Geochemical evolution of peraluminous plutons in southern Nova Scotia, Canada—a pegmatite-poor suite     

K. L. Currie  J. B. Whalen  W. J. Davis  F. J. Longstaffe  B. L. Cousens   《Lithos》1998,44(3-4):117-140

Three southern Nova Scotia plutons crystallized rapidly at 375 Ma from magma containing both mantle and crustal components. Isotopic and chemical data suggest that the crustal contribution included both lower crustal material and Cambro-Ordovician turbidites of the host Meguma Group. Despite local evidence of mixing and mingling of magmas, the bulk of the plutons evolved by assimilation and fractional crystallisation. Evolved portions of the plutons have compositions appropriate for development of rare-metal pegmatite fields, but pegmatites are relatively rare and little differentiated. Like parental plutons, pegmatites fall into biotite+plagioclase and muscovite+potassium feldspar assemblages. The latter locally contain Mn-rich garnet+biotite, giving calculated P–T conditions of pegmatite crystallisation of 620°C, 0.44 GPa under water-saturated conditions. Host rocks at the time of emplacement experienced P–T conditions varying from <500° to 620°C at 0.44 GPa. Beryl-bearing pegmatites occur only where host rocks were below sillimanite-grade, and pegmatites of any kind are scarce in sillimanite-grade host rocks. Rarity of pegmatites can be ascribed to a combination of insufficient amounts of F, Li, and B in the magma with rapid cooling which prevented extensive fractionation and undercooling. Our data suggest rather that peraluminous suites, produced by rapid heating due to incursions of lithospheric mantle into supracrustal rocks, and typified by biotite-rich, cordierite-bearing plutons, are not favorable locales for major rare-metal-enriched pegmatite fields. Such fields appear to require relatively prolonged anatexis resulting from crustal thickening, or an areally extensive mafic underplate,  相似文献   

湖南省主要稀有稀土金属矿床特征   总被引：4，自引：0，他引：4  

申志军谢玲琳  权正钰 《湖南地质》2003,22(1):30-33,63

湖南省主要有铌、钽、铷、铯、锂、铍、锆等稀有金属及稀土金属矿床．矿床类型以岩浆晚期分异交代型、气成热液型、佛晶岩型、风化壳型和砂矿型为主．稀有稀土金属矿床在空间分布与成因上，与东山期花岗岩体密切相关，往往具有水平分带和垂向分带规律．  相似文献   

云蒙山变质核杂岩抬升过程中伸展拆离和岩浆底辟联合作用的证据   总被引：3，自引：0，他引：3  

张家声  C.W. Passchier  J. Konopasek  牛向龙  黄雄南 《地学前缘》2007,14(4):26-39

北京地区云蒙山变质核杂岩在白垩纪阶段抬升的早期,伴随着沿四合堂剪切带由北向南的拆离滑脱和大型花岗闪长岩的垂向侵位,晚期变形发生在花岗闪长岩岩基周边及其邻近围岩中,形成云蒙山剪切带,并伴随大量同构造的花岗岩和伟晶岩岩脉灌入。剪切带中所有的岩脉都随时间发生了不同程度的变形,较老的岩脉形成紧闭的圆柱状褶皱,枢纽与剪切带的线理和面理接近平行。岩脉与剪切带中L-S组构的平行化作用主要是由于这种转动的结果。岩脉的成分和长英指数随它们的变形程度发生变化,说明持续的岩浆分异作用与韧性剪切变形是同时发生的。云蒙山剪切带由岩浆底辟引起的上盘岩石重力所驱动,并不断得到同构造侵位岩脉的补充,起到存储和不断改造侵位岩脉的作用。早期伸展体制下形成的四合堂剪切带局部遭受云蒙山剪切带的改造或复合。该地区的岩石、构造和同构造岩脉的变形几何学和运动学证据表明,太古宙结晶基底的抬升是下部岩浆底辟与上部地壳伸展拆离共同作用的结果。  相似文献   

