ISSN 1009-6248CN 61-1149/P 双月刊

主管单位:中国地质调查局

主办单位:中国地质调查局西安地质调查中心
中国地质学会

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    新疆西昆仑孜洛依铁矿床地质特征、形成时代及矿床成因探讨

    Geology, Formation Age, and Genesis of the Ziluoyi Iron Deposit in the Western Kunlun, Xinjiang

    • 摘要: 孜洛依铁矿床是新疆西昆仑塔什库尔干铁矿带北段规模最大的磁铁矿矿床。矿体呈层状、似层状赋存于布伦阔勒群变火山–沉积岩系中,与围岩为整合接触关系。矿石类型以条带状磁铁矿矿石为主,主要发育磁铁矿–阳起石–黑云母、磁铁矿–碳酸盐(方解石+白云石)–黑云母两类矿物组合,与塔什库尔干铁矿带南段矿床的矿石特征存在明显差异。然而,相较于南段矿床已具备较高的研究程度,孜洛依铁矿在地质特征、成矿时代及矿床成因类型等方面的认识仍较为薄弱。笔者对孜洛依铁矿的矿床地质特征进行了详细解剖,并选取与铁矿体整合产出的顶、底板围岩开展锆石U-Pb定年和微量元素分析,旨在约束其形成时代,探讨成矿构造背景与矿床成因类型。根据矿体底板变沉积岩中最年轻碎屑锆石年龄(518±16 Ma)及顶板变英安岩中岩浆锆石的加权平均年龄(504.3±5.9 Ma),首次将矿床的形成时代约束至寒武纪第二世—苗岭世(518~504 Ma)。碎屑锆石年龄峰值分布与变英安岩岩浆锆石的微量元素特征揭示,孜洛依地区布伦阔勒群原岩主要由一套弧火山岩和沉积岩共同组成,其中沉积岩物源主要来自麻扎尔–甜水海地体的大陆弧岩浆物质,整体形成于弧前伸展构造背景。综合成矿时代、构造背景和矿床地质特征分析,认为孜洛依矿床的形成可能与海相火山岩或与海底火山热液系统相关的喷流沉积作用有关。与塔什库尔干铁矿带南段矿床相比,孜洛依矿床可能距离海底火山通道或热液喷口更远,并在铁质沉积后遭受了高绿片岩相变质作用。

       

      Abstract: The Ziluoyi iron deposit is the largest magnetite deposit in the northern segment of the Taxkorgan iron ore belt in the western Kunlun orogen, Xinjiang. Layered and stratoid orebodies are hosted in the meta-volcanic-sedimentary rock series of the Bulunkuole Group and show conformable contacts with host rocks. The magnetite ores feature banded structures with two dominant mineral assemblages of magnetite-actinolite-biotite and magnetite-carbonate (calcite + dolomite)-biotite, showing notable differences in ore characteristics relative to deposits in the southern segment of the Taxkorgan iron-ore belt. Nevertheless, compared with the well-documented deposits in the southern segment, knowledge of the Ziluoyi iron deposit, including its geological features, formation age, and genetic type, is still limited. In this study, the geological features of the Ziluoyi iron deposit are dissected in detail. Zircon U-Pb geochronology and trace-element analyses on hanging-wall and foot-wall rocks conformable with iron orebodies are carried out to constrain their formation age and unravel their tectonic setting and genetic type. Using the youngest detrital zircon age (518±16 Ma) from ore-foot-wall metasedimentary rocks and the weighted-mean magmatic zircon age (504.3±5.9 Ma) from hanging-wall metadacite, the deposit's metallogenic age is constrained to the Cambrian Series 2–Miaolingian (518–504 Ma). Detrital-zircon age-peak patterns and magmatic zircon trace-element signatures from meta-dacite indicate that the protoliths of the Bulunkuole Group in the Ziluoyi area were generated within a fore-arc extensional setting. They predominantly consist of arc volcanic rocks and sedimentary rocks derived from continental-arc magmatic materials of the Mazar-Tianshuihai terrane. Combining its metallogenic age, tectonic setting, and geological characteristics, we suggest that the Ziluoyi deposit originated from exhalative-sedimentary processes linked to marine volcanic rocks or submarine volcanic-hydrothermal systems. Located distally from submarine volcanic conduits or hydrothermal vents, the deposit underwent high-greenschist-facies metamorphism after iron precipitation.

       

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