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Petrography and geochemistry of the Mesoarchean Bikoula banded iron formation in the Ntem complex (Congo craton), Southern Cameroon: Implications for its origin

Petrography and geochemistry of the Mesoarchean Bikoula banded iron formation in the Ntem complex (Congo craton), Southern Cameroon: Implications for its origin
Petrography and geochemistry of the Mesoarchean Bikoula banded iron formation in the Ntem complex (Congo craton), Southern Cameroon: Implications for its origin
Precambrian banded iron formations (BIFs) represent an important source of mineable iron, as well as an archive recording secular changes in the chemistry of the Earth’s early oceans. Here we report petrographic and geochemical characteristics of unweathered drill core samples from the Bikoula BIF, a virtually uncharacterized oxide facies iron formation, hosted in the Mesoarchean Ntem complex, southern Cameroon. The BIF is cross-cut with syenitic veins. The entire succession is highly deformed and metamorphosed under granulite facies conditions. The BIF is characterized by alternating micro-bands of magnetite, quartz and pyroxene. Sulfides (pyrite, pyrrhotite, and chalcopyrite), oligoclase, ferro-pargasite, biotite and ilmenite occur as minor phases. The presence of pyroxene, ferro-pargasite and oligoclase, relatively high contents of major elements such as Al2O3 (0.76–7.52 wt.%), CaO (1.95–4.90 wt.%), MgO (3.78–5.59 wt.%), as well as positive correlations among Al2O3, TiO2, HFSEs, LILEs and transition metals (V, Cr, Ni, Cu and Zn), suggest that the BIF protolith included a significant amount of clastic material. Several samples have preserved seawater-like PAAS-normalized REE-Y patterns, including LREE depletion, and positive La and Y anomalies. Positive Eu anomalies observed in some of the analyzed samples indicate influx of hydrothermal fluids (possibly including Fe and Si) within the basin where the BIF precipitated. However, few samples show unusual negative Eu anomalies that likely result from a large proportion of clastic contamination. The lack of Ce anomalies suggests that the Bikoula BIF was deposited in a basin that was (at least partly) anoxic or suboxic, where it was possible to transport and concentrate dissolved Fe2+.
Bikoula BIF, Ntem complex, Granulite-facies metamorphism, Hydrothermal fluids, Seawater
0169-1368
267-288
Teutsong, Tessontsap
bf0d0b35-ea99-4a37-8a4b-cddb7d07f8f9
Bontognali, Tomaso R.R.
055816bf-d77b-4102-b0f4-a305048eadbe
Ndjigui, Paul-Désiré
da3c63e3-2a1c-48e2-91ee-2712d07aa2b2
Vrijmoed, Johannes C.
06c8d8d9-a75d-47ce-b281-a24713bcf33e
Teagle, Damon
396539c5-acbe-4dfa-bb9b-94af878fe286
Cooper, Matthew
54f7bff0-1f8c-4835-8358-71eef8529e7a
Vance, Derek
9c0575d3-caf4-4d57-b08b-b7a81f6c107c
Teutsong, Tessontsap
bf0d0b35-ea99-4a37-8a4b-cddb7d07f8f9
Bontognali, Tomaso R.R.
055816bf-d77b-4102-b0f4-a305048eadbe
Ndjigui, Paul-Désiré
da3c63e3-2a1c-48e2-91ee-2712d07aa2b2
Vrijmoed, Johannes C.
06c8d8d9-a75d-47ce-b281-a24713bcf33e
Teagle, Damon
396539c5-acbe-4dfa-bb9b-94af878fe286
Cooper, Matthew
54f7bff0-1f8c-4835-8358-71eef8529e7a
Vance, Derek
9c0575d3-caf4-4d57-b08b-b7a81f6c107c

Teutsong, Tessontsap, Bontognali, Tomaso R.R., Ndjigui, Paul-Désiré, Vrijmoed, Johannes C., Teagle, Damon, Cooper, Matthew and Vance, Derek (2017) Petrography and geochemistry of the Mesoarchean Bikoula banded iron formation in the Ntem complex (Congo craton), Southern Cameroon: Implications for its origin. Ore Geology Reviews, 80, 267-288. (doi:10.1016/j.oregeorev.2016.07.003).

Record type: Article

Abstract

Precambrian banded iron formations (BIFs) represent an important source of mineable iron, as well as an archive recording secular changes in the chemistry of the Earth’s early oceans. Here we report petrographic and geochemical characteristics of unweathered drill core samples from the Bikoula BIF, a virtually uncharacterized oxide facies iron formation, hosted in the Mesoarchean Ntem complex, southern Cameroon. The BIF is cross-cut with syenitic veins. The entire succession is highly deformed and metamorphosed under granulite facies conditions. The BIF is characterized by alternating micro-bands of magnetite, quartz and pyroxene. Sulfides (pyrite, pyrrhotite, and chalcopyrite), oligoclase, ferro-pargasite, biotite and ilmenite occur as minor phases. The presence of pyroxene, ferro-pargasite and oligoclase, relatively high contents of major elements such as Al2O3 (0.76–7.52 wt.%), CaO (1.95–4.90 wt.%), MgO (3.78–5.59 wt.%), as well as positive correlations among Al2O3, TiO2, HFSEs, LILEs and transition metals (V, Cr, Ni, Cu and Zn), suggest that the BIF protolith included a significant amount of clastic material. Several samples have preserved seawater-like PAAS-normalized REE-Y patterns, including LREE depletion, and positive La and Y anomalies. Positive Eu anomalies observed in some of the analyzed samples indicate influx of hydrothermal fluids (possibly including Fe and Si) within the basin where the BIF precipitated. However, few samples show unusual negative Eu anomalies that likely result from a large proportion of clastic contamination. The lack of Ce anomalies suggests that the Bikoula BIF was deposited in a basin that was (at least partly) anoxic or suboxic, where it was possible to transport and concentrate dissolved Fe2+.

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Teutsong_etal_2017_OreGeolRev_Bikoula_BIF_Cameroon_Revised_Open_Access_lite.pdf - Accepted Manuscript
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Accepted/In Press date: 5 July 2016
e-pub ahead of print date: 7 July 2016
Published date: 1 January 2017
Keywords: Bikoula BIF, Ntem complex, Granulite-facies metamorphism, Hydrothermal fluids, Seawater
Organisations: Geochemistry

Identifiers

Local EPrints ID: 402616
URI: http://eprints.soton.ac.uk/id/eprint/402616
ISSN: 0169-1368
PURE UUID: 4c065393-bde4-41ed-b743-b3be4690bc07
ORCID for Damon Teagle: ORCID iD orcid.org/0000-0002-4416-8409
ORCID for Matthew Cooper: ORCID iD orcid.org/0000-0002-2130-2759

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Date deposited: 10 Nov 2016 16:43
Last modified: 09 Jan 2022 05:26

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Contributors

Author: Tessontsap Teutsong
Author: Tomaso R.R. Bontognali
Author: Paul-Désiré Ndjigui
Author: Johannes C. Vrijmoed
Author: Damon Teagle ORCID iD
Author: Matthew Cooper ORCID iD
Author: Derek Vance

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