胶西北三山岛伟晶岩型脉状钼矿化成因及对胶东钼成矿的指示意义   总被引：2，自引：1，他引：1  

文博杰  范宏瑞  胡芳芳  杨奎锋  刘玄  蔡亚春  孙之夫  孙宗锋 《岩石学报》2015,31(4):1002-1014

胶东是我国重要的金矿集中区,同时也是重要的铜钼多金属成矿区。胶东中东部地区分布有一些不同规模的钼矿床,但是在胶西北地区,尚没有钼矿化的报道。随着深部探矿工作的不断推进,近来在胶西北三山岛金矿区,已发现含辉钼矿化的伟晶岩发育于胶东群和玲珑岩体内。伟晶岩主要由钾长石、石英、白云母、辉钼矿、萤石、黄铁矿组成,此外还含有少量的斜长石、黄铜矿、闪锌矿和赤铁矿等矿物。辉钼矿Re-Os模式年龄为149.9~151.3Ma,加权平均值为150.0±1.0Ma,Re-Os等时线年龄为149.7±1.5Ma,表明伟晶岩形成于约150Ma。钾长石中还发育有大量的矿物包体,包括黄铁矿、方铅矿、赤铁矿、金红石、氧化铬、重晶石、萤石、天青石、碘化锑以及一些含Fe、Mn、Mg、Ca、Sb的碳酸盐矿物,表明原始流体富含金属元素,具备形成金属矿床的潜力。石英中流体包裹体主要有两种类型:纯CO2包裹体和CO2-H2O包裹体,并且一些包裹体中存在少量的CH4、N2等组分。显微测温结果显示,纯CO2包裹体初熔温度的分布范围为-57.3~-56.6℃,部分均一温度的分布范围为18.5~25.1℃,包裹体的密度为0.71~0.79g/cm3。CO2-H2O包裹体的初熔温度为-57.4~-56.6℃,部分均一温度为9.4~31.1℃,笼合物消失温度为4.1~8.3℃,均一温度分布范围为279~350℃,其对应的盐度为3.33%~10.33%NaC leqv,包裹体的密度为0.74~1.00g/cm3。显微测温结果表明流体为富含挥发分、中低盐度的H2O-CO2-NaC l型热液。石英中流体包裹体的δD值的范围为-69.6‰~-56.3‰,δ18O值的分布范围为3.2‰~5.6‰,黄铁矿的δ34S值的范围为4.1‰~5.0‰,表明伟晶岩的形成与岩浆热液关系密切。钾长石的Pb同位素分析结果:206Pb/204Pb=16.7212~17.0287,207Pb/204Pb=15.4093~15.5139,208Pb/204Pb=37.4811~37.9003,其特征与玲珑花岗岩相似,而与胶东群变质岩和中生代脉岩的Pb同位素组成不同。辉钼矿Re含量变化范围为4.66×10-6~29.20×10-6,平均15.49×10-6。Re含量介于壳源与壳幔混源之间,但更偏向壳源,表明成矿物质主要来自于地壳。综合以上的研究成果,本文认为伟晶岩形成于玲珑花岗岩岩浆期后热液,其中辉钼矿化的出现对胶东钼矿化具有重要的指示意义。  相似文献   

The baryte-bearing beryl-phosphate pegmatite Plössberg—A missing link between pegmatitic and vein-type barium mineralization in NE Bavaria, Germany     

Harald G. Dill  Berthold Weber  Reiner Botz 《Chemie der Erde / Geochemistry》2011,71(4):377-387

Pegmatites and aplites enriched in P, Be, Nb, Ta and Li occur in the high-temperature metamorphic lithological units of the NE Bavarian Basement, SE Germany. They are accompanied by Ba mineralization, in vein-type deposits in the basement as well as in its foreland. Locally, Ba minerals are encountered in the late Variscan pegmatites and aplites too. The shallow discordant stock-like pegmatites (Hagendorf-type) are barren as to Ba, but in the tabular, concordant aplites and pegmatites Ba was concentrated (Plössberg-type). These concordant pegmatites and aplites are supposed to be the root zone of the intrusive pegmatites. In the rare case of low sulfur fugacity, Ba forms Ba–Zr–K–Sc phosphates/silicates in the pegmatites (transition of magmatic into the hydrothermal stages I/II). Under high sulfur fugacity, Ba is accommodated within the same stages in the structure of baryte. Barium is not accommodated in the lattice of phosphates during or in the immediate aftermaths of the emplacement of these Be–P–Nb–Ta pegmatites (stage III). This element shows up again in APS minerals during supergene alteration under acidic conditions (stage IV). Considering the host rocks of baryte mineralization, the Sr contents of baryte increased from the early Paleozoic to the Late Triassic. The Sr contents of baryte are a function of the depth below ground in the vein-type deposits and in the shear-zones bounding the tabular concordant pegmatites. Beryl is not only a marker mineral for the shear-zone-hosted pegmatites but can also be used as a tool for the geodynamic positioning of these pegmatites using its oxygen isotopes. A subdivision of the pegmatites into intrusive and shear-zone hosted may be achieved by its REE and minor elements.  相似文献   

