Discriminating ore fertile and barren granites using zircon Ce and Eu anomalies – Perspective from late Mesozoic (Yanshanian) granites in South China

Abstract

Redox conditions are widely considered to be important to magma fertility, and have been estimated using different proxies, notably the biotite Fe3+/Fe2+ ratios and zircon Ce and Eu anomalies. In this research, we compiled a large number of zircon REE data from both the fertile (Cu–(Au)–Mo, Cu–Pb–Zn, W–Sn, W and Sn) and barren Yanshanian (Jurassic-Cretaceous) granites from South China to test whether zircon REE compositional differences can differentiate various deposit types and discriminate fertile intrusions from barren ones. We propose a modified method to calculate Ce anomalies (CeN/CeN*, chondrite-normalized) using all MREEs and HREEs (except Eu) to calculate CeN*. The zircon Ce anomalies calculated by this method, together with the Eu anomalies (EuN/EuN*) of the Yanshanian granites suggest that those related to Cu–(Au)–Mo mineralization have the highest oxygen fugacity (fO2) (proxied by CeN/CeN* and EuN/EuN*), followed by those related to Cu–Pb–Zn mineralization, and finally by those related to W–Sn, W and Sn mineralization. Furthermore, within a particular Cu–(Au)–Mo mineral district, the ore-related granites have higher fO2 (CeN/CeN*) than the barren ones. Besides, although reducing magmas generally favor Sn mineralization, some of the most-reduced granites in the Sn mineral districts are actually barren, which indicates that an extreme drop of fO2 could inhibit Sn mineralization.