Geological and Geochemical Characteristics of Sharote Copper Deposit Kohistan Island Arc, Gilgit Baltistan

Abstract

This study presents first report on hydrothermal polymetallic ore deposit in the Sharote Valley some 29
km North-West from Gilgit city in the northern Kohistan Island Arc Gilgit Baltistan. The deposit is formed of
extending sulphide veins. The minerals in associated rocks are identified as quartz, biotite, muscovite, epidote,
plagioclase and hornblende amphibole with accessory minerals chlorite, sericite with opaques. The XRF analysis
of investigated rocks shows that the major oxides are Na2O (6.10-6.70 wt. %), CaO (2.73-5.49 wt. %), SiO2 (66.69
68.10 wt. %), Fe2O3 (1.0-3.92 wt. %) Al2O3 (4.55-8.59 wt. %), and K2O (2.1-2.28 wt. %), which indicate that the
associated rock is quartz monzonite which is more Calc-alkaline and less tholeiitic based on AFM diagram. Based
on the analysis of ore samples using Atomic Absorption Spectroscopy, the trace elements Cr, Zn, Co, Pb, Fe, Mn,
Ni, Au, and Ag are investigated. The concentration (Wt.%) of Au, Ag, Cu, Cr, Pb, Ni, Co, Zn are 0.04-0.296, 4.2
42.55, 851.25-20025, 2.25-12.9, 2.1-1105, 0.1-28.25, 78.75-252.5 and 17.45-280.45. Cu shows positive trends
with Co, Cr, Zn, Ag and Pb. These geochemical signatures, petrographic results and field observations show that
sulphide veins dominated by chalcopyrite and bornite, accompanied by secondary azurite and malachite, and
hosted within quartz monzogranite are best interpreted as products of a magmatic-hydrothermal system linked to
the emplacement and crystallization of the granitic intrusion. As magma evolved, metals such as Cu, Au, Pb, and
Fe, along with volatiles (H₂O, S, Cl, and CO₂), became progressively concentrated in the residual melt. Upon
reaching fluid saturation, metal-bearing hydrothermal fluids were exsolved from the crystallizing quartz
monzogranite. These fluids, enriched in Cu–Au complexes, constituted the primary source of the sulphide
mineralization.