Geophysical Mapping by Electromagnetic Induction of Gold Occurrences in Birimian Formations of Liptako: Case of Sorbon Haoussa Sector (Souhwest Niger)

Abstract

The survey zone corresponds to the Sirba greenstone belt, one of Liptako Birimian Formations (LBF) of Niger. Previous aeromagnetic and geochemical works reveal the significant gold occurrences. The present study integrates geophysical mapping of these occurrences by electromagnetic induction on field. A multi-frequencies system of 10 frequencies was used for depth and subsurface investigation of resistive anomalies. The interpretation of obtained results shown two types of resistive anomalies, corresponding to the conductive units: deep anomalies obtained with low frequencies and subsurface anomalies detected with high frequencies. The subsurface anomalies were detected around the 15 meters and the deep anomalies were recorded beyond 80 meters. All of the detected resistive anomalies are in a lenticulars shapes oriented N-S or E-W. The analysis of combined resistivity map from all frequencies shown three zones of resistive anomaly presenting a high potential in conductive metals: The first zone Z1 (most important), located in Eastern studied zone covering, covering a surface of 3.5 Km2, the second zone Z2 is located in West and covers an area of 2.9 Km2 and the third anomaly zone Z3 is located in South with a surface of 0.96 Km2. On field, these conductive units correspond to auriferous quartz veins and/or highly altered manganese schists, exploited by using the artisanal mining wells, up to 20 meters in depth.