Hart’s resignation comes less than a week after the company announced the suspension of two of its three Duketon gold operations in Western Australia in the wake of flooding.

His resignation is effective immediately.

The company said the COO role would be overseen by managing director Mark Clark with help from chairman Nick Giorgetta and non-executive director Frank Fergusson, until a suitable replacement could be found.

No reason was given for Hart’s sudden departure, though the company’s Garden Well mine has grappled with operational issues since it was commissioned in late 2012.

“The board would like to thank Mr Hart for his enormous contribution to the company over the past four-and-a-half years and wishes him the best in his future endeavours,” Regis said.

Hart was elected a director in 2009 along with Clark and Giorgetta as part of a successful board spill.

All three, plus Fergusson, comprised the team behind successful gold miner Equigold, which merged with Lihir Gold in 2008.

The team got back together and have taken Regis from an explorer with a share price of less than 20c to an ASX 100 gold producer with three operating mines and a current market capitalisation of $1.3 billion.

Hart is the company’s eighth-largest shareholder with a 1.9% stake.

Shares in Regis underperformed against its peers, falling 3.8% to $A2.63.