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Theme Magazines and Fact Sheets
Download "Geology and Ore no. 9, February 2007" go09.pdf (~5.5 mb)
GOLD ENVIRONMENTS
AND FAVOURABILITY
in the Nuuk area of
southern West Greenland
No. 9 - February 2007
SOFar the interplay between the mag-
matic, tectonic and metamorphic evo-
lutions and their mineralising events
has been the main resource evaluation.
matic, tectonic and metamorphic evo-
lutions and their mineralising events
has been the main resource evaluation.
During the last couple of years,
focus on the primary geological envi-
ronment hosting the mineral deposits
has started to improve the evalua-
tions. Multidisciplinary, spatial, quan-
titative analysis of geo-data is used
for this purpose. The construction of
quantitative, favourability maps for a
specific element, such as gold, is a
result of this.
ronment hosting the mineral deposits
has started to improve the evalua-
tions. Multidisciplinary, spatial, quan-
titative analysis of geo-data is used
for this purpose. The construction of
quantitative, favourability maps for a
specific element, such as gold, is a
result of this.
The "new" approach has been used
in the Nuuk region in West Greenland,
where the statistical, spatial analysis
has been used to evaluate the gold
potential. The analysis also provides
valuable input to the interpretation of
the mineralisation and the primary geo-
logical environments.
where the statistical, spatial analysis
has been used to evaluate the gold
potential. The analysis also provides
valuable input to the interpretation of
the mineralisation and the primary geo-
logical environments.
Geological environments and
mineralisation in the Nuuk region
mineralisation in the Nuuk region
The Nuuk region, located within the Archa-
ean North Atlantic craton (the Nain craton
in Canada), comprises several different
tectono-stratigraphic terranes, which had
independent, geological evolution until they
were tectonically assembled at c. 2.7 Ga.
The terranes host several supracrustal belts;
the oldest is the Isua greenstone belt with
an age of c. 3.8 Ga and younger belts are
Mesoarchaean. The different belts and areas
are described according to their dominating
environment.
ean North Atlantic craton (the Nain craton
in Canada), comprises several different
tectono-stratigraphic terranes, which had
independent, geological evolution until they
were tectonically assembled at c. 2.7 Ga.
The terranes host several supracrustal belts;
the oldest is the Isua greenstone belt with
an age of c. 3.8 Ga and younger belts are
Mesoarchaean. The different belts and areas
are described according to their dominating
environment.
The investigations of the environments
require the combination of detailed geo-
logical mapping, geochemistry, petrography
work, isotope work and geochronological
studies.
logical mapping, geochemistry, petrography
work, isotope work and geochronological
studies.
Island-arc environment
Recently volcaniclastic rocks of andesitic
composition were discovered in the region.
The belt forms major parts of the Meso-
archaean, amphibolite facies supracrustal
belt around Qussuk bay, on central and
eastern Bjørneøen and on central Storø
Recently volcaniclastic rocks of andesitic
composition were discovered in the region.
The belt forms major parts of the Meso-
archaean, amphibolite facies supracrustal
belt around Qussuk bay, on central and
eastern Bjørneøen and on central Storø
(3071 Ma). Meta-volcanic rocks have been
subject to intense synvolcanic hydrothermal
alteration associated with gold-copper
mineralisation (grab samples with up to 2
g/t Au). Later hydrothermal events may
also have affected the occurrences of gold
in certain areas.
subject to intense synvolcanic hydrothermal
alteration associated with gold-copper
mineralisation (grab samples with up to 2
g/t Au). Later hydrothermal events may
also have affected the occurrences of gold
in certain areas.
The Ivisaartoq supracrustal belt, with a
maximum age of 3075 Ma, is interpreted
as a forearc supra-subduction environ-
ment. This belt underwent at least two
stages of calc-silicate, metasomatic alter-
ation between 3075 and 2963 Ma attrib-
as a forearc supra-subduction environ-
ment. This belt underwent at least two
stages of calc-silicate, metasomatic alter-
ation between 3075 and 2963 Ma attrib-
2
The Qingaaq gold prospect at Storø located within a
supracrustal sequence. The prospect is currently
being drilled and evaluated by NunaMinerals A/S. The lake in the lower left corner is 470 m above
sea level. The top in the background is the mountain Qingaaq (1616 m. a.s.l.), and the top in the
foreground is Little Qingaaq (1070 m.a.s.l). Photo courtesy: NunaMinerals A/S.
being drilled and evaluated by NunaMinerals A/S. The lake in the lower left corner is 470 m above
sea level. The top in the background is the mountain Qingaaq (1616 m. a.s.l.), and the top in the
foreground is Little Qingaaq (1070 m.a.s.l). Photo courtesy: NunaMinerals A/S.
Volcaniclastic, meta-andesitic rock from
Bjørneøen with fiamme textures.
