June 17 (Reuters) - Canada’s main stock index opened lower on Thursday, dragged down by a 2.5% fall in mining stocks, as bullion prices were pressured by stronger U.S. dollar after the Federal Reserve signaled earlier-than-expected interest rate increase. * At 9:30 a.m. ET (13:30 GMT), the Toronto Stock Exchange’s S&P/TSX composite index was down 28.73 points, or 0.14%, at 20,202.23. Reporting by Amal S in Bengaluru; Editing by Rashmi Aich Our Standards: The Thomson Reuters Trust Principles.