The Paleoproterozoic (Birimian) domain of the West African Craton (WAC) contains numerous economic gold deposits, some of which have been known since antiquity and others exploited since the 20^th century, such as the famous Ashanti deposit in Ghana [1] - [7] . Currently, West Africa is one of the largest gold provinces of Paleoproterozoic age, with a production and cumulative resources of over 10,000 tonnes of gold (or 321 Moz) [8] . Thus, the largest deposits that provide the majority of global gold production are orogenic gold deposits and placers and/or paleoplacers [9] [10] [11] [12] . The Witwatersrand gold deposit in South Africa is the largest placer gold deposit currently known (≈90,000 tonnes of gold) [13] [14] [15] [16] . Bache [13] , points out that placer deposits account for 67.5% of the world’s gold stock, thanks to the phenomenal old placer, the Witwatersrand, which alone is thought to contain almost 58%. Orogenic deposits are those associated with the Eburnean orogeny (2.2 - 1.6 Ga) [17] [18] . These deposits have been the subject of several classifications, the best known of which are those of Milési et al. [19] , who define five (5) types of deposit according to geometry, host structures and mineral paragenesis; Milési et al. [20] , who distinguish three (3) categories based on their relationship with the Eburnean orogeny: 1) pre-orogenic deposits, 2) syn-orogenic deposits and 3) late-orogenic deposits [13] [21] - [25] . That of Boyle [21] , is based on the nature of the surrounding rock. Bache [13] , in addition to the nature of the host rock, also takes into account the geostructural setting and mineralogical association. However, that of Milési et al. [20] , which takes into account the geodynamic context, is a simplified classification, based on a reference period constituted by the Eburnean orogeny (2.2 - 1.6 Ga) and remains the global model for Birimian deposits on the scale of the WAC.

In Senegal, like several provinces of the WAC, the Kédougou-Kéniéba Inlier (KKI) is also home to numerous gold deposits and resources. This is confirmed by recent discoveries of major new deposits in the KKI. These include the Massawa (Randgold-Endeavour Mining), Makabingui (Bassari Resources), Petowal (Toro Gold) and Boto (Iamgold) deposits. Almost all of these deposits are characterized by their location close to major shearing faults such as the MTZ, the Senegalo-Malian shear zone (SMSZ) and the Sabodala Shear Zone [26] - [34] . Numerous geological and metallogenic studies have also highlighted the close relationship between mineralization and geological structures. For this reason, lithostructural data are an essential lever for characterizing the control of gold mineralization.

The Douta gold project is located in eastern Senegal, in the administrative region of Kédougou, in the Saraya department. More precisely, it is located in the commune of Khossanto, near the villages of Mandankholy, Sambarabougou and Douta (Figure 1).

The aim of the present paper is to define the lithological and structural characters of the geological formations hosting the gold mineralization in the Douta permit and to propose a gîtological model in comparison with other deposits of the KKI and WAC in general. But before that, we will first present the geological context of the study area.

The Douta gold project is located in the KKI, western part of the WAC (Figure 2). The latter has been subdivided into three majors Precambrian lithostructural units [35] [36] : 1) in the North, the Reguibat Shield which extends from Mauritania to Algeria; 2) in the South, the Leo Shield which extends over several countries such as Liberia, Sierra-Leone, Mali, Guinea, Ghana, Burkina Faso, Niger and Ivory Coast; and 3) the Kédougou-Kéniéba and Kayes Inliers located between these two entities. The two Shield (Reguibat and Leo) are composed of both Archean (western part) and Paleoproterozoic (eastern part) formations, whereas the Inliers are formed solely of Paleoproterozoic-age terrane. These Paleoproterozoic formations are generally referred to as “Birimian” [1] . The KKI consists exclusively of Paleoproterozoic (Birimian) formations subdivided into two groups separated by the MTZ [19] [37] [38] [39] [40] (Figure 2(b)): 1) to the West, the volcanic-dominated Mako group, intruded by the Badon-Kakadian batholith dated around 2199 ± 68 Ma and 2168 Ma respectively by Bassot and Caen-Vachette [41] , and Dia [42] ; and 2) to the east, the sedimentary-dominated Dialé-Daléma group, cut by the Saraya granite dated at 2079 ± 2 Ma and 2064 ± 30 Ma according to respectively Hirdes and Davis [43] and Delor et al. [44] , and the Boboti massif dated at 2080 ± 0.9 Ma by Hirdes and Davis [43] . Previous studies [37] [42] [45] - [49] and recent works [40] [50] [51] [52] [53] in the Mako volcanic belt showed the bimodal character of volcanism: tholeiitic in the west and andesitic or calc-alkaline in the east. The majority of gold deposits discovered in the KKI are currently located in this Mako volcanic belt, as clearly illustrated in Figure 2(b). The Dialé-Daléma group, located to the east of the Mako group, is distinguished by its detrital character, with slightly metamorphosed sedimentary formations (metasediments) such as greywackes, shales, conglomerates, cipolins, and so on. Carbonate levels are found mainly in the southern parts of the Dialé-Daléma basin. These are essentially the Bandafassi banded marbles and the Ibel and Boundoukodi conglomeratic marbles.

