Gold vs Copper Deposits: Types, Ratios and Economics

Yes, often. In porphyry and iron oxide copper-gold (IOCG) deposits, gold and copper arrive in the same hot fluids and end up in the same rock, so a copper mine often produces some gold. At Freeport’s Indonesian mill, fed by the Grasberg district, the ore milled in 2024 averaged 1.27% copper and 1.00 g/t gold (Freeport-McMoRan 10-K, 2025 filing). But the pairing is not universal. Orogenic and most epithermal gold deposits are valued for gold (and silver), not copper, and some giant porphyries such as Morenci in Arizona carry almost no gold. This guide compares gold vs copper deposits by type, shows copper-to-gold ratios for named mines, and explains what the numbers mean for exploration and for the money a project can make.

Gold vs copper deposits: the four types side by side

Four deposit types explain much of the gold-and-copper overlap. They differ in the rock they sit in, the depth at which they formed and the metal that pays the bills. The table gives the main differences, with the grade figures that the cited geological surveys publish.

The USGS porphyry model, the USGS IOCG model and the USGS epithermal model are the basis for the first three rows (Cox and Singer, USGS Open-File Report 2007-1155; USGS epithermal gold-silver model). For orogenic gold, the standard classification paper places these deposits in regionally metamorphosed terranes of all ages, formed during compression at convergent margins (Groves and others, 1998, Ore Geology Reviews).

Porphyry deposits: how much gold sits with the copper

A porphyry copper deposit is a very large body of rock cut by thousands of small veins and sprinkled with copper sulfide. Grade is the amount of metal per tonne of rock: copper in per cent (%), gold in grams per tonne (g/t). Porphyry grades are low but the tonnage is huge, so mines are open pits or block caves that move tens of thousands of tonnes a day.

The USGS sorts porphyries into subtypes by their gold and molybdenum content: a porphyry is classed as copper-gold when the ratio of gold (in parts per million) to molybdenum (in per cent) is 30 or more, and as copper-molybdenum when it is 3 or less (USGS Scientific Investigations Report 2010-5070-B). That is why the gold answer depends on which porphyry you mean. Bingham Canyon in Utah holds 3,230 million tonnes (Mt) at 0.882% Cu and 0.38 g/t of gold, so a mill there sees roughly one gram of gold for every 23 kg of copper. Freeport’s Grasberg district mill and Oyu Tolgoi in Mongolia carry gold at 0.47 to 1.0 g/t. Butte, Montana (0.042 g/t) and Morenci (0.028 g/t) carry almost none.

The USGS epithermal model notes that these deposits commonly represent the shallow parts of larger hydrothermal systems, and in some districts a high-sulfidation gold deposit and an underlying porphyry copper-gold deposit formed in the same long-lived magmatic system. Our guide to porphyry copper deposits covers alteration zones and discovery history in more depth.

Copper-to-gold ratios in porphyry and IOCG deposits

The copper-to-gold ratio used here is simple: per cent copper divided by grams per tonne of gold. A ratio of 2 means 0.8% Cu goes with 0.4 g/t Au. A low ratio marks a gold-rich system, a high ratio a copper-dominant one. The table lists named deposits from government and company filings. The figures come from different years and reporting bases (resource, reserve or mill feed), so compare orders of magnitude, not decimals.

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Copper-to-gold ratio of selected deposits

Per cent copper divided by grams per tonne gold; resource, reserve or mill-feed basis as in the table

Three patterns stand out. First, the well-known gold-rich porphyries sit at a ratio of about 3 or less, and most large IOCG and porphyry mines cluster near 1 to 3. Second, a ratio above 15 means gold is a footnote: at El Teniente the model lists 0.005 g/t Au, so gold adds little revenue. Third, IOCG deposits are not richer in gold than porphyries per tonne. Their median gold grade is close to Bingham Canyon’s. What sets them apart is the iron oxide host rock, which gives a strong gravity and magnetic signal, and the uranium, silver and other metals that can come along.

Sources for the grade data: USGS porphyry model (SIR 2010-5070-B), Geoscience Australia’s mineral resources review (Australia’s Identified Mineral Resources) and the Freeport-McMoRan annual report.

