Geochronology and Geochemistry of Li(Be)-Bearing Granitic Pegmatites from the Jiajika Superlarge Li-Polymetallic Deposit in Western Sichuan, China

Strategic emerging minerals such as lithium,beryllium,niobium and tantalum are the most important rare metals currently,especially with the increasing demand of emerging industries on rare metals in China.The Jiajika deposit with a complete Li-Be-Nb-Ta metallogenic series is the largest pegmatite type rare metal deposit in China at present.In this paper,systematic researches of geochronology and petrogeochemistry were carried out to understand the genetic relationships between mineralization and magma evolution in the Jiajika deposit,which might be helpful to further rare-element prospecting in Songpan-Garze area.Zircon LA-ICP-MS U-Pb dating yields a concordia age of 217±1.1 Ma and a weighted mean 206 Pb/238 U age of 217±0.84 Ma for the aplite from the No.308 pegmatite.Cassiterite LA-MC-ICPMS dating yields concordant ages of 211±4.6 Ma for the No.308 pegmatite vein and198±4.4 Ma for the No.133 pegmatite vein,indicating that the rare metal mineralization mainly occurred in the Late Indosinian Period, further suggesting that the granites, aplites and pegmatites in Jiajika formed during a relatively stable stage after the intense orogeny of the Indosinian cycle.The rare metal-bearing granitic rocks and pegmatites show a clear linear relationship between A/CNK and A/NK and are enriched in total alkalis and depleted in CaO,FeO,MnO,MgO,Ba and Sr.All barren rocks and mineralized rocks feature similar rare earth element and trace element geochemical patterns.Thus,these characteristics indicate that the aplites and pegmatites represent the highly differentiated products of the two-mica granite(MaG)in this area, which is the most likely parent magma.During the evolution of magma,strong alkali metasomatism occurred between the melt phase and the volatile-rich fluid phase; as a result,large-scale rare metal mineralization occurred in certain structural zones of the pegmatite veins in the Jiajika deposit.