The Bayan Obo large REE-Nb-Fe deposit in Inner Mongolia has been exploited for nearly 70 years.The shallow iron ore resources have been exhausted,so it is urgent to find deep resources.Using electromagnetic methods to find out the connection state and occurrence characteristics of deep orebodies in the main mine and the east mine is of great significance for further understanding the metallogenic model of the Bayan Obo deposit and searching for deep resources.However,the structure,strata,lithology and topography of this area are relatively complex,which brings great challenges to electromagnetic exploration.The analysis of the key observation elements by means of numerical modeling and simulation is helpful for exploration design and data interpretation.Based on the existing geological and borehole data,the three-dimensional(3D)geoelectric model of the main and east mine and their junction area in Bayan Obo deposit is constructed,and then the 3D numerical simulation of the grounded-wire source short-offset transient electromagnetic method(SOTEM)is carried out by using the time-domain edge-based finite element algorithm.The influence of pit topography on observation data and the 3D electromagnetic response characteristics and detection ability of deep orebody under different transmitter-receiver devices are analyzed.The results indicate that the mine pit can lead to an increase in the response value of the SOTEM electromagnetic field.Placing a source on the west side of the main mine is more conducive to achieving effective detection of the orebody below the connection area.This work can provide a basis for the optimization of acquisition parameters and data interpretation in the field observation in the future.
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