The Metallogenesis Research Of Yaojialing Zn-Au Polymetallic Deposit In Tongling, Anhui Province

As a typical compound deposit of porphyry, skarn and hydrothermal vein types, theYaojialing Zn-Au polymetallic deposit, located in the east of the Tongling ore depositconcentration area, is closely related to granodiorite porphyry. Field investigation,microscopic observation and geochemical analysis have been carried out on the deposit,with a focus on an analysis of ore deposit characteristics and magmatic-hydrothermalprocesses so as to set up a mode for the formation of the compound deposit of porphyry,skarn and hydrothermal vein types.The following are major achievements obtained in this dissertation.1. Yaojialing intrusion is dated at 141.0±1.7 Ma, showing its formation in the EarlyCretaceous. Emplacement of crust-mantle syntactic magma results in the formation of thisintrusion. Temperature and pressure of the magma crystallization are estimated to be 558 to739℃and 50 to 250 MPa, respectively.2. An evident temporal and spatial zoning exists in the Yaojialing ore deposit. Thereoccur porphyry copper-gold, skarn iron-copper and hydrothermal vein lead-zinc oredeposits in order from deep to shallow. Alteration and mineralization of the Yaojialing oredeposit may be divided into three (early, middle and late) periods, including seven stages.3. The ore-forming fluid has middle-high temperature (200 ~400℃), middle-lowsalinity (1.9~ 23.7%), and pressure (14.4~52.2 MPa), corresponding to depth of 0.53 to1.93km. The early ore-forming fluid is predominated by magmatic water, whereas the lateore-forming fluid is a mixing fluid of magmatic water with meteoric water.4. Carbon, oxygen, sulfur and lead isotopic data of the ores support derivation ofore-forming materials mainly from the crust-mantle syntactic magma. At the same time,lead model ages (138~155 Ma) of ores are close to U-Pb ages (136~166 Ma) of zircongrains from the granodirite porphyry, indicating no difference between metallogenic timeand rock-forming time.5. The Yaojialing ore deposit was formed by a complex process. Rapid emplacement ofthe crust-mantle syntactic magma from deep level to shallow level of crust along fault belt,followed by cooling and crystallization of the magma and replacement of high temperature hydrothermal fluid, is responsible for the formation of the porphyry type deposit in theporphyry. Contact metasomatism and middle-high temperature hydrothermal alteration leadto the formation of skarn type deposit in limestone xenoliths. Late middle-low temperaturehydrothermal filling and replacement result in the formation of the hydrothermal vein typedeposit in interstratified fissures of limestone xenoliths.