Located in the southeastern parts of the BaouléMossi domain of the West African Craton,the Birimian terrane in Ghana is known to consist of predominantly juvenile crust emplaced during the Eburnean orogeny.Here w...Located in the southeastern parts of the BaouléMossi domain of the West African Craton,the Birimian terrane in Ghana is known to consist of predominantly juvenile crust emplaced during the Eburnean orogeny.Here we present novel coupled zircon U-Pb and Lu-Hf isotope data from nine Birimian granitoids intruding different domains from northwestern,western and southeastern Ghana.Sub-chondriticε_(Hf)-values indicating reworking of Archaean crust are recorded in zircon from both northwestern and southeastern Ghana.As a conservative estimate 71%of all analysed zircon grains spanning in age from2220 Ma to 2130 Ma require contribution from a reworked Archaean source,contradicting the common belief that the Birimian terrane consist of predominantly juvenile crust.A minimumε_(Hf)-value of-10.5 at2139 Ma suggests a Palaeoarchaean to late Mseoarchaean component as the contributing ancient source.Combined with previously reported heavy zirconδ^(18)O signatures from Birimian river zircon in Ghana,our new data suggests reworking of Archaean aged sediments during subduction initiated crustal growth in the vicinity of one,or possibly in between two Archaean aged cratons.展开更多
Located in the southwestern of the Oume-Fettekro greenstone belt, the Agbahou gold deposit is controlled by structural factors. Geophysics, teledetection and core data suggest the presence of NE and NW faults. However...Located in the southwestern of the Oume-Fettekro greenstone belt, the Agbahou gold deposit is controlled by structural factors. Geophysics, teledetection and core data suggest the presence of NE and NW faults. However, the NE-faults define two major shear zones (ATZ: Agbahou Tectonic Zone and WTZ: West Tectonic Zone) that control the Agbahou gold mineralization. These first order structures are subparallel to the regional tectonic grain mostly north-east oriented. They seem to respectively develop on the both arms (eastern and western) of an anticline moderately plunging ~25° towards northeast. Each shear-zone contains several second-order shear-zones or lenses of variable direction and of 50° - 80° dip. NW-faults however correspond to strike-slip faults and their development should be related to transcurrent tectonics. They acted as control channels on the distribution of gold mineralizations. The ductile-brittle character of shear-zones favored the ascent of hydrothermal fluids and the formation of multiple auriferous quartz veins: veins Type IIa and veins Type IIb relating respectively to the shear-veins and extensional veins. However, Agbahou also shows the existence of a disseminated sulphides-bearing mineralization within host-rocks. At Agbahou, the precipitation of gold probably occurred in a post to late ductile-brittle deformation period.展开更多
The Oudiane Elkharoub Zone is one of the major areas of the Reguibat Shield due to its position in the extreme northeast of the Birimian formation (dated between 1.6 and 2.7 Ga) within the Reguibat Shield, coupled wit...The Oudiane Elkharoub Zone is one of the major areas of the Reguibat Shield due to its position in the extreme northeast of the Birimian formation (dated between 1.6 and 2.7 Ga) within the Reguibat Shield, coupled with its closeness to with the Archean Domain in the Shield’s southern portion and with the Taoudeni Basin to the east. The results of field mapping, together with chemical (Fire Assay) and XRF (fluorescence spectrometer X-ray) analyses, shows significant Au, Ag, Cu, Pb, Mn, Cr, Ni, Th and Y anomalies in samples taken from the Oudiane Elkharoub Zone. The results of those analyses will allow us to build a geochemistry maps for the anomalous metal for the study area, understand the relationships between different rock units and the mineralization and the mineralization control and their style, such as structural or lithological control. This context reflects a structural control of the Mineralization according to the conducted analyses and the observation on the field. The mineralization auriferous mainly hosted in quartz vein or quartz-carbonate vein with sulfide (pyrrhotite and pyrite) alteration.展开更多
Mount Fouimba and Mount Goma (Seguela) greenstone belts petro-structural studies combine remote sensing, geophysics, petrography and structural analysis. In view of establishing mapping details of paleoproterozoic geo...Mount Fouimba and Mount Goma (Seguela) greenstone belts petro-structural studies combine remote sensing, geophysics, petrography and structural analysis. In view of establishing mapping details of paleoproterozoic geological formations, geological setting rocks observed are essentially magmatic formations, such as two-mica granite, granodiorites, and porphyritic basalts;and a few metamorphics which are metatonalite, amphibolites and amphibo-lopyroxenites. Remote sensing, such as Landsat 8 OLI satellite imagery and geophysical data, has been combined to show regional NNE-SW shear zone. Tectonic structures and microstructures have enabled to identify two main deformation phases: D1 phase corresponding to compression, and D2 is a transpression phase. Mechanisms responsible for deformations are respectively flattening and transpression. Geological formations derived from mantle origin but contain crustal components, and their tectonic setting occurred during subduction.展开更多
This study focused on the interpretation of geophysical data collected from the Sissedougou prospect which is located at the southern end of the Korhogo-M’Benguebirimian trench. The geophysical surveys were carried o...This study focused on the interpretation of geophysical data collected from the Sissedougou prospect which is located at the southern end of the Korhogo-M’Benguebirimian trench. The geophysical surveys were carried out on two grids with two magnetometers and an induced polarisation unit composed of a transmitter and a receiver. The magnetic data allowed on one side the mapping of basic, intrusive and volcanic formations, weakly magnetic rocks produced by meta-sediments to be showed, and on the other hand to identify the continuity of the shear corridor observed southward and northward of the prospect. Induced polarisation data revealed the signature of sulphide and disseminated mineralization. The synthesis of the obtained results showed that deep NE-SW, NNE-SSW and N-S oriented fractures promoted the late rise of sulphide fluids. The setting of sulphide and gold mineralization in the southern part of the Boundiali trench is therefore controlled by ductile and brittle shearing.展开更多
