Trace-element and multi-isotope geochemistry of Late-Archean black shales in the Carajas iron-ore district, Brazil

A. R. Cabral, R. A. Creaser, T. Naegler, B. Lehmann, A. R. Voegelin, B. Belyatsky, J. Pasava, A. A. Seabra Gomes, Jr., H. Galbiatti, M. E. Boettcher, P. Escher

35 Citationer (Scopus)

Abstract

The 250-300-m-thick Carajas Formation in the Carajas 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 delta S-34-isotope ratios of TRIS are between +0.3 to +10.7 parts per thousand, 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
OriginalsprogEngelsk
TidsskriftChemical Geology
Vol/bind362
Udgave nummerSI
Sider (fra-til)91-104
Antal sider14
ISSN0009-2541
DOI
StatusUdgivet - 20 dec. 2013

Emneord

  • Serra Sul
  • Carajas
  • Brazil
  • Black shale
  • Re-Os
  • Mo isotopes

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