How Gold Is Mined from Ore to Bar: From Rock to Bullion 2026

Understanding how gold is mined from ore to bar means following rock through a chain of stages: it is found, blasted out of the ground, crushed and ground to a powder, chemically separated from the surrounding waste, smelted into a rough bar called doré, then refined and cast into a stamped bar. Almost no finished bar is ever made at the mine itself.

Here is the whole chain in ten steps.

1. Exploration: geologists map veins, drill core, assay samples and size the deposit before any digging begins.
2. Feasibility: engineers model the mine, mill and cost base, then test whether the ore earns more than it costs.
3. Extraction: ore is drilled, blasted, loaded and hauled out, either from an open pit or from underground.
4. Crushing: run-of-mine rock is broken down in jaw and gyratory crushers until the pieces are small enough to mill.
5. Grinding: mills grind the crushed rock to a fine powder, using steel balls and water to keep it suspended.
6. Concentration: gravity separators and froth flotation pull gold-bearing particles away from the surrounding waste.
7. Cyanidation: a dilute sodium cyanide solution dissolves the fine gold, which is then adsorbed onto activated carbon.
8. Smelting: the loaded carbon is burned off and the remaining gold and silver melt together into a doré bar.
9. Refining: Miller and Wohlwill processes strip out the remaining silver, copper and lead, leaving 99.99% pure gold.
10. Casting and hallmarking: the metal is poured into moulds, weighed, numbered, assayed and hallmarked for sale.

Figures below reflect published mining practice and reference sources, and they were last checked in October 2026. Costs, grades and recoveries vary widely between deposits, so treat every number as a range rather than a rule.

How Gold Is Mined from Ore to Bar: The Process

The route rock takes is rarely a straight line. A heap leach operation skips crushing and flotation entirely, an underground mine may run gravity and flotation only, and a refractory deposit adds a roasting step before anything can be leached. What every route shares is the same logic: remove gold from a very large mass of rock, then concentrate that gold into a small, pure, saleable form.

How gold is mined from ore to bar, stage by stage

Metallurgists call the sequence comminution, recovery, smelting and refining, but the useful way to read it is as a series of separations. Each stage strips away one more layer of unwanted material.

Stage	What happens	What comes out	Typical duration
Exploration and drilling	Core drilling and mapping test the deposit	A resource estimate with a grade range	3 to 10 years
Feasibility and permitting	Mine plan, mill flowsheet and cost model are tested	A financed construction decision	1 to 3 years
Extraction	Drilling, blasting, loading and hauling	Run-of-mine ore plus waste rock	Hours per shift, decades of mine life
Crushing	Jaw and gyratory crushers reduce rock size	Semi-crushed ore, often 10 to 30 mm	Seconds to minutes per tonne
Grinding	SAG and ball mills grind with steel balls and water	Ore pulp, typically 70 to 150 micrometres	Minutes per tonne
Gravity and flotation	Dense particles settle; sulphides float in froth	Gold concentrate and a tailings stream	Hours to a few days per batch
Cyanidation and carbon capture	Leach solution dissolves gold; carbon adsorbs it	Pregnant solution and loaded carbon	12 to 48 hours of leaching
Smelting	Carbon is burned off in a furnace	A doré bar, roughly 85 to 90 percent gold	1 to 3 days
Refining	Chlorination and electrolysis strip out impurities	Refinery fine gold, 99.99 percent	Several days
Casting and hallmarking	Metal is poured, cooled, weighed, numbered, assayed	A serialised, hallmarked bullion bar	Hours, plus transport to a buyer

That table describes a hard rock operation. Placer and heap leach projects skip most of the middle rows, which is why two mines reporting the same metal price can have completely different cost structures.

What Is Gold Ore and How Much Gold Does It Contain?

Ore is any rock carrying enough gold to be worth processing. Waste rock, or gangue, is everything else blasted out of the pit that goes straight to a dump. The difference between them is decided on the spot by a geologist or a grade-control technician sampling the face before it is loaded.

Five terms get confused constantly, so it is worth separating them cleanly.

