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.     

新疆坡北镁铁-超镁铁杂岩体中橄榄石成分特征及其成因意义

橄榄石的矿物化学成分可以很好的反映母岩浆成分、岩浆分异结晶及硫化物熔离作用等信息.坡北镁铁-超镁铁杂岩体中橄榄石电子探针成分分析表明:橄榄石均为贵橄榄石,其化学成分与寄主岩石类型密切相关,其中橄榄辉长岩中橄榄石的Fo值在74～81之间,橄长岩或橄榄单斜辉石岩中橄榄石Fo=75～82.7,异剥橄榄岩或橄榄岩中橄榄石Fo值为83.6～86.3,暗示橄榄岩结晶早于橄榄辉长岩.橄榄石Ni含量变化范围为(174～2281)×10-6.利用最高Fo含量的橄榄石成分计算得到坡北岩体母岩浆MgO=14.38％,为高镁玄武岩浆.橄榄石分离结晶和硫化物熔离模拟显示:坡北岩体主要发生了～25％的橄榄石分离结晶,在橄榄石结晶程度为2％～4％的过程中,发生过硫化物熔离作用,但熔离程度较低(～0.2％).总体来看,该区成矿远景不佳.     

新疆东天山土墩基性-超基性杂岩体橄榄石成分特征及其成因意义

橄榄石通常是玄武质岩浆最早结晶出的矿物之一,其化学成分可以很好地反演母岩浆成分、岩浆结晶分异、硫化物熔离等成岩及成矿信息。本文以土墩镁铁质-超镁铁质杂岩体为研究对象,采用电子探针对岩体中的橄榄石矿物颗粒进行化学成分测试。利用橄榄石的Fo值和其中Ni含量,计算得到土墩杂岩体母岩浆中Mg O含量约为12.95%,是一种富镁的玄武质岩浆。同时,定量模拟结果表明,土墩杂岩体母岩浆中硫化物熔离几乎与橄榄石结晶作用同时进行,早阶段由橄榄石结晶(分离结晶程度约2%)而导致硫化物的熔离程度为0.2%。随后,橄榄石分离结晶程度在6%~7%时,硫化物熔体的熔离程度仅为0.01%。这些表明土墩杂岩体发生过一定程度的硫化物熔离,但成矿前景不是很好。此外,部分数据显示出Ni-Fo的负相关性,表明少许富铁橄榄石和晶间硫化物熔浆发生了Fe-Ni物质交换反应,这对橄榄石的成分有重要影响。     

新疆东天山镁铁-超镁铁岩体中橄榄石成分特征及其成因意义:以黄山东和图拉尔根为例

新疆东天山发育有十多个与铜镍硫化物成矿有关的镁铁-超镁铁杂岩体,对选取于黄山东和图拉尔根岩体岩体内不同岩性中的新鲜橄榄石进行了矿物化学成分测试.黄山东岩体角闪辉长岩相的橄榄角闪辉长岩中橄榄石Fo为67～73,超镁铁岩相的角闪(斜长)橄榄岩、角闪二辉橄榄岩和斜长单辉橄榄岩中橄榄石Fo为81～84,Ni含量为308～1762 μg/g;图拉尔根岩体中橄榄石Fo为82～85,Ni含量变化范围为857～1818μg/g.利用最高Fo含量的橄榄石成分计算得到黄山东岩体母岩浆MgO为10.3％,图拉尔根岩体母岩浆MgO为11.47％.橄榄石分离结晶和硫化物熔离模拟结果显示,黄山东岩体发生了19％的橄榄石分离结晶,由橄榄石分离结晶导致硫化物熔离的程度约为0.3％,晶间硫化物熔浆的物质交换作用对黄山东橄榄石的成分有重要影响;图拉尔根岩体发生了9％左右的橄榄石结晶,由橄榄石结晶导致出熔的硫化物熔体大约为0.5％.     

Olivine in the Udachnaya-East Kimberlite (Yakutia, Russia): Types, Compositions and Origins

