The origin of giant lode gold deposits of Mesozoic age in the North China craton (NCC) is enigmatic because high-grade metamorphic ancient crust would be highly depleted in gold. Instead, lithospheric mantle beneath the crust is the likely source of the gold, which may have been anomalously enriched by metasomatic processes. However, the role of gold enrichment and metasomatism in the lithospheric mantle remains unclear. Here, we present comprehensive data on gold and platinum group element contents of mantle xenoliths (n = 28) and basalts (n = 47) representing the temporal evolution of the eastern NCC. The results indicate that extensive mantle metasomatism and hydration introduced some gold (<1–2 ppb) but did not lead to a gold-enriched mantle. However, volatile-rich basalts formed mainly from the metasomatized lithospheric mantle display noticeably elevated gold contents as compared to those from the asthenosphere. Combined with the significant inheritance of mantle-derived volatiles in auriferous fluids of ore bodies, the new data reveal that the mechanism for the formation of the lode gold deposits was related to the volatile-rich components that accumulated during metasomatism and facilitated the release of gold during extensional craton destruction and mantle melting. Gold-bearing, hydrous magmas ascended rapidly along translithospheric fault zones and evolved auriferous fluids to form the giant deposits in the crust. INTRODUCTION The subcratonic lithospheric mantle (SCLM) underneath Archean crust mostly formed by high degrees of partial melting (Griffin et al., 2009). The SCLM is thus refractory and strongly depleted in incompatible elements and many metals like Au, reducing its potential as a source for later giant deposits. However, magmas and fluids derived from the convecting mantle, and particularly subducted materials, may have metasomatized and replenished the SCLM in volatiles, metals, and other elements (e.g., Lorand et al., 2013; O’Reilly and Griffin, 2013). The metasomatized SCLM is often assumed to be anomalously enriched in Au and to represent the source for the formation of large Au provinces (Hronsky et al., 2012; Griffin et al., 2013; Tassara et al., 2017), including Carlin-type Au deposits (sediment-hosted disseminated gold deposits) (Muntean et al., 2011). Giant Au deposits in the North China craton (NCC), which are globally noteworthy for their large-scale reserves (>5000 tons), are likely the best case in the world to clarify this model. The lithospheric mantle of the NCC was intensely metasomatized and hydrated over 2 billion years by partial melts and subducted components of different ages (Paleozoic, Triassic, Jurassic) before its extensive destruction at ca. 130–120 Ma (Zhu et