云南腾冲摆夷寨地区透锂长石伟晶岩的厘定与找矿指示

Identification of petalite pegmatites in Baiyizhai area, Tengchong, Yunnan Province and its implication for mineral exploration

中文关键词:透锂长石  高温低压环境  伟晶岩型锂矿  摆夷寨  滇西地区

keywords:Petalite  high-T and low-P environment  pegmatite-type lithium deposit  Baiyizhai  western Yunnan area

中文摘要:伟晶岩型锂矿是全球锂资源供给的重要来源，锂辉石、锂云母和透锂长石是伟晶岩型锂矿床中主要的工业矿物。中国伟晶岩型锂矿床多为锂辉石型伟晶岩，仅有少数伟晶岩中有锂云母和透锂长石。滇西地区发育众多与花岗岩有关的伟晶岩，且在多条伟晶岩脉中发现了锂矿化。本次工作对研究区2条代表性伟晶岩脉中富锂矿物进行了厘定，74个LA-ICP-MS测点数据显示富锂矿物的w（SiO₂）介于76.53%~78.10%，平均值77.17%；w（Al₂O₃）介于16.81%~18.34%，平均值17.74%；w（Li₂O)=4.25%~5.12%，大部分在4.7%~5.0%，平均值4.84%；与典型透锂长石的化学成分特征吻合，表明摆夷寨地区伟晶岩中含锂矿物主要为透锂长石。透锂长石Li-Al-Si三组分关系以及Al³⁺/Li⁺>1、Li⁺和Al³⁺均与Si⁴⁺呈负相关的特征，反映透锂长石中Li⁺存在被Si⁴⁺、Al³⁺替换。摆夷寨地区透锂长石伟晶岩的发现，反映该地区伟晶岩形成于高温低压环境，其形成温度可能高于北部贡山地区以锂辉石、铁锂云母为主的含锂伟晶岩。透锂长石伟晶岩的首次厘定，为区域矿产勘查部署提供了新的找矿方向。

Abstract:Pegmatite-type lithium deposits are the important source of lithium resources in the world, with spodumene, lepidolite, and petalite being the main ore minerals in these deposits. Most pegmatite-type lithium deposits in China are spodumene-type pegmatites, with only a few pegmatites containing lepidolite and petalite. In western Yunnan area, numerous pegmatites associated with granite and many pegmatite veins hosting lithium mineralization have been discovered. Based on detailed field geological surveys, this study carried out LA-ICP-MS analysis on Li-bearing minerals from two pegmatite veins located in the Baiyizhai area. The 74 results of the samples show that the w(SiO₂) content ranges from 76.53% to 78.10%, 77.17% in average; w(Al₂O₃) content ranges between 16.81% and 18.34%, with an average of 17.74%; w(Li₂O) content ranges from 4.25% to 5.12%, mostly between 4.7% and 5.0%, 4.84% in average. These data are the typical composition of petalite, indicating that the petalite is the main Li-bearing mineral in pegmatite veins. The Li-Al-Si three component relationship of petalite, Al³⁺/Li⁺> 1, Li⁺ and Al³⁺ showing negative correlation with Si⁴⁺, all these characteristics reflect the existence of Li⁺ being substituted by Si⁴⁺ and Al³⁺ in petalite. The discovery of large amounts of petalite in pegmatites in the Baiyizhai area indicates that the pegmatites in the area were formed in a high-T and low-P environment. The temperature may be higher than that of the pegmatites in the Gongshan area north of the Baiyizhai area, which are rich in spodumene or lepidolite. The first identification of petalite pegmatite provides new ideas and directions for Li mineral exploration in this region.