MT - Studying

What is the typical grade for Cu deposits?

0.2-2% Cu grades are typical

What is the typical grade for Ni deposits?

0.7-3% Ni grades

What is the mineral formula for Pyrrhotite (po)?

Fe_1-xS

What is the mineral formula for Pentlandite (pn)?

(Fe, Ni)₉S₈

How much Sulphur is in the peridotite magma in ppm?

~250 ppm S

What wt% MgO is komatiite melts?

>18wt% MgO

What ages are Komatiite deposits limited to? Why?

Are Archean (>2.5 Ga) in age

• Hotter mantle in early Earth that allowed for extensive mantle melting (30-50%)

What is the age of the latest Komatiite deposits?

1.88 Ga - Paleoproterozoic

What temperatures are komatiite melts?

1600’C

What are 2 examples of Ni-Cu-PGE deposits and their ages?

1. Sudbury, Ontario - Meteorite impact (1.85Ga)

2. Thompson

3. Raglan

4. Voisey’s Bay

5. Kambalda, Western Australia - Greenstone belts (2.7 Ga)

Are magmatic Ni-Cu-PGE deposits restricted to a certain geological interval of geologic time?

Usually from the Archean to the Proterozoic, but not restricted to a specific period. Only need mafic to ultramafic magmatic

What are 2 examples of Komatiite-associated Ni deposits?

• Kambalda

• kotselvaara

• Murrin Murrin

• Damba-Silwane

• Langmuir

• Marbridge

• Trojan

Draw and label Komatiite Ni ore-forming environment/deposit? Involve the following:

• Scale

• textures

• location of sulphides

• Ore elements present

V scale = 10-100m

H scale = 100-100,000m

What is the source of metals in Ni-Cu-(PGE) Deposits?

Some of the S is the peridititic upper mantle (except for Sudbury where it is all crustal)

What is the transport of metals in Ni-Cu-(PGE) Deposits?

The metals and S are transported in solution as basaltic/komatiitic magmas ascend from the mantle through the crust

What is the traps of metals in Ni-Cu-(PGE) Deposits?

Embayments and irregularities at the base of flows or within conduit systems are critical for collecting sulphide liquids into larger bodies.

• Collected sulphide melts can fractionate and produce Cu, Pt, Pd, Au-rich residual liquids

• Sulphide melts crystallize and produce po-pn-cp during cooling

How does sulphide liquid saturation in magmas at high levels in the crust?

1. Sulphide saturation, in most cases, is triggered by contamination (addition of crustal S)

2. The amount of sulphide liquid produced upon saturation is small (<1% of the total mass of silicate magma)

3. Metals (Ni-Cu-PGE) partition strongly into sulphide melt.

What are the Platinum Group Minerals (PGM)?

• Speryllite

• Braggite

• Cooperite

• Merenskyite

What is the mineral formula for Speryllite?

PtAs₂

What is the mineral formula for Braggite?

(Pt, Pd)S

What is the mineral formula for Cooperite?

PtS

What is the mineral formula for Merenskyite?

PdTe₂

What is Tulameenite and what is the mineral formula?

Platinum- Copper Alloy

• Pt₂CuFe

What is the mineral formula for Laurite?

RuS₂

What are the 2 types of PGE deposits?

1. Reef Type - stratiform sulphide-bearing ore zones rich in PGE in LMI

2. Magmatic Breccia Type - large zones of disseminated sulphide in a mafic magmatic host

What are 2 examples of Reef Type Deposits and their ages?

1. Merensky reef, Bushveld (2.057 Ga)

2. J-M Reef, Stillwater (2.709 Ga)

What are 2 examples of Magmatic Breccia Type Deposits?

1. Platreef - Bushveld

2. Lac des Illes, Ontario

What age are most PGE deposits?

mostly Paleoproterozoic (2.5 Ga) to Neoarchean (2.8 Ga) in age

What are the PGE grades for the Merensky reef?

5-7 g/t (Pd/Pt ~0.5)

What are the sulphide grades for the Merensky reef?

