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1.
藏南过铝花岗岩中电气石的矿物化学特征及成因意义   总被引：2，自引：0，他引：2  
讨论了藏南过铝花岗岩中电气石的地质产状、矿物学和矿物化学特征。结果表明:(1)在以氧原子数为24.5计算的化学式中,电气石的(Fe+Mg)/Mg比值在2.32~5.37之间,指示花岗岩和伟晶岩中的电气石均为黑电气石系列,而且属镁电气石—铁电气石系列中的较富铁电气石的成员;(2)电气石的FeO/(FeO+MgO)值高达0.70~0.89,与贫Li花岗岩接近,Al-Al50Fe50-Al50Mg50图解和Fe-Mg-Ca图解投点均位于贫Li花岗岩区,属于贫Li花岗岩有关的电气石;(3)TiO2-MnO/CaO-MgO/FeO三元图解可判定属于第Ⅰ类,即MgO和FeO含量同步消长,且较贫Mg富Fe,而MnO和TiO2含量为异步消长,这与电气石的FeO/(FeO+MgO)值所反映的性质相同;(4)地质产状、矿物学及矿物化学揭示的成因信息表明藏南过铝花岗岩中的电气石为酸性侵入体岩浆期后热液成因。  相似文献   

2.
Summary Tourmaline is an ubiquitous constituent in the Pinilla de Fermoselle rare-element pegmatite (Zamora, Spain), as well as in barren pegmatitic and quartz–tourmaline veins inside the associated leucogranite. The rare-element pegmatite shows internal zoning, evolving from a barren facies, in the lower border zone, in contact with the leucogranite, to a Li-rich facies in the upper border zone, close to the host-rocks.Tourmalines from the veins within the leucogranite have highest Mg contents, and belong to the schorl–dravite series. The tourmalines from the rare-element pegmatite mostly belong to the schorl–elbaite series, with chemical compositions within the range of the end-members, whereas the tourmalines associated with the most evolved zone in the pegmatite belong to the elbaite–rossmanite series. The broad compositional range shown by the tourmalines correlates quite well with the pegmatite zoning. The most plausible substitution mechanism for the chemical evolution of tourmalines during crystallization seems to be Mg–1Fe2+1, [X]–1YAl–1XNa–1YFe2+1, for the foitite–schorl series; YFe2+–3YAl1.5YLi1.5, for the schorl–elbaite vector; XNa–1YLi–0.5[X]1YAl0.5, for the elbaite–rossmanite series; and, (OH)1F1 for all the tourmalines except the pink elbaites. This chemical variation in tourmaline is consistent with a crystal fractionation model for the evolution of the Pinilla pegmatite.  相似文献   

3.
稀有金属矿物记录了花岗伟晶岩成岩成矿的重要信息。喜马拉雅是全球著名的淡色花岗岩带,库曲岩体位于喜马拉雅东段的特提斯喜马拉雅岩系中。本文调查了库曲岩体的二云母花岗岩、白云母花岗岩、电气石花岗岩和花岗伟晶岩,其中,花岗伟晶岩涉及花岗岩的伟晶岩相和独立伟晶岩脉。库曲岩体产出的稀有金属矿物包括锂辉石、锂绿泥石、绿柱石、铌铁矿-钽铁矿、钇铀钽烧绿石和细晶石,它们主要赋存于似文象伟晶岩、石英-钠长石-白云母伟晶岩、块体长石-钠质细晶岩、块体长石-电气石钠质细晶岩、锂辉石-块体长石-细晶岩、白云母花岗岩的伟晶岩相以及电气石花岗岩内。显微镜观察、电子探针和LA-ICP-MS测试结果显示锂辉石具有四种产状,包括粗粒锂辉石自形-半自形晶、细粒锂辉石-石英镶嵌晶、中细粒锂辉石-钾长石-钠长石-云母镶嵌晶以及发育锂绿泥石的粗粒锂辉石,揭示了其形成时复杂的熔流体动荡结晶环境。绿柱石背散射电子图像（BSE）下呈均一结构和不均一结构（蚀变边、不规则分带和补丁分带）,元素替代机制包括通道-八面体替代、通道-四面体替代以及通道中碱金属阳离子间的置换。铌铁矿族矿物包括原生、蚀变边和不规则分带结构,部分被钇铀钽烧绿石和细晶石交代。与原生铌铁矿相比,蚀变边和不规则分带铌铁矿族矿物总体上富钽贫锰,显示了结晶分异、过冷却引起的过饱和以及流体作用。根据稀有金属矿物揭示的成因信息,独立伟晶岩脉（似文象伟晶岩）、白云母花岗岩的伟晶岩相和电气石花岗岩在岩浆分异程度、经历的演化过程、以及流体活动方面存在差异,很可能是不同期次岩浆活动的产物。库曲岩体绿柱石的Rb和Zn含量、以及铌铁矿族矿物的Sc2O3、SiO2和PbO含量,与已有指示标志存在相关性,作为潜在指示标志仍需开展更多的研究工作。综合含锂辉石伟晶岩的产出、岩浆分异演化程度、多期花岗质岩浆活动、复杂的流体作用以及所属锂丰度高值区等因素,库曲岩体是喜马拉雅东段找锂的有利地段。  相似文献   