Bjørneøen with fiamme textures.
GEOLOGY AND ORE 9 / 2007
GOLD ENVIRONMENTS AND
FAVOURABILITY
FAVOURABILITY
in the Nuuk area of southern West
Greenland
GO_09.qxp 23/02/07 12:48 Page 2
64°30'N
65°N
52°W
51°W
Isukasia
Fiskefjord
50°W
Inland
Ice
Davis
Strait
Strait
Godthåbsfjord
Godthåb
sfj
ord
Nuuk
Ame
ralik
Qo
oqqut
Storø
Bjørneøen
Ivisaartoq
25 km
Qussuk
Q
A
Isua Greenstone
belt
S
Nordlandet
Sermitsiaq
Sillissianguit
North
Atlantic
craton
Nagssugtoqidian
orogen
Ketilidian
Ketilidian
orogen
orogen
Ketilidian
orogen
Nuuk
region
Gneiss -
infracrustal
infracrustal
Major faults and
shear zones
shear zones
Supracrustal
environments:
environments:
Unknown
Island Arc
Ocean Floor
Magmatic
Groups of gold
showings:
showings:
Isua gold group
Bjørneøen gold group
Storø gold group
Ungroup showings
Bjørneøen gold group
Storø gold group
Ungroup showings
uted to seafloor hydrothermal alteration.
The Ivisaartoq belt hosts volcanic massive
sulphide deposits (semi-massive to massive
pyrite-pyrrhotite) and disseminated tung-
sten in altered komatiites (channel samples
with 0.44% WO
The Ivisaartoq belt hosts volcanic massive
sulphide deposits (semi-massive to massive
pyrite-pyrrhotite) and disseminated tung-
sten in altered komatiites (channel samples
with 0.44% WO
3
over 2.5 m). Showings
with up to 3.5 g/t Au are recorded within
the Ivisaartoq belt.
the Ivisaartoq belt.
Ocean-floor environment
The 3.8 Ga Isua greenstone belt represents
an ocean-floor environment. The dominat-
ing rock types in this belt are pillow-struc-
tured tholeiitic and high Mg-basaltic rocks
with intercalated, extensive bands of chert
and banded iron formation, turbidites as
well as garnet-mica schist representing
metamorphosed sediments. Gold occur-
rences have been found in several settings
within the Isua greenstone belt.
The 3.8 Ga Isua greenstone belt represents
an ocean-floor environment. The dominat-
ing rock types in this belt are pillow-struc-
tured tholeiitic and high Mg-basaltic rocks
with intercalated, extensive bands of chert
and banded iron formation, turbidites as
well as garnet-mica schist representing
metamorphosed sediments. Gold occur-
rences have been found in several settings
within the Isua greenstone belt.
· In silicate facies iron formation
(up to 1.2 g/t Au)
· In fuchsite-stained quartz-rich rocks
(up to 3.1 g/t Au over 3 m)
· In shear-zone hosted, carbonate-
altered ultrabasic rocks (grab samples
with up to 100 g/t Au).
with up to 100 g/t Au).
A hydrothermal episode affected a c.
3.8 Ga intrusive tonalite sheet in the west-
ern part of the Isua greenstone belt. The
belt contains up to 14% combined Pb and
Zn with up to 6.8 g/t Au and 180 g/t Ag.
ern part of the Isua greenstone belt. The
belt contains up to 14% combined Pb and
Zn with up to 6.8 g/t Au and 180 g/t Ag.
Well-preserved, volcanic successions
interpreted as environments dominated by
ocean-floor settings are described from
several other areas in the Nuuk region. Bi-
modal, volcanic succession in greenschist
facies is described from the `Nunatak 1390'
in the Tasiuarsuaq terrane. Voluminously
layered amphibolites and well-preserved
pillow lava at Bjørneøen, associated with
homogenous, metagabbroic amphibolite
are also interpreted as a primary ocean
floor environment. A small VMS showing
is located in the south-western part of the
belt at Bjørneøen. This showing contains
up to 3.55% Zn, 1.33% Pb, 33 g/t Ag
and 0.153 g/t Au.
ocean-floor settings are described from
several other areas in the Nuuk region. Bi-
modal, volcanic succession in greenschist
facies is described from the `Nunatak 1390'
in the Tasiuarsuaq terrane. Voluminously
layered amphibolites and well-preserved
pillow lava at Bjørneøen, associated with
homogenous, metagabbroic amphibolite
are also interpreted as a primary ocean
floor environment. A small VMS showing
is located in the south-western part of the
belt at Bjørneøen. This showing contains
up to 3.55% Zn, 1.33% Pb, 33 g/t Ag
and 0.153 g/t Au.
