滇西含锡花岗岩特征标志及判别

本文根据滇西含锡花岗岩时、空间分布规律及含锡花岗岩的岩石学、岩石化学、地球化学和同位素特征,将岩体划分为母体含锡花岗岩及非母体含锡花岗岩。并以十个典型含锡岩体和六个非含锡岩体为模型,对其进行定量判别。分别以四个氧化物指标,五个微量元素指标及八个综合指标建立三个判别式,判别岩体的含锡性,对预测和找矿具有实际意义。     

新疆辉长岩类及其含矿性

新疆辉长岩类按成因、共生组合及岩石特征划分为幔源(包括蛇绿岩类、铜镍硫化物类、层状杂岩类)、壳幔混合源(包括造山花岗岩类、变质成因类、裂谷类)、深源碱性等3个系列,再细分为7个类型,14个岩石序列.文中对各类型辉长岩的特征和含矿性进行了叙述.指出其里特曼指数、固结指数、Mg/(Fe)、Mg/Ca″、K_2O、TiO_2+P_2O_5等方面的鉴别特征.     

滇西地区S型和I型花岗岩类的岩石化学特征

花岗岩物质成分的差异,是区分不同成因类型花岗岩最本质的因素。参照B·W·Chappell和J·R·White对S型和I型花岗岩的分类方法,通过对滇西地区494件花岗岩类岩石化学分析资料的计算与统计,获得了该区S型和I型岩类的主要岩石化学指数:A1_2O_3/(K_2O+Na-2O+CaO)S型>1,I型<1;K_2O/Na_2O S型>1.2—1.3,I型<1.2—1.3;Fe~(3+)/(Fe~(3+)+Fe~(2+)) S型0.1—0.6,I型0.2—0.75;SiO_2 S型65—77％,I型56—69％。据以上标准,在已有分析资料的112个岩体中,可分出S型岩体77个,I型岩体30个。上述划分经ACF及Al—K—Na,Ca和Fe~(2+)+Mg(原子数)图解判别,其结果均基本一致。滇西地区含锡及具锡、钨矿化的岩体,都具有S型岩类固有的特征。     

福建上杭地区晚中生代花岗质岩体黑云母的地球化学特征及成因意义

用电子探针对福建省上杭地区才溪岩体、四方岩体中黑云母进行了分析.结果表明,才溪二长花岗岩中的黑云母介于高铁黑云母和高镁黑云母之间,而四方花岗闪长岩中的黑云母为高镁黑云母;在由黑云母成分确定的物质来源图上,二者均落入壳幔混源区域,表明两个岩体都是壳-幔混源型花岗岩,但才溪花岗岩中的黑云母的MF值比四方花岗闪长岩中的黑云母的MF值低,显示后者形成过程中有更多幔源物质的加入,正因如此,使其成为紫金山矿床的含矿母岩.     

伊春地区晚印支期Ⅰ型花岗岩带特征及其构造背景

晚印支期花岗岩岩石类型主要为一套含角闪石黑云母二长花岗岩及含黑云母正长花岗岩,岩石中暗色闪长质岩包体发育较普遍,富含角闪石及镁质黑云母,副矿物以榍石、磁铁矿、磷灰石常见,Al2O3/(Na2O K2O CaO)＜1.1,显示出Ⅰ型花岗岩特征.利用岩石矿物组合、岩石化学特征判别其产于碰撞后构造环境,认为造山后伸展体制是这期花岗岩形成的重要原因.岩石(87Sr/86Sr),及δEu值反映其源区为壳幔过渡区,氧同位素(δ18O)测定值在5.5‰～10‰之间,具壳幔混源的特点,表明岩石来源于下地壳或壳幔过渡部分,与下地壳的部分熔融或壳幔过渡区部分熔融作用有关.     

花岗岩成因类型划分与地球化学图解判别综述

花岗岩是出露最广的侵入岩,是研究地壳运动的主要岩石类型。花岗岩的成因类型主要有3种划分方法:S-I-M-A型、壳幔同熔型-陆壳改造型-幔源型、磁铁矿系列-钛铁矿系列。花岗岩浆活动的板块构造背景一般划分为:同碰撞花岗岩(S-COLG)、火山弧花岗岩(VAG)、洋中脊花岗岩(ORG)、板内花岗岩(WPG)。花岗岩的成因类型与板块构造环境可根据常量元素、稀土元素、微量元素进行图解判别,常用图解为R_1-R_2图解、稀土元素分配型式图、微量元素蛛网图、非活动性元素(Rb-Yb+Ta、Rb-Y+Yb、Ta-Yb、Nb-Y)系列图解。     

含锡花岗岩类包裹体特征及其在岩体成矿性评价中的应用

通过对湘桂粤赣地区主要含锡花岗岩类岩体和部分非含锡岩体矿物中包裹体各项特征的研究,提出以复杂的包裹体类型、高CO_2含量、低Cl~-/F~-摩尔比值以及流体高浓度等特征,作为成锡岩体的判别标志.     

