翡翠的矿物组成特征及其质量

通过翡翠的矿物组成研究 ,其主要由辉石族的矿物 (硬玉、绿辉石、霓石、钠铬辉石 )组成 ,还有少量的闪石族矿物、长石族矿物以及绿泥石和铬铁矿、褐铁矿、赤铁矿等组成 ,他们的含量变化直接影响着翡翠的种类。在矿物组成中 ,硬玉呈不同的绿色 ,这些颜色的多少与分布特征直接影响着翡翠的颜色特征和档次。绿辉石、钠铬辉石含量少 ,在翡翠中呈黑绿色 ,它们的存在使翡翠的档次降低。闪石族矿物主要是蓝色的钠铝质闪石 ,翡翠中的飘“蓝花”就是由于它们造成的。长石族矿物主要是钠长石 ,颗粒细小 ,在翡翠中其含量 1.0 %～ 8.0 %。翡翠中主要的矿物形态以粒状为主 ,矿物的颗粒越细 ,翡翠的透明度、质地也越好。建议将翡翠定义为 :“在地质作用过程中主要由钠质或钠钙质辉石组成的达到玉级的集合体。”     

碱性长石微结构特征与岩体冷却速率的关系

前人的研究(主要为实验研究)表明:岩体冷却速率越慢,隐纹长石出溶叶片周期越大。但笔者在研究中发现:如把不同地区的不同岩石按冷却速率的变化梯度排列起来,其隐纹长石出溶叶片周期变化为:熔结凝灰岩中300nm±,熔岩流中150nm±,较窄岩脉中100nm±,较宽岩脉中50nm±,火山颈相次火山岩中12nm±。可见随着冷却速率的变慢,碱性长石出溶叶片周期反而变小,这明显与前人的实验结果相矛盾。该结果可能由两个因素造成:一是以往的实验结果只是对由拐点分解形成的出溶叶片周期的研究,不适用于解释由非均匀成核及均匀成核形     

百花脑花岗岩风化壳:潜在超大型的铷、铯、钇、钪、石英和钠长石矿床

研究表明，新生代滇西百花脑碱长花岗岩风化壳是一个罕见的超大型Rb,Cs,Y,Sc，石英和钠长石综合矿床，T,aNb,Sn,W等可附带回收，岩浆作用是矿床成岩与成矿的主导因素，矿床的矿石储量极其巨大，有用组分众多，易采，易选，易炼，经济潜值惊人，除Rb外，其他矿化元素品位稍偏低。在西部大开发中，反思矿床的经济－技术条件，探索采、选、冶新途径，具有重要意义。     

松辽盆地北部中——深层砂岩的次生孔隙研究

松辽盆地北部中——深层砂岩的次生孔隙主要是由不稳定的骨架颗粒组分溶解而成,按结构系列,次生孔隙可划分为八种类型。斜长石的溶解是造成次生孔隙的主要原因,它可以在埋藏浅处开始溶解,在1000-1500m 深处溶解变得集中和剧烈。钾长石的溶解一般发生在埋藏较深处。钾长石溶解和浊沸石溶解大大丰富了深层砂岩的孔、渗条件。次生孔隙的形成不仅取决于酸性介质环境,而偏碱性的孔隙溶液对长石的溶解亦具有重要意义。     

天然碱性长石的高分辨电镜观察

利用高分辨电子显微镜观察了产于河北汉诺坝玄武岩中碱性长石的精细结构。不同取向的高分辨像清楚地显示了钾、钠长石形成的片层状多重紧密连生体以及各种调制结构。钾、钠长石的连生界面一般为(601)晶面。其超微结构特征与在中等冷却速率下钾钠长石中按旋节分解机制产生的熔离结构相符。以(010)面为孪晶界面的多重连生微孪晶构成了平均周期约为8*d_(010)的调制结构。     

新疆西天山莫托萨拉热水沉积型铁锰矿床矿物学与地球化学特征

莫托萨拉铁锰矿床位于西天山阿吾拉勒成矿带东端,研究程度相对薄弱,在矿床成因方面存在热水沉积、沉积-热液改造、胶体化学沉积等争论。本文详细研究了莫托萨拉最上层锰矿及其围岩的矿物组成、结构构造和地球化学特征,并综合前人资料对整个铁锰矿床的成因做了进一步探讨。本研究首次在矿区发现了热液长石岩,其主要由钠长石、钾长石以及少量重晶石、霓石、锌铁黄长石等矿物组成,类似于"白烟型"热水沉积岩。莫托萨拉最上层锰矿主要由锰橄榄石、褐锰矿、红硅锰矿、磁锰铁矿以及少量重晶石、方铁锰矿等矿物组成,发育有典型的热水内碎屑结构,指示其沉积于海底热液喷流口附近。该层锰矿的Al/(Al+Fe+Mn)值很低(0～0.02)、Si/Al值较高(7.9～10.9)、Fe/Ti值很高(428～1353),通过UCC标准化后发现明显富集Zn、Ba、Pb等元素,而Co、Ni、Cu等元素未见富集,以上地球化学特征与现代海底热液成因铁锰沉积物一致。在Fe/Ti-Al/(Al+Fe+Mn)、Si O2-Al2O3、10×(Co+Ni+Cu)-Fe-Mn、100×(Zr+Ce+Y)-15×(Cu+Ni)-(Fe+Mn)/4等判别图中,莫托萨拉的锰矿层和铁矿层样品均落在海底热液沉积区。锰矿层和铁矿层的稀土元素经PAAS标准化后具有明显的Ce负异常、Eu正异常和Y正异常,与现代海底热液成因铁锰沉积物的稀土配分模式非常相似。综合分析本次研究的矿物学、岩石学、地球化学特征以及前人资料,本文认为莫托萨拉铁锰矿床为海相热水沉积成因,成矿与同期海底火山的间歇性活动密切相关,海底热液的化学组分、温度高低和活动强弱都具有明显的脉动性。莫托萨拉矿区铁锰共存但各自独立成矿,且铁锰分离程度较高,这在显生宙沉积型锰矿中独具特色。鉴于前人曾报道莫托萨拉铁矿石中存在菌藻类微生物化石,我们推测,该矿床的铁锰分离过程除了受控于沉积环境的氧化还原条件变化外,微生物的选择性氧化沉淀可能也发挥了重要作用,值得开展深入研究。     

