Always put your samples in clean containers. Be especially careful that you do not get oil or grease in with a sample because if small particles are coated with these substances, they tend to float and this makes a gravity separation very difficult. If a small particle of gold is oil-coated, it may jump to the surface of the water and be carried into the tail rather than going into the gold concentrate.
The best containers in which to transport placer samples are metal or heavy cardboard drums with lids. A five gallon drum will hold seventy to eighty pounds of material. Large canvas sample bags or burlap sacks lined with two plastic trash bags — one inside the other — may be used.
As you sample, use a gold pan to gather additional information. With your gold pan you can determine the size range and shape of most of the gold particles. Visually stratified layers can be checked to see which carry value and which carry little or no value. This information will be important if the deposit is mined, but it may also be important to know before the samples are concentrated. For example, before the samples are concentrated they are classified, or screened to a certain size. If you have found particles of gold as large as 10 mesh, this information should be given to the person concentrating your samples so he will know that he must screen the sample no smaller than 10 mesh. If the particles of gold are very flat and flakey they will be harder to separate than more massive par¬ticles. Again, the person concentrating your samples should know this so he can run the sample accordingly.
Before samples can be concentrated they must be prepared.
This preparation includes weighing the sample, drying the sample, and screening the sample. The sample will be weighed before it is dried and then again after it is dried to find the percent moisture in it. Sometimes the percent moisture ¡s found by weighing and drying only a small part of the sample and then using that percent for the whole sample.
Before a satisfactory gravity separation can be made, the material in the sample must be classified or sized. Rocks the size of apples and fine sand can not be concentrated together with any reliable results. Larger particles act like the heavier small particles and may even crowd them out of the con¬centrate. The best concentration occurs when the particles are all similar in size. The material in the sample will be screened to a size that will include all of the particles of gold if they are not larger than can be successfully concentrated. The oversized material from the screening will be carefully examined to see if any gold is present. If some is found it will be picked out and saved and later added to the concentrate. Screening can be done either wet or dry, usually depending on which type of material the concentrating equipment must have.