The Transient Electromagnetic(TEM)method is a critical geophysical technique for subsurface exploration of metal ore bodies,primarily utilizing either loop or grounded transmitters.The Long Offset Transient Electromag...The Transient Electromagnetic(TEM)method is a critical geophysical technique for subsurface exploration of metal ore bodies,primarily utilizing either loop or grounded transmitters.The Long Offset Transient Electromagnetic(LOTEM)method employs a grounded-source transmitter,relying on a far-source observation mode and plane wave approximation for detection.However,LOTEM's far-source configuration weakens signal strength,and the plane wave approximation reduces precision,limiting effective detection depth to approximately 1000 m with a comprehensive error of about 15%.Recently,we have developed the grounded-source Short Offset Transient Electromagnetic(SOTEM)method,achieving greater detection depth and accuracy within the 500–2000 m depth range,a crucial interval for mineral resource exploration.This study explores the theoretical framework,instrumentation,data processing,and field applications of SOTEM.Based on a point charge element model,SOTEM accurately computes surface wave effects in EM field calculations,optimized for near-source observation.High-power,high-resolution,wide-bandwidth exploration equipment and an advanced three-dimensional hybrid inversion technique were also developed to enhance the method's effectiveness.Application of SOTEM to the deep exploration of the Zhou'an Ni-Cu-PGE deposit in Henan Province yielded high-resolution imaging of conductivity structures to about 2.5 km depth.These results,consistent with existing drill data,delineated mineralized ore bodies from surrounding formations,identified zones of mineralization potential,and suggested extensive resource prospects in the region.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.42030106,42274192)the National Key Research and Development Program of China(Grant No.2022YFC2903505)。
文摘The Transient Electromagnetic(TEM)method is a critical geophysical technique for subsurface exploration of metal ore bodies,primarily utilizing either loop or grounded transmitters.The Long Offset Transient Electromagnetic(LOTEM)method employs a grounded-source transmitter,relying on a far-source observation mode and plane wave approximation for detection.However,LOTEM's far-source configuration weakens signal strength,and the plane wave approximation reduces precision,limiting effective detection depth to approximately 1000 m with a comprehensive error of about 15%.Recently,we have developed the grounded-source Short Offset Transient Electromagnetic(SOTEM)method,achieving greater detection depth and accuracy within the 500–2000 m depth range,a crucial interval for mineral resource exploration.This study explores the theoretical framework,instrumentation,data processing,and field applications of SOTEM.Based on a point charge element model,SOTEM accurately computes surface wave effects in EM field calculations,optimized for near-source observation.High-power,high-resolution,wide-bandwidth exploration equipment and an advanced three-dimensional hybrid inversion technique were also developed to enhance the method's effectiveness.Application of SOTEM to the deep exploration of the Zhou'an Ni-Cu-PGE deposit in Henan Province yielded high-resolution imaging of conductivity structures to about 2.5 km depth.These results,consistent with existing drill data,delineated mineralized ore bodies from surrounding formations,identified zones of mineralization potential,and suggested extensive resource prospects in the region.
