Gold deposits of the Carajás mineral province: deposit types and metallogenesis

Abstract

The Carajas mineral province is located in the south-eastern part of the Amazon craton and is divided into the southern and northern tectonic blocks, which are referred to as the Rio Maria granitoid–greenstone terrane and the Itacaiunas shear belt, respectively. The geological evolution of this province occurred almost entirely in the Archean, with no tectonism from ~2.4 to 1.9 Ga and then an episode of very extensive intraplate granitic magmatism. Distinct types of gold deposits, most associated with Archean metavolcano-sedimentary sequences, including greenstone belts as old as 2.9 Ga, comprise (1) Fe-oxide-poor Cu–Au, (2) Fe-oxide–Cu–Au–U–REE, (3) shear-zone related lode-gold, and (4) sedimentary rock-hosted Au–PGE. The shear-zone related deposits are more typical of the Rio Maria granitoid–greenstone terrane, whereas the other types are more abundant in the Itacaiunas shear belt. The first type, represented by the Serra Verde deposit, shows most characteristics of volcanogenic massive sulfide (VMS) deposits, except for the dominance of chalcopyrite over pyrite and/or pyrrhotite. Some deposits of the second type (Igarape Salobo and Igarape Bahia) are also syngenetic, but their ore mineralogy and paucity of pyrite and/or pyrrhotite are inconsistent with, or at least unusual for, classic VMS deposits. Other Fe-oxide–Cu–Au–U–REE deposits, such as the Cristalino and Sossego, occur as epigenetic stockwork mineralization related to Archean granitoid stocks. Most shear-zone related lode-gold deposits are classified as orogenic gold deposits (e.g. Sapucaia, Babacu and Tucuma) that cut greenstone belt rocks. The Cumaru deposit is also hosted by a shear zone, but may have a genetic association with a granitoid intrusion. The Aguas Claras deposit, although also hosted in a shear zone and perhaps intrusion-related, differs from the orogenic gold deposits by its extensional tectonic setting, lack of CO2 in the ore fluids, and voluminous chalcopyrite. The sedimentary rock-hosted Serra Pelada Au–PGE deposit is structurally controlled and occurs in an Archean clastic-chemical sedimentary rock sequence.