The metavolcano-sedimentary rocks of the FGD represent a very deformed sequence of flysch type. In general, they strike NNW-SSE and dip steeply (50˚ to 90˚) towards SW. The main facies are metagreywackes, metasiltstones, meta-argillites, slates and schists. Samples were taken from the facies that could be studied in the polarized light microscope.

1) Amphibole bearing volcanoclastic metagreywacke: Sample 468 E4-a

On a macroscopic scale, the rock is dark grey, and varies from medium-grained (clasts of ≤0.5 mm) to coarse-grained (clasts up to 2 mm) with sub-rounded clasts of feldspar and quartz (Figure 4(a)). It contains carbonate as well as disseminated sulphides.

Under the microscope, the rock shows a granoblastic texture (Figure 4(b)). The clastic fraction of the rock is constituted of plagioclases, quartz and lithic fragments in a poorly sorted recrystallized matrix.

The plagioclases are the most abundant coarse clastic fraction of the rock, they are euhedral to subhedral, cloudy or brownish-coloured and altered. They show varying size, from micrometric to millimetric (0.5 to 2.1 mm) and can be identified by polysynthetic twins or zoning. Their alteration gives a mixture of sericite and epidotes. The quartz is micrometric, angular to sub-rounded; its size is up to 250 µm. The lithic fragments are mainly constituted by plagioclases fragments.

The matrix of the rock is made up of an inequigranular, fine-grained assemblage of minerals, composed predominantly of quartz, with a lower proportion of plagioclases, biotite, actinolite, chlorite, epidote, calcite and opaque minerals. Actinolite is randomly oriented; it is pleochroic in shades of green and developed on the clastic fraction of the rock. The mineral occurs dominantly as aggregates of elongated prismatic crystals, occasionally as hexagonal prisms. Its size varies from micrometric to millimetric (up to 2.3 mm), some crystals show twinning. Biotite is brown, micrometric to millimetric (0.07 to 1.3 m) but generally micrometric. It is sometimes pseudomorphosed by chlorite which can develop from biotite or amphibole.

The other minerals present but in low proportion are: epidote, sericite, calcite, apatite, rutile and opaque minerals.

2) Amphibole-sulphide bearing metagreywackes: Sample 579 E1-a

The rock color is grey and fine to medium-grained (Figure 4(c)). It contains sulphides and carbonates evidenced by their reaction with HCl.

Under the microscope, the rock shows granoblastic texture (Figure 4(d)), with random orientation of the clastic grains.

The clastic fraction of the rock is fine to medium-grained. It is composed of plagioclases, quartz, and lithic fragments embedded in a poorly sorted and recrystallized matrix. The matrix, very fine-grained consists of quartz, feldspars, calcite, epidote, chlorite and sulphides.

Feldspar is micrometric plagioclases, up to 300 µm. They are cloudy or brownish-coloured, much altered and often recrystallized into fine grains. Quartz is subrounded to subangular, it is micrometric in size, up to 600 µm and contains fluid inclusions. It appears as single crystal or polycrystalline, and both show undulose extinction as a result of strain. The boundaries between polycrystalline quartz are sometimes sutured. The lithic fragments are mainly composed of fragments of shale or slate. The rock contains also a fragment constituted of plagioclases laths set in an altered fine-grained groundmass; it is probably a volcanic rock fragment.

The matrix consists of fine-grained quartz, plagioclases, amphibole, chlorite, sulphides, and calcite. Some grains of plagioclases show polysynthetic twins. Amphibole is pleochroic in the shades of green; it is a micrometric hornblende, up to 450 µm, which developed on the quartz-feldspar grains. It occurs as euhedral to subhedral, sometimes it is replaced by chlorite. Calcite is micrometric and presents variable forms: some individuals have anhedral to subhedral shapes. Sulphides are micrometric up to 360 µm, they occur often as well shaped with square form, they are dominantly pyrite.

3) Amphibole—biotite bearing volcanoclastic metagreywacke: Sample 464 E1-f

The rock is light grey in color, medium to coarse-grained and is crossed by carbonate veins (Figure 4(e)).

Under the microscope, it shows an inequigranular granoblastic texture (Figure 4(f)); grains are randomly oriented. The clastic fraction of the rock consists mainly of plagioclases, and secondarily of quartz, all dispersed in a poorly sorted recrystallized matrix. Quartz and plagioclases show locally angular fragments, some with remnants of crystal faces.

