Doré Bar

A doré bar is an intermediate product of gold mining. Cast at the mine site itself, it contains gold and silver in a crude mixture—typically 70–90% gold, with the remainder mostly silver and trace base metals. It is neither ore nor pure bullion; it sits midway in the refining chain, waiting to be shipped to a specialist refinery for final purification.

Why mines make doré, not pure gold

Gold mining is not a matter of pulling nuggets from the ground. Ore contains gold dispersed through rock—often at concentrations of just a few grams per tonne. The mine must crush, concentrate, and process ore through several chemical and physical steps.

After initial concentration (which removes most waste rock), mines have a gold-bearing concentrate still laced with copper, zinc, arsenic, and other elements. To make an easily transportable product, the mine typically smelts this concentrate in a furnace. Gold and silver, being noble metals, preferentially separate from base metals during smelting. The furnace produces a liquid or semi-solid melt rich in gold and silver. When poured into moulds, this melt solidifies into bars—doré.

Doré is a practical intermediate. A mine could not economically refine gold to 99.9% purity on-site; the equipment and chemistry are specialist and expensive. Shipping crude ore to distant refineries was wasteful. Doré solves this by removing most waste at the mine, leaving a concentrated, shipment-ready alloy that is valuable enough to justify transport costs but crude enough to be produced at scale on-site.

Composition and impurities

A typical doré bar is 80–85% gold by weight, with 10–15% silver. The remainder includes copper, lead, zinc, and arsenic—metals concentrated from the ore or introduced during smelting. Some doré bars are cleaner; others are messier, depending on ore characteristics and the mine’s smelting practice.

The presence of silver is often welcome. Silver is valuable in its own right, and the combination of gold and silver in doré allows refineries to extract both metals. Some mines, particularly in producing countries with abundant copper ores, produce doré that is deliberately enriched in byproduct silver and copper; the refiner will be recompensed for both.

Base metals—especially arsenic and lead—are contaminants. They lower the doré bar’s purity and add refining costs. Mines with effective concentration stages produce cleaner doré. Mines with poor ore grades or aged equipment may produce messier doré that requires extra refining steps.

Transport and custody

Doré bars are typically 10–30 kilograms (22–66 pounds) each, a practical size for handling and transport. They are cast with identifying marks—the mine’s brand, weight, approximate fineness—stamped or embossed into the surface. Bars are usually packed into wooden or metal crates for shipment.

Because doré is partially refined and contains significant precious metal, it is valuable and must be guarded. Mines keep doré in secure vaults until shipment. Transport is often by armoured courier or via trusted bullion dealers. The doré is insured for its metal content value while in transit.

Once at the refinery, doré bars are weighed, sampled, and assayed to confirm gold and silver content. The refinery pays the mine (or the mine’s trading counterparty) based on the confirmed assay, less a processing fee.

The refining process

At the refinery, doré undergoes several stages to isolate pure gold and silver.

Parting is the critical first step. The alloy is dissolved in hot sulfuric or nitric acid, which dissolves base metals and silver but leaves gold behind (gold is nearly insoluble in these acids). The undissolved gold residue, called “gold mud,” is filtered and rinsed. The acid solution, now rich in silver and base metals, is treated separately to recover silver.

Gold purification follows. The gold mud is melted, cast into anode slabs, and purified through electrorefining. An electric current is passed through the gold anode in an acid bath; pure gold deposits on a cathode, while impurities either remain in the mud or dissolve into the bath. After several cycles, the refined gold reaches 99.95–99.99% purity—the standard for trade bullion.

Silver recovery is handled in parallel. The acid solution from parting is treated with copper or electrolysis to precipitate pure silver, which is also electrorefined.

The entire process takes weeks. The refinery produces bars of pure gold (called “good delivery” bars, meeting international standards) and silver, along with residual impurities that may be further processed or sold as byproducts.

Pricing and market

Doré is priced as a blend. The refinery calculates the value of gold and silver content (based on the assay) at the prevailing London Gold Fix (or LBMA Gold Price) and a silver benchmark. It deducts a refining fee (typically 0.5–2% of the metal value, depending on fineness and batch size) and pays the mine in cash or through a futures contract.

A mine might hedge doré revenues by selling futures contracts for the expected gold and silver content, locking in a price regardless of spot movements. This is a standard risk-management tool for mining companies.

Because doré is an intermediate—not yet bullion but no longer ore—it does not trade as openly as finished bullion or futures. It is almost always a bilateral transaction between a mine (or its trading partner) and a refinery. Some major bullion dealers and refineries maintain doré inventories and may trade it opportunistically, but it is not a retail or public market.

The economics of doré production

For a gold mine, making doré on-site versus shipping raw ore involves trade-offs:

On-site smelting requires capital investment in a furnace and ancillary equipment, plus ongoing operating costs. But it drastically reduces the mass shipped (ore may be 99% waste rock; doré is 80%+ metal). Transport costs—a significant line item for remote mines—fall sharply. Environmental permitting can be complex, but large mines usually invest in smelting to capture margin.

Shipping raw ore avoids smelting capex and complexity but incurs higher logistics costs and leaves the mine with lower realised prices (the buyer discounts ore heavily due to concentration work needed). Only small, remote, or low-grade mines typically ship ore directly.

Most commercial gold mines produce doré, at least for high-grade ores. It is the economically rational middle step.

See also