Metamorphism of the Bikou Group in the Shanxi-Gausu-Sichuan Border Region1

Abstract The Bikou Group on the Shaanxi-Gansu-Sichuan border is composed of Mid-Late Proterozoic metamorphosed bimodal volcanic rocks and flysch sediments. Its metamorphism may be divided into the blueschist and greenschist facies. Three metamorphic zones, i.e. zones A, B, and C, may be distinguished on the basis of the field distribution of metamorphic rocks and the variation of b₀ values of muscovite. Blueschists are characterized by coexistence of sodic amphiboles and epidote and occur as stripes or relict patches in extensive greenschists of zone A. Studies of metamorphic minerals such as amphiboles, chlorite, epidote and muscovite and their textural relationships indicate that blueschists and greenschists were not formed under the same metamorphic physico-chemical conditions. The blueschist facies was formed at temperatures of 300-400°C and pressures of 0.5–0.6 GPa. The greenschist facies in zones A and B has similar temperatures but its pressure is only 0.4 GPa or so. The transition from the blueschist to greenschist facies is a nearly isothermal uplift process. The rock and mineral assemblages of the Bikou Group indicate that the blueschist facies metamorphism of the group might be related to crustal thickening or A-subduction accompanying the closure of an intracontinental small ocean basin.     

应用X射线衍射-扫描电镜-光学显微镜鉴定黑龙江石墨尾矿中的绢云母

石墨尾矿作为一类二次资源,当云母类矿物的含量在10%以上时,具有回收利用价值。黑龙江某地石墨尾矿中含有10%以上的云母类矿物,但其细度(500~800目)低于常规的云母矿,本文采用X射线衍射(XRD)分析矿物组成,再结合化学分析、扫描电镜-能谱、光学显微镜与纯矿物进行对比,由此鉴定云母类矿物种属。XRD研究初步表明石墨尾矿含有的云母族矿物属于白云母亚类或黑云母亚类。扫描电镜分析表明尾矿中的云母矿物与纯绢云母矿物均以片状和鳞片状为主要存在形态,而纯黑云母主要以片状形式存在。尾矿的Si O2含量为5%~13%,Al2O3含量为4%~8%,与纯绢云母接近。光学显微镜鉴定显示在正交偏光下石墨尾矿中的云母颜色和纯绢云母类似,而与纯黑云母截然不同。综合以上结果最终可确定该地石墨尾矿中的云母族矿物为白云母亚类中的绢云母。本研究为后续石墨尾矿的选矿工艺奠定了基础,也可应用于类似细度绢云母的鉴定。     

The Slyudyanogorsk muscovite deposit in the Middle Ural

The Slyudyanogorsk muscovite deposit of the central Urals has been known since 1884, but little geologic data are available in the literature. The muscovite occurrences are restricted to pegmatites found near the contact of the Late Precambrian Slyudyanogorsk Formation and the unconformably overlying Kurta Formation of Ordovician age. The country rock is dominantly metasedimentary in origin. Migmatization of schists is common and migmatites may be traced into pegmatites. The pegmatites may be classified on the basis of form into lens- and net-like veins and pipes that may be concordant or discordant to schistosity. Conformable pegmatites usually have higher mica contents and are distinctive in their extension to great depths. Transverse cutting types of pegmatites taper rapidly downward and are usually mica-free. On the basis Of composition, pegmatites may be divided into plagioclase (albite-oligoclase) and microcline varieties. Commercial muscovite occurrences are restricted to plagioclase pegmatites, as are the accessory ore minerals (molybdenite, chalcopyrite, pyrrhotite). The mica-bearing pegmatites usually have a more complex structure (zonal, cellular) than the massive mica-free pegmatites. The character and structure of the mica-bearing pegrnatites, the relicts of biotite within sheet muscovite and muscovite aggregates, the enlargement and replacement of biotite by muscovite in the surrounding wall rock, and the high iron content of the muscovite .suggest that muscovite is metasomatic after biotite in pegmatites that have formed from the wall rock by migmatization, recrystallization, and metasomatism. — R. D. DeRudder.     

