Randgold Resources Ltd. (GOLD) Thursday said it has made a rival offer for Moto Goldmines Ltd. (MGL.T) in a deal that values the gold exploration firm at about CAD546 million ($488 million).

The deal would give it and AngloGold Ashanti Ltd. (AU) access to one of Africa's largest undeveloped mineral resources, the Moto Gold Project in the Democratic Republic of Congo.

Perth, Australia-based Moto in June agreed to a CAD513 million all-share acquisition by Red Back Mining Inc. (RBI.T), another Africa-focused mining firm with operations in Ghana and Mauritania.

"We're very mindful that bidding wars are destructive in Africa. We've put a lot of effort into delivering something that is different and we think significantly superior to what has been proposed to (Moto's) board," Randgold CEO Mark Bristow told Dow Jones Newswires.

Randgold, which is incorporated in the Channel Islands and mines in west Africa, said its offer represents a 7% premium to Moto's share price as of Wednesday and an 11% premium to the price ahead of the Red Back deal being announced.

It said it also has the support of Congo's government, as well as investors representing 36.1% of Moto's shares. That would be enough to block the Red Back transaction, which is subject to the approval of two-thirds Moto's shareholders.

Moto in a statement said it had received the offer.

"The board of directors of Moto are considering the offer to determine whether it is a superior offer to the plan of arrangement that has been agreed with Red Back Mining Inc.," Moto said.

Randgold said it is offering the equivalent of CAD5 a share for Moto, which would be paid with 0.07061 of a Randgold share for each Moto share or a cash alternative. The company could issue as many as 3.9 million shares, it said.

Red Back wasn't immediately available to comment.

Moto's board has backed Red Back's offer and agreed to pay a break fee of CAD15.25 million to the Canadian company in certain circumstances, and has granted Red Back the right to match competing offers.

"In our opinion, Red Back will have to content itself with the $15.3 million break fee," Scotia Capital analyst Trevor Turnbull said in a research note. Randgold's offer "firmly tops" the smaller miner's, he added.

Moto's shares in London closed up 19 pence, or 7.3%, at 273 pence, and Randgold's were down 47 pence, or 1.2%, at 3,824 pence, roughly in line with the sector. AngloGold was down 1.7% at 295.01 rand.

AngloGold, Africa's largest producer of the precious metal, has agreed to part-fund the acquisition in exchange for an indirect 50% stake in Moto, and separately said it will pay $244 million after Randgold closes its deal.

"Our agreement to acquire for cash a 50% joint venture interest on closing enables Randgold Resources to present terms to Moto which make its offer clearly superior to those already offered by Red Back Mining," said AngloGold Chief Executive Mark Cutifani.

-By Robb M. Stewart, Dow Jones Newswires; +27 11 783 7848; robb.stewart@dowjones.com

(Jeffrey Sparshott in London contributed to this article.)