Oct 13 (Reuters) - Canada's main stock index opened lower on Tuesday after a long weekend, dragged by materials sector that shed 2% on weaker gold prices.

* At 9:34 a.m. ET (13:34 GMT), the Toronto Stock Exchange's S&P/TSX composite index was down 20.31 points, or 0.12%, at 16,542.5.

(Reporting by Amal S; Editing by Vinay Dwivedi)