Geochemistry of rhodonite in the Luziyuan Pb − Zn skarn deposit, Southwestern China

The Luziyuan skarn deposit is the second largest Pb − Zn deposit in the Baoshan block, Yunnan Province, Southwestern China. Rhodonite is a widespread skarn mineral in the host rock, occurring as coarse-grained crystals and veins, and is closely associated with Pb − Zn mineralization. In-situ elemental analysis of rhodonite from three levels (1220 m, 1265 m and 1495 m above sea level) by laser ablation-inductively coupled plasma-mass spectrometry and Sm − Nd isotopic dating of the rhodonite − calcite pair were conducted to constrain the compositions and the timing of Pb − Zn mineralization. The new Sm − Nd isotopic data reveal that the Luziyuan deposit formed during the Early Jurassic (183 ± 2.3 Ma; MSWD = 0.72). These chronological constraints, combined with regional tectonic evolution, suggest that the Luziyuan Pb − Zn mineralization is genetically linked to eastward subduction of the Shan Boundary Ocean beneath the Baoshan block during the Meso-Tethys period. Furthermore, all examined rhodonite samples contain relatively high concentrations of MnO (34.7 − 43.0 wt%) and Zn (536 − 2117 ppm), but generally low contents of FeO (1.07 − 6.08 wt%), Cu, Co, Ni, Ga, Mo, Sn, W and Pb. A positive correlation between Zn and MnO contents among different skarn deposits and nearly chondritic Y/Ho ratio (~ 28) in the Luziyuan rhodonite suggests that this mineral formed from magmatic fluids and its Zn enrichment was controlled by the fluid chemistry. The same data also suggest that Zn-rich rhodonite in skarns may be used as an indicator mineral for Zn exploration when combined with other geological, geophysical, and geochemical criteria.