Characterization of Alluvial Gold Bearing Sediments of Betare Oya District-East Cameroon, Implication for Gold Exploration and Recovery

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.

PALEOGENE(?) DEPOSYSTEMS AND BASIN EVOLUTION IN THE EASTERN TIBETAN PLATEAU: NANGQIAN AND XIALAXIU BASINS

Paleogene sedimentary basins exposed across much of the central and eastern Tibetan Plateau may record the early history of plateau uplift related to the Indo\|Asian collision. We conducted sedimentological and stratigraphic investigations in the northeastern Qiangtang terrane, eastern Tibetan Plateau. Our results indicate development of several nonmarine basins during Paleogene(?) time, probably synchronous with northeast\|southwest contractional deformation. The Nangqian and Xialaxiu basins (96°～97°E, 32°～33°N) are composed of 500～ 20000m thick successions of primarily clastic sediment indicative of lacustrine and alluvial\|fan depositional processes. Paleocurrent measurements and sediment compositional data indicate local sediment source areas composed of Carboniferous\|Triassic carbonate and sandstone and minor Tertiary volcanic rocks. The large variability of provenance and facies types suggest that each basin evolved independently, as opposed to regional development of a single integrated basin which was partitioned by later deformation.

Sedimentary model reconstruction and exploration significance of Permian He 8 Member in Ordos Basin,NW China

Based on the Late Paleozoic geological background and the latest exploration achievements of the Ordos Basin and North China platform, it is concluded that during the sedimentary period of Permian He 8 Member, the area in concern had multiple material sources, multiple river systems, flat terrain, shallow sedimentary water, widely distributed fluvial facies sand body and no continuous lake area, so alluvial river sedimentary system developed in the whole region. Based on stratigraphic correlation and division, and a large number of drilling and outcrop data, a comprehensive analysis of lithofacies and sedimentary facies types and distribution was carried out to reconstruct the ancient geographic pattern of the He 8 Member sedimentary period. The results of paleogeography restoration show that the area of Ordos Basin was the "runoff area" in the sedimentary slope in the western part of the North China platform during the sedimentary period of He 8 Member, the whole region was mainly alluvial plain sedimentation featuring alternate fluvial facies, flood plain facies and flood-plain lake facies. According to the results of flume deposition simulation experiment, a new sedimentary model of "alluvial river & flood-plain lake" is established, which reveals the genesis of large area gravel sand body in He 8 Member of this area and provides geological basis for the exploration of tight gas in the south of the basin.

Coarse grain deposit feature of Guantao formation in western depression Shuyi area of Liaohe basin

The extensive distribution of coarse-grained clastic rock of Guantao formation in Shuyi area of Liaohe basin was considered as a result of fluvial deposit. According to the comprehensive analysis of seism data, well log, core observation and experimental data, this kind of clastic rock is composed of pebblestone-cobblestone, microconglomerate, sand conglomerate, medium-coarse grained sandstone and fine-sandstone. According to the clast composition, sedimentary texture, structure and rock type, 3 kinds of sediment facies can be recognized ie the mixed accumulation-conglomerate dominated debris flow, pebblestone-cobblestone dominated gradient flow and sandstone dominated braided stream. Vertically, the bottom gradient current deposit and top braided stream deposit form fining-upward sediment sequence, and the debris flow deposit distributes in them at random. The sedimentary feature of coarse grain clastic of Guantao formation in Shuyi area is accordant with proximal wet alluvial fan deposited in wet climate at foreland and this kind of alluvial fan is different from the traditional one.

