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A mixed seawater and hydrothermal origin of superior-type banded iron formation (BIF)-hosted Kouambo iron deposit, Palaeoproterozoic Nyong series, Southwestern Cameroon: Constraints from petrography and geochemistry.
- Source :
-
Ore Geology Reviews . Jan2017, Vol. 80, p860-875. 16p. - Publication Year :
- 2017
-
Abstract
- The Kouambo iron deposit contains banded iron formations (BIFs) and is located in the northwestern margin of the Congo craton. The BIFs are hosted in Palaeoproterozoic Nyong series, a dominantly metasedimentary formations, which were metamorphosed into greenschist to granulite facies. The Kouambo BIFs are medium- to coarse-grained banded rocks consisting of alternation of Si-rich and Fe-rich mesobands, and belong to oxide facies iron formations. Geochemistry analyses reveal that these iron formations are composed of > 96 wt% Fe 2 O 3 and SiO 2 and have low concentrations of Al 2 O 3 , TiO 2 and trace HFSE, suggesting chemical precipitates of silica and iron. Moreover, these BIFs have low concentrations of Al 2 O 3 , TiO 2 and trace HFSEs (high field strength elements, e.g., Zr, Hf, Ta, Pb and Th), suggesting that terrigenous detrital materials contributed insignificantly to the sedimentation. The Post-Archean Australian Shale (PAAS)-normalized REE-Y patterns display seawater-like profile: minor LREE depletion and HREE enrichment, positive Y anomalies. However, they display positive Eu and negative Ce anomalies, and low Y/Ho ratio (average 29), which suggest the influence of the hydrothermal fluids. The weak positive Eu/Eu*( PAAS ) ratio (average 1.5), associated with the low V (17.5 ppm), Co (6.1 ppm) and Ni (27.5 ppm) contents similar to other Superior-type BIFs worldwide, are consistent with the deposition of the Kouambo BIFs in continental marginal sea or back-arc basin environment. In summary, the Kouambo BIFs show a seawater-like REE + Y signature, however, the positive Eu anomalies and reduced Y/Ho ratios relative to seawater indicates a possible mixing with hydrothermal fluids (∼ 0.5%). [ABSTRACT FROM AUTHOR]
- Subjects :
- *HYDROTHERMAL deposits
*GEOLOGICAL formations
*IRON ores
*IRON mining
*FACIES
Subjects
Details
- Language :
- English
- ISSN :
- 01691368
- Volume :
- 80
- Database :
- Academic Search Index
- Journal :
- Ore Geology Reviews
- Publication Type :
- Academic Journal
- Accession number :
- 119076560
- Full Text :
- https://doi.org/10.1016/j.oregeorev.2016.08.021