Tourmaline geochemical and boron isotopic compositions of the Bailongshan rare-metal pegmatite deposit: Implications for magmatic-hydrothermal evolution of the West Kunlun Orogen (NW China)

doi:10.1016/j.oregeorev.2024.105894

	Zhang, Xiao-Yu 1,2; Wang, He1 ; Bai, Hong -Yang 1,2; Wang, Kun-Yu 1,2; Huang, Liang 1,2
	Tourmaline geochemical and boron isotopic compositions of the Bailongshan rare-metal pegmatite deposit: Implications for magmatic-hydrothermal evolution of the West Kunlun Orogen (NW China)
Source Publication	ORE GEOLOGY REVIEWS
ISSN	0169-1368
	2024-03-01
Volume	166 Pages:19
DOI	10.1016/j.oregeorev.2024.105894
Language	英语
WOS Research Area	Geology ; Mineralogy ; Mining & Mineral Processing
Abstract	The Bailongshan in the West Kunlun Orogen (northern Tibet) is a newly-discovered super-large rare-metal (Li-Rb(-Be-Ta-Nb)) pegmatite deposit. Tourmaline occurs widely in muscovite granites and pegmatites at Bailongshan, but comprehensive study is yet to be done on the geochemical evolution of tourmaline from the magmatic to the hydrothermal stages. Here, we present a systematic study of in-situ major, trace elemental and boron isotopic variations of tourmaline from Bailongshan deposit, and discuss the tourmaline genesis and how boron isotopes change during the magmatic to hydrothermal stage. Three types of tourmaline have been identified at Bailongshan deposit, including disseminated tourmaline in the muscovite granite, medium-coarse-grained euhedral tourmaline in the barren pegmatite, and multicolored medium-coarse-grained tourmaline in the ore-bearing pegmatite. EPMA and LA-ICP-MS geochemical analyses reveal that the tourmaline samples belong mainly to alkali group, with the tourmalines from the muscovite granite and the barren pegmatite falling into the schorl solid-solution series and the ore-bearing pegmatite falling into elbaite. There is a major chemical change from Fe-rich compositions with moderate Al in the Y-sites (muscovite granite and barren pegmatite) to Li-rich compositions with high Al-Y and relatively high F (ore-bearing pegmatite). Most trace element contents vary over several orders of magnitude with median concentrations of 0.1-10 mu g/g. High concentrations are found for Ga, Zn, Be, Sc, Sn and Li (several tens to thousands of mu g/g), whereas low concentrations (<0.1 mu g/g) are found for V, Rb, U, Th, W, and Hf. The tourmalines from muscovite granite and barren pegmatite yielded delta B-11 = -8.9 to -7.5 parts per thousand and -8.7 to -6.0 parts per thousand, respectively, whilst the tourmaline in the ore-bearing pegmatite show a wider delta B-11 range (-8.8 to -5.2 parts per thousand). The B isotopic values indicate a source of the continental crust in a post-collisional setting. The estimated delta B-11 value of parental granitic magma is -10.0 parts per thousand. The overlap in delta B-11 values between muscovite granite and barren pegmatite indicates a little isotopic fractionation between tourmaline and melt. Rayleigh fractionation results in the observed delta B-11 decrease from zone I (-6.9 parts per thousand) to zone V (-8.0 parts per thousand). After the barren-pegmatite-hosted tourmaline formation, the delta B-11 value of boron-rich magma would have been about -11.5 parts per thousand. The intragrain delta B-11 variation of tourmaline in the ore-bearing pegmatite is 2.7 parts per thousand, much larger than that from the other zones, indicating the rim of the tourmaline crystallized from fluid exsolved. We calculated the boron-isotope fractionation (between fluid and melt) to be 4.2-5.7 parts per thousand at 600-450 degrees C. Chemical variations in tourmaline are continuous in the muscovite granite and barren pegmatite, consistent with fractional crystallization, whereas the tourmaline from the ore-bearing pegmatite may have formed during the magmatic-hydrothermal transition. The boron isotopic variations could be attributed to fractionation between melt-tourmaline, melt-fluid and tourmaline-fluid and Rayleigh fractionation.
Keyword	Tourmaline Boron isotopes Bailongshan rare-metal pegmatite deposit West Kunlun Orogen Major elements Magmatic-hydrothermal evolution
WOS ID	WOS:001203112400001
Indexed By	SCI
Citation statistics
Document Type	期刊论文
Identifier	http://ir.gig.ac.cn/handle/344008/77134
Collection	中国科学院矿物学与成矿学重点实验室
Corresponding Author	Wang, He
Affiliation	1.Chinese Acad Sci, Guangzhou Inst Geochem, CAS Key Lab Mineral & Metallogeny, Guangzhou 510640, Peoples R China 2.Univ Chinese Acad Sci, Beijing 100049, Peoples R China
Recommended Citation GB/T 7714	Zhang, Xiao-Yu,Wang, He,Bai, Hong -Yang,et al. Tourmaline geochemical and boron isotopic compositions of the Bailongshan rare-metal pegmatite deposit: Implications for magmatic-hydrothermal evolution of the West Kunlun Orogen (NW China)[J]. ORE GEOLOGY REVIEWS,2024,166:19.
APA	Zhang, Xiao-Yu,Wang, He,Bai, Hong -Yang,Wang, Kun-Yu,&Huang, Liang.(2024).Tourmaline geochemical and boron isotopic compositions of the Bailongshan rare-metal pegmatite deposit: Implications for magmatic-hydrothermal evolution of the West Kunlun Orogen (NW China).ORE GEOLOGY REVIEWS,166,19.
MLA	Zhang, Xiao-Yu,et al."Tourmaline geochemical and boron isotopic compositions of the Bailongshan rare-metal pegmatite deposit: Implications for magmatic-hydrothermal evolution of the West Kunlun Orogen (NW China)".ORE GEOLOGY REVIEWS 166(2024):19.

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