Reducing samples

In many cases the sample is too large to be sent to laboratory. So it’s necessary to reduce it, but it has to be done in a way that the reduced sample is identical to the original (or the least different). 

The simplest sample reducer is a brass cross to divide the amount in four equal parts. What is most commonly used is the “Jones” sample divider, made of a metallic box divided in two by furrows the separate the material alternately from one side to another.

Like it can be seen in fig. 10, there are two methods to “quarter” a sample, as long as you have three or two metallic boxes and a mixing pallet. 

The sample that is got will be approx. 10-20 grams and it will be sent to the laboratory for analysis.

If transportation costs are cheap, the rest of the sample can be kept, for eventual future analysis or for panning. 

It’s important to clean the quarter well with a brush, when going from one sample to another to avoid contamination.

Milling and grinding
In this case the quartering will be longer to obtain a 50g sample, which will then be milled and ground leaving no residue.

The granulation to be obtained depends on the type of analysis (40 microns for quantimetric analysis & 80 micros for humid chemical analysis, atomic absorption, & spectrometric emission.

You have to be careful not to grind too much the softer parts, so mill more frequently.

Carefully clean the mortar with a brush between samples.

F) Pits  

They are small study & sample evidence pits, made in tabular horizontal or semi horizontal deposits (bauxite, phosphates).

These can be isolated or organized with a square or rectangular like net, depending on the prospecting phase & evidence shape.

They are normally hand made pits, of 0.70 - 0.80m in diameter, where the sampling is made through vertical furrows on excavation’s the walls or floor, every meter or 50cm.

In the first case the work is like it has been described above; in the second case (in the case of homogenous minerals & of low commercial value such as bauxite, Fe or Mn minerals, the metric amounts will be put in a spiral form around the pit and numbered with rods and cards, indicating the number of pit and depth (fig. 11).  

In this case the sample reduction will be done the way it was described above, with the difference that the milling, because of the larger amount, will be done preferably with crushers working with a gas motor.

Drilling with motor perforator

For evidence or deposits of certain soft or plastic substances, like powder, a light motor perforator is used (like the one in fig. 13), capable of sampling up to 15cm deep.

G) Sampling book

Each sample sent to the lab must be numbered, logically. Like we have shown with petrographic samples, there are various methods, depending on the mission’s situation.

Each prospector must take note in a specific book, possibly making two copies using carbon paper, where the following is mentioned:

• sample number
• name of the area or sector
• the most precise location possible: besides the geographic coordinates, locate it based on the “toponymy” of the area. 
• Write, if the determination is possible, the nature of the take sample, maybe putting an interrogation sign if the determination is uncertain.

For the samples that are to be analyzed it is shown the method used to sample (by furrows, heaps, etc.) and the original weight of the sample (even estimated).

It’s always best to put the samples, especially loose material, in two bags with a plastic card specifying the number, between one bag and the other, besides writing the number with a marker on the bag itself.