|
|
|||||||||||||||||||||||
|
||||||||||||||||||||||||
Theme Magazines and Fact Sheets
Download "Geology and Ore no. 10, January 2008" go10.pdf (~4.5 mb)
No. 10 - January 2008
Pegmatites and their
potential for mineral
exploitation in Greenland
potential for mineral
exploitation in Greenland
Pegmatites are important suppliers of
many commodities world wide. In
Greenland pegmatites are well-
known, but their economic potential
has only been explored at a few local-
ities. This review provides an over-
view of the genesis and general eco-
nomic potential of pegmatite occur-
rences in Greenland. Field observa-
tions, archive information as well as
maps of stream sediment samples that
are enriched in elements characteristic
of pegmatites are the base for the
presentation. The prospective areas
for pegmatite-hosted mineral occur-
rences in Greenland are outlined, and
examples of prominent pegmatite
minerals are demonstrated.
many commodities world wide. In
Greenland pegmatites are well-
known, but their economic potential
has only been explored at a few local-
ities. This review provides an over-
view of the genesis and general eco-
nomic potential of pegmatite occur-
rences in Greenland. Field observa-
tions, archive information as well as
maps of stream sediment samples that
are enriched in elements characteristic
of pegmatites are the base for the
presentation. The prospective areas
for pegmatite-hosted mineral occur-
rences in Greenland are outlined, and
examples of prominent pegmatite
minerals are demonstrated.
Introduction
Pegmatites are suppliers of rare metals like
beryllium, lithium and tantalum. Pegmatites
also represent an important source of gem-
stones such as emerald and tourmaline, and
some pegmatites are even mined for their
large, clean crystals of quartz and feldspar.
Pegmatites are abundant in Greenland, but
few have been described or studied in detail
and hence their economic potential is large-
ly unknown at present.
beryllium, lithium and tantalum. Pegmatites
also represent an important source of gem-
stones such as emerald and tourmaline, and
some pegmatites are even mined for their
large, clean crystals of quartz and feldspar.
Pegmatites are abundant in Greenland, but
few have been described or studied in detail
and hence their economic potential is large-
ly unknown at present.
In a broader sense, the term pegmatite is
used for any coarse-grained vein of granitic
composition, with or without a connection
to an intrusive complex. Medium- to coarse-
grained granitic to pegmatitic veins may be
derived from partial melting of their host
rocks during progressive high-grade meta-
morphism. Such veins are also termed
migmatitic veins.
used for any coarse-grained vein of granitic
composition, with or without a connection
to an intrusive complex. Medium- to coarse-
grained granitic to pegmatitic veins may be
derived from partial melting of their host
rocks during progressive high-grade meta-
morphism. Such veins are also termed
migmatitic veins.
Mineralogically, pegmatites are termed sim-
ple when they essentially consist of quartz,
feldspar and biotite, and complex when
they carry a range of accessory minerals like
tourmaline, fluorite, lepidolite, spodumene
or beryl. Also molybdenite, scheelite, urani-
nite and rare earth element-bearing miner-
als may occur in complex pegmatites.
ple when they essentially consist of quartz,
feldspar and biotite, and complex when
they carry a range of accessory minerals like
tourmaline, fluorite, lepidolite, spodumene
or beryl. Also molybdenite, scheelite, urani-
nite and rare earth element-bearing miner-
als may occur in complex pegmatites.
Pegmatites in exploration and
exploitation
exploitation
Exploration is generally straightforward,
because large, potentially economic peg-
matites are often easily recognised in the
field, and they are often shown on geologi-
cal maps. Furthermore, pegmatites may
sometimes be located directly from aerial
photographs due to their distinct appear-
ance. In the geological mapping of the
Precambrian basement of Greenland,
coarse-grained veins are commonly termed
pegmatites when their dimensions exceed
0.5 m in width and 2 m in length, regard-
less of their origin.
because large, potentially economic peg-
matites are often easily recognised in the
field, and they are often shown on geologi-
cal maps. Furthermore, pegmatites may
sometimes be located directly from aerial
photographs due to their distinct appear-
ance. In the geological mapping of the
Precambrian basement of Greenland,
coarse-grained veins are commonly termed
pegmatites when their dimensions exceed
0.5 m in width and 2 m in length, regard-
less of their origin.
Of economic importance are especially
mine rals containing lithium, beryllium, scan-
dium, uranium and REE, which are com-
modities with a variety of high-technology
uses. Quartz, feldspars and mica are used as
industrial minerals. Several pegmatite min -
eral species may also be used as gemstones.
mine rals containing lithium, beryllium, scan-
dium, uranium and REE, which are com-
modities with a variety of high-technology
uses. Quartz, feldspars and mica are used as
industrial minerals. Several pegmatite min -
eral species may also be used as gemstones.
Greenland itself only comprises one exam-
ple of pegmatite exploitation which is how-
ever outstanding, namely the cryolite
deposit adjacent to an alkaline granite of
Mesoproterozoic Gardar age at Ivittuut in
South Greenland. This deposit supported an
ple of pegmatite exploitation which is how-
ever outstanding, namely the cryolite
deposit adjacent to an alkaline granite of
Mesoproterozoic Gardar age at Ivittuut in
South Greenland. This deposit supported an
extremely profitable mining operation for
around 130 years. Apart from this hallmark
of pegmatite use in Greenland only limited
pegmatite exploration has been carried out.
around 130 years. Apart from this hallmark
of pegmatite use in Greenland only limited
pegmatite exploration has been carried out.
