内蒙古白乃庙金矿含金石英脉LA-ICP-MS锆石U-Pb测年及其地质意义

    LA-ICP-MS zircon U-Pb dating of the gold-bearing quartz veins in the Bainaimiao Au deposit of Inner Mongolia and its geological significance

    • 摘要: 为了厘定内蒙古白乃庙金矿床的成矿时代,对矿区主要含金石英脉中热液蚀变锆石进行了LA-ICP-MS U-Pb测年。结果表明,锆石热液蚀变特征明显,具有清晰的核—幔—边结构,锆石核、幔均为岩浆锆石或变质锆石,热液蚀变增生边呈自形—半自形结构,Th/U值集中于0.2~0.5之间,测年数据为421.4~447.6Ma,认为金矿形成时代为志留纪。从区域成矿规律分析,初步认为白乃庙金矿床的形成与早古生代古亚洲板块向华北地块强烈俯冲引起的构造—岩浆活动密切相关。

       

      Abstract: Cathodoluminescence image (CL) and zircon LA-ICP-MS U-Pb dating techniques were used to study the metallogenic age of the Bainaimiao gold deposit.According to the results obtained, all zircons from the gold-bearing quartz veins show clear core-mantle-rim texture, the core-mantles are of magmatic and metamorphic characteristics,the rims of zircons show the features of hydrothermal zircon with clear core-mantle-rim texture, non-luminescent rim, and euhedral and subhedral crystals, Th/U ratios vary in the range of 0.2~0.5,and the results of the rim dating are 421.4~447.6Ma, suggesting that the Bainaimiao gold deposit formed in Silurian. The ages are accordant to ages of granodiorite porphyry, which has similar zircon core-mantle CL features. It is thus held that the gold deposit was closely related to tectonic-magmatism, post-magmatic hydrothermal activities and durative orogenesis resulting from the intense subduction of Early Paleozoic paleo-Asian oceanic plate towards the northern margin of North China craton.

       

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