WEEK 4: Mining & mineral Deposits

ore

a mineral deposit containing valuable material that can be extracted economically.

ore grade

the concentration of valuable material within an ore.

what determines whether a mineral deposit is worth mining

• grade

• size

• depth

• accessibility

• tech

• location

• mineral price

why minerals aren’t evenly distributed across earth

geological processes that form mineral deposits vary from place to place.

3 major processes that form mineral deposits

igneous, sedimentary, metamorphic processes

magmatic deposit

a mineral deposit formed through processes involving magma & crystallization

how can magma form mineral deposits

As magma cools, different minerals crystallize at different times, allowing certain minerals to become concentrated.

What are precious metals?

Gold (Au), silver (Ag), and platinum (Pt).

What are base metals?

Common economically important metals such as iron (Fe), nickel (Ni), copper (Cu), lead (Pb), and zinc (Zn).

hydrothermal deposit

A mineral deposit formed when hot fluids transport dissolved elements and minerals later precipitate.

hydrothermal

hot fluids/water

How hydrothermal fluids form mineral deposits

Hot fluids dissolve and transport elements, then changes in temperature, pressure, or chemistry cause minerals to precipitate.

black smokers

underwater hydrothermal vents where hot, mineral-rich fluids escape onto the seafloor.

VMS Deposits

Volcanogenic Massive Sulfide deposits, which form from hydrothermal activity and can contain metals such as copper, lead, zinc, gold, and silver.

VMS deposits commonly associate

divergent/extensional enviro & hydrothermal systems such as black smokers

porphyry copper deposits

Large copper deposits associated with magma and hydrothermal fluids.

What tectonic setting is commonly associated with porphyry copper deposits?

Convergent boundaries/subduction zones.

metamorphism

the solid-state alteration of rock caused by heat, pressure &/or fluids

does metamorphism require melting

no, rock remains solid

metasomatism

chemical alteration of a rock by fluids

evaporite example

salt

evaporite deposit

a deposit formed when water evaporates & leaves dissolved minerals behind.

placer deposit

concentration of heavy minerals transported & deposited by water

why gold can form placer deposits

gold is dense, so flowing water can transport sediment while concentrating the heavier gold particles.

where gold placer comes from

found in rocks released through weathering & erosion, transported by water then concentrated in sediment.

leaching

the dissolving & removal of material by water

reprecipitation

when dissolved material becomes a solid mineral again

residual deposit

deposit formed when weathering removes other materials & leaves certain minerals concentrated behind.

BIF stands for

banded iron formation

why is iron economically important

used to produce steel

magmatic deposits

minerals concentrate through magma cooling/crystallization

hydrothermal deposits

minerals are transported & deposited by hot fluids

placer deposits

minerals are transported & concentrated, commonly by water

residual deposits

weathering removes other materials, leaving certain minerals behind

Why does grade matter in mining?

A higher grade means more valuable material is present in a given amount of rock, generally making extraction more economically attractive.

basic process of placer deposit

Weathering → erosion → transportation → deposition → concentration of heavy minerals.

basic process of evaporite

Mineral-rich water → evaporation → minerals remain behind

basic process of hydrothermal deposit

Hot fluid → dissolves/transport elements → fluid changes/cools → minerals precipitate

basic process of magmatic deposit

Magma cools → minerals crystallize → certain minerals become concentrated.