隐伏含矿花岗岩的寻找标志

尼日利亚北部Banke和Ririwai两个较年青的花岗岩杂岩体中花岗岩岩浆期后蚀变和矿化表明,Li、F和Rb的含量以及Ba/Rb、Rb/Sr值可以作为寻找隐伏含矿花岗岩的标志。Banke和Ririwai两个杂岩体主要是火成活动的花岗岩的深成相组成。这些环状花岗岩杂岩与Sn-Nb矿化伴生,具有Li、F、Rb的含量及Rb/Sr值高,而Ba、Sr的含量及Ba/Rb值低的特征。     

赣南大田重稀土花岗岩的特征与成因

大田重稀土花岗岩是由燕山中期三次花岗岩浆侵入形成的复式岩体,其中γ_5~(2-2)花岗岩风化壳构成风化壳离子吸附型重稀土矿床。γ_5~(2-2)花岗岩中,SiO_2、MnO、∑REE和Rb含量高,而Sr、Ba和δEu值均低。岩浆成分呈“弧形”演化。一系列特征表明重稀土花岗岩的岩浆来源较深,源岩物质系经受多次熔融作用后于晚期形成。     

西秦岭造山带早中生代花岗岩成分多样性及形成机制

花岗质岩体产状及组成上的差异主要受控于源区性质和岩浆过程。以西秦岭造山带内几个代表性早中生代花岗岩为例,简要介绍其形成中所记录的岩浆过程,探讨花岗岩成分多样性的原因。西秦岭造山带内S型花岗岩是变泥质岩部分熔融的产物; 根据地球化学特征可分为两类,即高Sr含量、低Rb/Sr值和稀土元素总含量的Group A,及低Sr含量、高Rb/Sr值和稀土元素总含量的Group B,其分别可由白云母水致熔融和脱水熔融形成。糜署岭岩体的暗色微粒包体中发育3类晶形和成分不同的锆石,其与寄主岩石的锆石具有一致的U-Pb年龄; 其中,暗色微粒包体中的类型3锆石与寄主岩石中锆石具有一致的晶形和ε_Hf(t)值,捕获于寄主岩石,而类型1和类型2锆石具有较高的Th/U值和ε_Hf(t)值,结晶于混合程度不同的基性岩浆,其基性端元可能来自幔源岩浆; 因此,糜署岭岩体的暗色微粒包体记录了壳-幔岩浆混合过程。中川岩体由形成时代没有明显差异的5个岩相呈同心环状产出; 边部的似斑状花岗闪长岩被含斑中粒黑云母二长花岗岩侵入,中粒黑云母二长花岗岩被中粒电气石二云母花岗岩侵入,后者又被细粒黑云母二长花岗岩侵入; Rb-Sr-Ba微量元素特征显示各岩性之间不存在成分分异趋势; 因此,中川岩体的环带结构是由多期次岩浆侵位、聚集形成的。     

江西赣州隆木花岗岩体年龄、成分特征及其构造意义

为了查明江西赣州隆木花岗岩形成时代及演化过程,对隆木岩体中的黑云母花岗岩与似斑状黑云母二长花岗岩进行LA-ICP-MS锆石U-Pb定年和同位素地球化学研究。结果表明：黑云母花岗岩与似斑状黑云母二长花岗岩的锆石U-Pb定年结果分别为（457±6）、（450±9）Ma,表明岩体形成于晚奥陶世;岩体铝饱和指数为1.11～1.29,K2O与Na2O含量（质量分数）之比为0.97～1.51,属强过铝质及高钾钙碱性岩石;根据ACF图解,岩体投影于S型花岗岩区域内;岩体Rb、Th＋U、La＋Ce、P、Nd、Zr＋Hf＋Sm相对富集,而Ba、Nb、Sr、Ti相对亏损,总体上属于低Ba、低Sr的花岗岩;岩体Rb与Sr含量之比为0.60～2.82,平均值为1.68,明显高于大陆地壳与上地壳的平均值,具壳源花岗岩特征;根据A/MF-C/MF图解,岩体物源区为砂质岩;岩体稀土元素含量总量偏低,为（113～176）×10-6,轻稀土元素富集明显,配分模式明显呈右倾型,Eu异常为0.38～0.67,Eu亏损程度中等偏高;化学成分显示,岩体属于强过铝质高钾钙碱性S型花岗岩,是一种壳源花岗岩,岩浆源区为成熟上地壳的砂质岩源区;构造判别图解、年龄信息及野外特征表明,岩体形成于后碰撞伸展构造环境。总之,隆木岩体形成于早古生代晚期的加里东构造运动,是华夏古陆块与扬子古陆块在新元古代碰撞拼贴之后裂解、在中奥陶世再次发生陆内碰撞使得地壳加厚部分重融、造山后期地壳伸展减薄、熔融物质上升侵位形成的岩体。     

