Classification, Tectonic Setting, and Mineralization Potential of Ayetoro and Sasaro Syenitic Plutons in Igarra Schist Belt, Southwestern Nigeria

Petrographic and geochemical studies of syenite-looking Ayetoro and Sasaro plutons within Igarra Schist Belt were carried out in order to classify them and determine their tectonic setting and mineralization potential. Petrographic study and geochemical classification revealed that while Ayetoro boss is microgranite constituting an aggregate of medium grained muscovite, quartz and biotite minerals, Sasaro stock is micromonzonite made up of medium grained albite, orthoclase, biotite, hornblende and pyroxene. Geotectonic setting showed the boss and stock are orogenic, probably derived from the same upper mantle magma as Igarra batholith that got contaminated by crustal materials responsible for their difference in lithology. Their mineralization potential showed that the massive Ayetoro microgranite with no appreciable trace-element contents cannot serve as host of any metallic deposit, and should be suitable for industrial applications. Whereas, the silicified, highly sheared Sasaro monzonite, with elevated level of some trace elements contents as Ag, Au and Cu, could harbor Ag-Au-Cu deposit.

Peraluminous A-type granites formed through synchronous fractionation,magma mixing,mingling,and undercooling:evidence from microgranular enclaves and host Mesoproterozoic Kanigiri granite pluton,Nellore Schist Belt,southeast India

The field and microstructural features coupled with mineral chemical data from microgranular enclave(ME)and host Mesoproterozoic Kanigiri granite(KG)pluton of Nellore Schist Belt(NSB),Southeastern India,have been documented in order to infer the likely processes responsible for the origin and evolution of ME and host KG magma.The ME and host KG bear the same mineral assemblages barring the KG which does not contain amphibole;however,they are modally disequilibrated.The ME in KG is originated due to multiple intrusions of ME magmas into the crystallizing host KG magma chamber.Field and textural features indicate the dynamic magma flow,mingling,and undercooling of the ME against a relatively cooler surface of host KG magma.The presence of NSB country rock xenoliths and its diffuse boundaries suggest the intrusive relation and marginal assimilation by the intruding KG magma.The occasional cumulate texture in the ME appears to have formed by the accumulation of early-formed minerals that crystallized rapidly in the ME magma globules.The ME shows the magmatically deform features developed due to the flowage and erosion by the subsequent intrusions of ME magma pulses into the crystallizing host KG magma chamber.The ME amphiboles show unusual composition as ferro-edenitic hornblende to potassian-hastingsitic hornblende,that crystallized in the subalkaline-alkaline transition,low fO_(2)(reducing to mildly oxidizing)magma.The unusual extremely low Mg/Mg+Fe^(t)=0.015(avg.)of ME amphiboles may be related to the changing physico-chemical(P,T,fO_(2),and H_(2)O)condition of the ME magma or they might have crystallized in equilibrium with more evolved KG magma.The KG(FeOt/MgO=37.04,avg.)and ME(FeO~t/MgO=77.72,avg.)biotites are siderophyllite,and buffered between QFM and NNO syn-crystallizing in the water undersaturated(H_(2O)≈3.58 wt.%in KG;≈3.53wt.%in ME),alkaline anorogenic(A-type)host magmas that were emplaced at mid-crustal(4–5 kbar;17 km)depth.Field,microtextural and mineral chemical evidences suggest that the alkaline KG magma originated from crustal source and evolved through synchronous fractionation,mixing,and mingling with coeval ME magmas in the KG magma chamber.

Geochemical Orientation Study of Stream Sediment Samples in the Southern Part of Nuggihalli Schist Belt: Ore Mineral Phases and Their Implications on the Bedrock Potential for Ores

