Die Bedeutung des intermediär oxidierten Schwefels für die Genese hydrothermaler Sulfat‐Sulfid‐Lagerstätten

Abstract

What one observes in hydrothermal ore deposits and their wall rock are sulfates (baryte, anhydrite, alunite) and sulfides (pyrite, galena etc.). The nature of the ore forming solution has to be extrapolated. Many authors maintain that sulfur occurs in solution in the extreme oxidation states S6+ and S2− only. However, theoretical considerations and experiments show that intermediate oxidized sulfur species (IOSS) are more frequent than generally assumed. Under hydrothermal conditions (p, T, po2) sulfate will be reduced stepwise; IOSS are dominant. Oxidation, reduction and disproportionation lead to the formation of sulfides and/or sulfates. Sulfate‐acceptors resp. sulfide‐acceptors keep the disproportionation going. IOSS provide a new model to explain the transport of metals and sulfur in the same hydothermal solution and the simultaneous crystallization of sulfates and sulfides. A further advantage of this model is the fact that heavy metals and earth alkali metals are more soluble by orders of magnitude as IOSS than as sulfate and sulfide.