西昆仑白龙山伟晶岩型稀有金属矿床地质特征及成矿时代

Geological Characteristics and Metallogenic Age of the Rare Metal Pegmatite Deposit in Bailongshan,West Kunlun

白龙山锂铷伟晶岩型稀有金属矿床位于西昆仑造山带甜水海地体,是一新发现的超大型锂‒铷‒(铍‒钽‒铌)矿床。本文对白龙山矿区伟晶岩的区域和内部分带进行了详细划分,发现大多数贫矿伟晶岩靠近白龙山花岗岩体,而矿化伟晶岩相对离岩体较远。白龙山伟晶岩型稀有金属矿床中锡石LA-MC-ICP-MS U-Pb同位素定年结果显示,矿化伟晶岩(石英‒锂辉石带)和未矿化伟晶岩脉(石英‒长石‒白云母带)分别得到211 Ma和213 Ma年龄,表明白龙山稀有金属伟晶岩形成于晚三叠世。结合二者区域分带的空间连续性和前人研究,认为矿区矿化和未矿化伟晶岩应属于同一构造‒岩浆事件的产物,它们均形成于碰撞后的伸展环境。在区域上,甜水海地体是松潘‒甘孜地块的西延展,西昆仑稀有金属成矿带可能与松潘‒甘孜稀有金属成矿带相连,构成一个超过2000 km的巨型稀有金属成矿带。

The Bailongshan is a newly discovered superlarge Li-Rb-(Be-Ta-Nb)rare metal pegmatite deposit located in the Tianshuihai terrane of the West Kunlun orogenic belt.In this study,the regional and internal zoning of pegmatites in the Bailongshan area were delineated.Most of the barren pegmatites are located near the Bailongshan granite pluton,whereas the ore-bearing pegmatites are relatively far from the pluton.LA-ICP-MS cassiterite U-Pb age represents the crystallization time of the pegmatites.Cassiterite from ore-bearing and barren pegmatites yield Tera-Wasserburg lower intercept ages of 211 Ma and 213 Ma,respectively,demonstrating that the Bailongshan rare metal pegmatites were formed in the Late Triassic.Considering the spatial continuity of the regional zoning,these ages may indicate that the formation of the ore-bearing and barren pegmatites in the Bailongshan area was related to the same tectonic event in a post-collisional extensional environment.Integrated with previous research,we highlight a Late Triassic rare-metal metallogenic event in the West Kunlun orogenic belt in a post-collision environment that is closely related to the evolution of the Paleo-Tethys.Regionally,the Tianshuihai terrane is the western extension of the Songpan-Ganze block,and the Western Kunlun rare metal metallogenic belt may be connected to the Songpan-Ganze rare metal metallogenic belt,forming a giant rare metal metallogenic belt of more than 2000 km in longth.