Geochemical criteria for identify-
ing economic pegmatite occur-
rences
ing economic pegmatite occur-
rences
The regional distribution of certain ele-
ments may indicate where pegmatites are
located. Large parts of Greenland outside
the Inland Ice have been covered by
stream sediment surveys. Most samples
have been analysed by neutron activation,
and several of the elements that are easy
to determine by this method are usually
concentrated in pegmatites; the elements
of interest in this context are Cs, Mo, La,
Yb, Hf, Ta, Th and U.
ments may indicate where pegmatites are
located. Large parts of Greenland outside
the Inland Ice have been covered by
stream sediment surveys. Most samples
have been analysed by neutron activation,
and several of the elements that are easy
to determine by this method are usually
concentrated in pegmatites; the elements
of interest in this context are Cs, Mo, La,
Yb, Hf, Ta, Th and U.
The distribution of Cs reflects the distribu-
tion of granitic and syenitic rocks, and the
highest values suggest areas favourable
for finding pegmatites. These high values
form clusters in meta-sedimentary rocks in
several geological environments in
Greenland.
tion of granitic and syenitic rocks, and the
highest values suggest areas favourable
for finding pegmatites. These high values
form clusters in meta-sedimentary rocks in
several geological environments in
Greenland.
2
Pink pegmatite related to the Qôrqut granite complex. Godthåbsfjord, Nuuk region
GEOLOGY AND ORE 10 / 2008
Pegmatites and their potential for
mineral exploitation in Greenland
mineral exploitation in Greenland
3
P E G M A T I T E S I N GREENLAND
Nassuttooq
Ardencaple Fjord
Godthåbsfjord
(Nuuk region)
(Nuuk region)
Major lithostratigraphi-
cal and tectonic division
of Greenland.
cal and tectonic division
of Greenland.
Lithium (Li) is the most economically valu-
able of the lithophile elements because of
its rarity and use in the electronics indus-
try. The Geological Survey (GEUS)' stream
sediment database does not contain data
for Li, but the distribution of Cs serves as
a good indicator of environments general-
ly enriched in lithophile elements including
Li. In South Greenland, both granitic and
alkaline intrusions have high Cs contents;
hence the possibility of finding concentra-
tions of Li minerals seems to be good.
able of the lithophile elements because of
its rarity and use in the electronics indus-
try. The Geological Survey (GEUS)' stream
sediment database does not contain data
for Li, but the distribution of Cs serves as
a good indicator of environments general-
ly enriched in lithophile elements including
Li. In South Greenland, both granitic and
alkaline intrusions have high Cs contents;
hence the possibility of finding concentra-
tions of Li minerals seems to be good.
The Ta distribution patterns show that the
Gardar province is strongly enriched in Ta,
but interestingly, high Ta is alsOFound in
samples from streams draining metasedi-
mentary and sedimentary rocks in East
Greenland. The few scattered stream sedi-
ment samples with high Ta in West
Greenland coincide with known occur-
rences of Ta-Nb bearing carbonatites (i.e.
not pegmatites).
Gardar province is strongly enriched in Ta,
but interestingly, high Ta is alsOFound in
samples from streams draining metasedi-
mentary and sedimentary rocks in East
Greenland. The few scattered stream sedi-
ment samples with high Ta in West
Greenland coincide with known occur-
rences of Ta-Nb bearing carbonatites (i.e.
not pegmatites).
In simple pegmatites related to granites
the minerals allanite and monazite are
commonly enriched in REE (rare earth ele-
ments), whereas a whole range of rare
REE minerals occurs in alkaline pegma-
tites. The light REE La and Ce are geo-
chemically very similar, so that a high con-
the minerals allanite and monazite are
commonly enriched in REE (rare earth ele-
ments), whereas a whole range of rare
REE minerals occurs in alkaline pegma-
tites. The light REE La and Ce are geo-
chemically very similar, so that a high con-
centration of La also indicates high Ce.
The heavy REE Yb is similar to Y, which is
economically more interesting. There is an
interesting difference in the distribution
patterns of the light and heavy REE, exem-
plified by La and Yb. Thus, in metasedi-
mentary environments, La is enriched in
the Rinkian fold belt, while Yb is enriched
in south-eastern Ketilidian and Caledonian
orogens. Many of the Gardar rock units
are enriched in both light and heavy REE.
The heavy REE Yb is similar to Y, which is
economically more interesting. There is an
interesting difference in the distribution
patterns of the light and heavy REE, exem-
plified by La and Yb. Thus, in metasedi-
mentary environments, La is enriched in
the Rinkian fold belt, while Yb is enriched
in south-eastern Ketilidian and Caledonian
orogens. Many of the Gardar rock units
are enriched in both light and heavy REE.
Granitic pegmatites
The most common pegmatites in the
Precambrian basement of Greenland are
approximately granitic in composition.
They essentially consist of very coarse-
grained quartz, alkali feldspar and mica;
the amount and variety of additional min-
erals depend on the origin of the peg-
matite in question. Magnetite, zircon and
allanite are commonly seen, while min -
erals such as monazite, tourmaline, fluo-
rite, apatite, sulphides, uraninite, beryl or
topaz are rarer.
Precambrian basement of Greenland are
approximately granitic in composition.
They essentially consist of very coarse-
grained quartz, alkali feldspar and mica;
the amount and variety of additional min-
erals depend on the origin of the peg-
matite in question. Magnetite, zircon and
allanite are commonly seen, while min -
erals such as monazite, tourmaline, fluo-
rite, apatite, sulphides, uraninite, beryl or
topaz are rarer.
Genetically, most pegmatites in the
Precambrian basement are results of melt-
ing during prograde metamorphism. Their
mineralogy and economic potential
Precambrian basement are results of melt-
ing during prograde metamorphism. Their
mineralogy and economic potential
depend to a large extent on the character
of the source rock. Pegmatites derived
from reworking of tonalitic to granitic
orthogneiss usually have a simple mineral-
ogy of quartz, alkali feldspar and biotite,
and are commonly named as simple peg-
matites.
of the source rock. Pegmatites derived
from reworking of tonalitic to granitic
orthogneiss usually have a simple mineral-
ogy of quartz, alkali feldspar and biotite,
and are commonly named as simple peg-
matites.
