The Elogo region has been subjected to craft industry and semi-industrial mining for gold-bearing placers, since the colonial times. It is actually undergoing an intensive exploration for a primary gold deposit. The g...The Elogo region has been subjected to craft industry and semi-industrial mining for gold-bearing placers, since the colonial times. It is actually undergoing an intensive exploration for a primary gold deposit. The goal of this study is to contribute to the exploration of the primary gold deposit in the Elogo Region (North-West of Congo Republic). The methodology consisted of characterization of placers deposits by their lithology, mineralogy and the gold grains shape, in order to constrain the source of gold with the respect to the local geology. The results obtained show that alluviums are polygenic and yields seventeen mineral species composed of zircon, olivine, magnetite, ilmenite, gold, garnet, rutile, coltan, cassiterite, monazite, apatite, amphibole, tourmaline, pyrite, limonite, chromite, and amphibole. The morphoscopy of gold grain shows single grains and grains with quartz inclusions that suggest their relationship with quartz veins. The gold grains are flattened, sub-flattened, and rounded. The northern region of Elogo characterized by a dominance of coarser quartz-included gold grains indicates a proximal proparte origin (less than 50 m), while the southern region, showing less coarse and more evolved grains with choc marks, appears to be associated with a distal pro-parte origin (more than 300 m). The multivariate statistical analysis shows seven classes of samples corresponding to the mineralogical paragenesis suggesting various sources, consisting of high-grade metamorphic, granitoids, pegmatites, basic and ultrabasic rocks, and BIFs that provided minerals to the placers. Gold mainly comes from hydrothermal quartz veins and probably from the peptization of gold from the weathering of sulfides occurring in the BIF. In the Elogo region, gold exploration for primary deposits should look for and follow the hydrothermal system developed in this region. Chemical analysis for the gold grains and associated minerals is necessary to better guide the proposed geochemical prospecting.展开更多
The practice has proved that it is an economic and effective method to investigate placer gold deposit by using multi-level information sources of remote sensing and multi-variate analysis methods, especially for the ...The practice has proved that it is an economic and effective method to investigate placer gold deposit by using multi-level information sources of remote sensing and multi-variate analysis methods, especially for the area with a sparse population and difficult condition like the Da Hinggan Mountains, China.The information sources used in our work includes Landsat TM, aerial infrared photography and their mosaic image maps and enlarged photos with different scales. According to statistic data, in the study area the gold-bearing rocks are mainly granite, alaskite, granodiorite and some old metamorphic rocks. On gold-bearing geological structures, the fault zones in the four directions (NE, NNE, NW and EW) are obvious, in which NNE and EW are the most key fault zones. On fluvial geomorphology the flow courses stored placer are in the tributaries of the 4th and 5th levels, especially in straight or slight curve reaches. On the basis of analysis the interpretative signs were set up, and the interpretative展开更多
Many gold placers located in the Coastal Range of south-central Chile have been exploited commercially during the past decades;nevertheless and until now, there are not any exploration studies of these placers and the...Many gold placers located in the Coastal Range of south-central Chile have been exploited commercially during the past decades;nevertheless and until now, there are not any exploration studies of these placers and their basement. In order to provide an overview of exploratory potential, the stream sediments that are part of several gold placers in the northwest area of the BioBío region are analyzed, which have been registered on the basis of empirical evidence from artisanal mining activities. The overview consists of two goals: 1) determine the presence of auriferous occurrences (stream sediments and basement) and 2) identify potentially favorable areas to find gold placer deposits. Through optical microscopy this study characterized the metallic and non-metallic mineralogy of the basement, along with geochemical analyses of stream sediments and surrounding rocks of the placer deposits. The geochemical results show two sectors with high precious metal contents in sediments (up to 24 ppm of Au and 8 ppm of Ag) and two rocky outcrops with Au (757 and 41 ppb). Additionally, there are depressions in the study area that have received large amounts of sediments (reaching up to 170 m-thick), which are favorable places for the accumulation of auriferous sediments from nearby valleys due to the tectonic and structural conditions where they are located. Then, these results show an exploratory potential for gold placers and can be useful to delineate future exploration strategies in the Coastal Range of south-central Chile.展开更多
