1. Introduction

OJG

Open Journal of Geology

2161-7570

Scientific Research Publishing

10.4236/ojg.2023.132005

OJG-122915

Articles

Earth&Environmental Sciences

Petrochemical Studies of Fouimba and Goma Mounts, Central-West of Cote d’Ivoire: Implication on Petrogenesis Tectonic Setting

Allialy

Marc Ephrem

¹^*Siogbo

Davy Bedel

²Kouadio

Fossou Jean Luc

¹Houssou

N’guessan Nestor

¹Kouassi

Brice Rolland

¹Konan

Félix Oufouet

¹Diakité

Sekou

Laboratoire GRME, UFR STRM, University Félix Houphou&#235;t-Boigny de Cocody Abidjan, Abidjan, C&#244;te d’Ivoire

DGMG, Ministère des Mines de C&#244;te d’Ivoire, Abidjan, C&#244;te d’Ivoire

09022023

13029110631, December 20226, February 2023 9, February 2023

2014

This work is licensed under the Creative Commons Attribution International License (CC BY). http://creativecommons.org/licenses/by/4.0/

Petrogeochemical analysis of mafic rocks of Fouimba and Goma Mount in the Séguéla region (central-western C ôte d’Ivoire) is the subject of this study. This analysis combines remote sensing, geophysics, petrography and geochemistry, in order to determine the major characteristics of the mafic formations in the said area, and above all to participate in the detailed mapping of all the Ivorian terrains. The mafic formations encountered in this region are essentially metatonalites to metadiorites, amphibolites, amphibole bearing pyroxenites and porphyry basalts. Chemical analysis indicates that these mafic formations are tonalitic to monzonitic. They are thought to have derived from mantle depleted magmas.

Petrography Geochemistry Mount Fouimba and Goma Seguela Côte d’Ivoire

1. Introduction

Known for its diamond fields fed by kimberlite and lamprophyre dykes, the Séguéla area, located in the central-western part of Côte d’Ivoire, has a certain number of structural, stratigraphic, lithological, magmatic and metamorphic features in its greenstone belts, which at first glance seem to favour the development of significant mineral concentrations.

These numerous particular features have recently attracted the attention of major mining companies, which have acquired a mining exploration permit covering an area of 350 km² and including the two main mountains in the said zone, namely Mounts GOMA and FOUIMBA. Furthermore, it is clear that Côte d’Ivoire does not yet have detailed geological maps covering the entire country, which would enable all the above-mentioned features to be understood, as few detailed studies have been carried out. It is therefore clear that the establishment of a detailed geological map of the Ivorian terrain is more than necessary. It is therefore in this spirit of necessity that the present study aims to highlight, in a detailed manner, all the petro-structural characteristics of the geological formations in the Seguela area, by means of a 1:50,000 scale map.

2. Study Framework2.1. Geographic Location

The town of Seguela is located in the centre-west of Côte d’Ivoire, between longitudes 6˚30'00"W and 7˚00'00"W and latitudes 7˚45'00"N and 8˚15'00"N, with an average altitude of 350 m above sea level. Séguéla is 516 km from Abidjan, the economic capital, and is above all the capital of the Worodougou region, covering an area of 11,427 km² (Figure 1).

2.2. Geologie of Man Shield and Study Area

The West African Craton (WAC) is, according to [1]; subdivided into three distinct zones (Figure 2): Reguibat Ridge northern part formed by Archean formations (3.0 - 2.7 Ga) separated from Paleoproterozoic formations (~2 Ga) Zednes Fault (a northern extension of the Sassandra Fault), and outcropping in Algeria, Morocco and Mauritania. Man or Leo ridge in the southern part formed Archean series of Liberian Shield, and Paleoproterozoic (Birimian) formations of Baoulé-Mossi Domain covering Ghana, Côte d’Ivoire, Guinea, southern Mali, Burkina Faso, and western Niger. Liberian basement and Birimian series are separated by an Archean-Proterozoic transition zone [2], corresponding to a large complex fault: Sassandra submeridian fault [1] [3]. In an intermediate position between the two ridges are two buttonholes, including the Kayes buttonhole in western Mali and the Kenieba-Kédougou buttonhole on either side of Senegal-Malian border. These buttonholes are formed exclusively by Birimian series.