大兴安岭中南段燕山期两类不同成矿花岗岩类角闪石的化学成分及其成岩成矿意义

大兴安岭中南段燕山期两类不同成矿花岗岩类岩体中角闪石主要为钙质角闪石。角闪石的主化学成分表明本区燕山早期早阶段与铜成矿有关的花岗岩类主要为壳幔型花岗岩：而与Sn多金属成矿有关的花岗岩类可能为壳源成因。燕山期两个不同期次不同成矿系列的花岗岩中角闪石的化学成分明显不同，燕山早期早阶段与铜成矿有关的斜长花岗斑岩其角闪石相对以富镁、硅贫铁为特征，M变化于0．24－0．54之间，平均值为0．37；燕山晚期早阶段与锡、铅、锌多金属矿化有关的花岗斑岩类岩体角闪石以富铁贫硅、镁为特征。角闪石的M为0．10－0．27，平均值为0．19。角闪石的化学成分及不同成矿岩体的微量元素和同位素特征是区分区内两类不同成矿岩体的有效判别标志。     

南岭地区加里东期花岗岩地球化学特征、岩石成因及含矿性评价

南岭地区加里东期花岗岩从岩石学上可划分为三类岩石组合,分别是石英(或英云)闪长岩-花岗闪长岩-二长花岗岩组合,以花岗闪长岩为主;花岗闪长岩-二长花岗岩组合,以二长花岗岩为主;二长花岗岩-二云母花岗岩组合,以二长花岗岩为主,分别对应于HSS型、HS型以及S型三种成因类型。地球化学上,这三类花岗岩大体上具有过铝,适度富碱(6.26%~8.06%),K2O>Na2O(比值多在1.5左右),不同程度地富集大离子亲石元素(Rb、Cs、Th、U)的共同特点。同位素组成上,三类花岗岩都表现出高ISr值和低εNd值的特性,而且εNd值还呈现出连续过渡的特征。岩石成因上,第三类花岗岩主要起源于纯陆壳变沉积岩的部分熔融;第一类花岗岩可能是壳源岩浆与幔源岩浆近等比例混合的产物;第二类花岗岩以壳源岩浆为主,但也混合了少量幔源岩浆。在含矿性评价方面,第三类岩体,尤其是越城岭、苗儿山岩体,具有较好的成钨潜力,在第二类彭公庙岩体南部和其他加里东岩体内部及接触带附近的断裂发育区,分别有一定的钨多金属矿的找矿空间。     

湖南锡田复式花岗岩体岩石学、岩石地球化学特征——兼对岩石成因类型、岩体侵位机制的探讨

锡田岩体位于南岭中西段北东向钨锡A型花岗岩带(由花山、姑婆山、九嶷山、骑田岭岩体组成)北端,主要由晚三叠世和晚侏罗世花岗岩组成。本文对锡田岩体进行了岩石学、岩石地球化学特征研究,研究表明锡田岩体为钾质、高钾质,亚碱性,过铝质的碱钙性岩石,SiO2、(K2O+Na2O)含量较高,微量元素Y富集、Ba、Sr亏损,具较低的87Sr/86Sr值、高εNd(t)值(-8)和低tDM模式年龄值等特征;在地球化学判别图解上,锡田岩体显示为A型花岗岩,其晚三叠世花岗岩侵位于印支运动的主碰撞之后,形成于碰撞后伸展构造体制下;而晚侏罗世花岗岩可能与古太平洋板块的俯冲消减引起的拉张环境有关,为后造山花岗岩。在野外地质资料的收集及详细调查的基础上,对岩体的接触关系、接触带特征、分布形态,岩体中发育的流面构造、捕虏体及其边缘向斜进行了研究,结合航片、卫片图像特征,认为锡田岩体以气球膨胀方式底辟上升侵位,而部分晚期的侵入次侵位可能受断裂的控制。     

Zircon and granite petrology

The typologic study of zircon populations from granitic rocks lead to the proposition of a genetic classification with three main divisions: (1) granites of crustal or mainly crustal origin [(sub) autochthonous and aluminous granites)]; (2) granites of crustal+mantle origin, hybrid granites (calc-alkaline and sub-alkaline series granites); (3) granites of mantle or mainly mantle origin (alkaline and tholeiitic series granites). In detail, there are many petrogenetic variants of each of the following granitic rocks: granodiorite, monzogranite and alkaline granite. The variations observed with zircon typology are accompanied petrographically by modifications of associations of other main and accessory minerals, and on the field by the presence or absence of basic microgranular xenoliths, associated microgranites, rhyolites or basic rocks. In the typologic diagram, some endogenous non granitic rocks (i.e. migmatites, tonalites, rhyolites ...) show a logical distribution with regard to different genetic stocks of granitic rocks.     

