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

Okunlola, Olugbenga Akindeji; Ajibola, Oluwabusayo Mary; Olisa, Olusegun Gbenga

doi:10.2478/rmzmag-2021-0018

Figures & Tables

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

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.

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.

(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) 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

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

Figures & Tables

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Chemical composition of the REE minerals in charnockites and syenites_

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

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

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

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