TORONTO, July 24 (Reuters) - Canada's main stock index ended lower on Monday, with Barrick Gold Corp ABX.TO falling nearly 5 percent after a company it majority owns, Acacia Mining, was hit by a bill for $190 billion in unpaid taxes in Tanzania. Toronto Stock Exchange's S&P/TSX composite index .GSPTSE unofficially closed down 54.44 points, or 0.36 percent, at 15,128.69, with eight of its 10 main sectors ending in the red.