滇中牟定大弯山地区新元古代变质玄武岩中Sc富集的发现及其地质意义

Discovery of scandium enrichment and its geological significance in the Dawanshan Neoproterozoic metamorphic basalts from the Mouding area in Central Yunnan Province,China

钪(Sc)是世界各国竞相争夺的关键金属矿产资源之一。滇中牟定大弯山变质玄武岩厚度>36.5m,出露面积0.5km^(2),形成时代为新元古代南华纪(781.3±1.9Ma)。本文对该变质玄武岩开展了全岩地球化学分析、全自动矿物分析(TESCAN TIMA)观测、NPPM薄片区域面扫和单矿物原位LA-ICPMS分析等研究,结果显示变质玄武岩全岩Sc含量为47.0×10^(-6)~97.9×10^(-6),平均含量为69.1×10^(-6),钪氧化物(Sc_(2)O_(3))平均含量为106×10^(-6),变质玄武岩空间Sc矿化特征稳定,具有形成钪矿资源的潜力。同时,变质玄武岩共伴生有钛和铁矿化,全岩TiO_(2)含量为2.57×10^(-2)~6.13×10^(-2),平均为4.25×10^(-2);TFe含量为13.3×10^(-2)~23.7×10^(-2),平均为17.7×10^(-2)。Sc可能存在类质同象和离子相两种赋存形式,类质同象形式Sc主要赋存于钛铁矿和金红石矿物中,钛铁矿中Sc含量为70.0×10^(-6)~168×10^(-6),平均值为108×10^(-6);金红石中Sc含量高达297×10^(-6);而磁铁矿、黑云母等矿物中Sc含量较低,均低于全岩Sc含量,对全岩Sc矿化贡献较小。牟定大弯山Sc矿化与以往报道侵入岩及其风化壳中Sc矿化在富集特征、赋存岩性和载体矿物等方面不同,是变质火山岩中新发现的Sc矿化信息,显示了较好的找矿潜力,对Sc资源勘查和研究具有重要指示意义。

Scandium(Sc)is one of the critical mineral resources that countries around the world are competing for.The Dawanshan metamorphic basalt in Mouding County,central Yunnan,has a thickness of more than 36.5m,an exposed area of 0.5km^(2),and a formation age(781.3±1.9Ma)of Neoproterozoic Nanhua Period.In this paper,the whole rocks geochemical analysis,full automatic mineral analysis(TESCAN TIMA)observation,NPPM thin section regional surface scanning and single mineral in-situ LA-ICPMS analysis were carried out for the metamorphic basalt.The results show that the Sc contents of the metamorphic basalts range from 47.0×10^(-6) to 97.9×10^(-6),with an average content of 69.1×10^(-6),and with an average scandium oxide(Sc_(2)O_(3))content of 106×10^(-6).As the Sc mineralization has stable spatial distribution characteristics,so it has the potential to form Sc deposit.At the same time,the metamorphic basalts are accompanied by Ti and Fe mineralization,with the TiO_(2) contents of 2.57%~6.13%(average 4.25%);The TFe contents range from 13.3%to 23.7%,with an average content of 17.7%.There are two types of Sc existence state:ionic phase and isomorphism phase.The Sc in the form of isomorphism mainly exists in ilmenite and rutile minerals,and the contents of Sc in ilmenite range from 70.0×10^(-6) to 168×10^(-6),with an average value of 108×10^(-6);Sc contents in rutile can up to 297×10^(-6).However,the contents of Sc in magnetite,biotite and other minerals are lower than that of the whole rocks,which makes little contribution to Sc mineralization in the whole rocks.The Dawanshan Sc mineralization in Mouding is different from the previous reported Sc mineralization in intrusive rocks and weathered rock crusts in terms of rock occurrence and mineral occurrence.It is newly discovered Sc mineralization information in volcanic rocks,demonstrating good prospecting potential,which has important guiding significance for the exploration and research of Sc deposits.