26th International Geological Congress Paris 1980

Precambrian ores of the northern part of Norrbotten county, northern Sweden

Guide to excursions 078 A+C, Part 1 (Sweden)

Edited by Rudyard Frietsch

Geological Survey of Finland Espoo 1980 26th International Geological Congress Paris 1980

PRECAMBRIAN ORES OF THE NORTHERN PART OF NORRBOTTEN COUNTY, NORTHERN SWEDEN

Guide to excursions 078 A + C, Part 1 (Sweden)

EDITED BY RUDYARD FRIETSCH

GEOLOGICAL SURVEY OF FINLAND ESP00 1980 Frietsch, Rudyard (Editor), 1980. Precambrian ores of the northern part of Norrbotten county, northern Sweden. Guide to excursions 078 A+ C, Parf l (Sweden). 26" International Geological Congress, Paris 1980.

The following Precambrian ore deposits in northern Sweden and their geological setting are described: the Kiirunavaara, Luossavaara, Nukutus- vaara, Rektor, Gruvberget, Kiilavaara, Saivo and Mertainen iron ores, and the Viscaria, Gruvberget and Aitik copper ores.

Key words: economic geology, ore deposits, metallogenic provinces, iron, copper, Precambrian, Northern Sweden

Rudyard Frietsch, Sveriges geologiska undersckning, Box 670, S-75128 Uppsala, Sweden

ISBN 951-690-115-8

Helsinki 1980. Valtion painatuskeskus CONTENTS

Precambrian ores of the northern part of Norrbotten county. northern Sweden -Budyard Frietscb ...... Introduction ...... Geological setting ...... Ore deposits ...... Iron ores ...... Copper ores ...... Geology of the Kiruna area -- Pad Ford and Lisbetb Godin ...... Geology and ores of the Svappavaara area -- Rtldyard Frietsch ...... Geological setting ...... Ore deposits ...... Saivo iron ore -- Rtldyard Frietscb ...... Mertainen iron ore -- Rdyard Friefscb ...... Aitik copper ore -- Ham ZweifeZ ...... Introduction ...... Geological setting ...... The ore ...... References ...... DAILY ROUTES

Excursion 078A: 27th June-5th July, 1980 Excursion 078C: 19th July-27th July, 1980

In Sweden (Part 1) First day 27th June 19th July Kiruna area ...... 13 Second day 28th June 20th July Kiruna area...... 19 Third day 29th June 218t July Kiruna-Svappavaara-Saivo-Kiruna 20 Fourth day 30th June 22nd July Kiruna-Mertainen-Aitik-Gallivare . 27

In Finland (Part 2)

Fifth day let July 23rd July Galhare-Kerni-Oulu ...... 6 Sixth day 2nd July 24th July Oulu-Vihanti-Oulu ...... 14 Seventh day 3rd July 25th July Oulu-Otanmaki-Kuopio ...... 25 Eighth day 4th July 26th July Kuopio-Outokumpu-Kuopio ...... 33 Ninth day 5th July 27th July Kuopio-Kotalahti-Kuopio-Helsinki 42

Excursion leaders: In Sweden: Paul Forsell, LKAB Prospektering AB, 3-98104 Kiruna, Sweden Ru&ard Frietsch, Sveriges geologiska undersokning, Box 670, 3-75128 Uppala, Sweden Lisbeth Godin, L KAB Prospekterifig AB, S-98 104 Kirama, Sweden Hans Zweife, Boliden Metall AB, S-93050 Boliden, Sweden In Finland: Auh Hiikli, Outokumpu Oy, Box 27, SF-02201 Espoo 21, Finland 0le Lifidholm, Rautaruakki Oy, Ampubaukantie 4, SF-90250 Oulu 25, Finland Excursion route and daily stops. PRECAMBRIAN ORES OF THE NORTHERN PART OF NORRBOTTEN COUNTY, NORTHERN SWEDEN - by Rudyard Frietsch

