Integrated geophysical exploration for the Longtoushan Ag-Pb-Zn deposit in the southeast of the Da Xing’an Ling mountains, Inner Mongolia, northern China

Abstract

Geophysical and geological studies attempting to search and explore new mineralisation resources were carried out in the Longtoushan area, Inner Mongolia, northern China. The Longtoushan area is located within a large alteration zone, which is covered by a variety of altered lava, bioclast limestone and Quaternary sediments. In this case study, ground geophysical surveys played an important role in defining the mineralised structures beneath Quaternary sediment cover. The aim of this study was to investigate the subsurface mineralisation in the area using a combination of very low frequency electromagnetic (VLF-EM), Stratagem EH4 and controlled source audiofrequency magnetotelluric (CSAMT) measurements. These successful surveys in the area revealed that the VLF, Stratagem EH4 and CSAMT methods were effective in detecting the unseen mineralised system and results from the different methods confirmed each other. VLF measurements at 2875 stations along 35 lines identified the principal mineralised shear system as two sub-parallel linear conductive belts, tracing the principal mineralised system for a further 650 m of strike length beneath cover loess, in a NW–SE-trending direction. The subsequent Stratagem EH4 soundings along four parallel traverses perpendicular to the mineralised trend indicated that the principal mineralised shear structure, extending for more than 600 m in the dip direction, was almost vertically dipping above the 200 m level but changed to the SSW direction at a steep angle at depth. A CSAMT survey on two lines confirmed that the ore-bearing mineralised zone was a conductive belt and contained a low resistivity anomaly of less than 500 Ωm.