龙门山冲断带盆山体系地下水循环特征分析——以石亭江流域绵竹段为例

山区与平原区水资源联系密切,探究山区-盆地地下水循环可为水资源开发和合理利用提供科学依据。龙门山冲断带及川西前陆盆地是中国典型的盆山系统代表,结合现场采样及前人研究结果,采用水文地质调查、水化学特征、氢氧同位素和聚类分析等技术方法,阐明了绵竹市境内石亭江流域龙门山冲断推覆体与前陆盆地形成的盆山体系的地下水循环特征。研究认为:大气降水为山区及平原区浅层地下水的主要补给来源,其中J_3l~3地层还接受石亭江水的侧向补给;地形对山区浅层地下水径流具有主控作用,主要沿北西、南东方向发生径流,对近平原区的浅层地下水给予少量补给;平原区浅层还接受地表水、河渠水补给,地下水自北西向南东发生运移,在玉泉镇至板桥镇附近以泉的形式进行排泄。NW向断裂构造沟通盆山体系,来源于研究区北西侧更高山区的地下水沿断裂带形成深部径流带,形成具有较高矿化度的热水。研究成果可为类似山区-盆地地下水循环系统研究提供参考。

Distribution and land use characteristics of alluvial fans in the Lhasa River Basin,Tibet

In Lhasa River Basin(LRB),land suitable for settlement or living is experiencing a shortage of resources.Alluvial fans have the potential to alleviate this problem.However,basic information,such as the distribution and land use types of alluvial fans,is rarely studied.In this study,Google Earth,ArcGIS and visual interpretation were used to obtain the outlines,areas,quantities and distribution of alluvial fans.Meanwhile,to show the utilisation potential of alluvial fans,we analysed the land use,their distance from the roads,places(town and village)and rivers.The results showed 826 alluvial fans exist in LRB,with a total area of 1166.03 km2.The number of alluvial fans with areas between 0.1 and 1 km2 is 517,accounting for 62.59%of the total number of alluvial fans.Grassland is the dominant land use type,accounting for 68.70%of the total area of alluvial fans.The cropland area accounted for 2.16%of alluvial fans and accounted for 18.98%of the total cropland area in LRB.Exactly 93.70%,53.63%and 61.86%of the total number of alluvial fans were located within 5 km from the tertiary road,village,and river,respectively.To sum up,our survey results showed that alluvial fans are important land resources in LRB and may have huge utilisation potential.

Machine learning-based identification for the main influencing factors of alluvial fan development in the Lhasa River Basin,Qinghai-Tibet Plateau

Alluvial fans are an important land resource in the Qinghai-Tibet Plateau with the expansion of human activities. However, the factors of alluvial fan development are poorly understood. According to our previous investigation and research, approximately 826 alluvial fans exist in the Lhasa River Basin(LRB). The main purpose of this work is to identify the main influencing factors by using machine learning. A development index(Di) of alluvial fan was created by combining its area, perimeter, height and gradient. The 72% of data, including Di, 11 types of environmental parameters of the matching catchment of alluvial fan and 10 commonly used machine learning algorithms were used to train and build models.The 18% of data were used to validate models. The remaining 10% of data were used to test the model accuracy. The feature importance of the model was used to illustrate the significance of the 11 types of environmental parameters to Di. The primary modelling results showed that the accuracy of the ensemble models, including Gradient Boost Decision Tree,Random Forest and XGBoost, are not less than 0.5(R^(2)). The accuracy of the Gradient Boost Decision Tree and XGBoost improved after grid research, and their R^(2) values are 0.782 and 0.870, respectively. The XGBoost was selected as the final model due to its optimal accuracy and generalisation ability at the sites closest to the LRB. Morphology parameters are the main factors in alluvial fan development, with a cumulative value of relative feature importance of 74.60% in XGBoost. The final model will have better accuracy and generalisation ability after adding training samples in other regions.