The study area is dominated to the east by metasedimentary formations (greywackes, sandstones, shales, graphitic shales, cherts, quartzites, claystones, and so on). Volcano-sedimentary terms represented by carbonate and silicate breccias are also very present. These epizonal metamorphic formations are cut by mafic intrusions of dolerite and gabbro. Felsic intrusions are also noted, especially to the NE of the permit, and are related to the late-tectonic Sambarabougou granite [54] located close to the study area. In the western part of the study area, mafic formations of the Mako group are more common.

The geology of the Douta permit is dominated by alterites (lateritic cuirass, colluvium, alluvium, erosion, etc.). These mask the rock formations in several places. For this reason, outcrops are quite rare, although a few can be observed. However, the trenches and the various Auger, RAB, RC and Core drilling have enabled us to better study the lithological, petrographic, structural, geochemical and metallogenic characteristics of the main facies in the study area.

The main lithological units in the study area, both in outcrop and in trenches and drillholes (Figure 3 & Figure 4) are meta-greywackes, shales, graphitic

shales, sedimentary breccias (conglomerates), tuffs, claystones, cherts and quartzites. These metasedimentary rocks constitute the host of numerous mafic magmatic rocks (dolerites and gabbros), as well as felsic rocks. Airborne geophysical data indicate strong potassic alteration that could be identified with subcrop granite at Makosa. Thin sections and polished sections were made in the United Kingdom (UK) for microscopic studies. These blades and polished sections correspond for the most part to core samples taken in the target zones (high-grade zones). Petrographic, mineralogical, microstructural and metallogenic studies were carried out using a conventional transmitted and reflected light microscopy, a Scanning Electron Microscope (SEM) and an X-Ray Diffractometer (XRD).

Meta-greywackes: They are more common in outcrops in the southern part of the study area. These metasediments present several hues (Figure 3(a) & Figure 3(b)) and a very variable grain size of the constituents. They consist of millimeter-sized grains of quartz and albite (felsic plagioclase) (Figure 4(a)), cemented in a fine matrix rich in sericite, muscovite and chlorite (Figure 4(b)). Albite minerals are affected by strong sericitization (Figure 4(b) & Figure 4(c)). Thus, albite can be completely replaced by sericite as illustrated in Figure 4(c). XRD analysis of these rocks confirms the presence of quartz, albite, muscovite, chlorite and calcite. Quartz and albite grains are generally monocrystalline and exhibit grain flattening and preferred orientation. Partially recrystallized chalcedony (cryptocrystalline quartz) is also present between quartz and albite clasts. Anatase and sphene are the two most common accessory minerals (Figure 4(d)). They were probably formed from the alteration of ferrotitanium oxides (ilmenite and titaniferous magnetite). The rock is traversed by several generations of veins/veinlets and is very rich in sulphides (Figure 3(a), Figure 3(b) & Figure 4(a)).

Shales: They are among the most abundant facies in the study area, both in outcrop and in drillholes. These facies are of varied origin and may be graphitic, pelitic or greywackous (Figure 3(c) & Figure 3(d)). These rocks are composed of very fine grains corresponding mainly to albite, quartz and graphite, in a matrix rich in sericite and chlorite (Figure 5(a) & Figure 5(b)). The shales are interbedded with the meta-grauwackes and the contact between the two lithologies is generally clear (Figure 5(a)). These metasediments are cut by several quartz/chlorite veins and veinlets, generally parallel to the schistosity, sometimes sheared (Figure 3(c) & Figure 3(d)). However, there are other veins intersecting the major structures. Fine and disseminated sulphides are also present in these rocks.

