* Copper down 12 percent, iron loses 5 percent on the year
* Metals price move makes Rio more expensive for Glencore
* Anglo, Antofagasta, Kaz, also hard hit by copper slump
By Silvia Antonioli
LONDON, Jan 14 (Reuters) - A sudden plunge in the price of copper pulled the shares of global miner Glencore to their lowest level on record on Wednesday and risks frustrating any intention to make a fresh move on larger rival Rio Tinto.
Copper prices slid to their lowest in 5-1/2 years after a downward revision to global growth forecasts by the World Bank and shares in Glencore lost as much as 12 percent to 236.20 pence on Wednesday.. Glencore, among the large diversified miners, has the largest exposure to copper.
BREAKINGVIEWS-Copper collapse accurately indicates global
If sustained, the steeper fall in copper prices compared with that of iron ore so far this year, might derail any potential move by Glencore to take over Australian miner Rio Tinto , which is heavily exposed to iron ore.
After Glencore's first takeover approach was rebuffed by Rio last summer, the market was widely expecting Swiss-based Glencore to make another attempt this year.
The steeper fall last year in prices of iron compared with base metals made Rio a more affordable target for Glencore.
That has been partially reversed this year.
Copper has lost almost 12 percent of its value, while iron ore has lost less than 5 percent
"The fall in copper prices makes it much harder for Glencore to take over Rio as the share exchange ratio is not in their favour," said London-based analyst Paul Gait at Bernstein Research. "The issue is that Glencore's commodity mix hasn't played in its favour in the last few weeks and Rio is looking more expensive as a consequence."
Gait however, like many other analysts, thought fundamentals for copper looked much better that those of iron ore and expected this situation to be short-lived.
Glencore's stock, first listed in London in 2011, was the worst loser among the blue-chip FTSE-100 companies on Wednesday, indicated down 11.5 percent at 238.05 pence at 1345 GMT.
The second biggest loser was Anglo American, with the second-largest exposure to copper among the diversified miners. Its shares were down 10 percent at 10.31 pounds.
Rio Tinto and BHP Billiton , with smaller exposure to copper, were down 6 and 8 percent, respectively.
Other stocks battered by the steep fall in copper prices were pure copper miners such as Kaz Minerals, a relatively high-cost producer in Kazakhstan which lost more than 22 percent, Chile's Antofagasta down more than 6 percent and First Quantum, down more than 7 percent. (Editing by Elaine Hardcastle)