The Chronological Characteristics and Geological Significance of Calcite in the Xiong’er Mountains Kangshan Gold Mine in Western Henan Province

The Kangshan gold deposit in the Xiong’er Mountains of western Henan represents a typical gold deposit along the southern margin of the North China Craton. During mining operations in recent years, a series of calcite veins have been discovered within certain fault zones. These veins intersect and interweave with the main ore bodies formed during the primary mineralisation phase, exhibiting distinct differences from the carbonate veins developed during the late stage of primary mineralisation. Although the genesis, tectonic control characteristics, and enrichment mechanisms of the gold deposit have been extensively studied, the relationship of the calcite veins with the mineralisation process or their potential as indicators of mineralisation remain unclear. Therefore, this study investigates the fluid characteristics and formation age of the calcite veins in the Kangshan gold deposit through fluid inclusion thermometry and Laser in-situ U-Pb isotope dating of calcite. Laser in-situ U-Pb isotope dating of the calcite veins yields ages ranging from 46.3 to 45.4 Ma, confirming them as products of Cenozoic hydrothermal activity. Quartz inclusions from the primary mineralisation phase exhibit homogenization temperatures of 181.6-345.0°C and salinities of 3.55-15.67% NaCl eqv, indicating low-to-medium temperature and medium-salinity fluids. Therefore, the Kangshan deposit is a low-to-medium temperature hydrothermal gold deposit. The homogenization temperatures of calcite inclusions from the secondary mineralisation phase range from 152.4 to 223.6°C, with salinities of 1.57-9.86% NaCl eqv, indicating low-temperature, low-salinity fluids. From the geological features and mineralisation ages, the Kangshan gold deposit can be ascertained to have experienced superimposed multi-phase hydrothermal activity. Following Yanshanian mineralisation, the deposit was influenced by Cenozoic hydrothermal events. Nevertheless, the Cenozoic hydrothermal activity was relatively weak. While it may have locally enriched mineralisation, it should not be considered a primary exploration target for regional gold deposits because of its limited scale.