甘肃干沙鄂博稀土矿床熔体和流体包裹体对成矿的制约

甘肃天祝干沙鄂博稀土矿床产于霓辉正长岩和霓辉正长斑岩中,矿体形态呈不规则脉状、透镜状和板状。成矿过程可分为岩浆期、岩浆-热液期、热液期和表生期,其中岩浆-热液期为主要成矿期。本矿床中的包裹体有熔体包裹体、流体-熔体包裹体、H_2O包裹体、CO_2包裹体、CO_2-H_2O包裹体、含子矿物H_2O包裹体和含子矿物CO_2-H_2O包裹体7类,并以富含流体-熔体包裹体、CO_2-H_2O包裹体为显著特征。包裹体组合从熔体包裹体→流体-熔体包裹体、H_2O包裹体、CO_2包裹体和CO_2-H_2O包裹体→H_2O包裹体的变化,反映本矿床的形成经历了从岩浆→岩浆+热液→热液的演化过程。岩浆期熔体包裹体均一温度为780℃;岩浆-热液期均一温度为191~700℃,盐度为5.26%~22.24%,属中低盐度,成矿压力为68~95 MPa,相应的成矿深度为2.6~3.6 km;热液期均一温度为129~225℃,盐度为0.35%~7.73%,为低盐度。从岩浆期到岩浆-热液期再到热液期,温度逐渐降低,矿化作用主要发生在岩浆-热液期,属中高温、中深成岩浆-热液过渡型矿床。     

岩浆到热液演化的包裹体记录——以骑田岭花岗岩体为例

骑田岭花岗岩是燕山期花岗岩早期多阶段侵入复式岩体,岩石化学的研究表明它是富碱的、高分异的A型花岗岩,形成于板内拉张的构造环境。在其第二阶段中细粒黑云母花岗岩内广泛发育着厘米级至米级似伟晶岩囊状体和石英晶洞, 它们是富挥发份岩浆固结的产物,代表岩石形成过程经历了明显的岩浆-热液过渡阶段。包裹体显微岩相学研究在骑田岭黑云母花岗岩的石英中发现熔体-流体包裹体和流体包裹体共存,这一结果进一步证实骑田岭中细粒黑云母花岗岩中的似伟晶岩囊状体和石英晶洞是花岗质熔体在岩浆-热液过渡阶段的产物。显微测温结果显示,熔体-流体包裹体的捕获温度大于530℃,说明岩浆热液过渡阶段的温度不低于该温度;闪锌矿中流体包裹体的均一温度在285~417℃之间,盐度为11.7% NaCleqv,代表了成矿流体的温度和盐度;流体包裹体的均一温度为172~454℃,代表热液阶段流体的温度。从中细粒黑云母花岗岩到似伟晶岩囊状体再到石英晶洞,岩浆-热液体系经历了富挥份熔体→熔体+高盐度流体→高盐度流体→低盐度流体的完整演化过程,形成了CaCl₂-NaCl-H₂O-CO₂体系的岩浆热液流体。包裹体岩相学及激光拉曼探针分析结果显示,在流体包裹体和多晶熔体-流体包裹体中含有长石、方解石、金红石及金属氧化物等子矿物,暗示其所捕获的流体具有较强的成矿能力。     

萤石中流体-熔融包裹体的研究

在四川冕宁稀土矿床霓辉重晶石伟晶岩型矿体早期萤石中笔者发现了大量的流体-熔融包裹体。矿物的光学性质及激光拉曼光谱特征表明,流体-溶融包裹体内晶体矿物为重晶石。萤石中流体-熔融包裹体的“均一化”温度为493.7—502.3℃,其捕获温度更高,这说明主矿物萤石的形成温度很高,笔者认为这类萤石是由富含挥发分,以氟化钙、硫酸钡为主要成分的盐熔体直接结晶而成的,即该类萤石以及与之共生的重晶石具有岩浆成因的特征。     