• Ore grade is the amount of gold in the rock, usually quoted in grams per tonne.
• Concentrate is a processed intermediate where the gold has been upgraded from grams per tonne to a fraction of a percent or more.
• Tailings are the residue that leaves the plant after the recoverable gold has been taken out.
• Doré is a rough bar of gold mixed with silver and a little base metal, produced at the mine or at a smelter.
• Refined bullion is metal refined to a stated fineness such as 999.9, cast and stamped by a refinery.

As broad examples rather than hard rules, large low-grade open pit and heap leach operations commonly work between 0.4 and 1.5 grams per tonne, conventional open pit mines run nearer 1 to 2 grams per tonne, and underground operations that chase narrower veins can see 3 to 8 grams per tonne. For context, one open pit project studied publicly in recent years reported an average ore grade of about 1.04 grams per tonne. Placer deposits are described differently again, in grams per cubic metre of gravel, because the volume is not rock at all.

Grade is only one number in the economics, and frequently the least important one on its own. Recovery rate, operating cost, the mineralogy of the ore, how much byproduct silver or copper is credited against costs, and whether the deposit can be mined safely all move the answer. A 1.2 gram per tonne deposit that recovers 94 percent of its gold and sits next to existing road and power infrastructure can beat a 3 gram per tonne deposit that is hard to leach and 400 kilometres from a port.

A worked example: how much rock for one ounce?

Here is the calculation that most public explainers skip. A troy ounce of gold weighs 31.1035 grams. Take an ore averaging 1.5 grams per tonne with a 90 percent recovery, which sits comfortably inside normal practice for a large open pit operation.

Each tonne of ore therefore yields 1.5 grams of contained gold, and 90 percent of that reaches the doré stage: 1.35 grams of recovered gold per tonne of ore. Dividing 31.1035 by 1.35 gives about 23 tonnes. So it takes roughly 23 tonnes of ore to produce one recovered ounce of gold.

That is the ore figure only. Add the waste rock that has to be moved to reach it, and the totals climb sharply. Reference works commonly quote a figure near 79 tonnes of mine waste per ounce of gold once overburden and barren rock are counted. Anyone who has seen a pit that looks enormous for its output is looking at exactly this arithmetic.

How Is Gold Found Before Mining Begins?

Gold is found by looking for the conditions that concentrate it, not by looking for gold itself. It is too scarce to see in most rock, and the visible speckles in a stream are the leftovers of an erosion process, not a guide to the source.

Geologists build a model of the geology first, using mapping, aerial photography, geochemical sampling of soil and stream sediments, and geophysical surveys that sense differences in rock density, conductivity and magnetism. Drilling then tests the model. A core drill cuts a narrow cylinder of rock, which is split, logged and sent to an assay laboratory.

Assaying is where the number comes from. A laboratory fires a small, precisely weighed sample and measures the gold content, with results returned in grams per tonne. Thousands of those results are modelled into a resource estimate, and an independent geologist signs it off before any of it becomes a number investors can trade on.

After that comes the feasibility stage, where the resource meets engineering. The study asks two questions: can the ore be processed at a recovery rate that makes the grade pay, and can the mine be built and run within a cost structure that survives a lower metal price than today? Only after that does a shovel normally appear.

How Is Gold Extracted from the Ground?

Extraction is the part everyone pictures, and it is the most straightforward stage in the chain. Ore is drilled with rigs that punch or blast holes, loaded with explosives, and then broken. Front shovels or loaders fill haul trucks, which take the rock to a primary crusher at the pit or underground at the portal.

Underground mining does the same job with a different shape. Rather than stripping everything above the ore, miners drive declines and levels into the rock, fill stopes and draw the broken ore up through shafts. It suits steep, narrow, high-grade veins that would be uneconomic to chase from the surface, and it carries far more ground-control risk.

Between the blast and the mill sits grade control. Crews sample the face, mark high and low zones on the haul route, and direct material to different destinations. Sending low-grade rock to the mill at all is the most expensive decision an operation makes, so that sorting is a continuous, unglamorous discipline.