Olivine is the principal mineral of kimberlite magmas, and isthe main contributor to the ultramafic composition of kimberliterocks. Olivine is partly or completely altered in common kimberlites,and thus unavailable for studies of the origin and evolutionof kimberlite magmas. The masking effects of alteration, commonin kimberlites worldwide, are overcome in this study of theexceptionally fresh diamondiferous kimberlites of the Udachnaya-Eastpipe from the Daldyn–Alakit province, Yakutia, northernSiberia. These serpentine-free kimberlites contain large amountsof olivine (50 vol.%) in a chloride–carbonate groundmass.Olivine is represented by two populations (olivine-I and groundmassolivine-II) differing in morphology, colour and grain size,and trapped mineral and melt inclusions. The large fragmentalolivine-I is compositionally variable in terms of major (Fo_85–94)and trace element concentrations, including H₂O content (10–136ppm). Multiple sources of olivine-I, such as convecting andlithospheric mantle, are suggested. The groundmass olivine-IIis recognized by smaller grain sizes and perfect crystallographicshapes that indicate crystallization during magma ascent andemplacement. However, a simple crystallization history for olivine-IIis complicated by complex zoning in terms of Fo values and traceelement contents. The cores of olivine-II are compositionallysimilar to olivine-I, which suggests a genetic link betweenthese two types of olivine. Olivine-I and olivine-II have oxygenisotope values (+ 5·6 ± 0·1 VSMOW, 1 SD)that are indistinguishable from one another, but higher thanvalues (+ 5·18 ± 0·28) in ‘typical’mantle olivine. These elevated values probably reflect equilibriumwith the Udachnaya carbonate melt at low temperatures and ¹⁸O-enrichedmantle source. The volumetrically significant rims of olivine-IIhave constant Fo values (89·0 ± 0·2 mol%),but variable trace element compositions. The uniform Fo compositionsof the rims imply an absence of fractionation of the melt'sFe²⁺/Mg, which is possible in the carbonatite melt–olivinesystem. The kimberlite melt is argued to have originated inthe mantle as a chloride–carbonate liquid, devoid of ‘ultramafic’or ‘basaltic’ aluminosilicate components, but becameolivine-laden and olivine-saturated by scavenging olivine crystalsfrom the pathway rocks and dissolving them en route to the surface.During emplacement the kimberlite magma changed progressivelytowards an original alkali-rich chloride–carbonate meltby extensively crystallizing groundmass olivine and gravitationalseparation of solids in the pipe. KEY WORDS: kimberlite; olivine; partial melting; carbonatitic melt; oxygen isotopes; H₂O     

含水对富铁橄榄石流变性的影响

橄榄石是下地壳上地幔最丰富的造岩矿物,橄榄石集合体的高温高压流变性对地幔动力学过程有着很大的影响。以往对橄榄石单晶和集合体进行过的流变性实验研究,涉及了温度、压力、氧逸度、含铁量以及含水等因素的影响,本文研究了含水对富铁橄榄石集合体流变性能的影响,首先,利用高精度 Paterson 气体介质变形装置对含水富铁橄榄石集合体(Mg_(0.9),Fe_(0.1))_2SiO_4、(Mg_(0.7),Fe_(0.3))_2SiO_4和(Mg_(0.5),Fe_(0.5))_2SiO_4进行了高温三轴压缩蠕变试验,变形试验条件为:温度1323～1473K,围压300MPa,差应力10～300MPa,应变率10~(-7)～10~(-4)s~(-1),每个试件的最大变形量为20%。利用三维非线性拟合方法对蠕变试验数据进行分析,结果表明,含水富铁橄榄石集合体的微观变形机制为扩散域和位错域,对三种铁含量,扩散域的应力指数为1。位错蠕变域中,Fo_(50)应力指教为3.8,活化能为444kJ/mol;Fo_(70)应力指数为3.7,活化能为479kJ/mol,Fo_(90)应力指数为3.6,活化能为514kJ/mol。将实验结果与不含水富铁橄榄石集合体的强度进行对比,发现含水使富铁橄榄石的强度明显下降,舍铁量相同时,含水橄榄石集合体的流变强度比干燥时小至少一个数量级。从而得到了含水对含铁量不同的橄榄石集合体粘性(强度)影响的初步试验结果。     

The Occurrence of Forsterite and Highly Oxidizing Conditions in Basaltic Lavas from Stromboli Volcano, Italy

We report the occurrence of unusual, high-magnesium (Fo₉₆) olivinephenocrysts in a basaltic lava and an ejected lithic block fromthe Upper Vancori period (13 ka) and the recent activity (2002–2003)of Stromboli volcano, Italy. The samples that contain this distinctivemineral chemistry are a shoshonitic basalt and a basaltic andesitewith anomalous bulk-rock chemical characteristics in which theiron is highly oxidized (6–8 wt % Fe₂O₃ and <1 wt %FeO). In other respects these samples are similar to the majorityof Stromboli basalts, characterized by the coexistence of olivine,clinopyroxene, plagioclase and Fe–Ti oxides as phenocrysts,and clinopyroxene, plagioclase and Fe–Ti oxides in thegroundmass. In the high-magnesium olivine samples, Fe–Tioxides (pseudobrookite) typically occur as symplectitic intergrowthswith the olivine phenocrysts, indicating simultaneous growthof the two phases. We propose, as a paragenetic model, thatthe Fo₉₆ olivine phenocrysts crystallized from a highly oxidizedbasaltic magma in which most of the iron was in the ferric state;hence, only magnesium was available to form olivine. The highlyoxidized state of the magma reflects sudden degassing of volatilephases associated with instantaneous, irreversible, transientdegassing of the magma chamber; this is postulated to occurduring periods of sudden decompression induced by fracturingof the volcanic edifice associated with paroxysmic activityand edifice collapse. KEY WORDS: Stromboli; Mg-rich olivine; oxygen fugacity; redox state of magmas; irreversible processes     

