Last year, gold mines produced nearly 1 t of carbon dioxide (CO2) for every ounce of gold produced, says business intelligence company Standard & Poor’s (S&P) Market Intelligence research.
To gather insight into greenhouse-gas (GHG) emissions in the gold mining industry, the firm reviewed sustainability reports from more than 90 gold mines across the world to compare their CO2 emissions to a variety of production values.
The firm notes that South Africa's gold mines are excluded from this study as the country is an outlier with anomalously high GHG emissions, owing to its coal-heavy power grid, above-average needs for ventilation owing to its deepening mines and falling ore grades.
The research finds that openpit mines emitted, on average, more than twice as much CO2 equivalent (CO2e) per ounce of gold produced as underground mines, at 0.85 tCO2e/oz and 0.40 tCO2e/oz, respectively.
S&P Market Intelligence also reveals that openpit mines processed roughly five times the amount of ore at an average grade of about 1.05 g/t of gold for the population evaluated, versus 3.25 g/t of gold for underground mines.
The firm notes that these figures support the assumption that openpit mines emit greater amounts of GHGs than underground mines at a similar level of production.
“While there are more factors in GHG emissions than simply the volume of material moved and processed, there is a direct correlation between the two when we evaluate emissions as a function of production,” states S&P Market Intelligence.
Further, underground mines, which operate at higher grades and process less material, generally have lower GHG footprints than their larger openpit counterparts. As such, for every ounce of gold produced, underground mines emit less than half the amount of CO2e that openpits do.
However, despite the difference in scale, openpit mines emit one-third more CO2 and have an average grade one-third lower than underground mines. Both types of mines generate on average similar GHG intensities when looking at CO2 emissions as a function of ore processed.
S&P Market Intelligence notes that CO2 emissions per kilotonne of ore processed are generally more contained to a similar range for openpit mines but tend to be much more variable at underground mines as a result of that shift in perspective.
A related report published by S&P Market Intelligence also reveals that lower 2019 emissions are linked to higher free cash flows experienced that year.
The firm notes that while the largest gold producers have the capacity to generate the largest amount of free cash, a large production base also comes with higher emissions. Consequently, S&P Market Intelligence reveals that some producers and some jurisdictions see better-than-average returns per tonne of emissions.
As such, underground mines with higher grades and lower emissions generate far more free cash per tonne of CO2e emissions than equivalent-producing openpit mines. With their higher population of underground mines, S&P Market Intelligence says this is clearest in Canada and Central/East Africa, which generate the most free cash per tonne of emissions.
“In contrast, Latin America, with its higher population of lower-grade openpits, generate the least free cash per tonne of emissions.”