SOURCE OF LEAD IN BASE-METAL AND PRECIOUS -METAL DEPOSITS AND THEIR VOLCANIC HOST-ROCKS FROM THE TERTIARY EPITHERMAL DISTRICT OF W-SARDINIA

Lead isotope analyses have been performed on sulphides and host-rock s amples from the Tertiary auriferous and base-metal epithermal system o f W Sardinia. No lead-isotopic evidence of any filiation or mixing phe nomena between the Tertiary district and the nearly Cambrian metalloge nic province (Iglesiente) has been detected. Lead in Tertiary base-met al and precious ores is interpreted to be derived from mixing processe s between a mantle-derived component and a crustal end-member shown to imprint the Pb isotopic compositions of the studied volcanic rocks.