al., 2012; Wu et al., 2019). The cratonic destruction was essentially coeval with the eruption of mantle-derived magmas and the formation of giant lode Au deposits in the eastern NCC (Li et al., 2012; Zhu et al., 2015). These hydrothermal deposits are mostly hosted in amphiboliteto granulite-facies metamorphic rocks and in Mesozoic felsic plutons. They are difficult to designate as crustal metamorphism-related orogenic Au deposits because they formed prior to 1.8 Ga after high-grade metamorphism of the crust, which would have been strongly depleted in gold and fluids (Goldfarb and Santosh, 2014; Goldfarb and Groves, 2015). Instead, it is assumed that the lithospheric mantle of the NCC metasomatized by subducted materials may have played a key role in the large-scale Au mineralization (Goldfarb and Groves, 2015; Li et al., 2012; Zhu et al., 2015). However, the extent of gold enrichment in the SCLM after metasomatism and the mechanism and scope of its contribution to giant Au deposits have rarely been directly tested. Here, we present Au and platinum group element (PGE) contents of the peridotite xenoliths and basalts in the NCC, which reflect different evolutionary episodes of the mantle from the Archean to Cenozoic. This allows us to fully assess the impact of metasomatism on the Au contents of the SCLM and define the links among mantle metasomatism, mantle-derived hydrous magmas, and the origin of giant Au deposits in the NCC. SAMPLES Primitive alkaline picrites and high-Mg basalts with Mg# of 71–75 were erupted coeval with (125–119 Ma) (Fig. 1), or slightly earlier than the peak period of Au mineralization (Gao et al., 2008; Liu et al., 2008). They have been extensively studied and are characterized by high volatile contents (e.g., 2–4 wt% water), arc basalt–like trace element patterns, and radiogenic Sr-Nd-Hf-Os isotopic compositions (referred to hereafter as 130–120 Ma basalts; Zhang et al., 2002; Gao et al., 2008; Liu et al., 2008; Xia et al., 2013; Meng et al., *E-mail: zaicongwang@cug.edu.cn Published online 22 November 2019 Downloaded from https://pubs.geoscienceworld.org/gsa/geology/article-pdf/48/2/169/4927129/169.pdf by guest on 14 February 2020 170 www.gsapubs.org | Volume 48 | Number 2 | GEOLOGY | Geological Society of America 2015; Huang et al., 2017; Geng et al., 2019a, 2019b). They have been well accepted to have mainly originated from metasomatized, hydrated and isotopically enriched SCLM with insignificant input of crustal contamination (see details in the GSA Data Repository1). We analyzed the Au and PGE contents of many 130–120 Ma basalts, and younger basalts that erupted after the formation of the gold deposits. The younger basalts erupted later than 110 Ma and are melts derived from the