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| DOI | 10.1016/j.oregeorev.2024.105894 |
| 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) | |
| 发表日期 | 2024 |
| ISSN | 0169-1368 |
| EISSN | 1872-7360 |
| 起始页码 | 166 |
| 卷号 | 166 |
| 英文摘要 | 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. |
| 英文关键词 | Tourmaline; Boron isotopes; Bailongshan rare-metal pegmatite deposit; West Kunlun Orogen; Major elements; Magmatic-hydrothermal evolution |
| 语种 | 英语 |
| WOS研究方向 | Geology ; Mineralogy ; Mining & Mineral Processing |
| WOS类目 | Geology ; Mineralogy ; Mining & Mineral Processing |
| WOS记录号 | WOS:001203112400001 |
| 来源期刊 | ORE GEOLOGY REVIEWS
 |
| 文献类型 | 期刊论文 |
| 条目标识符 | http://gcip.llas.ac.cn/handle/2XKMVOVA/306830 |
| 作者单位 | Chinese Academy of Sciences; Guangzhou Institute of Geochemistry, CAS; Chinese Academy of Sciences; University of Chinese Academy of Sciences, CAS |
| 推荐引用方式 GB/T 7714 | . 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],2024,166. |
| APA | (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. |
| MLA | "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). |
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