Prograde metamorphism of clastic sedi-
mentary rocks with significant contents of
clay minerals leads to progressive dehydra-
tion and generation of metamorphic
fluids, and when high amphibolite facies
conditions are reached, pegmatites are
commonly formed. They are more alumi-
nous than the simple pegmatites and
therefore typically also contain muscovite,
tourmaline and garnet in addition to
quartz, alkali feldspar and biotite. Besides
common accessory minerals such as mag-
netite, apatite and zircon, which are also
found in simple granitic pegmatites, they
may comprise additional beryl, topaz and
fluorite in order to accommodate minor
elements like B, Be or F from their pelitic
precursors. These pegmatites are therefore
often named as complex pegmatites.
Some of the minerals found in this group
may potentially be of gem quality.
mentary rocks with significant contents of
clay minerals leads to progressive dehydra-
tion and generation of metamorphic
fluids, and when high amphibolite facies
conditions are reached, pegmatites are
commonly formed. They are more alumi-
nous than the simple pegmatites and
therefore typically also contain muscovite,
tourmaline and garnet in addition to
quartz, alkali feldspar and biotite. Besides
common accessory minerals such as mag-
netite, apatite and zircon, which are also
found in simple granitic pegmatites, they
may comprise additional beryl, topaz and
fluorite in order to accommodate minor
elements like B, Be or F from their pelitic
precursors. These pegmatites are therefore
often named as complex pegmatites.
Some of the minerals found in this group
may potentially be of gem quality.
Alkaline pegmatites
Alkaline magmatic rocks result from crys-
tallisation of melts generated in the litho -
spheric mantle and are often associated
with crustal-scale rifting. Magmas formed
in this way are often silica-undersaturated
and characterised by high concentrations
of the alkali metals K and Na. Related
pegmatites are enriched in high field
strength elements such as Y, Zr, Hf, and
Nb, Ta and REE. The concentration of
these elements may reach economically
interesting levels both in pegmatites and
in non-pegmatitic rock units in the sur-
roundings of the alkaline complexes.
Alkaline rocks contain rare minerals that
have a value as specialised industrial min-
erals or in the mineral collectors' market.
In addition, certain minerals have found
use as semi-precious stones, e.g. ama-
zonite and tugtupite.
I
tallisation of melts generated in the litho -
spheric mantle and are often associated
with crustal-scale rifting. Magmas formed
in this way are often silica-undersaturated
and characterised by high concentrations
of the alkali metals K and Na. Related
pegmatites are enriched in high field
strength elements such as Y, Zr, Hf, and
Nb, Ta and REE. The concentration of
these elements may reach economically
interesting levels both in pegmatites and
in non-pegmatitic rock units in the sur-
roundings of the alkaline complexes.
Alkaline rocks contain rare minerals that
have a value as specialised industrial min-
erals or in the mineral collectors' market.
In addition, certain minerals have found
use as semi-precious stones, e.g. ama-
zonite and tugtupite.
I
4
P E G M A T I T E S I N GREENLAND
GEOLOGY AND ORE 10 / 2008
Large black crystals of arfvedsonite up to 60 cm long are intergrown with equally large crystals of
white feldspar. Pegmatite in the margin of the alkaline Ilímaussaq complex, South Greenland.
white feldspar. Pegmatite in the margin of the alkaline Ilímaussaq complex, South Greenland.
5
P E G M A T I T E S I N GREENLAND
Locations of stream sedi-
ment samples with high
concentrations of Cs and
Hf in the < 0.1 mm frac-
tion. Green dots mark
location of samples
analysed by neutron acti-
vation.
ment samples with high
concentrations of Cs and
Hf in the < 0.1 mm frac-
tion. Green dots mark
location of samples
analysed by neutron acti-
vation.
In Greenland, the largest and most impor-
tant group of alkaline rocks is the Meso -
proterozoic Gardar province in South
Greenland. Others include the Palaeogene
alkaline province in East Greenland.
tant group of alkaline rocks is the Meso -
proterozoic Gardar province in South
Greenland. Others include the Palaeogene
alkaline province in East Greenland.
Selected pegmatite occurrences
Most of the information about pegmatites
in Greenland is found in the published
geological maps and field diaries in the
archives of the Survey. The regions
addressed in the following are selected
due to a demonstrated and/or expected
potential.
in Greenland is found in the published
geological maps and field diaries in the
archives of the Survey. The regions
addressed in the following are selected
due to a demonstrated and/or expected
potential.
Rinkian fold belt
The Palaeoproterozoic Karrat Group com-
prises large areas of amphibolite to gran-
ulite facies metagreywacke of the Nukav -
sak Formation together with quartzite and
marble. Pegmatites are most abundant in
The Palaeoproterozoic Karrat Group com-
prises large areas of amphibolite to gran-
ulite facies metagreywacke of the Nukav -
sak Formation together with quartzite and
marble. Pegmatites are most abundant in
the northern part close to the Prøven
igneous complex. A swarm of peralumi-
nous granite pegmatite dykes cuts
gneiss and Karrat Group rocks in the
central part of the southern Rinkian
fold belt. The pegmatites have quartz-
rich centres and are associated with
quartz veins, and are composed of
quartz, muscovite, biotite, feldspar,
garnet and variable tourmaline.
