Geological settings and metallogenesis of high-grade iron deposits in China

The predominant types of high-grade iron deposits in China include skarn, sedimentary metamorphic (banded iron-formation, BIF-type), continental/submarine volcanic-hosted and magmatic Fe-Ti-V oxide deposits. Based on a comprehensive review of current studies on these deposits, this paper suggests that the oxygen concentration in atmosphere played an important role for the formation of BIFs, whereas the tectonic setting and deep magmatic differentiation processes are more important for the other types. Notably, both high temperature and high pressure experiments and melt inclusion studies indicate that during the differentiation, high temperature magmas could develop iron-rich magma via liquid immiscibility but not pure oxide melt (“iron ore magma”). Fe-P melt could be generated directly by liquid immiscibility under hydrous and oxidized condition. The formation of high-grade iron deposits is mostly associated with the processes related to multiple stages of superimposition, e.g., desiliconization and iron enrichment, removal of impurity, and remobilization and re-precipitation of iron. According to the temporal evolution, the high-grade iron deposit could be divided into multi-episode superimposition type (temporally discontinuous mineralization) and multi-stage superimposition type (temporally continuous mineralization). The former is represented by the sedimentary metamorphic iron deposit, and the latter includes those related to magmatic-hydrothermal fluids (e.g., skarn, volcanic-hosted and magmatic types).