湖北鸡笼山矽卡岩型金铜矿床铅同位素地球化学研究

Pb Isotope Geochemistry of the Jilongshan skarn-host Au-Cu Deposit in Hubei Province

湖北鸡笼山金铜矿床是长江中下游铁铜金多金属成矿带鄂东南成矿区中典型的矽卡岩矿床,对其成矿物质来源的专门研究相对贫乏。对鸡笼山矽卡岩带的11件黄铁矿、2件方铅矿和2件闪锌矿样品进行了铅同位素分析,结果显示206Pb/204Pb为17.358～18.589,207Pb/204Pb为15.414～15.745,20 8Pb/204Pb为37.956～39.094,矿石铅属异常铅,其单阶段模式年龄(136.3～707.3 Ma)不能代表成矿年龄,但其分布特征反映了铅的多源混合特征。同位素构造模式图上投点的线性分布特征显示了花岗闪长斑岩、矽卡岩、大理岩中的铅同位素演化具有很好的继承性和相应性,但各类铅同位素组成在20 8Pb/204Pb-206Pb/204Pb图上均落在下地壳和地幔之间,指示其具有来自壳幔边界附近的深源的特点。鸡笼山金铜矿床、丰山洞铜钼矿床、城门山铜金矿床、铜绿山铜铁矿床4个相似矿床的铅同位素组成进行对比,显示整体成矿物质来源在主体相似的背景下也具有局部的差异性。

Jilongshan Au-Cu deposit is a typical skarn deposit in the southeastern Hubei metallogenic region of the Middle-Lower Yangtze River Fe-Cu metallogenic belt. Few studies have been made on the ore-forming mate- rial sources of this deposit. Fifteen samples were collected from the Jilongshan deposit for Pb isotope analyses. The ranges of the Pb isotopic compositions are from 17. 358 to 18. 589 for ^206Pb/^204Pb, 15. 414 to 15. 745 for ^207Pb/^204Pb and 37. 956 to 39. 094 for ^208Pb/^204Pb, which are anomalous and their single-stage model ages can- not be used as a criterion for metallogenic epoch. However, the distributing characteristics of the single-stage model ages suggest that the Pb of the ore derives from different sources. The linear distribution of Pb isotope in tectonic model diagram reflects the consistent relation of granodiorite porphyry, skarn, marble and ore, which is also a good proof that the ore-forming materials are partly from the magma. The comparison of the Pb isotopic characteristics of Jilongshan Au-Cu deposit, Fengshandong Cu-Mo deposit, Chengmenshan Cu-Au deposit and Tonglushan Cu-Fe deposit shows that the ore-forming materials of the four deposits have different characteristicsin parts although they are very similar on the whole.