Organic Matter Alteration in Kupferschiefer: The Role of NSO Compounds during Mineralization

The Late Permian Kupferschiefer in north-central Europe is one of the world’s most significant sediment-hosted stratabound copper (SSC) deposits, with mining of copper and other base metals dating back to the Middle Age (Borg, 2012; Paul, 2006).

Organic matter (OM) is thought to play a key role in the mineralization process, as previous studies have indicated pronounced alteration patterns in bulk parameters and non-polar biomarkers in mineralized rocks, using conventional analytical methods. However, subtle changes in organic composition may remain undetected using these approaches. Moreover, the exact mechanisms governing OM transformations during mineralization remain unresolved (e.g. Bechtel et al., 2002). Poetz et al. (2022) expanded the traditional approach by integrating polar compounds containing nitrogen, sulfur and oxygen (NSO) using high-resolution mass spectrometry (FT-ICR-MS), as these compounds are more reactive than hydrocarbons. They observed alteration of the oxygen containing compounds that correlated with the metal content but did not find significant differences in NSO compound composition between Cu mineralized rocks and Zn-Pb mineralized rocks. Building on this, we have analyzed samples with varying degrees of mineralization and thermal overprint by combining bulk and molecular parameters obtained through conventional analytical methods (GC-MS, GC-IRMS, ICP-MS, and Rock-Eval pyrolysis) with FT-ICR-MS data, aiming to provide a more comprehensive understanding of OM alteration and its dynamics during mineralization. Preliminary data suggest next to an enhanced OM alteration in the highly mineralized sample, an enhanced aromaticity which may resulted from oxidative processes.