The moment in which, perhaps after hours of tiring walking, an interesting mineral is identified is certainly a source of priceless emotions for every researcher.
But it is also a delicate moment:
extracting a sample without adequate knowledge of excavation techniques can in fact irremediably compromise the quality, if not even make one's efforts useless.
Here is a series of general indications on how to deal with the most common types of rocks and on how to handle the tools essential for excavation..
At first, some advice for those who want to sift the metals from the sands and, finally, a short trip - for the more experienced - in the fascinating world of gold mining in rivers.
After reaching the chosen location, it is necessary to immediately set up a small base camp where each member of the group will arrange their backpack and any other personal items.
The base camp must be located close enough to the workplace, on a possibly flat site, judged to be free of potential dangers and therefore far from possible fragments, stone falls, precipices, gorges (deep gorges with vertical walls), steep slopes.
If it is available in the immediate vicinity, it is preferable to use any sufficiently safe natural or artificial shelter.
The next operation (essential if the locality is not well known) is the accurate reconnaissance of the area of interest.
To better use the time available and have a better chance of success, it is advisable to divide the areas to be explored among the various members of the group.
By doing so, all the necessary information will be acquired in a short time and it will be possible to start the real research in the most correct way and with good prospects.
During the survey it is necessary to carefully evaluate the various factors that could condition your research :
such as: quality and position of the rock or how the mineral is presenting itself; and of course the location of the most promising points.
Indeed, the choice of the most suitable equipment to use depends on the result of these evaluations.
Since there are usually several points suitable for research in each locality, it is advisable that each perform their work separately and at a safe distance from the others to avoid accidents.
Of course, in case of need, each member of the group should be able to rely on the collaboration of each fellow partners.
Even if the execution of these operations is strictly linked to personal experience, it is strongly conditioned by a very variable series of objective situations, some general indications can be very useful .
When the rock to be worked is partially buried, it will be necessary and convenient to highlight it more by removing the surrounding soil.
In this way it is possible to notice any continuation of the veins or mineralized cavities observed on the surface.
The method of attack on the rock mass varies substantially according to the nature and position of the rock itself and the minerals that needs to be extracted.
A good general rule is to tackle the rock with sledgehammer , using precise sparse strokes.
The same also applies when using tools such as chisels or wedges , which must, however , first be pushed very firmly into the slots to prevent the kickbacks of the tool.
The removal of druse or geodes from rocks such as granite , porphyry trachyte requires a lot of patience and perseverance.
It is in fact necessary to dig with a good pointed chisel around the cavity of interest (and at a safe distance from the crystals) a deep enough groove, in order to weaken the source rock and thus be able to extract the sample still whole.
In some metamorphic rocks such as gneiss , micascists and serpentinites , the mineralized lithoclases are often arranged perpendicular to the rock schistosity.
In this case it is necessary to try to remove as much mineralized portion as possible.
In doing so, it is necessary to introduce the chisels and then the wedges at a short distance from each other, on the same line and in the sense of the schistosity, beating them alternately until the desired effect is obtained.
Acting directly perpendicular to the schistosity would be a waste of effort, because the rock would hardly break.
Basalts and other volcanic rocks frequently contain cavity-rich inclusions filled with beautiful materials, immersed in a usually sterile (non-metallic) matrix.
In these cases it is advisable to first remove the inclusion from the matrix and then break it.
Pegmatitic veins and other types of Filonian rocks should be preferably split by attaching them to the side, non-butt , using sufficiently long chisels, or rather the crowbar, as a lever to move the pieces obtained.
In the case of stratified sedimentary rocks ( limestones , dolomites and similar), which may sometimes have a mineralogical interest for the presence of calcite , dolomite and pyrite nodules or marcasite , you have to act according to the situation and the position of the layers:
that is by lifting portions of surface rock layers with the help of the lever, which will then be crushed, or, in the case of layers stacked to form vertical walls, splitting laterally .
Particular caution is required when breaking rocks containing delicate minerals (such as tufts of artinite , of fibrous zeolites , of aragonite , etc.):
too intense blows should be avoided and, when the rock tends to break, it is necessary to act manually with a lever to facilitate cracking and not cause damage to the samples.
In some active quarries of gneiss or granite you can discover walls rich in crystals, however impossible to remove completely because they are unreachable.
The use of the so-called grapple , which allows you to remove at least a part of the cavity, can then be helpful.
A particular case is represented by the isolated crystals of quartz (very rarely of other minerals) which are found dissolved and mixed with the earth.
In this circumstance, for those who are not satisfied with the crystals already on the surface, the possible excavation becomes quite simple because it takes place on a soil that is usually soft and free of rocks.
However, at least one pick and one small shovel are required to move the soil.
It is usually the gold of rivers and certain hard and heavy stones ( zircon , garnets , ilmenite ) from the disintegration of igneous rocks.
For zircon and other minerals the operation is quite simple :
The sand is abundantly washed in a basin with running water, shaking slightly to completely remove the silt and the lighter parts;
then it is dried and sieved with sieves with gradually narrower meshes, each time examining small portions of what passes through the sieve.
The various minerals are recognized by their shape, color, shine and can be separated manually with the help of tweezers and lenses.
For magnetite you can resort to the use of a magnet.
The separation of gold, on the other hand, is longer and more complex and requires specific equipment , as well as particular research methods.
It basically involves placing certain quantities of gold sand, duly screened and sieved, on a long and narrow wooden board, with lateral edges and equipped with various transverse and parallel grooves, called canaletta (italian-equipment) .
This tool is then placed in the river or stream so that a weak stream of water constantly passes over it.
The gold dust, due to its high density, settles in the grooves, together with other heavy minerals.
The gold concentrate is then purified using a special dish called batea (italian-equipment) or with other tools such as trulla (a kind of square shovel with raised edges) or bacile (similar to the trulla, but without a handle).