Petrogenesis of amazonite granite and its constraints on rubidium mineralization in Jiangjunshan,Xinjiang Altai
The Xinjiang Altai is well known for the abundance of rare metal pegmatites,but lacks a considerable number of highly differentiated granites.The Jiangjunshan amazonite granite is the only known Rb-rich granite in Xinjiang Altai.However,its petrogenesis,Rb occurrence and its relationship with the surrounding pegmatites are still unclear,which restricts the understanding on Rb enrichment mechanism and the assessment of ore-forming potential.To address these issues,whole rock composition,chronology,isotope and mineralogy of amazonite granite and pegmatite in Jiangjunshan area were studied.Results demonstrate that the amazonite granite is a highly differentiated A-type granite with monazite U-Pb age of 276.9±2.7Ma,indicating that it was formed in the Early Permian.The monazite Nd isotope composition(εNd(t)=+4.15～+6.05,tDM2=548～708Ma)has the characteristics of the depleted source,indicating the source from juvenile crust or mixed with mantle-derived materials.The amazonite granite is spatially,temporally and compositionally related to the surrounding amazonite pegmatite,indicating that they have a genetic relationship in differentiation and evolution.The geochemical type of the amazonite granite and the mineral assemblage of the amazonite pegmatite both support the NYF(Nb,Y,F-rich)affinity of the amazonite.The Jiangjunshan amazonite granite and the pegmatite both show Rb mineralization,with major ore minerals of amazonite and phengite.From granite to pegmatite,the Rb contents in amazonite and phengite both increase gradually.High degree differentiation of magma is the dominating mechanism for Rb mineralization in the amazonite granite and pegmatite,but the mineralization degree is limited by the source derived from juvenile crust or mixed by mantle materials.Besides amazonite granite,we suggest that potassium feldspar and mica minerals in rare metal pegmatite should be paid attention to the exploration of Rb resources in Xinjiang Altai in the future.
万方数据
维普