新疆阿图什彻依布拉克锡多金属矿点地质特征

南天山是重要的锡锑多金属成矿带，目前已发现几处锡矿床(点)和大量锡化探异常，具有良好的成矿前景．彻依布拉克锡多金属矿点赋存于塔木岩体围岩的夕卡岩中．塔木碱长花岗岩侵入时代为晚二叠世，化学成分具有富Si、富碱，贫Mg、Al的特点，Ga／Al比值大，富轻稀土，具强Eu负异常，具有A型花岗岩的特点．矿体严格受夕卡岩带控制，呈似层状、透镜状，与夕卡岩产状一致，二呈渐变过渡关系，矿体变化较大．矿石类型有：锡铁矿石、金(铜)矿石、锡矿石和锌铜矿石．成矿具有多阶段性，划分为夕卡岩阶段硼酸盐阶段、硫化物阶段和表生阶段，其中硼酸盐阶段是锡成矿的主要阶段．岩浆活动为成矿提供了热源和主要物质来源．     

熔融制样X射线荧光光谱法测定钠长石钾长石中多元素

采用熔融制样X射线荧光光谱法测定钠长石和钾长石中的Na2O、MgO、Al2O3、SiO2、P2O5、K2O、CaO、TiO2、Fe203、Rb、Sr、Y、Zr、Ba14个成分的含量，所得结果与化学分析结果相符，各组分测定33次的仪器RSD为0．10％～4．67％。在试验过程中，对功率为1kW和4kW的两种波长色散型X射线荧光光谱仪的灵敏度和检出限进行了比较，并对仪器的精密度和长期稳定性进行了考察。     

Crustal uplift in the southern Superior Province, Canada, revealed by paleomagnetism

A change in the polarity of magnetization with depth in the 2.45 Ga Matachewan dyke swarm is used to document vertical crustal movements that occurred at 1.9–2.3 Ga along the Kapuskasing Structural Zone, a 500-km-long fault zone that transects the Archean Superior Province of Canada. At shallow crustal levels dykes have a primary magnetization dominantly of one polarity, but at greater depths (20 km down) a polarity change occurs associated with the growth of exsolved magnetite in feldspar due to slow crustal cooling after cessation of Matachewan igneous activity. Regions of the dyke swarm with one dominant polarity are separated from those with opposite polarity by major faults. Using this polarity distribution and associated variations in the intensity of feldspar clouding and hydrous alteration, maps of the southern Superior Province are produced that display regional crustal tilting on which are superimposed more local fault-bounded blocks associated with the Kapuskasing zone. Some of these blocks have been recognized for the first time as a result of this study.The paleomagnetic work has also shown that the Matachewan swarm is regionally distorted both within and north of the Kapuskasing zone, and originally had a more radial disposition. This widespread distortion suggests that the lower crust was still relatively ductile at the time of deformation, perhaps due to high heat flow associated with the waning stages of the Matachewan mantle plume beneath.     

Thermodynamic modeling of post-entrapment crystallization in igneous phases

Inclusions of quenched silicate liquid in igneous phenocryst phases represent important windows into the pre-eruption chemistry of volcanic rocks. Melt inclusions are subject to a variety of potential modifications after entrapment, which obscure the connection between final inclusion composition, and entrapment conditions. We concentrate on the effects of post-entrapment crystallization (PEC) in the cooling inclusion. PEC is neither an isobaric nor an isochoric process. Pressure decreases between 2 and 27 bars per degree of cooling, depending on the chemistry of melt and host and on the degree of PEC. In the equilibrium case, between about 50% and 65% of this pressure effect is due to thermal expansivity of the liquid, 10–35% from thermal expansivity of the host, and 5–40% from mass transfer between the inclusion and host. This complicates the application of simple element-partitioning schemes for back-calculating the effects of post-entrapment crystallization except in the simplest cases. We present a thermodynamic algorithm for PEC correction. This method is based on the self-consistent thermodynamic model set used in the MELTS software package. The algorithm moves backward through the PEC process, incrementally adding equilibrium crystal composition to the liquid while accounting for consequent variations in pressure and oxygen fugacity. Entrapment conditions are assumed to have been reached when the instantaneous liquidus solid composition most closely matches that of the bulk host crystal. Besides giving information on the degree of PEC and initial inclusion composition, the proposed algorithm can provide constraints on the pressure, temperature and oxygen fugacity at the time of entrapment. Olivine- and orthopyroxene-hosted inclusions from Popocatépetl, Mexico help constrain pre-eruption conditions for mixed magmas from recent eruptive products. Feldspar-hosted inclusions from Satsuma-Iwojima, Japan suggest that these magmas were substantially undersaturated with respect to supercritical vapor phase at the time of entrapment and underwent on the order of 29% post-entrapment crystallization. Quartz-hosted inclusions can potentially be employed in more silicic compositions, but this will require refinement of existing thermodynamic models.