黔东南铬尖晶石特征及金刚石原生矿找矿分析

本文介绍和分析近几年来在黔东南特别是清水江水系亮江支流的黎平敖市,中黄及锦屏同古等出土金刚石地区,利用重砂,地质寻找金刚石原生矿取得的新成果,主要对铬尖晶石矿物形态。     

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。     

山东蒙阴金伯利岩中尖晶石族矿物特征及种类划分

山东蒙阴金刚石矿区金伯利岩中的尖晶石族矿物究竟是铬铁矿还是尖晶石一直倍受争议,为了确定山东蒙阴矿区形态复杂的尖晶石族矿物种类,项目组对矿区的尖晶石族矿物进行了系统的采样,利用电子探针对50件尖晶石族矿物MgO、FeO、TiO2、Al2O3、MnO、Cr2O3进行微区化学成分分析,结果显示,山东蒙阴金刚石矿区金伯利岩中尖晶石族矿物A、B端元成分复杂,不存在单纯的铬铁矿或尖晶石矿物种,以化学分子式分类为基础得到的尖晶石族矿物种类主要有:铁镁-铬铁钛、镁铁-铬铁铝钛、铁镁-铬铝铁、镁铁-铬铝铁、铁镁-铬铁钛铝、镁铁-铬铝、铁镁-铬铝7个亚种。山东蒙阴金伯利岩中尖晶石族矿物的主要端元组分为MgAl2O4、MgCr2O4、FeCr2O4,矿物化学成分分析表明,Mg质量分数较高(7.3%~11.8%),其中Fe、Mg离子数比近于1:1,构成富镁的铬铁矿。     

金伯利岩中铬尖晶石的特征及与其它岩类中铬尖晶石之对比

本文根据我国金伯利岩中铬尖晶石的a_0、比重、红外光谱分析、穆斯堡尔谱分析、湿法化学分析、探针分析和稀土元素分析资料及其它岩类中的铬尖晶石类的化学成分资料,研究了各金伯利岩区之间及其区内各岩体的铬尖晶石的差异,指出了作为粗晶、原生基质矿物、金刚石中的包体、金伯利岩深源包体中的矿物产出的铬尖晶石特征,将金伯利岩中的铬尖晶石与其它岩类中的铬尖晶石作了对比。研究表明,地球上,所有铬尖晶石中,以金刚石中铬尖晶石包体的Cr_2O_3组分最高。同时,随着金伯利岩中金刚石含量增加,岩石中粗晶铬尖晶石的Cr_2O_3组分增加,625—645cm~(-1)及500—525cm~(-1)红外吸收谱带向低频率方向移动,IS[Fe~(3+)(B)]穆斯堡尔参数增高,QS[Fe~(3+)(B)]及QS[Fe~(2+)(A)]穆斯堡尔参数降低。     

铬尖晶石的谱学研究及其地质意义

一、引言铬尖晶石是含矿(铬)超基性岩体中的主要矿物,对造矿铬尖晶石和附生铬尖晶石在化学成分、稀土元素分布特征等方面的研究成果二十多年来已经有很多报导,但是由于铬铁矿成矿作用的复杂性和多样性,往往在不同岩体的造矿和附生铬尖晶石的元素成分(如Mg/Fe值等),可以有截然不同的标型特征.所以仅以岩石地球化学和矿物化学成分的差异来作为造矿铬尖晶石的矿物标型特征已不能满足.近年来国内外对铬尖晶石类矿物开始进行矿物波谱学的研究,试图在铬尖晶石内寻找其所携带的铬矿形成过程中的微观信息,用以探索和解释铬铁矿的成矿作用.     