4.
Subhorizontally layered pegmatite-aplite bodies are characterized by fine-grained, sodic to granitic aplite that is usually juxtaposed abruptly above by much coarser-grained, commonly graphic potassic pegmatite. Although well studied, there currently is little concensus as to how such dikes form. The Little Three dike near Ramona, California, is representative of such zoned bodies in this and other regions, and contains discontinuous miarolitic pockets near the base of the graphic pegmatite zone. Tourmaline, garnet, biotite, and muscovite show no changes in major- or minor-element compositions indicative of progressive magmatic fractionation until the immediate vicinity of the main miarolitic zone, where they record abrupt and extreme enrichments in Li, F, and Mn. There is no correlation of chemical changes in the dike with the appearance of small miarolitic vugs well below the main miarolitic zone, nor is there any indication that the aplite, graphic pegmatite, or miarolitic pockets represent separate magma injections. The chemistries of tourmaline, garnet, and micas, however, preclude conventional models of Rayleigh fractionation or traditional zone refining. Textural features and modeled cooling histories indicate that the dike cooled quickly and might have solidified partially or totally to glass before crystallization commenced. Geothermometry based on the compositions of coexisting plagioclase and homogeneous, nonperthitic K-feldspar indicates inward crystallization of the dike, from ∼400–435 °C at the margins to ∼350–390 °C within 20–30 cm of the pocket horizon, then a sharp decrease to 240–275 °C in the pockets where K-feldspar is perthitic. We interpret the feldspar geothermometry (except perhaps in the miarolitic cavities) to reflect the temperatures at crystallization fronts that advanced into the pegmatite, first from the foot wall and eventually joined by a similar front downward from the hanging wall. Crystallization down from the hanging wall may have commenced after ∼70–80% of the foot wall aplite had crystallized. The very abrupt increases of Li, Mn, and F in tourmaline and garnet near the miarolitic zone appear to be explained best by the process of constitutional zone refining, in which a fluxed crystallization front sweeps an incompatible element-enriched boundary layer through a solid or semi-solid. After these two highly fluxed boundary layers merged near the main miarolitic zone, compositional evolution could have proceeded by crystal-melt fractionation. Received: 24 March 1998 / Accepted: 10 March 1999  相似文献   