Molybdenite is commonly found close
to the margins of the veins, and 0.1
0.5 % MoS
igneous complex. A swarm of peralumi-
nous granite pegmatite dykes cuts
gneiss and Karrat Group rocks in the
central part of the southern Rinkian
fold belt. The pegmatites have quartz-
rich centres and are associated with
quartz veins, and are composed of
quartz, muscovite, biotite, feldspar,
garnet and variable tourmaline.
Molybdenite is commonly found close
to the margins of the veins, and 0.1
0.5 % MoS
2
has been recorded.
The Nagssugtoqidian orogen
The Nagssugtoqidian orogen in central
West Greenland mainly comprises
Archaean crust that has been partly
reworked during Palaeoproterozoic heat-
ing and deformation, besides Palaeo -
proterozoic supracrustal rocks and rem-
nants of two magmatic arcs. Both
Archaean and Palaeoproterozoic peg-
matites occur, and examples of both simp -
le and complex pegmatites are known.
The Nagssugtoqidian orogen in central
West Greenland mainly comprises
Archaean crust that has been partly
reworked during Palaeoproterozoic heat-
ing and deformation, besides Palaeo -
proterozoic supracrustal rocks and rem-
nants of two magmatic arcs. Both
Archaean and Palaeoproterozoic peg-
matites occur, and examples of both simp -
le and complex pegmatites are known.
Pink pegmatites are common in the outer
fjord zone from Kangaatsiaq to south of
Attu, where the Archaean orthogneiss is
intruded by granite and simple pink peg-
matites of un-known age. The pegmatites
occur mostly as discordant up to metre-
thick bodies within the gneiss, commonly
fjord zone from Kangaatsiaq to south of
Attu, where the Archaean orthogneiss is
intruded by granite and simple pink peg-
matites of un-known age. The pegmatites
occur mostly as discordant up to metre-
thick bodies within the gneiss, commonly
6
GEOLOGY AND ORE 10 / 2008
P E G M A T I T E S I N GREENLAND
Pegmatite of residual granitic origin with pink
feldspar, white quartz and black biotite
feldspar, white quartz and black biotite
from
the Ndr. Strømfjord (Nassuttooq) area.
Aggregate of black allanite crystals in red peg-
matite from the Ndr.Strømfjord (Nassuttooq)
area. Scale bar: 1 cm.
matite from the Ndr.Strømfjord (Nassuttooq)
area. Scale bar: 1 cm.
7
P E G M A T I T E S I N GREENLAND
at contacts between major lithological
units. The dominant minerals are coarse-
grained K-feldspar, quartz, biotite and
subordinate allanite, titanite, apatite, mag-
netite and Fe-sulphides.
White pegmatites are generally concor-
dant to the foliation of the adjacent coun-
try rocks. The white pegmatites are 520
m wide and 50200 m long, with a gen-
eral trend of NWSE all over the Nordre
Strømfjord and Ussuit areas, and normally
contain plagioclase and biotite with accu-
mulations of monazite.
units. The dominant minerals are coarse-
grained K-feldspar, quartz, biotite and
subordinate allanite, titanite, apatite, mag-
netite and Fe-sulphides.
White pegmatites are generally concor-
dant to the foliation of the adjacent coun-
try rocks. The white pegmatites are 520
m wide and 50200 m long, with a gen-
eral trend of NWSE all over the Nordre
Strømfjord and Ussuit areas, and normally
contain plagioclase and biotite with accu-
mulations of monazite.
Pegmatite dykes, veins and schlieren occur
throughout the southern Nagssugtoqidian
boundary area, and vary considerably.
Locally, simple quartz-feldspar-pegmatites
host garnet and apatite.
throughout the southern Nagssugtoqidian
boundary area, and vary considerably.
Locally, simple quartz-feldspar-pegmatites
host garnet and apatite.
Archaean basement in the Nuuk
region
region
The Nuuk region represents the highest
crustal level of the North Atlantic craton in
crustal level of the North Atlantic craton in
southern West Greenland, and pegmatites
are abundant and voluminous in some
areas, especially within supracrustal rocks
at the western part. Pegmatites were
are abundant and voluminous in some
areas, especially within supracrustal rocks
at the western part. Pegmatites were
formed during several thermal episodes in
the time interval c. 27502600 Ma, and
again at around 2550 Ma in connection
with the intrusion of multiple Qôrqut
granite sheets.
the time interval c. 27502600 Ma, and
again at around 2550 Ma in connection
with the intrusion of multiple Qôrqut
granite sheets.
Pre-Qôrqut granite pegmatites are leuco-
cratic and dominated by quartz and white
feldspar, and they contain a variety of
accessory minerals including biotite, mag-
cratic and dominated by quartz and white
feldspar, and they contain a variety of
accessory minerals including biotite, mag-
Monazite in biotite rich pegmatite from the Ndr.Strømfjord (Nassuttooq) area. Scale bar: 1 cm.
Brown siderite, grey cryolite and white quartz in a pegmatite vein from the cryolite deposit of the
alkaline granite at Ivittuut, South-West Greenland.
alkaline granite at Ivittuut, South-West Greenland.
Black tourmaline crystals (dravite) from peg-
matite on the island of Sermitsiaq, Nuuk,
region. Scale bar: 1 cm.
matite on the island of Sermitsiaq, Nuuk,
region. Scale bar: 1 cm.
netite, garnet, tourmaline, allanite and
uraninite. Pegmatites in the Ivisaartoq area
to the east are known for local finds of
beryl (var. aquamarine), which at one
locality has delivered large, well-shaped
crystals of up to 4 x 17 cm. Tourmaline
(var. dravite) is well known from the
Sermitsiaq island and in the southern part
of the Nuuk region around Ameralik. A
typical feature of this tourmaline is its
black colour; the well-developed crystal
faces with shiny surfaces and the large
sizes. Crystals of up to nearly 2 kg each
have been recorded.
uraninite. Pegmatites in the Ivisaartoq area
to the east are known for local finds of
beryl (var. aquamarine), which at one
locality has delivered large, well-shaped
crystals of up to 4 x 17 cm. Tourmaline
(var. dravite) is well known from the
Sermitsiaq island and in the southern part
of the Nuuk region around Ameralik. A
typical feature of this tourmaline is its
black colour; the well-developed crystal
faces with shiny surfaces and the large
sizes. Crystals of up to nearly 2 kg each
have been recorded.
