Bernhard Bühn

Bernhard Bühn
University of Brasília | UnB · Institute of Geosciences

About

44
Publications
8,909
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1,831
Citations
Citations since 2016
4 Research Items
955 Citations
2016201720182019202020212022050100150
2016201720182019202020212022050100150
2016201720182019202020212022050100150
2016201720182019202020212022050100150
Additional affiliations
August 2004 - present
University of Brasília
Position
  • Professor (Associate)

Publications

Publications (44)
Conference Paper
Full-text available
Turmalina é um importante depósito de ouro-orogênico localizado na região NW do Quadrilátero Ferrífero. O depósito está hospedado no greenstone belt arqueano Pitangui (correlato ao Rio das Velhas) e é composto por orto-anfibolitos e pelitos com intercalações de tufos, metamorfisados na fácies anfibolito e intrudidos por um stock granítico. Os corpo...
Conference Paper
Full-text available
Turmalina is an important orogenic gold deposit hosted in an Archean greenstone belt, intruded by a granite stock, and located in the Quadrilátero Ferrífero, Brazil. Three deformation events are recognized (D1 to D3). The three generations of garnet observed (Fig. 1) show that Grt1 blastesis is pre- to syn-D1 and Grt2 growth during the late to post...
Article
The Urucum iron and manganese formation (IF and MnF) in the Neoproterozoic Santa Cruz Formation, Brazil, provides unique insights into Neoproterozoic seawater and the habitat for the evolution of the Ediacaran fauna. Pure Urucum IF drill core samples, i.e. chemical sediments that are devoid of any syn- or post-depositional alteration, are reliable...
Article
Total and dissolved rare earth element (REEs) and U concentrations were determined for waters from Lake Paranoá (Brasilia, Brazil) sampled in the dry (November 2012) and wet seasons (July 2013). Shale-normalized REE patterns of all samples display the M-type lanthanide tetrad effect and large positive Gd anomalies, but only the total REE pool shows...
Article
This work presents the first sulfur isotope data for the Tapira, Araxá, Salitre, Serra Negra, Catalão I and Catalão II alkaline–carbonatite complexes of the Alto Paranaiba Igneous Province (APIP) and the Jacupiranga complex of the Ponta Grossa Province, in central and southeast Brazil, respectively. The APIP complexes are composed of al-kaline sili...
Article
Full-text available
Este trabalho abrange o estudo de química mineral e geocronologia U-Pb de grãos de monazita, composicionalmentehomogêneos, provenientes de várias jazidas explotadas pelas Indústrias Nucleares do Brasil (INB) em placers marinhos da região de Buena,litoral norte fluminense. A área está localizada na região da Bacia de Campos e, geologicamente, perten...
Article
Mass-independent sulfur isotope fractionation (MIF) has been observed in rocks of the geological record older than about 2.45 Ga, a characteristic which is thought to be related to processes in the Neoarchean atmosphere. Samples recording a MIF effect therefore have to contain sulfur of the exogenic sulfur cycle, while endogenic sulfur should not s...
Article
The Vazante Group show varied U–Pb provenance patterns along the basin. Zircon ages range from 936 to 3409Ma, but Paleo- and Mesoproterozoic terrains constitute the main sources of the original sediments. The youngest population (~930Ma) establishes the maximum depositional age of the group. Sm–Nd TDM data show the predominance of Paleoproterozoic...
Article
Full-text available
The “Americano do Brasil” Complex (ABC) is part of a cluster of coeval synorogenic mafic–ultramafic intrusions emplaced during the Brasiliano/Pan-African Orogenic Cycle in Brazil. The medium-sized ABC consists of interlayered dunite, peridotite, websterite, and gabbronorite. High Fo values of olivine (up to Fo88) and the crystallization sequence of...
Article
Full-text available
The Camaguey district, Cuba, is known for its epithermal precious metal deposits in a Cretaceous volcanic arc setting. Recently, the La Union prospect was discovered in the southern part of the district, containing gold and minor copper mineralization interpreted as porphyry type. Mineralization is hosted in a 73.0 1.5 Ma calc-alkaline I-type oxidi...
Article
Full-text available
The Lutetium-Hafnium isotopic system represents one of the most innovative and powerful tools for geochronology and isotopic studies. Combined U-Pb and Lu-Hf in situ analyses on zircon by LA-MC-ICP-MS permit to characterize isotopically the host magma from which it crystallized furnishing significant information for sediment provenance and crustal...
