Characteristics and metallogenic model of the Pulang superlarge porphyry copper deposit in Yunnan,China

Abstract

The westward subduction of the Ganze-Litang Paleo-ocean occurred earliest in the late Early Triassic,and up to the Late Triassic,the plate of the Ganze-Litang Paleo-ocean subducted in a large-scale beneath the Zhongza massif to lead to the formation of the Yidun island arc belt(YIAB).The Pulang porphyry copper deposit is just located at the southern end of YIAB,and is regarded as the typical Triassic porphyry copper deposit in China up to now.The deposit is hosted in a composite intrusion in the form of a stock consisting of quartz diorite porphyry and quartz monzonite porphyry.The host intrusion is quartz monzonite porphyry occupying an area of 1.09 km2.By Re-Os dating for molybdenite and K/Ar,Ar/Ar dating for thermal minerals,such as biotite and orthoclase,and whole rock from the Pulang porphyry copper deposit,the mineralization period of the porphyry copper deposit is determined for the first time.The duration of thermal activity involving patassic silicates(biotite and K-feldspar) alteration ranges from(235.4±2.4) Ma to(221.5±2.0) Ma determined by K-Ar dating.The age of the quartz-molybdenite stage is (～213±3.8) Ma by molybdenite Re-Os dating,the plateau ages(214.58±0.91) Ma to(216.0±1) Ma of the biotite from the main Cu-bearing orebody and Cu-Mo-bearing orebody of the Pulang district are the Late Triassic Norian,consistent with the Re-Os dating.These data suggest that the ore-formation of the Pulang porphyry copper deposit developed in Indosinian.The host intrusion has a distinct alteration zoning from the centre outward,formed the strong silisification zone(locally) →potassic silicate(K-felspar + biotite) zone→phyllic zone→propyllic zone(locally developed illite-carbonate zone).The industrial orebodies are mainly hosted within the zones of potassic silicate and phyllic of the quartz monzonite porphyry.The deposit is of the three-storeyed model which consists of the orebodies with structures of dissaminated at the lower part,veinlet-stockwork at the middle-upper part,and the vein or lode at the top.Up to now,the proved copper resources of the deposit is up to the superlarge scale of copper deposit.The characteristics of the intrusion,element assemblage,and mineralization of the deposit can be compared with the Oyu Tolgoi porphyry copper deposit in Mongolia.