Introduction and Malmberget have been known since the latter part of the 17th century. Most of the iron Within the Precambrian in the northern part ore deposits were found at the end of the 19th of the county of Norrbotten, some of the most century and during and immediately after the important ore deposits of Sweden are found. First World War. Early in the 1930's some This region contains about 80 % of the iron ore copper deposits were discovered of which the reserves of the country (4 billion tons out of a most important is Aitik. More recently several total of 5 billion tons) and about 95 of the iron ores and some copper ores such as Viscaria iron reserves (2 billion tons out of a total of at Kiruna, have been found. 2.35 billion tons). About 85 of the total iron ore production of Sweden comes from Norr- Geological setting botten; in 1974, 30.5 million tons iron ore, con- centrate and pellets were produced, and in 1976, In the Precambrian of the northen part of 25.5 million tons. The Aitik copper deposit Norrbotten county supracrustal rocks (including contains about 10 % of the metal content of the gneisses derived from these) and igneous rocks sulphide ores of Sweden and produces about have approximately the same aerial extents (Fig. 60 % of the annual quantity of mined sulphide 1). The supracrustals form belts orientated ore in Sweden. Other deposits are of such size N-S and NNE-SSW with a less distinct NW-SE and quality or have such a geographical position orientation. The internal relationships between that they cannot be exploited economically. the different rock types are uncertain and radio- Limited mining of limestone-dolomite, feld- metric age determinations are few. However spar, quartzite and ultrabasic rock also takes regional mapping conducted during the last place. decade (Offerberg 1967, Padget 1970, 1977, Several hundered deposits and occurrences of Witschard 1970, 1975, Eriksson and Hallgren ore are known of which the earliest discovered 1975) have elucidated many of these problems were the copper ores at Gruvberget, Svappa- so that a relatively detailed stratigraphic division vaara (in 1654) and some others further north can now be ascertained. in the latter part of the 17th century. At this The earlier subdivision by Odman (1957) of time some iron ores were also known at Masugns- the Precambrian into an older, Svecofennian byn (in 1644) and Gruvberget, Svappavaara (in cycle and a younger, Karelian cycle has been 1654). At Masugnsbyn a blast furnace was abandoned in the light of radiometric age datings. erected a few years later and was the most At present the Precambrian is divided into two northerly situated blast furnace of its kind in main units. The first is the Archean fold belt, the world. The vast iron ore deposits at Kiruna more than 2 700-2 800 Ma old, covering a I J K L M Fig. 1. The iron ore and copper ore deposits in the northern part of the Norrbotten county. restricted area in the north. Younger than this formation is the lowest part of the Greenstone is the Svecokarelian fold belt which makes up group, formed as an epicontinental facies in the the rest of the Precambrian. In other parts of Svecokarelian development. The Greenstone Sweden the Svecokarelian folding came to an group is dominated by spilitic, often pillow- end about 1 800 Ma ago. In Norrbotten some bearing effusives of basaltic composition. In igneous and volcanic rocks were formed 1 500- addition andesites and peridotites are present. 1 600 Ma ago thus indicating a clear post- All these rocks are sub-alkaline to alkaline orogenic age in relation to the Svecokarelian. As (Frietsch 1980) and hypabyssal rocks of similar these rocks have been folded and metamorphosed composition occur sporadically. In the basic it means that post-Svecokarelian orogenic events volcanics, mostly in the higher stratigraphic may taken place. The metamorphism is possibly parts, occur intercalations of tuff, tuffite, phyllite, related to the formation of late granites about graphite-bearing schist, limestone-dolomite, mar1 1 500 Ma ago. and chert. These formations were deposited in a All rocks suggest intermediate metamorphic closed basin environment at the border of the conditions dominated exclusively by amphibolite Archean craton during the evolutionary phase facies assemblages. A typical feature for the of the Svecokarelian orogeny. Similar rocks in northern part of Norrbotten county is that the Finland have yielded radiometric ages in the rocks rather commonly contain scapolite result- 2 000-2 200 