Epithermal Vein Deposits Unearth Gold in Areas of Active Volcanic Activity

To begin to understand the formation of epithermal vein deposits and their propensity for gold it is necessary to first understand their origins. Epithermal veins are hydrothermal deposits composed of either metal or stone ores. These ores form when water, brine and a heated substance, typically volcanic magma, come into contact with one another. Together these ingredients combined with presence of metals or minerals form hydrothermal deposits. These hydrothermal deposits can then be subcategorized into three types:

Hypothermal
Mesothermal
Epithermal

These three types of vein deposits can then be re-classified in accordance with whether their veins are formed by an open space filling process or crack seal growth process.

To sum up the ideal conditions for the formation of these veins we recognize the following factors:

Brine
Hot liquids: usually magma
Presence of a mineral or metal
Open spaces within the ore that will allow for the travel of these heated liquid solutions

These four factors result in the chemical reaction that allows for one of the three types of hydrothermal deposits to occur.

Shallow Heat Deposits: Another Name for Epithermal Deposits

Epithermal veins, when identified by their proper name are hardly recognizable to the general public as it takes a geologist or another similar professional within the field to be able to identify them. People are usually surprised to find that epithermal veins are close in nature to hot springs or geysers which make them the most common type of hydrothermal deposit.

Ores and minerals generally found in epithermal vein deposits:

Gold
Sulphite
Zinc lead
Molybdenum
Bismuth
Nickel
Cobalt
Antimony
Mercury
Quartz
Calcite
Fluorite barite
Chalcedony
Rhodochrosite
Dolomite

Epithermal Gold Deposits

Many of the world's most well-known gold mines are comprised of epithermal vein deposits. The gold minerals are typically found within and around the vein area which in most cases are found close to the surface but can also go as deep as 600 metres.

Interesting facts regarding epithermal gold deposits are:

Found in areas with active volcanoes
Process of gold mineralization to occur in a 1-2 km range from the surface
Fluid responsible for the mineral deposits range in temperature from 100C to 300C
Gold is carried through the ore fractures by one of two chemical fluids: low sulphidation and high sulphidation
Low sulphidation produces more silver and gold as well as lead, zinc, copper, quartz, carbonate, pyrite, sphalerite, and galena
High sulphidation yields less gold and silver and tends to have higher concentrations of arsenic and copper as well lesser amounts of alunite, pyrite, quartz and enargite