Magmatic environment
The Nordlandet and Fiskefjord areas are
dominated by mafic to ultramafic sequences
including dunite, peridotite, pyroxenite,
norite and amphibolites hosted by tona-
litic and trondhjemitic gneisses. In many
cases relict magmatic layering is preserved.
The Nordlandet and Fiskefjord areas are
dominated by mafic to ultramafic sequences
including dunite, peridotite, pyroxenite,
norite and amphibolites hosted by tona-
litic and trondhjemitic gneisses. In many
cases relict magmatic layering is preserved.
This area comprises probably both primary
magmatic environments and relicts of
greenstone belts. The mafic to ultramafic
complexes south of Fiskefjord show en-
hanced values of Au and PGE. The Seqi
Olivine Mine operated by Minelco AB is
located just north of central Fiskefjord.
The deposit contains at least 100 million
tonnes of high-quality olivine and is host-
ed within a large dunite body.
magmatic environments and relicts of
greenstone belts. The mafic to ultramafic
complexes south of Fiskefjord show en-
hanced values of Au and PGE. The Seqi
Olivine Mine operated by Minelco AB is
located just north of central Fiskefjord.
The deposit contains at least 100 million
tonnes of high-quality olivine and is host-
ed within a large dunite body.
The supracrustal belt at central Storø is
of a complex character and much debated.
It seems that this belt may contain charac-
teristics of both continental and oceanic
volcanic and sedimentary rocks. The area
is furthermore affected by intense folding
and major shearing, making straight inter-
pretations even more difficult. The area may
represent an accretion environment along
boundaries of different terranes (amalga-
mated around 2.7 Ga). Central Storø hosts
the Qingaaq Gold prospect which is inves-
tigated and drilled by NunaMinerals A/S.
Several gold bearing structures, 436 m
wide, have been found at Qingaaq with
grades from 0.5 to 6 g/t Au and locally
24 m wide zones with grades up to 20
g/t Au.
It seems that this belt may contain charac-
teristics of both continental and oceanic
volcanic and sedimentary rocks. The area
is furthermore affected by intense folding
and major shearing, making straight inter-
pretations even more difficult. The area may
represent an accretion environment along
boundaries of different terranes (amalga-
mated around 2.7 Ga). Central Storø hosts
the Qingaaq Gold prospect which is inves-
tigated and drilled by NunaMinerals A/S.
Several gold bearing structures, 436 m
wide, have been found at Qingaaq with
grades from 0.5 to 6 g/t Au and locally
24 m wide zones with grades up to 20
g/t Au.
3
GOLD ENVIRONMENTS AND FAVOURABILITY
Simplified schematic geo-
logical map of the Nuuk
region with general indi-
cation of different geo-
logical environments.
logical map of the Nuuk
region with general indi-
cation of different geo-
logical environments.
Outlines of the rock units
are from digital versions
of 1:100 000 and 1:2
500 000 scale geological
maps published by the
Survey.
Q: Qingaaq;
A: Aappalaartoq;
S: Seqi Olivine mine.
are from digital versions
of 1:100 000 and 1:2
500 000 scale geological
maps published by the
Survey.
Q: Qingaaq;
A: Aappalaartoq;
S: Seqi Olivine mine.
The statistically defined
groups of gold showings
in the region are also
indicated (a gold show-
ing is defined as a locality
where in situ rock sam-
ples yielded 1 g/t Au).
groups of gold showings
in the region are also
indicated (a gold show-
ing is defined as a locality
where in situ rock sam-
ples yielded 1 g/t Au).
GO_09.qxp 23/02/07 12:48 Page 3
Mineral potential - addressing
multivariable datasets
multivariable datasets
Visual inspection and comparison of e.g.
lithological, topographical, geochemical
and geophysical maps are necessary ways
of interpreting geological features across
poorly exposed or little explored areas. In
mineral exploration the maps and data are
used visually to identify anomalies believed
to reflect the existence of mineral occur-
rences. However, if the regional data are
widely spaced, and if the occurrences are
of limited size or poorly exposed, the ano-
malies may be too subtle to be recognised
by a simple visual approach. In such cases,
statistical data analyses may help identify
deviations from the background variations
and trends in the data. Furthermore, visu-
ally based correlation between distributions
is often limited to a few parameters and
with the wealth of to-day's digital data,
multivariable relationships are easily over-
looked or not possible to deduce visually.
lithological, topographical, geochemical
and geophysical maps are necessary ways
of interpreting geological features across
poorly exposed or little explored areas. In
mineral exploration the maps and data are
used visually to identify anomalies believed
to reflect the existence of mineral occur-
rences. However, if the regional data are
widely spaced, and if the occurrences are
of limited size or poorly exposed, the ano-
malies may be too subtle to be recognised
by a simple visual approach. In such cases,
statistical data analyses may help identify
deviations from the background variations
and trends in the data. Furthermore, visu-
ally based correlation between distributions
is often limited to a few parameters and
with the wealth of to-day's digital data,
multivariable relationships are easily over-
looked or not possible to deduce visually.