Sedimentary breccias: They are formed of sub-angular lithoclasts of variable size, cemented by a matrix very rich in silica or carbonate. These are sedimentary breccias. Lithoclasts are generally of variable nature and size, making them heterometric polygenic conglomerates (Figure 3(e)). Lithoclasts dominated by quartz, carbonate and fragments of other rocks are generally oriented and elongated in a preferential direction. The sulphides are dominated by pyrite and arsenopyrite. Sericite and hematite are also present in these rocks.

Cherts: These siliceous facies are widespread in the form of highly silicified benches often referred to as cherts or jaspes. They are more common in outcrops in the central part of the study area, where they are associated with greywackes, sandstones and quartzites (Figure 3(f)). They form small hills, generally elongated following the NE direction (N40). Their mineralogy is dominated by silica (chalcedony and/or opal).

Quartzites: They are more common in the southern part of the permit,

where they are associated with meta-greywackes. Elsewhere, they disappear beneath the lateritic cover. The mineralogy is dominated by quartz but other minerals such as pyrite, arsenopyrite, sericite and hematite are also present.

The various metasedimentary formations described above constitute the host of numerous mafic and felsic magmatic intrusions.

Magmatic intrusions: These correspond mainly to mafic sills and/or dykes of dolerites and gabbros cutting the metasediments (Figures 3(g)-(j)). These rocks outcrop discontinuously in several parts of the Douta permit (Figure 3(h) & Figure 3(i)). They have a microgranular to granular porphyritic texture. These formations are intersected at depth by the majority of drillholes (Figure 3(g) & Figure 3(j)). They are greenish-black hue, more or less speckled with white, and are composed of pyroxenes, plagioclases and secondarily, amphiboles and biotite. In the southern part of the permit, gabbro outcrops present a pegmatitic granular texture with plagioclase megacrysts up to 20 cm in size (Figure 3(i) & Figure 3(j)). Quartz veins are also noted in several areas of the permit.

The Douta gold project is located along the Main Transcurrent Shear Zone (MTZ) [19] [37] [38] [55] , which is a large sinistral ductile shear zone trending broadly NE-SW and becoming N-S towards the north. This regional structure has recorded a long and complex history of tectonic deformation, hydrothermal alteration and gold mineralization. The Douta perimeter is marked by shear corridors. The deformation is evidenced by the presence of numerous brittles, semi-ductile and ductile structures. These tectonic structures are essentially fractures, faults, veins and veinlets, schistosities, boudinages, lineations, shear zones, and so on. The structural study of the study area was based on field data and microscopic laboratory analyses.

The study of the characteristics of gold mineralization in the KKI has provided an overview of the types of mineralization and their similarities to the orogenic model, but also their specificities and variations from one deposit to another. However, the majority of gold deposits discovered in the KKI remain concentrated for the moment in the Mako volcanic belt [27] [28] [30] [32] [34] . The aim here is to present the highlighting of the gold mineralization, the mineralized structures, the bearing lithologies and the paragenesis of the mineralization based on the results of geochemical prospecting, trenching and the various drillholes (Auger, RAB, RC and Diamond core).

The Douta gold mineralization is hosted by Birimian metasediments (mainly meta-greywackes and shales) of eastern Senegal. It is formed by metamorphic and hydrothermal processes thought to be related to the Sambarabougou granitic intrusion. Gold is associated with a paragenesis consisting of quartz/carbonate-sericite-epidote-fine and disseminated pyrite and arsenopyrite ± albite ± chlorite ± hematite (Figure 4, Figure 5, Figure 7 & Figure 17). In fact, all the alteration phases and associated mineral parageneses are located in ductile to ductile-brittle deformation corridors associated with veins such as the NE Makosa shear corridor shown in Figure 15. The mineralization trends NE, i.e. sub-parallel to the Makosa shear zone, and dips steeply (75˚ to 85˚ to the NW) (Figures 10-19). This demonstrates the fundamental role played by the structural in controlling mineralization at Douta. In addition, the gold mineralization is mainly hosted by two (2) lithologies (meta-greywackes and shales). The numerous results obtained argue in favor of lithostructural control of the Douta gold mineralization and its similarity to the orogenic and hydrothermal deposits model. This model of gold vein mineralization associated with disseminated sulphides would correlate with type 5 in the classification of Milési et al. [19] , which corresponds to the late-orogenic deposit in the classification of Milési et al. [20] (Figure 18). It would be comparable to type 4 (veins in a sedimentary host) and type 3 (unconformable veins, stockworks in a volcano-sedimentary or sedimentary context) in the classifications drawn up by Boyle [21] and Bache [13] respectively. This type of deposit has been reported in Canada (Noranda, Lamaque, and Madsen Red Lake), California in the USA (Mother Lode), Australia (Kalgoorlie, Bendigo-Ballarat) and Zimbabwe (Cam and Motor) [13] . It also would correlate with type 2 in the classification of Béziat et al. [24] , which is based on the geometry and style of mineralization. The mineralized veins are thought to have developed in a structural context subsequent to the development of the regional structures. This organization clearly demonstrates the late-orogenic character of Douta’s gold mineralization.

