辽宁弓长岭铁矿床磁铁矿稀土元素特征及其地质意义

辽宁弓长岭铁矿床是我国著名的沉积变质型铁矿床,其二矿区的磁铁富矿达大型规模,属国内之最.为探讨弓长岭铁矿床铁矿的物质来源、形成环境和富矿成因,本文以二矿区六个铁矿体的贫铁矿石和富铁矿石中磁铁矿单矿物为研究对象,利用电感耦合等离子体质谱进行了系统的稀土元素测试.结果表明,所有样品中磁铁矿的稀土元素总量(∑REEs)和Y具有非常一致的特征:稀土元素总量较低,Y/Ho比值较高;经太古界后平均澳大利亚页岩( PAAS)标准化呈现重稀土相对富集、轻稀土相对亏损的分馏模式,大部分呈现La正异常,所有样品都有明显的Eu和Y正异常,这些特征表明研究区的磁铁矿成矿物质主要来源于海底高温热液和海水;虽然磁铁矿的Ce/Ce*为0.69～ 0.97,但大多数样品缺乏真正意义的Ce负异常,这暗示其沉积于还原的海水环境;富铁矿石磁铁矿的稀土元素总量和Eu含量明显高于贫铁矿石的磁铁矿,而且含富矿的上含铁带Eu异常明显较高,表明富铁矿石磁铁矿具有更明显的热液特征,是在贫铁矿石的基础上受热液活动形成的.     

辽宁凤城翁泉沟硼铁矿床磁铁矿的成因研究

辽宁凤城翁泉沟硼铁矿床产于卉元古代辽吉裂谷带,赋存于下辽河群的含硼岩系里尔峪组中。其矿石矿物主要为硼镁铁矿、磁铁矿和硼镁石等：脉石矿物主要为蛇纹石、白云石、金云母等。翁泉沟硼铁矿床中的磁铁矿分为3种类型：变质形成的粗粒磁铁矿（I型）、热液蚀变而成的细粒磁铁矿（Ⅱ型）和网脉状磁铁矿（Ⅲ型）,其中,I型显示均质性,Ⅱ、Ⅲ型显示非均质性。均质性磁铁矿的镁、铝元素含量高于非均质性磁铁矿,硅含量低于非均质性磁铁矿,导致前者硬度高于后者。元素含量差异可能是磁铁矿发生非均质化的原因。研究结果表明,翁泉沟矿床的成矿过程包括了沉积变质和后期热液叠加作用。     

磁化率各向异性的原理及应用实例

磁化率各向异性(AMS)在地质领域中的应用极为广泛,可以用来研究古流向造成的磁性矿物的定向排列,以及构造应力作用引起的岩石内磁性矿物的定向重结晶、定向排列及韧性变形。本文介绍了AMS的基本原理和参数,并并介绍了前人及作者应用AMS详细分析研究了二个实例:(1)以假多畴(MD)高钛磁铁矿为主要载磁矿物的玄武岩样品的AMS变化及其对构造运动的响应;(2)以MD磁铁矿为主要载磁矿物的湖泊沉积物样品在沉积过程中AMS变化。AMS可以灵敏地检测样品中磁性矿物的定向排列,因此在在地质领域中具有很好的应用前景。     

磁铁矿系列花岗岩含金差异性及其评价准则—以豫西地区为例

本文以豫西地区小秦岭、外方山为例，将磁铁矿系列花岗岩进一步划分为两大类：一类与金矿具密切的空间关系，本文命名为M1型花岗岩，以文峪岩体、合峪岩体为代表；另一类成金能力较差的岩体，本文命名为MS型花岗岩，以华山岩体、太山庙岩体为例。两类岩体在化学成分、矿物含量、同位素组成等方面均有一定差异。M1和MS型花岗岩的源岩是一致的，均为陆内腐冲碰撞地壳板块冲下插作用所产生的物质，其成分及含矿性差异与源岩部分熔融程度、岩浆演化及其分熔序列有关。M1型花岗岩是在下地壳源岩分离熔融晚阶段、源岩部分熔融程度较高、环境较氧化的条件下形成的。     