The northeastern region of Côte d’Ivoire is characterised by a granitic basement mainly composed of biotite granite rocks. According to mapping work in the Gbabédjou and Doropo areas, these Birimian gra...The northeastern region of Côte d’Ivoire is characterised by a granitic basement mainly composed of biotite granite rocks. According to mapping work in the Gbabédjou and Doropo areas, these Birimian granitoids are cut by gabbro dykes and amphibolite enclaves, which are the subject of this study. In order to better understand the role and the implication of mafic rocks in the Doropo basement emplacement, a multidisciplinary methodology integrating microscopic observations and geochemical analyses of major and trace elements was carried out on 4 samples considered representative of the outcrops studied. Green hornblende, clinopyroxene, and accessory sphene minerals are found in mafic mineral phases, according to petrographic research. Whole-rock analyses reveal that mafic samples with TiO<sub>2</sub> contents 1.1 ratios giving them an orogenic granite nature (I-type). Their REE patterns are moderately fractionated (La/Sm)<sub>N</sub> = 2.66 - 6.13 and (La/Yb)<sub>N</sub> = 11.17 - 43.70) with a very negative Eu anomaly (Eu/Eu* = 0.75 - 0.97). The multi-element diagrams are characterized by negative Nb-Ta anomalies and geotectonic studies have identified them as volcanic arc formations. All these characteristics allowed us to distinguish the Doropo mafic rocks as formations originating from the juvenile continental crust, emplaced under the Archean tectonics model with significant crustal contamination in the source. Magma driven by mantle diapir has been injected at the base of the continental crust and the heat induces the partial melting of the overlying crust giving rise to mixed liquids. This magma now enriched in LILE was immediately drained to the upper crust to form the mafic rocks from the studied area.展开更多
The Tarkwaian deposits of the Birimian belt of Houndé are located in the Baoule-Mossi Paleoproterozoic area of the West African Craton. The sedimentary units consist of sandstone heterometric pelitic feldspthic s...The Tarkwaian deposits of the Birimian belt of Houndé are located in the Baoule-Mossi Paleoproterozoic area of the West African Craton. The sedimentary units consist of sandstone heterometric pelitic feldspthic sandstone with locally interbedded breccias, puddings and polygenic conglomerates. Lithic pebbles and macroscopic fragments that are similar to vein type originated quart castings and andesitic-dacitic projections, felsic sub-volcanic rocks evolving from microdioritic to microgranite composition are detected in terrigenous sediments. The volcanic packages form a linear strip composed of basic to intermediate rocks and andesitic to dacitic volcaniclastites. The contacts between these units are not clearly exposed but the different facies between the polygenic conglomerates and sandstones show discordant tectonic contacts with the Tarkwaian and the Birimian. The geochemical nature of these Tarkwaian formations is strongly influenced by the relative decline of the dominant quartz of feldspars and phyllites. The improperly classified and immature feldspathic sandstones show context affinities of island arc probably dictated by Birimian lithic products. Sedimentologically, the cross-bedded stratification and the predominance of sandstone terrigenous lands indicate a deposition in a fluvio-deltaic hydrodynamic setting along intermontane Birimian rift. The similarities between these Tarkwaian formations and the typical Tarkwaian of the Tarkwa basin in Ghana are probably limited to petrographic and not stratigraphic aspects, which lead to likening them to flyscho?d or molassic tardi Birimian deposits.展开更多
The dependence of groundwater quality on borehole depth is usually debatable in groundwater studies, especially in complex geological formations where aquifer characteristics vary spatially with depth. This study ther...The dependence of groundwater quality on borehole depth is usually debatable in groundwater studies, especially in complex geological formations where aquifer characteristics vary spatially with depth. This study therefore seeks to investigate the relationship between borehole depth and groundwater quality across the granitoid aquifers within the Birimian Supergroup in the Ashanti Region. Physicochemical analysis records of groundwater quality data were collected from 23 boreholes of public and private institutions in the Ashanti Region of Ghana, and the parametric values of iron, fluoride, total hardness, pH, nitrate, and nitrite were used to study the groundwater quality-depth relationship. The results showed that the depth-to-groundwater quality indicated a marginal increase in water quality in the range of 30 to 50 m, which is mathematically represented by the low-value correlation coefficient (r<sup>2</sup> = 0.026). A relatively significant increase occurs in the depth range of 50 to 80 m, which is given by a correlation coefficient of r<sup>2</sup> = 0.298. The mean percent parameter compatibility was 74%, 82%, 89%, and 97% at 50, 60, 70, and 80 m depths, respectively. The variations in groundwater quality per depth ratio ranged from 1.48, 1.37, 1.27, and 1.21 for 50, 60, 70, and 80 m depth, respectively. The recommended minimum borehole depth for excellent groundwater quality is suggested with a compatibility per meter depth ratio of 1.37. This results in a range between 50 and 70 m as the most desirable drilling depth for excellent groundwater quality within the granitoids of the Birimian Supergroup of the Ashanti Region in Ghana.展开更多
