Mineral magnetic discrimination between diagenetic and hydrogenetic iron-manganese concretions

Marine iron-manganese concretions are metal-containing biogeochemical precipitates abundantly encountered in the seafloors of the world ocean. Their importance in paleoenvironmental reconstructions as well as a source for critical metals has been recently realized. Diagenetic and hydrogenetic concretions, however, have different compositions and subsequently can have differing capacities for recording oceanographic processes and for economic utilization. Therefore, their genetic classification can provide crucial information for both environmental and economic applications. Traditionally discrimination of different marine iron-manganese concretion origins has been achieved with geochemical methods, such as investigating their rare earth element content. It is now evident that iron-manganese concretions also host magnetic minerals that are likely formed by facilitation by microbial processes. Currently it is unknown if the different genetic backgrounds of iron-manganese concretions are reflected in their magnetic properties.  

We compared the geochemical and magnetic properties of diagenetic iron-manganese concretions from the Baltic Sea to hydrogenetic concretions from the Pacific. While the commonly utilized geochemical indicators differentiate the concretions found from the two localities as diagenetic and hydrogenetic, it also appears that concentration dependent magnetic parameters such as saturation magnetization and anhysteretic remanent magnetization effectively discriminate between the different types of concretions. Mineral magnetic methods are fast and cost-effective and may provide an alternative tool to quickly screen out diagenetic from hydrogenetic precipitates.

This research is part of the Fermaid project, funded by the Academy of Finland grant 332249.