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

Abstract：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.