Method	What it suits	Typical grade	Typical recovery	Main limitation
Placer	Alluvial gravel in streams and terraces	Grams per cubic metre	Often well below 90 percent	Shallow and limited in volume
Heap leach	Oxidised, low-grade, large-tonnage ore	0.4 to 0.8 g/t	60 to 75 percent	Long leach cycles, slow to pay back
Open pit	Large, shallow or gently dipping orebodies	0.8 to 2 g/t	85 to 95 percent	Huge waste rock volumes
Underground	Narrow, steep, high-grade veins	3 to 8 g/t	85 to 95 percent	Ground control and development cost
By-product	Copper, lead or zinc operations carrying gold	Varies widely	Varies widely	Gold output is not the business driver

Recovery figures in that table come from published developer studies and pilot campaigns rather than marketing material. Recent base-case studies commonly assume about 95 percent recovery, while heap leach pilots have targeted nearer 70 percent at pilot scale.

How Is Gold Separated from Ore?

Separation is where the volume of rock becomes a volume of gold. Nothing clever happens in a single step; each method takes advantage of a different physical property that the gold or its host minerals happen to have. It is also the longest stretch of how gold is mined from ore to bar, and where most of the operating cost sits.

Comminution: why gold is never mined straight from rock

Crushing breaks the rock, but grinding is what actually sets the processing route. In a SAG mill, large steel balls tumble with the ore, and a second stage of ball mills fine-grinds it until gold grains are freed from the surrounding mineral. The practical target is a grind where roughly 80 percent of the pulp passes 150 micrometres or finer. Grind any coarser and locked gold stays buried in the particles; grind finer and the mill burns power it does not need to.

Crushers usually sit right at the mine mouth, which cuts the haul distance and lets the pit run at a steadier rate. Grinding happens at the mill, next to the concentrator.

Gravity, flotation and amalgamation before cyanide

Because gold is dense, it responds to water. Jigs, shaking tables and spiral ramps separate heavy particles from light ones, recovering coarse free gold cheaply and with no chemicals at all. That is how most placer gold is found: panning is just this idea done by hand.

Froth flotation takes the opposite approach. In a tank of slurry, air bubbles float up through water and carry only the water-repellent mineral particles with them. Gold is not usually the target, but many gold deposits are hosted in sulphide minerals such as pyrite, so the plant floats the sulphide concentrate and recovers the gold from it later. The froth overflows into a thickener, the concentrate goes to a smelter or a roaster, and the underflow becomes tailings.

Amalgamation, where gold is trapped in liquid mercury, is a third older method. It is fast and works on very small operations, and it is the single most damaging practice in the sector, because mercury vapour is toxic to the people doing the work. International programmes have pushed artisanal and small-scale mining off it over two decades, but it persists in parts of the world where formal processing is unavailable.

Cyanidation and carbon capture: CIL, CIC and heap leach

Most of the world production now runs on cyanidation. Gold dissolves in a dilute sodium cyanide solution, typically a few hundredths of a percent, when the ore is fine enough, the solution is alkaline enough to keep the cyanide stable, and enough oxygen is present. Leaching can take 12 to 48 hours.

Rather than recovering the dissolved gold from solution, modern plants attach it to activated carbon, which is essentially charcoal engineered to grab molecules. The loaded carbon is stripped with a hot caustic solution, the gold is precipitated out of that, and the now-empty solution goes back to leaching. Sodium hypochlorite or ozone destroys any remaining cyanide before water is discharged, and cyanide-bearing solution is never released untreated.

Two circuit layouts dominate. In carbon-in-pulp, the slurry is leached and adsorbed in the same tanks. In carbon-in-column, the slurry is leached first, the clear solution passes through columns packed with carbon, and the carbon is stripped separately. Heap leaching is the third variant, quite different in character: crushed ore is stacked on a lined pad, a weak cyanide solution is dripped through it for weeks or months, and pregnant solution is collected from the bottom.

Not every ore will give up its gold to cyanide. Refractory ore traps gold inside sulphide crystals where the solution cannot reach it, so it is roasted to burn off the sulphides, pressure-oxidised, or biologically oxidised first. That adds a plant, time and cost, and it is often the difference between a deposit that works and one that does not.

What Happens to Gold Concentrate and Doré?

Concentrate and doré are both intermediates, and confusing them with a finished bar is the most common misunderstanding in this whole chain.

Flotation concentrate may be roasted on site to drive off sulphides and carbon, or it may leave by truck or rail to a smelter if the mine is far from a refinery. Either way, the concentrate arrives as a fine powder carrying a small percentage of gold rather than grams per tonne.

