Hydrothermal Ore Deposits

Question 1

Define Hydrothermal fluid.

Answer 1

A hot, aqueous fluid containing dissolved metals in a solution.

Question 2

What are the Three Key Requirements to Form a Hydrothermal Fluid?

Answer 2

A Source of Heat:

• Volcanic / Magmatic
• Radioactive decay
• Geothermal gradient
• Metamorphism

A Source of Water:

• Seawater
• Groundwater / Meteoric
• Magmatic
• Metamorphism

A Source of Metals:

• Magma
• Country rocks

Question 3

What is a Disseminated ore?

Answer 3

When ore minerals precipitate into pore spaces and cavities within the rock.

Question 4

How do Hydrothermal Veins Form?

Answer 4

1) Magma intrudes and starts to crystallize minerals containing, Si, Al, K, Na, Ca.
2) Incomplete elements stay dissolved in the hydrothermal fluid which begins to rise.
3) The intrusion cools and contacts, producing cooling joints that allow fluids to escape.
4) Fluid can percolate through porus permeable rock leading to a disseminated ore.
5) Fluid travels along joints, faults and bedding planes to produce mineral veins.

Question 5

Why Does Limestone Contain More Ore?

Answer 5

• Has joints and bedding planes allowing fluid to percolate through.
• Reacts with hydrothermal fluid causing precipitation of metals.