Sept 28 (Reuters) - Canada’s main stock index retreated on Tuesday, as a 1% drop in gold prices weighed on miners, while technology stocks tracked a slide in the U.S. tech-heavy Nasdaq. At 9:31 a.m. ET (13:31 GMT), the Toronto Stock Exchange’s S&P/TSX composite index was down 112.86 points, or 0.55%, at 20,350.56. (Reporting by Amal S in Bengaluru; Editing by Krishna Chandra Eluri) Our Standards: The Thomson Reuters Trust Principles.