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Volcanic Rocks
Also called extrusive rocks, volcanic rocks are those that formed through volcanic eruption. Eruptions
on the sea floor, where the crust is thinner are generally mafic, while volcanic rocks associated with
thick continental crust are more likely to be felsic.
Examples:
• Seafloor volcanics: Volcanogenic Massive Sulfide deposits
• Continental volcanics: Rhyolite-hosted Tin Deposits
Intrusive Rocks
Intrusive rocks are those formed from the cooling of magma bodies that have never erupted to the
surface, but have instead been exposed through erosion or uplift. These rocks generally have a more
crystalline appearance since they have the opportunity to cool more slowly than volcanic rocks and the
crystalline minerals can more fully form.
Examples:
• Layered Mafic Instrusions: Bushveld PGM deposits
• Granitic REE Deposits

This pink coloured
felsic intrusive rock
contains “rafts” of
mafic wall rock
which likely broke
off into the felsic
magma body.
Sedimentary Rocks

Sedimentary rocks are formed from the erosion of older intrusive, volcanic rocks or even other
sedimentary rocks. They may also be formed through biologic processes, such as coral reef
formation. Mineral deposits may form in sedimentary rocks through the erosion of ore-bearing rocks or
through the mobilization of ore-bearing fluids through sedimentary rock.
Examples:
• Sediments eroded from older rocks: Sandstone hosted copper
• Carbonates (Limestone, Dolostone): MVT Lead-Zinc Deposits
Surface Sediments
Surface sediments can also host a variety of mineral deposits. Ore minerals in these sediments are
concentrated through the flow of surface fluids such as rainwater or rivers.
Laterites
Laterites are red colored iron-rich soils that have been leached through tropical weathering processes.
They can host important mineral deposits including Iron, Nickel, Bauxite (Aluminum) and REE’s.

Laterite Soils, Karajini National Park, Western Australia
Examples:
• REE-bearing Laterites: China
• Lateritic Nickel: New Caledonia
Placer Deposits
Mineral deposits formed by the concentration of moving
particles through wind or water action are called placer
deposits.
Examples:
• Gold: Alaska and Yukon
• Diamonds: Namibia, Africa
Metamorphic Rocks

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