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Rare Earth Element Geochemistry and Abundances in Syenites and Charnockitic Rocks of Selected Locations within Southwestern Nigeria

Olugbenga Akindeji Okunlola
Olugbenga Akindeji Okunlola
, 
Oluwabusayo Mary Ajibola
Oluwabusayo Mary Ajibola
 and 
Olusegun Gbenga Olisa
Olusegun Gbenga Olisa
   | Aug 28, 2023
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Article Category: Original Scientific Article
Published Online: Aug 28, 2023
Page range: 75 - 84
Received: Apr 08, 2022
Accepted: Jun 03, 2022
DOI: https://doi.org/10.2478/rmzmag-2021-0018
Keywords
© 2022 Olugbenga Akindeji Okunlola et al., published by Sciendo
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

Figure 1

Geological map of southwestern Nigeria showing the sampling points. (Modified after the Nigerian Geological Survey Agency [5]).
Geological map of southwestern Nigeria showing the sampling points. (Modified after the Nigerian Geological Survey Agency [5]).

Figure 2

Photomicrograph of syenites from: (a) Okeho showing B = biotite, P = plagioclase, Ol = Oolivine, My = mymerkite, O = opaque, G = garnet (b) Iwo showing Q = qQuartz, M = microcline, P = plagioclase, Py = pyroxene (c) Kajola showing P = plagioclase, B = biotite, Or = orthoclase, H = hornblende.
Photomicrograph of syenites from: (a) Okeho showing B = biotite, P = plagioclase, Ol = Oolivine, My = mymerkite, O = opaque, G = garnet (b) Iwo showing Q = qQuartz, M = microcline, P = plagioclase, Py = pyroxene (c) Kajola showing P = plagioclase, B = biotite, Or = orthoclase, H = hornblende.

Figure 3

Photomicrographs of charnockite from a) Akure showing Q = quartz, B = biotite, Opx = orthopyroxene, P = plagioclase, O = opaque; b) Ikere showing Q = quartz, B = biotite, Pl = plagioclase, H = Hornblendeh; and c) Ado showing Q = quartz, B = biotite, P = plagioclase, H = hornblende.
Photomicrographs of charnockite from a) Akure showing Q = quartz, B = biotite, Opx = orthopyroxene, P = plagioclase, O = opaque; b) Ikere showing Q = quartz, B = biotite, Pl = plagioclase, H = Hornblendeh; and c) Ado showing Q = quartz, B = biotite, P = plagioclase, H = hornblende.

Figure 4

(a and b): Back-scattered electron (BSE) image of REE-bearing minerals in the rims of zoned apatite from charnockites; (c and d): BSE image of REE-bearing minerals in syenites.
(a and b): Back-scattered electron (BSE) image of REE-bearing minerals in the rims of zoned apatite from charnockites; (c and d): BSE image of REE-bearing minerals in syenites.

Figure 5

a) Plots of Zr/Y vs Th/Yb for charnockites of the study areas showing three sampling points (after Ross and Bédard [14]; b) Plots of Zr/Y vs Th/Yb for syenites of the study area (after Ross and Bédard [14]); c) Chondrite normalised REE distribution pattern for the syenites (after Boynton [13]); d) Chondrite normalised REE distribution pattern for the charnockites (after Boynton [13]).
a) Plots of Zr/Y vs Th/Yb for charnockites of the study areas showing three sampling points (after Ross and Bédard [14]; b) Plots of Zr/Y vs Th/Yb for syenites of the study area (after Ross and Bédard [14]); c) Chondrite normalised REE distribution pattern for the syenites (after Boynton [13]); d) Chondrite normalised REE distribution pattern for the charnockites (after Boynton [13]).

Chemical composition of the REE minerals in charnockites and syenites.

