Mining investors know that grade is crucial, yet not simple.
Because what's high for copper porphyry may be low for vein systems and so on.
Hence, here is your primer on grades by metal and deposit type.
(I promise you'll want to bookmark this)
Because what's high for copper porphyry may be low for vein systems and so on.
Hence, here is your primer on grades by metal and deposit type.
(I promise you'll want to bookmark this)
First, types of deposits* can be classified as:
• Hydrothermal: Porphyry, VMS, SEDEX, meso & epithermal, etc
• Magmatic: PGE, nickel & copper, kimberlites, pegmatites
• Sedimentary: Placer, evaporites, laterites, BIF, coal, clays & brines
(detailed breakdown 👇)
• Hydrothermal: Porphyry, VMS, SEDEX, meso & epithermal, etc
• Magmatic: PGE, nickel & copper, kimberlites, pegmatites
• Sedimentary: Placer, evaporites, laterites, BIF, coal, clays & brines
(detailed breakdown 👇)
Range is simply the typical variation in grades found in assays, resources or reserves.
Anything at or below the lower end of the range is low grade, in the middle is average, and anything at or above the high end is high-grade (hence highly sought).
Anything at or below the lower end of the range is low grade, in the middle is average, and anything at or above the high end is high-grade (hence highly sought).
Typical ranges vary with time, and the technology used.
As tech improves, we can process lower grades.
Meaning what was considered 'waste' 50 years ago, can be profitably processed today.
Higher is generally better.
Units used are most commonly grams per ton or percent.
As tech improves, we can process lower grades.
Meaning what was considered 'waste' 50 years ago, can be profitably processed today.
Higher is generally better.
Units used are most commonly grams per ton or percent.
Additionally, a grade that is 'just right' for one type of deposit, may not be enough for another type, due to:
• depth
• impurities
• strip ratios
• processing method
• applicable extraction techniques, etc
Let's go over each type and optimal grade ranges:
• depth
• impurities
• strip ratios
• processing method
• applicable extraction techniques, etc
Let's go over each type and optimal grade ranges:
Porphyries can host gold, copper, and molybdenum plus silver, tin and tungsten.
Grade range:
Gold (Au): 0.1-1.0g/t
Silver (Ag): 1.0-3.0g/t
Copper (Cu): 0.25-1.0%
Molybdenum (Mo): 0.01-0.1%
Example: Los Azules $MUX
Grade range:
Gold (Au): 0.1-1.0g/t
Silver (Ag): 1.0-3.0g/t
Copper (Cu): 0.25-1.0%
Molybdenum (Mo): 0.01-0.1%
Example: Los Azules $MUX
VMS (also called VHMS) can host gold, silver, copper, zinc and lead.
Grade range:
Gold (Au): 0.5-2g/t
Silver (Ag): 15-30g/t
Copper (Cu): 1-2.5%
Zinc (Zn): 2.0-6.0%
Lead (Pb): 0.5-2.0%
Example: McIlvenna Bay $FOM
Grade range:
Gold (Au): 0.5-2g/t
Silver (Ag): 15-30g/t
Copper (Cu): 1-2.5%
Zinc (Zn): 2.0-6.0%
Lead (Pb): 0.5-2.0%
Example: McIlvenna Bay $FOM
SEDEX can host zinc and lead, plus silver, and copper.
Grade range:
Zinc (Zn): 4.0-8.0%
Lead (Pb): 2.0-6.0%
Silver (Ag): 30-60g/t
Copper (Cu): 0.0-1.0%
Example: McMillan Pass/Tom & Jason $FWZ
Grade range:
Zinc (Zn): 4.0-8.0%
Lead (Pb): 2.0-6.0%
Silver (Ag): 30-60g/t
Copper (Cu): 0.0-1.0%
Example: McMillan Pass/Tom & Jason $FWZ
Epithermal deposits can host gold, silver, copper, zinc, lead.
Grade range:
Gold (Au): 1.0-15+g/t, +25g/t bonanza sporadically
Silver (Ag): 0.0-200+g/t (silver only at the high end)
Copper (Cu): up to 2.0%
Zinc (Zn): up to 2.0%
Lead (Pb): up to 2.0%
Example: Diablillos $ABRA
Grade range:
Gold (Au): 1.0-15+g/t, +25g/t bonanza sporadically
Silver (Ag): 0.0-200+g/t (silver only at the high end)
Copper (Cu): up to 2.0%
Zinc (Zn): up to 2.0%
Lead (Pb): up to 2.0%
Example: Diablillos $ABRA
Mesothermal deposits can host gold and silver. Also referred to as greenstone/shear-zone-hosted and orogenic.
Grade range:
Gold (Au): 3.0-20.0g/t
Silver (Ag): 4.0-20+g/t
Example: Herbert $GPG
Grade range:
Gold (Au): 3.0-20.0g/t
Silver (Ag): 4.0-20+g/t
Example: Herbert $GPG
Intrusion related can host gold, silver, copper, zinc and lead.
