Mineralogy,M-type tetrad effect and radioactivity of altered granites at the G. Abu Garadi shear zone,central Eastern Desert,Egypt

The G. Abu Garadi area is covered mainly by metasediments, alkali feldspar granites and stream sediments. The alkali feldspar granite is traversed by a major strike-slip fault trending in an N-S direction as well as two subordinate sets of faults trending NW to WNW for the first one and NE for the second one. These faults represent the shear zones affected by magmatic (syngenetic) as well as hydrothermal (epigenetic) activities causing alteration of the granitic rocks. The most common alteration features are albitization, greisenization and koalinitization. The mass balance calculations of the studied altered samples show enrichments in Zr, Y, Ni, U, Th and Ga and depletions in Zn, Sr, Nb, Ba, Pb, Cu and V. Only the greisenized samples exhibit a significant enrichment in Nb, ∑REE budget and pronounced lanthanide tetrad effect (M-type), especially TE1,4, while weakly expressed tetrad effects are for the other albitized and koalinitized samples. Mineralogically, the common accessory minerals in the altered samples include samarskite-(Y), betafite, uranothorite, zircon, fluorite and cassiterite. The greisenized granites contain high eU and eTh than the other altered types, where they are characterized by an assemblage of the radioactive minerals; samarskite-(Y), betafite, uranothorite in addition to zircon. The inter-element relationships between U and Th and also their ratios illustrate that the radioelement distribution in these granites is mainly governed by magmatic processes, in addition to post-magmatic ones. The distribution of chemical elements and the fractionation of some isovalents within the shear zone are largely controlled by the newly formed mineral phases. With respect to uranium mobilization, uranium migrated from the host alkali feldspar granites of G. Abu Garadi, while the shear zones acted as traps for the migrated uranium. Moreover, U migrated in the shear zone during greisenization and albitization, and migrated out during koalinitization.     

大兴安岭伊勒呼里山早白垩世碱长花岗岩年龄、地球化学特征及其地质意义

对大兴安岭伊勒呼里山早白垩世碱长花岗岩进行了岩相学、地球化学、LA-ICP-MS锆石U-Pb定年研究。伊勒呼里山地区碱长花岗岩主量元素具有富Si、富碱,贫Mg、Ca的特征;微量元素亏损Sr、P、Eu、Ti,富集K、Rb、Th等不相容元素,元素地球化学特征表明,岩体为铝质A型花岗岩(A/CNK=0.88~1.21,A/NK=0.94~1.49)。测年结果显示,粗中粒碱长花岗岩的锆石年龄为140.3±1.0Ma,细中粒碱长花岗岩锆石年龄为137.9±0.8Ma,均形成于早白垩世。结合区域研究资料,伊勒呼里山地区碱长花岗岩岩体的形成与蒙古-鄂霍茨克洋闭合后的岩石圈伸展密切相关,其岩浆源区可能为地壳物质的部分熔融。     

Composition, age, and origin of the ~620?Ma Humr Akarim and Humrat Mukbid A-type granites: no evidence for pre-Neoproterozoic basement in the Eastern Desert, Egypt

The Humr Akarim and Humrat Mukbid plutons, in the central Eastern Desert of Egypt, are late Neoproterozoic post-collisional alkaline A-type granites. Humr Akarim and Humrat Mukbid plutonic rocks consist of subsolvus alkali granites and a subordinate roof facies of albite granite, which hosts greisen and Sn–Mo-mineralized quartz veins; textural and field evidence strongly suggest the presence of late magmatic F-rich fluids. The granites are Si-alkali rich, Mg–Ca–Ti poor with high Rb/Sr (20–123), and low K/Rb (27–65). They are enriched in high field strength elements (e.g., Nb, Ta, Zr, Y, U, Th) and heavy rare earth elements (La _n /Yb _n ?=?0.27–0.95) and exhibit significant tetrad effects in REE patterns. These geochemical attributes indicate that granite trace element distribution was controlled by crystal fractionation as well as interaction with fluorine-rich magmatic fluids. U–Pb SHRIMP zircon dating indicates an age of ~630–620?Ma but with abundant evidence that zircons were affected by late corrosive fluids (e.g., discordance, high common Pb). εNd at 620?Ma ranges from +3.4 to +6.8 (mean?=?+5.0) for Humr Akarim granitic rocks and from +4.8 to +7.5 (mean?=?+5.8) for Humrat Mukbid granitic rocks. Some slightly older zircons (~740?Ma, 703?Ma) may have been inherited from older granites in the region. Our U–Pb zircon data and Nd isotope results indicate a juvenile magma source of Neoproterozoic age like that responsible for forming most other ANS crust and refute previous conclusions that pre-Neoproterozoic continental crust was involved in the generation of the studied granites.     

