Characteristics of strong reducing metallogenic porphyry and its constraints on the genesis of the rare metal-tin-polymetallic deposit in Weilasituo, Inner Mongolia

DU Lihua; HUANG Yu; GAO Xiong; NIU Xingguo; ZHENG Guoqiang; CHEN Feifei; CAO Jindong; ZHAO Dan; ZHONG Shihua

doi:10.12097/gbc.2024.07.001

2025 Vol. 44, No. 4

Article Contents

Article navigation > Geological Bulletin of China > 2025 > 44(4): 633-648

Next Article Previous Article

DU Lihua, HUANG Yu, GAO Xiong, NIU Xingguo, ZHENG Guoqiang, CHEN Feifei, CAO Jindong, ZHAO Dan, ZHONG Shihua. 2025. Characteristics of strong reducing metallogenic porphyry and its constraints on the genesis of the rare metal-tin-polymetallic deposit in Weilasituo, Inner Mongolia. Geological Bulletin of China, 44(4): 633-648. doi: 10.12097/gbc.2024.07.001

Citation:

DU Lihua, HUANG Yu, GAO Xiong, NIU Xingguo, ZHENG Guoqiang, CHEN Feifei, CAO Jindong, ZHAO Dan, ZHONG Shihua. 2025. Characteristics of strong reducing metallogenic porphyry and its constraints on the genesis of the rare metal-tin-polymetallic deposit in Weilasituo, Inner Mongolia. Geological Bulletin of China, 44(4): 633-648. doi: 10.12097/gbc.2024.07.001

Characteristics of strong reducing metallogenic porphyry and its constraints on the genesis of the rare metal-tin-polymetallic deposit in Weilasituo, Inner Mongolia

1.
Comprehensive Survey Team of Non-ferrous Geological Exploration Bureau of Inner Mongolia Autonomous Region, Hohhot 010011, Inner Mongolia, China
2.
College of Marine Geosciences/Key Lab of Submarine Geosciences and Prospecting Techniques, MOE and Ocean University of China, Qingdao 266100, Shandong, China

More Information

Corresponding author: ZHONG Shihua, zhongshihua@ouc.edu.cn

Received Date: 01 July 2024

Revised Date: 16 October 2024

Publish Date: 15 April 2025

Abstract

Abstract

Objective
Since the discovery of the Weilasituo rare metal−tin−polymetallic deposit in Inner Mongolia, the genesis of its ore deposits has been a central focus of geological inquiry. Oxygen fugacity ($f_{{\mathrm{O}}_2} $) has been identified as playing a pivotal role in the processes of tin element migration and enrichment. Accurate characterization of $f_{{\mathrm{O}}_2} $ in granites is essential for constraining the genesis of the Weilasituo tin polymetallic deposit.
Methods
This study employs LA−ICP−MS zircon U−Pb dating, whole−rock geochemical analyses, and zircon trace element studies to investigate granites closely associated with mineralization at the Weilasituo deposit.
Results
Zircon U−Pb dating reveals concentrated crystallization ages of the granites at approximately 120.2±1.6 Ma and 125.9±1.9 Ma, indicative of multiple magmatic episodes in this area. Zircon trace element analyses show that the Ce/Ce^* average value for granites at Weilasituo is 400.87, with an average Eu/Eu^* value of 0.062. The ${\mathrm{log}}f_{{\mathrm{O}}_2 } $ predominantly ranges from −26 to −20, and ΔFMQ values are concentrated between −6 and −1, suggesting a predominantly reducing ore−forming environment. The obtained age data closely align with previously proposed late−stage magmatic activity, indicating that these ore−forming magmas retained low $f_{{\mathrm{O}}_2} $ characteristics.
Conclusions
In summary, it is concluded that oxygen fugacity is the key factor controlling the formation of Verastor deposit. The low oxygen fugacity of Verastor metallogenic magma inhibits the premature saturation of Sn in the deep crust, which enables Sn to accumulate in the magma and eventually form large−scale Sn mineralization.
- rare metal /
- tin /
- oxygen fugacity /
- zircon U−Pb dating /
- granite /
- Weilasituo /
- Inner Mongolia

FullText(HTML)

