Open Cast Gold Mining: 7 Steps With Real Costs

Open cast gold mining removes the rock above a gold deposit and digs the ore out in stepped layers, so the finished hole looks like an upside-down cone. The cost sits in the waste as much as the ore. A real 2025 feasibility study for an Idaho pit puts total site cost at US$10.52 per tonne of ore processed, and about US$1,480 per ounce all-in (Forte Dynamics for Integra Resources, DeLamar technical report, 8 December 2025). World mine output was about 3,300 tonnes of gold in 2025, with the United States at 160 tonnes (USGS, Mineral Commodity Summaries 2026).

This guide walks through the seven steps in the order a mine follows them. Each step uses numbers from that DeLamar report and from engineering literature, so you can see what the choices cost. A calculator near the end lets you test your own pit with your own numbers. In gold mining, open cast is used as another name for the open pit method: extracting a near-surface ore deposit with horizontal benches while dumping waste outside the final pit (Altiti and colleagues, IntechOpen).

Step 1: Prove the ore body before you design anything

Every pit starts with evidence that enough gold sits close enough to the surface. Teams combine geological mapping, geochemical sampling, geophysical surveys, satellite and airborne imagery, and finally drilling to fix the shape, depth and grade of the mineralised rock. Grade is the gold content per tonne of rock, measured in grams per tonne (g/t).

Satellites cannot see gold itself. They map the iron-oxide, clay and silica alteration that hot fluids leave around many gold systems, which helps a team choose where to put the first drill holes. Satellite-based mineral detection gives exploration targets, which still need ground sampling and drilling before anyone can call them a resource. Licence owners who want a quote can use the mining query form.

The DeLamar project shows what a drilled deposit looks like on paper. Its measured and indicated resources total 245.8 million tonnes at 0.37 g/t gold, which is 2.945 million ounces of gold, plus silver (DeLamar technical report, 2025). That grade is low, and it still supports a pit because the ore is near the surface and suited to heap leaching. A resource is an estimate of what is in the ground; a reserve is the part a study shows can be mined at a profit.

Step 2: Design the pit and test the economics

Engineers use pit optimisation software to find the largest shell where each block of rock still pays for its own mining and processing. The key idea is the cut-off grade, the lowest grade worth sending to the plant. At DeLamar, in-pit oxide resources are reported at 0.17 g/t gold-equivalent, while sulfide material needs 0.3 g/t at DeLamar and 0.2 g/t at Florida Mountain because it costs more to process (DeLamar technical report, 2025). Gold-equivalent counts silver as an extra amount of gold at a set price ratio.

The design also sets the stripping ratio, the tonnes of waste that must be removed to uncover one tonne of ore. A lower ratio means less waste handling. The break-even stripping ratio, where the profit margin is zero, sets the outer limit of the pit (IntechOpen). The DeLamar reserves were optimised at US$2,000 per ounce of gold and a mining cost of US$2.50 per tonne, while the study’s base case uses US$3,000 per ounce, so the design keeps a margin if the price falls.

Design also covers access roads, waste dumps, water control and the leach pads or tailings facility. Permit conditions shape these choices: in the DeLamar case the footprint was reduced by about 25% through successive studies, and the report expects further optimisation during permitting. The Bureau of Land Management published its Notice of Intent for the environmental impact statement in the Federal Register in May 2026, and the final statement and Record of Decision are targeted for the third quarter of 2027 (Integra Resources news release, 29 May 2026).

Step 3: Strip the overburden and cut the benches

Overburden is the soil and waste rock above and around the ore. Excavators and trucks remove it, and topsoil is stored separately so it can be put back later. Pre-stripping, the waste removed before any ore is sold, is a capital cost: DeLamar budgets US$9.6 million for it.

Chart

Stripping ratio at the DeLamar project

Tonnes of waste per tonne of material processed

The pit is cut in benches, horizontal steps that make the walls stable and give trucks room to work. Bench height is usually set as high as the equipment allows without creating a safety problem, from about 15 m in large mines to 1 m in small ones (IntechOpen). Height matters for stability. In a numerical model of an open pit limestone mine, raising the bench height from 5 m to 12 m cut the static safety factor by 43.78% (Scientific Reports, bench geometry study). That result comes from limestone, not gold ore, but it shows why geotechnical drilling comes before a final wall angle.

The stripping ratio differs a lot between pits, even inside one project, as the chart shows.

Step 4: Drill, blast, load and haul

Drill rigs bore holes in a planned pattern, explosives break the rock, and shovels or loaders fill trucks that carry ore to the crusher and waste to the dump. This cycle repeats on every bench, so small savings per tonne matter. At DeLamar, mining costs US$2.55 per tonne of rock moved, which is US$3.95 per tonne of ore once the waste is counted.