老挝Boneng砂锡矿地质特征及矿床成因分析

Boneng砂锡矿区Ⅰ、Ⅲ区属残坡积型,Ⅱ、Ⅳ区属冲洪积型。前者分布于山麓及其缓坡地带,矿层较厚,品位变化大;后者分布于现代河床及两侧,规模不大,厚度l-10米,品位变化较大。一般情况下,在残坡积层中铁锰结核以及褐铁矿含量越高,锡的品位越高。

Alluvial sedimentation and tectonostratigraphic evolution in a narrow extensional zigzag basin margin (northern Teruel Basin, Spain)

The northern part of the eastern margin of the extensional Neogene Teruel Basin(central-eastern Spain)consists of a non-linear,zigzag fault zone made of alternating ca.2 km long,NNW-SSE trending segments and shorter NNESSW ones.Good outcrop conditions made possible a comprehensive integrated stratigraphic and structural study,especially focused on coarse clastic sediments deposited along the basin margin.Well-exposed stratal relationships with boundary faults,allowed the analysis of tectonic influence on sedimentation.Synsedimentary deformation includes growth faulting,rollover anticlines,and monoclines and associated onlap stratal terminations,angular unconformities,and other complex growth strata geometries.One of them is the onlap-over-rollover bed arrangement described here for the first time,which reveals the competition between tectonic subsidence and sedimentary supply.Both,the structural inheritance(dense Mesozoic fracture grid)and the dominant,nearly‘multidirectional’(σ1 vertical,σ2≈σ3),Pliocene extensional regime withσ3 close to E-W,are considered to have controlled the margin structure and evolution.Tectono-stratigraphic evolution includes:(i)reactivation of inherited NNW-SSE faults and development of W-SW-directed small alluvial fans(SAF)while NNE-SSW segments acted as gentle relay ramp zones;(ii)progressive activation of NNE-SSW faults and development of NW-directed very small alluvial fans(VSAF);during stages i and ii sediments were trapped close to the margin,avoiding widespread progradation;(iii)linking of NNW-SSE and NNE-SSW structural segments,overall basin sinking and widespread alluvial progradation;(iv)fault activity attenuation and alluvial retrogradation.The particular structure and kinematic evolution of this margin controlled alluvial system patterns.Size of alluvial fans,directly set up at the border faults,was conditioned by the narrowness of the margin,small catchment areas,and proximity between faults,which prevented the development of large alluvial fans.The size of the relay zones,only a few hundred meters wide,acted in the same way,avoiding them to act as large sediment transfer areas and large alluvial fans to be established.These features make the Teruel Basin margin different to widely described extensional margins models.

^(10)Be in quartz gravel from the Gobi Desert and evolutionary history of alluvial sedimentation in the Ejina Basin,Inner Mongolia,China

Reconstructing the evolutionary history of the Gobi deserts developed from alluvial sediments in arid regions has great significance in unraveling changes in both tectonic activity and climate.However,such work is limited by a lack of suitable dating material preserved in the Gobi Desert,but cosmogenic 10Be has great potential to date the Gobi deserts.In the present study,10Be in quartz gravel from the Gobi deserts of the Ejina Basin in Inner Mongolia of China has been measured to assess exposure ages.Results show that the Gobi Desert in the northern margin of the basin developed 420 ka ago,whereas the Gobi Desert that developed from alluvial plains in the Heihe River drainage basin came about during the last 190 ka.The latter developed gradually northward and eastward to modern terminal lakes of the river.These temporal and spatial variations in the Gobi deserts are a consequence of alluvial processes influenced by Tibetan Plateau uplift and tectonic activities within the Ejina Basin.Possible episodes of Gobi Desert development within the last 420 ka indicate that the advance/retreat of alpine glaciers during glacial/interglacial cycles might have been the dominant factor to influencing the alluvial intensity and water volume in the basin.Intense floods and large water volumes would mainly occur during the short deglacial periods.

