The present work aims to identify flood hazards and risks, particularly to the Attanagalu Oya river basin in Gampaha district, the western province in Sri Lanka. Attanagalu Oya river catchment area periodically faced ...The present work aims to identify flood hazards and risks, particularly to the Attanagalu Oya river basin in Gampaha district, the western province in Sri Lanka. Attanagalu Oya river catchment area periodically faced flood hazards. The flood is categorized by complex like 2008, 2010, 2016, 2017, and it chose 2016 as the primary flood event. Study areas have been selected depending on data availability. Attanagalu Oya river basin is mainly focused as a study area. However, here selected only four Grama Niladhari Divisions are as a sample area. Those are;Kirindivita, Ambanvita, Thammita West, Gonagaha1. Furthermore, many flood hazards can be identified when considering the flood events history. But here selected only two years were 2010 and 2016. These two years were selected with high flood events. For the study, that flood series used 1 feet elevation contours used to identify flood levels and used LiDAR image to identify risk areas in the study site. Due to the blockage of the main waterways that discharge water into the Negombo Lagoon, limited water transportation, low lying land reclamation for development, mainly affect paddy lands and roads, and flood as a major problem identified temporarily and spatially. Eventually, the study could identify flood-prone areas and map the risk zones within the study area.展开更多
Sedimentological methods such as granulometry, morphoscopy and heavy minerals analysis have been carried out to characterize alluvial gold deposits of Betare-Oya and its surroundings, with the aim to determine their o...Sedimentological methods such as granulometry, morphoscopy and heavy minerals analysis have been carried out to characterize alluvial gold deposits of Betare-Oya and its surroundings, with the aim to determine their origin and conditions in which they are formed and also to determine the mineralogical content of these deposits, their nature and distribution. It came out from this study the following: The alluvial deposits studied are sand, constituting of coarse fraction (grains), medium grains in abundant and fine grains. The average values of sorting index (S0) and coefficient of asymmetry (A) are respectively 2.53 and 0.73. These values indicate that the sand is poorly arranged and poorly sorted with a better classification or arrangement in the coarse fraction (grains). These are sediments that are deposited together by high competent currents. It would therefore probably be torrential deposits and or streams from short transport. Unused grains are dominating (80.5%) which translate a proximal source of the sediments. So it would be probably from the dismantling of the surrounding landforms. The heavy minerals studied revealed the presence of the following minerals;zircon, gold, sphene, green hornblende, tourmaline, rutile, augite, hypersthene, sillimanite, glau-cophane, biotite, staurotide, and the opaque. These minerals belong to the cortege of plutonic and metamorphic rocks from a single proximal distributing province.展开更多
Field studies (location Au pits, sampling of different layers of sedimentary sequences filling the pits, panning of sediments), litho-stratigraphic investigations, grain size analysis and outlining of depositional con...Field studies (location Au pits, sampling of different layers of sedimentary sequences filling the pits, panning of sediments), litho-stratigraphic investigations, grain size analysis and outlining of depositional conditions revealed a characteristic fining upward sequence in all the sections of 08 Au-pits within the Betare Oya basin. A typical profile is 2.5 to 4.5 m thick and is composed of a 30 to 50 cm organic topsoil layer, underlain by a 1.5 m thick reddish brownish gold free saprolite, which is underlain by 1.5 m sandy section. From litho-stratigraphic investigations and grain size analysis results a quartz dominated gravelly 1.4 m thick layer consisting in boulders (275 mm), cobbles (2-−0.0148x2 + 1.2187x + 2.0344, R2 = 0.6929 (sandy layer);2) y = 0.0617x2 + 1.0849x + 0.8097, R2 = 0.8694 (gravelly layer);and y > R2 is satisfied in both cases. This implies that Au recovery from these layers could be effective through gravity separation using sieves mounted on classifiers of 7 cm (sandy layer) and 10 cm (gravelly layer) diameter.展开更多
