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Evolution of porphyry-fertile magmatic cycles inferred from trace element profiles in zircons

Massimo Chiaradia 1, Hugo Carrasco1, Jing-Jing Zhu2, You-Wei Chen2, Dian-Zhong Wang2, Angelo Aguilar3, Sergio Pichott3, Sergio Cubelli3, Carolina Rodríguez3

  • Affiliations: 1Department of Earth Sciences, University of Geneva, 1205, Geneva, Switzerland; 2Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, P.R. China; 3Corporación Nacional del Cobre de Chile (CODELCO), Huérfanos 1270, Santiago, Chile 

  • Presentation type: Poster

  • Presentation time: Tuesday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 28

  • Programme No: 4.1.19

  • Theme 4 > Session 1

Abstract

Magmatic systems associated with supergiant porphyry Cu deposits (PCDs) undergo a multi-million-year maturation in the deep continental crust. This evolution is recorded also by zircon, the most used mineral to infer magma fertility in porphyry Cu systems due to its resistance to hydrothermal alteration. Nonetheless, zircon analyses are almost always limited to one or two spots and miss to convey information on changing magmatic conditions during its crystallization. This information is valuable to better understand the evolution of the fertile magmatic system and can be obtained through detailed core-to-rim profiles. We report nanoSims trace element (Eu, Gd, Ce, Ti, U) profiles in 48 zircons from 8 samples of pre- to syn-mineralization magmatic rocks associated with the supergiant Llurimagua PCD (Ecuador). Zircons span a range of ages between ~23 and ~6.3 Ma. Mineralization occurs at the end of this magmatic cycle, typical of supergiant PCDs, between ~7.28 and ~6.22 Ma. Between ~23 and ~10 Ma, profiles indicate zircon crystallization from magmas cooling at shallow crustal levels in concomitance with plagioclase fractionation. The cores of the ~23-10 Ma zircons also indicate that these zircons crystallised from magmas that have progressively evolved at deep crustal levels through time, under increasing PH2O and fO2 conditions. After ~10 Ma zircon profiles display both cooling and heating patterns suggest the onset of a more dynamic magmatic plumbing system characterised by recharges and suggesting an increased magma transfer from deep to shallow levels, which is ultimately responsible for the subsequent mineralization from ~7.3 to ~6.2 Ma.