藏南拿日雍措片麻岩穹窿淡色花岗岩稀有金属的富集

Rare Metal Enrichment in Leucogranite within Nariyongcuo Gneiss Dome, South Tibet

拿日雍措穹窿(错那洞穹窿)位于北喜马拉雅穹窿的东部,穹隆内花岗岩种类较多,有淡色花岗岩、含石榴子石淡色花岗岩、片理化淡色花岗岩、含石榴子石和含绿柱石伟晶岩.这些花岗岩为经历了斜长石、锆石、独居石、磷灰石、富Ti矿物等分离结晶作用而形成的高度演化花岗岩,相对于维氏世界花岗岩平均值,富集Bi、Cs、Li、Sn、Be、Pb、B、W、Ta等稀有金属成矿元素,略贫Nb元素.同时,围岩也相对富集稀有金属元素.全岩地球化学分析表明,引起拿日雍措穹隆淡色花岗岩富集稀有金属成矿元素的因素是分离结晶作用和热液交代作用.高度演化淡色花岗岩在喜马拉雅造山带广泛分布,铌铁矿、钽铁矿、锡石和绿柱石等稀有金属矿物已在多处露头被识别,暗示了喜马拉雅淡色花岗岩是未来稀有金属矿产勘探的重要靶区.

The Nariyongcuo gneiss dome,located to eastern Tethyan Himalaya, consists of many types of granites, containing two-mica granite, foliated leucogranites, garnet-bearing leucogranite, garnet-bearing pegmatite, and beryl -bearing pegmatite. All the Nariyongcuo leucogranites are evolved granites and resulted from various degrees of collective fractional crystallization of plagioclase, zircon, monazite, apatite and Ti-rich mineral phases. Comparing with Victorinox value of granites, these granites are enriched in rare metal elements of Bi, Cs, Li, Sn, Be, Pb, B, W, Ta, but relatively depleted in Nb. In addition, the wall rocks are also enriched in rare metal elements. Whole rock geochemical data imply that fractional crystallization and hydrothermal metasomatism resulted in rare metal mineralization within the Nariyongcuo gneiss dome. In the Himalayan belt, high evolved granites are widely distributed, and commonly contain rare metal-bearing minerals (niobite, tapiolite, cassiterite, beryl),suggesting that the Himalaya belt could be another new important target for the exploration of race metal deposits.