We present an overview of an ambitious geophysical program undertaken by Vale to characterize both tailings storage facilities (TSF) properties around existing mine sites as well as an exploration program for iron ore. This resulted in 23 survey blocks being flown. There are a large number of mines in Minas Gerais where technical approaches and surviving records for TSF properties are not at the same standard as at modern mines. In some cases, there are no records regarding dam construction. Geophysics presents a non-invasive, cost-effective method of characterizing these dams. However, in places, ground geophysics is not permitted because of HSE concerns. Also, given the number of mine sites, ground geophysics would be an onerous endeavor. Airborne geophysics is thus a compelling solution. There are two main reasons for airborne acquisition: (1) HSE for conducting ground surveys on top of the existing earth dams and tailing ponds and (2) speed of acquisition. To properly characterize the site, data must be collected in multiple lines over the dam, pond and the immediate surrounding area. To characterize the dam, very near surface information is required. Frequency domain EM presents the best available near-surface sensitivity of airborne geophysical techniques. The Resolve system was used due to its wide frequency range of 400Hz to 140 kHz. In order to enhance sensitivity to magnetic material in the ground, Resolve was flown with a transverse horizontal magnetic gradiometer. To ensure the correct interpretation of the complete earth response in these topographically complex settings, the data is being modelled with a 3D inversion program. A cooperative joint inversion is being conducted between the magnetics and the EM, and where available, surface, geotechnical and borehole information is being incorporated.

Open-Access Online Publication: May 29, 2023