IOCG and Porphyry-Cu deposits in Northern Finland ... - IAGS 2011
IOCG and Porphyry-Cu deposits in Northern Finland ... - IAGS 2011
IOCG and Porphyry-Cu deposits in Northern Finland ... - IAGS 2011
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FIELD EXCURSION<br />
<strong>IOCG</strong> <strong>and</strong> <strong>Porphyry</strong>-<strong>Cu</strong> <strong>deposits</strong><br />
<strong>in</strong> <strong>Northern</strong> F<strong>in</strong>l<strong>and</strong><br />
<strong>and</strong> Sweden
<strong>IOCG</strong> <strong>and</strong> <strong>Porphyry</strong>-<strong>Cu</strong> <strong>deposits</strong> <strong>in</strong><br />
<strong>Northern</strong> F<strong>in</strong>l<strong>and</strong> <strong>and</strong> Sweden<br />
Excursion guide, 27 - 28 August <strong>2011</strong><br />
25th International Applied Geochemistry Symposium <strong>2011</strong><br />
22-26 August <strong>2011</strong> Rovaniemi, F<strong>in</strong>l<strong>and</strong><br />
Tero Niiranen<br />
Publisher: Vuorimiesyhdistys - F<strong>in</strong>nish Association of M<strong>in</strong><strong>in</strong>g <strong>and</strong> Metallurgical<br />
Eng<strong>in</strong>eers, Serie B, Nro B92-12, Rovaniemi <strong>2011</strong>
Niiranen, T. <strong>2011</strong>. Iron oxide-copper-gold <strong>and</strong> porphyry-<strong>Cu</strong> <strong>deposits</strong> <strong>in</strong> <strong>Northern</strong> F<strong>in</strong>l<strong>and</strong> <strong>and</strong> Sweden.<br />
Excursion guide <strong>in</strong> the 25th International Applied Geochemistry Symposium <strong>2011</strong>, 22-26 August <strong>2011</strong>,<br />
Rovaniemi, F<strong>in</strong>l<strong>and</strong>. Vuorimiesyhdistys - F<strong>in</strong>nish Association of M<strong>in</strong><strong>in</strong>g <strong>and</strong> Metallurgical Eng<strong>in</strong>eers, Serie<br />
B92-12, 40 pages.<br />
Layout: Irma Varrio<br />
ISBN 978-952-9618-86-6 (Pr<strong>in</strong>ted)<br />
ISBN 978-952-9618-87-3 (Pdf)<br />
ISSN 0783-1331<br />
© Vuorimiesyhdistys<br />
This volume is available from:<br />
Vuorimiesyhdistys ry.<br />
Kaskilaaksontie 3 D 108<br />
02360 ESPOO<br />
Electronic version:<br />
http://www.iags<strong>2011</strong>.fi or http://www.vuorimiesyhdistys.fi/julkaisut.php<br />
Pr<strong>in</strong>ted <strong>in</strong>:<br />
Pa<strong>in</strong>atuskeskus F<strong>in</strong>l<strong>and</strong> Oy, Rovaniemi
<strong>IOCG</strong> <strong>and</strong> <strong>Porphyry</strong>-<strong>Cu</strong> <strong>deposits</strong> <strong>in</strong><br />
<strong>Northern</strong> F<strong>in</strong>l<strong>and</strong> <strong>and</strong> Sweden<br />
Tero Niiranen<br />
Geological Survey of F<strong>in</strong>l<strong>and</strong>, P.O. Box 77, 96101 Rovaniemi, F<strong>in</strong>l<strong>and</strong>, e-mail<br />
tero.niiranen(at)gtk.fi<br />
Abstract<br />
The field excursion visits the iron <strong>and</strong> iron-copper-gold <strong>deposits</strong> <strong>in</strong> Kolari-Pajala<br />
area currently under development by Northl<strong>and</strong> Resources S.A. <strong>and</strong> the Aitik <strong>Cu</strong>-<br />
Ag-Au m<strong>in</strong>e <strong>in</strong> Gällivare operated by New Boliden Ab.<br />
At Kolari we will visit the Hannuka<strong>in</strong>en Fe-<strong>Cu</strong>-Au deposit which was operated<br />
by Rautaruukki Oyj <strong>and</strong> subsequently by Outokumpu Oyj between 1981 <strong>and</strong><br />
1990 total production be<strong>in</strong>g about 4.5 Mt @ 43% Fe, 0.48% <strong>Cu</strong>, <strong>and</strong> 0.29 g/t Au.<br />
Northl<strong>and</strong> Resources has been develop<strong>in</strong>g the Hannuka<strong>in</strong>en deposit s<strong>in</strong>ce 2005 <strong>and</strong><br />
the current resource estimate for the Hannuka<strong>in</strong>en is 110 Mt @ 33.9% Fe <strong>and</strong> 0.17%<br />
<strong>Cu</strong> (measured + <strong>in</strong>dicated, 15% Fe, cut off) with additional 88 Mt <strong>in</strong>ferred resources.<br />
The Hannuka<strong>in</strong>en deposit is controlled by a thrust zone which is part of the crustalscale<br />
Kolari-Pajala shear zone system. The ore is hosted by altered varieties of 1.86<br />
Ga diorite <strong>in</strong>trusion <strong>and</strong> 2.2-2.05 Ga mafic volcanic rocks. The deposit has been suggested<br />
to belong to <strong>IOCG</strong> class.<br />
At Pajala the excursion visits two iron <strong>deposits</strong>, the Sahavaara <strong>and</strong> Tapuli.<br />
Both <strong>deposits</strong> are skarn-hosted magnetite <strong>deposits</strong>. The resource estimate for the Tapuli<br />
is 101 Mt @ 26.9% Fe (measured & <strong>in</strong>dicated). For the Sahavaara, the current<br />
resource estimate is 64.9 Mt @ 42.5% Fe (measured & <strong>in</strong>dicated) with additional<br />
34.7 Mt <strong>in</strong> <strong>in</strong>ferred category. Both the Tapuli <strong>and</strong> Sahavaara <strong>deposits</strong> are hosted<br />
by 2.4-1.98 Ga sedimentary sequence of dolomitic marbles, phyllites, <strong>and</strong> graphitic<br />
schists.<br />
At Gällivare, we will visit the Aitik <strong>Cu</strong>-Ag-Au m<strong>in</strong>e which is one of Europe’s<br />
largest copper producers. M<strong>in</strong><strong>in</strong>g at Aitik started at 1968 <strong>and</strong> s<strong>in</strong>ce then about<br />
500 Mt of ore has been m<strong>in</strong>ed from a open pit operation. The total ore reserves <strong>in</strong><br />
2009 were 747 Mt grad<strong>in</strong>g 0.25% <strong>Cu</strong>, 1.7 g/t Ag, <strong>and</strong> 0.14 g/t Au. In 2010 the ore<br />
production was 27.6 Mt. The Aitik deposit is hosted by gneissic varieties of regionally<br />
wide spread calc-alkal<strong>in</strong>e Hapar<strong>and</strong>a Suite <strong>in</strong>trusives <strong>and</strong> co-magmatic volcanic<br />
rocks. The geological features for the Aitik deposit suggest that it is a metamorphosed<br />
porphyry-copper deposit.
Excursion program <strong>and</strong> route<br />
Introduction 8<br />
Geological <strong>and</strong> tectonic evolution of the northern part of the Fennosc<strong>and</strong>ian Shield 9<br />
Iron oxide <strong>and</strong> iron oxide-<strong>Cu</strong>-Au <strong>deposits</strong> <strong>in</strong> the Kolari-Pajala district 17<br />
Aitik <strong>Cu</strong>-Au-Ag M<strong>in</strong>e 24<br />
References 31<br />
Saturday, 27th August<br />
Stop 1. Hannuka<strong>in</strong>en Fe-<strong>Cu</strong>-Au deposit, Kolari. About 190 km, 2 h 30 m<strong>in</strong>. We will visit the two old open pits<br />
at Hannuka<strong>in</strong>en <strong>and</strong> waste rocks piles next to them. Possibility to see the ore, host rock, <strong>and</strong> wall rock boulders<br />
of the Hannuka<strong>in</strong>en deposit.<br />
Stop 2. Northl<strong>and</strong> Resources S.A. drill core facilities <strong>in</strong> Äkäsjokisuu. About 20 km drive (30 m<strong>in</strong>) from Hannuka<strong>in</strong>en.<br />
Drill core display of the Northl<strong>and</strong>s targets <strong>in</strong> the Kolari <strong>and</strong> Pajala districts<br />
Stop 3. Kolari Hotel, about 18 km (20 m<strong>in</strong>). Lunch <strong>and</strong> Northl<strong>and</strong>’s presentation of the projects <strong>in</strong> Kolari <strong>and</strong><br />
Pajala areas.<br />
Stop 4. The Stora Sahavaara deposit, Pajala, Sweden. About 40 km drive (45 m<strong>in</strong>). Possibility to see the ore<br />
<strong>and</strong> host rock boulders taken from a bulk sample drive made by Northl<strong>and</strong> <strong>in</strong> 2006.<br />
Stop 5. Optional. Tapuli deposit (about 5 km). Depend<strong>in</strong>g on the operations <strong>in</strong> there, possibility to see the host<br />
rock assemblage rocks.<br />
Stop 6. Gällivare, Sweden. 160 km, about 2 hours. Accommodation to Gr<strong>and</strong> Hotel Lapl<strong>and</strong> <strong>and</strong> d<strong>in</strong>ner <strong>in</strong> the<br />
even<strong>in</strong>g at the hotel.<br />
Sunday, 28th August<br />
8:00 Check out from the hotel, short drive to the New Boliden’s Aitik m<strong>in</strong>e (about 25 km drive). Company<br />
geologists presentation on the geology <strong>and</strong> m<strong>in</strong><strong>in</strong>g operations at Aitik. Visit to the open pit. The exact localities<br />
to be visited <strong>in</strong> the open cut depend on the accessibility to different parts of the m<strong>in</strong>e which changes rapidly as<br />
a consequence of the m<strong>in</strong><strong>in</strong>g activities.<br />
14:00 Drive to Rovaniemi. About 280 km, about 4 hours. If necessary we’ll drive through the airport where<br />
we’ll expect to arrive around 6 p.m. The buss will also stop at the Hotels down town Rovaniemi.<br />
Weather <strong>and</strong> cloth<strong>in</strong>g:<br />
Weather <strong>in</strong> late August can vary considerably - the temperature range is <strong>in</strong> between 0 to 25ºC, be<strong>in</strong>g typically<br />
around 15ºC <strong>in</strong> daytime. It is recommended that one should have a weatherproof jacket <strong>in</strong> case of ra<strong>in</strong>.<br />
The field targets <strong>in</strong> both Kolari <strong>and</strong> Pajala are easily accessed <strong>and</strong> one can manage with regular shoes. Dur<strong>in</strong>g<br />
the visit to Aitik safety boots, hard hat <strong>and</strong> safety classes are provided by the company.
SAFETY INSTRUCTIONS:<br />
The <strong>in</strong>structions of your guides <strong>and</strong> hosts MUST be followed at all times. Be aware of loose boulders <strong>in</strong> the<br />
waste rock piles <strong>and</strong> open cut walls. Be aware of heavy mach<strong>in</strong>ery, hard hat <strong>and</strong> safety boots provided <strong>in</strong> the<br />
Aitik m<strong>in</strong>e must be worn all the time.<br />
Mobile numbers of your guides:<br />
Tero Niiranen: +358 503 487 621<br />
Tuomo Kar<strong>in</strong>en: +358 504 369 360
8<br />
Introduction<br />
Pär Weihed, Olof Mart<strong>in</strong>sson<br />
Luleå University of Technology, Luleå, Sweden<br />
Pasi Eilu<br />
Geological Survey of F<strong>in</strong>l<strong>and</strong>, Espoo, F<strong>in</strong>l<strong>and</strong><br />
The Fennosc<strong>and</strong>ian Shield forms the north-westernmost<br />
part of the East European craton <strong>and</strong> constitutes<br />
large parts of F<strong>in</strong>l<strong>and</strong>, NW Russia, Norway,<br />
<strong>and</strong> Sweden (Fig. 1). The oldest rocks yet found<br />
<strong>in</strong> the shield have been dated at 3.5 Ga (Huhma et<br />
al. 2004) <strong>and</strong> major orogenies took place <strong>in</strong> the Archaean<br />
<strong>and</strong> Palaeoproterozoic. Younger Meso- <strong>and</strong><br />
Neoproterozoic crustal growth took place ma<strong>in</strong>ly <strong>in</strong><br />
the western part, but apart from the anorthositic Ti<strong>deposits</strong><br />
<strong>in</strong> SW Norway, no major ore <strong>deposits</strong> are<br />
related to rocks of this age. The western part of the<br />
shield was reworked dur<strong>in</strong>g the Caledonian Orogeny.<br />
Economic m<strong>in</strong>eral <strong>deposits</strong> are largely restricted<br />
to the Palaeoproterozoic parts of the shield.<br />
Although Ni–PGE, Mo, BIF, <strong>and</strong> orogenic gold <strong>deposits</strong>,<br />
<strong>and</strong> some very m<strong>in</strong>or VMS <strong>deposits</strong> occur <strong>in</strong><br />
the Archaean, virtually all economic examples of<br />
these deposit types are related to Palaeoproterozoic<br />
magmatism, deformation <strong>and</strong> fluid flow. Besides<br />
these major deposit types, the Palaeoproterozoic<br />
part of the shield is also known for its Fe-oxide <strong>deposits</strong>,<br />
<strong>in</strong>clud<strong>in</strong>g the famous Kiruna-type Fe-apatite<br />
<strong>deposits</strong>. Large-tonnage low-grade <strong>Cu</strong>–Au <strong>deposits</strong><br />
(e.g., Aitik), are associated with <strong>in</strong>trusive rocks <strong>in</strong><br />
the northern part of the Fennosc<strong>and</strong>ian Shield. These<br />
<strong>deposits</strong> have been described as porphyry style <strong>deposits</strong><br />
or as hybrid <strong>deposits</strong> with features that also<br />
warrant classification as iron oxide–copper–gold<br />
(<strong>IOCG</strong>) <strong>deposits</strong> (Weihed 2001, Wanha<strong>in</strong>en et al.<br />
2005).<br />
Dur<strong>in</strong>g this field trip we will visit the iron<br />
<strong>and</strong> iron oxide-<strong>Cu</strong>-Au <strong>deposits</strong> straddl<strong>in</strong>g the national<br />
border between F<strong>in</strong>l<strong>and</strong> <strong>and</strong> Sweden (Fig. 2)<br />
as well as the giant Aitik <strong>Cu</strong>-Au deposit <strong>in</strong> Sweden.<br />
Fig. 1. Simplified geological map of the Fennosc<strong>and</strong>ian<br />
Shield with major tectono-stratigraphic units<br />
discussed <strong>in</strong> text. Map based on Koist<strong>in</strong>en et al.<br />
(2001), tectonic <strong>in</strong>terpretation after Laht<strong>in</strong>en et al.<br />
(2005). LGB = Lap¬l<strong>and</strong> Greenstone Belt, CLGC<br />
= Central Lapl<strong>and</strong> Granitoid Complex, BMB =<br />
Belomorian Mobile Belt, CKC = Central Karelian<br />
Complex, IC = Iisalmi Complex, PC = Pudasjärvi<br />
Complex, TKS = Tipasjärvi–Kuhmo–Suomussalmi<br />
green¬stone complex. Shaded area, BMS =<br />
Bothnian Megashear.
