Active stream bed sampling technique
In warm countries and in most tropical countries with fortuitous bed-rock, the chippings on riverbed are easily accessible. At any rate, samples must be done both on riverbank areas and on land.
A) Equidistance of samples or density in km2
The equidistance varies from 1km and 500 meters, along with the density of 1 to 5 samples per km2, is determined before the mission depending on the region’s geological context and the type of existing hydrographical reticulate.
B) Sampling technique
Each sample will be made up by two samples made at two points, several meters from one another, and highlighted by its concentration of heavy minerals, where the chippings are strong and least moldy possible.
The chippings (gravel) are sampled at a variable depth of 10 & 40cm if it isn’t possible to reach the bed-rock directly and it’s placed on a net sift of 5mm.
Two vats are filled (trays or pans) knowing the volume of each, to be able to determine in the future different textures; at any rate each one must contain at least 5 liters of sand.
The remains on the sifter are visually checked to verify the presence of large mineralized elements; the same is done is done of little gravel that area washed in buckets taking them out manually.
The sand that stays, very clean from the limo-clayey fractions, is washed with circular movements having the outer parts fallout in order to get a concentrate of heavy minerals with a good fraction of medium density minerals (the exact techniques are shown in field work).
The concentrates of both vats are put together in one bag or cup to be sampled, with the proper label (see further on the principles of sample numerating).
C) Organization & material
In a team the following is necessary:
1 prospector or team leader
1 or 2 sample workers
1 shovel
1 pickaxe
1 5mm sifter (30cm of diameter)
2 vats or pans of 8 liters, of stainless steel
- Recipients, bags & labels for samples
- 5-10 carriers, in the case of isolated areas or tropical jungle
1 hunter (possible)
What is related to the instrument to work with, we recommend a pan that has a crease on the side of the way, which works as a trap for heavy minerals. It normally has the following dimensions: 45cm
 17cm
Performance varies depending on the area. In an area with a good interstate network, you can get up to 10 to 12 samples in an 8 hour working day. In subtropical areas, considering access difficulty, performance can decrease to 2-4 samples by 8-10 linear km on the map, or an average of 1-2 samples per km2, better said; one alluvium sample for every two geochemical samples in a mixed prospecting mission, which is how they are usually done.
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