Structure and composition of the weathering crust on the terrigenous-carbonate rocks in diamondiferous regions

Carried out complex research indicated that in the course of weathering of terrigenous-carbonate rocks of basic diamondiferous regions of the Siberian Platform a dissolution of carbonates and decomposition of trioctahedral laminated silicates took place first. Because of such process and sequential washing out the individual elements from various levels of thick eluvial layers, sufficient alteration of physical-mechanical properties and structural-textural specific features of primary rocks can be observed. Fast destruction of carbonates and trioctahedral minerals leads to development of cavities and large pores with high permeability, providing leaching of potassium, abundance of silica and other unstable in the zone of hypergenesis elements. Redistribution of elements provides a local decrease of medium pH and subsequent relative accumulation of aluminum, which is the most important element necessary for new formation of kaolinite. Some intermediate phases (gypsum, aluminite, basaluminite, jarosite and others) may crystallize in the formed caverns and fractures. A very intensive process of superimposed secondary formation of sulphate minerals due to infiltration of rich in sulphur waters is an important feature of hypergene alteration of terrigenous-carbonate rocks in the basic diamondiferous regions of the Siberian Platform. It allows referring such crust of weathering to sulfuric type, apart from the Pre-Early Jurassic crust of alkaline type.