Spatial Variations in Mineral Chemistry of the Haobugao Zn-Pb Skarn Deposit, Northeast China

Abstract

Zinc-Pb skarn typically represents the distal, lower-temperature end member of a skarn system, implying that higher-temperature mineralization may exist closer to the intrusion center. Establishing deposit-scale zonation using mineral chemistry is essential for predicting the location of such proximal ores. In this study, garnet, pyroxene, and sphalerite from the Haobugao Zn-Pb skarn deposit in Northeast China reveal clear mineralogical and geochemical zonation from proximal to distal zones. The proximal garnet is more reddish brown and grossular rich (Ad18–98Gr0–74Pyr1–11, where Ad = andradite, Gr = grossularite, and Pyr = pyralspite), associated with diopside-dominated pyroxene (Di70–98, where Di = diopside); the distal garnet is yellowish green with a narrower composition range (Ad73–99Gr0–25Pyr1–11), and pyroxene becomes more Fe rich (Hd31–81, where Hd = hedenbergite). Economic metals shift from Fe and Cu rich to Zn-Pb rich with increasing distance from the intrusion. Vertically, the concentrations of Cu and In in sphalerite decrease upward; laterally, In significantly decreases, whereas Cd slightly increases outward. The generally decreased In highlights its potential as a reliable indicator for localizing hydrothermal centers. Sphalerite δ34S values generally increase from –1.8‰ near the intrusion to +4.4‰ away from it. Considering that the causative biotite granite is relatively oxidized whereas the limestone is organic matter bearing, Haobugao can be classified as an oxidized intrusion-reduced carbonate skarn system. This redox contrast, alongside variations in fluid temperature and composition, likely controlled the observed spatial zonation in mineral chemistry and sulfur isotopes. The well-zoned skarn minerals and sphalerite geochemistry at Haobugao may also apply to other Zn-Pb skarns, providing valuable exploration guidance for targeting new, high-temperature orebodies.