Integrated U–Pb, Lu–Hf and (U–Th)/He analysis of zircon from the Banxi Sb deposit and its implications for the low-temperature mineralization in South China

Low-temperature Sb (Au–Hg) deposits in South China account for more than 50% of the world’s Sb reserves, however, their genesis remains controversial. Here we report the first study that integrates U–Pb and Lu–Hf analysis by LA-(MC)-ICPMS and conventional (U–Th)/He analysis, all applied to single zircon crystals, in an attempt to constrain the origin and timing of world-class Sb (Au–Hg) deposits in Banxi (South China). Zircon separated from a quartz-stibnite ore and an altered country rock samples revealed similar U–Pb age spectra defining two major populations – Paleoproterozoic (~1900–2500 Ma) and Neoproterozoic (~770 Ma), which are characterized by variable εHf(t) values (–10.7 to 9.1 and –16.5 to 11.2, respectively) and Hf crustal model ages (TDM C) (2.48 to 3.24 Ga and 0.97 to 2.71 Ga, respectively). The U–Pb age and Hf isotopic features of the zircons are consistent with the Banxi Group in the region, indicating that the zircons involved in the low-temperature hydrothermal system were originally from the Banxi Group country rocks. Thirty-three mineralization-related zircon crystals yielded a mean (U–Th)/He age of 123.8
3.8 Ma, which is interpreted to represent the timing of the latest low-temperature mineralization stage of the Banxi Sb deposit. The combined U–Pb, Lu–Hf and (U–Th)/ He data suggest that Precambrian basement rocks were the major contributors to the low-temperature mineralization, and that Early Cretaceous (130–120 Ma) could be the most important ore-forming epoch for the Sb deposits in South China. This study also demonstrates the analytical feasibility of integrated U–Pb - Lu–Hf - (U–Th)/He “triple-dating”, all applied to single zircon crystals. This approach reveals the full evolution of zircon, from its origin of the magmatic source, through its crystallization and low-temperature cooling. Although this study demonstrates the usefulness of this integrated approach in dating low-temperature mineralization, it has great potential for zircon provenance and other studies that may benefit from the large amount of information that can be extracted from single zircon crystals.