Metamorphism and PGE-Au content of chromitite from the Ipanema mafic/ultramafic Complex, Minas Gerais, Brazil
Nenhuma Miniatura disponível
Data
2001-01-01
Orientador
Coorientador
Pós-graduação
Curso de graduação
Título da Revista
ISSN da Revista
Título de Volume
Editor
Springer
Tipo
Artigo
Direito de acesso
Acesso restrito
Resumo
The Santa Cruz massif, which forms part of the Ipanema mafic/ultramafic Complex, Minas Gerais, Brazil, has an exposed upward sequence of metadunite, metaharzburgite (including three separate chromitite layers), metapyroxenite, metagabbro, and metaanorthosite. Primary igneous chromite grains in the main chromitite layer are poikiloblastic and tectonically fragmented, and have a narrow (10-20 mum) margin of chromian spinel. Cataclased chromite fragments are extensively replaced and mantled by chromian spinel; they have a composite margin comprised of an inner zone of more aluminous spinel and an euhedral outer zone of more Cr-rich spinel, representing granulite and amphibolite facies metamorphic events, respectively. The contents of platinum-group elements (PGE) and Au in chromite separates are relatively high (Os 45, Ir 23, Ru 136, Rh 19, Pt 98, Pd 63, and Au 83 ppb), and significantly enriched (similar to 4x) over whole rock values. Platinum-group minerals are not observed and micrometre-sized inclusions of sulfide minerals (chalcopyrite and pentlandite) in relict chromite are rare. However, comparison of mineral proportions in the separated chromite and whole rock shows that the precious metals are hosted predominantly in the relict igneous chromite grains, rather than the secondary chromian spinel and primary and secondary Mg-rich silicates. The major element composition and average chondrite-normalized PGE pattern of the separated chromite correspond to S-poor stratiform chromitite. We suggest that the precious metals accumulated with chromite during crystallization of a S-poor magma, and were not remobilized in the relict chromite during the subsequent high grade metamorphism.
Descrição
Palavras-chave
Idioma
Inglês
Como citar
Mineralogy and Petrology. Vienna: Springer-verlag Wien, v. 71, n. 3-4, p. 173-194, 2001.
