Lithofacies associations and structural evolution of the Archean Rio das Velhas greenstone belt, Quadrilátero Ferrífero, Brazil: A review of the setting of gold deposits

摘要: Abstract The Rio das Velhas greenstone belt is located in the Quadrilatero Ferrifero region, southern extremity of Sao Francisco Craton, central-southern part State Minas Gerais, SE Brazil. metavolcano–sedimentary rocks Supergroup this region are subdivided into Nova Lima and Maquine Groups. former occurs at base sequence, contains major Au deposits region. New geochronological data, along with a review geochemical data for volcanic sedimentary rocks, suggest least two generations belts, dated 2900 2780 Ma. Seven lithofacies associations identified, from bottom to top, encompassing (1) mafic–ultramafic volcanic; (2) volcano–chemical–sedimentary; (3) clastic–chemical–sedimentary, (4) volcaniclastic association four lithofacies: monomictic polymictic breccias, conglomerate–graywacke, graywacke–sandstone, graywacke–argillite; (5) resedimented association, including three sequences graywacke–argillite, north eastern, greenschist facies south, amphibolite metamorphic facies; (6) coastal sandstone medium- large-scale cross-bedding, ripple marks, herringbone sandstone–siltstone; (7) non-marine conglomerate–sandstone, coarse-grained sandstone, fine- medium-grained sandstone. Four structures recognized: first second Archean compressional, driven NNE SSW; third extensional attributed Paleoproterozoic Transamazonian Orogenic Cycle; fourth E W, related Neoproterozoic Brasiliano Cycle. Gold structurally controlled occur associated hydrothermal alterations thrust shear zones generation structures. Sedimentation occurred during episodes. Cycle 1 interpreted have between 2800 2780 Ma, based on ages mafic felsic volcanism, comprises predominantly chemical intercalated flows. It includes volcano–chemical–sedimentary association. cycle initial stage formation, deposition sediments contemporaneous flows that formed submarine plains. 2 encompasses clastic–chemical–sedimentary distal turbidites eastern sector Ferrifero. was deposited stages volcanism. sector, advanced subduction. In it also possible recognize stable shelf environment. Following 3 associations, largely northern area. characteristics both indicate fan environment transitional successions edifices formation island arcs. 4 made up clastic belonging They as braided plain alluvial retroarc foreland basin supply debris previous cycles.