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1.
采用偏光显微镜薄片观察、电子探针及背散射图像、阴极发光等方法,分别对伟晶岩矿脉和顺层剪切带矿脉两种产出状态的云南麻栗坡祖母绿进行了系统的包裹体特征研究。结果表明,云南麻栗坡祖母绿具有产地特征的包裹体有黑色镁电气石、含钒的白云母、具有环带的钾长石、毒砂、镁质黑云母、白钨矿包裹体。伟晶岩脉和顺层剪切带中的祖母绿均含有钾长石、钠长石、电气石、萤石、祖母绿(绿柱石)、黑云母、榍石、磷灰石、黄铁矿、绿泥石、绿帘石包裹体。白云母、方解石、石英、锆石、毒砂、闪锌矿、方铅矿、透辉石仅出现在伟晶岩脉中的祖母绿包裹体中;而白钨矿仅出现在顺层剪切带中的祖母绿包裹体中。对云南不同产状祖母绿矿物包裹体的研究不仅对祖母绿的产地鉴定具有宝石学意义,也对揭示云南麻栗坡祖母绿的成因类型具有重要意义。  相似文献   

2.
The genesis of gem-quality deep green emeralds of Zabara, Sikait and Umm Kabo (South Eastern Desert, Egypt) is to date a controversial topic. The emerald-bearing biotite schists and quartz lenses are interpreted alternatively as a product of (i) thrust-fault-shear zone – controlled large scale alkali-metasomatism driven by post-magmatic fluid flow or of (ii) a large scale interaction between syntectonic pegmatitic magma or hydrothermal fluids with pre-existing basic to ultrabasic rocks, or of (iii) a syn- to post-tectonic regional metamorphism and small scale blackwall metasomatism. Detailed microstructural and chemical analyses of the Egyptian emeralds and their host rocks show that three generations of beryl can be distinguished: a colourless pegmatitic beryl; a pale green Cr-poor beryl crystallized from pegmatite-related hydrothermal fluids; and a deep green Cr- and Mg-rich emerald. The crystallization of the Cr- and Mg-rich emerald was controlled by the very local availability of Cr, Mg and Be-rich metamorphic fluids during the Pan-African tectono-thermal event. Emerald-rich quartz lenses demonstrate that those fluids locally did mobilize quartz, too. The pale green emeralds found within the pegmatites in association with colourless beryl are the product of a mobilization of colourless pegmatitic beryl and/or phenakite by late pegmatitic fluids slightly enriched in Cr by an interaction with the Cr-rich country rocks. The late pegmatitic fluids are typically Na-rich as is demonstrated by the pervasive albitization of the pegmatites. The complex interplay of magmatic and regional metamorphic events during the genesis of the Egyptian emeralds/beryls makes it impossible through stable oxygen isotope data to relate their genesis to the one or the other event.  相似文献   

3.
The fluid composition, δD of channel H2O, and δ18O of lattice oxygen have been determined in beryl and emerald from a variety of geological environments and used to constrain the origin of the parental fluids from which beryl has grown. Step-heating analyses performed by quadrupolar mass spectrometry were used to quantify the composition of the fluid phases in beryl from granitic pegmatites and greisens and emerald from Brazil, Colombia, and Afghanistan. An important conclusion is that beryl and emerald have a similar fluid composition, with concentrations of H2O being greater than 90% of the total water in the mineral irrespective of the age of formation (2.0 Ga to 32 Ma) and tectonic settings. However, the Brazilian Santa Terezinha shear-zone emerald deposit contains abundant CO2, up to 13 wt% of the total fluid. A second conclusion is that the channel H2O content for some Brazilian emeralds is higher than the range defined for beryl in the literature, especially for those related to the shear-zone type (2.99 lt; H2O < 3.16 wt%) and the pegmatite type from the Pombos, Pela Ema, and Pirenopolis deposits (2.78 < H2O < 3.01 wt%). Colombian emeralds have very low H2O contents (1.30 < H2O < 1.96 wt%), among the lowest in the world.

