Porphyry copper-type mineralization and geosynclinal tectonic evolution in the Chilean Andes
Abstract
A tectonic palaeogeographic scheme is summarized indicating some important relationships between the geological evolution of the Chilean Andean region, especially during the Middle Triassic to Recent Andean Tectonic Cycle, and the genesis and location of porphyry type copper mineralization.
The study of the Andean Chain suggests that the location of the porphyry copper deposits is related to the transition zone which separates the eugeosynclinal and miogeo-synclinal zones throughout the length of the Andean basin (mesodorsal, Frutos, 1973). The porphyry copper deposits are specifically related to the eastern fringe, located parallel to the axis of the basin, in which, due principally to the Mid-Late Cretaceous and Lower Tertiary diastrophic phases some important overthrustings occurred, with a partial riding of the mesodorsal zone on the miogeosynclinal furrow.
The spatial location of the Mid-Late Cretaceous and Tertiary magmatic processes involved in the evolution of the geosynclinal basin, the sedimentary physicochemical environment, and the tectonic structures directly associated with the porphyry copper deposits, obviously have a direct relation with the aforementioned tectonic phenomenon and with the evolution of the western margin of the continent.
It seems that the geological-geographical location of the porphyry copper deposits and also the copper-bearing tourmaline breccia pipes could be related to the following factors:
a) The miogeosynclinal Upper Jurassic to Lower Cretaceous andesitic volcanic facies, parallel marine sediments and evaporitic facies.
b) The important Cretaceous-Lower Tertiary compressive structures.
c) The Cretaceous-Pliocene transcurrent fault system, cutting diagonally the Andean Chain, with NE and NW general directions.
d) The Upper Cretaceous-Cainozoic acid hypabyssal magmatism.
e) The relatively uplifted mesodorsal zones, especially those of the Upper Tertiary, that have enhanced secondary enrichment.
Mention is also made of some plate tectonic metallogenetic models, emphasizing the volcanic characteristics observed in the youngest ore bodies.