4.12.1.1Resources and Reserves

Diamond resources are limited in the world. Up to now diamonds have been found in all the continents except Antarctica, but diamond deposits are found only in about 40 countries. Generally, Africa, Oceania and Asia are endowed with more diamond resources. According to the report of the US Bureau of Mines, the world's diamond reserve base is 1900 million carats. The countries with more reserves are in successive order Australia, Congo (Kinshasa), Botswana, South Africa and Russia. Among the major producers, the production of gem diamonds in Namibia accounts for over 90% of the total annual production, in Russia about 26%, in South Africa about 25%, in Botswana about 19%, and in Australia and Congo (Kinshasa) about only 5%.

China is one of the countries whose diamond resources are scarce. Although diamonds have been found in 17 provinces (regions), explored reserves are available only in Liaoning, Shandong, Hunan and Jiangsu. Up to the end of 1997, 24 diamond occurrences have been explored throughout China, with categories B+C+D diamond reserves of 4,746.69 kg (or 23.7335 million carats), of which categories B+C reserves are 2,480.23 kg (or 12.4012 million carats). Except the Xiaobuling placer diamond mine at Tancheng County, Shandong Province, which has been closed, there are 23 diamond occurrences with retained reserves; they have categories B+C+D retained diamond reserves of 4,145.13 kg (or 20.7257 million carats), of which categories B+C retained reserves are 1,889.83 kg (or 9.4492 million carats). In comparison with the diamond reserve bases of some countries, China ranks about 9th to 10th. But the levels of exploration and availability of China's retained diamond occurrences are relatively high. The reserves of the occurrences that have undergone target exploration, detailed reconnaissance and general reconnaissance account for 78.6%, 20.2% and 1.2% of the total reserves respectively. The retained reserves that have been used and can be used in the near future take up 84% of the total reserves and those that are difficult to use amount to 16% of the total. China's explored diamond reserves were mainly obtained in the period from 1964 to 1980, and after 1985, although the explored reserves did not increase, marked progress was made when great efforts were made to implement the diamond prospecting plan. For example, two diamond-bearing kimberlite bodies (Nos. 109 and 110) were found in eastern Liaoning, and their industrial value remains to be further ascertained; diamond and pyrope were found in a volcanic terrain at Xiaobuling, Shandong; diamond was found in 17 provinces (regions) such as Shandong, Hunan, Liaoning, Jilin, Shanxi, Hebei, Guizhou, Jiangsu, Jiangxi, Xinjiang, Inner Mongolia and Tibet; lamproite was found in Guizhou, Hebei, Hubei, Hunan and Shanxi, and diamond was found in lamproite at Taoyuan, Hunan; diamond-bearing peridotite was found in Tibet. All these indicate that China has the geological conditions for forming both kimberlite-type and lamproite-type primary diamond deposits.

4.12.1.2 Characteristics of Resources

China's diamond resources are characterized by the paucity of resources, concentrated distribution, dominance of kimberlite-type primary deposits, low grade and good quality. The diamond deposits are suited for combined open-pit mining and underground mining.

(1) Resources paucity and concentrated distribution

China's diamond deposits are mainly of medium and small sizes. The largest Wangcun diamond deposit at Mengyin, Shandong, has retained diamond reserves of only 65.79 kg, which cannot  compared with large deposits in other countries. China's retained diamond (mineral) reserves account for only 0.1% of the world's diamond reserve base, and the per-capita diamond reserves are very scarce. Owing to limited explored reserves and insufficient occurrences that can be developed and mined, diamond has long been one of the deficient mineral resources.

The explored diamond reserves are concentrated in Liaoning, Shandong, Hunan and Jiangsu provinces, mainly clustered at Liaoning and Shandong. In 1997 the retained diamond reserves of Liaoning and Shandong were 2,169.74 kg and 1,863.31 kg respectively, accounting for 52.34% and 44.95% of the total reserves respectively, both amounting to 97.29% of the total; whereas the sum of the retained reserves of Hunan and Jiangsu was 112.08 kg, making up 2.71% of the total. The index of the distribution of diamond occurrences in China is shown in Table. 4.12.1.

Liaoning Province is the largest source of diamond in China. In the province there are nine diamond occurrences, all located at Wafangdian City (Fuxian County), of which six are primary ones (three large occurrences, two medium-sized occurrences and one small occurrence); besides, there are three placer diamond occurrences (one medium-sized occurrence and two small occurrences).

Shandong Province is the second largest source of diamond in China and also the locality where the first primary diamond deposit was discovered. In the province, there are nine diamond occurrences, of which five (two large and three small) occurrences are primary ones, all distributed at Mengyin County; in addition there are four placer diamond occurrences, all small-sized, distributed at Tancheng County.

In Hunan Province diamond resources were developed earlier. There are four occurren-ces, all of which are placer deposits. Of the four occurrences, the Dingjiagang diamond deposit at Changde and the Taoyuan diamond deposit at Taoyuan County are medium-sized and the other two are both small ones.

