What is the metasomatism in geology ?

Metasomatism : definition

Metasomatism is the process by which a chemical transfer is established from one solid to another without the intervention of the liquid state (we speak of metasomatosis). Considered by some authors as a special case of metamorphism, metasomatosis is accompanied by a change in the overall chemical composition of the original rocks, due to the contribution of certain chemical elements (Mg, Fe, etc...) and to departure of others (K, Na, Si, etc...). This process is the result of the circulation of reactive fluids in the rocky material, inducing the external contribution or the departure of certain chemical elements.
 
This element mobility can lead to very significant replacements (dolomite massifs are frequently formed by magnesium metasomatosis of limestones), as well as to notable mineral concentrations, such as certain zinc or lead deposits in the carbonate domain.