三方晶系直氟碳钙铈矿在我国的发现及其透射电…

运用透射电镜方法，在山东郗山稀土矿床的钙－铈氟碳酸盐系列矿物中发现了三方晶系直氟碳钙铈矿的存在，其晶胞参数为α＝０．７１２ｎｍ，ｃ＝５．６１６ｎｍ，衍射符号为３ｍＲ－ｃ－。通过与加拿大魁北克某矿区产出的单斜晶系的直氟碳钙铈矿的对比研究，确认为本矿区产出的直氟碳钙铈矿为其同质二象变体。     

氟碳钙铈矿6R2新多型的高分辨电镜研究

用电子衍射和高分辨电子显微镜技术研究了钙稀土氟碳酸盐系列矿物中氟碳钙铈矿及其衍生体的微结构,发现了氟碳钙铈矿的６Ｒ２新多型体,确定了其亚结构晶胞呈六方（Ｈ）对称α＇＝０．４１２ｎｍ,ｃ＇＇＝０．４７１ｎｍ,超结构晶胞呈菱面体（Ｒ）对称,ａ＝０．７１４ｎｍ,ｃ＝８．４７８ｎｍ,可能的空间群为Ｒ３＾－ｃ和Ｒ３ｃ,［１２１０］取向的高分辨结构像显示出该多型体结构单元层沿ｃ轴的有序堆垛及重复周期。［０００     

氟碳铈矿和氟铈矿晶体结构的精确测定

用强功率四圆单晶衍射仪精确地修正了氟碳铈矿和氟铈矿的晶体结构．氟碳铈矿（ｂａｓｔｎａｅｓｉｔｅ，Ｃｅ（ＣＯ３）Ｆ）属六方晶系，其晶胞参数为：ａ＝０．７１４３８（９）ｎｍ，ｃ＝０．９８０８（２）ｎｍ，γ＝１２０°，Ｚ＝６，空间群Ｐ６－２ｃ．使用３６７个（Ｆ≥３σ（Ｆ））独立衍射点，经多轮最小二乘法修正后，最终获得偏离因子Ｒ＝０．０４９９．氟碳铈矿的晶体结构特征表现为［ＣＯ３］平面三角形平行ｃ轴分布，铈的配位数为９，Ｃｅ－Ｏ（Ｆ）平均键长为０．２５１５ｎｍ，Ｃ－Ｏ平均键长０．１３２７ｎｍ，每个氟原子与周围三个铈原子相连．氟铈矿（ｆｌｕｏｃｅｒｉｔｅ，ＣｅＦ３）属六方晶系，其晶胞参数为：ａ＝０．７１４１２（２１）ｎｍ，ｃ＝０．７２９８９（２１）ｎｍ，γ＝１２０°，Ｚ＝６．其空间群为：Ｐ３－ｃ１（Ｎｏ．１６５）．使用３２１个（Ｆ≥３σ（Ｆ）））独立衍射点，经多轮最小二乘法修正后，最终获得偏离因子Ｒ＝０．０５４２．氟铈矿的晶体结构表现为每个氟原子与周围三个铈原子相连接，每个铈原子与周围９个氟原子相连，铈的配位数为９，Ｃｅ－Ｆ平均键长为０．２４６８ｎｍ．     

氟碳钙铈矿结构中晶体缺陷的高分辨电镜研究

用高分辨电子显微术（ＨＲＥＭ）研究了氟碳钙铈矿（ＢＳ）晶体结构中的无序堆垛和体衍交生现象，结果表明该矿物的衍生多晶体是由钙－铈氟碳酸盐矿物中不同组分的氟碳铈矿（Ｂ）和直氟碳钙铈矿（Ｓ）结构单元层沿ｃ方向无序堆垛而成。高分辨结构象揭示出氟碳钙铈矿衍生多晶体的微结构特征。讨论了氟碳钙铈矿结构中的堆垛层错等晶体缺陷现象。     

