• 主管:

      天津市地质矿产勘查开发局

    • 主办:

      天津地热勘查开发设计院

    • ISSN

      1001-1412  CN 12-1131/P

    班公湖-怒江成矿带东段达翁铜金矿花岗斑岩的年代学、地球化学特征及其地质意义

    Geochronology and Geochemical Characteristics of Granitic Porphyry from the Daweng Cu-Au Deposit in the Eastern Segment of the Bangong-Nujiang Metallogenic Belt and Their Geological Significance

    • 摘要: 达翁铜金矿位于班公湖-怒江成矿带东段,矿区主要出露花岗斑岩、二长岩、正长斑岩,花岗斑岩为含矿岩石,矿区广泛发育绢云母化蚀变,其次是黏土化,局部见碳酸盐化、钾化、硅化蚀变,蚀变呈现围绕中酸性小岩体集中发育的面状分布特征,金属矿化主要有黄铁矿化、黄铜矿化、金矿化、闪锌矿化、赤铁矿化、褐铁矿化。LA-ICP-MS锆石U-Pb测年结果显示,花岗斑岩206Pb/238U加权平均年龄为(116.64±0.68)Ma、(116.90±0.74)Ma,表明岩体形成时代为早白垩世。花岗斑岩成因类型为I型花岗岩,铝饱和指数(A/CNK)平均为1.00,强烈富集大离子亲石元素Rb、Ba,轻微亏损高场强元素Ta、Nb,发育明显的Nb-Ta负异常,Sr显著富集,呈现弱Eu负异常,弱的Ce负异常,显示形成于汇聚板块俯冲构造环境,岩浆体系富挥发分与流体活动,为富水岩浆,具有典型弧岩浆岩地球化学特征。成矿作用与俯冲造山背景下的岩浆热液活动密切相关,推测为班公湖-怒江特提斯洋盆的南向俯冲作用下,由洋壳板片脱水产生的富含水和成矿物质的高氧逸度流体,交代下地壳形成含矿岩体上侵,属于斑岩浅成低温热液成矿系统。

       

      Abstract: The Daweng Cu-Au mineralization occurrence is located in the eastern segment of the Bangong Co-Nujiang metallogenic belt. The mining area mainly exposes granite porphyry, monzonite, and syenite porphyry, with granite porphyry as the ore-bearing rock. Sericitic alteration is widely developed, followed by argillic alteration; locally, carbonatization, potassic alteration, and silicification are also observed. The alteration shows a planar distribution concentrated around small intermediate-acidic intrusions. Metallic mineralization mainly includes pyritization, chalcopyritization, gold mineralization, sphaleritization, hematitization, and limonitization. LA-ICP-MS zircon U-Pb dating yields 206Pb/238U weighted mean ages of (116.64±0.68) Ma and (116.90±0.74) Ma for the granite porphyry, indicating an Early Cretaceous emplacement age. The granite porphyry is genetically classified as I-type granite, with an average aluminum saturation index (A/CNK) of 1.00. It is strongly enriched in large-ion lithophile elements (LILE) Rb and Ba, slightly depleted in high-field-strength elements (HFSE) Ta and Nb with pronounced Nb-Ta negative anomalies, and significantly enriched in Sr, showing weak Eu and Ce negative anomalies. These features indicate formation in a convergent plate subduction tectonic setting; the magma system was volatile-rich and characterized by active fluid circulation, representing a hydrous magma with typical geochemical signatures of arc magmatic rocks. The mineralization is closely related to magmatic-hydrothermal activity in a subduction orogenic setting. We infer that during southward subduction of the Bangong Co-Nujiang Tethys oceanic basin, high-oxygen-fugacity fluids rich in water and ore-forming materials, generated by dehydration of the oceanic slab, metasomatized the lower crust, forming ore-bearing magmas that ascended and emplaced. The mineralization belongs to a porphyry-epithermal metallogenic system.

       

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