The principles of the statistical
methodology
All spatial datasets are converted info a
form, where they can be compared and
subjected to statistical analysis. Each data-
set is presented as a regular grid using a
common grid cell size denoted a pixel. In
methodology
All spatial datasets are converted info a
form, where they can be compared and
subjected to statistical analysis. Each data-
set is presented as a regular grid using a
common grid cell size denoted a pixel. In
the case of gold potential in a region, pix-
els with and without gold showings are
registered. To construct a gold favourabili-
ty map includes analysing the characteris-
tic data signatures of the pixels, with and
without gold showings, in multiple data-
sets and then integrating the data signa-
ture to calculate the gold showing proba-
els with and without gold showings are
registered. To construct a gold favourabili-
ty map includes analysing the characteris-
tic data signatures of the pixels, with and
without gold showings, in multiple data-
sets and then integrating the data signa-
ture to calculate the gold showing proba-
bility for each pixel. Besides enabling the
quantification of the gold favourability in
a certain area, the statistical approach pro-
vides quantitative signatures of specific
geological features, e.g. the gold show-
ings, which can be used and integrated in
geological models and interpretations.
quantification of the gold favourability in
a certain area, the statistical approach pro-
vides quantitative signatures of specific
geological features, e.g. the gold show-
ings, which can be used and integrated in
geological models and interpretations.
4
GOLD ENVIRONMENTS AND FAVOURABILITY
Deformed pillow lava from
southern part of Bjørneøen.
southern part of Bjørneøen.
Rusty chromite-magnetite banding from magmatic layered
norite in the Fiskefjord area.
GEOLOGY AND ORE 9 / 2007
GO_09.qxp 23/02/07 12:48 Page 4
Data
No. of showings
Showings
No showings
Empirical distribution
functions are calculated
for different datasets one for
'showings', one for 'no showings'
functions are calculated
for different datasets one for
'showings', one for 'no showings'
?
?
?
? ? ? ? ? ? ? ? ? ?
?
?
?
? ? ? ? ? ?
? ? ?
?
?
?
? ? ? ? ? ? ? ? ? ?
? ?
? ? ? ? ? ? ? ? ? ?
?
?
?
? ? ? ? ?
? ? ? ?
?
?
?
? ? ? ? ? ? ? ? ? ?
?
?
?
Quantified signatures
in different datasets
A search for similar signatures
is carried out.
The degree of similarities is
used to construct mineral
potential maps
is carried out.
The degree of similarities is
used to construct mineral
potential maps
Mineral potential map
high
low
favourability for showings
Geoscientific data sets are pixelated
2
1
4
3
Au
Au
Au
5
GOLD ENVIRONMENTS AND FAVOURABILITY
Illustration of the statistical approach:
1: Regional datasets and gold showings (Au) are referred
to a
common grid with fixed cell size; a pixel.
common grid with fixed cell size; a pixel.
2: Empirical distribution functions for pixels with and
without
known gold showings are used to establish the signatures of
the showings in each dataset.
known gold showings are used to establish the signatures of
the showings in each dataset.
3: Likelihood ratiOFunctions for all datasets are
calculated on
the basis of the two previous functions, expressing the likeliness
of a showing to be present. Groupings of gold showings are
based on constructed mineral potential maps for each showing.
Pixel by pixel, these maps outline the predicted favourability for
data signatures similar to the selected showing, i.e. the poten-
tial for a similar showing to be present.
the basis of the two previous functions, expressing the likeliness
of a showing to be present. Groupings of gold showings are
based on constructed mineral potential maps for each showing.
Pixel by pixel, these maps outline the predicted favourability for
data signatures similar to the selected showing, i.e. the poten-
tial for a similar showing to be present.
4: Finally, mineral potential maps are calculated for
each identi-
fied group of showings. These maps are based on the signa-
tures found to be indicative for each of the different groups.
fied group of showings. These maps are based on the signa-
tures found to be indicative for each of the different groups.
GO_09.qxp 23/02/07 12:48 Page 5
6
GEOLOGY AND ORE 9 / 2007
Rust zone in massive sulphide occurrence at
Ivisaartoq.
GOLD ENVIRONMENTS AND FAVOURABILITY
Gold favourability map for the
Nuuk region
Nuuk region
Data analysed
Sixty-nine different geoscientific datasets
including location of known gold show-
ings, data from geological maps, stream
sediment geochemistry, aeromagnetic data,
aeroradiometric data and data from linea-
ment analysis have sOFar been included in
the statistical analysis. All datasets are pix-
elated. A gold showing is in the current
study defined as a locality where a rock
grab sample has yielded> 1 g/t Au.
