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Fluid inclusion and stable isotope constraints on the source and evolution of ore-forming fluids in the Bailongshan pegmatitic Li-Rb deposit, Xinjiang, western China
Lithos ( IF 2.9 ) Pub Date : 2021-01-01 , DOI: 10.1016/j.lithos.2020.105824 Zeyang Zhang , Yuhang Jiang , Hecai Niu , Pan Qu
Lithos ( IF 2.9 ) Pub Date : 2021-01-01 , DOI: 10.1016/j.lithos.2020.105824 Zeyang Zhang , Yuhang Jiang , Hecai Niu , Pan Qu
Abstract The newly discovered Bailongshan pegmatitic lithium–rubidium (Li Rb) deposit in West Kunlun–Karakorum (western China) is a world-class Li deposit. In this paper, we present detailed field observations and fluid inclusion (FI) data for four major mineral zones at Bailongshan; i.e., the fine albite (FAZ), blocky feldspar (BFZ), quartz–muscovite (QMZ), and spodumene–quartz (SQZ) zones. FIs are abundant in quartz and spodumene, and include four types: (1) two-phase L-type, (2) two-phase V-type, (3) three-phase S-type, and (4) three-phase (CO2–H2O–NaCl) or two-phase (CO2-rich) C-type. Quartz contains all four FI types, whereas spodumene contains mainly C-type FIs. Microthermometric measurements show that the L-type FIs in the FAZ, BFZ, and SQZ homogenised at 283–338, 156–224, and 223–421 °C, respectively, with corresponding salinities of 15.4–26.5, 4.4–10.4, and 10.5–30.6 wt% NaCl equivalent. The S-type FIs in the FAZ and SQZ homogenised at 183–285 and 214–298 °C, respectively. The C-type FIs in spodumene and quartz homogenised at 256–321 and 234–286 °C, with corresponding salinities of 4.4–18.1 and 4.4–12.6 wt% NaCl equivalent, respectively. The ore-forming fluids were of medium–low-temperature and medium–low-salinity, and no systematic fluid compositional variations were identified in each zone. The average CO2 densities and trapping pressures were estimated at 0.72–0.91 g/cm3 and 3.00–3.75 kb, respectively, corresponding to mineralisation depths of 9–11 km. Supercritical fluids likely contributed to the concentration of ore-forming elements in the fluids, and fluid boiling may have led to CO2 degassing and Li ore deposition. H O isotope data show that quartz grains from all four zones have δ18OV-SMOW values of 8.6‰–10.2‰ and δDV-SMOW values of −38‰ to 107‰. The ore-forming fluids were likely sourced from pegmatitic magmas.
更新日期：2021-01-01
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