Germanium concentration associated to sphalerite recrystallization: an example from the Pyrenean Axial Zone

Alexandre Cugerone (1) , Bénédicte Cenki-Tok (1) , Emilien Oliot (1) , Manuel Munoz (1) , Alain Chauvet (1) , Fabrice Barou (1) , Kalin Kouzmanov (2) , Stefano Salvi (3) , Vincent Motto-Ros (4) , Elisabeth Le Goff (5)

1 Géosciences Montpellier
2 UNIGE - Université de Genève = University of Geneva
3 GET - Géosciences Environnement Toulouse
4 iLM - SPECTROBIO - iLM - Spectrométrie des biomolécules et agrégats
5 BRGM - Bureau de Recherches Géologiques et Minières (BRGM)

Germanium (Ge) is often found as trace element in undeformed sphalerite (ZnS). However, the presence of Ge-minerals (oxides, chloritoids and/or sulphides with up to 70 wt% Ge) is remarkable in Pb-Zn deposits from the Variscan Pyrenean Axial Zone. Their abundance is controlled by the chemical and/or the mechanical processes that affect rare element concentration from sulphides which have undergone deformation and metamorphism. In this study, we document the microstructures and chemical heterogeneities in sphalerite, based on EBSD (electron backscatter diffraction) coupled to LA-ICPMS in situ analyses. Deformation induces the dynamic recrystallization of sphalerite. Recrystallized domains have low Ge contents (1-50 ppm Ge) whereas porphyroclastic sphalerite grains commonly show higher Ge concentrations (up to 650 ppm Ge). Ge-minerals (up to 70 wt% Ge) are exclusively hosted by the Ge-poor recrystallized domains. We propose that Ge was removed from the sphalerite crystal lattice during sulphide recrystallization, and was subsequently concentrated in Ge-minerals, leaving behind a Ge-depleted fine-grained recrystallized sphalerite matrix. Numerous sulphide ore types enriched in rare elements like Pyrenean deposits may present recrystallization features and we suggest evaluating the potential of such deposits by integrating chemical and structural informations at the micrometer scale using state-of-the-art analytical techniques in exploration methods.

Mots clés: Geologie

Domaines: Planète et Univers [physics]; Sciences de la Terre

Alexandre Cugerone, Bénédicte Cenki-Tok, Emilien Oliot, Manuel Munoz, Alain Chauvet, et al.. Germanium concentration associated to sphalerite recrystallization: an example from the Pyrenean Axial Zone. 15th SGA Biennial Meeting on Life with Ore Deposits on Earth, Aug 2019, Glasgow, United Kingdom. ⟨hal-02915316⟩