TORONTO -- Endeavour Mining Corp. is offering to buy Centamin PLC in a stock-swap deal that values the gold miner at roughly $2.5 billion, based on stock values just prior to the announcement.

Endeavour says it made the offer after several unsuccessful attempts to engage with the board of Centamin regarding a possible merger.

Toronto-listed Endeavour, which has gold mines in Africa, is offering 0.0846 of an Endeavour share for each share of Centamin.

Endeavour stock was down about three per cent at $24.90 in early trading while Centamin stock gained nearly 12 per cent to $2.20 at the Toronto Stock Exchange after the offer was disclosed.

Under the deal, Endeavour shareholders would own approximately 52.9 per cent of the combined company while Centamin shareholders would own about 47.1 per cent.

Centamin's principal asset is the Sukari gold mine in Egypt, but the company also has projects in Burkina Faso and Cote d'Ivoire.

Centamin says its board has reviewed the proposal and determined it doesn't adequately reflect the contribution that it would make to the merged company and that it would be better positioned to deliver shareholder returns as an independent firm.

The Endeavour offer follows a friendly deal Monday that saw Chinese company Zijin Mining Group Co. Ltd. buy Continental Gold for $1.4 billion.

Continental is developing the Buritica gold project in Colombia.