陕西柞山地区穆家庄铜矿铅同位素地球化学与成矿物质来源

Lead isotope geochemistry and source of ore materials of the Mujiazhuang copper deposit,Zhashui-Shanyang area,Shaanxi

穆家庄铜矿床位于南秦岭造山带柞(水)山(阳)地区的泥盆系中。矿体产于红岩寺—黑山复式向斜南翼金井河—胡家沟次级背斜南翼近轴部断裂中,赋矿岩石为泥盆系青石垭组中上部白云质岩,其空间展布明显受背斜陡倾南翼(倒转翼)近轴部的层间断裂-裂隙带构造控制,矿石主要有团块状和网脉状,其后生成矿现象非常明显。本文从铅同位素地球化学出发,来探讨产于秦岭泥盆系中铜矿的成矿物质来源和矿床成因等问题。研究表明,穆家庄铜矿矿石铅和近矿围岩岩石铅具有极高的放射性成因铅特点。通过对矿石铅、近矿围岩岩石铅与测定的寒武系碳硅质岩岩石全岩铅进行综合对比,发现它们的组成特征类似,说明穆家庄铜矿铅源来自于寒武系。

The Mujiazhuang copper deposit is located in the Devonian strata in the Zhashui-Shanyang area of the South Qinling orogenic belt. Orebodies occur in a fault near the axial region in the southern limb of the Jinjinghe-Hujiamiao inverted secondary anticline in the southern limb of the Hongyansi-Heishan composite syncline. Host rocks are dolomitic rocks in the middle and upper parts of the Devonian Qingshiya Formation. Their spatial distribution is obviously controlled by an interlayer fracture-fissure zone near the axial region in the steeply dipping southern limb （inverted limb） of an anticline. Ores are dominantly of nodular and stockwork types and the feature of epigenetic mineralization is very pronounced. This paper discusses the sources of ore-forming materials and ore genesis of copper deposits in the Devonian in the Qinling Mountains through a study of lead isotope geochemistry. The lead isotope study shows that ores of the Mujiazhuang copper deposit and the host rocks contain very high radiogenic lead. On the basis of an integrated comparison of ore lead, host rock lead and whole-rock lead in Cambrian carbonaceous-siliceous rocks, it is found that their compositional features are similar, suggesting that lead in the Mujiazhuang copper deposit was derived from the Cambrian.