Without any doubt, gold panning is the oldest prospecting tool and concentration device employed by prospectors. The method is based on the difference of specific gravity among gold and other minerals. Pans can be found in several presentations and the prospector must select the most appropriate according to gold mineralization. The typical gold pan is 16 inch diameter and 2 to 3 inches depth. Some pans have riffles a long one half and they are an extra help to enhance the separation of light and heavy particles.
Basically, gold and heavy metals remain at the bottom and the other minerals are discharged due to they are lighter. Before adding material into the pan, it must be classified with 6 mesh screen so that all the coarser particles can be separated. The finer particles will be processed by panning. It is important to mention that the appropriate skill can be only obtained with practice. In this way, the prospector will recognize minerals and minimize losses.
If the material does not have homogeneous particle distribution, some problems can be expected during the panning. For this operation the sample must be classified in 1000-500 g charges and each charge must be panned. Ideally, the sample must be mixed with water in order to prepare slurry at 30-35% solids. The water will be added slowly over the ore so that all the lumps can be broken. At the moment of adding water the supernatant layer will be dark and a lot of fine particles (slimes) will be floating. At this moment is important to shake the pan repeatedly several time in order to create a preliminary separation between slimes and the other particles, tilt the pan and discharge some dirty water and add more clean water. Repeat this procedure until the water is totally clear.
Now, the separation between heavy and lighter particles must be performed. For this, the pan must be inclined and shaken from side to side by making a circular movement. It is important to add water in each operation in order to observe the minerals and make easy the separation. Elimination of light particles is helped by moving the lip of the pan down and up. A gentler wash action is required as the amount of wash dirt remaining decreases. The previous operation must be repeated until only a small area (circle of 2.5-4.5 cm radio) of fine material can be observed.
Gold Panning
If the material has free gold particles, they will be observed easily at the bottom of the pan. Most the time, by processing samples from placers, at the last part of the process will be observed black particles such as magnetite and zircon. Magnetite can be separated by using a magnet.
At the end of the process is important to be careful with the shaking motion due to there are flattened and tiny gold particles that tend to floats easily. For this reason, it is important to be careful during the panning. If the panning is perform with samples taken in a placer or any place without performing a classification or size reduction, the opportunity of watching a gold nugget is high and the coarse material must be rejected carefully, otherwise some free gold will be lost. For this reason is important to prepare the sample by crushing and screening operations. In other words, if the sample has homogeneous size distribution, losses are reduced.
It is important to mention that gold particles can be found in nature under different presentation such as large pieces coarser than 2.0 mm; fine particles, 2 - 100 µm, microcrystalline particles, 100 – 1 µm; sub-microcrystalline particles, associated with sulphides; and tellurium compounds.