论斜长石超结构——关于e衍射参数及其矢量模的一些探讨

矿物的单位晶胞的晶体结构研究,曾使矿物学从外观形态描述进入微观研究。现代对矿物的非布拉格衍射--“卫星”衍射的研究,揭示了矿物具有超结构,从而使矿物学进入了新的发展阶段。矿物的超结构研究,表明矿物不是单位晶胞的简单重复,每一种矿物从宏观到微观,在单位晶胞,超晶胞等不同数量级范围内,都具有各自的组合、分布规律。无疑,超结构研究更能解释矿物的各种物理和化学性质,因而它具有深远的矿物学意义。     

铬尖晶石类质同象系列的×射线粉末法鉴定

一、引言铬铁矿是我国急需矿种之一,我所地质科技人员自建所以来,在陕、甘、宁、青、新等地区对铬铁矿的物质成分与成矿规律作了研究工作,随着地质科研的深入,对铬尖晶石类质同象系列正确定名的要求也越来越迫切,能否通过X射线粉晶鉴定来解决这个问题,成了大家关心的课题。近十年来,我们收集了楼房沟、松树沟、绿梁山、金川、大道尔吉、萨尔托海等地的铬尖晶石类矿物X射线粉晶分析数据,通过与91个有化学分析资料的铬尖晶石进行对比、统计及数据处理,初步获得晶胞大小与矿物物质成分的关系,可以按晶胞值的大小,大致划分六种铬尖晶石类矿物。同时推导了铬尖晶石晶胞值的近似经验计算公式,从而对铬尖晶石巴甫洛夫分类与晶胞大小关系的规律有了进一步     

广西大厂长坡锡石硫化物矿床锡石晶胞参数的初步研究

矿床为高中温热液型锡石硫化物矿床,通过研究知道随成矿温度由高到低,成矿阶段由锡石—石英经锡右硫化物到锡石—方解石,锡石晶胞的轴长,特别是c轴长和晶胞体积都有增大趋势。锡石中含有Fe等杂质元素,它们可以类质同像代替Sn,由于这些元素离子半径小,类质同像代替结果导致晶胞变小。而在高温条件下,元素类质同像代替较易进行,这就造成了高温阶段形成的锡石晶胞小,低温阶段形成的锡石晶胞大。     

豆荚状铬铁矿床的成因——以西藏自治区罗布莎铬铁矿床为例

本文以西藏自治区罗布莎铬铁矿床为例并结合世界其它地区同类矿床实例,讨论了豆荚型铬铁矿床的成因机制。研究表明,铬铁矿与纯橄岩-斜辉辉橄岩都是由同一原始地幔岩(尖晶石二辉橄榄岩)经不同程度熔融的产物。铬铁矿及纯橄岩是这一过程中高度熔融的最终产物。其熔融的机制是两种辉石(斜方辉石和单斜辉石)不一致熔融转变为橄榄石和铬尖晶石,并伴随着副矿物铬尖晶石及造岩矿物成分的调整和再造,从而导致铬铁矿床与纯橄岩的紧密伴生。该研究成果对认识世界上同类矿床的成因有普遍意义。     

超基性岩体中橄长岩-异剥辉长岩分异脉岩与铬铁矿的成因联系

1958年袁棨林在我国北部一地槽区曾注意到有两类超基性岩体。第Ⅰ类有橄长岩-异剥辉长岩分异脉岩(以下简称分异脉岩)的岩体,其造矿铬尖晶石为较富铝的富铬尖晶石亚种和富铁富铬尖晶石亚种,组成低品位冶金级矿石;第Ⅱ类为无分异脉岩的岩体,其中合富铬贫铝的铬铁矿亚种和富铁铬铁矿亚种,组成高品位冶金级矿石。它们虽然都是镁质超基性岩,同样是以斜辉辉撖岩为主的纯橄榄岩-辉橄岩杂岩体,而且都显示了较强的动力分异作用,只是由于出现或不出现与晚期岩浆铬铁矿有成因关系的分异脉岩,而使造矿铬失晶石成分有明显地不同。     

