Metasomatized Lithospheric Mantle for Mesozoic Giant

https://doi.org/10.1130/G46662.1 Manuscript received 19 June 2019 Revised manuscript received 18 October 2019 Manuscript accepted 21 October 2019 © 2019 The Authors. Gold Open Access: This paper is published under the terms of the CC-BY license. Published online 22 November 2019 Metasomatized lithospheric mantle for Mesozoic giant gold deposits in the North China craton Zaicong Wang1*, Huai Cheng1, Keqing Zong1, Xianlei Geng1, Yongsheng Liu1, Jinhui Yang2, Fuyuan Wu2, Harry Becker3, Stephen Foley4 and Christina Yan Wang5 1 State Key Laboratory of Geological Processes and Mineral Resources (GPMR), School of Earth Sciences, China University of Geosciences, Wuhan 430074, China 2 Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China 3 Institut für Geologische Wissenschaften, Freie Universität Berlin, Berlin 12249, Germany 4 Department of Earth and Environmental Sciences, Macquarie University, North Ryde, NSW 2109, Australia 5 Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China ABSTRACT to designate as crustal metamorphism-related The origin of giant lode gold deposits of Mesozoic age in the North China craton (NCC) is orogenic Au deposits because they formed prior enigmatic because high-grade metamorphic ancient crust would be highly depleted in gold. to 1.8 Ga after high-grade metamorphism of the Instead, lithospheric mantle beneath the crust is the likely source of the gold, which may have crust, which would have been strongly deplet- been anomalously enriched by metasomatic processes. However, the role of gold enrichment ed in gold and fluids (Goldfarb and Santosh, and metasomatism in the lithospheric mantle remains unclear. Here, we present comprehensive 2014; Goldfarb and Groves, 2015). Instead, it data on gold and platinum group element contents of mantle xenoliths (n = 28) and basalts is assumed that the lithospheric mantle of the (n = 47) representing the temporal evolution of the eastern NCC. The results indicate that NCC metasomatized by subducted materials extensive mantle metasomatism and hydration introduced some gold (<1–2 ppb) but did not may have played a key role in the large-scale lead to a gold-enriched mantle. However, volatile-rich basalts formed mainly from the meta- Au mineralization (Goldfarb and Groves, 2015; somatized lithospheric mantle display noticeably elevated gold contents as compared to those Li et al., 2012; Zhu et al., 2015). from the asthenosphere. Combined with the significant inheritance of mantle-derived volatiles However, the extent of gold enrichment in the in auriferous fluids of ore bodies, the new data reveal that the mechanism for the formation SCLM after metasomatism and the mechanism of the lode gold deposits was related to the volatile-rich components that accumulated during and scope of its contribution to giant Au depos- metasomatism and facilitated the release of gold during extensional craton destruction and its have rarely been directly tested. Here, we mantle melting. Gold-bearing, hydrous magmas ascended rapidly along translithospheric present Au and platinum group element (PGE) fault zones and evolved auriferous fluids to form the giant deposits in the crust. contents of the peridotite xenoliths and basalts in the NCC, which reflect different evolution- INTRODUCTION Tassara et al., 2017), including Carlin-type Au ary episodes of the mantle from the Archean The subcratonic lithospheric mantle (SCLM) deposits (sediment-hosted disseminated gold to Cenozoic. This allows us to fully assess the underneath Archean crust mostly formed by deposits) (Muntean et al., 2011). impact of metasomatism on the Au contents of high degrees of partial melting (Griffin et al., Giant Au deposits in the North China craton the SCLM and define the links among mantle 2009). The SCLM is thus refractory and strong- (NCC), which are globally noteworthy for their metasomatism, mantle-derived hydrous magmas, ly depleted in incompatible elements and many large-scale reserves (>5000 tons), are likely the and the origin of giant Au deposits in the NCC. metals like Au, reducing its potential as a source best case in the world to clarify this model. The for later giant deposits. However, magmas and lithospheric mantle of the NCC was intensely SAMPLES fluids derived from the convecting mantle, and metasomatized and hydrated over 2 billion years Primitive alkaline picrites and high-Mg ba- particularly subducted materials, may have by partial melts and subducted components of salts with Mg# of 71–75 were erupted coeval metasomatized and replenished the SCLM in different ages (Paleozoic, Triassic, Jurassic) be- with (125–119 Ma) (Fig. 1), or slightly ear- volatiles, metals, and other elements (e.g., Lo- fore its extensive destruction at ca. 130–120 Ma lier than the peak period of Au mineralization rand et al., 2013; O’Reilly