An Isotopic (Sr, Nd and Pb) Tracer Study on the Xiaoxinancha Gold-rich Copper Deposit in Yanbian, China: Implication for the Geodynamic Model of Diagenesis and Metallogenesis

An isotopic study was systemically carried out on the granitic complex, diorite-porphyrite, ores and ore minerals of the 103 Ma Xiaoxinancha gold-rich copper deposit in Jilin province to determine the geodynamic model of diagenesis and metallogenesis. Results show that the initial Nd and Sr isotopic compositions of the granitic complex are in the range of 0.70425–0.70505 for (87Sr/86Sr)i , 0.51243–0.51264 for INd, and –1.31 to +2.64 for εNd(t); those of the diorite-porphyrite are in the range from 0.70438–0.70448 for (87Sr/86Sr)i, 0.51259–0.51261 for INd, and +1.56 to +2.09 for εNd(t). For ores and sulfides, the (87Sr/86Sr)i , INd, and εNd(t) values are in the range from 0.70440–0.70805, 0.51259–0.51279 and +1.72 to +5.56, respectively. The Pb isotopic ratios of the granitic complex range from 18.2992–18.6636 for 206Pb/204Pb, from 15.5343–15.5660 for 207Pb/204Pb, and from 38.1640–38.5657 for 208Pb/204Pb. For diorite-porphyrite, the isotopic ratios of 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb are 18.3919, 15.5794 and 38.3566, respectively, whereas those of the ores and ore sulfides vary from 18.2275–18.3770 for 206Pb/204Pb, from 15.5555–15.5934 for 207Pb/204Pb and from 38.1318–38.3131 for 208Pb/204Pb. The results indicate that the mineralization was correlated to the formation and evolution of the granitic complex and the diorite-porphyrite. Combining with the reported data in petrologic characteristics, elemental geochemistry and chronology, conclusions can be drawn that the geodynamic settings of diagenesis and metallogenesis of this deposit were consistent with the subduction of the Izanagi oceanic plate during the Early Cretaceous. The diorite-porphyrite was formed by the emplacement of the adakitic magma triggered by partial melting of the enriched mantle, which originated from the derivative continental lithospheric mantle metasomatized by dehydration fluids from the subducting oceanic crust. The granitic complex was produced by fractional crystallization of the mixture between the adakitic magma and the high-K calc-alkaline acidic magma, which were generated by the remelting of the lower crust in the course of intraplate upwelling of the adakitic magma. The ore-bearing fluid reservoir convened in a late stage of the evolution of the mixed magma chamber.     

吉林小西南岔金铜矿床流体包裹体及成矿作用研究

该矿床流体包裹体丰富，为２相气液、１相液体、少数含子晶多相和含液态ＣＯ＿２三相包裹体。包裹体液相中富Ｎａ￣＋、Ｃｌ￣－和ＳＯ，气相中Ｈ＿２Ｏ占优势，ＣＯ＿２次之。属ＮａＣｌ－Ｈ＿２Ｏ体系。包裹体同位素分析表明，成矿流体为岩浆水和大气降水的混合流体。在温度高于３６０～４００℃的中性—弱酸性热流体中，Ａｕ和Ｃｕ的络合物呈迁移状态，在温度低的弱酸—酸性的较还原环境下，围岩产生广泛的石英－绢云母化，导致Ａｕ、Ｃｕ络合物分解，沉淀出大量Ａｕ和Ｃｕ。     

吉林省小西南岔金铜矿床稀土元素地球化学特征

小西南岔金铜矿床岩石、矿石及矿物的稀土元素特征表明：成矿作用与海西期闪长岩和燕山期闪长玢岩脉密切相关；矿石及矿物稀土总量北山矿段明显高于南山矿段，显示出成矿作用的地质分带性；不同成矿阶段的石英稀土元素地球化学特征具有明显的差异和变化规律，从早期成矿阶段至主成矿阶段到晚期成矿阶段，稀土配分模式由重稀土富集型→轻稀土富集型→轻稀土明显富集型，铕异常由显著负异常→明显负异常→不明显负异常，ΣＲＥＥ及Ｓｍ／Ｎｄ比值由高到低，ΣＣｅ／ΣＹ及（Ｌａ／Ｓｍ）＿Ｎ比值由小到大。     

