共查询到19条相似文献，搜索用时 250 毫秒
1.
新疆阿尔泰可可托海3号伟晶岩脉岩浆-热液过程:来自电气石化学组成演化的证据 总被引：2，自引：0，他引：2
新疆阿尔泰可可托海3号脉不同结构带及其蚀变围岩中电气石化学组成电子探针(EMPA)分析结果显示,蚀变围岩、外接触带和内接触带中电气石为是富钙-铁的镁电气石,电气石化伟晶岩中电气石为富镁-铁的锂电气石,伟晶岩早期结构带(Ⅰ-Ⅳ带)中电气石为黑电气石-锂电气石系列,而伟晶岩晚期结构带(Ⅴ-Ⅶ带)中电气石为锂电气石。蚀变围岩、外接触带和内接触带中电气石以Y位中低Al,高Mg、Ca以及显著低的Al/(Al+Fe)、Fe/(Fe+Mg)比值为特征,主要存在R3++O2-=R2++OH-的置换;伟晶岩内部结构带(Ⅰ-Ⅶ带)中电气石以Y位上极低Mg、Ca,高Fe、Al、Li以及显著高的Al/(Al+Fe)、Fe/(Fe+Mg)比值为特征,主要存在+Al3+=Na++Fe(Mg)2+和Li++Al3+=Fe(Mn)2++Mg2+的置换。蚀变围岩、外接触带和内接触带中电气石化学组成特征指示存在围岩-流体、围岩-熔体相之间的相互作用。伟晶岩早期结构带(Ⅰ-Ⅳ带)中电气石无明显组成分带,为岩浆成因;晚期结构带(Ⅴ-Ⅶ带)中电气石显示振荡环带,形成于岩浆-热液过渡阶段体系。随着伟晶岩由外向里固结,温度逐渐降低,伟晶岩内部结构带中电气石显示Y位上Al、Li、Mn及Fe/(Fe+Mg)比值逐渐增大的演化趋势;内部结构带中电气石几乎不含Mg,指示3号伟晶岩脉岩浆-热液演化是在相对封闭体系中进行的。 相似文献
2.
以小虎斯特91号伟晶岩脉中的不同结构带及蚀变围岩、交代岩、锂云母细脉中云母矿物为研究对象,通过电子探针(EMPA)和激光剥蚀等离子体质谱(LA-ICP-MS)对各结构带不同产状的云母进行主微量成分分析.研究表明,91号脉从围岩蚀变带、伟晶岩边缘带、外侧带、中间带到核部带,依次发育黑云母、白云母、富锂白云母和锂云母,伟晶岩中云母类矿物显示由白云母向锂云母演化趋势.Li在白云母和富锂云母(锂白云母和锂云母)中的置换机制不同,分别可能为2SiⅣ+ LiⅥ(←→)3A1Tot和Si+Li(←→)AlTot+Fe (Zn,Mn,Mg)(白云母)和3LiⅥ(←→)AlⅥ+ 2□Ⅵ(富锂云母,□代表空位).小虎斯特91号伟晶岩脉经历了岩浆-热液的演化过程,随着演化进行,云母中K/Rb、Mg/Li比值显著降低,Li、Rb、Cs、F含量显著增大,指示分离结晶作用是晚期熔体相Li、Rb、Cs、F富集的主要机制.但云母类矿物的主、微量元素特征显示小虎斯特91号脉岩浆-热液过渡阶段特征不明显,伟晶岩演化很快由正岩浆阶段转化为热液阶段. 相似文献
3.
