Caracterização metalogênica da Jazida Aurífera Satinoco, Conceição do Pará/MG

Abstract

In the Pitangui region, extreme NW in the Quadrilátero Ferrífero-MG, meta-volcano-sedimentary rocks outcrop, characteristics of a greenstone belt sequence type contained in the Group Nova Lima (Rio das Velhas Supergroup), which host the auriferous deposit Satinoco. Conventional petrographic and SEM analysis, of the host rock, of hydrothermal alteration zones, and of mineralized rock as well as specific chemical analysis in pyroxene, garnet, amphibole, feldspar, chlorite and sulphides were performed to characterize the metallogenic evolution of the mineralizing processes in Satinoco and determine the equilibrium conditions during prograde metamorphism, of the metamorphic peak and retro-metamorphism. The metamorphic peak paragenesis is marked by mineral associations almandine ± biotite ± hornblende ± grunerita-cummingtonite, hornblende ± plagioclase and by pyroxene recrystallization. The mineral association combined with mineral chemistry revealed evidence of metamorphism in conditions of facies amphibolite with temperature of 663 oC to 717 oC (geothermometer plagioclase - amphibole), as well as pressure on roughly 9 Kbares (Al-Amphibole). The tectonometamorphic events may have occurred during the Neo-Archean to the Proterozoic generating two dominant Sn foliation and Sn+1 of crenulation and transpressive transcurrent structures activation. To these structures, hydrothermal processes and polymetallic mining of orogenic type were linked which generated deposition the auriferous ore of Satinoco. The ore mineral is docked as discontinuous bodies arranged in transpressive shear zone with orientation of 306°-315°/45°-60°E. The mineralization in Satinoco is arranged stratigraphically within the basal sequences of the Nova Lima Group, structurally controlled in the direction NW-SE, hosted on metapiroxenite at the base and mica-amphibole schist at the top, and associated with areas of hydrothermal alteration. Minerals derived from fluid - host rocks interactions were associated with processes of silicification, sulfidation, chloritization, epidotization, carbonation, sericitization, and uralitization. Such effects are spatially distributed according to the shear zone deformation. The auriferous ore geneses is related to two pulses of mineralizing fluids: i) sulphides of Fe, As, Cu, Zn, Pb, and ii) a second generation of sulfides of Fe, As, Au, Cu. According to the chlorite composition characteristics, it was formed in a temperature between 390 oC and 457 oC. These temperatures would be indicative of chemical equilibrium conditions during retrograde metamorphism that reached greenschist facies metamorphic, and of the conditions under which acted hydrothermal processes derived from the fluids percolation during ore genesis, reaching greenschist metamorphic facies. We postulate that the auriferous deposit in Satinoco has metallogenetic features of epigenetic type, similar to the deposits of orogenic gold type, comparable to the metallogenetic features of other exploited deposits in the Quadrilátero Ferrífero, which are considered largest deposits.