Magmatism and formation conditions of the Urma helvite-bertrandite deposit,West Transbaikal berillium province

The relationships between mineralization and magmatism during the formation of the Early Mesozoic West Transbaikal beryllium province are exemplified in the Urma helvite-bertrandite deposit. The deposit is drawn toward granitoids of elevated alkalinity, which belong to the Tashir Complex. Mineralization is related to leucogranite and characterized by patched distribution controlled by localization of metasomatic alteration. The latter is identified owing to replacement of feldspar with microcline and albite followed by silicification related to fracture zones. Helvite and bertrandite are the major Be minerals at the deposit. The Be grade of the ore is nonuniform and varies from 740 to 25000 ppm. Zircon, malacon, monazite, allanite, bastnaesite, columbite, and xenotime occur in metasomatic rocks together with Be minerals. Geochemical characteristics of alkali granites and metasomatic rocks are similar in a wide range of incompatible elements. Both are characterized by lowered Ba, Sr, P, and Eu contents and enriched in Th, U, Pb, Zr, and Hf. The degree of enrichment is the highest in the ore. The Be content in the ore correlates with concentrations of a number of other rare metals typical of host granite, which form their own mineralization against the background of metasomatic alteration, including Zr and REE minerals. Similarity in geochemistry of granitic rocks and Be ore indicates that the Urma deposit was related to the evolution of magmatic melt. Regional correlation shows that the ore-magmatic system of the Urma deposit is close to that of the Orot deposit, one of the largest in the central segment of the West Transbaikal metallogenic province. Both deposits are characterized by a similar composition of granitoids and comparable localization of ore zones in the structure of plutons. This similarity supports the high ore resource potential of Early Mesozoic alkali granites in the western Transbaikal region. Taking into account that these granitoids are widespread in the West Transbaikal Rift Zone that controls the metallogenic province, one can expect the discovery of new deposits therein.     

High heat producing radioactive granites of malani igneous suite at northeast of Jodhpur,northwestern India

The Malani igneous suite, a terrain showing crustal formation as late as in Neoproterozoic, shows some pink and grey granites in the northeast of the desert city of Jodhpur, in northwestern, India. The average heat generation value of 15.925 HGU for these granites that is much higher than the average known value (3.8 HGU) for the continental crust has been reported here. The concentration of uranium determined is four times higher than the average continental crust. Thorium is still higher than U and K. The radioelement concentration (Ur) varies from 15.58 to 73.48 in the granites with an average of 45.671, clearly indicates a ‘hot crust’. Hence it is favourable for the formation of mineralization of HFS elements like, Nb, Ce, REE and U and Th, which need to be explored in the terrain as an economic deposit.     