云南龙陵县黄连沟钽铌铍矿床地质特征     

邢永辉  李学仁 《云南地质》2014,(4):544-549

黄连沟钽、铌、铍矿产于燕山晚期花岗伟晶岩脉中,伟晶岩脉即为矿体、矿化体,该矿为明显的稀有金属伟晶岩脉矿床.矿区花岗伟晶岩脉众多,成群出现,单个脉体规模较大,加之铌、钽重砂异常明显,这些不仅显示了本区有很好的找矿前景,同时为今后的勘查提供了直接的找矿标志.  相似文献   

An overview of the pegmatitic landscape from the pole to the equator – Applied geomorphology and ore guides     

《Ore Geology Reviews》2017

Pegmatites and aplites share the common major constituents with the granitoid suite as well as various gneissic lithologies, e.g., orthogneisses, aplitic gneisses. Not surprising, the pegmatitic landscape has landforms resembling some found in landscapes derived from metamorphic and granitic rocks that genetically next of kin of pegmatites. The wealth of rare minerals, the peculiar shape, the zonation into a rim extremely vulnerable to weathering and a hard silica core renders pegmatites strikingly different from the afore-mentioned crystalline rocks and account for a landscape type of its own. The primary features of pegmatites, shape and composition, the key elements of the CMS classification scheme (Chemical composition-Mineral assemblage-Structural geology) also are critical for the secondary alteration of these rocks and the evolution of a pegmatitic landscape. The 1st order landscape formation, involving geomorphology sensu stricto and weathering contributes to the built-up of five morphological types (erosional type I, alteration type II, mixed type III, composite type IV (erosion-transport-deposition), hidden type V (under an intact roof rock or under clastic overburden)). The minerals produced by chemical weathering are accountable for type II and III, whereas the relic minerals are accountable for type I, III, IV and V. Morphological type IV leads to different placer deposits. The 2nd order landscape formation is governed by the climate giving rise to discrete zones arranged from the pole to the equator and two genetic types, the plain and valley types. Both types can genetically be correlated with the wet-and-dry and the tropical humid climates. Placers developed a clastic apron around pegmatites abundant in relic minerals whereas minerals newly formed during chemical weathering lead to clay deposits resting immediately on top of pegmatites. In terms of applied geomorphology, reading and understanding a pegmatitic landscape means creating an “ore guide” to the pegmatites, to their argillaceous supergene deposits in the apical part and their cogenetic placer deposits around. The current overview is a supplement to the review Dill (2015a).  相似文献   

莫桑比克阿尔特里哥纳伟晶岩区概貌     

叶水泉  黄建平  夏明飞 《江苏地质》2006,30(1):10-12

莫桑比克阿尔特里哥纳是世界著名的伟晶岩区之一,蕴藏着丰富的稀有金属、稀土、水晶和宝石等矿产资源。伟晶岩脉及其矿体的分布受北北东—北东向和北西向断裂控制,北北东—北东向分布的伟晶岩矿床以稀有金属矿种为主,北西向分布的伟晶岩矿床以稀土金属矿种为主。伟晶岩体及其矿体呈脉状和透镜状等,规模大,富含钽铁矿、铌铁矿、锂云母、锂辉石、绿柱石、独居石、铌钇矿、烧绿石和泡铋矿等矿物。伟晶岩年龄410M a~560M a,是泛非构造运动的产物。按岩浆凝固浓度等分类,伟晶岩类型为稀有金属伟晶岩,部分为浅成、晶洞状伟晶岩;按化学成分等分类,伟晶岩以钠锂型为主,部分为钾型。伟晶岩体有明显的结构分带。  相似文献