Gold Extraction From Soil: Methods, Borax and Arsenic Ores

Gold extraction from soil means concentrating the gold first, then recovering it. For loose placer soil, that usually means washing and screening, gravity concentration with a pan or sluice, and smelting the concentrate with a flux such as borax. Fine or chemically locked gold needs milling and leaching at a permitted plant. Before you buy equipment, get an assay: the grade decides whether any of this pays.

This guide covers the steps, the throughput of small equipment, what borax really does, why arsenic-bearing ore needs a different route, and how to test the economics with your own numbers. It is written for consultants, claim owners and small operators who need to judge a site.

How to extract gold from soil in six steps

1. Confirm your right to work the ground. Get the landowner’s permission and the licence, claim or permit that applies where you are. Water use and discharge often need separate approval.
2. Sample and assay. Take samples across the area and at depth, and send them to an accredited laboratory. An assay measures how much gold is in a sample. Results come in grams per tonne (g/t), parts per million (ppm, the same number as g/t) or parts per billion (ppb).
3. Find out what kind of gold you have. Visible flakes in a test pan point to gravity methods. A good assay with no visible gold suggests very fine or locked gold, so ask a metallurgist for a recovery test.
4. Wash and screen. Break up the clay with water and remove oversize stones so that the heavy minerals can settle.
5. Concentrate by gravity. The US EPA explains that most concentration methods rely on gold’s high density. Options include pans, sluices, shaking tables, spirals and centrifuges.
6. Recover the metal. Smelt a high-grade concentrate with a flux, or send material to a permitted leaching operation. Sell through a refiner or licensed buyer, and rehabilitate the ground as your permit requires.

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From soil to gold in 4 stages

1. 1AssayProve the grade across the ground.
2. 2WashBreak up clay and screen out stones.
3. 3ConcentrateUse gravity to collect the heavy minerals.
4. 4RecoverSmelt rich concentrate or use a permitted plant.

A satellite image cannot measure the gold in soil. It can help a consultant plan the fieldwork by showing access, drainage, old workings and disturbed ground before a sampling crew travels to site.

Gold extraction from soil: which soils are worth working

Not every gold-bearing soil is ore. Ore is material that can be mined and treated at a profit, and the same soil can pass or fail that test as prices and costs change. Three types of ground lead to very different decisions.

Placer soil and gravel

A placer is a deposit of loose sediment in which water has concentrated gold particles. These are the best candidates for simple washing and gravity recovery, because the gold has already separated from the rock. Washington State’s placer mining guide remains a clear introduction to the equipment and to where such gold collects. Our guide to gold deposits in the United States shows where the main districts are.

Residual soil over a lode

Weathering can leave gold in soil directly above a hard-rock vein, called a lode. Such soil is often more useful as a pointer to the source than as a mining target. In exploration, a soil survey measures gold in ppb and maps where values rise.

Oxidized low-grade material

Weathered, oxidized ore may suit heap leaching, in which a solution trickles through a lined pile of ore. The EPA’s 1994 gold technical report says heaps are typically built from lower-grade oxidized ore. This is an industrial process that needs engineering, liners and permits. It is not a backyard method.

Reading a soil assay against ore grades

The table shows why a single high sample proves little. A soil result must hold up across a measured volume of ground before it can support a mining decision.

Equipment for small-scale soil and gravel recovery

Throughput often decides the method. A pan is good for testing, but it cannot move enough material for most production. Washington’s 1979 guide gives these working figures for loose material, and your rate will vary with clay content, gold size and crew.

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How much material small equipment can wash

Cubic yards per 10 hours, upper reported figures for loose material

The EPA notes that sluices treat large amounts of material quickly but often do not produce a rich concentrate, so a second step such as panning usually follows. For a wider view of mechanised digging, see our surface mining methods for gold and these cost-effective strategies for gold extraction.

Borax gold extraction: what the method really does

Borax does not pull gold out of soil. It is a flux used in the last step, direct smelting, after gravity concentration has already done most of the work. The EPA’s description is the clearest public summary:

• Concentrate and a flux, such as borax, go into a crucible, a high-temperature bowl made for smelting.
• The flux lowers the melting temperature and viscosity of the non-gold minerals, so they separate more easily. It does not change the melting point of gold.
• Batches are small, usually around 50 to 100 grams of concentrate.
• The charge is heated to 1,065 degrees Celsius, the temperature at which gold melts, usually with a blow torch.
• Good concentrate can yield doré, a semi-pure gold alloy, that can reach upwards of 95% purity.
• Poor concentrate may need a further pour to separate the slag, which can still contain gold worth reprocessing.

Why miners choose it over mercury

The main case for smelting is that it avoids mercury. The World Health Organization lists kidney and nervous system damage among mercury’s health effects. A published review citing the UN’s 2018 global assessment gives an estimate of 838 tonnes of mercury released to air each year by artisanal and small-scale gold mining, about 38% of human-caused air emissions. Our page on the risks of mercury in gold extraction covers this further.

Where borax falls short

Smelting only works well on a rich concentrate. If gravity methods lost the fine gold to the tailings, borax cannot bring it back. The method also involves extreme heat, so use proper protective equipment and good ventilation, keep other people away and follow local rules. Published recovery rates depend heavily on the concentrate, so test your own material and weigh the results instead of relying on a general percentage.