巴尔哲超大型稀有稀土矿床富晶体的流体包裹体初步研究

巴尔哲矿床是一个超大型稀有稀土多金属矿床,它受巴尔哲碱性花岗岩体（株）控制,稀有稀土矿体分布在巴尔哲岩体上部的钠长石碱性花岗岩中。本文在钠长石碱性花岗岩的石英中发现了大量的富晶体的流体包裹体,并对其进行了初步的激光拉曼光谱和显微测温研究。与一般含盐类晶体矿物的三相流体包裹体不同,巴尔哲富晶体的流体包裹体的晶体不是盐类矿物,而是长石、云母等硅酸盐矿物;同时,该类包裹体内还广泛分布着稀土碳酸盐矿物。富晶体的流体包裹体的发现从微观角度揭示了巴尔哲含矿钠长石碱性花岗岩的形成与岩浆-热液过渡阶段有直接的成因联系,并为阐述巴尔哲岩体稀土元素及氧同位素的地球化学特征提供了新思路。稀土碳酸盐矿物在富晶体的流体包裹体中广泛地分布则充分说明。巴尔哲碱性花岗岩演化到岩浆-热液过渡阶段体系内的稀土元素已经达到足以形成独立稀土矿物的富集程度,其稀土元素矿化受岩浆-热液过渡阶段的制约。     

Linkam热台与热液金刚石压腔的熔体包裹体均一实验对比研究

熔体包裹体均一实验是利用熔体包裹体研究原始岩浆演化和挥发分组成的基础。目前,开展包裹体均一温度实验的设备主要为Linkam系列的高温热台,而热液金刚石压腔(HDAC)是近年来才被应用到熔体包裹体均一实验中的。文章以义兴寨金矿床石英斑岩为例,对比研究了Linkam TS1500高温热台和HDAC在熔体包裹体均一实验应用中的优劣。利用Linkam TS1500高温热台得出熔体包裹体的均一温度范围为943~1190℃,而HDAC的测试结果为780~890℃。实验研究表明:HDAC能够在加热的同时提供接近熔体捕获条件的外压,更适于开展富挥发分的高内压熔体包裹体的均一实验。实验过程中得到的熔体包裹体固相初熔温度范围,可为估算义兴寨金矿床石英斑岩原始岩浆晚期结晶的压力提供依据。     

熔体包裹体挥发分应用的研究进展

挥发分(例如H2O、CO2、F、Cl和S)是地幔的重要组成部分,虽然它们在地幔中的含量很低,但是在地幔熔融和熔体演化、地幔不均一、地幔流变学、地幔地震特性和电导率等研究方面具有重要作用。对矿物熔体包裹体和玻璃挥发分的研究已经成为当前的研究热点。其中,熔体包裹体研究凭借其独特的优势成为研究地幔和岩浆挥发分组成的重要手段。熔体包裹体直接捕获了矿物形成时岩浆中的成分,且由于寄主矿物的存在使得熔体包裹体能够保持独立演化而不受外界环境影响,因此能够较为完整地保存岩浆中的挥发分信息。同时,研究熔体包裹体中的挥发分是恢复岩浆喷发前挥发分含量最直接的途径。如果通过现代分析方法(如扫描电镜、电子探针和离子探针等)对熔体包裹体进行详细的岩相学观察以及对后期可能影响熔体包裹体原始挥发组分的作用(地壳混染、岩浆去气、扩散和水化作用)进行评估,并结合实验研究熔体包裹体被捕获后发生的变化而对数据进行矫正,那熔体包裹体对研究岩浆体系中的挥发分将大有可为。基于此,本文系统介绍了熔体包裹体挥发分研究的现状及主要研究内容,主要包括熔体包裹体挥发分的测试方法、挥发分在岩浆中的溶解度、判断挥发分数据可靠性和挥发分研究的经典应用等4个方面。     

单矿物中熔体包裹体研究进展及地质指示意义

熔体包裹体是矿物在生长过程中捕获的原始岩浆,能有效的保留大量主矿物结晶和周围岩浆介质的物理化学信息,是岩浆演化和成矿过程的良好指示刺.文章从熔体包裹体在主矿物中的赋存状态,均一化试验和测试技术等方面总结了目前的研究进展,并结合具体的矿床揭示熔体包裹体对岩浆和成矿方面的指示意义.同时笔者也建议,将熔体包裹体信息和岩石学、地球化学、找矿学联系起来,可以加深对岩浆演化过程的了解程度,提高勘查找矿的效果.熔体包裹体作为一种较新的微区分析对象具有十分广阔的应用前景.     

