BUZZ-Silver Wheaton Corp: To buy back shares
** Shares of company, which invests in miners in exchange for silver and gold, up 4.6 pct at C$15.44
** Company says it will buy back for cancellation up to 20.2 mln shares on the Toronto and New York stock exchanges
** Shares represent 5 pct of outstanding as of Sept. 11
** Up to Monday's close, stock had fallen 37.5 pct this year on the Toronto Stock Exchange
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