Abstract
Semi-airborne transient electromagnetic (S-ATEM) method is a hybrid method which employs a grounded electrical or a loop source and an airborne receiver. It has greater investigation depth compared to the airborne electromagnetic method due to its higher transmitting power and more flexibility and efficiency compared to ground electromagnetic method due to its airborne receiving equipment. A new S-ATEM system based on unmanned helicopter is introduced. Besides some information on the technical specifications of the S-ATEM system and data processing technique, a case study of the investigation of Changyi banded iron formation deposit is illustrated. Within the survey area, the ground magnetic method has found a clear magnetic anomaly, whose location has a good correspondence with a ore-body. In order to investigate the underground electrical characteristics and reveal the relationship of ore-body location, subsurface magnetic field anomaly and underground resistivity distribution, a S-ATEM investigation was conducted in January 2016. During the survey, underground resistivity distribution from ground level to a depth of 400 was reconstructed and it was inferred that a strong gran- ite intrusion in the middle of the survey area influenced the ore-body burial depth and magnetic distribution. Although the effect of in- trusion on magnetic field is not as significant as that of the ore-body, the intrusion uplifted and deformed the ore-bearing strata, reducing the burial depth and changing the tilt angle, which indirectly affect the magnetic field distribution of the survey area.
Highlights
Electromagnetic (EM) method was considered as an important technique for geophysical exploration
Transient EM method is characterised by a limited investigation depth in low resistivity coverage area and it is seriously affected by EM noise due to the transmitting power limitation
We describe the characteristics of the regional geology, banded iron formation (BIF) deposit, lithology, and magnetic field in the survey area
Summary
Electromagnetic (EM) method was considered as an important technique for geophysical exploration. Ground EM method is widely used to achieve underground resistivity investigation it is not suitable for low resistivity coverage, strong EM noise, and unreachable regions exploration both in frequency and time domain [Nabighian et al, 2005; Zhdanov et al, 2010]. Semi-airborne transient EM (S-ATEM) is a hybrid method which employs a grounded electrical source or a fixed-loop source for large transmitting power and an airborne receiving for flexibility and efficiency. It was further developed by Elliott [1996] and Mogi et al [1998] with fixed-loop source and grounded electrical source, respectively. We delineate the geoelectrical structure and ore-body distribution of the survey area by combining the S-ATEM result with prior geo-information
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