at Yangxian and Xixiang, Shaanxi, are minable.

The retained bentonite reserves in North China make up 17% of the total. Large deposits at Xuanhua County, Hebei, and Xinghe County, Inner Mongolia, and small deposits at Ningcheng County, Inner Mongolia, have been mined. These areas are also main bentonite producers of China. In addition, medium-sized and small deposits at Hunyuan, Shanxi Province, Longhua, Hebei Province and the Urad Front Banner, Inner Mongolia, are minable.

The retained bentonite reserves in Northeast China take up 6% of the total. Medium-sized and small deposits at Jiutai City and Changchun City, Jilin Province, and Heishan County, Faku County and Lingyuan City, Liaoning Province, have been mostly mined and some of them have been mined for many years. These areas are China's main bentonite producers too. A medium-sized deposit in which bentonite is associated with zeolite at Hailin County, Heilongjiang Province, has been mined, and small deposits at Baiquan County and Boli County are minable.

The retained bentonite reserves in Southwest China only account for 1% of the total. Eight small deposits at Santai, Yanting and Renshou counties, Sichuan Province, have been mined and a medium-sized deposit at Xuanwei, Yunnan, is minable.

Bentonite deposits of China may be classified into the volcanic-sedimentary type, weathering residual type and hydrothermal type. Volcanic-sedimentary type deposits are widespread. Sedimentary environments include neritic, oxbow lake, valley piedmont and saline lake ones. The bentonite horizon is persisitent and flat. Continental volcanic-sedimentary

Fig. 4.23.1Distribution of bentonite deposits in China
1. Ulan Linge-Riyuelei, Hobksar County, Xinjiang; 2. Ke'erjian, Toksun County, Xinjiang; 3. Sarhu, Hami City, Xinjiang; 4. Baimiaozi zeolite mine (bentonite associated with zeolite), Urad Front Banner, Inner Mongolia; 5. Baiyin Qagan, Xin Barag Left Banner, Inner Mongolia; 6. Gaomiaozi, Xinghe County, Inner Mongolia; 7. Yanjiagou, Xuanhua, Hebei Province (associated bentonite); 8. Yixunhegou zeolite mine (bentonite associated with zeolite), Longhua County, Hebei Province; 9. Reshuitang, Lingyuan City, Liaoning Province; 10. Xinsheng, Baiquan County, Heilongjiang Province; 11. Hailin County zeolite mine (bentonite associated with zeolite), Heilongjiang Province; 12. Yinkuangshan bentonite-zeolite mine, Jiutai City, Jilin Province; 13. Shibailing, Changchun City, Jilin Province (associated bentonite); 14. Liufangzi, Gongziling, Jilin Province (associated bentonite); 15. Shili, Heishan County, Liaoning Province; 16. Suntun, Heishan County, Liaoning Province; 17. Hongquan, Jinchang City, Gansu Province; 18. Yangxian County, Shaanxi Province; 19. Yangheba, Xixiang County, Shaanxi Province; 20. Qianfengling, Hunyuan County, Shanxi Province; 21. Yongquanzhuang, Weixian County, Shandong Province; 22. Yujiachuang, Weifang, Shandong Province; 23. Longwangshan-Mudian attapulgite clay mine (bentonite associated with clay), Xuyi County, Jiangsu Province; 24. Liujiachong pearlite mine (bentonite associated with pearlite), Xinyang, Henan Province; 25. Yangjiawan pearlite mine (bentonite associated with pearlite), Luoshan County, Henan Province; 26. Jiashan, Jiurong County, Jiangsu Province; 27. Balingshan, Jiangling County, Hubei Province; 28. Shangxiong, Jiangxia District, Wuhan City, Hubei Province; 29. Lines 0-8, Shangxiong mine, Jiangxia District, Wuhan City, Hubei Province; 30. Hongmiao, Anji County, Zhejiang Province; 31. Pingshan, Lin'an County, Zhejiang Province; 32. Baitengkou, Laiyang City, Shandong Province; 33. Qiushan, Yuhang County, Zhejiang Province; 34. Dashuode, Yangchang, Xuanwei County, Yunnan Province; 35. Tiandong, Tiandong County, Guangxi; 36. Ningming, Ningming County, Guangxi; 37. Wujiayu gypsum mine (bentonite associated with gypsum), Lixian County, Hunan Province; 38. Danaopu, Yangxin County, Hubei Province; 39. Xintan, Huangshan City, Anhui Province; 40. Dashan, Xiuning County, Anhui Province; 41. Dongyuan ore sector, Wukou ore district, Leping County, Jiangxi Province; 42. Lijia, Guangfeng County, Jiangxi Province; 43. Zhongshan, Wuping County, Fujian Province; 44. Dashaba, Meixian County, Guangdong Province.

