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

2009 - 200912010 - 20201

Configurações

Autor: search.filters.author.Fallick, Anthony Edward

Resultados da Pesquisa

Agora exibindo 1 - 2 de 2
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    Stable isotopes and fluid inclusion constraints on the fluid evolution in the Bacaba and Castanha iron oxide-copper-gold deposits, Carajás Mineral province, Brazil.
    (2020) Pestilho, André Luiz Silva; Monteiro, Lena Virginia Soares; Melo, Gustavo Henrique Coelho de; Moreto, Carolina Penteado Natividade; Juliani, Caetano; Fallick, Anthony Edward; Xavier, Roberto Perez
    The evolution of the Bacaba and Castanha iron oxide-copper-gold deposits, located in the Carajás Mineral Province, Brazil, is discussed based on petrography, scanning electron microscopy, stable isotopes, and fluid inclusion analyses. The Castanha deposit is mainly hosted by ca. 2.75 Ga subvolcanic and volcanic rhyodacitic rocks, and gabbros. Early sodic (albite, scapolite) alteration was followed by high-temperature calcic-iron (actinolite-magnetite), potassic (biotite), and minor chlorite and sericite alteration. Calcite, REE carbonate, and epidote represent a late and proximal alteration to ore bodies. Ore breccias with Durchbewegung structure comprise chalcopyrite + pyrrhotite + pyrite ± cobaltpentlandite ± sphalerite ± marcasite and are notable due to their nickel-(zinc) enrichment. The Bacaba Deposit is hosted by the ca. 3.00 Ga Bacaba Tonalite, 2.85 Ga Serra Dourada Granite, and gabbro bodies. Early (ca. 2.70 Ga) alteration at Bacaba includes sodic (albite, scapolite), iron (magnetite), and potassic-iron (K feldspar-magnetite, biotite) associations. Well-developed late chlorite, albite, sericite, calcite-hematite-(musketovite) alteration formed during a Paleoproterozoic overprinting (ca. 2.06 Ga). The Bacaba ore is composed of (I) chalcopyrite ± magnetite ± bornite, and (II) chalcopyrite ± pyrite ± hematite/musketovite, related to early potassic-iron and late alteration, respectively. The Castanha deposit was formed from magmatic fluid (δ18OH2O = 9.5 ± 0.5‰ to 5.2 ± 1.0‰, at 500 to 400 °C) and sulfur (δ34S = 0.1–3‰) sources, with a limited contribution of externally-derived fluids during its evolution. Ore precipitation progressed under considerably low fS2 and fO2 conditions, at relatively high temperatures (> 370 ± 50 °C). Fluid inclusion analyses indicate greater proximity of the Castanha deposit to the source of a hot overpressured magmatic fluid, suggesting its formation in a high-temperature hydrothermal center. Fluidrock interaction coupled with increasing pH might have been the critical factors in destabilizing the metalchloride complex in the Castanha deposit. The Bacaba deposit evolved from a fluid-mixing between hot (> 450 °C) hypersaline CaCl2-NaCl-bearing magmatic brine (> 30 mass % equivalent) and a less saline, colder, and 18O-depleted and D-enriched fluid (e.g., seawater or low-latitude meteoric water). Mixing resulted in an oxidizing environment, dilution (salinities between 35 and 4 mass % equivalent), and temperature drop (160–190 °C), triggering the ore precipitation. At Bacaba, the slightly higher δ34S values (1.3–5.4‰) may reflect an additional contribution of externally-derived sulfur through the thermochemical reduction of oxidized sulfur species. In the Southern Copper Belt, the regional spatial distribution of the sulfur isotope compositions shows the highest δ34Ssulfide values close to the Paleoproterozoic Sossego Orebody and the Alvo 118 deposit. This might suggest significant involvement of externally-derived components (e.g., diluted fluids and sulfur) during late stages of a protracted hydrothermal evolution in the Carajás IOCG deposits.
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    Geoquímica de isótopos estáveis (C, S e O) das rochas encaixantes e do minério de Cu(Au) do depósito cristalino, província mineral de Carajás, Pará.
    (2009) Ribeiro, Andreza Aparecida; Suita, Marcos Tadeu de Freitas; Sial, Alcides da Nóbrega; Fallick, Anthony Edward; Eli, Fabrício; Goulart, Luís Emanoel Alexandre
    Descrevemos dados de isótopos estáveis de rochas encaixantes e de minérios sulfetados do depósito de Cu(Au) do Cristalino (DC), Província Carajás, Brasil. Analisamos calcita de rocha total e de sulfetos de vulcânicas máficas a félsicas e “brechas hidrotermais”. O DC, um depósito arqueano (ca. 2.7Ga) IOCG, ocorre em supracrustais hidrotermalizadas (e.g., alcalinização; carbonatação; sulfetação; etc.) do Supergrupo Itacaiúnas. Dioritos cortam estas rochas e podem relacionar ao minério de Cu. Assinaturas isotópicas de ä34S e ä13C e ä18O plotam nos sulfetos do manto e campo primário dos carbonatitos, respectivamente. Os fluidos do minério podem ser derivados de uma intrusão granítica ou diorítica ou lixiviados de rochas vulcânicas máficas do tipo-MORB.