祁连山西段新元古代晚期花岗质片麻岩成因及LA-ICP-MS锆石U-Pb定年

祁连山西段吊大坂新元古代花岗质片麻岩出露于北大河岩群二云母片麻岩中。地球化学特征显示,吊大坂新元古代花岗质片麻岩主要为碱性、弱过铝质花岗岩(A/CNK=1.04~1.12)。岩石主体Rb含量较低,Sr和Ba含量高,K/Rb值介于179~225之间,说明吊大坂新元古代花岗质片麻岩不是高分异花岗岩,但明显的负Eu异常(Eu/Eu*=0.25~0.35),说明该岩浆经历了弱的分离结晶作用。在(Al_2O_3+TFe O+Mg O+Ti O_2)-Al_2O_3/(TFe O+Mg O+Ti O_2)图解中,未经历强烈分异的花岗质岩石样品点落入地壳杂砂岩或中性岩浆岩源区。未经历强烈分异的样品富集强不相容元素,并且在Y-Nb和(Y+Nb)-Rb图解中,主体落入板内花岗岩区域。吊大坂花岗质片麻岩LA-ICP-MS锆石206Pb/238U年龄为736±5Ma,该年龄被解释为花岗质片麻岩的形成时代,说明祁连山存在750~730Ma的岩浆作用记录,可能为新元古代晚期伸展背景下的产物。祁连山新元古代岩浆活动记录了新元古代早期汇聚、新元古代晚期伸展到裂解的长期演化过程。     

东昆仑祁漫塔格地区花岗岩类时空变化的构造控制——来自钾钠含量变化的证据

系统收集东昆仑祁漫塔格地区花岗岩类岩石化学数据,统一采用Collins,et al.（1982）提出的K2ONa2O分类图解法,获得各个地史时期花岗岩的成因类型。结果表明,晋宁期以S型为主,优势方位不明显。加里东期优势方位为北东向,以A型为主,北西向处于次要地位,以I型为主。海西印支期,优势方位为北西向,岩石类型在海西早、中期以I型为主,海西晚期至印支期以A型为主。此时北东向处于次要地位,岩石类型以A型为主。燕山期,整个祁漫塔格地区昆中断裂以北均为A型,以南形成新的构造岩浆岩带,岩石类型主要为I型。并且,燕山期昆中断裂以北早期以北西向为主,晚期以北东向为主。上述情况说明,至少自加里东期以来,该区花岗岩的空间展布、发育规模、成因类型等诸方面都始终受到北东向和北西向两组构造带的活动强度、力学性质交替变化的控制,并且由老到新总体上存在着由北向南逐渐迁移的变化趋势。因此,祁漫塔格岩浆岩带并非同一构造机制下形成的岩浆弧,而是由北东向和北西向两组构造岩浆活动带交替作用控制的、成因类型不同的花岗岩类共同组成的复合构造岩浆岩带。     

河南省商城埃达克质花岗岩地球化学特征及成因

河南信阳商城花岗岩体属于高钾钙碱性系列,具有岛弧花岗岩特征,其岩石地球化学具有与adakite岩相似的特征。这些岩石的SiO2含量均56%(67.32%~69.38%),Al2O3的含量除一个样品为14.92%外,其余均15%(15.03%~15.47%)、富含Na2O(3.5%~4.75%)、Na2OK2O,Na2O/K2O比值在1.1~1.4之间,具低MgO(1.10%~2.05%),低Cr(4.8×10-6~22×10-6)、Ni(1.7×10-6~5.6×10-6),具有高Sr(475.3×10-6~896.7×10-6,平均均400×10-6,平均为785.14×10-6),低Y(7.53×10-6~15.5×10-6,平均10.3×10-6,18×10-6),Sr/Y值40(平均84.4)、低Yb(0.58×10-6~1.55×10-6,平均0.87×10-6,1.8×10-6)。该花岗岩体在稀土元素配分曲线图上具有弱Eu负异常,稀土元素分异强烈,属轻稀土富集重稀土亏损;在微量元素蛛网图上具Ba、Sr正异常,而Nb、Ta的负异常较为明显。岩石类型为石英二长岩,花岗闪长岩、花岗岩。矿物成分以更长石、正长石、镁质黑云母、石英为主,副矿物为磁铁矿+榍石-锆石+磷灰石组合,富含暗色闪长质包体,属I型花岗岩类。表明商城埃达克质花岗岩形成可能与增厚下地壳熔融有关。     

