The control of natures and processes of mantle on the ophiolite-type chromite mineralization

The ophiolite-type chromitite deposit represents the major direction for making breakthrough of the Cr deposit exploration in China, as China’s dependence on foreign Cr sources reached as high as 99%. However, within the ophiolites in the same orogenic system, the observed mineralization scale of ophiolite-type chromitite deposits in China is always at least 1-2 orders less than those in foreign countries. Whether this phenomena is caused by the insufficient natural endowment of chromitites in Chinese ophiolites (primarily no ores as congenital deficiency) or by the unclear understanding of the structures and compositions of Chinese ophiolites with metallogeneic potential of chromitite (with ore deposits, but not found) is a big challenge for geoscientific researchers. The issues including the natures and processes of mantle sources for chromitites, the distributions of mantle melt channel’s interface, and their spatiotemporal relationships with the enrichment and mineralization of chromitites are crucial questions to be urgently solved. In this paper, through the clarification of research progresses of ophiolites that recorded the mantle material origins, mantle melt channel systems, and crust-mantle and intra-mantle lithological interfaces, and by providing two case study examples with one from the Luobusa ophiolite in Xizang (hosting high Cr-type chromitite) and the other one from the Hegenshan ophiolite in Inner Mongolia (hosting high Al-type chromitite), it is revealed that the mantle melt extraction and migration channel system beneath the oceanic spreading centers actually controlled the “source-transport-sink” mineralization system for the ophiolite-type chromitite deposits. It is also found that the chromite enrichment and mineralization in proper locations of lithosphere are resulted from the “melt-channel-interface controlled mineralization”, which was co-operated by the “mantle source contributions” “melt extraction and migration” and “the chromite enrichment triggered by the melt-channel interfaces”.