23/01/2026
Many black sands contain microscopic gold that cannot be seen with the naked eye. This gold is often trapped inside iron minerals or sulfides. Therefore, the process goes through several essential stages:
1. Concentration:
First, the black sand is thoroughly washed in a pan or sluice to remove light materials and concentrate the heavy minerals (magnetite, hematite, ilmenite, etc.). The goal is to reduce volume and increase the percentage of gold-bearing minerals.
2. Magnetic separation:
A strong magnet is used to remove most of the magnetite and iron minerals, since gold is not magnetic. This step makes the sample cleaner and easier to treat.
3. Roasting:
The concentrate is dried and then roasted at moderate to high heat in a metal container and in an open, well-ventilated area.
At this stage:
β Organic matter burns off.
β Sulfides break down.
β Iron minerals oxidize.
This process destroys the coatings and structures that trap microscopic gold, allowing it to be released.
4. Grinding after roasting:
Once cooled, the material is finely ground. This further frees any remaining gold locked inside the grains.
5. Re-washing and concentration:
The material is washed again to separate the now-free gold, which settles at the bottom because of its high density.
6. Collection and smelting (to obtain relatively pure free gold):
The heavy concentrate is collected and smelted with borax to remove impurities, producing free, visible gold with much better purity.
Important note: roasting and smelting must always be done outdoors with proper protection, as some black sands can release toxic gases.
In this way, roasting is not used to extract gold directly, but to liberate it first, making concentration and smelting possible.
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