Characterization of Gold Bearing Placers and Associated Minerals in the Elogo Region (North-West Congo Republic)

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.

Reconstruction of the Indigenous Sources of Gold of the Glu-Kharinsky Placer (Kolyma River Basin, Magadan Region, Russia)

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.

THE APPLICATION OF REMOTE SENSING TECHNIQUE ON GEOLOGICAL INVESTIGATION OF PLACER DEPOSIT

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

Global placer中框约束问题非线性共轭梯度算法的改进

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。

Exploring Placer Gold Deposits through Integrated Geophysical and Geochemical Techniques at the Confluence of the Indus and Kabul Rivers,NW Pakistan

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.

Niobium–tantalum oxide minerals in alluvial placer deposits from the Ngoura area,East-Cameroon

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.

Exploratory Potential for Gold Placer Deposits in the Coastal Range, BioBío Region, South-Central Chile

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.

Mineralogical Characteristics and its Prospecting Significance of Gold-Mercury Minerals in Davao Gold Placer in Mindanao Islands, Philippines

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.

基于Innovus混合放置的布局规划方法优化

随着集成电路后端设计中宏单元数量增多,传统布局规划方法效率低且耗时,而自动布局规划的混合放置(MP)技术存在物理规则违例数量多、电压降大和功耗高等问题。针对传统方式和MP方式的不足,提出了一种优化的MP布局规划方法,通过控制宏单元通道空间和标准单元密度大小、固定边界宏单元位置及脚本修复TSMC芯片集成检查(TCIC)违例的方法解决MP技术存在的问题。研究结果表明,优化的MP方式保留了MP技术的性能、功耗和面积(PPA)优势,且相比于传统方式布线长度优化了28%,时序违例优化了65%,功耗优化了609%。该方案可为多宏单元大规模设计的布局规划提供参考。

金属砂矿勘查中基本分析项目与地质品位的确定--讨论及建议

基本分析项目与地质品位的确定是金属砂矿勘查中基础且重要的环节,对我国金属类砂矿开发与利用产生直接影响。我国现有砂矿地质品位确定方法存在一定差异性,模糊性或矛盾性,对这些重要问题进行讨论是有必要的。本文以多年来滨浅海金属类砂矿调查经验为基础,结合前人研究成果,介绍目前勘查中砂矿品位的主流表示与计算方法,分析其优缺点,继而提出面向新一轮找矿突破要求的改进方法并探讨其可行性。结果表明:金属砂矿勘查品位确定应遵循与时俱进、正确对待误差、综合评价原则,并寻求勘查成本与勘查风险的最佳结合点。建议不采用传统重矿物淘洗+鉴定方法作为基本分析获得矿物品位,推荐视勘查阶段、勘查主要目的、勘查类型灵活选用重矿物含量(THM%)测定、化学分析法换算、自动矿物分析(如MLA)3种方法作为基本分析项目。圈定矿体的边界品位与最低工业品位可直接利用“重矿物含量”或采用“综合圈矿指标”。应选取重点研究区,将其与传统方法进行对比研究与验证,同时对砂矿勘查技术规范体系相关内容进行广泛深入讨论,寻求共识,以求加快补充修订。

