Magmatic Ore-Forming Processes - Additional Lecture
Magmatic Ore-Forming Processes - Additional Lecture
Magmatic Ore-Forming Processes - Additional Lecture
Pauline.jeanneret@geo.uu.se
❖ Magmatic Ore Deposits
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
Chemical classification of volcanic rocks in the TAS diagram wt% Na2O + K2O
versus wt% SiO2; after Le Bas et al. (1992); q = normative proportion of quartz,
ol = normative proportion of olivine
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
❑ Classification of
igneous rocks
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
❑ Classification of
igneous rocks
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
❑ Classification of
igneous rocks
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
❑ Magmas and metallogeny Magmatic deposits can roughly be divided into 3 groups:
(1) Deposits associated with primitive magmas that originate directly from the Earth’ mantle such as basalt. Such basic
and ultrabasic magmas can form deposits of chromium, nickel, platinum, iron, titanium, and vanadium. Includes the
huge layered mafic intrusions (LMIs) such as Bushveld (South Africa), Great Dyke (Zimbabwe), and Sudbury (Canada) that
are among the most important deposits of all. It also includes komatiites, and Kiruna-type deposits.
(2) Deposit related to acidic melts. They can be formed by strong fractionation from a primitive melt originally derived
from the mantle or by melt formation in the crust. Of economic interest are the late magmatic residual melts that may
contain high contents of rare elements such as lithium, beryllium, rare-earth elements (REEs), niobium, tantalum,
uranium, and thorium. The main focus of such interest is on pegmatites that have particularly large crystals.
(3) alkali-rich magmas/rocks that occur at continental rifts and hotspots. Form under special conditions in the Earth’
mantle. Fractionation allows them to develop into very special and diverse alkaline rocks some of which have very high
contents of rare elements such as REEs, niobium, zirconium, and uranium. In addition to silicate magmas, carbonatites
also play a role. They are responsible for the most important REE and niobium deposits. Phosphate, copper, iron,
zirconium, are also extracted from carbonatites.
➢ Understanding ore genesis processes, therefore, requires a knowledge of lithospheric architecture, and also of the
origin and nature of the igneous rocks in this section of the Earth.
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
Oceanic crust, which covers 2/3 of the Earth surface, is thin (<10
km) and has a composition and structure that is relatively simple
and consistent over its entire extent. 0.4 km thick
Main layers:
1–.5 km thick
(1) 0.4 km thick of pelagic sediments
(2) 1–.5 km thick layer of Pillow lavas and sheeted dikes =
dominantly basaltic in composition
(3) Main body of oceanic crust, plutonic in character and formed
by crystallization and fractionation of basaltic magma. This
cumulate assemblage comprises mainly gabbro, pyroxenite, and
peridotite.
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
❑ Magmas and metallogeny: types of ore deposits that one might expect to find associated with ophiolitic rocks
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
The lower crust is not necessarily compositionally different from the upper crust, but exists at higher metamorphic grades.
Some of the lower crust may be more mafic in composition, comprising material such as amphibolite, gabbro, and
anorthosite.
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
❑ Magmas and metallogeny types of ore deposits that one might expect to find hosted in rocks of continental crust
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
Zou et al.2013
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
1. Concentration of ore minerals by partial melting and fractional crystallization: during partial melting of rock certain
elements preferentially enter the melt while others remain behind. As soon as crystals form during cooling the composition of
the remaining melt changes and continues to do so as crystallization progresses. Separating crystals from the melt (fractional
crystallization) results in rock with a completely different composition.
2. Separation of sulfide or oxide liquids from otherwise silicate-dominated magmas due to liquid immiscibility upon cooling.
Sometimes liquid immiscibility occurs in which magma is separated into 2 differently composed melts. Such processes lead to
effective fractionation that can enrich certain elements to such an extent that an ore deposit is formed.
heating
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
Fractional crystallisation of basic magmas can lead to concentration of oxidic ore minerals, such as chromite, ilmenite and
Ti- magnetite as well as of platinum-group minerals.
Ores of this type are frequently related to layered intrusions of gabbro or norite as well as to their differentiates that are
represented by ultramafic rocks, such as dunite, peridotite or pyroxenite, or by genetically related felsic rocks, such as
anorthosite.
