Geochemical Characteristics of Granodioritefrom Manley-Mandah Cu-Au Metallogenic Belt in South Gobi of Mongolia and Its Geological Significance

The studying area is located in South Gobi and the northern part of East Gobi province of Mongolia, which belongs to Manley-Mandah Cu-Au metallogenic belt of southern Mongolia metallogenic area. The Hercynian granodiorite, granite and Carboniferous-Permian volcanic rocks were occurred in this area, with quartz vein type, porphyry type and alteration-rock type copper-gold mineralization. The nearly EW-direction regional structures control the diagenesis and mineralization, and the granodiorite intrusion is closely related to the origin and temperal-spatial distribution of copper-gold mineralization in this area. The main orebodies are occurred in altered granodiorite. The geochemical results show that these granodiorites have high SiO₂ (61.3%~67.2%), calc-alkaline (Rittman indexes range from 2.07 to 2.34, all samples fall into the calc-alkaline area in AR-SiO₂ diagram), Sr (491×10^-6~631×10^-6) and Sr/Y (42.7~80.9), but they have low Yb (0.8×10^-6~1.2×10^-6) and Y (7.8×10^-6~13×10^-6), with depleted HREE and no obvious negative Eu anomalies, showing the characteristics of adakitic rocks. Based on the regional metallogenetic study, it can be concluded that this area has the potential for prospecting large porphyry copper-gold deposits.