Archaean basement in the
FiskenæssetPaamiut region
FiskenæssetPaamiut region
In the southern part of the Archaean cra-
ton, quartz- and plagioclase-rich peg-
matites intrude both the orthogneisses
and the Fiskenæsset anorthosite complex,
where they typically form conformable
bodies along lithological contacts within
the complex. Numerous light coloured
quartz-plagioclase-biotite pegmatites with
varying sizes up to 30 m wide often have
accessory (up to 10 vol%) allanite.
ton, quartz- and plagioclase-rich peg-
matites intrude both the orthogneisses
and the Fiskenæsset anorthosite complex,
where they typically form conformable
bodies along lithological contacts within
the complex. Numerous light coloured
quartz-plagioclase-biotite pegmatites with
varying sizes up to 30 m wide often have
accessory (up to 10 vol%) allanite.
Molybdenite and beryl are rarely seen, and
the pegmatites are considered barren in
an economic geological context.
the pegmatites are considered barren in
an economic geological context.
Palaeoproterozoic Ketilidian
orogen
orogen
The evolution of the Palaeoproterozoic
Ketilidian orogen and the subsequent
Mesoprotero-zoic Gardar igneous province
in South Greenland has favoured the for-
mation of pegmatites, both simple ones
related to granitic magmas, simple and
complex pegmatites formed by melting of
metasedimentary rocks, and pegmatites
related to alkaline intrusions. The most
interesting pegmatite-forming events are
late-kinematic Ketilidian granites related
to the Julianehåb batholith and the gran-
ites contemporaneous with the late- to
post-kinematic rapakivi suite, both of
Palaeoproterozoic age, and the Meso -
proterozoic Gardar magmas.
The late to post-kinematic rapakivi intru-
Ketilidian orogen and the subsequent
Mesoprotero-zoic Gardar igneous province
in South Greenland has favoured the for-
mation of pegmatites, both simple ones
related to granitic magmas, simple and
complex pegmatites formed by melting of
metasedimentary rocks, and pegmatites
related to alkaline intrusions. The most
interesting pegmatite-forming events are
late-kinematic Ketilidian granites related
to the Julianehåb batholith and the gran-
ites contemporaneous with the late- to
post-kinematic rapakivi suite, both of
Palaeoproterozoic age, and the Meso -
proterozoic Gardar magmas.
The late to post-kinematic rapakivi intru-
P E G M A T I T E S I N GREENLAND
8
GEOLOGY AND ORE 10 / 2008
White pegmatites within Archaean supracrustal rocks on central Storø, Nuuk region.
P E G M A T I T E S I N GREENLAND
9
sive suite of granites also comprises small
volumes of microcline granite and biotite
granite. Pegmatites and aplites associated
with these granites are locally enriched in
gold, and have a potential of being
enriched in Li as they have high concen-
trations of the other lithophile elements
Rb and Cs. The type locality for allanite is
Aluk in South Greenland, located within
the rapakivi suite.
volumes of microcline granite and biotite
granite. Pegmatites and aplites associated
with these granites are locally enriched in
gold, and have a potential of being
enriched in Li as they have high concen-
trations of the other lithophile elements
Rb and Cs. The type locality for allanite is
Aluk in South Greenland, located within
the rapakivi suite.
Mesoproterozoic Gardar
province
province
A number of the Gardar intrusions have
attracted various grades of exploration.
The Ilímaussaq intrusive complex and the
Ivittuut granite stock appear to have the
best potential for economic use of their
pegmatites.
attracted various grades of exploration.
The Ilímaussaq intrusive complex and the
Ivittuut granite stock appear to have the
best potential for economic use of their
pegmatites.
Ilímaussaq intrusive complex
The Ilímaussaq intrusive complex compris-
es a series of syenites formed by crystalli-
sation of silica-undersaturated, alkaline to
peralkaline magmas rich in volatiles. The
pegmatites were formed as networks of
veins near the roof and along the sides of
The Ilímaussaq intrusive complex compris-
es a series of syenites formed by crystalli-
sation of silica-undersaturated, alkaline to
peralkaline magmas rich in volatiles. The
pegmatites were formed as networks of
veins near the roof and along the sides of
the chamber within the early naujaite-
foyaite stage of nepheline syenites. The
pegmatites are commonly rich in the Zr
mineral eudialyte and other minerals con-
taining Nb, Ta and REE, and pegmatites
rich in Li and Be minerals occur locally. In
the late magmatic lujavrite (mafic nephe -
line syenite) stage, other pegmatites were
developed as irregular veins and patches,
and they are particularly enriched in F, U
and Th, Be, Li, Zr, Nb and Ta. The Ilímaus -
saq complex has become famous among
mineral connoisseurs for its large number
of rare mineral species, which are com-
monly found in its pegmatites.
foyaite stage of nepheline syenites. The
pegmatites are commonly rich in the Zr
mineral eudialyte and other minerals con-
taining Nb, Ta and REE, and pegmatites
rich in Li and Be minerals occur locally. In
the late magmatic lujavrite (mafic nephe -
line syenite) stage, other pegmatites were
developed as irregular veins and patches,
and they are particularly enriched in F, U
and Th, Be, Li, Zr, Nb and Ta. The Ilímaus -
saq complex has become famous among
mineral connoisseurs for its large number
of rare mineral species, which are com-
monly found in its pegmatites.