南海及邻域砂矿资源分布特征及成矿模式

南海及邻域具有多样的地形地貌和丰富的物源,为海洋固体矿产资源的形成和分布提供了物质来源和堆积环境。为系统查明南海及邻域砂矿资源分布情况,本文通过对南海及邻域2606个站位表层沉积物样品进行粒度测试、碎屑矿物鉴定,以及重矿物的品位计算,分析了南海及邻域有用矿物砂矿资源以及建筑用砂资源分布特征并预测了远景区,总结了砂矿成矿模式。结果表明,南海及邻域具有远景的矿种主要有锆石、钛铁矿、金红石、锐钛矿、独居石和石榴子石等;重矿物高品位矿点主要集中在南海东北陆架、菲律宾海盆、南部陆架,重矿物异常区主要位于周缘陆架浅水区以及越东外陆架浅水海域、菲律宾海盆。锆石品位异常区的范围最大,达到工业品位的面积也最大;其次是磁铁矿、钛铁矿、独居石的异常区;锐钛矿、金红石异常区的面积相当;石榴子石品位异常范围最小。根据砂矿的分布规律、大地构造背景、成矿条件以及成矿元素特征,圈定了24个有用重矿物砂矿成矿远景区和6个成矿带。沉积物中砂(0.063~2 mm)含量大于50%的建筑用砂的远景区9个,主要分布于海南岛西南面到台湾海峡南部一线以北海域,其次为南海南部礼乐滩、万安滩、曾母暗沙附近海域,其余海域极为罕见。基于南海砂矿资源分布特征,初步建立了近岸型、潮流砂脊型、古河道埋藏型、峡口型、陆架坡折带型等五种砂矿成矿模式,为海砂资源进一步勘查提供方向和建议。

Provenance studies on the heavy mineral placers along the coastal deposits of Odisha,eastern India

The coastal deposits along the eastern part of the Indian Peninsula are known for the high abundance of heavy minerals. The present study, as discussed here, has been undertaken along the southwestern coastal part of Odisha, India, adjoining the charnockite-migmatite zone of the Eastern Ghat Mobile Belt(EGMB). The composition of the placers along the study area is primarily controlled by the detritus from the proximal hinterland rock type(s). The weathering index has been established based on the grain morphology, major element concentration and radioelement ratios. Petrological characteristics and grain morphology of monazite, zircon, ilmenite and rutile have been presented respectively, and their implications are discussed. The provenance study of these coastal placers is based on the abundance of rare earth elements(REE) and radioactive elements in the placer sands and the rock types in the study area. The tectonic implications are based on the major element abundance of the beach sands.

威海市东部滨海新城海域海砂资源分布及特征

对威海东部滨海新城海域海底底质样品、浅地层剖面、地质钻探、多波束测量等资料进行了分析,探讨了该区海砂资源的类型、分布特征及沉积环境。结果表明:研究区海砂资源主要分布于鸡鸣岛和苍家岛潮沟附近,均为埋藏砂矿,以粉砂和细砂为主,含泥量较高,可用作回填用砂。研究区埋藏砂矿主要形成于晚更新世末期,成因类型主要有古冲积、残留和海积等类型。

The freeze-thaw metallogenic model of regenerated gold placers under cold low temperature conditions

LOCATED in the mined-out areas of primary gold placers, the regenerated gold placers in permafrost zonesare a kind of special low temperature deposit formed under modem cold climate conditions. Although theregeneration phenomenon was first discovered in South America, the scale and periodicity of the regeneration are more evident in permafrost environment of Northern Hemisphere.

方格网法在资源量估算中的应用探索——以宁夏某建筑用砂矿为例

本文以宁夏某地建筑用砂矿详查项目为研究背景,采用方格网法(fgwtf)建立DEM模型估算资源量,并选取块段采用垂直投影平行断面法进行校验,证实该方法估算结果可靠。通过应用实践,表明方格网法(fgwtf)适宜范围不规则矿区的资源量估算,且具有微地形控制程度高、估算过程简单可视、数据精度高、估算效率更高的优点。

Study on Seed Bank Composition and Seedling Emergence Regularity in Placer Iron Ore Soil

The mining of placer iron ore greatly influences the surrounding desert grassland.In Agdala Town,Qinghe County,Xinjiang,the soil seed bank is severely damaged,and the utilization and productivity of desert grasslands are almost zero,which seriously affects the safety of the ecological environment and the development of local animal husbandry.It is very important to supplement soil seed banks to enhance the species composition of desert grasslands after ecological restoration.In this study,the effects of the seed bank,species composition,and seed burial depth on the seedling emergence rate at placer iron ore site before and after artificial seed bank replenishment were compared using the germination tray method.The original soil seed bank in the study area contained only four species,which were all annual plants.The dominant species were Salsola ruthenica and Corispermum orientale,and the soil seed bank density was very small.The emergence regularity of the soil seed bank was closely related to water content,and the emergence of annual vegetation was explosive.Seed burial depth affected the emergence rate of perennial grass,and we determined that a burial depth of 0–5 cm was the most effective for emergence.This indicates that seedling emergence of artificially supplemented soil seed bank can be completed within 7 days if the sowing depth is appropriate;sowing depths greater than 5 cm affect seed germination.These findings provide a basis for selecting species to populate large areas.