岩浆岩中的熔体包裹体

熔体包裹体是岩浆岩矿物生长过程中捕获的天然岩浆珠滴 ,它们有效地保存了大量有关其主矿物形成时周围岩浆介质的物理化学信息 ,所以它们是其主矿物结晶演化史的忠实记录员 ,它们能够提供岩浆系统成分和演化的重要信息。文中对熔体包裹体研究的若干基本原理进行了讨论 ,它们涉及 :(1)熔体包裹体的一般特征 ;(2 )熔体包裹体封闭过程中和封闭后的演化 ;(3)熔体包裹体的均一化研究 ;(4 )熔体包裹体化学成分和挥发组分研究。熔体包裹体研究可以对岩浆岩石学中的一些重要问题进行更为深入的探索 :(1)重建天然岩浆结晶演化的热历史 ;(2 )提供有关岩浆沿下降液相线的成分数据 ;(3)查明天然岩浆结晶演化过程中化学成分的变迁规律 ;(4 )解决岩浆岩石学中的一些疑难问题 ,如岩浆不混溶作用、岩浆混合作用、岩浆混染作用、岩浆中硫的性状、地幔部分熔融和地幔交代作用等方面的问题。将熔体包裹体数据和常规的岩石学、地球化学和实验岩石学信息综合一体 ,可以提高我们模拟岩浆作用过程的能力。熔体包裹体研究已经成为现代岩浆岩石学的一个独立的分支 ,其前景十分广阔。     

福建永定大坪铌钽矿化花岗斑岩体的流体演化对铌钽富集的制约

福建永定大坪铌钽矿化花岗斑岩体位于永定县城南部的大石凹-蓝地火山喷发盆地,对斑岩型铌钽矿床的产出具有重要的指示意义。本文通过岩相学、显微测温和激光拉曼等实验对大坪岩体ZK10001和ZK10401钻孔不同深度岩石样品中的流体和熔体包裹体进行了研究,试图揭示岩体的熔体-流体演化过程,分析铌钽等成矿元素的富集机制。观测结果表明,大坪岩体主要发育气液两相盐水溶液包裹体和硅酸盐熔体包裹体。流体包裹体均一温度集中在175～225℃,盐度集中在3%～7%NaCleq,密度集中在0.75～0.95g/cm~3,成矿流体主要为中低温、低盐度和低密度的流体,总体属于H_2O-NaCl体系。熔体包裹体主要分布于石英斑晶雪球结构的环带中,含有钠长石、石英和钽铁矿等子矿物。熔体包裹体完全均一温度较高,能够代表早期原始岩浆的组成。研究表明,大坪岩体的原始岩浆富铌钽等成矿元素和碱性组分,大坪岩体的铌钽矿化是岩浆高度分异的产物,铌钽的富集过程经历了斑晶阶段和基质阶段等两阶段结晶分异过程:在早期斑晶结晶阶段,少量铌钽矿物与斑晶一起结晶,并被斑晶包裹;岩浆演化晚期发生流体出溶现象,但未分异出大量流体,F等挥发分促进了铌钽在结晶残余熔体中富集,并在基质间隙中沉淀。大坪矿化岩体的存在指示出斑岩型铌钽矿床存在的可能性。     

黑龙江乌拉嘎金矿的次火山岩浆-热液成矿:熔体-流体包裹体证据

黑龙江乌拉嘎金矿是我国陆相火山岩区的重要金矿之一。构造位置处于古亚洲构造域与滨太平洋构造域交接复合部位的东北缘,矿体主要分布于团结沟斜长花岗斑岩接触带部位的隐爆角砾岩带和黑龙江群变质岩的层间裂隙中。斜长花岗斑岩的石英斑晶中发育3类包裹体:熔体包裹体、原生的L-V包裹体(及少量的L-V-S包裹体)和次生的L-V包裹体。玻璃质熔体包裹体相当于酸性殘浆的成分(SiO2达69.5%～73.8%),其捕获温度大于800℃。石英斑晶中次生L-V包裹体均一温度集中在210～350℃、盐度5%～7%NaCleqv,代表了次火山岩浆热液的特征,与黄铁矿-早期白色玉髓状石英阶段中Q1的包裹体均一温度范围很接近,而盐度略高于白色玉髓状石英Q1的。乌拉嘎金矿的金成矿可划分3个成矿阶段,发育盐水溶液包裹体:(1)黄铁矿-早期白色玉髓状石英阶段,包裹体均一温度为154～355℃,集中在190～330℃,盐度为1.3%～8.2%NaCleqv,密度为0.53～0.88g/cm3。(2)烟灰色玉髓状石英-多金属硫化物阶段,石英中包裹体均一温度为159～196℃,集中在170～190℃,盐度为2.2%～3.2%NaCleqv,密度0.79～0.92g/cm3。(3)碳酸盐-石英阶段,方解石中包裹体均一温度集中在170～270℃;盐度0.5%～2.9%NaCleqv。成矿流体以中低温、低盐度、贫CO2的盐水体系为特征,与国内外陆相火山-次火山热液矿床十分相似。石英斑晶中熔体、流体包裹体及其共存反映了次火山岩浆活动晚期,由硅酸盐熔体通过不混溶产生含矿的盐水溶液的可能,说明了金成矿与斑岩的成因联系,乌拉嘎金矿应该属于陆相火山-次火山活动有关的中低温浅成热液金矿床。     

