18. Expenses by nature

 For the period
 from 1 January 2014
to 31 December 2014
from 1 January 2013
to 31 December 2013
Depreciation of property, plant and equipment and amortisation of intangible assets: 818 768
of which :    
    Depreciation of property, plant and equipment 803 759
    Amortisation of intangible assets 15 9
Employee benefits expenses 3 022 2 946
Materials and energy  5 870 5 740
   including purchased copper-bearing materials 3 688 3 471
External services 1 378 1 516
Taxes and charges 1 896 2 200
   including the minerals extraction tax* 1 520 1 856
Advertising costs and representation expenses 51 46
Property and personal insurance 21 23
Research and development costs not capitalised in intangible assets  9 8
Other costs, of which: 28 7
  Write-down of inventories 5 7
  Reversal of impairment losses on property, plant and equipment - (25)
  Losses from the disposal of financial instruments 7 9
  Business trip expenses 13 10
 Other operating costs 3 6
Total expenses by nature 13 093 13 254
Cost of merchandise and materials sold (+)  136 288
Change in inventories of finished goods and work in progress (+/-) 34 594
Cost of manufacturing products for internal use (-) (143) (166)
Total cost of sales, selling costs and administrative expenses 13 120 13 970
of which:    
Cost of sales 12 265 13 173
Selling costs 120 126
Administrative expenses 735 671