Ivorian Precambrian basement is a characteristic part of the Man Ridge and is essentially composed of a western Archean domain and an eastern Proterozoic domain. Archean-Proterozoic transition of the Ivory Coast is, according to [1] [3], materialised by a large complex fault called Sassandra Submeridian Fault, with an N-S to NNW-SSE orientation. [4] [5] subdivide this transition zone into three sub-domains, including the Boundiali domain or Northern domain, located north of parallel 9˚; Séguéla-Vavoua domain or Central domain, located between parallels 7˚ and 9˚, in which the present study area is located; and SASCA domain or Southern domain, which extends from parallel 7˚N, to Atlantic coast.

The present study area is based on a thread-like trench called Séguéla-Vavoua, oriented N-S, and the geological formations encountered there are essentially composed of volcano-sedimentary units (greenstone belt) generally oriented N-S to NE-SW. These are essentially, metagranites, metamonzonites, biotite and/or hornblende metagranodiorites, gabbros and metagabbros, metadiorites, amphibolites lamprophyres, tonalites, and biotite granites (Figure 3).

3. Analytical Methods

• Major and REE Elements Analysis

The geochemical data were realized within the analytical laboratory of the CRPG (Nancy, France). Major oxide analyses were obtained using emission spectroscopy on ICP-AES whereas trace-element geochemistry was determined by mass spectroscopy on ICP-MS. Results for both major and trace elements are given in Table 1. Samples were chipped and cleaned in acid before being crushed and powdered. Powders were mixed by coning several times to ensure homogeneity. 300 mg of the powdered sample were considered for determination of loss on ignition by living the samples in a muffle furnace at 1000˚C for 12 hours. For preparation of glass fusion discs, the sample was mixed with lithium tetraborate (LiBO3) and the mixture was heated in a furnace to 1050˚C and cast in carbon dies to form the discs.

Major elements, together with V, Cr, Ni, Zn, Ga, Rb, Sr, Y, Zr, Nb, Ba, La, Ce, Pb, and Th were analyzed on the prepared discs by X-Ray fluorescence (XFR) spectrometer at the Centre de Recherche Pétrographique et Géochimique de Nancy (France) using spectrometer ICP-AES Jobin Yvon JY70 for major elements (Si, Al, Fe total, Mn, Mg, Ca, Na, K, P, Ti).

4. Results4.1. Tele-Analytical Data

Two main types of remote sensing data have been used in this paper. These include satellite imagery data and aeromagnetic data.

• Major and REE Elements Analysis

The processing of the satellite images and the systematic analysis of the lineaments obtained allowed us to identify 4 major directions of the structures, of which the main one is oriented NNE-SW, the secondary direction NE-SW, the tertiary one is oriented WNW-SE and the quaternary one is oriented NNW-SSE. In fact, the lineaments between [N0˚- N45˚] constitute about 28.88%; the lineaments between [N46˚- N90˚] constitute about 25.26%; the lineaments between [N90˚- N135˚] constitute about 23.64%; and the lineaments between [N135˚- N180˚] constitute about 22.22%. These so-called major lineament directions are distributed in a very homogeneous manner over the entire study area, and for the most part do not occupy any preferential quadrants in the study area (Figure 4).

• Geophysic

■ Mapof the Reduced Magnetic Field at the Equator

The analysis and interpretation of the map of the reduced field at the equator made it possible to identify the major structural features of the study area (Figure 5).

4.2. Lithology

The geological survey carried out in the study area revealed a range of rock outcrops from which samples were taken for a more detailed petrographic study. Metamorphic formations of the surveyed area are essentially composed of metatonalites, amphibolites and amphibolo-pyroxenites, located mainly on Mount Fouimba.

• Metatonalites

The Metatonalite has been encountered at Sifié (North-West), Béna and Forona (North-East). It is mesocratic with a grainy oriented texture. The Bena sample shows a grouping of light minerals (quartz and feldspars) forming leucozomes and dark minerals (biotites and amphiboles) forming melanozomes, materialising the foliation in the rock. Microscopic examination of this rock has enabled us to identify its mineral paragenesis, which is as follows (Figure 6).

• Amphibolites

They were observed mainly in the Fouimba and Goma mountains, more precisely in the centre of the study area. These formations are hard and compact, moderately to slightly altered, greenish in colour and fine to medium grained. Under the microscope, these rocks have a grano-nematoblastic texture with the following mineralogy (Figure 7).

