Mesoarchean (3.0 and 2.86 Ga) host rocks of the iron oxide-Cu-Au Bacaba deposit, Carajas Mineral Province:U-Pb geochronology and metallogenetic implications

摘要

The Bacaba iron oxide-copper-gold deposit, situated within a WNW-ESE-striking shear zone in the Carajas Domain, Carajas Mineral Province, is hosted by the Serra Dourada Granite, the Bacaba Tonalite, and crosscut-ting gabbro intrusions, which were intensely affected by sodic (albite-scapolite), potassic, chloritic, and hydrolytic hydrothermal alteration. This deposit is located 7 km northeast of the world-class Sossego iron oxide-copper- gold deposit and might represent a distal and deeper portion of the same or related hydrothermal system. The U-Pb laser ablation inductively coupled plasma-mass spectrometry data for zircon from a sodically altered sample of the Serra Dourada Granite yielded a 2,860 ± 22 Ma (MSWD = 11.5) age. Three samples from the Bacaba Tonalite, including one with potassic alteration and two with Cu-Au mineralization, rendered the 3,001.2 ± 3.6 Ma (MSWD = 1.8), 2,990.9 ±5.8 Ma (MSWD = 1.9), and 3,004.6 ± 9 Ma (MSWD = 2.2) ages, respectively. The ca. 2.86 and ca. 3.0 Ga ages are inteipreted as the timing of the igneous crystallization of the Serra Dourada Granite and the Bacaba Tonalite, respectively, and represent the oldest magmatic events recognized in the Carajas Domain. The Serra Dourada Granite and the Bacaba Tonalite are interpreted to greatly predate the genesis of the Bacaba deposit. A genetic link is improbable in the light of the similarities with the Sossego deposit, which is also hosted by younger ca. 2.76 Ga metavolcano-sedimentary units of the Itacaiunas Supergroup. In this context, the iron oxide-copper-gold deposits in the southern sector of the Carajas Domain could be mainly controlled by important crustal discontinuities, such as a regional shear zone, rather than be associated with a particular rock type. These results expand the potential for occurrences of iron oxide-copper-gold deposits within the Mesoarchean basement rocks underlying the Carajas Basin, particularly those crosscut by Neoarchean shear zones.