新疆阿尔泰协库斯特伟晶岩中锂的矿物学行为及其启示

协库斯特伟晶岩位于新疆阿尔泰可可托海镇,属于典型的Li-Cs-Ta(LCT)伟晶岩,发育大量锂的磷酸盐矿物和硅酸盐 矿物。文章利用电子探针和X射线衍射等分析手段,结合野外观察,系统研究了协库斯特伟晶岩中锂的矿物学行为,探讨 花岗质岩浆-热液过程中锂矿物的结晶演变与热液蚀变过程。研究表明：协库斯特伟晶岩中锂矿物结晶于两个阶段,花岗 质岩浆阶段,锂矿物主要有锂辉石、磷锂铝石与磷锰锂矿,而锂电气石、多硅锂云母、锂白云母等形成于岩浆-热液过渡 阶段至热液阶段。磷锰锂矿与羟磷锂铝石团块包体反映协库斯特伟晶岩中锂的磷酸盐熔体与硅酸盐熔体的不混溶机制。磷 锰锂矿逐渐蚀变形成黄白色-红色的结构相似的矿物相,揭示了磷锰锂矿的氧化过程以及锂的释放过程。早期锂辉石、磷 锰锂矿、磷锂铝石等锂矿物热液蚀变释放出Li进入热液,这种富Li热液作用形成了次生富锂矿物,显示了协库斯特伟晶岩 内部Li的地球化学循环过程。     

新疆阿尔泰协库斯特伟晶岩中锂的矿物学行为及其启示

协库斯特伟晶岩位于新疆阿尔泰可可托海镇，属于典型的Li-Cs-Ta(LCT)伟晶岩，发育大量锂的磷酸盐矿物和硅酸盐 矿物。文章利用电子探针和X射线衍射等分析手段，结合野外观察，系统研究了协库斯特伟晶岩中锂的矿物学行为，探讨 花岗质岩浆—热液过程中锂矿物的结晶演变与热液蚀变过程。研究表明：协库斯特伟晶岩中锂矿物结晶于两个阶段，花岗 质岩浆阶段，锂矿物主要有锂辉石、磷锂铝石与磷锰锂矿，而锂电气石、多硅锂云母、锂白云母等形成于岩浆—热液过渡 阶段至热液阶段。磷锰锂矿与羟磷锂铝石团块包体反映协库斯特伟晶岩中锂的磷酸盐熔体与硅酸盐熔体的不混溶机制。磷 锰锂矿逐渐蚀变形成黄白色—红色的结构相似的矿物相，揭示了磷锰锂矿的氧化过程以及锂的释放过程。早期锂辉石、磷 锰锂矿、磷锂铝石等锂矿物热液蚀变释放出Li进入热液，这种富Li热液作用形成了次生富锂矿物，显示了协库斯特伟晶岩 内部Li的地球化学循环过程。     

Multistage Growth of a Rare-Element, Volatile-Rich Microgranite at Argemela (Portugal)

The small Argemela microgranite body in central Portugal displaysmany of the mineralogical and chemical features characteristicof peraluminous, Li, P-rich, rare-element pegmatites. Its mineralogyconsists predominantly of quartz, albite, white mica (partlyreplaced by lepidolite) and a phosphate of the amblygonite series.K-feldspar is noticeably absent or scarce. Cassiterite, beryland columbite are the main accessories. The microgranite showsextreme enrichment in incompatible elements such as F, P, Rb,Cs, Li, Sn and Be, and extreme depletion in Sr, Ba, Zr and REE.It is highly sodic and strongly peraluminous. The micrograniteoverall is interpreted as a mixture of two components: a crystalmush injected from below (seen in narrow dykes intersected duringdrilling, composed of quartz, albite and phengite) and interpretedas ‘feeders’, overprinted by a second highly evolvedcomponent dominated by Li, F, P (Rb, Cs, Be, Sn, Nb, Ta, etc.)considered as a ‘lubricant’ medium for the ascendingmush and occasionally quenched (quartz, albite, skeletal lepidoliteand amblygonite). This second component has the mineralogicaland chemical characteristics of rare-element pegmatites. Allthese petrological characteristics are magmatic. Only a fewnarrow cross-cutting veinlets with quartz, K-feld-spar and F-pooramblygonite are considered as fluid derived. A model of crystallizationin successive steps is proposed where concentration in fluxingagents (F, Li, P, etc.) is progressively enhanced up to saturationwith the crystallization of magmatic lepidolite and amblygonite. KEY WORDS: petrogenesis; microgranite; pegmatite; volatiles; Portugal ^*Corresponding author.     