Ore-forming mechanism for the Xiaoxinancha Au-rich Cu deposit in Yanbian,Jilin Province,China: Evidence from noble gas isotope geochemistry of fluid inclusions in minerals

The Xiaoxinancha Au-rich copper deposit is one of important Au-Cu deposits along the continental margin in Eastern China. The deposit consists of two sections: the Beishan mine (North), composed of altered rocks with veinlet-dissemination sulfides and melnicovite-dominated sulfide-quartz veins, and the Nanshan mine (South), composed of pyrrhotite-dominated sulfide-quartz veins and pure sulfide veins. The isotope compositions of noble gases extracted from fluid inclusions in ore minerals, i.e. ratios of 3He/4He, 20Ne/22Ne and40Ar/36Ar are in the ranges of 4.45―0.08 Ra, 10.2―8.8 and 306―430, respectively. Fluid inclusions in minerals from the Nanshan mine have higher 3He/4He and 20Ne/22Ne ratios whereas those from the Beishan mine have lower 3He/4He ratios. The analysis of origin, and evolution of the ore fluids and its relations with the ore-forming stages and the ages of mineralization suggests that the initial hydrothermal fluids probably come from the melts generated by partial melting of oceanic crust with the participation of fluids from the mantle (mantle-plume type)/aesthenosphere. This also corresponds to the continental margin settings during the subduction of Izanagi ocaneic plate towards the palaeo-Asian continent (123―102 Ma). The veinlet-dissemination ore bodies of the Beishan mine were formed through replacement and crystallization of the mixed fluids generated by mixing of the ascending high-temperature boiling fluid with young crustal fluid whereas the melnicovite-dominated sulfide-quartz veins were formed subsequently by filling of the high-temperature ore fluid in fissures. Pyrrhotite-dominated sulfide-quartz veins in the Nanshan mine were formed by filling-deposition-crystallization of the moderate-temperature ore fluids and the pure sulfide veins were formed later by filling-deposition-crystallization of ore substance-rich fluids after boiling of the moderate-temperature ore fluids. The metallogenic dynamic processes can be summarized as: (1) formation of fluidand ore substance-bearing Adakitic magma by degassing, dewatering and partial melting during subduction of the Izanagi plate; (2) separation and formation of ore fluids from the Adakitic magma; and (3) success-sive ascending of the ore fluids and final formation of the Au-rich Cu deposit of veinlet-dissemination and vein types by secondary boiling.     

吉林珲春小西南岔金-铜矿床控矿因素研究

小西南岔金-铜矿位于兴蒙造山带东端,其矿化类型可分为大脉型及细脉带型。矿脉空间产出主要受北北西向压扭性断裂构造控制,矿体则由充填于断裂裂隙中的含金-铜石英-多金属硫化物脉及其两侧围岩中的细脉浸染状矿化体构成。断裂构造是控制小西南岔金铜矿床主要的控矿因素,尤其区内北西向断裂构造控制矿体展布,与矿体规模呈正相关关系。区内闪长岩和闪长玢岩脉与成矿关系密切,是矿体直接围岩。矿体赋存在闪长玢岩脉上下盘中和其内部,所以岩浆活动为金、铜成矿提供了物质来源。     

小西南岔金铜矿床地质特征及成因机制

小西南岔金铜矿床产于下古生界五道沟群与华力西晚期闪长岩内接触带中.矿化类型为含金石英硫化物脉型及密集细脉型.矿体受近S-N向断裂、NW向断裂及裂隙构造带控制,矿床成因类型为岩浆热液型.     

吉林小西南岔金-铜矿床成矿流体地球化学特征及矿床成因研究

小西南岔金-铜矿床产于海西期花岗闪长岩-石英闪长岩体之中,其矿化类型以石英大脉及石英细脉带型金-铜矿化为主,局部地段叠加发育有石英脉型辉钼矿化。流体包裹体研究结果表明,矿区金-铜矿脉及辉钼矿脉石英中均主要发育含NaCl子矿物三相、气相-富气相及气液两相三种类型的原生流体包裹体,同类包裹体均一温度、盐度等参数相近,显示两类矿化成矿流体具有相似的地球化学性质,氢-氧同位素研究结果反映它们均主要来源于岩浆热液。辉钼矿Re-Os同位素定年研究表明区内辉钼矿化主要发生于109Ma±,而金-铜矿脉石英的40Ar-39Ar同位素定年结果表明金-铜矿化则主要发生于123.35±0.8Ma。结合矿区已有的岩浆岩年代学研究成果,提出小西南岔矿区金-铜矿化主要与燕山晚期细粒(花岗)闪长岩活动有关,而辉钼矿化则与其后侵位的隐伏花岗斑岩活动有关的认识。     