The objective of this work is to contribute to the crustal evolution during the Paleoproterozoic in the Northeast of Côte d’Ivoire through the structural study of the Bondoukou-tanda locality. To do this, we pro...The objective of this work is to contribute to the crustal evolution during the Paleoproterozoic in the Northeast of Côte d’Ivoire through the structural study of the Bondoukou-tanda locality. To do this, we proceeded by a macroscopic observation of the outcrops for the identification of the structures (schistosity, fold, shear, and lineation). The structures indicated the direction of the main constraints and the relative correlations between the lithologies. The structural measurements, in particular the direction and the dip obtained, were all processed by the GEOrient software to draw up the stereographic projections for a static interpretation of the measurements. Given the rarity of rock outcrops in the study area, the teleanalytical data were of considerable support in the structural analysis. The various treatments carried out on the ENVI 5.2 software made it possible to identify a total of 471 lineaments. They cover the entire area and are of variable lengths (1.24 to 9.73 km). The different directions highlighted from this methodology are a main direction: NNW-SSE to NW-SE;a secondary direction: NNE-SSW to NE-SW;a tertiary direction: ENE-WSW to E-W. Associated with the lithology map, the teleanalytical map shows that the lineaments are unevenly distributed throughout the study area. The lineaments appear more compact in the volcano-sedimentary and sandstone-conglomeratic units than in the granitoid intrusives. However, the Bondoukou granodiorite appears to be the least fractured lithology.展开更多
The semi-industrial permit of Koffissiokaha, south-eastern area of Katiola, is located in the northern part of Fêtêkro Birimian Greenstone Belt (Côte d’Ivoire). This permit, applicated by the comp...The semi-industrial permit of Koffissiokaha, south-eastern area of Katiola, is located in the northern part of Fêtêkro Birimian Greenstone Belt (Côte d’Ivoire). This permit, applicated by the company Blue-Hill Exploration Sarl (BHEX), is in the southern continuity area of Lafigué permit (Endeavour Mining). Blue-Hill will have to work to highlight potential gold mineralization, quantify it (resource calculation) and initiate administrative procedures to obtain a Semi-Industrial Exploitation Authorization (AESI). Our recent works, including field mapping coupled with petrographic and microstructural studies, are therefore intended to contribute to the knowledge of the geology and to the evaluation of the gold potential of this permit. They suggest that Koffissiokaha permit includes four major lithologic units: 1) a sedimentary unit formed by metaarenites and metasiltites, 2) a unit of mafic pyroclastites (cinerites, tuffs and volcanic breccias) 3) a plutonic unit of metagabbro and finally, 4) a lode-type unit made up of metarhyodacites. The metamorphism that affected the volcano-sedimentary rocks is of low grade to greenschist facies. On the structural level, deformations with variable gradients are noted. The major planary structure, the schistosity, is oriented N20 - 40 with weak (°), moderate (50°- 60°) and steep dips (>70°) or subvertical. The faults generally correspond to narrow dextral or senestral shear-zones (75°) towards south-east or subvertical. They are most often intersected by late strike-slip faults-oriented NW-SE, NNW-SSE and N-S. Quartz veins are associated with faults or deformation zones. They are generally oriented N20 to N40, with weak (°), moderate (55°- 65°) and steep dips (>75°). Orientations of joints and fractures are mostly subparallel to the plans of schistosity, shears and most of quartz veins. However, ENE, WNW and N-S fractures are also distinguished. The sulphide paragenesis consists of pyrites (and pyrrhotites), arsenopyrites and chalcopyrites. Gold mineralization is controlled by both structural and hydrothermal parameters.展开更多
The Mako area, located in eastern Sénégal</span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verda...The Mako area, located in eastern Sénégal</span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">,</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> constitute</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">s</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> a segment of Paleoproterozoic (Birimian) formations of the Kédougou-Kéniéba Inliers (KKI) in the western part of the West African craton.</span></span></span><span><span><span style="font-family:""> </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">The basic volcanism of the Birimian formations of the KKI has long been considered to be related to a single magmatic event associated with a Mid Oceanic Ridge Basalts (MORB) setting.</span></span></span><span><span><span style="font-family:""> </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">The aim of this paper is to demonstrate on the basis of the architectural characteristics of the granitoids dark enclaves, the occurrence of at least two distinct phases of basic Magamtism in the Birimian of the KKI.</span></span></span><span><span><span style="font-family:""> </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">The methodology consists of a cartography, a petrographic and architectural characterization of the dark enclaves within the Mako granitoids, in order to constrain their spatial and temporal relationships with the granitic magma. The results obtained are compared with those of the bibliography. We have pinpointed two types of enclaves depending on their shapes and the characteristics of their edge with the enclosing rocks: angular enclaves with straight edges (ante-granitoids) and the soft enclaves with uneven edges (syn-granitoids).