新疆可可托海稀有金属矿床矿物和岩石热红外光谱特征

当前新型材料、新能源在各个领域应用不断深化,稀有金属矿床迎来了世界范围内的研究与勘探热潮。新疆可可托海稀有金属矿床是我国最早开发利用稀有金属矿产资源的重要基地,但对其典型矿物和围岩的热红外反射光谱的认识还很缺乏,制约了对同类型矿床开展遥感地质调查和遥感地质学研究工作的推进。本文采用便携式热红外光谱仪,对可可托海3号脉的典型矿物岩石开展热红外光谱特征研究。结果表明:热红外光谱可以有效识别锂辉石、锂云母、绿柱石、电气石等典型的稀有金属矿物。其中,与锂云母相比,含锂云母伟晶岩产生了新的特征峰;含锂辉石伟晶岩、含电气石伟晶岩相比于各自单晶矿物,其反射特征峰均明显向短波方向偏移;含绿柱石伟晶岩光谱曲线反射特征峰比绿柱石单晶反射特征峰明显向长波方向偏移。本文初步建立了可可托海典型矿物和岩石热红外光谱特征数据库,总结了以锂辉石、锂云母等稀有金属矿床矿物、含矿伟晶岩及围岩的热红外光谱特征,可为热红外光谱进行稀有金属矿物的识别及花岗伟晶岩型矿床的勘探提供必要的基础数据支撑。     

Conditions of pocket formation in the Oktyabrskaya tourmaline-rich gem pegmatite (the Malkhan field, Central Transbaikalia, Russia)

Coexisting melt (MI), fluid-melt (FMI) and fluid (FI) inclusions in quartz from the Oktaybrskaya pegmatite, central Transbaikalia, have been studied and the thermodynamic modeling of PVTX-properties of aqueous orthoboric-acid fluids has been carried out to define the conditions of pocket formation. At room temperature, FMI in early pocket quartz and in quartz from the coarse-grained quartz–oligoclase host pegmatite contain crystalline aggregates and an orthoboric-acid fluid. The portion of FMI in inclusion assemblages decreases and the volume of fluid in inclusions increases from the early to the late growth zones in the pocket quartz. No FMI have been found in the late growth zones. Significant variations of solid/fluid ratios in the neighboring FMI result from heterogeneous entrapment of coexisting melts and fluids by a host mineral. Raman spectroscopy, SEM EDS and EMPA indicate that the crystalline aggregates in FMI are dominated by mica minerals of the boron-rich muscovite–nanpingite CsAl₂[AlSi₃O₁₀](OH,F)₂ series as well as lepidolite. Topaz, quartz, potassium feldspar and several unidentified minerals occur in much lower amounts. Fluid isolations in FMI and FI have similar total salinity (4–8 wt.% NaCl eq.) and H₃BO₃ contents (12–16 wt.%). The melt inclusions in host-pegmatite quartz homogenize at 570–600 °C. The silicate crystalline aggregates in large inclusions in pocket quartz completely melt at 615 °C. However, even after those inclusions were significantly overheated at 650±10 °C and 2.5 kbar during 24 h they remained non-homogeneous and displayed two types: (i) glass+unmelted crystals and (ii) fluid+glass. The FMI glasses contain 1.94–2.73 wt.% F, 2.51 wt.% B₂O₃, 3.64–5.20 wt.% Cs₂O, 0.54 wt.% Li₂O, 0.57 wt.% Ta₂O₅, 0.10 wt.% Nb₂O₅, 0.12 wt.% BeO. The H₂O content of the glass could exceed 12 wt.%. Such compositions suggest that the residual melts of the latest magmatic stage were strongly enriched in H₂O, B, F, Cs and contained elevated concentrations of Li, Be, Ta, and Nb. FMI microthermometry showed that those melts could have crystallized at 615–550 °C.

