Concordant baddeleyite and rutile analyses from mineralized Nipissing diabase at Gowganda's Castle mine yield a U–Pb age of [Formula: see text]. Baddeleyite is a primary phase of the diabase; therefore the age dates the magmatic emplacement. The genesis of rutile is less certain: rutile could have formed during an episode of alteration, veining, and Ag mineralization, in which case the U–Pb age would also date the secondary event and demonstrate that Ag mineralization was related to the Nipissing magmatism. However, a primary magmatic origin of the rutile cannot be completely excluded for now; thus the U–Pb age may not constrain the time of Ag mineralization. Further research is needed to clarify this point.