The Złoty Stok deposit in Sudetes (European Variscides, SW Poland): Sources of Fe, As, Au and W, and the role of organic matter in the formation of nephrite and metallic mineralization

• The Złoty Stok deposit hosts dolomite-related nephrite, and Fe, As, Au and W. • Marbles were transformed into skarns and nephrite under three fluid influx events. • Fluids source was the Kłodzko-Złoty Stok pluton, and not Jawornik granitoids. • An involvement of (ultra)mafic veins in fluids formation caused enrichment in Fe. • Calcite δ 13 C values (−16.0 ‰ to −9.1 ‰) link a nephrite formation with organic matter. The Złoty Stok deposit in Central Sudetes hosts nephrite, Fe-As-Au-mineralization and minor W-mineralization. Dolomite-related origin of nephrite is evidenced by low Cr (<14 ppm), Ni (0.4–39.3 ppm) and Co (9.2–71.0 ppm) contents, although the nephrite is unusually rich in Fe 2 O 3 (4.19–14.93 wt%) likely due to an involvement of mafic/ultramafic intrusions in fluids formation. Two subduction-related, coeval, syn- to late-tectonic intrusions suites are adjacent to the deposit, but, of them, only the Kłodzko-Złoty Stok pluton was involved in the fluids formation, whereas Jawornik granitoids were uninvolved. A broad span of nephrite F/Cl (55.6–202.3), δD (−95 ‰ to −68 ‰), δ 18 O (δ 18 O tremolite + 3.6 ‰ to +10.9 ‰, δ 18 O calcite + 7.0 ‰ to +20.4 ‰) and δ 37 Cl (−0.4 ‰ to +0.6 ‰) values, reflect a transformation of marbles into skarns and nephrite under three fluid influx events: 1) tremolite, diopside and arsenopyrite precipitation from fluids derived from granitoids of the Kłodzko-Złoty Stok pluton (ca. 340 Ma), 2) Fe-enriched tremolite and diopside, talc and löllingite precipitation from fluids, related with clinopyroxenites, gabbros, monzonites, lamprophyres and syenites, of the Kłodzko-Złoty Stok pluton (ca. 340 Ma), 3) quartz, calcite and clinozoisite veins formation and precipitation of scheelite, talc and minor tremolite, diopside and arsenopyrite, under the influence of fluids from post-tectonic granitoids of the Kłodzko-Złoty Stok pluton (∼305 Ma). Nephrite and Fe-As-Au-mineralization preferentially precipitates from hydrothermal fluids when they reach an organic matter-rich horizon in marbles, as evidenced by highly negative δ 13 C values (−16.0 ‰ to −9.1 ‰) of calcite from nephrites and skarn, suggesting a crucial role of organic matter in the formation of dolomite-related nephrite deposits.