Geochemical and geochronological study of beryl-bearing granitic pegmatite in the Mount Shisha Pangma Himalaya region
The Himalayan leucogranite,an essential product of the collisional orogenesis between the Indian and Eurasian plates,has drawn significant attention in studies related to orogenic evolution and plateau uplift.Recent research has revealed its highly fractionated nature and close association with large rare metal(e.g.,Li,Be,Rb,Cs)deposits.This study presents mineralogical,geochemical and geochronological data related to the beryl-bearing pegmatites associated with the Shisha Pangma leucogranite in the central Himalayas.The beryl in these pegmatites typically exhibits euhedral texture,mostly enclosed within major rock-forming minerals like feldspar and quartz,indicating characteristics of magmatic crystallization.Mineral chemistry reveals that the trace elemental changes in beryl are dominated by channel-octahedral and channel-tetrahedral substitution.It has a similar geochemical composition to that of beryl in Be-mineralized pegmatite,and a lower Li2O,Cs2O and Na/Li ratio than beryl in Himalayan Li-mineralized pegmatite,highlighting the attributes of Be mineralization in the host rock.It is consistent with the whole rock geochemical characteristic of high beryllium and low lithium in pegmatite.Additionally,rubidium,cesium and tin in pegmatite were also enriched.The strong positive correlation between rare metal elements and the Rb/Sr ratio in the pegmatite indicates that their enrichment is mainly controlled by fractional crystallization.U-(Th)-Pb dating of monazite indicates that these pegmatites primarily formed at ca.18~17Ma,consistent with the age of the Shisha Pangma leucogranite.Monazite in the beryl-bearing pegmatites also records ages of ca.25~23Ma and ca.21 Ma,representing two other regional magmatic events.In the central Himalayan region,the widespread occurrence of these three stages of leucogranitic magmatic events,along with rare metal mineralization,further emphasize the contribution of the generation and differentiation of leucogranite to the mineralization of pegmatite in the Himalayas.
HimalayaShisha PangmaLeucograniteBerylFractional crystallizationRare metal mineralization