</span></span></span><span><span><span style="font-family:""> </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">The enclaves with straight and well-defined rectilinear edges (ante-granitoids) would be linked to a basic magma which is already consolidated before being fragmented, torn and carried away as enclaves in the granitoids. These enclaves would come from enclosing outcrops of metabasalts and metagabbros which are locally cross-cut</span></span></span><span><span><span style="font-family:""> </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">by the granitoids.</span></span></span><span><span><span style="font-family:""> </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">The soft enclaves with uneven edges (syn-granitoids) were co-magmatic and not solid during their incorporation into the granitoids. They come from a basic magma which is contemporaneous to the granitic one.</span></span></span><span><span><span style="font-family:""> </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">Thus, the occurrence of two generations of dark enclaves </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">is</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> related to</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">,</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> at last, two different phases of basic magmatism in the Birimian formations of the KKI.展开更多
The manganese deposit of North Téra is located in the western side of the Diagorou-Darbani greenstone belt in the Niger Liptako Province(Northeastern part of Man Schield,West African Craton).Manganese mineralizat...The manganese deposit of North Téra is located in the western side of the Diagorou-Darbani greenstone belt in the Niger Liptako Province(Northeastern part of Man Schield,West African Craton).Manganese mineralization bearing rocks are mainly gondites(a kind of garnet-rich quartzite of the spessartine type)whose borders consist of a high concentration of Mn oxide concretions.The methodological approach implemented consisted of a field study followed by a polarizing microscopic analysis in transmitted and reflected light and a geochimical analysis.North Téra gondites originate from Birimian manganese-rich sediments metamorphism in amphibolite facies.The supergene alteration,more or less important,has developed on the protore of gondites,a saprolitic profile whose setting up conditions were recently described in our previous work.The macroscopic analysis of the manganese deposits samples combined with the metallographic microscopic and geochemical analysis confirms that manganese mineralization originated from weathering processes.The first oxide that forms around the garnets is nsutite,while the mesostasis is invaded by pyrolusite with lenses of lithiophorite destabilizing in favor of pyrolusite.In the botryoidal concretions,the latter forms an alternation with the psilomelane rich in Ba(8,101ppm)in the uppermost levels.The abundance diagram shows that the normalize Rare Earths compared to PAAS derived from a plagioclase-rich quartzitic source.This observation is corroborated by a positive anomaly in Eu.Otherwise,the high levels of transition elements(Ni,V,Co and Cr)highlight the involvement of a basic source.The contents of major elements show a significant leaching,with an increase in those of Mn and Al during the increasing weathering.The CIA and PIA indices move in the same direction towards high values leading to the Al2O3 pole on the Al2O3-CaO*+Na2O-K2O diagram.This indicates an increasing alteration along the profile,according to an alteration path comprising plagioclase-smectite-kaolinite and illite to kaolinite.展开更多
This study focuses on the petrographic and structural characteristics of the geological formations of the Alépé region in the Comoé basin. The petrographic characterization allows us to retain that the ...This study focuses on the petrographic and structural characteristics of the geological formations of the Alépé region in the Comoé basin. The petrographic characterization allows us to retain that the study area abounds in a variety of lithologies: amphibole metagranite, metadiorite, amphibolite and metagrauwacke. The lineament map attests that the study area was affected by polyphase tectonics (ductile and brittle), all these deformations have NW-SE to NNW-SSE;NW-ESE to NW-SE;ENE-OSW and NE-SW directions. Coupled geochemical data show that the protoliths of the studied rocks evolve between granites and gabbros that are weakly to moderately be altered. They would originate from continental crust and mantle and would be emplaced in collision contex.展开更多
The region of Toumodi, located in the heart of the West African Craton, is renowned for its geological complexity. This geochemical study delves into the origin of siliciclastic sediments and the geodynamic context of...The region of Toumodi, located in the heart of the West African Craton, is renowned for its geological complexity. This geochemical study delves into the origin of siliciclastic sediments and the geodynamic context of their formation. The study reveals that Toumodi’s sediments exhibit an intriguing mineralogical composition, with indications of a dual source of parent rocks, one rich in quartz and the other poor in quartz. Furthermore, geochemical analysis highlights a variation in sediment maturity from west to east, indicating the coexistence of distinct geotectonic environments in the region. In the eastern part of the Toumodi region, a passive margin is defined characterized by sediments with an abundance of quartz, while to the west, an active margin is observed with sediments having a lower quartz content. This arrangement suggests the presence of a potential suture zone in the region. This geological complexity underscores the importance of further research to better understand the origin of sediments and the processes that have shaped them. Moreover, this study sheds new light on the fascinating geology of Toumodi, but many questions remain to be explored.展开更多
