| The Carlin-type gold deposits in the Youjiang Basin are characterized by extensive decarbonation and recarbonation of the host rocks. The multi-stage calcite veins commonly developed in the deposits are direct evidence of decarbonation and recarbonation. The Getang gold deposit, one of the most representative Carlin-type gold deposits in the Youjiang Basin (with a gold reserve of up to 30 t), has two stages of hydrothermal calcite veins (Cal-Ⅰ during the mineralization period and Cal-Ⅱ in the late mineralization period). This study conducted in-situ micro-area chemical composition and single mineral C-O-Sr isotope analysis on the two stages of calcite veins to reveal the evolution process of the ore-forming fluid and the mechanism of gold enrichment. The results of calcite composition analysis show that Cal-Ⅰ has a relatively high Mn content, while the Fe, Y and rare earth element (REE) contents of Cal-Ⅱ are significantly higher than those of Cal-Ⅰ. The REE distribution patterns of both stages of calcite indicate Eu negative anomalies due to their formation in a low-temperature environment (<250℃). The Ce anomaly changes from mostly weak negative in Cal-Ⅰ to generally negative in Cal-Ⅱ, directly indicating a shift from a weakly oxidizing to a strongly oxidizing environment. Compared with Cal-Ⅱ, the enrichment of middle rare earth elements (MREE) in Cal-Ⅰ is attributed to acidic hydrothermal fluids. The C-O-Sr isotopic composition of Cal-Ⅰ (δ13CV-PDB：-1.55‰~+0.09‰；δ18OV-SMOW：+6.71‰~+11.53‰；87Sr/86Sr：0.707865~0.707981) is close to that of acidic granites, suggesting a close genetic relationship between the formation of calcite during the mineralization period and the acidic magmatic fluids. The upwelling of acidic magmatic fluids and their reaction with the host rocks led to decarbonation, increasing the secondary porosity of the rocks and allowing Ca2+, Fe2+ and other ions to enter the fluids, where they combined with HCO3- and Au(HS)2-carried by the fluids, eventually precipitating along fractures to form gold-bearing pyrite and Cal-Ⅰ calcite veins. The isotopic composition of Cal-Ⅱ (δ13CV-PDB -2.86‰~+1.42‰；δ18OV-SMOW：+5.18‰~+24.09‰；87Sr/86Sr：0.708970~0.709601) indicates that the fluids of this stage were also acidic magmatic fluids, but to varying degrees mixed with signals from marine carbonate rocks. During the infiltration of atmospheric precipitation, the carbonate rocks in the host rocks were continuously leached, carrying HCO3- from the strata into the late-stage hydrothermal fluids, resulting in a decrease in fluid temperature and an increase in oxidation, eventually crystallizing to form Cal-Ⅱ calcite veins. Calcite in this stage usually does not participate in gold enrichment, and its appearance marks the end of the entire mineralization process. Therefore, the calcite formed during the mineralization period with characteristics of MREE enrichment, high Mn content, weak negative Ce anomaly and acidic hydrothermal fluid isotopic signals in Carlin-type gold deposits can be used as an important indicator for regional exploration of Carlin-type gold deposits. |