长江中下游富钠闪长岩类与铁矿系列的成因联系

长江中下游成矿带内,铁矿系列与中生代燕山期岩浆活动有十分密切的关系,其形成主要与富钠闪长岩类成岩过程中发育的钠硅质异常演变相联系。富钠闪长岩类和与其密切相伴的矿浆贯入-残浆气液交代充填-接触交代(矽卡岩)-热液交代充填型铁矿系列,是深部同源岩浆顺序演化的产物。     

铁锰结核的矿物相变和其它次生变化

本文通过对太平洋中部61个铁锰结核的研究,发现在结核形成后,发生了渐近相变、退化相变和Mn、Ni、Cu的次生富集作用。渐近相变是,随着结核成岩作用的增强(伴随着氧化还原电位由高到低的变化),锰矿物发生了由原生δ-MnO_2→环带状、薄层状钠水锰矿和钡镁锰矿→块状磷片状钡镁锰矿集合体的相变。在这一相变系统中钠水锰矿是相变的过渡阶段,钡镁锰矿是相变的高级阶段。退化相变:具层纹构造的原生δ-MnO_2在底层水(可能贫Mn、Ni、Cu而富Fe)的作用下,其中一部分Mn、Ni、Cu等被水带走而沉淀下Fe,形成新的富Fe、δ-MnO_2或非晶质水合铁锰氧化物。Mn、Ni、Cu的次生富集作用。结核在重结晶作用或由结核成岩作用到成岩后生作用过程中均发生了Mn、Ni、Cu的次生富集作用。它不仅表现在由原生δ-MnO_2→环带状钠水锰矿和钡镁锰矿→块状钡镁锰矿过程中,而且还表现在由早期到后期形成的δ-MnO_2成分上。     

桐柏-大别山南缘志留纪黄羊山碱性杂岩的暗色矿物

黄羊山碱性杂岩体位于桐柏-大别山南缘,其SHRIMP U-Pb年龄为(439±6) Ma.该杂岩体由石英正长岩和碱性花岗岩组成,其中以石英正长岩为主体,从中心到边缘粒度变化由粗到细.利用电子探针对该杂岩体中的特征暗色矿物的分析结果表明,角闪石和辉石的成分变化较小,角闪石显示出从铁钠透闪石到钠铁闪石的成分演化趋势,辉石主要为霓石,另外岩体中大量出现三斜闪石.根据矿物间的相互接触关系、环带结构、矿物组合的相平衡关系等识别了原生的岩浆矿物组合和次生的岩浆期-岩浆期后矿物组合,建立了矿物结晶顺序,重建了过碱性岩浆或流体的成分、温度、氧逸度的演化历史.从矿物组合的相平衡关系角度表明,黄羊山碱性杂岩体为大陆裂谷环境的产物.     

http://www.sciencedirect.com/science/article/pii/S1674987114000425

Na-metasomatism in the form of albitisation is regionally extensive in the Precambrian crust of southern Scandinavia and is particularly widespread in the Bamble Sector, the Kongsberg-Modum Sector and the Norwegian part of the Mylonite Zone. Sites of albitisation outside these belts are associated with hy- drothermal breccia pipes and fracture-bound alteration. The albitites are composed of near end-member sodic plagioclase （Ano 5Ab94-99） with minor carbonate （calcite and dolomite）, rutile, clinopyroxene （En30Fs21-23W047 49）, amphibole （edenite-pargasite）, quartz, titanite, tourmaline, epidote （Fe3＋ - 0.20 -0.85 a.p.f.u） and chlorite （Mg# = 0.81-0.89）. The albitites have been studied in detail in the region around the town of Kragem, and are described as albitisation along veins, as breccias, alhitic felsites, massive carbonate-bearing albitites and megascale clinopyroxene-titanite-bearing albitite. The strong fluid control on their formation is illustrated by the veining and mineral replacement reactions, showing fluid transport by a H20-CO2 fluid rich in Na, depleting Fe and Mg from the host rock, in accordance with calculated mass transfer. A study of the mineralogical replacement reactions in combination with a regional compilation has demonstrated the relationship between metasomatic processes and the for- mation of apatite, ruti｜e and Fe deposits. The albitites occur spatially associated with other metasomatic rocks such as scapolitised metagabbros. We document that metasomatism is an important mineral- and rock-forming process in the continental crust, which in the Bamble Sector is a part of the tectonome- tamorphic evolution of the Sveconorwegian orogen.     

福建省永安市佛仔岬钠长石矿床地质特征及成因探讨

通过对福建省永安市佛仔岬钠长石矿床的野外勘查，查明钠长石矿体呈脉状和透镜状成群分布于鸡公岩复式岩体中，且多发育带状构造；矿石自然类型可分为钠长石矿石、石英钠长石矿石、石英钾钠长石矿石三种类型。显微镜下发现钠长石中保留环带结构假象、残留辉绿结构以及残留辉石矿物等现象，显示矿区经历广泛而强烈的钠交代作用。研究表明钠交代作用是矿床形成的主要成矿作用，矿床成因类型为酸性岩浆环境中的岩浆-热液矿床。