Geochemical indicators of the genesis of the Panimba gold deposit at the Yenisei Ridge (Siberia, Russia)

The paper provides the data of study of rare and trace elements as well as precious metals distribution in sulfides and gold of the Panimba deposit (Yenisei Ridge). Our previous studies show that vein quartz of the deposit was formed by Mg-Na-Cl-containing watercarbon dioxide-hydrocarbon fluids with the salinity of 8-23 wt. % NaCl-eq., in the range of temperatures and pressures of 180-410°С, 0.2-3.3 kbar, respectively. The temperatures of sulfide formation fall within the range: arsenopyrite 300-460°С, pyrrhotite 258-359°С; and the peak temperatures of the carbonaceous substance formation in quartz (248-587°С) and slate (201-610°С) are insignificantly higher. Based on the dating performed the absolute age of quartz vein-veinlet gold-sulfide-disseminated mineralization has been determined, which is within 817.2±5.3-744±17 Ma (as per muscovite, Ar-Ar method) and 815.0±37.6-762.3±33.3 Ma (as per zircon from ore slate, U-Pb-method). The mineralogical and geochemical studies show that the studied specimens of arsenopyrite of the deposit are characterized by systematic iron deficit and sulfur over arsenic predominance. Structural disorder is typical for the mineral, expressed in the formation of iron positions with the nearest-neighbor environment, with the predominance of sulfur and arsenic; meanwhile, the share of iron atoms with sulfur predominance is higher, which agrees with the data of the chemical composition. Pyrrhotite of the deposit differs in weak deficiency of iron. Pyrite is extremely stoichiometric, which is confirmed by the Moessbauer data indicating that 98 % of iron atoms are in the environment corresponding to the mineral. Native gold of the deposit is high-carat (902-908 ‰) and has significant silver impurities only. Arsenopyrites of the deposit are saturated with microinclusions foremost (ore and rock-forming minerals as well as minerals-carriers of rare and trace elements). There are significantly less microinclusions in pyrite and pyrrhotite, and they are absent in native gold. The distribution of trace elements demonstrates the similarity of compositions for the groups of minerals: arsenopyrite, pyrite and pyrrhotite, gold. Arsenopyrite is characterized by more similar microelement composition in relation to hoisting rocks. Native gold and arsenopyrite are similar in the distribution of Sb, W and Sn. Arsenopyrite and iron sulfides have similar trends of nickel, cobalt and antimony distribution. All studied minerals are characterized by elevated antimony grades. The data on the study of rare elements distribution received allows assuming the integrated source of the ore substance. REE patterns indicate the inheritance of the composition of hoisting rocks, the metamorphogenic nature of the fluid and presence of a deep source. The isotopy of sulfide sulfur speaks to the mineralization relation to granite intrusions and involvement of sedimentary sulfur in the process. The presence of highly mineralized fluids in secondary inclusions of quartz of the deposit speaks to the mineralization relation to granitoid magmatism, too. Ore-bearing fluids of medium and low temperatures were characterized by strong reduction nature, which is confirmed by the presence of positive cerium anomalies and negative europium anomalies; the Th/U>1 value, the alkane to alkene ratio in sulfides and quartz of the deposit (over one) and the predominance of chloride complexes. The gold-silver ratio in sulfides (0.18-0.72) and native gold (9.18-9.82) indicates the possibility of detection in the ores of silver and gold sulfides (for example acanthite, yutenbogaardtite, etc.). The data received testifies to the correlation of grades of rare and trace elements with the number of microinclusions in arsenopyrite, which shall be taken into account during such studies.

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