Formation of carbonate-hosted magnesite in the Eastern Alps: Insights from the Hochfilzen mining district (Austria)

Carbonate-hosted sparry magnesite is the most important raw material for the production of magnesia sinter (MgO), which is essential for the refractory industry. In one of the most significant magnesite mining districts of the Eastern Alps near Hochfilzen (Austria), fine-grained magnesite occurs in two settings: (1) as minable deposits in Silurian to Devonian dolostones and (2) in Permian breccias of red beds in the hanging wall. Despite the far-reaching implications of a possible genetic relationship between these groups on both the timing and the mechanism of sparry magnesite formation in the Eastern Alps, there is no comparative analytical data available. To decipher their relationship, we used electron probe microanalysis, laser ablation inductively coupled plasma mass spectrometry, micro-X-ray fluorescence mapping and Raman spectroscopy. Paragenetic parallels, comparable rare earth element patterns, similar trace element contents and enrichment patterns point towards a common mineralizing fluid of the two magnesite groups. Based on our results, we suggest that a Mg-rich, seawater-derived brine descended into the subsurface, migrated through the red beds, magnesitized the Permian breccias, entered the underlying pre-Permian footwall along fault planes and formed the magnesite deposits – the magnesite groups are therefore related by a common fluid. We contextualize this formation model with the Permian-Triassic metallogenetic epoch in the Eastern Alps and argue for a Triassic age of the magnesite.