Deposit types explained (and why it matters to mining investors) [Twitter thread unrolled]

Here’s your ‘Mineral deposit types 101’

(plus why you, as an investor, should care):

Let’s define mineral deposit:

A body of rock that hosts a ‘HIGH concentration’* of valuable minerals that may be extracted at a profit, given current technology and reasonable metal prices.

*aka grade, is a moving target. We’ll get back to that shortly.

Note that a mineral deposit is not the same as an ore deposit.

The difference is basically, reserves vs resources.

Only deposits with reserves should be referred to as ore deposits.

But I digress… let’s get back into it.

Several natural processes increase the concentration of a mineral in a particular location.

And you need a source, a transportation method & a place where the minerals are deposited.

Hence, the ‘deposit’.

Now, let’s dive deeper (yes, pun, I can’t help myself).

These natural processes are:

• Hydrothermal
• Magmatic
• Sedimentary

Let’s expand, and mention examples of typical types of deposits within each one.

(You’ll see why this is crucial for investors shortly)

1) Hydrothermal:

Most metal deposits. Formed via circulation of hot metal-bearing fluids through the crust.

Hot fluids/water can dissolve and carry metals like gold, copper, silver & zinc.

Fluids travel from hot to cool areas, from high to low pressure via faults & fractures.

Deposit types

• Porphyry
• Skarn
• Volcanic Massive Sulphide, VMS
• Sedimentary Exhalative, SEDEX
• Mesothermal, epithermal, intrusive-related gold & silver
• Uranium, unconformity, sandstone-hosted
• Mississippi Valley Type, MVT
• Iron Ore Copper Gold, IOCG

2) Magmatic:

These deposits form when minerals of interest crystallize directly out of a magma.

This occurs in low viscosity magmas w/high background level of nickel, copper & PGE.

Either via sulfide metals creating massive bodies or layered rocks that sink to the bottom.

Deposit types:

• Magmatic platinum group elements, PGE
• Magmatic nickel & copper
• Kimberlites (diamond)
• Pegmatites (boron, cesium, lithium, molybdenum, niobium, tantalum, tin, tungsten, beryllium, and also gems such as emeralds and aquamarine)

3) Sedimentary:

These deposits form by accumulation of minerals or plant material on the surface of the earth.

Deposit types

• Placer (alluvial gold)
• Evaporites (lithium, boron, gypsum)
• Laterites (nickel, aluminum/bauxite)
• Banded Iron Formation, BIF 📷
• Coal

Now, does it matter, if a deposit is a copper porphyry vs skarn, or epithermal vs mesothermal gold, or VMS vs IOCG?

Yes, it ABSOLUTELY does.

Remember when I said that grade is a moving target?

That’s actually the crux of the matter.

It matters because a ‘good grade’ is not absolute, plus it conditions decisions.


1) economic grade
2) CAPEX range
3) mining method

Will vary w/each type, existing technology and metal prices. A stellar grade in one type may not be economic in another!

1 tweet summary ↓

Deposit types

• Hydrothermal: Porphyry, VMS, SEDEX, meso & epithermal, intrusive-related gold & silver, skarn, uranium, MVT, IOCG
• Magmatic: PGE, nickel & copper, kimberlites, pegmatites
• Sedimentary: Placer, evaporites, laterites, BIF, coal

Good grades = type-dependent

I will be breaking down each deposit type with currently economic grades in future threads.

So make sure you are following me @paola_rojas to catch them first.

Thanks for reading 🧐

📊 Graphics

@NotreDame‘s lecturer Dr. Clive R. Neal:

I don’t personally have the book the lecture is based on, but you can check it out here if you like.

(and yes, geology books are expensive, that’s just how it is!)

If this was useful, please retweet the start of the thread.

Follow me @paola_rojas for more on metals, markets and tech.


Investing in metals & tech and not on our distribution list? Let’s fix that. Link in bio.

Originally tweeted by Paola Rojas 🐝 (@paola_rojas) on July 23, 2022.

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