Immiscibility of high salinity fluids in volcanic rocks and the mechanism of magma degassing in the Dongying sag, eastern China

Fluid inclusions that bear halite daughter minerals were discovered in volcanic rocks at Pingnan area in the Dongying sag. The samples of the fluid inclusions collected from the BGX-15 well drill cores are hosted in quartz of diorite-porphyrite. The daughter minerals are identified as NaCl crystals after being observed under a microscope and analyzed by in situ Raman spectroscopy at −185°C. The results of micro-thermal analysis show that the homogenization temperatures of primary fluid inclusions are between 359 and 496°C, and the salinities of fluid inclusions are from 43.26 to 54.51 wt-%. All fluid inclusions in the studied samples can be divided into five types including primary fluid inclusions and secondary fluid inclusions. The fact that five types of fluid inclusions were symbiotic in the same quartz grain implies that immiscibility happened in magma. Due to the decrease in temperature and pressure during the ascent of magma, the fluids became intensively immiscible. This process accelerates the degassing of CO₂ from magma, but the remnant fluids with high salinity are preserved in fluid inclusions. Thus, the primary fluid inclusions are mainly in NaCl-H₂O fluids and poor in CO₂. The results of our study indicate that the degassing of magma and accumulation of CO₂ gas at the Pingnan area are relative to the immiscibility of high salinity fluids. This discovery is important because it can help us have a further understanding of the mechanism of magma degassing and accumulation of the inorganic CO₂ in eastern China. Translated from Acta Geologica Sinica, 2006, 80(11): 1699–1705 [译自: 地质学报]     

Melt inclusions in basalts of Ross Island area,Antarctica

There are many melt and fluid inclusions (mainly CO₂-rich) in olivine and pyroxene phenocrysts in basalts from the Ross Island area. The melt inclusions can be classified as follows: (1) crystalline melt inclusions (type I), (2) fluid-melt inclusions (type II) and (3) glass inclusions (type III). The daughter minerals in type I include olivine, plagioclase, ilmenite, etc. Fluid-melt inclusions are a new type which represent the immiscibility of magma and fluid at a particular stage of evolution. Three types of fluid-melt inclusions were examined in this study: a) crystal + liquid + gas, b) inclusions coexisting with glass inclusions and fluid inclusions, and c) crystal + daughter mineral (dissolved salt) + gas. Both primary and secondary melt inclusions are recognizable in the samples. The secondary melt inclusions were formed during healing of fractures in the host minerals in the process of magma rise. The homogenization temperatures (both Leitz 1350 stage and quench method were used) of melt inclusions in basalts range from 1190 to 135°C at high pressure (about 7 kbars), indicating that the basalts may have come from the upper mantle. Melt-fluid immiscibility in basaltic magma shows that the CO₂-rich fluids may be the main fluid phase in the upper mantle, which are of significance in understanding the evolution of magma and various processes in the deep levels of the earth. The homogenization temperatures of melt and aqueous fluid inclusions in granites and metamorphic rocks in this area vary from 980 to 1100°C and 279 to 350°C, respectively.     