Ivittuut alkaline granite stock
The Gardar intrusion at Ivittuut comprises
a stock of alkaline granite (Ivigtût granite)
with a pegmatitic facies developed into
cryolite-, quartz- and quartz-feldspar peg-
matites. The now totally exploited cryolite
ore body had the shape of an irregular,
flattened dome measuring about 50 x 155
m horizontally and 70 m in depth. The
main ore body of cryolite and siderite was
followed downwards by a siderite zone,
which was mixed with a fluorite shell to
The Gardar intrusion at Ivittuut comprises
a stock of alkaline granite (Ivigtût granite)
with a pegmatitic facies developed into
cryolite-, quartz- and quartz-feldspar peg-
matites. The now totally exploited cryolite
ore body had the shape of an irregular,
flattened dome measuring about 50 x 155
m horizontally and 70 m in depth. The
main ore body of cryolite and siderite was
followed downwards by a siderite zone,
which was mixed with a fluorite shell to
the west. At still deeper levels a huge
mass of more or less pure quartz with
accessory sulphide minerals separated the
body from the underlying granite. Late
feldspar-quartz pegmatites have been
recognised in the upper part of the ore
body. Typical complex pegmatite minerals
such as topaz, cassiterite, columbite and
wolframite occur, together with a suite of
rare and unusual fluoride and oxide min-
erals, around 100 different minerals in all.
mass of more or less pure quartz with
accessory sulphide minerals separated the
body from the underlying granite. Late
feldspar-quartz pegmatites have been
recognised in the upper part of the ore
body. Typical complex pegmatite minerals
such as topaz, cassiterite, columbite and
wolframite occur, together with a suite of
rare and unusual fluoride and oxide min-
erals, around 100 different minerals in all.
The cryolite deposit was mined from
18561987, with at total production of
3.7 million t of ore averaging 58% cryo-
lite. The mode of formation of the cryolite
mass adjacent to the Ivigtût granite is still
a matter of discussion. One of the accept-
ed theroies considers the cryolite to repre-
sent an extreme pegmatitic and/or pneu-
matolytic phase derived from the crystal -
lising granitic magma. This unique occur-
rence was the result of accumulated fluo-
rine-rich gases trapped in the central up -
per part of the already solidified granite
stock.
18561987, with at total production of
3.7 million t of ore averaging 58% cryo-
lite. The mode of formation of the cryolite
mass adjacent to the Ivigtût granite is still
a matter of discussion. One of the accept-
ed theroies considers the cryolite to repre-
sent an extreme pegmatitic and/or pneu-
matolytic phase derived from the crystal -
lising granitic magma. This unique occur-
rence was the result of accumulated fluo-
rine-rich gases trapped in the central up -
per part of the already solidified granite
stock.
The major cryolite, cryolite/siderite and
Close-up of white pegmatite, clearly intrusive into deformed grey gneiss, central Storø, Nuuk region.
P E G M A T I T E S I N GREENLAND
10
GEOLOGY AND ORE 10 / 2008
quartz phases of the cryolite deposit are
considered to have crystallised in close
succession, while subsequent fluorite-
cryolite- and fluorite-dominated phases
were formed when late fluids reacted with
previously crystallised rocks.
considered to have crystallised in close
succession, while subsequent fluorite-
cryolite- and fluorite-dominated phases
were formed when late fluids reacted with
previously crystallised rocks.
Nunarssuit alkaline complex
This large intrusive complex comprises sev-
eral intrusive phases of saturated to over-
saturated alkaline rocks. Very high Y and
Yb concentrations in stream sediment sug-
gest that pegmatites with yttrium minerals
may occur in the intrusive complex. Well
crystallised amazonite occurs in several
pegmatites of the complex, and a limited
exploitation has been carried out directed
to its use as gemstone.
This large intrusive complex comprises sev-
eral intrusive phases of saturated to over-
saturated alkaline rocks. Very high Y and
Yb concentrations in stream sediment sug-
gest that pegmatites with yttrium minerals
may occur in the intrusive complex. Well
crystallised amazonite occurs in several
pegmatites of the complex, and a limited
exploitation has been carried out directed
to its use as gemstone.
Igaliko alkaline complex
A pegmatite at the locality Narsaarsuk has
been famous for a large number of new
and very rare minerals with REE.
A pegmatite at the locality Narsaarsuk has
been famous for a large number of new
and very rare minerals with REE.
Caledonian orogen in East
Greenland
Greenland
The basement to the Caledonian orogen
in central East Greenland is dominated by
grano-dioritic to tonalitic orthogneisses of
Archaean and Palaeoproterozoic age,
in central East Greenland is dominated by
grano-dioritic to tonalitic orthogneisses of
Archaean and Palaeoproterozoic age,
respectively, north and south of 73° N.
Palaeoproterozoic granites are known, e.g.
a body of pegmatitic muscovite granite
near the margin of the Inland Ice at Char -
cot Land. The granite/ pegmatite body
intrudes both basement and supra crustal
Palaeoproterozoic granites are known, e.g.
a body of pegmatitic muscovite granite
near the margin of the Inland Ice at Char -
cot Land. The granite/ pegmatite body
intrudes both basement and supra crustal
rocks. In Milne Land a pegmatite several
metres wide with large crystals of tourma-
line and beryl (var. aquama-rine) is hosted
by Proterozoic migmatitic gneiss and pos-
sibly related to nearby Caledonian granite.
Scheelite and cassiterite with W and Sn,
metres wide with large crystals of tourma-
line and beryl (var. aquama-rine) is hosted
by Proterozoic migmatitic gneiss and pos-
sibly related to nearby Caledonian granite.