Article
The Mara Rosa arc constitutes the northern portion of the Goiás Magmatic Arc, an important tectonic component of the Brasília Belt that represents the result of the convergence of the Amazonian and San Francisco cratons between 900 and 600 Ma. New in situ zircon U–Pb and Lu–Hf isotope data by LA-MC-ICP-MS on representative magmatic rocks permitted...
Article
Full-text available
The Palaeoproterozoic era was the most important stage of crustal accretion in the South American Platform, being responsible for the development of several magmatic arcs, which represent approximately 35% of the present-day continental crust. The recently mapped Campinorte volcano-sedimentary sequence and associated plutonic rocks represent this P...
Article
This paper presents the first U–Pb and Sm–Nd data for the gneisses of the high-grade Uruaçu Complex, exposed in the northern part of the Neoproterozoic Brasília Belt, central Brazil. Previous studies have interpreted this complex as the exposure of Archaean or Paleoproterozoic continental crust, included, therefore, in the so-called Goiás Massif, a...
Article
Full-text available
Age determinations using the 235U and 238U radioactive decay series to the daughter isotopes 207Pb and 206Pb, respectively, using the mineral zircon (ZrSiO4), are widely used to decipher geological processes. A new method developed in the last couple of years, the laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-IC...
Article
Full-text available
Two bimodal carbonatite complexes in Namibia of Cretaceous age are explored as to the presence and composition of a coexisting carbonatitic fluid. The Kalkfeld and Ondurakorume complexes contain both Ca- and Mg/Fe-carbonatites, composed of calcite alone or calcite with ferroan dolomite, fluorapatite and strontianite. The major element evolution in...
Article
Associated with the Cretaceous Okorusu carbonatite complex (Namibia) is a hydrothermal fluorite mineralization hosted in Pan-African country rock marbles, which resulted from fluid–rock reaction between the marbles and orthomagmatic, carbonatitic fluids expelled from the carbonatite. Yellow fluorite I was deposited in veins up to 5 cm away from the...
Article
We compare the petrogenetic and chemical signatures of two alkali silicate suites from the Cretaceous Damaraland igneous province (Namibia), one with and one without associated carbonatite, in order to explore their differences in terms of magma source and evolution. The Etaneno complex occurs in close spatial proximity to the Kalkfeld bimodal carb...
Article
Full-text available
Basanite intrusions from the Early Cretaceous Erongo complex, Namibia, have compositions consistent with near-primary mantle melts derived from a depth of at least 100 km. These rocks provide a key reference for the mantle component(s) involved in breakup-related magmatism in this region. Initial Sr-Nd-Pb isotope ratios of the Erongo basanites and...
Article
The Okorusu fluorite deposit occurs in Pan-African carbonaceous rocks of the Damara Sequence in northern Namibia. The epigenetic mineralization formed from fluids expelled from the Cretaceous Okorusu carbonatite, which is part of the Damaraland igneous province related to the South Atlantic oceanic opening. The fluorites contain abundant high-field...
Article
Full-text available
. Magmatic fluorapatites of five African carbonatite complexes were analyzed for rare-earth (REE) and trace elements by electron microprobe and high-resolution synchrotron micro-XRF to explore the fluorapatite composition during different stages of carbonatite magma evolution. Early crystallized fluorapatites have La concentrations mostly below 1,5...
Article
Full-text available
The Otjisazu Carbonatite Complex intruded crustal rocks of the Damara Orogen in central Namibia close to the Okahandja Lineament. The igneous complex consists of a suite of mela-syenites, syenites and alkali feldspar syenites, and a carbonatite suite comprising clinopyroxenites with calcite and calcite-garnet lenses, feldspathic clinopyroxenites an...
Article
Full-text available
Anorogenic granites of the Brandberg igneous complex in NW Namibia formed during early Cretaceous rifting and continental break-up of Gondwana. A metaluminous series [SiO2 = 62-77 wt %, molar (Na + K)/Al = 0.8-0.95] includes an early monzonite body, major biotite-hornblende granite, late biotite granite segregations and peripheral dykes of trachyda...