氟碳钙铈矿晶体结构解析探索

氟碳钙铈矿从１８３５年发现至今已有一百五十多年的历史。然而迄今还没有人深度用结构因子计算法成功测定其晶体结构，只有推测结构模型与部分原子位，本文第一次用结构因子计算法完成该矿物二级亚晶胞ａ＇ｃ＇的结构测定。晶体简易化学式Ｃｅ２ＣａＦ２［ＣＯ３］３，ａ＇ｃ＇亚晶胞空间群为Ｐ６３２２，晶胞参数ａ＇＝ｂ＇＝０．４１０１ｎｍ（ａ＝０．７１０４（１）ｎｍ，ａ＇＝１／√３ａ），ｃ＇＝２．７９０１（４）ｎｍ，ｒ     

关于钙-稀土氟碳酸盐矿物名称的汉译问题

钙-稀土氟碳酸盐矿物属六方球霞石(Vaterite)型碳酸盐。已命名的有四种矿物,即Bastnacsitc,Parisite,Roentgenite和Synchysite。由新矿物及矿物命名委员会审订的汉译名分别为:氟碳铈矿,氟碳钙铈矿,伦琴石和直氟碳钙铈矿。与此相关的还有Bastnaesite-(Y),Synchysite-(Y),Synchysite-(Nd)等变种矿物分别译为氟碳钇矿、直氟碳钙钇矿和直氟碳钙钕矿。这些汉译名显然是遵循几个不同的原则确定的,     

我国产出的砷铅矿族矿物的研究

砷铅矿族矿物是一族六方晶系的类质同象系列矿物，包括砷铅矿、钒铅矿和磷氯铅矿。砷铅矿呈淡黄色、浅黄绿色和灰白色六方柱状晶体产出，Ｈｍ＝３．５，Ｄ≥６．７５ｇ／ｃｍ３，一轴晶负光性，Ｎ＞２，晶胞参数为ａ０＝１．０２５１ｎｍ，Ｃ０＝０．７４４ｎｍ，Ｚ＝２。广西德保矿区产出的砷铅矿的化学成分为（ｗｔ．％）：ＰｂＯ７４．９４，Ａｓ２Ｏ５１９．５３，Ｐ２Ｏ５２．３１，ＣｕＯ０．３６，Ｃｌ２．４１，总量为９９．５５。云南个旧矿区产出的钒铅矿呈桔红色至红褐色，六方短柱状自形晶，Ｈｍ＝３．０，Ｄｘ＝６．９５ｇ／ｃｍ３，一轴晶负光性，Ｎ＞２，晶胞参数为ａ０＝１．０３１ｎｍ，Ｃ０＝０．７４３ｎｍ，Ｚ＝２，空间群为Ｐ６３／ｍ，其化学成分为（ｗｔ．％）：ＰｂＯ７９．９８，Ｖ２Ｏ５１８．９４，Ｃｌ２．６１，总量为１０１．５３。广西阳朔产出的磷氯铅矿，呈暗绿色六方柱状晶体产出，Ｈｍ＝３．５，Ｄ＝６．９８ｇ／ｃｍ３，一轴晶正光性，Ｎ＝２±，平均化学成分为（ｗｔ．％）：ＰｂＯ８１．６４，Ｐ２Ｏ５１５．０８，Ａｓ２Ｏ５０．１０，ＣｕＯ０．２０，Ｃｌ２．６７，总量为９９．６９。     

直氟碳钙铈矿6R,3R多型及其微孪晶结构的透射电镜研究

运用透射电镜技术，发现了三方晶系直氟碳钙铈矿（Synchysite）多型和微孪晶的存在，确定其中的多型有两种，即6R和3R多型，在3R多型中发现有微孪晶存在，这种微孪晶属（0001）孪晶面的面律（旋转）孪晶。由于直氟碳钙铈矿是钙铈氟碳酸盐系列矿物的一个端员组分，因此，对其多型和微孪晶的研究，有助于揭示该系列中间组分矿物多型和微孪晶的形成机理。     

