藏南拉隆穹窿的厘定及其稀有多金属成矿作用新发现

拉隆穹窿位于特提斯喜马拉雅构造带东南缘，与错那洞穹窿、库局穹窿构成平行于拉轨岗日穹窿带的另一条重要穹窿带.穹窿被上下拆离断层分割为核部单元、过渡带和盖层.核部单元主要由花岗片麻岩、淡色花岗岩和伟晶岩组成，花岗片麻岩锆石U-Pb年龄为474.3±5.5 Ma，淡色花岗岩主要包括二云母花岗岩和黑云母花岗岩两类；过渡带由石榴石片岩、十字石片岩、红柱石片岩、蓝晶石片岩，以及大理岩、矽卡岩化大理岩、矽卡岩等组成，由内向外显示出巴罗型变质分带特征；盖层由中生界浅变质碎屑沉积岩组成.拉隆穹窿中新发现有3类稀有多金属矿化作用，第1类为伟晶岩型铍矿化，主要富铍矿物为绿柱石，伟晶岩的独居石U-Pb年龄为23.19±0.12 Ma；第2类为矽卡岩型铍、钨、铌、钽稀有多金属矿化，矽卡岩型稀有多金属矿化产于白云母花岗岩与大理岩接触带，白云母花岗岩独居石U-Pb年龄为23.23±0.27 Ma；第3类为受构造控制的热液铜铅锌银矿化.拉隆稀有多金属矿化显示出以淡色花岗岩为核心向外的Be、Be-W-Nb-Ta、Cu-Pb-Zn-Ag矿化分带特征.拉隆穹窿的厘定表明特提斯－喜马拉雅成矿带存在一条“双穹窿”构造带，拉隆穹窿稀有多金属成矿作用的发现，进一步证实特提斯喜马拉雅成矿带具有巨量稀有金属找矿潜力，有望成为我国继华南和新疆阿尔泰之后第3条稀有金属成矿带. 

Determination of Lalong Dome in South Tibet and New Discovery of Rare Metal Mineralization

The Lalong dome is located in the southeast margin of the Tethys-Himalayan tectonic belt, which constitutes another important dome belt parallel to the North Himalayan dome belt along with Cuonadong dome and Kuju dome. The dome is separated by fault into a core unit, a transitional zone and a caprock. The core unit is mainly composed of granitic gneiss, leucogranites and pegmatite. The zircon U-Pb age of granitic gneisses is 474.3±5.5 Ma. Leucogranties mainly consist of two-mica granite and muscovite granite. The transitional zone is composed of garnet schist, cross schist, andalusite schist, kyanite schist, marble, skarn and so on. The caprock is composed of Mesozoic epimetamorphic clastic sedimentary rocks. Three types of rare metal mineralization are recognized. The first type is pegmatite beryllium mineralization. The main beryllium-bearing mineral is beryl. The monazite U-Pb age of pegmatite is 23.19 ±0.12 Ma. The second type is skarn beryllium, tungsten, niobium and tantalum with rare polymetallic mineralization. The monazite U-Pb age of muscovite granite in the contact zone with skarn is 23.23±0.27 Ma. The third type is tectonically controlled hydrothermal Cu-Pb-Zn-Ag mineralization. The rare polymetallic mineralization in Lalong dome shows the zonation characteristics of Be, Be-W-Nb-Ta, Cu-Pb-Zn-Ag mineralization with leucogranite as the core. The determination of the Lalong dome indicates the existence of a "double dome" structural belt in the Tethys-Himalayan metallogenic belt. The discovery of rare polymetallic mineralization in the Lalong dome further confirms that the Tethys-Himalayan metallogenic belt has a huge potential for rare metal prospecting and is expected to become the third rare metal metallogenic belt after South China belt and Altai Xinjiang belt.