大别山榴辉岩富流体退变质阶段的白色云母

大别山榴辉岩的退变质过程可分为贫流体、弱流体和富流体3个阶段。贫流体阶段的主要作用是榴辉岩造岩矿物的重结晶、同质多象转变和固溶体出溶;弱流体阶段有少量流体参与,并且其压力、温度较高,形成的白色云母主要为多硅白云母;富流体阶段在大量流体参与下,形成大量的低压含水矿物,其中包括多种白色云母。富流体阶段早期的白色云母主要为多硅白云母,其Si原子数介于6．5pfu和7．2pfu之间;晚期白色云母成分复杂,包括钠云母、白云母和珍珠云母。黑云母是退变质作用最晚期形成的云母。退变质云母具环带结构,其内带为钠云母,中带为白云母和珍珠云母的交生体,外带为黑云母。     

云母类矿物的活化释钾性能

通过对３个典型二八面体型的云母类矿物,即白云母,绢云母和伊利石的活化释钾试验,发现云母类矿物热自理产物酸化后钾能大量释放;探讨了云母类矿物的活化释钾性能。虽然白云母释钾的活化条件相对较高压有利于晶包有机质释放但其释钾量明显大于绢云母和伊利石。     

SEDIMENTS FROM BAY ST. GEORGE, NEWFOUNDLAND

Sediments cored to a depth of about 1 m in Bay St. George, Newfoundland, were examined for grain-size distribution and minerals. The sediments are light brown silty clays, the principal minerals of which are chlorite and muscovite mica. The scarce sand consists of fresh detrital grains of blue-green amphibole, biotite, epidote, zoisite, magnetite, garnet, hypersthene, apatite, chlorite, and scarce zircon. Quartz, plagioclase feldspar, and muscovite are abundant. These minerals are all present in the rocks of the adjacent land areas and have been deposited in the sediments with little alteration or change due to weathering. The clay minerals of the sediments are predominantly muscovite and chlorite with a slight admixture of vermiculite and montmorillonite. There is very little mixed-layering of these minerals. Montmorillonite may be due to diagenetic changes after deposition of these clays in the marine environment of the bay.     

Mica Inclusions inside Host Mica Grains from the Sutlej Section of the Higher Himalayan Crystallines, India—Morphology and Constrains in Genesis

Abstract: Biotite and muscovite inclusions inside mica host minerals from the Sutlej section of the Higher Himalayan Crystalline were studied under an optical microscope. These inclusions formed possibly by local recrystallization of mica grains during regional prograde metamorphism, with some affected by top-to-SW shear leading to parallelogram shapes. Recrystallization may have been assisted by solution transfer along the cleavage planes of the host grains. The relative competency of deformed phyllosilicate inclusions with the same or different composition to the host depends on the size and orientation of (001) cleavage planes of the inclusions relative to the host. Shearing of mica inclusions led to their parallelogram geometries within the contained mica inclusions. Some of the sheared inclusions deflect cleavage planes in the host minerals and define flanking microstructures. Trapezoid-shaped inclusions are a new finding that deserves more attention for their genesis. These structurally anisotropic inclusions did not originate from sub-grains, secondary infillings or retrogression. These inclusions are also not related to pseudomorphism, isomorphism, folding of the bulk rock etc. Some of the inclusions formed by recrystallization of the host mineral during top-to-SW ductile shear.     

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...     

Geochemistry of sodic waters in the Datong intermountain basin,Shanxi Province,northwestern China

The paper presents a critical analysis of current concepts of the origin of sodic waters. The example of the Datong Basin with widespread sodic waters is employed to demonstrate that these waters typically have salinities of 0.6–4.5 g/l at pH of 7.8–8.8. It was determined that sodic waters are in equilibrium with calcite and clay minerals (montmorillonite and kaolinite) and, sometimes, also with analcime but are never in equilibrium with anorthite, albite, forsterite, microcline, and muscovite; i.e., the water-rock system is in equilibrium-unequilibrium state. The degree of evaporation concentration of salts is in places as high as a few tens. The complex analyses of conditions under which sodic waters are formed indicates that these waters are produced during a certain weathering stage of aluminosilicates, after the groundwaters have reached equilibrium with calcite. The time when this equilibrium can be reached is controlled by the intensity of the water exchange. Original Russian Text ? S.L. Shvartsev, Yanxing Wang, 2006, published in Geokhimiya, 2006, No. 10, pp. 1097–1109.     