Plagioclases are coarse-grained and abundant in the clastic fraction. They are micrometric to millimetric and they reach 2.5 mm. They show different shape, from euhedral to subhedral type, prismatic to angular. Most of the euhedral ones are strongly zoned. Quartz, of micrometric size up to 250 µm is abundant in the fine-grained matrix. It is angular to subrounded with locally some straight borders and discrete gulf corrosion. Some grains present undulose extinction. The lithic fragments are composed of an assemblage of dominant plagioclases and minor quartz.

The matrix is fine-grained and poorly sorted. It is composed of quartz, plagioclases, amphibole, biotite chlorite, calcite epidote and opaques minerals. Amphibole is micrometric to millimetric, up to 1.5 mm, it occurs either as free or in an aggregate. It is replaced mainly by chlorite and appears locally retromorphic. Biotite is brown, micrometric up to 880 µm, sub-automorphic and strongly pleochroic. It contains occasionally rutile. Biotite is quite often replaced by chlorite, which replaces amphibole as well.

Secondary minerals such as calcite, epidote and opaques minerals are also present in small amounts.

4) Sulphide bearing quartzofeldspathic schist: Sample 468 E1-b

The rock is grey in colour, medium-grained, and consists mainly of quartz with a dissemination of sulphides in the matrix (Figure 4(g)). The rock is cut by veinlets (~1 - 2 mm) composed of the quartz-carbonate-sulphide association.

Under the microscopic, the rock shows a foliated texture (Figure 4(h)); marked by orientation of elongate quartz and rare plagioclases.

The clastic fraction of the rock consists of dominant quartz and very minor altered plagioclases. The quartz is stretched and micrometric, in general up to 550 µm. It shows locally polycrystalline form composed of granoblastic grains with triple junction at 120˚. The rare grains of plagioclases, up to 300 µm, are unrecognizable, most of them are strongly altered and give a mixture of micrometric grains of sericite and epidote.

The matrix consists of very fine-grained quartz, feldspar, sericite, carbonate, epidote and opaque sulphide-type minerals.

5) Andalusite hornfels: Sample 464 E2-b

The rock is dark-coloured and made up of very fine unrecognizable grains with the naked eyes or with a magnifying glass (Figure 5(a)).

Under the microscope, the rock presents a granoblastic texture (Figure 5(b)). It mainly contains porphyroblasts of andalusite and secondary grains of quartz and plagioclases, both are embedded in a very fine clay matrix that appears dark and indistinct.

The porphyroblasts of andalusite are altered, many of them occur as euhedral to anhedral and appear in rhombic-shaped to weakly elongated. They are micrometric, (up to 500 µm), and colourless in plane-polarized light; in cross-polarized light, they show a mixture of sericite, chlorite and opaque minerals. Andalusite shows locally numerous dark inclusions arranged in the centre, and propagate towards the diagonals, drawing a typical cruciform pattern of graphite rich inclusions. This type of andalusite is commonly called chiastolite.

The quartz is more dominant than the plagioclases in the matrix or groundmass possibly former glass. It is micrometric (up to 250 µm) and appears more or less flattened with undulose extinction, the plagioclases show sometimes twinning.

The clay matrix is composed of very fine-grained components which are indistinct.

6) Andalusite slate: Sample 037 E1-e

It is a dark-coloured metasedimentary rock made up of very fine grains not identifiable with the naked eye or with a magnifying glass (Figure 5(c)) which alternates with light medium-grained (Figure 5(e)) and fine-grained rocks (Figure 5(g)) identified respectively as feldspathic metagreywacke and feldspathic metasiltstone.

Under the microscope the rock presents a foliated texture outlined by the orientation of elongate altered andalusite in very fine dark grained indistinct matrix (Figure 5(d)).

7) Feldspathic metagreywacke: Sample 037 E1-e

Under the microscope, the medium-grained light layer of the sample shows a more or less oriented granoblastic texture (Figure 5(f)). It is made up of abundant quartz grains and feldspar dispersed in a very fine-grained matrix composed of quartz, plagioclases, calcite, and opaque minerals.

