Occurrence of chromiferous horizon in the Trincheira Complex, municipality of Corumbiara, southeast of the State of Rondônia, Brazil

Abstract

The Trincheira Mafic-ultramafic Complex comprises a Mesoproterozoic layered intrusion hosted in metasedimentary rocks of the southwestern portion of the Amazonian Craton. This intrusion has an outcropping area of approximately 35 km2 , however, it has been associated to a larger ellipsoidal magnetic anomaly with N-S elongated shape. The Trincheira Complex is com-posed of partially metamorphosed pyroxenites, websterites, gabbros and anorthosites. The complex hosts Cr-rich layers associated to relevant concentrations of Ni. High concentrations of Cu, Co and V have also been detected. Preliminary analysis performed with portable X-ray diffraction indicates up to 13% Cr and occurrence of cochromite, a special variety of chromite enriched in cobalt, nickel and iron, whereas ICP-MS analyses returned concentrations of up to ~3600 ppm Cr.