A semi-regional study was carried out in the Yaounde-Sangmelima area, a densely vegetated tropical region of southern Cameroon located in the Central Africa Fold Belt (CAFB)/Congo Craton (CC) transition zone. Towards ...A semi-regional study was carried out in the Yaounde-Sangmelima area, a densely vegetated tropical region of southern Cameroon located in the Central Africa Fold Belt (CAFB)/Congo Craton (CC) transition zone. Towards structural lineaments and predictive hydrothermal porphyry deposits mapping, an integrated analysis of Landsat-8 OLI data, aeromagnetic, geological and mineral indices maps was performed. The Remote sensing using False colour composite images involving bands combinations and Crosta method (features oriented principal components analysis) enabled the mapping of the gneisses and schists domains without a clear differentiation between the Yaounde and Mbalmayo schists;despite the reflectance anomalies evidenced NW of Akonolinga, hydrothermal alterations in the study area failed to be detected. Besides, aeromagnetics depicted a moderately fractured northern zone (the CAFB) contrasting with a high densely fractured zone (the CC, known as Ntem complex). The Ntem complex displays signatures of a meta-igneous, an intrusive complex, greenstone relics south of Sangmelima and hydrothermal activity. Indeed, CET porphyry analysis tool detected many porphyry centres. In general, the study revealed many lineaments including contacts, fractures faults zones and strike-slips. The major aeromagnetics structures are SW-NE to WSW-ENE and WNW-ESE to NW-SE while those from Landsat-8 are NE-SW, WNW-ESE, NW-SE, WSW-ENE and NW-ESE to NNW-SSE. Together, these structures depict trans-compressions or trans-tensions corresponding to a broad NE-SW strike-slips channel that affect both the CAFB and the Ntem Complex, and they control the intrusions thus confirming a pervasive hydrothermal activity within the Ntem Complex. The proximity or coincidence of these porphyry centres with some mapped Iron-Gold affiliated mineral indices and porphyry granites indicate the possible occurrence of many hydrothermal ore deposits. These results show the high probability for the Ntem complex to host porphyry deposits so they may serve to boost mineral exploration in the Yaounde-Sangmelima region and in the entire southern Cameroon as well.展开更多
The purpose of this work is to characterize the sediments of the Babouri-Figuil<span style="font-family:""><span style="font-family:Verdana;"> Basin from a diagenetic point of view...The purpose of this work is to characterize the sediments of the Babouri-Figuil<span style="font-family:""><span style="font-family:Verdana;"> Basin from a diagenetic point of view, the protolith context and weathering conditions, u</span><span><span style="font-family:Verdana;">sing major element geochemistry and mineralogy of the sedimentary rocks. Microscopic observations of diagenetic phenomena (on and around detrital grains of the basin), and the study of precipitation of the cement show that these sediments have undergone phenomena of compaction, dissolution, recrystallization and cementation. Cementation of quartz by silica is controlled by the rate of precipitation of silica, which is closely related to temperature than pressure. Thus, the sediments of the basin could be influenced by hydrothermalism during diagenesis, which would have inhibited their reservoir quality by generalized cementation phenomena. Geochemical features of the sediments show high contents in SiO</span><sub><span style="font-family:Verdana;">2</span></sub><span style="font-family:Verdana;"> (47.49 wt</span><span style="color:#4F4F4F;font-family:Verdana;">%</span></span></span><span style="font-family:""> </span><span style="font-family:Verdana;">-</span><span style="font-family:""> </span><span style="font-family:""><span style="font-family:Verdana;">90.79 wt</span><span style="color:#4F4F4F;font-family:Verdana;">%</span><span style="font-family:Verdana;">), Al</span><sub><span style="font-family:Verdana;">2</span></sub><span style="font-family:Verdana;">O</span><sub><span