Firebrand politician Julius Malema has been barred by police from addressing striking workers at South Africa's Marikana mine.Some 2,000 miners had gathered at a stadium near the mine, about 60 miles (100km) north-west of Johannesburg.Strikes have already halted production at several gold and platinum mines in the resource-rich country.South African President Jacob Zuma said that the disruption had cost the industry $548m (£337m) in lost output.Speaking before a conference of the Congress of South African Trade Unions (Cosatu) he said that this year's strikes had taken nearly $388m from the national treasury.Last week, the government warned it would act "swiftly" against the incitement and threats of violence crippling the mines.'Opportunism'After arguing with police at the stadium, Mr Malema was escorted away by a special police protection unit.According to the Associated Press, two armoured police vehicles drove alongside Mr Malema's vehicle and a police helicopter hovered above until he reached a two-lane highway.He has called for a nationwide strike after earlier saying the mines should be made "ungovernable".Some have accused Mr Malema, who was expelled from the African National Congress (ANC) earlier this year, of political opportunism amid seething anger over last month's deaths at Marikana mine.Forty-four people died at the Lonmin-owned platinum mine in mid-August, among them 34 miners shot in a single day by police.A commission of inquiry is looking into events at that mine, but observers say the issue is tapping into disquiet over the ruling ANC's links to big business and alleged neglect of the working classes that have made up its historical support base.Sidumo Dlamini, the president of South Africa's trade union movement, said again on Monday that growing inequality was to blame for the recent killings and continuing unrest in the country's mining industry.The London-registered Lonmin firm announced on Monday that is was halting construction of a new mine shaft, putting 1,200 people out of work.Mr Malema, the former head of the ANC Youth League, is also under investigation for alleged corruption - which he denies.But he is continuing to make waves in South Africa - articulating the anger of many following last month's killings, says BBC Africa correspondent Andrew Harding.His fiery rhetoric is hugely popular, especially given the relative silence from other quarters, our correspondent says.