山西中条山地区篦子沟、南河沟铜矿云母^(40)Ar-^(39)Ar同位素年龄及其对成矿构造背景的约束

Mica^(40)Ar-^(39)Ar isotopic chronology of Bizigou and Nanhegou copper deposit in Zhongtiao Mountain region,Shanxi Province,and its constraint on metallogenic tectonic setting

篦子沟、南河沟铜矿床位于华北克拉通中部造山带南缘,是山西中条山地区胡篦型铜矿的典型代表,因严格受地层控制,呈层状、似层状产出,也被认为是沉积岩型层状铜矿床。这些矿床的成矿年龄仍未被精确测定,成矿时代长期存在争议。在矿床学研究的基础上,对篦子沟、南河沟铜矿内与矿化有关的蚀变黑云母开展了高精度的^(40)Ar-^(39)Ar测年。获得篦子沟铜矿床黑云母^(40)Ar-^(39)Ar坪年龄为1825±13 Ma(MSWD=8.86),对应的等时线年龄为1820±13Ma(MSWD=5.67),反等时线年龄为1820±13 Ma(MSWD=5.63);南河沟黑云母^(40)Ar-^(39)Ar坪年龄为1861±14 Ma(MSWD=8.17),对应的等时线年龄为1864±16 Ma(MSWD=8.31),反等时线年龄为1865±16 Ma(MSWD=8.47)。2个矿床的成矿年龄在误差范围内一致,表明胡篦型铜矿热液期矿化年龄限定在1850 Ma左右。此年龄与中部造山带约1.85 Ga峰期变质和退变质作用时间一致,综合已有研究成果推测,该期成矿事件与碰撞造山事件耦合。区域上,在侵入中条群的基性岩内发育含矿石英脉,对脉内与硫化物伴生的白云母进行^(40)Ar-^(39)Ar定年,获得其坪年龄1851±13 Ma(MSWD=7.47),对应的等时线年龄为1844±19 Ma(MSWD=7.30),反等时线年龄为1844±19 Ma(MSWD=7.28),说明基性岩内的含矿石英脉与矿区内的热液期矿化为同一地质事件的产物,印证了碰撞造山过程中产生的变质流体广泛作用于区域各地质体,且影响范围广泛。

The Bizigou and Nanhegou copper deposits are located in the southern margin of the Trans-North China Orogen of the North China Craton.They are typical of the Hubi type copper deposits in the Zhongtiao Mountain area of Shanxi Province.Because they are controlled by strata and like stratified,they are also considered as the sediment-hosted stratiform copper deposits.However,the mineralization age of these deposits has not been determined and remain controversial.In this paper,high-precision^(40)Ar-^(39)Ar dating of mica in Bizigou and Nanhegou copper deposits was carried out.The plateau age of Bizigou copper deposit sample was 1825±13 Ma(MSWD=8.86),and the corresponding isochron age was 1820±13 Ma(MSWD=5.67),inverse isochron age of 1820±13 Ma(MSWD=5.63).The samples from Nanhegou copper deposit obtained plateau age of 1861±14 Ma(MSWD=8.17),the corresponding isochron age is 1864±16 Ma(MSWD=8.31),and the inverse isochron age is 1865±16 Ma(MSWD=8.47).The mineralization ages of the two deposits are consistent within the error range,indicating that the hydrothermal mineralization time of the Hubi type copper deposit is limited to ca.1850 Ma.This age is consistent with the peak metamorphism and retrometamorphism of ca.1.85 Ga in the Trans-North China Orogen.After that,it was found ore bearing quartz veins were developed in the mafic rocks of Zhongtiao Group.^(40)Ar-^(39)Ar dating of muscovite associated with sulfide in veins obtained the plateau age of 1851±13 Ma(MSWD=7.47),the corresponding isochron ages of 1844±19 Ma(MSWD=7.30)and inverse isochron ages of 1844±19 Ma(MSWD=7.28),indicating that the mineralization is the product of the same geological event as the hydrothermal mineralization in the mining area.It is proved that metamorphic hydrothermal fluid widely acted on geological bodies throughout the region during the collision orogeny.