What is AISC?

All-In Sustaining Cost, or AISC, is the most widely used measure of what it costs a mining company to produce an ounce of gold, a pound of copper, or a tonne of any other commodity on a fully-loaded, ongoing basis. It was introduced by the World Gold Council in 2013 to give investors a more complete picture of the true cost of mining than older metrics like cash cost or C1 cost provided.

Before AISC, companies would report simple cash costs that excluded large categories of spending. A gold miner might report $600 per ounce in cash costs, but after accounting for exploration, corporate overhead, and the capital needed to keep the mine running, the real cost was closer to $1,000. AISC was designed to close that gap.

The standard AISC calculation starts with direct mining and processing costs, often called site costs or cash costs. On top of that, it adds several categories that reflect the full cost of sustaining current operations:

Mining costs cover the direct expenses of extracting ore from the ground, including drilling, blasting, loading, and hauling. Processing costs include crushing, grinding, and the metallurgical processes that extract the valuable mineral from the ore. General and administrative expenses (G&A) include corporate overhead, management salaries, and head-office costs that support the operations.

Sustaining capital expenditure is the money spent to maintain current production levels. This includes replacing worn-out equipment, extending mine life within existing operations, and infrastructure maintenance. It is distinct from growth capital, which funds new mines or major expansions. Royalties and production taxes are government-imposed costs based on revenue or production volume. By-product credits are subtracted from the total. A gold mine that also produces silver will credit the silver revenue against its gold AISC, reducing the reported cost per ounce.

Despite the World Gold Council guidance, AISC is not a standardized accounting metric. It is a non-GAAP measure, meaning each company decides exactly what to include. The WGC framework is a recommendation, not a rule.

This creates real comparability problems. One company might include corporate development costs in AISC while another excludes them. The treatment of stockpile adjustments, non-cash reclamation provisions, and lease payments under IFRS 16 varies significantly. Some companies include exploration spending in AISC while others treat all exploration as growth capital.

The line between sustaining and growth capital is particularly subjective. A brownfield expansion that extends mine life could be classified as sustaining capital by one company and growth capital by another. This single classification decision can move AISC by $50 to $100 per ounce for a gold miner.

This is precisely why ProveMines tracks the definition of AISC separately for each company and each year. When a company changes what it includes in its AISC calculation, that change is recorded, and the year-over-year comparison is flagged as potentially affected by a methodology change rather than a genuine operational improvement or deterioration.

AISC is always expressed in a currency per unit of the commodity being produced. For gold miners, the standard unit is US dollars per troy ounce ($/oz). For copper producers, it is US cents per pound (c/lb) or US dollars per pound ($/lb). For iron ore, it is dollars per tonne.

ProveMines uses commodity-specific AISC metrics to avoid confusion. Rather than a single generic AISC field, the system tracks aisc_au for gold, aisc_cu for copper, aisc_ag for silver, and so on. This prevents the common data problem where a diversified miner has multiple AISC figures reported in different units, all labelled the same way.

AISC is most useful as a relative measure. Comparing one company's AISC trend over time reveals whether operations are becoming more or less efficient. Comparing AISC across companies in the same commodity shows which operations have structural cost advantages.

However, AISC comparisons require caution. A company with a low AISC might simply be deferring sustaining capital, which will eventually catch up. A company with a rising AISC might be investing heavily in sustaining capex that will pay off in future years. The direction of change matters as much as the absolute level.

AISC also drives margin analysis. When the gold price is $2,000 per ounce and a company's AISC is $1,200 per ounce, the margin is $800 per ounce. If the gold price rises 10% to $2,200, the margin expands to $1,000 per ounce, a 25% increase in margin from a 10% price move. This is the operational leverage that makes mining stocks more volatile than the underlying commodity.