In the mafic intrusive bodies, ore minerals can occur as massive layers but they can also be distributed in the mafic host
rock as volumetrically subordinate constituents. A feature typical of layered intrusions are cumulate structures.
heating
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
o However, some of the rocks are found Why do Rocks Melt on Earth and where ?
entirely molten within the Earth.
❖ Magmatic Ore Deposits
ToC prevailing in the Earth’ mantle are normally below the solidus
Adiabatic
of peridotite; hence the mantle is not molten.
Decompression
A melt is generated when the ToC of the mantle is unusually high or
when the melting ToC is reduced by the presence of water. H20 increase
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
Anorthite
❑ Partial melting and Fractional crystallization as ore-forming processes
Melts originating from the mantle almost always have the composition
of basalt
➢ How is melt composition defined? Forsterite
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
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Melts originating from the mantle almost always have the composition
of basalt
➢ How is melt composition defined?
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
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A distribution coefficient can be specified for all elements according to which they
either preferentially enter the melt or remain in the peridotite.
Elements that tend to remain in the rock are called compatible such as chromium
and nickel. Elements enriched in the melt are called incompatible.
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits The brown stripe marks the border between
compatible and incompatible
❑ Partial melting and Fractional crystallisation as ore-forming (from Okrusch and Matthes 2009)
processes
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
Magmatic series :
Ex: Basalts of the mid-ocean ridges = tholeiitic trend:
iron and titanium are strongly enriched while SiO2 and alkalis
hardly change; hence basalts become rich in iron.
It is only later that SiO2 and alkalis are enriched (i.e., after
magnetite starts to be crystallized). The tholeiitic trend mid-ocean ridges
assumes low oxygen fugacity, which delays the oxidation of Subduction
iron and thus the crystallization of magnetite.
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits STUDY CASE – PhD 2016: Behavior of U-bearing phases: Monazite
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits STUDY CASE – PhD 2016: Behavior of U-bearing phases: Monazite
M2-D2
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits STUDY CASE – PhD 2016: Behavior of U-bearing phases: Monazite
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
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(1)Silicate melt–iron oxide melt: concerns basaltic magmas that follow tholeiitic fractionation in which iron accumulates
strongly in the melt. Size of the gap and thus the composition of the two melts depend on the oxygen content and the
content of phosphorus, titanium, and iron. Ex: segregation in the groundmass of tholeiitic basalts where iron-rich melt has a
significant silicate content. IOA (kiruna type) type?
(2) Silicate melt–sulfide melt : segregation between silicate and sulfide melt is of greater importance and often happens when
it comes to basic magmas. During segregation elements such as copper, nickel, cobalt, gold, and platinum (chalcophile and
siderophile elts) effectively fractionate into the sulfide melt as long as of course they are present in the melt. This is the most
important process in the formation of nickel and platinum deposits.
(3)Silicate melt–carbonatitic melt: third miscibility gap occurs mainly in alkali-rich and silica-undersaturated (alkaline)
magmas. If they have a very high CO2 content, then a carbonate melt (carbonatite) may be segregated.
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
Mentimeter time
Go to www.menti.com
❖ Magmatic Ore Deposits
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
Two giant Ni-Cu districts stand out above all the rest in the world:
Sudbury, Ontario, and Noril’sk-Talnakh, Russia. Other major Ni-Cu
districts include the Thompson, Voisey’s Bay, and Raglan districts in
Canada, Kambalda (Australia).
FIGURE 4. Grade and tonnage plots of global magmatic Ni-Cu sulphide deposits.
(A) Tonnages vs. Ni grades; (B) Tonnages vs. Cu grades; (C) Tonnages vs. PGE
grades. (Prepared from data in Eckstrand et al., 2004: in some cases modifi ed.)
Inclined contours show quantities of contained metals in each fi gure; tonnes
for Ni and Cu, and kg for PGE.
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits Zientek, 2012, USGS
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
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❑ Tectonic setting
generally occur in intracratonic settings associated
with mantle plume activity.