Corundum from basaltic terrains: a mineral inclusion approach to the enigma

 This paper investigates the origin of corundum megacrysts that occur in many basaltic terrains, and which are considered to be eroded from basaltic rocks. Geochemical data for over 80 primary mineral inclusions within corundum megacrysts are used to gain a new insight into the petrogenetic history of the corundum megacrysts. A wide spectrum of minerals is present as inclusions in the corundum; the most common are Nb−Ta oxides (such as titaniferous columbite and uranpyrochlore), alkali feldspar, low-Ca plagioclase (albite-oligoclase) and zircon. Rare inclusions include Fe,Cu-sulphide (low in Ni), cobalt-rich spinel, Th,Ce-rich phosphate and uraninite. The similar chemistry of some inclusion minerals from corundum occurring in widely separated areas suggests that the corundum megacrysts in basalts have a similar petrogenesis. Geochemical characteristics of the inclusions indicate a bimodal grouping, which is best explained by a mixing-hybridisation process. This study indicates that the corundum megacrysts are not cogenetic with their basaltic hosts but are crustal fragments accidentally incorporated into the erupting magma. It is suggested that interactions between a silicic component and an intruding carbonatitic or similar Si-poor magma is responsible for Al-oversaturation, resulting in locally distributed lenses of corundum-bearing rock of mixed paragenesis (“hybrid rock hypothesis”). Feldspar exsolution textures provide strong evidence that this hybridisation occurred at mid-crustal levels. Subsequent volcanic eruptions brought the corundum-bearing rocks (later disintegrated in the magma) up to the Earth's surface. This petrogenetic model for corundum megacrysts is experimentally testable. Received: 15 March 1995 / Accepted: 30 June 1995     

Crystallization conditions of the alkaline-basic dike from the Yllymakh Massif,Central Aldan: Evidence from melt inclusion data in minerals

Alkaline-basic dike from the Yllymakh Massif (Central Aldan) has been studied. Its partially crystallized matrix contains corroded phenocrysts of olivine and hypidiomorphic phenocrysts of clinopyroxene and pseudo-, epileucite. It was found that phenocrysts of clinopyroxene contain abundant primary inclusions, Ti-magnetite and apatite bear only single inclusions, whereas olivine is enriched in secondary inclusions, which are confined to the cleavage of host mineral (along second and third pinacoids) and its cracks. The homogenization temperatures of the primary inclusions in clinopyroxene and secondary inclusions in olivine are approximately equal and lie within 1260–1240°C. The compositions of melt inclusions in olivine and clinopyroxene are also similar and corresponded to the malignite-pseudoleucite phonolite-monzonite pulaskites, which are developed at the Yllymakh Massif. Unheated inclusions in apatite and Ti-magnetite compositionally approach monzonites and nepheline syenites—tinguaites, respectively. It was concluded that the alkaline basaltoid magma was presumably parental magma for the entire rock complex of the Yllymakh Massif. Its crystallization and differentiation presumably provided all observed rock variety from ultrabasics (early derivatives located at depth) and malignites (later derivatives) to leucite phonolites, monzonites, and alkaline pulaskites, which were obtained during subsequent stages of the melt evolution. The parental magma, and especially its derivatives, were enriched in BaO (0.8–0.1 wt %), Cl (0.1–0.3 wt %) and trace elements (primarily, LREE and MREE), which are several times higher than mantle values. At the same time, ion microprobe (SIMS) study showed that derivative melts were dry: contained only 0.01–1.13 wt % H₂O. The trend of melts conserved in the minerals and the massif rocks corresponds to the evolution of alkalinebasaltoid magma with increase in Si, Al, alkalis and decrease in Mg, Ca, and Fe, i.e. the Bowen trend. The considered alkaline-basic dike was presumably formed from the derivative of leucite-phonolite melt, which during emplacement captured olivine xenocrysts from previously fractionated ultrabasic rocks. The parental magma was presumably derived by high-degree melting of garnet-spinel-facies depleted mantle at some influence of crustal material.     

Rare Earth and Rare Metal Elements Mobility and Mineralization During Magmatic and Fluid Evolution in Alkaline Granite System: Evidence from Fluid and Melt Inclusions in Baerzhe Granite,China