Influence of the olivine additive fineness on the oxidation of magnetite pellets

Olivine is used as an additive in Luossavaara–Kiirunavaara AB (LKAB) blast furnace pellets. The LKAB iron ore is magnetite which oxidizes to hematite during the sintering process. Olivine retards the oxidation of magnetite pellets if the threshold temperature of magnesioferrite formation is exceeded.In this study, we have developed a thermogravimetric measuring method to study the relationship between the olivine reactivity in green pellets and the olivine fineness. A less reactive olivine makes the pelletizing process more tolerant of excessively high temperatures in the green pellets during oxidation.The reactivity of olivine decreases when the amount of fine tail in olivine is decreased. The top size is limited by balling. Grinding tests in pilot scale show that if the olivine additive is ground in closed circuit with a ball mill keeping good control over the top size, the olivine fineness can be appreciably decreased without disturbing balling. The olivine reactivity can be decreased by 40% compared to the reference olivine in the production plant. Also, savings can be made on both the grinding energy and grinding media consumption. The results in both pilot scale and full production scale show that better oxidation in the grate due to a coarser olivine additive improves the low temperature reduction strength (LTD, ISO 13930) in pellets.The measuring method developed for the olivine reactivity enabled evaluation of different particle-sizing methods for olivine characterisation. The screening size fraction %−45 μm showed a good correlation to olivine reactivity in green pellets within a very large measuring range. The correlation of laser diffraction analysis to the olivine reactivity showed, however, that the laser diffraction measuring method is affected too much by variations in the large particles.     

鄂东南程潮铁矿多世代叠加成矿作用:磁铁矿证据

湖北程潮铁矿是长江中下游成矿带最大的矽卡岩型铁矿床,主要产于早白垩世中酸性侵入岩与三叠系地层的接触带上。为了进一步探讨其富铁矿的形成机制,本文对该矿床中不同产状的磁铁矿和不同岩性侵入岩中的副矿物磁铁矿进行了详细的野外地质观察和显微结构分析,发现在多数磁铁矿矿石和矿化矽卡岩中均存在多世代磁铁矿矿化叠加现象。根据显微观察和BSE图像特征,程潮铁矿中热液期磁铁矿可以划分为四个世代,即Mt1、Mt2、Mt3、Mt4,其中Mt1颗粒表面不均匀,溶解-再沉淀现象明显;Mt2沿Mt1边缘生长,颗粒表面均匀,环带发育;Mt3沿Mt2边缘生长,颗粒表面均匀,环带不发育;Mt4多呈板条状或他形粒状,环带不发育。电子探针分析结果表明:同一世代不同产状或同一产状不同世代磁铁矿之间具有明显的成分差异,其中以Si、Al、Ca、Mg等含量较高的元素差异最为明显,而Ti、Cr、V、Zn、Ni等含量较低的元素差异则相对较小。这些差异性可能与磁铁矿结晶时成矿流体氧逸度、温度、元素浓度和水岩反应比例密切相关。不同世代热液磁铁矿与矿区岩体副矿物磁铁矿对比发现,二者在矿物结构和微量元素组成上存在明显差异,特别以微量元素Ti含量差异最大。程潮铁矿与不同成因类型矿床中的磁铁矿成分对比分析结果,进一步暗示出程潮铁矿中的磁铁矿为接触交代成因,并非矿浆成因。半定量模拟计算结果表明,Mt1、Mt2、Mt3在整个成矿过程中贡献了至少96%的铁质,对成矿起到了决定性作用。多世代磁铁矿矿化叠加过程不仅为揭示程潮大型铁矿的富集过程提供了重要依据,同时也为进一步理解矽卡岩型富铁矿的成矿机制提供了重要启示。     

The detection of single-domain greigite (Fe3S4) using rotational remanent magnetization (RRM) and the effective gyro field (Bg): mineral magnetic and palaeomagnetic applications

The intensity of rotational remanent magnetization (RRM) acquired by single-domain greigite at a rotation frequency of 5 rps was combined with measurements of anhysteretic remanent magnetization (ARM) to calculate the effective biasing field ( Bg ) that produced the RRM. Samples of single-domain greigite had Bg values between -137 and -84 μT, and a MDF_RRM of c. 80 mT. By contrast, a suite of natural and synthetic ferrimagnetic iron oxide samples, including single-domain magnetite and y Fe₃O₄ tape particles, acquired Bg values between -3 and -14 μT, and MDF_RRM ranged between 43 and 68 mT (when RRM was acquired). Multidomain magnetite did not acquire a RRM. Bg values at 5 rps were calculated from previously published data for magnetite particles of different grain sizes, which revealed a minimum Bg value of -24 μT and a MDF_RRM of 57 mT for the finest fraction (0.2-0.8 μm in diameter). In a geological example, measurements of Bg and MDF_RRM were used to detect the presence of greigite in a 4 m long Late Weichselian sediment core. Variations in inclination, declination and the intensity of the natural remanent magnetization (NRM) correlate with changes in magnetic mineralogy.     