西天山阿吾拉勒东南部晚石炭世—中二叠世中酸性小岩体成因及地质意义

西天山阿吾拉勒东南部艾肯达坂花岗岩和2752高地闪长玢岩浅成小岩体侵入于石炭系火山 沉积岩中,岩石无变形,呈均一块状,具斑状/似斑状结构,属准铝质到弱过铝质高钾钙碱性花岗岩类,富集Rb、Th、U、K和Pb等大离子亲石元素,贫Zr、Hf等高场强元素,显示中等到弱的负Eu异常,亏损Nb、Ta、P、Ti和Sr等元素,具壳源岛弧区岩浆作用的地球化学特征。这两个岩体锆石均为正ε_Hf(t)值和新元古代Hf陆壳模式年龄,指示其主要源自新元古代陆壳物质的部分熔融,个别锆石ε_Hf(t)值明显高表明岩体形成过程还有幔源岩浆物质的加入。LA-ICP-MS锆石U-Pb定年分别获得2752高地闪长玢岩307 Ma和艾肯达坂花岗岩282 Ma的形成年龄,与区域上同期小岩体一同对应于西天山大规模壳-幔花岗岩浆活动末期,证明在晚石炭世—中二叠世期间,伴随着西天山大规模花岗岩浆活动的减弱,出现一期重要的小规模中酸性岩浆活动。综合分析西天山晩石炭世—中二叠世各类岩浆作用,该时期中酸性小岩体为后碰撞向陆内伸展拉张过渡阶段岩浆活动的产物,指示西天山晚石炭世晚期深部动力学背景和构造环境发生了重要转折。     

内蒙古乌兰五台地区三叠纪铝质A型花岗岩年代学及地球化学特征

基于1∶50 000区域地质调查工作,在内蒙古乌兰五台地区识别出铝质A型花岗岩。通过研究该套斑状二长花岗岩LA-ICP-MS锆石U-Pb年龄及地球化学特征,分析其成因类型,探讨早—中三叠世该区大地构造环境特征。结果表明:内蒙古乌兰五台地区斑状二长花岗岩单颗粒锆石U-Pb年龄加权平均值为(231.84±0.99)Ma,是印支期岩浆活动的产物,其岩石组合为中细粒、细粒斑状二长花岗岩;岩石地球化学特征属于高钾钙碱性系列,主量元素与微量元素表现为高硅、高碱,w(K₂O)/w(Na₂O)>1,A/CNK值为1.01～1.10的特点;Eu负异常明显,Rb、Th、K、Pb相对富集,Sr、Ti亏损;Ba、Nb、Sr、Ti呈现明显负异常,Rb、Th、K、Pb呈现明显正异常,w(Rb)/w(Sr)、w(Rb)/w(Ba)值高,w(Sr)/w(Ba)值低。上述特征显示该花岗岩为中—下地壳脱水部分熔融形成的岩浆侵位,可能形成于后碰撞挤压环境下的局部拉张构造环境,标志着大规模碰撞造山运动的结束和新的板内构造运动演化阶段的开始。     