一株产铁载体细菌的筛选及其与云母的相互作用

        产铁载体细菌与云母类矿物相互作用的研究有助于了解矿物生物风化和土壤形成的演化规律和机理。采用纯培养法 自南京龙山废钾矿区酸模根际土壤分离筛选到一株高产荧光铁载体的细菌Z6,通过16S rDNA 序列分析和生理生化反应将其 鉴定为假单胞菌属（Pseudomonas sp.）;通过室温静置培养试验研究Z6 菌株与云母的相互作用结果表明,细菌生长代谢前期 （8~15 d）快速产生大量铁载体,菌株与矿物共培养75 d 后,产铁载体细菌对云母类矿物确实产生了风化作用,黑云母组发 酵液中Fe 含量增加了211 倍,Si 含量增加了约27.8 倍,SEM 显示云母表面出现溶蚀坑,细菌可以在矿物表面形成生物膜或 矿物- 细菌复合物。不同矿物对共培养体系中细菌数量、荧光铁载体含量、溶液pH 的影响不同。     

西武夷地区早古生代浅色花岗岩的厘定及其造山意义

西武夷地区的付坊超单元是一套白云母／二云母花岗岩组合,岩性包括白云母／二云母花岗闪长岩和白云母／二云母二长花岗岩,年龄为４７２～４４６Ｍａ。它是下生代华夏古陆向扬子板块爷冲、华夏板块内部武夷地块与罗霄地块接俣过程中形成的陆内俯冲花岗岩,两地块的接合部位－雩山接合带是一条陆内俯冲带。     

Intermediate sodium–potassium mica in hydrothermally altered rocks of the Waterloo deposit,Australia: a combined SEM-EMP-XRD-TEM study

Metastable intermediate Na–K mica represents a product of hydrothermal alteration in volcanic rocks from the alteration halo of the Waterloo massive sulfide deposit, Australia. The XRD pattern of this solid solution between paragonite and muscovite is characterized by a rational series of basal reflections with d values intermediate between the end members. Transmission electron microscopy revealed that the intermediate Na–K mica forms thick stacks that belong to a two-layer polytype. Na-rich intermediate Na–K mica typically occurs together with paragonite whereas K-rich intermediate Na–K mica is intergrown with muscovite. The intermediate Na–K mica is interpreted to have formed as a result of the incomplete transformation of K-rich mica to Na-rich mica through dissolution and recrystallization processes driven by compositional changes of the hydrothermal fluids interacting with the volcanic rocks. Alteration must have proceeded under non-equilibrium conditions because the composition of the solid solution falls into the miscibility gap separating paragonite and muscovite.Editorial responsibility: T.L. Grove     

Development of slaty cleavage in a mudstone unit from the Cantabrian Mountains, northern Spain

A 200 m thick mudstone unit in the Carboniferous of the Cantabrian Mountains, northern Spain, exhibits an increase in intensity of the slaty cleavage from top to bottom which appears to be correlated with a decrease in the mean grain size, average bed thickness and quartz: mica ratio. Anastomosing cleavage domains, formed by pressure solution and by kinking and rotation of the detrital micas, become closer spaced, wider and more continuous towards the finer-grained base of the unit. Growth of strongly oriented new micas within the cleavage domains also appears to be correlated with the intensity of the domain development and hence with the initial lithology. Clay minerals have been completely replaced throughout the mudstone by muscovite, paragonite and pyrophyllite during low-grade metamorphism. The growth of an oriented mica fabric, however, is restricted to samples with well-developed cleavage domains.     

Cs-dominant polylithionite in the Koktokay#3 pegmatite,Altai, NW China: in situ micro-characterization and implication for the storage of radioactive cesium

Except forming two Cs-rich minerals like pollucite and londonite, cesium generally occurs in trace amounts in potassium-bearing minerals owing to its very low Clarke value and large ionic radius. However, in the Koktokay#3 pegmatite (Altai, NW China), lepidolite is extremely enriched in cesium (typically 21–26 wt% Cs₂O). Cs-enriched lepidolite is restricted to the inner of the pegmatite, where four types of occurrence are characterized by using in situ techniques (EMP: electron microprobe, micro-XRD: micro-area X-ray diffractometer and Raman probe: micro-area Raman spectrometer) as: (1) outer zones on Cs-poor lepidolite cores; (2) fine overgrowths on muscovite veinlets; (3) veinlets in Cs-poor lepidolite and (4) veinlets in elbaite. There is an inverse correlation between K and Cs and in terms of ^VIAl versus Cs/(K+Cs), the Cs-dominant micas are an analog of the Li-rich mica polylithionite. Micro-XRD patterns and micro-Raman spectra indicate that Cs-dominant polylithionite structurally corresponds to minerals of the lepidolite series. According to its distribution and compositional characteristics, the Cs-dominant polylithionite seems to have formed at the magmatic to hydrothermal transition stage of pegmatitic magma evolution as a result of marginal replacement of early-formed lepidolite by Cs-rich fluids. Alternatively, it may have formed through direct precipitation from Cs-rich fluids. The results of the present study have important implications for the storage of nuclear waste in that Li mica such as polylithionite is a good candidate for immobilizing high-level radioactive cesium waste.     