磁铁矿铁同位素标准物质的研制

中国地质科学院地质研究所研制了磁铁矿铁同位素标准物质,将其命名为CAGS-MAG.研制过程中使用单因素方差分析法对CAGS-MAG进行均匀性检验,使用趋势检验对其在30个月中5次分析数据进行长期稳定性检验,结果显示均匀性和稳定性良好,满足标准物质的要求.CAGS-MAG的特征值采用多家实验室协作定值的方法确定.协作定值...     

塔什库尔干陆块磁铁矿多源信息特征及成矿预测

新疆塔什库尔干陆块近年来陆续发现了乔普卡里莫、老并、吉尔铁克沟等一系列大型一超大型磁铁矿床,在一直未有找矿突破的达布达尔以南至岔河口地段,又新发现了乌如克铁矿及新的磁铁矿点。该类矿床主要赋存于布伦阔勒岩群黑云石英片岩岩性段内,为一种特殊的膏铁建造,具有明显的区域高磁和化探异常。矿床成因类型为海相火山沉积型,后期受区域变质作用叠加改造。该成果对丰富世界沉积铁矿床的类型和指导同类型铁矿床的找矿工作都具有重要的参考意义。     

Ilmenite, Magnetite and Chromite Beach Placers from South Maharashtra, Central West Coast of India

The heavy mineral placer deposits of the coastal sediments in south Maharashtra stretch for 12.5 km from Pirwadi in the north to Talashil in the south. The area is a sand bar represented by a narrow submergent coastal plain lying between the Achara and Gad Rivers. The sediments in the area are mainly sands which are moderately well sorted to well sorted. The heavy mineral concentration in the surficial sediments ranges between 0.69 and 98.32 wt % (28.73 wt % in average). The heavy mineral concentration shows an increasing trend from north to south. The heavy mineral suite consists predominantly of opaque minerals (ilmenite, magnetite and chromite), garnet, pyroxene, amphibole, zircon, tourmaline, rutile, staurolite, etc. Ilmenite grains are fresh whereas magnetite grains show the effect of weathering and alteration. The chromite grains are rounded to sub-rounded with alteration at the margin of the grains. The surficial textures of the opaque minerals show mechanical breaking that indicates limited distance of transportation. Ilmenite has TiO₂ in the range between 40.04 and 46.6 wt %. Based on ore microscopy studies, the magnetite grains appear to be of two types: pure magnetite and titano-magnetite. Compositionally, the total magnetite fractions have Fe₂O₃ between 32 and 46 wt %, FeO between 19.0 and 25 wt % and TiO₂ between 14.3 and 23.9 wt %. The chromite grains are an admixture of two varieties, ferro-chromite and magnesio-chromite. The chromite grains have 32.06–47.5 wt % of Cr₂O₃ with total iron between 23.86 wt % (4.73% Fe₂O₃ and 19.13% FeO) and 27.89 wt % (4.36% Fe₂O₃ and 23.53% FeO) and MgO between 12 and 40 wt %. The observed variations in the distribution of heavy minerals in the area are due to differences in the sediment supply, their specific gravity and oceanographic processes all of which result in a selective sorting of the sediments. The observed mineral assemblages of transparent heavy minerals (pyroxene, amphibole, tourmaline, kyanite, garnet, zircon and olivine) are suggestive of their derivation from a heterogeneous provenance comprising of igneous rocks, high grade metamorphic rocks and reworked Kaladgi sediments. The chromite grains appear to have been derived from ultrabasic rocks present in the upper reaches of the Gad River. The inferred reserves of ilmenite, magnetite and chromite are 0.175, 0.395 and 0.032 million tons, respectively.