Evolution of ore-forming fluids in a post-collisional porphyry Cu-Au system: A case study from the Bučim deposit, Republic of North Macedonia

•The Bučim deposit represents a post-collisional porphyry Cu-Au system.•Oxidation of Fe2 + to Fe3 + in the potassic alteration zone promoted sulphate reduction.•The barren phyllic alteration zone records infiltration of hot and saline magmatic fluids.•The chlorite alteration zone reflects a lithostatic/hydrostatic transition.•The barren argillic alteration zone records incursion of a cold and diluted meteoric fluid.