Crystallization of quartz–feldspar pegmatite matrix leads to the formation of H₂O-, B- and F-enriched residual melts and associated fluids (prototypes of pockets). Fluids of different compositions and residual melts of different liquidus–solidus P–T-conditions would form pockets with various internal fluid pressures. During crystallization, those melts release more aqueous fluids resulting in a further increase of the fluid pressure in pockets. A significant overpressure and a possible pressure gradient between the neighboring pockets would induce fracturing of pockets and “fluid explosions”. The fracturing commonly results in the crushing of pocket walls, formation of new fractures connecting adjacent pockets, heterogenization and mixing of pocket fluids. Such newly formed fluids would interact with a primary pegmatite matrix along the fractures and cause autometasomatic alteration, recrystallization, leaching and formation of “primary–secondary” pockets.     

Geological Evolution of Selected Granitic Pegmatites in Myanmar (Burma): Constraints from Regional Setting,Lithology, and Fluid-Inclusion Studies

Pegmatite deposits commonly occur in the 1500 km long, N-S-trending, tungstentin-bearing granitoid belt in Myanmar. Pegmatites are emplaced as veins and dikes that cut granitoid, migmatite, granitoid gneiss, gneiss, and schist. The pegmatite veins and dikes are mostly 2 to 5 meters wide and 30 to 150 meters long, and some are traceable over a distance of 300 meters.

The pegmatites are composed of quartz, orthoclase, albite, microcline microperthite, and muscovite, with minor biotite, tourmaline, beryl, garnet, topaz, lepidolite, magnetite, wolframite, cassiterite, and rare columbite. They are commonly zoned, feldspars and muscovite being more abundant in the center and quartz more common at the margin. The zoning pattern is rather distinct in the pegmatite body, where tourmaline is present. The light-colored felsic minerals are confined to the core zone and the dark-colored tourmaline crystals to the outer zone.

Numerous fluid inclusions have been found in quartz, topaz, and beryl. Most of the inclusions are rounded to elliptical, with a variable degree of liquid filling. All inclusions are aqueous, two-phase (liquid and vapor) inclusions with no daughter minerals. Homogenization temperatures of 173 fluid inclusions were measured in this study.

Geothermometric studies indicate that the pegmatites were formed over a homogeniza-tion temperature range of 230° to 410°C. Salinities of fluid inclusions in pegmatite minerals yielded from 1.0 to 10.8 NaCl equiv. wt‰. Topaz and quartz single crystals (several cm across) from the Sakangyi pegmatite provide an opportunity to extract the fluids trapped in these minerals. The Na/K ratios of the fluid inclusions in two topaz samples were 3.0 to 4.9, and those of two quartz samples were 2.9 to 10.5, suggesting the presence of substantial potassium in the pegmatite-forming fluids. In this study, evidence for phase separation of the pegmatite-forming fluids was not observed. The post-magmatic, hydrothermal fluids responsible for the pegmatite veins evidently emanated from cooling S-type granitoids, with which they are spatially associated.     

In situ analyses of micas in the Yashan granite,South China: Constraints on magmatic and hydrothermal evolutions of W and Ta–Nb bearing granites