松辽盆地中生代火山岩中的氟碳钙铈矿特征及成因意义

在松辽盆地深层发育的中生代酸性火山岩中首次发现氟碳钙铈矿.氟碳钙铈矿的寄主岩为球粒流纹岩、流纹岩、流纹质熔结凝灰岩、流纹质凝灰岩,其寄主岩分布深度为2 930～3 830m,形成时代为早白孚世晚期.氟碳钙铈矿常与石英、碳酸盐、钠铁闪石、钠长石、绿泥石、绿帘石、粘土矿物等次生矿物共生,并与天然气储层有着一种内在的联系.氟碳钙铈矿是岩浆后期热液和大气降水多阶段、多次作用萃取的产物,这种相互作用是多无体系参与并经历了多阶段演化,氟碳钙铈矿形成于富Ca2+抖和CO23;的流体及还原环境.松辽盆地周边地区广泛发育的中生代火山岩与松辽盆地深层中生代火山岩十分相似,松辽盆地周边地区是否存在一个巨大的氟碳钙铈矿潜在资源,值得注意.     

我国首次发现的砷钙锌石和羟砷锌石的矿物学特征及其意义

我国首次发现的砷钙锌石和羟砷锌石产于内蒙古自治区额济纳旗老硐沟金矿脉氧化带矿石的空洞中。砷钙锌石多呈半自形或自形晶体，绿或淡绿色，透明，比重４．３２（计算）。Ｎｇ＝１．７７８，Ｎｍ＝１．７６０，Ｎｐ＝１．７５６，二轴晶（＋），２Ｖ＝４６°。化学分子式为Ｃａ０．９９（Ｚｎ０．９４Ｃｕ０．０７）１．０１［（ＡｓＯ４）０．９７（ＣＯ３）０．０３］１．００（ＯＨ），其中（ＣＯ３）２－取代部分（ＡｓＯ４）３－为红外光谱分析所证实，这不同于国外报道的砷钙锌石。据Ｘ射线粉末衍射分析的主要谱线，计算得其晶胞参数：ａ＝０．７４７３ｎｍ，ｂ＝０．９０１７ｎｍ，ｃ＝０．５９１６ｎｍ。羟砷锌石常呈集合体或单个晶体产出，淡黄绿色或无色，透明，比重４．４４（计算）。Ｎｇ＝１．７６１，Ｎｍ＝１．７３８，Ｎｐ＝１．７１９，二轴晶（＋），２Ｖ＝８７°。化学分子式为（Ｚｎ１．９７Ｃａ０．０２）１．９９（ＡｓＯ４）（ＯＨ）。据Ｘ射线粉末衍射分析的主要谱线，计算得其晶胞参数：ａ＝０．８３０４ｎｍ，ｂ＝０．８５１６ｎｍ，ｃ＝０．６０５４ｎｍ。氧化矿石的主要矿物组合为：臭葱石＋褐铁矿＋针铁矿＋砷钙锌石＋羟砷锌石＋自然金＋自然银＋石英＋方解石＋蛋白     

地幔超高压条件下镍黄铁矿的一种新结构相——菱面体相: 辽宁金刚石包体的镍黄铁矿晶体结构

从金刚石中获取的包体矿物经电子探针分析其成分与镍黄铁矿相同, 该包体矿物晶体形态完好, 外形为三(六)方对称.用CCD单晶衍射仪对该矿物进行了单晶德拜衍射, 得到的39个衍射峰, 经粉末法指标化程序判别和计算, 这些衍射峰分别属于两种结构的镍黄铁矿的衍射峰: 一套为菱面体结构(六方定向)镍黄铁矿的衍射; 另一套属于立方结构的镍黄铁矿结构的衍射.菱面体结构镍黄铁矿的晶胞参数: a＝0.690 62 nm, c＝1.720 95 nm, V＝0.710 85 nm3(六方定向); a_R＝0.698 61 nm, α＝59.244 5°, V＝0.236 95 nm3(菱面体定向).菱面体结构的衍射表明该镍黄铁矿在地幔超高压环境中形成, 出现立方结构的衍射, 反映了金刚石破碎后, 该镍黄铁矿包体在常压下相变的结果.      