IOCG deposits: Olympic Dam and the breccia-hosted group

IOCG stands for iron oxide copper-gold. The USGS IOCG model replaces the older Olympic Dam Cu-Au-U model, and Olympic Dam in South Australia is its best-known example, with copper, uranium, gold and silver in a large iron oxide body (Cox and Singer, 2007; Geoscience Australia). BHP’s 2009 statement, reproduced by Geoscience Australia, lists total resources of 9,080 Mt at 0.87% Cu, 0.27 kg/t U3O8 and 0.32 g/t Au, and reserves of 589 Mt at 1.81% Cu and 0.66 g/t Au. Reserves are richer than resources because only the best ore is mined first; that is the same reason a resource ratio can differ from a mill-feed ratio.

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Gold grade of eight selected deposits

Grams per tonne; selected deposits, not a full census

The USGS database of 33 IOCG deposits splits the type in two. Twelve fault- and vein-hosted deposits are small (median 3.5 Mt) but rich: median 2.3% Cu and 1 g/t Au. Twenty-one breccia- and fault-zone-hosted deposits are much larger (median 120 Mt) and leaner at 1.1% Cu and 0.48 g/t gold (Cox and Singer, 2007). The Cu:Au ratio is nearly the same in both groups, about 2.3, so the ratio tells you the fluid chemistry and the grade tells you the size of the plumbing.

Orogenic and epithermal gold: where copper drops out

Orogenic gold deposits form when metamorphic fluids move up faults during mountain building. The gold travels in quartz veins, and the ore is valued for gold, not copper.

Epithermal deposits form much closer to the surface. The USGS model gives a depth of about 50 to 1,500 m below the water table and temperatures of 100 to 300 °C. Gold content runs from 0.1 to over 30 g/t, but the bulk-mined deposits are mostly under 1 to about 3 g/t, recovered by heap leach or carbon-in-pulp at over 90% in oxidised ore. Because epithermal ore forms in the shallow part of larger systems, epithermal gold can still point towards a copper-gold porphyry at depth. See our epithermal gold guide for the styles and clues.

What gold-copper ratios mean for exploration

A ratio is only useful when both metals are assayed. Many old copper drill programmes sampled only for copper, and many old gold programmes ignored copper, so a district can look like a gold camp or a copper camp mostly because of what was measured. These checks follow from the deposit data above.

• Assay both metals in every hole. A Cu:Au ratio of 1 to 3 in a new intercept points to a copper-gold porphyry or IOCG system; a ratio over 15 points to a copper-only system, and gold with little copper points to an orogenic or epithermal system.
• Match the search to the host. IOCG targets are often found where gravity and magnetic surveys show dense iron oxide bodies, which is how the Gawler Craton of South Australia is searched.
• Look up and down. Epithermal gold at the surface can sit above a porphyry; a barren copper-molybdenum porphyry can have no gold at any depth.
• Check the rock first. Alteration (the chemical change hot fluid makes to rock) and structures come before assays. Iron oxide, clay and silica are visible from space.

Satellite imagery cannot see copper or gold itself. It maps the iron-oxide stain, clay minerals and faults that these systems leave. A satellite screen helps a licence owner decide which blocks to sample first, before paying for drilling. Our overview of satellite-based mineral detection explains what the maps can and cannot show, and the mining query form is the way to ask for a quote on your own licence area.

▶ Explains how satellites map the iron stains, clays and faults around gold and copper systems. · 4:25

What gold and copper deposits mean for project economics

Scale matters first. In the United States, about 7% of 2025 gold output was recovered as a by-product of base-metal ores, chiefly copper ores, while Nevada alone made about 64% of domestic gold from gold mines (USGS Mineral Commodity Summaries, 2026). Arizona, home to Morenci and its low-gold porphyries, produced about 70% of US copper (USGS copper summary, 2026). So copper mines add gold at the margin in the US, while elsewhere, as at Grasberg, the by-product is a large part of revenue.

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Grasberg mill ore grade, 2021 to 2025

Copper in per cent, gold in grams per tonne; Freeport Indonesia mill; axis starts at 0.3

Revenue depends on grade, recovery and price. Copper grades of 0.3% to 1.3% mean 3 to 13 kg of copper per tonne of ore, while gold grades of 0.3 to 1 g/t mean less than one gram. The price per tonne of metal decides how much each adds.

Prices change daily. On 28 October 2026 Trading Economics showed gold at about US$4,046 per troy ounce and copper (COMEX) at about US$6.62 per pound (gold, copper). Freeport’s Indonesian mines show how large the gold share can be. In 2025 they sold 1,205 million pounds of copper at an average realised US$4.53 per pound and 1,050 thousand ounces of gold at US$3,418 per ounce (Freeport-McMoRan 10-K). On our arithmetic that is about US$5.5 billion of copper and US$3.6 billion of gold, so gold was roughly 40% of the value of the two metals even though it was only a by-product.

