Hydrothermal mineral deposits

Hydrothermal ActivityHydrothermal Activity• The circulation of water through hot

volcanic rocks and magma• Forms fumarolesfumaroles – volcanic vents

emitting gases, some charged with dissolved minerals

• Forms geysersgeysers – heated hydrothermal waters under pressure, that intermittently erupts at the surface

• Provides the source for Geothermal Geothermal EnergyEnergy.

Hydrothermal Mineral DepositsHydrothermal Mineral Deposits

Most of the metallic minerals mined in the world, such as copper, gold, silver, lead, and zinc, are associated with volcanism

Magmas may get the metallic components from:

– Partial melting of the mantle at mid-ocean ridges and subduction zones

– From the subducted slab

– Melting of the crust as magma rises through it

Image from the article: The role of Magmas in the formation of Hydrothermal Ore Deposits, by Hendenquist and Lowenstern, Nature, Vol. 370, 1994

Rising magma does not always reach the surface to erupt; instead it may slowly solidify beneath the volcano

As the magma body cools, the metallic elements become concentrated in the residual fluids called HYDROTHERMAL SOLUTIONS

Groundwater or seawater can also come in contact with the magma body and form hydrothermal solutions

Hydrothermal Systems Hydrothermal Systems Water enters the ground by Water enters the ground by

infiltration infiltration

Hydrothermal Systems Hydrothermal Systems Water enters the ground by Water enters the ground by

infiltration infiltration

Heated water Heated water begins to rise begins to rise

Hydrothermal Systems Hydrothermal Systems Water enters the ground by Water enters the ground by

infiltration infiltration

Heated water Heated water begins to rise begins to rise

Hot Springs:Hot Springs: form when form when heated groundwater reaches the heated groundwater reaches the

surface surface

Hydrothermal Systems Hydrothermal Systems Water enters the ground by Water enters the ground by

infiltrationinfiltration

Heated water Heated water begins to risebegins to rise

Hot Springs:Hot Springs: form when form when heated groundwater reaches the heated groundwater reaches the

surfacesurface

Geysers:Geysers: form where a form where a complicated plumbing system complicated plumbing system

allows steam pressure to be built allows steam pressure to be built up, causing intermittent eruptions up, causing intermittent eruptions

The magma body heats and circulates the hydrothermal solutions carrying the metallic compounds

The metals become

concentrated by

circulating hot fluids

When the fluids become cooler (near surface or away from the magma body), the metallic minerals are deposited to form rich mineral veins

Oatman, AZGold bearing

hydrothermal vein deposit

Large quantities of sulfide deposits form at mid-ocean ridges and other undersea volcanoes in this manner

* Sulfides are the most common of the metallic ores* Sulfides are the most common of the metallic ores

Some Copper OresSome Copper Ores

Kennecott Open Pit Copper Mine, Utah