Fig. 2. Hannuka<strong>in</strong>en deposit open pits <strong>in</strong> Kolari, F<strong>in</strong>l<strong>and</strong> dur<strong>in</strong>g w<strong>in</strong>ter 2009.<br />
Photo courtesy of Northl<strong>and</strong> Resources S.A.<br />
Geological <strong>and</strong> tectonic evolution<br />
of the northern part of the<br />
Fennosc<strong>and</strong>ian Shield<br />
Stefan Bergman<br />
Geological Survey of Sweden, Uppsala, Sweden<br />
Pär Weihed, Olof Mart<strong>in</strong>sson<br />
Luleå University of Technology, Luleå, Sweden<br />
Pasi Eilu<br />
Geological Survey of F<strong>in</strong>l<strong>and</strong>, Espoo, F<strong>in</strong>l<strong>and</strong><br />
Markku Ilj<strong>in</strong>a<br />
Geological Survey of F<strong>in</strong>l<strong>and</strong>, Rovaniemi, F<strong>in</strong>l<strong>and</strong><br />
Regional geology<br />
The oldest preserved cont<strong>in</strong>ental crust <strong>in</strong> the<br />
Fennosc<strong>and</strong>ian Shield was generated dur<strong>in</strong>g the<br />
Saamian Orogeny at 3.1–2.9 Ga (Fig. 1) <strong>and</strong> is<br />
dom<strong>in</strong>ated by gneissic tonalite, trondhjemite <strong>and</strong><br />
granodiorite. Rift- <strong>and</strong> volcanic arc-related greenstones,<br />
subduction-generated calc-alkal<strong>in</strong>e volcanic<br />
rocks <strong>and</strong> tonalitic-trondhjemitic igneous rocks<br />
were formed dur<strong>in</strong>g the Lopian Orogeny at 2.9–2.6<br />
Ga. Only a few Archaean economic to subeconom<br />
ic m<strong>in</strong>eral <strong>deposits</strong> have been found <strong>in</strong> the shield,<br />
<strong>in</strong>clud<strong>in</strong>g orogenic gold, BIF <strong>and</strong> Mo occurrences,<br />
<strong>and</strong> ultramafic-to mafic-hosted Ni-<strong>Cu</strong> (Frietsch et al.<br />
1979, Gaál 1990, Weihed et al. 2005).<br />
Dur<strong>in</strong>g the Palaeoproterozoic, Sumi-Sariolian<br />
(2.5–2.3 Ga) clastic sediments, <strong>in</strong>tercalated with<br />
volcanic rocks vary<strong>in</strong>g <strong>in</strong> composition from komatiitic<br />
<strong>and</strong> tholeiitic to calc-alkal<strong>in</strong>e <strong>and</strong> <strong>in</strong>termediate to<br />
felsic, were deposited on the deformed <strong>and</strong> metamorphosed<br />
Archaean basement dur<strong>in</strong>g extensional<br />
events. Layered <strong>in</strong>trusions, most of them with Cr,<br />
Ni, Ti, V <strong>and</strong>/or PGE occurrences, represent a major<br />
magmatic <strong>in</strong>put at 2.45–2.39 Ga (Amel<strong>in</strong> et al. 1995,<br />
Mutanen 1997, Alapieti & Laht<strong>in</strong>en 2002). Periods<br />
of arenitic sedimentation preceded <strong>and</strong> followed<br />
extensive komatiitic <strong>and</strong> basaltic volcanic stages at<br />
about 2.2, 2.13, 2.05 <strong>and</strong> 2.0 Ga <strong>in</strong> the northeastern<br />
part of the Fennosc<strong>and</strong>ian Shield dur<strong>in</strong>g extensional<br />
events (Mutanen 1997, Lehtonen et al. 1998, Rastas<br />
et al. 2001). Associated with the subaquatic extrusive<br />
<strong>and</strong> volcaniclastic units, there are carbonate<br />
rocks, graphite schist, iron formation <strong>and</strong> stratiform<br />
sulphide occurrences across the region.<br />
Svecofennian subduction-generated calcalkal<strong>in</strong>e<br />
<strong>and</strong>esites <strong>and</strong> related volcaniclastic sedimentary<br />
units were deposited around 1.9 Ga <strong>in</strong> the<br />
northern Fennosc<strong>and</strong>ia <strong>in</strong> a subaerial to shallowwater<br />
environment. In the Kiruna area, the 1.89 Ga<br />
Kiirunavaara Group rocks (formerly Kiruna Porphy<br />
9
10<br />
ries) are chemically different from the <strong>and</strong>esites <strong>and</strong><br />
are geographically restricted to this area. The Svecofennian<br />
porphyries form host to apatite-iron ores<br />
<strong>and</strong> various styles of epigenetic <strong>Cu</strong>-Au occurrences<br />
<strong>in</strong>clud<strong>in</strong>g porphyry <strong>Cu</strong>-style <strong>deposits</strong> (Weihed et al.<br />
2005).<br />
The up to 10 km thick pile of Palaeoproterozoic<br />
volcanic <strong>and</strong> sedimentary rocks was multiply<br />
deformed <strong>and</strong> metamorphosed contemporaneously<br />
with the <strong>in</strong>trusion of the 1.89–1.87 Ga granitoids.<br />
Anatectic granites were formed dur<strong>in</strong>g 1.82–1.79<br />
Ga, dur<strong>in</strong>g another major stage of deformation <strong>and</strong><br />
metamorphism. Large-scale migration of fluids of<br />
variable sal<strong>in</strong>ity dur<strong>in</strong>g the many stages of igneous<br />
activity, metamorphism <strong>and</strong> deformation is expressed<br />
by regional scapolitisation, albitisation <strong>and</strong><br />
albite-carbonate alteration <strong>in</strong> the region. For example,<br />
scapolitisation is suggested to be related to felsic<br />
<strong>in</strong>trusions (Ödman 1957), or to be an expression of<br />
mobilised evaporates from the supracrustal successions<br />
dur<strong>in</strong>g metamorphism (Tuisku 1985, Frietsch<br />
et al. 1997, Vanhanen 2001).<br />
S<strong>in</strong>ce Hietanen (1975) proposed a subduction<br />
zone dipp<strong>in</strong>g north beneath the Skellefte district,<br />
many similar models have been proposed for<br />
the ma<strong>in</strong> period of the formation of the crust dur<strong>in</strong>g<br />
the Svecokarelian (or Svecofennian) orogeny roughly<br />
between 1.95 <strong>and</strong> 1.77 Ga (e.g. Rickard & Zweifel<br />
1975, Pharaoh & Pearce 1984, Berthelsen & Marker<br />
1986, Gaál 1986, Weihed 1992). This orogeny <strong>in</strong>volved<br />
both strong rework<strong>in</strong>g of older crust with<strong>in</strong><br />
the Karelian craton <strong>and</strong>, importantly, subduction towards<br />
NE, below the Archaean, <strong>and</strong> the accretion of<br />
several volcanic arc complexes from the SW towards<br />
NE. Recently, substantially more complex models<br />
for crustal growth at this stage of the evolution of<br />
the Fennosc<strong>and</strong>ian Shield have been proposed (e.g.<br />
Nironen 1997, Laht<strong>in</strong>en et al. 2005). The most recent<br />
model for the Palaeoproterozoic tectonic evolution<br />
of the Fennosc<strong>and</strong>ian Shield <strong>in</strong>volv<strong>in</strong>g five partly<br />
overlapp<strong>in</strong>g orogenies was presented by Laht<strong>in</strong>en et<br />
al. (2005). This model builds on the amalgamation<br />
of several microcont<strong>in</strong>ents <strong>and</strong> isl<strong>and</strong> arcs with the<br />
Archaean Karelian, Kola <strong>and</strong> Norrbotten cratons <strong>and</strong><br />
Fig. 1. Simplified geological map of the Fennosc<strong>and</strong>ian<br />
Shield with major tectono-stratigraphic units<br />
discussed <strong>in</strong> text. Map based on Koist<strong>in</strong>en et al.<br />
(2001), tectonic <strong>in</strong>terpretation after Laht<strong>in</strong>en et al.<br />
(2005). LGB = Lap¬l<strong>and</strong> Greenstone Belt, CLGC<br />
= Central Lapl<strong>and</strong> Granitoid Complex, BMB =<br />
Belomorian Mobile Belt, CKC = Central Karelian<br />
Complex, IC = Iisalmi Complex, PC = Pudasjärvi<br />
Complex, TKS = Tipasjärvi–Kuhmo–Suomussalmi<br />
green¬stone complex. Shaded area, BMS =<br />
Bothnian Megashear.