• Amphibolo-pyroxenites

The outcrops encountered are generally in the form of blocks. They have been found mainly in Monts Fouimba and Goma. They are massive, very dense and greenish in colour. Microscopically, they generally have a granonematoblastic texture with the following mineralogical composition (Figure 8).

4.3. Geochemistry4.3.1. Classification and Geochemical Nature of Fouimba and Goma Greenstones

Chemical compositions of samples from basic formations are plotted into rocks classification diagrams. Inserted in the Na₂O + K₂O (wt%) versus SiO₂ (wt%) diagram of [6], all the basic formations of the study area show mostly gabbroic and dioritic compositions (Figure 9) and (Table 1). A minority of the basic formations are tonalitic to monzonitic.

Table 1 Major elements composition in Séguéla greenstones

Sample	SB4	SB7	SB11B	SB13	SB17A	SB17B	SB18A	SB18B	SB19A	SB19B	SB24B
SiO₂	52.38	47.66	53.37	53.12	49.92	50.27	50.51	49.1	49.05	51.98	51.14
Al₂O₃	13.12	15.35	15.04	5.25	13.44	14.49	14.66	14.94	14.89	13.66	14.6
Fe₂O₃	12.82	13.32	10.79	10.87	15.61	11.62	11.4	13.15	10.77	11.46	10.67
CaO	14.45	11.4	9.16	12.77	11.08	11.94	11.12	9.86	10.96	9.83	8.13
MgO	4.65	7.67	5.53	15.81	6.61	8.34	7.67	8.12	8.15	8.84	7.44
Na₂O	0.24	1.16	3.85	0.87	1.24	0.79	2.15	1.36	1.81	1.56	3.95
K₂O	0.06	0.03	0.86	0.27	0.12	0.04	0.07	0.05	0.06	0.08	1.8
MnO	0.13	0.19	0.17	0.25	0.23	0.16	0.17	0.17	0.17	0.18	0.22
TiO₂	1.11	1.07	0.86	0.36	1.42	0.84	0.97	1	0.75	0.78	0.92
P₂O₅	0.09	0.09	0.14	0.06	0.11	0.06	0.08	0.08	0.06	0.06	0.5
Cr₂O₃	0.03	0.03	0.02	0.08	0.02	0.04	0.03	0.03	0.03	0.05	0.03
LOI	1.19	2.92	0.6	1.41	0.73	2.24	1.77	2.65	3.41	2.23	0.66
Total	100.27	100.89	100.39	101.12	100.53	100.83	100.6	100.51	100.11	100.71	100.06
Ba	26	54	182	110	49	34	32	20	39	22	536
Be	<1	<1	<1	<1	2	<1	<1	<1	<1	<1	3
Co	40.4	57.9	40.6	75.1	53.7	45.8	42.3	56.8	46	43.5	41.6
Cs	0.3	<0.1	0.7	0.7	<0.1	<0.1	<0.1	0.1	<0.1	<0.1	1.1
Ga	22.9	15.8	16.8	7.8	16	13.6	14	13.7	12.6	12	15.7
Hf	1.7	1.6	2.5	1.7	2.1	1.4	1.5	1.7	1.3	1.4	5.9
Nb	2.7	2.6	3.2	1.8	3.2	2	1.9	2.3	1.7	1.8	9.4
Rb	1.8	0.4	29.7	7.6	1.4	0.4	0.4	0.2	0.3	0.4	68.5
Sn	<1	<1	<1	<1	<1	<1	<1	<1	<1	<1	3
Sr	111.5	130.9	356.6	96.2	95.7	75.6	103.5	88.1	89.8	68.6	403.1
Ta	0.2	0.2	0.2	0.1	0.2	0.1	0.1	0.1	0.1	0.1	0.5
Th	0.4	0.3	3.6	2.4	0.5	0.3	0.2	<0.2	0.2	0.3	6.4
U	0.1	<0.1	1	0.5	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	2
V	290	285	212	161	371	255	268	269	231	219	216
W	0.5	0.5	<0.5	3.5	0.5	0.7	<0.5	<0.5	<0.5	<0.5	<0.5
Zr	60.6	59.7	91.1	50.3	77.3	48.8	50.6	51.6	43.6	46.1	214.8
Y	47.4	21.9	17.4	16.8	28.2	19	18.2	18.7	17.4	16.8	22.8
La	101.7	4.3	19.8	10.1	6.8	3.8	2.9	3	3.9	3.4	33
Ce	16.2	9.8	47.5	21.4	12.5	8.3	7.4	7.4	7.6	8	75.8
Pr	30.44	1.44	5.41	3.21	2.06	1.26	1.17	1.15	1.26	1.18	10.51
Nd	112.4	6.9	21.4	14.8	10.4	6.2	6.6	6.1	5.9	6.1	44.3
Sm	19.03	2.22	3.95	3.73	3.15	1.91	1.99	1.94	1.79	1.81	8.25
Eu	5	0.85	1.22	0.84	1.17	0.69	0.81	0.72	0.7	0.72	2.27
Gd	13.74	3.19	3.47	3.68	4.24	2.53	2.72	2.77	2.49	2.45	6.89
Tb	2.03	0.58	0.53	0.57	0.75	0.47	0.5	0.51	0.46	0.43	0.87
Dy	10.45	3.71	3.12	3.23	4.81	3.19	3.14	3.2	3.01	2.88	4.59
Ho	1.97	0.84	0.66	0.65	1.15	0.65	0.72	0.72	0.66	0.61	0.81
Er	5.07	2.5	1.96	1.86	3.17	2.12	2.06	2.14	2.02	1.89	2.33
Tm	0.72	0.37	0.28	0.26	0.45	0.29	0.29	0.32	0.28	0.28	0.31
Yb	4.44	2.33	1.87	1.6	3.01	1.91	1.88	2.09	1.89	1.84	2.07
Lu	0.61	0.37	0.3	0.25	0.45	0.3	0.3	0.31	0.29	0.28	0.3
Mo	0.1	0.3	0.4	<0.1	0.3	0.2	0.3	0.2	0.1	<0.1	0.4
Cu	37.1	126.2	57.6	67.4	138.3	83.4	115.7	122.6	112.8	81.1	13.8
Pb	0.7	0.2	2.6	0.8	0.4	0.3	0.2	0.3	0.1	0.2	3
Zn	18	54	41	14	32	39	35	53	38	40	75
Ni	21	141.9	33	100.7	38	61.2	80.2	144.3	92.7	64.6	49.6

