3D magnetic interpretation of the Regis kimberlite pipe, Minas Gerais, Brazil

摘要

In the present work, high-resolution ground magnetic data are used to unveil the structure of the Regis kimberlite pipe, which is located in a well-known diamondiferous province in the central portion of Brazil. The main tectonic feature of the area is a NW-SE major crustal fracture zone, extending for more than 3000 km within Brazil, along which Regis and several other kimberlite pipes have intruded. The area is located at low magnetic latitude (inclination approximately 27° south) and the ground magnetic anomaly associated with the Regis pipe appears as an isolated asymmetric dipole-like source caused by magnetization primarily in the direction of the Earth's magnetic field. We inverted this high-resolution magnetic data set in order to recover the 3D effective susceptibility model of the studied pipe. We obtained an asymmetric conical-shaped strongly magnetized body (35 × 10 -3 SI units) extending from 50-720 m depth. Prior to the inversion, the data were upward continued to 30 m above the surface to attenuate high-frequency noise and mitigate inversion artefacts. Our results were used to better define the subsequent drilling positions to thoroughly evaluate the economic potential of the Regis pipe. One available borehole drilled approximately in the centre of the structure corroborates our interpretation.