1 2 3 4 5 6 7 8 9
F   2.41   2.57   2.41
Na2O   1.88   3.6
MgO   0.4   0.52   0.61   0.37   0.86
Al2O3 13.46 13.17 13.3 15.74   1.7   0.49
SiO2 28.39 27.91 29.48   0.75   0.63   0.16 38.14   3.78   4.94
P2O5   5.25   5.85 7 39.4 39.7 40.57   1.87 32.45 25.65
Cl   0.12   0.17   0.12
CaO 18.06 20.12 19.04 57.32 56.94 56.73 12.86 10.9   8.92
Fe2O3 14.22 13.76 12.72 11.85   0.32 12.6
La2O3   5.88   4.91   4.83   4.36 16.99 13.36
Ce2O3 11.01 10.54   8.52   8.66 28.13 25.92
Nd2O3   3.33   3.21   2.62   2.55   5.38   7.25
Total 100 99.99 100 100 100.01 99.99 100
Mineral Monazite Monazite Monazite Apatite Apatite Apatite Monazite

Comparison of the REE concentration in the syenites of the study area with other related rock types (all values in ppm).

1 2 3 4 5 6
REE RANGE AVERAGE AVERAGE Mean RANGE AVERAGE
La 81.72-111.4 257 93.36 42.07 5082-94810 449.5
Ce 150.2-290.2 450 214.36 60.57 7021-90630 798
Pr 18.32-39.02 N/A N/A 5.01 510-5835 75.5
Nd 63.5-149.2 304 105.51 13.04 1592-16418 43.5
Sm 9.75-24.25 66.5 16.72 1.18 110-1147 265.5
Eu 2.19-2.67 7.1 3.69 0.36 22.8-236.5 39
Gd 7.73-10.29 54.8 9.43 1.9 53-513 1.9
Tb 0.83-1.44 6 N/A 0.28 26-52 26
Dy 4.2-6.02 N/A 5.2 1.77 29-338 2.9
Ho 0.73-1.06 N/A 0.98 0.47 23-40 12.5
Er 1.89-2.85 N/A 2.31 1.56 36-395 2.35
Tm 0.28-0.41 N/A N/A 0.15 6-7 5.95
Yb 1.82-2.45 14.4 1.51 1.61 3-52 0.85
Lu 0.28-0.36 2.55 0.21 0.29 0.5-10 0.8
ΣLREE 325.66-648.24 1084.6 433.64 122.23 N/A 1655.4
ΣHREE 16.88-26.91 77.75 19.64 8.03 N/A 29.89
REE 342.54-674.85 1162.35 453.28 130.26 14458-199154 1685.3
ΣLREE/ΣHREE 18.01-24.11 13.95 22.07 15.22 N/A 55.38

Comparison of the REE concentration in the charnockites of the study area with other related rock types (all values in ppm).

1 2 3 4 5 6
REE RANGE RANGE AVERAGE AVERAGE AVERAGE RANGE
La 50.8-195.6 40.9-147 280.38 136 80.5 20.7-81.7
Ce 93.3-338.4 85.3-287 26.24 301 182.5 28.0-159.0
Pr 11.66-41.96 10.4-31.9 85.5 35.3 N/A N/A
Nd 37.7-150.7 46.9-123 13.62 146 95.5 6.9-66.0
Sm 4.81-23.06 9.7-20.3 4.33 26 20 0.76-15.9
Eu 2.11-4.31 2.35-3.85 12.55 5.8 2.5 1.23-3.17
Gd 3.46-18.72 8.2-15.1 1.95 17.7 18.5 6.0-19.4
Tb 0.42-2.39 1.2-1.8 12.28 2.4 2.95 0.08-0.78
Dy 2.05-12.51 5.9-9.2 2.41 12.6 N/A N/A
Ho 0.37-2.23 1.1-1.6 6.65 2.2 N/A N/A
Er 1.08-5.73 3.1-4.2 0.97 5.7 N/A N/A
Tm 0.22-0.77 0.43-0.54 6.47 0.75 1.445 0.03-2.25
Yb 0.98-4.64 2.6-3.2 0.95 4.2 8.2 0.27-13.8
Lu 0.14-0.71 0.37-0.51 30 0.63 1.13 0.21-1.91
ΣLREE 211.26-754.03 196.7-611 422 650.1 381 57.59-325.77
ΣHREE 8.64-47.7 25.9-36.3 61.7 46.18 32.23 6.59-38.14
ΣREE 219.69-801.73 220.02-647.96 484 696.28 413.23 64.18-363.91

