Antiskarn to skarn: Garnet insights into dual carbonatite-related metasomatism at Huayangchuan, NW China

Antiskarn refers to skarn-like assemblages formed by reactions between carbonatite melts and silicate wall rocks and provides critical insights into carbonatite petrogenesis and related mineralization. Here we report calc-silicate assemblages associated with Triassic (229−206 Ma) carbonatite dikes at Huayangchuan, Qinling orogen, central China. Two texturally distinct andradite-rich garnets are distinguished. Fine-grained euhedral garnets yield a U-Pb age (213 ± 5 Ma) coeval with carbonatite emplacement and represent syn-magmatic “antiskarn” reactions between carbonatite melt and silicate wall rocks. Euhedral garnets intergrown with sulfides yield a U-Pb age of 130.0 ± 5.2 Ma, identical to nearby granite (132 ± 1 Ma), and possibly represent a later skarn reaction between granite-derived fluids with solidified carbonatite rocks. Mineral paragenesis in the Triassic assemblages defines three successive stages, reflecting the melt and fluid evolution during carbonatite solidification. These results demonstrate that direct geochronology is essential for distinguishing syn-magmatic antiskarnisation from later hydrothermal modification in carbonatite-related systems.