Stream sediment sampling is a significant tool in geochemical exploration. The stream sediment composition reflects the bedrock geology, overburden cover, and metalliferous mineralization. This research article focuses on assessing selected trace element concentrations in stream sediments and interpreting their inter-element relationships using multivariate statistical methods. Tagadur Ranganathaswamy Gudda and its surroundings in the Nuggihalli schist belt of southern India have been investigated in the present work. The geology of the study area is complex, with a diverse range of litho units and evidence of strong structural deformation. The area is known for its mineralization potential for chromite, vanadiferous titanomagnetite, and sulfides. The topography of the region is characterized by an undulating terrain with a radial drainage pattern. Most part of the schist belt is soil covered except the Tagadur Ranganathaswamy Gudda area. For this study, a discrete stream sediment sampling method was adopted to collect the samples. Stream sediment samples were collected using a discrete sampling method and analyzed for trace elements using an ICP-AES spectrophotometer: Fe, Cr, Ti, V, Cu, Ni, Zn, Pb, Mn, Cd, and As have been analyzed. The analytical data were statistically treated using the SPSS software, including descriptive statistics, normalization of data using natural log transformation, and factor analysis with varimax rotation. The transformed data showed a log-normal distribution, indicating the presence of geochemical anomalies. The results of the study provide valuable insights into the geochemical processes and mineralization potential of the study area. The statistical analysis helps in understanding the inter-element relationships and identifying element groups and their implications on bedrock potential mineralization. Additionally, spatial analysis using inverse distance weighting interpolation provides information about the distribution of geochemical parameters across the study area. Overall, this research contributes to the understanding of stream sediment geochemistry and its application in mineral exploration. The findings have implications for future exploration efforts and can aid in the identification of potential ore deposits in the Nuggihalli schist belt and similar geological settings.

柴北缘茶卡北山伟晶岩型锂铍矿变质围岩时代及原岩特征

茶卡北山锂铍矿床位于青海南山西部,区域构造上处于宗务隆山陆缘裂谷带东段。矿体赋存于花岗伟晶岩脉中,围岩为低角闪岩-高绿片岩相变质岩组合,该套变质岩作为锂铍矿体围岩,对于探讨柴北缘锂铍矿成矿规律及成矿预测具有重要意义。依据岩石组合,将其单独厘定为茶卡北山片岩岩组,通过对片岩开展锆石阴极发光图像特征研究和锆石U-Pb(LA-ICP-MS)测年,限定形成时代为南华纪—奥陶纪,为宗务隆山陆缘裂谷带新发现的新元古代—早古生代地层。锆石Hf同位素分析结果显示,εHf(t)值分布范围在-19.62~-3.07之间,表明源区岩石源自古元古代—新太古代上地壳物质的部分熔融。片岩SiO_(2)含量介于61.33%~70.57%之间,FeO含量为3.58%~5.13%,TFe2O_(3)含量为5.2%~7.95%,MgO含量为1.89%~4.95%。球粒陨石稀土元素配分曲线表现为右倾,重稀土元素曲线趋于平缓,具有弱Eu亏损和轻稀土元素富集特征。微量元素富集Th、U、Nd、Zr、Hf、Nb、Ti等高场强元素,亏损Ba、Sr等亲石元素。综合岩石年龄和地球化学特征,认为茶卡北山片岩形成于新元古代—早古生代弧后盆地环境,原岩遭受弱风化剥蚀作用,化学组分稳定,确定为泥质砂岩,物质主要来源于岛弧环境的长英质火成岩,构造环境为大陆岛弧,与矿区含锂铍矿伟晶岩脉源区一致。

循环加卸载下黑云母石英片岩的弹性模量与能量演化特征研究

黑云母石英片岩是一种典型的各向异性岩石,为研究其损伤演化规律及各向异性表现特征,针对含0°,45°,90°3种片理角度的试样,开展了等塑性应变循环加卸载试验。结果表明:不同片理面角度试样的破坏模式有所不同,0°片理面试样中的张拉破裂现象与45°片理面中的剪切破坏现象尤为明显。随着塑性应变增加,黑云母石英片岩的弹性模量表现出先强化、后弱化的现象,这一现象在高围压下更为明显。在弱化阶段中,弹性模量演化的转折点与裂纹起裂强度σci稳定时对应塑性应变一致。弹性模量作为岩石损伤劣化过程的评价指标较完整性系数受片理面角度的影响更小。在岩石内部能量演化过程中,耗散能大小与片理面角度的关系为0°>90°>45°,耗散能、弹性能下降的速率大小关系为45°>90°>0°,其降至稳定时与岩石损伤强度σcd稳定时对应塑性应变一致。该研究借助弹性模量和能量演化规律分析,探究了黑云母石英片岩的损伤演化力学行为。

干湿循环作用下片岩片理面抗剪性能劣化实验设计

为揭示片岩片理面在干湿循环作用下抗剪性能劣化规律,选取云母石英片岩设计相应的直剪实验方案进行研究,并将该方案应用于实验教学。实验结果表明:干湿循环作用下,片理面抗剪性能劣化明显,干湿循环20次后,粘聚力和内摩擦角分别下降49.05%、15.34%,粘聚力下降幅度约为内摩擦角的3.2倍;片理面不断渗出黄褐色物质浸染岩样,使片理面逐渐显化,且逐渐沿片理面产生裂隙并不断向岩石内部扩展发育;片理面是水进出片岩内部的良好通道,水可将片理面间的泥质胶结物和可溶性矿物溶解并带出,使得片理面间胶结物及胶结面积逐渐减少,抗剪性能逐渐劣化。该实验教学对培养学生科研创新思维及理论联系实际能力具有重要意义。

