Aug 13 (Reuters) - Canada’s main stock index opened higher on Friday, lifted by mining shares, and was set to deliver its fourth straight weekly gain as investors took comfort on the back of a strong batch of corporate earnings. * At 9:30 a.m. ET (13:30 GMT), the Toronto Stock Exchange’s S&P/TSX composite index was up 30.76 points, or 0.15%, at 20,551.36. Reporting by Amal S in Bengaluru, Editing by Sherry Jacob-Phillips Our Standards: The Thomson Reuters Trust Principles.