References

[1]	Belousova E A, Griffin W L, Pearson N J. 1998. Trace element composition and catholuminescence properties of southern African kimberlitic zircons[J]. Mineralogical Magazine, 62: 355−366. doi: 10.1180/002646198547747 CrossRef Google Scholar
[2]	Boynton W V. 1984. Cosmochemistry of the Rare Earth Elements: Meteorite Studies[J]. Developments in Geochemistry, 2: 63−114. Google Scholar
[3]	Du A D, Qu W J, Wang D H, et al. 2007. Subgrain−size decoupling of Re and ¹⁸⁷Os within molybdenite[J]. Mineral Deposits, 26(5): 572−580 (in Chinese with English abstract). Google Scholar
[4]	Fan Z Y, Qiu H Y, Fu X, et al. 2017. Discovery and exploration of Weilasituo large porphyry−type tin−polymetal deposit in Inner Mongolia and its geological significances[J]. Gold Science and Technology, 25(1): 9−17 (in Chinese with English abstract). Google Scholar
[5]	Ferry J M, Watson E B. 2007. New thermodynamic models and revised calibrations for the Ti−in−zircon and Zr−in−rutile thermometers[J]. Contributions to Mineralogy and Petrology, 154: 429−437. doi: 10.1007/s00410-007-0201-0 CrossRef Google Scholar
[6]	Gao X, Zhou Z H, Karel B, et al. 2019. Ore formation mechanism of the Weilasituo tin−polymetallic deposit, NE China: Constraints from bulk−rock and mica chemistry, He−Ar isotopes, and Re−Os dating[J]. Ore Geology Reviews, 109: 163−183. doi: 10.1016/j.oregeorev.2019.04.007 CrossRef Google Scholar
[7]	Gehrels G E, Valencia V A, Ruiz J. 2008. Enhanced precision, accuracy, efficiency, and spatial resolution of U−Pb ages by laser ablation−multicollector–inductively coupled plasma–mass spectrometry[J]. Geochemistry, Geophysics, Geosystems, 9(3): Q03017. Google Scholar
[8]	Guo G H, Zhong S H, Li S Z, et al. 2023. Constructing discrimination diagrams for granite mineralization potential by using machine learning and zircon trace elements: Example from the Qimantagh, East Kunlun[J]. Northwestern Geology, 56(6): 57−70 (in Chinese with English abstract). Google Scholar
[9]	Guo G J. 2016. Discussion on geological characteristics and metallogenic origin of Weilasituo Sn polymetal deposit in Inner Mongolia[D]. Master's Thesis of China University of Geosciences (Beijing) (in Chinese with English abstract). Google Scholar
[10]	Ishihara S. 1981. The granitoid series and mineralization[J]. Econ. Geol., 75th Anniv.: 458−484. Google Scholar
[11]	Keppler H, Wyllie P J. 1991. Partitioning of Cu, Sn, Mo, W, U, and Th between melt and aqueous fluid in the systems haplogranite H₂O−HCl and haplogranite−H₂O−HF[J]. Contributions to Mineralogy & Petrology, 109(2): 139−150. Google Scholar
[12]	Lei W Y, Shi G H, Liu Y X. 2013. Research progress on trace element characteristics of zircons of different origins[J]. Earth Science Frontiers, 20(4): 273−284 (in Chinese with English abstract). Google Scholar
[13]	Liu J Q, Zhong S H, Li S Z, et al. 2023. Identification of mineralized and barren magmatic rocks for the pophryry−skarn deposits from the Qimantagh, East Kunlun: Based on machine learning and whole−rock compositions[J]. Northwestern Geology, 56(6): 41−56 (in Chinese with English abstract). Google Scholar