铌钽铁矿族矿物(CGM)是重要铌、钽矿石矿物,记录了花岗伟晶岩型稀有金属矿床的岩浆热液演化过程.扎乌龙位于四川省西部石渠县,为大型花岗伟晶岩型稀有金属矿床.文章以扎乌龙14号伟晶岩脉为研究对象,开展了系统的铌钽铁矿族矿物研究工作.14号伟晶岩脉分带良好,从边部到中心可划分为云母石英电气石带(Ⅰ带)、斜长石带(Ⅱ带)、钠长石锂辉石带(Ⅲ带)和石英锂辉石带(Ⅳ带),均发育有铌钽铁矿族矿物.根据矿物内部结构和化学成分,推断14号伟晶岩脉存在2个阶段铌钽矿化:早阶段在各带内均形成铌铁矿-铌锰矿(CGM-1),内部呈现均一结构或振荡环带,指示以铌结晶为主的岩浆阶段;晚阶段在Ⅲ带和Ⅳ带内形成钽铁矿和少量富钽的铌铁矿-铌锰矿(CGM-2),围绕早阶段铌铁矿-铌锰矿再生长或穿切、交代早阶段铌钽矿物,指示以钽结晶为主的岩浆-热液过渡阶段.铌钽铁矿族矿物呈现出2种演化趋势,分别为早阶段铌铁矿-铌锰矿的Mn/(Mn+Fe)比值随着Ta/(Ta+Nb)比值升高而增加,晚阶段富钽矿物Mn/(Mn+Fe)比值随着Ta/(Ta+Nb)比值升高而不变,指示扎乌龙14号伟晶岩脉总体为中等程度分异,早期岩浆阶段各带内连续、晚期岩浆-热液阶段发生跳跃的不连续演化过程,并指示早阶段演化受岩浆结晶分异的控制、晚阶段演化主要受结晶分异、富Li流体环境和其他含Fe-Mn矿物共同控制的地球化学行为. 相似文献
4.
本文利用电子探针和背散射电子成像技术系统地研究了新疆阿尔泰可可托海3号伟晶岩脉各结构带中的铝铁矿族矿物。研究表明,本区伟晶岩脉中铌铁矿族矿物主要为铌锰矿-钽锰矿。成分特征显示从岩脉边部带到核部,Ta/(Nb Ta)比值呈近垂向演化,但Mn/(Fe Mn)比值没有明显变化。另一方面,铌铁矿族矿物在早期正岩浆阶段(Ⅰ-Ⅳ带)的成分变化非常局限,而在晚期的岩浆-热液过渡阶段(Ⅴ-Ⅶ带)的成分变化非常大。背散射电子成像技术观察还表明本区铌铁矿族矿物在正岩浆阶段没有环带构造特征,而在岩浆-热液过渡阶段有明显的环带构造特征,而且随着伟晶岩固结过程的进行,环带构造主要沿着渐变环带构造→韵律环带构造→交代构造的趋势变化。研究认为,本区铌铁矿族矿物在不同结构带的成分变化和在单颗粒中的环带构造是热液流体参与铌铁矿族矿物结晶的反应,环带构造的类型主要是由热液流体参与结晶的程度所控制。 相似文献
5.
磷铁锂矿与磷锰锂矿是一完全类质同象系列中两个端员矿物。磷锰锂矿在我国新疆伟晶岩中已有大量发现。笔者于1984年在福建南平稀有金属花岗伟晶岩中发现了典型的磷铁锂矿。此外,早在1980年笔者还在新疆青河富铍伟晶岩中发现了成分介于该类质同象系列中间的磷锰铁锂矿。对后两个产状的矿物进行了较详细的矿物化学成分和物理性质研究。结合前人的资料,文中系统地讨论了国内所发现的六个产状的磷铁锂矿-磷锰锂矿系列矿物的化学成分特征及变化规律,化学成分与光学性质、物理性质、晶胞参数等之间的相互关系,并系统地引用了大量国外资料作对比。讨论了矿物中Mg、Ca等含量对这些特征的影响。另外,笔者还研究了该系列矿物成分与红外光谱之间的关系,指出矿物的红外吸收谱带频率与铁锰比值间呈良好的线性关系,并给出了相关关系式。 相似文献
6.