Most rare-metal granites in South China host major W deposits with few or without Ta–Nb mineralization. However, the Yashan granitic pluton, located in the Yichun area of western Jiangxi province, South China, hosts a major Nb–Ta deposit with minor W mineralization. It is thus important for understanding the diversity of W and Nb–Ta mineralization associated with rare-metal granites. The Yashan pluton consists of multi-stage intrusive units, including the protolithionite (-muscovite) granite, Li-mica granite and topaz–lepidolite granite from the early to late stages. Bulk-rock REE contents and La/Yb ratios decrease from protolithionite granite to Li-mica granite to topaz–lepidolite granite, suggesting the dominant plagioclase fractionation. This variation, together with increasing Li, Rb, Cs and Ta but decreasing Nb/Ta and Zr/Hf ratios, is consistent with the magmatic evolution. In the Yashan pluton, micas are protolithionite, muscovite, Li-mica and lepidolite, and zircons show wide concentration ranges of ZrO₂, HfO₂, UO₂, ThO₂, Y₂O₃ and P₂O₅. Compositional variations of minerals, such as increasing F, Rb and Li in mica and increasing Hf, U and P in zircon are also in concert with the magmatic evolution from protolithionite granite to Li-mica granite to topaz–lepidolite granite. The most evolved topaz–lepidolite granite has the highest bulk-rock Li, Rb, Cs, F and P contents, consistent with the highest contents of these elements and the lowest Nb/Ta ratio in mica and the lowest Zr/Hf ratio in zircon. Ta–Nb enrichment was closely related to the enrichment of volatile elements (i.e. Li, F and P) in the melt during magmatic evolution, which raised the proportion of non-bridging oxygens (NBOs) in the melt. The rims of zoned micas in the Li-mica and topaz–lepidolite granites contain lower Rb, Cs, Nb and Ta and much lower F and W than the cores and/or mantles, indicating an exotic aqueous fluid during hydrothermal evolution. Some columbite-group minerals may have formed from exotic aqueous fluids which were originally depleted in F, Rb, Cs, Nb, Ta and W, but such fluids were not responsible for Ta–Nb enrichment in the Yashan granite. The interaction of hydrothermal fluids with previously existing micas may have played an important role in leaching, concentrating and transporting W, Fe and Ti. Ta–Nb enrichment was associated with highly evolved magmas, but W mineralization is closely related to hydrothermal fluid. Thus these magmatic and hydrothermal processes explain the diversity of W and Ta–Nb mineralizations in the rare-metal granites.     

Genesis of apatite-fluorite rock in the Burpala pluton

Burpala is a unique peralkaline pluton known to the world. Alkaline pegmatites of the pluton contain about 70 rare-metal minerals. A new scheme of rock crystallization is offered: shonkinite → nepheline syenite → alkali syenite → quartz syenite → vein rocks: mariupolite, rare-metal pegmatite, apatite-fluorite, and alkali granite. Investigation of fluid inclusions in fluorite from the apatite-fluorite rocks established the high temperatures (520–560°C) of homogenization of multiphase salt inclusions. Fluids from inclusions are dominated by hydrocarbonates and chlorides as anions and sodium and calcium as cations; microelements include strontium, barium, boron, iron, manganese, lithium, rubidium, and cesium, i.e., components characteristic of magmatogenic fluids. These rocks are analogous to foskorites of carbonatite complexes in the high calcium content, but calcite is replaced with fluorite along with other foskorite minerals such as apatite, magnetite, mica, and pyroxene.     

Compositional controls on <Superscript>40</Superscript>Ar/<Superscript>39</Superscript>Ar ages of zoned mica from a rare-element pegmatite

A high spatial resolution Ar–Ar dating study of compositionally zoned micas using UV laser extraction has been used to investigate the effect of composition and compositional boundaries upon argon diffusion in mica. The crystals are characterised by muscovite cores and Li–F–Rb–Cs-rich lepidolite rims produced by the interaction of a residual melt-vapour phase with the original muscovite during the late stages of pegmatite crystallisation. Single crystals exhibit dramatic intra-grain age variations, with a maximum range of 2,880–2,117 Ma. Backscattered electron images combined with UV-laser analyses reveal that apparent ages younger than 2,600 Ma are directly associated with the compositionally distinct rims, suggesting that Ar diffusion was faster in the lepidolite than in muscovite. Although it is not possible to be fully quantitative using the present data, it seems that argon diffusion rates in lepidolite are similar to those in biotite. Major rearrangements of the crystal structure needed to accommodate high concentrations of lithium, fluorine and large interlayer cations (Rb⁺, Cs⁺) in muscovite account for lower argon retentivity of the crystal rims. In most cases the age profiles show no disturbance at the compositional boundary, despite the transition from a di-octahedral to tri-octahedral mica, indicating that in general the boundaries do not act as fast diffusion pathways. However, in some cases there is a clear drop in ages at the compositional boundary, which acts as an effective sub-grain boundary. The difference between the two types may be related to the internal structure of the compositional boundaries or their degree of contact with the grain boundary network of the rock.     

