Mining companies operating in Zambia have failed to show how higher taxes introduced this year will affect their profitability despite objecting to the new framework, a senior government official said on Thursday. The country, Africa’s second-largest copper producer, increased its sliding scale for royalties of 4 to 6 percent by 1.5 percentage points from Jan. 1 and introduced a new 10 percent tax when the price of copper exceeds $7,500 per tonne.