西秦岭大水金矿的花岗岩成矿作用特征

西秦岭大水金矿是西秦岭造山带南缘三叠系浅海相碳酸盐岩中新近发现的一类独特的特大型金矿床。矿区侵入岩属花岗岩大类 ,δ <4,ASI >1,属中性—中偏基性过铝质钙碱系列岩石 ,具深源浅成的特征。岩石化学成分δ τ图解以及稀土元素的w(Rb) w (Yb +Nb)和w(Rb) w(Yb +Ta)图解显示其属造山带同碰撞构造环境。金矿石的碳、氢、氧、硅同位素测试结果显示成矿物质来源于深部。矿石为轻稀土富集型 ,配分模式与岩浆岩接近。全岩K Ar同位素年龄表明格尔括合岩体为 190 0～ 190 5Ma ,矿化脉岩为 182 6～ 184 7Ma ,说明成岩与成矿具同源性但主成矿期滞后于脉岩的形成。花岗岩的成矿作用主要体现为 :( 1)沟通深部矿源场和成矿场 ;( 2 )岩浆高热能和岩浆水参与成矿流体的循环 ;( 3)花岗岩的就位机制为“气球膨胀”式 ,并通过就位扩容压缩围岩产生的张性断裂构造控制金矿体的产出。     

湘东北构造活化期花岗岩形成构造环境及成因

华南大陆从印支期进入陆内活化阶段,形成一系列沿断裂分布的印支期花岗岩。该期花岗岩代表陆内活化期的开始,在岩石地球化学和形成构造环境上以及岩石的形成方式上都与该期以后的花岗质岩石存在一定的差异。表明华南中生代陆内活化构造环境的复杂性和多阶段性。本文以湘东北印支期花岗质侵入岩为例,分析其成岩构造环境,用以反映该区陆内开始活化时的构造环境和活化方式。湘东北印支期花岗质岩石以花岗闪长岩-二长花岗岩岩石系列为主,以相对较低的SiO2、K2O和较高的TiO2、P2O5及负铕异常不明显区别于中生代其它侵入期次岩石,具有陆壳重熔型花岗岩特征,其形成为陆内俯冲导致陆壳物质在俯冲前缘重熔的结果,表明陆内俯冲作用是导致湘东北陆内开始活化的主要方式之一,其构造环境以逆冲式推覆挤压为主。     

Oxygen-isotope systematics of a strongly recrystallized granitic rock complex,Grenvillian Belt,SW Sweden

In the eastern, external part of the Grenvillian Belt in SW Sweden, five formations of granitic rocks were found in the basement of the Dalslandian Supracrustal Group. The granitic rocks have been strongly recrystallized but have preserved most of their granitic texture in the process. Most magmatic crystals have been pseudomorphed by metamorphic minerals: quartz, albite, chlorite, biotite, white mica, epidote, titanite, hematite, pyrite and carbonate. Two of the formations have subsequently been affected by a cataclastic deformation and at present consist of mylogneisses. ¹⁸O whole-rock values for the granitic rocks vary from +3.0 to +11.1. Quartz-apatite, quartz-zircon and quartz-titanite pairs show ¹⁸O/¹⁶O fractionations corresponding to equilibrium temperatures of 550–700° C, which are believed to reflect in the main continued closed-system isotopic exchange at high temperatures following solidification. In contrast highly positive ¹⁸O/¹⁶O fractionations for quartz-K-feldspar, quartz-biotite, quartz-chlorite and quartz-sericite pairs in some granitic samples indicate that these rocks have exchanged oxygen with heated, meteoric, H₂O dominated fluids. Other granitic samples, however, show virtually undisturbed magmatic ¹⁸O/¹⁶O fractionation values for the same mineral pairs, even though these rocks are equally altered.It is concluded that all granitic rock units recrystallized under greenschist facies conditions during the infiltration of fluids under the influence of hydrothermal convection systems set up by the intrusion of the granitic plutons. The fluids probably had a range of ¹⁸O values from ca. -14 to ca. +10, indicating the mixing of distinct fluid reservoirs, one of meteoric origin and the others of magmatic and/or metamorphic origin. The temperature of alteration is estimated at 450–500° C.Estimation of pre-alteration ¹⁸O whole rock values for the five granitic units suggests that three units should be assigned a dominantly S-type origin, where as the other two units may partly or wholly have an I-type origin.     