The Indonesian mill grades below show how the gold side moves. Copper grade varied between 1.10% and 1.30% over five years, while gold fell to 0.77 g/t in 2025, the year of the September mud rush incident that disrupted mining (Freeport-McMoRan). A project built on a Cu:Au ratio of 1.3 is far more exposed to the gold price than one at a ratio of 19.

Two costs also matter. Gold in sulfide ore is more costly to recover than gold in oxidised ore (USGS). And a gold-only mine can run profitably at grades of 1 to 3 g/t only if the tonnage is large and mining is cheap. Use the calculator below to test a grade pair against your own prices and recoveries.

▶ Follows gold from rock to refined metal, step by step. · 5:27

A worked example: same copper, different gold

Take two ore bodies with the same copper grade of 0.8% Cu. Ore A carries 0.8 g/t gold (a ratio of 1) and ore B carries 0.05 g/t gold (a ratio of 16). At the 28 October 2026 prices above and before any recovery loss, a tonne of either ore holds about US$117 of copper (8 kg, or 17.6 lb, at US$6.62 per pound). The gold in ore A is worth about US$104 per tonne and in ore B about US$6.5. Ore A is therefore worth around US$221 per tonne and ore B around US$123, a difference of 80% from a gold grade that most drill logs treat as a side note.

The same arithmetic runs the other way. If gold falls by a quarter, ore A loses about US$26 per tonne while ore B loses under US$2. That is why it pays to read the Cu:Au ratio alongside the headline copper grade, and to check whether the gold has been assayed with the same care as the copper. Recoveries differ too: Freeport reported 87.9% copper recovery and 75.7% gold recovery in the Indonesian mill in 2025, so the metals in the bag are less than the metals in the ground.

For a wider view across every metal, see our guide to types of ore deposits.

Frequently asked questions

Does copper and gold go together?

In porphyry copper-gold and IOCG deposits, yes: gold travels with copper and is recovered as a by-product or co-product. At Freeport’s Indonesian mines, gold was about 40% of the value of copper plus gold sold in 2025 (Freeport-McMoRan 10-K, our arithmetic). In orogenic gold deposits and most epithermal deposits, copper is minor or absent.

What is a copper-to-gold ratio?

It compares copper grade with gold grade. This page uses per cent copper divided by grams per tonne of gold. Bingham Canyon is 0.882 / 0.38 = 2.3; Morenci is 0.524 / 0.028 = about 19.

Which has more gold, a porphyry or an IOCG deposit?

Neither type always wins. The median breccia-hosted IOCG deposit grades 0.48 g/t gold (USGS); the Grasberg district mill, Oyu Tolgoi and Bingham Canyon grade between 0.38 and 1.0 g/t. Butte and Morenci, both porphyries, grade under 0.05 g/t.

Is gold always a by-product at copper mines?

Mostly, but the split is mine-specific. Newcrest’s Cadia district resource is 1,212 Mt at 0.32% Cu and 0.75 g/t gold (USGS), so on simple grade-times-price arithmetic at the 28 October 2026 prices quoted above and before recoveries, gold is worth roughly twice as much as copper per tonne there. The wider Cadia Province resource is 44 million ounces of gold and 8 million tonnes of copper in 3 billion tonnes of ore (Geoscience Australia, 2009).

What is an orogenic gold deposit?

It is a gold-bearing vein system formed in metamorphic rock during mountain building at a convergent plate margin (Groves and others, 1998). Copper is not the main metal.

How deep do epithermal gold deposits form?

From about 50 m to 1,500 m below the water table, at temperatures between 100 and 300 °C (USGS Scientific Investigations Report 2010-5070-Q).

What do IOCG and porphyry deposits have in common?

Both are large copper-gold systems linked to intrusions and hot fluids. Porphyries are veined and disseminated rock around intrusions; IOCG deposits are iron oxide-rich breccias and shear zones. The Cu:Au ratio is similar, about 1 to 3, for the examples in this guide.

Do these deposits carry other metals?

Yes. Olympic Dam also contains uranium oxide and silver (World Nuclear Association; Geoscience Australia), and porphyries often carry molybdenum and silver.

Can satellite data tell a gold deposit from a copper deposit?

Not by itself. Satellites map alteration minerals, iron oxide and structures; the metal split needs rock sampling and assays. The imagery helps rank which ground to sample first.

How can a licence owner request a screen of a licence area?

Send the boundary through the mining query form or contact us. Results are exploration targets that sit ahead of a resource estimate.