新疆昭苏布合塔铜(金)矿化区花岗质岩石锆石U-Pb年龄、地球化学特征及其成因

布合塔铜（金）矿化区位于新疆昭苏境内,大地构造位于那拉提构造带北缘西段。矿化区主要被二长花岗岩及石英闪长岩呈岩株状侵入,在花岗岩体边缘及与围岩接触带内均有铜（金）矿化。研究区2种岩体的锆石 LA-ICP-MS U-Pb测年结果分别为（434.5±4.6）Ma（二长花岗岩）、（445.7±5.1）Ma（石英闪长岩）,为晚奥陶世—早志留世;元素地球化学测试结果显示,二者均属过铝质钾玄岩系列;二长花岗岩A/CNK值为1.35~1.42,石英闪长岩A/CNK值为1.47~1.71,具S型花岗岩特征;二者稀土元素特征较为相近,均显示轻稀土相对富集、具Eu负异常（δEu=0.67~0.80）,微量元素均显示富集Ba、Th、U,亏损Nb、Ta等;地球化学分析表明,岩浆源岩主要为变杂砂岩,以部分熔融作用为主。结合区域大地构造背景及相关研究,总体认为该矿化区花岗质岩浆是由中天山板块与伊犁板块碰撞闭合之后的中下地壳部分熔融而成。     

辽东凤城地区早白垩世花岗岩的锆石U-Pb年龄、地球化学特征及地质意义

辽东凤城地区出露的大面积花岗岩一直是华北克拉通北缘岩石圈减薄的研究热点,但花岗岩的岩石年龄、成因及构造环境等方面的研究尚不够深入.以辽东凤城地区帽盔山二长花岗岩、蛟羊峪花岗闪长岩、清凉山二长花岗岩为研究对象,采用岩石学、岩石地球化学及LA-ICP-MS锆石U-Pb测年方法,讨论了花岗岩的岩石成因及构造意义.帽盔山二长花岗岩、蛟羊峪花岗闪长岩、清凉山二长花岗岩中锆石具有典型的岩浆振荡生长环带和较高的钍铀比（Th/U>0.4）,LA-ICP-MS锆石U-Pb年龄分别为127.2±0.6 Ma、122.9±1.1 Ma、129.0±0.8 Ma,均形成于早白垩世.岩石地球化学特征显示帽盔山二长花岗岩和清凉山二长花岗岩为高钾钙碱性A型花岗岩,具有富Si、富碱,贫Al、Fe、Ca、Mg的特征,Eu负异常较为明显;蛟羊峪花岗闪长岩为准铝质到过铝质岩石,微量元素富集Nd、Tb、La,亏损Sr、P、Ti.构造环境判别结果显示,上述3个花岗岩体均形成于伸展拉张的构造环境.以上研究表明,辽东凤城地区在早白垩世时期处于非造山的伸展环境,是华北克拉通岩石圈减薄和克拉通破坏作用的缩影.      

大兴安岭中段早白垩世花岗质岩石锆石U-Pb年龄及地球化学特征

大兴安岭地区显生宙花岗岩分布广泛,但区内中生代花岗岩的研究相对薄弱.通过对大兴安岭中段扎兰屯以西的毕家店岩体和神山岩体进行年代学和地球化学研究,探讨了本区早白垩世花岗岩的成因及构造背景.其中毕家店岩体主要由正长花岗岩和花岗斑岩组成,神山岩体主要由碱长花岗岩组成.毕家店岩体的锆石U-Pb年龄为136±3 Ma、139.5±0.9 Ma和128.1±0.8 Ma,神山岩体为119.3±0.8 Ma,均形成于早白垩世.地球化学特征上,两岩体均呈现高硅、低钙、富碱、Eu负异常等特征,亏损Nb、Ta,富集Rb、Th和U,属于弱过铝质高钾钙碱性系列,为岩浆演化晚期的高分异I型花岗岩.两岩体具有活动大陆边缘构造属性,结合大兴安岭地区同时期I型、A型花岗岩特征,认为早白垩世花岗质岩石的形成与太平洋板块俯冲背景下的拆沉作用密切相关.     

