东秦岭卢氏稀有金属伟晶岩的绿柱石矿物学特征及其指示意义

绿柱石是重要的铍矿石矿物,记录了花岗伟晶岩型稀有金属矿床的成岩成矿过程。东秦岭伟晶岩区是我国重要的稀有金属产地之一。本文调查了东秦岭卢氏伟晶岩区中的南阳山矿区(703号脉锂矿化伟晶岩和302号脉铍矿化伟晶岩)、七里沟-前台矿区(前台锂矿化伟晶岩)、蔡家沟矿区(大西沟和韭菜沟锂矿化伟晶岩)和瓦窑沟矿区(西山沟和瓦窑沟铍矿化伟晶岩)的伟晶岩内部结构分带,认为东秦岭稀有金属伟晶岩主要为过铝质LCT型伟晶岩,属于稀有金属(REL)类REL-Li亚类。其中,703号脉、韭菜沟和大西沟伟晶岩属复杂型锂辉石亚型,前台伟晶岩属钠长石-锂辉石型,302号脉、瓦窑沟和西山沟伟晶岩属绿柱石型绿柱石-铌铁矿亚型。电子探针结果表明绿柱石富碱金属,贫铁和镁。绿柱石元素替代机制包括通道-八面体替代、通道-四面体替代以及通道中碱金属阳离子间的置换。西山沟和瓦窑沟绿柱石的替代机制分别是Na(Fe~(2+),Mg)_(-1)Al_(-1)和NaLi_(-1)Be_(-1)。302号脉、前台、大西沟和韭菜沟绿柱石的替代机制为(Na,Cs) Li_(-1)Be_(-1)。703号脉绿柱石的替代机制包括NaFe~(2+)_(-1)Al_(-1)、NaCs_(-1)和(Na,Cs)Li_(-1)Be_(-1)。绿柱石的Cs2O含量和Na/Cs值揭示伟晶岩分异演化程度序列(由低至高)为瓦窑沟矿区→302号脉铍矿化伟晶岩→蔡家沟矿区→前台→703号脉锂矿化伟晶岩。铍矿化伟晶岩岩浆分异演化程度低于锂矿化伟晶岩岩浆。背散射图像显示绿柱石内部分带多样,包括均一结构、条带状、正/反蚀变边、补丁分带和复杂不规则分带。与铍矿化伟晶岩相比,锂矿化伟晶岩产出的绿柱石内部分带复杂多样,反映更为强烈的液相不混溶和交代作用。随伟晶岩岩浆分异演化程度升高,绿柱石FeO含量降低,内部分带更为复杂,发育蚀变边结构、补丁分带和不规则分带等。绿柱石FeO含量和内部分带特征可作为花岗伟晶岩分异演化程度的潜在指示标志。锂矿化伟晶岩中绿柱石的化学组成和内部分带特征表明岩浆就位时是高度分异演化的稀有金属伟晶岩岩浆。大西沟、韭菜沟和前台锂矿化伟晶岩岩浆就位后未经历明显分异演化过程,而南阳山703号脉伟晶岩岩浆就位后经历了较充分的分异演化,导致稀有金属的进一步富集。锂矿化伟晶岩的稀有金属成矿机制是结晶分异和液相不混溶。     

Organic material accumulation of Carnian mudstones in the North Qiangtang Depression,eastern Tethys: Controlled by the paleoclimate,paleoenvironment, and provenance

The Late Triassic mudstones are considered to be the most significant hydrocarbon source rocks (TOC: 0.54%–3.29%) in the North Qiangtang Depression, eastern Tethys. Here, we present geochemical data from the Woruo Mountain Carnian mudstones, in order to investigate their paleoclimate, paleoenvironment, and provenance and to analyze the mechanism of organic material accumulation. The paleoclimate condition was warm and humid during the Carnian mudstones deposition, as indicated by moderate chemical index of alteration (CIA; 73–76), which may be connected with the Late Triassic Carnian stage global climate event in the Tethys. The low U/Th (0.17–0.25) and C_org/P_tot (7–33) ratio values and moderate manganese contents, reflect the oxidizing conditions during the Carnian mudstones deposition. The relatively high primary productivity in this study is supported by the relatively high P concentrations. The Al₂O₃–(CaO* + Na₂O)–K₂O ternary plot and Th/Sc–Zr/Sc crossplot reflect that the source areas have undergone a medium chemical weathering with weak sedimentary recycling. The TiO₂–Zr, Co/Th–La/Sc, La/Th–Hf, and La/Yb–∑REE bivariate diagrams indicate that the provenance of Carnian mudstones was primarily from felsic igneous rocks. The collision setting has been identified based on the multi-major elements discriminate plots in the present study. The Riwanchaka and Mayigangri masses to the southwest and south of the study area consisting mainly of Middle-Triassic granodiorite and Late-Triassic granite are likely responsible for supplying provenance to the Woruo Mountain Carnian mudstones, which have similar REE patterns. The relatively high TOC contents of Carnian mudstones are related to high paleoproductivity and fast sedimentation rates, which will lead to preservation of some organic matter even when bottom waters are completely oxidizing. The detrital input during the Carnian mudstones deposition would result in dilution of organic matter.     

