Porphyry Cu-Mo systems emplaced under contrasting tectonic regimes: examples from central Chile and SE China
Piquer, J and Cooke, DR, Porphyry Cu-Mo systems emplaced under contrasting tectonic regimes: examples from central Chile and SE China, Abstracts from the FUTORES II Conference - Future Understanding of Tectonics, Ores, Resources, Environment and Sustainability, 04-07 June 2017, James Cook University, Townsville, QLD, pp. 94. (2017) [Conference Extract]
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The formation of porphyry Cu-Mo systems is commonly thought to be favoured by compressive to transpressive tectonic regimes, which lead to a diminution in the rate of volcanic output and to the entrapment of magmas and volatiles in the upper crust. Two cases are presented here for which the tectonic regime during mineral deposit formation is studied, based on the analysis of syn-tectonic hydrothermal minerals (Fig. 1): central Chile and SE China. In both porphyry belts, syn-tectonic magmatic and hydrothermal activity was strongly localized by pre-existing structures oblique to the orogenic belts and magmatic arcs, in particular by the intersections of pairs of regional-scale conjugate faults, and in turn fault ruptures were promoted by high fluid pressures. However, differences exist in the tectonic regime prevalent during mineralisation. Porphyry Cu-Mo deposits of central Chile were formed during the culminating stage of tectonic inversion of an intra-arc volcano-tectonic basin under transpressional conditions, with σ1 trending E-W to ENE, sub-parallel to the convergence direction. These are typical conditions for porphyry Cu-Mo formation. On the other hand, porphyry Cu-Mo deposits in SE China were formed under transtensional to extensional conditions, with sub-vertical σ1, demonstrating that at least medium-sized porphyry Cu-Mo systems and associated high-sulfidation epithermal Cu-Au deposits can form in extensional volcanic arcs with a retreating trench, such as the Yanshanian arc of SE China. This has important implications for the exploration of other extensional arcs, which are commonly considered non-prospective for porphyry Cu-Mo deposits.
porphyry, copper, high sulfidation, gold, geodynamics, extension, compression