Application of “EH4+high magnetic” model in iron ore exploration in Liberia

The Liberian iron ore deposit, is a typical sedimentary magnetite deposit, located in the Archean metallogenic area of the Man Earth Shield in the southern part of the West African Craton.High precision magnetic survey, EH4 magnetotelluric sounding and drilling verification are used to carry out geological exploration and research on the selected iron ore body in the study area.It is inferred that the magnetic anomaly is related to the exposed surface or shallow ore body based on the high-precision magnetic survey results.And then the EH4 magnetotelluric sounding results are used to analyze the magnetic anomaly to infer the favorable metallogenic area, which is verified successfully by drilling.The geological geophysical model of the study area is established in combination with the geological background, geophysical results and drilling.The results show that the magnetic anomalies in this area basically show the obvious characteristics of positive negative positive magnetic anomaly zoning.Through drilling verification, the positive magnetic anomaly is the response of the surface outcrop (or certain coverage), and the negative magnetic anomaly is the downward extension of the ore body and the core area of the syncline.The magnetic anomaly in this area basically presents the obvious characteristics of positive magnetic-negative magnetic-positive magnetic anomaly zoning.Through drilling verification, the positive magnetic anomaly is the response of the surface outcrop (or certain coverage), and the negative magnetic anomaly is the downward extension of the ore body and the core area of the syncline.The comprehensive high-precision magnetic survey and EH4 magnetotelluric survey results show that the rock formation in the area is a syncline structure, and the ore body occurs in the syncline.The geological geophysical model of the study area is established combined with comprehensive geophysical methods and geological engineering.This model has certain reference significance for discussing the genesis of sedimentary metamorphic iron deposits and searching for the same type of deposits in the periphery and region of the mining area.At the same time, the groundwater level in the study area is not deeply buried, and the reasons such as groundwater enrichment, polymetallic chemical halo and sulfide enrichment caused by hydrothermal activities should be comprehensively considered when analyzing the geophysical prospecting results.According to this study, it is found that the distribution of ore bodies in this area is complex, and the magnetic anomaly is weak or even not obvious in some sections.Therefore, in the subsequent work or in the search for the same type of ore bodies, the density difference and gravity measurement can be used to determine the location.