不同含水率下变片理倾角云母石英片岩波速变化规律

对不同含水率条件下变片理倾角云母石英片岩试样进行波速测试,结合偏光显微镜和电镜扫描观察,探究声波在云母石英片岩中传播的变化机制。试验结果显示:当声波通过云母石英片岩时,其内部孔隙、裂隙沿片理面方向定向分布的特征以及矿物组构导致波速随其入射方向与片理面的夹角增大而减小;吸水过程中,水逐渐取代空气介质填充在云母石英片岩的空隙中导致波速总体随含水率的上升而增大,在水饱和度从50%上升到70%的阶段,由于水对云母石英片岩的软化作用和水分子自由振动的影响,声波传播速度下降,孔隙、裂隙的分布特征导致饱和状态下云母石英片岩波速受片理倾角影响减小、各向异性指数降低;脱水过程中,云母石英片岩表面的水分和孔隙、裂隙中的自由水蒸发,声波经过的空气介质增多,波速呈快速下降的趋势,但随着水的软化作用减弱,波速出现回升,且片理倾角越小的试样波速变化幅度越大。

干湿循环作用下云母石英片岩抗剪强度损伤劣化模型

为探究干湿循环作用对片岩抗剪特性的影响,以鄂西北广泛分布的云母石英片岩为研究对象,通过直剪试验揭示其在干湿循环作用下抗剪性能的劣化规律,并建立损伤劣化模型。结果表明:云母石英片岩抗剪性能在干湿循环作用下劣化效应明显,且前期劣化速率较快、幅度较大,后期劣化速率减慢、幅度降低;干湿循环20次后,云母石英片岩不同法向应力下峰值剪应力劣化度为16.27%~29.59%,黏聚力、内摩擦角劣化度分别为26.58%、15.36%,黏聚力对干湿循环作用的影响更为敏感。基于Lemaitre损伤理论与统计损伤本构模型,建立起云母石英片岩抗剪强度损伤劣化模型,计算所得峰值剪应力预测值与试验值相对误差为1%~6%,可有效预测干湿循环作用下云母石英片岩的抗剪强度变化。

片石置换法在软土浅基坑工程中的应用

在公路工程中常采用抛石挤淤法来加固处理含水量高、孔隙比大、透水性弱及抗剪强度低的软弱地基。基于抛石挤淤法提出软土浅基坑工程的片石换填技术。采用有限元分析软件PLAXIS 3D对基坑开挖及基底加固过程进行数值模拟,分析了不同的片石换填厚度对基坑承载能力及变形的影响,并将计算结果与实测数据进行对比,验证了有限元计算结果。

基于核磁共振技术云母石英片岩干湿循环损伤特性研究

为研究片岩在干湿循环作用下的微观损伤特性,对不同干湿循环作用下云母石英片岩试样进行核磁共振测试,并定量分析其损伤变量变化规律。结果表明:不同干湿循环作用下云母石英片岩孔隙之间连通性较好,孔径较小孔隙集中发育,随着干湿循环次数的增加,孔径逐渐扩展增大;云母石英片岩孔径发育具有关联性,干湿循环5次前小孔、中孔数量增加较快,5~10次循环后小孔数量趋于饱和,部分中孔发育扩展为大孔,导致中孔数量减少,大孔数量从5次干湿循环后开始显著增加;云母石英片岩受干湿循环影响损伤明显,损伤变量曲线在前5次干湿循环作用下近似呈直线上升,试样内部孔隙、裂隙发育扩展较快,5次干湿循环后,孔隙、裂隙的大小和数量发育减缓,云母石英片岩损伤变量增速逐渐变缓。

黑云母石英片岩骨料在巴塘水电站工程中的应用研究

通过对巴塘水电站开挖弱风化黑云母石英片岩进行云母含量检测及混凝土力学性能试验,并结合类似工程研究成果进行分析,确定了采用工程开挖弱风化黑云母石英片岩作为混凝土骨料的料源方案。据此对工程的料源规划及总布置进行调整,大幅节省了工程投资,减轻了工程建设对环境的影响。