Scheelite and cassiterite with W and Sn,
Bluish green amazonite and graphic granite with grey quartz and white feldspar, from a pegmatite associated with the Nunarssuit alkaline complex,
South-West Greenland. Scale bar: 1 cm.
South-West Greenland. Scale bar: 1 cm.
Migmatitic veins in the Krummedal metasediments at Ardencaple Fjord, North-East Greenland
respectively, besides fluorite and tourma-
line have been recorded in a sub-concor-
dant pegmatite presumed to be associated
with a Cale-donian granite at Forsblad
Fjord. Here also Li (200 ppm), Be (50
ppm). up to 2 ppm Au (in arsenopyrite)
occur in samples from the contact zone
between pegmatite and metasedimentary
rocks. The finding suggests that peg-
matites related to the Caledonian granites
have a potential for Li minerals.
line have been recorded in a sub-concor-
dant pegmatite presumed to be associated
with a Cale-donian granite at Forsblad
Fjord. Here also Li (200 ppm), Be (50
ppm). up to 2 ppm Au (in arsenopyrite)
occur in samples from the contact zone
between pegmatite and metasedimentary
rocks. The finding suggests that peg-
matites related to the Caledonian granites
have a potential for Li minerals.
Palaeogene alkaline intrusions in
East Greenland
East Greenland
Mineral research related to the Palaeo -
gene alkaline intrusions in central East
Greenland has mostly been attracted by
hydrothermal alteration that is very pro-
nounced within and around preserved
gene alkaline intrusions in central East
Greenland has mostly been attracted by
hydrothermal alteration that is very pro-
nounced within and around preserved
roof zones of several large intrusions.
Many pegmatites have however also been
observed, and in general terms they have
a potential for rare minerals enriched in Li,
Be, Zr, Hf, Nb, Ta, REE and Y, U and Th.
Many pegmatites have however also been
observed, and in general terms they have
a potential for rare minerals enriched in Li,
Be, Zr, Hf, Nb, Ta, REE and Y, U and Th.
The Gardiner intrusion comprises many
pegmatites, and pegmatites also occur in
the nearby Kangerlussuaq intrusion. An
undersaturated alkaline pegmatite occurs
at Bagnæsset. At Kræmer Island, a quartz
vein contains large crystals of aegirine,
arfvedsonite, astrophyllite, and abundant
small zircon crystals and amazonite. The
Caledonian alkaline intrusion at Batbjerg
contains large pegmatites with crystals of
Cr-diopside, phlogopite and `moonstone'
feldspar.
pegmatites, and pegmatites also occur in
the nearby Kangerlussuaq intrusion. An
undersaturated alkaline pegmatite occurs
at Bagnæsset. At Kræmer Island, a quartz
vein contains large crystals of aegirine,
arfvedsonite, astrophyllite, and abundant
small zircon crystals and amazonite. The
Caledonian alkaline intrusion at Batbjerg
contains large pegmatites with crystals of
Cr-diopside, phlogopite and `moonstone'
feldspar.
Concluding remarks
Favourable areas in West Greenland for
complex pegmatites of granitic composi-
tion with economic potential occur where
partial melting of metasedimentary rocks
has taken place. Published geological
maps at scale 1:100 000 show the distri-
bution of supracrustal rocks and peg-
matites. Additional information is provided
by stream sediment geochemical maps,
which can be used to outline areas
favourable for concentrations of specific
elements within complex pegmatites.
Favourable units with this potential could
be the fore-arc basin of the Ketilidian oro-
gen in South Greenland. Other units con-
sidered favourable are underlain by
Archaean supracrustal rocks e.g. in the
Nuuk region in the Archaean craton.
complex pegmatites of granitic composi-
tion with economic potential occur where
partial melting of metasedimentary rocks
has taken place. Published geological
maps at scale 1:100 000 show the distri-
bution of supracrustal rocks and peg-
matites. Additional information is provided
by stream sediment geochemical maps,
which can be used to outline areas
favourable for concentrations of specific
elements within complex pegmatites.
Favourable units with this potential could
be the fore-arc basin of the Ketilidian oro-
gen in South Greenland. Other units con-
sidered favourable are underlain by
Archaean supracrustal rocks e.g. in the
Nuuk region in the Archaean craton.
P E G M A T I T E S I N GREENLAND
11
Geological map of South Greenland with names. Geological formations in
green, fjords in blue, settlements in grey, and other place names in black
text.
green, fjords in blue, settlements in grey, and other place names in black
text.
Alkaline pegmatites occur abundantly
within the Gardar alkaline province in
South Greenland and the intrusions of the
Palaeogene igneous province in East
Greenland. Successful exploitation of peg-
matites in Greenland has sOFar only been
within the Gardar alkaline province in
South Greenland and the intrusions of the
Palaeogene igneous province in East
Greenland. Successful exploitation of peg-
matites in Greenland has sOFar only been
related to alkaline rocks. However, com-
modities of interest hosted by alkaline
rocks are not confined to pegmatites, so
that the entire alkaline complexes are tar-
get areas for detailed exploration for spe-
cific elements or minerals.
modities of interest hosted by alkaline
rocks are not confined to pegmatites, so
that the entire alkaline complexes are tar-
get areas for detailed exploration for spe-
cific elements or minerals.
Bailey, J.C., Bohse, H., Gwozdz, R. & Rose-
Hansen, J. 1993:
Li in minerals from the
Ilímaussaq alkaline intrusion, South Greenland.
Bulletin of the Geological Society of Denmark
40
, 288299.
Bailey, J.C., Larsen, L.M. & Sørensen, H. (eds)
1981:
The Ilímaussaq intrusion, South Greenland:
a progress report on geology, mineralogy, geo-
chemistry and economic geology. Rapport
Grønlands Geologiske Undersøgelse
103
, 130
pp.
