Ore-forming fluids ultimately precipitate Fe-bearing sulfides and oxides in hydrothermal ore deposits and the Fe isotopic composition of these minerals can trace magmatic-hydrothermal evolution. Here, we report on the Fe isotopic compositions of a suite of hydrothermal minerals (magnetite, pyrite, and chalcopyrite) and granodiorite porphyry from the giant Duolong porphyry Cu-Au deposit (Bolong and Duobuza section), central Tibet. Most magnetite grains with potassic alteration show only minor delta Fe-57 variation (0.38 +/- 0.07 parts per thousand to 0.52 +/- 0.04 parts per thousand in Bolong and 0.68 +/- 0.02 parts per thousand to 0.77 +/- 0.08 parts per thousand in Duobuza), consistent with the equilibrium fluid delta Fe-57 (similar to-0.3 parts per thousand and similar to-0.1 parts per thousand, respectively) at similar to 550-480 degrees C. The equilibrium fluids have lighter Fe isotope signatures than the Duolong granodiorite porphyry (delta Fe-57 = 0.03 +/- 0.06 parts per thousand to 0.07 +/- 0.02 parts per thousand), corroborating the hypothesis that exsolved fluids should have a lighter Fe isotopic composition relative to parental magmas. Chalcopyrite from the mineralized Bolong and Duobuza porphyries have relatively consistent delta Fe-57 values of -0.60 +/- 0.07 parts per thousand to -0.42 +/- 0.07 parts per thousand and -0.40 +/- 0.08 parts per thousand to -0.30 +/- 0.05 parts per thousand, respectively, with equilibrium fluids at similar to 450-350 degrees C having lighter delta Fe-57 values of similar to-0.7 parts per thousand and similar to-0.6 parts per thousand. The trend of decreasing delta Fe-57 values in evolved fluids likely reflects Rayleigh fractionation of magnetite enriched in heavy Fe isotopes. This supposition is supported by the lighter delta Fe-57 value (0.25 +/- 0.07 parts per thousand) recorded in magnetite that equilibrated with a lighter delta Fe-57 fluid (similar to-0.5 parts per thousand) at similar to 470 degrees C. Compared to chalcopyrite, pyrite from the Bolong and Duobuza sections have heavier delta Fe-57 values of 0.35 +/- 0.06 parts per thousand to 0.71 +/- 0.06 parts per thousand and 0.53 +/- 0.06 parts per thousand to 0.71 +/- 0.07 parts per thousand, respectively. The pyrite values correlate variably with the Fe isotopic composition of ore-forming fluids (delta Fe-57 -0.6 parts per thousand to -0.7 parts per thousand), likely due to variations in the degree of Fe isotope exchange between pyrite and fluid. Moreover, combined with previously published Fe isotopic compositions of hydrothermal minerals from oxidized and reduced ore deposits, the results show that chalcopyrite in oxidized hydrothermal deposits always has a lighter Fe isotopic composition than chalcopyrite from reduced hydrothermal deposits. This is likely controlled by melt composition and precipitation of magnetite/pyrrhotite-bearing mineral assemblages. Therefore, the Fe isotopic composition of chalcopyrite could be a useful diagnostic tool for distinguishing oxidized from reduced fluids in hydrothermal systems. (C) 2018 Elsevier Ltd. All rights reserved.