Paragenetic evolution and fluid regime in the Cu-Co Tarzan system, Carajás Province

Author(s)

Rafaela Santeiro de Campos Pinheiro

• Document type: Master's Dissertation
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Geociências
• Defense date: 2019-05-16

Examining board members

Carolina Penteado Natividade Moreto; Diego Fernando Ducart; Gustavo Henrique Coelho de Melo

• Advisor: Roberto Perez Xavier; Carolina Penteado Natividade Moreto

Abstract

The Carajás Domain, in the northern sector of the Carajás Province (Pará - Brazil), is recognized worldwide as one of the largest and most important metallogenetic provinces. Carajás Province hosts an extensive number of iron-copper-gold oxide deposits (IOCG) and Cu-Au-(W-Bi-Mo-Sn) deposits. The Tarzan Cu-Co rich deposit is hosted by mudrocks, fine-grained to coarse-grained lithic greywackes and polymictic pebble-conglomerates all related to the top sequence of the Itacaiúnas Supergroup (Igarapé Cigarra Formation), as well as subordinate diorite. Pyrrhotite with cobalt or chalcopyrite nodules and chalcopyrite layers are concordant to the bedding of silstones and rhythmites. Chloritization is the predominant hydrothermal alteration, which is marked by chlorite ± sericite ± quartz. The main mineralization stage is marked by disseminations, systems of veins of calcite + pyrrhotite + chalcopyrite + quartz + cobaltite ± chlorite ± biotite ± muscovite ± pyrite ± marialite ± tourmaline ± magnetite, and hydrothermal breccias and venules in stockwork zones constituted of chlorite ± sericite ± quartz ± pyrite ± chalcopyrite. The presence of sulfide nodules and layers that are concordant to sedimentary bedding suggests the formation of syngenetic sulfides in the Tarzan deposit, which is coeval to the deposition of the marine sedimentary sequences of the Itacaiúnas Supergroup. Microthermometric studies in calcite veins point to two distinct hydrothermal fluids: (i) saline (13.2 a 23.7 wt.% NaCleq), moderately hot (135.7 to 331.5 °C) and aqueous fluid with Na+, Ca2+, Mg2+ and Li+; and (ii) hypersaline (39.1 to 68.6 wt.% NaCleq), hot (312 to 562.8 ºC) and aqueous saturated fluid composed by Na+ and Ca2+. The hypersaline fluids, which would have been responsible for transporting metals, would have been mixed with less saline fluids, favoring ore precipitation. . ?34S values in sulfur of veins, disseminations and nodules indicate sulfur from a hybrid source with magmatic and externally derived component, e.g., seawater sulfates. C and O isotopes analysis in calcite samples from veins revealed magmatic source for the carbon and oxygen of calcite and fluids of magmatic derivation. The Tarzan deposit is extremely relevant from a metallogenetic view, where epigenetic Cu-Co rich hydrothermal mineralizations overlap the formation of Neoarchean syngenetic sulfides (ca. 2.7 Ga) (AU)

• FAPESP's process: 17/25114-0 - Paragenetic evolution and fluid regime in the Cu-Co Tarzan system, Carajás Province
• Grantee: Rafaela Santeiro de Campos Pinheiro
• Support Opportunities: Scholarships in Brazil - Master