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| Description
| - The 250–300-m-thick Carajás Formation in the Carajás mineral province, northern Brazil,consists of banded iron formation (including giant high-grade iron-ore deposits) and minor black shale, overlying a thick pile (2–3 km) of about 2.75-Ga-old metabasalt. Carbonaceous shale with pyrite- and locally pyrrhotite-rich patches from drillcore of the Serra Sul exploration project has up to 29 ppm Mo; iron-speciation analysis indicates essentially ferruginous and for some samples likely euxinic depositional conditions. Positive δ34S-isotope ratios of TRIS are between +0.3 to +10.7 promile, with heavy data restricted to pyrrhotite-free samples. The data suggest microbial sulfate reduction under, at least partially, sulfate-limiting conditions with later overprint by migrating solutions. The black shale is affected by pronounced low-temperature potassium metasomatism (K2O/Na2O > 100; up to 10 wt.% K2O as adularia) related to diagenetic processes at <100°C, and low-grade metamorphic overprint. We studied in detail a 20-cm-black-shale drillcore interval from the middle part of the Serra Sul BIF sequence in detail. Five samples with the most euxinic signature give a Re–Os regression of 2710 ± 38 Ma (2σ) with an initial ratio of -0.37 ± 0.40 (MSWD = 3.3), whereas the full data set (n=11), including black-shale samples from the top and bottom of the BIF sequence, gives a regression of 2661 ± 110 Ma (MSWD = 121). Molybdenum-isotope patterns suggest mixing between a clastic end member, with about 0.2 promile δ98/95Mo for continental input (TDM of 2.8–3.1 Ga according to Nd-isotope data), and 0.9 promile δ98/95Mo for a hydrogenous component. Black-shale samples from the bottom of the BIF sequence have heavy Mo-isotope composition of up to 1.8 promile δ98/95Mo. The significant Mo-isotope fractionation is either the result of an early and transient %22whiff of oxygen%22 at 2.7 Ga, or the result of hydrothermal fluid overprint.
- The 250–300-m-thick Carajás Formation in the Carajás mineral province, northern Brazil,consists of banded iron formation (including giant high-grade iron-ore deposits) and minor black shale, overlying a thick pile (2–3 km) of about 2.75-Ga-old metabasalt. Carbonaceous shale with pyrite- and locally pyrrhotite-rich patches from drillcore of the Serra Sul exploration project has up to 29 ppm Mo; iron-speciation analysis indicates essentially ferruginous and for some samples likely euxinic depositional conditions. Positive δ34S-isotope ratios of TRIS are between +0.3 to +10.7 promile, with heavy data restricted to pyrrhotite-free samples. The data suggest microbial sulfate reduction under, at least partially, sulfate-limiting conditions with later overprint by migrating solutions. The black shale is affected by pronounced low-temperature potassium metasomatism (K2O/Na2O > 100; up to 10 wt.% K2O as adularia) related to diagenetic processes at <100°C, and low-grade metamorphic overprint. We studied in detail a 20-cm-black-shale drillcore interval from the middle part of the Serra Sul BIF sequence in detail. Five samples with the most euxinic signature give a Re–Os regression of 2710 ± 38 Ma (2σ) with an initial ratio of -0.37 ± 0.40 (MSWD = 3.3), whereas the full data set (n=11), including black-shale samples from the top and bottom of the BIF sequence, gives a regression of 2661 ± 110 Ma (MSWD = 121). Molybdenum-isotope patterns suggest mixing between a clastic end member, with about 0.2 promile δ98/95Mo for continental input (TDM of 2.8–3.1 Ga according to Nd-isotope data), and 0.9 promile δ98/95Mo for a hydrogenous component. Black-shale samples from the bottom of the BIF sequence have heavy Mo-isotope composition of up to 1.8 promile δ98/95Mo. The significant Mo-isotope fractionation is either the result of an early and transient %22whiff of oxygen%22 at 2.7 Ga, or the result of hydrothermal fluid overprint. (en)
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| Title
| - Trace-element and multi-isotope geochemistry of Late-Archean black shales in the Caraj´as iron-ore district, Brazil
- Trace-element and multi-isotope geochemistry of Late-Archean black shales in the Caraj´as iron-ore district, Brazil (en)
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| skos:prefLabel
| - Trace-element and multi-isotope geochemistry of Late-Archean black shales in the Caraj´as iron-ore district, Brazil
- Trace-element and multi-isotope geochemistry of Late-Archean black shales in the Caraj´as iron-ore district, Brazil (en)
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| skos:notation
| - RIV/00025798:_____/13:00000516!RIV15-MSM-00025798
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| http://linked.open...avai/riv/aktivita
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| http://linked.open...avai/riv/aktivity
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| http://linked.open...iv/cisloPeriodika
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| http://linked.open...vai/riv/dodaniDat
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| http://linked.open...aciTvurceVysledku
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| http://linked.open.../riv/druhVysledku
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| http://linked.open...iv/duvernostUdaju
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| http://linked.open...titaPredkladatele
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| http://linked.open...dnocenehoVysledku
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| http://linked.open...ai/riv/idVysledku
| - RIV/00025798:_____/13:00000516
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| http://linked.open...riv/jazykVysledku
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| http://linked.open.../riv/klicovaSlova
| - Serra Sul, Carajás, Brazil, black shale, Re–Os, Sm–Nd, Mo isotopes, S isotopes, iron speciation, trace elements (en)
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| http://linked.open.../riv/klicoveSlovo
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| http://linked.open...odStatuVydavatele
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| http://linked.open...ontrolniKodProRIV
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| http://linked.open...i/riv/nazevZdroje
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| http://linked.open...in/vavai/riv/obor
| |
| http://linked.open...ichTvurcuVysledku
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| http://linked.open...cetTvurcuVysledku
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| http://linked.open...UplatneniVysledku
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| http://linked.open...v/svazekPeriodika
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| http://linked.open...iv/tvurceVysledku
| - Pašava, Jan
- Nagler, T.
- Voegelin, A.
- Cabral, Alexandre
- Galbiatti, Henry
- Lehmann, Bernd
- Belyatsky, Ba
- Bottcher, Ma
- Creaser, Robert
- Escher, Pa
- Seabra Gomes Jr., An
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| http://linked.open...ain/vavai/riv/wos
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| issn
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| number of pages
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| http://bibframe.org/vocab/doi
| - 10.1016/j.chemgeo.2013.08.041
|
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