style="font-family:Verdana;">3</span></sub><span style="font-family:Verdana;"> (2.92 wt</span><span style="color:#4F4F4F;font-family:Verdana;">%</span></span><span style="font-family:""> </span><span style="font-family:Verdana;">-</span><span style="font-family:""> </span><span style="font-family:""><span style="font-family:Verdana;">23.18 wt</span><span style="color:#4F4F4F;font-family:Verdana;">%</span><span style="font-family:Verdana;">), Fe</span><sub><span style="font-family:Verdana;">2</span></sub><span style="font-family:Verdana;">O</span><sub><span style="font-family:Verdana;">3</span></sub><span style="font-family:Verdana;"> (0.2 wt</span><span style="color:#4F4F4F;font-family:Verdana;">%</span></span><span style="font-family:""> </span><span style="font-family:Verdana;">-</span><span style="font-family:""> </span><span style="font-family:""><span style="font-family:Verdana;">6.22 wt</span><span style="color:#4F4F4F;font-family:Verdana;">%</span><span style="font-family:Verdana;">) and alkali and alkaline earth metals (>3</span><span style="color:#4F4F4F;font-family:Verdana;">%</span><span style="font-family:Verdana;">). The chemical alteration index varies between 30.92</span><span style="color:#4F4F4F;font-family:Verdana;">%</span><span style="font-family:Verdana;"> and 95.08</span><span style="color:#4F4F4F;font-family:Verdana;">%</span><span style="font-family:Verdana;"></span><span style="font-family:Verdana;">. This variation in the CIA values reflects the variation in the proportion of feldspars and different clay minerals in these sediments. How</span></span><span style="font-family:""><span style="font-family:Verdana;">ever, the ICV calculation and the ICV versus CIA show compositional immature to mature sediments, with </span><span style="font-family:Verdana;">low to intense weathering character of these sediments. Petrographic and</span><span style="font-family:Verdana;"> geo</span><span style="font-family:Verdana;">chemical characteristics of sediments of the basin are compatible with the</span><span style="font-family:Verdana;"> composition of the granitic and gneissic surrounding bedrocks.</span></span>展开更多
The Douala-Buea Region(DBR;4°-5°N,9°-10°30’E),a portion of the southern Cameroon passive margin,developed on the Proterozoic granito-gneissic basement and the Cretaceous to Recent volcanosedimenta...The Douala-Buea Region(DBR;4°-5°N,9°-10°30’E),a portion of the southern Cameroon passive margin,developed on the Proterozoic granito-gneissic basement and the Cretaceous to Recent volcanosedimentary cover,was explored in order to evaluate the lithology and tectonics controls on its landscape usingthequalitativeandquantitative geomorphological analyses based on 30 m resolution Digital Elevation Models(DEM)and field evidences.This area displays an uneven and complex landscape differentiated into four morphological units:Douala,Nkondjock,Kumba and Buea Units.The Douala Unit corresponds to the Coastal Plain and is extended on the Douala-Kribi/Camposedimentarybasin.The Nkondjock Unit represents a middle plateau developed on a Proterozoic granito-gneissic basement.The Kumba Unit matches with the southernmost volcanic Western Cameroon High Plateau.The Buea Unit corresponds to the Mount Cameroon stratovolcano.The relief analysis through mountain-front sinuosity(Smf,1.19–1.43)and relative relief ratio(Rr,0.10–2.31)vary from one unit to another.The drainage network analysis including drainage patterns,stepped longitudinalriverprofiles,theassociated morphometric indexes,notably the concavity index(IC,0.56–0.88),deviation(D,267–2912 m),basin asymmetry factor(A_(F),6.37–42.12),hypsometric integral(HI,0.10–0.29),valley floor width to valley height ratio(V_(f),0.36–2.75),elongation ratio(R_(e),0.30–0.50),watershed slope(S,6.88–88.88)and stream length gradient index(SL,0–3332)vary from one basin to another too.These results also show the heterogeneous and uneven DBR landscape controlled by its lithology and active tectonics.The drainage system reveals concave to concavo-convex longitudinal river profile shapes with knick points,asymmetric basins,and fault reactivations,and highlights the tectonics activity that used to occur through the time and their control on the morphology.Together,they document the lithostructural controls on the DBR landscape evolution,extendable in the whole SW Cameroon margin.展开更多