白云母成分对富锂铍伟晶岩成因的指示：以卡鲁安稀有金属矿田为例

新疆阿尔泰造山带是我国重要的稀有金属矿床矿产资源基地,尤以富Li和富Be伟晶岩型矿床广泛发育为特色。本研究选择阿尔泰造山带卡鲁安-阿祖拜矿田富Li和富Be伟晶岩型矿床开展典型解剖,以贯穿岩浆阶段-伟晶岩阶段的白云母矿物为研究主线,探讨不同矿化类型伟晶岩中云母的成分演化规律、花岗岩与伟晶岩的成因联系。矿物学特征显示富Be伟晶岩中发育大量磷酸盐矿物,而富Li伟晶岩含较多橙色锰铝榴石、锂云母而缺乏典型的Fe-Mn磷酸盐。白云母成分分析显示,从白云母花岗岩→富Be伟晶岩→富Li伟晶岩,白云母总体呈Nb含量和Nb/Ta值降低,指示白云母花岗岩、富Be伟晶岩经历了不同程度的分离结晶作用,也代表了富Li伟晶岩的岩浆分异演化程度更高。尽管利用云母成分变化(尤其是K、Rb、Cs等大离子亲石元素)模拟岩浆结晶演化过程,显示可由初始花岗质岩浆经瑞利分离结晶作用依次形成白云母花岗岩→富Be伟晶岩→富Li伟晶岩的假设。但研究区年代学、矿物学、同位素证据指示富Li伟晶岩和富Be伟晶岩具有不同的熔体性质和形成时代。因此,应用云母成分探讨伟晶岩的成因联系应当建立在花岗岩-伟晶岩系统具有合理的时空分布和其它支持源自同一...     

新疆拜城波孜果尔东矿区侵入岩矿物学特征

新疆拜城县波孜果尔东矿区侵入岩为富含铌、钽、铀、钍、稀土、锆、铷、铯、锂等有用元素的含矿岩体.通过偏光显微镜、电子探针(EPMA)分析, 对拜城波孜果尔东矿区侵入岩的矿物学特征进行了详细的研究, 并对岩浆形成的构造背景进行了初步探讨, 这对成岩、成矿作用研究有一定参考意义.研究结果表明, 波孜果尔东矿区侵入岩为黑云母碱性花岗岩, 主要造岩矿物包括石英、钠长石、钾长石、钠铁闪石、锂云母和黑云母等.其中, 黑云母为锂铁叶云母, 以富Si富Fe、低Al贫Mg为特征; 锂云母以富Si、高Li低Al为特征, 它们为黑云母-锂铁云母系列的不同成员, 均属三八面体型.钠铁闪石以富含Fe2+为特征.副矿物包括烧绿石、星叶石、氟铈矿、独居石、钍石、萤石、锆石、铌铁矿等.岩石形成于非造山的板内构造环境, 且具高温、无水、低氧逸度的成岩特点.      

四川阿坝州党坝超大型锂辉石矿床成矿规律及深部和外围找矿方向

党坝矿区位于松潘-甘孜稀有金属成矿带东段,可尔因矿田的东南部,是我国超大型锂辉石矿床之一.为了解该矿床地质特征及成矿规律,查明工作区深部及外围地质找矿方向,梳理了现有工作成果和野外地质观察结果,总结工作区岩浆岩岩相的空间变化特征、控岩控矿构造力学特征,对成矿规律进行了深入分析.研究表明:（1）党坝矿区主矿脉Ⅷ是2期成矿作用叠加、复合形成的钠长石锂辉石+锂云母型伟晶岩脉,每期伟晶岩脉内构造分带明显,自外向内分别是锂云母钠长石伟晶岩带、白云母钠长石伟晶岩带、锂辉石钠长石伟晶岩带;（2）主成矿期的应力场为EW向挤压,形成了矿区内的NW向和NEE向2组剪裂隙,伟晶岩脉充填其中,形成了呈"X"型分布的伟晶岩脉带;（3）以Ⅵ矿脉为成岩成矿中心,NW走向的伟晶岩矿脉带向南东侧伏,NE走向的伟晶岩矿脉带向北东侧伏,为工作区开展深部及外围地质找矿指明了方向.      

