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Cited by 969Paleontology and Stratigraphy of FossilsGeochemistry and Elemental AnalysisGeological and Geochemical Analysis

Some Precambrian banded iron-formations (BIFs) from around the world: Their age, geologic setting, mineralogy, metamorphism, geochemistry, and origins

Klein, C.·2005·American Mineralogist
DOI 10.2138/am.2005.1871
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Abstract

Banded iron-formations (BIFs) occur in the Precambrian geologic record over a wide time span. Beginning at 3.8 Ga (Isua, West Greenland), they are part of Archean cratons and range in age from about 3.5 until 2.5 Ga. Their overall volume reaches a maximum at about 2.5 Ga (iron-formations in the Hamersley Basin of Western Australia) and they disappear from the geologic record at about 1.8 Ga, only to reappear between 0.8 and 0.6 Ga. The stratigraphic sequences in which BIFs occur are highly variable. Most Archean iron-formations are part of greenstone belts that have been deformed, metamorphosed, and dismembered. This makes reconstruction of the basinal setting of such BIFs very difficult. The general lack of metamorphism and deformation of extensive BIFs of the Hamersley Range of Western Australia and the Transvaal Supergroup of South Africa allow for much better evaluations of original basinal settings. Most Archean iron-formations show fine laminations and/or microbanding. Such microbanding is especially well developed in the Brockman Iron Formation of Western Australia, where it has been interpreted as chemical varves, or annual layers of sedimentation. BIFs ranging in age from 2.2 Ga to about 1.8 Ga (e.g., those of the Lake Superior region, U.S.A., Labrador Trough, Canada, and the Nabberu Basin of Western Australia) commonly exhibit granular textures and lack microbanding. The mineralogy of the least metamorphosed BIFs consists of combinations of the following minerals: chert, magnetite, hematite, carbonates (most commonly siderite and members of the dolomite-ankerite series), greenalite, stilpnomelane, and riebeckite, and locally pyrite. Minnesotaite is a common, very low-grade metamorphic reaction product. The Eh-pH stability fields of the above minerals (and/or their precursors) indicate anoxic conditions for the original depositional environment. The average bulk chemistry of BIFs, from 3.8 through 1.8 Ga in age, is very similar. They are rich in total Fe (ranging from about 20 to 40 wt%) and SiO 2 (ranging from 43 to 56 wt%). CaO and MgO contents range from 1.75 to 9.0 and from 1.20 to 6.7 wt%, respectively. Al 2 O 3 contents are very low, ranging from 0.09 to 1.8 wt%. These chemical values show that they are clean chemical sediments devoid of detrital input. Only the Neoproterozoic iron-formations (of 0.8 to 0.6 Ga in age) have very different mineralogical and chemical make-ups. They consist mainly of chert and hematite, with minor carbonates. The rare-earth element profiles of almost all BIFs,with generally pronounced positive Eu anomalies, indicate that the source of Fe and Si was the result of deep ocean hydrothermal activity admixed with sea water. The prograde metamorphism of iron-formations produces sequentially Fe-amphiboles, then Fe-pyroxenes, and finally (at highest grade) Fe-olivine-containing assemblages. Such metamorphic reactions are isochemical except for decarbonation and dehydration. The common fine lamination (and/or microbanding) as well as the lack of detrital components in most BIFs suggest that such are the result of deposition, below wave base, in the deeper parts of ocean basins. Those with granular textures are regarded as the result of deposition in shallow water, platformal areas. Carbon isotope data suggest that for a long period of time (from Archean to Early Proterozoic) the ocean basins were stratified with respect to δ 13 C (in carbonates) as well as organic carbon content. In Middle Proterozoic time (when granular BIFs appear) this stratification diminishes and is lost. The Neoproterozoic BIFs occur in stratigraphic sequences with glaciomarine deposits. These BIFs are the result of anoxic conditions that resulted from the stagnation in the oceans beneath a near-global ice cover, referred to as “Snowball Earth”. All of the most “primary” mineral assemblages appear to be the result of chemical precipitation under anoxic conditions. There are, as yet, no data to support that BIF precipitation was linked directly to microbial activity. The relative abundance of BIF throughout the Precambrian record is correlated with a possible curve for the evolution of the O 2 content in the Precambrian atmosphere.

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  • Manganese is the most abundant redox-sensitive element in IF after Fe.

    “Manganese, the most abundant redox-sensitive element in IF after Fe (Klein, 2005)”

    From Iron formations: A global record of Neoarchaean to Palaeoproterozoic environmental history (2017) · cites this paper as Klein, 2005

  • Iron formations are iron-rich (15-40 wt%) and siliceous (40-60 wt%) sedimentary deposits that precipitated from seawater throughout much of the Archean and Paleoproterozoic (3.75-1.85 Ga).

    “Iron formations (IF) are iron-rich (15-40 wt%) and siliceous (40-60 wt%) sedimentary deposits that precipitated from seawater throughout much of the Archean and Paleoproterozoic (3.75-1.85Ga) (James, 1954;Trendall, 2002;Klein, 2005).”

    From Trace elements at the intersection of marine biological and geochemical evolution (2016) · cites this paper as Klein, 2005

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Authors
Klein, C.
Affiliations
University of New Mexico (US)
Corresponding author
Klein, C.
Venue
American Mineralogist
Publisher
Mineralogical Society of America
Published
2005-10-01
Volume
90
Issue
10
Pages
1473-1499
ISSN
0003-004X (ISSN-L)
DOI
10.2138/am.2005.1871
OpenAlex
W2030996811
Cited by
969
References
73
Citations by year
2026: 38 · 2025: 67 · 2024: 53 · 2023: 58 · 2022: 66 · 2021: 60 · 2020: 58 · 2019: 56 · 2018: 65 · 2017: 62 · 2016: 72 · 2015: 60 · 2014: 47 · 2013: 47 · 2012: 56
FWCI
7.72
Type
journal article
Language
en
Open access
closed
Locations
  • American Mineralogist (publishedVersion)
  • Helmholtz Centre for Ocean Research Kiel (GEOMAR) (acceptedVersion)
Topics
  • Physical Sciences › Earth and Planetary Sciences › Paleontology › Paleontology and Stratigraphy of Fossils
  • Physical Sciences › Earth and Planetary Sciences › Geochemistry and Petrology › Geochemistry and Elemental Analysis
  • Physical Sciences › Earth and Planetary Sciences › Geophysics › Geological and Geochemical Analysis
Keywords
banded iron formations, Precambrian, Archean, Proterozoic, greenstone belts, Hamersley Basin, Transvaal Supergroup, siderite, greenalite, riebeckite, anoxic depositional environment

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