▶ How gold moves from rock to refined metal, step by step · 5:27

Arsenic gold extraction: treating refractory ore

Arsenic is not used to extract gold. The phrase refers to recovering gold from ore that contains arsenic, often in the sulfide mineral arsenopyrite. Such ore is usually called refractory. A 2025 paper in REM, International Engineering Journal classes an ore as refractory when cyanide leaching recovers less than 80% of the gold. Sulfides can lock the gold inside their crystals, where the leach solution cannot reach it.

This work belongs in an engineered plant, and it is not a soil method for small operators. WHO warns that long-term arsenic exposure can cause cancer and skin lesions. If an assay shows high arsenic, stop and take specialist advice before any heating or crushing.

Roasting, pressure oxidation and bacterial oxidation compared

The REM paper reports that acid POX typically recovers 90% to 95% of the gold, and that autoclave recovery typically runs 5 to 10% higher than recovery after roasting. In its own laboratory work on a composite from the Faina project in Brazil, an acid test reached 98.40%. That is a test result on one prepared concentrate, not plant performance. Older reviews such as the North Carolina Geological Survey’s gold circular also describe bacterial leaching as an alternative to roasting.

Why the arsenic must be managed

Mined sulfide rock can also harm water. The USGS describes how old mine materials and rock exposures can erode and affect streams. Project budgets should therefore include waste characterisation and long-term water management from the start. Arsenic can also occur in weathered minerals: the USGS describes scorodite as an iron-arsenic mineral derived from weathering.

▶ The main environmental impacts of mining, explained in clay · 2:31

Leaching and recovery rates compared

Leaching dissolves gold into a solution. It is the route for gold too fine for gravity, and it needs trained staff and proper containment. The EPA says chemical leaching has been increasingly adopted in small-scale mining, and that it works best when gravity pre-concentration comes first. See our explainer on cyanide heap leaching for how a heap is run.

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Reported gold recovery by route

Percent of contained gold, low and high of each reported range

Recovery differs widely by route. The EPA’s 1994 report gives 60 to 80% for heap and valley fill leaching and 92 to 98% for tank methods. Tanks recover more but need milling, which is why the same report links lower-grade ore with heaps and higher-grade ore with tank circuits. A higher recovery is only worth paying for when the extra gold covers the extra cost.

Is gold extraction from soil profitable?

It can be, but only when grade, volume, recovery and costs work together. Gold price helps. The USGS estimated an average of US$3,300 per troy ounce in 2025, up from US$2,388 in 2024. An annual average is only a guide, so use a current quote from your buyer or refiner in any estimate.

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Annual average gold price

US$ per troy ounce; 2025 is a USGS estimate

A strong price does not rescue a poor site. Work through this list before you commit money:

• Grade: is the average based on many samples, or on one good result?
• Volume: how many tonnes can you actually dig, including overburden?
• Recovery: has a test on your own material measured it?
• Water: is there a legal and reliable supply?
• Title: does your licence cover mining, or only exploration?
• Closure: what will rehabilitation and bonding cost?

The calculator below gives a first screen. It does not replace a metallurgical test or a professional estimate. For scale, compare your figures with the world’s highest gold mines by reserves.

Other pages from Farmonaut cover fleet management, carbon footprinting, product traceability, loan and insurance verification, the large-area admin app, the mobile app and the developer API.

▶ What owning a gold claim does and does not give you · 3:19

Frequently asked questions

How do you extract gold from soil at home?

Small-scale testing usually means panning a soil sample after washing out the clay, where you have permission. Heating, smelting and chemical work are hazardous and may be regulated, so they do not belong in a home. Never use mercury.

What is the borax method of gold extraction?

It is direct smelting of a gold concentrate with borax as a flux. The EPA describes small batches of about 50 to 100 grams, heated to 1,065 degrees Celsius in a crucible. The flux helps the other minerals separate as slag.

Does borax lower the melting point of gold?

The EPA says the flux lowers the melting temperature and viscosity of the non-gold minerals. The charge is still heated to the temperature at which gold melts, 1,065 degrees Celsius.

Can borax extract gold directly from soil?

No. Soil must be concentrated first, because the EPA’s method uses only small batches of concentrate. Borax comes at the end of the process.

What is arsenic gold extraction?

It is the treatment of gold ore that contains arsenic, often in arsenopyrite. Roasting, pressure oxidation or bacterial oxidation breaks down the sulfides so that leaching can reach the gold.

What makes a gold ore refractory?

The REM paper defines refractory ore as one where cyanide leaching recovers less than 80% of the gold. Common causes include gold locked in sulfides and carbon that absorbs dissolved gold.

How much gold is in normal soil?

Very little. The EPA’s 1994 report puts the average for the Earth’s crust at 0.003 to 0.004 ppm. Local soils vary, and only assays can tell you what your own ground contains.

What grade of soil is worth mining?

There is no fixed figure. The EPA’s report said deposits could be economic with as little as 0.69 to 1.37 ppm at 1994 prices, but placer operators often work in volume units and their break-even depends on digging cost, recovery and today’s price.

Which gold extraction method recovers the most?

Among the routes the EPA’s 1994 report compares, tank methods reached 92 to 98%, against 60 to 80% for heap leaching. Tanks are costlier and suit higher grades, so the highest recovery is not always the most profitable choice.

Do I need a permit to extract gold from soil?

Usually, yes, although the rules vary by country, state and land type. Check with the mining regulator and the environmental agency before you disturb ground or use water.