Quartz of micrometric size (up to 850 µm) contains many fluid inclusions. It presents variable shapes (subrounded, subangular, stretched), and shows often an undulose extinction. It is in monocrystalline dominant form, or secondarily in a polycrystalline form. The plagioclases are also micrometric (up to 600 µm). They are heavily altered, partly or completely recrystallized but the residual grains are still recognizable by their characteristic twins.

The matrix contains very fine-grained quartz and feldspars. Subordinate minerals are represented by epidote, sericite, calcite, and opaques (well disseminated) minerals. All of these minerals are micrometric in size.

8) Feldspathic metasiltstone: Sample 037 E1-e

Under the microscope, the fine-grained light layer of the sample shows a more or less oriented granoblastic texture (Figure 5(h)). It is made up of abundant quartz grains and subordinate feldspar, both are dispersed in a very fine-grained matrix composed of indistinct quartz and plagioclases, epidote, sericite and leucoxene.

The clasts of quartz are micrometric in size and reach rarely 100 µm. They present variable shapes (subrounded, subangular, stretched), and show often an undulose extinction. The plagioclases are smaller than quartz, they are often inferior to 70 µm. Some of the clasts are still recognizable by their twining.

The dominant very fine-grained matrix contains indistinct quartz and feldspars. Subordinate minerals are epidote, sericite, leucoxene.

Numerous quartz-feldspar veins occur within the altered metavolcano-sedimentary rocks and plutonic intrusive rocks of the open-pits as well on the drill cores. Their dimensions vary in width and length, from millimetre to centimetre in width and from centimetre to decimetre in length. In the open-pits, their length can reach 3 m. Their contacts with their hosts are clear and they are occasionally interconnected.

1) Brecciated quartz-feldspar vein: Sample 576 E1-d

It corresponds to a filling of fracture of intrusive rock by brecciated quartz-feldspar vein (Figure 6(a)).

Under the microscope, the rock shows a granoblastic texture marked by an association of quartz and plagioclases in a minor poorly sorted matrix of micrometric size (Figure 6(b))

The quartz is anhedral, micrometric to millimetric (up to 4 mm), highly strained with undulose extinction. It is also cloudy because of the great numbers of fluid inclusions. The Plagioclases crystals are subhedral with a micrometric to millimetric size (up to 1.8 mm). They show both simple and multiple twins, the twins are occasionally bended. Some of the plagioclases are partly recrystallized.

The matrix is composed of rare micrometric chlorite, sericite and epidote.

2) Sulphide-bearing chlorite-quartz vein: Sample 468 E5-a

It is a filament of milky-white quartz, made up mainly of quartz veinlets, sulphides, chlorites and carbonates, observable with the naked eyes (Figure 6(c)).

Under the microscope the vein shows a granular texture formed mainly by the spectacular development of sutured crystals of quartz in a matrix composed of quartz, plagioclases, chlorite, calcite, sericite, epidotes and opaque minerals (Figure 6(d)).

The dominant crystals of quartz are millimetric and may exceed 5 mm in length. They are anhedral, sutured and strained. They expose undulose extinction and occasionally some subgrains. The phenocrystals of plagioclases are micrometric, up to 600 µm and subhedral.

Calcite has variable shape; it occurs in free form or in an aggregate of grains which cut the crystals of quartz. This shows its late character compared to quartz. The chlorite has a dark blue interference colour in crossed-plane polarized. It is associated with sericite, epidote, sulphides and carbonates.

3) Quartz-carbonate vein: Sample 468 E6-a

It is a milky-white vein, composed mainly of quartz and carbonates (Figure 6(e)).

The rock shows a granular texture under the microscope and displays dominant quartz in a matrix composed of quartz, carbonates, and rare muscovite (Figure 6(f)).

Quartz is micrometric in size and occurs as anhedral strained crystals which display undulose extinction or subgrains.

The matrix is poorly sorted with dominant micrometric grains of carbonates which intersect or grow between the quartz.

1) Tonalite: Sample 468 E2-c

The tonalite is a leucocratic rock with a granular texture (Figure 7(a)).

Under the microscope, the rock presents a granular porphyritic texture, consisting of altered phenocrysts of plagioclases, quartz, amphibole and biotite dispersed in recrystallized groundmass of feldspar, quartz, amphibole, biotite, chlorite, epidote, calcite, rutile and opaque minerals (Figure 7(b)). The inequigranular matrix consists of quartz, plagioclases, biotite, chlorite and calcite.

