Geochemical and mineralogical investigation of germanium-rich chalcopyrite veins from the Cu-Ag Kupferschiefer deposit, Poland

• Germanium enrichment is common in epigenetic massive chalcopyrite veins and breccias from the Cu-Ag Kupferschiefer deposit in Poland. • Micro-XRF mapping reveal dendritic and oscillatory-like distribution of germanium in massive chalcopyrite. • Role of overpressured fluids in germanium accumulation in sulphide ores is proposed. The underlying geological processes responsible for germanium enrichment across various mineralization types remain elusive, posing a significant obstacle to the development of a comprehensive genetic models. The investigation of germanium-rich epigenetic sulfide-calcite veins from the Cu-Ag Kupferschiefer deposit in Lubin-Sieroszowice ore district in Poland provides new insights into the mechanisms of germanium concentration in sulfide ores. Petrographic observations at macro- and microscale levels suggest that this mineralization style is consistent with single or multiple brecciation episodes likely related to natural hydraulic fracturing by overpressured fluids. Electron microprobe microanalysis (EPMA), TESCAN Integrated Mineral Analyzer (TIMA), and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) reveal that chalcopyrite, a predominant mineral in the veins, is also the primary host of germanium, containing up to 5 016 mg/kg of Ge. Typical associations include calcite, bornite, sphalerite, galena, and tennantite, with less common occurrences of luzonite, gersdorffite, betekhtinite, and anhydrite. Micro X-ray fluorescence (micro-XRF) mapping of massive chalcopyrite demonstrates that germanium distribution is inhomogeneous exhibiting two distinct spatial distribution patterns: dendrite-like and apparent oscillatory zoning. It is hypothesized that a rapid fluid pressure drop could be an important factor in formation of germanium-enriched sulphide ores.