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Geology, Geochemistry, and Geochronology of Gabbro from the Haoyaoerhudong Gold Deposit, Northern Margin of the North China Craton

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Geology, Geochemistry, and Geochronology of Gabbro from the Haoyaoerhudong Gold Deposit, Northern Margin of the North China Craton minerals Article Geology, Geochemistry, and Geochronology of Gabbro from the Haoyaoerhudong Gold Deposit, Northern Margin of the North China Craton Jianping Wang *, Xiu Wang, Jiajun Liu, Zhenjiang Liu, Degao Zhai and Yinhong Wang School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China; [email protected] (X.W.); [email protected] (J.L.); [email protected] (Z.L.); [email protected] (D.Z.); [email protected] (Y.W.) * Correspondence: [email protected]; Tel.: +86-10-8232-2264 Received: 5 December 2018; Accepted: 17 January 2019; Published: 21 January 2019 Abstract: The Haoyaoerhudong gabbro is a mafic intrusion located in the Haoyaoerhudong gold deposit, which is a giant gold deposit (148 t Au) hosted in Proterozoic strata on the northern margin of the North China Craton. In this paper, we present integrated SHRIMP U–Pb, geochemical and Sr–Nd isotopic data from gabbro of the Haoyaoerhudong gold deposit to reveal the magmatic processes behind its origin. SHRIMP zircon U–Pb dating constrains the timing of crystallization of the Haoyaoerhudong gabbro to 278.8 ± 0.81 Ma. Whole-rock geochemical results indicate that the Haoyaoerhudong gabbro has calc-alkaline features with enrichments of large-ion lithophile elements (LILE) and light rare-earth elements (REE) as well as depletions of high-field strength elements 87 86 (HFSE). The relatively high ( Sr/ Sr)i (0.7053 to 0.7078) and low "Nd(t) (−4.6 to −15.1) values of the gabbro indicate the involvement of crustal materials. Low Ce/Pb ratios (1.35 to 7.38), together with nearly constant La/Sm and Th/Yb ratios and variable Ba/Th and Sr/Nd ratios, suggest that the ancient mantle was modified by slab dehydration fluids. Based on new geochemical data and regional geological investigations, we propose that both the Haoyaoerhudong gold deposit and the Haoyaoerhudong gabbro formed in a post-orogenic extensional setting. Keywords: geochemistry; U–Pb zircon age; Sr–Nd isotopes; Haoyaoerhudong gabbro; Inner Mongolia 1. Introduction The North China Craton (NCC) is a well-known Precambrian block in China [1–3]. The amalgamation between the eastern and western blocks ca. 1.85 Ga marked the cratonization process of the NCC [4]. Its northern margin underwent a strong rifting process, forming the Langshan–Zhaertaishan Rift and the Bayan Obo Rift during the Proterozoic era. Affected by the evolution of the Central Asian Orogenic Belt (CAOB), a giant magmatic rock belt formed along the northern margin of the NCC during the Paleozoic era (Figure1) [ 5–8]. Several large orogenic gold deposits, including the Zhulazhaga and Haoyaoerhudong gold deposits, formed during the Paleozoic orogenic process. The Haoyaoerhudong gold deposit is a super large (148 t Au) low-grade deposit in the western part of the NCC. Gold is hosted by pyrite and pyrrhotite, which were mainly deposited on bedding and schistosity planes of the Proterozoic black shales [9]. Hercynian intrusions are common in the Haoyaoerhudong gold district. A small gabbro intrusion is located west of the Haoyaoerhudong gold deposit (called the Haoyaoerhudong gabbro below). Most previous research focused on the gold deposit itself and the granitoids around the deposit [10–14], but little is known about the Haoyaoerhudong gabbro. Minerals 2019, 9, 63; doi:10.3390/min9010063 www.mdpi.com/journal/minerals Minerals 2019, 9, 63 2 of 18 Minerals 2018, 8, x FOR PEER REVIEW 2 of 18 FigureFigure 1.1. (a)(a) Tectonic frameworkframework of China,China, showingshowing thethe locationlocation ofof ((b)b) DistributionDistribution ofof PaleozoicPaleozoic magmaticmagmatic rocks along along the the northern northern margin margin of of the the No Northrth China China Craton Craton (NCC) (NCC) (modified (modified after after [6]). [TC,6]). TC,Tarim Tarim Craton; Craton; YC, YC,Yangtze Yangtze Craton. Craton. MaficMafic rocks,rocks, althoughalthough inin aa smallsmall volumevolume onon the earth’searth’s surface, are very important study subjects toto exploreexplore deepdeep mantlemantle heterogeneity,heterogeneity, crust-mantlecrust-mantle interactionsinteractions [[15],15], andand thethe tectonictectonic propertiesproperties ofof differentdifferent blocksblocks inin ancientancient orogensorogens [[16].16]. The presencepresence of thethe HaoyaoerhudongHaoyaoerhudong gabbro givesgives usus anan opportunityopportunity toto investigate investigate the the composition composition of theof ancientthe ancient mantle, mantle, crust-mantle crust-mantle interaction, interaction, and crustal and differentiationcrustal differentiation [17] of the [17] northern of the marginnorthern of themargin NCC. of We the report NCC. new We data report of whole-rocknew data of geochemistry, whole-rock zircongeochemistry, U–Pb dating, zircon and U–Pb Sr–Nd dating isotopes, and Sr–Nd of the Haoyaoerhudongisotopes of the Haoyaoerhudong gabbro with the gabbro goal of with constraining the goal theof constraining petrogenesis the and petrogenesis timing of the and gabbro timing as well of the as the gabbro geodynamic as well settingas the ofgeodynamic the Permian setting magmatism of the andPermian related magmatism gold mineralization. and related gold mineralization. 