文摘A semi-regional study was carried out in the Yaounde-Sangmelima area, a densely vegetated tropical region of southern Cameroon located in the Central Africa Fold Belt (CAFB)/Congo Craton (CC) transition zone. Towards structural lineaments and predictive hydrothermal porphyry deposits mapping, an integrated analysis of Landsat-8 OLI data, aeromagnetic, geological and mineral indices maps was performed. The Remote sensing using False colour composite images involving bands combinations and Crosta method (features oriented principal components analysis) enabled the mapping of the gneisses and schists domains without a clear differentiation between the Yaounde and Mbalmayo schists;despite the reflectance anomalies evidenced NW of Akonolinga, hydrothermal alterations in the study area failed to be detected. Besides, aeromagnetics depicted a moderately fractured northern zone (the CAFB) contrasting with a high densely fractured zone (the CC, known as Ntem complex). The Ntem complex displays signatures of a meta-igneous, an intrusive complex, greenstone relics south of Sangmelima and hydrothermal activity. Indeed, CET porphyry analysis tool detected many porphyry centres. In general, the study revealed many lineaments including contacts, fractures faults zones and strike-slips. The major aeromagnetics structures are SW-NE to WSW-ENE and WNW-ESE to NW-SE while those from Landsat-8 are NE-SW, WNW-ESE, NW-SE, WSW-ENE and NW-ESE to NNW-SSE. Together, these structures depict trans-compressions or trans-tensions corresponding to a broad NE-SW strike-slips channel that affect both the CAFB and the Ntem Complex, and they control the intrusions thus confirming a pervasive hydrothermal activity within the Ntem Complex. The proximity or coincidence of these porphyry centres with some mapped Iron-Gold affiliated mineral indices and porphyry granites indicate the possible occurrence of many hydrothermal ore deposits. These results show the high probability for the Ntem complex to host porphyry deposits so they may serve to boost mineral exploration in the Yaounde-Sangmelima region and in the entire southern Cameroon as well.
文摘The purpose of this work is to characterize the sediments of the Babouri-Figuil<span style="font-family:""><span style="font-family:Verdana;"> Basin from a diagenetic point of view, the protolith context and weathering conditions, u</span><span><span style="font-family:Verdana;">sing major element geochemistry and mineralogy of the sedimentary rocks. Microscopic observations of diagenetic phenomena (on and around detrital grains of the basin), and the study of precipitation of the cement show that these sediments have undergone phenomena of compaction, dissolution, recrystallization and cementation. Cementation of quartz by silica is controlled by the rate of precipitation of silica, which is closely related to temperature than pressure. Thus, the sediments of the basin could be influenced by hydrothermalism during diagenesis, which would have inhibited their reservoir quality by generalized cementation phenomena. Geochemical features of the sediments show high contents in SiO</span><sub><span style="font-family:Verdana;">2</span></sub><span style="font-family:Verdana;"> (47.49 wt</span><span style="color:#4F4F4F;font-family:Verdana;">%</span></span></span><span style="font-family:""> </span><span style="font-family:Verdana;">-</span><span style="font-family:""> </span><span style="font-family:""><span style="font-family:Verdana;">90.79 wt</span><span style="color:#4F4F4F;font-family:Verdana;">%</span><span style="font-family:Verdana;">), Al</span><sub><span style="font-family:Verdana;">2</span></sub><span style="font-family:Verdana;">O</span><sub><span style="font-family:Verdana;">3</span></sub><span style="font-family:Verdana;"> (2.92 