Application of Prognosticating Methods of Placer Gold Resources——Taking the Upper Regions of the Nenjiang River as an Example

On the basis of analysing and studyingthe mineralizing conditions and content ratinglaws, the authors infer the geology and oresnear old placers by applying the remote sens-ing technology and analogous method,

西藏多龙尕尔勤——一个遭受过剥蚀的浅成低温热液金矿床

西藏具有形成巨型斑岩铜成矿系统的地质背景。浅成低温热液型金矿常发育于斑岩铜成矿系统上部,极具经济价值,但由于形成深度较浅,易于剥蚀,目前西藏地区尚未发现独立的浅成低温热液型金矿床。多龙超大型铜金矿集区位于西藏班公湖-怒江成矿带西段,产出有大型-超大型斑岩-浅成低温热液型铜金矿床,而是否存在独立的浅成低温热液型金矿,既是重大科学问题,也是勘查的重点方向。文章运用超景深高分辨数码显微镜、扫描电镜及电子探针等手段,系统研究了多龙矿集区尕尔勤矿区内的残坡积物和外围水系沉积物中746颗砂金的大小、形貌、核部元素及不透明矿物包体特征,发现尕尔勤矿区内广泛分布的砂金不是表生环境下生物化学或化学成因金,而是尕尔勤产出的金矿(化)体剥蚀的产物。砂金普遍含有较高的w(Bi)、极低的w(Cu),部分含有高的w(Hg)、w(Te);砂金w(Ag)变化较大(0.05%~40.21%);金成色变化范围较大(588~999);砂金富含Bi-Pb-Te-S系列矿物包体等,显示尕尔勤矿区可能存在一个遭受过剥蚀的浅成低温热液金矿床。

沉积型钛铁矿品位计算方法

沉积型钛铁矿品位计算中时常出现简化计算公式,忽视钛铁矿中TiO2实际含量和钛物相分布中钛铁矿占比等因素,导致钛铁矿品位计算数据偏差,影响钛铁矿储量计算和项目经济测算。为了减少钛铁矿品位计算的错误,本文以莫桑比克和马拉维钛铁矿项目勘查资料数据为基础,论述钛铁矿物中TiO2实测含量及钛物相分析中钛铁矿占比的意义,正确运用钛铁矿品位计算公式,使沉积型钛铁矿品位计算更接近实际,为提升钛铁矿砂矿资源储量和项目经济性测算的准确性提供重要支撑。

国外某滨海砂矿锆钛高效回收选矿试验研究

国外某海滨砂矿中TiO_(2)、ZrO_(2)含量分别为7.55%和0.74%,其中钛主要以钛铁矿、金红石等工业可利用矿物形式存在,锆主要以锆英石形式存在,嵌布粒度范围主要集中在0.04~0.16 mm,属于物理选矿适宜回收的粒度范围,是典型的锆钛共生砂矿。针对该矿,进行了工艺矿物学和选矿小型试验研究,采用“锆钛矿物重选预富集—钛铁矿与非磁性锆钛矿物磁选分离—锆钛矿物重选再富集—金红石与锆英石干式磁电选分离”的全工艺流程,分别获得了钛品位大于52%的钛铁矿精矿、钛品位大于77%的含铁金红石精矿、钛品位大于75%的金红石精矿以及锆品位大于63%的锆英石精矿,钛锆回收率分别达到了81%和74%,实现了该矿床中钛锆资源的高效利用,可为同类矿山的开发利用提供借鉴。