The Troia–Pedra Branca mafic–ultramafic complex, Borborema Province, Brazil: Records of 2.04 Ga post–collisional Alaskan–type magmatism and PGE mineralization

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Felipe Grandjean da Costa
Wagner da Silva Amaral
Hector Rolando Barrueto
João Luiz Carneiro Naleto
Joseneusa Brilhante Rodrigues
Iaponira Paiva Gomes


The Troia–Pedra Branca complex is the most extensive exposure of mafic–ultramafic rocks in the Borborema Province, northeastern Brazil. These rocks have been known for a long time, particularly because of their platinum group element (PGE) mineralization associated with chromitites. The Troia–Pedra Branca complex consists of a succession of serpentinites (after dunite), metachromitites, metaperidotites, hornblendites and metagabbros. PGE–bearing metachromitites are hosted by the serpentinite–peridotite unit, occurring as dispersed blocks, well preserved from weathering. However, host metadunites are poorly preserved, and are only accessed by drill core samples. Scanning Electron Microscopy (SEM) analysis in thin sections of selected metachromitite samples revealed that most of the platinum group minerals (PGM) occur in the chlorite–serpentine matrix, generally in contact with chromite grains. The main PGM are sperrylite (PtAs2), cooperite (PtS), irarsite ((Ir,Pt,Rh)AsS) and hollingworthite ((Rh,Pd,Pt,Ru)AsS). Within chromite grains, very few PGM were found, and sulfide inclusions are mainly chalcopyrite (CuFeS2), pentlandite ((Fe,Ni)9S8) and bornite (Cu5FeS4). Whole–rock geochemical data reveal that metagabbros are LILE–enriched and show subduction–related signature similar to that of Alaskan–type intrusions. Mineral chemistry of chromite and olivine is also compatible with arc–related Alaskan–type complexes. The U–Pb SHRIMP zircon age for a metachromitite sample yielded an upper intercept age of 2036 ± 27 Ma, which we interpret as the crystallization age. However, dispersion in the data implies that zircons lost variable amounts of radiogenic Pb at around 749 ± 54 Ma (lower intercept), which may be related to Neoproterozoic metamorphism. The age obtained for the Troia–Pedra Branca metachromitites (2036 Ma) is younger than the 2190–2130 Ma arc–related plutons of the area, and it is closely related in age to the 2.10–2.04 Ga syn– to late–collisional plutonism and high–temperature metamorphism. Therefore, this Alaskan–type mafic–ultramafic magmatism may be related to the post–collisional setting of the 2.2–2.0 Ga Eburnean/Transamazonian orogeny.

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Grandjean da Costa, Felipe, Wagner da Silva Amaral, Hector Rolando Barrueto, João Luiz Carneiro Naleto, Joseneusa Brilhante Rodrigues, and Iaponira Paiva Gomes. 2021. “The Troia–Pedra Branca mafic–ultramafic Complex, Borborema Province, Brazil: Records of 2.04 Ga post–collisional Alaskan–type Magmatism and PGE Mineralization”. Journal of the Geological Survey of Brazil 4 (2).
Research Papers
Author Biographies

Felipe Grandjean da Costa, Geological Survey of Brazil

Graduated in Geology at the State University of Campinas (UNICAMP) in 2006 and master's degree in Geosciences and Natural Resources at the UNICAMP in 2008. Since 2008, Felipe works as research geologist in the Geological Survey of Brazil - CPRM, and in 2018 got his PhD at the Federal University of Pará (UFPA), working with crustal evolution and gold metallogenesis in the Troia Massif, CE. In the first half of 2018 developed a split-site Phd fellowship program (6 months) in the University of Cape Town, South Africa, working with C, O and H stable isotopes.

Wagner da Silva Amaral, Unicamp - Universidade Estadual de Campinas, Brazil

From 2013 to present work as PhD - Professor at the Department of Geology and Natural Resources of UNICAMP.

Hector Rolando Barrueto, Codelco Mineração do Brasil

From 2018 to present works at the CODELCO DO BRASIL MINERAÇÃO LTDA as coordinator geology, directly responsible for setting new areas for mineral exploration, from initial geological mapping to reaching drilling operations.

João Luiz Carneiro Naleto, Geological Survey of Brazil

From 2010 to present works as Geologist / Researcher in Geosciences (Remote Sensing and Geophysics Division - DISEGE).