Ma range. ing from a relatively late stage regional meta- The Greenstone group is overlain by mica- somatic process. schists and conglomerates of moderate thick- To the north of Kiruna the Archean (pre- nesses. This Schist-conglomerate group (Paha- Svecokarelian) basement is found. It is a biotite- kurkkio group, Kiilavaara quartzite group) is of bearing, weakly schistose, rnicrocline-porphyritic restricted extent but forms a distinct marker granite with a U/Pb radiometric age of about horizon. Examples exist at Kiruna (Kurravaara 2 750-2 800 Ma (Welin et al. 1971). Farther to conglomerate) and include the metasediments at the north and to the east, adjacent to the Finnish Tiirendo (Padget 1970) and Lainio (Witschard border, vast areas are covered by gneisses which 1970). also possibly belong to the basement (Lindroos The Porphyry group, which is the following and Henkel 1978). In the northernmost area, unit in the sequence, is composed of predorni- abundant dykes of serpentinized ultrabasites nantly sodic or sodium-potassium intermediate, occur which are not deformed by the Archean rhyolitic and trachytic rocks of sub-alkaline to folding and possibly represent an intraorogenic alkaline composition; all the acid rocks are sub- magmatism, pre-dating the formations of Sveco- alkaline (Frietsch 1980). The Porphyry group karelian age. occurs mainly in the western and central parts Within the Svecokarelian four supracrustal of the county; in addition it appears in restricted groups can be ascertained but no major uncon- areas to the east around Tarendo, Pajala and formity has been observed between them. Oldest Lannavaara. Locally porphyritic and other vol- among the supracrustal is the Greenstone group canic textures are well preserved, but mostly (Kiruna greenstone group, Vittangi greenstone they have been obliterated due to the later group, Veikkavaara greenstone group, Suorsa metamorphism which has resulted in the trans- greenstone group). On the granite-gneiss base- formation of the rocks to fine-grained, equi- ment, under the main part of the Greenstone granular rocks or more rarely to somewhat coarser group, occur narrow horizons of quartz-bearing gneissic rocks. Narrow intercalations of meta- conglomerate and quartzite, occasionally siltstone sediments occur to some extent, especially among and limestone-dolomite. This Tjarro quartzite the intermediate volcanics. Mostly agglomerates, conglomerates, tuffs, tuffites, sandstones and pegmatites and aplites. The formation of the mudstones are encountered; occasionally also granites is associated with an intense gneissifica- limestones. The age of the volcanics at and south- tion. Thus the supracrustal rocks have over large west of Kiruna is 1 605-1 635 Ma (Rb/Sr age areas been transformed into gneisses, particularly determination, Welin et al. 1971). in the eastern part of the county along the coast In the eastern part of the county restricted and the Finnish border. Radiometric age deter- areas are covered by metasediments (amphibole- mination~of the Lina granite, which is the most schists, conglomerates, limestones, pelitic and widespread of the granites belonging to this basic schists; the Kalix-alv group) which are group, have given a Rb/Sr age of about 1 565 Ma possibly of the same age as the Porphyry group (Welin 1970, Welin et al. 1971). For some (Padget 1970). granitoids, however, an age of 1 820 Ma has The youngest supracrustal unit is the Quart- been recorded. The distribution between the zite group (Upper Hauki complex, Mattavaara younger and older Lina granites is not known. quartzite group, Rissavaara quartzite, Kuusi- The older ones probably belong to the same vaara quartzite) which is composed of quartzitic phase as the Granodiorite group. sandstone with occasional phyllitic intercalations. Restricted areas among the younger granitoids It is of limited extent and mostly bounded by are covered by perthite granites and perthite dislocations, indicating a formation in subsiding monzonites. As pointed out by Geijer (1931 a) grabens. West of Malmberget, near the Cale- and Witschard (1975) these show a close chemical donides, other, possibly more transgressive and genetical relationship with the rocks of the sedimentary conditions must have prevailed. The Porphyry group. Rb-Sr isotope data show that quartzites (Snavva-Sjofall quartzites) have a the age of these granitoids is 1 535-1 565 Ma thickness of up to 10 000 m and extend to the (Gulson 1972). south for a distance of some hundreds of kilo- It should be pointed out