High Sulphidation Deposits
High sulphidation deposits comes about due to fluids, which are mainly gases such as SO2, HF, HCl, channeled straight from a hot magma. The fluids interact with groundwater and the result is strong acids. These acids then decompose and melt the nearby rock and all that is left then is silica, it usually has sort of a spongy characteristic to it and is also known as vuggy silica. Gold and at times brines with copper also rise from the magma and then precipitate their metals inside of the spongy vuggy silica bodies. The shape of these mineral deposits mainly depends on the distribution of vuggy silica. Now and then the vuggy silica can be extensive if the acid fluids ran across a broad permeable geologic unit. In this case it is frequent to stumble upon big bulk tonnage mines with lower grades.
The acidic fluids are neutralized by the rock little by little the more they move away from the fault. The rocks on the other hand, are changed by the fluids into gradually more neutral stable minerals the more they move away from the fault. Consequently, delineated areas of alteration minerals are approximately always formed into layers that look similar to shells surrounding the fault zone. On average the cycle is to move from vuggy silica (the middle of the fault) making progress through quartz alunite to kaolinite-dickite, illite rich rock, to chlorite rich rock at the external contact of alteration.
Alunite, which consists of a sulphate mineral, as well as kalonite, dickite, illite and chlorite, which consist of clay minerals, are usually whitish or in some cases have a yellowish color to them. The clay and sulphate alteration, which is known as acid-sulphate alteration, in high sulphidation systems is able to leave enormous spots, in some cases up to 100 square kilometers of visually extraordinarily highlighted in color rocks.
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