The plagioclases phenocrysts are elongated and heavily altered. They vary in size (approximately 1 to 2.5 mm) and are transformed in a mixture of feldspar, quartz, sericite, chlorite, opaque and epidotes. The feldspars present in the groundmass are micrometric and granular. The quartz occurs in the form of anhedral grains of micrometric size (50 to 450 µm). The amphibole is generally retromorphic, biotite is brown, micrometric in size (200 to 400 µm).

Chlorite occurs in micrometric size (200 to 920 µm) with varying shapes. Some individuals show an elongated subhedral form. Chlorite is weakly pleochroic in the shades of light green. It pseudomorphosed both amphibole and biotite. Calcite is anhedral and granular; its size varies between 60 to140 µm. It intersects the chlorite and therefore appears to postdate it.

The accessory minerals are rutile and leucoxene.

2) Microtonalite: Sample 037 E2-a

It is a leucocratic rock with a fine-grained structure. It is made up of visible dark chlorite and light feldspars (Figure 7(c)).

Under the microscope, the rock presents a porphyritic microgranular texture, consisting of relics of weathered plagioclases, dispersed in a recrystallized matrix of plagioclases, quartz, epidote, chlorite, calcite, zircon, leucoxene, and opaque minerals (Figure 7(d)).

Residual plagioclases are completely altered; alteration gives a mixture of chlorite, sericite, epidote. Some phenocrysts show occasionally twining which allow them to be identified.

The matrix of the rock is composed of plagioclase, quartz, chlorite, epidote and opaque minerals. The plagioclases vary in size (50 - 300 µm); many of them are euhedral and show a twining, some of them form an association in a cluster that looks like a bouquet of flowers. Chlorite occurs in the form of small aggregate grains of micrometric size (<50 µm). It invades and pseudomorphoses massively a former crystal which could be amphibole. Opaque minerals are abundant and dispersed in the micrometric matrix. The calcite shows poorly crystallized grains but it still identifiable by its high birefringence and by the presence of cleavages on the well-formed sections. Epidote is often seen with chlorite.

The accessory minerals are zircon and leucoxene.

3) Quartz diorite: Sample 466 E2-d

The rock is mesocratic, fine-grained; it is made up of quartz, plagioclases, amphibole and biotite, all visible to the naked eyes (Figure 7(e)).

The rock shows a porphyritic granular texture (Figure 7(f)) with a dominant plagioclases, amphibole and biotite.

The plagioclases are altered and micrometric, up to 900 µm. The alteration obliterates their original form; it gives a mixture of white mica (sericite) and epidote. Very rare phenocrysts show twining. No K-Feldspar has been observed. The amphiboles are micrometric to millimetric (up to 3 mm), prismatic or elongate, free or in aggregate. They are pleochroic from pale to green pale and develop on quartz and plagioclases. Biotite is micrometric to millimetric (up to 1 mm), brown-coloured and occurs as subhedral, it replaces locally amphibole.

The recrystallized matrix of the rock is formed mainly of quartz, plagioclase, biotite, calcite chlorite, epidote, apatite and opaque minerals. Quartz is micrometric; it presents xenomorphic form and shows discrete undulose extinction. Chlorite is also micrometric and has variable forms; it pseudomorphoses both amphibole and biotite.

The accessory minerals are apatite and opaques; apatite in elongated (up to 1.5 mm) or hexagonal sections (up to 230 µm).

4) Quartz diorite: Sample 466 E1-c

It is a dark coloured rock, medium-grained with a granular porphyric texture (Figure 7(g)). The facies are cut by carbonate veins and locally contains carbonates in the matrix.

Under the microscope, the rock consists of phenocrysts of plagioclases, amphiboles and biotite dispersed in a recrystallized matrix (Figure 7(h)).

Plagioclases are heavily altered and give a mixture of sericite and epidotes. The weakly damaged crystals show a millimetric size up to 2.3 mm. The older phenocrysts are generally replaced by new grains of plagioclases largely present in the matrix. Amphiboles are micrometric to millimetric (0.6 - 3.5 mm), and slightly pleochroic in the brown tones. The phenocrysts are in elongated or hexagonal prismatic form. The elongated crystals could attain 3.5 mm. Both are twinned and pseudomophosed locally by biotite. Quartz is micrometric to millimetric (up to 1.3 mm), it shows undulose extinction. Biotite is micrometric to millimetric, up to 2.2 mm, and subhedral. It is brown in plane-polarized light and it contains a lot of needle-like rutile inclusions. Locally, it is pseudomorphosed by chlorite which takes its form. Chlorite is in association with epidotes and rutile.