Brazilian, Colombian, and Afghanistani emeralds have contrasting and restricted ranges of δ18O values. In Brazil, emeralds related to pegmatites have a systematic δ18O inter-deposit variability (+6.3 < δ18O < +12.4‰). The calculated δ18O of the fluid was buffered by the host ultrabasic rocks during fluid-rock interaction. Emerald and cogenetic phlogopite related to shear-zone-type deposits have a quite restricted δ18O range (+12.0 < δ18O 7lt; +12.4‰); the calculated is interpreted to represent the original isotopic composition of the hydrothermal fluid. Relative to Brazil, the δ18O of Colombian and Afghanistani emeralds shows strong enrichment in 18O (+13.4 < δ18O < +23.6‰), and the high calculated δ18O of the fluid suggests extensive reaction with 18O-rich sedimentary or metasedimentary rocks.

In Brazil, the δD composition of channels in emerald and the calculated δ18OH2O for phlogopite are compatible with both magmatic and metamorphic origins. A magmatic origin is supported for emeralds associated with the pegmatitic Socotó and Carnaiba deposits (mean δD = ?37.8 ± 8‰) and a metamorphic origin is suggested for the Santa Terezinha shear-zone type (mean δD = ?32.4 ± 3‰). A metamorphic origin is proposed for Colombian emeralds. Afghanistani emeralds have a δD composition of channels (mean δD = ?46.3 ± 1.3‰) that is compatible with both magmatic and metamorphic origins.  相似文献   

4.
天然祖母绿与合成祖母绿的成分及红外吸收光谱研究   总被引：2，自引：2，他引：0  
申柯娅 《岩矿测试》2011,30(2):233-237
祖母绿是一种高档名贵的宝石,其矿物学名称为绿柱石,化学成分为铍铝硅酸盐。鉴别天然祖母绿和人工合成祖母绿,已成为祖母绿宝石鉴定中的一个重要课题。文章采用常规宝石学研究方法、激光剥蚀-电感耦合等离子体质谱法和红外光谱技术对天然祖母绿(包括哥伦比亚祖母绿和巴西祖母绿)、合成祖母绿(包括助熔剂法合成祖母绿和水热法合成祖母绿)样品进行了系统的分析和研究。结果表明,天然祖母绿与合成祖母绿的主要致色微量元素Cr的含量越高,祖母绿的绿色越浓艳;天然祖母绿与合成祖母绿的红外吸收光谱特征具有明显的差异;根据祖母绿中是否含水、水的赋存状态以及氯的吸收峰,可作为准确鉴别天然祖母绿和合成祖母绿的重要依据。等离子体质谱法化学成分分析不能确定祖母绿是天然形成还是人工合成,需在常规宝石学检测的基础上,综合研究祖母绿的红外吸收光谱特征及内含物特征,才能准确地鉴别天然祖母绿、水热法合成祖母绿和助熔剂法合成祖母绿。  相似文献   

5.
The Ianapera emerald deposit is located in the Neoproterozoic Vohibory Block of southern Madagascar. The local geology consists of intercalated migmatitic gneissic units and calcareous metasedimentary rocks, containing boudinaged metamorphosed mafic/ultramafic lenses, all intruded by pegmatite veins. These units occur near the hinge of the tightly folded Ianapera antiform, within a few kilometers of the Ampanihy shear zone. Emerald mineralization is hosted by metasomatic phlogopite veins, and bodies developed within the mafic/ultramafic rocks. Based on field and textural relationships, we distinguish proximal and distal styles of mineralization. Proximal mineralization occurs at the contact of pegmatite veins with mafic/ultramafic units; in the distal style, pegmatites are not observed. Three types of emeralds could be distinguished, mainly on the basis of color and mineral zoning. Some of these emeralds have the most Al-depleted and Cr-rich composition ever recorded. Another characteristic feature to the Ianapera deposit and, to our knowledge, yet unreported, is the association of some emeralds with scapolite in metasomatised mafic rocks. Mineral inclusions are common in most emeralds and include phlogopite, carbonates, barite, K-feldspar, quartz, pyrite, zircon, monazite, bastnaesite, phenakite, plus Fe and Cr oxides. However, feldspar and rare earth element-bearing minerals occur predominantly in proximal emeralds, which also have a more incompatible trace-element signature than distal emeralds. We propose a model related to syn- to post-tectonic magmatic-hydrothermal activity. Pegmatitic bodies intruded units of the Ianapera antiform probably during tectonic relaxation. Exsolution of fluids rich in halogens and incompatible elements from the cooling pegmatites caused hydrothermal metasomatism of Cr-bearing mafic/ultramafic rocks in direct contact with the pegmatites. Local fracturing favored fluid infiltration, permitting the formation of distal mineralization. Emerald composition was controlled by the chemistry of the host rock. The presence of carbonate mineral inclusions in the emeralds and the high F-activity indicated by elevated F-contents in newly formed minerals suggest transport of Be as a fluoride-carbonate complex. It seems likely that beryl formation was triggered by precipitation of F-rich phlogopite, which removed the complexing ligand from the fluid.  相似文献   

