Mineralization Regularities And Prediction Of Targets Of Porphyry Copper Deposits In East Junggar, Xinjiang, China

The Junggar porphyry copper deposit belt (PCDB), as one of the important part of the huge central Asian PCDB, has good potential to find large copper depodits. Many porphyry copper deposits (PCDs) were discovered in this PCDB recently, however, their research level were lower. Basing on detailed research on metallogenic fluid-structures, alteration, ore and deposit types, and mineralization chronology, mineral deposit models were set up for three typical PCD, includingHersai PCD, Mengxi PCD and Yuleken Halasu PCD in east Junggar in this dissertation. Moreover, regional metallogenic conditions were analyzed, tectonic setting, ore types and spatial distribution of PCD in east Junggar were discussed, and their formation regularity were summarized. Finally, integrated prediction models were proposed and some potential targets for PCD were suggested. Hersai PCD had experienced several stages of magma intrusion, and the sulfide-rich albite porphyry formed in 418Ma was possible late magmatic deposit with some distinct magmatic textures among ore-forming minerals. Formation of granitic porphyries and associated Cu-Mo deposit in the Mengxi district were evidently controlled by fault structures. Four mineralization types including volcanic- sedimentary sulfide mineralization, vein-disseminated mineralization associated with granite porphyry, mineralization related to diorite porphyry and their combination mineralization were recognized in the Mengxi copper deposit. The Mengxi porphyry Cu-Mo deposit was formed at about 411Ma (molybdenite Re-Os age), the ore-forming granitic porphyry has U-Pb age of about 413Ma, the corresponding ore-forming material were derived from magma and mineralization fluids were low salinity hydrothermal solutions. Data of U-Pb age of zircons from mylonitic granodiorite porphyry and Re-Os age of molybdenite from different ore types in Yuleken Halasu PCD show that the Yuleken PCD had gone through reforming and superimposed mineralization. The reforming mineralization related to ductile deformation occurred at about 360-362Ma, while the later post-collision gold and copper mineralization associated with the potassium alteration occurred at about 332Ma.The PCDs in East Junggar were formed in two different tectonic setting, the Halasu porphyry Cu- Au deposit belt was formed in the Sawuer island arc, while the Qiongheba porphyry Cu- Mo belts were formed in continental arc. Basing on ore textures and structures, they can be classified into three types, including Hersai porphyry copper deposit, porphyry copper deposit related to fault structure, and reforming and superimposed PCD. After field surveying, I found that the Hongliuxia ductile shear zone was an oblique thrusting one and cut through the north-western Zhifang ophiolite belt. SIMS U-Pb dating of zircons from granitic ultramylonite showed that the Hongliuxia ductile shear zone was formed at about 343Ma, implying that mineralization later after 343Ma were syn- or post- collision mineralization. Many U-Pb zircon dating indicate that magmatic activity in East Junggar can be divided into four stages: 1) formation of the Yemaquan-Qiongheba continental arc at 460- 400Ma; 2) formation of the Sawuer island arc at 400- 360 Ma; 3) collision between continental arc and island arc between 360- 340 Ma; and 4) post-collision stage at 340- 260Ma.It was suggested that Halasu-Karaxianger and Mengxi-Hersai were two potential large porphyry copper porphyry ore districts with copper resource of about 336 Mt in total, in which nine prospecting targets were predicted.