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 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 Fe₂O₃ (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 ‰), δ¹⁸O (δ¹⁸O_tremolite +3.6 ‰ to +10.9 ‰, δ¹⁸O_calcite +7.0 ‰ to +20.4 ‰) and δ³⁷Cl (−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 δ¹³C 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.