介绍H.B.巴甫洛夫著“铬尖晶石类矿物的化学成分与超基性岩侵入体岩石成分之间的关系”一书

H.B.巴甫洛夫著:铬尖晶石类矿物的化学成分与超基性岩侵入体岩石成分之间的关系。陆培芳等译、鲍明道校。     

高压相变晶体化学Ⅱ.高压下镁硅酸盐和氧化物中硅氧离子的半径变化和迁移行为

考查了高压下镁硅酸盐和硅镁氧化物(橄榄石、硅镁尖晶石、钙钛矿及后钙钛矿)中氧、硅的离子半径,发现在压力增加的条件下,不论相变是否发生,氧离子半径总是随压力增加而逐渐缩小的,但对于阳离子硅来说,相变导致它从配位数低的多面体向配位数高的多面体迁移时,其离子半径是逐渐增大的.这种现象与SiO2在高压相变时硅离子增大的趋势完全一致.这种现象可能是在高压下离子化合物逐渐向金属相化合物转变引起的.     

西藏某铬矿床成因分析

对于铬矿床,特别是对“非层状”超基性岩体内的铬矿床的成因和成矿规律,是一个尚未解决的地质问题。笔者在学习前人成果的基础上,根据1975—1977年的野外观察及室内鉴定分析,结合附生及造矿铬尖晶石类型、成矿与岩相及构造的关系,对西藏某铬矿床的成因进行了分析研究。     

X 射线粉末法晶胞参数修正的微计算机程序设计

X 射线粉末法,不仅可利用其粉末图来鉴定矿物,而且,可利用粉末法求出的晶胞参数来研究矿物的化学组成、结构和成因。晶胞参数计算和修正是 X 射线粉末法的一项不可缺少的重要工作之一。利用指标化的 d 值或θ角进行最小二乘方修正的方法,已经比较成熟.在晶系和空间群未知情况下,仅仅利用 d 值进行指标化并计算其晶胞常数,虽然已经进行了许多研究,并取得了很大进展,但成功率并不令人满意。     

华北磷块岩的矿物化学

在华北磷矿的研究項目中,我們做了些磷酸鈣矿物及其相伴生的矿物的鑑定工作。大家知道磷酸鈣矿物的类别是不易确定的,不同的学者对磷矿物的认識,分歧很大。A.B.卡查柯夫认为,所有磷酸鈣矿物都是氟磷灰石与高度分散状态的方解石的混合物,其主要依据是磷块岩与氟磷灰石的粉末照象实际上是极其相似的。据哥尔德斯密特对磷酸鈣矿物的晶体化学的研究,六方格架和Ca与F原子在通道中的排列情况使氟磷灰石构造十分稳定。Cl^-（1.81（?））和OH^-（1.4-1.6（?））的离子半径比F^-（1.33（?））大,因而稳定性較差。     

铬尖晶石和石榴石的相变:大陆科学钻探CCSD-PP3孔超镁铁岩超高压变质作用的证据

PP3超镁铁岩主要岩石类型有纯橄岩和石榴石橄榄岩,两者为渐变,主要矿物为橄榄石、铬尖晶石、石榴石、单斜辉石和斜方辉石.铬尖晶石的Cr#[Cr/(Cr+Mg) ×100]从51~89变化,TiO₂和MnO₂值分别低于0.26%和0.46%.铬尖晶石矿物表现为4期次演化的特点,反映了从岩浆期、榴辉岩相、角闪岩相和绿片岩相演化特征.随着超镁铁岩的演化,铬尖晶石表现为Cr#不断增大,而Mg#[Mg×100/(Mg+Fe2+) ]不断减少、氧逸度不断增加的过程.PP3铬尖晶石反映了地幔来源,为大陆岩石圈超镁铁岩特征,后期随折返而演化.从石榴石与铬尖晶石相互转变过程看出,PP3超镁铁岩经历了深度加大的过程,超镁铁岩曾经到达100km以上的岩石圈地幔深处.在绿片岩相-绿片角闪岩相变质过程中,铬尖晶石中Cr、Mg和Al减少,Fe相对增加,产生富Cr尖晶石变质作用样式.晚期剪切变形等次生变化影响了铬尖晶石矿物成分.      

