Vein (geology)

Veins form when mineral constituents carried by an aqueous solution within the rock mass are deposited through precipitation.

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 km (2–3 mi).

Crack-seal veins are thought to form quite quickly during deformation by precipitation of minerals within incipient fractures.

[2] On the macroscopic scale, the formation of veins is controlled by fracture mechanics, providing the space for minerals to precipitate.

In all cases except brecciation, therefore, a vein measures the plane of extension within the rock mass, give or take a sizeable bit of error.

In ductilely deforming compressional regimes, this can in turn give information on the stresses active at the time of vein formation.

Today's mining, which uses larger machinery and equipment, forces the miners to take low-grade waste rock in with the ore material, resulting in dilution of the grade.

However, today's mining and assaying allows the delineation of lower-grade bulk tonnage mineralisation, within which the gold is invisible to the naked eye.