Regis Resources said it won't match a rival US$3.9 billion bid for Vault Minerals made by Genesis Minerals, as a planned merger would no longer meet its thresholds for value and returns.

Regis Resources and Vault Minerals agreed in May to combine in an all-stock merger that valued Vault at roughly A$4.61 a share, equivalent to US$3.21. Last week, that deal was trumped by an offer from Genesis Minerals that valued Vault at roughly A$5.27 a share and was found by Vault directors to be superior to the Regis deal.

"The Regis board concluded that the terms that would be required to match the Genesis proposal do not meet the value and return thresholds that Regis applies to all growth opportunities," Regis said Monday. By merging with Vault, Regis had aimed to become one of Australia's biggest gold stocks, adding scale and relevance in global markets.