Magmatic transition in the Ningwu iron oxide-apatite (IOA) ore district, eastern China: Implications for ore fertility of magmas

Iron oxide-apatite (IOA) deposit is an important source of Fe ores, characterized by a huge amount of Fe oxide ores associated with byproducts of considerable critical mineral resources. The Ningwu ore district is a well-defined IOA ore district in eastern China, containing more than 30 IOA deposits. Four volcanic cycles occurred over approximately 10 Ma (134–126 Ma), forming two types of primary intrusive rocks (i.e., diorite porphyry and granitic rocks). The IOA deposit is typically associated with the diorite porphyry that was intruded at the end of the second volcanic cycle. In this study, the trace element abundances of zircon grains from syn-mineralization intrusive rocks and post-mineralization intrusions are distinguishable and record magmatic transitions during multistage volcanic activity. The zircon trace element abundances imply that the syn-mineralization magmas had greater oxygen fugacity (ΔFMQ > +0.5), higher water content (Eu/Eu* > 0.35, Dy/Yb < 0.21), elevated magma evolution (Zr/Hf < 50), and a high proportion of enriched mantle magma sources that are related to oceanic subduction, which significantly differed from those of the post-mineralization intrusions, reflecting a magmatic transition during multistage volcanic activity. They could also be valuable tools for identifying potential fertile magmas of IOA deposits.