Types of dispersion

There are two kinds of dispersion:

• “Primary dispersion”, joined by formation phenomena’s or mineral arrival, for example, hydrothermal alterations or magmatic differentiations. The study of these “primary abnormalities” is done during the discovery of a deposit by rock sampling (along with the drilling and cutting samples).
• Through the election of element “parameter”, being one of the main structures of the box rock and metallic elements of mineralization, it is possible to trace the “halos” & determine the gradients & polarity close to the deposit.
• “Secondary dispersion”, joined by phenomena’s superficial & geomorphologic alteration (fig. 20A, B, fig. 21A-B, C, D, E).
• In this case the dispersion through the movement of clastic fragments occurs mainly on the surface, where the erosion happens. 
• The main force that is responsible of this mechanical dispersion is gravity. It’s important to know that the movement of fragments & rocks happen in the lightest inclinations (“creeping” or ceep”).
• In warm and humid weather the movement is made easy by the lubricating effect of humidity. If the mobilization increases, it can cause a flow of water mixed material that can move catastrophically. In this case soil geochemical abnormalities can be moved or covered.  
• These dispersions, sometimes mechanical, sometimes chemical, starting from the mineralized area, unstabilized by oxidation, cause “areolas” and “secondary eluvials” that cover larger surfaces than those produced by the intersection with the mineral concentration surface hidden by different recovers. 

In all cases of geochemical prospecting, be it strategic or tactical, these secondary areolas that try to highlight the chemical analysis of soil samples, from water flow sediments, along with more or less disintegrated rocks.

It’s important to consider that the elements associated with a deposit can have totally different mobility and can begin abnormalities that can’t be superimposed.

For example Pb & Zn are normally linked with deposits & in superficial alteration conditions zinc is much more lixiviated than lead and can be transported to long distances compared to Pb that instead causes abnormalities directly on the mineralization.

The chemical makeup of a secondary abnormality doesn’t directly reflect the chemical behavior of an underlying deposit, but is the result of the following phenomenon:  

• primary chemicals
• oxidation & mobile conditions
• presence of “traps”

Therefore it must be studied carefully without jumping to conclusions on deposits only looking at the abnormal parameters.

The means used are then sampling of floors, river sediments & rocks, but there are also other types, used in specific cases:

• Hydro geological: by water analysis, but it has the problem of having an analytical threshold (traces in ppb). Its generally used for fluorine & uranium.
• Phyto geochemical: through the analysis of certain vegetable ash.
• Analysis of the vat concentrate: in the case that the prospecting is oriented to certain metal minerals.  

Throughout this chapter we will not give topics theoretical perspectives (based on geochemistry), but the practical application of different methods.