Defect distribution and dissolution morphologies on low-index surfaces of α-quartz

The dissolution of prismatic and rhombohedral quartz surfaces by KOH/H₂O solutions was investigated by atomic force microscopy. Rates of dissolution of different classes of surface features (e.g., steps, voids, and dislocation etch pits) were measured. The prismatic surface etched almost two orders of magnitude faster than the rhombohedral surface, mostly due to the difference in the number and the rate of dissolution of extended defects, such as dislocations. Because of the presence of imperfect twin boundaries, defect densities on the prismatic surface were estimated at 50-100 μm⁻², whereas the rhombohedral surface possessed only ∼0.5-1.0 μm⁻², mostly in the form of crystal voids. Crystal voids etched almost one order of magnitude faster on the prismatic surface than on the rhombohedral surface due to differences in the number and the density of steps formed by voids on the different surfaces. In the absence of extended defects, both surfaces underwent step-wise dissolution at similar rates. Average rates of step retreat were comparable on both surfaces (∼3-5 nm/h on the prismatic surface and ∼5-10 nm/h on the rhombohedral surface). Prolonged dissolution left the prismatic surface reshaped to a hill-and-valley morphology, whereas the rhombohedral surface dissolved to form coalescing arrays of oval-shaped etch pits.     

First carbonatite hosted REE deposit from India

Based on geological mapping and grid channel geochemical sampling, a carbonatite plug hosted REE deposit has been discovered at Kamthai, Barmer district, Rajasthan. The main REE minerals hosted by carbonatite plug are bastanesite (La), basnaesite (Ce), synchysite (Ce), carbocernaite (Ce), cerianite (Ce), ancylite and parisite. The highest value of LREE is 17.31%, whereas, mean works out 3.33% and weighted average is 2.97%. The carbonatite plug covers 19475 sq. meters and the resources have been estimated upto 84 m depth under Proved, Probable and Possible categories. The total resource estimation for carbonatite plug and other carbonate sills, dykes and veins is 4.91 million tons, making this as truly world class deposit. The TMC of individual LREO (lower rare earth oxide) calculated for carbonatite plug only are La=52196 tonnes, Ce =66026 tonnes, Nd = 13663 tonnes, Pr = 5415 tonnes, Sm = 920 tonnes and Eu = 207 tonnes. Besides these REE, the Kamthai resource will produce 551 tonnes of Ga, 44 tonnes of Ge and 1,12,830 tonnes of SrO during its mining life.     

Bristen granite: a highly differentiated,fluorite-bearing A-type granite from the Aar massif,Central Alps,Switzerland

Bristen granite is a body of fine-grained leucogranite occurring in the Gotthard rail base tunnel in the Central Alps. During construction of the tunnel, Bristen granite (Brgr) has been drilled along a 600 m long section. The aplite-granite belongs to the suite of Variscan granitoid intrusions of the Aar massif and contains a variety of accessory minerals typical of highly differentiated granites. Rock forming fluorite, partly enriched in yttrium (Y) and rare earth elements (REE), is intergrown with the late Y- and REE-bearing carbonate mineral synchysite. The granite contains a variety of Ti- and Y-REE-niobates, thorite, and zircon. Compared with the calc-alkaline central Aar granite (cAgr), Bristen granite is strongly depleted in Ti, P, Mg, Sr, and Ba and shows a remarkable enrichment in incompatible elements such as Rb, Th, U, Nb, Y, HREE and F. Bristen granite is the most evolved granitoid rock of the Aar massif. The composition of Brgr is typical of post-collisional reduced (ferroan) A-type granites. The Brgr melt formed in the lower crust and crystallized from a highly differentiated melt at the cotectic point in the quartz-feldspar system close to 100 MPa and 700 °C. The Brgr intruded as a small isolated stock pre-Variscan gneisses with sharply discordant contacts. The primary igneous host of Nb, Ta, Y, U, Th and REE is biotite in addition to minor amounts of allanite, and zircon. The presence of Y-REE-fluorite, synchysite, parisite and Y- and Ti-niobates and other REE-minerals can be related to reaction of igneous biotite and primary fluorite with hydrothermal fluids. The reaction is associated with alpine metamorphism, because Y-bearing fluorite and synchysite have been reported from Alpine fissures. The transformation of primary biotite to chlorite and muscovite released the heavy metal oxides under lower greenschist facies conditions that formed the Alpine diagnostic mineral stilpnomelane at about 300 °C.     

