湖北省鸡笼山金铜矿床煌斑岩地球化学、矿物学特征及其地质意义

Geochemistry and Mineralogy of Lamprophyre from the Jilongshan Au-Cu Ore Deposit, Hubei Province, and Its Geological Significance

湖北省鸡笼山金铜矿床位于长江中下游地区铁铜成矿带西部的九瑞矿集区的丰山矿田中。本文对产于鸡笼山岩体北部的煌斑岩脉进行采样,共计5件样品。在对煌斑岩脉样品进行详细镜下岩相学观察后,开展了全岩地球化学分析,并对其中主要造岩矿物角闪石进行了电子探针成分分析。研究表明,鸡笼山煌斑岩为钙碱性煌斑岩,从角闪石基质到斑晶,由早到晚,角闪石由富Mg、Ti端元向富Fe、Al方向演化;计算得知,鸡笼山煌斑岩中角闪石基质温压条件均明显低于角闪石斑晶,煌斑岩形成时的岩浆体系,从早期到晚期,氧逸度逐渐降低;鸡笼山煌斑岩中角闪石的钛含量明显高于有关报道的煌斑岩中角闪石中的钛含量;结合区域构造演化体制,认为煌斑岩的形成受控于古太平洋板块的俯冲作用,引发软流圈地幔上升,继而在上升减压过程中发生了部分熔融作用,从而形成煌斑岩。

The Jilongshan Au-Cu deposit is located in the western part of Jiurui area along the Late Mesozoic Middle–Lower Yangtze River Metallogenic Belt(YRMB),eastern China.The authors collected five samples of lamprophyre dikes from the Jilongshan intrusion.The whole rock geochemical analysis and electron microprobe analysis of amphibole in lamprophyre were conducted based on the systematic observation under the microscope.The results show that the lamprophyres are calc-alkaline lamprophyres,and from matrix to phenocryst,the composition of amphibole varies from Mg-,Ti-rich to Fe-,Al-rich.According to the calculation result,the temperature and pressure of amphibole matrix are lower than those of amphibole phenocryst,and oxygen fugacity decreases from the early stage to late stage.Based on the regional tectonic evolution history and the high Ti content of the amphiboles from the lamprophyres in the Jilongshan deposit,the authors hold that the lamprophyres were controlled by the subduction of paleo-pacific plate,which induced the asthenospheric mantle uprising and partial melting.