Article
A carbonatite-derived fluid trapped under closed-system conditions is preserved as fluid inclusions in quartzitic country rocks of the Kalkfeld carbonatite complex, Namibia. The fluid inclusion population provides a unique opportunity of investigating in situ the composition of a natural, volatile-rich carbonatitic fluid with all components trapped...
Article
Full-text available
Burbankite, ideally (Na,Ca) 3(Sr,REE,Ba)3(CO3)5, is a rare REE carbonate mineral that until now had been encountered only at a few localities including highly alkaline silicate rocks, carbonatites, and lacustrine sediments. It was identified as an abundant solid phase in fluid inclusions that repre- sent fluids derived from the Kalkfeld carbonatite...
Article
Full-text available
The genesis of manganese and iron formations (MnF and IF) is a closely related process during the Proterozoic, in which oceanic crustal venting provided metal-rich solutions to be deposited on adjacent continental shelves. Their deposition in condensed marine sequences occurred when continental break-up initiated a major transgression and provided...
Article
Extract Manganese mineralization is diverse in occurrence, origin, mineralogy and geochemistry. These variations reflect differences in the processes of formation and depositional environments, which in turn are a response to changes in the land-ocean-atmosphere system over geological time. As such, manganese deposits can act as markers of major ev...
Article
Full-text available
Manganiferous chemical sediments of Neoproterozoic age in Namibia were subjected to high-T-low-P metamorphism during the Damara Orogeny and display unique phase assemblages. The manganese formations are embedded in iron formations and siliciclastic country rocks. This sequence is petrographically subdivided into restricted lithotypes which bear spe...
Article
Full-text available
Lower Paleozoic volcanic members have been investigated by geological, petrographical and geochemical means in a traverse across the Ossa-Morena Zone (OMZ) in south-west Spain. The volcanism lasted from the Early Cambrian to the Early Ordovician, with a peak in the Middle Cambrian. The volcanism is bimodal, starting up with acidic and ending with b...
Article
Full-text available
The Late Proterozoic Damare sequence exposed in the Otjosondu manganese mining area has been affected by three ductile deformational events which resulted in different styles of superposed folding in rheologically highly variable lithostratigraphic units. All deformation events are regionally correlated along tectonic strike on the Damara inland be...
Article
Full-text available
The Otjosondu manganese mining area is located at the eastern exposed extent of the inland branch of the late Proterozoic Damara orogen. In spite of intense deformation and a high-grade metamorphic overprint, the sedimentological interpretation of the manganese-rich rocks and their associated lithologies has led to a paleoenvironmental model which...
Article
Full-text available
Fluorapatite is a frequent liquidus phase in carbonatite magmas, and is also known to crystallize throughout carbonatite fractionation. In principle, its abundance and common occurrence in carbonatitic rocks favours fluorapatite as a petrogenetic and geochemical indicator mineral. We have analyzed magmatic fluorapatites of six African carbonatite c...

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Archived project
O objetivo e resultado desejado dessa pesquisa é a determinação quantitativa e quantitativa da poluição ambiental durante os últimos 50 anos no Distrito Federal. A análise isotópica pode mostrar as fontes dos elementos, em comparação com locais de uma outra história de urbanização e industrialização. Um foco desse trabalho vai ser a escolha de locais de amostragem, ou seja, a identificação dos focos poluentes no DF. Com a separação do material orgânico em madeira e casca, poder-se-á também distinguir o tipo de transporte do material poluente (poluentes em solução versus partículas poluentes). O estabelecimento dos procedimentos científicos e dos métodos analíticos possibilitará a ampliação da pesquisa para outros espécies e situações ambientais distintas melhorando o potencial de avaliação de fontes poluidoras na região do cerrado.