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Abstract:
Critical elements are the indispensable strategic resource for global high-tech industries,and the mechanisms for the enrichment and mineralization for such elements is currently one of the key areas in the international mineral deposit studies. In the Gyirong and Yadong areas along the Himalayan orogen,a systematic geochemical study of leucogranites indicate that the leucogranites which invaded the Southern Tibet Detachment System (STDS) contain a relatively elevated content of Sn,Cs,Tl,Be,W,B,Li and Bi. Whole-rock element geochemical data indicate that (1) these leucogranites are enriched in critical elements; (2) they represent the residual melts,which resulted from fractional crystallization of plagioclase,zircon,monazite,apatite,and mica of more primitive magmas; and (3) enrichment and mineralization of critical elements are closely related to the evolution of such highly fractionated granites. As magmas evolved into high SiO2 and volatile magmas by intensive fractional differentiation,critical elements with a high fluid compatibility are enriched in the residual melt and might eventually form economic ore deposits. Due to geochemical similarity,Cs and Tl are incorporated into mica by replacement of K or Rb. These granites enriched with critical elements are syntectonic granites spatially and temporally associated with the STDS whose activities promote extensive fractional crystallization of the more primitive magmas and later enrichment of critical elements such as Rb,Cs,and Tl.
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