5.
A detailed study of the chemical composition and substitutions in calcium tourmalines from a scapolite-bearing rare-metal pegmatite vein from the Sol’bel’der River basin has shown that their species attribution is determined by occupancy of octahedral site Y. The composition of the yellow tourmaline most abundant in the central part of the pegmatite bodyis rather constant and characterized by the ideal formula Ca(Mg2Li)Al6(Si6O18)(BO3)3(OH)3F. Variations in the chemical composition of zonal tourmaline crystals from the contact part of the pegmatite are controlled by abrupt change in the chemical medium during their formation. The yellow cores of these crystals are close in composition to tourmaline from the central part of the pegmatite vein. The Mg content abruptly decreases toward the crystal margin: Mg2+ → Fe2+, 2Mg2+ → Li+ + Al3+, and Mg2+ + OH → Al3+ + O2−. The composition of dark green marginal zones in tourmaline is characterized by the ideal formula Ca(Al1.5Li1.5)Al6(Si6O18)(BO3)3 (OH2O)(F). The results indicate specific formation conditions of pegmatite. The crystallochemical formulas of the studied tourmalines allow us to regard them as new mineral species in the tourmaline group.  相似文献   

6.
Reported in this paper are the results of geological and fluid inclusion studies of gem-grade tourmaline in pegmatite veins from Altay, Xinjiang. The homogenization temperatures of fluid inclusions in the tourmaline range from 230° to 350°C with a salinity of 0.2−4.5 NaCl% equiv. The composition of fluids corresponds to the NaCl-CaCl2-H2O system in terms of the measurements of first melting temperature of fluid inclusions. By comparing the homogenization temperatures of different color zones in the gem tourmaline, it is suggested that it has undergone an intermittent growth process. Careful observation of the section parallel to thec axis of greenish blue tourmaline provides evidence of the occurrence of cat-eye tourmaline similar to that found in Brazil and other parts of the world. Attention should be paid to such kind of tourmaline as viewed from its economic importance.  相似文献   

7.
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.  相似文献   

8.
东秦岭地区是我国重要的花岗伟晶岩区及稀有金属成矿区.电气石在东秦岭各类花岗伟晶岩中广泛发育,通常在无矿化伟晶岩、铍矿化及锂矿化伟晶岩中呈黑色-深蓝色.本文旨在通过各类伟晶岩中电气石的对比研究揭示电气石地球化学特征对东秦岭伟晶岩矿化类型的指示作用.本文所研究电气石为作为东秦岭各类伟晶岩贯通矿物的黑电气石系列.在双峰村、碾...  相似文献   

9.
The Qiman Tagh W-Sn belt lies in the westernmost section of the East Kunlun Orogen, NW China, and is associated with early Paleozoic monzogranites, tourmaline is present throughout this belt. In this paper we report chemical and boron isotopic compositions of tourmaline from wall rocks, monzogranites, and quartz veins within the belt, for studying the evolution of ore-forming fluids. Tourmaline crystals hosted in the monzogranite and wall rocks belong to the alkali group, while those hosted in quartz veins belong to both the alkali and X-site vacancy groups. Tourmaline in the walk rocks lies within the schorl-dravite series and becomes increasingly schorlitic in the monzogranite and quartz veins. Detrital tourmaline in the wall rocks is commonly both optically and chemically zoned,with cores being enriched in Mg compared with the rims. In the Al-Fe-Mg and Ca-Fe-Mg diagrams,tourmaline from the wall rocks plots in the fields of Al-saturated and Ca-poor metapelite, and extends into the field of Li-poor granites, while those from the monzogranite and quartz veins lie within the field of Li-poor granites. Compositional substitution is best represented by the MgFe_(-1), Al(NaR)_(-1), and AlO(Fe(OH))_(-1) exchange vectors. A wider range of δ~(11)B values from -11.1‰ to -7.1‰ is observed in the wall-rock tourmaline crystals, the B isotopic values combining with elemental diagrams indicate a source of metasediments without marine evaporates for the wall rocks in the Qiman Tagh belt. The δ~(11)B values of monzogranite-hosted tourmaline range from -10.7‰ and-9.2‰, corresponding to the continental crust sediments, and indicate a possible connection between the wall rocks and the monzogranite. The overlap in δ~(11)B values between wall rocks and monzogranite implies that a transfer of δ~(11)B values by anataxis with little isotopic fractionation between tourmaline and melts. Tourmaline crystals from quartz veins have δ~(11)B values between -11.0‰ and-9.6‰, combining with the elemental diagrams and geological features, thus indicating a common granite-derived source for the quartz veins and little B isotopic fractionation occurred. Tourmalinite in the wall rocks was formed by metasomatism by a granite-derived hydrothermal fluid, as confirmed by the compositional and geological features.Therefore, we propose a single B-rich sedimentary source in the Qiman Tagh belt, and little boron isotopic fractionation occurred during systematic fluid evolution from the wall rocks, through monzogranite, to quartz veins and tourmalinite.  相似文献   

