Abstract

Tin distribution patterns in granitic and rhyolitic rock suites from the central Andes (northern Chile, northwestern Argentina, Bolivia) imply a regionally variable bulk tin distribution coefficient, with systematic tin enrichment trends as a function of magmatic evolution in the Bolivian tin belt, and little or no tin enrichment outside of the tin province. The tin enrichment trends in the igneous rocks of the Bolivian tin belt can be understood as a consequence of the ilmenite series affiliation of these rocks, i.e., their low oxidation state, and of fractional crystallization. A geochemical tin anomaly in either the source or the country rocks of the Bolivian tin granites and tin porphyries is not likely. The tin ore deposits are seen as a result of effective hydrothermal redistribution (f (sub O 2 ) below to magnetite-pyrite-pyrrhotite buffer) of magmatically preenriched tin in a shallow environment.

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