Magmatic evolution and genesis of the giant Reko Diq H14-H15 porphyry copper-gold deposit, District Chagai, Balochistan-Pakistan

• Main Author: Razique, Abdul
• Language: English
• Published: University of British Columbia 2013
• Online Access: http://hdl.handle.net/2429/44621

Reko Diq porphyry Cu-Au-Mo deposit in the western Chagai belt, Pakistan, is one of the world’s largest porphyry ore deposits, containing a global resource of 5,900 million metric tons @ 0.41 % Cu and 0.22 g/t Au. The Reko Diq volcanic complex hosts a cluster of eighteen porphyry centers within a NW trending, ~10-long mineralized corridor bounded by the Drana Koh fault system to the north and Tuzgi fault to the south. The western porphyry complex at Reko Diq is linked to a distinct tectono-magmatic event of middle-late Miocene (12.9-11.9 Ma) age, which formed four economic porphyry Cu deposits and remains the focus of this study. The Reko Diq western porphyry deposits are spatially and temporally associated with a series of medium-K calc-alkaline granodiorite and quartz-diorite intrusions forming H79, H15, H14 and H13 deposits, which are spatially distributed from north to south. High Sr/Y and low Y adakitic signature and petrochemical variations in the intrusive rocks suggest normal basalt-andesite-dacite-rhyolite magmas derived from a tholeiitic to calc-alkaline suite arc magma with significant upper crustal interaction. Combination of U-Pb-zircon and Re-Os-molybdenite geochronology and zircon mineral chemistry suggests that a short lived (~1 Ma) fractionated magmatic-hydrothermal system with sustained mafic recharge and efficient hydrothermal fluid flow was involved in the formation of the giant H15 and H14 porphyry deposits. Much of the high-grade (up to 2.0 % Cu and 1.5 g/t Au) Cu-Au mineralization is associated with intense hydrothermal potassic alteration and early quartz “A-type” veins in the early-mineral granodiorite and intra-mineral quartz-diorite intrusions and adjacent host rocks. The main ore-stage potassic alteration is typically associated with high temperature, hypersaline magmatic-hydrothermal fluids. Fluid inclusions with co-existing vapor and brine suggest a boiling phase of two immiscible fluids responsible for the copper ore precipitation. The intensity of potassic alteration and Cu-Fe-sulfide mineralization decreases with the emplacement of late-mineral and late-barren stage quartz-diorite intrusions forming a low grade core in H15 and H14 porphyry deposits. The decline in Cu-Au grades with time is interpreted as a manifestation of the underlying magma chamber depleted in metals and volatiles.