东昆仑大格勒地区富铌橄榄岩中的含铌矿物组成

Niobium-bearing mineral compositions of niobium-rich peridotites in the Dagele area of the East Kunlun Mountains

铌(Nb)是我国极度紧缺的战略性矿产资源,对外依存度非常高。近期本研究团队在东昆仑大格勒地区发现了志留纪–泥盆纪碱性岩–碳酸岩型铌、磷矿化杂岩体,岩石类型主要为橄榄岩、单斜辉石岩、橄榄辉长岩、角闪石岩和碳酸岩等。橄榄岩中Nb_(2)O_(5)品位为0.5%~0.8%,平均为0.6%,是原始地幔Nb丰度(0.713×10^(-6))的数千倍,显示了Nb元素的超常富集。本文在光学显微镜岩相学研究的基础上,应用电子探针背散射图像、能谱分析及电子探针定量分析技术,对橄榄岩中含铌矿物类型、共生关系及其化学组成进行研究。结果表明,橄榄岩中含铌矿物主要为烧绿石、(铈)铌钙矿、(铈)钙钛铌矿、褐铈铌矿和含铌钛铁矿,其中烧绿石含量最高(约1%)。5种矿物中Nb_(2)O_(5)含量依次为:烧绿石(71.45%~74.50%)、(铈)铌钙矿(50.96%~55.26%)、(铈)钙钛铌矿(43.27%~47.73%)、褐铈铌矿(41.63%~44.26%)以及含铌钛铁矿(4.63%~4.99%)。烧绿石呈半自形粒状晶,充填于磁铁矿等矿物粒间。本研究为东昆仑造山带碱性–碳酸岩型铌矿成矿潜力分析、成矿规律总结以及下一步矿产勘查部署提供了依据。

Niobium(Nb)is an extremely scarce strategic mineral resource in China,and its dependence on foreign countries has exceeded 99%in recent years.Recently,we discovered a Silurian-Devonian alkaline rock-carbonate-type Nb and phosphate mineralized complex in the Dagele area of East Kunlun.The rock types are mainly peridotite,clinopyroxenite,olivine gabbro,hornblende rock,and carbonate.The Nb_(2)O_(5)grade in the peridotite ranges from 0.5%to 0.8%,with an average of 0.6%,which is thousands of times higher than the primary mantle Nb abundance(0.713´10−6),indicating an extraordinary enrichment of Nb.The types,paragenesis,and chemical compositions of Nb-rich minerals in the peridotite are studied using electron microprobe backscatter images,energy spectrum analyses,and electron microprobe quantitative analyses based on optical microscopy petrography.The results show that the main Nb-rich minerals in the peridotite are pyrochlore,cerium niobium,(cerium)calcium niobite,(cerium)perovskite niobium ore,and Nb-bearing ilmenite.Among these minerals,pyrochlore had the highest Nb content(up to 1%).The Nb_(2)O_(5)contents in the five minerals were as follows:pyrochlorite(71.45%-74.50%),cerium niobium(50.96%-55.26%),(cerium)calcium niobite(43.27%-47.73%),(cerium)perovskite niobium ore(41.63%-44.26%),and Nb-bearing ilmenite(4.63%-4.99%).Pyrochlore is mainly composed of subhedral fine-grained crystals filled between mineral grains such as magnetite.This study provides a basis for the analysis of the metallogenic potential of alkaline-carbonate niobium ore in the East Kunlun orogenic belt and provides a summary of metallogeny and the next step of mineral exploration and deployment.