So what exactly is Xstrata? It’s an outfit that rewards some close scrutiny.

See, while Rio and BHP might be every bit the lying multi-national bullies that Xstrata is, at least they’re actually genuine mining companies.

But Xstrata makes more sense as a Swiss investment vehicle that has become a major force in mining around the world by acquisition, rather than real growth.

The dominant (34%) shareholder in Xstrata is a privately-held outfit called Glencore. Glencore was founded and run by Marc Rich, the indicted tax evader and embargo-breaker who was notoriously pardoned by Bill Clinton at the end of his term in office. Rich sold out in the 1990s to two of his lieutenants, Ivan Glasenberg and Willy Strothotte.

The CIA has accused Glencore of sanctions-busting deals with Saddam Hussein’s Iraq, among other rogue states, and the company has a history of human rights controversies, particularly in South America. Xstrata has long been involved in attempts to de-unionise its Australian workforce and force them onto individual contracts (the Xstratafacts website details the company’s ongoing campaign against its workforce).

But Glencore has more than a proprietorial relationship with Xstrata. Strothotte is chairman of both Glencore and Xstrata, and Xstrata shareholders revolted in May against his re-election, with a quarter opposing him (CEO Mick Davis’s generous remuneration package was also savaged). Glencore CEO Ivan Glasenberg is also on the Xstrata board.

More particularly, Glencore extracts huge marketing agent fees from Xstrata, worth $80 million in 2008, and acts as Xstrata’s distributor for a number of products (and in some cases collects fees regardless of whether it sells Xstrata products or not). The close relationship between Glencore and Xstrata was a key reason for a mooted merger with Vale falling over two years ago, with complaints from other Xstrata shareholders that Glencore had wrecked the deal.

According to Xstrata’s 2009 annual report, it gets only 26% of its revenue from Australasia, compared to more than 50% from the Americas. Despite its limited exposure to Australia, its share price fell 10% in May, significantly under-performing local miners with much higher exposures to the government’s proposed RSPT.

You might have noticed that, for all its vociferous attacks on the RSPT, Xstrata, led by its South African CEO Mick Davis, hasn’t had much to say in the debate about effective tax rates.

That might be because Xstrata is headquartered in Zug, a small canton in Switzerland. Zug is one of the tax avoidance capitals of Europe, boasting “some of the lowest tax rates available in any stable democracy”. Glencore is headquartered there as well. Look at BHP’s or Rio’s annual reports and they produce figures showing they pay 30% tax on their global operations — which leaves out generous deductions and concessions they receive in Australia, but that’s another story. Xstrata’s figures show they pay 25% globally, courtesy of their use of a tax haven.

It appears Glencore and Xstrata are very sensitive about tax. No wonder they’ll say and do anything to ward off the RSPT.