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 magmaticbelt (CMB) in Pakistan's western margin, Balochistan. This arc exists on the west segment of the Tethyan metallogenicbelt in the south-west of Pakistan. Tethyan metallogenic belt is widely spread over 12,000 km from east to westdirection from Indochina, Tibet, Pakistan, Iran, Turkey and Alpine mountain range in Europe. During the last thirty toforty years several porphyry deposits have been reported in the Chagai magmatic arc, including the very large RekoDiq H14-H15, large Saindak, Tanjeel, H35, H8 and medium Dasht-e-Kain porphyry deposits and many small porphyrycopper deposits. These porphyry deposits were developed within the phase of calc-alkaline type magmatism in theChagai arc. Tonalite, quartz diorite, and monzonite host the porphyry deposits within the adjacent sedimentary wallrock units of Sinjrani Volcanic Group, Juzzak, Saindak, and Amalaf Formations. The concentric zonal pattern ofhydrothermal alteration in these porphyry deposits of the Chagai magmatic arc follows the world's major porphyrydeposits' 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 mineralizationin these deposits is of copper, gold, silver, molybdenum, and minor constituents of other base metals that have beenreported to occur within hydrothermal alteration zones in the Miocene porphyry Chagai magmatic arc.