Source of ore-forming substances and theoretical problems of metallogeny relevant to the Bayan Obo Fe-REE ore deposits in Inner Mongolia, China

摘要

The source of rare earth elements (REE) ore-forming substances is identified to be extremely distinct from that of iron ores. The Bayan Obo Fe-REE ore deposits were generated by a composite process of both crustal and mantle source mineralization. The original iron bodies are of a sedimentary deposit from supergenesis, while the REE ores have been formed by mantle fluid metasomatism superimposed upon the pre-existing iron bodies. It is believed that the REE ore deposit would be controlled by intracontinental hot spot. The H_8 dolomite in mine regions belongs to normal sedimentary carbonate rock, its C and O isotopic composition rules out the possibility comparable with magmatic carbonatite. The Sm-Nd isochrons of separated REE minerals have shown two REE peak mineralization periods: early-middle Proterozoic (1 700 Ma ±480 Ma) and Caledonia (424- 402Ma).