asthenosphere (Liu et al., 2008; Meng et al., 2015). We used these basalts as a measure for the fraction of gold released from the asthenospheric mantle compared to the 130–120 Ma basalts, which were mainly from the metasomatized SCLM. Mantle xenoliths with Archean to Paleoproterozoic (Hebi and Mengyin) and Phanerozoic (Shanwang) Re depletion model ages (Zheng et al., 2005; Chu et al., 2009; Liu et al., 2011) were also analyzed to assess temporal changes in the Au contents of the SCLM. We obtained the gold and PGE contents of bulk rocks of mantle xenoliths (n = 28, three locations; Fig. 1), and 130–120 Ma and <110 Ma basalts (n = 47, seven locations), after Carius tube digestion in reverse aqua regia and chromatography separation (Cheng et al., 2019). The PGE contents were determined by isotope dilution methods, and gold contents were determined by internal standardization to platinum and/or standard addition method (Tables DR1–DR2 in the Data Repository). Reference materials and sample replicates indicated 10%–15% (2 standard deviations) uncertainty for Au, with blanks of 5 ± 5 pg (Figs. DR1–DR3). Such low blanks are essential for analyzing low-Au samples. The Au and PGE contents and other information about the analyzed samples are given in Tables DR1–DR3, and the main results are shown in Figures 2 and 3. LIMITED RE-ENRICHMENT OF GOLD IN METASOMATIZED MANTLE Gold is more incompatible, and also more mobile, in fluids than Pd and other PGEs (Maier et al., 2012; Pokrovski et al., 2013), and so melt and/or fluid metasomatism should elevate the Au/ Ir and Pd/Ir ratios of the refractory SCLM, and also Au/Pd, which is a well-documented feature of peridotites (e.g., Fischer-Gödde et al., 2011; Maier et al., 2012). The Mengyin mantle xenoliths hosted by 480 Ma kimberlites, and the Hebi mantle xenoliths hosted by 4 Ma basalts, represent the relics of Archean–Paleoproterozoic SCLM (low Os/Osinitial of 0.1089–0.1164, high Mg# of > 92; Fig. 2). They have undergone extensive metasomatism, as indicated by highly enriched light rare earth elements (REEs; Zheng et al., 2005), radiogenic Sr/Srinitial, and unradiogenic Nd/Ndinitial (Zhang et al., 2008; Chu et al., 2009). The Mengyin harzburgite xenoliths contain 140–510 ppm S, which is much higher than that for refractory peridotites (Chu et al., 2009), and variably elevated Au/Pd(N) (normalized to the primitive mantle [PM]), indicating the addition of sulfides and gold during metasomatism. However, these samples still contain relatively low Au contents of 0.06–0.50 ppb, as well as low Pd and Cu contents compared to the PM (Fig. 2). This is also true for the Hebi peridotites (La/Yb(N) of 16–38 and Au of 0.03–0.11 ppb; Fig. 2). These results indicate that metasomatism introduced