Analysis of the anomalous magnetic mineral intensities and geochemistry for placer gold deposits are presented for those of the Attock area at the confluence of the Indus and Kabul rivers in northwestern Pakistan.Two ...Analysis of the anomalous magnetic mineral intensities and geochemistry for placer gold deposits are presented for those of the Attock area at the confluence of the Indus and Kabul rivers in northwestern Pakistan.Two grids covering an area of 10 x18 m2 and 8 x10 m2 were analyzed using a G-858 Cesium Vapor Magnetometer.The anomalous zones obtained were plotted on contour maps,2 D and 3 D magnetic intensity maps.Based on the magnetic anomalies,grid-1 of the study area was sampled at three different anomalous zones for geochemical analysis.These zones contain gold concentrations,ranging from 2.11 ppm to 6.109 ppm with an average of 4.01 ppm.Increase in gold concentration in the subsurface within the anomalous zones indicates that magnetometer survey followed by a geochemical analysis can potentially narrow down the gold-bearing anomalous zones.展开更多
Global placer其实是一个矩形框约束问题。关于如何改进当前的无约束非线性共轭梯度算法来应用于矩形框约束问题,本文提出了一个实用的改进方法并且通过一些数学方法解决了程序实现执行中数据精度和稳定性问题。改善当前无约束的共轭梯...Global placer其实是一个矩形框约束问题。关于如何改进当前的无约束非线性共轭梯度算法来应用于矩形框约束问题,本文提出了一个实用的改进方法并且通过一些数学方法解决了程序实现执行中数据精度和稳定性问题。改善当前无约束的共轭梯度求解算法是非常有价值的,可以帮助客户缩短产品进入市场的时间周期和减少最后的总成本如最后总的布局布线的导线长度。展开更多
A comparative analysis of typomorphic features of gold placers and indigenous sources of gold was carried out for the Glukharinsky ore-placer node (the Nadezhda deposit and Glukharinskoye, Tyomnoye, and Tyi-Jurye ore ...A comparative analysis of typomorphic features of gold placers and indigenous sources of gold was carried out for the Glukharinsky ore-placer node (the Nadezhda deposit and Glukharinskoye, Tyomnoye, and Tyi-Jurye ore occurrences). A correlation between fineness of placer native gold and composition of relic minerals preserved inside gold particles was obtained for the first time. This made it possible to establish mineral parageneses of native gold from potential indigenous sources. The study of placer gold fineness in combination with com-position of mineral inclusions allowed us to identify seven types of gold paragenesis: petzite-hessite with a fineness of 855‰, pyrite-polybasite-galena (a fineness of 670‰), bismuth telluride (900‰), cosalite-vikingite (790‰), galena (870‰), glaucodot (950‰), and hydrohematite (840‰). It was also shown that the placer contains the material from ore occurrences of different formation: gold-quartz-porphyry occurrences in granitoids (Au-Te-Bi type) and gold-silver occurrences. The method developed by us allows one to estimate the percentage of each ore source in placer formation.展开更多
This work presents a preliminary mineralogical characterization of Nb-Ta oxide minerals from alluvial placers located in the Ngoura area,eastern Cameroon.The heavy minerals are characteristic of short hydromechanical ...This work presents a preliminary mineralogical characterization of Nb-Ta oxide minerals from alluvial placers located in the Ngoura area,eastern Cameroon.The heavy minerals are characteristic of short hydromechanical transport and highlight the stability of Nb-Ta oxides during the weathering and transport.Nb-Ta mineralization in placer deposits from the Ngoura area may derive from local sedimentation.The assemblage of Nb-Ta oxides in the studied placers consists of tapiolite-(Fe)and tantalite-(Mn).Tapiolite-(Fe)exhibits high concentrations in Ta2O5(78.07-80.46 wt%)and FeO(12.18-13.66 wt%)and plots within a narrow range of Ta*(0.900-0.933)and Mn*(0.037-0.119),which correspond to the ranges typically observed in tapiolite-(Fe)worldwide.Tantalite-(Mn)shows Ta2O5 contents ranging from 62.17 to 69.45 wt%,Nb2O5 from 12.09 to 17.37 wt%,MnO from 7.63 to 12.49 wt%and FeO from 1.48 to 6.62 wt%.It is also characterized by a wider range of Mn<sup>*(0.538-0.891)and relatively homogeneous Ta/(Ta+Nb)(0.683-0.779)ratios.Texturally,the studied Nb-Ta minerals exhibit oscillatory zoning characterized by bright Ta-rich zones alternating with dark Nb-rich zones.This oscillatory zoning is progressive in some minerals and the alternating bands may appear regular to wavy with gradual transitions.Oscillatory zoning in Nb-Ta oxides from the Ngoura placers is considered to be a primary magmatic feature and is tentatively explained as a result of magmas mixing,rapid cooling or degassing/decompression of the igneous system.The geomorphology and the tropical humid climate of the eastern region offer suitable conditions for the deposition of alluvial placers.Therefore,niobium-tantalum minerals from the Ngoura placers must have been sourced from the weathering and erosion of alkaline granites and pegmatites widespread in the study area.展开更多