Baerzhe Be–Nb–Zr–REE deposit is hosted in alkaline granite (125 Ma) which intrudes in the late Jurassic Baiyingaolao Formation in the middle of the Great Hinggan Metallogenic Belt in China. The ore‐forming granite consists of three lithological facies: arfvedsonite‐bearing alkaline granite at the bottom, aegirine‐bearing albite aplite in the middle and pegmatite crust on the top. The albite aplite is the main orebody. We recognized three magmatic‐hydrothermal stages: orthomagmatic stage, late‐magmatic stage and hydrothermal stage, with the late‐magmatic stage being divided into two substages, the pegmatite substage and the aplite substage. Petrographic study on the granite, the microthermometric study on fluid inclusions and in situ laser‐ablation inductively coupled plasma mass spectrometry analysis for quartz‐hosted melt inclusions reveal the process of magmatic‐hydrothermal evolution. The finding indicates that primary magma evolved to more peralkaline by fractional crystallization, with synchronously increasing high field strength elements. An extremely high content of Zr and Nb are in the melt inclusions from last stage albite aplite (Zr, min 52 548 ppm, and Nb, min 4104 ppm). This implies that the residual magma directly formed the orebody of rare metal elements. Meanwhile, volatility was increasing during the magma evolution process and F‐bearing aqueous fluid was oversaturated at temperatures higher than 800°C. The separation of fluid from magma caused Li‐REE enrichment in F‐bearing fluid and depletion in residual melt, and led to the difference of the Y/Ho ratio between whole rock compositions and melt inclusion data. Fluid separated into a high‐salinity liquid and a low density vapor phase above 697°C, and enriched REE in the high‐salinity liquid. The oxygen isotope data shows mixing between primary magmatic‐hydrothermal fluid and meteoric water. The ubiquitous pseudo‐secondary fluid inclusions have a wide range of salinity below 462°C, which is similar to the melting temperatures of REE‐bearing daughter minerals. A model involving the mixing by meteoric water could be a mechanism for precipitation of REE minerals.     

川西甲基卡花岗伟晶岩型锂矿床中熔体、流体包裹体固相物质研究

川西甲基卡二云母花岗岩和伟晶岩内发育大量原生熔体包裹体和富晶体流体包裹体。为了查明甲基卡成矿熔体、流体性质与演化特征,运用激光拉曼光谱和扫描电镜鉴定了甲基卡花岗伟晶岩型锂矿床中二云母花岗岩及伟晶岩脉不同结构带内的原生熔体、流体包裹体的固相物质。分析结果表明,甲基卡二云母花岗岩石英内熔体包裹体的矿物组合为磷灰石+白云母、白云母+钠长石、白云母+石墨;伟晶岩绿柱石内富晶体流体包裹体的矿物组合主要为刚玉、富铝铁硅酸盐+刚玉+锂辉石、锂辉石+石英+锂绿泥石;伟晶岩锂辉石内富晶体流体包裹体的矿物组合主要为磷灰石、锡石、磁铁矿、石英+钠长石+锂绿泥石、萤石、富钙镁硅酸盐+富铁铝硅酸盐+富铁硅酸盐+石英;花岗岩浆熔体与伟晶岩浆熔体(流体)具有一定的差异,成矿熔体、流体成分总体呈现出碱质元素(Na、Si、Al)、挥发分(F、P、CO_2)含量增高及基性元素(Fe、Mg、Ca)降低的特征;包裹体中子矿物与主矿物的化学成分具有一定的差别,揭示出伟晶岩熔体(流体)存在局部岩浆分异作用,具不混溶性及非均匀性。因此认为,伟晶岩熔浆(流体)为岩浆分异与岩浆不混溶共同作用的产物,挥发分含量的增高(F、P、CO_2)使伟晶岩能够与稀有金属组成各类络合物或化合物,这对于稀有金属成矿起到了至关重要的作用。     

Compositions of magmas and carbonate–silicate liquid immiscibility in the Vulture alkaline igneous complex, Italy

This paper presents a study of melt and fluid inclusions in minerals of an olivine-leucite phonolitic nephelinite bomb from the Monticchio Lake Formation, Vulture. The rock contains 50 vol.% clinopyroxene, 12% leucite, 10% alkali feldspars, 8% hauyne/sodalite, 7.5% nepheline, 4.5% apatite, 3.2% olivine, 2% opaques, 2.6% plagioclase, and < 1% amphibole. We distinguished three generations of clinopyroxene differing in composition and morphology. All the phenocrysts bear primary and secondary melt and fluid inclusions, which recorded successive stages of melt evolution. The most primitive melts were found in the most magnesian olivine and the earliest clinopyroxene phenocrysts. The melts are near primary mantle liquids and are rich in Ca, Mg and incompatible and volatile elements. Thermometric experiments with the melt inclusions suggested that melt crystallization began at temperatures of about 1200 °C. Because of the partial leakage of all primary fluid inclusions, the pressure of crystallization is constrained only to minimum of 3.5 kbar. Combined silicate–carbonate melt inclusions were found in apatite phenocrysts. They are indicative of carbonate–silicate liquid immiscibility, which occurred during magma evolution. Large hydrous secondary melt inclusions were found in olivine and clinopyroxene. The inclusions in the phenocrysts recorded an open-system magma evolution during its rise towards the surface including crystallization, degassing, oxidation, and liquid immiscibility processes.     