other pre-1.92 Ga components. The Karelian craton<br />
experienced a long period of rift<strong>in</strong>g (2.5–2.1 Ga)<br />
that f<strong>in</strong>ally led to cont<strong>in</strong>ental break-up (c. 2.06 Ga).<br />
The microcont<strong>in</strong>ent accretion stage (1.92–1.87 Ga)<br />
<strong>in</strong>cludes the Lapl<strong>and</strong>-Kola <strong>and</strong> Lapl<strong>and</strong>-Savo orogenies<br />
(both with peak at 1.91 Ga) when the Karelian<br />
craton collided with Kola <strong>and</strong> the Norrbotten cratons,<br />
respectively. It also <strong>in</strong>cludes the Fennian orogeny<br />
(peak at c. 1.88 Ga) caused by the accretion of the<br />
Bergslagen microcont<strong>in</strong>ent <strong>in</strong> the south. The follow<strong>in</strong>g<br />
cont<strong>in</strong>ental extension stage (1.86–1.84 Ga) was<br />
caused by extension of hot crust <strong>in</strong> the h<strong>in</strong>terl<strong>and</strong>s<br />
of subduction zones located to the south <strong>and</strong> west.<br />
Oblique collision with Sarmatia occurred dur<strong>in</strong>g the<br />
Svecobaltic orogeny (1.84–1.80 Ga). After collision<br />
with Amazonia, <strong>in</strong> the west, dur<strong>in</strong>g the Nordic<br />
orogeny (1.82–1.80 Ga), orogenic collapse <strong>and</strong> stabilization<br />
of the Fennosc<strong>and</strong>ian Shield took place at<br />
1.79–1.77 Ga. The Gothian orogeny (1.73–1.55 Ga)<br />
at the southwestern marg<strong>in</strong> of the shield ended the<br />
Palaeoproterozoic orogenic development. <strong>in</strong>g cont<strong>in</strong>ental<br />
extension stage (1.86–1.84 Ga) was caused<br />
by extension of hot crust <strong>in</strong> the h<strong>in</strong>terl<strong>and</strong>s of subduction<br />
zones located to the south <strong>and</strong> west. Oblique<br />
collision with Sarmatia occurred dur<strong>in</strong>g the Svecobaltic<br />
orogeny (1.84–1.80 Ga). After collision with<br />
Amazonia, <strong>in</strong> the west, dur<strong>in</strong>g the Nordic orogeny<br />
(1.82–1.80 Ga), orogenic collapse <strong>and</strong> stabilization<br />
of the Fennosc<strong>and</strong>ian Shield took place at 1.79–1.77<br />
Ga. The Gothian orogeny (1.73–1.55 Ga) at the<br />
southwestern marg<strong>in</strong> of the shield ended the Palaeoproterozoic<br />
orogenic development.<br />
Palaeoproterozoic 2.45–1.97 Ga<br />
greenstone belts<br />
The Palaeoproterozoic Lapl<strong>and</strong> Greenstone Belt,<br />
which overlies much of the northern part of the Archaean<br />
craton, is the largest coherent greenstone terra<strong>in</strong><br />
exposed <strong>in</strong> the Fennosc<strong>and</strong>ian Shield (Fig. 1). It<br />
extends for over 500 km from the Norwegian northwest<br />
coast through the Swedish <strong>and</strong> F<strong>in</strong>nish Lapl<strong>and</strong><br />
<strong>in</strong>to the adjacent Russian Karelia <strong>in</strong> the southeast.<br />
Due to large lithostratigraphic similarities <strong>in</strong> different<br />
greenstone areas from this region <strong>and</strong> the ma<strong>in</strong>ly<br />
tholeiitic character of the volcanic rocks, Pharaoh<br />
(1985) suggested them to be coeval <strong>and</strong> represent<strong>in</strong>g<br />
a major tholeiitic prov<strong>in</strong>ce. Based on petrological<br />
<strong>and</strong> chemical studies of the mafic volcanic rocks <strong>and</strong><br />
associated sediments, an orig<strong>in</strong>ally cont<strong>in</strong>ental rift<br />
sett<strong>in</strong>g is favoured for these greenstones (e.g., Lehtonen<br />
et al. 1985, Pharaoh et al. 1987, Huhma et al.<br />
1990, Olesen & S<strong>and</strong>stad 1993, Mart<strong>in</strong>sson 1997).<br />
It <strong>in</strong>cludes the Central Lapl<strong>and</strong> Greenstone Belt <strong>and</strong><br />
Kuusamo <strong>and</strong> Peräpohja Schist Belts <strong>in</strong> F<strong>in</strong>l<strong>and</strong> <strong>and</strong><br />
the Kiruna <strong>and</strong> Masugnsbyn areas <strong>in</strong> Sweden. The<br />
lithostratigraphy of the F<strong>in</strong>nish part of the Lapl<strong>and</strong><br />
Greenstone Belt, the Central Lapl<strong>and</strong> Greenstone<br />
Belt, is presented <strong>in</strong> Fig. 2.<br />
In northern Sweden, a Palaeoproterozoic<br />
succession of greenstones, porphyries <strong>and</strong> clastic<br />
sediments rests unconformably on deformed,<br />
2.7–2.8 Ga, Archaean basement. Stratigraphically<br />
lowest is the Kovo Group. It <strong>in</strong>cludes a basal conglomerate,<br />
tholeiitic lava, calc-alkal<strong>in</strong>e basic to <strong>in</strong>termediate<br />
volcanic rocks <strong>and</strong> volcaniclastic sediments.<br />
Sedimentary rocks were deposited along a<br />
coastl<strong>in</strong>e of a mar<strong>in</strong>e rift bas<strong>in</strong>, <strong>and</strong> material <strong>in</strong>put<br />
was provided through a number of alluvial fans<br />
(Kumpula<strong>in</strong>en 2000). The Kovo Group is overla<strong>in</strong><br />
by the Kiruna Greenstone Group which is dom<strong>in</strong>ated<br />
by mafic to ultramafic volcanic rocks. An albite diabase<br />
(albitised dolerite), <strong>in</strong>trud<strong>in</strong>g the lower part of<br />
the Kovo Group, has been dated at 2.18 Ga (Skiöld<br />
1986), <strong>and</strong> gives a m<strong>in</strong>imum depositional age for<br />
this unit. The Kovo Group is suggested to be c. 2.5–<br />
2.3 Ga <strong>in</strong> age (Sumi-Sariolan) whereas the Kiruna<br />
Greenstone Group is suggested to be 2.2–2.0 Ga <strong>in</strong><br />
age (Jatulian <strong>and</strong> Ludikowian). The upper contacts of<br />
the Kovo Group <strong>and</strong> the Kiruna Greenstone Group<br />
are characterised by m<strong>in</strong>or unconformities <strong>and</strong> clasts<br />
from these units are found <strong>in</strong> basal conglomerates <strong>in</strong><br />
overly<strong>in</strong>g units.<br />
In F<strong>in</strong>l<strong>and</strong>, the lowermost units of the greenstones<br />
also lie unconformably on the Archaean, <strong>and</strong><br />
are represented by the Salla Group rocks <strong>in</strong> the<br />
Central Lapl<strong>and</strong> Greenstone Belt (CLGB; Fig. 2), a<br />
polymictic conglomerate <strong>in</strong> the Kuusamo Schist Belt<br />
<strong>and</strong> the Sompujärvi Formation of the Peräpohja Schist<br />
Belt. Recently, a new group, the Vuojärvi Group was<br />
recognized <strong>in</strong> CLGB area (Fig. 2). This consists of<br />
quartz-feldspar <strong>and</strong> quartz-sericite schists that may<br />
represent metamorphosed clastic sedimentary rocks<br />
<strong>and</strong>/or felsic volcanic rocks. The current stratigraphic<br />
relation between the Vuojärvi <strong>and</strong> Salla Groups<br />
is uncerta<strong>in</strong>. The Vuojärvi <strong>and</strong> Salla Groups is followed<br />
by sedimentary units which precede the c. 2.2<br />
Ga igneous event <strong>and</strong> comprise the Kuusamo <strong>and</strong><br />
Sodankylä Group rocks <strong>in</strong> the CLGB <strong>and</strong> the Kuusamo<br />
schist belt. The latter lithostratigraphic group<br />
also hosts most of the known Palaeoproterozoic syngenetic<br />
sulphide occurrences <strong>in</strong> the CLGB.<br />
The Savukoski Group mafic to ultramafic<br />
volcanic <strong>and</strong> shallow-mar<strong>in</strong>e sedimentary units<br />
were deposited dur<strong>in</strong>g 2.2–2.01 Ga <strong>in</strong> the CLGB,<br />
<strong>and</strong> similar units were also formed <strong>in</strong> the Kuusamo<br />
<strong>and</strong> Peräpohja belts (Lehtonen et al. 1998, Rastas<br />
et al. 2001). Age determ<strong>in</strong>ations of the Palaeo<br />
proterozoic greenstones exist ma<strong>in</strong>ly from F<strong>in</strong>l<strong>and</strong><br />
(e.g. Perttunen & Vaasjoki 2001, Rastas et al. 2001,<br />
Väänänen & Lehtonen 2001) <strong>and</strong> suggests a major<br />
11
12<br />
magmatic <strong>and</strong> rift<strong>in</strong>g event at c. 2.1 Ga with the f<strong>in</strong>al<br />
break up tak<strong>in</strong>g place at c. 2.06 Ga. Extensive occurrence<br />
of 2.13 <strong>and</strong> 2.05 Ga dolerites also support<br />
these dates. Thick piles of mantle-derived volcanic<br />
rocks <strong>in</strong>clud<strong>in</strong>g komatiitic <strong>and</strong> picritic high-temperature<br />
melts are restricted to the Kittilä-Karasjok-<br />
Kautoke<strong>in</strong>o-Kiruna area <strong>and</strong> are suggested to represent<br />
plume-generated volcanism (Mart<strong>in</strong>sson 1997).<br />
The rift<strong>in</strong>g of the Archaean craton, along a l<strong>in</strong>e <strong>in</strong> a<br />
NW-direction from Ladoga to Lofoten, was accompanied<br />
by NW-SE <strong>and</strong> NE-SW directed rift bas<strong>in</strong>s<br />
(Saverikko 1990) <strong>and</strong> <strong>in</strong>jection of 2.1 Ga trend<strong>in</strong>g<br />
dyke swarms parallel to these (Vuollo 1994). Eruption<br />
of N-MORB pillow lava occurred along the rift<br />
marg<strong>in</strong>s (e.g., Åhman 1957, Pekkar<strong>in</strong>en & Lukkar<strong>in</strong>en<br />
1991). The Kiruna greenstones <strong>and</strong> dyke swarms<br />
north of Kiruna outl<strong>in</strong>e a NNE-trend<strong>in</strong>g magmatic<br />
belt extend<strong>in</strong>g to Alta <strong>and</strong> Repparfjord <strong>in</strong> the northernmost<br />
Norway. This belt is almost perpendicular<br />
to the major rift, <strong>and</strong> may represent a failed rift arm<br />
related to a triple junction south of Kiruna (Mart<strong>in</strong>sson<br />
1997). The rapid bas<strong>in</strong> subsidence, accompanied<br />
by eruption of a 500–2000 m thick unit of MORBtype<br />
pillow lava is suggested to be an expression of<br />
the development of this rift arm.<br />
Rift<strong>in</strong>g culm<strong>in</strong>ated <strong>in</strong> extensive mafic <strong>and</strong><br />
ultramafic volcanism <strong>and</strong> the formation of oceanic<br />
crust at c. 1.97 Ga. This is <strong>in</strong>dicated by the extensive<br />
komatiitic <strong>and</strong> basaltic lavas of the Kittilä Group of<br />
the CLGB <strong>in</strong> the central parts of the F<strong>in</strong>nish Lapl<strong>and</strong><br />
Fig. 2. Stratigraphy of the Central Lapl<strong>and</strong> greenstone belt.<br />
After Hanski et al. (2001) <strong>and</strong> the <strong>2011</strong> version of the GTK digital bedrock database.<br />
(Fig. 2). The 1.97 Ga stage also <strong>in</strong>cluded deposition<br />
of shallow- to deep-mar<strong>in</strong>e sediments, the latter<br />
<strong>in</strong>dicat<strong>in</strong>g the most extensive rift<strong>in</strong>g <strong>in</strong> the region.<br />
Fragments of oceanic crust were subsequently emplaced<br />
back onto the Karelian craton <strong>in</strong> F<strong>in</strong>l<strong>and</strong>, as<br />
<strong>in</strong>dicated by the Nuttio ophiolites <strong>in</strong> central F<strong>in</strong>nish<br />
Lapl<strong>and</strong> <strong>and</strong> the Jormua <strong>and</strong> Outokumpu ophiolites<br />
further south (Kont<strong>in</strong>en 1987, Sorjonen-Ward et al.<br />
1997, Lehtonen et al. 1998).<br />
Svecofennian complexes<br />
The Palaeoproterozoic greenstones are overla<strong>in</strong> by<br />
volcanic <strong>and</strong> sedimentary rocks compris<strong>in</strong>g several<br />
different but stratigraphically related units. Regionally,<br />
they exhibit considerable variation <strong>in</strong> lithological<br />
composition due to partly rapid changes from<br />
volcanic- to sedimentary-dom<strong>in</strong>ated facies. Stratigraphically<br />
lowest <strong>in</strong> the Kiruna area are rocks of<br />
the Porphyrite Group <strong>and</strong> the Kurravaara Conglomerate.<br />
The former represents a volcanic-dom<strong>in</strong>ated<br />
unit <strong>and</strong> the latter is a ma<strong>in</strong>ly epiclastic unit (Offerberg<br />
1967) deposited as one or two fan deltas<br />
(Kumpula<strong>in</strong>en 2000). The Sammakkovaara Group<br />
<strong>in</strong> northeastern Norrbotten comprises a mixed volcanic-epiclastic<br />
sequence that is <strong>in</strong>terpreted to be stratigraphically<br />
equivalent to the Porphyrite Group <strong>and</strong><br />
the Kurravaara Conglomerate, <strong>and</strong> the Pahakurkio<br />
Group, south of Masugnsbyn. The Muorjevaara
Group <strong>in</strong> the Gällivare area is also considered to be<br />
equivalent to the Sammakkovaara Group <strong>in</strong> the Pajala<br />
area <strong>and</strong> is dom<strong>in</strong>ated by <strong>in</strong>termediate volcaniclastic<br />
rocks <strong>and</strong> epiclastic sediments. In the Kiruna<br />
area, these volcanic <strong>and</strong> sedimentary units are overla<strong>in</strong><br />
by the Kiirunavaara Group that is followed by<br />
the Hauki <strong>and</strong> Maattavaara quartzites constitut<strong>in</strong>g<br />
the uppermost Svecofennian units <strong>in</strong> the area.<br />
In northern F<strong>in</strong>l<strong>and</strong>, pelitic rocks <strong>in</strong> the<br />
Lapl<strong>and</strong> Granulite Belt were deposited after 1.94<br />
Ga (Tuisku & Huhma 2006). Svecofennian units<br />
are ma<strong>in</strong>ly represented by the Kumpu Group <strong>in</strong> the<br />
CLGB (Lehtonen et al. 1998) <strong>and</strong> by the Paakkola<br />
Group <strong>in</strong> the Peräpohja area (Perttunen & Vaasjoki<br />
2001). The molasse-like conglomerates <strong>and</strong> quartzites<br />
compris<strong>in</strong>g the Kumpu Group were deposited <strong>in</strong><br />
deltaic <strong>and</strong> fluvial fan environments after 1913 Ma <strong>and</strong><br />
before c. 1800 Ma (Rastas et al. 2001). The Kumpu<br />
rocks apparently are equivalent to the Hauki <strong>and</strong><br />
Maattavaara quartzites, <strong>and</strong> Porphyrite Group rocks<br />
<strong>and</strong> the Kurravaara Conglomerate of the Kiruna area.<br />
With the present knowledge of ages <strong>and</strong> petrochemistry<br />
of the Porphyrite <strong>and</strong> Kumpu Groups,<br />
