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<p>This study investigates the occurrence and distribution of invisible gold in arsenian pyrite from two contrasting mineral systems: the Western Mecsek uranium deposit (Hungary) and the Bakyrchik Au deposit (Kazakhstan). The comparison highlights how pyrite evolution influences Au fixation under different geochemical conditions: organic-rich sedimentary diagenesis versus high-temperature hydrothermal mineralization. Eleven samples were analyzed for arsenian pyrite morphologies, As contents, and Au concentrations using XRPD, WD-XRF, and EMPA-EDS-BSE for mineralogy and elemental composition, aqua regia digestion with ICP-OES for extractable elements, and LA-ICP-MS on pyrite grains. The results show distinct pyrite forms and geochemical signatures. W-Mecsek pyrite is predominantly framboidal, cement, and euhedral, formed under low-temperature conditions (~ 144&#xa0;°C), with pyrite grains containing up to 4.3&#xa0;wt% As and 0.46&#xa0;ppm Au and extractable Au up to 0.63&#xa0;ppm, whereas Bakyrchik pyrite is framboidal, hexahedral, and cubic/euhedral, formed at higher temperatures (~ 340&#xa0;°C), with pyrite grains containing up to 12.5&#xa0;wt% As and 0.52&#xa0;ppm Au, extractable Au up to 4.13&#xa0;ppm, and often associated with arsenopyrite. Au occurs both as structurally bound invisible gold within pyrite grains and as readily extractable gold in the two studied deposits. Invisible gold occurs primarily within arsenian pyrite, with early framboidal growth linked to bacterial sulfate reduction and initial Au adsorption, while later recrystallization and hydrothermal overprinting enhance Au incorporation. Mineralogical controls differ between deposits, with organic matter and low-temperature diagenesis dominant in W-Mecsek, and As-rich fluids and high-temperature hydrothermal activity critical in Bakyrchik. These findings provide new insights into invisible gold distribution and guide exploration in similar deposits.</p>

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Geochemical controls on invisible gold fixation in arsenian pyrite: Evidence from the Western Mecsek and Bakyrchik deposits

  • 期刊论文

  • 发表日期：

    2026年3月13日

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  • Medet Junussov,
  • Maxat K. Kembayev,
  • Akmaral Baisalova,
  • Manshuk Kokkuzova,
  • Yerkhozha Mamanov,
  • Gulnur Mekenbek,
  • Salima Cherkeshova

摘要

This study investigates the occurrence and distribution of invisible gold in arsenian pyrite from two contrasting mineral systems: the Western Mecsek uranium deposit (Hungary) and the Bakyrchik Au deposit (Kazakhstan). The comparison highlights how pyrite evolution influences Au fixation under different geochemical conditions: organic-rich sedimentary diagenesis versus high-temperature hydrothermal mineralization. Eleven samples were analyzed for arsenian pyrite morphologies, As contents, and Au concentrations using XRPD, WD-XRF, and EMPA-EDS-BSE for mineralogy and elemental composition, aqua regia digestion with ICP-OES for extractable elements, and LA-ICP-MS on pyrite grains. The results show distinct pyrite forms and geochemical signatures. W-Mecsek pyrite is predominantly framboidal, cement, and euhedral, formed under low-temperature conditions (~ 144 °C), with pyrite grains containing up to 4.3 wt% As and 0.46 ppm Au and extractable Au up to 0.63 ppm, whereas Bakyrchik pyrite is framboidal, hexahedral, and cubic/euhedral, formed at higher temperatures (~ 340 °C), with pyrite grains containing up to 12.5 wt% As and 0.52 ppm Au, extractable Au up to 4.13 ppm, and often associated with arsenopyrite. Au occurs both as structurally bound invisible gold within pyrite grains and as readily extractable gold in the two studied deposits. Invisible gold occurs primarily within arsenian pyrite, with early framboidal growth linked to bacterial sulfate reduction and initial Au adsorption, while later recrystallization and hydrothermal overprinting enhance Au incorporation. Mineralogical controls differ between deposits, with organic matter and low-temperature diagenesis dominant in W-Mecsek, and As-rich fluids and high-temperature hydrothermal activity critical in Bakyrchik. These findings provide new insights into invisible gold distribution and guide exploration in similar deposits.