The key role of mica during igneous concentration of tantalum

Igneous rocks with high Ta concentrations share a number of similarities such as high Ta/Nb, low Ti, LREE and Zr concentrations and granitic compositions. These features can be traced through fractionated granitic series. Formation of Ta-rich melts begins with anatexis in the presence of residual biotite, followed by magmatic crystallization of biotite and muscovite. Crystallization of biotite and muscovite increases Ta/Nb and reduces the Ti content of the melt. Titanium-bearing oxides such as rutile and titanite are enriched in Ta and have the potential to deplete Ta at early stages of fractionation. However, mica crystallization suppresses their saturation and allows Ta to increase in the melt. Saturation with respect to Ta and Nb minerals occurs at the latest stages of magmatic crystallization, and columbite can originate from recrystallization of mica. We propose a model for prediction of intrusion fertility for Ta.     

河南铝土矿矿物成因及其演化序列

[摘 要]豫西铝土矿是我国喀斯特型铝土矿的典型代表。本文选取豫西典型的喀斯特型铝土矿为研究对象,通过XRD 分析、扫描电镜-能谱分析、电子探针分析和差热分析多种手段,探测铝土矿的物质组成及其赋存状态,并且分析其矿物成因,总结矿物演化序列。研究显示,豫西铝土矿的主要矿物成分包括硬水铝石、伊利石、锐钛矿、高岭石、针铁矿、赤铁矿、金红石等。硬水铝石主体为简单结晶成因。伊利石主体为风化过程中产物,部分为后期硬水铝石硅质交代的结果。锐钛矿和硬水铝石同期结晶形成于还原环境下。大部分高岭石形成于陆源期风化阶段,少部分为后期硬水铝石硅化转变形成。针铁矿和赤铁矿形成于两个阶段,第一阶段为成矿前风化作用形成的铁质风化壳;第二阶段为铝土矿成岩晚期出现了一期铁质流体活动形成了大量的赤铁矿和针铁矿。重砂矿物金红石和锆石等主要是母岩风化作用的残留物。豫西铝土矿中矿物形成演化可归纳为如下五个阶段:陆源期、同生期、成矿期、成矿后期和表生期。     

松树岗钽铌钨锡矿床石英脉的矿物学研究——云母和黑钨矿成分对热液成矿过程的制约

矿石矿物和脉石矿物的成分演化蕴含了热液成矿过程的详细信息。本文基于岩相学观察,从云母和黑钨矿着手,利用电子探针和LA-ICP-MS分析技术,对赣东北松树岗Ta-Nb-W-Sn矿床的浅部热液成矿过程开展了研究。结果表明,松树岗矿床浅部的钨锡矿体的石英脉,从早到晚,由深至浅,可以划分为黑钨矿石英脉、锡石石英脉、硫化物石英脉和贫矿石英脉。4类石英脉中都含有早期的铁锂云母和晚期的白云母与铁的氧化物集合体,深部早期脉中的云母以铁锂云母为主,而浅部晚期脉中的云母以白云母为主。与早期铁锂云母相比,晚期白云母具有明显较低的Ti、Na、Rb、Cs、W、Nb、Zn、Li_2O含量和明显较高的Pb、Cu、B含量。从深部早期脉到浅部晚期脉,云母成分存在如下演化趋势:Ti、Na、W、Nb含量降低,Pb、Zn、Cu、Li_2O、B含量增高。不同深度的黑钨矿石英脉中含有两种不同成分的黑钨矿,属同一期演化早晚形成。相对于热液流体早期沉淀的黑钨矿,晚期黑钨矿具有明显较低的Nb、Ta、Zr、Hf、Ti、Sn、U、In、Sc含量和明显较高的Mo含量和Fe O/MnO值。云母和黑钨矿主微量元素成分的演化揭示了在松树岗矿床浅部的热液成矿早期以岩浆热液为主,晚期由于水岩反应的加强有较多围岩物质贡献。     

