* LME/SHFe arb: tmsnrt.rs/2oQ5nm2 (Recasts, adds quotes, updates with closing prices)
By Peter Hobson
LONDON, April 21 (Reuters) - Copper suffered a third week of losses amid a broad decline for industrial metals on Friday as worries over political instability and global demand prompted investors to cut bets on higher prices.
Investors have overestimated global growth and the impact of supply disruptions at major copper mines, said Norbert Rucker, head of commodity research at Julius Baer. Copper could slip to $5,200 a tonne in the next three months, he said.
"The technicals don't look very good," said INTL FCStone analyst Edward Meir. "The downtrend is pretty sharp for most of the metals ... You're going to see a sideways to lower drift."
* LME COPPER: Three-month copper on the London Metal Exchange closed flat at $5,622.50 a tonne, leaving it down 1.2 percent this week. The metal used in the power and construction sectors went as low as $5,530 on Wednesday, its weakest since Jan. 4.
* COPPER SUPPLY: The global refined copper market had a 51,000 tonne surplus in January, up from a 44,000 tonne surplus in January last year, the International Copper Study Group (ICSG) said. But the strike at the Escondida mine in February-March meant "next month's report should reflect a tighter market", analysts at ING said.
* FREEPORT EXPORTS: Freeport McMoran Inc's Indonesia unit has been granted a permit to export 1.11 million wet metric tonnes of copper concentrate until February of next year, a trade ministry official said.
* FREEPORT STRIKE: Freeport also warned that it would punish workers for absenteeism at its Indonesian operation, a day after one of its main unions announced plans for a one-month strike over employment conditions.
* RIO TINTO: Rio on Thursday cut full-year copper production guidance to 500,000-550,000 tonnes from up to 665,000 tonnes because of the Escondida strike in Chile and output cuts at the Grasberg mine in Indonesia.
* COPPER STOCKS: On-warrant inventories at LME-registered warehouses MALSTX-TOTAL fell 9,025 tonnes to 150,950 tonnes. Stocks in warehouses monitored by the Shanghai Futures Exchange declined 11.5 percent to 240,191 tonnes from a week ago.
* NICKEL SPREAD: The discount of LME cash nickel to the three-month contract CMNI0-3 shrank to $50 a tonne from $67.50 late last month, the largest since January 2015. A smaller discount indicates tighter supply.
* OTHER METALS: Aluminium finished 0.5 percent down at $1,932.50. Nickel lost 1.5 percent to $9,345. Zinc closed 1.8 percent lower at $2,584, with lead falling 0.8 percent to $2,142 and tin down 0.6 percent at $19,750.
Additional reporting by James Regan; Editing by Edmund Blair and David Goodman