There are four important tin-producing districts in east central Bolivia, in the provinces of Potosi, Oruro, and La Paz. The region lies on the high plateau (elevation, 12,000 feet) and the principal mines are near or in the mountains on the east of the pampa rather than in the western range of the Cordillera. Schists, slates, and quartzites have been intruded by acid igneous rocks, and the tin deposits are found in the granites, the quartz porphyries, and the sedimentary rocks near the contacts. The quartz veins are strong and carry between 3 and 8 per cent. tin in most of the productive mines, though some bodies of ore have carried as much as 40 per cent. tin. Some of the mines were worked for silver by the Spanish, but the silver ores seem to be limited to the upper zones, the lodes becoming relatively richer in tin at depth. Wolframite and bismuth are won as by-products at some of the mines. Pyrite, sphalerite, chalcopyrite, and galena are usually abundant in the tin ores, and tourmaline and fluorite are not uncommon.
The Bolivian deposits are of considerable future importance. Many mines and prospects, either through lack of knowledge or finances, have not been developed; the local management of most of the mines has been notoriously poor; and it is thought that with proper technical direction the output of tin can be greatly increased.
Dutch East Indies.
—On the islands of Banca, Billiton, and Singkep, south of the Malay Peninsula, are important tin mines. As will be seen from [Table 60] the output of tin from these islands has been approximately 21,000 tons a year. Mining began on Banka about 1718, but the Billiton deposits were not worked until about 1860. The mines of Banka are worked by the government, but on Billiton and Singkep the deposits are leased by private concerns, mostly Dutch. At Banka the Dutch government operates smelters having a yearly capacity of 16,000 tons. The concentrates produced on Billiton and Singkep are in part sent to the Straits Settlements for treatment, but some are smelted locally.
Practically all of the tin mined in the Dutch East Indies is from placer deposits, some of which are alluvial. There is, however, a little lode mining on Billiton. The cassiterite was formed in greisenized granite and sediments, and the original deposits are similar to those of the Malay Peninsula. A little tungsten and gold are obtained as by-products of the tin mining.
China.
—Tin deposits in the Mengtze district, near Kochiu, Province of Yunnan, southeastern China, have been worked for many years. During recent years about 8,000 tons of tin have been exported, and it is known that considerable tin ore produced from these deposits is smelted locally, the metal being consumed in China. The exports go out through the French port of Haifong. The mining industry is entirely under Chinese control. Most of the tin ore is obtained by placer and open-cut methods from decomposed granitic and pegmatitic lodes which are found near the contact of granite that is intrusive into limestone. There are less important tin deposits in the Fuchuan and Tungchwan districts, the former producing a very pure metal.
The tin concentrates exported go mostly to Hong Kong and the Straits Settlements for treatment, so the Chinese tin output is more or less at the disposal of England.
Siam.
—In that part of Siam lying in the Malay Peninsula, tin deposits, similar in origin and occurrence to those in the British provinces, are being worked, and as shown by [Table 60] are yearly becoming larger factors in the world’s output. The largest operations are near Renong and Tongkah, where dredging by British companies is active. The chief producing companies are Tongkah Harbor Tin Dredging Co., Tin Benbong, Bangnon Valley, Ronpibon Extended, Beebook Dredging Co., and Katoo Syndicate.