Most common Metal analysis methods

The most used methods for geochemical prospecting are fundamentally:

• Emission spectrometry with a plasma source (spectrometry plasma), where the powder sample is burnt in an arch of direct current, an a highly exiting gas (plasma).

Normally 12 priority elements are analyzed:

Cu, Pb, Zn, Ag, W, Sb, Ba, Ni, Mn, Fe, Cr, Sn,

Along with 10 useful elements, because they are accessory elements, or by their geological cartography: 

V, P, As, Mo, B, Be, Cd, Co, Ni, Y.

• Direct reading optical spectrometry emission, it can read 7 elements simultaneously and outline more than 26:

SiO2, Al2O3, Fe2O3, MgO, CaO, Na2O, K2O, / Mn, P, Ti, Zr, B, Ba, Sr, La, Y, Nb, Pb, Zn, Cu, Ag, Cd, As, Sb, Bi, Li, Sn, W, Mo, Cr, Co, V, Ni.

• Atomic absorption: is the most used method for common mono-element analysis, it has low levels of detection and the equipment is relatively cheap.

The results of the analysis are normally shown as p.p.m. (part per million, this is grams per ton) or sometimes as p.p.b. (part per billion, this is milligrams per ton). For the present elements in larger quantity they will be shown as percentages (%).

Suggestions

Different analysis methods have different sensibilities depending on the analyzed minerals; which is why it is impossible to compare results coming from different methods. This is why that on a geochemical sampling campaign the same analytical method must be used. To control analysis productivity and precision double samples must be interchangeable or samples with known tenure measurements of 1 for every 100. When sampling it is recommended to provide numbers without samples.

Execution of different prospecting stages

Once your objectives are set and the prospecting method of execution, with the help of a geochemical advisor, the prospector, geologist or technologist will begin the execution of the tasks on the terrain.

No matter what the state of the prospecting is, the tasks will consist mainly of the following operations:

• tracing of itineraries & sample positions
• taking & numbering samples
• preparing & shipping samples

Itineraries & position of samples

In the “exploration” phase or “general reconnaissance”, the largest amount of space in the shortest amount of time must be covered, so existing communication routes will be used, land or water. When there aren’t any, you will need to trace out routes with a compass.

In the “strategic” phase the objective is to locate abnormalities on where to conduct more detail prospecting, therefore the regularity of sampling is prioritized. 

The classic sampling is that of alluvial sediments. The most logical routes are those done throughout the secondary hydrographic net.

With trying to keep a constant density of samples its recommended to pre-select sample point on a topographic map or aerial photos, eventually imposing a kilometric grid.

Now it is important to accurately position the possible sample points on the terrain for future recognition.
Leaving marks next to each sample point, that can be made up of a plastic tape with a bright color with a written sample number, tied to a branch if it’s a wooded area or the sample number written on the closest outcrop.

In the “tactical” phase the objective is delimitate the exact surroundings of the abnormality to construe its location and the most probable kind of mineralization. The method consists of taking samples using a regular grid, being square or rectangle, along parallel profiles, when direction of the alignments of the abnormality is known.  The sampled material is always a soil or, the limit of a crumbled rock.

The location of sampling is joined to the materialization over the terrain of the prospecting grid. With a compass a base and perpendicular line will be traced from this one, other parallel lines, according to the dimension of the net. The sampling points are marked with rods, which are placed with a card or color tape with the sample number written on it. In this phase a fast topographic removal might also be needed.