Sixty-nine different geoscientific datasets
including location of known gold show-
ings, data from geological maps, stream
sediment geochemistry, aeromagnetic data,
aeroradiometric data and data from linea-
ment analysis have sOFar been included in
the statistical analysis. All datasets are pix-
elated. A gold showing is in the current
study defined as a locality where a rock
grab sample has yielded> 1 g/t Au.
Grouping of gold showings
Instead of treating all known gold show-
ings as one group, it is statistically ana-
lysed whether the showings should be split
into groups according to common signa-
tures in the datasets. For the Nuuk region,
this analysis resulted in the identification
of at three main groups of gold showings:
the Storø, the Bjørneøen and the Isua
group.
Instead of treating all known gold show-
ings as one group, it is statistically ana-
lysed whether the showings should be split
into groups according to common signa-
tures in the datasets. For the Nuuk region,
this analysis resulted in the identification
of at three main groups of gold showings:
the Storø, the Bjørneøen and the Isua
group.
Resulting gold favourability map
By using the identified common signature
for gold showings, it is possible to estimate
the probability for similar data signatures
within all pixels. It is not surprising that
By using the identified common signature
for gold showings, it is possible to estimate
the probability for similar data signatures
within all pixels. It is not surprising that
areas immediately surrounding known gold
showings are predicted as favourable, but
more interestingly, a number of favourable
areas are also predicted outside areas with
known gold showings.
showings are predicted as favourable, but
more interestingly, a number of favourable
areas are also predicted outside areas with
known gold showings.
Gold bearing rustzone in the Qussuk area.
GO_09.qxp 23/02/07 12:48 Page 6
7
GOLD ENVIRONMENTS AND FAVOURABILITY
Fis
ke
fjord
Inland
Ice
Davis
Strait
Strait
Go
dth
åb
sf
jor
d
God
thå
bsfjord
Amer
alik
Qo
oqqut
Fis
ke
fjord
Inland
Ice
Davis
Strait
Strait
Go
dth
åb
sf
jor
d
God
thå
bsfjord
Ameralik
Qooqqut
Nuuk
region
Q
A
Q
A
64°30'N
65°N
52°W
51°W
Isukasia
Q
A
Q
A
50°W
Se
rm
its
iaq
Nuuk
Storø
Bjørneøen
Ivisaartoq
25 km
64°30'N
65°N
52°W
51°W
Isukasia
Q
A
Q
A
50°W
Serm
its
ia
q
Nuuk
Storø
Bjørneøen
Ivisaartoq
25 km
Top 685 km
2
most gold favourable area (5% of entire study
area)
Top 137 km
2
most gold favourable area (1% of entire study
area)
Gneiss
Ice
Amphibolite
Metasediment
Ultramafic rock
Metasediment
Ultramafic rock
Fault and shear zones
Late Archaean granites
Storø showings
Bjørneøen showings
Isua showings
Ungrouped showings
Isua gold group
The top 137 km
2
and 685 km
2
most favourable areas for:
Bjørneøen gold group
Storø gold group
Simplified geological maps with the top
rated 137 km
rated 137 km
2
and 685 km
2
(respectively
1% and 5% of the analysed area) outlined
as most gold favourable area for the three
groups of gold showings (Isua, Bjørneøen
and Storø groups). Outlines of the rock
units are from digital versions of 1:100 000
and 1:2 500 000 scale geological maps
published by GEUS.
as most gold favourable area for the three
groups of gold showings (Isua, Bjørneøen
and Storø groups). Outlines of the rock
units are from digital versions of 1:100 000
and 1:2 500 000 scale geological maps
published by GEUS.
GO_09.qxp 23/02/07 12:48 Page 7
Some of the most notable areas out-
lined as most favourable for gold are east
of the fjord Qooqqut, areas at Storø, areas
at Sermitsiaq, areas south and west of
Isuakasia and areas in outer and inner part
of Fiskefjord. Especially in the latter area,
hardly any prospecting for gold has been
done, but the area comprises both
supracrustal rocks and structures that are
similar to those in areas with known gold
showings. Field work in the inner part of
Fiskefjord recently revealed a strong alter-
ation of the country rock in that area;
mainly bleaching, silicification and epidoti-
zation. Rocks from the area yield elevated
gold content with up to 0.377 g/t Au in
amphibolite-hosted quartz veins.
of the fjord Qooqqut, areas at Storø, areas
at Sermitsiaq, areas south and west of
Isuakasia and areas in outer and inner part
of Fiskefjord. Especially in the latter area,
hardly any prospecting for gold has been
done, but the area comprises both
supracrustal rocks and structures that are
similar to those in areas with known gold
showings. Field work in the inner part of
Fiskefjord recently revealed a strong alter-
ation of the country rock in that area;
mainly bleaching, silicification and epidoti-
zation. Rocks from the area yield elevated
gold content with up to 0.377 g/t Au in
amphibolite-hosted quartz veins.
