June 30 (Reuters) - Canada’s main stock index opened lower on Wednesday as mining stocks fell, while official data showed the nation’s economy likely contracted again in May, following its first decline in a year last month. * At 9:30 a.m. ET (13:30 GMT), the Toronto Stock Exchange’s S&P/TSX composite index was down 23.27 points, or 0.12%, at 20,147.75. (Reporting by Amal S in Bengaluru; Editing by Vinay Dwivedi) Our Standards: The Thomson Reuters Trust Principles.