Geochronology and geochemistry of the Shilu Cu–Mo deposit in the Yunkai area, Guangdong Province, South China and its implication
Geochronology and geochemistry of the Shilu Cu–Mo deposit in the Yunkai area, Guangdong Province, South China and its implication
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DOI：
10.1016/j.oregeorev.2014.12.009
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发表时间：
2015-06
影响因子：
3.3
通讯作者：
Wei Zheng;J. Mao;F. Pirajno;Hai-jie Zhao;Cai‐sheng Zhao;Zhihao Mao;Yong-Jian Wang
中科院分区：
文献类型：
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作者：
Wei Zheng;J. Mao;F. Pirajno;Hai-jie Zhao;Cai‐sheng Zhao;Zhihao Mao;Yong-Jian Wang
石路是位于广东省中国南部云开地区的一个大型斑岩夕卡岩型矿床。矿区石鲁花岗岩是与铜矿化成因有关的花岗闪长岩。花岗闪长岩中的斜长石具有带状结构，主要为安山石，少量拉斑玄武岩，而钾长石呈卡尔斯巴德孪生，部分还具有带状结构的特征。花岗闪长岩中的钾长石具有较高的OR含量(87-92wt.%)和少量的Ab(8-13wt.%)，而0-0.3wt.%的值可以忽略不计。黑云母属磁黑云母，具有富镁[镁/(镁+铁)=0.54-0.60]和低铝(平均值=0.11)的特征。角闪石主要为镁角闪石和闪锌矿。石鲁花岗闪长岩的La-ICP-MS锆石U-Pb年龄为107.00±10.7 Ma，与辉钼矿Re-Os年龄104.1±11.3 Ma相吻合。地球化学资料表明，石鲁花岗闪长岩富硅(SiO_2=63.43~65.03%)、富碱(K_2O_3+Na_2O_3=55.45~6.05%)，富钙(CaO_2=94.76~5.1%)。微量元素地球化学结果表明，大离子亲石元素(如Rb、K和Ba)富集，一些高场强元素(如Nb、P、Ta和Ti)亏损。花岗闪长岩稀土元素总量低(∑和REE=200ppm)，具有轻稀土富集性[(La/Yb)N&Gt；9ppm]和中度负Eu异常(Eu/Eu*x=0.83-0.90)的特征。这些矿物学、年代学和地球化学结果表明，石鲁花岗闪长岩具有壳幔混合源，与I型花岗岩具有地球化学亲和力。角闪石的温压测定得出岩浆结晶温度为686-785℃，结晶压力在1.0-2.34kbar之间，转换为3.31-7.71kbar的深度。黑云母温压测量得出的温度和压力相似，分别为680-780℃和0.8-2kbar(深度2.64-6.6公里)。母岩浆的氧逸度很高。石鲁花岗闪长岩具有较低的εNd/t-t值和较高的(87Sr/86Sr)i值，获得了969~1590 Ma的两阶段亏损地幔模式年龄。我们的新资料结合前人的研究表明，花岗闪长岩及其伴生的石鲁铜钼矿床形成于伸展环境，与侏罗纪残余俯冲板片的重熔密切相关。
Shilu is a large porphyry–skarn deposit in the Yunkai district in Guangdong Province, South China. The Shilu granitic intrusion in the mine area is a granodiorite which is genetically related to Cu mineralization. Plagioclase in the granodiorite has a zoned texture and is mainly andesine with minor amounts of labradorite, whereas the K-feldspars exhibit Carlsbad twins and some are also characterized by a zonal texture. K-feldspars from the granodiorite show high contents of Or (87–92 wt.%) with minor Ab (8–13 wt.%) and negligible An value of 0–0.3 wt.%. Biotite can be classified as magnesio-biotite, and is characterized by Mg-rich [Mg/(Mg + Fe) = 0.54–0.60] and AlVI-low (average values = 0.11). Hornblende is chiefly magnesiohornblende and tschermakite. LA-ICP-MS zircon U–Pb age of the Shilu granodiorite is 107 ± 0.7 Ma, which is consistent with molybdenites Re–Os age of 104.1 ± 1.3 Ma. Geochemical data indicate that the Shilu granodiorite is silica-rich (SiO2= 63.43–65.03 wt.%) and alkali-rich (K2O + Na2O = 5.45–6.05 wt.%), as well as calcium-rich (CaO = 4.76–5.1 wt.%). Trace element geochemistry results show enrichments in large ion lithophile elements (e.g., Rb, K, and Ba) and depletions in some high field strength elements (e.g., Nb, P, Ta, and Ti). The total rare earth element (REE) content of the granodioritic rocks is low (∑ REE < 200 ppm), and is characterized by light REE enrichment [(La/Yb)N> 9] and moderately negative Eu anomalies (Eu/Eu* = 0.83–0.90). These mineralogical, geochronological, and geochemical results suggest that the Shilu granodiorite has a mixed crust–mantle source with a geochemical affinity to I-type granitoids. Hornblende thermobarometry yielded magmatic crystallization temperatures of 686–785 °C and crystallization pressures between 1.0 and 2.34 kbar, which is converted to depths in a range of 3.31 to 7.71 km. Biotite thermobarometry yielded similar temperatures and lower pressures of 680–780 °C and 0.8–2 kbar (depth 2.64–6.6 km), respectively. The parent magma had a high oxygen fugacity. The Shilu granodiorite has a relatively low εNd/t–t value and high (87Sr/86Sr)ivalue, and Nd isotopes yield two-stage depleted mantle Nd model ages of 969–1590 Ma. Our new data, combined with previous studies, imply that the granodiorite and the associated Shilu Cu–Mo deposit was formed in an extensional environment, closely related to remelting of residual subducted slab fragments in the Jurassic.