* TSX falls 0.46 percent to 13,907.32
* Barrick to buy Equinox for more than C$7 billion
* Barrick falls to 3-week low, top heavyweight decliner
* 6 of index's 10 sectors weaker, materials falls 6.4 pct (Updates to close)
TORONTO, April 25 (Reuters) - Toronto's main stock index ended a three-day upswing on Monday as investors dumped Barrick Gold Corp ABX.TO after it struck an all-cash deal to buy an Australian copper miner.
Barrick ABX.TO, the world's largest gold miner, plunged more than 6 percent to C$49.44, its lowest point in more than three weeks, after it said it will to buy Equinox Minerals EQN.TO EQN.AX for about C$7.3 billion. That bid topped an offer from China's Minmetals Resources 1208.HK and was seen as a big bet on soaring copper demand.
Barrick finished down 6.73 percent at C$49.50, suggesting not all investors back its move to diversify. The gold miner was the index's top decliner, and had six times more drag on the overall index than Canadian Natural Resources CNQ.TO, the next heaviest loser.
Equinox surged 12 percent early on, then pared gains to finish up 11.6 percent at C$8.37.
"Barrick explains the move down," said Francis Campeau, broker at MF Global Canada in Montreal. "I'm wondering if the gold players are going to steer away from Barrick to get to a more gold play."
But almost all gold-mining issues came under pressure on Monday, driving down the index's gold subsector by 10.52 percent.
The Toronto Stock Exchange's S&P/TSX composite index .GSPTSE ended down 64.70 points, or 0.46 percent, at 13,907.32. Six of the index's 10 main groups were weaker, led by a 6.39 percent drop in the materials group, which fell on the steep selloff in gold-mining issues.
($1=$0.95 Canadian) (Reporting by Ka Yan Ng; editing by Peter Galloway)