磁测模型的AMT约束反演在沉积型磷矿勘查中的应用OA

Conventional audio-frequency magnetotelluric(AMT)inversion methods suffer from insufficient vertical resolution and low accuracy in orebody localization for sedimentary phosphate ore exploration.To address this issue,this work proposes an AMT constrained inversion approach that constructs an initial model based on magnetic survey data.The method was applied to the exploration of the Yangchang super-large concealed phosphate deposit in Yunnan Province.First,the magnetic survey data were processed using potential field separation to extract the regional magnetic field component.A geological model reflecting the deep syncline structure was then constructed through 2.5-dimensional forward modeling.This model was then introduced as prior information into the AMT inversion,with resistivity constraints set for key stratigraphic boundaries.These boundaries include the Cambrian Qingxidong Formation and Jindingshan Formation,the Jindingshan Formation and Niutitang Formation,and the Niutitang Formation and Dengying Formation,with constraint values of 400 Ω·m,20 Ω·m,and 200 Ω·m,respectively.The constrained inversion was performed using the two-dimensional nonlinear conjugate gradient method.The results show that the AMT inversion constrained by the magnetic survey model achieved a root mean square error(RMS)of 3.018,which is better than that of the unconstrained inversion(RMS=3.157).After further incorporating borehole constraints,the RMS decreased to 3.001,and the number of iterations reduced from 200 to 89.Validation was performed using three boreholes(ZK0801,ZK0808,and ZK0816).The phosphate-bearing strata(Cambrian Meishucun Formation)identified by the inversion occur at depths of 750～1150 m.These depths are consistent with the actual ore positions revealed by drilling(e.g.,900～950 m in borehole ZK0801,980-1030 m in ZK0808,and 850～900 m in ZK0816),with an overall error within 5%.This constrained inversion method effectively improves the identification accuracy of deep stratigraphic interfaces,suppresses low-resistivity interference from fault structures,and provides a reliable electrical basis for deep phosphate exploration in sedimentary environments.