The rock matrix is essentially formed of quartz, relics of older plagioclase, chlorite, calcite, epidote, opaque minerals.

The other accessory minerals are apatite, rutile, and opaque minerals. Apatite is the dominant accessory mineral. It is in the form of elongated euhedral prismatic crystals or in a hexagonal section. The elongated crystals are micrometric to millimetric, up to 1.5 mm.

The rocks of the FGD exhibit steeply dipping foliation, the main marker of this deformation is the foliation-S1. In the open-pits, it developed remarkably in the fine-grained facies on the west side. The foliation-S1 has been identified and measured in the open-pits (N = 195) and on the drill cores (N = 40). In both cases, it is parallel to the stratification-S₀ (Figure 9(a) and Figure 9(b)). This parallelism defines an S₀ - S₁ composite surface which trajectories are fairly homogeneous in the open-pits and on the drill cores. In either case, it strikes between N130˚ and N180˚. Its dip direction fluctuates between SW to W and its values range from 50˚ to 90˚ (Figure 10 and Figure 12). On average, S₀ - S₁

strikes NNW-SSE and dips steeply towards the WSW. It is the major deformation of the deposit.

A stretched quartz and andalusite have been identified respectively on thin sections of the quartzofeldspathic and andalusite schists (Figure 4(h) and Figure 5(d)). They are probably carried by the foliation plane. Both are interpreted as a result from the same ductile deformation.

In the FGD, there are two types of bodies of minerals which have been precipitated into the fracture within rocks: 1) en-echelon tension gashes, 2) and a quartz vein arrays. The former marks the ductile-brittle deformation recognized in the deposit.

The tension gashes are organized en-echelon, some of them are curveted (Figure 9(c)). They have been observed locally at the west side of the main open-pit at its level 365 m. They extend to the length of 1.4 m, with an opening of a few cm thick (7 - 20 cm). In the open-pits, shear fabrics indicate dextral movement in the NE-SW direction (Figure 9(c)).

The quartz vein arrays have been observed and measured in the open-pits (N = 187) as well on the drill cores (N = 42). They intersect all the lithologies of the deposit and seem to be later. The quartz vein arrays have a millimetric to centimetric thickness and rarely reach the meter. However, locally in the open-pits, some veins show a length varying between 1 and 3 m. In the open-pits two sets of quartz vein arrays are secant on the S₀ - S₁ surface (Figure 9(d) and Figure 9(e)), while one is parallel to it (Figure 9(b)). On the drill cores, quartz-carbonate

veinlets are observed parallel to the S₀ - S₁ and microfolding affects them (Figure 11).

The measurements of the orientation of the quartz vein arrays shows three sets of populations (Figure 10 and Figure 12):

• a first set of population named QV₁: it strikes N140 to N180 (NW-SE to N-S) and dips steeply (50˚ - 80˚) towards the SW or W;

• a second set of population labelled QV₂: it strikes N40 to N80 (NE-SW to ENE-WSW) and dip more steeply (65˚ - 85˚) towards the SE, NW or SSE;

• a third set of population designated QV₃ with an E-W trending and a dip varying between 6˚ to 70˚ towards the S or N.

Some shifts between the quartz vein arrays have been observed locally in the open-pits, in particular between QV₂ and QV₃, the latter being shifted in a dextral movement. However, most of veins crosscut each other; they seem to be contemporaneous, even if field observations do not allow an obvious relative chronology to be established between the three sets of populations. The most mineralized veins show an NE-SW trending with a dip toward SE [71].

It is marked by faults and fractures which have only been observed and measured in the open-pits (Figure 9). They display several directions; some of them are sub-parallel to the S₀ - S₁, others are totally sequent.

Structural analysis of the trending of the faults shows two (2) main directions (Figure 10):

• NNW-SSE trending with a shallow dip to the ENE;

• ENE trending with a shallow dip to the SSE.

The NNW-SSE faults correspond to reverse faults while the ENE directions seem to be linked to a shear zone.

The fractures show late characters, they cut the quartz vein arrays. Analysis of the density of the poles of the fractures does not show any preferential orientation on the stereogram, and on the rosette (Figure 10).

