Audiomagnetotelluric 3D imaging of the Regis kimberlite pipe, Minas Gerais, Brazil

Kimberlite pipes are significant source rocks that form primary diamond deposits. Usually, the low resistivity of kimberlite produces a significant contrast in electrical resistivity, which can be mapped using electromagnetic EM methods. The Regis kimberlite is located in a well-known diamondiferous province in central Brazil. The main tectonic feature of the area is a northwest-southeast major crustal fracture zone that extends for more than 3000 km within the Brazilian territory, where Regis and several other kimberlites have intruded. In this paper, we present an audiomagnetotelluric (AMT) study at the Regis pipe. AMT data were collected in the 10 Hz-100 kHz frequency range at 111 stations on a grid, and three-dimensional (3D) inversions were used to generate a resistivity model of the pipe. Our interpretation was corroborated by available geological information of six drill holes. The final model shows an asymmetric conically shaped body with a conductivity range of 2 to 70 ohm.m and a depth of 0 to 550 m. These conductive sources were associated with crater lake sediments in the upper part and the main kimberlite diatreme at depth.