6.
Gold-bearing quartz veins fill late-Alpine brittle structures in Pennine nappes of Austria (in the Tauern window) and in northern Italy. The veins formed in the latter stages of uplift of the Alps. Fluid inclusions in veins sampled from Böckstein, Austria, and Valle Anzasca, Italy have a wide variety of compositions, ranging from aqueous brine (about 5 wt% NaCl equiv.) to about 50 mol% CO2. At room temperature, the inclusions range with increasing CO2 content from two-phase aqueous, through three-phase in which the CO2 homogenizes to vapour, to three-phase with CO2 homogenizing to liquid. This wide range of inclusion compositions is interpreted as evidence for fluid immiscibility, with most inclusions being accidental mixtures of the two end-member immiscible fluids. The homogenization temperatures of the aqueous inclusions, 200–280°C, gives the best estimate of temperature of formation of the veins. Vein formation fluid pressure at Böckstein and Valle Anzasca was about 1 kbar, and Böckstein veins formed at lower pressure than Valle Anzasca veins. Fluid immiscibility may have contributed to deposition of gold at both Valle Anzasca and Böckstein, and possibly many other uplift-related Alpine gold localities.  相似文献   

7.
Mineralogical, geochemical and fluid inclusion studies reveal two favorable environments for the localisation of beryl mineralisations in the Precambrian rocks of Egypt: (1) emerald-schist; and (2) beryl-specialised granitoid associations. Emerald occurs within the mica schists and is typically confined to the Nugrus major shear zone. However, beryl associated with granitoids occurs in pegmatite veins, greisen bodies, and cassiterite quartz veins cutting the granites and the exocontacts of the volcanosedimentary country rocks.Compositionally, emerald is of octahedral type and its cell edge is lengthened along the a-axis, while beryl associated with granitoids is normal in composition and structural constants. Emerald is thought to be formed as the result of epitactic nucleation of Be, Al and alkali-rich solutions on the mica of the schist country rocks. Fluid inclusion studies show that the solutions are saline (8–22 wt% NaCl equiv.) and the reactions proceeded in the temperature range 260–382°C. On the other hand, aqueous inclusions in beryl associated with granitoids show the following sequence of formation with decreasing temperatures and salinities: beryl pegmatite (320–480°C and 7–16 wt% NaCl equiv.)→greisen bodies (190–400°C and 4–7 wt% NaCl equiv.)→cassiterite-quartz veins (190–380°C and 2–4 wt% NaCk equiv.).This study suggests that factors such as the chemistry of the Be-bearing fluids (rather than that of the bulk host schists) and syn-tectonic intrusions of leucogranites and pegmatites (Bederiving sources) along major ductile shear zones are the important factors controlling emerald formation. However, the endogreisens and exogreisens are the most important targets characterising the metasomatically- and magmatically-specialised, Be-granitoids, respectively. The aqueous inclusions examined in greisen beryls of metasomatised granites show a shorter range of homogenisation temperatures (260–390°C) and salinities(4.8-7 wt% NaCl equiv.) as compared to those of magmatically-specialised granitoids (190–400°C and 4–7 wt% NaCl equiv.). This phenomenon can be partly attributed to the late development of the fracture system during the crystallisation history of the metasomatised granites, where little or no contribution from meteoric waters occurred.  相似文献   

