Magnetic analysis of AbaetÉ diamondiferous district (MG) and its possible primary sources

Abstract

This work studies the origin of the diamonds from the important mining region, Abaeté Diamondiferous District (MG). The discovery of pipes with micro diamonds and/or crater facies kimberlites in the entire Alto Paranaíba Igneous Province (macro region of Abaeté District) enhanced the interest about understanding the diamonds origins. The diamonds from this district usually show few cleavages, present more than 100 carats (ct) and are associated to numerous indicator minerals for kimberlite, suggesting proximity between their primary and current sources. In order to corroborate with the area geophysics knowledge, high resolution maps were prepared using airborne magnetic data integrated with geology and field studies. The products were used to: suggest the continental fracture zones which allowed the ascent of alkaline magma; correlate magnetic responses with stratigraphic and tectonic features; indicate the magnetic responses of the lineaments that govern the diamantiferous drainages; suggest possible kimberlite clan rocks; and estimate the basement depth by Euler Deconvolution. The crystalline basement is concave and the sedimentary rocks thickness may achieve about 3,000 m. The magnetic anomalies selected as possible kimberlite clan rocks were detailed using ground magnetic surveys and their Analytic Signal was adopted to estimate the magnetic source geometries by Euler Deconvolution. These possible kimberlitic pipes look like each other and presenting depths of up to 200 m and diameters of up to 300 m.