Bolivian Tin Deposits

tin-ore deposits located in western Bolivia. They form an ore belt that stretches along the Eastern Andes for 800 km. The most productive section of this length, approximately 250 km, is in the central part of the belt and is bounded to the north by the Oruro mine and to the south by the Potosí mine. The Bolivian tin deposits have been worked for the mining of silver since the 16th century and for tin since the end of the 19th century. In 1966, 26,000 tons of tin (about 20 percent of the world production) were mined.

The tin belt is made up of Paleozoic, Mesozoic, and Cenozoic sedimentary and volcanic rocks that were crumpled into folds and broken by faults of various sizes and orientations during the Laramie and Alpine folding. Along the belt there are numerous masses of intrusive and surface magmatic rocks, principally of granite and graniteporphyritic composition, with which ore deposits are associated. The ore bodies form bundles of veins and stockworks; the length of the veins is 100 m to 10 km, and the thickness is several cm to 1 m (occasionally up to 10 m). The tin content in the ores decreases sharply from 3–10 percent to 0.5–0.7 percent at a depth of 400–600m. The formation of ore came about in the Cenozoic era from rising hot mineral waters and was accomplished in two primary stages. First, at high temperature, cassiterite, quartz, tourmaline, topaz, fluorite, wolframite, bismuthinite, arsenopyrite, pyrite, and pyrrhotite were deposited; later, tetrahedrite, stannite, chalcopyrite, galenite, sphalerite, and other rarer minerals precipitated out from lower-temperature solutions. The ores of the Bolivian tin deposits are complex and rich in tin and silver; gold, tungsten, lead, zinc, antimony, and bismuth are also obtained from them.