A influência de fluidos cambrianos em depósitos de ouro orogênico arqueanos, leste do Quadrilátero Ferrífero: geoquímica, geocronologia e geologia isotópica dos metaturbiditos e rochas associadas do Supergrupo Rio das Velhas

Abstract

The Archean orogenic gold deposits of the eastern sector of the Quadrilátero Ferrífero, one of the main metallogenetic provinces in the world, are hosted mainly by metasedimentary clastic sequences that make up the Rio das Velhas greenstone belt (RVGB). The mineralized bodies in this region are associated with the Córrego do Sítio Lineament, a remarkable NE-SW structural feature of about 15 km in length. The host rocks compose turbiditic sequences, recognized as the Ressedimented Association, represented by metagrawackes and metapelites, in association with metamafic dikes and sills. The main ore bodies, named Carvoaria, Laranjeiras and Cachorro Bravo have similar petrographic characteristics, with arsenopyrite as the predominant sulfide and bertiherite and stibnite sulfossalts with associated gold, in veins or disseminated. In the Pilar deposit, east of the Córrego do Sítio Lineament, the mineralization is hosted by the Quebra Osso Group, which comprises ultramafic rocks (talc schists), and in metamafic and metapelitic rocks, described as carbonate-albite-chlorite-quartz schist, quartz- chlorite schist and carbonaceous schist, and by the BIF's, of the Nova Lima Group. Robust U-Pb geochronological data obtained in situ (SHRIMP) in hydrothermal monazite crystals in different deposits suggest a persistent modification of Ediacaran-Cambrian age (~ 510 and 540 Ma), possibly related to the collapse stage of the Araçuaí Orogen, on the Archean rocks that host the mineralizations. Although the strong Cambrian imprint by hydrothermal fluids is observed, the geochemical signature of rare earth elements does not indicate considerable disturbance in relation to the original sedimentary signature. Isotopic Nd analysis indicate the importance of TTG Complexes as source areas for RVGB metaturbidites, with TDM model ages of 3.0 to 3.2 Ga and de direção NE-SW ENd (2.7 Ga) = -1 to -3.