8.
Alpine-type fissure vein mineralization in the Hiddenite area of western North Carolina, USA consists mostly of quartz, but locally contains Cr-bearing beryl (emerald) or Cr-bearing spodumene (hiddenite). These gem minerals occur in mineral-lined cavities and may be accompanied by euhedral crystals of quartz, calcite, muscovite, rutile, albite, pyrite, siderite and dolomite. Chabazite-Ca occurs as a late stage phase in spodumene-bearing veins, but is absent in emerald-bearing veins. Chabazite-Ca occurs as simple penetrating twins of pseudocubic rhombohedra and as the lens-shaped variety, phacolite. Chabazite-Ca from Hiddenite contains minor amounts of Na, Mg, Fe and K. Phacolitic chabazite-Ca shows Fe-enriched but Mg-depleted cores relative to the rims. Chemical zoning is absent in rhombohedral chabazite. The Hiddenite chabazite apparently precipitated under low temperature (< 250°C) and low pressure (< 2 kbar) conditions during the waning stages of crystallization of an alkaline hydrothermal fluid.  相似文献   

9.
The Sorkhe-Dizaj orebody is located 32 km southeast of Zanjan within the Tarom subzone of the Alborz-Azarbaijan structural zone. It is hosted mainly in quartz monzonite-monzodiorite and, to a lesser extent, in volcanoclastic rocks. Mineralization occurs in the form of stockwork and veins, comprising predominantly magnetite and actinolite, with minor pyrite and chalcopyrite. Two generations of magnetite and apatite are inferred: the first as disseminations in the host rock and the second mainly as an alteration product of actinolite, secondary K-feldspar, silica, sericite, chlorite and epidote. Fluid inclusion studies were carried out on second-generation apatite, and late-stage quartz to understand the geochemical evolution of the ore-bearing fluids. Fluid inclusions are of three types, i.e. primary, secondary, and pseudo-secondary. These inclusions are liquid or vapour single-phase, two-phase rich in liquid or vapour, and three-phase. Homogenization temperatures of second-generation apatite are inferred to be between 209°C and 520°C (mostly between 290°C and 320°C), indicating salinities of 9.08–21.61 wt.% NaCl equiv. At 342°C, the δ18O values range from 9‰ to 11.32‰ for the second-generation magnetite associated with coeval apatite. Fluid inclusions in the late-stage quartz veins are inferred to have homogenized between 186°C and 263°C, with δ18O values ranging between 2.5‰ and 7.4‰ at 220°C. Oxygen isotopes in the late-stage carbonate veins have values of 3.28–6.14‰ at 100°C. These data in the late-stage veins imply introduction of a cooler, less saline, isotopically depleted fluid, probably meteoric water. Field observations, mineral parageneses, and fluid inclusion?+?oxygen isotope data suggest that the magnetite-apatite veins formed from a predominantly magmatic-derived fluid. Introduction of cooler meteoric water in the final stage of mineralization reduced δ18O values, facilitating precipitation of sulphides, quartz, and carbonate veins.  相似文献   

10.
Emerald, the green gem variety of beryl (Be3Al2Si6O18), is the third most valuable gemstone after diamond and ruby. The green colour appearance of the crystal is due to trace of Cr3+ and V3+, which replaces Al3+ ions in the crystal lattice of beryl. The hue of green colour of emerald depends on the quantity of Cr3+ and V3+ present in the crystal. Be is incorporated along with Cr and/or V during the process of crystallization. Since Be is relatively rare in the upper continental crust, therefore specific geological and geochemical parameters are required for Be to be incorporated in the crystal lattice of emerald.The present work was carried out to understand the lithological and structural control of emerald occurrences in and around Gurabanda area within the Singhbhum shear zone (SSZ) of Singhbhum crustal province, eastern India. The biotite and serpentine schist belong to the Paleoproterozoic Dhanjori Group and constitute the major lithology of the area. Pegmatite and biotite schist contains a variety of gem minerals in abundance in the area and the gem quality emerald occur at the contact zone of quartz vein and mica-schist. Lithology and structure are the main controlling factors of gem-mineralization in the study area. The study indicates that regional metamorphism and deformation processes along the shear zone played a significant role in the formation of emerald deposits. It is inferred that Singhbhum shear zone facilitated a favourable condition, where the Be bearing pegmatites interacted with Cr bearing mica schist or ultramafic rocks to produce emerald crystal.  相似文献   

