UPDATE 1-Iamgold files offer for France's Euro Resources

(Adds details; in U.S. dollars unless noted)

TORONTO, Aug 29 (Reuters) - Mid-tier Canadian gold producer Iamgold Corp (IMG.TO) said on Friday it has filed a cash offer for the rest of Euro Resources (EURR.PA) it does not already own in a bid worth about 71 million euros ($104 million).

Euro Resources currently holds a royalty on production from Iamgold's Rosebel gold mine in Suriname, which the acquisition would effectively eliminate. Based on current gold prices, that would result in a reduction in cash costs at the mine of about $50 an ounce, Iamgold said.

The offer filed in France is for 1.20 euros per share, a premium of about 30 percent over Paris-based Euro Resources' closing price on the Euronext exchange on Thursday.

Iamgold already owns a 4.9 percent stake in Euro Resources, which has about 60.6 million shares outstanding, plus up to 1.9 million shares in potential options.

Euro Resources said it will make its recommendation to shareholders once it has reviewed the full details of the unsolicited bid.

Iamgold said that the offer is expected to open on or about Sept. 17 and is conditional on acceptance by at least 50 percent plus 1 of Euro Resources' shareholders, including its own stake. (Reporting by Leah Schnurr; editing by Rob Wilson)