[14]	Liu R L, Wu G, Li T G, et al. 2018a. LA−ICP−MS cassiterite and zircon U−Pb ages of the Weilasituo tin−polymetallic deposit in the southern Great Xing'an Range and their geological significance[J]. Earth Science Frontiers, 25(5): 183−201 (in Chinese with English abstract). Google Scholar
[15]	Liu R L, Wu G, Chen G Z, et al. 2018b. Characteristics of fluid inclusions and H−O−C−S−Pb isotopes of Weilasituo Sn−polymetallic deposit in southern Da Hinggan Mountains[J]. Mineral Deposits, 37(2): 199−224 (in Chinese with English abstract). Google Scholar
[16]	Liu Y F, Fan Z Y, Jiang H C, et al. 2014. Genesis of the Weilasituo−Bairendaba porphyry−hydrothermal vein type system in Inner Mongolia[J]. Acta Geologica Sinica, 88(12): 2373−2385 (in Chinese with English abstract). Google Scholar
[17]	Liu Y F, Jiang S H, Bagas L. 2016. The genesis of metal zonation in the Weilasituo and Bairendaba Ag−Zn−Pb−Cu−(Sn−W) deposits in the shallow part of a porphyry Sn−W−Rb system, Inner Mongolia, China[J]. Ore Geology Reviews, 75: 150−173. doi: 10.1016/j.oregeorev.2015.12.006 CrossRef Google Scholar
[18]	Liu Y S, Hu Z C, Zong K Q, et al. 2010. Reappraisement and refinement of zircon U−Pb isotope and trace element analyses by LA−ICP−MS[J]. Chinese Science Bulletin, 55(15): 1535−1546. doi: 10.1007/s11434-010-3052-4 CrossRef Google Scholar
[19]	Loucks R R, Fiorentini M L, Henríquez G J. 2020. New magmatic oxybarometer using trace elements in zircon[J]. Journal of Petrology, 61(3): egaa034. doi: 10.1093/petrology/egaa034 CrossRef Google Scholar
[20]	Ludwig K R. 2012. User’s manual for Isoplot 3.75: A geochronological toolkit for Microsoft Excel[J]. Berkeley Geochronology Center Special Publication, 5: 1−75. Google Scholar
[21]	Maniar P D, Piccoli P M. 1989. Tectonic discrimination of granitoids[J]. GSA Bulletin, 101(5): 635−643. doi: 10.1130/0016-7606(1989)101<0635:TDOG>2.3.CO;2 CrossRef Google Scholar
[22]	Meng Q R. 2003. What drove late Mesozoic extension of the northern China−Mongolia tract?[J]. Tectonophysics, 369(3/4): 155−174. Google Scholar
[23]	Müller B, Frischknecht R, Seward T, et al. 2001. A fluid inclusion reconnaissance study of the Huanuni tin deposit (Bolivia), using LA−ICP−MS micro−analysis[J]. Mineralium Deposita, 36(7): 680−688. doi: 10.1007/s001260100195 CrossRef Google Scholar
[24]	Murakami T, Chakoumakos B C, Ewing R C, et al. 1991. Alpha−decay event damage in zircon[J]. American Mineralogist, 76(9/10): 1510−1532. Google Scholar
[25]	Niu J H, Tian F Q, Qiu D F, et al. 2023. Zircon U−Pb age of granitoids in the Jiudian gold deposit, Shandong Province and constraints on the magmatic activity patterns in the southern section of the Zhaoping fault[J]. Geological Bulletin of China, 42(5): 813−827 (in Chinese with English abstract). Google Scholar
[26]	Pan X F, Guo L J, Wang S, et al. 2009. Laser microprobe Ar−Ar dating of biotite from the Weilasituo Cu−Zn polymetallic deposit in Inner Mongolia[J]. Acta Petrologica et Mineralogica, 28(5): 473−479 (in Chinese with English abstract). Google Scholar