The first stage of deformation is ductile. It is characterized by structural features developed only in the metavolcano-sedimentary rocks and include mostly NNW-SSE foliation trending. It is marked by the parallelism between schistosity and stratification which suggests an isoclinal folding context. It is responsible for the crustal thickening of the metavolcano-sedimentary rocks and is linked to a compression event-oriented ENE-WSW. It is the major deformation of the deposit and it has a regional extent.

Similar striking of S₀ - S₁ have been reported for the Kalana gold deposit with however opposite dipping direction [69] [73]. The opposition of the dip directions of S₀ - S₁ at Faboula and Kalana suggests that the two deposits are located on either side of a syncline where the Kalana area occupies the western limb of the fold and the Faboula the oriental one. This assertion is in line with the analysis of the attitude of the tension gashes observed in the two deposits.

Across the WAC, isoclinal folding has been described. In the near ca. 2125 - 2090 Ma Bagoé basin, composite surface S₀ - S₁ has been reported by [15]. According to these authors, it presents similar strike (NNW-SSE) but dips steeply towards the ENE at the Bagoé Bridge, outside the village of Niamala and in the Banifing River. In the adjacent ca. 2115 - 2090 Ma Siguiri basin NNW-SSE oriented folds, due to ENE-WSW compression, have been described by [49].

This stage is poorly expressed in the field. It has been identified through the interpretation of the sigmoidal en-echelon tension gashes filled by quartz. Its extent remains unclear, and there is no evidence of the presence of a large regional shear zone in the deposit.

The development of the tension gashes is related to the stress field underwent by the rocks when they were buried. It is well known that sigmoidal gashes are related to shear zones which develop at an acute angle (45˚) to the direction of maximum compressive stress given by the tip of the gashes. In the deposit, the curvature of the sigmoidal gashes indicates a dextral movement in the NNE-SSW direction which results from an ENE-WSW regional shortening.

In the Kalana deposit, a set of sinistral sigmoid tension gashes related to an ENE-WSW compressive stress has been identified by [76]. The opposition between the kinematics of shearing at Faboula and Kalana suggests that these two deposits are located on opposite limbs of the same fold as evidenced by the similar strike of S₀ - S₁ and its opposite dip direction.

At the scale of southern Mali and the Leo-Man Shield, shearing has also been described from neighbouring NNE-SSW Siekorolé dextral shear zones [77] and the NE-SW to NNE-SSW Banifing sinistral Shear Zone in the Bagoé basin [3] [15] [62] [74] [75]. In the bordering Siguiri basin, at its southern edge not too far from the FGD ductile deformation along sinistral faults occurred after the crystallization of the granodiorites, around 2.08 Ga [8]. These authors related it to a Late Eburnean ENE-WSW shortening. Further in the south, sinistral shearing has also been reported for the Sassandra Shear Zone at the border of the Archean of Kénéma-Man and the Birimian of Baoulé-Mossi domain [55].

Numerous quartz vein arrays show three different orientations within the FGD. One type (NW-SE to N-S) is parallel to the regional composite surface S₀ - S₁, while two others (NE-SW to ENE-WSW and E-W) crosscut it. Quartz veins arrays have been reported in the Kalana gold deposit; they are controlled by the intrusive granitic rocks [78].

According to [73], there are two groups of quartz veins crosscutting a bedding-parallel schistosity surface, striking N170 and dipping steeply towards the E: 1) a first set of groups which show more irregular measured strikes, roughly N-S but some of them are oriented NE-SW and others E-W; 2) a second set of groups, more homogeneous than the other, with closely spaced veinlets striking NE-SW. Both are coeval according to the authors, a point of view shared by Kusters [76] and [78]. The latter suggested that there are many parallel veins, stacked on top of each other, due to their different strikes and dips, some of them must cross and cut each other.

According to [70], the gold mineralization of the Faboula deposit occurs in the form of free gold and is associated with NE- SW quartz veins steeply dipping to SE, which in this study corresponds to the second set of population labelled QV₂. A major phase of mineralization commonly associated with quartz veining during a D₃ deformation linked to WSW-ENE shortening and formation of the dextral Siekorole shear zone is described by [77]. In the neighbouring Siguiri basin, gold mineralization is associated with one main and, at least, three minor sets of auriferous quartz veins; the main quartz-vein set shows remarkably consistent easterly to northeasterly trends and steep southerly to subvertical dips throughout the Siguiri Mining Complex [79]. In the Siguiri Gold District, gold-bearing mineral occurrences are formed along subvertical N-S reverse faults, NE-trending dextral shear zones, WNW-trending sinistral faults, and E-trending normal relay faults developed or reactivated early-D₃ [49].