广西大厂地区笼箱盖黑云母花岗岩与区内晚白垩世锡多金属成矿作用在时空上密切相关。岩相学特征表明,笼箱盖黑云母花岗岩中的电气石可以分为三类:1)浸染状电气石; 2)石英-电气石囊; 3)电气石-石英脉。本文利用电子探针和激光剥蚀等离子体质谱系统测定三种不同产状电气石的化学组成。分析结果显示,三种产状的电气石均具有高的Fe/(Fe+Mg)和Na/(Na+Ca)比值,主体属于碱基亚类铁电气石。浸染状电气石为岩浆晚期结晶,其Fe/(Fe+Mg)比值变化于0. 85～0. 94,随着岩浆分异,电气石逐渐富集Li、F、Fe和Sn等元素。与浸染状电气石相比,石英-电气石囊中早阶段电气石具有低的Fe/(Fe+Mg)比值,高的V、Co和Sr含量,可能反映了岩浆演化晚期出现的不混溶富硼熔/流体对早期黑云母和长石的交代作用,从而使囊中早阶段电气石继承部分被交代矿物的化学组成特征;石英-电气石囊中晚阶段电气石的化学组成变化较大(如Li、F、Mg、Al、V、Fe和Zn),与热液成因电气石的推论一致。与浸染状和囊状电气石相比,石英脉中的电气石具有高的Fe/(Fe+Mg)和Na/(Na+Ca)比值;微量元素组成与囊状电气石相似。就成矿元素锡而言,三种产状的电气石均具有相对高的锡含量,与其他地区锡成矿花岗岩中电气石的成分特征相似。但是,从岩浆晚期到热液阶段,大厂地区电气石的锡含量并没有显著升高,可能反映了早期岩浆热液流体对熔体锡有限的萃取作用。 相似文献
7.
川西扎乌龙花岗伟晶岩型锂矿床位于甘孜-松潘造山带内,为大型锂矿床.前人基于对扎乌龙系统的流体包裹体研究,认为扎乌龙锂矿形成于500～580℃,压力350 MPa的环境.然而,对于扎乌龙成矿流体的来源及其何种流体挥发分对成矿起主导作用,仍缺乏有效制约.锂辉石型伟晶岩脉是扎乌龙锂矿最富集的类型,脉体内部分带性良好,可划分为4个带:石英-白云母带、斜长石带、钠长石-锂辉石带和石英-锂辉石带.根据地质现象和流体包裹体的岩相学观察,扎乌龙锂辉石型伟晶岩脉可划分为伟晶岩阶段和热液阶段2个主要阶段,锂矿化集中于伟晶岩阶段.文章对扎乌龙成矿流体的来源及成分开展了研究,即对锂辉石型伟晶岩各阶段的流体包裹体进行了激光拉曼光谱、群体包裹体和氢、氧、碳同位素分析.流体包裹体成分揭示,成矿流体由伟晶岩阶段的高温(500～580℃)、低盐度(w(NaCleq)0.8％～8.5％)、富挥发分(Li、P、B等)、弱碱性的硅酸盐水体系,向晚期中高温(300～400℃)、低盐度(w(NaCleq)4.4％～9.6％)、富CO2、弱酸性的盐水体系热液演化.氢、氧同位素组成表明早期成矿流体以岩浆水为主,晚期无明显的大气降水加入.碳同位素分析结果表明,二氧化碳主要来源于岩浆出溶.结合已有的研究成果,笔者认为相对封闭的成矿环境导致挥发组分的大量聚集和弱碱性环境,是扎乌龙锂矿富集与沉淀的主要控制因素.晚期贫F、富Cl的弱酸性热液流体有利于锂辉石的保存. 相似文献
8.
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
9.
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
10.
11.
Paul Keller François Fontan André-Mathicu Fransolet 《Contributions to Mineralogy and Petrology》1994,118(3):239-248
Minerals of the triphylite-lithiophilite, Li(Fe, Mn)PO4, and the triplite-zwieselite-magniotriplite series, (Mn, Fe, Mg)2PO4F, occur in the late stage period of pegmatite evolution. Unfortunately, neither are the genetic relationships between these phosphates fully understood nor are thermodynamic data known. Consequently, phosphate associations and assemblages from 8 granitic pegmatites — Clementine II, Rubicon II and III, and Tsaobismund (Namibia); Hagendorf-Süd and Rabenstein (Germany); Valmy (France); Viitaniemi (Finland) — have been tested for compositional zoning and intercrystalline partitioning of main elements by electron microprobe techniques. Although the selected pegmatites display varying degrees of fractionation, and the intergrowth textures indicate different genetic relationships between the phosphates, the plots of mole fractions X
Fe=Fe/(Fe+Mn+Mg+Ca), X
Mn=Mn/(Fe+Mn+Mg+Ca), and X
Mg=Mg/(Fe+Mn+Mg+Ca) can be fitted relatively well with smooth curves in Roozeboom diagrams. Their deviations from symmetrical distribution curves are mainly dependent upon X
Mg or X
Ca, and upon non-ideal solutions. Surprisingly small differences between the partition coefficients were detected for intergrowths of different origin. However, the partitioning of shared components among coexisting phases is clearly dependent upon the conditions of formation. Compositional zoning is observed only when both Fe–Mn phosphates are intergrown mutually or with other Fe–Mn–Mg mineral solid-solutios. Thus, the zoning does not seem to be due to continuous crystallization, but to later diffusion processes. The triplite structure has preference for Mn, Mg, and Ca, while Fe prefers minerals of the triphylite series. A quantification of main element fractionation between minerals of the triphylite and the triplite series is possible in the cases where diffusion can be excluded. For the Fe/(Fe+Mn) ratios of core compositions an equation with a high correlation coefficient (R=0.988) was determined: Fe/(Fe+Mn)Tr=[Fe/(Fe+Mn)Li]/{2.737-(1.737)[Fe/(Fe+Mn)Li]} (Tr=triplite series, Li=triphylite series). Consequently, the Fe/(Fe+Mn) ratio of the triplite series can now also be used in the interpretation of pegmatite evolution, just like that of the triphylite series which has been successfully applied in the past. 相似文献
12.
