Resumo

GERARDO, N. Páez et al. Volcanostratigraphy of the Martha Mine silver bearing deposit, Deseado Massif, Santa Cruz Province. Rev. Asoc. Geol. Argent. [online]. 2010, vol.67, n.1, pp.77-90. ISSN 0004-4822.

Martha Mine is located in the southwestern portion of the Deseado Massif, close to the city of Gobernador Gregores, Santa Cruz Province, Argentina. On the area, two main geological units are recognized: the Bahia Laura Group (J) and the Monte Leon Formation (Tc). Detailed mapping and sampling allows defining nine volcanic units for the Jurassic of the study area. Volcanic stratigraphy of Martha Mine is characterized by episodic pyroclastic volcanism dominated by crystal rich ash flow tuffs, interbedded with reworked pyroclastic sediments representing pauses in the volcanism. This episodic volcanism was interrupted by a highly explosive volcanic event, related to the development of a 12 km wide collapse caldera and the deposition of a thick sequence of lithic rich ash flow tuffs. This caldera volcanism occurred as result of mingling of two compositionally different kinds of magma, an andesitic magma similar in composition to the Bajo Pobre Formation, and a rhyolitic magma related to the compositions of the Chon Aike Formation. This mingling is preserved into the lithic tuffs as two textural and compositionally different pumice fragments. The coexistence of two different kinds of pumice into the same flow unit (correlated to the Bajo Pobre and Chon Aike formations), implies the need of reviewing the classical stratigraphic scheme for the Deseado massif.

Palavras-chave : Volcanism; Jurassic; Bahía Laura Complex; Mingling; Epithermal deposit.

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