秦志军,周豹,苌笙任,苏建辉,邵辉

• 1:湖北省地质调查院
• 2:湖北省地质勘查工程技术研究中心
• 3:中国地质大学(武汉)资源学院
• 4:中国地质大学(武汉)地球科学学院

摘要(Abstract)：

位于南秦岭武当地区的杀熊洞铌-稀土矿床是我国典型的碳酸岩-碱性岩型铌-稀土矿床，虽已有不少研究，但对于该矿床中铌的富集、结晶及后期流体改造矿物学方面的研究仍较为薄弱，制约了铌富集机理的精细刻画。采用偏光显微镜、光学阴极发光和背散射电子进行了详细的岩相学观察，查明了矿物的结构、组分和共生关系，并用电子探针分析了2类烧绿石的成分，探讨了铌富集机理。研究表明：杀熊洞碳酸岩-碱性岩杂岩体发育有一套完整的蚀变辉石岩-正长岩-碳酸岩岩性组合，三者在空间上紧密共生。杀熊洞杂岩体中铌矿物主要为烧绿石，主要在岩浆演化最晚期的碳酸岩相中结晶，为碱性岩浆演化晚期富集的产物。烧绿石包括原生(Pcl1)和蚀变(Pcl2)两种类型，前者呈自形、粒度大、发育震荡环带，被认为是直接从碳酸岩熔体中结晶的岩浆烧绿石；而后者则为原生烧绿石被热液交代后形成，其形状不规则，在背散射电子(BSE)图像中表现为不均匀的亮白色。利用电子探针对两类烧绿石进行了原位成分分析，两类烧绿石的B、Y位置分别以Nb、F元素为主导，而A位置以Ca为主导，Na次之，因此将大部分烧绿石定名为氟钙烧绿石，少数定名为氟钠烧绿石。两类烧绿石的Nb与F均存在较好的线性正相关关系，说明氟作为挥发分，可能对Nb在碱性岩浆-热液体系中的富集起到了关键的作用，与前人实验模拟结果一致。另一方面，两者也存在一定成分差别，与原生烧绿石相比，蚀变烧绿石具有明显较低的Nb_2O_5、CaO、Na_2O、F等以及较高的UO_2、Ta_2O_5、SrO、SiO_2等含量，这些差异说明交代烧绿石的流体具有更富Sr、Si和U但贫Na和Ca的特征。此外，在交代过程中，局部存在明显的铌活化与丢失。

关键词(KeyWords)： 烧绿石;铌-稀土矿化;碳酸岩;杀熊洞

Abstract:

Keywords:

基金项目(Foundation): 中国地质调查局项目“湖北三稀资源现状和潜力分析”(1212011220811);; 湖北省地质局科技项目“南秦岭地区古生代Nb-Ta-REE成矿岩浆的关键性质与过程”(KJ2020-54);; 湖北省地质局项目“汉江生态经济带(湖北段)西北端战略性矿产资源综合评价”(KCDZ2022-17)

作者(Author): 秦志军,周豹,苌笙任,苏建辉,邵辉

DOI: 10.19509/j.cnki.dzkq.2022.0197

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