天水坪道花岗岩体的地球化学特征及构造环境

坪道岩体由早期到晚期可分出斜长花岗岩→花岗闪长岩→黑云二长花岗岩→含斑黑云二长花 岗岩→正长花岗岩共5期岩浆活动。岩体碱值为0.49～0.62,ANKC大于1,多见白云母,CIPW计算 中多见刚玉,属钙碱性铝过饱和型。随SiO2增加,TiO2,TeO,MgO,CaO,Na2O均逐渐缓慢减少,而 Fe2O3,K2O剧增。岩石化学显示其源岩为上地壳杂砂岩类、碎屑岩类。岩体相对富集轻稀土,δEu值 为0.35～0.7,铕亏损强烈。岩体贫Ba,Rb,Sr,Y,Cu,Zr,Ga,Ni,富Nb,Ta,Bi,Th,Cr,Sn,Mo,Hf,Sc, 异常富Hf,Sn,Sc。构造地球化学信息显示岩体是大陆裂谷型花岗岩。     

龙首山直沟门岩体特征及构造环境

直沟门岩体(年龄374±38Ma)侵入于华北板块西缘的龙首山岩群,主要由花岗岩、二长花岗岩 等岩性组成。根据野外产状和岩相学特征可划分为3个单元,从早到晚依次为:直沟门单元、湾湾圈单 元和马路湾单元。岩体的w(SiO2)65.94%～75.18%,w(K2O)2.36%～4.35%,w(Na2O)3.53%～ 5.47%,总体上w(Na2O)≈w(K2O)。随w(SiO2)增大w(CaO),w(TFeO),w(MgO)减少,所有岩 石均具铝弱过饱和,ANKC=1.01～1.09,岩浆类型属钙碱性系列,σ=1.99～2.64,皮可克指数为55.6。 Li,Cs,Rb质量分数较低,而Ba,Sr较高,从早到晚大体存在Rb/Sr减少,而Sr,Ba,Co和Ba/K增加。 湾湾圈和马路湾单元在ΣREE((152.11～171.94)×10-6),ΣLREE/ΣHREE(24.81～26.92),δEu (0.91～1.10)以及配分模式等方面是相似的,与其相比,直沟门单元的ΣREE(46.62×10-6),ΣLREE/ ΣHREE(3.52)低,而δEu(1.60)高。w(La)与w(La)/w(Sm)大体存在正相关,δEu,ΣREE与DI变化 也相一致。直沟门岩体形成于祁连造山带碰撞阶段之后,属后碰撞花岗岩。在w(CaO)/w(Na2O)对 w(Al2O3)/w(TiO2)图上,与拉克伦褶皱带后碰撞花岗岩的投影区相近。直沟门岩体的岩浆可能源自 祁连褶皱带下冲火山岩。     

河南内乡牧虎顶花岗岩特征及与金矿的关系

东秦岭造山带的二郎坪－夏馆地区，发育一套火山－碎屑岩建造，并有大量花岗岩侵入体分布。重点研究了牧虎顶花岗岩的特征及与金矿的关系。该岩体副矿物含量高，组合复杂；SiO2含量高，变化大；Au、Ag等成矿元素和Sr、Ba等微量元素含量高而Rb、Co、Ni等含量低；富轻稀土，具中等负铕异常。据上述特征并结合其他许多资料综合分析表明，牧虎顶花岗岩属加里东期陆壳改造重熔型花岗岩。本区花岗岩与金矿有密切成因联系。矿床地质地球化学研究表明，金矿床的部分成矿金属物质和成矿流体及全部硫源来自花岗岩或岩浆热液，岩浆活动并为地层中金的活化迁移和聚集提供了热动力，因而花岗岩是本区金矿形成的重要因素，今后应主要在含矿花岗岩体及其附近开展金矿勘查工作。     

日本飞弹变质带庄川岩体的岩石成因

主要从岩石学方面对飞弹变质带西北部的庄川岩体的成因进行探讨。该区侏罗纪岩体由闪长岩-石英闪长岩(以下简称D-Qd)和花岗闪长岩-石英二长岩(以下简称Gd-Ad)两类岩石构成。在野外,Gd-Ad侵入于D-Qd之中。D-Qd和Gd-Ad,其Sr含量随Rb/Sr的变化倾向,以及[Eu/Eu~*),(La/Lu)cn随SiO_2含量的变化倾向明显不同,所以,两者可能是由不同的岩浆生成的。Gd-Ad的微量元素和稀土元素(REE)含量的分散现象可能是由飞弹变质岩类或(和)广泛分布飞弹变质带中的古期灰色花岗岩的混合作用引起的。     