The spatial distribution
The spatial distribution of all outlined favour-
able areas suggests the existence of a main
regional tract favourable for gold and gold
mineralising environments. Most of the fa-
vourable areas for the different groups of
known gold showings are situated within a
The spatial distribution of all outlined favour-
able areas suggests the existence of a main
regional tract favourable for gold and gold
mineralising environments. Most of the fa-
vourable areas for the different groups of
known gold showings are situated within a
GOLD ENVIRONMENTS AND FAVOURABILITY
8
GEOLOGY AND ORE 9 / 2007
Vertical gradient of total magnetic
intensity field [nT/m]
-0.6 -0.4 -0.2
0.0 0.2
0.4 0.6
Normalised frequency
0.0
2.0
4.0
6.0
8.0
Cs [ppm]
6
Normalised frequency
0.0
0.8
1.6
2.4
3.2
3
4
5
2
Ni/Mg ratio
5
15
25
35
45
55
Normalised frequency
0.00
0.04
0.08
0.12
0.16
As [ppm]
2
6
10 14 18 22 26 30
Normalised frequency
0.0
0.2
0.4
0.6
0.8
Isua grou p
Bjørneøen grou p
Storø grou p
Background
Four examples of statistically derived data signatures
for the three main groups of gold showings in
the Nuuk region, displayed together with the background signature(pixels without any gold show-
ings).
the Nuuk region, displayed together with the background signature(pixels without any gold show-
ings).
Rust zone with 377 ppb Au in quartz-veined amphibolite,
central Fiskefjord.
GO_09.qxp 23/02/07 12:48 Page 8
NNE-trending tract from the town of Nuuk
to Isukasia. The tract embraces most of
the previously known gold showings in
the region as well as geochemical gold
anomalies, and the zone has previously
been suggested as being prospective for
gold.The NNE-trending tract outlined as
being favourable for gold is common to
the general orientation of the supracrustal
belts in this area and to the regional large-
scale faults. In general, supracrustal units
outside the tract constitute similar propor-
tions, but these are not indicated as being
within the most favourable areas by the
present statistical analysis. This indicates
that the supracrustal units within the tract
deviate from those outside.
to Isukasia. The tract embraces most of
the previously known gold showings in
the region as well as geochemical gold
anomalies, and the zone has previously
been suggested as being prospective for
gold.The NNE-trending tract outlined as
being favourable for gold is common to
the general orientation of the supracrustal
belts in this area and to the regional large-
scale faults. In general, supracrustal units
outside the tract constitute similar propor-
tions, but these are not indicated as being
within the most favourable areas by the
present statistical analysis. This indicates
that the supracrustal units within the tract
deviate from those outside.
Signatures of gold showings
The systematic construction of data signa-
tures of showings and the background
draw attention to the significance of par-
ameters that are not immediately or tradi-
tionally regarded as indicative of gold min-
eralisation. It has previously been estab-
lished that the combination of elevated As
in stream sediment and gold mineralisation
has not been found outside Storø. How-
ever, the possible significance of the Ni/Mg
ratio in relation to gold has not previously
been substantiated in a quantitative way.
This observation is an incentive to conduct
further studies of host rock properties in
terms of their Ni and Mg behaviour. The
rare and unique As signature of the Storø
The systematic construction of data signa-
tures of showings and the background
draw attention to the significance of par-
ameters that are not immediately or tradi-
tionally regarded as indicative of gold min-
eralisation. It has previously been estab-
lished that the combination of elevated As
in stream sediment and gold mineralisation
has not been found outside Storø. How-
ever, the possible significance of the Ni/Mg
ratio in relation to gold has not previously
been substantiated in a quantitative way.
This observation is an incentive to conduct
further studies of host rock properties in
terms of their Ni and Mg behaviour. The
rare and unique As signature of the Storø
group poses a problem in the search for
areas holding a potential for new show-
ings. Since this signature exists on Storø
solely, this area will be outlined as favour-
able only for the Storø group. Consequent-
ly, the As data are omitted in the calcula-
tion of pixels with a potential for Storø-
type showings. It has before been argued
that Cs may be considered a pathfinder
element for gold mineralisation associated
with granite-related, hydrothermal alter-
ation. The signature for Cs in stream sedi-
ment confirms that the gold at Storø and
Bjørneøen is indeed located in a Cs-rich
environment, but also suggests that the
mineralisation at Isua has a different nature.
areas holding a potential for new show-
ings. Since this signature exists on Storø
solely, this area will be outlined as favour-
able only for the Storø group. Consequent-
ly, the As data are omitted in the calcula-
tion of pixels with a potential for Storø-
type showings. It has before been argued
that Cs may be considered a pathfinder
element for gold mineralisation associated
with granite-related, hydrothermal alter-
ation. The signature for Cs in stream sedi-
ment confirms that the gold at Storø and
Bjørneøen is indeed located in a Cs-rich
environment, but also suggests that the
mineralisation at Isua has a different nature.