The study of Birimian granitoids is of great importance because it allows us to understand the architecture of the West African crust and the processes that shaped it. In order to contribute to the improvement of know...The study of Birimian granitoids is of great importance because it allows us to understand the architecture of the West African crust and the processes that shaped it. In order to contribute to the improvement of knowledge on the geodynamic context of the emplacement of certain granitoids of the West African craton, this article addresses some essential problems of the Birimian, namely distinguishing the real nature of the magmas and the mechanisms that generated this Birimian crust. On the West African craton, there are intrusive granites in volcano-sedimentary furrows, in meta-sedimentary basins and granites that form batholiths separating these structures. To provide an answer to this scientific concern, we conducted a comparative study of the granitoids of the Comoé basin (Tiassalé region) and those of the large batholith of Ferkessédougou (Daloa region). From this study, it appears that these Birimian granitoids have been identified as granites, granodiorites and tonalites in the Tiassalé region while in Daloa, they are assimilated to anatexites and granites. They present very diverse aspects and contexts of emplacement: the granitoids of the Comoé basin have characteristics of type I granite, indicating direct crystallization of mantle magmas in a syntectonic emplacement, while in the Daloa region, some granitoids are magmatic, others migmatitic or metasomatic, reflecting a certain complexity relating to their genesis.展开更多
基金Financial support provided by the Swedish Research Council(grant VR#2008-3447 and VR#2012-4531 to A.Schersten)Per Westlings minnesfond to A.Petersson
文摘Located in the southeastern parts of the BaouléMossi domain of the West African Craton,the Birimian terrane in Ghana is known to consist of predominantly juvenile crust emplaced during the Eburnean orogeny.Here we present novel coupled zircon U-Pb and Lu-Hf isotope data from nine Birimian granitoids intruding different domains from northwestern,western and southeastern Ghana.Sub-chondriticε_(Hf)-values indicating reworking of Archaean crust are recorded in zircon from both northwestern and southeastern Ghana.As a conservative estimate 71%of all analysed zircon grains spanning in age from2220 Ma to 2130 Ma require contribution from a reworked Archaean source,contradicting the common belief that the Birimian terrane consist of predominantly juvenile crust.A minimumε_(Hf)-value of-10.5 at2139 Ma suggests a Palaeoarchaean to late Mseoarchaean component as the contributing ancient source.Combined with previously reported heavy zirconδ^(18)O signatures from Birimian river zircon in Ghana,our new data suggests reworking of Archaean aged sediments during subduction initiated crustal growth in the vicinity of one,or possibly in between two Archaean aged cratons.
文摘Located in the southwestern of the Oume-Fettekro greenstone belt, the Agbahou gold deposit is controlled by structural factors. Geophysics, teledetection and core data suggest the presence of NE and NW faults. However, the NE-faults define two major shear zones (ATZ: Agbahou Tectonic Zone and WTZ: West Tectonic Zone) that control the Agbahou gold mineralization. These first order structures are subparallel to the regional tectonic grain mostly north-east oriented. They seem to respectively develop on the both arms (eastern and western) of an anticline moderately plunging ~25° towards northeast. Each shear-zone contains several second-order shear-zones or lenses of variable direction and of 50° - 80° dip. NW-faults however correspond to strike-slip faults and their development should be related to transcurrent tectonics. They acted as control channels on the distribution of gold mineralizations. The ductile-brittle character of shear-zones favored the ascent of hydrothermal fluids and the formation of multiple auriferous quartz veins: veins Type IIa and veins Type IIb relating respectively to the shear-veins and extensional veins. However, Agbahou also shows the existence of a disseminated sulphides-bearing mineralization within host-rocks. At Agbahou, the precipitation of gold probably occurred in a post to late ductile-brittle deformation period.
文摘The Oudiane Elkharoub Zone is one of the major areas of the Reguibat Shield due to its position in the extreme northeast of the Birimian formation (dated between 1.6 and 2.7 Ga) within the Reguibat Shield, coupled with its closeness to with the Archean Domain in the Shield’s southern portion and with the Taoudeni Basin to the east. The results of field mapping, together with chemical (Fire Assay) and XRF (fluorescence spectrometer X-ray) analyses, shows significant Au, Ag, Cu, Pb, Mn, Cr, Ni, Th and Y anomalies in samples taken from the Oudiane Elkharoub Zone. The results of those analyses will allow us to build a geochemistry maps for the anomalous metal for the study area, understand the relationships between different rock units and the mineralization and the mineralization control and their style, such as structural or lithological control. This context reflects a structural control of the Mineralization according to the conducted analyses and the observation on the field. The mineralization auriferous mainly hosted in quartz vein or quartz-carbonate vein with sulfide (pyrrhotite and pyrite) alteration.
文摘Mount Fouimba and Mount Goma (Seguela) greenstone belts petro-structural studies combine remote sensing, geophysics, petrography and structural analysis. In view of establishing mapping details of paleoproterozoic geological formations, geological setting rocks observed are essentially magmatic formations, such as two-mica granite, granodiorites, and porphyritic basalts;and a few metamorphics which are metatonalite, amphibolites and amphibo-lopyroxenites. Remote sensing, such as Landsat 8 OLI satellite imagery and geophysical data, has been combined to show regional NNE-SW shear zone. Tectonic structures and microstructures have enabled to identify two main deformation phases: D1 phase corresponding to compression, and D2 is a transpression phase. Mechanisms responsible for deformations are respectively flattening and transpression. Geological formations derived from mantle origin but contain crustal components, and their tectonic setting occurred during subduction.
