Arc-Related Cu–Pb Mineralization in the Hanzal Granite, Kohistan Batholith, Pakistan: Petrological and Geochemical Constraints

Abstract

The Hanzal Cu-Pb polymetallic quartz vein system, emplaced within the Kohistan Batholith of northern Pakistan, constitutes a well-preserved example of arc-related magmatic-hydrothermal mineralization developed in the Kohistan Island Arc during collisional orogenesis. The study area encompasses a composite lithotectonic assemblage of calc-alkaline plutonic rocks (granite to granodiorite), metavolcanic sequences (basalt to basaltic andesite), and metasedimentary units (marble and slate), reflecting a complex magmatic and tectonometamorphic evolution. This study integrates detailed field mapping, petrography, and whole-rock geochemistry to constrain the petrogenetic evolution of the Hanzal granitoids and the metallogenic processes responsible for Cu-Pb mineralization. Ore mineralization is structurally controlled and predominantly confined to quartz veins and veinlet networks, comprising a hypogene sulfide assemblage of chalcopyrite, galena, sphalerite, and pyrite, overprinted by supergene phases including malachite, azurite, hematite, and limonite. Petrographic characteristics indicate that the host intrusions range from monzogranite to granodiorite, dominated by quartz, plagioclase, and K-feldspar, with accessory biotite, muscovite, amphibole, and zircon. Microtextural features, including myrmekitic intergrowths, oscillatory zoning in plagioclase, and brittle deformation of quartz, exhibits progressive magmatic differentiation, syn- to post-emplacement deformation, and pervasive hydrothermal overprinting. Geochemically, the granitoids exhibit calc-alkaline affinity and are interpreted to have originated from partial melting of a metasomatized continental crustal source in a subduction-modified, collision-related tectonic regime. Trace element systematics and compositional variability indicate polyphase magma generation and incremental emplacement, accompanied by fluid exsolution and evolving magmatic-hydrothermal systems. The Cu-Pb mineralization is genetically linked to these magmatic processes, with ore-forming fluids likely derived from late-stage magmatic devolatilization, subsequently modified by fluid-rock interaction and meteoric ingress. The Hanzal system displays key attributes consistent with intrusion-related and porphyry-style mineralization.