[27]	Peccerillo A, Taylor S R. 1976. Geochemistry of Eocene calc−alkaline volcanic rocks from the Kastamonu area, Northern Turkey[J]. Contributions to Mineralogy and Petrology, 58: 63−81. doi: 10.1007/BF00384745 CrossRef Google Scholar
[28]	Qin F, Liu J M, Zeng Q D, et al. 2009. Petrogenetic and metallogenic mechanism of the Xiaodonggou porphyry molybdenum deposit in Hexigten Banner, Inner Mongolia[J]. Acta Petrologica Sinica, 25(12): 3357−3368 (in Chinese with English abstract). Google Scholar
[29]	Robinson P T, Zhou M F, Hu X F, et al. 1999. Geochemical constraints on the origin of the Hegenshan Ophiolite, Inner Mongolia, China[J]. Journal of Asian Earth Sciences, 17(4): 423−442. doi: 10.1016/S1367-9120(99)00016-4 CrossRef Google Scholar
[30]	Shao J A. 2007. Uplift of the Great Xing'an Range and its geodynamic background[M]. Beijing: Geological Publishing House: 150−178 (in Chinese with English abstract). Google Scholar
[31]	Sun S S, McDonough W F. 1989. Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes[J]. Geological Society, London, Special Publications, 42: 313−345. Google Scholar
[32]	Taylor J R, Wall V J. 1993. Cassiterite solubility, tin speciation, and transport in a magmatic aqueous phase[J]. Economic Geology, 88(2): 437−460. doi: 10.2113/gsecongeo.88.2.437 CrossRef Google Scholar
[33]	Wang C Y. 2015. Lead−zinc polymetallic metallogenic series and prospecting direction of Huanggangliang−Ganzhuermiao metallogenic belt, Inner Mongolia[D]. Doctoral Thesis of Jilin University (in Chinese with English abstract). Google Scholar
[34]	Wang F X, Bagas L, Jiang S H, et al. 2017. Geological, geochemical, and geochronological characteristics of Weilasituo Sn polymetal deposit, Inner Mongolia, China[J]. Ore Geology Reviews, 80: 1206−1229. doi: 10.1016/j.oregeorev.2016.09.021 CrossRef Google Scholar
[35]	Wang X Y, Hou Q Y, Wang J, et al. 2013. SHRIMP geochronology and Hf isotope of zircons from granitoids of the Weilasituo deposit in Inner Mongolia[J]. Geoscience, 27(1): 67−78 (in Chinese with English abstract). Google Scholar
[36]	Wang Y, Wang X, Zhang W, et al. 2024. Fresh insights into the onset of big mantle wedge beneath the North China Craton[J]. Acta Geochimica, 44: 142−160. Google Scholar
[37]	Wu F Y, Sun D Y, Ge W C. 2011. Geochronology of the Phanerozoic granitoids in northeastern China[J]. Journal of Asian Earth Sciences, 41(1): 1−30. doi: 10.1016/j.jseaes.2010.11.014 CrossRef Google Scholar
[38]	Wu G, Liu R L, Chen G Z, et al. 2021. Mineralization of the Weilasituo rare metal−tin−polymetallic ore deposit in Inner Mongolia: Insights from fractional crystallization of granitic magmas[J]. Acta Petrologica Sinica, 37(3): 637−664 (in Chinese with English abstract). doi: 10.18654/1000-0569/2021.03.01 CrossRef Google Scholar
[39]	Xiao L Y, Yang X Z. 2022. Ce−in−zircon oxybarometer and the redox state of the early earth[J]. Geological Journal of China Universities, 28(4): 484−492 (in Chinese with English abstract). Google Scholar
