Geochemical Data of Major and Trace Elements of the BIF of ZD Fm of the RGB

Published: 26 April 2023| Version 2 | DOI: 10.17632/n9thzj2f8y.2
Lowanika Victor Tibane


Whole rock geochemical data (wt.%) of the 20 selected samples of Banded Iron Formation (BIF) of the Zandrivierspoort Formation (Fm) of the Rhenosterkoppies Greenstone Belt (RGB) in a descending order are: SiO2 > FeO > MgO > CaO > MnO > Al2O3 > P2O5 > K2O > Na2O > BaO > Cr2O3 > ZrO2 > TiO2 > SrO > V2O5. The trace elements data (ppm) are highest for Ba (476.13), Co (21), and V (129.34), Ni (56,79), and lowest for U (0.20), Sb (0.28), and Cd (0,10). No significant enrichment observed, nonetheless, some transition elements were enriched and their variations are: Ni (1.10 – 56.79), Cu (0.30 – 25.89), Pb (0.10 – 13.00), Ta (0.08 – 11.35), W (1.91 – 17.32). The RGB BIF Fe deposits are depleted in high field strength elements (HFSE) with averages of Ta (1.62), Th (1.34), Sc (4.01), Y (6.00), Zr (9.18). Large ion lithophile elements (LILE) and their average contents are relatively elevated, e.g. Rb (11.11), Sr (6.24), Ba (87.54). The average concentrations (ppm) of the rare earth elements (REE) of BIF samples of the RGB in a descending order are: Ce (10.95), La (10.38), Nd (8.81), Y (6.00), Sm (1.94), Yb (0.67), Eu (0.71), Tb (0.29), and Lu (0.10). The enrichment of light rare earth elements (LREE) relative to heavy rare earth elements (HREE) is shown by the ratios of chondrite normalized (La/Sm)n, (La/Yb)n, and (Tb/Yb)n. Chondrite-normalised REE show strong LREE fractionation with (La/Yb)n 18.10 on average. The RGB BIF REE patterns show enrichment in LREE with (La/Sm)n = 3.52 relative to the HREE with (Tb/Yb)n = 2.75. Correspondingly, the RGB BIF samples show a very weak (+) Eu anomaly with Eu/Eu* = Eu(n)/(0.67Sm(n) + 0.33Tb(n)) = 0.09 when normalized against chondrite values by multiplying Anders and Grevesse (1989) values by the factor 1.36, following after (Boynton; 1985; Taylor and McClennan, 1985). In comparison, the REE data show a weak negative (-) Ce anomaly (Ce/Ce* = Ce/Ce* = log[Cen/(La(n) x Nd(n))1/2] = -0.82 (Ndema et al., 2020; Chombong et al., 2017; Akagi and Masuda, 1998). Pearson’s correlation matrix and binary plots display negative correlations of FeO with La, Ce, Nd, Sm, Eu, Tb, Y, Yb, and Lu. Conversely, unlike FeO, SiO2 shows a positive correlation with La, Ce, Nd, Sm, Eu, Tb, Y, Yb, and Lu.


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Ten samples of BIF were collected from the field using a geological pick and another 10 BIF samples were taken from borehole ZDRP and ZDRT. The BIF samples were sun dried for 2 days at room temperature, crushed to ~95% of 3.0 mm diameter particles using a steel jaw crusher. The materials were milled to <150 μm powder, using a tungsten-carbide swing-disk milling pot. Both the crusher and the pot were periodically cleaned with quartz grains between sample preparations to avoid contamination. Milling was performed for 2-4 minutes and the materials were sieved to get particles target milling of ~95% of ~150 μm. The mixture was pressed into powder pellets using compressive pressure of 50 bars for 2-3 minutes before oven drying for 120 minutes to measure the loss on ignition (LOI) and analysed using X-ray fluorescence (XRF) method. The LOI was estimated by allowing the samples to cool and ultimately measuring the decrease in sample weight. The accuracy of major oxides data for the BIF standard were within typical uncertainty of the XRF data with a detection limit with precision (2σ standard deviation) of major oxide elements calibrated at 0.005 wt.%. The raw data for major oxides including FeO, SiO2, Al2O3, K2O, P2O5, MnO, CaO, MgO, TiO2, Na2O, V2O5, BaO, Cr2O3, SrO, ZrO2 are reported in weight percent (wt.%). Most of the oxides recorded an analytical error of <0.15%, with a loss on ignition (LOI) calculated after oven drying the samples at the temperature >650 °C. Volumetric titration was used to control the quality of FeO(t) content following after Beyeme-Zogo (2009). Trace elements and rare earth elements (REE) data for 20 BIF samples were obtained using inductively coupled plasma mass spectrometry (LA-ICP-MS), using part of the crushed and milled powder materials. About 5 g was prepared using fusion in graphite crucibles at 950 °C and used to measure the content of trace elements and REE (ppm), with the detection limits ranging from 0.1 to 1.0 ppm, with Vanadium (V) being an exception (8.00 ppm). The accuracy of REE analyses for the BIF were within normal uncertainty of the ICP-MS data, whereas the precision of REE was within 15% of the analytical concentrations. Magnetic data was obtained from the 20 BIF samples using a magnetic separation procedure after the samples have been sun-dried for ~48 hours to avoid excessive heating of the powder samples. Portions of the crushed materials were separately blended into a 3-point milling curve established to determine milling time required in a swing-disk mill to achieve a target optimum mill of ~95% passing at ~150 μm particle size using Satmagan technique. About 20 g pulverised aliquot of the principal samples was analysed using a Satmagan technique version 135 at the detection limit of 0.1% at the temperature of 10-40 °C, humidity of <95% in 60 seconds.


Geology, Geochemistry