Abstract

Formation of the tin deposits of Bolivia is discussed relative to recognition of two distinct types of granites in the Cordillera Real. One type is a microcline granite of probable metasomatic origin; the other is a later magmatic granite, considered anatectic in origin, whose emplacement in Devonian and older formations in late Triassic-early Jurassic time at high temperatures was accompanied by intense contact metamorphism and widespread tin, boron, and tungsten mineralization. A second phase of Sn-B mineralization, associated with Tertiary rhyolitic volcanism in the southern part of the orogenic zone, was not necessarily independent of the first; the rhyolitic magma may have represented a deep-seated residue of the anatectic granitic magma.

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