The Alteration and Mineralization Characteristics of Miocene Porphyry Cu-Au Deposits of Chagai Magmatic Belt, District Chagai, Balochistan, Pakistan

Abstract

Subduction related Miocene porphyry type deposits are found in the east-west trending Chagai magmatic
belt (CMB) in Pakistan's western margin, Balochistan. This arc exists on the west segment of the Tethyan metallogenic
belt in the south-west of Pakistan. Tethyan metallogenic belt is widely spread over 12,000 km from east to west
direction from Indochina, Tibet, Pakistan, Iran, Turkey and Alpine mountain range in Europe. During the last thirty to
forty years several porphyry deposits have been reported in the Chagai magmatic arc, including the very large Reko
Diq H14-H15, large Saindak, Tanjeel, H35, H8 and medium Dasht-e-Kain porphyry deposits and many small porphyry
copper deposits. These porphyry deposits were developed within the phase of calc-alkaline type magmatism in the
Chagai arc. Tonalite, quartz diorite, and monzonite host the porphyry deposits within the adjacent sedimentary wall
rock units of Sinjrani Volcanic Group, Juzzak, Saindak, and Amalaf Formations. The concentric zonal pattern of
hydrothermal alteration in these porphyry deposits of the Chagai magmatic arc follows the world's major porphyry
deposits' alteration pattern. Zones of hydrothermal alteration from distal to proximal part includes a potassic alteration,
sericitic-clay-chlorite alteration, sericitic alteration, argillic alteration and propylitic alteration. Major ore mineralization
in these deposits is of copper, gold, silver, molybdenum, and minor constituents of other base metals that have been
reported to occur within hydrothermal alteration zones in the Miocene porphyry Chagai magmatic arc.