Elemental and stable isotopes geochemistry of Paleoproterozoic dolomites from Fecho do Funil Formation, Quadrilátero Ferrífero - Brazil
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2017
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Abstract
Geochemical and stable isotopic characteristics of thirteen samples taken from Paleoproterozoic Fecho
do Funil Formation, Quadril atero Ferrífero, Brazil have been analyzed to investigate the depositional
conditions and source of rare earth elements (REEs) in Cumbi quarry dolomites. The major oxides such as
CaO and MgO show variable compositions ranging from 20 to 29 wt % and 14e21 wt % respectively in
most of the samples. The contents of loss on ignition (LOI) are lower (26e42 wt %) than that of the pure
dolomite (~48 wt %). These mass discrepancies are compensated by other oxides including Al2O3 (1.9
e18.7 wt %), Fe2O3 (1.2e6.1 wt %), and K2O (0.5e6.8 wt %) that had been incorporated into the dolomite
samples by the contamination of terrigenous input. Further, SREE contents (20e101 ppm) display significant
variation that also corroborate with contamination of studied samples by detrital materials. The
regression lines of SREE against Al2O3 (R2 ¼ 0.96), Fe2O3 (R2 ¼ 0.65), Ni (R2 ¼ 0.94), Cr (R2 ¼ 0.95), Th
(R2 ¼ 0.98), and Sc (R2 ¼ 0.98) show positive correlation which is probably associated with the input of
terrigenous materials during the deposition of Cumbi quarry dolomites. On the other hand, a negative
correlation between SREE and CaO combined with a large variation in Y/Ho (27e50) is also interpreted
as the sea-water like REE patterns have been masked by the contribution of variable amounts of
terrigenous materials in Cumbi quarry dolomites. All the dolomite samples analyzed from the Fecho do
Funil Formation exhibit a subtle negative cerium anomaly (Ce/Ce* ¼ 0.85e0.95). The dolomites from
Cumbi quarry e Fecho do Funil Formation show narrow variations in Eu anomalies (Eu/Eu* ¼ 1.02 to
1.25). The positive correlation between Eu with Zr, Th and Y supports the non diagenetic influence on this
element (R2 ¼ 0.94, 0.98, 0.84 respectively). Eu contents, in this study show significant positive correlation
with Al2O3 (R2¼0.96), suggesting the detrital origin.
The d13CVPDB (þ6.0 to þ7.2‰) and d18OVPDB ( 10.9 to 10.4‰) values in our samples display a narrow
range which are identical to those shown by successions, characterized by positive carbon excursions,
deposited during the Lomagundi event. We infer that the elevated carbon isotope values of the Fecho do
Funil dolomites likely reflect primary carbon isotope compositions.
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Keywords
C-O isotopes, Rare earth elements
Citation
NOGUEIRA, L. B. et al. Elemental and stable isotopes geochemistry of Paleoproterozoic dolomites from Fecho do Funil Formation, Quadrilátero Ferrífero - Brazil. Brazil. Journal of South American Earth Sciences, v. 79, p. 525-536, nov. 2017. Disponível em: <https://www.sciencedirect.com/science/article/pii/S0895981116302541>. Acesso em: 11 fev. 2019.