it is possible to attribute these rocks completely to<br />
the same event of collisional tectonics <strong>and</strong> juvenile<br />
convergent marg<strong>in</strong> magmatism. This period of convergence<br />
was manifested by the numerous <strong>in</strong>trusions<br />
of Jörn- (south of the craton marg<strong>in</strong>) <strong>and</strong> Hapar<strong>and</strong>a-<br />
(with<strong>in</strong> the craton) type calc-alkal<strong>in</strong>e <strong>in</strong>trusions, as<br />
described by Mellqvist et al. (2003). With<strong>in</strong> a few<br />
million years, this period of convergent marg<strong>in</strong> magmatism<br />
was followed by a rapid uplift recorded <strong>in</strong><br />
extensive conglomeratic units, more alkal<strong>in</strong>e <strong>and</strong><br />
terrestrial volcanism (Vargfors-Arvidsjaur Groups<br />
south of the craton marg<strong>in</strong> <strong>and</strong> the Kiirunavaara<br />
Group with<strong>in</strong> the craton) <strong>and</strong> plutonism (Gallejaur-<br />
Arvidsjaur type south of the craton marg<strong>in</strong>, Perthite<br />
Monzonite Suite with<strong>in</strong> the craton). This took place<br />
between 1.88 <strong>and</strong> 1.86 Ga <strong>and</strong> the ma<strong>in</strong> volcanic<br />
episode probably lasted less than 10 million years.<br />
The evolution after c. 1.86 is ma<strong>in</strong>ly recorded<br />
by an extensive S-type magmatism (c. 1.85 Ga<br />
Jyryjoki, <strong>and</strong> 1.81–1.78 Ga L<strong>in</strong>a-type <strong>and</strong> the Central<br />
Lapl<strong>and</strong> Granitoid Complex) derived from anatectic<br />
melts <strong>in</strong> the middle crust. In the western part of the<br />
shield, extensive I- to A-type magmatism (Revsund-<br />
Sorsele type) formed roughly N-S trend<strong>in</strong>g batholiths<br />
(the Transc<strong>and</strong><strong>in</strong>avian Igneous Belt) coeval with the<br />
S-type magmatism. Scattered <strong>in</strong>trusions of this type<br />
<strong>and</strong> age also occur further east (e.g. Edefors <strong>in</strong> Sweden,<br />
Nattanen <strong>in</strong> F<strong>in</strong>l<strong>and</strong>). The period from c. 1.87<br />
to 1.80 Ga possibly also <strong>in</strong>volved a shift <strong>in</strong> orogenic<br />
vergence from NE-SW to E-W <strong>in</strong> the northern part<br />
of the Shield as suggested by Weihed et al. (2002).<br />
Palaeoproterozoic magmatism<br />
Early rift<strong>in</strong>g <strong>and</strong> emplacement<br />
of layered igneous complexes<br />
The beg<strong>in</strong>n<strong>in</strong>g of the rift<strong>in</strong>g period between 2.51<br />
<strong>and</strong> 2.43 Ga is <strong>in</strong>dicated by <strong>in</strong>trusion of numerous<br />
layered mafic igneous complexes (Alapieti et<br />
al. 1990, Weihed et al. 2005). Most of the <strong>in</strong>trusions<br />
are located along the marg<strong>in</strong> of the Archaean<br />
granitoid area, either at the boundary aga<strong>in</strong>st the<br />
Proterozoic supracrustal sequence, totally enclosed<br />
by Archaean granitoid, or enclosed by a Proterozoic<br />
supracrustal sequence. Most of the <strong>in</strong>trusions<br />
are found <strong>in</strong> W-trend<strong>in</strong>g Tornio-Näränkävaara belt<br />
of layered <strong>in</strong>trusions (Ilj<strong>in</strong>a & Hanski 2005). Rest<br />
of the <strong>in</strong>trusions are found <strong>in</strong> NW Russia, central<br />
F<strong>in</strong>nish Lapl<strong>and</strong> <strong>and</strong> NW F<strong>in</strong>l<strong>and</strong>. These Palaeoproterozoic<br />
layered <strong>in</strong>trusions are characteristic to<br />
northern F<strong>in</strong>l<strong>and</strong> as only one of them, the Tornio<br />
<strong>in</strong>trusion, be<strong>in</strong>g partly on the Swedish side of the<br />
border. Alapieti <strong>and</strong> Laht<strong>in</strong>en (2002) divided the<br />
<strong>in</strong>trusions <strong>in</strong>to three types, (1) ultramafic–mafic, (2)<br />
mafic <strong>and</strong> (3) <strong>in</strong>termediate megacyclic. They also <strong>in</strong>terpret<br />
the ultramafic–mafic <strong>and</strong> the lowermost part<br />
of the megacyclic type to have crystallised from a<br />
similar, quite primitive magma type, which is characterised<br />
by slightly negative <strong>in</strong>itial e Nd values <strong>and</strong><br />
relatively high MgO <strong>and</strong> Cr, <strong>in</strong>termediate SiO 2, <strong>and</strong><br />
low TiO 2 concentrations, resembl<strong>in</strong>g the bon<strong>in</strong>itic<br />
magma type. The upper parts of megacyclic type<br />
<strong>in</strong>trusions <strong>and</strong> most mafic <strong>in</strong>trusions crystallised<br />
from an evolved Ti-poor, Al-rich basaltic magma.<br />
Amel<strong>in</strong> et al. (1995) suggested two age<br />
groups for the <strong>in</strong>trusions for Fennosc<strong>and</strong>ian Shield,<br />
the first with U–Pb ages at 2.505–2.501 Ga, <strong>and</strong> the<br />
second at 2.449–2.430 Ga. All F<strong>in</strong>nish layered <strong>in</strong>trusions<br />
belong to the younger age group. The <strong>in</strong>trusions<br />
were later deformed <strong>and</strong> metamorphosed dur<strong>in</strong>g<br />
the Svecofennian orogeny.<br />
Mafic dykes<br />
Mafic dykes are locally abundant <strong>and</strong> show a variable<br />
strike, degree of alteration <strong>and</strong> metamorphic<br />
recrystallisation which, with age dat<strong>in</strong>g, <strong>in</strong>dicate<br />
multiple igneous episodes. Albite diabase (a term<br />
commonly used <strong>in</strong> F<strong>in</strong>l<strong>and</strong> <strong>and</strong> Sweden for any albitised<br />
dolerite) is a characteristic type of <strong>in</strong>trusions<br />
that form up to 200 m thick sills. They have a coarsegra<strong>in</strong>ed<br />
central part dom<strong>in</strong>ated by albitic plagioclase<br />
<strong>and</strong> constitute laterally extensive, highly magnetic<br />
units north of Kiruna.<br />
Extensive dyke swarms occur <strong>in</strong> the Archaean<br />
doma<strong>in</strong> north of Kiruna; the swarms are dom<strong>in</strong>ated<br />
by 1–100 m wide dykes with a metamorphic m<strong>in</strong>eral<br />
assemblage but with a more or less preserved<br />
igneous texture (Ödman 1957, Mart<strong>in</strong>sson 1999a,b).<br />
The NNE-trend<strong>in</strong>g dykes that are suggested to represent<br />
feeders to the Kiruna Greenstone Group (Mar-<br />
13
14<br />
t<strong>in</strong>sson 1997, 1999a,b). Scapolite-biotite alteration<br />
is common <strong>in</strong> the dykes with<strong>in</strong> Svecofennian rocks<br />
(Offerberg 1967) <strong>and</strong> also <strong>in</strong> feeder dykes with<strong>in</strong><br />
the lower part of the Kiruna Greenstone Group<br />
(Mart<strong>in</strong>sson 1997).<br />
In northern F<strong>in</strong>l<strong>and</strong>, albite diabases, both<br />
sills <strong>and</strong> dykes, form age groups of 2.2, 2.13, 2.05<br />
<strong>and</strong> 2.0 Ga (Vuollo 1994, Lehtonen et al. 1998, Perttunen<br />
& Vaasjoki 2001, Rastas et al. 2001). These<br />
dates also reflect extrusive magmatism <strong>in</strong> the region.<br />
The dykes vary <strong>in</strong> width from
orig<strong>in</strong> is supported by the abundant occurrence of<br />
mafic-ultramafic complexes northwest of Kiruna,<br />
which possibly def<strong>in</strong>e the plume centre.<br />
L<strong>in</strong>a Suite<br />
Intrusions of the L<strong>in</strong>a Suite are extensive <strong>in</strong> northern<br />
Norrbotten where they typically occur as granite,<br />
pegmatite <strong>and</strong> aplite of ma<strong>in</strong>ly m<strong>in</strong>imum melt<br />
composition generated by crustal melt<strong>in</strong>g. In F<strong>in</strong>l<strong>and</strong>,<br />
they appear to form most of the volume of the<br />
Central Lapl<strong>and</strong> Granitoid Complex (Fig. 1), <strong>and</strong><br />
are also present as smaller <strong>in</strong>trusions <strong>in</strong> many areas<br />
across northern F<strong>in</strong>l<strong>and</strong> (Lehtonen et al. 1998). However,<br />
the seismic appearance of the Central Lapl<strong>and</strong><br />
Granitoid Complex is <strong>in</strong>consistent with this area as<br />
an <strong>in</strong>trusion-rich belt, <strong>and</strong> it may have a composition<br />
comparable with the supracrustal belts to the north<br />
<strong>and</strong> south (Patison et al. 2006). The L<strong>in</strong>a Suite is<br />
composed of monzo-, syeno-granites, <strong>and</strong> adamellite,<br />
<strong>and</strong> is characterised by its restricted SiO 2 range<br />
at 72–76 wt. %. It is peralum<strong>in</strong>ous <strong>and</strong> a high content<br />
of Rb <strong>and</strong> depletion of Eu are characteristic.<br />
The heat source generat<strong>in</strong>g the magmas<br />
might be the cont<strong>in</strong>ent-cont<strong>in</strong>ent collision events<br />
to the south <strong>and</strong> west (Öhl<strong>and</strong>er et al. 1987b, Öhl<strong>and</strong>er<br />
& Skiöld 1994, Laht<strong>in</strong>en et al. 2005) or the<br />
contemporaneous TIB 1 magmatism (Åhäll & Larsson<br />
2000). Age determ<strong>in</strong>ations <strong>in</strong>dicate a relatively<br />
large span <strong>in</strong> the emplacement age at 1.81–1.78 Ga<br />
for the L<strong>in</strong>a Suite (Huhma 1986, Skiöld et al. 1988,<br />
Wikström <strong>and</strong> Persson 1997b, Perttunen & Vaasjoki<br />
2001, Rastas et al. 2001, Väänänen & Lehtonen<br />
2001, Bergman et al. 2002).<br />
A- <strong>and</strong> I-type <strong>in</strong>trusions<br />
This is the youngest of the described <strong>in</strong>trusive suites<br />
<strong>and</strong>, <strong>in</strong> the west, it forms part of the Transc<strong>and</strong><strong>in</strong>avian<br />
Igneous Belt (TIB). Two generations (c. 1.8<br />
<strong>and</strong> 1.7 Ga) of <strong>in</strong>trusions belong<strong>in</strong>g to the TIB exist<br />
<strong>in</strong> northern Sweden <strong>and</strong> adjacent areas of Norway.<br />
They commonly show quartz-poor monzonitic<br />
trends, <strong>and</strong> gabbroic-dioritic-granitic components<br />
are relatively common. (Romer et al. 1992, 1994,<br />
Öhl<strong>and</strong>er & Skiöld 1994)<br />
Across northern F<strong>in</strong>l<strong>and</strong>, the suite is represented<br />
by the Nattanen-type granitic <strong>in</strong>trusions dated<br />
at 1.80–1.77 Ga (Huhma 1986, Rastas et al. 2001).<br />
They form undeformed <strong>and</strong> unmetamorphosed, multiphase,<br />
peralum<strong>in</strong>ous, F-rich plutons which sharply<br />
cut across their country rocks. Their Nd <strong>and</strong> Hf isotopic<br />
ratios <strong>in</strong>dicate a substantial Archaean component<br />
<strong>in</strong> their source.<br />
In northern Norrbotten, monzonitic to syenitic<br />
rocks give ages between 1.80 <strong>and</strong> 1.79 (Romer<br />
et al 1994, Bergman et al. 2001), whereas granites<br />
range from 1.78–1.77 <strong>and</strong> 1.72–1.70 Ga (Romer<br />
et al. 1992). Further south, the age of the granitic<br />
Ale massif <strong>in</strong> the Luleå area is 1802±3 Ma <strong>and</strong><br />
1796±2 Ma for the core <strong>and</strong> the rim of the massif,<br />
respectively (Öhl<strong>and</strong>er & Schöberg 1991). This is<br />
similar to the 1.80 Ga age of Edefors type monzonitic<br />
to granitic rocks (Öhl<strong>and</strong>er & Skiöld 1994).<br />
This suite can be classified as a quartz<br />
monzodiorite–quartz monzonite–adamellite–granite<br />
suite <strong>and</strong> shows a metalum<strong>in</strong>ous to peralum<strong>in</strong>ous<br />
trend with alkal<strong>in</strong>e aff<strong>in</strong>ity (Ahl et al. 2001). Lithophile<br />
elements are enriched <strong>in</strong> this suite, e.g. Zr is<br />
strongly enriched <strong>in</strong> the Edefors granitoids (Öhl<strong>and</strong>er<br />
& Skiöld 1994).<br />
Characteristic for the 1.8 Ga monzonitic to<br />
syenitic rocks is the occurrence of augite <strong>and</strong> locally<br />
also orthopyroxene <strong>and</strong> oliv<strong>in</strong>e demonstrat<strong>in</strong>g an<br />
orig<strong>in</strong> from dry magmas (Ödman 1957, Öhl<strong>and</strong>er &<br />
Skiöld 1994, Bergman et al. 2001). The Transsc<strong>and</strong><strong>in</strong>avian<br />
Igneous Belt (TIB) has been suggested to have<br />
formed <strong>in</strong> response to eastward subduction (Wilson<br />
1980, Nyström 1982, Andersson 1991, Romer et al.<br />
1992, Weihed et al. 2002), possibly dur<strong>in</strong>g a period<br />
of extensional conditions (Wilson et al. 1986, Åhäll<br />
& Larsson 2000). The Edefors granitoids are <strong>in</strong>terpreted<br />
as products of plate convergence <strong>and</strong> a mantle<br />
source is suggested for these rocks based on Sm-Nd<br />
isotopic characteristics. Mafic magmas may have<br />
formed by mantle melt<strong>in</strong>g <strong>in</strong> an extensional sett<strong>in</strong>g<br />
caused by a 1.8 Ga collisional event follow<strong>in</strong>g northward<br />
subduction. These magmas were subsequently<br />
contam<strong>in</strong>ated with cont<strong>in</strong>ental crust <strong>and</strong> crystallised<br />
as monzonitic to granitic rocks (Öhl<strong>and</strong>er & Skiöld<br />
1994).<br />
The related plate-tectonic sett<strong>in</strong>g may also<br />
be that of the f<strong>in</strong>al orogenic collapse, decompression<br />
<strong>and</strong>/or thermal resett<strong>in</strong>g <strong>in</strong> the term<strong>in</strong>al stages of<br />
the orogenic development, follow<strong>in</strong>g the cont<strong>in</strong>entcont<strong>in</strong>ent<br />
collisional stage (Laht<strong>in</strong>en et al. 2005)<br />
Deformation <strong>and</strong> metamorphism<br />
The Palaeoproterozoic rocks <strong>in</strong> the northern part of<br />
the Fennosc<strong>and</strong>ian Shield have undergone several<br />
phases of deformation <strong>and</strong> metamorphism. Metamorphic<br />
grades vary from greenschist to granulite<br />
facies.<br />
