Mining firm OceanaGold has agreed to buy Romarco Minerals for about $CA856 million.
Romarco's shareholders will get roughly a quarter of an OceanaGold share for one of their own.
That equates to 68 Canadian cents per Romarco share, 73 percent above Romarco's closing share price on Wednesday.
Romarco is building an open-pit gold mine in South Carolina, which is expected to produce around 540,000 ounces of gold a year by 2017.
Separately, OceanaGold lost $US1 million in the three months to June, mainly due to changes in the value of hedges and higher costs.
At midday, OceanaGold's shares had fallen 17 percent, down 54 cents to $2.61.