Authigenic minerals

Authentic, in contrast to terrigenous, is called minerals of sedimentary rocks, which are formed (grow) in the process of accumulation, diagenesis and lithification of sediment. Authigenic are minerals formed at the place of their location - in sediment or rock. They are the main indicators of the environment in which the formation of this breed took place. Among the most common authigenic minerals in detrital rocks, mention should be made of carbonates ( calcite and dolomite ), chlorites , clay minerals, sericite , quartz , chalcedony , epidote , prenite , and actinolite .

Among them, the leading place in the steppe zone belongs to carbonates, mainly calcite , sulfates and chlorides occupy a subordinate position.

In deserts, the role of sulfates and chlorides is intensified, where they often become the main rock-forming minerals. Here, gypsum often forms coarse-grained aggregates ( desert roses ), which is not observed in modern steppes.

Ore carbonates ( malachite and azurite ) are formed, apparently, in any climatic zone, if there are lime - bearing rocks in the vicinity of sulfide copper ore deposits. In the steppes for the formation of malachite and azurite, compliance with this condition is not necessary, because calcium carbonate in the weathering zone of rocks in the steppes is almost always present as an authigenic mineral. In the steppes, the conditions for the conservation of malachite and azurite on the surface are most favorable, where the processes of their dissolution are slowed down. Therefore, it is much easier to search for copper ores from precipitations of these bright, highly visible minerals in the steppes than in the forest zone.