André -Mathieu Fransolet Paul Keller François Fontan 《Contributions to Mineralogy and Petrology》1986,92(4):502-517
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
13.
Encarnación Roda-Robles Romeu Vieira Alfonso Pesquera Alexandre Lima 《Mineralogy and Petrology》2010,100(1-2):23-34
Granitic pegmatites are widespread within a schist-metagreywacke complex in the Fregeneda-Almendra area (Central Iberian Zone). They intrude pre-Ordovician metasedimentary rocks and show a zonal distribution relative to the Meda-Penedono-Lumbrales granitic complex, from barren bodies to those enriched in Li, F, Sn, Nb>Ta, P and Be. Based on mineralogical criteria, these pegmatites are classified into three main categories: barren, intermediate and rare-element pegmatites, with each type including various subtypes. Phosphates are present in many pegmatites that usually occur as fine-grained accessory minerals. The most complex association of such minerals includes numerous Fe–Mn phosphates that occur in intermediate pegmatites. Al-phosphates are characteristic of Li-rich pegmatites. Electron microprobe analyses of representative phosphates reflect compositional differences depending on the pegmatite type. The Fe/(Fe+Mn) ratio of phosphates tends to decrease as the evolution degree of the pegmatites increases. 相似文献
14.
15.
The Igarapé Bahia gold deposit has developed from weathering of a near-vertical hydrothermal Cu (Au) mineralization zone. The unweathered bedrock composed of chlorite schists is mainly metamorphosed basalts, pyroclastic and clastic sedimentary rocks and iron formation. Contents and Fe/(Fe + Mg) ratios of chlorites increase from distal country rock towards the mineralization zone, which can be attributed to different water/rock ratios and locations in a hydrothermal system. In the hydrothermal system high salinity fluids convected through basin-floor rocks, stripping metals from the recharge zones with precipitation in discharge zones. The chlorite with lower Fe/(Fe + Mg) ratios indicates alteration by relatively unreacted Mg-rich fluids, occurring within recharge zones. By contrast, the chlorite with higher Fe/(Fe + Mg) ratios in the mineralization zone formed from solutions rich in Fe, Mn, Au, Cu, H2S and SiO2 within a discharge zone. The iron formation could also be formed within the discharge zone or on the basin floor from the Fe-rich fluids. The distal country rock with less chlorite content is a hydrothermal product at low water/rock ratios whereas the proximal country rock and the host rock with more chlorite content formed at high water/rock ratio conditions. The Al(IV) contents of chlorites indicate that the formation temperatures of these rocks range from 204 to 266 °C, with temperatures slightly increasing from distal country rock towards the mineralization zone. 相似文献
16.