北秦岭马河钼矿区花岗岩类的锆石U-Pb年龄、地球化学特征及其地质意义

本文对北秦岭马河钼矿区桃官坪中-细粒二长花岗岩和西沟斑状二长花岗岩进行了LA-ICP-MS锆石U-Pb年龄测定,分别获得了157±1Ma(NSWD=13)和153±1Ma(NSWD=14)的谐和年龄,表明其为晚侏罗世侵入体。马河钼矿的形成与这两个侵入体密切相关,据此限定该钼矿床成矿时代略晚于157~153Ma,为侏罗世晚期成矿。桃官坪和西沟花岗岩具有高硅(68.12%~76.33%),富碱(Na₂O+K₂O=6.35%~10.38%)的特征,K₂O/Na₂O变化较大(0.91~1.89),A/CNK在0.85~1.14之间,为准铝质-弱过铝质高钾钙碱性系列。微量元素上富集U、Pb、Hf等高场强元素,亏损Rb、Ba、K、Sr、P等大离子亲石元素。稀土元素配分曲线为轻稀土相对富集的右倾型,多数具有弱的负铕异常(δEu=0.5~0.9),少数样品具有弱正铕异常(δEu=1.05~1.08)。与华北地块南缘与钼矿有关的花岗岩相比,二者均具有高硅、高钾、富碱的特征。但马河钼矿区成矿花岗岩比华北地块南缘的稍基性,这可能是导致马河钼矿的矿床规模比华北地块南缘较小的原因之一。     

Trend surface analysis of Th,U, and K,and heat production in three related granitic plutons,Farsund area,south Norway

The radioelement concentrations and their distributions in the light (biotite hornblende) Farsundite and dark (charnockitic) Farsundite suggests that they are distinct plutons and not comagmatic. The trend surfaces of radioelement concentrations, coupled with available gravity data indicates that the light Farsundite has a closer relationship to the Holum granite than to the dark Farsundite. Average radioelement concentrations for the three plutons suggests they are all part of a low heat production province which may be related to the low radioelement contents in the rocks of the Egersund area to the west.     

内蒙古济沁河林场晶洞花岗岩锆石U-Pb年龄及地球化学特征

对大兴安岭中部济沁河林场地区晶洞二长花岗岩进行了锆石U-Pb同位素年代学及地球化学研究,并对其成岩时代、成因及构造意义进行讨论.从阴极发光图像上来看,该晶洞二长花岗中锆石具有典型岩浆成因的振荡生长环带,高Th/U比值也印证了其岩浆成因.LA-ICP-MS锆石U-Pb定年结果显示,岩体形成于113.1~115.1 Ma的早白垩世晚期.二长花岗岩具有高硅、富碱的特征,Eu异常较小,弱过铝质,富集U、Th,强烈亏损P和Ti,微量元素中富集Rb、Th、La、Zr、Hf,而亏损Ba、Sr、P、Ti.上述特征表明晶洞花岗岩是高分异的I型花岗岩,其形成于华北板块、西伯利亚板块、北美板块和古太平洋板块四者汇聚之后的后碰撞伸展构造环境.     

Geophysical and radiometric studies of the Northern Units of the Leinster Intrusion

The Leinster intrusion, S.E. Ireland, is one of a group of Caledonian granites, sensu lato, of Siluro-Devonian age, which typically exhibit strong geophysical and geochemical contrasts with their host rocks. New gravity data supplement previous road-based data and define, over the Northern Units of the intrusion, a closed residual anomaly (-160 g.u.) with steep gradients. The Northern Units are shown to comprise a large volume of low-density material extending to a depth of 8 km, and hence to constitute a significant contribution to Caledonian crustal growth. The sub-surface form of the intrusion is essentially vertical-sided having no broad root, in contrast with other Siluro-Devonian granites (s.l.). Radioelement concentrations in the Northern Units were mapped quantitatively by in situ gamma-ray spectrometry. The mean concentrations of 4·2 per cent K₂O, 3·0 ppm U and 8·1 ppm Th measured are lower than those typical of the Siluro-Devonian granites (s.l.), suggesting depletion associated with high-level fractionation, and in addition a possible Th-depleted source region. Complex areal radioelement distributions reflect both the multiple intrusive event, and later secondary remobilization, particularly of U. This is demonstrated using fission-track radiography which shows that U, at least, is located in both primary and secondary minerals.     