文摘This study focused on the interpretation of geophysical data collected from the Sissedougou prospect which is located at the southern end of the Korhogo-M’Benguebirimian trench. The geophysical surveys were carried out on two grids with two magnetometers and an induced polarisation unit composed of a transmitter and a receiver. The magnetic data allowed on one side the mapping of basic, intrusive and volcanic formations, weakly magnetic rocks produced by meta-sediments to be showed, and on the other hand to identify the continuity of the shear corridor observed southward and northward of the prospect. Induced polarisation data revealed the signature of sulphide and disseminated mineralization. The synthesis of the obtained results showed that deep NE-SW, NNE-SSW and N-S oriented fractures promoted the late rise of sulphide fluids. The setting of sulphide and gold mineralization in the southern part of the Boundiali trench is therefore controlled by ductile and brittle shearing.
文摘The northeastern region of Côte d’Ivoire is characterised by a granitic basement mainly composed of biotite granite rocks. According to mapping work in the Gbabédjou and Doropo areas, these Birimian granitoids are cut by gabbro dykes and amphibolite enclaves, which are the subject of this study. In order to better understand the role and the implication of mafic rocks in the Doropo basement emplacement, a multidisciplinary methodology integrating microscopic observations and geochemical analyses of major and trace elements was carried out on 4 samples considered representative of the outcrops studied. Green hornblende, clinopyroxene, and accessory sphene minerals are found in mafic mineral phases, according to petrographic research. Whole-rock analyses reveal that mafic samples with TiO<sub>2</sub> contents 1.1 ratios giving them an orogenic granite nature (I-type). Their REE patterns are moderately fractionated (La/Sm)<sub>N</sub> = 2.66 - 6.13 and (La/Yb)<sub>N</sub> = 11.17 - 43.70) with a very negative Eu anomaly (Eu/Eu* = 0.75 - 0.97). The multi-element diagrams are characterized by negative Nb-Ta anomalies and geotectonic studies have identified them as volcanic arc formations. All these characteristics allowed us to distinguish the Doropo mafic rocks as formations originating from the juvenile continental crust, emplaced under the Archean tectonics model with significant crustal contamination in the source. Magma driven by mantle diapir has been injected at the base of the continental crust and the heat induces the partial melting of the overlying crust giving rise to mixed liquids. This magma now enriched in LILE was immediately drained to the upper crust to form the mafic rocks from the studied area.
文摘The Tarkwaian deposits of the Birimian belt of Houndé are located in the Baoule-Mossi Paleoproterozoic area of the West African Craton. The sedimentary units consist of sandstone heterometric pelitic feldspthic sandstone with locally interbedded breccias, puddings and polygenic conglomerates. Lithic pebbles and macroscopic fragments that are similar to vein type originated quart castings and andesitic-dacitic projections, felsic sub-volcanic rocks evolving from microdioritic to microgranite composition are detected in terrigenous sediments. The volcanic packages form a linear strip composed of basic to intermediate rocks and andesitic to dacitic volcaniclastites. The contacts between these units are not clearly exposed but the different facies between the polygenic conglomerates and sandstones show discordant tectonic contacts with the Tarkwaian and the Birimian. The geochemical nature of these Tarkwaian formations is strongly influenced by the relative decline of the dominant quartz of feldspars and phyllites. The improperly classified and immature feldspathic sandstones show context affinities of island arc probably dictated by Birimian lithic products. Sedimentologically, the cross-bedded stratification and the predominance of sandstone terrigenous lands indicate a deposition in a fluvio-deltaic hydrodynamic setting along intermontane Birimian rift. The similarities between these Tarkwaian formations and the typical Tarkwaian of the Tarkwa basin in Ghana are probably limited to petrographic and not stratigraphic aspects, which lead to likening them to flyscho?d or molassic tardi Birimian deposits.
文摘The dependence of groundwater quality on borehole depth is usually debatable in groundwater studies, especially in complex geological formations where aquifer characteristics vary spatially with depth. This study therefore seeks to investigate the relationship between borehole depth and groundwater quality across the granitoid aquifers within the Birimian Supergroup in the Ashanti Region. Physicochemical analysis records of groundwater quality data were collected from 23 boreholes of public and private institutions in the Ashanti Region of Ghana, and the parametric values of iron, fluoride, total hardness, pH, nitrate, and nitrite were used to study the groundwater quality-depth relationship. The results showed that the depth-to-groundwater quality indicated a marginal increase in water quality in the range of 30 to 50 m, which is mathematically represented by the low-value correlation coefficient (r<sup>2</sup> = 0.026). A relatively significant increase occurs in the depth range of 50 to 80 m, which is given by a correlation coefficient of r<sup>2</sup> = 0.298. The mean percent parameter compatibility was 74%, 82%, 89%, and 97% at 50, 60, 70, and 80 m depths, respectively. The variations in groundwater quality per depth ratio ranged from 1.48, 1.37, 1.27, and 1.21 for 50, 60, 70, and 80 m depth, respectively. The recommended minimum borehole depth for excellent groundwater quality is suggested with a compatibility per meter depth ratio of 1.37. This results in a range between 50 and 70 m as the most desirable drilling depth for excellent groundwater quality within the granitoids of the Birimian Supergroup of the Ashanti Region in Ghana.
