* Mounting stocks cast shadow over copper prices
* Nickel prices likely to fall on improved H2 supply - Citi
* Jump in China zinc concentrate imports a one-off -Macquarie (Updates with closing prices)
By Eric Onstad
LONDON, Aug 25 (Reuters) - Nickel slumped to the lowest in over six weeks on Thursday after worries eased that an environmental crackdown on mines in the Philippines would create shortages of metal.
Nickel had surged 32 percent from the beginning of June until it hit a one-year peak in early August as authorities in the Philippines launched a campaign to close mining operations that failed to meet environmental regulations.
"It did feel that the market got ahead of itself looking further ahead than it perhaps needed to," said Caroline Bain, senior commodities economist at Capital Economics.
With only several mines having been closed or suspended, worries about a blanket ban seem to have been unfounded, analysts said.
"Despite the closure of eight small-scale producers so far, we could see imports stabilise, belying any concerns of supply constriction from the Philippines that has recently riled markets, artificially boosting nickel prices," Citi said in a note.
Three-month nickel on the London Metal Exchange CMNI3
closed down 1.5 percent at $9,845 a tonne, the weakest since July 11 and extending a 2.6 percent slump from the previous session.
There is also increased focus on a surge in exports from Indonesia of ferronickel, an intermediate stage of the metal that contains both nickel and iron. are also available to supply the market, Bain said. "One thing always in the background is that even though stocks have fallen recently, they are still high. So there's no immediate panic about supply."
LME nickel stocks total 372,414 tonnes.
Base metals got little direction from a rangebound dollar index .DXY ahead of the global central bankers' gathering in Jackson Hole, Wyoming, at which Federal Reserve Chair Janet Yellen may offer new clues on U.S. monetary policy. USD/
Zinc CMZN3 ended up 1 percent at $2,298 as investors continued to bet that lower mine output would create shortages.
Macquarie analyst Vivienne Lloyd said a spike in Chinese zinc concentrate imports in July was likely a one-off.
"A continued resurgence in zinc concentrate imports should be very difficult to achieve... Not a zinc shortage as yet, but we are approaching the turning point," she said in a note.
LME copper CMCU3 fell 0.1 percent to $4,626, following a 1.7 percent loss in the previous session, when it fell to its weakest since July 24.
Copper has been under pressure from a rise in LME copper stocks, which added another 9,175 tonnes on Thursday, bringing total stocks to 263,875, a jump of 72 percent since June 1. MCUSTX-TOTAL
Aluminium CMAL3 dipped 0.1 percent to finish at $1,644.50 after touching $1,632, the weakest since Aug. 5, lead CMPB3 closed up 0.4 percent at $1,862, while tin CMSN3 fell 0.5 percent to $18,750.
PRICES
Three month LME copper
CMCU3
Most active ShFE copper
SCFcv1
Three month LME aluminium
CMAL3
Most active ShFE aluminium
SAFcv1
Three month LME zinc
CMZN3
Most active ShFE zinc
SZNcv1
Three month LME lead
CMPB3
Most active ShFE lead
SPBcv1
Three month LME nickel
CMNI3
Most active ShFE nickel
SNIcv1
Three month LME tin
CMSN3
Most active ShFE tin
SSNcv1