克拉玛依油田六区克下组冲积扇岩石相及储层质量差异

在准噶尔盆地克拉玛依油田六区11口取心井岩心描述的基础上,将该区克下组冲积扇岩石相划分为7种类型。结合沉积微相分析,应用岩心分析化验资料对冲积扇内部储层质量差异及其分布特征进行了研究。分析表明,研究区克下组储层以原生粒间孔隙为主,沉积组构对储层质量差异起控制作用;粗砂岩相和细砾岩相储层为研究区克下组冲积扇中最好的储层;各微相储层质量差异显著,辫流水道和流沟储层质量最好,砂砾坝次之,砾石坝和径流水道较差,漫洪砂体最差;流沟以窄条带状镶嵌于砾石坝和砂砾坝之中,为扇根和扇中内带储层中的高渗通道。

鄂尔多斯盆地西南地区上三叠统延长组沉积相及石油地质意义

鄂尔多斯盆地三叠系延长组主要发育东北和西南两大沉积体系 ,东北的河流三角洲体系已为大量的勘探研究资料所证实 ,而西南体系因受勘探程度限制 ,目前研究不够。本文通过最新钻探成果 ,结合盆地西南部露头资料 ,确立盆地西南地区三叠系延长组为冲积扇 -扇三角洲沉积体系 ,发育冲积扇、扇三角洲、湖泊(浊积 )相。冲积扇以西南缘平凉崆峒山和水河剖面为代表 ,扇三角洲及湖泊 (浊积 )相为区内钻井剖面所证实。长 6—长 8为区内主力油层组 ,地层保存完整 ,钻探程度相对较高。扇三角洲前缘砂体类型以水下分流河道为主 ,局部发育河口坝。浊积体以厚层块状为主。长 8亚期为扇三角洲前缘亚相最发育期 ,横向形成自西南向东北延伸的三支前缘砂体带 ,是石油聚集的重要区带 ;长 7亚期随着湖盆沉降 ,周边抬升强烈 ,湖岸较陡 ,大量发育浊积体系 ;长 6亚期湖退导致扇三角洲再次发育 ,但规模较长 8亚期小。扇三角洲前缘砂体单层厚度大 ,砂岩粒度较粗 ,颗粒分选及物性好 ,是石油富集的最有利相带。

一个片流过程控制的冲积扇——太原盆地风峪沟冲积扇

风峪沟冲积扇位于太原盆地西北侧,面积较大,平面形态十分开阔。野外考察表明,在该冲积扇顶部出露了典型的、具平行层理结构的沉积物剖面。说明该冲积扇主要由高流态的片流过程形成的。片流沉积物由厚度小、侧向延伸长的中、细砾石坝沉积物和相对粒度较细的坝间沉积物所组成。风峪沟冲积扇流域的地质地貌特征表明,由于该段吕梁山地较大幅度的抬升给冲积扇的发育提供了充分的可容空间,这可能是风峪沟冲积扇上片流沉积物发育的主要原因。

成都盆地新生代大邑砾岩的沉积特征

通过对龙门山前陆盆地大邑砾岩的发育层序、沉积特征及物源的分析 ,建立其垂向相序 ,总结出大邑砾岩的沉积具冲积扇相的特点 ;恢复大邑砾岩发育时期的古地貌 ,推断其至少由三个冲积扇组成 :古岷江扇 ,古青衣江扇 ,古玉溪扇。同时 ,结合测年资料 ,指出大邑砾岩是上新世 -早更新世的整合沉积相 ,有别于全球其他地区同期的不整合事件。大邑砾岩沉积之后 。

甘肃酒泉盆地河流地貌与新构造运动

通过对甘肃酒泉盆地北大河、洪水坝河、丰乐河、马营河的阶地进行了野外形态量计，获得了它们的阶地纵剖面，对洪水坝河的阶地年龄进行了测定和估计，并通过卫星像片解译对这些河流的洪积扇进行了制图。作者认为酒泉盆地河流阶地纵剖面的形态和洪积扇的迁移受断层控制，河流在距今大约１６万年和４万年发生的两次由加积转化为下切的事件可能代表两次构造抬升相对强烈时期。