To assess the water quality in the locality of Bétaré-Oya affected by an intensive artisanal and semi mechanized mining activities, 71 samples were collected from sixteen points during the 2015-2016 hydrolog...To assess the water quality in the locality of Bétaré-Oya affected by an intensive artisanal and semi mechanized mining activities, 71 samples were collected from sixteen points during the 2015-2016 hydrological year. These points include: three in Lom river which is the main stream of the study area, five in Mari river which is one of the left bank tributaries of the Lom, in Bétaré-Oya and eight in the left and the right bank of Mari. Different physicochemical parameters such as pH, electrical conductivity (EC), alkalinity, turbidity, total suspended solids (TSS), cyanide (CN-), major elements and heavy metals (Pb, Zn, Cd, Fe, Cu, As, Mn and Cr) were analyzed. Water Quality Indices (WQI), Heavy metal Pollution Index (HPI), sodium adsorption ratio (SAR) and percent sodium (Na%) were also computed to evaluate the suitability of water for drinking and irrigation. The results showed that the surface water from Bétaré-Oya was acidic to basic (5.40 < pH < 8.84), weakly mineralized (11.60 < EC < 122.10 μS/cm) with a high concentration of TSS (2 < TSS < 8996.00 mg/L) and turbidity (1.22 to 4758.00 NTU). The WQI scores show excellently to unsuitable quality in almost all the sampling sites. The water quality is found to be most deteriorated in Lom river and in the downstream of Mari river where an extensive mining activity is carried out, with the high WQI value of 5137.40. Based on heavy metal pollution index, the mean value was 1195.36 and thus under the critical pollution index. We thus notice a serious physical degradation by organic and mineral suspended particles as well as chemical degradation by heavy metals. This results from mining activities in the Lom river and its main tributaries such as the Mari river in the upstream part of the Sanaga basin. According to the percentage of sodium and SAR, these waters can be used for irrigation purposes in almost all types of soils.展开更多
Physicochemical characterization and pollution evaluation were performed on six gold mining sites at the locality of Bétaré-Oya in Cameroon. Twelve samples of twenty two sampled show contamination with arsen...Physicochemical characterization and pollution evaluation were performed on six gold mining sites at the locality of Bétaré-Oya in Cameroon. Twelve samples of twenty two sampled show contamination with arsenic, nickel and lead. Granulometric analysis performed on all samples show a predominance of coarse particle (>250 μm) and PH varying from 5.4 to 7. The pollution index and pollution load index show that primary gold exploitation site of Mbal, Nakayo and Kpawara are contaminated. The highest pollution index is recorded on releases from the primary gold mining sites of Mbal, Kpawara and Nyondéré, which means that one must have a watchful eye to the discharges produced by primary gold mining. Sorting the samples in descending order of pollution index yields: Mb3 > Kp1 > Kp2 > Mb2 > Mb1 > Mb4 > Kp3 > Na5;meaning that special emphasis should be placed on the monitoring of wash sludge such as those from the Mbal site (Mb3), where pollution index is equal to 36.29, as well as washed and waste rock.展开更多
Exploration for primary gold in tropical settings is often problematic because of deep weathering and the development of a thick soil cover. In this paper we present the results of both chargeability and resistivity s...Exploration for primary gold in tropical settings is often problematic because of deep weathering and the development of a thick soil cover. In this paper we present the results of both chargeability and resistivity surveys carried out over the Belikombone hill gold prospect (14?00' - 14?25'E, 5?25' - 6?00'N) in the Betare Oya area (eastern Cameroon), where previous soil sampling had identified gold anomalies. The geophysical data were obtained using Syscal Junior 48 resistivity meter and the Schlumberger configuration array for both the vertical electrical soundings (VES) and horizontal profiling. These data were further built into a GIS framework and the continuity of favourable gold-bearing structures at depth modeled using WINSEV, RED2INV and SURFER extensions softwares. IP (Induced Polarization)-chargeability and resistivity data combined, have identified irregular anomalous zones trending NE-SW. This trend is consistent with the attitude of most auriferous quartz veins exposed in artisanal pits and parallel to the regional shear zone system and foliations. The high resistivity anomalies correspond to quartz veins while the relatively high IP anomalies correspond to low sulphide ± gold concentrations in the quartz veins. Modeling IP-chargeability and resistivity data prepared as contours and 3D maps, culminated to the development of an inferred, irregular and discontinuous mineralized body at depths of up to 95 m. The size and shape of this mineralized body can only later be tested by drilling to ascertain the resource.展开更多