Evolution of 2:1 layered silicates in low-grade metamorphosed Liassic shales of Central Switzerland

White mica from the Liassic black shales and slates in Central Switzerland was analysed by transmission electron microscopy (TEM) and electron microprobe to determine its textural and compositional evolution during very low-grade prograde metamorphism. Samples were studied from the diagenetic zone, anchizone and epizone (T ≈100°–450 °C). Phyllosilicate minerals analysed include illite/smectite (I/S), phengite, muscovite, brammallite, paragonite, margarite and glauconite. Textural evolution primarily is towards larger, more defect-free grains with compositions that approach those of their respective end-members. The smectite-to-illite transformation reduced the amounts of the exchange components SiK_?1Al_?1, MgSiAl_?2, and Fe³⁺Al_?1. These trends continue to a lesser degree in the anchizone and epizone. Correlations between the proportion of smectite in I/S and the composition of I/S indicate that smectite layers may contain a high layer charge. Illite in I/S bears a compositional resemblance to macrocrystalline phengite in some samples, but is different in others. Paragonite first appears in the upper diagenetic zone or lower anchizone as an interlayer-deficient brammallite, and it may be mixed with muscovite on the nanometre scale. Owing to the small calculated structure factor for paragonite-muscovite superstructures, conventional X-ray powder diffraction cannot distinguish between mixed-layer structures and a homogeneous compositionally intermediate solid solutions. However, indirect TEM evidence shows that irregularly shaped domains of Na- and K-rich mica exist below 10 nm. Subsequent coarsening of domains at higher grades produced discrete paragonite grains at the margins of muscovite crystals or in laths parallel to the basal plane of the host muscovite. Margarite appears in the epizone and follows a textural evolution similar to paragonite in that mixtures of margarite, paragonite, and muscovite may initially occur on the nanometre scale. However, no evidence of interlayer-poor margarite has been found.     

内蒙古红花尔基钨钼矿云英岩化白云母Ar-Ar定年及其地质意义

红花尔基钨多金属矿是近年在大兴安岭中北部地区发现的一处大型钨多金属矿床,主要矿化蚀变为云英岩化、绢英岩化,主要有用金属矿物为白钨矿和辉钼矿,岩体内辉钼矿与白钨矿有上钼下钨的带状分布特点,地质特征显示该矿床为一高温热液型钨(钼)矿床。为准确限定成矿热液活动时间,本文对矿区典型蚀变矿物——云英岩化蚀变带白云母进行Ar-Ar同位素定年,获得Ar-Ar坪年龄为174.4±1.2 Ma,等时线年龄为173.2±4.3 Ma。根据矿区云英岩化带与钨钼矿化带空间上重合和密切共生的关系,可知白云母的形成是与白钨矿、辉钼矿形成同源、同时,且辉钼矿Re-Os年龄(176.8±2.2 Ma)与Ar-Ar年龄在误差范围内具有一致性,该年龄代表了钨钼矿热液成矿时代。结合野外地质特征及锆石U-Pb、辉钼矿Re-Os年龄,进一步限定该矿床成矿时代为早中侏罗世,属燕山期构造岩浆活动的产物。     

Deformation of biotite and muscovite: Optical microstructure

An optical comparison illustrates the difference in behaviour of the two mica minerals biotite and muscovite; their response to deformation, and to chemical processes such as grain dissolution. Non-passive mechanical rotation, segmentation of deformed grains by a recovery-recrystallization type process and syntectonic growth of the phyllosilicates all contribute to the development of a strong tectonic foliation within a deformed pegmatite from the Italian Alps. There are significant mechanical differences between the two micas. Biotite readily deforms by kinking whereas muscovite forms sinusoidal folds and seldom kinks. If kink-like structures (deformation zones) are present in muscovite they are generally accompanied by fracturing. Fracturing and displacements are obvious in most deformed muscovites both parallel to axial surfaces and between (001) cleavages. Fracturing is occasionally recognised in biotite. However, it is often obscured by extensive dissolution and new grain nucleation. Evidence for dissolution processes in biotite is more abundant than in muscovite.