Characterisation of Two New Reference Materials: STL-1, the Stewart Lepidolite and ZA-1, the Zapot Amazonite

The analysis of granitic pegmatites still remains a challenge because suitable natural reference materials are scarce or not available. Two new reference materials were prepared at the Smithsonian Institution, to provide an avenue to pursue the geochemical analysis of micas and feldspars in granitic pegmatites: STL-1, the Stewart lepidolite (NMNH 174041) and ZA-1, the Zapot amazonite (NMNH 174042). STL-1 was prepared from lepidolite collected from the lithium-rich Stewart pegmatite, San Diego County, California (33°22'52'N, 117°03'41'W). ZA-1 was prepared from an amazonite from the topaz-bearing Zapot pegmatite, Mineral County, Nevada, (38° 41'N, 118 °33'W). The results of this study indicated that STL-1 and ZA-1 are homogeneous and could be used as reference materials that would allow the expansion of calibration curves in XRF analysis up to 16000 μg g⁻¹ for Rb, 2000 μg g⁻¹ for Cs and 100 μg g⁻¹ for Tl. STL-1 and ZA-1 also contain unusually high concentrations of Ga and Tl, and STL-1 of Nb.     

浙江临安石室寺NYF型伟晶岩中稀有稀土金属的矿物学行为与成矿过程

浙江临安石室寺伟晶岩位于河桥岩体西北面,属于典型的Nb-Y-F （NYF） 型伟晶岩,富含大量稀有稀土矿物。本文在野外考察和显微镜观察的基础上,结合电子探针背散射电子图像观察与矿物化学成分分析,系统鉴定了石室寺NYF 型伟晶岩中的稀有稀土矿物,揭示了稀有稀土元素的富集、迁移、结晶与成矿过程。研究结果表明：（1） 石室寺伟晶岩中的稀有稀土矿物有铌钽矿物（铌铁矿、铌锰矿、重钽铁矿、细晶石等）、钇矿物（褐钇铌矿、黑稀金矿）、钨矿物（黑钨矿、 白钨矿、铌钨矿物）、铈矿物（独居石、氟铈矿、氟碳铈矿） 和钍矿物等。（2） 铌钨系列矿物的WO3含量在8.30~70.51 wt%之间呈规律变化,可能为铌铁矿与黑钨矿之间形成的一系列多体矿物。（3） 铌铁矿LA-ICP-MS U-Pb 定年结果显示,石室寺伟晶岩的形成年龄为133±2 Ma,与河桥花岗岩具有成因联系。（4） 石室寺NYF 型伟晶岩中稀有稀土元素的成矿过程与其岩浆的结晶演化密切相关：岩浆阶段,锆石、钍石与独居石等矿物最早晶出;岩浆—热液阶段,黑稀金矿、铌铁矿、褐钇铌矿、氟铈矿等稀有稀土矿物逐渐结晶;热液阶段,黑钨矿、铌钨矿物相继形成,同时早期的独居石、氟铈矿受晚期热液交代形成次生铈矿物。     

Sc- and REE-bearing ixiolite and associated minerals from the Sosedka pegmatite vein in the Malkhan pegmatite field, central Transbaikal region

Composition and localization of REE mineralization in miarolitic pegmatites and its role in the pegmatite formation were studied at the Malkhan gem deposit (jewel-quality tourmaline, morganite, danburite, and hambergite) in the central Transbaikal region. The chemical composition of Ti-, Ta-, Nb- and REE-bearing minerals, their relationships with rock-forming and accessory minerals indicate that two geochemically specialized stages of pegmatite formation are distinguished. The early stage gave rise to the crystallization of quartz-feldspar aggregates including K-feldspar block zone with Sc and REE mineralization. The rare-metal (Li, Cs, F, B, Be) albite-lepidolite-cleavelandite complex with pockets of gem mineralization was formed at the late stage.     

