Developing a Technique to Determine Iron-Bearing Mineral Composition in Hydrothermal Plumes Using Optical Backscattering Sensors

It is largely unknown to what extent hydrothermal vents contribute to ocean iron cycling and to iron-containing deposits on the ocean floor. We are working to develop a method using optical backscattering sensors that will allow the oxide vs. sulfide composition of iron-containing mineral mineral particles to be easily calculated from in situ measurements at different points in the plume. We investigated the wavelength-dependent optical backscattering of suspensions of iron-containing mineral particles, such as pyrite, hematite, and chalcopyrite, that are commonly found in high-temperature hydrothermal vent plumes. We observed particles’ backscattering behavior at varying concentrations and particle sizes. Measurements were made using commercially-available optical backscattering sensors (BB-RTD, WETLabs). Iron oxides and sulfides exhibited different wavelength dependences in their backscattering patterns that were consistent with their light absorption properties. Backscattering sensors rated for high pressures could provide a time and labor-efficient means of determining relative proportions of iron oxide and sulfide minerals at high resolution in hydrothermal plumes.