Petrographic and Geochemical Characteristics of the Pouni Palaeoproterozoic Formations North of the Léo Square Degree (Burkina Faso, West Africa)

The Pouni area is made up of basalts belonging to the Boromo belt, lamprophyres and granitoids. These geological formations are similar to geological formations of the same type in other regions of the Palaeoproterozoic domain of the Man/Leo shield. This study, which focused on the petrographic and geochemical characteristics of these geological formations, led to the following main conclusions: The lamprophyres are basic plutonic rocks that cut through other geological formations. The basalt belongs to the northern part of the Borormo belt and is thought to be a relic of overthickened oceanic plateaus. There are two groups of granitoid rocks. The granodiorite has a geochemical signature close to that of Archean TTGs and is metaluminous in character. It has a low potassium content. The minor element and rare earth element spectra indicate that it could be derived from partial melting of basic magmatic rocks. Biotite granites are peraluminous and highly potassic. Minor element contents and rare earth spectra indicate that they could be derived from partial melting of felsic materials. Geotectonic diagrams show that the granitoids identified in the Pouni zone were emplaced in an active tectonic context, similar to that of present-day subduction zones.

Insight from Lithostructural and Aeromagnetic Data from the Léo Square Degree, Central-Western Burkina Faso

This study, carried out in the Léo square degree (west-central Burkina Faso) in the Palaeoproterozoic domain of the Man/Léo ridge, aims to define the shapes and positions of granitic plutons and the organisation of deformation structures using aeromagnetic data. These data have shown that there are small sub-circular granitic bodies to the north of the granitic masses in this region, and a large sub-circular granitic body to the south, around which are other smaller granitic bodies. The lineament map shows that the deformation structures are organised along three main directions and largely form these sub-circular plutonic bodies. We suggest that the granitic plutons are coalescent, pending identification of the internal structures of these granites to further refine the geodynamic model.

Petrographic and Geochemical Characteristics of the Granitoids in the South of Godé (North of the Square Degree of Léo-Burkina Faso, West Africa)

South of Godé, in the central-western region of Burkina Faso, granitoids of Paleoproterozoic age are similar to those of the Man/Leo shield. This study focused on the petrographic and geochemical characteristics of these granitoids, with the following results: 1) The tonalite that outcrops in the south-west of the study area belongs to the TTG group or first generation granitoids. They are most often ribboned at outcrop and have a geochemical signature close to that of Archean TTGs. Tonalite has a metaluminous character and the REE spectrum indicates that it may be derived from partial melting of basic magmatic rocks. 2) Biotite granites have no outcrop structure. They are weakly metaluminous to peraluminous and potassic to highly potassic. Their rare earth spectra indicate that they may be derived from the partial melting of TTG granitoids. 3) Geotectonic diagrams show that the granitoids studied to the south of Godé were emplaced in an active tectonic context similar to that of present-day subduction zones.

Geochemical Mobility Associated to Gold and Base Metal Occurrences of Mangodara Sector, in Southern Burkina Faso, Banfora Greenstone Belts (West African Craton)

In the Mangodara area within the Banfora greenstone belts (Baoulé-Mossi domain of the West African Craton), our study focused on geochemical assessment of the mobility of major and trace elements. Gold and base metal occurrences are hosted in highly metamorphic felsic (metarhyolite) and intermediate (metadacite and metaandesite) formations. Common mineral assemblages made up of staurolite - kyanite - pyrophyllite are interpreted to represent the metamorphosed equivalent of aluminous hydrothermal alteration. Associated felsic and intermediate volcanic rocks are enriched in Fe2O3, K2O (metaandesite, metarhyolite) and depleted in MgO, Al2O3, CaO, P2O5, Na2O (metarhyolite) and Fe2O3, MgO, CaO (metaandesite). Al2O3 depletion in mineralized kyanite-staurotide bearing metarhyolites suggests corroded minerals. Mineralized metarhyolites show enrichment in Au, Ag, Ba, Bi, Cr, Cu, Eu, La, Mo, Ni, Pb, S, Sc, V and depletion in As Sb Co, Sn, Zn while mineralized metaandesites show enrichment in Au, Ag, As, Mo, S, Sb and depletion in Co, Sn, Zn, Bi, Cr, Cu, Eu, Ni, Pb, Sc. Ba, La, V are immobile in metaandesites. Finally, Ag, As, Sn appear as geochemical vectors for gold exploration in the study area since gold mineralization is characterized by Au + Ba + Cu + Eu + La + Mo + Ni + S association in metarhyolites and Au + S + Sb + As + Ag + Bi in metaandesites.

