PETROCHEMISTRY AND PETROGENESIS OF THE MAGMATIC ROCKS OF THE DEXING COPPER AND YINSHAN Cu-Pb-Zn MINES AND ORE-FORMING MECHANISM OF THE RELATED ORE DEPOSITS
德兴铜矿、银山铜铅锌矿床的岩浆岩岩石化学特征及其成岩成矿机理探讨

The Dexing porphyry copper deposit and the Yinshan Cu-Pb-Zn deposit occur to the northwest of the northeastern Jiangxi deep fracture, in a transitional zone between the Jiangnania oldland and the Qiantang depression. The Dexing porphyry copper deposit is genetically re'ated to the Yanshanian hy-pabyssal granodiorite porphyry intrusion (169 Ma), The intrusion is of low-Si sodic magmatic association. Its aluminian parameter AA=Al- (K + Na+ 2Ca)] ranges from -13 to 93, exhibiting the feature of alumina-subsaturation to - unsaturation, and the mafic parameter B (B=Fe + Mg + Ti) ranges from 100 to 265. The functional relation between both displays a trend line of magma-tic evolution with a negative slop, suggesting that the magma originated from the upper mantle or lower crust. The formation of the Yinshan deposit is related to the Yanshanian (145-142 Ma), continental volcanism-subvolcanism, i. e. related to a complete old volcanic apparatus consisting of rhyolitic and dacitic agglomerates, volcanic breccias and tuffs with transitional rock types as well as subvolcanic rocks such as dacite and quartz porphyry formed in the late stage of the volcanic cycle. The volcanic series that is characterized by high Si and K contents has its aluminuian parameter A varying from 7 to 176 and the mafic parameter B from 60 to 120, which show a trend line of magmatic evolution with a positive slope, indicating the magma resulted from anatexis of the sialic crust.The REE and trace elements such as Cu, Pb, Zh, Cr, Ni,Co and U of the magmatic rocks in the two districts are similar in characters,but the contents of Rb and Sr of the magmatic rocks in the Dexing district are consistent with average contents of diorite from Vinogladov (1962),and in the Yinshan district with one of granite.