Program > Browse abstracts by speaker > Filgueiras Bernardo

Zinc plays a vital role in industry and human health, making it a critical global resource, and understanding the geological conditions of Zn-mineral formation is essential for Zn-resource discovery. While Zn-sulfides dominate global zinc resources, they are poor indicators of the physical and chemical conditions of Zn mobilization and concentration into ore deposits. In contrast, non-sulfide Zn-minerals potentially offer clearer insights, in particular those with willemite (Zn₂SiO₄) given the stronger crystal-chemical control on composition in silicates. This study investigates willemite formation conditions and its potential as a geological tracer of fluid and element sources using its trace element fingerprint. This requires a detailed understanding of its trace element partitioning. We determined partitioning systematics in willemite-synthesis experiments in trace-element-doped melts, enclosed in quartz capsules, at 1500˚C in a 1-atm furnace. Quenched samples were imaged and analyzed using SEM-EDS and laser-ablation ICP-MS, and resulting partition coefficients (D values) were interpreted in light of Lattice strain theory. High-temperature X-ray diffraction and ab-initio Density Functional Theory calculations provided insights into the response of the crystal structure to pressure and temperature, and indicate that, above 200°C and 2 kbars, the two Zn sites of willemite diverge in size, which should allow for a larger range of elements to be incorporated. Experimental results show compatibility of Mg, Co, Ag and Cd (2 ≤ D > 1) and incompatibility of Mn, Fe, Pb and Ge (D < 1). However, these latter elements have been reported at high concentration in natural willemite. This suggests that reported compositions may suffer from micro-inclusions or that an additional, interstitial site aids their incorporation. This research provides the crystal-chemical framework for evaluating the potential of willemite as a probe of the formation conditions of Zn deposits, and thereby provide the insights needed for effective exploration for this critical resource.