湖南花垣矿集区李梅铅锌矿床闪锌矿Rb-Sr定年与成矿物质示踪

李梅铅锌矿床位于扬子克拉通东南缘花垣矿集区北段,预测铅锌储量为300×10⁴ t,是该区铅锌矿床的典型代表。该矿床铅锌矿体呈层状、似层状,受地层与构造的控制,主要赋存于下寒武统清虚洞组下段第三亚段地层藻灰岩中。为获得该矿床的成矿年龄,探讨其成矿物质来源,采用闪锌矿Rb-Sr定年方法,对主成矿期形成的闪锌矿单矿物进行Rb-Sr同位素组成测定,获得的等时线年龄为(464±12)Ma(平均标准权重偏差为0.97),成矿时代为中奥陶世,成矿早于花垣矿集区南段的狮子山铅锌矿床(成矿时间为(410±12)Ma)和柔先山铅锌矿床((412±6)Ma),推断在花垣矿集区范围内发生了郁南运动和广西运动导致的两期成矿事件,整个矿集区成矿时限跨度大约为70 Ma。李梅铅锌矿床成矿时代明显晚于赋矿地层时代,该矿床的形成可能与郁南运动形成伸展构造引起的构造热液活动有关。闪锌矿的⁸⁷Sr/⁸⁶Sr值为0.709 56～0.711 14,(⁸⁷Sr/⁸⁶Sr)_i值为0.709 380±0.000 018,成矿流体具有高于赋矿围岩的高Sr同位素比值,推断成矿物质应主要源自具有高⁸⁷Sr/⁸⁶Sr值和高Pb、Zn丰度的下伏寒武系石牌组和牛蹄塘组。     

个旧含锡花岗岩浆杂岩体的成因演化及成矿

根据个旧含Sn花岗岩的Rb-Sr年代学、Sr和Pb同位素地质学、Rb和Sr以及REE地球化学资料,讨论了该岩体的成因、演化和成矿作用。个旧含Sn花岗岩,是陆壳重熔岩浆在深部长期分异演化的产物,并伴随有明显的同化混染和混合作用。其成岩及其成矿作用具有多期、多阶段性。含Sn花岗岩浆的逐步分异和演化有利于Sn富集成大型富矿。个旧白云山碱性岩不是由神仙水花岗岩演化而来,而可能是基性岩浆在深部分异演化的结果。     

Strontium hydrogeochemistry of thermal groundwaters from Baikal and Xinzhou

This paper reports our work on the strontium hydrogeochemistry of thermal groundwa-ters in the Baikal Rift System (BRS) in Russia and Mongolia and the Xinzhou basin of the Shanxi Rift System (SRS) in northern China. Though similar in geological background, groundwaters from the BRS and the Xinzhou basin have different strontium isotope compositions. Both the strontium contents and the 87Sr/86Sr ratios of thermal water samples from Xinzhou are higher than those of most samples from Baikal. The major reason is the difference in hostrock geochemistry. The hos-trocks of the Xinzhou waters are Archaean metamorphic rocks, while those of the Baikal waters except the Kejielikov spring are Proterozoic or younger rocks. In the study areas, cold groundwaters usually show lower 87Sr/86Sr ratio due to shorter water-rock interaction history and lower equilibration degree. Strontium hydrogeochemistry often provides important information about mixing processes. Ca/Sr ratio can be used as an important hydrogeochemical pa     

