EM - Escola de Minas

URI permanente desta comunidadehttp://www.hml.repositorio.ufop.br/handle/123456789/6

Notícias

A Escola de Minas de Ouro Preto foi fundada pelo cientista Claude Henri Gorceix e inaugurada em 12 de outubro de 1876.

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Filtros

2020 - 20212

Configurações

Assunto: search.filters.subject.Boron isotopes

Resultados da Pesquisa

Agora exibindo 1 - 2 de 2
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    The Santa Lúcia Cu-Au deposit, Carajás Mineral Province, Brazil : a Neoarchean (2.68 Ga) member of the granite-related copper-gold systems of Carajás.
    (2021) Hunger, Raphael Bianchi; Melo, Gustavo Henrique Coelho de; Xavier, Roberto Perez; Moreto, Carolina Penteado Natividade; Talavera, Cristina; Su, Zhi-Kun; Zhao, Xin-Fu
    The Santa Lúcia copper-gold deposit lies in the southeastern portion of the Carajás Mineral Province, along NW-SE splays of the Carajás Fault. The deposit is hosted by a rhyolitic subvolcanic rock, which is crosscut by pegmatite intrusions. The paragenetic evolution at Santa Lúcia encompasses an early stage of chlorite alteration, followed by potassic alteration with microcline, greisenization (quartz-muscovite-tourmaline), copper-gold ore precipitation, and late sericite and hematite vein formation/ fracture infill. Copper mineralization is dominantly represented by chalcopyrite-sphalerite-pyrrhotite-pentlandite-pyrite breccias, which are spatially associated with greisen alteration and characterized by the enrichment of light rare earth elements (LREE), Ni, Co, and Cr. The alteration types, mineralization styles, and ore assemblage suggest that the Santa Lúcia deposit could represent a member of the Paleoproterozoic (ca. 1.88 Ga) granite-related copper-gold systems of Carajás (e.g., the Breves and Estrela deposits). However, the in situ U-Pb analyses of ore-related monazite yield a weighted average 207Pb/206Pb age of 2688 ± 27 Ma, thereby constraining the timing of mineralization at Santa Lúcia to the Neoarchean. Moreover, tourmaline from the pegmatite and within the ore zones has a range of δ11B values from − 3.7 to − 0.6‰, therefore linked to a magmatic boron source. Collectively, these results indicate that the Santa Lúcia deposit is the first reduced magmatic-hydrothermal, iron oxide–poor system formed in the Neoarchean, coeval with the 2.72–2.68 Ga metallogenic event responsible for the genesis of important iron oxide copper-gold (IOCG) deposits in the Carajás Mineral Province.
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    Geochemistry and δ11B evolution of tourmaline from tourmalinite as a record of oceanic crust in the Tonian Ibaré ophiolite, southern Brasiliano Orogen.
    (2020) Arena, Karine da Rosa; Hartmann, Leo Afraneo; Lana, Cristiano de Carvalho; Queiroga, Gláucia Nascimento; Castro, Marco Paulo de
    The isotopic and geochemical evolution of tourmaline constrain the processes of paleo-oceanic lithosphere in ophiolites. The Brasiliano Orogen is a major structure of South America and requires characterization for the understanding of Gondwana supercontinent evolution. We made a pioneering investigation of tourmaline from a tourmalinite in the Ibaré ophiolite by integrating fi eld work with chemical analyses of tourmaline by electron microprobe (EPMA) and δ11B determinations via laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS). Remarkably massive tourmalinite (>90 vol.% tourmaline, some chlorite) enclosed in serpentinite has homogeneous dravite in chemical and isotopic composition (δ11B = +3.5 to +5.2‰). These results indicate a geotectonic environment in the altered oceanic crust for the origin of the tourmalinite. This fi rst δ11B characterization of tourmaline from tourmalinite sets limits to the evolution of the Neoproterozoic to Cambrian Brasiliano Orogen and Gondwana evolution.