The brittle deformation is linked to the late emplacement of faults and fractures. Fractures are present in number in the area, their measure show that they are randomly oriented. They disrupt the main S₀ - S₁ and the quartz vein arrays and are clearly post faulting. Faults are more regularly oriented than the fractures. They show orientation similar to the most important attitudes seen in the quartz veins arrays: NNW-SSE and ENE-WSW. The NNW-SSE faults correspond to reverse faults while the ENE directions seem to be linked to a shear zone. They could mark the continuation of the brittle-deformation or they might be a result of a concomitant event developed during a compressive event.

In the Faboula gold deposit, there is an association of ductile, brittle-ductile and brittle deformations. The essential question is whether these deformations belong to different phases or are they the result of a progressive deformation starting with the ductile type and ending with the brittle type?

The sequence of deformations recognized in the deposit shows a ductile deformation marked by isoclinal folding developed during an ENE-WSW compression event which is also at the origin of a brittle-ductile deformation whose sigmoidal en-echelon tension gashes indicate a dextral movement in the NNE-SSW direction. Thus, the folding and the shearing are related to the same greatest compressive stress σ1. The brittle ductile-deformation is localized in the limb, its whole data set (tension gashes, reverse faults, strike slip faults) is consistent with Riedel’s shear structures developed in a compressive regime; the orientations of the faults are in accordance with the R and R’ structures.

This type of deformation with folding and shearing, related to the same ENE-WSW compressive stress, could occur simultaneously during a transpressive mechanism. Our interpretation is supported by the fact that the reverse faults strike perpendicular to the main compressive stress σ1 in the same direction as the folds and foliation. Indeed, transpression is a combination of strike-slip faulting, thrust-reverse faulting, and folding [80]. It is the spectrum of combinations of strike-slip and coaxial strain involving shortening perpendicular to the zone [81]. Transpression is commonly associated with oblique plate convergence.

Due to its characteristics, and also because it corresponds more to the D₂ or D₃ than the D₁ tectonic phases, at the scale of the Leo-Man Shield, we will call it D_2Fb. Indeed, no relic of a first tectonic phase D₁ has been identified in the deposit, even if a first ductile event marked by cryptic tight recumbent folds linked to N-S compression, was recognized by [49] in the adjacent District of Siguiri.

The transpressive dextral D_2Fb highlighted at Faboula could be equivalent to the regional D₂ or D₃ deformations recognized at the scale of the Leo-Man Shield. It could be correlated with D₃ of [3], D2 of [79], D3 of [77]; D_2S of [49] and D₃ of [15]. All these middle phases of the Eburnean orogeny are bracketed between ca. 2115 - 2074 Ma [3] [15]. The deformation of [77] which best matches the D_2FB is D₃. The latter is linked to ENE-WSW shortening and the genesis of the dextral Siekorole Shear Zone associated with the development of mineralized quartz veins. In the neighbouring Massigui region, dextral D₃ is indicated by the tension gashes [3]. This phase brittle/ductile in character, is highlighted by fracture cleavage, microfaults and vein arrays; its regional fault drag patterns into the Banifing Fault Zone are consistent with a component of dextral displacement [15]. The folding and shearing associated within the D_2Fb are also in agreement with the D₂ of [79] which is the main deformation phase of the Siguiri Mining Complex. The D₂ deformation of this author shows N-S trending strike-slip and reverses faults anastomosing around and enveloping open-to tightly folded domains. The D_2Fb dextral transpressive deformation corresponds to the main and second deformation (D_2S) of [49], which would result from an E-W to ENE-WSW directed compressions. According to these authors, it was responsible for the generation of the dominant N-trending of the Siguiri Gold District.

The abundance of quartz veins arrays and their relationship with the deformation structures indicates probably that the mineralization is structurally controlled during a hydrothermal event. They could be related to relaxation or orogenic collapse immediately after the D₄ [77], which is a tectonic event linked with to NW-SE shortening and on-going magmatism.