西秦岭大桥金矿区晚三叠世岩浆活动--锆石U-Pb定年及Lu-Hf同位素证据

    Late Triassic magmatic activity in the Daqiao gold deposit of West Qinling belt: Zircon U-Pb chronology and Lu-Hf isotope evidence

    • 摘要: 西秦岭是中国金矿的重要集中区之一。该区大桥金矿近年已达到超大型规模。最新矿床成因研究认为,成矿可能与矿区岩浆活动有关。矿区采集的4个花岗闪长岩样品LA-ICP-MS锆石U-Pb年龄测试结果主要集中于228Ma、206Ma两组,对应于晚三叠世。相应的Hf同位素组成基本相似,也可分为2个单元。εHft)主体分布在-8~0之间,TDM2主体为1300~1900Ma,推测壳源源区为古-中元古代古老地壳岩石,岩浆主要来源于下地壳古老物质重熔,成岩过程可能有少量地幔组分的参与。结合稀土和微量元素研究结果,认为矿区存在2期印支晚期岩浆活动。大桥金矿可能为西秦岭地区印支晚期晚三叠世区域岩浆活动引发成矿作用的产物。

       

      Abstract: The West Qinling area is one of the important gold ore concentration areas in China. The Daqiao gold deposit, located in the middle of the West Qinling area, has become a superlarge deposit with the growing Au reserves. Recent research reveals that the metallogenic process may be associated with magmatic activity in the area. The zircons LA-ICP-MS U-Pb dating results of 4 granodiorite samples collected in the mining area are concentrated mainly at 228Ma and 206Ma, forming two groups obviously and corresponding to the Late Triassic. The corresponding Hf-isotopic compositions of zircons show similar phenomena and can also be divided into two units. The εHf(t) values are from -8 to 0, and the TDM2 values are from 1300Ma to 1900Ma. It is inferred that the source came from the old crustal rocks of the Paleoproterozoic-Proterozoic period, and most of the ancient lava was derived from remelting process of the old materials, which came from the lower crust, mixed probably with a small amount of mantle components which were involved in diagenetic process. In combination with REE and trace elements researches, the authors hold that there probably existed two phases of magmatic activity in late Indosinian period in the mining area. The Daqiao gold deposit is the product of metallogenic activity caused by regional magmatism in the late Indosinian epoch in West Qinling belt.

       

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