The Altay Orogenic Belt (AOB), an important part of the Central Asian Orogenic Belt (CAOB), comprises the Russia Gorny Altay, Kazakhstan Rudny Altay, Chinese Altay and Mongolia Altay. Previous work show that there are nearly one hundred thousand pegmatite veins in this area (~ 20,000 km2), in which most of the rare-metal pegmatites are concentrated in the Chinese Altay.

Since 2008, Professor ZHANG Hui’s research group from IGCAS has been devoting itself to the study of the formation and evolution of pegmatite, metallogenesis of rare metal ore deposit, and tectonic evolution of AOB. The group has achieved the following significant research progress:

(1) Pegmatites and their associated rare-metal ore deposits from the Chinese Altay were mainly formed in the Permian and Triassic, that is, 280-260 Ma and 250-205 Ma, respectively; few of them were formed in the Jurassic (200~180 Ma) according tozircon U-Pb dating.

(2) Pegmatites are characterized by lower positive Hf isotope (εHf(t)=+0.03~+2.39) and older TDM (1102~1225 Ma) in their zircons, similar to those in Paleozoic granites (εHf(t)=-1.41~+4.13, TDM=1164~1515 Ma), and Mesozoic granites (εHf(t)=+1~+4, TDM=1007~1196 Ma) from the Chinese Altay, indicating that pegmatites and granites were originated from a common source, that is, derived from partial melting of ancient crust with mantle-derived residual materials.

(3) It was put forward that large-scale distribution of pegmatites in the Chinese Altay was resulted from tectonic decompression melting after crustal thickening in the Triassic continental collision setting.

(4) Based onzircon U-Pb dating, the time limitation for the magmatic, magmatic–hydrothermal transition and hydrothermal stages were first determined in the natural pegmatite system: the Kelumute No. 112 pegmatite in the Chinese Altay. A long-term evolution process of three stages, with durations of ~5 Ma, ~23 Ma and ~22 Ma respectively, cannot be explained by undercooling and rapid crystallization model.

Some of the above research progress was published in Lithos, an international petrology journal. 

(By ZHANG Hui’s research group)