吉林省小西南岔-农坪金-铜-钨成矿区控矿因素及找矿方向

简要介绍了小西南岔-农坪金-铜-钨成矿区的成矿地质背景及主要矿床的地质特征,重点阐述了控矿因素,分析了区内下古生界五道沟群、华力西晚期至燕山期侵入岩（尤其是浅成侵入体）以及主要断裂构造与成矿作用的关系,指出了该区今后找矿方向.     

延边小西南岔大型富金铜矿床矿区内暗色脉岩的锆石年代学及其地质意义

本文对小西南岔富金铜矿床矿区内与成矿空间密切的成矿前辉绿辉长岩、成矿期闪长玢岩岩脉进行了单颗粒锆石SHRIMP、LAICPMS UPb年龄的测定。实验数据表明：辉绿辉长岩的16个锆石或单点有387.0±11.8Ma、292.0~251.1Ma (加权平均值270±14Ma, n=10)、129.8±2.6 Ma、107.0～95.4Ma（加权平均年龄为103±13Ma,n=3）和46.8±2.6Ma五组谐和年龄; 闪长玢岩的11个锆石、12个单点仅获一组谐和年龄,变化在108～98Ma之间（加权平均值102.1±2.2Ma）。结合CL图像特征,初步厘定成矿前辉绿辉长岩形成于早二叠世晚期（270±14Ma,n=10;273±14Ma,n=6）,岩浆上侵过程中捕获了少量的泥盆世碎屑锆石,在成岩后的早白垩世、新生代始新世中期曾被热液改造;而闪长玢岩则形成于早白垩世晚期。考虑到伴生闪长玢岩的年龄与辉绿辉长岩的107.0～95.4Ma相匹配,且辉绿辉长岩的热液锆石年龄在103~95.4Ma之间,进而限定该富金铜矿床的成矿热事件应发生在108～98Ma,成矿作用发生在晚中生代地壳强烈伸展、减薄作用末期,经晚白垩世—古近世的后期抬升被剥露于现今地表,其成矿滞后于中国东北部晚中生代岩浆热液金矿床大规模成矿峰期（120Ma）约10Ma。     

Two periods of mineralization in Xiaoxinancha Au–Cu deposit,NE China: evidences from the geology and geochronology

The Xiaoxinancha Au–Cu deposit is located at the eastern segment of the Tianshan–Xingmeng orogenic belt in northeast China. The deposit includes porphyry Au–Cu orebodies, veined Au–Cu orebodies and veined Mo mineralizations. All of them occur within the diorite intrusion. The Late Permian diorite, Late Triassic granodiorite, Early Cretaceous granite and granite porphyry are developed in the ore area. The studies on geological features show that the porphyry Au–Cu mineralization is related to the Late Permian diorite intrusion. New geochronologic data for the Xiaoxinancha porphyry Au–Cu deposit yield Permian crystallization zircon U–Pb age of 257 ± 3 Ma for the diorite that hosts the Au–Cu mineralization. Six molybdenite samples from quartz + molybdenite veins imposed on the porphyry Au–Cu orebodies yield an isochron age of 110.3 ± 1.5 Ma. The ages of the molybdenites coeval to zircon ages of the granite within the errors suggest that the Mo mineralization was genetically related to the Early Cretaceous granite intrusion. The formation of the diorite and the related Au–Cu mineralization were caused by the partial melting of the subduction slab during the Late Palaeozoic palaeo‐Asia Ocean tectonic stage. The Re contents and Re–Os isotopic data indicate that the crustal resource is dominated for the Mo mineralization during the Cretaceous extensional setting caused by the roll‐back of the palaeo‐Pacific plate. Copyright © 2014 John Wiley & Sons, Ltd.