The Chailag-Khem fluorite-barium-strontium rare earth carbonatite occurrence, the Western Sayan Range, Russia

The geological and mineralogical data on the Chailag-Khem F-Ba-Sr-REE occurrence in the Western Sayan Range, Russia, are discussed. The chemical compositions of rocks, ores, and minerals (ICP-MS, Link) are reported. The occurrence is localized in a tectonic crush zone composed of Cambrian quartz-sericite slates intruded by quartz syenite porphyry. Ore mineralization occurs as veins, cement of tectonic breccia, and metasomatic disseminations in host rocks. Massive ore consists of calcite, strontianite, and quartz; impregnations of euhedral fluorite, ankerite, and bastnaesite crystals; and fine-grained barite aggregate. Accessory minerals include parisite, synchysite, barytocelestine, sulfides, rutile, and uraninite. Late metasomatic calcite and strontianite segregations and veinlets are abundant. In genetic, mineralogical, and geochemical features, the Chailag-Khem occurrence is similar to the Late Mesozoic carbonatite deposits of Central Tuva, of which the Karasug Fe-F-Ba-Sr-REE deposit is the largest and best known. All carbonatite deposits and occurrences are located within a longitudinal zone transverse to the major tectonic elements of the region.     

碱性花岗岩中稀土矿物微观地质异常及其意义

四川冕西霓石碱性花岗岩中的稀土矿物主要为钙稀土氟碳酸盐矿物系列，通过选区电子衍射（SAED）和高分辨透射电子显微术（HRTEM）研究发现该系列矿物晶体结构中广泛发育复杂多样的微观地质异常现象，其主要类型有：（1）由该系列两个端员矿物氟碳铈矿结构层（B）与直氟碳钙铈矿结构层（S）以不同比例沿C轴方向有序堆垛形成的BmSn型规则混层结构；（2）无序堆垛形成的有序一无序结构晶畴；（3）由堆垛层错形成的无序混层结构，氟碳钙铈矿中不同多型体间的共格连生结构和相转变等；（4）氟碳铈矿结构中的平行于[001]方向的平移畴及一维无公度调制结构，该类调制结构可能是由于矿物中原子占位有序度的变化而形成的无序结构状态。     

Spheroidal dolomites in a Visean karst system – bacterial Induced origin?

Spheroidal dolomite crystals occur in the karstified top of a Dinantian dolomite sequence in eastern Belgium. The spheroidal dolomite crystals are best developed at the base of the karst system. The dolomite crystals are characterized by a spherulitic or dumb-bell inclusion pattern, and are overgrown by dolomite cements with a rhombohedral outline. They are considered to be bacterially related precipitates based on, (1) textural similarities with documented bacteriogenic precipitates, (2) the presence of ‘bacterial’microspheres and framboidal pyrite embedded within the dolomite, and (3) their general geological setting. The geochemical characteristics of the dolomites and associated minerals support a bacterial origin. The ubiquity of framboidal pyrite, depleted in ³⁴S (δ³⁴S=— 22.4 to — 25.5%oCDT), testifies to a period of bacterial sulphate reduction. The isotopic composition of the spheroidal dolomites (δ¹³C=— 2.4 to - 3.2%oPDB and δ¹⁸O=— 3.8 to - 3.4%oPDB) suggest a contribution from oxidized organic carbon produced during bacterial sulphate reduction. Sulphate reduction may also result in a concomitant ¹⁸O depletion if the system is nearly closed. It is however, evident from the sulphur isotopic composition of associated framboidal pyrite that the system was fairly open. The ¹⁸O depletion of the spheroidal dolomite crystals (δ¹⁸O=— 3.8 to — 3.4%oPDB) and their occurrence adjacent to, and within karst cavities suggests a mixing zone origin, with a significant proportion of freshwater in it. The rhombohedral cement-overgrowths have calculated δ¹⁸O values in the range of 0 to +5.3%oPDB, which reflect precipitation from normal to slightly evaporated contemporaneous seawater.     

