Open Space Filling
Open space filling is the hallmark of epithermal vein systems, such as a stockwork, in greisens or in certain skarn environments. For open space filling to take effect, the confining pressure is generally considered to be below 0.5 GPa, or less than 3-5 kilometers. Veins formed in this way may exhibit a colloform, agate-like habit, of sequential selvedges of minerals which radiate out from nucleation points on the vein walls and appear to fill up the available open space. Often evidence of fluid boiling is present. Vugs, cavities and geodes are all examples of open-space filling phenomenon in hydrothermal systems.
Alternatively, hydraulic fracturing may create a breccia which is filled with vein material. Such breccia vein systems may be quite extensive, and can form the shape of tabular dipping sheets, diatremes or laterally extensive mantos controlled by boundaries such as thrust faults, competent sedimentary layers, or cap rocks.
Read more about this topic: Vein (geology)
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