东准噶尔贝勒库都克铝质A 型花岗岩 地球化学特征及锡矿化

本文通过对新疆东准噶尔卡拉麦里地区贝勒库都克岩体的地球化学研究,初步探讨贝勒库都克A型花岗岩与锡矿的关系。研究表明贝勒库都克黑云母花岗岩具有高硅、低铝、贫钙镁、富碱的特征,FeOt/MgO值高,富集Rb、K、Th等大离子亲石元素及Zr、Hf等高场强元素,亏损Ba、Sr、Nb、Eu等元素,Eu的负异常极强,稀土元素配分模式呈平坦的V字型,属于典型的铝质A型花岗岩。该岩体含Sn普遍都比较高,已圈出8条含锡构造蚀变带,为锡的成矿物质来源和锡矿矿床学的深入探索提供了有利的证据。     

Age of granite emplacement in the Norseman region of Western Australia

Ion probe U‐Th‐Pb dating of zircons from the Late Archaean granites of the Norseman region of the southeastern Yilgarn shows the existence of two distinct magmatic episodes. Large regional tonalite and granodiorite plutons were emplaced between 2685 and 2690 Ma, whereas large regional granite, and small tonalite and leucogranite plutons that intrude the greenstones have ages of 2660–2665 Ma. A small body of granite that intrudes the western edge of the greenstones has an inferred emplacement of 2672 ± 7Ma, and contains inherited zircon that is ～2800 Ma. The monzogranite core from a second pluton in a similar structural position also contains ～2800 Ma zircon; this age is similar to published Sm‐Nd and Rb‐Sr whole rock ages for banded gneisses associated with other members of this suite of domal plutons and is interpreted as representing the age of a significant component within the source region for these distinctive rocks.

Available geochemical and isotopic data are interpreted as indicating derivation of both the older granodiorite and younger granite suites through anatexis of pre‐existing crust of broadly andesitic composition, whereas both the domal granites and the small, late tonalite plutons could have been derived by anatexis of heterogeneous material similar to that represented by the banded gneisses.

If regional metamorphism was related to the emplacement of large volumes of felsic magma within the upper crust, as suggested by Binns et al. (1976), then the Norseman area has probably undergone two periods of regional metamorphism of comparable intensity at approximately 2660 and 2685 Ma.     

湖北麻城市四道河地区面理化含榴花岗岩的成因

野外和室内研究结果表明,四道河地区面理化含榴花岗岩由古生代沉积岩变质而成。在元素地球化学特征上,具有与岩浆成因的碱性花岗岩一致的特点:高硅(SiO2=75.24%～77.23%)、富碱(Na2O+K2O=6.87%～8.84%)、低铝(Al2O3=11.00%～12.78%);富Rb、Ba、Th、U等大离子亲石元素和Pb,贫Nb、Ta、Zr、Hf等高场强元素;稀土元素含量较高(∑REE=101.08～180.1μg/g),轻稀土元素相对富集(LREE/HREE=3.1～6.8),铕有中等负异常(δEu=0.30～0.68);锆石成因类型及定年结果表明,老核(继承锆石)是异地多时代(元古代-古生代),其寄主岩的原岩是沉积岩,时代不会早于古生代。     