The gold mineralization of Douta presents characteristics comparable to those of other deposits in the KKI, especially in terms of mineralization type, mineralized structures, nature of host rocks and metalliferous paragenesis. Indeed, the lithostructural control of the Douta gold mineralization is similar to that of the Massawa (>4 Moz) [40] [56] [57] [58] and Makabingui (>1 Moz) [54] [59] [60] deposits located 4 km to the West and 1.5 km to the East respectively. Thus, the

characteristic parageneses of these deposits are generally rich in quartz, carbonate, sericite and sulphides (pyrites and arsenopyrites). The fine, disseminated pyrites and arsenopyrites that characterize much of the mineralization at Massawa are highly visible at Douta. Their presence is indicative of gold mineralization in the Douta project. However, studies show that pyrite crystallized from arsenopyrite at Douta, whereas at Massawa, arsenopyrite predates pyrite.

Similar mineral parageneses have also been reported in other KKI deposits including Sabodala [26] [32] [34] [61] [62] [63] [64] .

The brittle-ductile to ductile deformation structures controlling the mineralization at Douta are similar to those described in the Sabodala, Petowal and Boto deposits by Sylla [34] , Dème [62] and Lincoln et al. [64] , respectively. Figure 18 compares the 2D mineralization model for Douta with that for Massawa. These models show many similarities, especially with regard to the geometry of the mineralization. The NNE to NE orientation and subvertical dip (75˚ to 85˚ to the NW direction) of the Douta mineralization (Figure 18(a) & Figure (19)) is almost identical to that of Massawa (Figure 18(b)). It clearly confirms the parallelism with the majors’ structures-oriented NNE to NE in the Douta perimeter. Figure 19 is a 3D model of gold mineralization at Douta. It shows four (4) mineralization lodes with variable grades, all oriented NNE to NE and exhibiting a subvertical dip.

At the WAC scale, similar features appear in a certain number of deposits [31] , notably in the Kalana metasediments [24] [65] [66] , the Loulo [20] [27] [28] [67] and Yatela [68] deposits in Mali, the Wassa and Julie deposits [5] [6] [69] [70] in Ghana, the Poura sandstones in Burkina Faso.

However, some variations, especially in relation to the nature of the host rocks and the age of emplacement, are worth noting. According to Perrouty et al. [5] and Parra-Avila et al. [6] , the gold mineralization at Wassa is pre- to syn-D1 (Eoeburnean) and was emplaced between 2187 and 2158 Ma, unlike that at Douta, which presents a metamorphic and late-orogenic character, correlating with the D2 deformation phase (Figure 20). Indeed, most of the vein-type WAC

deposits [3] [19] [20] [24] correspond to steeply dipping quartz veins or families of veins with an orientation parallel to that of the regional foliation [71] .

Comparable features have also been described in Central Africa, particularly in the Archean Etéké belt in Gabon, where mineralization is contained in veins forming stockworks associated with a hydrothermal event [72] .

The authors would like to thank the Managers, Engineers and Technicians of the African Star Resources et Thor Explorations Companies, who facilitated the realization of this paper.

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

Ndour, M., Ndiaye, P.M., Ekra, K.F., Ndong, A., Faye, M. and Ndour, P. (2024) Lithostructural Control of the Gold Mineralization of the Douta Permit of African Star Resources (Kédougou-Kéniéba Inlier, Southeastern Senegal). International Journal of Geosciences, 15, 303-333. https://doi.org/10.4236/ijg.2024.154017