By Rhiannon Hoyle

Genesis Minerals has made a rival bid for Vault Minerals that values the Australian gold miner at US$3.9 billion, trumping an agreed merger with Regis Resources.

Under the Genesis offer, Vault shareholders would receive 0.7629 new Genesis shares plus 47.5 Australian cents, equivalent to 33.0 U.S. cents, in cash for each Vault share held.

The offer values Vault at A$5.6 billion, or roughly A$5.27 a share, the companies said Monday in separate statements.

Vault said its directors unanimously found the offer to be superior to the all-stock deal with Regis that was agreed in May and valued Vault at roughly A$4.61 a share.

Regis and Vault's planned merger aims to transform the pair into one of Australia's biggest gold stocks, adding scale and relevance in global markets. Regis has five business days to match or beat Genesis's offer, should it choose to do so, Vault said.

There has been a flurry of dealmaking in the gold sector as miners seek to attract investor attention and replace depleting reserves. Vault was itself formed by the 2024 merger of Red 5 and Silver Lake Resources.

Genesis said a combination of its own assets with Vault's would create a gold company with "the profile, management team, scale, liquidity and quality of cash flows sought after by global investors."

Both companies said there would be operational and administrative benefits from combining the businesses. Genesis said it estimates so-called synergies valued at over A$2.0 billion, in big part from sharing infrastructure at their nearby operations.

Under its proposal, Genesis shareholders would own roughly 60% of the enlarged company, with Vault investors holding the remainder. Genesis said it intends to offer Vault shareholders a mix-and-match facility that would enable them to opt for more or less cash or stock, subject to limits.

Write to Rhiannon Hoyle at rhiannon.hoyle@wsj.com