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Geochemistry of shales of the Middle Buanji Group in the Kimani area, Southwest Tanzania: Implication to provenance and depositional environment
  • Almachius Mutasingwa,
  • Michael Msabi,
  • Jagarlamudi Seetharamaiah
Almachius Mutasingwa
University of Dodoma

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Michael Msabi
University of Dodoma
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Jagarlamudi Seetharamaiah
University of Dodoma
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Abstract

Major and trace element proxies of the shale samples from the Middle Buanji Group of the Upper Paleoproterozoic (∼1.67 Ga) are reported in this paper to decipher the provenance and depositional environment in the study area. The analytical results of shales in the Middle Buanji Group indicates relatively low percentage of major oxides compositions such as; SiO2 (38.84 – 54.26 %), Al2O3 (6.8 – 10 %), K2O (2.22 – 3.04 %), TiO2 (0.21 – 0.28 %) and CaO (0.15 – 0.51 %) and moderately high Fe2O3 (4.34 – 10.4 %) and P2O5 (1.62 – 2.01 %). The trace element composition of the analyzed shale samples displays wide concentration variation such as Mn (29 -19600 ppm), Ti (468 - 35600 ppm), P (370 – 4610 ppm), Ba (400 – 7730 ppm), and S (5 – 2350 ppm), V (130 – 290 ppm), Zn (5 – 100 ppm), Sr (40 – 160 ppm), As (2 – 70 ppm), and Cr (100 – 250 ppm). Measured proxies of major oxides Al2O3 /TiO2 (10.86 to 15.31) and K2O/Al2O3 (0.23 – 0.35). Variation of Cr concentrations in the shale samples indicates diverse source compositions in the study area ranging from; ultramafic, mafic, intermediate, to feldspar-rich rocks. The measured Mn values in shales have an average of 2527.65 ppm, and proxies of V/Cr: 0.65 – 1.7, V/ (V + Cr): 0.39 – 0.63, and CuO/Zn: 0.004 – 1.7 elements suggest that shales and dominant clay minerals (illite and chamosite) were deposited in marine environment under oxidizing conditions.