THE LATERITIC BAUXITE DEPOSIT OF RONDON DO PARA: A NEW GIANT DEPOSIT IN THE AMAZON REGION, NORTHERN BRAZIL

Detailed geologic surveys (including mapping, drillings, trenches, and mineralogical and chemical analyses) have delimited a new giant lateritic bauxite deposit with 642 million metric tons (Mt) of 42.7% Al2O3 (available) in the world-renowned Amazon Province, northern Brazil. The mineral resource is part of a mature laterite profile and consists of reddish to mottled clay at the base that narrows upward to massive bauxite, followed by ferruginous bauxite, and is capped by an iron horizon (nodular and columnar ferruginous crust) and nodular bauxite with a clayey matrix; a thick clay cover sealed the profile after abrupt contact. The bauxite ore is composed of gibbsite in addition to goethite, hematite, and kaolinite. In general, the ore has high concentrations of Al2O3 (avg 52.4% in massive bauxite and 39.9% in ferruginous bauxite) and Fe2O3 (avg 14.8% in massive bauxite and 35.1% in ferruginous bauxite) and low concentrations of SiO2 (avg 4.33% in massive bauxite and 3.21% in ferruginous bauxite) and is therefore of metallurgical grade. Geologic contact features together with REE distribution patterns indicate that the horizon successions were formed in situ via alteration of the basal sedimentary rocks through polyphasic bauxitization events. These features are comparable with those of other world-class bauxite deposits in this province, such as Trombetas, Juruti, and Paragominas. The Rondon do Para bauxite orebody consists of massive bauxite and ferruginous bauxite layers. The last layer is a differentiated horizon that is not always present in other deposit profiles; when it is present, however, it is not classified as ore. Correlation with other Amazonian bauxite deposits demonstrates that the Rondon do Para deposit is of lateritic origin, was formed during the Paleocene-Eocene, and was reworked in the Miocene.