中国东部新生代玄武岩中橄榄石的矿物化学

作者搜集了中国东部新生代玄武岩及其包体中橄榄石化学成分278个,通过计算、投影,研究了它们的矿物化学特征,并与国内外金伯利岩及其包体中橄榄石化学成分20个进行了对比,分析了它们的地质、找矿意义及固-液平衡问题.     

The Role of Pre-existing Mechanical Anisotropy on Shear Zone Development within Oceanic Mantle Lithosphere: an Example from the Oman Ophiolite

Structural and fabric analysis of the well-exposed Hilti mantlesection, Oman ophiolite, suggests that shear zone development,which may have resulted from oceanic plate fragmentation, wasinfluenced by pre-existing mantle fabric present at the paleo-ridge.Detailed structural mapping in the mantle section revealed agently undulating structure with an east–west flow direction.A NW–SE strike-slip shear zone cuts across this horizontalstructure. The crystal preferred orientation (CPO) of olivinewithin the foliation is dominated by (010) axial patterns ratherthan more commonly observed (010)[100] patterns, suggestingthat the horizontal flow close to the Moho involved non-coaxialflow. Olivine CPO within the shear zone formed at low temperatureis characterized by (001)[100] patterns and a sinistral senseof shear. The olivine CPO becomes weaker with progressive mylonitizationand accompanying grain size reduction, and ultimately developsinto an ultra-mylonite with a random CPO pattern. The olivine[010]-axis is consistently sub-vertical, even where the horizontalfoliation has been rotated to a sub-vertical orientation withinthe shear zone. These observations suggest that the primarymechanical anisotropy (mantle fabric) has been readily transformedinto a secondary structure (shear zone) with minimum modification.This occurred as a result of a change of the olivine slip systemsduring oceanic detachment and related tectonics during cooling.We propose that primary olivine CPO fabrics may play a significantrole in the subsequent structural development of the mantle.Thus, the structural behavior of oceanic mantle lithosphereduring subduction and obduction may be strongly influenced byinitial mechanical anisotropy developed at an oceanic spreadingcenter. KEY WORDS: mantle lithosphere; anisotropy; shear zone; olivine CPO; Oman ophiolite     

湘西通道地区新元古代长界橄榄辉石岩中单斜辉石矿物学特征及其板内裂谷成因论证

湘西通道地区长界橄榄辉石岩主要组成矿物为单斜辉石、橄榄石和斜长石,还具有少量的Ti—Fe氧化物。本文利用电子探针对江南造山带西段湘西通道地区长界橄榄辉石岩单斜辉石进行了详细的矿物学研究,研究结果表明单斜辉石属于顽透辉石和普通辉石。长界橄榄辉石岩单斜辉石较富镁而贫铁,并且还具有高硅、贫碱、低钙的特征,其母岩浆属于拉斑玄武系列。单斜辉石温压计算结果显示,橄榄辉石岩的形成温度为1260～1383℃,压力为1.5～2.6GPa,深度为50～86km,平均深度为73km。整体来看,长界橄榄辉石岩形成的温度基本与软流圈地幔的温度(1280～1350℃)相当,其形成深度为约73km的地幔深处,且在这种温压条件下,软流圈地幔可以发生减压熔融。单斜辉石的成分特征显示示长界橄榄辉石岩是板内拉斑玄武岩,指示其构造背景为裂谷环境。另外,单斜辉石具低的Al_2O_3(0.02%～5.51%)、TiO_2(0～0.46%)和Na_2O(0.01%～1.44%)的特征,这可能是单斜辉石寄主岩石岩浆源区受到俯冲熔体/流体的交代改造作用所导致。结合作者和前人的研究结果,我们推测长界橄榄辉石岩源区为软流圈地幔,其形成可能与裂谷作用导致软流圈物质上涌并发生熔融有关,且在形成长界橄榄辉石岩之前,软流圈地幔已经遭受过俯冲熔体/流体的交代改造作用。