Table 4.12.1 The diamond occurrences in China

¢ÙAccording to the Reference Manual of Industrial Requirements of Mineral Resoruces (revised edition) compiled by the office of the former China National Mineral Reserves Committee, deposits with primary diamond reserves of 200,000 to 1,000,000 carats or placer diamond reserves of 100,000~500,000 carats are classified as medium-sized deposits, those with reserves larger than the above-mentioned upper limit are classified as large deposits and those with reserves smaller than the above-mentioned lower limit are classified as small deposits

In Jiangsu Province there is only one placer diamond occurrence, located at Wangyu, Xinyi City. Its explored reserves are scanty, being only 0.089 kg. Further work may be done in this occurrence.

(2) Dominance of kimberlite-type primary deposits

Diamond deposits of China may be classified into magmatic-type (i.e. kimberlite-type), primary diamond deposits and placer diamond deposits. The retained reserves of the former make up over 95% of the total, while those of the latter only nearly 5%.

According to the morphologies of orebodies, i.e. diamond-bearing kimberlite bodies, primary diamond deposits may be divided into the pipe type, dike type and sill type.

More than 20 kimberlite pipes have been found in China, mainly distributed in Shandong and Liaoning. The section of the pipes is generally round, elliptical and irregular in shape and a few to a few hundred meters in diameter with a ratio of long diameter to short diameter of about 2¡Ã1 to 4¡Ã1. They show a pinch-and-swell structure in section and become dikes to a certain depth. The pipes generally dip very steeply at dip angles of 75¡ãto 85¡ã. They have a high diamond potential. Most primary diamond deposits in China belong to this type.

Over 400 kimberlite dikes have been discovered in China, occurring in Liaoning, Shandong and Guizhou. Part of them contain diamond, but few of them are of industrial value. Up to now it is known that only the Hongqi Nos. 1 and 5 kimberlite dike primary diamond deposits at Mengyin, Shandong, have industrial value.Kimberlite sills are present in Shandong and Henan. They are intruded gently (generally at a dip angle of 10¡ã) along the bedding of the country rocks. The sills have a low ore potential and seldom form industrial deposits.

According to the formation ages, diamond deposits may be divided into ancient placer deposits and modern (Quaternary) placer deposits. Placer diamond deposits of industrial va-lue in China are all modern (Quaternary) placer deposits, distributed in Shandong, Hunan, Liaoning and Jiangsu. They include eluvial, hillside, deluvial and elluvial placer deposits.

(3) Low grade of ore

The average ore grade of placer diamond deposits of China ranges from 4 to 8 mg/m3, and only the ore of the Toudaogou placer deposit at Wafangdian City, Liaoning Province, reaches an average grade 14.6 to 16.5 mg/m3. The ore grade of primary diamond deposits is higher in occurrences of Shandong than in occurrences of Liaoning. The average ore grades of diamond occurrences at Mengyin, Shandong, are 53.57 to 672.313 mg/m3; among these occurrences the Wangcun diamond deposit has the highest average grade of ore. The average ore grades of primary diamond occurrences at Wafangdian, Liaoning, are in the range of 29.8 to 462 mg/m3, with the ore of pipe No. 68 of Toudaogou having the highest grade.   

(4) Good quality of ore

Diamond products of China are generally good in quality. Especially diamonds produced in Liaoning are of excellent quality. According to the statistics of the geological grade, gem diamonds take up only 30%, but according to the statistics of the annual production, gem diamonds may account for over 70% of the annual production. Among the diamond products of Shandong Province, gem diamonds make up about 15 to 20%. The content and granularity of gem diamonds from placer diamond deposits are notably higher than those from primary diamond deposits. Gem diamonds from placer deposits in Hunan, Liaoning and Shandong account for 60%, 50% and 30% of the total production respectively, but famous large-grained diamonds are mostly found in Shandong, and the crystals are relatively intact.

II-type diamonds occupy a certain proportion in diamond deposits of China. Preliminary analysis of diamond samples from part of diamond orebodies gave the following results: the content of II-type diamonds from the Shengli No. 1 pipe in the Wangcun deposit, Mengyin County, Shandong Province, is 18.67% of the total diamond samples weight, of which the IIb type makes up 24.67% of the II type; the content of II-type diamonds from orebody Nos. 50, 51, 68 and 74 in the Toudaogou deposit, Wafangdian, Liaoning, is 3.86% of the total weight, of which the IIb type takes up 5% of the II type; the content of II-type diamonds from the Dingjiagang placer deposit, Changde, Hunan, is 2.6% of the total sample weight, all the diamonds being of IIa type.

(5) Be suited for combined open-pit mining and underground mining

The diamond reserves of kimberlite pipe-type primary deposits occupy an absolutely dominant position in the national total reserves. The pipes generally occur as subvertical tubular bodies going up straight to the ground surface. Their section on the ground surface is round or elliptical, mostly covering an area of a few hundred to a few thousand square kilometers, and toward the depth, the section becomes smaller and smaller, the ore grade becomes low and the diamond quality becomes poor. The upper part of the diamond-bearing pipe is generally open-cut mined, and underground mining is done when the pipe is mined to a certain depth.