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
❑ Tectonic setting
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits pyrrhotite (Po) and pentlandite (Pn)
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits pyrrhotite (Po) and pentlandite (Pn)
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
The great majority of magmatic sulfide deposits form from much the same sequence of three processes:
2) Physical separation of a mixture of sulfide liquid droplets and cumulus silicate minerals from this emulsion;
Solubility of sulfur in silicate magma depends not only on the temperature but also on the redox state (oxygen fugacity)
and FeO content of the melt. Accordingly, other processes can trigger segregation in addition to cooling. A simple
possibility is contamination with external sulfur. Many sediments have a significant sulfur content. If they are melted by
and mixed with basic magma, then sulfur saturation can easily be exceeded. Under certain circumstances the mixing of
two different magmas can also lead to a composition that is exactly right for segregation. Finally, segregation can also be
triggered by crystallization of an FeO-rich phase such as magnetite.
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
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Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
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Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
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❑ ORE-FORMING PROCESSES: Sulfide rich NI-CU-PGE deposit Sulfide saturated Sulfide undersaturated magma
magma
❖ Generation of Sulfide Liquids
Mantle-derived magmas having potential to form Ni-Cu-
PGE deposits must have been produced by relatively high
degrees of partial melting and S-undersaturation
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
For platinum that are only present in small amounts in the magma but fractionate strongly in segregated melts the so-
called R factor plays a role in addition to the distribution coefficient.
R factor describes the quantitative ratio between silicate magma and sulfide magma in equilibrium. If a small amount
of sulfide magma exchanges elements with a lot of silicate magma, then elements such as platinum are enriched in the
sulfide melt to particularly high concentrations. A significant deposit forms when sulfide melts segregate relatively
early during fractional crystallization of the original magma.
In order to achieve ore grade sulfide mineralization a very high R-factor is required: the sulfide liquid must equilibrate
with significant quantities of metal-bearing silicate magma. In the case of Ni and Cu, they are in sufficient abundance in
mantle-derived magmas that they only require R-factors of 100s to 1000s to yield ore grade mineralization. In contrast,
low concentration elements like Pt (and other PGE) require significantly higher R-factors, ~10000 or higher, to achieve ore
grade
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
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Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
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Figure 2. R-factor models for various Ni, Cu, and Pt (DNi = 500 ,
DCu = 1500, and DPt = 10,000). Also shown is an approximate
ore grade for the various commodities.
this diagram illustrates the importance of both the starting
concentration of an element (Co) and also how increased R-
factor is required to generate ore grade mineralization.
Also evident is that for PGE-rich deposits the R-factor requires
is an order of magnitude higher (or more) than it is for the base
metals Ni and Cu, and explains why many PGE-rich deposits are
associated with large igneous provinces with high volumes of
magmatism.
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
Wang et al.2018
❖ Magmatic Ore Deposits
Mechanism of mixing two magmas both of which are at or close to sulfide-liquid saturation can give rise to a hybrid
magma with transient sulfide supersaturation. This process has been invoked to explain the origin of PGE reefs associated
with major magma influxes in large chambers, such as the Merensky Reef of the Bushveld Complex.
Addition of external S is regarded as the dominant process in the formation of all komatiite-hosted ores and in the great
majority of intrusion-hosted deposits. A variety of mechanisms exist for incorporating external S, but direct melting of
physically incorporated sulfidic country-rock fragments (xenoliths) to form sulfide ‘xenomelts’ is the fastest and most
effective.
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
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Great diversity of form in the magma bodies that host Ni–Cu-dominant, sulfide-rich orebodies. All represent the products of
magma flowing through restricted conduits or channels, leaving behind an accumulated residue of sulfide liquid and cumulus
silicate minerals.
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
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Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
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❑ Ni-Cu-PGE Magmatic Sulphide Deposits : Relation between LIP and these deposit
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
❑ Ni-Cu-PGE Magmatic Sulphide Deposits : Relation between LIP and these deposit
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
Ni-Cu deposits of the rift and continental flood basalt subtype are the products of the
magmatism that accompanies intracrustal rifting events. Include the largest deposit,
Noril’sk-Talnakh, (12.6 Mt of contained Ni)
Features that these deposits tend to have in common: associated with large magma
systems, and that within these systems the Ni-Cu sulphide ores tend to be associated
with conduits or feeders to the larger igneous masses. Much of the sulphide has been
derived by contamination of the magma through incorporation of S from adjoining
wall rocks.
