Copper porphyries explained to help you add the metal to your portfolio (for mining investors) [Twitter thread unrolled]

Copper is crucial for decarbonisation, yet we’ve been underinvesting for over a decade.

To be copper-ready we must step up.

Here's the skinny on porphyry deposits to help you take advantage of this lifetime opportunity.

Today I'll cover some copper porphyry basics including:

• characteristics
• location
• grades
• tonnage
• must & nice to haves
• mining methods
• size and mineralisation
• minerals present
• origin
• examples

Let's dive in.

Porphyry copper deposits are:

• massive
• low to medium in grade
• host copper, gold & molybdenum
• hydrothermal deposits related to igneous intrusions
• dominant mineralisation is Cu, Mo sulphide in fractures, stockworks, veins and disseminations

Let's break it down.

Porphyries are the world's major source of copper and molybdenum and a significant source of gold.

Found around the world but most deposits are in the circum-pacific belt, also known as the 'ring of fire' due to its volcanic activity (makes sense, huh?).


Map of the ring of fire

Each deposit type has an associated grade and tonnage range that can be economic, i.e. mined at a profit.

Typical grades for porphyry* are:

• Copper: 0.25-1%
• Gold: 0.1-1 g/t
• Molybdenum: 0.01-0.1%
• Silver: 1-3g/t

*may also host tin & tungsten.

On the other hand, the ore tonnage range for porphyries is 10-1000MT, with a typical ~100MT.

Larger examples are also known.

Do not confuse tonnage with resources or reserves.

There are some examples in the range in this list, including @resolutioncu

A worthy porphyry:

• grades in range
• intersections start near surface ~100m like $ABRA.V 📊
• hundreds m in all directions
• tens to hundreds of m in length

• open at depth
• large zones of mineralisation at 200-400m
• 10-50m zones at top of grade range

Results from the first hole drilled by AbraSilver at their La Coipita copper project in San Juan province. The results show copper mineralisation starting very close to surface, at 25m

Given their low grade and large size, porphyry deposits are mined via open pit.

Like Kennecott, also known as $RIO's Bingham Canyon mine in Utah.

A few use block caving, which despite being an underground method permits high tonnage and low-cost production.

📷 @globaldataplc

Bingham copper mine, view of the open pit

The ideal deposit is oval or spherical in form, while some are pipe-shaped.

Can extend hundreds to thousands of m in each direction.

Minerals are disseminated within host rock or in fractures, veins and breccia.

A common style of mineralisation is stockwork.

📷 @PampaMetals


Dominant economic minerals are sulphides including chalcopyrite, bornite, chalcocite and molybdenite.

Gold is found in its native state and in electrum (natural alloy of gold + silver).

In deposits with a supergene zone, copper oxide minerals and native copper may be present.

Thought to originate from hydrothermal fluids on top of a cooling magma at depths between 1-5km.

Hot fluids move upwards.

Minerals crystallise out of fluids mainly as a result of cooling.

Cause a fracture network and the characteristic stockwork texture.

📊 Stephen Marshak

Considerable gold or silver-gold deposits are formed on top of porphyries.

CEOs often say they are looking to hit the porphyry.

Even if it's too deep to target directly, its genesis helps predict how it may present and where.

Predicting is essential when you can't see!

Among producing and closed copper mines we can mention:

• Escondida
• El Teniente
• Alumbrera (c)
• Chuquicamata
• Bingham Canyon

For other advanced projects in the pipeline see my thread

And that's a wrap!

By digesting these concepts you can more confidently allocate capital to copper explorers.

My absolute favourite is deposit formation. Think like a geologist but with an investor's perspective.

Keen to dig deeper? Visit my blog:

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

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

#GeologyForInvestors #MiningForInvestors #ExplorationForInvestors

Originally tweeted by Paola Rojas 🐝 (@paola_rojas) on September 19, 2022.


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