The behavior of trace elements during the chemical evolution of the H2O-, B-, and F-rich granite–pegmatite–hydrothermal system at Ehrenfriedersdorf, Germany: a SXRF study of melt and fluid inclusions

Detailed melt and fluid inclusion studies in quartz hosts from the Variscan Ehrenfriedersdorf complex revealed that ongoing fractional crystallization of the highly evolved H₂O-, B-, and F-rich granite magma produced a pegmatite melt, which started to separate into two immiscible phases at about 720°C, 100 MPa. With cooling and further chemical evolution, the immiscibilty field expanded. Two conjugate melts, a peraluminous one and a peralkaline one, coexisted down to temperatures of about 490°C. Additionally, high-salinity brine exsolved throughout the pegmatitic stage, along with low-density vapor. Towards lower temperatures, a hydrothermal system gradually developed. Boiling processes occurred between 450 and 400°C, increasing the salinities of hydrothermal fluids at this stage. Below, the late hydrothermal stage is dominated by low-salinity fluids. Using a combination of synchrotron radiation-induced X-ray fluorescence analysis and Raman spectroscopy, the concentration of trace elements (Mn, Fe, Zn, As, Sb, Rb, Cs, Sr, Zr, Nb, Ta, Ag, Sn, Ta, W, rare earth elements (REE), and Cu) was determined in 52 melt and 8 fluid inclusions that are representative of distinct stages from 720°C down to 380°C. Homogenization temperatures and water contents of both melt and fluid inclusions are used to estimate trapping temperatures, thus revealing the evolutionary stage during the process. Trace elements are partitioned in different proportions between the two pegmatite melts, high-salinity brines and exsolving vapors. Concentrations are strongly shifted by co ncomitant crystallization and precipitation of ore-forming minerals. For example, pegmatite melts at the initial stage (700°C) have about 1,600 ppm of Sn. Concentrations in both melts decrease towards lower temperatures due to the crystallization of cassiterite between 650 and 550°C. Tin is preferentially fractionated into the peralkaline melt by a factor of 2–3. While the last pegmatite melts are low in Sn (64 ppm at 500°C), early hydrothermal fluids become again enriched with about 800 ppm of Sn at the boiling stage. A sudden drop in late hydrothermal fluids (23 ppm of Sn at 370°C) results from precipitation of another cassiterite generation between 400 and 370°C. Zinc concentrations in peraluminous melts are low (some tens of parts per million) and are not correlated with temperature. In coexisting peralkaline melts and high-T brines, they are higher by a factor of 2–3. Zinc continuously increases in hydrothermal fluids (3,000 ppm at 400°C), where the precipitation of sphalerite starts. The main removal of Zn from the fluid system occurs at lower temperatures. Similarly, melt and fluid inclusion concentrations of many other trace elements directly reflect the crystallization and precipitation history of minerals at distinctive temperatures or temperature windows.     

Characteristics of Pegmatite-Related Fluids and Significance to Ore-Forming Processes in the Zhaxikang Pb-Zn-Sb Polymetallic Deposit, Tibet, China

