—In the extreme southwest of England is the famous Cornwall tin region, which includes the Camborne, St. Austell, and Liskeard districts, in Cornwall, and the Tavistock district, in Devon. The mines have produced about 8,000 tons of concentrates a year, but at present the output seems to be diminishing; in 1915 the production of metallic tin was approximately 5,000 tons, but in 1918 was only about 4,000 tons.
Tin mining in Cornwall dates back to prehistoric times. In the sixteenth century the mines produced about 700 tons of tin a year; the maximum output was reached in the period 1860 to 1890, when about 10,000 tons was produced annually. It is estimated that the total output of tin from this district is approximately 1,750,000 tons. The mining companies are without exception controlled by British capital.
The second largest tin-smelting capacity in the world is in the Cornwall district. The following companies, Williams Harvey & Co., Penpoll, Cornish Tin Smelting Co., Copper Pass, Redruth Tin Smelting Co., and the London Smelting Co. operate smelters having a combined output of approximately 31,100 tons of tin a year.
The tin deposits of Cornwall and Devon lie about five masses of granite, which are intruded into slates (killas) and greenstones. Quartz porphyry dikes are closely connected with the granite, and the tin lodes are found in both slates and granite, being particularly abundant near intrusive contacts with low dips. The principal lodes are wide zones of fissured rock that are tourmalinized, the less important fissures containing tin and gangue minerals. Copper and tungsten minerals are produced from these lodes, and arsenic is an important by-product of smelting. The lodes in slates are as a rule richer in copper than in the granite, and in depth the lodes contain a larger proportion of tin than nearer the surface. The mines about the Camborne granite mass yield about 85 per cent. of the tin mined, those about the Lands End granite mass 12 per cent., and the mines about St. Austell, Bodmin Moor, and Dartmoor about 1 per cent. each.
Practically all of the tin produced in recent years has been from lodes, but placer tin was mined near St. Austell. The lodes have been worked to a depth of 3,000 feet, which seems to be about the greatest depth to which commercially profitable ore extends. As considerable ground above this level remains to be developed, the district should be productive for some time.
Other Nations.
—Outside of the British Empire the principal tin deposits of the world are in Bolivia, the Dutch East Indies, China, and Siam, named in the order of their importance as producers in 1918. There are small outputs of tin from deposits in Japan, Spain, Portugal, and the United States, and tin deposits are known in Germany, Italy, Russia, Belgian-Congo, and Southwest Africa.
Bolivia.
—Practically all of the tin ore shipped from Bolivia is mined from lodes. Mining began late in the last century. Exports are in the form of barilla, a tin concentrate carrying 60 to 65 per cent. and averaging about 62 per cent. tin. The output has been steadily increasing, and since 1913 Bolivia has been the second largest producer of tin in the world. (See [Table 60], and [Figure 9]). The majority of the companies working in Bolivia are controlled by Chilean or local capital, though a little English, French, Swiss, and German capital was invested in Bolivian tin mines before the war. Recently English and American capital has become interested in the deposits.
Prior to the war practically all of the barilla was sent to Germany and England to be smelted, but lately exports have been to the United States and England. A small Chilean-owned smelter, estimated capacity 900 tons a year, has recently been built at Arica to handle the concentrates from one of the larger mines.