11.
祖母绿是一种名贵彩色宝石,其产地来源对祖母绿价值的评定具有重要影响。祖母绿的产地鉴别因而成为宝石实验室的重要技术,也是宝石学领域的研究热点。祖母绿的包裹体、谱学特征和化学成分是常用且关键的产地鉴别信息,但随着祖母绿产地研究数据的积累,传统的产地鉴别方法备受挑战。文章系统整理和归纳分析了全球各产地祖母绿的宝石学特征、包裹体信息、谱学特征和主微量成分数据,在综述前人研究结果的基础上,系统阐明了目前祖母绿产地鉴别的研究现状,总结了不同产地祖母绿的宝石学特征和包裹体特征,划分了紫外-可见光-近红外(UV-VIS-NIR)光谱类型,揭示了各产地祖母绿的成分指纹信息,并以案例的形式阐明区分祖母绿常见重要产地的方法。全球尺度的对比虽然表明不同产地祖母绿包裹体种类多数雷同、光谱趋同、成分含量范围重叠明显,但也从包裹体出现频率、UV-VIS-NIR光谱样式类型、重水吸收样式和成分投图参数的选择上提供了产地鉴别的新思路。综上所述,文章旨在促进祖母绿鉴别技术的发展,为祖母绿的产地溯源提供科学依据。  相似文献   

12.
邹平地区与火山岩浆热液作用有关的铜矿床主要可划分为2种类型：一类为斑岩-火山角砾岩型,另一类为浅成低温热液型;代表性矿床分别为王家庄斑岩一火山角砾岩型铜（钼）矿床和南洞子浅成低温热液型铜（金）矿床。流体包裹体研究表明：王家庄铜（钼）矿床成矿流体的均一化温度和盐度偏高,出现了富气相的两相水溶液包裹体、富液相的两相水溶液包裹体和含子晶的三相水溶液包裹体共存现象,加温后,富气相包裹体均一到气相,同期富液相包裹体均一到液相的特征,这表明成矿流体在形成和演化过程中曾发生过沸腾作用。南洞子铜（金）矿床成矿流体均一温度和盐度偏低,以上3种包裹体共存的现象不明显,说明成矿流体在形成和演化过程中沸腾作用不强。上述2类矿床矿化脉石英中的δ^18OH2O-δD投影点飘离岩浆水范围,参照流体包裹体研究结果,证明邹平地区与火山岩浆热8液作用有关的铜矿成矿流体主要来源于岩浆水,后期混人大气降水。相比之下,浅成低温热液铜矿成矿流体中的大气降水混入量多。  相似文献   

13.
文章对印度尼西亚索林帕萨铜多金属矿含矿石英脉流体包裹体进行了显微测温与氢氧同位素测定,发现石英脉中含有3种类型的流体包裹体:A.纯液相水溶液包裹体;B.富液相气液两相水溶液包裹体和C.富气相气液两相水溶液包裹体,其中以B类为主.三种流体包裹体同时出现,表明石英脉形成时流体可能发生过沸腾作用.成矿流体均一温度为198.9℃～356.4℃,冰点温度为-0.6℃～-2.3℃,相应流体盐度变化范围为0.94%～3.76%NaCleq..质谱测定显示成矿流体的氢氧同位素组成分别为占δDH2O=-61.0‰～-81.0‰,δ18OH2O=-3.08‰～0.17‰,表明成矿流体主要为大气降水,不排除有少量岩浆水加入.根据成矿流体地球化学与围岩蚀变类型,初步推断该矿属于酸性-硫酸盐(高硫)型的浅成低温多金属矿床,沸腾作用是成矿物质沉淀的主要因素.  相似文献   

14.
黑龙江省铜山斑岩铜矿床流体包裹体研究   总被引：14，自引：4，他引：10  
武广  刘军  钟伟  朱明田  糜梅  万秋 《岩石学报》2009,25(11):2995-3006
铜山大型铜矿床位于小兴安岭西北部,是中亚-兴蒙造山带北东段最著名的斑岩型铜矿床之一,矿体产于加里东期花岗闪长岩和中奥陶世多宝山组安山岩、凝灰岩中,铜矿化与硅化-绢云母化关系密切.流体包裹体研究表明,铜山铜矿床主要发育气液两相包裹体、含CO_2包裹体和含子矿物多相包裹体.成矿流体在形成过程中经历了早、中、晚3个阶段的演化.成矿早阶段发育气液两相水溶液包裹体和少量含子矿物多相包裹体,均一温度介于420℃～＞5500C之间,流体盐度介于13.72 wt%～59.76 wt%NaCl eqv之间;中阶段为铜山矿床的主成矿阶段,发育气液两相水溶液包裹体和含CO_2包裹体,均一温度为241℃～417℃,流体盐度介于2.96 wt%～14.04 wt%NaCl eqv之间,主成矿期成矿流体总体上属H_2O-CO_2-NaCl体系;晚阶段仅发育气液两相水溶液包裹体,均一温度为122℃～218℃,盐度介于3.71 wt%～15.96 wt%NaCl eqv之间,表明晚阶段有大气降水的混入.成矿早、中阶段的流体均为不混溶流体,流体沸腾作用是金属硫化物大量沉淀的主要机制.铜山矿床形成于陆缘弧环境.  相似文献   