Blast design affects the pit wall as well as the broken rock. The limestone study above recorded flying fragments travelling 20 to 50 m from blasts, and it found that blast vibration limits must be set for each slope rather than one value for the whole mine (Scientific Reports). Exclusion zones, vibration monitoring and trained crews are the practical response.

Step 5: Crush, leach and recover the gold

Ore is crushed, then gold is dissolved and caught. Cyanide leaching has been the dominant gold extraction method since the 1970s, using a dilute solution of 100 to 500 parts per million cyanide, and the two most common routes are heap leaching and milling with carbon-in-leach (Society for Mining, Metallurgy and Exploration). In heap leaching the crushed ore is stacked on a lined pad and sprayed with solution; in carbon-in-leach the ore is ground and the dissolved gold is adsorbed on activated carbon.

Chart

Where the all-in cost goes at one open pit

US$ per ounce of gold-equivalent, co-product basis, life of mine

DeLamar plans a heap leach at 35,000 tonnes a day, with a life-of-mine gold recovery of 72.3% and a processing cost of US$5.02 per tonne. Recovery varies by ore type, from 45% to 95% for gold in the study’s cut-off calculations. Processing is the largest single block of the all-in cost, as the chart shows.

Cyanide is managed under the Cyanide Code, a voluntary programme for gold and silver miners and cyanide suppliers. It has more than 240 signatory companies and requires independent audits every three years (International Cyanide Management Institute).

▶ How gold is mined and refined, from rock to ring. · 5:27

What a real open pit costs per tonne and per ounce

The table below turns the DeLamar study into per-tonne costs, all in US dollars. Use it as one worked example, not an industry average. Costs depend on rock hardness, haul distance, water, power and labour.

Converted to ounces, the study gives a total cash cost of US$1,179 and an all-in sustaining cost of US$1,480 per ounce of gold-equivalent, with pre-production capital of US$347.0 million and a payback of 1.8 years at the study’s US$3,000 base gold price (DeLamar technical report, 2025). Prices change daily, so test your own pit with a current price in the calculator.

Step 6: Rehabilitate while you mine

Progressive reclamation means each area is restored as soon as it is no longer needed, for example waste rock piles once they reach their permitted size (IntechOpen). The usual sequence is recontouring the ground to a stable, draining shape, capping with a soil layer that plants can grow in, and revegetating. The goal is a site that is safe, stable, non-polluting and able to support an agreed land use afterwards.

Money is set aside for this from the start. DeLamar’s study carries US$65.5 million of reclamation cost over the life of the project, including US$26.4 million for water treatment after closure.

▶ A plain-language claymation on the seven environmental impacts of mining. · 2:31

Step 7: Close the pit and hand the land back

Closure ends with removal of buildings, covers on waste and tailings, long-term water monitoring and an agreed use for the land and the pit void. It can take years. The earlier DeLamar pits operated from 1977 to 1998, closure work began in 2003 and was nearly complete by 2014, and monitoring and bonds are still in place (DeLamar technical report, 2025). That history is a useful reminder that the closure budget and the community plan belong in the first feasibility study, not the last year of production.

For related reading on gold projects and licensing, see gold mines in Nunavut and their claim rules, gold deposits in Saskatchewan and a gold mine in Nova Scotia and its licence. For help with a site, contact the team via contact us.

If this topic matters to you, read Open Pit Mining Advantages and Disadvantages: Real Costs next.

Related reading on this site: Gold Mining KPIs: 12 Metrics With Real Mine Data.

Frequently asked questions

What is open cast gold mining?

It is surface mining of a gold deposit in benches after the overburden is removed. World gold mine production was about 3,300 tonnes in 2025 (USGS), and surface pits and underground mines both contribute to that total.

What is a stripping ratio and what is a good one?

It is the tonnes of waste removed per tonne of ore. DeLamar’s pits range from 0.47 at Florida Mountain to 1.16 in the DeLamar area, with a life-of-mine ratio of 0.54. The right figure is the one where the pit still earns a margin, which is the break-even ratio.

How much does it cost to run a gold open pit?

For DeLamar, US$10.52 per tonne of ore processed, made up of US$3.95 mining, US$5.02 processing and US$1.54 administration. All-in sustaining cost is US$1,480 per gold-equivalent ounce. Your site will differ, so use the calculator with your own numbers.

Is cyanide used in open pit gold mines?

Often, in dilute solution, in heap leach and carbon-in-leach plants. Companies that sign the Cyanide Code are audited independently every three years.

What happens to the pit after mining ends?

Waste areas are recontoured, capped with soil and replanted, water is monitored, and the pit void may be left as a lake or a managed landform under the agreed closure plan. The money for this is set aside during operations.