| 贺兰山北段牛头沟金矿床成矿流体和成矿物质来源:来自H-O-S-Pb同位素的证据 |
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| 引用本文： | 张道涵,魏俊浩,付乐兵,王大钊,刘金科.贺兰山北段牛头沟金矿床成矿流体和成矿物质来源:来自H-O-S-Pb同位素的证据[J].大地构造与成矿学,2017,41(2). |
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| 作者姓名： | 张道涵 魏俊浩 付乐兵 王大钊 刘金科 |
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| 作者单位： | 1. 中国地质大学(武汉)资源学院,湖北武汉,430074;2. 中国地质大学(北京)地球科学与资源学院,北京,100083;3. 宁夏地质工程院,宁夏银川,750021 |
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| 基金项目： | 国家自然科学基金，中央高校基本科研业务费专项基金 |
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| 摘 要： | 贺兰山北段牛头沟金矿床为华北克拉通西北缘新发现的金矿床,包括构造破碎带蚀变岩型和石英脉型两种矿化类型,后者可进一步细分为低缓石英脉型和陡窄石英脉型2个亚类。矿区所有矿体均赋存在古元古界贺兰山群变质杂岩和混合花岗岩内,受主干断裂F_1及其上盘次级断裂体系控制。综合本文及前人研究成果表明,破碎带蚀变岩型石英流体包裹体以纯液相水溶液包裹体为主,而低缓石英脉型和陡窄石英脉型石英流体包裹体则以气液两相水溶液包裹体为主,不同矿化类型成矿流体均为中低温(160~210℃)、中低盐度(6%~12%NaCl_(eq))的H_2O-NaCl流体。对矿区内3种矿化类型石英流体包裹体和硫化物分别开展的H-O和S-Pb同位素研究显示:破碎带蚀变岩型和陡窄石英脉型流体包裹体δD_(H2O)组成相近,分别为-75.2‰~-89.3‰和-87.0‰~-93.8‰,而低缓石英脉型流体包裹体则具有较高的δD_(H2O)值(-45.7‰~-67.7‰);流体包裹体δ~(18)O_(H2O)值则由破碎带蚀变岩型(3.7‰~4.4‰)→低缓石英脉型(1.9‰~3.3‰)→陡窄石英脉型(0.5‰~0.9‰)依次降低。破碎带蚀变岩型和陡窄石英脉型δ~(34)S组成均为正值,分别为1.3‰~6.9‰和2.2‰~5.8‰,而低缓石英脉型则具有较低的δ~(34)S值(-5.1‰~-2.6‰)。低缓石英脉型金矿具有明显不同的δD_(H2O)和δ~(34)S组成,可能与含矿断裂性质及其距离导矿构造F_1断裂较远等因素所共同导致的成矿流体氧逸度升高有关。3种矿化类型对应的矿石均表现出明显富集Th放射成因Pb的特点,~(206)Pb/~(204)Pb(16.467~17.994)和~(207)Pb/~(204)Pb(15.382~15.582)组成相对均一,而~(208)Pb/~(204)Pb变化较大(37.413~42.345)。总体上,石英流体包裹体H-O同位素组成表明成矿流体均为岩浆水和大气降水形成的混合流体,其大气降水比例自破碎带蚀变岩型→低缓石英脉型→陡窄石英脉型依次升高;矿石S-Pb同位素指示成矿物质为深部岩浆和具有高Th/U比的基底围岩双重来源。结合区域构造–岩浆演化,笔者将牛头沟金矿床成矿过程概括为晚古生代裂陷盆地形成阶段、中晚侏罗世区域挤压推覆阶段和晚侏罗世至早白垩世岩浆热液活动阶段等3个阶段。
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| 关 键 词： | 金矿化 流体包裹体 矿床成因类型 矿床成因模式 |
H-O-S-Pb Isotopic Constraints on Sources of the Ore-forming Fluids and Ore Metals in the Niutougou Gold Deposit in Northern Helanshan |
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| ZHANG Daohan,WEI Junhao,FU Lebing,WANG Dazhao,LIU Jinke.H-O-S-Pb Isotopic Constraints on Sources of the Ore-forming Fluids and Ore Metals in the Niutougou Gold Deposit in Northern Helanshan[J].Geotectonica et Metallogenia,2017,41(2). |
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| Authors: | ZHANG Daohan WEI Junhao FU Lebing WANG Dazhao LIU Jinke |
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| Abstract: | The Niutougou gold deposit was recently discovered in the northwestern margin of the North China Craton (NCC). It consists of structurally fractured metasomatic type and quartz vein type ores, and the latter can be further divided into gently dipping and steeply dipping quartz vein subtypes. All of the orebodies are hosted in the Paleoproterozoic Helanshan metamorphic complex and migmatite, and are controlled by main fault F1 with the strike of NNW to NNE direction and its secondary faults. Combining the fluid inclusion results of this and previous studies, fluid inclusions in the quartz from the structurally fractured metasomatic type ores are mainly liquid aqueous inclusions, whereas those from quartz type ores are predominantly two-phase of liquid-rich inclusions. The ore-forming fluids of various ore types are medium-low temperatures (160–210℃) in H2O-NaCl fluid systems with medium-low salinities of 6%–12%NaCleq. H-O isotopic compositions of fluid inclusions in quartz and S-Pb isotopic compositions of sulfides show that the structurally fractured metasomatic type and steeply dipping quartz vein type have similarδDH2Ovalues ranging from?75.2‰ to?89.3‰ and from?87.0‰ to?93.8‰, respectively, while the gently dipping quartz vein has relatively higherδDH2Ovalues of?45.7‰to?67.7‰. Their calculatedδ18OH2Ovalues decrease sequentially from structurally fractured metasomatic type (3.7‰–4.4‰), through gently dipping quartz vein type (1.9‰–3.3‰), to steeply dipping quartz vein type (0.5‰–0.9‰). The ores of structurally fractured metasomatic type and steeply dipping quartz vein type have positiveδ34S values of 1.3‰–6.9‰ and 2.2‰–5.8‰, respectively; whereas the ores of gently dipping quartz vein type have distinctly negativeδ34S values of?5.1‰ to?2.6‰. TheδDH2O andδ34S composition peculiarity of the gently dipping quartz vein type ores may be related to the relatively high oxygen fugacity of ore-forming fluid, which due to either difference of its ore-controlling structures or its deposition site away from the ore-transmitting structure (F1 fault). Sulfides from the three ore types are enriched in the Th-radiogenic Pb, with rather homogeneous 206Pb/204Pb (16.467–17.994) and207Pb/204Pb (15.382–15.582) compositions but a wide range of208Pb/204Pb (37.413–42.345). In general, H-O isotopic compositions of fluid inclusions in quartz from the three different ore types indicate their ore-forming fluids consist of magmatic fluid and paleometeoric water, with the proportion of the latter consistently increase from structurally fractured metasomatic type, through gently dipping quartz vein type, to steeply dipping quartz vein type. S-Pb isotopic compositions of sulfides imply that the ore-forming materials were derived from both the underlying magmatic rocks and their country rocks with high Th/U ratios. Taking the regional tectono-magmatic evolution into consideration, we suggest that the ore-forming process of the Niutougou gold deposit includes three stages, i.e., rift-basin formation stage in the Late Paleozoic, regional compressive thrusting stage in the Late Jurassic, and magmatic-hydrothermal stage in the Late Jurassic to Early Cretaceous. |
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| Keywords: | gold mineralization fluid inclusion ore deposit genesis metallogenic model |
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