It is surprising that the Bolivian tin belt does not cross the national frontiers either north into Peru or south into Argentina. Lithologic and tectonic controls can explain this anomaly. The length of the belt is about 1,000 km.

Three metallogenetic cycles of different age can be distinguished. The oldest is in the northern part of the High Cordillera and is related to pegmatites and pneumatolytic veins in granitic batholiths of Triassic-Jurassic age. South of the latitude of La Paz is the Miocene metallogenetic cycle with its abundant tin and wolframite veins, from the vicinity of Viloco to Colquiri. South

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of Oruro, the lode deposits are related to small stocks and dikes of dacite and rhyolite of Pliocene age. The belt widens (100 km) and forms the famous polymetallic province, unique in the world because of the rare associations of tin, silver, and other minerals such as teallite, franckeite, aramayoite, andorite, argirodite, etc. (Chocaya).

Inexplicably the deposits are of shallow depth; in most cases their root zones are in the lower part of the hills and the vertical difference in elevation of the zones is not more than 1,000 m (Chorolque).

There is zonal arrangement from tin, wolframite, bismuth to lead, silver and zinc, to the outer zone of quartz and stibnite. In the southern province, the zonal arrangement is more local (Tasna).

There are approximately 750 tin mines, 2,000 lead mines, 250 antimony mines, and about 30 mines for bismuth, most of them are small and shallow. The wealth of some of these mines is extraordinary. The production of Llallagua (Catavi) is estimated as 600,000 tons of tin. There remains one million tons of proven and indicated reserves, 75 percent of which belongs to Corporacion Minera de Bolivia (COMIBOL).

The tin veins are exploited by selective underground methods despite high mining costs. The grade averages of the deposits have declined to limits which now can be considered marginal.

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