At the smelter, the concentrate is smelted and the gold and silver it carries melt together into an unrefined bar, typically around 85 to 90 percent gold with the balance mostly silver plus copper, lead or zinc. That bar is doré, and it is a tradeable intermediate that no serious buyer treats as investment metal. It still has to be refined before it means anything as bullion.

Modern smelters also capture the sulphur dioxide, arsenic and mercury released from the charge, which is a large part of why modern facilities are expensive to build and tightly permitted.

Product	Typical fineness	Where it is made	Who buys it
Concentrate	Often a few percent gold, variable	Concentrator at the mine	Roaster or smelter
Doré bar	About 85 to 90 percent	Mine smelter or custom smelter	Refinery or trader
Refinery fine gold	99.99 percent	Specialist refinery	Mints, bullion dealers, banks
Minted bullion bar	999.9 fineness or better	Mint or refiner	Retail investors and banks

How Is Refined Gold Turned into a Bar?

Refining is the step that turns a mixed metal into a defined product, and it is the last, least mine-side part of how gold is mined from ore to bar. The doré arrives, gets remelted, and then goes through two refining processes that have barely changed in principle since the nineteenth century.

The Miller process, patented in 1867, blows chlorine through the molten metal. Gold reacts with chlorine and dissolves as gold chloride while most base metals either volatilise or stay behind, and the gold is then precipitated out of solution. It is fast and inexpensive, and it typically takes the metal to about 99.5 percent.

The Wohlwill process, patented in 1878, then takes it the rest of the way. An impure gold anode is dissolved in an electrolyte and the gold plates out onto a cathode in a controlled electrolytic cell, while silver and copper stay in solution or fall as sludge. The result is the 99.99 percent that investment-grade bullion requires. Every modern refinery runs both, and the electrolysis step is what makes the claim on a bar defensible.

From there the metal is cast. Molten gold is poured into moulds, often under vacuum or inert gas to keep oxides out, and it is allowed to cool under controlled conditions. Bars are then trimmed, weighed, given a serial number, and hallmarked with the refiner’s mark, the fineness and the weight. A sample goes to an independent assay office, which issues a certificate for the batch. London Good Delivery bars, the international trading standard, weigh 400 troy ounces and require three good refiners, each holding a minimum stock of refined metal, to certify the metal.

Provenance is the part buyers should care about most. The serial number, hallmark and assay certificate let anyone trace a bar back to a refiner and check its weight and fineness, and reputable dealers will show you the certificate before the bar leaves the counter. A bar that arrives without any of that is just metal in a shape.

What Is the Difference Between a Gold Bar and a Gold Coin?

A bar and a coin usually contain the same purity, and the difference is mostly in how they are made, shaped and sold. Both are bullion, but they behave differently in the market.

A bar is cast from refined metal, so it carries no minting premium beyond the cost of casting and stamping. It usually comes in a heavier weight, and heavier bars are typically priced closer to the underlying metal. A coin is struck, not cast, which adds a manufacturing step, and popular designs such as American Eagles, Krugerrands or Maple Leafs can also carry a collector premium that moves independently of the metal.

That premium cuts both ways. Coins are easier to resell in small, convenient amounts and are widely accepted, but you may pay above the metal value and give some of it back when you sell. Bars usually trade at a tighter spread, which makes them the simpler choice for holding metal and the worse choice for the moment you want to sell a small amount. A 400 ounce bar is a different product from a 1 ounce bar in more than weight: the smaller one is what most individual buyers actually want.

For anyone checking value, the useful habit is to read the fineness stamp and the assay before the shape. 999.9 means 99.99 percent pure, which is the same number whether it is struck into a coin or cast into an ingot.

Frequently Asked Questions

Conclusion

The chain runs from a mapped deposit, through blasting, crushing, grinding, concentration, cyanidation and carbon capture, to a doré bar at the smelter and a 99.99 percent bar at the refinery. Grade, recovery and cost are the three numbers that decide whether that chain is worth running, and they explain why two mines producing the same metal can have very different economics.

If you want one practical starting point, learn to tell the four material types apart: ore, concentrate, doré and refined bullion. A product’s fineness stamp, serial number and assay certificate tell you which stage it came from, and that is a far better basis for judging a gold product than its shape, weight or finish.

Source: https://www.pgm-blog.com/how-gold-is-mined-from-ore-to-bar/