Grade range:
Gold (Au): 0.5-3g/t, higher grades known
Silver (Ag): up to 20+g/t
Copper (Cu): 0.0-1.5%
Zinc (Zn): 0.0-1.5%
Lead (Pb): 0.0-1.5%
Example: Rogue $SGD
Grade range:
Gold (Au): 0.5-3g/t, higher grades known
Silver (Ag): up to 20+g/t
Copper (Cu): 0.0-1.5%
Zinc (Zn): 0.0-1.5%
Lead (Pb): 0.0-1.5%
Example: Rogue $SGD
Unconformity and sandstone-hosted uranium host... uranium
Grade range:
Uranium (U): 0.05%-3.0%, up to 20% in Athabasca basin deposits
Example: Wheeler River $DML
Grade range:
Uranium (U): 0.05%-3.0%, up to 20% in Athabasca basin deposits
Example: Wheeler River $DML
Carbonate replacement, MVTs & skarn can host gold, zinc, silver and lead plus tungsten, iron, molybdenum & tin.
Grade range:
Gold (Au): 5.0-500+g/t
Silver (Ag): replacement deposits are silver rich
Zinc (Zn): 2.0-10%
Lead (Pb): 2.0-10%
Example: possibly Medicine Springs $RSLV
Grade range:
Gold (Au): 5.0-500+g/t
Silver (Ag): replacement deposits are silver rich
Zinc (Zn): 2.0-10%
Lead (Pb): 2.0-10%
Example: possibly Medicine Springs $RSLV
IOCGs can host gold, silver, copper, zinc and lead plus iron, cobalt, rare earth elements, bismuth, barium, phosphorous and uranium.
Grade range:
Gold (Au): 0.2-1.0g/t
Copper (Cu): 0.5-1.5%
Uranium (U): 0.5% (Olympic Dam)
Example: La Higuera $TRBC
Grade range:
Gold (Au): 0.2-1.0g/t
Copper (Cu): 0.5-1.5%
Uranium (U): 0.5% (Olympic Dam)
Example: La Higuera $TRBC
Magmatic nickel & copper can host gold, nickel, and copper.
Grade range:
Gold (Au) + PGE (Pt, etc): 1.0g/t
Nickel (Ni): 0.5-3.0%
Copper (Cu): 0.5-3.0%
Example: Cassini $MCR
Grade range:
Gold (Au) + PGE (Pt, etc): 1.0g/t
Nickel (Ni): 0.5-3.0%
Copper (Cu): 0.5-3.0%
Example: Cassini $MCR
Also, with nickel, here's @equivestinvest breaking down the difference between laterite vs sulphide.
Sulfide is easier to process (conventional mining, smelting and refining), vs to laterite requiring intensive hydrometallurgical processing, hence more energy & chemicals.
Sulfide is easier to process (conventional mining, smelting and refining), vs to laterite requiring intensive hydrometallurgical processing, hence more energy & chemicals.
Magmatic PGE can host gold, and PGEs.
Grade range:
Gold (Au) + PGE (Pt, etc): 4.0-10.0g/t
Example: Stillwater-Sibanye $SBSW
Grade range:
Gold (Au) + PGE (Pt, etc): 4.0-10.0g/t
Example: Stillwater-Sibanye $SBSW
Lithium is a bit of a maverick. It can be found in multiple sources and deposit types.
Concentration/grade range for the most common are:
a) Brines: 250mg/l and higher**
Example: Pastos Grandes $LAC
Concentration/grade range for the most common are:
a) Brines: 250mg/l and higher**
Example: Pastos Grandes $LAC
b) Hard rock in pegmatites such as spodumene & lepidolite: 1.0-3.0%
By-products may include tantalite (primary source of tantalum) or tin.
Example: Pilgangoora $PLS
By-products may include tantalite (primary source of tantalum) or tin.
Example: Pilgangoora $PLS
c) Sedimentary rocks (such as clays and evaporites): approx 1,000-4,000ppm, still new as source
May also contain potassium, boron.
Example: Thacker Pass $LAC
May also contain potassium, boron.
Example: Thacker Pass $LAC
Other minor sources are geothermal and oilfield brines.
**Lower grades may be economic with DLE and other non-traditional extraction methods.
Some additional context into lithium main sources:
**Lower grades may be economic with DLE and other non-traditional extraction methods.
Some additional context into lithium main sources:
And that's it for now!
Making sure grades are within these ranges will help derisk your investments, especially with early-stage explorers.
Bookmark this for future reference.
PS: I will expand on other types in the future.
Making sure grades are within these ranges will help derisk your investments, especially with early-stage explorers.
Bookmark this for future reference.
PS: I will expand on other types in the future.
*notes:
- Not an exhaustive list
- Accurate classification may take years
- Some deposit types can straddle categories
- Grade is crucial but not the only consideration
- A project can include several deposits of different types. This is used during exploration as a pathfinder
- Not an exhaustive list
- Accurate classification may take years
- Some deposit types can straddle categories
- Grade is crucial but not the only consideration
- A project can include several deposits of different types. This is used during exploration as a pathfinder
If this was interesting or useful to you, please retweet the start of the thread.
Follow me @paola_rojas for commentary on the energy transition and the metals and minerals that are making it possible.
Follow me @paola_rojas for commentary on the energy transition and the metals and minerals that are making it possible.
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