陕北斜坡店塔地区铬尖晶石特征

前人已在鄂尔多斯盆地陕北斜坡圈出了铬尖晶石指示矿物的异常区和远景区,研究表明,区内店塔地区铬尖晶石具幔源特征,铬尖晶石表面具阶梯状小立方体结晶纹理结构,与国外含金刚石岩体中铬尖晶石表面特征具有相似性,表明店塔地区铬尖晶石可能与含金伯利岩岩体有关。     

山东金伯利岩中镁钛铁矿特征及其与非金伯利岩中钛铁矿的区别

该文主要论述山东金伯利岩中镁钛铁矿特征和国内外含矿金伯利岩中钛铁矿特征基本一致。同时与非金伯利岩钛铁矿特征进行对比,可以看出山东金伯利岩中镁钛铁矿、特别是富铬高镁钛铁矿有明显标型特征,是寻找金刚石原生矿的标型矿物。     

铬尖晶石的谱学研究及其地质意义

一、引言铬尖晶石是含矿(铬)超基性岩体中的主要矿物,对造矿铬尖晶石和附生铬尖晶石在化学成分、稀土元素分布特征等方面的研究成果二十多年来已经有很多报导,但是由于铬铁矿成矿作用的复杂性和多样性,往往在不同岩体的造矿和附生铬尖晶石的元素成分(如     

黔东施秉下翁哨地区金刚石指示矿物地球化学特征及其地质意义

对黔东施秉下翁哨地区金刚石指示矿物镁铝榴石、铬尖晶石分别进行了电子探针（EMPA）主量元素和LA- ICP- MS微区原位微量元素测试,结果表明：镁铝榴石主要属于G9型（约占87%）,次为G12型（约占11%）和G3型（约占2%）,源区为二辉橄榄岩和异剥橄榄岩,当其与橄榄石共生,获得平衡温度（tNi）为686~1225℃,压力（PCr）为1.9~4.0 GPa,少数落在形成金刚石的主要温压范围内（压力约4.0~6.5 GPa,温度约950~1300℃）;铬尖晶石主要来源于橄榄岩尖晶石捕虏晶（Xen）（约占90%）,少量为铬铁矿（Chr）（约占10%）,个别落在全球原生金刚石中铬铁矿包裹体的范围内。研究认为,恢复区域加里东期造山运动以来的古地貌,寻找金刚石指示矿物的母岩体/新岩体及开展其矿物间的对比研究工作,特别是对加里东期以来区域的地幔物质组成、岩石圈厚度和热状态等进行深入研究,将对扬子克拉通的演化、深部地幔结构剖析和金刚石成矿事件等具有重要的科学研究意义。     

山东蒙阴县西峪矿区深部与外围金刚石指示矿物——利用金刚石指示矿物预测金伯利岩的含矿性

金伯利岩中的石榴子石、铬铁矿和铬透辉石是寻找金刚石矿的重要指示矿物,根据这些指示矿物的含量可大致推断金刚石原生矿的存在及含矿性。石榴子石中G10组指示金伯利岩中金刚石的存在,其含量越高,岩体中金刚石品位相对较富。由西峪G10组含量小于常马G10组含量,可推断西峪金刚石品位小于常马金刚石品位,事实证明推断正确;S1、S2、S6组铬铁矿是与金刚石共生的铬铁矿,西峪矿区62粒S6组和1粒S7组铬铁矿与深源捕虏体橄榄岩有关,几乎全部来自金伯利岩,具有重要指示意义;Cr_2O_3≥1.2%的铬透辉石含量越多,金刚石品位越高。通过统计分析,地表铬透辉石中Cr_2O_3≥1.2%含量略大于岩管深部,西峪矿区深部矿体平均品位略低于地表矿体平均品位,说明可通过铬透辉石定性地推断金伯利岩的含矿性。结合CSAMT和钻探等地质工作,在西峪岩管群深部-205m以下找到金刚石原生矿,在外围通过槽探工程发现红旗15-1岩脉,并在选矿样中选获18颗金刚石,充分证明了根据金刚石指示矿物找矿方法定性预测金伯利岩含矿性的有效性和可行性。     

再谈黎平敖市金刚石异常——贵州省当前最佳金刚石找矿靶区分析

诸多迹象表明,敖市金刚石异常为一浓集异常,且叠加在一辉石重砂异常之上,显示出强烈的近源补给特征,其补给源极有可能是具工业价值的金刚石原生矿.鉴于湘黔金刚石成矿区内已知的含金刚石钾镁煌斑岩及其相关岩体的同位素年龄值均在375～475 Ma范围,其成矿期显然属加里东晚期,而紧邻敖市异常尚有后加里东盖层残留,作为幔源火山作用...     

