The state of critical elements: valency and distribution of Ge in colloform sphalerite

Sphalerite (ZnS) is a significant host for critical elements (Ge, Ga, In, Co) and Ge elemental composition is used to determine the temperature of ore emplacement and the fractionation of Ge isotopes is related to temperature, redox conditions, and/or sphalerite crystal structure. Two types of sphalerite crystal fabrics are generally observed: euhedral and colloform. In euhedral coarse sphalerite crystals, Ge is generally incorporated in the sphalerite crystal lattice as tetravalent cation.
Colloform sphalerite is composed of a mix of acicular and euhedral crystals. Germanium is hosted in halogen-rich nanoscale fluid inclusions rather than in the crystal lattice. However, no investigation of Ge redox state has been performed in colloform sphalerite. This proposal aims to investigate the valency of Ge in colloform and euhedral sphalerite. Micro-XRF mapping and XANES-EXAFS of Ge will be performed on sphalerite to evaluate the influence of incorporation mechanisms on Ge redox state.