that the stratigraphic metres (Odman 1957). succession of the Kiruna area presented by Two groups of granitoids with different ages Forsell and Godin on p. 13 in the present can be discerned. Younger than the Greenstone publication in many respects deviates from that group is a differentiated series with gabbro, described above. According to several authors diorite and granodiorite; the latter member (Lundbohm 1910, Geijer 1931 a, Offerberg 1967, dominating. The distribution of this Grano- Frietsch 1979) the rocks in the Kiruna area occur diorite group (or the Haparanda >>granite)) in a monoclinal sequence which, from the oldest series) is tectonically controlled and occurs pre- to the youngest, comprises: (basement granite- dominantly in the eastern part of the county quartz-bearing conglomerate and quartzite)- mainly associated with rocks of the Greenstone Kiruna greenstone-Kurravaara conglomerate- and Schist-conglomerate groups. Radiometric syenite-porphyry, quartz-bearing porphyry and Rb/Sr age determinations on granitoids in the volcanics of the Lower Hauki formation (com- coastal area round Haparanda give an age of plex, series)-conglomerate, phyllite and quart- about 1 880 Ma (Welin 1970, Welin et al. 1970). zitic sandstone of the Upper Hauki formation Whether similar granitoids in other areas of the (complex, series). county have the same age is still an open ques- tion. Ore deposits The younger intrusive group, which transects all the supracrustal rocks and the rocks of the The ores in the Precambrian, present in the older intrusive group, is composed of late- northern part of the county of Norrbotten, are kinematic potassium-granites accompanied by almost totally restricted to supracrustal rocks and occur in these both as syngenetic as well The apatite-bearing iron ores are considered as epigenetic formations. The igneous rocks and to be closely associated with the volcanics in the gneisses are mostly devoid of mineral which they occur and to have originated by a deposits. magmatic differentiation in which volatiles played an important role. While the main part of the magma crystallized the ore remained in Iran orer solution and was injected as a late, separate phase The main part of the iron ore deposits (Geijer 1910, 1931 b, 1935, Geijer and odman occur in a broad zone which extends from the 1974, Frietsch 1973 b, 1978). The magmatic Caldonides west of Kiruna eastwards to the origin is indicated by the fact that the ore be- Finnish border (Fig. 1). South of this zone haved as a younger igneous body; the nore scattered occurrences are present around 6811i- breccia,) is a primary, magmatic structure. The vare. The following iron ore types can be phosphorus-rich type is thought to have formed discerned: apatite-bearing iron ore (of the at a somewhat later stage in the differentation Kiruna type), skarn iron ore, quartz-banded process when there was an men higher content iron ore and metasomatic, mostly hematitic of volatiies. In the near vicinity and southwest impregnations. of Kiruna there are some economically unim- The apatite-bearing iron ores occur in inter- portant apatite-free, siliceous hematite ores that mediate and acid volcanics of the Porphyry replace acid volcanics. This ore type is consid- group having a tendency to appear relatively low ered to be a late hyiIrotherma1 formation related in the stratigraphic sequence. The ores consist to the same process that produced the apatite- of magnetite and less commody of hematite bearing ores; it is characterized by the presence together with varying amounts of apatite. The of barite and an intense metasomatic alteration apatite contains mostly 2.5-3 F, but in (sericitization) of the wall rock. some deposits it is chlorine-rich with 1-2 % C1 In the apatite-bearing iron ores magnetite is (Frietsch 1974). The content of phosphorus in the primary iron oxide from which hematite has the ore is mostly around 1 X,but some deposits, been formed by oxidation (Frietsch 1967 b). or parts of deposits, are low in phosphoras. The This is due to metasomatic processes occurring apatite occurs evenly distributed or as more or as a late phase in the activity that gave the ore. less distinct layers. Apatite-rich ores, with be- The volcanic wall rock was altered to quartz and tween 2 and 5 % P, are found in the vicinity of sericite and sometimes also calcite and chlorite. Kiruna (Rektor, Hauki, Nukutus, Henry and In addition small amounts of tourmaline, fluorite, Lappmalmen) and SW of Kiruna (Pattok). Other barite and allanite occur