地震作用下绢云母片岩高路堤中土工格栅效用分析

对于采用绢云母片岩土石混合料为填料的高路堤而言,通常会出现地震作用下路堤变形严重等问题,加筋为通常做法。文中依托十巫北高速公路项目,以绢云母片岩土石混合料填筑的高路堤进行地震动力响应分析。结果表明,土工格栅具有分担部分应力,减小路堤动力加速度,以及抑制其变形的作用。对于路堤整体而言,加筋路堤的最大应力相对于未加筋路堤所承受应力较小;相比于无筋路堤,路堤加筋后加速度和速度明显减小,在路堤同一高度上土工格栅加筋土路堤的水平向峰值加速度和速度比未加筋路堤的水平向峰值加速度和速度小;土工格栅加筋对路堤整体的纵向沉降和侧向位移具有抑制效果,显著地减弱路堤在地震作用下的破坏程度。

地应力影响下钠长岩-片岩物理力学特征随赋存深度变化规律研究

以西南地区凉山州拉拉铜矿的钠长岩-片岩物理力学特征为研究对象,研究物理力学特征随赋存深度变化规律,在标高+1 890~1 760 m共开展54个点的工程地质调查工作,标高+1 880~1 760 m 10次地应力测试,并在标高+1 984~1 760 m进行钠长岩、片岩的岩块取样,完成岩样的物理性质、单轴抗压强度、单轴压缩变形试验,获取各标高岩样的密度、孔隙率、单轴抗压强度、弹性模量、泊松比及岩体的节理间距、地应力测试数据。结果表明:该矿山钠长岩和片岩的单轴抗压强度、弹性模量、密度及泊松比均随赋存深度增加而增加,孔隙率及节理间距随赋存深度增加而减小。随着岩石的赋存深度增加,地应力值随之增加,直接改变了岩石的应力环境,岩体节理间距的变化同时反映了应力环境的改变。这也引起岩石孔隙率、密度的改变,进而组成岩石的矿物颗粒受到挤压,导致岩石的结构逐渐致密,岩石力学强度特性提高。

大姚县秀水河铜金矿成矿地质条件及找矿前景探讨

大姚县秀水河铜金矿矿体主要赋存于花岗质片麻岩、糜棱岩化白云英片岩中,受构造破碎带控制,岩石劈理、节理裂隙发育,较破碎,具硅化、碳酸盐化等特征,矿化主要为铜矿化及褐铁矿化,见孔雀石、褐铁矿呈细脉状、薄膜状、浸染状沿破碎带分布,局部可见少量黄铜矿、蓝铜矿、斑铜矿呈散点状分布。通过区内土壤地球化学测量工作,发现区内元素组合异常与已知矿化带吻合较好,异常浓集中心与已知矿点相对应,且异常强度高,指示该区具有良好的成矿地质条件及较大的找矿前景。

绿片岩集料在高速公路面层的可持续应用与改进策略研究

针对绿泥石片岩与沥青集料黏附性差导致混合料的水稳定性不佳的问题,论文以武汉至大悟高速公路项目为依托,基于绿泥石片岩集料的特性分析,研究了绿片岩集料、沥青界面黏附机制与分析模型,以及绿泥石片岩沥青混合料的配合比设计方法,同时提出了绿泥石片岩集料沥青混合料的改进措施和评价方法,有效解决了绿泥石片岩集料与沥青黏附性差、混合料水稳定性不足等问题。

强风化云母石英片岩原位直剪试验研究

强风化片岩难以采取原状试样开展室内试验获取岩体力学强度参数,原位直剪试验是获取强风化片岩抗剪强度参数的可靠途径。原位直剪试验研究表明,强风化片岩整体呈弹塑性破坏特征,在抗剪断强度达到峰值后,剪切位移急剧增大,剪应力未出现陡降,即残余强度效应不明显。同时,强风化片岩抗剪断内摩擦角呈显著的各向异性,随预设剪切面与层理面夹角的增大而增大,当夹角为零即沿层理面剪切时内摩擦角值最小;强风化片岩的黏聚力与剪切方向相关性不明显,主要受岩体内石英、云母等矿物成分含量的高低影响。基于原位直剪试验成果,开展强风化片岩高边坡防护工程优化设计的成功实践表明,加大勘察成本投入,通过原位试验获取可靠的抗剪强度参数,可保证高边坡支护设计方案的安全性和经济性。