wt</span><span style="color:#4F4F4F;font-family:Verdana;">%</span></span><span style="font-family:""> </span><span style="font-family:Verdana;">-</span><span style="font-family:""> </span><span style="font-family:""><span style="font-family:Verdana;">23.18 wt</span><span style="color:#4F4F4F;font-family:Verdana;">%</span><span style="font-family:Verdana;">), Fe</span><sub><span style="font-family:Verdana;">2</span></sub><span style="font-family:Verdana;">O</span><sub><span style="font-family:Verdana;">3</span></sub><span style="font-family:Verdana;"> (0.2 wt</span><span style="color:#4F4F4F;font-family:Verdana;">%</span></span><span style="font-family:""> </span><span style="font-family:Verdana;">-</span><span style="font-family:""> </span><span style="font-family:""><span style="font-family:Verdana;">6.22 wt</span><span style="color:#4F4F4F;font-family:Verdana;">%</span><span style="font-family:Verdana;">) and alkali and alkaline earth metals (>3</span><span style="color:#4F4F4F;font-family:Verdana;">%</span><span style="font-family:Verdana;">). The chemical alteration index varies between 30.92</span><span style="color:#4F4F4F;font-family:Verdana;">%</span><span style="font-family:Verdana;"> and 95.08</span><span style="color:#4F4F4F;font-family:Verdana;">%</span><span style="font-family:Verdana;"></span><span style="font-family:Verdana;">. This variation in the CIA values reflects the variation in the proportion of feldspars and different clay minerals in these sediments. How</span></span><span style="font-family:""><span style="font-family:Verdana;">ever, the ICV calculation and the ICV versus CIA show compositional immature to mature sediments, with </span><span style="font-family:Verdana;">low to intense weathering character of these sediments. Petrographic and</span><span style="font-family:Verdana;"> geo</span><span style="font-family:Verdana;">chemical characteristics of sediments of the basin are compatible with the</span><span style="font-family:Verdana;"> composition of the granitic and gneissic surrounding bedrocks.</span></span>
文摘The Douala-Buea Region(DBR;4°-5°N,9°-10°30’E),a portion of the southern Cameroon passive margin,developed on the Proterozoic granito-gneissic basement and the Cretaceous to Recent volcanosedimentary cover,was explored in order to evaluate the lithology and tectonics controls on its landscape usingthequalitativeandquantitative geomorphological analyses based on 30 m resolution Digital Elevation Models(DEM)and field evidences.This area displays an uneven and complex landscape differentiated into four morphological units:Douala,Nkondjock,Kumba and Buea Units.The Douala Unit corresponds to the Coastal Plain and is extended on the Douala-Kribi/Camposedimentarybasin.The Nkondjock Unit represents a middle plateau developed on a Proterozoic granito-gneissic basement.The Kumba Unit matches with the southernmost volcanic Western Cameroon High Plateau.The Buea Unit corresponds to the Mount Cameroon stratovolcano.The relief analysis through mountain-front sinuosity(Smf,1.19–1.43)and relative relief ratio(Rr,0.10–2.31)vary from one unit to another.The drainage network analysis including drainage patterns,stepped longitudinalriverprofiles,theassociated morphometric indexes,notably the concavity index(IC,0.56–0.88),deviation(D,267–2912 m),basin asymmetry factor(A_(F),6.37–42.12),hypsometric integral(HI,0.10–0.29),valley floor width to valley height ratio(V_(f),0.36–2.75),elongation ratio(R_(e),0.30–0.50),watershed slope(S,6.88–88.88)and stream length gradient index(SL,0–3332)vary from one basin to another too.These results also show the heterogeneous and uneven DBR landscape controlled by its lithology and active tectonics.The drainage system reveals concave to concavo-convex longitudinal river profile shapes with knick points,asymmetric basins,and fault reactivations,and highlights the tectonics activity that used to occur through the time and their control on the morphology.Together,they document the lithostructural controls on the DBR landscape evolution,extendable in the whole SW Cameroon margin.
