Zonas de alteração hidrotermal e paragênese do minério de cobre do Alvo Bacaba, Província Mineral de Carajás (PA)

Abstract

The Bacaba prospect is located at 7 km from the Sossego iron oxide-copper-gold deposit in the Carajás Mineral Province. It represents a satellite copper deposit associated with the Sossego deposit. This study aims the identification of hydrothermal alteration patterns, which might represent distal portions of the Sossego hydrothermal system. The results permitted the recognition of hydrothermal alteration zones represented by early albitization, intense scapolitization, potassic alteration, magnetite formation, chloritization, copper mineralization, and sericitization. These alteration stages were recognized in different host rocks (granite and gabbro). The copper mineralization was late and spatially related to potassic alteration with predominance of potassic feldspar. Temperature (~500 oC to < 300 oC) and salinity decrease, coupled with increase of fO2 conditions could have favored metal deposition from the metalliferous fluid. Ore and gangue minerals (chalcopyrite, galena, bornite, chalcocite, melonite, hessite, altaite, magnetite, hematite, uraninite, cassiterite, ferberite, allanite, apatite, monazite, and cheralite) reflect a Cu-Fe-Ni-Te-Ag-Pb-U-Sn-W-ETR-Th-P signature. The identified sequence of hydrothermal alteration stages in the Bacaba prospect is similar to that described for the Sossego deposit, despite scapolite abundance at Bacaba. This suggests that these deposits represent different portions of a single hydrothermal system. Influx of diluted, meteoric fluids might be more important at Sossego causing a higher efficiency in copper deposition in that site.