抽水蓄能电站云母石英片岩各向异性特性试验研究

云母石英片岩的各向异性特征对抽水蓄能电站地下洞室围岩稳定性影响较大。通过岩矿鉴定、室内压缩实验、直剪试验、点荷载现场试验等手段,分析了云母石英片岩强度、变形的变化规律,研究了不同风化程度的云母石英片岩在不同加载方向上的各向异性特性。结果表明:在漫长地质历史过程中经历各种地质作用,云母石英片岩的矿物形成了强烈的定向排列结构,使云母石英片岩具有明显的片状构造,从而导致云母石英片岩在力学性质上具有明显的各向异性;在不同方向荷载作用下,云母石英片岩的抗压强度、变形模量、弹性模量均表现出一定的各向异性,随着水平与片理面夹角的增大,云母石英片岩的单轴抗压强度、变形模量、弹性模量先减小后增大,均呈现出“U”型的变化规律;水平与片理面夹角α为0°时,岩石破坏为压密剪切破坏,α为40°时,岩石破坏为复合剪切破坏,α为70°时,岩石破坏为典型层面剪切破坏,α为90°时,岩石破坏为劈裂张拉破坏;直剪试验指出片理面间的粘结强度较低,在荷载方向与片理方向平行时易产生错动,反应了云母石英片岩的各项异性;通过点荷载试验,不同风化程度不同加载方向的云母石英片岩点荷载强度呈现出明显的各向异性,平行片理面的强度主要由片理层间的胶结强度提供,而非云母石英片岩本身的力学强度特性,同时云母石英片岩的各向异性程度随着风化程度减弱而稍有减弱。

New Data on the Mineralogy of Chromite from the Nuggihalli Schist Belt,Western Dharwar Craton,Karnataka,India:Petrogenetic Implications

The occurrence of rhythmic layering of chromite and host serpentinites in the deformed layered igneous complexes has been noticed in the Nuggihalli schist belt （NSB） in the western Dharwar craton, Karnataka, South India. For this study, the chromitite rock samples were collected from Jambur, Tagadur, Bhakatarhalli, Ranganbetta and Byrapur in the NSB. Petrography and ore microscopic studies on chromite show intense cataclasis and alteration to ferritchromite. The ferritchromite compositions are characterized by higher Cr number （Cr/[Cr＋AI]） （0.68-0.98） and lower Mg number （Mg/[Mg＋Fe]） （0.33-0.82） ratios in ferritchromite compared to that of parent chromite. The formation process for the ferritchromite is thought to be related to the exchange of Mg, AI, Cr, and Fe between the chromite, surrounding silicates （serpentines, chlorites）, and fluid during serpentinization.

Correlations between ultrasonic pulse wave velocities and rock properties of quartz-mica schist

Physico-mechanical properties are critically important parameters for rocks. This study aims to examine some of the rock properties of quartz-mica schist（QMS） rocks in a cost-effective manner by establishing correlations between non-destructive and destructive tests. Using simple regression analysis, good correlations were obtained between the pulse wave velocities and the properties of QMS rocks. The results were further improved by using multiple regression analysis as compared to those obtained by the simple linear regression analysis. The results were also compared to the ones obtained by other empirical equations available. The general equations encompassing all types of rocks did not give reliable results of rock properties and showed large relative errors, ranging from 23% to 1146%. It is suggested that empirical correlations must be investigated separately for different types of rocks. The general empirical equations should not be used for the design and planning purposes before they are verified at least on one rock sample from the project site, as they may contain large unacceptable errors.

Dynamic response characteristics of dry and watersaturated schist under impact loading

Many geological engineering hazards are closely related to the dynamic mechanical properties of rock materials.However,most existing studies on the dynamic mechanical properties of rock materials were conducted on the hard rocks such as sandstone,granite,limestone,and marble,whereas soft rocks,such as schist,are less studied.Therefore,in this study,a series of triaxial impact tests were conducted on dry and saturated schist by employing a modified triaxial split Hopkinson pressure bar system to reveal the coupling effects of water,strain rate,and triaxial confining pressure on the mechanical properties of schist.The results show that schist is a type of watersensitive rock and the stress-strain curve of saturated schist has apparent ductility.The effects of strain rate on dynamic strain,deformation modulus and peak stress were analyzed.The results also show that the dynamic peak stress is affected by the combined softening effect and viscous effect of water under impact loading.Finally,it was found that the failure mode of schist belongs to typical axial tensile failure under uniaxial impact tests,and shear failure is the main failure mode under triaxial impact tests.With the increase in confining pressure,the failure modes of schist change from tensile failure to shear failure.This research can provide useful parameters for geological engineering hazard prevention in mountain areas.