文摘The present work aims to identify flood hazards and risks, particularly to the Attanagalu Oya river basin in Gampaha district, the western province in Sri Lanka. Attanagalu Oya river catchment area periodically faced flood hazards. The flood is categorized by complex like 2008, 2010, 2016, 2017, and it chose 2016 as the primary flood event. Study areas have been selected depending on data availability. Attanagalu Oya river basin is mainly focused as a study area. However, here selected only four Grama Niladhari Divisions are as a sample area. Those are;Kirindivita, Ambanvita, Thammita West, Gonagaha1. Furthermore, many flood hazards can be identified when considering the flood events history. But here selected only two years were 2010 and 2016. These two years were selected with high flood events. For the study, that flood series used 1 feet elevation contours used to identify flood levels and used LiDAR image to identify risk areas in the study site. Due to the blockage of the main waterways that discharge water into the Negombo Lagoon, limited water transportation, low lying land reclamation for development, mainly affect paddy lands and roads, and flood as a major problem identified temporarily and spatially. Eventually, the study could identify flood-prone areas and map the risk zones within the study area.
文摘Sedimentological methods such as granulometry, morphoscopy and heavy minerals analysis have been carried out to characterize alluvial gold deposits of Betare-Oya and its surroundings, with the aim to determine their origin and conditions in which they are formed and also to determine the mineralogical content of these deposits, their nature and distribution. It came out from this study the following: The alluvial deposits studied are sand, constituting of coarse fraction (grains), medium grains in abundant and fine grains. The average values of sorting index (S0) and coefficient of asymmetry (A) are respectively 2.53 and 0.73. These values indicate that the sand is poorly arranged and poorly sorted with a better classification or arrangement in the coarse fraction (grains). These are sediments that are deposited together by high competent currents. It would therefore probably be torrential deposits and or streams from short transport. Unused grains are dominating (80.5%) which translate a proximal source of the sediments. So it would be probably from the dismantling of the surrounding landforms. The heavy minerals studied revealed the presence of the following minerals;zircon, gold, sphene, green hornblende, tourmaline, rutile, augite, hypersthene, sillimanite, glau-cophane, biotite, staurotide, and the opaque. These minerals belong to the cortege of plutonic and metamorphic rocks from a single proximal distributing province.
文摘Field studies (location Au pits, sampling of different layers of sedimentary sequences filling the pits, panning of sediments), litho-stratigraphic investigations, grain size analysis and outlining of depositional conditions revealed a characteristic fining upward sequence in all the sections of 08 Au-pits within the Betare Oya basin. A typical profile is 2.5 to 4.5 m thick and is composed of a 30 to 50 cm organic topsoil layer, underlain by a 1.5 m thick reddish brownish gold free saprolite, which is underlain by 1.5 m sandy section. From litho-stratigraphic investigations and grain size analysis results a quartz dominated gravelly 1.4 m thick layer consisting in boulders (275 mm), cobbles (2-−0.0148x2 + 1.2187x + 2.0344, R2 = 0.6929 (sandy layer);2) y = 0.0617x2 + 1.0849x + 0.8097, R2 = 0.8694 (gravelly layer);and y > R2 is satisfied in both cases. This implies that Au recovery from these layers could be effective through gravity separation using sieves mounted on classifiers of 7 cm (sandy layer) and 10 cm (gravelly layer) diameter.
