Identification of Kimberlite Bodies in Brazil from a 3D Audio-Magnetotelluric Survey

Abstract

Summary We report on a successful identification of kimberlite bodies in Brazil through the use of the electromagnetic technique audio-magnetotelluric (AMT). Macnae (1979) writes that “In one large survey in South Africa, electromagnetic (EM) techniques have proven to be remarkably effective in detecting the presence of weathered clays or epiclastic kimberlite contained within the pipes.” Full tensor AMT data were acquired at 65 stations in a 3D configuration with frequencies ranging from 10 kHz to 1Hz in the NW portion of the Mato Grosso state, Brazil, an area of thick jungle coverage. During the AMT survey, few outcrops were seen, because of the dense forest cover. Usually, the occurrences found were of sand deposits, indicating the occurrence of Fazenda Casa Branca and Utiariti Formations and gravel from Salto das Nuvens Formation, widely used in paving trails in this region. In the area of the survey, three main targets were identified and confirmed by the 3D resistivity model in depth obtained from inversion of the AMT data, helping the exploration in a region of difficult logistics due to the dense jungle cover and remote location.