Rapid ore classification for real-time mineral processing optimisation at the Niederschlag multi-generation hydrothermal barite-fluorite vein deposit, Germany

Abstract

Fluorite is currently viewed as a critical raw material (CRM) by the European Commission (2017) as it is the main source of fluorine which is vital as a flux for metal ore smelting and the manufacture of hydrofluoric acid. In addition, it also contributes to the manufacture of fluorine-containing chemicals and their products. Due to supply risks and increasing industrial demand, investment in exploration and mining of European fluorite deposits has been encouraged to support European markets. The opening of the Niederschlag fluorite mine in the Erzgebirge, Germany, by Erzgebirgische Flussund Schwerspatwerke GmbH (EFS) in 2013, is a positive outcome of this initiative. EFS produces a fine-grained acid grade concentrate containing greater than 97% CaF2. The Niederschlag barite-fluorite mineralisation is a complex, multi-generation (Permian and Mesozoic) veintype deposit which has been modified by multiple synand post-genetic shearing and in the Paleogene-Neogene, local hydrothermal alteration and replacements caused by the emplacement of phonolite dykes and sills (Kuschka et al. 2002; Haschke et al. 2021). Each generation has its specific mineral paragenesis with distinctive mineral abundances and diversity, grain shapes and sizes and micro-scale mineral intergrowths. The combination of these complex features has greatly complicated the design and operation of mineral processing operations at the mine. The major aim of this study was to establish criteria for the rapid ‘real-time’ identification of the main vein generation in the ore to allow crucial adjustments and refinements to be made to the processing flowsheet, to achieve the best possible quality of fluorite concentrate. In addition, the trace element compositions of fluorite from the main generations were determined by laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) to confirm that they are genetically different, i.e. formed during separate phases of hydrothermal alteration and mineralisation. This information could also be used to further develop the deposit model for Niederschlag to aid in exploration for near-mine extensions or similar deposits in the area or worldwide. The study does not aim to provide insights into methodologies for fluorite processing.