Well Sampling Techniques

In certain plain areas in inter tropical regions, the viscous clayish deposits are very potent to the point where the active beds remains poor in heavy minerals. The meanders are numerous and the bed rock is usually not visible. In these conditions it will be necessary to carry out sampling through wells that go through the fluvial deposits and reach the subjacent bed rock. This type of prospecting is recommended especially in the search for diamonds by which it is normally necessary to wash anywhere from to 2 to 2 m3 of gravel for each sampling point.

Sampling locations

• In the first case a surface sample will without a doubt be sterile due to the fact that the surface sands cannot provide any idea of the heavy concentration of minerals in the water course. It is necessary in this case to dig wells: this is usually the case of the big water courses.
• In the second case we will say that we are in the ideal situation: with samples to be done on the convex bank, by means of the excavation of small wells to possibly reach the bed rock and sample right then and there.

In the third case it will be necessary to sample the riversides, in the alluviums and in some cases much further up the course of the river. However it is important to be careful of the possible traps of heavy minerals in the course of the river if they can be seen. Besides this, samples of old alluviums on a concave bank give important information about eventual placers. In the areas of rapids or with water falls, it is useless to carry out sampling in the areas around them, because the erosion in these areas is such that it is pushed down with the water into the valleys. A sample of the upstream of rapids is often times considered valid. It is also a good idea to control the nature of the bed rock as far as a stratification etc could act as traps for heavy minerals, and even more so if these are inclined towards the mountain, accomplishing in this way the role of a natural sluice.

Note: in the case of a course of water that goes through a highway or road it is necessary to carry out the sampling by at least 50 meters upstream, as far as a bridge it can hinder the natural relation of the minerals by the addition of foreign materials.