in these alteration minerals associated with the ore are tremolite- rocks. aainolite, diopside and in some deposits calcite. A palingenetic-sedimentary origin for the The content of titanium is less than 1 % and the apatite-bearing iron ores has been postulated by contents of manganese and sulphur less than Landergren (1948) and an exhalative-sedimentary 0.1 X. origin by Oelsner (1961) and Parkk (1975 a and The ore occurs as elongated, tabular bodies b). According to the latta author the ores in or in part as veinlets forming an irregular net- the Kiruna area were deposited in a volcano- work ())ore breccia))). The average content of sedimentary environment. The ores formed as a iron in the massive bodies is 55-65 % Fe and result of chemical and minor mechanical sec$- in the network parts 3545 0/,. The reserves are mentation in connection with the volcanism. about 3 billion tons of ore with more than This hypothesis of formation is supported by 50 % Fe. various observations, for example, quartzose, stratified ores grading into apatite-bearing ores; the order of formation being diopside-tremolite- in addition, the apatite-bearing ores occur as serpentine. fragments in the wall rock indicating that the The skarn ores have been considered as ore is older than part of the volcanics and, thus, pyrometasomatic (Geijer 1931 a, Geijer and not of intrusive origin. The ,,ore beccias,, are Magnusson 1952), the iron emanating from the considered to have formed by mobilization of older granitoids, or as volcanic-sedimentary sedimentary ore material which has been formed simultaneously with the host rocks directed into a fracture system. (Frietsch 1973 a, 1977). The main reasons for a The skarn iron ores occur in the Greenstone sedimentary mode of formation are that skarn group, mostly in the stratigraphic higher parts. iron ores and quartz-banded iron ores, of which The host rocks consist mainly of chemical or the latter are undoubtedly of sedimentary origin, detrital sediments, less commonly of the basic both occur in the same stratigraphic position in volcanics proper. In many cases the ores are the Greenstone group. In some deposits the two associated with limestones-dolomites and marls, types occur intermingled with each other. The or, at least occur in the same stratigraphic posi- skarn-layering and the more rare carbonate- tion. All the larger deposits are associated with a layering in the skarn iron ores is probably a sedimentary sequence. The ore forms lenses, up relict sedimentary texture. The skarn formation to 1-2 km long and 10-100 m across, which was possibly completed before the intrusion of are concordant with the host rocks. The domi- the older group of granitoids (Frietsch 1967 a). nant ore mineral is magnetite or, exceptionally, The magnetite in the skarn iron ores and in the hematite. The amount of iron varies in most quartz-banded iron ores has a similar trace cases between 30 and 40 X. The ore usually element distribution (Frietsch 1970); of special contains subordinate amounts of pyrite and interest is the relatively high content of mag- pyrrhotite and sometimes also chalcopyrite. The nesium (up to several percent) in both types. The sulphur content is a rule higher than 1 X.The skarn iron ores are therefore considered as iron- content of phosphorus, in the form of apatite, silica-carbonate-rich sediments which through is in most cases less than 0.1 X, but in some later metamorphic processes have attained their deposits the content is higher and rises locally present mineralogical composition. to 1 or 2 X. The content of manganese is usually The quartz-banded iron ores in the Green- less than 0.2 %. The reserves are about 500 mil- stone group are quartzites in which magnetite lion tons of ore with an average of 36 Fe. and skarn minerals occur in a more or less banded The ore is accompanied by large amounts of fashion. The ores, which are considered to be skarn silicates which are evenly distributed in the volcanogenic (Frietsch 1973 a, 1977), are locally ore or form independent masses or layers. Rather rather high in iron, but the average grade is common is an interlayering of magnetite and mostly below 20 %. The occurrences are small skarn minerals, or sometimes also calcite. The and the reserves are about 10 million tons of skarn silicates are either Ca-Mg-rich (tremolite- ore. The deposits have a large extension along actinolite, diopside, hornblende) or Mg-rich the strike but the width is only some tens of (phlogopite-biotite, olivine and serpentine). In metres. The