CARACTERIZAÇÃO ESTRUTURAL DOS VEIOS DE QUARTZO AURÍFEROS DA REGIÃO DE CUIABÁ (MT)

Abstract

STRUCTURAL CHARACTERIZATION OF GOLD QUARTZ VEINS IN THE CUIABÁ REGION, MATO GROSSO STATE, BRAZIL The gold mineralization in the Cuiabá region occurs in quartz veins found in metasedimentary rocks (phyllites, metasandstones, metadiamictites, marbles and metasiltstones) of the Cuiabá Group, internal zone of the Paraguai Fold Belt. Structural analyses carried out in areas located at the overturned limb (Jardim Itália and Casa de Pedra Mining), normal limb (CPA gold field) and hinge zone (Mineiro and Abdala gold fields) of the Bento Gomes Antiform, confirm the poliphase evolution (four deformation phases) and shows that this fold is a first phase (Dn) related structure with an axial plane slaty cleavage and a stretching/mineral lineation, interpreted as the X direction of the strain ellipsoid. Symmetrical linear features (pressure shadows and elongated clasts) is considered evidence that Dn flow was essencially coaxial. Three different quartz vein types were identified: parallel to S0 (type 1); parallel to Sn (type 2); perpendicular to Sn (type 3). The type 3 veins are also perpendicular to the stretching lineation, and appear to be late Dn tension fractures. They are both the most abundant and the richest, with 2-5 g/ton ore grade. So, kinematics and geometric constraints show that the type 3 veins formed related to Dn tension fractures, associated with metamorphic gold remobilisation during late Dn.