Dr. P. Černý Dr. R. Chapman R. Göd Dr. G. Niedermayr Dr. M. A. Wise 《Mineralogy and Petrology》1989,40(3):197-206
Summary Titanian ferrocolumbite is a rare accessory mineral in the spodumene-bearing pegmatites at Weinebene, Carinthia, Austria. It contains abundant exsolved niobian rutile and scarce inclusions of cassiterite that may be primary. The titanian ferrocolumbite is relatively homogeneous with Mn/(Mn + Fe) 0.24–0.33, Ta/(Ta + Nb) 0.09–0.13 (atomic ratios) and 0.47–0.88 Ti per 12 cations (2.7–5.0 wt.% TiO2). Natural specimens are considerably disordered but become more ordered on heating. Niobian rutile has Mn/(Mn + Fe) 0.00–0.04 and Ta/(Ta + Nb) 0.26–0.38; it concentrates Fe, Ta, Ti and Sn relative to the Mn- and Nb-enriched ferrocolumbite. The overall scarcity of Nb, Ta-oxide minerals in the spodumene-bearing pegmatites of southern Ostalpen conforms to their general features ranking them with the albite-spodumene type of rare-element pegmatites.With 4 Figures 相似文献
17.
Petrogenesis and geochemical composition of biotites in rare-element granitic pegmatites in the southwestern Grenville Province,Canada 总被引：2，自引：0，他引：2
D. Lentz 《Mineralogy and Petrology》1992,46(3):239-256
Summary Field, mineralogical, and chemical determinations of biotite from late-tectonic rare-element (U, Th, Mo, Nb, REE) Grenville pegmatites are used to characterize and evaluate their petrogenesis in part of the southwestern Grenville Province. These pegmatites occur within middle to upper amphibolite facies rocks along and adjacent to shear zones and have hybridized margins because of interaction with their host rocks. Endo- and exomorphic biotite forms by the mechanical incorporation or hydrothermal replacement of pre-existing biotite, hornblende, Ca pyroxene and/or feldspar; accompanied by chemical re-equilibration, an increase in grain size, and inherit some of the chemical characteristics of the pegmatite. In general, the Fe/(Fe + Mg) ratio ranges between 0.22 and 0.86. The most highly fractionated biotites have high Fe/(Fe + Mg), Al, Mn, Rb, Nb, and Zn and low Ba. The chemical compositions of biotite from unzoned, partially-zoned, and zoned pegmatites indicate a trend of increasing chemical fractionation based on LIL enrichment.Overlap in calculated log
(3.2 to 4.7) and log
(1.3 to 2.8) for biotite (@ 600°C) among the different pegmatites is extensive. Commonly, magnetite and microcline coexist with biotites having an Fe/(Fe + Mg) between 0.54 to 0.65. Volatile enrichment and vapor-phase saturation are probably responsible for the development of zonation in the pegmatites. The diffusive loss of H2 at or near H2O vapor saturation at high H2O/Fe2+ may be responsible for the oxidized nature of some pegmatites.Rare-element enrichment due to pegmatite fractionation combined with partitioning of rare-elements from the pegmatite melt into the volatile phase and subsequent interaction with the host rocks is key to the formation of these rare-element mineral deposits.
With 9 Figures 相似文献
Petrogenese und geochemische Zusammensetzung von Biotiten in seltenen Element-führenden granitischen Pegmatiten der südwestlichen Grenville Provinz, Kanada
Zusammenfassung Die Ergebnisse von Geländearbeiten, sowie von mineralogischen und geochemischen Untersuchungen an Biotit aus spättektonischen seltenen Element-Pegmatiten (U, Th, Mo, Nb, REE) von Grenville-Alter bilden die Basis einer Diskussion ihrer Petrogenese in der südwestlichen Grenville Provinz. Diese Pegmatite kommen in Gesteinen der mittleren bis oberen Amphibolit-Fazies längs und in der Nähe von Shearzonen vor und haben hybridisierte Ränder, die auf Interaktion mit ihren Wirtsgesteinen zurückgehen. Endo- und exomorphe Biotite sind durch mechanische Einschließung oder durch hydrathermale Verdrängung von Biotiten, Hornblenden, Kalziumpyroxenen und/oder Feldspäten gebildet worden. Dies wird durch chemische Reequilibrierung, eine Zunahme der Korngröße und durch Übernahme einiger chemischer Charakteristika der Pegmatite begleitet. Im allgemeinen schwanken die Fe/(Fe + Mg) Verhältnisse von 0.22 bis 0.68, die am stärksten fraktionierten Biotite haben hohe Fe/(Fe + Mg), Al, Mn, Rb, Nb und Zn Gehalte und niedrige Ba Gehalte. Die chemische Zusammensetzung von Biotit aus nicht zonierten, teilweise zonierten und zonierten Pegmatiten zeigt einen Trend mit zunehmend chemischer Fraktionierung, die auf einer Anreicherung von LIL-Elementen basiert.Beträchtliche überschneidungen in den berechneten log (3.2 bis 4.7) und log (1.3 bis 2.8) für Biotit (600°C) von verschiedenen Pegmatiten sind zu erkennen. Im allgemeinen koexistiert Magnetit und Mikroklin mit Biotiten von Fe/ (Fe + Mg) Verhältnissen zwischen 0.54 und 0.65. Anreicherung von volatilen Phasen und eine Sättigung der Dampfphase sind wahrscheinlich für die Entwicklung der Zonierung der Pegmatite verantwortlich. Der Verlust von H2 durch Diffusion im Bereich der H2O Dampfsättigung bei hohen H2O/Fe2+ Werten dürfte für die oxidierte Natur einiger Pegmatite verantwortlich sein.Wichtigster Faktor für die Bildung dieser Lagerstätten seltener Elemente ist die Anreicherung von seltenen Elementen durch Pegmatit-Fraktionierung, wobei diese von der Pegmatit-Schmelze in die volatile Phase gehen, und die anschließende Interaktion mit den Nebengesteinen.