2-4 vol.% sulphide

• low grade

What are the PGE grades for the J-M reef?

~18 ppm (g/t) with a Pd/Pt of ~3

• Higher grade than Merensky (Pd/Pt = ~0.5), but is smaller

What is the source of PGE-rich Reefs?

Peridotitic mantle

What is the Transport system in PGE-rich Reefs?

PGE are transported in solution in the magma until they reach upper crustal magma chambers

What is the trap of PGE-rich Reefs?

PGE are trapped from solution in PGM within a “reef“ (a broadly stratiform, but locally discordant, horizon in a layered intrusion)

What are the temperatures of basaltic magma?

1300’C

What are the temperatures of Komatiite magmas?

1600’C

What is the mineral formula for Spodumene? What REE element does this contain?

LiAlSi₂O₆

• Contains Lithium (Li)

What is the mineral formula for Petalite? What REE element does this contain?

LiAlSi₄O₁₀

• Contains Lithium (Li)

What is the mineral formula for Lepidolite? What REE element does this contain?

KLi₂Al(Al, Si)₃O₁₀(F, OH)₂

• Contains Lithium (Li)

What is the mineral formula for Pollucite? What REE element does this contain?

(Cs, Na)₂Al₂Si₄O₁₀*2H₂O

• Contains Cesium (Cs)

What is the mineral formula for Cassiterite? What REE element does this contain?

SnO₂

• Contains tin (Sn)

What is the mineral formula for Columbite and Tantalite? What REE element does this contain?

• (Mn, Fe)Nb₂O₆

• (Mn, Fe)Ta₂O₆

Contains Niobium (Nb) and Tantalum (Ta)

What is the mineral formula for Pyrochlore-Microlite? What REE element does this contain?

• Ca₂Nb₂O₆(F)₂

• Ca₂Ta₂O₆(F)₂

Contains Niobium (Nb) and Tantalum (Ta)

What is the mineral formula for Tapiolite? What REE element does this contain?

(Fe, Mn)Ta₂O₆

• contains tantalum (Ta)

What is the mineral formula for Niobian Rutile? What REE element does this contain?

(Ti, Nb, Fe)O₂

• Contains Niobium (Nb)

What is the mineral formula for Beryl? What REE element does this contain?

Be₃Al₂(SiO₃)₆

• Contains beryllium (Be)

What is the mineral formula for Tourmaline? What REE element does this contain?

Na(Mg, Fe, Li)₃Al₆(OH)₄B₃O₉Si₆O₁₈

• Contains Lithium

What is the temperature of pegmatitic granitic magmas?

T = 550-250

Draw an example of a pegmatite involving the relationship between pegmatites and granites. Involve the following:

• Pressures

• scale/depth

• locations of: miarolites, petalite, spodumene, beryl, ceramic, Li-Cs-Ta

Draw the internal structure of a layered pegmatite. Incorporate the following into your image:

• perthite

• miarolitic cavity

• qtz

• border/wall zone

• graphic perthite

• layered sodic apalite

• dike center line

• scale

What is an example of a pegmatite deposit? Provide the age. What type of pegmatite is it?

2.670 Ga Tanco pegmatite

• Lithium-Cesium-Tantalum (LCT) pegmatite

What is the source of rare metals in pegmatites?

Source = pre-existing continental crust that is partially melted to form granitic melts

What is the transport of rare metals in pegmatites?

Metals are transported when dissolved in granitic magmas

What is the trap of rare metals in pegmatites?

The pegmatite body itself.

• where crystals with unusual chemistry and size crystallize at low temperatures, volatile-rich magmas (± aqueous fluid)

What are 2 Rare Earth Element (REE) bearing minerals? and their formulas?

• Bastnasite: (La,Ce,Y)CO₃F

• Monazite: (Ce,La,Th)PO₄

What is the main transport system for metals in hydrothermal deposits?

aqueous hydrothermal fluids

• main transport medium for ore-forming metals