2.2. Geological Setting AA “double “double rift” rift” system system developed developed on onthe thenorthern northern margin margin of the of NCC the in NCC the Proterozoic in the Proterozoic era [18]. eraThe [ 18Langshan–Zhaertaishan]. The Langshan–Zhaertaishan Rift (inside) Rift (inside)and the andBayan the BayanObo Rift Obo (o Riftutside), (outside), host gigantic host gigantic thick thickProterozoic Proterozoic rift sediments rift sediments called called the Zhaertai the Zhaertaishanshan and Bayan and Bayan Obo OboGroups, Groups, respectively. respectively. The Thesupracrustal supracrustal succession succession of the of theZhaertaishan Zhaertaishan and and Bayan Bayan Obo Obo Groups Groups are are thought thought to bebe contemporaneouscontemporaneous with differentdifferent typestypes ofof magmatismmagmatism [[19–21].19–21]. CarbonatesCarbonates characterizedcharacterized thethe BayanBayan OboObo RiftRift [[22–24],22–24], whereaswhereas double-peakdouble-peak volcanismvolcanism occurred in the Langshan–ZhaertaishanLangshan–Zhaertaishan Rift [25]. [25]. TheThe giantgiant BayanBayan OboObo REE–Nb–FeREE–Nb–Fe depositdeposit isis locatedlocated inin thethe BayanBayan OboObo Group,Group, andand thethe superlargesuperlarge Langshan–ZhaertaishanLangshan–Zhaertaishan SEDEX (sedimentary exhalative)exhalative) Pb–Zn–Cu–S ore belt (including(including thethe Dongshengmiao,Dongshengmiao, Huogeqi, Tanyaokou, andand JiashengpanJiashengpan oreore deposits)deposits) isis hostedhosted inin thethe ZhaertaishanZhaertaishan Group.Group. Carbonate dikes and bimodal magmatism in indicatedicate that the northern margin of thethe NCCNCC experiencedexperienced rifting in thethe MiddleMiddle Mesoproterozoic,Mesoproterozoic, whichwhich is considered to be the result ofof thethe finalfinal breakupbreakup ofof thethe ColumbiaColumbia Supercontinent Supercontinent [21 [21],], and and induced induced the the formation formation of of the the Bayan Bayan Obo Obo REE–Nb–Fe REE–Nb– depositFe deposit and and the giantthe giant Langshan–Zhaertaishan Langshan–Zhaertaishan SEDEX SE oreDEX belt. ore Alongbelt. Along with the with evolution the evolution of the CAOB, of the theCAOB, northern the northern margin ofmargin the NCC of experiencedthe NCC experienced an orogenic an process orogenic with process strong with tectono-magmatism strong tectono- duringmagmatism the Paleozoic. during the Large Pale volumesozoic. Large of magmatic volumes rocks of magmatic currently rocks crop out currently along the crop northern out along margin the ofnorthern the NCC margin (Figure of the1). NCC Zhang (Figure et al. 1). [ 6 ]Zhang summarized et al. [6] threesummarized important three magmatic important events: magmatic Devonian events: (fromDevonian 400 to(from 360 Ma),400 to late 360 Early Ma), Carboniferouslate Early Carboniferous to Middle Permianto Middle (from Permian 330 to(from 265 Ma),330 to and 265 latest Ma), Permianand latest to Permian Triassic (fromto Triassic 250 to (from 200 Ma). 250 The to most200 Ma striking). The regionalmost striking structure regional is the Solonkerstructure sutureis the zone.Solonker This suture zone, zone. which This is composed zone, which of is ophiolites composed and of olistostromes,ophiolites and isolistostromes, thought to be is thethought remnants to be the remnants of the Paleo-Asian Ocean. Additional information about the regional tectonic evolution is given in references [2,26,27]. Minerals 2019, 9, 63 3 of 18 of the Paleo-Asian Ocean. Additional information about the regional tectonic evolution is given in referencesMinerals 2018 [,2 8,,26 x FOR,27]. PEER REVIEW 3 of 18 The geology of the Haoyaoerhudong gold deposit is similar to the northern margin of the NCC, whichThe is characterizedgeology of the by Haoyaoerhudong Proterozoic strata gold divided deposit by is Paleozoic similar to magmatic the northern rocks. margin The of Bayan the NCC, Obo Groupwhich is exposed characterized in the goldby Proterozoic district include strata the divided Jianshan, by Paleozoic Halahuogete, magmatic and Bilute rocks. formations The Bayan [ 9Obo,14]. TheGroup Bilute exposed Formation, in the gold which district is mainly include composed the Jian ofshan, black Halahuogete, shales (rich and in organic Bilute formations material, with [9,14]. an averageThe Bilute TOC Formation, of 3.4%), is which the major
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