侯马盆地冲积扇及其流域地貌发育规律

根据从DEM数据中提取的侯马盆地冲积扇及其流域的多项地貌指标,分析了各地貌指标的空间分布规律,并通过地貌指标的空间分布曲线与山前地形高程曲线形态的对比以及地貌指标相关性分析来揭示冲积扇及其流域地貌的发育规律。结果表明,在侯马盆地相对隆起部位的冲积扇及其流域的地貌指标与在盆地凹陷部位的冲积扇及其流域的地貌指标有较大差异;流域地貌指标的空间分布受到盆地边界断层构造活动性的影响;冲积扇的发育主要受到流域规模、山前构造活动以及盆地基准面等多种因素共同的影响;流域内岩性的差异不是造成研究区域内冲积扇地貌差异的主要因素。

新疆柴窝堡盆地地下水化学及稳定同位素研究

地下水是维持乌鲁木齐河流域社会经济发展和生态系统的最重要的水源,尤其是柴窝堡盆地因大量开采使得地下水水位下降、湖面萎缩,地下水系统动态特征发生了变化,所以研究区内地下水水流系统及其补径排关系对于深入研究盆地地下水流系统特征和合理开发利用地下水水资源能够提供重要的基础资料,尤其是对调整地下水资源的开采布局具有现实意义。本次研究主要以地质、水文地质背景资料为基础,结合地下水补给环境的差异,利用水化学和水的稳定同位素进行示踪研究,确定了柴窝堡盆地地下水的补给来源和排泄途径,区分出盆地排泄带不同点的补给区,包括东山、南山和西山补给区,对同一补给区又细分出不同的水流系统。

准噶尔盆地乌尔禾油田三叠系百口泉组储层敏感性评价

针对准噶尔盆地乌尔禾油田三叠系百口泉组低孔低渗的冲积扇储层,储层天然能量较差,未经储层改造难以获得工业油流的问题,采用水基压裂液改造后试油未能获得成功,而在W36井采用油基压裂液压裂后试油获得成功。依据储层分析技术和实验分析技术,参照碎屑岩储层评价标准,分析大量岩心流动实验测试数据,针对百口泉组冲积扇砂砾岩储层敏感性深入研究,指出分析储层敏感性和改善压裂工艺将对油层保护及开发起到关键作用。通过研究发现,伊/蒙混层和高岭石等粘土矿物含量高是造成储层具有较强敏感性的主要原因;百口泉组储层水敏感性、盐敏感性和体积流量敏感性中等偏强,速度敏感性较弱。通过研究结果和生产试验,建议采取脱水油基压裂液、压裂液盐度控制在6 000 mg/L以上、控制流速和体积流量等措施,有效地降低不同敏感性造成的储层伤害,提高油气产量。

鄂尔多斯盆地早侏罗世富县期冲积扇沉积

在综合研究野外露头、钻井剖面及室内编图、地层对比的基础上 ,指出鄂尔多斯盆地冲积扇 -河流沉积体系是侏罗纪富县期主要的古地理格局 ,富县期沉积受与古地貌密切相关的五条河谷控制。认为鄂尔多斯盆地侏罗纪富县期冲积扇沉积具进积型特征 ,其形成与古地形密切相关 ,分布于古甘陕。

同生逆断层对冲积扇沉积构型的控制作用:以准噶尔盆地西北缘三叠系下克拉玛依组为例

以新疆准噶尔盆地西北缘三叠系克拉玛依组冲积扇为例,综合应用岩心、测井、地震资料及邻近露头资料,通过沉积构型及构造-沉积响应分析,探讨挤压型盆地边缘与同生逆断层相关的冲积扇沉积构型特征。研究表明:挤压型盆地边缘冲积扇扇体的形态、规模和组合样式受到同生逆断层组合样式的控制。在多条平行盆地边缘的断层与顺源调节断层组合的条件下,调节断层走滑活动导致物源区溯源剥蚀,扇体呈快速退积而形成薄层条带溯源叠置组合。同时,调节断裂的平移活动会影响物源出口位置的侧向偏移,形成侧向迁移叠置扇体组合;在强烈活动的交叉状同生逆断层组合条件下,则形成多期厚层垂向叠置扇体组合。