This paper presents a study of a newly discovered pollucite-lepidolite-albite granite(PLAG)in the Himalayan leucogranite belt,which marks the first occurrence of pollucite,a major cesium silicate mineral,in the Himala...This paper presents a study of a newly discovered pollucite-lepidolite-albite granite(PLAG)in the Himalayan leucogranite belt,which marks the first occurrence of pollucite,a major cesium silicate mineral,in the Himalayan orogenic belt(China).The rock appears at the northern part of the Gyirong pluton,coexisting with the tourmaline-bearing two-mica granite(TMG).Primary rare-metal minerals include lepidolite(Li),spodumene(Li),pollucite(Cs),cassiterite(Sn),and microlite(Ta).Micas,mainly lithian muscovite to lepidolite,contain 4.07 wt.%Li_2O and 0.76 wt.%Rb_2O on average.The average Li_2O content of the spodumene is 7.95 wt.%.Pollucite not only has an average Cs_2O content of 34 wt.%,but also has an elevated Rb_2O content of about 0.16 wt.%.Notably,this granite attains industrial grades for rare metals,specifically with Li_2O,Rb_2O,and Cs_2O contents of 0.49–1.19 wt.%,0.12–0.24 wt.%,and 0.69–2.33 wt.%,respectively.Dating results of magmatic accessory cassiterite and monazite indicated that the PLAG was formed at 19–18 Ma,slightly later than the TMG(22–20 Ma)of the Gyirong pluton.Thus,these two types of granites may form within the same magmatic system considering their pulsating intrusive contact,formation ages,and whole-rock and mineral chemical compositions.Furthermore,the abundant presence of pollucite suggests that the PLAG experienced high degrees of magmatic fractionation.In comparison to the Pusila spodumene pegmatite in the Himalaya and the Yashan topaz-lepidolite granite in Jiangxi,South China,the Gyirong PLAG exhibits different whole-rock and mineral compositions,resulting from differences in source materials and fractionation processes.Notably,the difference in fluorine(F)content may determine the degree of rare-metal element enrichment.The discovery of Gyirong PLAG highlights multiple stages and types of rare-metal mineralization in the Himalayan leucogranite belt,which is controlled by the South Tibetan Detachment System.The Cs-bearing geyserite deposit exposed along the Yarlung-Zangbo River,together with Himalayan leucogranites,constitutes two systems of rare-metal elements migration and enrichment.These two systems reflect the interaction among Earth systems across time and space,emphasizing how the Himalayan orogeny controls mineralization.As a result,the Himalayan leucogranite belt has considerable prospecting potential for cesium and rubidium resources and may be a crucial area for future exploration and resource utilization.展开更多
Mica exhibits a relatively high Rb/Sr ratio and possesses a closure temperature for the Rb-Sr isotope system that is higher than the ore-forming temperature range of low-to medium-temperature deposits.Consequently,uti...Mica exhibits a relatively high Rb/Sr ratio and possesses a closure temperature for the Rb-Sr isotope system that is higher than the ore-forming temperature range of low-to medium-temperature deposits.Consequently,utilizing the laser ablation(LA)technique for in situ Rb-Sr dating in mica constitutes a significant methodology for resolving the mineralization chronology of low-to medium-temperature hydrothermal ore deposits.In this study,we employed a combination of a triple quadrupole inductively coupled plasma mass spectrometer(ICP-MS/MS)and 193 nm LA system with SF_6as the reaction gas to achieve interference removal of~(87)Rb~+on~(87)Sr~+.We then developed an in situ Rb-Sr dating method for mica.In addition,an investigation was conducted to identify the factors that could influence the analytical accuracy of the method.Subsequently,we applied the developed method to carry out in situ Rb-Sr dating for the ZBH-25 biotite,a national primary reference material(GBW04439)for K-Ar dating,and yielded a younger age(ca.12%,relative standard deviation,RSD)than the reference K-Ar age when using NIST SRM 610 as the reference material for external calibration.This finding indicated that in the process of determining Rb-Sr ages for mica by LA-ICP-MS/MS,there are significant matrix effects between the NIST SRM 610 and the mica samples,resulting in inaccurate Rb-Sr ages.In response to this issue,a two-step calibration method is proposed here.Based on external calibration using NIST SRM 610,ZBH-25 biotite is employed as a second external reference material to perform a second calibration of the sample data to correct the matrix effect between the glass standards and the natural mica samples,thereby improving the accuracy of Rb-Sr dating by LA-ICP-MS/MS.Using the proposed method,in situ Rb-Sr dating by LA-ICP-MS/MS was performed on mica samples from monzonite exposed in Mt.Dromedary,New South Wales,Australia,porphyritic granodiorite in Fangshan pluton and albionite granite in the Gyirong area of Xizang.The obtained Rb-Sr age results show agreement with the recommended values within the analytical uncertainty,which serves to validate the accuracy and effectiveness of the proposed method.展开更多
