Abstract

ECHEVESTE, Horacio. Structural control of the epithermal mineralization in the Manantial Espejo ore ditrict, Santa Cruz. Rev. Asoc. Geol. Argent. [online]. 2010, vol.66, n.3, pp.325-334. ISSN 0004-4822.

The structural analysis of the Manantial Espejo Au-Ag district allows to identify the existence of at least two brittle extensional deformation systems that were active before 159 Ma (Callovian). Rhyolitic volcanism and epithermal activity in the region were associated with these systems. The oldest of them was due to a main s1 NNO-SSE stress that produced two fracture systems: one at approximately 25° and the other at around 140°. These fractures hosted the rising rhyolitic magma, which generated dikes, and channeled of carbonate-rich waters associated with the presence of a hot spring type system, which formed calcite veins and travertine deposits on the surface. A second deformation system occurred after the former one and produced a simple shear system with a s1 ~ N 35° W similar to a conjugate Riedel shear system. The shear system has extension fractures between 120° and 150° that originated normal faults with NNE an SSW slope. These faults, with combined normal and dextral movements, cut and displaced the structures from the previous period and produced dilatational jogs, échelon type joints, and sigmoidal veins that created most of the new circulation channels of the now silica-saturated hydrothermal fluids. The decompression and consequent release of the CO2 of the mineralizing solutions produced by the reactivation of the fractures did generate the typical crustiform-colloform banded structures of the principal veins of the district. This last deformation system remained active until, at least, the Late Oligocene.

Keywords : Manantial Espejo; Extensional structures; Deseado Massif; Epithermal veins.

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