Uranium-lead dating of hydrothermal zircon and monazite from the Sin Quyen Fe-Cu-REE-Au-(U) deposit, northwestern Vietnam
Uranium-lead dating of hydrothermal zircon and monazite from the Sin Quyen Fe-Cu-REE-Au-(U) deposit, northwestern Vietnam
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越南西北部 Sin Quyen Fe-Cu-REE-Au-(U) 矿床热液锆石和独居石的铀-铅定年
DOI：
10.1007/s00126-017-0746-4
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发表时间：
2018
影响因子：
4.8
通讯作者：
MyDung Tran
中科院分区：
文献类型：
--
作者：
Li Xiao-Chun;Zhou Mei-Fu;Chen Wei Terry;Zhao Xin-Fu;MyDung Tran
越南西北部sinquyen矿床具有Cu、Au和LREE的经济富集和u的亚经济富集。该矿床在新元古代变质岩中赋存块状和带状替代矿石。共生序列包括钠蚀变（阶段1）、钙钾蚀变及其伴生的Fe-REE-(U)矿化（阶段2）、Cu-Au矿化（阶段3）和硫化物（石英-碳酸盐）脉化（阶段4）。仙泉矿床经历了广泛的矿后变质叠印作用，使成矿时代难以精确确定。利用锆石和独居石U-Pb年表和Rb-Sr等时线对成矿时间进行了限定。矿石中的锆石颗粒与II期热液矿物（如石榴石、allanite、hedenbergite）紧密共生或结构伴生。它们可能含有原生流体包裹体，在阴极发光（CL）图像上显示不规则的分带。锆石颗粒富集U (688 ~ 2902 ppm)，贫Th （0.2 ~ 2.9 ppm）。它们的δ 18ov - smow值在11.9 ~ 14.0‰之间，高于典型岩浆锆石。这些结构和成分特征表明，锆石来源于富18o和富u的热液，与II期矿物共生。独居石与II期磁铁矿和allanite密切相关，Th含量低（<2700 ppm），表明热液成因。热液锆石和独居石的U-Pb年龄分别为841±12和836±18 Ma，代表了Fe-REE成矿时间。Cu-Au矿化的时间没有直接的同位素限制，但地质观测表明，Cu-Au和Fe-REE矿石很可能形成于单一的热液演化过程中。在87rb /86Sr vs.87Sr/86Sr图中，大块矿石和从矿石中分离出来的黑云母的组成沿参考线排列30 Ma，与该地区变质作用的时间一致。新曲岩矿床成矿年龄在区域新元古代火成岩的整体年龄范围（740 ~ 860 Ma）内。结合硫化物矿物的岩浆样硫同位素（δ34SV-CDT=−0.8 ~ 3.1），表明成矿作用可能与新元古代火成岩活动有密切的成因联系。
The Sin Quyen deposit in northwestern Vietnam contains economic concentrations of Cu, Au and LREE, and sub-economic concentration of U. In this deposit, massive and banded replacement ores are hosted in Neoproterozoic metapelite. The paragenetic sequence includes sodic alteration (stage I), calcic-potassic alteration and associated Fe-REE-(U) mineralization (stage II), Cu-Au mineralization (stage III), and sulfide-(quartz-carbonate) veins (stage IV). The Sin Quyen deposit experienced an extensive post-ore metamorphic overprint, which makes it difficult to precisely determine the mineralization age. In this study, zircon and monazite U-Pb geochronometers and the Rb-Sr isochron method are used to constrain the timing of mineralization. Zircon grains in the ore are closely intergrown or texturally associated with hydrothermal minerals of stage II (e.g., garnet, allanite, and hedenbergite). They may contain primary fluid inclusions and display irregular zoning in cathodoluminescence (CL) images. Zircon grains are rich in U (688 to 2902 ppm) and poor in Th (0.2 to 2.9 ppm). Their δ18OV-SMOWvalues range from 11.9 to 14.0‰, higher than those of typical magmatic zircon. These textural and compositional features imply that zircon precipitated from18O- and U-rich hydrothermal fluids, coeval with the minerals of stage II. Monazite occurs in close association with stage II magnetite and allanite and has low contents of Th (<2700 ppm), indicative of a hydrothermal origin. Hydrothermal zircon and monazite have indistinguishable U-Pb ages of 841 ± 12 and 836 ± 18 Ma, respectively, representing the timing of Fe-REE mineralization. There is no direct isotopic constraint on the timing of the Cu-Au mineralization, but geological observations suggest that the Cu-Au and Fe-REE ores most likely formed within a single evolved hydrothermal process. In the plot of87Rb/86Sr vs.87Sr/86Sr, the composition of bulk-ore and biotite separates from ore lie along a reference line for 30 Ma, which is consistent with the timing of metamorphism in the region. The mineralization age of the Sin Quyen deposit falls within the overall age range (740 to 860 Ma) of the regional Neoproterozoic igneous rocks. This temporal linkage, in combination with the magmatic-like sulfur isotopes of sulfide minerals (δ34SV-CDT= −0.8 to 3.1), indicates that the mineralization may have a close genetic association with the Neoproterozoic igneous activity.