伊通上地幔剪切带捕虏体中富铝尖晶石的地球化学特征

伊通上地幔剪切带中辉石岩、二辉橄榄岩和易剥橄榄岩是3个主要地幔捕虏体,其中尖晶石的化学成分以富铝为特征。辉石岩中尖晶石在薄片下呈绿色,为铝含量高、铬含量低的铝尖晶石;与之相比,二辉橄榄岩和易剥橄榄岩中尖晶石在薄片下呈棕色,为铝含量相对较低、铬含量相对较高的富铝铬尖晶石。尖晶石的颜色与Al、Mg、Cr、Fe含量有关。在不同捕虏体中尖晶石成分具有不同的变化范围,尖晶石化学成分之间存在一定的相关性,Mg#与Cr#,Mg#与Fe2 和Cr与Al呈现负相关性,而Mg#与Al#呈现出正相关性,反映不同捕虏体中尖晶石具有同一来源和成因联系。在地幔岩石部分熔融和结晶过程中Cr和Al的分异明显。固溶体条件下基本服从八面体Cr Al替代关系,而不同地幔捕虏体中尖晶石的成分差异是岩浆部分熔融和结晶过程中元素分异、固溶体离子替代的结果。     

Petrogenesis of Dunite Xenoliths from Koolau Volcano, Oahu, Hawaii: Implications for Hawaiian Volcanism

Ultramafic xenoliths from Koolau Volcano on the island of Oahu,Hawaii, are divided into spinel lherzolite, pyroxenite, anddunite suites. On the basis of a study of the petrography andmineral compositions of 43 spinel lherzolites, 12 pyroxenites,and 20 dunites, the following characteristics of the dunitesin relation to the other nodule types and to Hawaiian lavasemerge. (1) The forstente content of olivines in the Koolaudunites (Fo_82.6-Fo_{89 7} ) overlap those of Hawaiian tholeiiticand alkalic lavas and are generally lower than those in abyssallherzolites and dunites and in Koolau spinel lherzolites. (2)Most of the dunites contain no orthopyroxene, all except twocontain chrome spinel, and a few contain interstitial plagioclaseand clinopyroxene. (3) Chrome spinels from the Koolau dunitesare distinctly higher in Cr/(Cr+Al), lower in Mg/(Mg+ Fe²⁺)and higher in TiO₂ than those from abyssal basalts and peridotites.Chrome spinels in the dunites correspond closely in compositionto chrome spinels in Hawaiian tholeiitic and alkalic lavas.(4) The abundance of dunite relative to other nodule types decreasesoutward from the central part of the volcano. The dunites areinterpreted not as residues of partial fusion of the mantlebut as crystal accumulations stored at shallow depths beneaththe central part of Koolau Volcano and derived from picriticmagmas parental to the shield-building tholeiitic lavas.     

Magmatic unmixing in spinel from late Precambrian concentrically-zoned mafic–ultramafic intrusions, Eastern Desert, Egypt

Spinel is widespread in the ultramafic core rocks of zoned late Precambrian mafic–ultramafic complexes from the Eastern Desert of Egypt. These complexes; Gabbro Akarem, Genina Gharbia and Abu Hamamid are Precambrian analogues of Alaskan-type complexes, they are not metamorphosed although weakly altered. Each intrusion is composed of a predotite core enveloped by pyroxenites and gabbros at the margin. Silicate mineralogy and chemistry suggest formation by crystal fractionation from a hydrous magma. Relatively high Cr₂O₃ contents are recorded in pyroxenes (up to 1.1 wt.%) and amphiboles (up to 1.4 wt.%) from the three plutons. The chrome spinel crystallized at different stages of melt evolution; as early cumulus inclusions in olivine, inclusions in pyroxenes and amphiboles and late-magmatic intercumulus phase. The intercumulus chrome spinel is homogenous with narrow-range of chemical composition, mainly Fe³⁺-rich spinel. Spinel inclusions in clinopyroxene and amphibole reveal a wide range of Al (27–44 wt.% Al₂O₃) and Mg (6–13 wt.% MgO) contents and are commonly zoned. The different chemistries of those spinels reflect various stages of melt evolution and re-equilibration with the host minerals. The early cumulus chrome spinel reveals a complex unmixing structures and compositions. Three types of unmixed spinels are recognized; crystallographically oriented, irregular and complete separation. Unmixing products are Al-rich (Type I) and Fe³⁺-rich (Type II) spinels with an extensive solid solution between the two end members. The compositions of the unmixed spinels define a miscibility gap with respect to Cr–Al–Fe³⁺, extending from the Fe³⁺–Al join towards the Cr corner. Spinel unmixing occurs in response to cooling and the increase in oxidation state. The chemistry and grain size of the initial spinel and the cooling rate control the type of unmixing and the chemistry of the final products. Causes of spinel unmixing during late-magmatic stage are analogous to those in metamorphosed complexes. The chemistry of the unmixed spinels is completely different from the initial spinel composition and is not useful in petrogenetic interpretations. Spinels from oxidized magmas are likely to re-equilibrate during cooling and are not good tools for genetic considerations.     

