The highest-cost major copper mine was BHP Billiton's Olympic Dam in Australia, which was ranked 11th highest by cost at $7,321 per ton. That's some $1,300 higher than three-month prices on the London Metal Exchange on Friday.
A BHP spokeswoman declined to comment on the study's findings beyond the company's first-half results in February. The mine also gets revenue from selling uranium oxide concentrate, gold and silver.
Miners often give costs for regions or divisions, but do not break down expenses for individual operations.
According to the methodology, GFMS calculated total costs based on copper sold and included mining, milling and treatment costs and on-site administrative expenses as well as depreciation charges and revenue from by-products.
It excluded royalties and taxes, capitalized development of stripping, head office costs and financing expenses. This is a better proxy for the outlay of sustaining production levels at a particular mine, GFMS said.
Close to break-even
Some producers have disputed the study's findings.
KGHM even said the GFMS estimate of $7,719 per tonne was too low for its five international assets, stretching from Sudbury in Canada to the Antofagasta region in Chile.
Fourth-quarter expenditure was actually higher than the GFMS estimate of $7,719 per tonne, a spokeswoman for the world's seventh-largest producer said.
Contrary to the GFMS study, which estimated costs had fallen by over 10 percent quarter-on-quarter, expenses were up due to stripping costs at its U.S. Robinson mine, she said.
Using the GFMS methodology, costs were $7,790 per ton, up from $6,512 in the prior quarter in 2014 and $6,268 in the fourth quarter of 2013, a spokeswoman said.
A Glencore spokesman said the company does not "recognize" GFMS's findings, which pegged costs for Cobar and Ernest Henry in Australia at $6,116 per ton.
Glencore's North Queensland operations had net costs, known in the industry as C1, after credits of $1.23 per lb in the final three months of last year, he said. That excludes depreciation charges.
North Queensland includes the near-century-old Mount Isa operation, Townsville refinery and Ernest Henry but excludes Cobar.