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首页> 外文期刊>Ore Geology Reviews: Journal for Comprehensive Studies of Ore Genesis and Ore Exploration >Differentiated rare-element mineralization in an ongonite-topazite composite dike at the Xianghualing tin district, Southern China: An electron-microprobe study on the evolution from niobium-tantalum-oxides to cassiterite
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Differentiated rare-element mineralization in an ongonite-topazite composite dike at the Xianghualing tin district, Southern China: An electron-microprobe study on the evolution from niobium-tantalum-oxides to cassiterite

机译：中国南方香花岭锡区的一个Ononite-topazite复合堤坝中的稀有元素矿化：电子-探针研究从铌-钽-氧化物向锡石的演化

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摘要

Our study characterizes in detail the mineralogical, textural and compositional features of a highly evolved, composite ongonite-topazite dike and its magmatic differentiation history. We present compositional data collected by established techniques, i.e. by electron microprobe and wet-chemical analysis, which provide a detailed framework for future studies that employ state-of-the-art analytical techniques. The studied dike (referred to as the No. 431 dike) crops out within the Xianghualing area in the Nanling Range of southern China, in close spatial association with Jurassic Sn-Nb-Ta granite plutons. The rock samples in the No. 431 dike were collected from a structurally lower drill hole and a trench at higher level. The ongonite is encountered throughout the dike, but the topazite is only revealed along the margin of the upper, near-surface dike. The results of whole-rock major and trace element analyses show that the rocks of the No. 431 dike are strongly peraluminous with an average ACNK value of similar to 1.5 for ongonite and >3.9 for topazite. They are enriched in F, 1.7 wt.% and 5.4 wt.% on average for ongonite and topazite, respectively. The rocks have low Zr/Hf and Nb/Ta ratios, and high levels of oreforming elements including Nb, Ta, Sn, and W. Silicate and oxide mineral assemblages, textures, and compositions are also distinct for the two rock types studied. In the lower ongonite of the dike, there are abundant phenocrysts of K-feldspar, quartz, and albite, and microphenocrysts of topaz and zinnwaldite in a matrix dominated by quartz, K-feldspar, and albite. Characteristic oxides are columbite-tantalite, tapiolite, and microlite, but cassiterite is absent. The upper ongonite of the dike has a silicate assemblage similar to the lower ongonite; columbite-(Mn), uranomicrolite, and limited amounts of cassiterite are the dominant accessory minerals. The topazite is characterized by large amounts of topaz and zinnwaldite intergrown with quartz, while K-feldspar, albite, and quartz phenocrysts have rounded shapes and are relatively rare. Cassiterite is the most abundant ore mineral, while Nb-Ta oxide minerals are less abundant. We interpret the whole-rock compositional trends, mineral textures, assemblages, and compositions to reflect the differentiation of an evolved, initially homogeneous magma that separated into aluminosilicate and hydrosaline melts, corresponding to crystallization of ongonite and topazite, respectively. The crystallization of Nb-Ta- and Sn-bearing ore minerals was strongly controlled by the separation of the two melt phases. We hypothesize that dike propagation/widening subsequent to the initial dike emplacement may have driven the separation of the aluminosilicate and hydrosaline melt phases that crystallized to ongonite in the core and topazite along the margins of the structurally higher part of the dike. (C) 2014 Published by Elsevier B.V.
机译：我们的研究详细描述了高度演化的复合型Ononite-Topazite堤的矿物学，质地和组成特征及其岩浆分化历史。我们将介绍通过既定技术收集的成分数据，即通过电子微探针和湿化学分析收集的成分数据，这些数据为采用最新分析技术的未来研究提供了详细的框架。所研究的堤防（称为431号堤防）与中国侏罗纪的Sn-Nb-Ta花岗岩岩体在空间上密切相关，在中国南部地区的香花岭地区种植。 431号堤防中的岩石样品是从结构较低的钻孔和较高高度的沟槽中收集的。在整个堤防中都遇到了gon石，但仅在上表面近堤防的边缘露出了黄玉。整块岩石的主要元素和痕量元素分析的结果表明，431号堤防的岩石具有强烈的高铝质特征，其平均ACNK值对于石墨和石灰石均接近1.5，而对于黄玉则大于3.9。对于on石和黄玉，它们分别平均富含F，1.7 wt。％和5.4 wt。％。这些岩石具有较低的Zr / Hf和Nb / Ta比，以及高含量的成矿元素，包括Nb，Ta，Sn和W。硅酸盐和氧化物矿物的组成，质地和成分在两种研究类型中也很不同。在堤坝下部的灰石中，在以石英，钾长石和钠长石为主的基质中，有丰富的钾长石，石英和钠长石晶状体，以及黄玉和锌长辉石的微晶型。特征性的氧化物是哥伦比-钽铁矿，黄铁矿和微晶石，但没有锡石。堤坝的上层云母具有与下层云母相似的硅酸盐组合物。钴矿（Mn），铀微晶石和少量锡石是主要的辅助矿物。该黄水晶的特征是大量的黄水晶和紫水晶和石英共生，而钾长石，钠长石和石英隐晶具有圆形形状，并且相对罕见。锡石是最丰富的矿石矿物，而Nb-Ta氧化物矿物则较少。我们解释了整个岩石的组成趋势，矿物质地，组合和组成，以反映演化的，最初是均质的岩浆的差异，该岩浆分为铝硅酸盐和碱盐水熔体，分别对应于on石和黄玉的结晶。含Nb-Ta-和Sn的矿石矿物的结晶受到两个熔体相分离的强烈控制。我们假设，在堤防初始位置之后堤防的传播/扩展可能已经驱动了硅铝酸盐和氢盐水熔体相的分离，这些相沿堤的结构较高部分的边缘结晶成核中的on石和黄玉。 （C）2014由Elsevier B.V.发布

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