10.
A detailed study was given to the composition and structure of alkali feldspars from the pockets of the Sosedka pegmatite vein, a large source of gems within the Malkhan tourmaline deposit. The vein is of concentric-zonal structure. Three types of pockets were recognized by mineral composition: A—quartz–lepidolite–Mn–Li–Al–tourmaline (± pollucite, hambergite, borocookeite, boromuscovite, danburite, light pink beryl); B—quartz–adularia–axinite (± laumontite); and C—quartz and laumontite (± B-containing cookeite). Each type of pockets contains feldspars of specific composition and structure. This evidences that pockets formed in strongly different conditions, though some pockets of different types are localized as close as 0.5–2 m from each other within a zone. The reported data disagree with the common model implying the formation of zonal pegmatite bodies as a result of crystallization differentiation within the vein.  相似文献   

11.
Six tourmaline samples were investigated as potential reference materials (RMs) for boron isotope measurement by secondary ion mass spectrometry (SIMS). The tourmaline samples are chemically homogeneous and cover a compositional range of tourmaline supergroup minerals (primarily Fe, Mg and Li end‐members). Additionally, they have homogeneous boron delta values with intermediate precision values during SIMS analyses of less than 0.6‰ (2s). These samples were compared with four established tourmaline RMs, that is, schorl IAEA‐B‐4 and three Harvard tourmalines (schorl HS#112566, dravite HS#108796 and elbaite HS#98144). They were re‐evaluated for their major element and boron delta values using the same measurement procedure as the new tourmaline samples investigated. A discrepancy of about 1.5‰ in δ11B was found between the previously published reference values for established RMs and the values determined in this study. Significant instrumental mass fractionation (IMF) of up to 8‰ in δ11B was observed for schorl–dravite–elbaite solid solutions during SIMS analysis. Using the new reference values determined in this study, the IMF of the ten tourmaline samples can be modelled by a linear combination of the chemical parameters FeO + MnO, SiO2 and F. The new tourmaline RMs, together with the four established RMs, extend the boron isotope analysis of tourmaline towards the Mg‐ and Al‐rich compositional range. Consequently, the in situ boron isotope ratio of many natural tourmalines can now be determined with an uncertainty of less than 0.8‰ (2s).  相似文献   

12.
The role of manganese in the chemical composition and coloring of tourmaline is discussed. It is shown that manganese tourmaline-tsilaisite is similar to tourmaline-elbaite in composition and condition formation. The miscibility in the sherlite-elbaite-tsilaisite system is complete, but in the sherlite-dravite-tsilaisite system there is a gap between the dravite and tsilaisite, similar to the relationship between dravite and elbaite.

Manganese may be present in tourmaline in the form of Mn2+ and Mn3+. The pink coloring of the tourmaline is caused by Mn3+. This conclusion has been drawn from data provided by many authors on the nature of pink coloring of tourmaline, the dyeing properties of Mn2+ and Mn3+, the possibility of the existence of Mn3+ during the crystallization of pink tourmaline, and the distribution of manganese in differently colored tourmaline. --auth.  相似文献   

