AMT方法在隐伏沉积型磷矿勘探中的预测定位研究OA

This work explores an effective geophysical technique combination for rapidly locating concealed sedimentary phosphorite deposits in northeastern Yunnan.Taking the Yangchang superlarge phosphorite deposit in Yunnan as the research object,two Audio-frequency Magnetotelluric(AMT)profile datasets were acquired and processed,and a comprehensive geophysical exploration method was established by integrating high-precision magnetic survey.Results show that the electrical structure of the study area is characterized by lateral blockiness and vertical layering,and displays significant resistivity differences among formations.The Niutitang Formation and the phosphate-bearing Meishucun Formation generally exhibit low resistivity(average resistivity of 85 Ω·m and 69 Ω·m,respectively),while the surrounding rocks such as the Qingxudong Formation and Jindingshan Formation have resistivities exceeding 1000 Ω·m.These resistivity differences provide a solid physical property foundation for AMT work.Through two-dimensional inversion using the nonlinear conjugate gradient method,profile L1 presents a three-layer"high-low-high"electrical structure,while profile L2 presents a five-layer"high-low-high-low-high"structure.By comparing the inversion results with borehole data in detail,an interpretation criterion was established.The phosphorite ore layer(Meishucun Formation)is located in the middle-lower part of the low apparent resistivity zone,with an apparent resistivity range of approximately 3.98～10 Ω·m.Based on this,the potential location of the phosphorite ore layer was delineated on the inverted profiles of the target mining area.The target ore layer was inferred to have a burial depth of around 200 m above sea level,with the shallowest part at about 1100 m and the deepest at about 1700 m,and a thickness of about 50 m.Concurrently,high-precision magnetic survey results show that local magnetic field jumps correspond well with major formation boundaries,such as those of the Qingxudong and Jindingshan Formations,which can be used for rapidly characterizing the stratigraphic framework.AMT can quickly identify the distribution of subsurface low-resistivity layers,and the lower part of the low-resistivity zone in its electrical profiles can serve as a target horizon for locating concealed phosphate-rich strata.In comparison,high-precision magnetic survey helps identify formation boundaries and assists in establishing the regional stratigraphic framework.The combined application of these two methods can effectively delineate the spatial position of phosphorite-rich strata,providing a reliable geophysical basis for the exploration and development of concealed sedimentary phosphorite deposits in northeastern Yunnan.