Head of communications Alexandra Buck has been appointed as interim managing director while the WIM board searched for a permanent replacement.
Buck is currently head of communications at Asanko Gold and has more than 15 years' experience in investor relations, corporate communications and crisis management in the mining industry.
She started her career at Brunswick, then moved to AngloGold Ashanti and co-founded specialist communications consultancy BuckBias before joining Asanko.
WIM chairman Carole Cable thanked McCulloch for her three-year stewardship, as well as her previous three-year role as head of its international committee.
"Nichole has been a passionate advocate of gender diversity and inclusion and a great ambassador for WIM," she said.