Role of CO2 in gold mineralization: A case study of the Rongdu gold deposit on the southeastern margin of the North China Craton

• The study reveals that the CO 2 -rich hydrothermal fluids responsible for gold mineralization in the Rongdu deposit originated from magma; • Due to the competitive mechanism between carbonates and pyrites, iron-rich dolomite may affect the gold grade in the ores; • The precipitation of carbonates and gold both attributed to phase separation; therefore, iron-poor dolomite can serve as an indicator for future prospecting. Lode gold deposits constitute one of the most important types of gold ore deposit, typically characterized by medium to low-temperature CO 2 -rich hydrothermal fluids, Consequently, it is commonly accompanied by the precipitation of abundant carbonates. However, research on key role of CO 2 in the transport and precipitation of gold. remains unclear. Here we discuss the genetic relationships between carbonate and gold associated with the Rongdu deposit, which is the largest gold deposit of Wuhe mining district along the south margin of NCC. The C-O isotope compositions of carbonates from different generations. suggest that the CO 2 -rich hydrothermal fluids of the gold deposit were derived from magma. The precipitation of carbonates preceded the formation of high-grade gold ores, possibly as a result of large-scale phase separation. After the formation of ankerite (Ank1), it underwent repeated magmatic hydrothermal fluid replenishment; however, external fluids were not introduced during this process. Simultaneously, the fluctuating anomalous Fe content in the carbonates suggests a competitive relationship for the incorporation of iron between sulfides and carbonates. The formation of carbonates hindered gold precipitation to some extent, but as an indicator of phase separation, it can serve as a prospecting indicator for gold in the area.