This paper has systematically researched mineral assemble and the characteristics of gold-mercury minerals in Davao Placer in Mindanao Islands, Philippines. The results show that reflection force of gold-mercury miner...This paper has systematically researched mineral assemble and the characteristics of gold-mercury minerals in Davao Placer in Mindanao Islands, Philippines. The results show that reflection force of gold-mercury minerals has a strong-weak-strong of changes features as mercury＇s content in minerals increased. Otherwise their hardness of gold-mercury minerals reduced. While the hardness of gold-mercury minerals, which have isometric crystal structure, they are gradually become larger, the goldmalgam and r-Goldmalgamite just be found to exist as natural edge of gold-mercury mineral grains. Overall, mercury content is gradually reduced from the edge to the centre of gold-mercury minerals particles, but mercury-bearing in edge of the grains is lower than in the middle. Combination of the background of geological mineralization, this paper suggests that there are mantle-derived deposits such as Platinum, chromium in Philippines, which accompanied ultramafic-mafic magmation. It＇s most likely to found some large or extra large scale polymetallic deposits of gold and mercury, as well as coastal placers of gold, platinum, etc.展开更多
文摘The Elogo region has been subjected to craft industry and semi-industrial mining for gold-bearing placers, since the colonial times. It is actually undergoing an intensive exploration for a primary gold deposit. The goal of this study is to contribute to the exploration of the primary gold deposit in the Elogo Region (North-West of Congo Republic). The methodology consisted of characterization of placers deposits by their lithology, mineralogy and the gold grains shape, in order to constrain the source of gold with the respect to the local geology. The results obtained show that alluviums are polygenic and yields seventeen mineral species composed of zircon, olivine, magnetite, ilmenite, gold, garnet, rutile, coltan, cassiterite, monazite, apatite, amphibole, tourmaline, pyrite, limonite, chromite, and amphibole. The morphoscopy of gold grain shows single grains and grains with quartz inclusions that suggest their relationship with quartz veins. The gold grains are flattened, sub-flattened, and rounded. The northern region of Elogo characterized by a dominance of coarser quartz-included gold grains indicates a proximal proparte origin (less than 50 m), while the southern region, showing less coarse and more evolved grains with choc marks, appears to be associated with a distal pro-parte origin (more than 300 m). The multivariate statistical analysis shows seven classes of samples corresponding to the mineralogical paragenesis suggesting various sources, consisting of high-grade metamorphic, granitoids, pegmatites, basic and ultrabasic rocks, and BIFs that provided minerals to the placers. Gold mainly comes from hydrothermal quartz veins and probably from the peptization of gold from the weathering of sulfides occurring in the BIF. In the Elogo region, gold exploration for primary deposits should look for and follow the hydrothermal system developed in this region. Chemical analysis for the gold grains and associated minerals is necessary to better guide the proposed geochemical prospecting.
文摘The practice has proved that it is an economic and effective method to investigate placer gold deposit by using multi-level information sources of remote sensing and multi-variate analysis methods, especially for the area with a sparse population and difficult condition like the Da Hinggan Mountains, China.The information sources used in our work includes Landsat TM, aerial infrared photography and their mosaic image maps and enlarged photos with different scales. According to statistic data, in the study area the gold-bearing rocks are mainly granite, alaskite, granodiorite and some old metamorphic rocks. On gold-bearing geological structures, the fault zones in the four directions (NE, NNE, NW and EW) are obvious, in which NNE and EW are the most key fault zones. On fluvial geomorphology the flow courses stored placer are in the tributaries of the 4th and 5th levels, especially in straight or slight curve reaches. On the basis of analysis the interpretative signs were set up, and the interpretative
文摘Many gold placers located in the Coastal Range of south-central Chile have been exploited commercially during the past decades;nevertheless and until now, there are not any exploration studies of these placers and their basement. In order to provide an overview of exploratory potential, the stream sediments that are part of several gold placers in the northwest area of the BioBío region are analyzed, which have been registered on the basis of empirical evidence from artisanal mining activities. The overview consists of two goals: 1) determine the presence of auriferous occurrences (stream sediments and basement) and 2) identify potentially favorable areas to find gold placer deposits. Through optical microscopy this study characterized the metallic and non-metallic mineralogy of the basement, along with geochemical analyses of stream sediments and surrounding rocks of the placer deposits. The geochemical results show two sectors with high precious metal contents in sediments (up to 24 ppm of Au and 8 ppm of Ag) and two rocky outcrops with Au (757 and 41 ppb). Additionally, there are depressions in the study area that have received large amounts of sediments (reaching up to 170 m-thick), which are favorable places for the accumulation of auriferous sediments from nearby valleys due to the tectonic and structural conditions where they are located. Then, these results show an exploratory potential for gold placers and can be useful to delineate future exploration strategies in the Coastal Range of south-central Chile.
