Shares in mining and trading company Glencore fell almost 30 percent and closed at a record low on Monday over concerns it is not doing enough to cut its debt to withstand a prolonged fall in global metals prices. About 3.5 billion pounds ($5.33 billion) in market value was wiped off the Swiss-based firm, whose $10 billion share offering in 2011 turned its managers into billionaire shareholders but left it saddled with debt – a growing problem as commodity prices fell.