基金supported by the Second Tibetan Plateau Scientific Expedition and Research(Grant Nos.2022QZKK0203,2019QZKK0802)the National Natural Science Foundation of China(Grant Nos.91755000,41888101,41902055)。
文摘This paper presents a study of a newly discovered pollucite-lepidolite-albite granite(PLAG)in the Himalayan leucogranite belt,which marks the first occurrence of pollucite,a major cesium silicate mineral,in the Himalayan orogenic belt(China).The rock appears at the northern part of the Gyirong pluton,coexisting with the tourmaline-bearing two-mica granite(TMG).Primary rare-metal minerals include lepidolite(Li),spodumene(Li),pollucite(Cs),cassiterite(Sn),and microlite(Ta).Micas,mainly lithian muscovite to lepidolite,contain 4.07 wt.%Li_2O and 0.76 wt.%Rb_2O on average.The average Li_2O content of the spodumene is 7.95 wt.%.Pollucite not only has an average Cs_2O content of 34 wt.%,but also has an elevated Rb_2O content of about 0.16 wt.%.Notably,this granite attains industrial grades for rare metals,specifically with Li_2O,Rb_2O,and Cs_2O contents of 0.49–1.19 wt.%,0.12–0.24 wt.%,and 0.69–2.33 wt.%,respectively.Dating results of magmatic accessory cassiterite and monazite indicated that the PLAG was formed at 19–18 Ma,slightly later than the TMG(22–20 Ma)of the Gyirong pluton.Thus,these two types of granites may form within the same magmatic system considering their pulsating intrusive contact,formation ages,and whole-rock and mineral chemical compositions.Furthermore,the abundant presence of pollucite suggests that the PLAG experienced high degrees of magmatic fractionation.In comparison to the Pusila spodumene pegmatite in the Himalaya and the Yashan topaz-lepidolite granite in Jiangxi,South China,the Gyirong PLAG exhibits different whole-rock and mineral compositions,resulting from differences in source materials and fractionation processes.Notably,the difference in fluorine(F)content may determine the degree of rare-metal element enrichment.The discovery of Gyirong PLAG highlights multiple stages and types of rare-metal mineralization in the Himalayan leucogranite belt,which is controlled by the South Tibetan Detachment System.The Cs-bearing geyserite deposit exposed along the Yarlung-Zangbo River,together with Himalayan leucogranites,constitutes two systems of rare-metal elements migration and enrichment.These two systems reflect the interaction among Earth systems across time and space,emphasizing how the Himalayan orogeny controls mineralization.As a result,the Himalayan leucogranite belt has considerable prospecting potential for cesium and rubidium resources and may be a crucial area for future exploration and resource utilization.
基金supported by the National Natural Science Foundation of China(Grant No.42173035)the Chinese Academy of Sciences“Key Technology Talent”Project。
文摘Mica exhibits a relatively high Rb/Sr ratio and possesses a closure temperature for the Rb-Sr isotope system that is higher than the ore-forming temperature range of low-to medium-temperature deposits.Consequently,utilizing the laser ablation(LA)technique for in situ Rb-Sr dating in mica constitutes a significant methodology for resolving the mineralization chronology of low-to medium-temperature hydrothermal ore deposits.In this study,we employed a combination of a triple quadrupole inductively coupled plasma mass spectrometer(ICP-MS/MS)and 193 nm LA system with SF_6as the reaction gas to achieve interference removal of~(87)Rb~+on~(87)Sr~+.We then developed an in situ Rb-Sr dating method for mica.In addition,an investigation was conducted to identify the factors that could influence the analytical accuracy of the method.Subsequently,we applied the developed method to carry out in situ Rb-Sr dating for the ZBH-25 biotite,a national primary reference material(GBW04439)for K-Ar dating,and yielded a younger age(ca.12%,relative standard deviation,RSD)than the reference K-Ar age when using NIST SRM 610 as the reference material for external calibration.This finding indicated that in the process of determining Rb-Sr ages for mica by LA-ICP-MS/MS,there are significant matrix effects between the NIST SRM 610 and the mica samples,resulting in inaccurate Rb-Sr ages.In response to this issue,a two-step calibration method is proposed here.Based on external calibration using NIST SRM 610,ZBH-25 biotite is employed as a second external reference material to perform a second calibration of the sample data to correct the matrix effect between the glass standards and the natural mica samples,thereby improving the accuracy of Rb-Sr dating by LA-ICP-MS/MS.Using the proposed method,in situ Rb-Sr dating by LA-ICP-MS/MS was performed on mica samples from monzonite exposed in Mt.Dromedary,New South Wales,Australia,porphyritic granodiorite in Fangshan pluton and albionite granite in the Gyirong area of Xizang.The obtained Rb-Sr age results show agreement with the recommended values within the analytical uncertainty,which serves to validate the accuracy and effectiveness of the proposed method.
