Copper dipped on Wednesday after Moody's downgrade of Portugal's credit rating revived investor concerns over the Eurozone's debt woes but supply disruptions at some of the world's top copper mines are expected to keep a floor under prices.
Three-month copper on the London Metal Exchange traded at $9,512 a tonne by 0945 GMT from $9,540 a tonne at Tuesday's close. The metal used in power and construction hit its highest since end-April on Tuesday at $9,565.
Moody's became the first ratings agency to cut Portugal's credit standing to junk, warning the country may need a second round of rescue funds before it can return to capital markets.
"The market wasn't expecting that ... People were still focused on Greece and hopes that gradually the situation was improving there," Nic Brown, head of commodity research at Natixis said. "It's clearly upset the market a little bit."
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The dollar was up against a basket of currencies.
A stronger dollar makes commodities like metals more expensive for holders of other currencies. Traders also said yesterday's options declaration day was pulling copper towards $9,500. Traders of calls and puts, the right to buy or sell a contract at a fixed price later, have to decide whether to exercise their options on the first Wednesday of each month during early LME trading hours.
Prices were being supported by supply disruptions in Chile and Indonesia. An unusually severe winter storm has hit operations at Collahuasi, the world's No 3 copper mine, with more heavy snow, wind and rain expected in Chile's copper-rich north.
Nickel traded at $23,399 a tonne from $23,300, supported by declining inventories, which fell to their lowest since April 2009 at 105,480 tonnes.
Tin was at $26,800 from $26,250, after touching its highest in just over a month while zinc, used in galvanizing was at $2,394 from $2,411 a tonne.
Aluminium was at $2,560 from $2,576 a tonne, having earlier hit a three-week high of $2,582.50.