Four zinc-lead showings are known from the Middle Ordovician Bay Fiord and Thumb Mountain formations at Rookery Creek on western Cornwallis Island. Mapping of the Rookery Creek area was updated at 1:50 000 scale. The geology is complex, with four fault sets superimposed on a broad anticlinorium. Three of four showings are at the intersection of a northwest-trending 'fulcrum fault', that forms the western edge of a half graben, with east-trending faults that offset stratigraphic units within the half graben. Despite the existence of three as yet untested areas in which mineralization might be expected, the attractiveness of Rookery Creek as an exploration target is reduced by the lack of a shale aquitard to mineralizing fluids, and by a low Pb/Zn ratio, suggesting a smaller fluid system than was present at Polaris mine. Other areas structurally similar to Rookery Creek and favourable for Zn mineralization, however, may be present elsewhere on the island.