type deposits make up 60% of the total deposits of China and contribute 70% of the total national reserves, as exemplified by the Pingshan deposit, Lin'an, Zhejiang, the Heishan deposit, Liaoning, and the Xintan deposit, Huangshan, Anhui. Marine sedimentary deposits are commonly large in size and high in grade, as exemplified by the Ke'erjian deposit, Toksun, Xinjiang. Peneplain colloid mineral deposits are generally small in size, distributed in Sichuan, Hubei etc. Bentonite beds of weathering residual deposits are thick and persistent and the bentonite is good in quality and has many uses. The mineralization depth is commonly near the water table, ranging from a few dozen centimetres to a few hundred metres. From above downwards bentonite shows gradational relationships with its parent rocks (various types of glassy lavas and clastic rocks). Ca-base bentonite predominates near the surface and Na-base bentonite only appears at depth. Bentonite deposits of different origins may be formed in the same tectonic environment and even in the same deposit. The example is the Qiushan deposit at Yushan, Zhejiang. For hydrothermal type bentonite deposits, only some occurrences are found in the Chating-Pingqiao area, Liyang County, Jiangsu.

More than half of bentonite deposits of China are distributed in the circum-Pacific volcanic belt, on the eastern continental margin of China, where there are parent rocks of bentonite. Bentonite deposits also occur in areas of volcanic rocks on paleoplate margins and in tectonically active belts in west-central China. The NE-trending downfaulted volcanic-sedimentary basins along the coast of eastern China, which possess the restricted, stable and alkali-rich water environment, are favorable areas for mineralization. The Liangzi Lake basin of Hubei, the down-faulted basin in the Qilian Mountains, the volcanic-sedimentary basin in the Tianshan Mountains and the Sichuan inland basin in west-central China are also favorable areas for bentonite formation. Bentonite deposits were formed from the Late Carboniferous to Tertiary, mainly in the Late Jurassic and Early Cretaceous.

Of the retained bentonite reserves of China, Ca-base bentonite accounts for 34%, Na-base bentonite 24%, and Al- and H-base bentonite and other types of bentonite 42%. Generally, bentonite formed at shallow depth in hot-humid areas in Guangdong, Guangxi etc. is naturally modified into Al-(CH-) bentonite; part of bentonite in arid areas in Gansu and Xinjiang is naturally modified into Na- and Mg-base bentonite; bentonite in other areas are mostly Ca-base one.

The grade of China's bentonite is generally above medium. According to the statistics of 61 occurrences, the bentonite grade (montmorillonite content) generally ranges from 33.3 to 97.27%, with a total average of about 65%. The highest average grade (97.27%) is found in the Mengjiayao mine, Hunyuan, Shanxi, which has retained bentonite reserves of 31,000 tons. Among other occurrences, 15 have an average grade of 84.5 to 70% with nearly 200 million tons of retained reserves (accounting for 11% of the total reserves of the occurrences participating in the statistics), mainly distributed at Xuanhua, Hebei Province, Tiandong, Guangxi Autonomous Region, Changchun, Jilin Province, Lingyuan, Liaoning Province and Xuyi, Jiangsu Province; 41 have an average grade of 70 to 50% with 1.27 billion tons of retained reserves (accounting for 73% of the total reserves of the occurrences participating in the statistics), mainly distributed at Ningming, Guangxi Autonomous Region, Huangshan, Anhui Province and Jiangxia, Hubei Province, as well as Faku and Heishan, Liaoning Province, Jiutai, Jilin Province, Jurong, Jiangsu Province, Yuhang, Zhejiang Province, and Xinyang and Luoshan, Henan Province; 4 have an average grade<50% with retained reserves of 280 million tons (accounting for 16% of the total reserves of the occurrences participating in the statistics), mainly distributed in Hoboksar, Xinjiang, and Yangxian, Shaanxi Province.

Among the useful associated minerals in bentonite of China, kaolin and illite are most common and have good dressing performance. In 24% of bentonite deposits, bentonite is associated with other mineral resources. In the Xuyi mine, Jiangsu Province, the associated useful minerals are attapulgite and clay; at Fuku, Liaoning Province, Dantu, Jiangsu Province, Xuanzhou, Anhui Province and Xinyang and Luoshan, Henan Province, bentonite is associated with pearlite; in the Wujiayu mine, Lixian County, Hunan Province, and the Zhongshan mine, Wuping County, Fujian Province, the associated mineral is gypsum; in Jilin, Heilongjiang and Hebei provinces, bentonite is associated with zeolite.

China's bentonite deposits are mostly located in hilly areas. They are shallow-buried, with 1 to 15 m thick overburdens, and mostly suited for open-pit mining, and some deposits in Zhejiang, Jilin and Liaoning are worked by underground mining.