[40]	Xue H M, Guo L J, Hou Z Q, et al. 2010. SHRIMP zircon U−Pb ages of the middle Neopaleozoic unmetamorphosed magmatic rocks in the southwestern slope of the Da Hinggan Mountains Inner Mongolia[J]. Acta Petrologica et Mineralogica, 29(6): 811−823 (in Chinese with English abstract). Google Scholar
[41]	Ying J F, Zhou X H, Zhang L C, et al. 2010. Geochronological framework of Mesozoic volcanic rocks in the Great Xing'an Range, NE China, and their geodynamic implications[J]. Journal of Asian Earth Sciences, 39(6): 786−793. doi: 10.1016/j.jseaes.2010.04.035 CrossRef Google Scholar
[42]	Zhai D G, Liu J J, Li J M, et al. 2016. Geochronological study of Weilasituo porphyry type Sn deposit in Inner Mongolia and its geological significance[J]. Mineral Deposits, 35(5): 1011−1022 (in Chinese with English abstract). Google Scholar
[43]	Zhang T F, Guo S, Xin H T, et al. 2019. Petrogenesis and Magmatic Evolution of Highly Fractionated Granite and Their Constraints on Sn−(Li−Rb−Nb−Ta) Mineralization in the Weilasituo Deposit, Inner Mongolia, Southern Great Xing'an Range, China[J]. Earth Science, 44(1): 248−267 (in Chinese with English abstract). Google Scholar
[44]	Zhao H., Feng C Y, Zhong S H, et al. 2023. Zircon fertility indicators compromised by mineral inclusion contamination: A case study from the Taoxikeng W deposit, South China[J]. Ore Geology Reviews, 162: 105714. Google Scholar
[45]	Zhao Z D, Liu D, Wang Q, et al. 2018. Zircon trace elements and their use in deep processes[J]. Earth Science Frontiers, 25(6): 124−135 (in Chinese with English abstract). Google Scholar
[46]	Zheng J P, O'reilly S Y, Griffin W L, et al. 1998. Nature and evolution of Cenozoic lithospheric mantle beneath Shandong peninsula, Sino−Korean craton, eastern China[J]. International Geology Review, 40(6): 471−499. doi: 10.1080/00206819809465220 CrossRef Google Scholar
[47]	Zhong S H, Seltmann R, Qu H Y, et al. 2019. Characterization of the zircon Ce anomaly for estimation of oxidation state of magmas: A revised Ce/Ce^* method[J]. Mineralogy and Petrology, 113(6): 755−763. doi: 10.1007/s00710-019-00682-y CrossRef Google Scholar
[48]	Zhou Z H, Gao X, Ouyang H G, et al. 2019. Formation mechanism and intrinsic genetic relationship between tin−tungsten−lithium mineralization and peripheral lead−zinc−silver−copper mineralization: Exemplified by Weilasituo tin−tungsten−lithium polymetallic deposit, Inner Mongolia[J]. Mineral Deposits, 38(5): 1004−1022 (in Chinese with English abstract). Google Scholar
[49]	Zhou Z H, Lü L S, Feng J R, et al. 2010. Molybdenite Re−Os ages of the Huanggang skarn Sn−Fe deposit and their geological significance Inner Mongolia[J]. Acta Petrologica Sinica, 14(3): 667−679 (in Chinese with English abstract). Google Scholar
[50]	Zhu X Y, Zhang Z H, Fu X, et al. 2016. Geological and geochemical characteristics of the Weilasito Sn−Zn deposit, Inner Mongolia[J]. Geology in China, 43(1): 188−208 (in Chinese with English abstract). Google Scholar
