But chief executive Ivan Glasenberg said the allegations, centred on its 73 per cent-owned Mopani copper and cobalt mine, were based on a 'helicopter view' of its finances.

NGOs including Canada's Mining Watch and Switzerland's Berne Declaration accused Glencore of 'financial and accounting manipulations' such as overstating operating costs, understating production volumes and manipulating pricing to avoid tax.

Their report, based on an audit international accounting firm Grant Thornton prepared for the Zambian government, alleged there was an unexplained US$380 million increase in operating costs at the mine in 2007 and that Glencore's reported volumes of extracted cobalt were 'stunningly low'.

'These people have failed to do a proper, detailed study of our business and that will come out shortly,' Glasenberg said.

Glencore - which made US$145 billion of sales last year and holds stakes in Oleg Deripaska's Hong Kong-listed aluminium supplier Rusal and Switzerland's Xstrata - has a long history of controversy.

Its billionaire founder, Marc Rich, was indicted by the US government in 1983 for evading over US$48 million worth of taxes and running illegal oil deals with Iran.

Rich fled to Switzerland to escape prosecution and sold Glencore to a group of his associates in 1994.

President Bill Clinton pardoned Rich during his last week in office.

Glencore's path to transformation from a clubby, private partnership to a public company accountable to shareholders has also not been smooth.

Last month, the firm's 71-year-old chairman Simon Murray, a familiar figure in Hong Kong as he formerly ran Hutchison, told a British newspaper he would not hire women for senior positions because 'pregnant ladies have nine months off'.

Meanwhile, Glencore's prospectus warned key staff could leave after the listing because of the impending 'cultural change'. The listing document also detailed environmental and political problems.

It said an acid plant at Mopani mine was releasing 'effluent discharge' into a nearby stream, causing 'possible contamination'.

And mines run by Kazzinc, Glencore's Kazakh associate, are emitting 'hazardous dust, containing metals, which could contaminate surrounding land'.

The company also warned it does business in countries where its assets could be nationalised.

Glencore is active in Bolivia, for example, where the government has ruled that mines should be run as joint ventures with the state.

The IPO has sold well in London. Bankers filled the massive order book in just one day.

But the mid-price listing valuation of US$61 billion fell short of analysts' initial predictions of US$70 billion.

Glencore is selling only 2.5 per cent of its shares to Hong Kong retail investors, at a price range of HK$61.25 to HK$79.18 a share.

The IPO will make five of the commodities giant's top staff billionaires. Glasenberg will own 15.8 per cent of the business after the float.

Some analysts have questioned why Glencore is selling shares to the public now.

Commodities prices have cratered in recent weeks on the back of slowing growth in China. London-traded copper hit a five-month low of US$8,615 per tonne yesterday.

Glasenberg insisted Glencore was not selling out at the peak.

'China is still growing,' he said. 'Demand continues to be strong.'

Major stake

Glencore owns 73 per cent of the Mopani copper mine in Zambia

A report for the Zambian government says there was an unexplained rise in operating costs at the mine in 2007 of: $380m