With 9 Figures 相似文献
18.
Nb-Ta-minerals from the cap de creus pegmatite field,eastern Pyrenees: distribution and geochemical trends 总被引：2，自引：0，他引：2
P. Alfonso Abella J. -C. Melgarejo i Draper M. Corbella i Cordomi 《Mineralogy and Petrology》1995,55(1-3):53-69
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.
With 6 Figures 相似文献
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
19.
Dirk Küster Rolf L. Romer Dandena Tolessa Desta Zerihun K. Bheemalingeswara Frank Melcher Thomas Oberthür 《Mineralium Deposita》2009,44(7):723-750
The Kenticha rare-element pegmatite, a globally important tantalite source in the Neoproterozoic Adola Belt of southern Ethiopia,
is a highly fractionated, huge (2,000 m long and up to 100 m thick), subhorizontal, sheet-like body, discordantly emplaced
in ultramafic host rock. It corresponds to the spodumene subtype of the rare-element pegmatite class and belongs to the lithium–cesium–tantalum
petrogenetic family. The Kenticha pegmatite is asymmetrically zoned from bottom to top into granitic lower zone, spodumene-free
intermediate zone, and spodumene-bearing upper zone. A monomineralic quartz unit is discontinuously developed within the upper
zone. Whole-rock data indicate an internal geochemical differentiation of the pegmatite sheet proceeding from the lower zone
(K/Rb ~36, K/Cs ~440, Al/Ga ~2,060, Nb/Ta ~2.6) to the upper zone (K/Rb ~19, K/Cs ~96, Al/Ga ~1,600, Nb/Ta ~0.7). The latter
one is strongly enriched in Li2O (up to 3.21%), Rb (up to 4,570 ppm), Cs (up to 730 ppm), Ga (up to 71 ppm), and Ta (up to 554 ppm). Similar trends of increasing
fractionation from lower zone to upper zone were obtained in muscovite (K/Rb 23–14, K/Cs 580–290, K/Tl 6,790–3,730, Fe/Mn
19–10, Nb/Ta 6.5–3.8) and columbite–tantalite (Mn/Mn + Fe 0.4–1, Ta/Ta + Nb 0.1–0.9). The bottom-to-top differentiation of
the Kenticha pegmatite and the Ta mineralization in its upper part are principally attributed to upward in situ fractionation
of a residual leucogranitic to pegmatitic melt, largely under closed system conditions. High MgO contents (up to 5.05%) in
parts of the upper zone are the result of postmagmatic hydrothermal alteration and contamination by hanging wall serpentinite.
U–Pb dating of Mn-tantalite from two zones of the Kenticha pegmatite gave ages of 530.2 ± 1.3 and 530.0 ± 2.3 Ma. Mn-tantalite
from the Bupo pegmatite, situated 9 km north of Kenticha, gave an age of 529.2 ± 4.1 Ma, indicating coeval emplacement of
the two pegmatites. The emplacement of the pegmatites is temporally related to postorogenic granite magmatism, producing slightly
peraluminous, I-type plutons in the area surrounding the Kenticha pegmatite field. Fractionated members of this suite might
be envisaged as potential parental magmas. 相似文献