| The Yidun Island Arc Belt (YIAB) is one of the important tectonic units in the archipelagic arc-basin system in the Sanjiang Area (the three rivers: Jinsha, Lanchang, and Nujiang River) , and is also a very important metallogenic belt of the polymetal as copper, lead, zinc, silver, gold, tungsten , tin, molybdenum, and so on, with a great resources potential. For over ten years, under the supporting of the programs granted by the Ministry of the Science & Technology, the Ministry of Land & Resources, and the China Geological Survey, the author conducted the studies about the formation and evolution of YIAB, metallogenic mechanism of the porphyry copper deposits within the Zhongdian Island Arc Belt (ZIAB) with the other scientific researchers including Professors Pan Guitang, Mo Xuanxue, Hou Zengqian, and Zeng Pusheng etc. This paper systematically depicts the characteristics of the Pulang supperlarge porphyry copper deposit in Zhongdian and establish the ore-forming model of the deposit. Furthermore, the author analysis the great copper resources potential of over 10 Mt, and delineate the targets for exploration.The YIAB is the product of the westward subduction of the Ganze-Litang Ocean, one of the four paleo-oceans(i.e., the Changning-Menglian, the Lancangjiang, the Jinshajiang, and the Ganze-Litang) of the Tethyan tectonic domain. The earliest westward subduction formed in Early Triassic (first suggested by this study), up to the Late Triassic, the slab of the Ganze-Litang Ocean dubducted beneath the Massif Zhongza, the slab was split and subducted with different angle for the differences of the fabric of the subducted slab and the varying velocity of subduction. In the north part, for the subduction with a relative rapid velocity and steep angle, there developed the extensional arc, the Changtai Arc, characterized by the intra-arc rift and the backarc basin, resulted in the Kuro-type massive sulfide deposits of Pb-Zn-Cu, and epithermal deposits of Au-Ag-Hg, whereas in the south part, the relative slow subduction with a gentle angle resulted in the compressional arc, the Zhongdian Arc, characterized by the andesitic volcanic rocks and intermediate-acid intrusions and resulted in the formation of the skarn and porphyry deposits. The TIAB experienced several orogenic stages including subduction of oceanic crust (238-208Ma), collision (238-208Ma), extension of the post-collision (138-75Ma), and strike-slip transfer (15-65Ma), each stage exists an individual deposit type.The Pulang porphyry copper deposit is the representative within the Zhongdian volcanic arc, and become one of the most important porphyry copper deposits in China succeed to the Yulong porphyry copper deposit in east Tibet Plateau. The Pulang porphyry copper deposit is consists of the two composite intrusions (blocks) in the north and the south, which represent relatively dependent porphyry copper centers. The two blocks are comprise of a series of quartz diorite porphyry and quartz monzonite porphyry stocks controlled by the NW-trend structures. Of which, the south one is 6.5 km~2 outcropped (contained monzonite of 1.09km~2) and the north one is 1.19km~2. The Pulang porphyry copper deposit was produced during Indosinian, and fill the blank of the Indosinian porphyry copper deposit in China (,different from the those porphyry copper deposits formed during Himalayan in the east Tibet Plateau, such as Gangdese Porphyry Copper Belt or Yulong Porphyry Copper Belt, and from those formed in the paleoasian metallogenic domain during Hercynian such as Tuwu-Yandong porphyry copper belt andthe Yanshanian Dexin porphyry copper belt in East China). By the field geological observation and the dating of the typical objectives of the Pulang district, such as Re-Os dating for molybdenite and K/Ar, Ar/Ar dating for thermal minerals, such as biotite and orthoclase, and whole rock from Pulang Porphyry Copper, the timing of mineralization of porphyry copper has systematically been determined first time. The duration of thermal activity involving patassic silicates (biotite and K-feldspar) alteration is ranging from 235.4±2.4Ma to 221.5±2.0Ma determined by K-Ar dating, and the timing of the quartz-molybdenite stage is — 213±3.8 Ma by molybdenite Re-Os dating, the plateau ages 214.58±0.91Ma to 216.0±1Ma of the biotite separates from the main Cu-bearing orebody and Cu-Mo-bearing orebody of the Pulang district are Late Triassic Norian, consistent with the Re-Os dating.The alteration zoning of the hosted intrusions of the Pulang porphyry copper deposit is distinct: from centre outward, occurring in order the intense silicification zone →K-felspar, biotite zone→quartz, sericite zone→propylitic zone (locally illitite,carbonate minerals developed).The ore body with economic value mainly developed within the K-felspar, biotite zone and quartz, sericite zpne. With a three-layered stair structure of the fmed-grained disseminated, veinlet-stockwork,and the veins, the preliminarily controlled the copper reserves 4.36 Mt with copper of 0.40%, accompanying the gold of 213 t with Au 0.18 g/t.
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