The last example illustrates the indicated
significance of the vertical gradient of the
total magnetic field intensity (denoted
VGTMI). This signature for the Storø and
Bjørneøen groups (0.2 to 0.1 nT/m) is iden-
tical to the background signature, and is
consequently regarded as non-indicative for
these groups. The Isua group has a more
dispersed signature (0.5 to 0.8 nT/m), with
an indicative positive and negative VGTMI
than the other groups. This probably reflects
local-scale changes in lithology. Other data-
sets, which yield a characteristic signature of
one or more of the groups of gold show-
ings, are the Au, Cs, Rb, La, Th, and U con-
centrations in stream sediment geochemisty.
total magnetic field intensity (denoted
VGTMI). This signature for the Storø and
Bjørneøen groups (0.2 to 0.1 nT/m) is iden-
tical to the background signature, and is
consequently regarded as non-indicative for
these groups. The Isua group has a more
dispersed signature (0.5 to 0.8 nT/m), with
an indicative positive and negative VGTMI
than the other groups. This probably reflects
local-scale changes in lithology. Other data-
sets, which yield a characteristic signature of
one or more of the groups of gold show-
ings, are the Au, Cs, Rb, La, Th, and U con-
centrations in stream sediment geochemisty.
GOLD ENVIRONMENTS AND FAVOURABILITY
9
Empirical simplified model of geological environments and
mineral occurrences present in the Nuuk region.
Basaltic
magmatism
Calc-alkaline
volcanism
Granite
TTG
Midoceanic
rift
Ivisaartoq
(~3.075 Ga)
Hydrothermal
Au, W
Hydrothermal
Au, W
Seqi
(~3.03 Ga)
Magmatic
Olivine
Magmatic
Olivine
Shield
Ultramafic-mafic
intrusions
Isuakasia
(~3.8 Ga)
BIF
Au, Fe
BIF
Au, Fe
Qussuk
Bjørneøen
Bjørneøen
(~3.07 Ga)
VMS, hydrothermal
Au, Cu, Zn, Pb
VMS, hydrothermal
Au, Cu, Zn, Pb
Bi-modal
volcanism
Island
arc
Ultramafic
intrusion
Sillissisanguit
(~3.03 Ga)
Magmatic
Ni, Cu, PGE
Magmatic
Ni, Cu, PGE
Qingaaq
Aappalaartoq
Aappalaartoq
(~2.85 Ga)
Hydrothermal,
Au
Hydrothermal,
Au
Fault-/shearzone
suture zone
Granite
intrusions
Ultramafic-
mafic intrusions
Continetal
margin
Back-arc
basin
Godthaabsfjord
(~2.63 Ga)
Pegmatite
Tourmaline, beryl,
U, Th, REE
Pegmatite
Tourmaline, beryl,
U, Th, REE
Qôrqut
granite
granite
Visible gold in drill core from the Storø prospect. Photo:
NiunaMinerals A/S.
GO_09.qxp 23/02/07 12:48 Page 9
Perspectives
The statistical approach has a potential of
identifying and mapping other types of
mineral occurrences as well as specific tec-
tonic units in poorly known areas and can
be used on local or regional scale, depend-
ing on the resolution of the involved data-
sets. The statistical approach has been used
to examine gold showings in a moderately
explored region.
identifying and mapping other types of
mineral occurrences as well as specific tec-
tonic units in poorly known areas and can
be used on local or regional scale, depend-
ing on the resolution of the involved data-
sets. The statistical approach has been used
to examine gold showings in a moderately
explored region.
The approach could also be applied to
economic deposits from well-known his-
toric or active mining camps. As shown in
the case in the Nuuk area, the statistical
approach should always be used in combi-
nation with other geological approaches.
toric or active mining camps. As shown in
the case in the Nuuk area, the statistical
approach should always be used in combi-
nation with other geological approaches.
The results of a statistical analysis should
be cross-validated and critically balanced
according to geological knowledge.
be cross-validated and critically balanced
according to geological knowledge.
Concluding remarks
The detailed investigations of primary geo-
logical environments of supracrustal rocks
in the Nuuk region have revealed a great
diversity in environments, which all carry
gold. The results from the statistical analy-
sis have been positive in the sense that
areas with high favourability for new gold
occurrences have been outlined.
logical environments of supracrustal rocks
in the Nuuk region have revealed a great
diversity in environments, which all carry
gold. The results from the statistical analy-
sis have been positive in the sense that
areas with high favourability for new gold
occurrences have been outlined.
