Metasomatism of Badenian sulphates of the Carpathian Foredeep and its palaeogeographic conditions

Abstract

The Miocene (Badenian) sulphate (gypsum and anhydrite) deposits in favourable structural conditions have undergone metasomatic transformation into limestones closely associated with native sulphur. The transformation process mobilized originally stable sulphate ions into highly mobile sulphide ions followed by their oxidation to elemental sulphur. It is possible to distinguish three stages of metasomatism which include (1) initial metasomatism (locally developed, often as crystal etching), (2) selective metasomatism (activated in the most susceptible parts of the sulphate deposits, e.g. along fractures, faults systems), and (3) complete metasomatism (the full alteration of a sulphate deposit with the preservation of original sulphate structures and textures). Except the structural pattern, the palaeogeographic conditions (areas lacking sulphates or where the sulphate horizon is substantially thinner) appear to be one of the important factors responsible for sulphate transformation. Intensity of the transformation process decreased with distance from such sedimentary discontinuities.