S, but only limited Au, into the SCLM from the Archean to 480 Ma, and even until 4 Ma in the central NCC (Hebi). A similar fashion of Au enrichment also occurred in the Finsch and Venetia peridotites in the Kaapvaal craton (e.g., high S contents of 280–1240 ppm and high Au/ Pd(N) of >1–13, but Au <0.9–1.4 ppb; Maier et al., 2012). The Shanwang peridotite xenoliths hosted in 18 Ma basalts represent juvenile lithospheric mantle that formed after the destruction of the NCC and Mesozoic Au mineralization (Chu et al., 2009). They contain 0.02–1.8 ppb Au and show a correlation with PGE contents, similar to refertilized massif-type peridotites representative of Phanerozoic lithospheric mantle (Figs. 2 and 3; Fig. DR4). 1GSA Data Repository item 2020048, methods, data quality, supplementary notes, Figures DR1– DR10, and Tables DR1–DR3, is available online at http://www.geosociety.org/datarepository/2020/, or on request from editing@geosociety.org. Figure 1. Sample locations on a simplified map of the North China craton (NCC). Analyzed mantle xenoliths and basalts (130–120 Ma and <110 Ma) are shown with eruption ages. Both mantle xenoliths and basalts from Hebi and Shanwang are included. Also shown are the major districts of Early Cretaceous lode gold deposits and the translithospheric Tanlu fault in the eastern North China craton (modified from Zhu et al., 2015). North China craton Qinling orogen Central Asian Orogenic Belt 128 E 0

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华北克拉通中生代巨型金矿床交代岩石圈地幔

华北克拉通（NCC）中生代巨型矿脉金矿床的成因是一个谜，因为高品位变质古地壳将高度枯竭金。相反，地壳下的岩石圈地幔可能是金的来源，金可能通过交代过程异常富集。然而，金在岩石圈地幔中的富集和交代作用仍不清楚。在这里，我们提供了地幔包体（n = 28）和玄武岩（n = 47）的金和铂族元素含量的综合数据，代表了华北克拉通东部的时间演化。结果表明，广泛的地幔交代和水合作用引入了一些金（<1-2 ppb），但没有导致富金地幔。然而，与来自软流圈的玄武岩相比，主要由交代岩石圈地幔形成的富含挥发物的玄武岩显示出明显升高的金含量。结合矿体含金流体中幔源挥发物的显着遗传，新资料揭示矿脉金矿床的形成机制与交代过程中积累并促进金释放的富挥发成分有关。在伸展克拉通破坏和地幔熔化期间。含金的含水岩浆沿着跨岩石圈断层带迅速上升，演化出含金流体，在地壳中形成巨大的矿床。引言 太古宙地壳下方的亚克拉通岩石圈地幔 (SCLM) 主要由高度部分熔融形成 (Griffin et al., 2009)。因此，SCLM 是难熔的，并且在不相容的元素和许多金属（如金）中严重枯竭，降低了其作为后来巨大矿床来源的潜力。然而，来自对流地幔的岩浆和流体，特别是俯冲物质，可能已经交代并补充了 SCLM 中的挥发物、金属和其他元素（例如，Lorand 等，2013；O'Reilly 和 Griffin，2013）。通常认为交代的 SCLM 异常富集 Au 并代表大 Au 省形成的来源（Hronsky 等人，2012 年；Griffin 等人，2013 年；Tassara 等人，2017 年），包括 Carlin-型金矿床（沉积物浸染型金矿床）（Muntean 等人，2011 年）。华北克拉通（NCC）巨型金矿床，以储量大（>5000吨）而享誉全球，可能是世界上最好的案例来阐明这个模型。NCC 的岩石圈地幔在 20 亿年的时间里被不同时代（古生界、三叠纪、侏罗纪）的部分熔融和俯冲成分强烈交代和水化，然后在大约 20 年被广泛破坏。130–120 Ma（朱等人，2012 年；吴等人，2019 年）。克拉通破坏基本上与华北克拉通东部地幔源岩浆的喷发和巨大矿脉金矿床的形成同时发生(Li et al., 2012; Zhu et al., 2015)。这些热液矿床主要位于角闪岩-麻粒岩相变质岩和中生代长英质岩体中。它们在地壳高级变质作用后形成于 1.8 Ga 之前，因此很难被指定为与地壳变质作用相关的造山金矿床，金和流体中的大量消耗（Goldfarb 和 Santosh，2014 年；Goldfarb 和 Groves，2015 年）。相反，假设被俯冲物质交代的华北克拉通岩石圈地幔可能在大规模金矿化中发挥了关键作用（Goldfarb and Groves, 2015; Li et al., 2012; Zhu et al., 2015） . 然而，交代作用后SCLM中金的富集程度及其对巨型金矿床的贡献机制和范围很少被直接测试。