GOLD ENVIRONMENTS AND FAVOURABILITY
10
GEOLOGY AND ORE 9 / 2007
Hydrothermal alteration with epidotization,
south of Ameralik fjord.
south of Ameralik fjord.
GO_09.qxp 23/02/07 12:48 Page 10
11
GEMSTONES OF GREENLAND
Drill cores are lifted by helicopter during
operation at Little Qingaaq. Photo courtesy:
NunaMinerals A/S.
operation at Little Qingaaq. Photo courtesy:
NunaMinerals A/S.
GO_09.qxp 23/02/07 12:48 Page 11
12
GEOLOGY AND ORE 9 / 2007
GEOLOGY AND ORE 7 / 2007
Key references
Appel, P.W.U., Coller, D., Coller, V., Heijlen,
W.,
Moberg, E., Polat, A.,Raith, J., Schjøth,
F.,
Stendal, H. & Thomassen, B. (2005):
Is
there
a gold province in the Nuuk region? Danmarks
og Grønlands Geologiske Undersøgelse Rapport
2005/27
, 79 pp., 1 CD-ROM.
Eilu, P., Garofalo, P., Appel, P.W.U. &
Heijlen,
W. (2006):
Alteration patterns in
Au-mineralised
zones of Storø, Nuuk region West Greenland.
Danmarks og Grønlands Geologiske Undersøgelse
Rapport
2006/30
, 73 pp.
Garde, A.A. (in press):
A mid-Archaean
island
arc complex in the eastern Akia terrane, Godt-
håbsfjord, southern West Greenland. Journal of
Geological Society.
Hollis, J.A., van Gool, J.A.M., Steenfelt, A.
&
Garde, A.A. (2005):
Greenstone belts in
the
central Godthåbsfjord region, southern West
Greenland. Geological Survey of Denmark and
Greenland Bulletin
7
, 6568.
Hollis, J.A., Schmid, S., Stendal, H., van
Gool,
J.A.M. & Weng, W.L. (2006):
Progress report
on
the 2005 field work: geological mapping,
regional
hydrothermal alteration and tectonic sections.
Danmarks og Grønlands Geologiske Undersøgelse
Rapport
2006/7
, 171 pp.
Juul-Petersen,A., Frei, R. Appel,
P.W.U.,
Persson,M. & Konnerup_Madsen, J. (in
press):
A sher zone related greenstone belt hosted gold
mineralization in the Archean of West
Greenland.
A petrographic and combined Pb-Pb and Rb-Sr
geochronological study. Ore Geology Reviews
(2007).
Stendal, H., Secher, K., Nielsen, B.M.,
Schøn-
wandt, H.K. & Thorning, L. (2005):
Greenland
geological environments and mineral resources.
Danmarks og Grønlands Geologiske Undersøgelse
Rapport
2005/8
, 207 pp.
Stensgaard, B.M., Chung, C., Rasmussen,
T.M.
& Stendal, H. (in press):
Assessment of
mineral
potential using cross-validation techniques and
statistical analysis: A case study from the
Paleoproterozoic of West Greenland. Economic
Geology,
101
.
Steensgaard, B.M., Steenfelt, A. &
Rasmussen,
T.M. (2006):
Gold potential of the Nuuk
region
based on multi-parameter spatial modelling.
Progress 2005. Danmarks og Grønlands Geo-
logiske Undersøgelse Rapport
2006/27
, 207
pp.
Polat, A., Appel, P.W.U., Frei, R., Pan, Y., Dilek,
Y.,
Ordóñes-Calderón, J.C., Fryer, B., Hollis,
J.A.
& Raith, J.G. (2007):
Field and
geochemical
characteristics of the Mesoarchean (~3075 Ma)
Ivisaartoq greenstone belt, southern West
Greenland: Evidence for seafloor hydrothermal
alteration in supra-subduction oceanic crust.
Gondwana Research
11
, 6991.
Front cover photograph
The mountain Aappalaartoq (1440 m)
named after the Greenlandic word for
red mountain in the background.
Several gold-bearing structures have
been located within the supracrustal
package making up the mountain. Photo
courtesy: NunaMinerals A/S.
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
B.M. Stensgaard & H. Stendal, GEUS
Editor
Karsten Secher, GEUS
Graphic Production
Carsten E. Thuesen, GEUS
Photographs
GEUS unless otherwise stated
Printed
January 2007 © GEUS
Printers
Schultz Grafisk
ISSN
1602-818x
Gold-mineralised quartz veins hosted in amphibolite at
the Qingaaq gold prospect,
central Storø.
central Storø.
GO_09.qxp 23/02/07 12:48 Page 12
Last modified: March 2, 2007
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