15.
祖母绿是由微量Cr和/或V致色的绿色绿柱石。位于云南省麻栗坡县的大丫口祖母绿矿床是中国重要的祖母绿矿床,近年来取得了一系列的研究进展,但与祖母绿相关的电气石的研究工作还未展开。本文以大丫口矿床含祖母绿矿脉和非矿脉中的电气石为研究对象,在详细的野外调查和岩相学研究基础上,对电气石进行成分测试,旨在探讨电气石成因、查明物质来源和流体演化过程,进一步探究大丫口祖母绿矿床的成矿机制。结果显示:含矿脉电气石单位分子中Na含量为0.62~0.79 apfu,Al含量为5.36~6.17 apfu,Fe/(Fe+Mg)值为0.31~0.41;非矿脉电气石单位分子中Na含量为0.64~0.76 apfu,Al含量为5.66~6.38 apfu,Fe/(Fe+Mg)值为0.14~0.34。大丫口电气石具有富Mg、Y位(Y-site)上呈低Al或无Al的特征,属于碱族镁电气石,但是含矿脉电气石则显示更高的Fe/(Fe+Mg)值。电气石成分的差异可能主要与形成环境有关,电气石的成分差异具有指示祖母绿是否富集的潜力。大丫口电气石具有成分分带且V2O3含量为0.65%~4.76%,其形成与持续的热液流体交代围岩有关。大丫口矿床是一个岩浆起源的动态热液体系,流体通过碱交代作用参与水岩反应萃取围岩中的成矿物质。早期流体的物质组成以源于花岗质熔体的Si、Al、Be、F、P为主,而随着演化的进行,Ca、V等来自地层的成分逐渐增加。研究表明,铍的氟化物或氟铍络合物是大丫口成矿流体中Be的一种重要的迁移方式。萤石、氟磷灰石等含氟矿物的结晶促使铍的氟化物或氟铍络合物分解,流体中氟元素的减少可能是大丫口祖母绿成矿的重要机制之一。  相似文献   

16.
卡尔却卡铜多金属矿床是青海省地质调查院于近几年在东昆仑西段祁漫塔格地区新发现的一个矿床,目前规模已达中型。文章通过对矿区西北部受岩体断裂破碎蚀变带控制的铜矿体中石英流体包裹体岩相学、显微测温和激光拉曼探针成分分析,表明铜矿化石英脉中发育气液两相、富气相、含子矿物三相、纯液相和纯气相5类包裹体;气液两相和含子矿物三相流体包裹体的盐度差异明显,但它们的均一温度比较一致(320~440℃),反映在成矿流体演化过程中发生了强烈的流体不混溶,对成矿起重要作用;流体包裹体气相成分主要为H2O和CO2,其次为CH4、N2、H2、H2S及烃类。综合流体包裹体研究和矿化、蚀变等地质特征,笔者认为矿区西北部矿化应为与高中温岩浆热液作用有关的斑岩型铜矿化,它与区内强烈发育的铜铅锌多金属矽卡岩矿化均为同一构造-岩浆作用的产物。  相似文献   

