LOMAGUNDI CARBON-ISOTOPE EXCURSION ON THE AMAZONIAN CRATON

The core of the Nuna (Columbia) supercraton assembled by 2.1-2.0 Ga and includes the following cratons: Amazonia, West Africa, São Francisco, Congo, Zimbabwe, Kaapvaal, North China, Volga-Uralia, and Sarmatia. Orogenic belts joining these cratons contain ~2.45-2.22 Ga juvenile crust, whereas sedimentary successions deposited on these cratons include detrital zircons with ages in this range. The Carajás Province of the southeastern Amazonia collided with West Africa at ~2.1-2.0 Ga forming the Maroni-Itacaiúnas orogenic belt. West Africa is richly endowed in the Paleoproterozoic mineral deposits: gold mineralization in greenstone belts and successor basins, sediment-hosted Mn and iron deposits. Although gold mineralization in structures potentially formed during the late Paleoproterozoic is known in the Carajás Province, iron and manganese deposits of the Paleoproterozoic age were not yet recognized. We studied dolostones from the lower part of the predominantly clastic Águas Claras Formation developed in the Serra Pelada area. Carbonates in several studied drill cores show consistently highly positive C-isotope values, up to +7.6‰ V-PDB, indicating deposition during the Paleoproterozoic, ~2.22-2.06 Ga Lomagundi carbon isotope excursion and underlie carbonaceous siltstones. The Águas Claras Formation of the Serra Pelada area (=Serra Pelada Sequence; SPS) hosting the Sereno Mn deposit has been correlated to the Águas Claras Formation in its type area of central Carajás (=Carajás Sequence; CS) that hosts world-class Azul Mn deposit in carbonaceous siltstones. Previously, the CS was considered to be Archean in age based on detrital zircon geochronology and U-Pb zircon dates for cross-cutting mafic sills. However, our data indicates a similar Archean provenance for the Paleoproterozoic SPS as for CS. In contrast, sandstones of the Paleoproterozoic Caninana Formation contain detrital zircons with a mode as young as 2055 Ma (Prado-Pereiro, 2009), derived from the Maroni-Itacaiúnas orogenic belt. Combined, our data points to a Paleoproterozoic passive margin succession in the Carajás Province that includes the CS and SPS and hosts the world-class Mn deposits. The SPS has been affected by the Transamazonian orogeny, resulting in gold and PGE mineralization of Serra Pelada.