在这里，我们展示了 NCC 中橄榄岩包体和玄武岩的 Au 和铂族元素 (PGE) 含量，它们反映了从太古代到新生代地幔的不同演化事件。这使我们能够充分评估交代作用对 SCLM 中金含量的影响，并确定地幔交代作用之间的联系，地幔来源的含水岩浆，以及 NCC 中巨大金矿床的起源。样品 原始碱性苦英岩和 Mg# 为 71-75 的高镁玄武岩与 (125-119 Ma) 同期喷发（图 1），或略早于 Au 矿化的高峰期（Gao 等，2008； Liu 等人，2008 年）。它们已被广泛研究并具有高挥发性含量（例如，2-4 wt% 的水）、弧形玄武岩样微量元素模式和放射性 Sr-Nd-Hf-Os 同位素组成（以下称为 130-120马玄武岩; Zhang et al., 2002; Gao et al., 2008; Liu et al., 2008; Xia et al., 2013; Meng et al., *E-mail: zaicongwang@cug.edu.cn 在线发表2019 年 11 月 22 日 来自 https://pubs.geoscienceworld.org/gsa/geology/article-pdf/48/2/169/4927129/169.pdf 的访客于 2020 年 2 月 14 日下载 170 www.gsapubs。组织| 第 48 卷 2 号 | 地质 | 美国地质学会 2015；黄等人，2017；耿等人，2019a，2019b)。它们已被广泛接受，主要源自交代化、水化和同位素富集的 SCLM，地壳污染的输入微不足道（参见 GSA 数据存储库中的详细信息1）。我们分析了许多 130-120 Ma 玄武岩以及金矿床形成后喷发的年轻玄武岩的 Au 和 PGE 含量。较年轻的玄武岩喷发时间晚于 110 Ma，是来自软流圈的熔体（Liu et al., 2008; Meng et al., 2015）。我们使用这些玄武岩作为衡量从软流圈地幔释放的金与主要来自交代 SCLM 的 130-120 Ma 玄武岩相比的比例。还分析了具有太古宙到古元古代（鹤壁和蒙阴）和显生宙（山旺）稀土耗竭模型年龄（Zheng 等，2005；Chu 等，2009；Liu 等，2011）的地幔包体，以评估SCLM 的 Au 含量。在 Carius 管消化后，我们获得了地幔包体（n = 28，三个位置；图 1）和 130-120 Ma 和 <110 Ma 玄武岩（n = 47，七个位置）的大块岩石的金和 PGE 含量。逆王水和色谱分离（Cheng 等，2019）。PGE 含量通过同位素稀释法测定，金含量通过铂内标和/或标准添加法测定（数据存储库中的表 DR1-DR2）。参考材料和样品复制品表明 Au 的不确定度为 10%–15%（2 个标准偏差），空白为 5 ± 5 pg（图 DR1–DR3）。如此低的空白对于分析低金样品至关重要。表 DR1-DR3 中给出了有关分析样品的 Au 和 PGE 含量以及其他信息，主要结果显示在图 2 和图 3 中。 , 在流体中而不是 Pd 和其他 PGEs (Maier et al., 2012; Pokrovski et al., 2013)，因此熔体和/或流体交代应该提高难熔 SCLM 的 Au/Ir 和 Pd/Ir 比率，并且Au/Pd，这是橄榄岩的一个有据可查的特征（例如，Fischer-Gödde 等人，2011 年；Maier 等人，2012 年）。480 Ma金伯利岩寄宿的蒙阴地幔包体和4 Ma玄武岩寄宿的鹤壁地幔包体，代表了太古宙-古元古代SCLM（低Os/Osinitial 0. 1089–0.1164，高 Mg# > 92；图2）。它们经历了广泛的交代作用，如高富集的轻稀土元素（REEs；Zheng 等，2005）、放射性 Sr/Srinitial 和非放射性 Nd/Ndinitial（Zhang 等，2008；Chu 等，2009）所示）。蒙阴菱镁矿捕虏体含有 140–510 ppm S，远高于耐火橄榄岩（Chu 等，2009），并且不同程度地升高 Au/Pd(N)（标准化为原始地幔 [PM]），表明在交代过程中加入硫化物和金。然而，与 PM 相比，这些样品仍然含有相对较低的 0.06-0.50 ppb 的 Au 含量，以及较低的 Pd 和 Cu 含量（图 2）。鹤壁橄榄岩也是如此（La/Yb(N) 为 16-38，Au 为 0.03-0.11 ppb；图 2）。这些结果表明交代作用引入了 S，但只有有限的 Au，从太古代进入 SCLM 到 480 Ma，甚至在 NCC 中部（鹤壁）直到 4 Ma。在 Kaapvaal 克拉通的 Finsch 和 Venetia 橄榄岩中也发生了类似的 Au 富集方式（例如，280-1240 ppm 的高 S 含量和 >1-13 的高 Au/Pd(N)，但 Au <0.9-1.4 ppb ; Maier 等人，2012 年）。18 Ma 玄武岩中的山旺橄榄岩捕虏体代表了北克拉通和中生代金矿化破坏后形成的年轻岩石圈地幔(Chu et al., 2009)。它们含有 0.02-1.8 ppb Au 并显示出与 PGE 含量的相关性，类似于代表显生宙岩石圈地幔的再肥化地块型橄榄岩（图 2 和图 3；图 DR4）。1GSA 数据存储库项目 2020048、方法、数据质量、补充说明、图 DR1-DR10 和表 DR1-DR3，可在 http://www. geosociety.org/datarepository/2020/，或应editing@geosociety.org 的要求。图 1. 华北克拉通 (NCC) 简化地图上的示例位置。分析的地幔捕虏体和玄武岩（130-120 Ma 和 <110 Ma）显示了喷发年龄。包括鹤壁和山旺的地幔捕虏体和玄武岩。还显示了华北克拉通东部早白垩世矿脉金矿床和跨岩石圈郯庐断裂的主要区域（修改自Zhu et al., 2015）。华北克拉通 秦岭造山带 中亚造山带 128 E 0 包括鹤壁和山旺的地幔捕虏体和玄武岩。还显示了华北克拉通东部早白垩世矿脉金矿床和跨岩石圈郯庐断裂的主要区域（修改自Zhu et al., 2015）。华北克拉通 秦岭造山带 中亚造山带 128 E 0 包括鹤壁和山旺的地幔捕虏体和玄武岩。还显示了华北克拉通东部早白垩世矿脉金矿床和跨岩石圈郯庐断裂的主要区域（修改自Zhu et al., 2015）。华北克拉通 秦岭造山带 中亚造山带 128 E 0