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
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Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
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Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
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Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
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A discontinuous, more mafic basal unit termed the sublayer contains most
of the Ni-Cu ores and abundant xenolithic clasts.
The melt also intruded some of the radiating breccia zones, forming many
km long quartz diorite dykes (offsets) extending outward from the SIC, and
these also contain Ni-Cu ores .
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits Rock is broken by shock waves and subsequent movement and is partly melted
(red). With large craters the center rebounds to form a central uplift. This is
known to collapse again with the result that very large craters have multiple
❑ Ni-Cu-PGE Magmatic Sulphide Deposits :
rings. Finally the ash cloud rains down and forms a tuff-like fallback breccia.
❖ Sulfide accumulation beneath a meteorite impact
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
2 main characteristics:
▪ Few economic PGE deposits in the world but size of their host intrusions is really huge. Mafic magmas have very low
contents of PGE. Despite the high R factor of PGE, the sulphide has apparently equilibrated with large proportions of
magma to form economic PGE deposits.
▪ Very small amount of sulphide (less than 3%) with which the PGE are associated. Sparsely disseminated sulphide is
mainly chalcopyrite, but also includes pentlandite and pyrrhotite. Pentlandite is the only common sulphide mineral
that contains a significant amount of any PGE, in this case Pd.
Small amount of sulphide appears due to the fact that the only S involved is the original mantle S, with little or no
addition from the intruded wall rocks. Because the solubility of S in mafic magmas is quite low, the amount of sulphide
produced when the magma reaches saturation is very small, resulting in small, sparsely dispersed sulphides.
Two distinct modes of PGE deposits are (1) the reef type, and (2) the magmatic breccia type. Of the two, only the reef
type has proved to be a major producer.
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
All PGE reefs are typically more or less conformable, relatively thin
layers (from less than one to a few metres) within the well-layered
sequence of the intrusions.
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
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Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
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Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
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Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
Barnes et al 2017 Elements
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❑ Exploration guide
Geology
Exploration methods
✓ First order target – mafic/ultramafic rocks
✓ Massive ores make good geophysical
✓ Regional scale targets, e.g.
• Continental Flood Basalt - Small differentiated intrusions that act • concentration of dense minerals,
as feeder systems in LICs
• contacts between conductive
• Komatiites minerals
• small to medium sized mafic/ultramafic sillls or flows
✓ Aeromagnetics for magnetite
• cluster along strike
• PGE – large mafic layered intrusions ✓ PGE – gravity and magnetics
✓ Sulphides – electromagnetics
✓ Local scale
• Gravitational settling, low in the sequence
• Ultramafic to mafic contact
• Decreases magma flow rate
• Low to high Ni or S concentrations
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
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❑ Resource use
❖ PGE
❖ Cu
❖ Ni • Catalysts
• Jewellery • Electrical industry
• Ni alloys (anticorrosive)
• Dentistry • Chemical industry – pest
• Steel
control
• Gas turbines • Electronics
• Engineering
• Catalysts • Chemical instruments
• Metallurgy – brass
• Rechargeable Ni-Cd batteries
❖ Cr • Coins
• Magnets
• Fe-Ni and Cu-Cr alloys • Telecommunications
• Coins
• Recycling 45% in the EU • Ferrochrome • Recycling contributes 30%
• Colour pigments
• Foundary sand
• Tanning leather and textiles
• Refractory industry
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
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Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
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➢ The way how these massive magnetite–apatite ore bodies have been
formed is still controversial.
2 theories:
(1) unusual phosphorus-rich iron oxide magma (Frietsch and Perdahl
1995; Harlov et al. 2002; Naslund et al. 2002; Hou et al. 2011).
(2) formed by hydrothermal solutions (Sillitoe and Burrows 2002; Jami et
al. 2007, 2009)
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
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Introduction
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits Ovalle 2018
field observations and magnetite geochemical data from surface or near surface
samples (e.g., Magnetite-Z and Magnetite-S) reflect a hydrothermal origin, magnetite
Introduction
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits Weis MSc thesis 2013
Introduction
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
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❑ Pegmatites
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
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❑ Pegmatites
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
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❑ Pegmatites
Although crystals several centimeters or decimeters in size are
the rule, even crystals several meters in size are not
uncommon. A single potassium feldspar in a pegmatite in
Colorado (USA) is said to have been 50 m long, 14 m wide, and
36 m high.
