Timing of hydrothermal activity associated with the Douzhashan uranium-bearing granite and its significance for uranium mineralization in northeastern Guangxi, China
Timing of hydrothermal activity associated with the Douzhashan uranium-bearing granite and its significance for uranium mineralization in northeastern Guangxi, China
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DOI：
10.1007/s11434-013-5986-9
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发表时间：
2013-07
影响因子：
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通讯作者：
Huan Hu;Rucheng Wang;Weifeng Chen;Peirong Chen;H. Ling;Guo-Qi Liu
中科院分区：
文献类型：
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作者：
Huan Hu;Rucheng Wang;Weifeng Chen;Peirong Chen;H. Ling;Guo-Qi Liu
桂东北庙儿山铀(铀)矿田是中国南部重要的花岗岩型铀矿床之一，与斗扎山含铀花岗岩关系密切。斗扎山花岗岩含有原生富铀副矿物，包括独居石(UO2=0.98-1.75wt%)和辉石(UO2=1.48-6.14wt%)。电子探针分析获得原生独居石和辉石的化学年龄分别为231±28 Ma和230±38 Ma，激光烧蚀-电感耦合质谱仪获得U-Pb同位素年龄分别为220±6 Ma和211±7 Ma。这些年龄表明斗扎山花岗岩形成于印支期岩浆活动期。背散射电子成像显示独居石和磷灰石常被蚀变为低铀正长石和磷灰石组合，这与铀在热液中的流失有关。次生磷灰石的U-Th-Pb分析获得了13 6±17 Ma的化学年龄，与中国南部白垩纪-第三纪地壳伸展的时间相对应。我们认为，成矿所需的热量和CO2是燕山期地壳伸展作用的结果，从而触发了斗扎山含铀花岗岩中富铀副矿物的分解。斗扎山花岗岩中的铀再活化作用为花岗岩和/或周围围岩中的成矿提供了物质。因此，印支挤压和燕山期伸展叠加共同作用形成了与斗扎山花岗岩有关的热液铀矿。
The Miaoershan uranium (U) ore field in northeastern Guangxi is one of the important granite-related U deposits in south China and is closely related to the Douzhashan U-bearing granite. The Douzhashan granite contains primary U-rich accessory minerals, including monazite (UO2= 0.98–1.75 wt%) and xenotime (UO2= 1.48–6.14 wt%). Primary monazite and xenotime yield chemical ages of 231 ± 28 Ma and 230 ± 38 Ma by electron microprobe analysis and U-Pb isotopic ages of 220±6 Ma and 211±7 Ma by laser ablation-inductively coupled-mass spectrometry respectively. These ages demonstrate that the Douzhashan granite formed during the period of Indosinian magmatic activity. Back scattered electron imaging shows that monazite and xenotime are commonly altered to assemblages of low-U synchisite and apatite, which was associated with loss of U to hydrothermal fluids. U-Th-Pb analyses of secondary apatite yielded a chemical age of 136 ± 17 Ma, which corresponds to the timing of Cretaceous-Tertiary crustal extension in south China. We suggest that the heat and CO2required for mineralization was the result of Yanshanian crustal extension, and that this triggered the breakdown of U-rich accessory minerals in the Douzhashan U-bearing granite. Uranium remobilization from the Douzhashan granite provided materials for mineralization within the granite and/or surrounding country rocks. Therefore, a combination of Indosinian compression and Yanshanian extensional overprint produced the hydrothermal U deposits associated with the Douzhashan granite.