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 mineralizations (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 sphalerite, and the crystallization of Ge-rich accessory minerals. Chemical and textural heterogeneity is common in sphalerite from various world-class deposits and a full understanding of these heterogeneities is now crucial to assess the rare metal potential, and associated extraction processes of deformed base-metal ores.