Stable isotope systematic applied to characterization of the hydrothermal systems associated with the Alvo Bacaba and Alvo Castanha copper deposits, Carajás Mineral Province, PA

Author(s)

Andre Luiz Silva Pestilho

• Document type: Master's Dissertation
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Geociências
• Defense date: 2011-08-26

Examining board members

Lena Virginia Soares Monteiro; Elson Paiva de Oliveira; Jorge Silva Bittencourt

• Advisor: Lena Virginia Soares Monteiro; Roberto Perez Xavier

Abstract

The Alvo Bacaba and Alvo Castanha copper deposits are located at the northern part of the Carajás Mineral Province, at a distant radius of about 8 km from the Sossego iron oxide-copper-gold deposit. These deposits occur along a regional shear zone 60 km wide, in the limit between the Itacaiúnas Supergroup and its basement represented mainly by migmatites of the Xingu Complex. Both deposits exhibits widespread hydrothermal alteration zones comprising albitization, scapolitization, iron oxide formation, sodic-calcic alteration, potassic alteration, tourmaline formation, sericitization, epidotization and carbonatization, although these two deposits show differences like sodic-calcic alteration, which is well developed in Alvo Castanha, but it is almost inexistant in Alvo Bacaba, being present only in its altered gabbros. Also the Alvo Bacaba shows ore minerals association essencialy composed by chalcopyrite±pyrite±bornite while the Alvo Castanha shows the association of chalcopyrite±pyrrhotite±pyrite. Paragenesis and stable isotope data indicate that the Alvo Bacaba and Alvo Castanha deposits have evolved with temperature decrease. However, the temperature drop in relation to the hydrothermal alteration succession was greater in Alvo Bacaba than the Alvo Castanha, and the oxygen fugacity was kept higher at Alvo Bacaba. The estimated temperature for ore deposition in the Alvo Bacaba was between 220 °C and 410 °C, while the Alvo Castanha it would have occurred between 350 °C and 420 °C. The isotopic evolution of the Alvo Bacaba is similar to that characterized for the Sossego deposit, with a steep temperature reduction accompanied by decrease of ?18O and increase of ?D values and fluid mixing evidences. In the Alvo Castanha, isotopic compositions of the hydrothermal fluids indicate predominance of magmatic sources. These characteristics and its similarities with those of the Sossego deposit could point to a contribution of magmatic and ocean waters in the hydrothermal system that originated all deposits (AU)

• FAPESP's process: 09/02747-0 - Stable isotope systematic applied to the characterization of the hydrothermal paleo-systems of the Alvo Bacaba and Alvo Castanha, Carajás Mineral Province, PA.
• Grantee: Andre Luiz Silva Pestilho
• Support Opportunities: Scholarships in Brazil - Master