Hydrothermal mineral deposit

They eventually produce metallic-rich fluids concentrated in a selected volume of rock, which become supersaturated and then precipitate ore minerals.

Discovery of mineral deposits consumes considerable time and resources and only about one in every one thousand prospects explored by companies are eventually developed into a mine.

Each hydrothermal mineral deposit has different distinct structures, ages, sizes, grades, geological formation, characteristics and, most importantly, value.

[3] Generally, porphyry-type mineral deposits form in hydrothermal fluid circulation systems developed around felsic to intermediate magma chambers and/or cooling plutons.

While, a skarn deposit is an assemblage of ore and calc-silicate minerals, formed by metasomatic replacement of carbonate rocks in the contact aureole of a pluton.

[4] Volcanogenic massive sulfide deposits form when mafic magma at depth, (perhaps a few kilometers beneath the surface), acts as a heat source, causing convective circulation of seawater through the oceanic crust.

[1] Porphyry-type ore deposits form in hydrothermal fluid circulation systems developed above and around high-level, subvolcanic felsic to intermediate magma chambers and/or cooling plutons.

An example for a typical arc-island porphyry deposit is described as follows:[1] Finally, volcanic activity ceased and erosion removed the upper portions of the volcano and exposed the intrusive rocks and stockwork mineralization that used to lie within.

[17] In contrast, those that occur in continental orogenic belts are typically rhyolitic in composition and carry copper, molybdenum and gold, and in some cases tin and/or tungsten.

Geologically speaking, a skarn deposit is an assemblage of ore and calc-silicate minerals, formed by metasomatic replacement of carbonate rocks in the contact aureole of a pluton.

Furthermore, various structures such as flexures in the contact or impermeable hornfels beds affected the distribution and ore grade of the skarn zones.

[28] Together, they comprise the single largest copper-gold mine in the world, with reserves of 2.8 billion tonnes grading 1.1% Cu and 1.1 g/t Au.

[10] They are commonly epithermal in origin, that is to say they form at relatively high crustal levels and moderate to low temperatures.

The fluids would have migrated upward and outward, following fractures in the solidified part of the granite pluton, precipitating ore minerals in veins and altering the wallrocks.

Thus, the shearing event may have been accompanied by the generation and movement of hydrothermal fluid as the crust was subjected to prograde devolatilization.

[35] Volcanogenic massive sulfide (VMS) are responsible for almost a quarter of the world's zinc production while contributing for lead, silver and copper as well.

VMS deposits tend to be of great size since they form over a long period of time and have a relatively high grade in valuable minerals.

Thus, VMS deposits are believed to be syngenetic or perhaps slightly diagenetic in age relative to their host volcanic rocks.

[37] Magma rises up from the mantle and then cools off in the crust and then releases volatile fluids that contain metals that are eventually transported up to the surface and over time these accumulations become mineral deposits.

As the high-temperature volatile fluids from the magma make contact with low-temperature liquids such as seawater that travel downwards via cracks and faults, producing, due to the large difference in temperature and chemical properties, mineral precipitation, yielding the black colour in the black smokers that end up showing up in the seafloor.

[39] Sedimentary exhalative (SEDEX) deposits account for 40% of total world zinc production, 60% of lead and a significant proportion of silver.

Hypothetical cross-section of an island arc volcano showing intrusions emplaced into the core of the volcano. During the development of porphyry-type ore, one or more intrusions would have generated a separate hydrothermal fluid phase and/or acted as a heat source to drive convection of meteoric waters (see red arrows).
Skarn Formation - three main stages of this mineral ore deposit formation
Ascending hydrothermal solutions rich in gold, sulfur and metals were channelled upward along major fracture and fault zones. Fluid that made it to the surface would have vented as hot springs and geysers. Localized erosion through the thrust sheet has formed windows into the underlying ore-bearing rocks. Adapted from Edwards and Atkinson (1985).
The origin of modern seafloor smokers and ancient volcanogenic massive sulfide deposits: mafic magma at depth (perhaps a few kilometers beneath the surface) acts as a heat source, causing convective circulation of seawater through the oceanic crust.
The petrogenetic model for the origin of the Red Sea sulfide deposits. Cold seawater (blue arrows) enters the seafloor via deep-seated fractures. As it descends, it heats up and leaches Si, metals and other solutes from the seafloor basalts.
MVT deposits petrogenetic model in general - Carbonate sand banks deposited on a shallow tropical marine platform separated very shallow water evaporite basins (landward) and deeper water muds (seaward).