A mineralização aurífera do depósito Córrego do Sítio e sua relação com o enxame de diques metamáficos no corpo Cachorro Bravo - Quadrilátero Ferrífero- MG

Abstract

Córrego do Sítio lineament is located in the Rio das Velhas greenstone belt (GBRV), Quadrilátero Ferrífero, Brazil and Cachorro Bravo is its principal orebody. It is an orogenic gold deposit as defined by Groves et al. (1998). The gold-only lodes are of hydrothermal origin and is characterized by quartz-carbonate veins with sulphidation in the wall rocks contact. The orebodies are hosted by clastic and turbiditic metasedimentary rocks of the upper portions of the GBRV. This research is developed at Cachorro Bravo orebody and its mineralization occurs in the metassedimentary sequences between mafic dykes swarms. There are two different mineralogical associations if near or far from these dykes. Hydrothermal alteration is descontinuous in metassedimentary sequences prevailing carbonatization in distal halos and sericitization in proximal halos. Sulphides of the lodes are mainly arsenic-pyrite and arsenopyrite. Near to the dyke contacts, hydrothermal alteration is represented by cloritization, carbonatization, sericitization and hydrothermal rutile and titanite. Arsenopyrite formed after pyrrotite. On both styles, gold is associated to arsenopyrite. The presence of antimonious minerals (berthierite and stibnite) suggests that the mineralization at Córrego do Sítio took place in a shalow environment, transition from mesozonal to epizonal, so far not registred in the Rio da Velhas greenstone belt. Local structures are a complex and there are three main structure families in Cachorro Bravo orebody. Bedding (S0) is easily observed in the metassedimentary sequences and underwent a deformation folding event (Fn) which prints an axial-planar foliation (Sn). Overprinting Sn occurs a spaced crenulation clivage (Sn+1). Another foliation plan is observed but its cronology before or after Sn+1 is not understood yet. Some of the rocks in Corrego do Sítio were submitted to intense hydrothermal alteration and transformed into a quartz-carbonate-white mica-chlorite association. Their protolites became unclear but by multi-elementar analysis it was possible to define Cr, Ni and P as guide of their metasedimentary and igneous origin.