Lead Isotopic Signature of the Hydrothermal Copper Mineralization in Drosh-Shishi Area, Chitral, Kohistan Arc Terrane, Northern Pakistan
Abstract
Copper mineralization in Drosh-Shishi area is a part of the upper crust of Kohistan arc terrane in Chitral, northern Pakistan. It is generally confined to the Gawuch formation in the area. This formation comprises of variably metamorphosed volcanics and sediments intruded by plutons of diorite and granodiorite. Copper mineralization is related to the hydrothermal activity and is mainly associated with altered diorites and quartz veins.
The lead isotopic ratios of three samples of galena from quartz veins in Drosh-Shishi area were determined. 206Pb/204Pb from 18.728 to 18.793, 207Pb/204Pb from 15.658 to 15.728 and 208Pb/204Pb from 39.040 to 39.285. These lead-isotopic ratios yield wide range of model ages of42 to 140 Ma. This mineralization is very young in terms of age and have values of 9.86 to 10.01. The studied galenas have comparable Pb-isotope ratios to that of Rossie-Type veins of USA and Canada and are more radiogenic to the conformable massive sulfides and less radiogenic to Mississippi Valley-Type sulfide deposits. The Lead isotopic data further suggest that the lead in galena may have been derived from the arc volcanics or pelagic sediments of ocean crust of Neo-Tethys or continental crust of Indian plate and may have relation with orogeny.
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