Inside the Refinery: How Gold Bars Are Accepted, Assayed and Settled

For many buyers, the refinery is a black box – gold goes in, payment comes out, and what happens in between is a mystery. Understanding the gold refining process removes that mystery and, more importantly, shows you why settlement on refinery assay is such a strong protection. This guide walks step by step through what actually happens to gold inside a refinery, from the moment a consignment arrives to the final settlement and documentation.

It is written from the perspective of a licensed operator that sources, refines and exports gold from the DRC and Uganda. For the supplier-side view, see our companion guide on supplying refinery-ready gold.

Why understanding the refinery matters

The refinery is where a gold consignment’s true value is established – objectively, by measurement, not by claim. When you know how acceptance and assay work, two things become clear: why you should never settle on a verbal purity claim, and why settlement on refinery assay protects both buyer and seller. The process is designed to remove trust from the equation and replace it with verification.

The gold refining process, step by step

1) Intake and security

The consignment arrives under secure, insured transport and is logged in against its documentation – assay report, bar list, certificate of origin and transport papers. Identity and paperwork are checked before anything else happens.

2) Weighing

The gold is weighed precisely on calibrated scales. Both gross weight and, ultimately, fine (pure-gold) weight matter – the fine weight is what settlement is based on.

3) Sampling

A representative sample is taken from the consignment. With mixed or cast material, careful sampling is essential, because the sample must accurately reflect the whole – this is a discipline in itself.

4) Assay

The sample is assayed to determine purity. Non-destructive XRF gives a fast surface reading for screening, while fire assay – the long-established reference method – provides the definitive result by determining the precise gold content. This assayed result is the figure everything else depends on. To learn how to read the resulting report, see our guide on verifying 999.9 gold from an assay report.

5) Melting and refining

To raise purity, the gold is melted and refined. Industry methods include the Miller process (chlorination, which removes base-metal impurities) and the Wohlwill process (electrolysis, used to reach the highest purities such as 999.9). Lower-purity material – dore, nuggets, dust, or 22K/23K gold – is refined upward toward investment-grade fineness through these steps.

6) Casting and serialisation

Refined gold is cast into bars (or minted into coins). Cast bars are stamped or recorded with a serial number and accompanied by a bar list, so each bar can be matched to its assay – the basis of the three-way match buyers rely on.

7) Settlement

Settlement is calculated on the confirmed fine weight and purity from the assay. Because it is based on measured results, the buyer pays for exactly the gold the refinery confirms is present – the heart of why refinery-assay settlement is fair to both sides.

8) Documentation

The refinery issues the final documentation – assay results, confirmed weight and purity, and settlement records – which complete the consignment’s paper trail and the chain of custody. See our guide on the gold chain of custody.

What this means for buyers

The refinery process is the reason serious transactions settle on assay rather than on a declared figure. The declared purity gets the deal moving; the assayed purity is what you actually pay on. For a buyer, this is reassurance: as long as your supplier is honest and the gold is genuine, the refinery’s objective measurement will confirm it – and any discrepancy is caught before final settlement. It is also why a supplier who resists refinery assay is a serious red flag, as covered in our guide on spotting gold trading scams.

How Congo Rare Minerals fits into the process

Congo Rare Minerals (Reg. No. CD 893220) sources responsibly at origin in the DRC and Uganda, tests before shipment, and supports settlement on final assay at the buyer’s nominated refinery. We can supply dore and raw gold for refineries that refine in-house, or refined gold in 22K, 23K and 24K (most commonly 22K and 23K), and our Refining service covers the process from raw material to certified output. Every consignment travels with assay documentation and full export paperwork through the documented Uganda/Tanzania corridor. You can review our operations on the About page.

Frequently asked questions

What is the gold refining process?

It is the sequence by which gold is accepted, weighed, sampled, assayed, melted and refined to raise purity, cast into bars, and settled on the confirmed weight and purity – with documentation issued at the end.

How do refineries test gold purity?

They use XRF for fast, non-destructive screening and fire assay as the definitive reference method to determine the precise gold content, on which settlement is based.

What are the Miller and Wohlwill processes?

The Miller process uses chlorination to remove base-metal impurities, and the Wohlwill process uses electrolysis to reach the highest purities, such as 999.9. Both are standard industrial refining methods.

Why is settlement based on refinery assay?

Because the assay objectively measures the actual gold content, settlement on assay means the buyer pays for exactly what is confirmed present – protecting both buyer and seller.

What happens to dore or lower-purity gold at the refinery?

It is refined upward toward investment-grade fineness through melting and refining, then cast into bars and documented with its assayed purity.

Does Congo Rare Minerals provide refining?

Yes. Our Refining service covers the process from raw material to certified output, and we support settlement on final assay at the buyer’s nominated refinery.