Porphyry Characteristics And Metallogenic Significance Of Pulang Porphyry Copper Deposit

The Pulang porphyry complex is located in the southern margin of the Yidun-Zhongdian island arc belt in Yunnan Province, southeastern China, and closely associated with the Pulang porphyry copper deposit. A chronological, petrological and geochemical study has been carried out on the Pulang porphyry complex, with a focus on analysis of its origin and metallogenic significance based on this study.The Pulang porphyry complex is divided into three stages of intrusions based on their contacting relationship and petrological characteristics. The lithologies of the intrusions include quartz dioritic porphyrite formed in the first stage, quartz monzonitic porphyrite in the second stage, and granodioritic porphyrite in the third stage. The crystallization ages of the intrusions were determined by using the single-grain zircon U-Pb method. The single-grain zircon U-Pb isotopic ages are defined as 221.0±1.0 Ma, 211.8±0.5 Ma; and 206.3±0.7 Ma for the first, second and third stages of intrusions, respectively.The porphyry rocks belong to a calc to alkaline series. They have high SiO2 and K2O content, and are rich in Rb, K, and Th, and poor in Nb, Ta, Ti, and Yb. There exist an evolution trend of SiO₂ and K₂O increasing and Al₂O₃, CaO and MgO decreasing in the rocks from early to late. The Sr, Nd isotopic data support derivation of the magma responsible for the formation of the complex from a mixing source of upper mantle with lower crust.The ore host rocks are firstly quartz monzonitic porphyrite, and secondly quartz dioritic porphyrite and granodioritic porphyrite. Compared with the ore-free porphyrites, the ore-bearing porphyrites are higher in magmatophile and mobile elements, and lower in REE, especially LREE, with no evident fractional distillation of REE. The cupper mineralization is associated with replacement of plagioclase by K-feldspar and precipitation of quartz. The peraluminous porphyrites with higher K₂O and lower Na₂O content have larger potential for the formation of porphyry copper deposit.