relationships, three mineralization stages (i.e., pre-ore, ore and supergene) have been identified in the Yangla deposit. The pre-ore stage is dominated by prograde skarn. The ore stage is characterized by the precipitation of hydrous silicate minerals, Fe-oxides, Fe-Cu-Mosulfides, quartz and calcite, whose mineral assemblages were formed in the early and late sub-ore stages. The early sub-ore stage is marked by retrograde alteration with the deposition of hydrous silicate minerals (e.g., actinolite, epidote and chlorite), Fe-oxides, abundant Fe-Cu-Mo-sulfides, quartz and minor calcite. Whilst, the late sub-ore stage, associated with silicic and carbonate alteration, is represented by widespread thick quartz or calcite veins with disseminated pyrite, chalcopyrite, galena and sphalerite. We present new carbon-oxygen (C-O) isotopic compositions of the ore-hosting marble and hydrothermal calcite of this deposit. The hydrothermal calcite in the Yangla deposit was precipitated from both the early and late sub-ore stages. Calcite I from the early sub-ore stage is anhedral, and occurs as spot in the skarn or locally replaces the skarn minerals. Calcite II from the late sub-ore stage is distinguished by being coarse-grained, subhedral to euhedral and its occurrence in thick veins. Calcite I contains lower delta C-13(pDB) (-7.0 parts per thousand to -5.0 parts per thousand) and delta O-18(smow) (7.2 parts per thousand to 12.7 parts per thousand than Calcite II (delta C-13(PDB) = -4.5%0 to-2.3%o; delta O-18(smow) =10.7%0 to 19.4%0). In the delta C-13(PDB) vs. delta O-18(smow) diagram, the Calcite I and Calcite II data fall close to the igneous carbonatite field and between the fields of igneous carbonatite and marine carbonates, respectively. This suggests a dominantly magmatic origin for the early sub-ore fluids, and there might have been increasing carbonate wall rock involvement towards the late sub-ore stage. The ore hosting marble (delta C-13(PDB) = 43 parts per thousand to 0.3 parts per thousand; delta 18O(smow) =10.2 parts per thousand to 23.9 parts per thousand) also shows a positive delta C-13(PDB) vs. delta O-18(smow) correlation, which is interpreted to reflect the decreasing alteration intensity during the interactions between the hydrothermal fluids and ore-hosting carbonates. Simulated calculation suggests that both the Calcite I and Calcite II precipitated at 350 degrees C to 250 degrees C and 250 degrees C to 150 degrees C, respectively. We proposed that CO2 degassing and water/rock interactions were likely the two major processes that precipitated the calcite and led to the observed C-O isotopic features of the Yangla Cu deposit.