基金financial support provided by the Department of Geology and the National Centre of Excellence in Geology,University of Peshawar。
文摘Analysis of the anomalous magnetic mineral intensities and geochemistry for placer gold deposits are presented for those of the Attock area at the confluence of the Indus and Kabul rivers in northwestern Pakistan.Two grids covering an area of 10 x18 m2 and 8 x10 m2 were analyzed using a G-858 Cesium Vapor Magnetometer.The anomalous zones obtained were plotted on contour maps,2 D and 3 D magnetic intensity maps.Based on the magnetic anomalies,grid-1 of the study area was sampled at three different anomalous zones for geochemical analysis.These zones contain gold concentrations,ranging from 2.11 ppm to 6.109 ppm with an average of 4.01 ppm.Increase in gold concentration in the subsurface within the anomalous zones indicates that magnetometer survey followed by a geochemical analysis can potentially narrow down the gold-bearing anomalous zones.
文摘A comparative analysis of typomorphic features of gold placers and indigenous sources of gold was carried out for the Glukharinsky ore-placer node (the Nadezhda deposit and Glukharinskoye, Tyomnoye, and Tyi-Jurye ore occurrences). A correlation between fineness of placer native gold and composition of relic minerals preserved inside gold particles was obtained for the first time. This made it possible to establish mineral parageneses of native gold from potential indigenous sources. The study of placer gold fineness in combination with com-position of mineral inclusions allowed us to identify seven types of gold paragenesis: petzite-hessite with a fineness of 855‰, pyrite-polybasite-galena (a fineness of 670‰), bismuth telluride (900‰), cosalite-vikingite (790‰), galena (870‰), glaucodot (950‰), and hydrohematite (840‰). It was also shown that the placer contains the material from ore occurrences of different formation: gold-quartz-porphyry occurrences in granitoids (Au-Te-Bi type) and gold-silver occurrences. The method developed by us allows one to estimate the percentage of each ore source in placer formation.
文摘This work presents a preliminary mineralogical characterization of Nb-Ta oxide minerals from alluvial placers located in the Ngoura area,eastern Cameroon.The heavy minerals are characteristic of short hydromechanical transport and highlight the stability of Nb-Ta oxides during the weathering and transport.Nb-Ta mineralization in placer deposits from the Ngoura area may derive from local sedimentation.The assemblage of Nb-Ta oxides in the studied placers consists of tapiolite-(Fe)and tantalite-(Mn).Tapiolite-(Fe)exhibits high concentrations in Ta2O5(78.07-80.46 wt%)and FeO(12.18-13.66 wt%)and plots within a narrow range of Ta*(0.900-0.933)and Mn*(0.037-0.119),which correspond to the ranges typically observed in tapiolite-(Fe)worldwide.Tantalite-(Mn)shows Ta2O5 contents ranging from 62.17 to 69.45 wt%,Nb2O5 from 12.09 to 17.37 wt%,MnO from 7.63 to 12.49 wt%and FeO from 1.48 to 6.62 wt%.It is also characterized by a wider range of Mn<sup>*(0.538-0.891)and relatively homogeneous Ta/(Ta+Nb)(0.683-0.779)ratios.Texturally,the studied Nb-Ta minerals exhibit oscillatory zoning characterized by bright Ta-rich zones alternating with dark Nb-rich zones.This oscillatory zoning is progressive in some minerals and the alternating bands may appear regular to wavy with gradual transitions.Oscillatory zoning in Nb-Ta oxides from the Ngoura placers is considered to be a primary magmatic feature and is tentatively explained as a result of magmas mixing,rapid cooling or degassing/decompression of the igneous system.The geomorphology and the tropical humid climate of the eastern region offer suitable conditions for the deposition of alluvial placers.Therefore,niobium-tantalum minerals from the Ngoura placers must have been sourced from the weathering and erosion of alkaline granites and pegmatites widespread in the study area.
文摘This paper has systematically researched mineral assemble and the characteristics of gold-mercury minerals in Davao Placer in Mindanao Islands, Philippines. The results show that reflection force of gold-mercury minerals has a strong-weak-strong of changes features as mercury＇s content in minerals increased. Otherwise their hardness of gold-mercury minerals reduced. While the hardness of gold-mercury minerals, which have isometric crystal structure, they are gradually become larger, the goldmalgam and r-Goldmalgamite just be found to exist as natural edge of gold-mercury mineral grains. Overall, mercury content is gradually reduced from the edge to the centre of gold-mercury minerals particles, but mercury-bearing in edge of the grains is lower than in the middle. Combination of the background of geological mineralization, this paper suggests that there are mantle-derived deposits such as Platinum, chromium in Philippines, which accompanied ultramafic-mafic magmation. It＇s most likely to found some large or extra large scale polymetallic deposits of gold and mercury, as well as coastal placers of gold, platinum, etc.
