Isotope analyses on leads in iron sulfides and trace galenas from two deposits (Big Ledge, British Columbia and Quemont Mine, Quebec) suggest that variations in the isotopic composition may be influenced by postmineralization alteration of ore. It is postulated that when the ore has been subject to regional metamorphism after emplacement, the metamorphism has homogenized the lead isotope ratios throughout the ore body as appears to have happened at Big Ledge, whereas, if postore activity is limited to minor hydrothermal alteration, as at Quemont, then the lead may be left with a wide range of isotopic composition.

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