13.
A detailed mineralogical investigation using the classical methods of identification by X-ray diffraction and by optical properties in thin sections, has revealed thirty one phosphate minerals occurring in the Tsaobismund pegmatite. This investigation is complemented by wet chemical and, mainly, electron microprobe analyses performed on the phosphates known to be typomorphic or considered to be relevant to the hydrothermal alteration. Additionally, microprobe analyses are also given for garnet, gahnite, and ferrocolumbite associated with the phosphates. On the basis of their chemical composition, particularly in terms of their Fe, Mn, and Mg contents, three types of triphylites are distinguished. Triphylite 1 only occurs as a primary phase, triphylite 2 shows exsolution lamellae of sarcopside, and triphylite 3 is partly replaced by a fluorophosphate of the triplite-zwieselite series. These minerals constitute three generations of the parent phases, which were progressively transformed by metasomatic processes, hydrothermal alteration, and by weathering, to give finally three types of complex associations. The Li(Fe,Mn)PO4 minerals appear to be more sensitive to such transformations than those of the (Fe,Mn)2PO4F series. Four main stages of hydrothermal alteration processes have been recognized in the Tsaobismund pegmatite: (i) the Mason-Quensel sequence results from a progressive oxidation of Fe and Mn, and a concomitant Li-leaching of triphylite yielding ferrisicklerite and heterosite, successively; (ii) the metasomatic exchange of Na for Li produces alluaudite; in the present case, the formation of hagendorfite from triphylite 2 is considered to be earlier than the generation of alluaudite-Na occurring in the three associations; (iii) the hydration phase mainly transforms the parent Li(Fe,Mn)PO4 phase into grey hureaulite, associated with barbosalite and tavorite; (iv) the formation of fluorapatite, not particularly widespread, replaces alluaudite-Na, as well as zwieselite s.l. The following crystallization sequence of the initially formed phosphate minerals is proposed: triphylite 1 triphylite 2 + sarcopside (associated with garnet) triphylite 3 + zwieselite s.l. The most prominent feature of this succession is the increase in the Mg and Zn contents in the composition of the phosphates, as well as the decrease in their Li contents. The variations of the Fe/Mn ratios in this sequence are discussed. The succession triphylite-zwieselite within weakly differentiated and Li-poor pegmatites is of general significance.  相似文献   

14.
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。  相似文献   

15.
Prosperous granite (Rb-Sr 2520±25 Ma) occurs as several plutons (1–380 km2 outcrop area) in a thick succession of metamorphosed greywacke-mudstone of the Yellowknife Supergroup. The average mineral content of the Sparrow pluton (in vol.%) is quartz (32), plagioclase (31), K-feldspar (24), muscovite (9), biotite (3), and apatite (<1). Average trace-element concentrations (in ppm) are Li (140), Be (4), B (28), Zn (47), Rb (250), Sr (76), Zr (75) and Ba (360). The central portion of the pluton is slightly richer in K, Sr, and Ba than the margin. Li is concentrated in mica (Li in biotite/Li in muscovite=4.7), and Be and B in muscovite and plagioclase. Countless pegmatite dikes occur in the Sparrow pluton and in schist-hornfels to the east; the outer limit is marked by the cordierite isograd, 9 km from the granite contact. Dikes vary greatly in size (1 km to a few cm in length), in mineral content (quartz, albite, K-feldspar, muscovite, tourmaline, beryl, spodumene), in major element composition (especially the NaK ratio), and in trace-element content (Li 18–5000 ppm, Be 5–260 ppm, B 20–150 ppm). Compared with Prosperous granite, the pegmatite bodies are richer in P and Rb, and poorer in Ti, Fe, Mg, Zr, and Ba. Dikes rich in tourmaline, beryl, and spodumene occur in overlapping zones situated progressively farther from the centre of the Sparrow pluton. The composition of tourmaline is related to host rock; the highest concentrations of Fe and Zn occur in crystals from pegmetite and the highest concentrations of Mg and V occur in crystals from tourmalinized schist, while those from granite and quartz veins occupy on intermediate position. Complex compositional zoning is present in some tourmaline crystals in pegmatite. Estimates of temperature (500°–600° C) and pressure (2–4 kb) of granite emplacement, based on the distribution of andalusite and sillimanite in the contact rocks, suggest that the final stage of granite emplacement occurred at sub-solidus conditions. A vaportransport model is proposed to explain the widespread distribution of the pegmatite dikes and their extreme compositional variability. Some of the pegmatite constituents, including Li, Be, and B, were possibly derived from Yellowknife graywacke and mudstone.  相似文献   

