A comprehensive comparative study of geological characteristics as well as aeromagnetic and aeroradiometric features of the Bayan Obo REE-Nb-Fe depoits and their implications for prospecting work

Through analyzing the aeromagnetic and aeroradiometric results obtained in the Bayan Obo REE-Nb-Fe deposit in combination with the comprehensive comparative study of its geological characteristics, the authors found that the Bayan Obo REENb-Fe ore deposit has unique and typical aeromagnetic and aeroradiometric characteristics. The aeromagnetic anomaly characteristics show that the ore deposit is characterized by a high-intensity banded and nearly EW positive magnetic anomaly associated with a parallel positive anomaly, which is the reflection of the contact between strong magnetic orebodies and poor magnetic wall rocks. The aeromagnetic ΔT_max value is over 5000 nT, and the ΔTmin value is about -2000 nT. There are over 30 survey lines which indicate obvious positive-negative magnetic anomaly development and show that the superimposed anomaly characteristics are the reflection of magnetic rocks of varying ages and intensities. It indicates that the ore deposit has experienced superposition and transformation activities of tectonic thermal events of varying ages. The scale of ore deposit decreases gradually with the increasing depth of downward extension, but it still shows obvious positive magnetic characteristics while aeromagnetic ΔT contour exhibits upward continuation to 3000 m, which indicates that the ore deposit has obvious mineralization in the depth. In addition, the aeroradiometric characteristics of the Bayan Obo ore deposit show marked high value halos of total counting rate and potassium and uranium and thorium elements, and they all show nearly EW banded distribution. The mining area is located in the high value zone, with values between 3000 and 15381 cps and partially in lumpy form, and the range of the high value zone exceeds the range of the mining area. The potassium content is high with values between 2.0% and 2.8%, and partially even reaching 2.8%-12% in the ore deposit and adjacent areas. The thorium values are in the range of 26×10^-6-223×10^-6, and the range of thorium high value zone is larger than the range of the second intrusive carbonatite that hosted the ore deposit in the middle Caledonian. The uranium values are generally in excess of 1.6×10^-6, with higher values between 2.8×10^-6 and 9.1×10^-6 in the ore deposit and adjacent areas. Through the comprehensive analysis, it is proved that the aeromagnetic and aeroradiometric characteristics are of highly consistent with ore deposit information. The aeromagnetic positive anomalies information can be used as favorable information to look for the iron-bearing polymetallic deposits, and the radioactive elements mainly including potassium, uranium and thorium with high values can be used as favorable information to look for rare earths ore. This understanding is of great guiding significance for the further prospecting work.