4.3.2. Traces Elements Geochemistry

The MgO vs. Harker Oxides diagrams shows a clustered distribution of representative points of the mafic rock samples from the study area. This distribution indicates positive correlations between MgO and the majority of elements including Al₂O₃, SiO₂, Fe₂O₃, CaO, TiO₂, P₂O₅. Negative correlations exist with SiO₂ but it is less clear with Na₂O which seems to be negative. In detail, the mafic formations of Seguela area show a similar composition (Figure 10).

The Seguela kimberlites have steep REE [7] patterns (Figure 11) with (La/Yb)n = 2 - 23 which is typical of MORB (Table 2). Comparative element abundance plots [8] normalized against primitive mantle values (Figure 12) show marked large-ion with pronounced positive Nb, Nd, and Sm anomalies, and negative K, Sr, P, Hf, and Zr lithophile element (LILE) and LREE enrichments (X > 100 times primitive mantle abundance) anomalies. These are all features previously documented for MORB and Primitive mantle [9]. These elemental abundance patterns indicate that amphibolites have a close affinity with MORB (Figure 13). Incompatibles elements contents are similar to those of N-MORB, intraplate basaltic rocks (e.g., non-DUPAL OIBs) [10] (Figure 14).

4.3.3. Tectonic Setting

[11] diagram indicates that most of mafic formations in the study area would have formed predominantly in mantle depleted context (Figure 15).

Table 2 Fouimba and Goma (Séguéla) greenstones traces elements ratios

Sample	SB4	SB7	SB11B	SB13	SB17A	SB17B	SB18A	SB18B	SB19A	SB19B	SB24B
La/Yb	22.91	1.85	10.59	6.31	2.26	1.99	1.54	1.44	2.06	1.85	15.94
Nb/La	0.03	0.6	0.16	0.18	0.47	0.53	0.66	0.77	0.44	0.53	0.28
Ce/Sr	0.15	0.07	0.13	0.22	0.13	0.11	0.07	0.08	0.08	0.12	0.19
Zr/Hf	35.65	37.31	36.44	29.59	36.81	34.86	33.73	30.35	33.54	32.93	36.41
Nb/Ta	13.5	13	16	18	16	20	19	23	17	18	18.8
Nb/Zr	0.04	0.04	0.04	0.04	0.04	0.04	0.04	0.04	0.04	0.04	0.04
Zr/Nb	22.44	22.96	28.47	27.94	24.16	24.4	26.63	22.43	25.65	25.61	22.85
Ce/Y	0.34	0.45	2.73	1.27	0.44	0.44	0.41	0.4	0.44	0.48	3.32

