Dolomite metasomatic

Mention may be made of the antimony deposit at Ardtche, which has been spoken of as sedimentary in origin (E). But it may ho an impregnation or a metasomatic alteration of the Triassic dolomite in which the deposit is found (C or D). 

Metasomatic dolomitization is a common process, which actively affects the composition of both rocks and ground water. Three major types of dolomite are distinguished primary, precipitated together with the rock, secondary in the form of cement and the third one at dolomitization of limestones. In the latter case it forms due to the substitution of Mg instead of Ca. Because of this the very substitution process is considered as a number of sequential reactions of dissolution and precipitation. However, total substitution of dolomite instead of calcite is rare. Usually form limestones at various dolomitization stages (magnesian calcite, protodolomite). In its substance this is isomorphism of cations with the same valence, which may be presented by equation... 

For this reason, metasomatic dolomitization is often considered a leading factor in the reservoir formation. 

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