Development of framboidal pyrite in the Upper Permian marly limestone of the NE-Hungarian Darnó Hill

The NE Hungarian Darnó Hill is geologically complex; it is composed of an accretionary mélange complex, which contains Permian, Triassic and Jurassic sedimentary and magmatic blocks. The succession can easily be correlated with the NW Dinarides, using evidences of the different evolutionary stages of the Neotethyan Ocean (rifting, marginal basin opening, closure). Several ore indications are known from this area, but their genesis is poorly understood, mostly because of the complexity of the geological structures. The present study deals with one of these indications from deep drilling. A framboidal pyrite bearing Permian-Triassic marly limestone series was investigated, which was previously described as a possible analogy of the Polish-German copper shales (Kupferschiefer). Framboidal pyrite, euhedral pyrite overgrowths (both with high Au content), disseminated euhedral and anhedral pyrite (without overgrowth), anhedral chalcopyrite, galena and sphalerite were recorded by detailed microscopy, EPMA and whole rock geochemical analyses. There is a slightly enriched total metal content of 100-200 ppm in the mineralized sediments compared to the unmineralized ones. The minerals formed under reducing, anoxic, marine sedimentary conditions, in several steps; during synsedimentary, early diagenetic and epigenetic processes. The characteristics confirmed by the research are typical of the weakly mineralized Kupferschiefer type.