most common skarn minerals some deposits there seems to be a tendency for are cummingtonite-grunerite, clinoenstatite-hy- the Ca-Mg-rich silicates to form independent persthene, hornblende and almandite. Small masses outside the ore and the Mg-rich silicates amounts of pyrite and pyrrhotite are also present to be distributed within the ore itself. There are and the sulphur content reaches some per cent. indications from some deposits that the Mg-rich The content of phosphorus is less than 0.1 X. silicates are later than the Ca-Mg-rich silicates, The manganese content is mostly low but rises in some deposits to 1-2 %. In these deposits pyrite. Exceptionally, as in the Viscaria occur- the silicates are manganese-bearing and dch in rence west of Kiruna, chalcopyrite is present in ferrous iron. economical amounts as a he banding, even The quartz-handed iron ores in the southern impregnation and veblets (cf. p. 17). part of the Norrbotten county differ in some Other occurrences of copper sulphides in the respects from those described above. They Greenstone group have a less marked relation- oceur in terrains with acid volcanics. The ship to certain stratigraphic horizons. In many wall rock is made up of metasediments such as cases the mineralizations are epigenetic, mostly mica-schist and quarrzites, but also the volcanics occurring in metasediments of different kinds. proper. The most common skarn minerals are In the Porphyry group the copper ores vary diopside, trernolite-aainolite, garnet, epidote depending on their geographical location. For and biotite. The content of manganese is in some example, at TjPrrojBkka, WSW of Kiruna, tuff deposits rather high, rising to 7 %. These ores intercalations in the porphyries contain strata- which most probably also are of volcanogenic bound mineralizations with chalcopyrite, bornite origin, are in many respects similar to the qnartz- and magnetite, In the Svappavaara-Gallivare banded iron ores of Central Sweden. The area chalcopyrite-bornite mineralizations occur reserves are somewhat more than 120 million in scapolitized supracrustal rocks. At Gruvber- tons of ore. get, Svappavaara, chalcopyrite and bornite are found in scapolite-altered trachytes (p. 23) and the mineralbations in the Gallivare area (Aitik copper oreJ and Nautanen) lie ia sericite-tourmaline-scapolite In the Precambrian of Not-rbotten county altered metasediments (biotite schism, quartzites copper ores are found in the Greenstone group and skarn gneisses). These rocks possibly belong and the Porphyry group and occur spowdically to the Schist-conglomerate group. The ore in gneiss'and granite. Copper sulphides are found minerals present are chalcopyrite, pyrite, pyr- rather frequently but tend to form weak miner- rhotite, magnetite, bornite and chalcocite which alization~of small size. The sulphides (mostly appear as impregnations or veinlets. The gangue chalcopyrite, with subordinate bornite and is composed of quartz, calcite, barite and fluorite. chalcocite) appear as disseminarions or fissure The only deposit of impoaance is Aitik, being fillings. Pyrite and magnetite, together with the greatest single copper deposit in Sweden. molybdenite in some deposits, commonly belong. The outcrop area is 300 000 m8 and the reserves to the association, and a small number of de- are 300 million tons of ore with 0.45 % Cu (p. posits contain sphalerite and sporadic galena. 28). About 5 km east of Aitik a similar but The skarn iron ores and the quartz-banded smaller mineralization occurs called Liikavaara E. iron ores in the Greenstone group contain small In the southern part of the county vein type amounts of iron sulphides (pyrrhotite and pyrite) deposits with chalcopyrite, magnetite, bornite, and subordinate amounts of chalcopyrite. The covellite and chalcocite are present in acid copper grades are mostly below 0.1 % Cu, but volcanics. Sphalerite is a relatively common some skarn iron ores contain up to 0.2-4.3 % constituent in some deposits within metasedi- Cu; the largest being Tervaskoski with 50 mil- ments and supracrustal gneisses. In these deposits lion tons of ore with 0.1 Cu. The graphite- small amounts of galena, molybdenite and bearing schists which occur in the same strati- arsenopyrite belong to the association. Some graphic position as the iron ores also contain the mineralizations occur in connection with brec- same ifon sulphides but are devoid of chalco- cias in basic-acid volcanin or metasediments. GEOLOGY OF THE KIRUNA AREA - by Paul Forsell and Lisbeth Godin

