Ore-controlling structure and deep prospecting of the Bayan Obo large-sized REE-Nb-Fe ore deposit, Inner Mongolia

Analysis on folds and faults of the Bayan Obo REE-Nb-Fe orefield indicates that its structural activities witnessed multi-stage evolution.There exist at least four periods of structural activities from Mesoproterozoic to Hercynian which control metallogenesis and diagenesis, including the nearly EW-trending litho-controlling fault (F1), the nearly EW-trending strike-slip fault (F2), the nearly EW-trending ductile shear zone and folds and the left lateral strike slip normal fault (F3).Based on a comprehensive analysis it is concluded that: a.The nearly EW-trending fault (F1) distributed along the boundary between dolomite carbonatite and hangingwall or footwall controls the intrusive occurrence and the formation of ore bodies; b.After the emplacement of dolomite carbonatite, the ore body was destroyed by the nearly EW-trending strike-slip faults (F2) for the first time.As a result, the deep ore bodies in the south of the Main and East mines moved from west to east, and the deep orebody encountered by borehole WK14-01 should be caused by the translation of deep orebody in the south of the Main mine; c.The post-ore NS-trending compression destroyed ore body for the second time and brought about tight folding of the Bayan Obo Group strata and lensing of ore body; d.The left lateral strike slip normal fault (F3) distributed between the main mine and east mine destroyed ore bodies for the third time and led to the dislocation of the Main mine and East mine.The above research results and understanding will be of great guiding significance to the prospecting in the deep and periphery of the mine.