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。     

Petrography,chemical composition,and Raman spectra of chrome spinel: Constraints on the diamond potential of the No. 30 pipe kimberlite in Wafangdian,North China Craton

Conventional diamond exploration seldom searches directly for diamonds in rock and soil samples. Instead, it focuses on the search for indicator minerals like chrome spinel, which can be used to evaluate diamond potential. Chrome spinels are preserved as pristine minerals in the early Paleozoic (∼465 Ma), hydrothermally altered, Group I No. 30 pipe kimberlite that intruded the Neoproterozoic Qingbaikou strata in Wafangdian, North China Craton (NCC). The characteristics of the chrome spinels were investigated by petrographic observation (BSE imaging), quantitative chemical analysis (EPMA), and Raman spectral analysis. The results show that the chrome spinels are mostly sub-rounded with extremely few grains being subhedral, and these spinels are macrocrystic, more than 500 µm in size. The chrome spinels also have compositional zones: the cores are classified as magnesiochromite as they have distinctly chromium-rich (Cr₂O₃ up to 66.56 wt%) and titanium-poor (TiO₂ < 1 wt%) compositions; and the rims are classified as magnetite as they have chromium-poor and iron-rich composition. In the cores of chrome spinels, compositional variations are controlled by Al³⁺-Cr³⁺ isomorphism, which results in a strong Raman spectra peak (A_1g mode) varying from 690 cm⁻¹ to 702.9 cm⁻¹. In the rims of chrome spinel, compositional variations result in the A_1g peak varying from 660 cm⁻¹ to 672 cm⁻¹. The morphology and chemical compositions indicate that the chrome spinels are mantle xenocrysts. The cores of the spinel are remnants of primary mantle xenocrysts that have been resorbed, and the rims were formed during kimberlite magmatism. The compositions of the cores are used to evaluate the diamond potential of this kimberlite through comparison with the compositions of chrome spinels from the Changmazhuang and No. 50 pipe kimberlites in the NCC. In MgO, Al₂O₃ and TiO₂ versus Cr₂O₃ plots, the chrome spinels from the Changmazhuang and No. 50 pipe kimberlites are mostly located in the diamond stability field. However, only a small proportion of chrome spinels from No. 30 pipe kimberlite have same behavior, which indicates that the diamond potential of the former two kimberlites is greater than that of the No. 30 pipe kimberlite. This is also supported by compositional zones in the spinel grains: there is with an increase in Fe³⁺ in the rims, which suggests that the chrome spinels experienced highly oxidizing conditions. Oxidizing conditions may have been imparted by fluids/melts that have a great influence on diamond destruction. Here, we suggest that chrome spinel compositions can be a useful tool for identifying the target for diamond potential in the North China Craton.     

山东蒙阴金伯利岩中铬铁矿电子探针波谱分析

铬铁矿是金伯利岩型金刚石矿床中主要的指示性矿物之一.准确分析出铬铁矿化学组分中FeO、MgO、Cr203、Al203、Ti02含量,不但对铬铁矿定名起决定性作用,对金伯利岩型金刚石矿床找矿也具有重要的指示意义.利用电子探针波谱技术对铬铁矿主量化学元素分析,通过所测样品微区化学成分含量推测矿物名称.25件单矿物样品微区化...     

新疆西准噶尔地区冶金型与耐火型铬铁矿床的特征及其成因研究

西准噶尔蛇绿岩中发育两类铬铁矿床(或矿化):一类是冶金型铬铁矿床,它以唐巴勒、萨雷诺海为代表;另一类是耐火型铬铁矿床,它以萨尔托海、鲸鱼、洪古勒楞为代表.冶金型矿床中的造矿与副矿物铬尖晶石以高Cr低Al为特征,耐火型则以高Al低Cr为特征.副矿物铬尖晶石的成分从二辉橄榄岩至纯橄岩均显示出向富Cr贫Al方向演化的趋势,两类造矿铬尖晶石成分位于该系列上的不同范围,显示了两者间的差异.豆荚状铬铁矿床的形成是原始地幔岩高度熔融的残余物,冶金型矿床的熔化程度高于耐火型矿床.豆荚体的聚集和分散则依靠上地幔的塑性剪切作用实现的.     

