Rare element geochemistry of the Mujiazhuang copper deposit in the Zhashan area, Shaanxi

Abstract：Although mineralization in the Devonian lead-zinc-gold polymetallic metallogenic belt in Qinling is related to hydrothermal exhalation-sedimentation. The Zhashan area is distinguished from the Fengtai area in its having a distinctive copper metallogenic setting. REE geochemical studies of rocks and ores in the Mujiazhuang copper deposit show that the REE compositions and distribution patterns of disseminated lean copper ores and near-ore country rocks are essentially consistent, suggesting that the disseminated lean copper ores represent the product of primary concentration of hydrothermal sedimentary rocks with small amount of sulfide formed by the hydrothermal sedimentary event during the Devonian. During this period the primary source bed of the Mujiazhuang copper deposit formed. Laminated siliceous rocks in country rocks might represent the nature of the Devonian hydrothermal sedimentary rocks. The REE composition of massive rich ores represents the result of fluid hydrothermal activity resulting from extensive continent-continent collisional orogeny. The hydrothermal activity not only modified the primary source bed in situ but also may have brought part of ore substances from other places and deposited them; the deposit was then subjected to modification and concentration at the appropriate structural site. Mujiazhuang copper deposit should be of modified origin.