UPDATE 1-Silver Wheaton to buy Silverstone Resources

* Silver Wheaton to buy Silverstone for C$190 mln in stock

* Offers 18 pct premium on Silverstone share price

* Deal adds 2.3 mln oz silver, 31,000 oz gold this year

TORONTO, March 12 (Reuters) - Canada's Silver Wheaton Corp SLW.TO said on Thursday it will acquire miner Silverstone Resources Corp SST.V in an all-stock deal valued at C$190 million ($147 million) to strengthen its position as the world's largest silver reseller.

Vancouver, British Columbia-based Silver Wheaton said the transaction would give Silverstone shareholders 0.185 of a Silver Wheaton share for each Silverstone share they own.

Silver Wheaton said the deal is worth C$1.47 per Silverstone share based on its closing stock price of C$7.94 on the Toronto Stock Exchange on Wednesday. It said its offer represents a premium of 18 percent on the closing price Silverstone shares on Wednesday.

Silver Wheaton, which buys silver produced by other mining companies and resells it, said the acquisition will give it additional production of 2.3 million ounces of silver and 31,000 ounces of gold this year.

Silver Wheaton said the deal has the approval of both Silverstone's board and its primary shareholder, Capstone Mining Corp CS.TO, which holds 24 percent of the company.

It said it expects the deal to close by the end of May.

Shares of Silver Wheaton rose 3.78 percent to $8.24 on the Toronto Stock Exchange on Thursday morning.

“This acquisition successfully consolidates the silver streaming industry and adds current production from low-cost, high-quality mines in politically stable jurisdictions,” Silver Wheaton Chief Executive Peter Barnes said.

Silver Wheaton expects its annual silver sales to increase to around 15 million to 17 million ounces in 2009 and to about 30 million ounces by 2013 from 11.1 million ounces in 2008.

$1=$1.29 Canadian Reporting by Claire Sibonney; Editing by Peter Galloway