and Griffin, 2013). (Zhu et al., 2012; Wu et al., 2019). The cratonic (Gao et al., 2008; Liu et al., 2008). They have The metasomatized SCLM is often assumed to destruction was essentially coeval with the erup- been extensively studied and are character- be anomalously enriched in Au and to represent tion of mantle-derived magmas and the forma- ized by high volatile contents (e.g., 2–4 wt% the source for the formation of large Au prov- tion of giant lode Au deposits in the eastern water), arc basalt–like trace element patterns, inces (Hronsky et al., 2012; Griffin et al., 2013; NCC (Li et al., 2012; Zhu et al., 2015). These and radiogenic Sr-Nd-Hf-Os isotopic compo- hydrothermal deposits are mostly hosted in am- sitions (referred to hereafter as 130–120 Ma phibolite- to granulite-facies metamorphic rocks basalts; Zhang et al., 2002; Gao et al., 2008; *E-mail: zaicongwang@cug.edu.cn and in Mesozoic felsic plutons. They are difficult Liu et al., 2008; Xia et al., 2013; Meng et al., CITATION: Wang, Z., et al., 2020, Metasomatized lithospheric mantle for Mesozoic giant gold deposits in the North China craton: Geology, v. 48, p. 169–173, https://doi.org/10.1130/G46662.1 Geological Society of America | GEOLOGY | Volume 48 | Number 2 | www.gsapubs.org 169 Downloaded from http://pubs.geoscienceworld.org/gsa/geology/article-pdf/48/2/169/4927129/169.pdf by guest on 30 September 2021 108 0E 112 0 E 116 0 E 120 0E 124 0E 128 0E Venetia peridotites in the Kaapvaal craton (e.g., 42 0N high S contents of 280–1240 ppm and high Au/ Central Asian Orogenic Belt Jianguo 100Ma Figure 1. Sample loca- Pd(N) of >1–13, but Au <0.9–1.4 ppb; Maier et al., Yixian125Ma tions on a simplified map 2012). The Shanwang peridotite xenoliths hosted 420 Sihetun 124Ma of the North China craton in 18 Ma basalts represent juvenile lithospheric (NCC). Analyzed mantle t mantle that formed after the destruction of the Beijing xenoliths and basalts 0 faul 38 N (130–120 Ma and <110 Ma) NCC and Mesozoic Au mineralization (Chu anlu T are shown with eruption et al., 2009). They contain 0.02–1.8 ppb Au and North China ages. Both mantle xeno- show a correlation with PGE contents, similar to 380 Shanwang craton 18Ma liths and basalts from refertilized massif-type peridotites representative Mengyin Hebi and Shanwang are 480Ma of Phanerozoic lithospheric mantle (Figs. 2 and Hebi Fangcheng included. Also shown are 34 0N 4Ma Feixian 125Ma 3; Fig. DR4). 119Ma the major districts of Early Cretaceous lode gold deposits and the trans- 0 34 lithospheric Tanlu fault in Qinling orogen the eastern North China 3 A l 0.13 130-120 Ma basalts craton (modified from Zhu initia Juvenile <110 Ma basalts et al., 2015). Os 0.12 188 Mantle xenoliths / 0.11 Ancient Early Cretaceous gold deposits 2 Os 187 90 92 94 1080 1120 1160 1200 (ppb) Mg# PM Au 1 Kaapvaal xenoliths Massif peridotites 2015; Huang et al., 2017; Geng et al., 2019a, (Figs. DR1–DR3). Such low blanks are es- Ancient Hebi Ancient Mengyin 2019b). They have been well accepted to have sential for analyzing low-Au samples. The Juvenile Shanwang mainly originated from metasomatized, hy- Au and PGE contents and other information 0 02468 drated and isotopically enriched SCLM with about the analyzed samples are given in Tables Al2O3 (wt.%) insignificant input of crustal contamination DR1–DR3, and the main results are shown in B 3 (see details in the GSA Data Repository1). We Figures 2 and 3. analyzed the Au and PGE contents of many 130–120 Ma basalts, and younger basalts that LIMITED RE-ENRICHMENT OF GOLD 2 erupted after the formation of the gold deposits. IN METASOMATIZED MANTLE (ppb) PM The younger basalts erupted later than 110 Ma Gold is more incompatible, and also more Au and are melts derived from the asthenosphere mobile, in fluids than Pd and other PGEs (Maier 1 (Liu et al., 2008; Meng et al., 2015). We used et al., 2012; Pokrovski et al., 2013), and so melt these basalts as a measure for the fraction of and/or fluid metasomatism should elevate the Au/ 0 gold released from the asthenospheric mantle Ir and Pd/Ir ratios of the refractory SCLM, and 0.01 0.11 10 100 compared to the 130–120 Ma basalts, which also Au/Pd, which is a well-documented feature La/Yb (N) were mainly from the metasomatized SCLM. of peridotites (e.g., Fischer-Gödde et al., 2011; C 10 Mantle xenoliths with Archean to Paleopro- Maier et al., 2012). The Mengyin mantle xe- Shanwang terozoic (Hebi and Mengyin) and Phanerozoic noliths hosted by 480 Ma kimberlites, and the 1 (Shanwang) Re depletion model ages (Zheng Hebi mantle xenoliths hosted by 4 Ma basalts, et al., 2005; Chu et al., 2009; Liu et al., 2011) represent the relics of Archean–Paleoproterozoic 0.1 187 188 were also analyzed to assess temporal changes SCLM (low Os/ Osinitial of 0.1089–0.1164, in the Au contents of the SCLM.

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