Identification of Groundwater Potential Zones in Samendeni Watershed in Sedimentary and Semi-Arid Contexts of Burkina Faso, Using Analytic Hierarchy Process (AHP) Method and GIS

Demand for water increases in Samendeni regarding the undertaken agricultural projects while pressure on surface water from global warming/evapotranspiration also increases. Thus, the need to evaluate the groundwater potential in the catchment is crucial as alternative supplier of water and resilience to climate hazards. The AHP was performed integrating ten influencing factors such as geomorphology, geology, soil, land use/land cover (lulc), slope, rainfall, drainage density, borehole rate & depth and piezometric level to generate groundwater potential zones (GWPZs) in Samendeni watershed (4420 km2). All the factors were processed and ranged into five (5) classes. Weight was assigned to each class of thematic layer. These thematic layers were then reclassified based on the normalized weight to be used in the calculation of groundwater potential zones (GWPZ). The final output, groundwater potential map, revealed a significant groundwater potential with very good (11%), good (31%), moderate (30%), poor (20%), and very poor (8%) of proportion. The interesting (very good, good) GWPZs in the study area are mostly in the central towards the east. The poor zones in term of groundwater potential are concentrated in the upper west region of the watershed. Besides the cross-validation with the relationship between different groundwater potential zones and the wells available in the study area, the overall accuracy was estimated to 88% provided from the result of the similarity analysis where 22 out of the 25 validation wells match with the expected yield classes of GWPZs. The statistics from that validation revealed the performance of AHP method to delineate groundwater potential zones at catchment level.

Experimental Evaluating of the Physical, Mechanical and Durability Properties of Natural, Recycled and Both Combined Aggregates Based Concretes

This experimental study aims at the reuse of recycled aggregates (RA), resulting from the demolition of concrete, cement block and cement mortar, in the manufacture of common construction in Burkina Faso. The RA can readily replace natural aggregates in concrete. Then five formulations of natural and recycled aggregates based concrete for characteristic strength of 25 Mpa were prepared in addition to the natural aggregates base concrete named reference concrete (BN): two types of recycled aggregates concrete (BR), three types of recycles and natural combined aggregates base concrete (BC). The properties of natural and recycled aggregates were characterized and the physical, mechanical strength and durability properties were also evaluated for all concrete specimens. All the studied concrete formulation present a density between 2000 kg/m3 ≤ ρ ≥ 2600 kg/m3 and an average slump of 4.9 ± 0.1 cm. The obtained results indicate that the recycled aggregates are suitable for current concrete. Two out of the five combinations studied, such as the natural (BN) and combined aggregate (BC2) based concretes satisfy the mechanical characteristics (Rc28 > 25 MPa) at 28 days of age and an average absorption coefficient of 2.93% and 3.98%. The recycled aggregate based concrete (BR1, BR2) and combined aggregate based concrete (BC1), gave respective average compressive strength of 21.55 MPa, 20.50 MPa and 20.30 MPa, i.e. a difference of 13.80% to 18.80% under the characteristic strength (25 MPa) aimed at 28 days of age. Thus, the recycled aggregates are in conformity with the normative prescriptions and their use for standard concrete gives adequate physical, mechanical and durability properties for the production of the C20/25 concrete series in the common civil engineering applications.

Characteristics of Gold Mineralization at the Baguiomo Gold Panning Site, Koudougou Region, Burkina Faso, West Africa

The Birimian Baguiomo formations are located in the northern part of the Boromo greenstone belt. In this belt, the volcanic rocks (tholeiitic basalt, calcalkaline basalt, andesite) hosting the gold mineralization are located in the Kwademen-Baguiomo shear zone. This mineralization, located only a few kilometers from the Kwademen gold deposit, is uncharacterized and, together with the latter, could constitute a gold potential capable of being economically exploitable. It is in this sense that this work is carried out with a view to characterizing the gold mineralization of the Baguiomo gold panning site. To carry out this work, we have made direct field measurements, combined with microstructures, and combined all this with data from geochemical rock analysis of the basalts that are the main host formations. Geochemical data show that tholeitic basalts formed from a mantle plume that was emplaced in an oceanic plateau context. Calc-alkaline basalts and andesites are comparable to Paleoproterozoic tholeitic basalts (PTH3), which are slightly enriched in light rare earths. Fertility tests show that these basalts concentrate between 3 and 6 ppb of gold at the time of accretion, which is sufficient for remobilization of this primary gold during the Eburnian orogeny to yield a deposit of around 4 - 5 Moz. Gold mineralization is associated with pyrite crystals when the latter are disseminated in the rock mass, whereas it is associated with hematite in quartz veins concordant with S1 shear deformation. It is mainly the pyrite crystals in the pressure shadows that contain the gold grains, whose development would be synchronous with micro-shear zone reactivation during the first phase of D1B deformation. The second phase of D2B deformation, which is a crenulation or fracture schistosity, does not significantly affect the shear deformation that controls mineralization.

