The Swiss mining company Xstrata said Thursday that it has been \"approached\" by raw materials giant Glencore regarding a merger that media reports say could be worth 80 billion dollars. According to regulations at the London Stock Exchange, where both companies are listed, Glencore has until March 1 to make a firm offer, a Xstrata statement said. In early London trading, Xstrata shares shot up by 12.13 percent to 1,260 pence, while Glencore showed a gain of 3.62 percent to 447.45 pence. The FTSE index was down meanwhile by 0.15 percen