用边界元法计算平面分层埋入体的电磁散射

本文结合平面边界元法和平面多极子展开法,求解平面分层埋入体的电磁散射。这种方法具有高速、占用内存少的优点。     

Textural re-equilibration,hydrothermal alteration and element redistribution in Fe-Ti oxide pods,Singhbhum Shear Zone,eastern India

This study describes textures and mineral chemistry of magnetite-ilmenite-bearing pods/pockets in mineralogically diverse feldspathic schist near Pathargora in the Singhbhum Shear Zone, eastern India. The textural and geochemical characteristics of the magnetite-ilmenite assemblage are the results of a protracted geological history involving magmatic crystallization and oxidation-exsolution of titanomagnetite, deformation-induced recrystallization and textural re-equilibration and hydrothermal fluid-induced hematitization of magmatic magnetite. The magnetite grains contain characteristic trellis and sandwich ilmenite lamella, which are interpreted to be the products of oxidation-exsolution of ulvöspinel component of magnetite-ulvöspinel solid solution. The exsolution process was accompanied by preferential partitioning of spinel elements such as Cr, Al and V in magnetite and Ti, Mn, Mg, HFS elements (Nb, Ta), transition elements (Sc, Co, Cu and Zn) and granitophile elements (Mo, Sn and W) in ilmenite. The deformed sandwich lamella is locally recrystallized and transformed into granular ilmenite close to fractures, micro-shear planes and magnetite grain boundaries. Coarse granules of ilmenite, within or associated with magnetite, are of two textural types: one invariably contains Fe-rich exsolved phase and may be of magmatic origin, while the other mostly formed by strain-induced, fluid-mediated expulsion (from the interior of magnetite to its boundary) and dynamic recrystallization of existing ilmenite lamella in magnetite, and dynamic recrystallization of primary ilmenite containing Fe-rich exsolved phases. Magnetite is variably hematitized. The highly porous nature and trace element geochemistry of hematite and mass-balance calculations suggest the hematitization was mostly redox-independent and was caused by infiltration of metal-rich, reduced and acidic fluid. The hematitization process was associated with significant enrichment and immobilization of U, Th, Pb, REEs, Cu, Mo and W and depletion of Ni, Cr, V in hematite.     

The Analytic Element Method for rectangular gridded domains,benchmark comparisons and application to the High Plains Aquifer

Groundwater studies face computational limitations when providing local detail (such as well drawdown) within regional models. We adapt the Analytic Element Method (AEM) to extend separation of variable solutions for a rectangle to domains composed of multiple interconnected rectangular elements. Each rectangle contains a series solution that satisfies the governing equations and coefficients are adjusted to match boundary conditions at the edge of the domain and continuity conditions across adjacent rectangles. A complete mathematical implementation is presented including matrices to solve boundary and continuity conditions. This approach gathers the mathematical functions associated with head and velocity within a small set of functions for each rectangle, enabling fast computation of these variables. Benchmark studies verify that conservation of mass and energy conditions are accurately satisfied using a method of images solution, and also develop a solution for heterogeneous hydraulic conductivity with log normal distribution. A case study illustrates that the methods are capable of modeling local detail within a large-scale regional model of the High Plains Aquifer in the central USA and reports the numerical costs associated with increasing resolution, where use is made of GIS datasets for thousands of rectangular elements each with unique geologic and hydrologic properties, Methods are applicable to interconnected rectangular domains in other fields of study such as heat conduction, electrical conduction, and unsaturated groundwater flow.     

ICP-AES光谱法测定铅锌矿石中Cu Pb Zn As Bi

铅锌矿经王水分解处理,标准溶液中配入与样品组分相匹配的标准物质,用电感耦合等离子体发射光谱法可稳定、准确地测定矿石中铜、铅、锌、砷、铋。     

塔中地区志留系砂岩元素地球化学特征与物源判别意义

通过分析塔中地区志留系砂岩的某些常量元素和微量元素含量的变化,研究了该地区砂岩的地球化学以及其物源特征。结果表明塔中地区志留系的沉积构造环境为活动大陆边缘和被动大陆边缘,物源主要来自再循环造山带。砂岩的矿物成分主要在石英、钾长石、斜长石、伊利石、绿泥石等矿物之间变化。化学风化作用指标(CIW)和化学蚀变作用指标(CIA)反映了该地区砂岩的碎屑成分受到了强烈的风化作用,风化作用强度为:依木干他乌组>塔塔埃尔塔格组>柯坪塔格组。化学组分变化指标(ICV)反映了有些砂岩中含有第一次旋回沉积物。A-CN-K三角图反映了砂岩的碎屑源岩中斜长石含量要高于钾长石含量,主要在花岗闪长岩和花岗岩之间变化,砂岩的碎屑成分在风化过程中受到了钾的交代作用,长石以及长石中的高岭石发生了伊利石化。稀土元素及其比值(La/Yb)_N、(La/Lu)_N等也反映了该地区砂岩来源于花岗闪长岩和花岗岩的混合物。     

