* Large LME position in aluminium supporting market
* U.S. markets reopen after long Labor Day weekend (Updates with closing prices)
By Eric Onstad
LONDON, Sept 2 Zinc climbed to a four-week high and aluminium neared an 18-month peak on Tuesday in markets driven by momentum-based speculators and computer-driven funds.
But analysts cautioned that both zinc and aluminium prices were moving ahead of supply/demand fundamentals as inventory levels remain high.
Aluminium prices, which have gained 13 percent over the past two months, have also been supported recently by one investor holding a large position of inventories and short-dated futures.
Three-month zinc on the London Metal Exchange closed at $2,378, up 0.9 percent, after touching a session high of $2,391.25, the strongest since Aug. 5.
"The big issue for me is that you've been seeing Chinese refined zinc production surging quite sharply since June, yet you have a relatively weak end-user sector in terms of construction activity," David Wilson, an analyst at Citi in London, said.
"Zinc has probably one of the biggest exposures to residential construction activity of any of the metals."
While investors are betting on shortages developing due to mine closures, inventories of zinc in LME-approved warehouses MZNSTX-TOTAL are giving the opposite signal, having surged by 13 percent over the last month to 739,400 tonnes.
Spot prices trading at a premium to the benchmark suggests more zinc could be delivered into LME inventories in coming weeks, broker Triland said. LME zinc cash traded at a $1.75 premium to benchmark prices, the highest in a month. CMZN0-3
LME benchmark aluminium closed 0.6 percent higher at $2,107 a tonne, trimming gains after touching a session high of $2,116, within shouting distance of last week's peak of $2,119.50 which was its most expensive since February 2013.
"We're surprised how far prices have risen," said analyst Ivan Szpakowski of Citi in Shanghai.
"A lot of it has been driven, we think, by CTAs (commodity trade advisers), momentum traders, and also macro trading on the more positive views of global economic growth. So, we don't think it's been as driven by fundamental factors. Our expectation is that prices bounce back lower."
Consumers have been restricted from accessing global stockpiles partly due to logjams at exchange warehouses.
Wilson said aluminium prices have been supported by one party holding up to 80 percent of LME stock warrants <0#LME-WHL>.
"That's clearly supportive of the front end of the market, but whether it's a reflection of the real physical market, I'm not so sure," he said.
Also fuelling interest in aluminium and zinc were expectations that central banks in Europe may be forced to act to shore up their economies after weak economic data.
On Tuesday, euro zone producer prices fell the most since April, underlining disinflationary pressures in the single currency area ahead of the European Central Bank's monetary policy meeting on Thursday.
"If we see more stimulus from the ECB, which is looking more and more likely, that's going to be a boost to commodity markets ... and it's helping to offset some of the more negative economic signals at the minute," said analyst James Glenn of National Australia Bank in Melbourne.
LME copper closed 0.5 percent higher at $6,973 a tonne, after losses of 0.6 percent in the previous session when it fell near support at $6,913.25 a tonne, the trough from Aug. 28, which was its weakest since Aug. 20.
Nickel ended 1 percent lower at $18,550 a tonne. brushing off threats of greater sanctions on Russia, one of the world's top producers of the metal, even though sister metal palladium has soared to a 13-1/2 year top.
Worries that sanctions could restrict supply of nickel, used in stainless steel, helped boost prices earlier this year.
Lead ended at $2,239 a tonne, up 0.3 percent and tin closed 0.5 percent lower at $21,515.
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
Three month LME tin
(1 US dollar = 6.1443 Chinese yuan) (Additional reporting by Melanie Burton, editing by David Evans and Susan Thomas)