Synchysite-(Y)–synchysite-(Ce) solid solutions from Markersbach, Erzgebirge, Germany: REE and Th mobility during high-T alteration of highly fractionated aluminous A-type granites

Summary The Ca,REE-fluorocarbonate synchysite, which forms anhedral grains hosted in albite, was identified in the Markersbach pluton (Erzgebirge, Germany) composed of F-rich, highly fractionated and autometasomatically altered granites. These granites were emplaced in a post-collisional setting and are of aluminous A-type affinity. The grains were identified by electron microprobe analysis as intermediate members of the probably complete solid-solution series between synchysite-(Y) and synchysite-(Ce). The rareearth elements likely were liberated upon complete destruction of magmatic monazite and xenotime during interaction with a F-CO₂-Ca-bearing, late-magmatic fluid at relatively high temperatures. The geochemical patterns of different granite samples from Markersbach indicate that the REE and Th were not trapped immediately at the site of their release but mobilized over distances of at least decimeters. During transport of the elements in the fluid, presumably as fluoride (HREE) and chloride (LREE) complexes, no significant fractionation took place among the REE. Received May 8, 2000; revised version accepted November 21, 2000     

Ree minerals of alkaline metasomatic rocks in the Main Sayan Fault

The composition of accessory REE minerals (allanite, chevkinite, fergusonite, and REE carbonates) in alkaline metasomatic rocks of the Main Sayan Fault (quartz-albite-microcline-riebeckite-aegirine, quartzalbite-microcline-magnetite, and clinopyroxene-albite) was studied using back-scattered scanning electron microscopy. Chevkinite occurs only in quartz-albite-microline metasomatic rock. The paragenesis of allanite and titanite is stable in clinopyroxene-albite metasomatic rocks. Allanite and fergusonite are typical of all zones of the metasomatic column. Chevkinite and allanite are often altered due to interaction with hydrothermal fluid and lose some amount of LREE. Secondary bastnaesite, synchysite, and ancylite are formed after allanite, while secondary monazite is developed after chevkinite. Presumably, the low-temperature alteration of allanite and chevkinite under effect of F^?, CO ₃ ^2? , and P ₄ ^3? -bearing fluids had not any significant manifestation in the total REE content in metasomatic rocks.     

Phase equilibria of bastnaesite,allanite, and monazite: Bastnaesite-out isograde in metapelites of the Vorontsovskaya group,Voronezh crystalline massif

Paleoproterozoic metapelites of the Vorontsovskaya structure contain accessory REE phosphates (monazite, xenotime, and REE-apatite), fluorine-carbonates (bastnaesite and synchysite), and silicate (allanite). Analysis of phase equilibria involving REE-bearing minerals indicates that bastnaesite is stable only in the greenschist facies and decomposes with the synthesis of monazite at temperatures below the staurolite isograde (490–500°C) at a pressure of 3 kbar. Monazite first appears in the greenschist facies, and its stability expands with increasing temperature, including the granulite facies. A diversity of reaction textures suggests that the mineral is formed in the garnet zone by a reaction of bastnaesite with apatite and by the partial decomposition of REE-bearing chlorite. Monazite is produced in the garnet and staurolite zones by a reaction of allanite with apatite and by a decomposition reaction of REE-bearing apatite.