Chrome spinels and accessory mineralization in the weathering crust of the Vladimir deposit,Varshavsky ultramafic massif,southern Urals

The paper presents the characteristics of chrome spinels from an ore-bearing packet of the Vladimir chromite deposit. Three main types of chrome spinels are distinguished by morphology and chemical composition: medium-chrome ore-forming, high-chrome transformed, and low-chrome relict accessory. The significant role of weathering conditions is expressed in alteration of accessory chrome spinel. The formation of high-chrome spinels is explained by the hydrothermal effect of the Varshavsky granitoid massif with accompanying dikes and talc–carbonate metasomatic rocks. Characteristic accessory minerals are represented by native gold and nickel, millerite, pentlandite, chalcopyrite, maucherite, PGE sulfides, and picroilmenite.     

辽宁瓦房店金伯利岩中尖晶石族矿物种类划分及指示意义

晶体矿物学理论认为不同成岩环境金伯利岩中尖晶石族矿物由于形成物理化学条件不同,其晶体结构和化学成分会发生明显的变化,通过对无矿、贫矿、富矿金伯利岩岩管中的尖晶石族矿物晶胞参数和化学成分的测定,研究尖晶石族矿物化学成分和晶胞参数变化与无矿、贫矿、富矿金伯利岩的内在关系,可以提高金伯利岩型金刚石矿床找矿效率。为了确定辽宁瓦房店金伯利岩中的尖晶石族矿物种属,探讨辽宁瓦房店金伯利岩中尖晶石族矿物化学成分和晶胞参数与金伯利岩含矿性关系,本文运用电子探针波谱仪对50件尖晶石族矿物中的MgO、FeO、TiO2、Al2O3、MnO及Cr2O3进行微区化学成分分析,运用单晶X射线衍射仪对136个尖晶石族矿物晶胞参数进行测定。数据统计显示:瓦房店金伯利岩中尖晶石族矿物为铬铁矿和镁铬铁矿,以化学分子式中A、B组主要阳离子占位特征为基础,可把矿区的尖晶石族矿物划分为10个亚种;如果用尖晶石族矿物化学成分中Cr2O3与(Cr2O3+Al2O3)含量的比值Cr'来表示尖晶石族矿物与金伯利岩含矿性的关系,金伯利岩岩体含矿性由富矿→中等含矿→贫矿,相应岩体中尖晶石族矿物Cr'值分别为89.5%、83.4%~87.1%和70.2%,逐渐变低;从无矿金伯利岩岩体→贫矿和中等含矿金伯利岩岩体→富矿金伯利岩岩体,金伯利岩体中第一世代尖晶石族矿物晶胞参数分别为0.831~0.832 nm、0.834~0.836 nm、0.837 nm,有逐渐变大的趋势。本文认为,辽宁瓦房店金伯利岩中第一世代尖晶石族矿物晶胞参数大小和Cr'参数可以作为判断辽宁瓦房店金伯利岩含矿性的指示标型。     

Electron probe microanalysis and microscopy: Principles and applications in characterization of mineral inclusions in chromite from diamond deposit

Electron probe microanalysis and microscopy is a widely used modern analytical technique primarily for quantifying chemical compositions of solid materials and for mapping or imaging elemental distributions or surface morphology of samples at micrometer or nanometer-scale. This technique uses an electromagnetic lens-focused electron beam, generated from an electron gun, to bombard a sample. When the electron beam interacts with the sample, signals such as secondary electron, backscattered electron and characteristic X-ray are generated from the interaction volume. These signals are then examined by detectors to acquire chemical and imaging information of the sample. A unique part of an electron probe is that it is equipped with multiple WDS spectrometers of X-ray and each spectrometer with multiple diffracting crystals in order to analyze multiple elements simultaneously. An electron probe is capable of analyzing almost all elements (from Be to U) with a spatial resolution at or below micrometer scale and a detection limit down to a few ppm.Mineral inclusions in chromite from the Wafangdian kimberlite, Liaoning Province, China were used to demonstrate the applications of electron probe microanalysis and microscopy technique in characterizing minerals associated with ore deposits, specifically, in this paper, minerals associated with diamond deposit. Chemical analysis and SE and BSE imaging show that mineral inclusions in chromite include anhydrous silicates, hydrous silicates, carbonates, and sulfides, occurring as discrete or single mineral inclusions or composite multiple mineral inclusions. The chromite–olivine pair poses a serious problem in analysis of Cr in olivine using electron probe. Secondary fluorescence of Cr in chromite by Fe in olivine drastically increases the apparent Cr₂O₃ content of an olivine inclusion in a chromite. From the chemical compositions obtained using electron probe, formation temperatures and pressures of chromite and its mineral inclusions calculated using applicable geothermobarometers are from 46 kbar and 980 °C to 53 kbar and 1130 °C, which are within the stability field of diamond, thus Cr-rich chromite is a useful indication mineral for exploration of kimberlite and diamond deposit. A composite inclusion in chromite composed of silicate and carbonate minerals has a bulk composition of 33.2 wt.% SiO₂, 2.5 wt.% Al₂O₃, 22.0 wt.% MgO, 7.5 wt.% CaO, 2.5 wt.% BaO, 0.8 wt.% K₂O, 25.5 wt.% CO₂, and 0.8 wt.% H₂O, similar to the chemical composition of the Wafangdian kimberlite, suggesting that it is trapped kimberlitic magma.     

