Gold: Extraction

From cyanide heaps to doré bars at the mine

Gold occurs in quartz-vein lode deposits, in disseminated low-grade orebodies such as Nevada's Carlin Trend, in river placers, and as a by-product of porphyry copper. Most ore is crushed and leached with cyanide in tanks or on heaps, recovered on carbon and smelted into doré, a mixed gold-silver bar sent for refining. In the US, Nevada supplied about 64% of 2025 mine output, and about 7% came as a by-product of base-metal ores. Worldwide, an estimated 15% of gold is a by-product. Artisanal mining, often using mercury, adds a large informal share in Africa and Latin America.

Gold reaches the market by four routes. Most comes from large open-pit or underground lode mines that grind ore and dissolve gold with cyanide in tanks. Low-grade oxide ore is stacked on heaps and sprayed with cyanide instead, which is cheaper but recovers less. A sizeable share is a by-product of copper mines, where gold rides in copper concentrate to smelters. Artisanal miners, often using mercury, add a large informal share in Africa, Latin America and Asia. Recycling of jewellery and scrap is the fifth source and, unlike mining, responds within weeks to price. All routes end at a refinery that produces bars to LBMA or exchange standards.

Methods compared

How each method works

Ore is crushed and ground to a fine slurry. Cyanide dissolves the gold in agitated tanks and activated carbon adsorbs it. Carbon is stripped, gold is electrowon and smelted into dore. Refractory sulphide ore needs roasting, pressure oxidation or bio-oxidation first.

High recovery and scale; high capital cost, cyanide handling and tailings dams.

Run-of-mine or crushed ore is stacked on lined pads and irrigated with dilute cyanide for weeks to months. Pregnant solution is collected and gold is recovered on carbon. Used widely in Nevada, Mexico and West Africa.

Low capital and fast to build; lower recovery and slow leach cycles, weather sensitive.

Gold in porphyry copper ore floats with copper minerals into concentrate. Smelters pay for the gold, which is recovered from anode slimes in copper refineries. Grasberg, Oyu Tolgoi and Chilean porphyries are large examples.

Supply set by copper economics, not gold price; very large orebodies.

Individuals and small crews dig alluvial or shallow hard-rock ore, crush it by hand or with small mills, and amalgamate gold with mercury, then burn off the mercury. Output often moves through informal traders to Dubai and other hubs.

Livelihoods for millions; mercury pollution, child labour, smuggling and conflict finance risks.

Refiners melt and assay old jewellery, dental gold and electronic scrap, then refine to bullion. Jewellery is most of it. In India, much old gold is exchanged at the jeweller for new pieces.

Price-responsive within weeks; depends on households choosing to sell.

Share produced as a by-product

Who does it: global

Who does it: India

India mines almost no gold: Hutti produces about 1-2 t a year against demand of 710.9 t in 2025 (WGC). The country is the second-largest consumer and imported 721 t worth $72.0 billion in FY2025-26. Value is added in refining (MMTC-PAMP and others) and jewellery making.