GEOLOGIA E RECURSOS MINERAIS DA SERRA DOS CARAJÁS

Abstract

The Serra dos Carajas iron-ore deposits, located in the southern part of the State of Para, about 550 km from the city of Belem, were discovered by Companhia Meridional de Mineracao geologists in August of 1967. The deposits occur in a series of elevated plateaus related to a peneplain which is presumed to be of Cretaceous age. The basement complex is composed of granite-gneissic rocks, and is unconformably overlain by the Grao Para Group, which consists of the Carajas Formation (itabirite, iron-ore, mafic dikes, sills, and intercalations), and underlying and overlying mafic rock units, A predominantly arenaceous clastic sequence, correlated with the Gorotire Formation, overlies the Grao Para Group, with angular discordance. A granite batholith occurs in the central part of the area. All the rock units are considered to be of Precambrian Age. The main structural feature of the district is a wide and complexly faulted synclinorium whose axis strikes and plunges to the northwest. The iron-ore consists mainly of martite and hematite, with significant quantities of magnetite. The typical ore is a platy, friable material which contains an average of 66.0% Fe, 0.05% P, 2.2% SiO 2 + Al 2 O 3 , and which has 2.0% LOI. The distribution for the most part is within a 0.1 to 6.35 mm size range (50 to 60% of the total). It represents a residual, enriched product of the original itabirite through leaching of the silica. The reserves are estimated at about 18 billion metric tons, of which 1.7 billion metric tons are measured ore.