A doré bar is a semi-pure gold/silver alloy bar produced at a mine site as the final saleable form before refining. Doré is typically 70–90% precious metals (Au + Ag) with the balance being base-metal impurities. It is the form mines ship to a refinery, where the alloy is separated into pure gold and pure silver.
How Doré Is Made
After electrowinning extracts gold and silver onto stainless-steel wool cathodes, the loaded cathodes go to the gold room. There the carbon is burned off, the residue is mixed with flux (borax, silica, soda ash), and the mixture is melted at ~1,100°C in a tilting-crucible furnace. Slag (impurities + flux) floats; molten gold/silver alloy is poured into a doré mold.
Typical Composition
Heap-leach gold doré: 80–95% Au + Ag, balance Cu, Fe, and trace base metals. Silver-dominant Merrill-Crowe doré: 70–85% Ag + Au, higher base-metal impurities. Each bar is sampled and assayed before shipping; the operator is paid by the refinery based on assayed metal content.
Shipping & Refining
Doré bars typically weigh 20–40 kg each and are shipped via secured logistics to a precious-metals refinery (Brink's, Loomis, etc., to LBMA-accredited refiners). The refinery separates the alloy into 99.99% gold and 99.9% silver, returns those metals or their cash equivalent to the operator, and charges refining + shipping costs.
The KCA Furnace Lineup
KCA fabricates three tilting-crucible furnace models: Model 225T (23 kg gold concentrate per charge), Model 430T (45 kg), and Model 800T (84 kg). All with matched off-gas scrubbing for SO₂ and particulate compliance. See Doré Bar Production.
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