Strontium hydrogeochemistry of thermal groundwaters from Baikal and Xinzhou

This paper reports our work on the strontium hydrogeochemistry of thermal groundwaters in the Baikal Rift System (BRS) in Russia and Mongolia and the Xinzhou basin of the Shanxi Rift System (SRS) in northern China. Though similar in geological background, groundwaters from the BRS and the Xinzhou basin have different strontium isotope compositions. Both the strontium contents and the⁸⁷Sr/⁸⁶Sr ratios of thermal water samples from Xinzhou are higher than those of most samples from Baikal. The major reason is the difference in hostrock geochemistry. The hostrocks of the Xinzhou waters are Archaean metamorphic rocks, while those of the Baikal waters except the Kejielikov spring are Proterozoic or younger rocks. In the study areas, cold groundwaters usually show lower⁸⁷Sr/⁸⁶Sr ratio due to shorter water-rock interaction history and lower equilibration degree. Strontium hydrogeochemistry often provides important information about mixing processes. Ca/Sr ratio can be used as an important hydrogeochemical parameter. Case studies at Xinzhou show that thermal waters with lowest Ca/Sr ratios are most weakly affected by mixing with shallow groundwaters, as supported by our hydrochemical and sulfur isotope studies.

     

Strontium isotopic geochemistry of the Changjiang estua-rine waters: Implications for water-sediment interaction

The Sr concentrations and 87Sr/86Sr ratios have been measured for the Changjiang es-tuarine waters with a main purpose to understand physical and chemical processes at the estuary. The result shows that the Changjiang River water has higher Sr concentration (150 ng/g) and lower 87Sr86Sr ratio (0.7105) when compared with the average values (0.7119 for 87Sr/86Sr and 78ppb for Sr, respectively) of large world rivers. In the mixing process, no simple mixing of two end-members has been found according to the variations of Sr concentration and isotope ratios. There is an abrupt rise of Sr isotope ratios at the salinity about 1 mg/g during river-sea water mixing at the estuary. This abrupt rise of Sr isotope ratios is mostly ascribed to the strong water-sediment interaction, because there exists the same rise of suspended particulate materials due to energetic resuspension of bottom sediments.     

滇西复式花岗岩体的时代及地质意义研究

对全岩Rb—Sr等时线年龄的研究,得到来利山复式岩体中不同期次岩石的同位素地质年龄：含紫苏辉石斑状黑云母二长花岗岩为84Ma,含斑黑云母钾长花岗岩为77Ma,等粒黑云母钾长花岗岩为52Ma表明来利山复式岩体形成于中生代晚期到新生代早期,说明其演化的比较充分,岩石化学成分的特征反映其物质来源于硅铝的熔融,在成因类型上相当于壳型、S型或改造型。     

Isotopic compositions of strontium in river water of Guizhou karst areas,China

We have carried out a study on the variation of strontium isotope composition of river waters, Wujiang and Yuangjiang River, in karst areas of Guizhou Province, China. The results obtained permit us to characterize the geochemistry of the river draining karst terrain and obtain a better understanding of main controls of catchment geology, chemical weathering of different rocks, and evaluate impact of human activities on the environment. The isotopic ratios of dissolved Sr in all rivers are between⁸⁷Sr/⁸⁶Sr=0.7077 and 0.7110, totally lower than the weighted average of⁸⁷Sr/⁸⁶Sr=0.7119 for the world large rivers. The Wujiang River waters have Sr concentrations from 1.0 to 6.1 μmol/L, while the Yuanjiang River waters have much lower Sr concentrations ranging from 0.28 to 1.3 μmol/L. Most of the river waters from the Wujiang river are characterized by low Ca/Sr and Mg/Sr, and⁸⁷Sr/⁸⁶Sr ratios, in which a majority of river waters are of⁸⁷Sr/⁸⁶Sr ratios lower than the average Sr isotope ratio (⁸⁷Sr/⁸⁶Sr=0.709) of present seawater. The higher⁸⁷Sr/⁸⁶Sr ratios are observed in the river waters in the lower reach of the Wujiang River, where the lithology is dominated by detrital rocks and dolomite. The water from Yuanjiang River show higher Ca/Sr, Mg/Sr and⁸⁷Sr/⁸⁶Sr ratios due to weathering of silicates, as compared to the river waters from Wujiang river.