Behavior of critical metals in metamorphosed Pb-Zn ore deposits: example from the Pyrenean Axial Zone

Abstract

Rare metals (Ge, Ga, In, Cd) are key resources for the development of green technologies and are commonly found as trace elements in base-metal mineral deposits. Many of these deposits are in orogenic belts and the impact of recrystallization on rare metal content and distribution in sphalerite needs to be evaluated. Based on laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses, and micro-imaging techniques such as laser-induced breakdown spectroscopy (LIBS) and electron backscattered diffraction (EBSD), we investigate the minor and trace element composition related to sphalerite texture for three types of mineralization from the Pyrenean Axial Zone (PAZ). Vein mineralization (type 2b) appears significantly enriched in Ge and Ga compared to disseminated and stratabound mineralization (type 1 and type 2a, respectively). In vein mineralization, the partial recrystallization induced by deformation led to the remobilization of Ge, Ga, and Cu from the sphalerite crystal lattice into accessory minerals. We propose that the association of intragranular diffusion and fluid-rock reaction were likely responsible for the formation of patchy-oscillatory zoning in

Variscan U-Th-Pb age for stratabound Pb-Zn mineralization in the Bossòst dome (Pyrenean Axial Zone)

“…Nonetheless, Bentaillou sphalerite seemed to have undergone recrystallization with presence of polygonal crystals or "foam textures" (Fig. 4C) contemporaneous of a low-grade metamorphism (<400 °C, Cugerone et al, 2021a). Low trace contents in Ga, Ge and In (<10 ppm) observed in the same sphalerite sample at Bentaillou is also a supporting clue of this metamorphic imprint (Cugerone et al, 2021a;Frenzel et al, 2016).…”

“…In the Victoria and the Horcall deposits, south and north-east of the Bossòst dome, respectively (Fig. 2A and B), stratabound mineralization is intensely folded by F2 folds but cross-cut metamorphic mineral assemblage such as gahnite as well as hosted in shadow pressure of garnet crystals (Cugerone et al, 2018b;Cugerone et al, 2021a;Cugerone et al, 2021b, submitted). The Bentaillou Pb-Zn deposit is located in low-grade marble and schists (Fert, 1976;Zwart, 1963b) and consequently is interpreted as part of the Suprastructure.…”

Trace-element imaging at macroscopic scale in a Belgian sphalerite-galena ore using Laser-Induced Breakdown Spectroscopy (LIBS)

“…Finally, although the presence of detectable gallium is not confirmed yet, it could be corroborated by the similarity of its distribution pattern to that of Cu and Ag, which could relate to the coupled substitution mechanism Ag + / Cu + + Ga 3+ ↔ 2 Zn 2+ (Cook et al, 2009;Cugerone et al, 2021).…”

“…The consistency of the results obtained so far suggests that, under the conditions we have used, matrix effects have no tangible influence. Another technique to tackle with spectral overlap, which was not used here because there are only two major mineralogical phases, is to use a different, overlap-free emission line of the same element for each mineralogical phase in the sample (e.g., Cugerone et al, 2021).…”

“…Note that depending on its design, a LIBS system can also operate at the microscopic scale, with a spot size down to 3 µm (e.g., Menut et al, 2003;Jolivet et al, 2019). LIBS thus appears as a very flexible technique and already finds a wide range of applications in earth sciences and mineral exploration (e.g., Senesi, 2014;Harmon et al, 2019), especially for geochemical mapping (e.g., Fabre et al, 2018;Rifai et al, 2018), including germanium in sphalerite (Cugerone et al, 2020;2021).…”