Solubility and complexation of nickel in hydrothermal fluids at conditions relevant for ore formation processes

• Applicants: Dr. Oliver Beermann; Dr. Christian Schmidt
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: from 2015 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 275543965

Nickel is among the least understood elements with respect to its behaviour in hydrothermal processes in the Earth¿s crust. Nickel is considered to be fairly immobile in hydrothermal environments because the few available experimental data indicate a low solubility in chloridic and sulfidic aqueous fluids. In contrast, the existence of many hydrothermal nickel deposits worldwide is evidence that this cannot generally be the case. However, it is unknown at which conditions nickel can be mobilised by hydrothermal fluids, which complexes transport Ni, and why there is a large variation in the Ni-Cu ratio of the mineralisations. Furthermore, arsenic could play a key role in these processes, which is nearly unexplored.In the proposed research, we intend to study the solubility of Ni, NiS and NiAs in aqueous fluids in comparison to that of Cu, and to identify the complexation of Ni. Particular attention is paid to conditions the relevance of which is indicated from the geologic observations, i.e. the presence of Fe, a large range of temperatures from 200 to 600 °C, low pH, and the availability of Cl, S, and As as ligands. Systematic Ni, Fe, and Cu solubility experiments will be carried out using cold-seal pressure vessels and a large-volume hydrothermal autoclave equipped for in situ fluid sampling, with additional application of the synthetic fluid inclusion technique. These experiments will be complemented by in situ Raman spectroscopic and synchrotron-radiation XRF and XANES analyses at high temperatures and pressures using hydrothermal diamond-anvil cells. The aim of the proposed project is to identify and quantify the parameters that cause increased solubility of Ni and separation of Ni and Cu in hydrothermal processes. The obtained results will be implemented in geologic models of hydrothermal Ni, Cu, and Fe mobilisation and mineralisation.

• DFG Programme: Research Grants
• Co-Investigators: Professorin Dr. Astrid Holzheid; Dr. Anke Watenphul