➢ Thus, pegmatites can be classified according to economic criteria such as gem-bearing, REE, and lithium pegmatites.
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
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❑ Pegmatites
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
Abyssal pegmatites are different
because they are not formed as the
residual melt of a granite but in situ by a
low degree of melting
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
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❑ Pegmatites
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
What is the use of niobium , tantalum, REEs, beryllium, lithium, cesium fluorine?
What is coltan?
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Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
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Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
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Exotic minerals can crystallize early in alkaline magmas resulting in fractionation leading in a different direction.
Water released by the magma plays an important role because large quantities of alkalis (together with chlorine, fluorine,
and other elements) can disappear from the magma. This water can in turn react with older igneous rocks and transform
them into completely different rocks.
Finally, the separation of immiscible carbonatite melt can also occur. If they have a very high CO2 content, then a carbonate
melt (carbonatite) may be segregated.
Accordingly, there is a whole catalog of different alkaline rocks. What they have in common is that they contain (1) minerals
low in silica such as olivine, feldspathoids (nepheline, sodalite, leucite) or melilite, and (2) Minerals rich in alkalis such as
aegirine (alkali pyroxene) or arfvedsonite (alkali amphibole).
➢ Only a fraction of these rocks are economically interesting such as carbonatites and agpaitic nepheline syenites.
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
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Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
Carbonatite is defined as igneous rock consisting of more than 50% carbonate minerals: calcite (calcite carbonatite:
coarse-grained, sovite; fie-grained, alvikite) or dolomite (dolomite carbonatite) typically dominates.
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
❑ Carbonatites and Alkaline rocks An unusual carbonatite is the Phalaborwa copper deposit
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
Foskorite are mainly mined for apatite the by-products of which are magnetite, zirconium, gold, silver, and PGEs.
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
Whole deposit is located within similarly old sediments (sandstone, slate) that had been deposited in a continental rift.
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
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❖ Magmatic Ore Deposits
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
❑ KImberlites
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
❑ KImberlites
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
❑ KImberlites
Kimberlites and lamproites are emplaced during highly explosive volcanic eruptions and form small, circular, funnel-shaped
craters called maars. Most kimberlites are restricted to continents, and diamond deposits occur preferentially near or at the
margins of stable Archean cratons.
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
❑ KImberlites
Most kimberlites are restricted to continents,
and diamond deposits occur preferentially
near or at the margins of stable Archean
cratons.
Several decades ago almost all diamond mines were located in southern Africa but many large and important deposits have
recently been found in Russia, Australia, and Canada. The small African country Botswana is now the world’ second largest
diamond producer (after Russia, measured by the values of the gems), followed by Canada
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
❑ KImberlites
Strictly speaking diamonds in kimberlites are not truly magmatic. They are
thought to be xenocrysts that were plucked from the sub-continental
lithospheric mantle as the kimberlite magma ascended from its deep source
to the surface.
Diamond is the stable form of carbon at the pressures and temperatures that
reign in the lower part the lithosphere. Given that carbon is relatively
abundant in mantle rocks, it is probable that this part of the mantle is a vast
reservoir of the gemstone. Kimberlite magma is merely a vehicle that
transports the diamonds rapidly to the surface
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
❑ KImberlites
Figure 19.21. Hypothetical cross section of an Archean craton with an extinct ancient mobile belt (once associated with subduction) and a
young rift. The low cratonal geotherm causes the graphite-diamond transition to rise in the central portion. Lithospheric diamonds
therefore occur only in the peridotites and eclogites of the deep cratonal root, where they are then incorporated by rising magmas
(mostly kimberlitic- “K”). Lithospheric orangeites (“O”) and some lamproites (“L”) may also scavenge diamonds. Melilitites (“M”) are
generated by more extensive partial melting of the asthenosphere. Depending on the depth of segregation they may contain diamonds.
Nephelinites (“N”) and associated carbonatites develop from extensive partial melting at shallow depths in rift areas.
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
❑ KImberlites
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites
❖ Magmatic Ore Deposits
Introduction Magmatic Ni-Cu-PGE REE pegmatite Carbonatite and Alkaline Intr. Kimberlites