* Fed projects a less aggressive path for rate rises
* OECD highlights threat to global growth (Adds closing prices)
By Pratima Desai
LONDON, Sept 22 (Reuters) - Copper rallied to a six-week high on Thursday as the dollar slipped after the U.S. central bank left benchmark interest rates unchanged, though gains were limited by worries about slow demand growth.
Benchmark copper on the London Metal Exchange ended up 1.9 percent to $4,855 a tonne, having touched $4,858.50, its highest since Aug. 12.
The Fed left rates on hold and projected a less aggressive path for rises over the coming years. That exerted pressure on the U.S. currency, a weakening of which makes dollar-denominated commodities cheaper for non-U.S. firms.
“Central banks are happy to support what economic growth there is with cheap money; that’s fuel for industrial metals,” said Societe Generale analyst Robin Bhar.
“But the market will struggle to sustain rallies because demand isn’t strong ... The OECD pointed out yesterday that the next leg lower could come from global trade.”
The Organisation for Economic Cooperation and Development on Wednesday warned that global economic growth will flounder this year and next because of slowing trade growth.
Also expected to weigh on metals is weak demand growth in China, which consumes nearly half of all industrial metals produced.
“We may get a seasonal pick-up in physical activity in the fourth quarter, but it’s not guaranteed. It may not come through if China continues to slow,” Bhar said.
Analysts also think the uncertainty created by the U.S. Presidential election in November could deter investment.
Three-month aluminium ended up 3.1 percent at $1,633, its highest since August 31.
Zinc gained one percent to $2,294, while lead rose 0.7 percent to $1,949 and tin climbed 0.9 percent to $19,485.
“We believe the bottom of the market for mined commodities was tested, and found, very early in 2016,” Investec analysts said in a note.
“Whilst this caught most analysts off-guard, the rally has proved to be sustainable despite many mining companies warning of difficult times to come.”
Nickel added 3.1 percent to end at a six-week high of $10,660. It has been boosted in recent weeks by worries about supplies from the Philippines, where the government is carrying out an environmental audit of mines.
Three month LME copper
Most active ShFE copper
Three month LME aluminium
Most active ShFE aluminium
Three month LME zinc
Most active ShFE zinc
Three month LME lead
Most active ShFE lead
Three month LME nickel
Most active ShFE nickel
Three month LME tin
Most active ShFE tin
Additional reporting by Melanie Burton and Eric Onstad; Editing by David Goodman