西秦岭阳山金矿带花岗斑岩元素及Sr-Nd-Pb同位素地球化学

甘肃阳山金矿带的花岗斑岩脉中含有石榴子石,A/CNK=1.65～3.65,属于强过铝质花岗岩类.花岗斑岩相对富集LILE和LREE,亏损Ba、Sr、Nb、Ta、P、Ti等,配分模式类似于典型同碰撞型花岗岩类;花岗斑岩ΣREE=54.35～124.01×10-6,(La/Yb)N=9.72-27.80,δEu=0.70～0.89,表明其岩浆形成时部分斜长石进入熔体,而非完全残留.花岗斑岩Isr值为0.70806～0.71756,平均0.71107;εNd(t)值变化于-2.9～-5.0,平均-3.4;Nd模式年龄(T2DM)为1.24～1.41Ga,平均1.34(Ga).以上同位素特征表明花岗斑岩岩浆应源自成熟度较低的中元古代基底地壳物质.花岗斑岩的(206pb/204Pb)220Ma、(207pb/204Pb)220Ma和(206pb/204Pb)220Ma的平均值分别为17.875、15.604和38.296,与秦岭微陆块的中元古代基底和碧口地体碧口群的Pb同位素组成一致.考虑到前人获得碧口群的年龄为1.235～1.367Ga,而秦岭微陆块沿勉略缝合带向南仰冲到碧口地体之上.我们认为由碧口群等组成的俯冲板片的变质脱水熔融作用导致了阳山金矿带花岗斑岩的形成.因此,阳山金矿带的花岗斑岩是扬子与华北大陆中生代碰撞造山过程中形成的同碰撞花岗岩类.     

吉林省西部草地土壤的化学元素含量及其特征研究

对吉林省西部草地土壤化学元素含量研究表明，吉林省西部草地土壤中富钾少磷；钙、镁含量丰富；硼、铜、铁、锰含量在剖面上表现为向下增加；土壤中氮、磷、钾、钙、铜含量随草地退化程度的加深而减少；土壤中硅、钠含量丰富，显示出较强的沙化、盐碱化趋势，其含量随草地退化程度的加深而增加，钴含量随草地退化程度加深而降低；钡含量随草地退化程度的加深有增加的趋势；而稀土元素总量低于土壤背景值，并随着草地退化程度的加深其含量有减少的趋势。     

安徽安庆铜铁矿床成因:矿床地质特征与元素地球化学约束

安庆铜铁矿床是产于长江中下游铜(金)、铁成矿带内安庆-贵池矿集区中的一典型矽卡岩矿床,矿体赋存于下三叠统南陵湖组大理岩与月山闪长岩体之间的接触带上。典型剖面系统取样分析显示,矿体与围岩在空间上具有显著的矿物组合分带与岩石化学分带特征,即靠近大理岩带发育致密块状磁铁矿矿石与团块状矽卡岩型矿石,远离大理岩带发育浸染状矽卡岩型矿石,靠近闪长岩带发育透辉石矽卡岩。从大理岩到磁铁矿体, Fe₂O₃^T含量显著增加,之后随着靠近闪长岩体,其含量呈逐渐降低趋势;而CaO显示了与Fe₂O₃^T相反的成分变异特征。矿物与全岩微量元素研究表明,致密块状磁铁矿矿石及团块状矽卡岩型矿石均具有岩浆成因的稀土元素配分模式;而浸染状矽卡岩型矿石显示了交代成因的稀土元素配分特征。矿体地质、矿相学与元素地球化学综合研究表明,矽卡岩成矿经历了矿浆贯入期与热液成矿期,前者包括氧化物阶段和硫化物-碳酸盐阶段,后者包括进化交代阶段、早退化蚀变阶段、石英-硫化物阶段和晚退化蚀变阶段。结合已有的区域岩浆岩成岩机制研究成果,认为安庆铜铁矿床应是矿浆贯入与接触交代复合成因的矽卡岩型矿床,由于高位岩浆房中岩浆不混溶作用形成的富Fe熔浆是该矿床中成矿元素的主要来源。