Dr. Adrian Fiege is a research scientist at the American Museum of Natural History, New York, USA. He is in charge of the Electron Micro-Probe and FTIR laboratories at the museum.
Dr. Fiege is an experimental petrologist and geochemist working on volatile and metal transport, redox processes, magma degassing, magma-magma interaction and (stable) isotope fractionation in magmatic-hydrothermal systems, both on Earth and in extraterrestrial environments. His research aims at a better understanding of the spatial, temporal, and geochemical relationship between magmatic/volcanic activity and mineral ore deposits formation.
Oxygen fugacity (fO2) is a key parameter, influencing metal transport, magma evolution, and even the style of volcanic eruptions (e.g., effusive vs. explosive). Sulfur is the third most abundant volatile in magmatic systems and because of its polyvalent properties (2- to 6+) it can modulate the redox state of a magmatic system through the addition or separation of S-rich fluids. In turns, the behavior of sulfur (partitioning, solubilities) is strongly redox-sensitive; for instance, sulfate (S6+) is typically more soluble in silicate melt when compared to sulfide (S2-). Sulfur strongly partitions into free (aqueous) volatile phases, where it may form complexes with (chalcophile) metals, resulting in their potential transport and enrichment. Furthermore, large amounts of sulfur are released by volcanic eruptions (mostly as SO2), impacting our climate. Thus, on many levels, understanding the budgets, sources, and transport processes of sulfur and tracing its state of redox in magmatic and hydrothermal environments can yield valuable insights into crustal processes, including but not limited to the lithospheric sulfur cycle, S-bearing ore deposit formation, and volcanic activities. Here, apatite may become a powerful tracer.
Apatite is a ubiquitous mineral in terrestrial and extraterrestrial magmatic and hydrothermal environments. Our group investigates the incorporation of S into apatite’s structure as a function of redox, using state of the art experimental, analytical and theoretical approaches. I will present experimental and computational results showing the high potential of S-in-apatite as both, a redox and a sulfur budget tracer. I will apply our data to lunar magmatism as well as to iron-oxide apatite ore deposit formation.