The Kupferschiefer in Spremberg, East Germany: Signals of Organic Matter Alteration from Hydrogen Isotopes and Nso Compounds

Abstract

Summary Ore forming processes in sediment-hosted sulfide deposits are widely regarded to involve organic matter (OM). However, the precise nature of interactions between OM and hydrothermal fluids are still debated as well as how the interconnected reactions develop over geological timescales. Here, we present results from an advanced characterization of organic matter in the Kupferschiefer from Spremberg in Northeast Germany with a focus on NSO (organonitrogen, sulfur and oxygen compounds) and compound specific hydrogen isotopes. The observed strong enrichment of D in the n-alkanes that is not linked with thermal maturity likely occurred due to intensive hydrogen exchange with an evaporitic brine with an initial high δD value. Signals of slight degradation and oxidation argue against interaction of the organic matter with strongly oxidizing and hot metal bearing brines. Further work is required to assess if the fluids have become less oxidised and cooler due to water-rock interactions during migration (and yet maintained copper in solution) or if different fluids were involved in the mineralization of the Spremberg Kupferschiefer.