Compositional variations of chromiferous spinel in Mg-rich rocks of the Deccan Traps,India

Composition of chromiferous spinel included in olivines of Mg-rich basalts and gabbros of the Deccan Traps (Gujarat and Western Ghats) are reported here. They vary from Al-rich compositions [Al₂O₃ = 53wt.%; Cr#, 100Cr/(Cr + Al) = 12] to Cr-rich compositions [Cr₂O₃ = 51wt.%; Cr# = 84], and from Cr-Al rich compositions towards Cr-rich Ti-magnetite (TiO₂ up to 23 wt.%, ulvöspinel up to 67mol.%). The Mg# [100Mg/(Mg + Fe²⁺)] of spinel decreases from 81 to nearly zero. The highest Cr# has been found in the Bushe Fm., Thakurvadi Fm., and some high-Ti basalts of the Pavagadh section, whereas some of the low-Ti basalts of Saurashtra have Al-rich compositions typical of spinels found in mid-ocean ridge basalts. The chemical composition of the Deccan Trap spinels is completely different compared to that observed in mantle spinel suites, with very few exceptions. The decreasing Al and increasing Fe and Ti of spinel seems to be mainly the result of decrease of Mg in the locally coexisting melts and favourable cationic substitutions in the lattice. There is barely any evidence of general relationships between the composition of the Deccan spinels and inferred mantle sources of the host magmas. Pyroxene inclusions in spinels may witness a high-pressure stage of crystallization, but the possibility of non-equilibrium crystallization, or even magma mixing, cannot be ruled out. Overall, the compositional ranges of chromiferous spinel in the Deccan Traps closely match those observed in the other Large Igneous Provinces having mafic/ultramafic intrusions and mafic magma compositions (e.g., Siberian Traps, Karoo, Emeishan).     

Non-Stoichiometric magnesian spinels in shale xenoliths from a native iron-bearing andesite at Asuk,Disko, central West Greenland

A strongly reduced native iron-bearing andesite breccia from Disko contains graphite-rich modified shale xenoliths with magnesian spinels. These spinels are free from or very poor in ferric iron and vary considerably within the MgO-FeO-Cr₂O₃-Al₂O₃ compositional space. Through a simple substitution of the type 3 (Mg, Fe)²⁺ ⇆ 2(Al, Cr)³⁺+□_vacancy, the spinels vary from stoichiometric (Mg, Fe)²⁺ (Al, Cr)³⁺ ₂O₄ towards (Al, Cr)₂O₃. The simple substitution of Cr for Al suggests that Cr was accepted into the spinel structure as Cr³⁺, despite the reduced nature of the enclosing andesite. The most magnesian spinels are cation deficient spinel_ss in the synthetic systems MgO-Al₂O₃ and MgO-Al₂O₃-Cr₂O₃. The absence of exolved (Al, Cr)₂O₃-component is probable due to rapid quenching.     

Effects of hydrothermal alteration on the compositions of chromian spinels

Chromite spinels in hydrothermally altered rocks from fracture-zone ultramafic rocks and from both ultramafic cumulate pods and sheeted dikes in the Josephine ophiolite, California, display a wide variety of compositions. Alteration of the spinel may not be visible in thin section. The primary composition changes accompanying hydrothermal alteration are increase in Cr/(Cr+Al) and/or Fe²⁺/(Fe²⁺+Mg). In general, altered spinel grains associated with hornblende and chlorite show an increase in Cr/(Cr+Al) from core to rim. Altered spinel grains associated with serpentine show an increase in Fe²⁺/(Fe²⁺+Mg) from core to rim but may not show an increase in Cr/(Cr+Al). The compositional zoning in some altered spinel grains appears to result both from reaction of clinopyroxene plus spinel to form hornblende, and from reaction of hornblende to form chlorite. These observations suggest that subsolidus hydrothermal metamorphic effects need to be considered when interpreting spinel compositions and the compositions should not be interpreted solely in terms of igneous processes. Further, the presence of highly altered spinels may be indicative of hydrothermal alteration in rocks where other evidence of such alteration is absent.     

