Tin- and tungsten-bearing quartz-tourmaline veins of the Caracoles district occupy predominantly northeast-striking fractures in the southeastern end of the Quimsa Cruz granodioritic batholith, emplaced in folded Paleozoic formations. Formation of the vein fractures may have been indirectly related to extension movements produced by northeast- southwest regional compression normal to the elongation of the batholith, and more directly to shifting secondary stress fields induced by stretching and arching. The more steeply dipping vein structures are interpreted as tension fractures, and the flatter ones as shear fractures. The vertical range of mineralization is only about 250 m, considerably less than in other mining districts of the Quimsa Cruz region, suggesting that ore precipitation within the fracture system was exceptionally rapid and was controlled by the chemistry and crystallization mechanism of the mineralizing solutions rather than by pressure and temperature gradients.

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