Project

radiogenic isotopes; amphibole partition coefficient for Cu; volcanic gases; arc magmatism; experimental petrology; high Sr/Y; geochronology; subduction; porphyry copper; arc magmas

Lead
Trois quarts du Cu mondial sont fournis par les gisements de type porphyre, associés avec les roches magmatiques d’arc. Tandis que les processus magmatiques et hydrothermaux à basse profondeur dans la croûte qui amènent à la précipitation des métaux dérivants du magma sont bien connu, les processus géodynamiques et magmatiques se passant à grande profondeur dans le manteau et la croûte terrestre, qui jouent un rôle essentiel dans la formation de ces gisements, sont peu connus.
Lay summary
Lead Trois quarts du Cu mondial est fourni par les gisements de type porphyre (incluant, le porphyre de Cu, les skarns, et la suite des gisements épithermaux). Ces gisements sont associés avec les roches magmatiques d’arc, produites par la subduction de la croûte océanique dessous la croûte continentale ou océanique. Tandis que les processus magmatiques et hydrothermaux à basse profondeur dans la croûte qui amènent à la précipitation des métaux dérivants du magma sont relativement bien connu, les processus géodynamiques et magmatiques se passant à grande profondeur dans le manteau et la croûte terrestre et qui jouent un rôle essentiel dans la formation de ces gisements sont peu connus.   Contenu et objectifs du travail de recherché Le but de ce projet est de mieux comprendre quelle est l’influence des processus profonds dans la formation des gisements de type porphyre. En particulier nous voulons mieux comprendre le lien entre la géodynamique des zones de subduction, la génération des magmas avec une géochimie particulière et la formation des gisements de type porphyre en étudiant des complexes magmatiques minéralisés et non-minéralisés et en les comparant entre eux.   Contexte scientifique et social du projet de recherche Notre travail générera des résultats qui nous aiderons à mieux comprendre la genèse des gisements de type porphyre et donc à raffiner les modèle génétiques qui sont à la base des campagnes d’exploration des compagnies minière pour la recherche des nouvelles ressources. Ils nous aiderons aussi à mieux comprendre l’évolution de la croûte et les échanges des métaux entre croute et manteau de la Terre.

Direct link to Lay Summary

Last update: 15.10.2013

Active participation

Title	Year

Number	Title	Start	Funding scheme

The present proposal is for a 2-year extension of the SNF project N. 200020_137663 “Magmas, ore deposits and geodynamic evolution at a convergent margin: the case of Ecuador”. Funds are asked for a 2-year PhD student salary, fieldwork and attendance to conferences by the PhD student and the applicant, as well as for analytical work. The PhD student will be engaged for this project from 1 January 2014.In the past years (SNF Projects N. 200021-109636, 200020-117616, 200020-126896, 200020_137663) we have investigated the time relationship between adakite-like rocks and mineralization (in Miocene porphyry-systems of Ecuador, in the giant porphyry-related Miocene system of Yanacocha and in the Oligocene skarn-porphyry mineralization of Coroccohuayco) and the petrogenetic significance of adakite-like rocks. We have also investigated the petrogenetic significance of the transition from normal calc-alkaline to adakite-like signatures that occurs during the Quaternary in several volcanic edifices of northern Ecuador. The main results of our previous investigations can be summarized as follows: (i) adakite-like rocks are formed by magmatic evolution at variably deep crustal levels and under hydrous conditions, favoring the stability of amphibole ± garnet but not that of plagioclase; (ii) porphyry-type deposits form in association with adakite-like rocks during a few Ma (~<1-3 Ma) towards the end of a several Ma long (=6 Ma) transition from normal to adakite-like magmatism.The results obtained in the previous years invite us to focus now on two specific questions (whose answers represent our objectives) about the association between adakite-like (high Sr/Y) magmas and porphyry systems: 1. Why porphyry systems occur in the final stages of a magmatic cycle characterized by a systematic increase in Sr/Y values through time? 2. Why magmatic cycles with increasing Sr/Y values associated with porphyry systems last several Ma as opposed to similar cycles in “barren” systems which last only 0.0X to 0.X Ma? A third point that we would like to address in synergy with the above ones is a more general: 3. Understanding of the magmatic behavior of Cu in active arc-related magmatic systems.Points 1 and 2 above will represent the focus of investigation of a PhD student (Subproject A: Magmatic and time-scale factors controlling the association of porphyry-type deposits with high Sr/Y magmas). They will be carried out in the giant porphyry-associated Au-Cu district of Yanacocha (northern Peru) and in the volcanic complex of Chachimbiro (northern Ecuador). Point 3 will be the research focus of the applicant in collaboration with Master students (Subproject B: Magmatic behavior of copper in arc-related systems) and will be carried out in the Aeolian islands of Vulcano, Stromboli and Lipari. At all sites we will monitor changes of some critical parameters such as metal (in particular Cu) and volatile (H2O, CO2, S, Cl, F) contents, oxidation state, depth of the reservoir during the temporal evolution of magmatic rocks of mineralized and non-mineralized systems from low to high Sr/Y values in order to better understand the role of high Sr/Y magmas in the formation of porphyry-type deposits. Investigation of the behavior of volatiles and metals like copper in “normal” barren systems (i.e., Aeolian islands) both in magmatic rocks and in volcanic gases will help us to better understand the factors which may lead to preferential association of porphyry-type deposits with high Sr/Y magmas.