新疆洪古勒楞蛇绿岩中铬尖晶石的化学成分变异及其意义

本文应用了洪古勒楞蛇绿岩中铬尖晶石的电子探针分析数据,讨论该蛇绿岩中不同岩石中铬尖晶石化学成分特征,显示出铬尖晶石的成分与寄主岩石有关。基本可将其分为三组:造矿铬尖晶石、堆积岩副矿物铬尖晶石和地幔橄榄岩副矿物铬尖晶石。它们在主要成分和微量成分方面均存在区别,化学成分的相关性也不一样。共生橄榄石-铬尖晶石对的元素分配说明二者基本为平衡矿物。     

A proton- and electron-microprobe study of gallium, nickel and zinc distribution in chromian spinel

Chromian spinels from a number of localities were analyzed by proton and electron microprobes to examine the variation of trace elements in different geological environments. Chromian spinels studied include those representing ophiolitic complexes, layered intrusions in continental areas, Alaskan-type complexes, komatiitic subvolcanic sills, Ni sulfide ores and metamorphosed mafic and ultramafic rocks.

Nickel concentrations range from 30 to 4690 ppm (proton microprobe), with a mean value of 943 ppm. Nickel, favouring the octahedral sites in the spinel structure, displays an overall increase with a decrease in the Cr/(Cr + Al + Fe³⁺) ratio. Nickel partitioning between chromian spinel and mantle silicates appears to be primarily dependent upon the major element composition of the chromian spinel.

Zinc concentrations range from 230 to 9810 ppm (proton microprobe), with a cluster around 500 ppm. Ophiolitic chromian spinels display the lowest overall Zn values. Zinc levels appear to discriminate between chromian spinels in chromitite samples from those occurring as accessory chromian spinel in dunites or other rock types. Chromian spinels that are enclosed in or adjacent to sulfide grains display higher concentrations of Zn. Zinc, strongly favouring the tetrahedral sites, displays a crude negative correlation with the Mg/(Mg + Fe²⁺) ratio and appears to vary as a function of temperature.

All the chromian spinel grains analyzed contain measurable quantities of Ga by proton microprobe, ranging from 10 to 208 ppm. There is a reciprocal relationship between the Ga concentration and the Cr/(Cr +Al + Fe³⁺) ratio and a crude positive correlation between the Ni and Ga concentrations. Measured Ga concentrations in chromian spinel and whole rock samples are supportive of the experimental mineral-melt partition coefficient of Malvin and Drake (1987). Similar to the peridotite xenoliths, mid-ocean ridge basalts and oceanic-island basalts, Ga correlates well with Al₂O₃ in the case of the ophiolitic chromian spinels and most of those representing layered complexes. The ophiolitic chromian spinels seem to have crystallized from melts whose compositions are similar to those of partial melts of the upper mantle.     

Scanning electron microscopy and Raman spectroscopy as combined methods for studying zoning in minerals: The case of spinels from Archean komatiites

Several types of both magmatic and metamorphic spinels have been found in Archean komatiites of the Sovdozero and Kostomuksha greenstone belts in the eastern part of the Fennoscandian Shield. Scanning electron microscopy and Raman spectroscopy revealed relics of cores of primary magmatic chrome-spinels with high Cr and Al contents. In the Sovdozero structure, the relics are better retained than those in the Kostomuksha structure, which is caused by a different degree of metamorphic transformation. The comparable 100 · Cr/(Al + Cr) values of spinel cores from Sovdozero and Kostomuksha reflect similar conditions of partitional melting in the mantle. These data agree with the fact that both komatiite complexes belong to the Al-undepleted petrogenic type. Wide variations in the Cr and Al contents in primary chrome-spinel cores together with a constant Mg/(Fe²⁺ + Mg) ratio correspond to low oxygen fugacity during magma crystallization. In general, the composition of these primary chrome-spinels is similar to that of accessory phases in peridotites from suprasubduction zones and agrees with hypothesis of komatiite complex formation in back-arc basins.