17.
Sn–W deposit of the Mueilha mine is one of many other Sn–W deposits in the Eastern desert of Egypt that associated with albite granite. Two forms of Sn–W mineralizations are known at the Mueilha Sn-mine area, namely fissure filling quartz veins and greisen. Cassiterite and/or wolframite, sheelite, and beryl are the main ore minerals in the greisen and quartz veins. Subordinate chalcopyrite and supergene malachite and limonite are also observed in the mineralized veins. To constrain the P–T conditions of the Sn–W mineralizations, fluid inclusions trapped in quartz and cassiterite, have been investigated. The following primary fluid inclusion types are observed: CO2-rich, two-phase (L?+?V) aqueous, and immiscible three-phase (H2O–CO2) inclusions. Low temperature and low salinity secondary inclusions were also detected in the studied samples. Microthermometric results revealed that Sn–W deposition seem to have taken place due to immiscibility at temperature between 260°C and 340°C, and estimated pressure between 1.2 to 2.2 kb. Microthermometric results of fluid inclusions in fluorite from fluorite veins illustrated that fluorite seems to be deposited due to mixing of two fluids at minimum temperature 140°C and 180°C, and estimated minimum pressure at 800 bars.  相似文献   

18.
云南大丫口祖母绿常出现颜色环带,且伴随明显成分变化,而目前颜色环带的成因仍存争议,相关的多阶段成矿假说尚缺少明确证据。文章通过电子探针和激光剥蚀电感耦合等离子质谱仪对大丫口祖母绿的颜色环带及黑色矿物包裹体进行主微量元素成分分析,并对不同类型岩脉祖母绿中流体包裹体进行显微测温分析,进而探讨祖母绿颜色环带成因与多阶段成矿的联系。成分测试结果表明,从浅绿白核部至绿色边部,V(970×10-6→10 077×10-6)、Rb(9.6×10-6→27.4×10-6)、Cs(535×10-6→3 108×10-6)、Fe(1 376×10-6→2 199×10-6)和Ga(4×10-6→14.7×10-6)等微量元素的含量急剧增加。结合绿色晶体边部中同生黑色富钒电气石包裹体的分布,有力证明了大丫口祖母绿颜色分带的形成与晶体的多阶段成矿有关。流体包裹体测试结果表明,含矿长石-方解石脉、含矿石英脉和伟晶岩-变粒岩接触带中矿物的流体包裹体盐度范围分别为3.39%~10.36%(NaCleq)、5.71%~12.29%(NaCleq)和8%~18.72%(NaCleq),指示了伟晶岩脉中祖母绿的多阶段结晶,且表明随结晶阶段演变,成矿流体的盐度逐渐升高。同时,成矿流体盐度升高也是晚期云英岩化阶段致色元素含量剧增的原因。  相似文献   

19.
Petrographic investigations in the area of the Capoeirana emerald deposit, Minas Gerais State, revealed two main lithostructural units. The first unit is comprised of gneissic rocks of granitic composition belonging to the basement complex, and the second is composed of a highly weathered metasedimentary-metavolcanic sequence represented by metapelitic schists, amphibolites, schists derived from ultramafic rocks, and quartzites. Quartz and pegmatoid veins appear near the contacts between the gneissic rocks and the mineralization metasedimentary-metavolcanic sequence. The emerald mineralization is dominantly concentrated within the intercalations of meta-ultramafic schists near the contact of the pegmatoid veins. Microthermometric studies of the fluid inclusions of the emerald grains indicate that crystallization occurred in the pressure and temperature ranges of 2000 to 2750 bar and 450 to 650 °C, respectively. These data suggest that the mineralizing solutions have had a late hydrothermal-pneumatolytic origin characterized by low pressures, suggestive of the paragenesis talc + tremolite + carbonate + biotite-phlogopite + chlorite of the emerald wall rocks.  相似文献   

20.
Given the wide range of oxygen isotopic composition of emerald from all over the world (δ18O between +6.2 and +24.7‰), the δ18OV-SMOW values of emeralds from the Sandawana mines in Zimbabwe (δ18O‰=+6.6 to +8.0), are relatively constant, among the lowest ever measured. These consistently low values can be explained by host-rock buffering in a very narrow emerald-bearing reaction zone between ultrabasic greenstones (metamorphosed komatiites) and albitised pegmatites. δ18O values of Sandawana emeralds overlap those of emeralds from Brazil, Austria, Australia and Madagascar, a fact indicating that, in these cases, oxygen isotope composition alone is not sufficient to determine the geographic origin of commercially available emeralds. However, stones with overlapping δ18O values may eventually be identified using a combination of physical properties, inclusion characteristics and chemical composition. To cite this article: J.C. Zwaan et al., C. R. Geoscience 336 (2004).  相似文献   

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