~(40)Ar/~(39)Ar dating for the Jiajika pegmatite-type rare metal deposit in western Sichuan and its significance

Abstract

The eastern part of the Qinghai-Xizang plateau (Tibet plateau) is an important area of pegmatite, and its importance is only next to the Altay ar ea in Xinjiang. It is also an important concentration area of rare metal resourc es, where the Jiajika rare metal deposit is the largest pegmatite-type Li-po lymetal deposit in China. Few studies have been finished for its remote location at high mountains and extremely unconventional traffic. New 40Ar/39Ar ages of m uscovite samples from the Jiajika rare metal pegmatite-type deposit are report ed, based on field investigation and isotopic geochronology study. The muscovite samples from the No.134 and No.104 pegmatite veins give Ar-Ar plateau ages of (195.7± 0.1) Ma and (198.9± 0.4) Ma, isochron ages of (195.4± 2.2) Ma and (1 99.4± 2.3) Ma, reverse isochron ages of (195.4± 1.9) Ma and (199.6± 2.1) Ma, respectively. This result suggests that the Jiajika pegmatite deposit formed at the early stage of Yanshanian, which is the relative stable period after the str ong Indo-China movement. That is to say, this pegmatite rare metal deposit for med at the interim from the Indo-China movement of plate-collision-style t o the Yanshanian movement of continental orogeny. Such feature is similar to man y pegmatite-type rare metal deposits at home and abroad.