白杨河超大型铍(铀)矿床中蓝柱石(BeAlSiO4(OH))的矿物特征与地质意义

蓝柱石作为一种较为罕见的含铍矿物,通常产在过铝-准铝性的岩浆-热液演化系统中,或发育于富铝质岩石的低级变质过程中。本文通过偏光显微镜、电子探针、X射线粉晶衍射、激光拉曼光谱和红外光谱等多种手段方法,在白杨河超大型铍(铀)矿床首次发现了除羟硅铍石以外的另一种含铍矿物-蓝柱石。系统的矿物学研究表明蓝柱石应由花岗斑岩岩浆分异的岩浆热液直接沉淀而成,且形成于富F环境中。结合前人关于矿床地质特征、成矿年代学和地球化学等方面的研究,认为白杨河矿床中的铍矿化应是花岗斑岩深部岩浆房分异的岩浆热液,在不断演化过程中形成的,而与后期流体(包括幔源流体和大气降水)的淋滤作用无关或关系很小。     

Petrological characteristics of podiform chromitites and associated peridotites of the Pan African Proterozoic ophiolite complexes of Egypt

Mafic-ultramafic fragments of a dismembered ophiolite complex are abundant in the late Precambrian Pan African belt of the Eastern Desert of Egypt and north-east Sudan. The ultramafic bodies in the Eastern Desert of Egypt are mostly characterised by the harzburgite–dunite–chromitite association. Because of their severe metamorphism, almost all primary silicates were converted to secondary minerals and we use the chrome spinel as a reliable petrogenetic indicator. The podiform chromitite deposits are common as small and irregularly shaped masses in the central and southern parts of the Eastern Desert. They strongly vary in texture, degree of alteration and chemical composition of chrome spinel. The podiform chromitites exhibit a wide range of composition from high Cr to high Al varieties. The Cr of chrome spinel ranges from 0.65 to 0.85 in dunite, quite similar in the high-Cr chromitite, whereas it is around 0.5 in harzburgite. Primary hydrous mineral inclusions, amphibole and phlogopite, in chrome spinel are reported for the first time from the Pan African Proterozoic podiform chromitites. The petrological characteristics of Pan African podiform chromitites and associated peridotites of Egypt are similar to those of Phanerozoic ophiolites. The Proterozoic podiform chromitites may have formed in the same way as the Phanerozoic ones, namely by melt-harzburgite reaction and subsequent melt mixing. The similarity of the mantle section of the late Proterozoic and the Phanerozoic ophiolites suggests that the thermal conditions controlling genesis of the crust–mantle system basically have not changed since the late Proterozoic era. The Pan African harzburgite is very similar to abyssal peridotite at fast-spreading ridges, and the high-Cr, low-Ti character of spinel in chromitite and dunite indicates a genetic link with a supra-subduction zone setting. The late Proterozoic ophiolites of Egypt are possibly a fragment of oceanic lithosphere modified by arc-related magmatic rocks, or a fragment of back-arc basin lithosphere. Received: 26 October 1999 / Accepted: 28 June 2000