* TSX down 53.08 points, or 0.41 percent, at 12,748.15 * Weaker resource shares offset firmer financials * BlackBerry slips 4.5 pct after Home Depot chooses iPhone * Cameco Corp down more than 3 percent after results By Alastair Sharp TORONTO, Feb 11 (Reuters) - Canada's main stock index fell on Monday, dragged down by weaker gold mining shares and a sharp fall in BlackBerry , which lost another major U.S. corporate customer to rival Apple. Cameco Corp, the world's biggest publicly traded uranium producer, also slipped after reporting a sharply lower quarterly profit and pointing to weaker earnings ahead. Gold miners were among the heaviest laggards on the index as commodity prices fell. Gold extended earlier losses to one-month lows after recent technical support broke down. The gold mining group, down 2.2 percent in the session, has also been hurt by rising production costs and limited discoveries. "There's too many companies out there digging holes and not coming up with anything encouraging, and then costs meanwhile keep picking up," said Levente Mady, a senior portfolio manager at PI Financial Corp. Mady added that he prefers government bonds to Canadian equities because he thinks valuations are too high at current levels. Goldcorp was the most influential decliner, down 2.4 percent to C$35.36, while Yamana Gold Inc fell 4.9 percent to C$15.77. Barrick Gold lost 1.5 percent to C$32.34. The Toronto Stock Exchange's S&P/TSX composite index ended the day down 53.08 points, or 0.41 percent, at 12,748.15. Seven of the 10 main sectors were in negative territory, including energy shares, down 0.5 percent. Shares of BlackBerry fell 4.5 percent to C$15.76 after U.S. home improvement retailer Home Depot Inc said it is replacing the BlackBerry smartphones it provides its executives and managers with Apple Inc's iPhone. Cameco knocked off 3 percent to C$21.05 after the company announced it took a C$168 million ($168 million) write-down on an Australian exploration project, and said the current quarter would likely produce weaker earnings as well. "We used to own Cameco ... my problem with Cameco is that I think the future of nuclear energy has been very much cast in doubt by fracking and tight oil," said David Baskin, president of Baskin Financial in Toronto. "Because there's so much petroleum-based energy available now than people thought say five years ago, and because of what happened in Fukushima in Japan, I think that the whole future of nuclear energy is very much up in the air." Slightly stronger financial and industrial shares helped to offset the broad declines. Manulife Financial Corp, a major insurer, was the top gainer, rising 3 percent to C$15.28.