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Rocks of Rio das Velhas Greenstone Belt subject of this paper are contained within the Quadrilátero Ferrífero region, Minas Gerais State, in the southeastern portion of Brazil. Volcanic rocks are represented by komatiites, basalts, andesites, dacites and volcaniclastic rocks, metamorphosed under greenschist facies. Despite intense deformation, these rocks preserve some original textural features like spinifex, variolitic, porphyritic and ophitic. Quench textures, pillow lavas and chemical sediments association (iron formation and metachert) indicate an ocean environment for mafic-ultramafic flows. The basalts geochemical patterns indicate that at least part of them formed from a mantle plume. The felsic volcanic and volcaniclastic rocks association indicates a subaerial explosive volcanism in an island-arc type environment.

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The Lamego orogenic gold deposit (440,742 Oz gold measured reserves and 2.4 million t measured resources, with an average grade of 5.71 Au g/t and the cut-off grade of 2.15 g/t Au; AGA personal communication, 2014) is located in the 5 km-long trend that includes the world-class Cuiabá deposit. It is hosted in the Neoarchean metavolcano-sedimentary rocks of the Rio das Velhas greenstone belt, Quadrilátero Ferrífero, Brazil. Mineralization is associated mainly with metachertbanded iron formation (BIF) and carbonaceous phyllites in the reclined Lamego fold, in which the Cabeça de Pedra orebody represents the hinge zone. Mineralization is concentrated in silicification zones and their quartz veins, as well as in sulfide minerals, product of BIF sulfidation. Hydrothermal alteration varies according to host rock, with abundant sulfide-carbonate in BIF, and sericite-chlorite in carbonaceous phyllite. Quartz veins classification according to structural relationships and host rocks identified three vein systems. The V1 system, mainly composed of smoky quartz (Qtz I) and pyrite, is extensional and crosscuts the S0 bedding of BIF, and is parallel to the fold axis. The V2 system, of same composition, is represented by veins that are parallel to the S1-2 foliation and S0 bedding. This system is also characterized by silicification zones in the BIF-carbonaceous phyllite contact that has its maximum expression in the hinge zone of folds. The V3 system has milky quartz (Qtz II) veins, which result from the recrystallization of smoky quartz, located mainly in shear zones and faults; these veins form structures en echelon and vein arrays. The most common ore minerals are pyrite, As-pyrite and arsenopyrite. Fluid inclusion-FI trapped in all quartz veins present composition in the H2O-CO2 ± CH4-NaCl system. Fluid evolution can be interpreted in two stages: i) aqueous-carbonic fluid trapped in Qtz I, of low salinity (~ 2% equiv. wt% NaCl), and ii) carbonic-aqueous fluid, of moderate salinity (average 9 % equiv. wt% NaCl) hosted in Qtz II. Both stages are characterized by decrepitation temperatures in the range of 200 to 300°C, and suggest a fluid of metamorphic origin. Applying the arsenopyrite geothermometer, the calculated formation temperature for the Cabeça de Pedra orebody is 300 to 375°C. The vertical intersection of the isochors allows a pressure calculation between 4 to 4.5 kbar. The composition of individual FIs of this orebody, obtained by LA-ICP-MS analyses, compared with results of FIs for the Carvoaria Velha deposit, Córrego do Sítio lineament, highlights a standard composition typical of metamorphic fluids with Na> K> Ca> Mg, which increase or decrease in concentration as a function of salinity in both deposits. Trace elements vary according to fluid-rock reactions, and are directly related to the host rock composition. The comparison of data sets of the two deposits shows that the Cabeça de Pedra FIs have a higher enrichment in Zn, while Cu, As and Sb are richer in Carvoaria Velha, suggesting influence of th...

The Caraja ´s Province presents several volcano-sedimentary sequences that comprise the Itacaiu ´nas Supergroup. The rocks represent bimodal volcanism, and clastic and chemical sedimentation in relatively unstable basins subject to recurrent structural events with subsidence and volcanism. The Gra ˜o Para ´Group represents one of these sequences with mafic volcanic rocks that enclose discontinuous jaspilite lenses, with development of large high-grade orebodies (Fe.65%). This unit is named the Caraja ´s Formation and presents peculiar characteristics compared with other iron districts in the world, thereby departing from the classic Lake Superior or Algoma iron formation types. Owing to the dense vegetation, lack of outcrops and harsh landscape, the structural analysis of the district can only be accomplished by combination of regional field work, detailed structural work on the open pits and remotely sensed image interpretation, in this case Landsat ETM7, JERS-1 images and the shuttle radar topography mission (SRTM) digital terrane model. The regional trend of the several sequences of the area is approximately N-S and the structure is dominated by a flattened flexural fold system with axes moderately dipping WNW, intersected by several strike-slip faults subparallel to their axial plane. The Serra dos Caraja ´s represents an s-shaped synform-antiform pair, herein named the Caraja ´s Fold. This regional structure is partially disrupted by the Caraja ´s Shear Zone that divides it in the northern (Serra Norte) and the southern (Serra Sul) Ranges and also probably prepared the terrane with the development of pathways for mineralising hydrothermal fluids forming large highgrade massive iron bodies. Syntectonic granitic bodies played an important role in the structural evolution of the area as well. They caused localised ductile flattening deformation and thermal contact metamorphism in surrounding terranes. The Estrela pluton, for instance, was responsible for the discontinuity of the regional trend between the Serras do Rabo and Leste. The Caraja ´s Province is regionally the upper crustal product of a very shallowly eroded dome-and-keel geometry of Neo-Archaean volcano-sedimentary units intruded by syntectonic calc-alkaline intrusives and overlying pre-existing infracrustal rocks. The lithostructural data suggest continental-margin back-arc basin development and closure in an oblique collision belt, with N-S shallow crustal shortening, parallel to the inferred pre-existing strike of the stratigraphy.