The formation of Luoboling porphyry Cu-Mo deposit: Constraints from zircon and apatite
The formation of Luoboling porphyry Cu-Mo deposit: Constraints from zircon and apatite
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罗波岭斑岩铜钼矿床的形成：锆石和磷灰石的制约
DOI：
10.1016/j.lithos.2016.12.003
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发表时间：
2017
期刊：
影响因子：
3.5
通讯作者：
Sun Wei-Dong
中科院分区：
文献类型：
--
作者：
Li Cong-ying;Hao Xi-luo;Liu Ji-qiang;Ling Ming-xing;Ding Xing;Zhang Hong;Sun Wei-Dong
罗布岭斑岩铜钼存款属于中国东南部晚白垩世紫金山铜金钼成矿区。罗布岭地区热液蚀变和风化作用强烈，难以采集新鲜的全岩样品进行地球化学和同位素研究。锆石和磷灰石是抵抗热液蚀变的副矿物。本文通过对比分析罗卜岭铜钼存款样品和含矿样品中锆石和磷灰石的微量元素和同位素组成，探讨了矿床的成因。锆石U-Pb LA-ICP-MS测年结果表明，萝卜岭斑岩形成于~ 100 Ma（100.3 ± 1.2Ma、100.6 ± 1.5Ma和98.6 ± 1.2Ma），属紫金山成矿田晚期成矿作用。中辽斑状花岗闪长岩的形成时代与该存款相同（99.5 ± 1.6 Ma）。四方花岗闪长岩的年龄稍老（109.7 ± 0.8Ma）。所有这些锆石颗粒具有高的Ce 4 +/Ce 3+比，表明高的氧逸度。含矿样品的εHf（t）为− 7.3至0.2，表明来源不均匀或两种不同岩浆的混合。有趣的是，贫瘠样品的Hf同位素组成系统性较高（εHf（t）为− 3.6至5.5），这意味着地壳物质的贡献较低。无矿样品（LBL 22 -03和SF 09 -05）磷灰石的OH摩尔百分比约为0.5，高于含矿样品（LBL 20 -01、LBL 20 -02和LBL 22 -02）磷灰石的OH摩尔百分比，表明岩浆中F、Cl含量较低或含水量较高。含矿样品中磷灰石的Sr含量高，表明没有斜长石结晶。与此相反，贫瘠的样品有不同的和较低的Sr，表明磷灰石结晶伴随着斜长石。这些图案是由水含量控制的，因为斜长石的结晶被岩浆中的高含水量抑制。含矿磷灰石的低OH值是由于岩浆中F、Cl含量较高所致。罗卜岭岩体的高氧逸度和高含水量是成矿的有利条件，同时也暗示了它们与板块俯冲作用的密切关系。
The Luobuling porphyry Cu–Mo deposit belongs to the Late Cretaceous Zijinshan Cu–Au–Mo mineralization field in southeastern China. Due to intensive hydrothermal alteration and weathering, it is very difficult to collect fresh whole rock samples for geochemical and isotopic studies in Luobuling. Zircon and apatite are accessory minerals that are resistant to hydrothermal alterations. In this study, we compared the trace element and isotope compositions of zircon and apatite from ore-bearing and barren samples to understand the formation of the Luoboling Cu–Mo deposit. Zircon U–Pb LA-ICP-MS dating shows that the Luoboling porphyries formed at ~ 100 Ma (100.3 ± 1.2 Ma, 100.6 ± 1.5 Ma and 98.6 ± 1.2 Ma), which belongs to the late stage mineralization of the Zijinshan mineralization field. Zhongliao porphyritic granodiorite has the same age as the deposit (99.5 ± 1.6 Ma). The age of barren Sifang granodiorite is slightly older (109.7 ± 0.8 Ma). All these zircon grains have high Ce4+/Ce3+ratios, indicating high oxygen fugacities. The ore-bearing samples show variable εHf(t) of − 7.3 to 0.2, suggesting either heterogeneous sources or mixing of two different magmas. Interestingly, the Hf isotope composition of barren samples is systematically higher (εHf(t) of − 3.6 to 5.5), implying a lower contribution of crustal materials. The OH mole percent of apatite grains from barren samples (LBL22-03 and SF09-05) is ~ 0.5, which is higher than that of apatite from the ore-bearing samples (LBL20-01 LBL20-02 and LBL22-02), indicating lower F, Cl contents or higher water contents in the magma. In apatite from the ore-bearing samples, Sr is high, indicating the absence of plagioclase crystallization. In contrast, barren samples have varied and lower Sr, indicating that apatite crystallization was accompanied by plagioclase. These patterns were controlled by water contents because the crystallization of plagioclase is suppressed by high water contents in magmas. It also suggests that the lower OH of ore-bearing apatite was resulted from higher F, Cl in the magma. High oxygen fugacity and water contents of Luoboling plutons are favorable for mineralization, which also implies their close relations to plate subduction.