滇西昌宁-孟连带三叠纪花岗岩地球化学、年代学及其意义

癞痢头山、云岭和耿马岩体位于昌宁-孟连带的中北段,主要岩性为二长花岗岩,锆石LA-ICP-MS U-Pb定年结果表明,这三个岩体几乎同期侵位于约231Ma。这三个岩体的SiO₂含量为65.65%～67.68%,富钾(K₂O/Na₂O=2.71%～1.42%)和较低钙CaO(1.35%～2.98%),铝饱和指数(A/CNK)为1.10～1.22,富集Rb、Ba、Th、U、K、La和LREE等元素,相对亏损Nb、Ta、Ti、Zr及Hf等高场强元素。这些特征表明3个岩体属于强过铝质高钾钙碱性S型花岗岩。这三个岩体负且变化范围大的锆石ε_Hf(t)值(-26.8～-8.2)和古老的Hf同位素地壳模式年龄(1.2～2.7Ga),表明它们主要来源于古老地壳物质(如含长石和黑云母且贫粘土的杂砂屑岩)的重熔,并有不同程度的幔源物质加入。它们可能侵位于后碰撞背景,可能指示缅泰马微陆块与思茅地块的主体碰撞在232Ma之前(即晚三叠世之前)已经发生。     

延边天佛指山花岗岩的形成时代及成因

延边天佛指山花岗岩年代学和地球化学研究表明,花岗岩中的锆石U-Pb年龄为(188.5±2.2)Ma,其侵位时间为早侏罗世。岩石总体上具有高硅、低铝、贫钙镁及富碱的特征,属高钾钙碱性系列I型花岗岩;富集轻稀土元素(LREE)和大离子亲石元素(LILE)Rb、Th、U、K等,相对亏损高场强元素(HFSE)Zr、Hf、Y、Yb等,显著亏损Ba、Nb、Ta、P、Ti等元素,δEu呈轻微程度负异常。该花岗岩岩浆源于地壳物质的部分熔融,可能形成于与古太平洋板块俯冲相关联的活动大陆边缘环境。     

新疆富蕴县恰库尔特—带碱性花岗岩的基本特征及形成的大地构造背景

恰库尔特一带的碱性花岗岩按侵入顺序和岩性可分为:晶洞(霓石)钾长花岗岩、(霓石)碱长花岗斑岩、霓石花岗岩.这些岩石大都含碱性暗色矿物.发育指示浅成特点的晶洞构造及文象结构,从矿物组合看岩石具贫水特征;岩石化学方面以高硅、高碱或过碱,贫铝、镁、钙为主要特征;岩石通常具有高的∑REE,其中以过碱性的霓石花岗岩为最高;轻稀土较重稀土富集,并具有强的负Eu异常;微量元素地球化学图谱表明,岩石相当于洋脊花岗岩,具有高钾、铷、钍的含量,而钡、钽、铌的富集程度相对较低.以上特征和区域构造分析表明,恰库尔特一带的碱性花岗岩为阿尔泰造山带造山作用结束以后于中晚三叠世的非造山环境下形成的A型花岗岩.     

西藏布姆松绒岩体地球化学特征及铀成矿前景

通过系统总结布姆松绒岩体的地质、地球化学特征,结合花岗岩型铀矿成矿理论及产铀花岗岩和非产铀花岗岩的判别标志,笔者认为该岩体符合产铀花岗岩的地质、地球化学特征,具有较好的铀成矿前景.其主要的找矿靶区是岩体内部的构造节点附近,找矿目标是以热液脉型为主的花岗岩型铀矿.     

华南印支期不同产铀能力花岗岩元素地球化学特征对比及其指示意义

笔者选取了华南印支期大部分花岗岩体,通过比较不同类型花岗岩的元素地球化学特征来确定产铀花岗岩的指示性特征.对比结果显示,花岗岩的源区和成因类型不同,是导致其产铀能力不同的主要因素.华南印支期产铀花岗岩的主要特征是：成岩年龄为219～250Ma,成岩温度和氧逸度低,属于S型花岗岩,其经历同碰撞的构造背景,主要分布在华夏地块内.产铀花岗岩以二云母花岗岩和黑云母花岗岩为主,蚀变作用强,副矿物组合复杂.花岗岩中结晶分异作用强,SiO2、K2O和P2O5含量高,而Al2O3、TiO2、FeO、MgO和CaO含量低,Th/U值低.这些指示性标志是指导铀矿勘查的重要线索.