投稿时间：2021-06-29
修订日期：2021-12-28
网络发布日期：2022-03-17
中文摘要:造山带铜镍矿床的地幔源区均经历过不同程度的俯冲交代作用和复杂的源区混染历史,造山带铜镍矿带内大量个体差异的矿床为源区和壳内混染的多样性提供了研究实例。中亚造山带天山-北山地区是中国众多造山带内铜镍矿数量最多、分布最广、总体储量最大的地域,这些矿化岩体普遍体现Nb-Ta亏损、高18O和锆石O-Hf同位素离散的特征,该宏大现象主要源自地幔源区不同比例的俯冲沉积物熔体和低温蚀变洋壳流体的交代改造;造山带铜镍矿床的初始岩浆在地壳尺度内上侵过程中,发生的分离结晶和硅铝质物质混染（AFC过程）,可以造成母岩浆发生硫化物饱和,然而AFC过程触发的硫化物饱和在时间上通常较晚,外源硫加入对岩浆早阶段大规模硫化物熔离是必要的;岩浆演化至晚阶段时,低比例的残余熔体可能经历壳源熔体加入,导致晚阶段矿物（如锆石）同位素组成与全岩成分明显不同。更为重要的是,造山带铜镍矿床的地幔源区具有潜在的高氧逸度特征,碳同位素和氧逸度研究显示还原性碳质物加入导致的岩浆还原作用,可能是造山带有别于板内环境铜镍矿床硫化物饱和的重要机制。总体来说,造山带铜镍矿床不同空间位置和尺度的混染模式和识别特征为:（1）源区混染,以Nb-Ta亏损、氧同位素不均一、O-Hf同位素离散为特征;（2）地壳尺度大规模混染,以多类别元素-同位素体系壳幔差异为特征,其中硅铝质混染以全岩混染为主,外源硫和还原性物质以选择性混染为主;（3）岩浆晚阶段粒间熔体混染,以同一岩相中不同矿物的同位素组成显著差异为特征。这3种模式中仅壳内大规模混染导致的成矿岩浆组分、硫含量以及氧逸度变化,有利于岩浆硫饱和形成不混溶的硫化物熔体;而晚阶段粒间熔体混染记录的地壳信息,不能反映与成矿密切相关的壳源混染事件。混染模式的精细识别为造山带广泛发育的镁铁-超镁铁岩体成矿潜力评价提供了重要的理论依据。
Abstract:The mantle sources of magmatic sulfide deposits in orogenic belts have commonly experienced various subduction-related metasomatism and complicated source contamination. Numerous Ni-Cu deposits with indivi-dual difference in Ni-Cu ore camps of orogenic belts can provide multiple research examples for shallow or crustal contamination. The Permian mafic-ultramafic complexes in the Tianshan-Beishan region of the southern Central Asian Orogenic Belt host the largest Ni-Cu deposit cluster in China. These mineralized intrusions are characterized by Nb-Ta depletion, highly elevated18O and divergent zircon O-Hf isotopes. Such unusual elemental and isotopic compositions are mainly inherited from a source mantle that was modified previously by subducted sediment-derived melts and slab-derived fluids. Fractional crystallization and siliceous crustal assimilation during magma ascending can trigger sulfide saturation. However, such sulfide saturation commonly took place too late in the magma crystallization history to generate the regional deposits, suggesting that the addition of crustal sulfur producing early sulfide saturation are necessary for the formation of significant Ni-Cu deposits. More importantly, magma reduction is most likely an important sulfide saturation mechanism to distinguish the ore genesis of magmatic sulfide deposits in orogenic belt from those within intraplate setting, because of the potential high oxygen fugacity of the mantle source in orogenic belts, as evidenced by magma oxygen fugacity and carbon isotopes.The minor interstitial liquid at late crystallization stage can also be contaminated by crustal melts, which may result in decoupling between late stage mineral（such as zircon） isotope and whole-rock compositions. Overall, contamination mechanism of Ni-Cu deposits in orogenic setting is as follows:（1） source contamination,（2） crustal contamination, including siliceous material contamination and crustal sulfur addition, and（3） interstitial contamination at late crystallization stage. The‘crustal character’of zircon formed by interstitial contamination cannot represent the true contamination history, and the subduction recycled materials and continental crust also give complicated information to contamination history. The study for contamination mechanism of magmatic sulfide deposits in orogenic belts will be conducive to improve the understanding of distinguished features for this type of deposit.
keywords:geology source contamination siliceous material contamination crustal sulfur/carbon addition interstitial contamination Ni-Cu deposits in orogenic belt Tianshan-Beishan
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基金项目:国家自然科学基金青年项目和面上项目(编号:41802076、42172076)和重点项目(编号:91855217)联合资助
引用文本：
薛胜超,王庆飞,唐冬梅,毛亚晶,姚卓森.2022.造山带岩浆铜镍硫化物矿床的混染模式——以天山-北山二叠纪铜镍矿为例[J].矿床地质,41(1):1~20XUE Sheng-chao,WANG Qing-fei,TANG Dong-mei,MAO Ya-jing,YAO Zhuo-sen.2022.Contamination mechanism of magmatic Ni-Cu sulfide deposits in orogenic belts: Examples from Permian Ni-Cu deposits in Tianshan-Beishan[J].Mineral Deposits41(1):1~20
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