U-pb e Re-Os geochronology applied to the metallogenetic evolution of the Southrn Copper Belt of the Carajás Mineral Province

Author(s)

Carolina Penteado Natividade Moreto

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Geociências
• Defense date: 2013-05-08

Examining board members

Lena Virginia Soares Monteiro; Marcio Martins Pimentel; Elton Luiz Dantas; Ticiano José Saraiva dos Santos; Maria José Maluf de Mesquita

• Advisor: Lena Virginia Soares Monteiro; Roberto Perez Xavier

Abstract

The Southern Copper Belt, Carajás Province, hosts several iron oxide-copper-gold (IOCG) deposits, including the Sossego (Sequeirinho-Pista-Baiano and Sossego-Curral orebodies), Cristalino, Alvo 118, Bacuri, Bacaba, Castanha, Visconde, and Jatobá deposits. These deposits are situated within a WNW-ESE shear zone in the southern contact between the Carajás Basin and basement rocks. Geological mapping combined with geochronological studies (U-Pb SHRIMP IIe and LA-ICPMS) allowed the characterization of the host rocks of the IOCG deposits in the central-west part of the Southern Copper Belt, which include: (1) 2.74 Ga Neoarchean units (Castanha Porphyry, Sossego granophyric granite and mafic intrusive rocks); (2) 2.87-2.84 Ga Mesoarchean units (Campina Verde Tonalite, Rio Verde Trondhjemite and the Serra Dourada Granite); (3) 2.97 Ga felsic metavolcanic rocks associated with metaultramafic lenses; (4) 3,0 Ga Mesoarchean granitic rocks (Bacaba Tonalite and Sequeirinho Granite). Hydrothermal alteration that affects these rocks consist in regional sodic (albite, scapolite and iron oxides), sodic-calcic (albite-actinolite), potassic (potassium feldspar and biotite), chlorite, and hydrolytic (sericite-muscovitehematite- quartz) alterations, silicification, and epidote-calcite-chlorite formation. However, the IOCG deposits display variations in the distribution of the hydrothermal alteration zones, pointing to distinct crustal levels in which the deposits were installed. Massive magnetite-rich and actinolite-rich bodies are recognized in deeper-emplaced deposits (Sequeirinho-Pista-Baiano orebodies and Castanha deposit), while chlorite and hydrolytic alteration zones are identified in shallower-emplaced deposits (Sossego- Curral orebodies and Alvo 118 deposit). Dating of hydrothermal monazite (U-Pb LA-MC-ICPMS) and molybdenite (Re-Os NTIMS) from the Sequeirinho and Pista orebodies and the Bacuri and Bacaba deposits rendered ages of ca. 2.71 to 2.68 Ga, whilst hydrothermal monazite from the Sossego and Curral orebodies yielded ages of ca. 1.90 to 1.87 Ga. Additionally, molybdenite crystals from Bacuri and monazite from Bacaba provided the ages of 2.76 Ga and 2.05 Ga, respectively. These data suggest that multiple discrete Neoarchean and Paleoproterozoic hydrothermal events were responsible for hydrothermal alteration and ore formation at the Southern Copper Belt. The development of deep IOCG hydrothermal systems (Sequeirinho-Pista, Bacaba, Bacuri, Visconde, and Castanha) at the Neoarchean (2.71-2.68 Ga), related to extensive scapolite-rich zones, was linked to the reactivation of shear zones due to the tectonic inversion of the Carajás basin. In the Orosinian (1.90-1.87 Ga), the establishment of IOCG hydrothermal system(s) in shallower crustal levels resulted in the formation of new deposits (Alvo 118) and orebodies (Sossego-Curral). This event was possibly associated with heat sources due to the emplacement of A-type granites at the province. This event would have caused ore re (mobilization) and overprint of hydrothermal alteration zones, with the formation of hydrolytic alteration over previously formed scapolite-rich zones. Therefore, the Southern Copper Belt presents an excellent example of recurrence of hydrothermal systems along the geological time, responsible for the genesis of world-class IOCG deposits (AU)

• FAPESP's process: 09/18371-0 - Geocronology and isotopic geochemistry applied on metallogenetic evolution of the Copper South Belt, Carajás Mineral Province
• Grantee: Carolina Penteado Natividade Moreto
• Support Opportunities: Scholarships in Brazil - Doctorate