Preservation of fluid copper isotope ratios in a Fe-Zn rich hydrothermal chimney

Project title

Preservation of fluid copper isotope ratios in a Fe-Zn rich hydrothermal chimney

Supervisors

Dr. Desiree Roerdink, Dr. Andreas Beinlich (Freie Universität Berlin, Germany)

Project description

Copper stable isotopes (δ65Cu) in deep-sea hydrothermal fluids have the potential to provide insights into ore-forming processes occurring below the seafloor, such as the dissolution of copper from igneous rocks, phase separation in fluids, and remobilization of copper from primary sulfides. However, the collection of high-temperature hydrothermal vent fluids for metal analyses is challenging due to the precipitation of sulfides in the sampler, which requires laborious procedures to reconstruct metal concentrations. In addition, high concentrations of dissolved salts complicate Cu isotope analyses from hydrothermal fluid-seawater mixtures, and require extensive purification in the clean laboratory. As a result, Cu isotope data on these fluids is currently scarce and most work has focused on sulfide-rich hydrothermal chimney samples, which show a large range in δ65Cu-values (up to 5‰). The origin of these variations remains debated, and may reflect temporal variations in fluid chemistry or low-temperature alteration and redox cycling. Recent work by the Centre for Deep Sea Research on a chalcopyrite-rich hydrothermal chimney suggests that only the innermost chalcopyrite minerals in a conduit preserve fluid copper isotope ratios (Samin et al, in prep.), but it remains unknown if this also applies to hydrothermal chimneys rich in iron and zinc-sulfides.

This project aims to determine Cu isotope variations through chimney walls with pyrrhotite and sphalerite minerals, collected from the Jan Mayen and Loki’s Castle vent fields on the Arctic Mid Ocean Ridges. It will generate Cu isotope data from sulfide minerals on microdrilled transects and compare these against mineralogical variations observed in thin sections, as well as previously measured Cu isotopic compositions of high-temperature hydrothermal fluids.