岩浆包裹体的成因和意义

本文从下述六个方面对岩浆包裹体的研究状况及意义进行评述:1.岩浆包裹体的形成机制和分类;2.岩浆包裹体的测温研究;3.岩浆包裹体的测压研究;4.岩浆包裹体的化学成分;5.利用岩浆包裹体进行实验岩石-矿物学研究:6.岩浆包裹体可做为矿化作用指示剂。虽然有几类异常岩浆包裹体(特别是在月岩样品中)还无法加以解释,但是。岩浆包裹体可以提供大量有关岩浆结晶演化、岩浆不混溶作用、岩浆混合作用、火成侵位时挥发组分的含量、性状及演化、玄武岩浆起源、以及岩浆岩体的潜在含矿标志等重要情报。其中有些资料,从其它来源无法获得。岩浆包裹体研究已经成为现代火成岩石学的一个不可缺少的独立分支,其前景十分广阔。     

岩浆包裹体化学成分研究

岩浆包裹体化学成分研究难度较大,为了获得可信的数据,应当注意:1.非演化型岩浆包裹体的化学成分可以代表其初始成分。演化型岩浆包裹体应先均一、淬火后再行测定。2.均一演化型岩浆包裹体应严格遵守加热规则,否则过热作用会使包裹体壁部分熔化,造成淬火后所测包裹体成分与其真正的初始成分并不相当。3.实测资料证明,“边界层效应”对于岩浆包裹体化学成分影响微不足道。4.岩浆包裹体的化学成分只能代表其主矿物结晶时周围岩浆的成分,即仅相当于岩浆液相线上的一个点。5。把显微冷热台测温、激光喇曼探针和电子探针分析技术结合使用,对查明单个包裹体中挥发组分的性状和浓度具有很大的潜力和前途。     

西藏甲玛铜多金属矿床成因研究——来自流体包裹体的证据

甲玛铜多金属矿床位于西藏冈底斯斑岩铜矿带东段,是近年来勘探发现的超大型斑岩-矽卡岩型铜多金属矿床。通过冷热台显微观察与测温、扫描电镜、激光拉曼探针测试,对甲玛矿床各成矿阶段典型矿物的流体包裹体研究表明,成矿流体富含挥发分,临界相均一的流体来自岩浆超临界流体出溶,主成矿阶段具有沸腾包裹体组合特征,有机质包裹体荧光效应显著。显微测温结果显示,岩浆-热液阶段斑岩中石英斑晶的流体包裹体均一温度范围为250～540℃,含石盐子晶高盐度包裹体盐度范围为35～61(wt%)NaCl.eq,中等盐度的临界均一的气液包裹体盐度范围为3～29(wt%)NaCl.eq,岩浆期后热液阶段斑岩、角岩中石英脉的流体包裹体均一温度范围为210～410℃,盐度范围为33～41(wt%)NaCl.eq,与其不混溶共生的中低盐度气液两相流体包裹体盐度范围为5～25(wt%)NaCl.eq。矽卡岩阶段矿物均一温度范围为130～360℃,盐度范围为3～41(wt%)NaCl.eq,从岩浆热液过渡阶段到石英-硫化物阶段均一温度与盐度呈阶梯式降低趋势。斑岩体石英的流体包裹体中含有较多黄铜矿子矿物,岩浆结晶分异过程中已经具成矿元素的富集。激光拉曼探针测试结果显示,成矿早期至主成矿期矿物流体包裹体气相成分主要为CO2、CH4和N2,各阶段矿物流体包裹体气相成分具有继承性。成矿流体为高温度高盐度,富含CO2、CH4的流体。成矿流体主要源于岩浆,后期混有大气降水。当岩浆热液上升时因压力的突然释放造成高温含矿热流体发生减压沸腾,CO2和CH4等气体大量逃逸,导致成矿物质快速沉淀。矿床在成因上与岩浆-热液成矿作用密切相关。