5. Discussion

The transition zone (Archean-Proterozoic) of Côte d’Ivoire is, according to studies by [12]; [4] subdivided into three domains: the Northern domain (Boundiali domain), the Central domain (Séguéla-Vavoua domain) and the Southern domain (SASCA domain). Compared to the other domains of the transition zone, the present study area (Séguéla-Vavoua domain) shows many similarities but above all important differences:

In the northern domain of the transition zone, [12]; [4] describe intrusive granitic massifs and amphibolites whose characteristics are similar to those described in the present area. In the southern part of the transition zone, [12]; [4] identify as a particular feature the coexistence of high-grade formations considered as Archean (anatexes, tonalitic orthogneisses more or less migmatitic.) and low-grade formations considered as Birimian (intrusive leucogranites, intrusive granodiorites, micaschists…). [13] identifies three major lithological units in this area, and more precisely at Bliéron (Grand-Béréby), which are not all identified in the Séguéla. Metabasites are characterised by metatonalites, gabbros, basalts and amphibolites. Low Nb/La and Ce/Sr ratios observed in the Seguela amphibolites show that also indicates protholite is not sediment recycling [14]. In this case greenstones alteration has caused elevated occupy of the MORB fields (Figure 13, Figure 14). The presence of lower content of Zr (<50 ppm), and higher Zr/Nb ratio (Table 2) varying from 22 to 28, support their MORB nature. A small amount of partial melting of a spinel-garnet-lherzolite source cannot produce lower La/Yb ratios. Lower La/Yb and significantly low Rb, Ba, and Nb represent higher degrees of partial melting.

Seguela ampibolites show relatively Low Rb, Ba, Nb and La/Yb ratios compared with MORB (N-MORB, E-MORB and OIB). Amphibolites, derived from relatively higher degrees of partial melting. Seguela kimberlites have high Zr/Nb ratio and low La/Yb ratios. Conventional interpretation indicates decreasing La/Yb ratios represent an increasing amount of partial melting. Thus it is evident that the Seguela amphibolites are formed by higher degrees of partial melting of the mantle source relative to MORB (N-MORB &e-MORB). The Ce/Y and Zr/Nb ratios are commonly used to infer the degrees of melting involved in the production of basaltic rocks from a peridotitic source. Rocks that derive from a similar source tend to show a decrease in Ce/Y with increasing Zr/Nb. Seguela amphibolites show that Ce/Y decreases with increasing Zr/Nb indicating that they are derived from the same source. The La/Yb ratios (1 to 23) of Seguela amphibolites are similar to MORB [11]. However, the lower concentrations of Rb, Ba and K in Seguela rocks may be indicative of no residual phlogopite in the source.

6. Conclusions

In view of all this, we can conclude that Seguela mafic formations are components of amphibolites, and amphibolo-pyroxenites, metaonalite, mostly affected by greenschist to amphibolite facies metamorphism. Significant hydrothermalism and weathering are marked on every rock. Hydrothermal weathering is proved by carbonation, sericitisation, chloritisation, epidotization, silicification and sulphudation.

Seguela mafic rocks derived from partial melting. Enrichment in incompatibles elements fractionated REE patterns and high volatile content pointed toward a primitive mantle origin. They have on average higher abundances of LILE and LREE. Geochemistry signatures are characterized by (La/Yb)n, Th/Yb, Zr/Nb, and Ta/Yb ratios which are similar to other Ivory Coast, and west African mafic rocks. Ratios reflect subduction zone environment, tholeitic magmas and MORB, IAT, OIB geochemical signatures related to mantle depleted magmas sources.

Conflicts of Interest

The authors declare no conflicts of interest regarding the publication of this paper.

Cite this paper

Ephrem, A.M., Bedel, S.D., Kouadio Fossou, J.L. Nestor, H.N., Rolland, K.B., Oufouet, K.F. and Sekou, D. (2023) Petrochemical Studies of Fouimba and Goma Mounts, Central-West of Cote d’Ivoire: Implication on Petrogenesis Tectonic Setting. Open Journal of Geology, 13, 91-106. https://doi.org/10.4236/ojg.2023.132005

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