Garde, A.A., Hamilton M.A., Chadwick B.,
Grocott J., & McCaffrey K.J.W. 2002:
The
Ketilidian orogen of South Greenland:
geochronology, tectonics, magmatism, and fore-
arc accretion during Palaeoproterozoic oblique
convergence, Canadian Journal of Earth Sciences
39
,765-793.
Harpøth, O., Pedersen, J.L., Schønwandt, H.K.
& Thomassen, B. 1986:
The mineral occurrences
of central East Greenland. Meddelelser om
Grønland Geoscience
17
, 139 pp.
Henriksen, N., Higgins, A.K., Kalsbeek, F. &
Pulvertaft, T.C.R. 2000:
Greenland from
Archaean to Quaternary. Descriptive text to the
Geological map of Greenland 1:2 500 000.
Geology of Greenland Survey Bulletin
185
, 93 pp.
Hollis, J.A., Schmid, S., Stendal, H., van Gool,
J.A.M. & Weng, W.L. 2006:
Supracrustal belts
in Godthåbsjord region, southern West
Greenland. Danmarks og Grønlands Geologiske
Undersøgelse Rapport
2006/7
, 171 pp., 1 DVD.
Kalsbeek, F. (ed.)1989:
Geology of the Ammassalik
region, South-East Greenland. Rapport Grønlands
Geologiske Undersøgelse
146
, 106 pp.
Nielsen, T.F.D. 1987:
Tertiary alkaline magmatism
in East Greenland: a review. In: Fitton, J.G. &
Upton, B.G.J. (eds): Alkaline igneous rocks
30
,
489515
Noe-Nygaard, A. & Ramberg, H. 1961:
Geo-
logical reconnaissance map of the country
between latitudes 69°N and 63°45 N, West
Greenland. Meddelelser om Grønland
123
, 9.
Petersen, O.V. 1989:
Der Narssârssuk-Pegmatit.
Mitteilungen der Österreichischen Mineralogis-
chen Gesellschaft
134
, 6372.
Petersen, O.V. & Gault, R.A. 1993:
Xenotime
from the Narssârssuk pegmatite, South
Greenland. Neues Jahrbuch für Mineralogie,
Monatshefte
Jahrg.1993
, 259264.
Petersen, O.V. & Secher, K. 1993:
The minerals
of Greenland. Mineralogical Record
24
, 165.
Sørensen, H. 1960:
Beryllium minerals in a peg-
matite in the nepheline syenites of Ilímaussaq,
south west Greenland. Rep. 21st int. geol. Congr.
Norden
1960
, 3135.
Sørensen, H., Rose-Hansen, J. & Petersen, O.V.
1981:
The mineralogy of the Ilímaussaq intru-
sion. Rapport Grønlands Geologiske Undersøgelse
103
, 1924.
Sørensen, H. 1992:
Agpaitic nepheline syenites:
a potential source of rare elements. Applied
Geochemistry
7
, 417427.
Steenfelt, A. 2001:
Geochemical atlas of
Greenland - West and South Greenland.
Danmarks og Grønlands Geologiske Undersøgelse
Rapport
2001/46
, 39 pp., 1 CD-ROM.
Steenfelt, A., Thorning, L. & Tukiainen, T. 1990:
Regional compilations of geoscience data from
the Nuuk-Maniitsoq area, southern West
Greenland. Thematic Map Series Grønlands
Geologiske Undersøgelse,
90/1
, 9 pp.
Steenfelt, A., Secher, K. & Garde, A.A .2007:
An overview of pegmatite occurrences in
Greenland and their economic potential,
Danmarks og Grønlands Geologiske Undersøgelse
Rapport
2007/2
, 46 pp.
Stendal, H., Secher, K. & Frei, R. 2006:
207
Pb-
206
Pb dating of magnetite, monazite and allan-
ite in the central and northern Nagssugtoqidian
orogen, West Greenland. Geological Survey of
Denmark and Greenland Bulletin
11
, 101114.
Upton, B.G.J. 1974:
The alkaline province of south-
west Greenland. In: Sørensen, H. (ed.): The alka-
line rocks, 221238. New York-London: Wiley.
van Gool, J.A.M., Connelly, J.N., Marker, M. &
Mengel, F. 2002:
The Nagssugtoqidian Orogen
of West Greenland: tectonic evolution and
regional correlations from a West Greenland per-
spective. Canadian Journal of Earth Sciences
39
,
665686.
12
GEOLOGY AND ORE 10 / 2008
Front cover photograph
Folded pegmatite in a metavolcanic
sequence of the supracrustal rocks from
the northern Ketilidian Border Zone in
Kobberminebugt, South-West Green-
land.
Bureau of Minerals and Petroleum
(BMP)
Government of Greenland
P.O. Box 930
DK-3900 Nuuk
Greenland
Tel: (+299) 34 68 00
Fax.: (+299) 32 43 02
E-mail: bmp@gh.gl
Internet: www.bmp.gl
Geological Survey of Denmark
and Greenland (GEUS)
Øster Voldgade 10
DK-1350 Copenhagen K
Denmark
Tel: (+45) 38 14 20 00
Fax.: (+45) 38 14 20 50
E-mail: geus@geus.dk
Internet: www.geus.dk
Author
K. Secher, A. Steenfelt & A.A. Garde,
GEUS
Editor
Karsten Secher, GEUS
Graphic Production
Henrik Klinge Pedersen, GEUS
Photographs
GEUS unless otherwise stated
Printed
January 2008 © GEUS
Printers
Schultz Grafisk
ISSN
1602-818x
Key literature
Last modified: February 13, 2008
|