Zinc-lead skarn deposits at Leadville, New South Wales, Australia, and their distinction from volcanic-hosted massive sulphides

Exploration of Zn-rich sulphide deposits at Leadville, northern Lachlan Fold Belt, New South Wales, for over two decades has been largely on the premise that the mineralisation represents felsic volcanic-hosted massive sulphides (VHMS). Deposits are hosted by ?Silurian felsic metavolcanic, psammopelitic and calcareous metasedimentary rocks which have been intruded by the late Carboniferous I-type Gulgong Granite. Evidence for an epigenetic replacement (skarn) origin of the deposits, rather than representing metamorphosed volcanogenic massive sulphides, includes the proximity of evolved granitic intrusives and reactive carbonate rocks, a skarn mineral assemblage (with characteristic prograde and retrograde stages), lack of textural or lithological indications of an exhalative origin, and gossan and sulphide compositions consistent with Zn-Pb skarns and atypical of Lachlan Fold Belt VHMS deposits. Furthermore, sulphide lead isotope ratios are significantly more radiogenic than signatures for VHMS deposits in the Lachlan Fold Belt. Carbonate δ¹³C and δ¹⁸O and sulphide δ³⁴S values are consistent with the interaction of magmatic hydrothermal fluids with Palaeozoic carbonate rocks and a largely magmatic source of sulphur. It is concluded that the Leadville deposits are of skarn type, genetically related to the Gulgong Granite.     

Moon—An albite depleted giant Skaergaard?

The chemical composition of 2188 terrestrial igneous rocks ranging from ultrabasic to granitic composition was analyzed statistically using the method of factor analysis (principal components). The resultant first and second factors were: $$\begin{gathered} {\text{ }}F_1 = 0.933{\text{ Na}}_{\text{2}} {\text{O + 0}}{\text{.143 SiO}}_{\text{2}} + 0.206{\text{ K}}_{\text{2}} {\text{O}} - 0.346{\text{ CaO}} - 0.263{\text{ MgO}} - \hfill \\ .203{\text{ FeO}} \pm \cdot \cdot \cdot \hfill \\ {\text{ }}F_2 = 0.979{\text{ Al}}_{\text{2}} {\text{O}}_{\text{3}} - 0.269{\text{ MgO}} - 0.151{\text{ SiO}}_{\text{2}} - 0.112{\text{ FeO}} \pm \cdot \cdot \cdot \hfill \\ \end{gathered} $$ where oxides are in weight percent. A plot of the first factor against the second results in a useful igneous variation diagram. When the compositions of the 2188 terrestrial rocks and 604 lunar rocks are plotted on this diagram, the two groups of rocks are clearly separated within an albite-anorthite-forsterite-fayalite-quartz polygon. None of the terrestrial differentiation trends are significant for lunar rocks. The major difference in the chemistry of lunar and terrestrial rocks lies in the former being albite poor. Removal of most of the albite from the compositions of terrestrial layered intrusives such as the Skaergaard results in an excellent match between the compositions of the two groups of rocks. Albite subtracted compositions of Skaergaard rocks in particular cover the entire range of chemical variation in the lunar rocks. The statistical results prompt us to speculate further on the similarity of the moon and Skaergaard. We note that the average composition of the moon (Wanke et al., 1974) is similar to the albite subtracted composition of the Skaergaard magma. The lunar crust and a significant part of the lunar interior may match the albite subtracted and somewhat Mg enriched Skaergaard magma.     

徐宿地区新元古代辉绿岩床的地球化学特征

同位素测年数据显示,徐宿地区的辉绿岩床是震旦纪早期和震旦纪晚期两次侵入的 产物。岩床多呈板状或楔状,为超浅成—浅成侵入体,其化学成分以高SiO2、CaO和低Al 2O3、MgO及(K2O+Na2O)为特征,属大陆拉斑玄武岩系列。稀土元素配分模式为轻 稀土富集型,但稀土元素分馏并不强烈。Rb、K、La等不相容元素富集,而Nb、Sr亏损明显 。δ18O值在6.63‰～9.93‰之间,多数>8‰。研究表明,该区基性岩浆来源于过 渡型地幔,主要通过部分熔融方式形成,在岩浆上侵过程中遭到陆壳或花岗质岩石的混染。