A sequence of ductile deformation events<br />
<strong>in</strong> central F<strong>in</strong>nish Lapl<strong>and</strong> is reported <strong>in</strong> Hölttä et<br />
al. (2007) <strong>and</strong> Patison (2007) <strong>and</strong> references there<strong>in</strong>.<br />
The earliest foliation (S1) is bedd<strong>in</strong>g-parallel <strong>and</strong><br />
can be seen <strong>in</strong> F2 fold h<strong>in</strong>ges <strong>and</strong> as <strong>in</strong>clusion trails<br />
<strong>in</strong> <strong>and</strong>alusite, garnet <strong>and</strong> staurolite porphyroblasts.<br />
The ma<strong>in</strong> regional foliation S2 is axial planar to tight<br />
15
16<br />
or isocl<strong>in</strong>al folds. It is mostly gently dipp<strong>in</strong>g to flat-.<br />
ly<strong>in</strong>g, <strong>and</strong> suggested to have been caused by horizontal<br />
movements related to thrust tectonics, e.g. along<br />
the Sirkka Shear Zone. The elongation l<strong>in</strong>eation generally<br />
trends NNE-SSW, <strong>and</strong> the movement direction<br />
was from SSW to NNE. The S-dipp<strong>in</strong>g Sirkka<br />
Shear Zone is composed of several sub-parallel<br />
thrusts <strong>and</strong> fold structures at the southern marg<strong>in</strong><br />
of the Central Lapl<strong>and</strong> Greenstone Belt. This NNEdirected<br />
thrust<strong>in</strong>g occurred dur<strong>in</strong>g D1-D2, with a<br />
maximum age of c. 1.89 Ga (Lehtonen et al. 1998),<br />
<strong>and</strong> was contemporaneous with S- to SW-directed<br />
thrust<strong>in</strong>g of the Lapl<strong>and</strong> Granulite Belt <strong>in</strong> the north.<br />
This thrust<strong>in</strong>g geometry is consistent with data<br />
from recent seismic reflection studies (Patison et al.<br />
2006). The D2 <strong>and</strong> earlier structures are overpr<strong>in</strong>ted<br />
by sets of late folds, collectively called F3-folds,<br />
with a variety of orientations. It is possible that some<br />
earlier-formed structures were reactivated dur<strong>in</strong>g<br />
D3. A m<strong>in</strong>imum age for the D3 deformation is given<br />
by post-collisional 1.77 Ga Nattanen-type granites.<br />
This age is also the maximium age for D4, which is<br />
characterised by discont<strong>in</strong>uous brittle shear zones.<br />
Ductile deformation <strong>in</strong> Sweden <strong>in</strong>cludes at<br />
least three phases of fold<strong>in</strong>g <strong>and</strong> also <strong>in</strong>volves the<br />
formation of major crustal-scale shear zones. The<br />
<strong>in</strong>tensity of deformation varies from a strong penetrative<br />
foliation to texturally <strong>and</strong> structurally well<br />
preserved rocks both regionally <strong>and</strong> on a local scale.<br />
Axial surface trace of the folds ma<strong>in</strong>ly trends <strong>in</strong> a SE<br />
or a SSW direction (Bergman et al. 2001). Locally,<br />
they <strong>in</strong>terfere <strong>in</strong> a dome <strong>and</strong> bas<strong>in</strong> pattern but more<br />
commonly either trend is dom<strong>in</strong>ant. The difference<br />
<strong>in</strong> the <strong>in</strong>tensity of deformation shown by <strong>in</strong>trusions<br />
of the Hapar<strong>and</strong>a Suite <strong>and</strong> the Perthite Monzonite<br />
Suite suggests an event of regional metamorphism<br />
<strong>and</strong> deformation at c. 1.88 Ga <strong>in</strong> northern Norrbotten<br />
(Bergman et al. 2001), correspond<strong>in</strong>g to D1–D2<br />
<strong>in</strong> F<strong>in</strong>l<strong>and</strong>. Evidence for an episode of magmatism,<br />
ductile deformation <strong>and</strong> metamorphism at c. 1.86–<br />
1.85 Ga from the Pajala area <strong>in</strong> the northeastern part<br />
of Norrbotten has been presented by Bergman et al.<br />
(2006). A third metamorphic event at 1.82–1.78 Ga<br />
is recorded by chronological data from zircon <strong>and</strong><br />
monazite <strong>in</strong> the same area. Movement along the Pajala-Kolari<br />
Shear Zone occurred dur<strong>in</strong>g this event.<br />
Major ductile shear zones <strong>in</strong> Sweden are represented<br />
by the NNE-trend<strong>in</strong>g Karesu<strong>and</strong>o-Arjeplog<br />
deformation zone, the N to NNE-directed Pajala-<br />
Kolari Shear Zone <strong>and</strong> the NNW-directed Nautanen<br />
deformation zone. The Pajala-Kolari Shear Zone has<br />
been given a major significance as represent<strong>in</strong>g the<br />
boundary between the Karelian <strong>and</strong> Norrbotten Cratons<br />
(Laht<strong>in</strong>en et al. 2005). These major shear zones<br />
show evidences to have been active at c. 1.8 Ga. In<br />
general the shear zones <strong>in</strong> the western part show a<br />
western-side-up movement whereas the shear<br />
zones <strong>in</strong> the eastern northern Norrbotten are characterised<br />
by an eastern-side-up movement (Bergman<br />
et al. 2001).<br />
One strik<strong>in</strong>g feature is that several of the<br />
crustal-scale shear zones are associated with abrupt<br />
changes <strong>in</strong> metamorphic grade, <strong>in</strong>dicat<strong>in</strong>g that these<br />
zones have been active after the peak of regional<br />
metamorphism. Moreover, many of the epigenetic<br />
Au <strong>and</strong> <strong>Cu</strong>-Au <strong>deposits</strong> also show a strong spatial<br />
relationship with these major shear zones, although<br />
their local control are the second- to fourth-order<br />
faults <strong>and</strong> shear zones. Geochronology <strong>and</strong> structural<br />
evidence <strong>in</strong>dicate late- to post-peak metamorphic<br />
conditions for many of the epigenetic <strong>Cu</strong>-Au<br />
occurrences <strong>in</strong> Sweden, whereas close to syn-peak<br />
metamorphic tim<strong>in</strong>g has been suggested for most<br />
of the occurrences <strong>in</strong> F<strong>in</strong>l<strong>and</strong> (Mänttäri 1995, Eilu<br />
et al. 2003), although very few age dates exist for<br />
m<strong>in</strong>eralisation <strong>in</strong> F<strong>in</strong>l<strong>and</strong><br />
The metamorphic grade ma<strong>in</strong>ly is of low-<br />
to <strong>in</strong>termediate- pressure type, <strong>in</strong> Sweden generally<br />
vary<strong>in</strong>g from upper-greenschist to upper-amphibolite<br />
<strong>and</strong> <strong>in</strong> F<strong>in</strong>l<strong>and</strong> from lower-greenschist to<br />
upper-amphibolite facies. Granulite facies rocks<br />
are only of m<strong>in</strong>or importance, except for the northern<br />
F<strong>in</strong>nish Lapl<strong>and</strong> <strong>and</strong> Kola Pen<strong>in</strong>sula with<strong>in</strong> the<br />
arcuate Lapl<strong>and</strong> Granulite Belt (Fig. 1).<br />
Regional metamorphic assemblages <strong>in</strong><br />
metaargillites <strong>and</strong> mafic metavolcanic rocks, <strong>in</strong>terpreted<br />
to be of Svecofennian age <strong>and</strong> generally <strong>in</strong>dicate<br />
that the metamorphism is of low to medium<br />
pressure type, 2–4 <strong>and</strong> 6–7.5 kbar, under temperatures<br />
of 510–570°C <strong>and</strong> 615–805°C, respectively.<br />
High T–low P regional metamorphism characterise<br />
large areas of Norrbotten, but as po<strong>in</strong>ted out by<br />
Bergman et al. (2001), the measured pressures <strong>and</strong><br />
temperatures are not constra<strong>in</strong>ed <strong>in</strong> time <strong>and</strong> could<br />
be related to different metamorphic events. Still<br />
the geochronology of the metamorphic history <strong>in</strong><br />
northern Sweden is rather sparse <strong>and</strong> the distribution<br />
<strong>in</strong> time <strong>and</strong> space is not well-known. Bergman<br />
et al. (2001) divided the pre-1.88 Ga rocks<br />
<strong>in</strong> northernmost Sweden <strong>in</strong>to low-, medium- <strong>and</strong><br />
high-grade areas follow<strong>in</strong>g the def<strong>in</strong>itions of W<strong>in</strong>kler<br />
(1979). It is <strong>in</strong>terest<strong>in</strong>g to note that most of<br />
the low-grade areas there (i.e. Kiruna, Rensjön <strong>and</strong><br />
Stora Sjöfallet) are located <strong>in</strong> the westernmost part<br />
of Norrbotten whereas the majority of medium to<br />
high grade metamorphic rocks are located <strong>in</strong> the<br />
central to eastern part where also the vast majority<br />
of the L<strong>in</strong>a type granites (c. 1.81 to 1.78 Ga) are<br />
situated. The strong spatial relationship between<br />
the higher-grade metamorphic rocks <strong>and</strong> the Stype<br />
granites is either a result of deeper erosional<br />
level of the crust <strong>in</strong> these areas or reflects areas
affected by higher heat flow at c. 1.8 Ga.<br />
In central F<strong>in</strong>nish Lapl<strong>and</strong>, the follow<strong>in</strong>g<br />
metamorphic zones have been mapped (Hölttä et al.<br />
2007): I) granulite facies migmatitic amphibolites<br />
south of the Lapl<strong>and</strong> Granulite Belt, II) high pressure<br />
mid-amphibolite facies rocks south of the zone<br />
I, characterised by garnet-kyanite-biotite-muscovite<br />
assemblages with local migmatisation <strong>in</strong> metapelites,<br />
<strong>and</strong> garnet-hornblende-plagioclase assemblages <strong>in</strong><br />
mafic rocks, III) low-pressure mid-amphibolite facies<br />
rocks south of the zone II, with garnet-<strong>and</strong>alusite-staurolite-chlorite-muscovite<br />
assemblages with<br />
retrograde chloritoid <strong>and</strong> kyanite <strong>in</strong> metapelites,<br />
<strong>and</strong> hornblende-plagioclase-quartz±garnet <strong>in</strong> metabasites,<br />
IV) greenschist facies rocks of the Central<br />
Lapl<strong>and</strong> Greenstone Belt, with f<strong>in</strong>e-gra<strong>in</strong>ed white<br />
mica-chlorite-biotite-albite-quartz <strong>in</strong> metapelites,<br />
<strong>and</strong> act<strong>in</strong>olite-albite-chlorite-epidote-carbonate <strong>in</strong><br />
metabasites, V) prograde metamorphism south of<br />
the zone IV from lower-amphibolite (<strong>and</strong>alusitekyanite-staurolite-muscovite-chlorite±chloritoid<br />
schists), to mid-amphibolite facies (kyanite-<strong>and</strong>alus-<br />
Iron oxide <strong>and</strong> iron oxide-<strong>Cu</strong>-Au<br />
<strong>deposits</strong> <strong>in</strong> the Kolari-Pajala district<br />
Tero Niiranen<br />
Geological Survey of F<strong>in</strong>l<strong>and</strong>, Rovaniemi, F<strong>in</strong>l<strong>and</strong><br />
Introduction<br />
The Kolari (F<strong>in</strong>l<strong>and</strong>) <strong>and</strong> Pajala (Sweden) areas<br />
have long been known for their iron <strong>deposits</strong>. Earliest<br />
records for the exploration <strong>and</strong> m<strong>in</strong><strong>in</strong>g of the<br />
iron oxide <strong>deposits</strong> <strong>in</strong> the district are from 17th<br />
century (Hiltunen, 1982). Small scale m<strong>in</strong><strong>in</strong>g was<br />
carried out <strong>in</strong> Juvakaisenmaa magnetite occurrence<br />
<strong>in</strong> Kolari around 1840. Modern exploration <strong>in</strong> Pajala<br />
area dur<strong>in</strong>g 1950s to 1960s by SGU <strong>and</strong> LKAB<br />
resulted discovery of around 10 magnetite occurrences<br />
of various size, however, at the time all of<br />
those were considered uneconomic. Exploration <strong>in</strong><br />
the Kolari area by Rautaruukki Oyj dur<strong>in</strong>g 1950s<br />
to 1980s resulted discovery of about 15 magnetite<br />
<strong>and</strong> magnetite-<strong>Cu</strong>-Au <strong>deposits</strong>. Two <strong>deposits</strong> at<br />
the Kolari area were exploited dur<strong>in</strong>g 1974-1992<br />
by Rautaruukki Oyj produc<strong>in</strong>g iron, copper, <strong>and</strong><br />
gold. In 2005 Northl<strong>and</strong> Resources SA staked the<br />
known occurrences <strong>in</strong> both Kolari <strong>and</strong> Pajala area<br />
the company has s<strong>in</strong>ce been develop<strong>in</strong>g the targets<br />
aim<strong>in</strong>g to start m<strong>in</strong><strong>in</strong>g <strong>in</strong> late 2012 (Northl<strong>and</strong> data).<br />
ite-staurolite-biotite-muscovite gneisses, <strong>and</strong> upper<br />
amphibolite facies garnet-sillimanite-biotite gneisses,<br />
VI) amphibolite facies pluton-derived metamorphism<br />
related with heat flow from central <strong>and</strong> western<br />
Lapl<strong>and</strong> granitoids.<br />
The present structural geometry shows an<br />
<strong>in</strong>verted gradient where pressure <strong>and</strong> temperature<br />
<strong>in</strong>crease up wards <strong>in</strong> the present tectonostratigraphy<br />
from greenschist facies <strong>in</strong> the zone IV through<br />
garnet-<strong>and</strong>alusite-staurolite grade <strong>in</strong> the zone III<br />
<strong>and</strong> garnet-kyanite grade amphibolite facies <strong>in</strong> the<br />
zone II to granulite facies <strong>in</strong> the zone I. The <strong>in</strong>verted<br />
gradient could be expla<strong>in</strong>ed by crustal thicken<strong>in</strong>g<br />
caused by overthrust of the hot granulite complex<br />
onto the lower grade rocks. Metamorphism <strong>in</strong> the<br />
Lapl<strong>and</strong> Granulite Belt occurred at 1.91–1.88 Ga<br />
(Tuisku & Huhma 2006), but the present metamorphic<br />
structure <strong>in</strong> central F<strong>in</strong>nish Lapl<strong>and</strong> may record<br />
later, postmetamorphic thrust<strong>in</strong>g <strong>and</strong> fold<strong>in</strong>g events<br />
(Hölttä et al. 2007).<br />
General Geology of the Kolari-Pajala area<br />
The bedrock of the Kolari-Pajala district is comprized<br />
by 2.44-1.91 Ga Karelian <strong>and</strong>
18<br />
Fig. 1. The ma<strong>in</strong> geological units of the Kolari-Pajala district <strong>and</strong> location of the known Fe <strong>and</strong> Fe-<strong>Cu</strong>-Au <strong>deposits</strong>.<br />
Modified after Fennosc<strong>and</strong>ian Bedrock map 1: 1 000 000.