文摘The objective of this work is to contribute to the crustal evolution during the Paleoproterozoic in the Northeast of Côte d’Ivoire through the structural study of the Bondoukou-tanda locality. To do this, we proceeded by a macroscopic observation of the outcrops for the identification of the structures (schistosity, fold, shear, and lineation). The structures indicated the direction of the main constraints and the relative correlations between the lithologies. The structural measurements, in particular the direction and the dip obtained, were all processed by the GEOrient software to draw up the stereographic projections for a static interpretation of the measurements. Given the rarity of rock outcrops in the study area, the teleanalytical data were of considerable support in the structural analysis. The various treatments carried out on the ENVI 5.2 software made it possible to identify a total of 471 lineaments. They cover the entire area and are of variable lengths (1.24 to 9.73 km). The different directions highlighted from this methodology are a main direction: NNW-SSE to NW-SE;a secondary direction: NNE-SSW to NE-SW;a tertiary direction: ENE-WSW to E-W. Associated with the lithology map, the teleanalytical map shows that the lineaments are unevenly distributed throughout the study area. The lineaments appear more compact in the volcano-sedimentary and sandstone-conglomeratic units than in the granitoid intrusives. However, the Bondoukou granodiorite appears to be the least fractured lithology.
文摘The semi-industrial permit of Koffissiokaha, south-eastern area of Katiola, is located in the northern part of Fêtêkro Birimian Greenstone Belt (Côte d’Ivoire). This permit, applicated by the company Blue-Hill Exploration Sarl (BHEX), is in the southern continuity area of Lafigué permit (Endeavour Mining). Blue-Hill will have to work to highlight potential gold mineralization, quantify it (resource calculation) and initiate administrative procedures to obtain a Semi-Industrial Exploitation Authorization (AESI). Our recent works, including field mapping coupled with petrographic and microstructural studies, are therefore intended to contribute to the knowledge of the geology and to the evaluation of the gold potential of this permit. They suggest that Koffissiokaha permit includes four major lithologic units: 1) a sedimentary unit formed by metaarenites and metasiltites, 2) a unit of mafic pyroclastites (cinerites, tuffs and volcanic breccias) 3) a plutonic unit of metagabbro and finally, 4) a lode-type unit made up of metarhyodacites. The metamorphism that affected the volcano-sedimentary rocks is of low grade to greenschist facies. On the structural level, deformations with variable gradients are noted. The major planary structure, the schistosity, is oriented N20 - 40 with weak (°), moderate (50°- 60°) and steep dips (>70°) or subvertical. The faults generally correspond to narrow dextral or senestral shear-zones (75°) towards south-east or subvertical. They are most often intersected by late strike-slip faults-oriented NW-SE, NNW-SSE and N-S. Quartz veins are associated with faults or deformation zones. They are generally oriented N20 to N40, with weak (°), moderate (55°- 65°) and steep dips (>75°). Orientations of joints and fractures are mostly subparallel to the plans of schistosity, shears and most of quartz veins. However, ENE, WNW and N-S fractures are also distinguished. The sulphide paragenesis consists of pyrites (and pyrrhotites), arsenopyrites and chalcopyrites. Gold mineralization is controlled by both structural and hydrothermal parameters.
文摘The Mako area, located in eastern Sénégal</span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">,</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> constitute</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">s</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> a segment of Paleoproterozoic (Birimian) formations of the Kédougou-Kéniéba Inliers (KKI) in the western part of the West African craton.</span></span></span><span><span><span style="font-family:""> </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">The basic volcanism of the Birimian formations of the KKI has long been considered to be related to a single magmatic event associated with a Mid Oceanic Ridge Basalts (MORB) setting.</span></span></span><span><span><span style="font-family:""> </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">The aim of this paper is to demonstrate on the basis of the architectural characteristics of the granitoids dark enclaves, the occurrence of at least two distinct phases of basic Magamtism in the Birimian of the KKI.</span></span></span><span><span><span style="font-family:""> </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">The methodology consists of a cartography, a petrographic and architectural characterization of the dark enclaves within the Mako granitoids, in order to constrain their spatial and temporal relationships with the granitic magma. The results obtained are compared with those of the bibliography. We have pinpointed two types of enclaves depending on their shapes and the characteristics of their edge with the enclosing rocks: angular enclaves with straight edges (ante-granitoids) and the soft enclaves with uneven edges (syn-granitoids).</span></span></span><span><span><span style="font-family:""> </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">The enclaves with straight and well-defined rectilinear edges (ante-granitoids) would be linked to a basic magma which is already consolidated before being fragmented, torn and carried away as enclaves in the granitoids. These enclaves would come from enclosing outcrops of metabasalts and metagabbros which are locally cross-cut</span></span></span><span><span><span style="font-family:""> </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">by the granitoids.</span></span></span><span><span><span style="font-family:""> </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">The soft enclaves with uneven edges (syn-granitoids) were co-magmatic and not solid during their incorporation into the granitoids. They come from a basic magma which is contemporaneous to the granitic one.</span></span></span><span><span><span style="font-family:""> </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">Thus, the occurrence of two generations of dark enclaves </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">is</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> related to</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">,</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> at last, two different phases of basic magmatism in the Birimian formations of the KKI.