Trace and rare elemental concentration in syenites and charnockites in selected locations in southwestern Nigeria (all values in ppm)

1 2 3 4 5 6 7 8 9 10
Ba 2495 1565 1493 1754 1429 1942 1915 1467 1144 2018
Ga 20.3 19.8 20.1 18.4 20 18.7 19 19.8 19 22.6
Hf 24.5 15.7 11.6 10.2 11.6 5.6 5.6 7.4 12.1 20.6
Nb 31.3 30.4 27.3 22.9 27.9 13 12.9 12.2 24.7 39.3
Rb 384 366.9 263.5 315.7 296 93.4 86 69.8 78.6 105.4
Sr 842 438.1 463.9 455.1 464.1 1062 1028 535.7 465.6 399.3
Th 79.6 60.7 30.8 36.1 45.7 7.6 6 16.6 9 16.4
U 5.9 4.8 4.9 3.9 3.4 1.5 1.1 2.2 1.6 0.8
V 90 60 76 51 64 88 85 59 88 116
W 0.7 1.8 2.2 1.7 1.1 0.9 0.7 <0.5 <0.5 0.8
Zr 1063 597 461 3867 441.6 223.6 220 301.5 531.3 895
Y 28 24.9 26.8 22 32.2 17 15.9 11 26.1 64.1
La 141 111.4 93.6 81.7 106.7 51.4 50.8 70.2 72.1 195.6
Ce 290 212.4 178.5 150.2 200.7 96.1 93.3 109.6 137.1 338.4
Pr 39 24.35 23.08 18.32 25.87 11.97 11.66 11.81 17.45 41.96
Nd 149 81.1 83.6 63.5 93.4 42.9 42.7 37.7 62.6 150.7
Sm 24 12.04 13.54 9.75 15.15 6.77 6.64 4.81 10 23.06
Eu 4.58 2.37 2.57 2.19 2.67 2.12 2.11 2.49 2.86 4.31
Gd 14 7.73 8.96 6.85 10.29 5.1 4.82 3.46 7.94 18.72
Tb 1.44 0.97 1.11 0.83 1.24 0.64 0.6 0.42 1.03 2.39
Dy 6.02 4.72 5.31 4.2 6.02 3.2 3.19 2.05 5.07 12.51
Ho 0.88 0.83 0.94 0.73 1.06 0.6 0.56 0.37 0.93 2.23
Er 2.21 2.11 2.4 1.89 2.85 1.63 1.54 1.08 2.49 5.73
Tm 0.32 0.32 0.33 0.28 0.41 0.22 0.22 0.14 0.33 0.77
Yb 1.95 2.03 2.12 1.82 2.45 1.4 1.35 0.98 1.99 4.64
Lu 0.28 0.32 0.31 0.28 0.36 0.21 0.2 0.14 0.31 0.71
Y 28 24.9 26.8 22 32.2 17 15.9 11 26.1 64.1
ΣLREE 648 443.66 394.89 325.66 444.49 211 207 236 302.11 754.03
ΣHREE 26 19.03 21.48 16.88 24.68 13 12.48 8.64 20.09 47.7
ΣREE 675 462.69 416.37 342.54 469.17 224 220 245 322 802
ΣLREE/ΣHREE 24 23.31 18.38 19.29 18.01 16.26 16.6 27.39 15.1 18.81
ΣREE+Y 703 487.59 443.17 364.54 501.37 241.26 235.59 256.25 348.3 865.83
Eu/Eu* 0.77 0.75 0.71 0.82 0.65 1.1 1.14 1.87 0.98 0.63
Ce/Ce* 0.94 0.98 0.92 0.93 0.92 0.93 0.92 0.92 0.93 0.9
(La/Yb)N 48 37 29.77 30.26 29.36 24.75 25.37 48.29 24.43 28.42
(La/Sm)N 3.66 5.82 4.35 5.27 4.43 4.78 4.81 9.18 4.54 5.34
(Ce/Yb)N 38 27.06 21.78 21.35 21.19 17.76 17.88 28.93 17.82 18.86
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