Table 1. Size <strong>and</strong> grade data of the selected <strong>deposits</strong> <strong>in</strong> Kolari-Pajala district. Table modified after Eilu et al., (<strong>in</strong> prep.).<br />
Subarea,<br />
Occurrence Tonnage (Mt) M<strong>in</strong>ed (Mt) Fe % <strong>Cu</strong> % Aug/t Ma<strong>in</strong> ore m<strong>in</strong>erals 1 Reference<br />
Pajala<br />
Palotieva 8.7 24.2 0.05 Mgt, Py, Po, Cpy L<strong>in</strong>droos et al.<br />
(1972), Baker &<br />
Lepley (2010)<br />
Ruutijärvi 8.3 40.9 Mgt L<strong>in</strong>droos<br />
& Johansson<br />
(1972)<br />
Stora Sahavaara 145 43.1 0.08 Mgt, Cpy, Py, Po Frietsch (1997),<br />
Northl<strong>and</strong> (2007)<br />
Södra Sahavaara 19.6 32.1 0.05 Mgt, Py, Po L<strong>in</strong>droos (1972)<br />
Suksivuoma 3.5 43.5 Mgt Frietsch (1997)<br />
Tapuli 116.1 26.1 Mgt, Py, Po L<strong>in</strong>droos et al.<br />
(1972), Baker &<br />
Lepley (2010)<br />
Kolari<br />
Hannuka<strong>in</strong>en 202.5 4.56 33.1 0.16 0.05 Mgt, Cpy, Py, Po Hiltunen (1982),<br />
Northl<strong>and</strong> (2010a)<br />
Kuervitikko 45 22.9 0.16 0.17 Mgt, Cpy, Py, Po Northl<strong>and</strong> (2010a)<br />
Rautuoja 1.9 36.7 0.19 0.34 Mgt, Cpy, Py Korkalo (2006)<br />
Rautuvaara M<strong>in</strong>e 13.3 11.6 2 46.8 0.2 Mgt, Cpy, Py, Po Hiltunen (1982)<br />
Rautuvaara SW 4.5 42.7 0.15 Mgt, Cpy, Py, Po Hiltunen (1982)<br />
Rautuvaara-<strong>Cu</strong> 2.8 21.8 0.48 0.2 Mgt, Cpy, Py, Po Hiltunen (1982),<br />
Niiranen et al.(2007)<br />
Mannakorpi 20 25 Mgt, Bary, Py, Po, Cpy Hiltunen (1982)<br />
Sivakkalehto 0.4 3 37 Mgt, Po, Py, Cpy Hugg & Heiskanen<br />
(1983)<br />
Taporova 7 28 Mgt, Hem, Bary Hiltunen (1982)<br />
1 Bary = baryte, Cpy = chalcopyrite, Mgt = magnetite, Hem = haematite, Po = pyrrhotite, Py = pyrite.<br />
2 <strong>in</strong>cludes the production from both Rautuvaara <strong>and</strong> SW Rautuvaara <strong>deposits</strong><br />
3 Massive ore of 0.4 Mt plus dissem<strong>in</strong>ated magnetite m<strong>in</strong>eralisation of about 200 Mt at 20−25 % Fe (Hugg & Heiskanen 1983).<br />
19
20<br />
The ore <strong>deposits</strong><br />
Total of about 25 <strong>deposits</strong> are known with<strong>in</strong> the area.<br />
The known <strong>deposits</strong> display considerable variation <strong>in</strong><br />
size, Fe, <strong>Cu</strong>, <strong>and</strong> Au grades, host rock assemblage,<br />
<strong>and</strong> m<strong>in</strong>eralization style (Table 1; Frietsch et al.,<br />
1979; Hiltunen 1982, Northl<strong>and</strong> data). The m<strong>in</strong>eralization<br />
style range from massive to semi-massive<br />
magnetite lenses to breccia hosted <strong>and</strong> to dissem<strong>in</strong>ated<br />
magnetite-<strong>Cu</strong>-Au ore bodies. The <strong>deposits</strong> occur<br />
with<strong>in</strong> the Karelian <strong>and</strong> Svecofennian supracrustal<br />
units as well as <strong>in</strong> the Hapar<strong>and</strong>a Suite <strong>in</strong>trusions.<br />
Typically the <strong>deposits</strong> are hosted by Ca-cl<strong>in</strong>opyrox-<br />
Fig. 2. Geological map of the Kolari area <strong>and</strong> location of the known Fe, <strong>and</strong> Fe-<strong>Cu</strong>-Au <strong>deposits</strong>.<br />
Modified after Digital bedrock database of the Geological Survey of F<strong>in</strong>l<strong>and</strong>.<br />
ene <strong>and</strong>/or act<strong>in</strong>olite, or serpent<strong>in</strong>e skarns. In addition<br />
there are <strong>deposits</strong> <strong>in</strong> the Kolari area <strong>in</strong> which the<br />
part or most of the Fe- <strong>and</strong> Fe-<strong>Cu</strong>-Au m<strong>in</strong>eralization<br />
occurs with<strong>in</strong> albite- <strong>and</strong> albite-biotite-act<strong>in</strong>olite altered<br />
country rocks (e.g. Hiltunen, 1982; Niiranen et<br />
al., 2007). The <strong>deposits</strong> <strong>in</strong> Kolari area (Fig. 2) display<br />
clear structural control be<strong>in</strong>g associated to the<br />
thrust <strong>and</strong> shear zones that comprise the crustal scale<br />
Pajala-Kolari shear zone which is sometimes also<br />
referred as Baltic-Bothnian megashear (Berthelsen<br />
& Marker, 1986; Hiltunen, 1982; Niiranen et al.,<br />
2007). For the Pajala <strong>deposits</strong> the structural geology<br />
is poorly described <strong>in</strong> the literature.
Hannuka<strong>in</strong>en deposit<br />
The Hannuka<strong>in</strong>en deposit is the largest known deposit<br />
<strong>in</strong> the Kolari area with current resource estimate<br />
about 200 Mt (Table 1). The deposit consists<br />
of five gently west dipp<strong>in</strong>g lenticular semi-massive<br />
magnetite lenses hosted by Ca-cl<strong>in</strong>opyroxene <strong>and</strong><br />
act<strong>in</strong>olite skarns (Fig. 3). The magnetite lenses <strong>and</strong><br />
the skarns overpr<strong>in</strong>t variably albitized Hapar<strong>and</strong>a<br />
Suite diorite <strong>and</strong> Savukoski Group tholeiitic volcanic<br />
rock (Figs. 2-3). The deposit is structurally controlled<br />
by one of the thrust zones of the Pajala-Kolari<br />
shear zone system.<br />
The <strong>Cu</strong>-Au m<strong>in</strong>eralization is dom<strong>in</strong>antly<br />
hosted by the magnetite-rich lenses, <strong>and</strong> partially<br />
by the skarns. Although <strong>Cu</strong> <strong>and</strong> Au occur <strong>in</strong> anomalous<br />
concentrations throughout the deposit, only part<br />
of the deposit is <strong>Cu</strong>-Au m<strong>in</strong>eralized. The richest<br />
<strong>Cu</strong>-Au grades are with<strong>in</strong> the Laur<strong>in</strong>oja ore body <strong>in</strong><br />
which the best reported <strong>in</strong>tercepts are ca. 0.8% <strong>Cu</strong><br />
<strong>and</strong> 0.3 g/t Au along 35 meter of core (Northl<strong>and</strong><br />
data). However, as all the reported resource estimates<br />
are based on iron cut off, the exact size <strong>and</strong><br />
grade of the <strong>Cu</strong>-Au-richest part is unknown.<br />
The ore m<strong>in</strong>erals at Hannuka<strong>in</strong>en are magnetite,<br />
pyrite, pyrrhotite <strong>and</strong> chalcopyrite bornite,<br />
tellurides, gold, molybdenite, <strong>and</strong> uran<strong>in</strong>ite (Hiltunen,<br />
1982; Niiranen et al., 2007). Native gold occurs<br />
<strong>in</strong> silicate gangue <strong>and</strong> <strong>in</strong>clusions <strong>in</strong> sulfides <strong>and</strong><br />
magnetite (Hiltunen, 1982;<br />
Fig. 3. Surface<br />
geology <strong>and</strong> a<br />
cross section of<br />
the Hannuka<strong>in</strong>en<br />
ore field. The deep<br />
Kivivuopio ore<br />
body is omitted<br />
from the surface<br />
geology. After<br />
Hiltunen (1982),<br />
redrawn by P.<br />
Kurki.<br />
21
22<br />
Alteration & geochemical f<strong>in</strong>gerpr<strong>in</strong>t<br />
Multi-stage <strong>and</strong> -style alteration has been dist<strong>in</strong>guished<br />
at Hannuka<strong>in</strong>en <strong>and</strong> can be divided <strong>in</strong>to five<br />
different styles that may temporally overlap (Hiltunen,<br />
1982; Niiranen et al., 2007). Early albitization<br />
is overpr<strong>in</strong>ted by skarn alteration (cpx-act-mgt). Potassic<br />
alteration, typically biotite-K-feldspar ± magnetite,<br />
cliopyroxene/act<strong>in</strong>olite zone occurs <strong>in</strong> places<br />
as <strong>in</strong>termediate zone to the m<strong>in</strong>eralization. Potassic<br />
alteration is also typical <strong>in</strong> <strong>in</strong>tensely sheared tholeiitic<br />
volcanic rocks at footwall. The <strong>Cu</strong>-Au m<strong>in</strong>eralization<br />
(sulfidization) is temporally late to the ma<strong>in</strong> magnetite<br />
stage. The sulfidization is <strong>in</strong> places accompanied<br />
with second generation of magnetite. Latest alteration<br />
phase is carbonation (calcite) which post-date the<br />
magnetite stage <strong>and</strong> probably also the <strong>Cu</strong>-Au stage.<br />
The metal association of the ore is Fe, <strong>Cu</strong>, S ± Au, Co,<br />
LREE, Mo, Te, U. Potassic alteration is typically accompanied<br />
with elevated Ba concentrations (
Fig. 4. Geology of the Sahavaara deposit, modified after Lundberd (1967).<br />
of semi-cont<strong>in</strong>uous tabular bodies that dip 45-60 degrees<br />
to NW. Substantial part of the m<strong>in</strong>eralization<br />
consists of breccia hosted magnetite bodies (Baker<br />
et al., 2010). The host rock sequence is (from hang<strong>in</strong>g<br />
wall to footwall) quartzite, dolomitic marble,<br />
graphitic phyllite, <strong>and</strong> mafic volcanic rock (Fig. 5).<br />
The metasomatic skarns <strong>and</strong> magnetite overpr<strong>in</strong>t the<br />
dolomitic marble <strong>and</strong> phyllite (Baker et al., 2010).<br />
The sole ore m<strong>in</strong>eral <strong>in</strong> Tapuli is magnetite<br />
with only trace amount of pyrite <strong>and</strong> pyrrhotite. The<br />
gangue consists of cliopyroxene, tremolite, act<strong>in</strong>olite,<br />
serpent<strong>in</strong>e, <strong>and</strong> carbonates.<br />
Alteration & geochemical f<strong>in</strong>gerpr<strong>in</strong>t<br />
Baker et al. (2010) classify the alteration at Tapuli<br />
<strong>in</strong>to three temporally different assemblages which<br />
are: cl<strong>in</strong>opyroxene-tremolite alteration (pre-dat<strong>in</strong>g<br />
the m<strong>in</strong>eralization), magnetite-act<strong>in</strong>olite alteration<br />
(m<strong>in</strong>eralization event), <strong>and</strong> serpent<strong>in</strong>e alteration<br />
(post-dat<strong>in</strong>g m<strong>in</strong>eralization). Baker et al. (2010) further<br />
state that at the higher Fe-grades the dom<strong>in</strong>ant<br />
skarn m<strong>in</strong>eral is serpent<strong>in</strong>e which may <strong>in</strong>dicate that<br />
serpent<strong>in</strong>e-alteration resulted upgrad<strong>in</strong>g of the Fegrades.<br />
They also note that <strong>in</strong> zones where protolith<br />
was silicate rock <strong>in</strong>dicated by higher alum<strong>in</strong>ium<br />
content the biotite- <strong>and</strong> albite-rich alteration assemblages<br />
are dom<strong>in</strong>ant.<br />
Besides the iron, the S, Co, <strong>and</strong> <strong>Cu</strong> occur <strong>in</strong><br />
slightly elevated grades only <strong>in</strong> the sulfur richer parts<br />
of the deposit. Baker et al. (2010) state that elevated<br />
concentrations of La <strong>and</strong> Ce have been detected <strong>in</strong><br />
Tapuli ore, <strong>and</strong> that Cl occurs locally at values over<br />
0.1%.<br />
Genetic models<br />
Several different genetic models have been proposed<br />
for the <strong>deposits</strong> <strong>in</strong> both Pajala <strong>and</strong> Kolari districts. In<br />
Sweden the skarn hosted <strong>deposits</strong> with<strong>in</strong> the Karelian<br />
greenstone formation have traditionally been<br />
referred as skarn iron ores <strong>and</strong> these have been considered<br />