The Zhaxikang Pb-Zn-Sb polymetallic deposit is one of the most important deposits in the newly recognized southern Tibet antimony-gold metallogenic belt.Compared to the porphyry deposits in the Gangdese belt,much less researches have addressed these deposits,and the genesis of the Zhaxikang deposit is still controversial.Based on field investigation,petrographic,microthermometric,Laser Raman Microprobe（LRM） and SEM/EDS analyses of fluid,melt-fluid,melt and solid inclusions in quartz and beryl from pegmatite,this paper documents the characteristics and the evolution of primary magmatic fluid which was genetically related to greisenization,pegmatitization,and silification in the area.The results show that the primary magmatic fluids were derived from unmixing between melt and fluid and underwent a phase separation process soon after the exsolution.The primary magmatic fluids are of low salinity,high temperature,and can be approximated by the H₂O-NaCl-CO₂ system.The presence of Mn-Fe carbonate in melt-fluid inclusions and a Zn-bearing mineral（gahnite） trapped in beryl and in inclusions from pegmatite indicates high Mn,Fe,and Zn concentrations in the parent magma and magmatic fluids,and implies a genetic link between pegmatite and Pb-Zn-Sb mineralization.High B and F concentrations in the parent magma largely lower the solidus of the magma and lead to late fluid exsolution,thus the primary magmatic fluids related to pegmatite have much lower temperature than those in most porphyry systems.Boiling of the primary magmatic fluids leads to high-salinity and high-temperature fluids which have high capacity to transport Pb,Zn and Sb.The decrease in temperature and mixing with fluids from other sources may have caused the precipitation of Pb-Zn-Sn（Au） minerals in the distal fault systems surrounding the causative intrusion.     

Theoretical studies of the alteration of spodumene,petalite, eucryptite and pollucite in granitic pegmatites: exchange reactions with alkali feldspars

The ratios Na/Li, K/Li, Na/Cs and K/Cs have been calculated for exchange equilibria among the Li and Cs silicates spodumene, petalite, eucryptite, and pollucite, and the alkali feldspars albite and K-feldspar plus quartz, in pure water and in chloride solutions at temperatures from 100° to 700°C and pressures from 0.5 to 4 kbar, using available thermodynamic data for minerals and the modified HKF equation of state for aqueous species. For exchange equilibria between Li-bearing aluminosilicates and the alkali feldspars, the activities of the alkali metals in solution under most of the conditions investigated follow the order Li>Na>K, and Na/Li and K/Li decrease with decreasing temperature. For exchange equilibria between pollucite and the alkali feldspars the order is Na>K>Cs in solution; Na/Cs and K/Cs increase strongly with decreasing temperature. The absolute values of these alkali metal ratios are in good agreement with the few available experimental data. The effect of chloride ion pairing on the calculated ratios is slight and does not consistently improve agreement between theory and experiment. These results suggest that the alteration of eucryptite, petalite or spodumene to albite and/or K-feldspar should be a normal consequence of the closed system evolution of rare element pegmatites upon cooling, in agreement with the ubiquity of such phenomena world-wide. On the other hand, alteration of pollucite to albite or K-feldspar upon cooling is only likely to occur if external fluids, with very high Na/Cs and/or K/Cs ratios, gain access to the pegmatite. Owing to the heterogeneity of rare element pegmatites, the fluid need not be external to the entire pegmatite, but could be simply external to the particular zone containing pollucite. Fluids in equilibrium with typical subsolidus rare metal pegmatite assemblages will invariably have high Li contents, thus explaining the common occurrence of Li-metasomatic halos about pegmatites. These same fluids are predicted to have relatively low Cs contents, in apparent agreement with the lesser role of Cs relative to Li in metasomatic halos. However, preferential formation of complexes of the alkali metals with fluoride, borate or aluminosilicate components potentially could alter the calculated alkali metal behaviors.     

河北平山阜平群夕线石钾长浅粒岩深熔作用的微区矿物学标志

河北省平山县阜平群是一套高角闪岩相岩石。根据宏观现象，某些地段曾经历过深熔作用过程。深熔效应以小觉地区的夕线石钾长浅粒岩最为典型。通过电子显微镜观测确认，所研究的夕线石钾长浅粒岩经受了深熔作用的改造，具有丰富而显著的微区矿物学标志。主要表现为前存矿物，如钾长石、条纹长石、石英、钠长石、黑云母和磁铁矿等，不同程度地被熔蚀，主要组成元素发生迁移和重组，沿矿物的解理、裂隙及粒间形成夕线石、石英、云母、长石、金红石等再结晶相。在深熔过程中，元素的迁移有两种可能形式：①选择性地从前存矿物晶格中移出；②通过前存矿物的熔融。Fe、Ti等元素从黑云母中移出，形成再结晶磁铁矿和金红石；Si、AI等元素则从黑云母和长石中移出，形成夕线石和再结晶石英。