文摘To assess the water quality in the locality of Bétaré-Oya affected by an intensive artisanal and semi mechanized mining activities, 71 samples were collected from sixteen points during the 2015-2016 hydrological year. These points include: three in Lom river which is the main stream of the study area, five in Mari river which is one of the left bank tributaries of the Lom, in Bétaré-Oya and eight in the left and the right bank of Mari. Different physicochemical parameters such as pH, electrical conductivity (EC), alkalinity, turbidity, total suspended solids (TSS), cyanide (CN-), major elements and heavy metals (Pb, Zn, Cd, Fe, Cu, As, Mn and Cr) were analyzed. Water Quality Indices (WQI), Heavy metal Pollution Index (HPI), sodium adsorption ratio (SAR) and percent sodium (Na%) were also computed to evaluate the suitability of water for drinking and irrigation. The results showed that the surface water from Bétaré-Oya was acidic to basic (5.40 < pH < 8.84), weakly mineralized (11.60 < EC < 122.10 μS/cm) with a high concentration of TSS (2 < TSS < 8996.00 mg/L) and turbidity (1.22 to 4758.00 NTU). The WQI scores show excellently to unsuitable quality in almost all the sampling sites. The water quality is found to be most deteriorated in Lom river and in the downstream of Mari river where an extensive mining activity is carried out, with the high WQI value of 5137.40. Based on heavy metal pollution index, the mean value was 1195.36 and thus under the critical pollution index. We thus notice a serious physical degradation by organic and mineral suspended particles as well as chemical degradation by heavy metals. This results from mining activities in the Lom river and its main tributaries such as the Mari river in the upstream part of the Sanaga basin. According to the percentage of sodium and SAR, these waters can be used for irrigation purposes in almost all types of soils.
文摘Physicochemical characterization and pollution evaluation were performed on six gold mining sites at the locality of Bétaré-Oya in Cameroon. Twelve samples of twenty two sampled show contamination with arsenic, nickel and lead. Granulometric analysis performed on all samples show a predominance of coarse particle (>250 μm) and PH varying from 5.4 to 7. The pollution index and pollution load index show that primary gold exploitation site of Mbal, Nakayo and Kpawara are contaminated. The highest pollution index is recorded on releases from the primary gold mining sites of Mbal, Kpawara and Nyondéré, which means that one must have a watchful eye to the discharges produced by primary gold mining. Sorting the samples in descending order of pollution index yields: Mb3 > Kp1 > Kp2 > Mb2 > Mb1 > Mb4 > Kp3 > Na5;meaning that special emphasis should be placed on the monitoring of wash sludge such as those from the Mbal site (Mb3), where pollution index is equal to 36.29, as well as washed and waste rock.
文摘Exploration for primary gold in tropical settings is often problematic because of deep weathering and the development of a thick soil cover. In this paper we present the results of both chargeability and resistivity surveys carried out over the Belikombone hill gold prospect (14?00' - 14?25'E, 5?25' - 6?00'N) in the Betare Oya area (eastern Cameroon), where previous soil sampling had identified gold anomalies. The geophysical data were obtained using Syscal Junior 48 resistivity meter and the Schlumberger configuration array for both the vertical electrical soundings (VES) and horizontal profiling. These data were further built into a GIS framework and the continuity of favourable gold-bearing structures at depth modeled using WINSEV, RED2INV and SURFER extensions softwares. IP (Induced Polarization)-chargeability and resistivity data combined, have identified irregular anomalous zones trending NE-SW. This trend is consistent with the attitude of most auriferous quartz veins exposed in artisanal pits and parallel to the regional shear zone system and foliations. The high resistivity anomalies correspond to quartz veins while the relatively high IP anomalies correspond to low sulphide ± gold concentrations in the quartz veins. Modeling IP-chargeability and resistivity data prepared as contours and 3D maps, culminated to the development of an inferred, irregular and discontinuous mineralized body at depths of up to 95 m. The size and shape of this mineralized body can only later be tested by drilling to ascertain the resource.