to represent metamorphosed syngenetic iron<br />
formations based on the observations that <strong>in</strong> places<br />
<strong>in</strong> Norrbotten area the skarn iron <strong>deposits</strong> appear to<br />
grade <strong>in</strong>to BIFs (e.g. Frietsch, 1997 <strong>and</strong> references<br />
there<strong>in</strong>). The Fe <strong>deposits</strong> <strong>in</strong> the Pajala area have<br />
been classified as “skarn iron ores” with similar genetic<br />
<strong>in</strong>terpretations ever s<strong>in</strong>ce the discovery of them<br />
(e.g. Griep <strong>and</strong> Frietsch, 1973). In F<strong>in</strong>l<strong>and</strong>, Hiltunen<br />
(1982) proposed that the Kolari <strong>deposits</strong> are metasomatic<br />
skarns related to the Hapar<strong>and</strong>a Suite <strong>in</strong>trusions<br />
based on the spatial association of the known<br />
ores close to the contacts of the <strong>in</strong>trusions. However,<br />
the U-Pb zircon <strong>and</strong> titanite ages from the <strong>in</strong>trusions<br />
<strong>and</strong> altered rocks at Kolari <strong>deposits</strong> <strong>in</strong>dicate that<br />
the m<strong>in</strong>eralization event(s) post-date the magmatic<br />
age of hang<strong>in</strong>g wall diorite <strong>and</strong> monzonite at Hannuka<strong>in</strong>en<br />
by ca. 60 million years, thus the <strong>deposits</strong><br />
are unrelated to the Hapar<strong>and</strong>a Suite magmatism<br />
(Niiranen et al., 2007). Based on the geochemistry,<br />
U-Pb age <strong>and</strong> fluid <strong>in</strong>clusion data as well as similarities<br />
with the Kolari Fe-<strong>Cu</strong>-Au <strong>deposits</strong> with some<br />
of the known <strong>IOCG</strong> <strong>deposits</strong> <strong>in</strong> Cloncurry district,<br />
Australia it has been proposed that the Kolari <strong>deposits</strong><br />
are examples of <strong>IOCG</strong> m<strong>in</strong>eralisation (Niiranen,<br />
2005 Niiranen et al. 2007).<br />
23
24<br />
Fig. 5. Cross section <strong>and</strong> a surface geology of the Tapuli deposit (www.northl<strong>and</strong>.eu).<br />
Aitik <strong>Cu</strong>-Au-Ag M<strong>in</strong>e<br />
Roger Nord<strong>in</strong><br />
Boliden M<strong>in</strong>eral AB, Boliden, Sweden<br />
Christ<strong>in</strong>a Wanha<strong>in</strong>en<br />
Luleå University of Technology, Luleå, Sweden<br />
Riikka Aaltonen<br />
M<strong>in</strong>istry of Trade <strong>and</strong> Industry, F<strong>in</strong>l<strong>and</strong><br />
Introduction<br />
The Aitik <strong>Cu</strong>-Au-Ag m<strong>in</strong>e is situated <strong>in</strong> Norrbotten<br />
County, northern Sweden, some 100 km north of<br />
the Arctic Circle <strong>and</strong> 17 km east of Gällivare town<br />
(Fig. 1). The m<strong>in</strong>e started operat<strong>in</strong>g <strong>in</strong> 1968 at a capacity<br />
of 2 Mt of ore annually. Subsequent expansions<br />
to 5 Mt (1970–72), 11 Mt (1979–81), have<br />
brought the capacity up to 16 Mt (1989–91). The<br />
next expansion will be operational <strong>in</strong> 2010–<strong>2011</strong><br />
<strong>and</strong> will br<strong>in</strong>g the capacity up to 33 Mt of ore <strong>in</strong><br />
2010, which will be ramped up to 36 Mt annually.<br />
production started <strong>in</strong> only 1969. (Juntunen 1971)<br />
M<strong>in</strong><strong>in</strong>g<br />
The Aitik m<strong>in</strong>e (Figs. 2 <strong>and</strong> 3) is a conventional<br />
large open-pit operation with an <strong>in</strong>-pit crusher (18.4<br />
Mt of ore m<strong>in</strong>ed 2006). The <strong>Cu</strong>-Au-Ag ore is moved<br />
by trucks carry<strong>in</strong>g 240 tonnes of ore to the crush<br />
ers. The ore is crushed, milled <strong>and</strong> processed <strong>in</strong> the<br />
flotation plant yield<strong>in</strong>g a chalcopyrite concentrate.<br />
The economic product is a <strong>Cu</strong>-(Au-Ag) concentrate<br />
with an average grade of 27–29 % <strong>Cu</strong>, 8 ppm Au<br />
<strong>and</strong> 250 ppm Ag. The concentrate is transported<br />
by truck to Gällivare <strong>and</strong> then railed 400 km to the<br />
Rönnskär <strong>Cu</strong> smelter east of Skellefteå, where LME<br />
(London Metal Exchange) grade <strong>Cu</strong> cathodes are<br />
produced. By-product gold <strong>and</strong> silver are also extracted<br />
at Rönnskär to produce metallic Au <strong>and</strong> Ag.<br />
Sulphur is captured by the smelter <strong>and</strong> converted<br />
<strong>in</strong>to sulphuric acid. In 2006, Aitik produced about<br />
29 % of the required feed of the Rönnskär smelter,<br />
or 240,000 tonnes of <strong>Cu</strong> concentrate. An average<br />
year at Aitik would yield some 60,000 tonnes<br />
of <strong>Cu</strong>-<strong>in</strong>-concentrate, 1.5–2 tonnes of Au, <strong>and</strong><br />
some 40–50 tonnes of Ag, from 17–18 Mt of ore.<br />
S<strong>in</strong>ce the start of m<strong>in</strong><strong>in</strong>g at Aitik <strong>in</strong> 1968,<br />
approximately 450 Mt of ore have been m<strong>in</strong>ed from<br />
a 3 km long, 1 km wide <strong>and</strong> 390 m deep open pit. In<br />
addition, some 400 Mt of waste rocks have been removed<br />
to expose the ore body. Proven <strong>and</strong> probable<br />
ore reserves at the start of 2007 were 625 Mt with<br />
0.28 % <strong>Cu</strong>, 0.2 ppm Au <strong>and</strong> 2 ppm Ag. Additional<br />
measured <strong>and</strong> <strong>in</strong>dicated m<strong>in</strong>eral resources were 858<br />
Mt with 0.24 % <strong>Cu</strong>, 0.2 ppm Au <strong>and</strong> 2 ppm Ag,<br />
with an additional 66 Mt of <strong>in</strong>ferred resources grad<strong>in</strong>g<br />
0.25 % <strong>Cu</strong>, 0.2 ppm Au <strong>and</strong> 2 ppm Ag (Boliden<br />
AB 2006). This makes Aitik the largest <strong>Cu</strong> deposit<br />
<strong>in</strong> the Fennosc<strong>and</strong>ian Shield <strong>and</strong> one of the largest<br />
Au-rich porphyry copper <strong>deposits</strong> <strong>in</strong> the world.<br />
The current m<strong>in</strong>e life, <strong>in</strong>clud<strong>in</strong>g the expansion to up<br />
to 36 Mt/a, will allow the m<strong>in</strong>e to cont<strong>in</strong>ue to operate<br />
until 2026. The f<strong>in</strong>al dimensions of the open<br />
pit <strong>in</strong> 2026 will be 5000 m long by 1400 m wide<br />
<strong>and</strong> 600 m deep. Exploration <strong>in</strong> the area is ongo<strong>in</strong>g.
Fig. 1. Geology of <strong>Northern</strong> Norrbotten with selected m<strong>in</strong>eral <strong>deposits</strong> <strong>in</strong>clud<strong>in</strong>g location of the Aitik m<strong>in</strong>e<br />
modified from Bergman et al. (2001).<br />
25
26<br />
Fig. 2. Local geology <strong>and</strong> excursion stops at the<br />
Aitik m<strong>in</strong>e. Geology from Wanha<strong>in</strong>en <strong>and</strong> Mart<strong>in</strong>sson<br />
(1999).<br />
M<strong>in</strong>e geology<br />
The local m<strong>in</strong>e geology at Aitik (Figs. 2 <strong>and</strong> 4) is<br />
divided <strong>in</strong>to 3 ma<strong>in</strong> parts, i.e. the hang<strong>in</strong>g wall, ma<strong>in</strong><br />
ore zone <strong>and</strong> the footwall complex. The hang<strong>in</strong>g wall<br />
is basically one unit of strongly b<strong>and</strong>ed hornblende<br />
gneisses. The ma<strong>in</strong> ore zone consists of three ma<strong>in</strong><br />
units, a muscovite schist, biotite schist <strong>and</strong> biotite<br />
gneisses. These rocks are strongly deformed <strong>and</strong> altered<br />
which obscure their primary character. However,<br />
their chemical character suggests a magmatic<br />
precursor of <strong>in</strong>termediate composition <strong>and</strong>, based on<br />
the knowledge from areas outside the m<strong>in</strong>e, a volcaniclastic<br />
orig<strong>in</strong> (Wanha<strong>in</strong>en & Mart<strong>in</strong>sson 1999).<br />
The most important footwall unit is the quartz monzodioritic<br />
<strong>in</strong>trusive. Other <strong>in</strong>trusives of <strong>in</strong>terest are<br />
the pegmatite dykes which cross cut the hang<strong>in</strong>g<br />
wall, ma<strong>in</strong> ore zone <strong>and</strong> the footwall complex.<br />
The ma<strong>in</strong> ore zone dips roughly 45° to the<br />
west (Figs. 3 <strong>and</strong> 4), <strong>and</strong> the lower ore contact consists<br />
of a gradational weaken<strong>in</strong>g of the copper grade<br />
at roughly 50° to the west. The lower contact is approximately<br />
where biotite gneisses change <strong>in</strong>to regional<br />
biotite-amphibole gneiss. Sporadic <strong>Cu</strong> m<strong>in</strong>eralisation<br />
of no economic <strong>in</strong>terest exists <strong>in</strong> these<br />
footwall gneisses. The footwall quartz monzodiorite<br />
<strong>in</strong> the southern part of the m<strong>in</strong>e is part of newly started<br />
series of push backs. Below follows a detailed<br />
description of the Aitik m<strong>in</strong>e rock units (see also the<br />
rock types depicted <strong>in</strong> Fig. 5)<br />
Hornblende-b<strong>and</strong>ed gneiss is a f<strong>in</strong>ely b<strong>and</strong>ed<br />
unit (mm to cm wide b<strong>and</strong>s) with alternat<strong>in</strong>g dark<br />
olive green <strong>and</strong> light grey layers. This unit is more<br />
than 250 m thick, <strong>and</strong> overlies the ma<strong>in</strong> ore zone. It is<br />
devoid of sulphides. M<strong>in</strong>eralogically it is dom<strong>in</strong>ated<br />
by hornblende, with biotite, quartz <strong>and</strong> m<strong>in</strong>or plagioclase.<br />
The light grey b<strong>and</strong>s have weak to moderate<br />
sericitic <strong>and</strong> chloritic alteration. The unit also shows<br />
a red-green microcl<strong>in</strong>e-epidote-alteration. Scapolite<br />
porhyroblasts of 1–5 mm <strong>in</strong> diameter occur throughout<br />
the unit. Other accessory m<strong>in</strong>erals are magnetite<br />
<strong>and</strong> tourmal<strong>in</strong>e. The f<strong>in</strong>e-gra<strong>in</strong>ed unit likely represents<br />
orig<strong>in</strong>al compositional variations, even though<br />
it is strongly metamorphosed. Based on field evidence,<br />
it is suggested that the f<strong>in</strong><strong>in</strong>g upwards of the<br />
layer<strong>in</strong>g shows that way-up is towards the west. The<br />
unit appears to have been tectonically emplaced over<br />
the ma<strong>in</strong> ore zone. The fault at the contact appears to<br />
be a thrust. The boundary between the ma<strong>in</strong> ore zone<br />
<strong>and</strong> the hornblende-b<strong>and</strong>ed gneiss is <strong>in</strong> places highly<br />
fractured, caus<strong>in</strong>g problems for drill<strong>in</strong>g. The border<br />
zone between hornblende b<strong>and</strong>ed gneisses <strong>and</strong> the<br />
ma<strong>in</strong> ore zone is also <strong>in</strong>truded by several pegmatite<br />
dykes up to 40 m wide.
