Project

copper and zinc isotopes; volcanic gases; geochronology; arc magmatism; clinopyroxene partition coefficient for Cu; subduction; high Sr/Y; Yanacocha; radiogenic isotopes; experimental petrology; amphibole partition coefficient for Cu; Chachimbiro; porphyry copper

Lead
Trois quarts du Cu mondial, et des quantités importantes des métaux comme Au, Re et Mo, sont fournis 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 connus, 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.
Lay summary
Lead Trois quarts du Cu mondial, et des quantités importantes des métaux comme Au, Re et Mo, sont fournis 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 connus, 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 (p. ex., valeurs Sr/Y élevées) et la formation des gisements de type porphyre en étudiant des complexes magmatiques minéralisés (au Pérou) et non-minéralisés (en Equateur et aux Iles Eoliennes) 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.   Keywords Subduction, arc magmas, porphyry systems, porphyry copper, skarn deposits, epithermal deposits, copper gold, andesite, adakite-like, Andes, Aeolian islands

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Last update: 14.10.2015

Geochemical and radiogenic isotope data of 86 new rocks from 13 volcanic edifices of Ecuador and Colombia

Author	Chiaradia, Massimo
Publication date	23.04.2020
Persistent Identifier (PID)	doi:10.6084/m9.figshare.7813940
Repository	figshare
Abstract

Geochemical and radiogenic isotope data of 86 new rocks from 13 volcanic edifices of Ecuador and Colombia produced in this study. Major and minor elements are expressed as oxides (wt.%) whereas trace elements are expressed as ppm; bdl = below detection limit; nm = not measured. Major and minor elements were measured by XRF, whereas all trace elements reported were measured by LA-ICPMS, except trace elements of Casitagua and Illiniza volcanoes which were measured by XRF. Radiogeni cisotopes were measured on a MC-ICPMS Neptune Plus. The epsilon-Nd value reported is calculated with respect to the CHUR reservoir, assuming a 143Nd/144Nd value of CHUR of 0.512638 (Wasserburg et al., 1981; Hamilton et al., 1983).

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The present proposal is for a 2-year extension of the SNF project N. 200020_149147 “Magmas, ore deposits and geodynamic evolution at convergent margins”. Funds are asked for a 2-year extension of the PhD salary of Ms. Maria Teresa Bellver Baca, fieldwork and attendance to conferences by the PhD student and the applicant, as well as for analytical work. Ms. Maria Teresa Bellver Baca has been engaged for this project since 1 February 2014.In the frame of this project we are focusing on two questions about the association between 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 are also addressing is a more general: 3. Understanding the behavior of Cu during magmatic processes and at the magmatic-hydrothermal transition in active magmatic arc systems.Points 1 and 2 above are the focus of investigation of the PhD project of Maria Teresa Bellver Baca (Subproject A: Magmatic and time-scale factors controlling the association of porphyry-type deposits with high Sr/Y magmas). They are carried out contemporaneously in the giant porphyry-associated Au(-Cu) district of Yanacocha (northern Peru) and in the barren volcanic complex of Chachimbiro (northern Ecuador): the magmatic evolution through time of these two systems is very similar but the timescales of evolution differ by an order of magnitude (~4 Ma long at Yanacocha and ~450 Ka long at Chachimbiro). The aim of sub-project A is to provide detailed petrogenetic models for the two magmatic complexes through acquisition of whole rock/mineral chemical and isotopic compositions as well as radiometric dating (U-Pb on zircons, 40Ar/39Ar on amphibole and biotite, 14C for the youngest samples on fossil wood contained in pyroclastic flows). Geochemical and isotopic data of whole rocks and minerals and radiometric ages will be used to quantify physical parameters of magmatic processes (e.g., size of the magmatic reservoir, magma fluxes) at the two sites and compare results to infer metallogenic implications. Detailed mineral (amphibole, clinopyroxene, apatite, magnetite, magmatic sulphides) and melt inclusion major and trace element compositions by in situ techniques (microprobe, LA-ICPMS, SIMS) will be used to reconstruct and compare the behavior of metals and volatiles during magmatic evolution (increasing Sr/Y) at the two sites. Experimental determination of partition coefficients of Cu for amphibole/clinopyroxene-andesite melt will be used to better characterize the behavior of this chalcophile metal during magmatic evolution in conjunction with Cu contents acquired on amphibole and clinopyroxene phenocrysts from the two magmatic complexes.Point 3 above is the current research focus of the applicant in collaboration with Master students (Subproject B: Magmatic behavior of copper in magmatic arc systems) and is/will be carried out both through literature surveys and statistical treatment of databases (e.g., Chiaradia, 2014: Nature Geoscience 7, 43-46) as well as through field-based studies in the Aeolian islands of Vulcano and Stromboli. Investigation of the behavior of metals like copper in barren systems with “normal” Sr/Y ratios (i.e., Aeolian islands) both in magmatic rocks/minerals and in volcanic gases will help us to further constrain the factors which may lead to the preferential association of porphyry-type deposits with high Sr/Y magmas.