Miners crash, Glencore at low as copper tumbles

Mining stocks sold off sharply on Wednesday, with Glencore falling to an all-time nadir, after copper plunged to a five-and-a half-year low.

Copper prices fell to their lowest levels since July 2009, sparked by a wave of selling after the World Bank revised down global economic growth, and continued weakness in the oil price. The metal tanked to trade around $5,353 per ton in mid-morning trade, before paring some losses, leveling at $5,536.

Read MoreInvestors go long gold, short copper in oil freefall

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Glencore, one of the world's largest copper producers, was hit hard, with its shares falling by as much as 12 percent to £2.44 ($3.71) — around half the price the group achieved at IPO in 2011. The stock came under additional pressure after Citigroup cut its target price on Wednesday for Glencore to £3.60 from £3.90.

Other miners hit by the commodity price fall included London-headquartered Anglo American, which fell by as much as 9 percent. BHP Billiton and Rio Tinto both tumbled by as much as 7 and 5 percent respectively.

"Part of copper's weakness can be explained by ongoing mine supply growth and broadening mining cost deflation, for example, from falling oil and steel prices as well as weakening producer currencies," said Carsten Menke, commodity analyst at Julius Baer, who added that the bank's basket of marginal producer currencies had fallen by around 11 percent over the past year.

"However, this hardly explains today's plunge, which was likely triggered by an overnight downgrade of global growth by the World Bank, leading to technical selling after prices broke below $6,000 per ton," he said.

Both Brent crude and WTI hit near six-year lows on Wednesday, extending losses after trading lower for seven straight weeks.

Since mid-2014, when oil has dropped close to 60 percent, copper has also fallen by around 25 percent. Julius Baer maintains a neutral view on copper but has cut its three- and twelve-month price targets to $5,900 and $5,800 per ton respectively.

The falling price of copper will likely have deeper implications for commodity currencies, analysts said.

Read MoreAussie dollar to keep falling - but how low can it get?

As Australia is a copper exporter, the strength of the Aussie dollar, for instance, is strongly linked to copper prices. It is also tied to iron ore prices, which have also turned lower in the last few trading sessions. The currency traded at $0.8035 against the dollar on Wednesday

"The broader weakness in commodity prices is going to fuel further weakness across the resource-exporting countries' currencies. So the Australian dollar-yen was the biggest G-10 foreign exchange mover overnight and Aussie dollar against the U.S. dollar has reversed almost all of the last week's rebound. Australian dollar against the dollar $0.80 remains, a major psychological support but in due course, this will break," said Société Générale global macro strategist Kit Juckes.