Fig. 3. Metal distribution at Aitik for copper (A) <strong>and</strong> gold (B) for the 100, 300 <strong>and</strong> 500 m horizontal levels. Class limits<br />
are chosen after the classification of m<strong>in</strong>eable to waste rock <strong>and</strong> low- to high-grade ore used by Boliden AB. From<br />
Wanha<strong>in</strong>en et al. (2003b).<br />
Fig. 4. Section across the Aitik deposit, view to the north, 200 m grid.<br />
27
28<br />
Quartz-muscovite (sericite) schist constitutes the<br />
upper part of the ma<strong>in</strong> ore zone. The unit is roughly<br />
200 m thick, <strong>and</strong> consist of a strongly foliated muscovite-rich<br />
matrix with quartz, biotite, microcl<strong>in</strong>e <strong>and</strong><br />
plagioclase. It is a light-buff coloured unit show<strong>in</strong>g a<br />
sharp contact with the overly<strong>in</strong>g hornblende-b<strong>and</strong>ed<br />
gneiss <strong>and</strong> a gradational lower contact grad<strong>in</strong>g <strong>in</strong>to<br />
biotite schist. Accessory m<strong>in</strong>erals <strong>in</strong> this unit are<br />
epidote, tourmal<strong>in</strong>e, magnetite <strong>and</strong> garnet. Magnetite<br />
occurs as occasional mm-scale porphyroblasts,<br />
<strong>and</strong> also as f<strong>in</strong>e dissem<strong>in</strong>ation (1–3 % magnetite).<br />
The sulphide m<strong>in</strong>erals are dom<strong>in</strong>ated by pyrite <strong>and</strong><br />
chalcopyrite (py > cpy > po). Total sulphur content<br />
can reach 5–7 %, correspond<strong>in</strong>g to 15–20 vol-% of<br />
sulphides. The muscovite schist has a Cpy:Py ratio<br />
rang<strong>in</strong>g from 1:2 to 1:7. The upper contact of the<br />
muscovite schist conta<strong>in</strong>s a sulphide rich zone, 5–40<br />
m wide with up to 20–25 % sulphides. Gold <strong>and</strong> copper<br />
zonation is shown <strong>in</strong> Figure 3. Gold <strong>and</strong> copper<br />
grades <strong>in</strong>crease at depth <strong>in</strong> the northern part of the<br />
pit. Pyrrhotite <strong>and</strong> molybdenite occur as less common<br />
sulphides. Pyrite typically occurs as large blebs,<br />
or along foliation planes, <strong>and</strong> as small ve<strong>in</strong>lets. The<br />
Ba content of the unit is quite high, <strong>in</strong> the order of<br />
1,000 – several 1,000s of ppm.<br />
Biotite schist constitutes the middle part of<br />
the ma<strong>in</strong> ore zone. It is gradational <strong>in</strong>to the biotite<br />
gneisses below as well as to the muscovite schists<br />
above. The thickness is on average 150 m. This unit<br />
is strongly foliated <strong>and</strong> sheared <strong>in</strong> a roughly northsouth<br />
direction. It conta<strong>in</strong>s pyrite <strong>and</strong> chalcopyrite<br />
dissem<strong>in</strong>ation <strong>and</strong> ve<strong>in</strong>lets, <strong>and</strong> chalcopyrite clots,<br />
with pyrite <strong>and</strong> chalcopyrite as equal volumes. Magnetite<br />
occurs as a f<strong>in</strong>e dissem<strong>in</strong>ation with gra<strong>in</strong>s<br />
commonly enclosed with<strong>in</strong> amphibole <strong>and</strong>/or garnet<br />
porphyroblasts. Molybdenite is present <strong>in</strong> the northern<br />
part of the m<strong>in</strong>eralisation. Biotite dom<strong>in</strong>ates over<br />
muscovite, <strong>and</strong> def<strong>in</strong>es a strong foliation. Th<strong>in</strong> ve<strong>in</strong>lets<br />
of quartz, commonly deformed, occur <strong>in</strong> this<br />
unit. Undeformed ve<strong>in</strong>lets with late zeolites <strong>and</strong> epidote<br />
occasionally occur with<strong>in</strong> the unit.<br />
Biotite gneisses constitute the lowermost<br />
part of the ma<strong>in</strong> ore zone, although the rock type is<br />
not always present. They commonly display zones<br />
of red garnet (spessart<strong>in</strong>e-alm<strong>and</strong><strong>in</strong>e) <strong>and</strong> more<br />
gneissic, coarser-gra<strong>in</strong>ed character than the strongly<br />
foliated biotite schist. M<strong>in</strong>eralisation is of the same<br />
style as <strong>in</strong> the biotite schist.<br />
Quartz monzodiorite is the dom<strong>in</strong>ant footwall<br />
unit, be<strong>in</strong>g up to 600 m thick. It shows medium-gra<strong>in</strong>ed<br />
equigranular, 2–5 mm phases as well<br />
as strongly porphyritic phases. Transition between<br />
these phases (= subphases of the quartz monzodiorite)<br />
is almost always gradational. The quartz monzodiorite<br />
conta<strong>in</strong>s plagioclase phenocrysts be<strong>in</strong>g up to<br />
7–9 mm <strong>in</strong> size. The plagioclase show compositional<br />
zon<strong>in</strong>g. The matrix of the quartz monzodiorite consists<br />
of a f<strong>in</strong>e-gra<strong>in</strong>ed mixture of plagioclase, quartz,<br />
biotite <strong>and</strong> m<strong>in</strong>or sericite. Alteration is commonly<br />
present as weak silicification <strong>and</strong> p<strong>in</strong>kish potassic<br />
alteration. M<strong>in</strong>eralisation is dom<strong>in</strong>ated by fracturecontrolled<br />
py-cpy±MoS 2, but f<strong>in</strong>ely dissem<strong>in</strong>ated<br />
sulphides are also present. A m<strong>in</strong>or accessory m<strong>in</strong>eral<br />
is epidote, which can conta<strong>in</strong> f<strong>in</strong>e gra<strong>in</strong>ed cpy.<br />
Hornblende <strong>and</strong> quartz-tourmal<strong>in</strong>e ve<strong>in</strong>lets occur<br />
throughout this unit. Ve<strong>in</strong><strong>in</strong>g of quartz, quartz-tourmal<strong>in</strong>e,<br />
gypsum, gypsum-fluorite <strong>and</strong> zeolites occur<br />
as mm–cm wide ve<strong>in</strong>lets. The zeolites present<br />
are stilbite, chabazite <strong>and</strong> desm<strong>in</strong>e, <strong>and</strong> calcite <strong>and</strong><br />
baryte have also been observed <strong>in</strong> this association.<br />
These stockwork ve<strong>in</strong>s cut each other at high angles,<br />
but zones of deformation are also present. The quartz<br />
monzodiorite has a zircon U-Pb age of ca. 1.89 Ga<br />
(Wanha<strong>in</strong>en et al. 2006), which fits well with reported<br />
ages for regional Hapar<strong>and</strong>a suite granitoids<br />
(Bergman et al. 2001).<br />
Feldspar-porphyritic <strong>and</strong>esitic <strong>in</strong>trusives<br />
occur as large dykes <strong>and</strong> occasionally show chilled<br />
marg<strong>in</strong>s. These types of <strong>in</strong>trusives occur throughout<br />
the entire stratigraphic column, but are more common<br />
<strong>in</strong> the footwall area. These dykes are strongly<br />
porphyritic <strong>in</strong> character, with large feldspar phenocryst<br />
laths, up to 25 mm long <strong>and</strong> 4–5 mm wide.<br />
They are set <strong>in</strong> a dark olive green matrix of hornblende,<br />
biotite, chlorite, <strong>and</strong> occasionally act<strong>in</strong>olite<br />
or tremolite. The f<strong>in</strong>e-gra<strong>in</strong>ed, equigranular variety<br />
of this rock is termed amphibolite <strong>in</strong> the m<strong>in</strong>e. Sulphides,<br />
when present, are typically pyrite-chalcopyrite<br />
at a 1:1 ratio, <strong>and</strong> they appear to be both remobilised<br />
from the adjacent rocks <strong>and</strong> to be present with<strong>in</strong><br />
the feldspar porphyritic unit.<br />
Amphibole <strong>and</strong> amphibole-biotite gneisses<br />
constitute a major part of the footwall unit. These<br />
rocks typically exhibit an anastomos<strong>in</strong>g weak network<br />
of 5–30 mm wide hornblende ve<strong>in</strong>lets or<br />
schlieren with a light-coloured feldspar (albite) rim.<br />
Biotite def<strong>in</strong>es a weak foliation, <strong>and</strong> porphyroblastic<br />
garnet is commonly present form<strong>in</strong>g 1–5 vol-%<br />
of the rock. Sporadic scapolite is present as small<br />
gra<strong>in</strong>s <strong>and</strong> as zones of <strong>in</strong>tense scapolitisation. Magnetite<br />
is a common accessory (1–3 %), <strong>and</strong> occurs as<br />
small porphyroblasts <strong>and</strong> as ve<strong>in</strong>lets.<br />
Th<strong>in</strong> pegmatite dykes are common; they<br />
may reach a maximum width of 40 m. Their distribution<br />
is varied with<strong>in</strong> the m<strong>in</strong>e area with the largest<br />
frequency of the dykes <strong>in</strong> <strong>and</strong> around the hang<strong>in</strong>g<br />
wall contact, where they are unm<strong>in</strong>eralised. At<br />
the hang<strong>in</strong>g wall contact, they are oriented roughly<br />
N-S <strong>and</strong> dip about 60º to the west. In the ma<strong>in</strong> ore<br />
zone, the pegmatite dykes occur less frequently,<br />
<strong>and</strong> one series of the dykes show a NNW orientation<br />
<strong>and</strong> a steep dip. The pegmatites commonly
have been <strong>in</strong>truded forcefully s<strong>in</strong>ce they can conta<strong>in</strong><br />
large fragments of the adjacent country rock. When<br />
they <strong>in</strong>trude m<strong>in</strong>eralised host rock they can also exhibit<br />
py-cpy m<strong>in</strong>eralisation. M<strong>in</strong>eralogically they<br />
are dom<strong>in</strong>ated by very-coarse gra<strong>in</strong>ed microcl<strong>in</strong>e,<br />
quartz <strong>and</strong> typically long prismatic black tourmal<strong>in</strong>e.<br />
Greenish muscovite flakes also are common. Accessory<br />
m<strong>in</strong>erals with<strong>in</strong> the pegmatites are molybdenite<br />
<strong>and</strong> fluorite.<br />
Genetic model<br />
The Aitik host rocks belong to the regionally widespread<br />
Hapar<strong>and</strong>a suite of <strong>in</strong>trusions <strong>and</strong> Porphyrite<br />
group of comagmatic volcanic rocks (Wanha<strong>in</strong>en<br />
& Mart<strong>in</strong>sson 1999, Wanha<strong>in</strong>en et al. 2006) which<br />
were generated dur<strong>in</strong>g subduction of oceanic crust<br />
beneath the Archaean craton around 1.9 Ga, dur<strong>in</strong>g<br />
the Svecokarelian orogeny (Weihed 2003). High-sal<strong>in</strong>ity<br />
fluids (30–38 eq. wt. % NaCl+CaCl2) responsible<br />
for chalcopyrite-pyrite m<strong>in</strong>eralisation <strong>in</strong> Aitik<br />
were released contemporaneously with quartz monzodiorite<br />
emplacement <strong>and</strong> quartz stockwork formation<br />
at ca. 1.89 Ga <strong>and</strong> caused potassic alteration of<br />
the <strong>in</strong>trusive <strong>and</strong> surround<strong>in</strong>g volcaniclastic rocks.<br />
The m<strong>in</strong>eralised quartz monzodiorite <strong>in</strong> the footwall<br />
is suggested to represent an apophyse from a larger<br />
<strong>in</strong>trusion at depth consistent with the porphyry copper<br />
model presented by Lowell <strong>and</strong> Guilbert (1970).<br />
Furthermore, zonation <strong>and</strong> alteration patterns, although<br />
disturbed, fit quite well with this model (Yngström<br />
et al. 1986, Monro 1988, Wanha<strong>in</strong>en 2005).<br />
However, all features of the ma<strong>in</strong> ore zone are not<br />
typical for a porphyry system, <strong>and</strong> Aitik is suggested<br />
to be hybrid <strong>in</strong> character with an aff<strong>in</strong>ity to both<br />
<strong>IOCG</strong> <strong>and</strong> porphyry-copper m<strong>in</strong>eralisation based<br />
on the character of the high sal<strong>in</strong>ity ore fluids, the<br />
alteration <strong>and</strong> m<strong>in</strong>eralisation styles, <strong>and</strong> on the 160<br />
Ma (Re-Os molybdenite <strong>and</strong> U-P titanite <strong>and</strong> zircon<br />
dat<strong>in</strong>g) evolution of the deposit (Wanha<strong>in</strong>en et<br />
al. 2003a, Wanha<strong>in</strong>en et al. 2005, Wanha<strong>in</strong>en et al.<br />
2006), <strong>in</strong>clud<strong>in</strong>g a regional m<strong>in</strong>eralis<strong>in</strong>g event of<br />
<strong>IOCG</strong>-type at ca. 1.8 Ga.<br />
29
30<br />
Fig. 5. Rock types at Aitik. A. Hornblende-b<strong>and</strong>ed gneiss – AIA1026 (HWC – at 19.40 m). F<strong>in</strong>ely b<strong>and</strong>ed unit with m<strong>in</strong>or coarser<br />
b<strong>and</strong>s. B. Muscovite schist – AIA1042 (MOZ) at 151.50 m. Display<strong>in</strong>g mixed nature with alternat<strong>in</strong>g muscovite <strong>and</strong> biotite-b<strong>and</strong>s.<br />
C. Biotite schist – AIA1042 (MOZ – 133.95 m) Dark grey rock with biotite b<strong>and</strong>s, display<strong>in</strong>g some muscovite. Garnet-porphyroblasts<br />
<strong>and</strong> dissem<strong>in</strong>ation of chalcopyrite, pyrite <strong>and</strong> pyrrhotite. D. Amphibole-biotite-gneiss – AIA1021 (MOZ – at 112.20 m).<br />
Metamorphic hornblende patches <strong>and</strong> schlieren. E. Diorite – AIA1042 (MOZ/FWC). Coarse-gra<strong>in</strong>ed <strong>and</strong> porphyritic. Overpr<strong>in</strong>t<strong>in</strong>g<br />
metamorphic amphibole alteration <strong>and</strong> silicification causes diffuse textures. F. Diorite – porphyritic with altered plagioclase<br />
phenocrysts (potassic alteration) – AIA1042 (at 505.30 m) Dioritic matrix. Potassic alteration <strong>and</strong> late gypsum ve<strong>in</strong>lets. G. M<strong>in</strong>eralised<br />
diorite. H. Feldspar porphyritic gabbro – AIA1042 (stratigraphic footwall at 609.40 m). Andesitic matrix. Plagioclase<br />
laths (5-15 mm).
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