[51]	Zi J W, Rasmussen B, Muhling J R, et al. 2022. In situ U−Pb and geochemical evidence for ancient Pb−loss during hydrothermal alteration producing apparent young concordant zircon dates in older tuffs[J]. Geochimica et Cosmochimica Acta, 320: 324−338. doi: 10.1016/j.gca.2021.11.038 CrossRef Google Scholar
[52]	杜安道, 屈文俊, 王登红, 等. 2007. 辉钼矿亚晶粒范围内Re和¹⁸⁷Os的失耦现象[J]. 矿床地质, 26(5): 572−580. doi: 10.3969/j.issn.0258-7106.2007.05.010 CrossRef Google Scholar
[53]	樊志勇, 邱慧远, 付旭, 等. 2017. 内蒙古维拉斯托大型斑岩型锡多金属找矿勘查及启示[J]. 黄金科学技术, 25(1): 9−17. doi: 10.11872/j.issn.1005-2518.2017.01.009 CrossRef Google Scholar
[54]	郭广慧, 钟世华, 李三忠, 等. 2023. 运用机器学习和锆石微量元素构建花岗岩成矿潜力判别图解: 以东昆仑祁漫塔格为例[J]. 西北地质, 56(6): 57−70. doi: 10.12401/j.nwg.2023158 CrossRef Google Scholar
[55]	郭贵娟. 2016. 内蒙古维拉斯托锡多金属矿床地质特征及成因探讨[D]. 中国地质大学(北京)硕士学位论文. Google Scholar
[56]	雷玮琰, 施光海, 刘迎新. 2013. 不同成因锆石的微量元素特征研究进展[J]. 地学前缘, 20(4): 273−284. Google Scholar
[57]	刘嘉情, 钟世华, 李三忠, 等. 2023. 基于机器学习和全岩成分识别东昆仑祁漫塔格斑岩−矽卡岩矿床成矿岩体和贫矿岩体[J]. 西北地质, 56(6): 41−56. doi: 10.12401/j.nwg.2023155 CrossRef Google Scholar
[58]	刘瑞麟, 武广, 李铁刚, 等. 2018a. 大兴安岭南段维拉斯托锡多金属矿床LA−ICP−MS锡石和锆石U−Pb年龄及其地质意义[J]. 地学前缘, 25(5): 183 201. Google Scholar
[59]	刘瑞麟, 武广, 陈公正, 等. 2018b. 大兴安岭南段维拉斯托锡多金属矿床流体包裹体和同位素特征[J]. 矿床地质, 37(2): 199−224. Google Scholar
[60]	刘翼飞, 樊志勇, 蒋胡灿, 等. 2014. 内蒙古维拉斯托−拜仁达坝斑岩−热液脉状成矿体系研究[J]. 地质学报, 88(12): 2373−2385. Google Scholar
[61]	牛警徽, 田福泉, 邱敦方, 等. 2023. 山东旧店金矿床花岗岩类锆石 U−Pb 年龄及对招平断裂带南段岩浆活动规律的约束[J]. 地质通报, 42(5): 813−827. doi: 10.12097/j.issn.1671-2552.2023.05.012 CrossRef Google Scholar
[62]	潘小菲, 郭利军, 王硕, 等. 2009. 内蒙古维拉斯托铜锌矿床的白云母Ar/Ar年龄探讨[J]. 岩石矿物学杂志, 28(5): 473 479. Google Scholar
[63]	邵济安. 2007. 大兴安岭的隆起与地球动力学背景[M]. 北京: 地质出版社: 150−178. Google Scholar
[64]	覃锋, 刘建明, 曾庆栋, 等. 2009. 内蒙古克什克腾旗小东沟斑岩型钼矿床成岩成矿机制探讨[J]. 岩石学报, 25(12): 3357−3368. Google Scholar
[65]	王承洋. 2015. 内蒙古黄岗梁−甘珠尔庙成矿带铅锌多金属成矿系列与找矿方向[D]. 吉林大学博士学位论文. Google Scholar
[66]	王新宇, 侯青叶, 王瑾, 等. 2013. 内蒙古维拉斯托矿床花岗岩类SHRIMP年代学及Hf同位素研究[J]. 现代地质, 27(1): 67−78. doi: 10.3969/j.issn.1000-8527.2013.01.007 CrossRef Google Scholar
[67]	武广, 刘瑞麟, 陈公正, 等. 2021. 内蒙古维拉斯托稀有金属−锡多金属矿床的成矿作用: 来自花岗质岩浆结晶分异的启示[J]. 岩石学报, 37(3): 637−664. Google Scholar
[68]	肖路毅, 杨晓志. 2022. 锆石Ce氧逸度计和早期地球的氧化还原状态[J]. 高校地质学报, 28(4): 484−492. Google Scholar
[69]	薛怀民, 郭利军, 侯增谦, 等. 2010. 大兴安岭西南坡成矿带晚古生代中期未变质岩浆岩的SHRIMP锆石U−Pb年代学[J]. 岩石矿物学杂志, 29(6): 811−823. doi: 10.3969/j.issn.1000-6524.2010.06.016 CrossRef Google Scholar
[70]	张天福, 郭硕, 辛后田, 等. 2019. 大兴安岭南段维拉斯托高分异花岗岩体的成因与演化及其对Sn−(Li−Rb−Nb−Ta)多金属成矿作用的制约[J]. 地球科学, 44(1): 248−267. Google Scholar
[71]	赵志丹, 刘栋, 王青, 等. 2018. 锆石微量元素及其揭示的深部过程[J]. 地学前缘, 25(6): 124−135. Google Scholar
[72]	翟德高, 刘家军, 李俊明, 等. 2016. 内蒙古维拉斯托斑岩型锡矿床成岩、成矿时代及其地质意义[J]. 矿床地质, 35(5): 1011−1022. Google Scholar
[73]	周振华, 高旭, 欧阳荷根, 等. 2019. 锡钨锂矿化与外围脉状铅锌银铜矿化的内在成因关系和形成机制: 以内蒙古维拉斯托锡钨锂多金属矿床为例[J]. 矿床地质, 38(5): 1004−1022. Google Scholar
[74]	周振华, 吕林素, 冯佳睿, 等. 2010. 内蒙古黄岗夕卡岩型锡铁矿床辉钼矿Re−Os年龄及其地质意义[J]. 岩石学报. 14(3): 667−679. Google Scholar
[75]	祝新友, 张志辉, 付旭, 等. 2016. 内蒙古赤峰维拉斯托大型锡多金属矿的地质地球化学特征[J]. 中国地质, 43(1): 188−208. doi: 10.3969/j.issn.1000-3657.2016.01.014 CrossRef Google Scholar