文摘The manganese deposit of North Téra is located in the western side of the Diagorou-Darbani greenstone belt in the Niger Liptako Province(Northeastern part of Man Schield,West African Craton).Manganese mineralization bearing rocks are mainly gondites(a kind of garnet-rich quartzite of the spessartine type)whose borders consist of a high concentration of Mn oxide concretions.The methodological approach implemented consisted of a field study followed by a polarizing microscopic analysis in transmitted and reflected light and a geochimical analysis.North Téra gondites originate from Birimian manganese-rich sediments metamorphism in amphibolite facies.The supergene alteration,more or less important,has developed on the protore of gondites,a saprolitic profile whose setting up conditions were recently described in our previous work.The macroscopic analysis of the manganese deposits samples combined with the metallographic microscopic and geochemical analysis confirms that manganese mineralization originated from weathering processes.The first oxide that forms around the garnets is nsutite,while the mesostasis is invaded by pyrolusite with lenses of lithiophorite destabilizing in favor of pyrolusite.In the botryoidal concretions,the latter forms an alternation with the psilomelane rich in Ba(8,101ppm)in the uppermost levels.The abundance diagram shows that the normalize Rare Earths compared to PAAS derived from a plagioclase-rich quartzitic source.This observation is corroborated by a positive anomaly in Eu.Otherwise,the high levels of transition elements(Ni,V,Co and Cr)highlight the involvement of a basic source.The contents of major elements show a significant leaching,with an increase in those of Mn and Al during the increasing weathering.The CIA and PIA indices move in the same direction towards high values leading to the Al2O3 pole on the Al2O3-CaO*+Na2O-K2O diagram.This indicates an increasing alteration along the profile,according to an alteration path comprising plagioclase-smectite-kaolinite and illite to kaolinite.
文摘This study focuses on the petrographic and structural characteristics of the geological formations of the Alépé region in the Comoé basin. The petrographic characterization allows us to retain that the study area abounds in a variety of lithologies: amphibole metagranite, metadiorite, amphibolite and metagrauwacke. The lineament map attests that the study area was affected by polyphase tectonics (ductile and brittle), all these deformations have NW-SE to NNW-SSE;NW-ESE to NW-SE;ENE-OSW and NE-SW directions. Coupled geochemical data show that the protoliths of the studied rocks evolve between granites and gabbros that are weakly to moderately be altered. They would originate from continental crust and mantle and would be emplaced in collision contex.
文摘The region of Toumodi, located in the heart of the West African Craton, is renowned for its geological complexity. This geochemical study delves into the origin of siliciclastic sediments and the geodynamic context of their formation. The study reveals that Toumodi’s sediments exhibit an intriguing mineralogical composition, with indications of a dual source of parent rocks, one rich in quartz and the other poor in quartz. Furthermore, geochemical analysis highlights a variation in sediment maturity from west to east, indicating the coexistence of distinct geotectonic environments in the region. In the eastern part of the Toumodi region, a passive margin is defined characterized by sediments with an abundance of quartz, while to the west, an active margin is observed with sediments having a lower quartz content. This arrangement suggests the presence of a potential suture zone in the region. This geological complexity underscores the importance of further research to better understand the origin of sediments and the processes that have shaped them. Moreover, this study sheds new light on the fascinating geology of Toumodi, but many questions remain to be explored.
文摘The study of Birimian granitoids is of great importance because it allows us to understand the architecture of the West African crust and the processes that shaped it. In order to contribute to the improvement of knowledge on the geodynamic context of the emplacement of certain granitoids of the West African craton, this article addresses some essential problems of the Birimian, namely distinguishing the real nature of the magmas and the mechanisms that generated this Birimian crust. On the West African craton, there are intrusive granites in volcano-sedimentary furrows, in meta-sedimentary basins and granites that form batholiths separating these structures. To provide an answer to this scientific concern, we conducted a comparative study of the granitoids of the Comoé basin (Tiassalé region) and those of the large batholith of Ferkessédougou (Daloa region). From this study, it appears that these Birimian granitoids have been identified as granites, granodiorites and tonalites in the Tiassalé region while in Daloa, they are assimilated to anatexites and granites. They present very diverse aspects and contexts of emplacement: the granitoids of the Comoé basin have characteristics of type I granite, indicating direct crystallization of mantle magmas in a syntectonic emplacement, while in the Daloa region, some granitoids are magmatic, others migmatitic or metasomatic, reflecting a certain complexity relating to their genesis.