16.
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。  相似文献   

17.
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.  相似文献   

18.
Summary A new subtype of complex rare-element granitic pegmatites, the elbaite subtype, is proposed to designate pegmatites in which most of Li is stored in tourmaline. Elbaite pegmatites are widespread in the Bohemian and Moravian parts of the Moldanubicum. Internal structure commonly is simple, progressing from a granitic border unit through a graphic unit to local pods of blocky K-feldspar. Patches of an albitic unit are associated with the blocky pods or pockets developed in the central parts of some dikes. A very low proportion of micas is typical. Tourmaline (schorl to elbaite) is an omnipresent subordinate to accessory phase. Elbaite is found at and within the pockets, or associated with albite ± lepidolite in massive pegmatite. Hambergite, danburite, datolite and boromuscovite have been found at some localities. Elbaite from the elbaite pegmatites is apparently enriched in Mn and F, and shows low vacancies in the X-site, relative to elbaite from the lepidolite subtype. Lepidolite from elbaite pegmatites is close to polylithionite, whereas lithium micas from pegmatites of the lepidolite subtype show highly variable compositions from lithian muscovite to lepidolite with a substantial amount of the trilithionite (up to polylithionite) component.Paragenesis and composition of the elbaite pegmatites indicate conditions of consolidation that are rather different from those of other subtypes of the complex pegmatites: high activity of B, increased alkalinity of the parent medium, and reduced activity of P.
Elbait-Pegmatite im Moldanubikum: Ein neuer Subtyp der Selten-Element Pegmatite
Zusammenfassung Um Pegmatite zu kennzeichen, in denen Li hauptsächlich an Li-führende Turmaline gebunden ist, wird ein Elbait Subtyp komplexer granitischer Selten-Element Pegmatite vorgeschlagen. Zusammen mit dem häufigeren und üblicherweise stärker Li-angereicherten Lepidolith-Subtyp, sind Elbait-Pegmatite im Moldanubikum Böhmens und Mährens weitverbreitet. Die Internstruktur ist allgemein einfach, beginnend mit einer granitischen Randzone, gefolgt von einer schriftgranitischen Zone mit Nestern mit blockigem K-Feldspat. Albit-reiche Zonen die sich im zentralen Teil der Pegmatitgänge entwickelten, sind mit diesen Nestern verbunden. Ein geringer Glimmeranteil ist typisch. Turmalin (Schörl bis Elbait) ist untergeordnet bis akzessorisch allgegenwärtig. Elbait kommt in den Taschen, oder vergesellschaftet mit Albit ± Lepidolith in den massigen Pegmatiten vor. Hambergit, Danburit, Datolith und Boromuscovit sind gelegentlich gefunden worden. Sie stellen späte Drusen-Minerale dar. Der Elbait aus den Elbait-Pegmatiten ist an Mn und F angereichert, und zeigt im Vergleich zum Elbait aus dem Lepidolith-Subtyp, wenig Leerstellen auf den X-Positionen. Lepidolith aus Elbait-Pegmatiten ähnelt Polylithionit, während Li-Glimmer aus Pegmatiten des Lepidolith-Subtyps sehr variable Zusammensetzungen von Li-betontem Muscovit bis Lepidolith mit erheblichen Anteilen von Trilithionit (bis Polylithionit) enthalten.Die Paragenese und Zusammensetzung der Elbait-Pegmatite verweisen auf Bildungsbedingungen, die sich erheblich von denen anderer Subtypen komplexer Pegmatite unterscheiden. hohe B-Aktivität, erhöhte Alkalinität der Fluidphase und niedrige P-Aktivität.

