Geochronology and petrogenesis of the Qibaoshan Cu-polymetallic deposit, northeastern Hunan Province: Implications for the metal source and metallogenic evolution of the intracontinental Qinhang Cu-polymetallic belt, South China
Geochronology and petrogenesis of the Qibaoshan Cu-polymetallic deposit, northeastern Hunan Province: Implications for the metal source and metallogenic evolution of the intracontinental Qinhang Cu-polymetallic belt, South China
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湘东北七宝山铜多金属矿床年代学和岩石成因：对华南秦航陆内铜多金属带金属来源和成矿演化的启示
DOI：
10.1016/j.lithos.2018.01.017
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发表时间：
2018-03
期刊：
影响因子：
3.5
通讯作者：
Yabin Yuan
中科院分区：
文献类型：
--
作者：
Shunda Yuan;Jingwen Mao;Panlao Zhao;Yabin Yuan
秦杭成矿带是华南地区新近发现的一条具有重要经济意义的中生代陆内斑岩-矽卡岩型铜多金属成矿带。然而，含矿岩浆的来源和控制QHMB中不同金属组合的主要因素仍然不清楚。七宝山存款矿床是位于青藏高原北方与中部交界处的大型铜金铅锌银铁存款矿床。本文结合新的锆石U-Pb年龄、Hf-O同位素年龄、辉橄榄岩Re-Os年龄和全岩地球化学资料，对七宝山存款含矿斑岩的成矿时代和成因进行了研究。锆石U-Pb和辉橄榄岩Re-Os年龄均为晚侏罗世（152.7 ~ 148.3Ma），表明该存款年龄明显小于以前估计的年龄（227-184 Ma）。七宝山含矿石英斑岩锆石εHf（t）值为负值（−14.8 ~ −5.5），δ 18 O值为8.4 ~ 10.8‰，Mg#值为69.1 ~ 73.0，表明其形成于幔源岩浆注入触发的古地壳部分熔融。两个极端端元混合的锆石Hf-O同位素模拟表明，岩浆源包括约70-80%的改造古地壳成分和约20-30%的亏损地幔成分。与QHMB中其他含矿斑岩相比，七宝山存款的高（Pb + Zn）/Cu值主要来自于壳源物质和相对较低的氧逸度（ΔFMQ −1.8 ~ ΔFMQ +0.8），而Pb、Zn和Ag主要来自于改造后的古地壳。虽然继承新元古代锆石（~800 Ma）的四种分析都具有不同的正εHf（t）值（0.72 ~ 11.21），表明七宝山含矿石英斑岩的形成与新元古代的新生地壳有关，相对较低的氧逸度（ΔFMQ −1.2 ~ ΔFMQ +0.4）表明，这些继承锆石的母岩浆不可能为七宝山铜多金属存款的成矿作用提供重要的金属铜。因此，七宝山铜多金属存款中的金属铜很可能是幔源岩浆注入的产物。由于氧逸度较低的成矿岩浆对Au的溶解度较低，故七宝山存款的大Au矿化可能与该区高背景值的Au有关。结合区域岩石地球化学数据，我们的数据表明，岩浆源对青藏高原矿床中不同金属组合具有一级控制作用。
The recently recognized Qinhang metallogenic belt (QHMB) is an economically important intracontinental Mesozoic porphyry-skarn Cu-polymetallic metallogenic belt in South China. However, the origin of the ore-bearing magma and the major factors controlling the different metal assemblages in the QHMB are still unclear. The Qibaoshan deposit is a large Cu–Au–Pb–Zn–Ag–Fe deposit located at the juncture between the northern and central parts of the QHMB. In this study, new zircon U–Pb ages, Hf–O isotopic data, molybdenite Re–Os ages, and whole-rock geochemical data are combined to constrain the timing of the mineralization and the origin and petrogenesis of the ore-bearing porphyry in the Qibaoshan deposit. The ages obtained from both zircon U–Pb and molybdenite Re–Os dating fall in the Late Jurassic (between 152.7 and 148.3 Ma), revealing that this deposit is significantly younger than previously estimated (227–184 Ma). The Qibaoshan ore-bearing quartz porphyry shows variable negative zircon εHf(t) values (−14.8 to −5.5), high δ18O values (8.4 to 10.8‰), and high Mg#values (69.1 to 73.0), indicating that it formed via the partial melting of ancient crust triggered by the injection of mantle-derived magma. Zircon Hf–O isotopic modeling of the mixing of two extreme endmembers indicates that the magmatic source comprised ~70–80% reworked ancient crustal components and ~20–30% depleted mantle components. Based on comparisons with other ore-bearing porphyries in the QHMB, a magmatic source dominated by crust-derived material and relatively low oxygen fugacities (ΔFMQ −1.8 to ΔFMQ +0.8) was responsible for the high (Pb + Zn)/Cu ratio in the Qibaoshan deposit, and the Pb, Zn and Ag were mainly derived from the reworked ancient crust. Although four analyses of inherited Neoproterozoic zircons (~800 Ma) have variable positive εHf(t) values (0.72 to 11.21), indicating that Neoproterozoic juvenile crust was involved in the formation of the Qibaoshan ore-bearing quartz porphyry, the relatively low oxygen fugacities (ΔFMQ −1.2 to ΔFMQ +0.4) of the parent magma of these inherited zircons suggest that this parent magma could not have provided significant metallic Cu for mineralization in the Qibaoshan Cu-polymetallic deposit. Therefore, the metallic Cu in the Qibaoshan Cu-polymetallic deposit was probably provided by the injection of the mantle-derived magma. Because ore-forming magmas with relatively low oxygen fugacities have low Au solubility, the large Au mineralization in the Qibaoshan deposit may be related to high background values of Au in this area. Our data, integrated with regional petrogeochemical data, indicate that the magmatic source exerted a first-order control on the different metal assemblages in the deposits in the QHMB.
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