Abstract
The southern portion of the Colangüil Batholith is formed by units of the Tocota Pluton, of Permian age, which intrude late Carboniferous-Permian (Asselian) sandstones. Sub-volcanic bodies with andesitic composition and tuffs of Cenozoic age, modern layers of piedmont sediments and both alluvial and glacier deposits also crop out. The region exhibits a set of metalliferous deposits (Cu-Au-As) and occasionally with bismuth. These are mostly filonian type. These are spatially associated with granodiorites, granite and sandstone. Their development is interpreted as belonging to the Gondwanan cycle.Within granitic rocks, mineralizations were formed between 139 ºC and about 400 °C, probably after the consolidation of the Tocota pluton and by the upward circulation of hydrothermal fluids, probably mixed with meteoric waters. In the host rock, mineralization occurred in an interval between 200 ºC and 350 °C, through hydrothermal activity detected in areas of phyllic-argillic alteration. The gangue constitutes mainly of quartz, tourmaline and and sometimes potassium feldspar and calcite. The mineralization pattern, in both the pluton and the sandstone, has been controlled by 1) a strong domain of ore filled faults and joints, with ENE and WNW as the more common strikes and NNW subordinated, 2) fault breccias and hydrothermal breccias, and 3) dykes of andesite composition with low metal content. The host rock mineralization is commonly emplaced in joints as well as finely disseminated, related to intense silicification. Such deposits contain hypogene minerals whose isotopic 34S/32S ratios are compatible with a granite-like filiation but other provenances cannot be ruled out.
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