Evaluating Sn mineralization potential at the Haobugao skarn Zn–Pb deposit (NE China) using whole-rock and zircon geochemistry

Abstract

The metal association in a skarn deposit is largely controlled by the magma redox state and fractionation degree. The Haobugao skarn deposit in northeastern China contains significant Zn–Pb sulfides, with subordinate by-products Cu and Fe ores. Recent explorations also found minor cassiterite occurring locally in the deposit, inspiring the speculation of Sn mineralization. To better evaluate the Sn mineralization potential at Haobugao, the geochemical compositions of the ore-related biotite granite porphyry and its magmatic zircons have been investigated to quantify the oxidation state and the degree of magmatic evolution, which provide constraints on the capability of the Haobugao intrusion to produce economic Sn mineralization.The causative biotite granite porphyry (~140 Ma) of the Haobugao skarn is a typical I-type granite that belongs to high-K calc-alkaline series. It contains 68.88–72.27 wt% SiO2 and 0.52–1.38 wt% MgO, and has a Rb/Sr ratio range of 0.82–2.07 and a Nb/Ta ratio range of 8.69–22.49, indicating that it is moderately fractionated. The zircon Ce and Eu anomalies have been used as proxies for magma redox state, and the results (CeN/CeN* = 36–213, EuN/EuN* = 0.17–0.52) suggest that the ore-forming magmas are relatively oxidized, with an estimated ΔFMQ range of −0.4 to +3.5 (+1.0 in average). This is also consistent with the high whole-rock Fe2O3/(FeO + Fe2O3) mass ratios (0.54–0.76) and the occurrence of abundant ferric garnet in the skarn (i.e., andradite). These results collectively show that the ore-related granitic intrusion at Haobugao is generally more oxidized but less evolved when compared with other intrusions responsible for typical skarn Sn mineralization worldwide. Therefore, it is unlikely for the Haobugao intrusion to produce Sn mineralization of economic significance. The present study demonstrates that the whole-rock and zircon geochemistry data are useful in evaluating the mineralization potential of metals like Sn in a given mineral deposit or prospect, which may help guide exploration.