Implication of Paleoproterozoic Basalt Fertility Related to Mantle Plume Activity in Nassara Gold Mineralization (Burkina Faso, West Africa)

The Birimian Nassara volcanic formations are located south of Gaoua in the southern part of the Boromo belt. Within these formations is the Nassara gold deposit where mineralization is hosted at the contact between basaltic volcanic rocks and sedimentary rocks. It is with the aim of understanding the geodynamic context of the basaltic rocks and the implication of their primary gold potential in the Nassara gold deposit that this work is carried out. To achieve our objectives, 28 samples of fresh basaltic rocks were geochemically analyzed for their major and trace element compositions. These analyses show that the Nassara basalts are Fe-rich tholeiitic basalts. Rare earth profiles (La/SmN = 0.75 - 1.50;La/YbN = 0.65 - 2.18) are fairly flat and without europium anomaly (Eu/Eu* = 0.90 - 1.09), nor niobium. In the Zr/Nb vs. Nb/Th and Nb/Y vs. Zr/Y binary diagrams, the Fe-rich tholeiitic basalts of Nassara, as well as those of the Houndé and Boromo belts, are placed in the field of oceanic plateau basalts related to a mantle plume system. A gold fertility test carried out on these basalts was positive. As other studies have already shown, the genetic link between gold deposits and mantle plumes appears to be a general rule. The scenario for the Nassara gold deposit is that it is the source magma that was already more or less enriched in gold and other related elements on its way up. The remobilization of this gold would have occurred during the Eburnean orogeny with the help of metamorphic, hydrothermal and deformation phenomena to be redeposited at the level of shear zones with economic grades. Through this analysis, we show that the fertility of the initial lithologies is very important for the formation of economic size deposits in the proximal shear zones. Exploration work should now integrate this dimension to define the best targets.

Lamprophyre Rocks in the Nassara Gold Deposit, Southwest Burkina Faso: Characteristics and Implication for Mining Exploration

The lamprophyres are late dykes that cut the formations hosting the gold mineralization in the Nassara deposit. They are geographically and spatially related to most orogenic gold deposits. It is with the aim of characterizing them and seeing their implications for exploration that this work is carried out. To achieve our objective, petrographic studies and chemical analyses of minerals (pyroxenes, amphiboles, feldspars, chromite) and geochemical analyses of total rock were carried out. These studies have enabled us to classify the Nassara lamprophyres as calc-alkaline lamprophyres of the spessartite type. The Cr, Co, Ni and Mg enrichment of these rocks would indicate a depleted mantle source, with LILE enrichment by fluids probably related to metasomatic activity. The various diagrams show that they are depleted in HREE and enriched in LREE. The high Nb/Ta ratios in our data indicate metasomatic activity probably linked to amphibole and rutile in the mantle prior to melting. The geodynamic context of spessartite-type lamprophyres indicates a signature linked to late-orogenic to post-collisional subduction. They are late-orogenic to post-collisional lamprophyres enriched in compatible elements (Cr, Ni, Co) and display a negative Ta-Nb-Ti (TNT) anomaly. The frequent association of these lamprophyre dykes with the deposits does not indicate the source of the gold for these deposits, but rather zones of crustal permeability capable of draining hydrothermal fluids at the time of emplacement. Good mapping of lamprophyre dykes, especially in shear zones, could therefore guide prospecting and identify potential zones of hydrothermal fluid circulation.

Alteration Typology and Geochemical Signatures of the Napélépéra Gold-Bearing Granodiorite in South-West Burkina Faso (West Africa)

The characterization of the relationships between mineralization and hydrothermal alteration is an essential element in understanding gold deposits. In south-west Burkina Faso, the Napélépéra mineralisation, the mobility of chemical elements and alteration-mineralization relationships were studied by means of selected core drilling and geochemical analyses using ICP-MS (Inductively Coupled Plasma Mass Spectrometry) and ICP-AES (Inductively coupled plasma atomic emission spectroscopy). The mineralised granodiorite is grey porphyroid with quartz, plagioclase, biotite and amphibole. It is metaluminous and located in the tholeiitic series. The Na2O + CaO versus Fe2O3 + MgO alteration diagram divides the samples according to alteration dominance. Chloritisation and carbonation are the main alterations. There is a relationship between gold mineralisation at Napélépéra and alteration, and the paragenesis of gold + pyrite ± carbonate ± silica ± sericite is the main characteristic. Carbonation is the result of fluid input in the shear corridor of the mineralised zone. The mass balance of comparative metals in the proximal and distal zones of the mineralisation shows the absence of metals, while As, Hg, Ag and Bi are strongly enriched from the distal zone to the mineralised zone. The oxides associated with the mineralisation are mainly NaO, SrO and CaO.