Caracterização tectono-metamorfica do deposito aurifero Ambrosio, Greenstone Belt do Rio Itapicuru - Bahia

AUTOR(ES)
DATA DE PUBLICAÇÃO

1996

RESUMO

The Ambrósio lode gold deposit, located in the northem sector ofthe lower Proterozoic (2.200 to 2.000 Ma) Rio Itapicuru greenstone belt, northeast Brazil, is enclosed within a narrow belt ofhighly deformed supracrustals, tightly squeezed between two syn-tectonic granitic batholiths (pedra Alta and Ambrósio domes). The deposit is hosted at the contact of amphibolites and clastic-chemical metasediments, which represent part ofthe mafic volcanic domain at the basal portion ofthe greenstone belt sequence. The metasediments and amphibolites comprise the footwall and hangingwall ofmineralization, respectively. The former are represented by andalusite-gamet-biotite schist and the latter consits mainly ofhomblende and plagioclase; these lithotypes show mylonite texture devoloped in amphibolites facies. The deposit is closely associated with structures developed in a ductile strike-slip duplexes system, in the offset region between two main shear zones at the boundary of the granite-gneiss domes. The gold mineralization occurs in centimetre-wide quartz veins containing disseminations of iron sulphides (arsenopyrite, pyrrhotite and pyrite), and subordinate amounts ofbiotite, plagioclase and muscovite. The veins were submitted to intense recrystallization processes and are controUed by: 1) transcurrent shear zone (NNE) and 2) drag folds with subhorizontal axis in the NNE direction. These minera1ized structures are related to early stages of evolution ofthe duplexes system, and are broadly synchronous with regional metamorphism and granite intrusions. CO2 - rich inclusions, mostly monophase at room temperature, are the dominant or virtually the only fluid inclusion type, in the quartz veios of the Ambrósio deposito The CO2 - rich inclusions appear restricted to intergranular trails, or along subgrain boundaries. Microthermometry and laser Raman microphobe data demonstrate that the carbonic fluids are composed of pure CO2. Fluid inclusions and petrographic studies suggest that gold was transported by tiocomplex in an original H20-C02 fluid, which was enriched in C02 by loss ofH20 during the vein formation and later deformation

ASSUNTO(S)

metamorfismo (geologia) - bahia geologia estrutural - bahia ouro - bahia

ACESSO AO ARTIGO

Documentos Relacionados