Coupling whole-rock geochemistry with trace elements and S-isotope analyses of pyrite to unravel distinct precipitation processes responsible for the Yaouré gold deposit formation (Côte d’Ivoire, West Africa)
摘要
Two distinct gold mineralization events were recognized from the structural evolution of the Yaouré deposit in central Côte d’Ivoire: The first gold-forming process was associated with fault-fill laminated veins (V1) within strike-slip faults, whereas the second mineralizing pulse was associated with fault-fill and tension veins (V2) within a shallow-dipping, reverse fault network. Whole-rock geochemical data coupled with in situ trace-element and isotopic studies on pyrite grains support the distinction of V1 and V2 hydrothermal events first established from structural constraints and crosscutting relationships. The same methodology is applied to another set of hydrothermal veins that are genetically related to the V2 veins from Yaouré based on structural criteria, occurring within the same host rocks, but 6 km east of the deposit at a locality named the Kossou Dam, whereby no fault or other structural permeability is noted. A comparison of δ34S values and trace element contents in pyrite from V1 and V2 events at Yaouré with that from the Kossou Dam systems, suggests variations in fO2 controlled gold precipitation during V1 formation, whereas cyclic fluid pressure fluctuations represented the preeminent factor in gold precipitation during the subsequent V2 episode. This work presents the importance of integrating structural and geochemical analyses across scales, with a particular focus on in situ trace element and δ34S analyses on sulfides cogenetic with gold mineralization, to increase confidence in delineating processes at play for gold precipitation in structurally complex environments.