235 International Geology Review, Vol. 49, 2007, p. 235–258. Copyright © 2007 by V. H. Winston & Son, Inc. All rights reserved. 0020-6814/07/921/235-24 $25.00 Yulong Deposit, Eastern Tibet: A High-Sulfidation Cu-Au Porphyry Copper Deposit in the Eastern Indo-Asian Collision Zone HOU ZENGQIAN, 1 Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, People’s Republic of China XIE Y ULING, Beijing University of Science and Technology, Beijing 100082, People’s Republic of China XU W ENYI, LI YINQING, Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, People’s Republic of China ZHU XLANGKUN, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, People’s Republic of China KHIN ZAW, Centre for Ore Deposit Research, Centre of Excellence in Ore Deposits, University of Tasmania, GPO Box 252-79, Private Bag 79, Hobart, Tasmania, Australia 7001 G. BEAUDOIN, Universitè Laval, Quèbec City, Quèbec, G1K 7P4, Canada RUI ZONGYAO, Institute of Mineral Resources, CAGS, Beijing 100037, People’s Republic of China HUANG W EI, AND LUOBU CIREN Xizang Bureau of Geology and Mineral Resources, Lhasa, 850000, People’s Republic of China Abstract The Yulong ore body is the largest Cu deposit (6.22 million metric tons [Mt] at 0.99% Cu) in the 300 km long Himalayan porphyry copper belt, and is controlled by major Cenozoic strike-slip faults in the eastern Indo-Asian collision zone. It is associated with a steeply dipping, pipe-like multi- phase (42–35 Ma) monzogranitic stock. The host rocks are potassic calc-alkaline or shoshonitic, and show geochemical affinities with adakites. They appear to have been derived from a thickened lower crustal source in East Tibet. The Yulong deposit consists of a ring-shaped, high-grade Cu-Au zone overlying and/or surround- ing a porphyry-type Cu-Mo ore body. Cu-Mo mineralization produced a steeply dipping, pipe-like, veinlet-disseminated ore body within the stock. Associated hydrothermal alteration produced K-sil- icate and quartz-sericite assemblages within the stock, and contemporaneous propylitic alteration in the Upper Triassic sandy-slate wall rock. Fluid inclusion and δ 18 O-δD data indicate that the ore-forming fluid was supercritical, and exsolved from a high-level magma chamber at >620°C; it then separated into a hypersaline aqueous liquid and a coexisting low-salinity vapor at 340°–600°C. The high-grade Cu-Au zone (3 Mt at 4.74% Cu, and 4.5 g/t Au) is dominated by a supergene chalcocite-malachite blanket resting on an underlying supergene/hypogene sulfide transition unit and a hypogene pyrite-chalcopyrite sulfide unit. The Cu-Au zone was controlled by a subhorizontal or gently outward dipping breccia horizon developed along the marginal fracture zone near the roof of the stock, produced by hydrothermal brecciation due to regional uplift and/or fluid boiling. Alter- ation associated with the hypogene Cu-Au mineralization was texture-destructive advanced argillic alteration, characterized by associations of quartz, kaolinite, dickite, endellite, montmorillonite, hydromica, and minor alunite. It mainly developed within the breccia horizons, and partially over- 1 Corresponding author; e-mail: houzengqian@126.com Downloaded By: [Canadian Research Knowledge Network] At: 22:32 8 April 2009