With 4 Figures  相似文献   

19.
Summary Internal structure and mineralogy facilitate distinction of four main pegmatite types at the eastern end of the Pyrenees. Three main trends in compositional variations in Nb-Ta-Sn-REE-Ti minerals have been established: a regional trend, with Ta/(Ta + Nb) ratio increasing towards the more evolved pegmatites, Mn/(Mn + Fe) being relatively low and increasing only slightly; a single-body trend, with similar enrichment toward the late pegmatite units; a single-crystal trend, with zoning related to both Ta/(Ta + Nb) and Mn/(Mn + Fe) ratios and a tendency toward Ta-enrichment in the late growth stages. The regional geochemical enrichment trends in the Mn/(Mn + Fe) ratios and Ta/(Ta + Nb) are those expected for a beryl-columbite pegmatite type. In a single pegmatite, the evolution depends on the simultaneous growth of other mineral species. Three factors seem to control the development of zoning in columbite-tantalite crystals: availability of Mn, Ta, Fe, Nb, significant differences in solubility between mineral group end members and re-equilibria with late pegmatite fluids.
Nb-Ta-Minerale aus dem Pegmatit-Feld vom Cap de Creus, östliche Pyrenäen: Verteilung und geochemische Trends
Zusammenfassung Am Ostrand der Pyrenäen können anhand des inneren Aufbaus und der Mineralogie vier Haupttypen von Pegmatiten unterschieden werden. Die Zusammensetzungen von Nb-Ta-Sn-SEE-Ti-Mineralen folgen drei Haupttrends: einem regionalen Trend, bei dem das Verhältnis Ta/(Ta + Nb) zu den höher entwickelten Pegmatiten hin zunimmt, während Mn/(Mn + Fe) relativ niedrig ist und nur leicht zunimmt; einem lokalen (auf das jeweilige Vorkommen beschränkten) Trend mit einer ähnlichen Anreicherung zu den spätpegmatitischen Einheiten hin; einem auf Einzelkristalle bezogenen Trend mit Zonierung in bezug auf die Verhältnisse Ta/(Ta + Nb) und Mn/(Mn + Fe) und einer Tendenz zur T a-Anreicherung in den späten Wachstumsphasen. Die regionalen geochemischen Anreicherungstrends in den Mn/(Mn + Fe)- und Ta/(Ta + Nb)-Verhältnissen entsprechen jenen, wie sie für den Beryll-Columbit-Pegmatit-Typ erwartet werden. In einem einzelnen Pegmatit hängt die Entwicklung vom gleichzeitigen Wachstum anderer Mineral-Spezies ab. Drei Faktoren scheinen die Ausbildung einer Zonierung in Columbit-Tantalit-Kristallen zu kontrollieren: das Angebot an Mn, Ta, Fe und Nb, deutliche Unterschiede in der Löslichkeit der Endglieder von Mineralgruppen und die Iteequilibrierung mit spätpegmatitischen Lösungen.

With 6 Figures  相似文献   

20.
Carbon dioxide-rich fluid and carbonate-rich aluminosilicate melt inclusions in tantalite-(Mn) from the Alto do Giz pegmatite in the Borborema Pegmatite Province, northeastern Brazil were investigated to constrain the formation of the host crystals. The results demonstrate that in the Alto do Giz pegmatite, water- and alkaline carbonate-rich fluids and melts are responsible for the transport and deposition of tantalite-(Mn) at temperatures around 600°C and about 4 kbar. Moreover, evidence is presented to show that during crystallization of the tantalite-(Mn), three different components coexisted, which are now trapped as separate inclusions: two immiscible silicate melts (types A and B melt inclusions) and a CO2-rich aqueous fluid. We hypothesize that immiscible fluid separation may have been a critical factor in producing the water- and alkaline carbonate-rich fluids and melts necessary for Ta and Nb transport. Since the tantalite-(Mn) crystallized during pegmatite formation, this mechanism must also have implications for pegmatite genesis in general.  相似文献   

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