The Kiruna area is exclusively underlain by the deposition of the ores is also supported by Precambrian rocks (Fig. 2). The oldest rock- the occurrence of a conglomerate (Fig. 5) be- complex, mostly consisting of gneisses, is found tween the syenite-porphyry and the iron ore. in the northern part of the Kiruna district (out- The main ore bodies, the Kiirunavaara- (4) side the map). Those rocks comprise the base- and Luossavaara-ores, comprise fine grained ment of Kiruna Volcanics, the oldest group of magnetite-ores, partly very rich in apatite. There which is the Kiruna Greenstone (spilite) with are two types of ores (Fig. 6), one is rich in apatite, intercalations of tuff, graphite-schist, limestone, often showing a distinct banding, and the other and albitite (l)'). Magnetite and sulphides is an almost apatite-free, massive type. The (mainly pyrrhotite and chalcopyrite) are com- apatite is rich in rare-earth-elements (about mon constituents of these sediments (1). Ultra- 0.5 X). Actinolite and calcite occur in very basic members are found in the western part subordinate amounts. The foot-wall contact is of the greenstone group. commonly very sharp (4). In the hanging-wall- The Kurravaara Conglomerate (2) is younger contact (4), however, a kaolinization of the than the siliceous basal porphyry (quartz-kerato- quartz-bearing porphyry is common. Recent phyre) and the syenite-porphyry (keratophyre). geological and geochemical data contradict the Sixty to seventy percent of the pebbles are com- magnetite-intrusive theory proposed by Geijer posed of silicic porphyries similar to those found (1931 b). A hypothesis of a volcanic-sedimentary east of the conglomerate. Pebbles of magnetite- origin of the ores has been proven to be more syenite-porphyry (see below) also indicate that consistent with known geological facts (Parhk the Kurravaara Conglomerate is younger than 1975 a). most of the syenite-porphyries. The conglom- The ore, as well as the above mentioned rocks, erate forms a synclinal fold (see cross-section). are often intersected by porphyry dykes, which The syenite (3) is found between the silicic chemically occupy a position between the syenite- porphyry and the syenite-porphyry. The eastern porphyries and the quartz-bearing porphyries. margin of the syenite is transitional into the The quartz-bearing porphyry (6, 7, 8, 9) syenite-porphyry. (quartz-keratophyre to rhyolite) forms the hang- The syenite-porphyry (3, 4, 5) often exhibits ing-wall of the main ores. It is locally rich in amygdaloidal structures. Tuffaceous intercala- xenoliths of apatite-magnetite ore (6). Sometimes tions are rarely found (3). In the upper parts of agglomeratic to conglomeratic layers are found the syenite-porphyry suite there occurs a rock (6). In one drillhole through the quartz-bearing consisting of albite-needles in matrix of mag- porphyry a 5 m long section of anhydrite was netite referred to as a magnetite-syenite-por- encountered. phyry. The syenite-porphyry sometimes contains The iron-ores of Hauki-type (Haukivaara, veins and fragments of magnetite, which some- Rektorn, Henry, Nukutusvaara and the deep- times form lean iron-ores. The amygdaloidal seated Lappmalmen) of the Lower Hauki-rocks types of syenite-porphyry (3) as well as the are often extremely apatite-rich hematite and tuffaceous parts sometimes show a pronounced magnetite varieties (7, 8, 9). They show great unconformity with the overlying ores (Figs. 3, similarities with the main ores and are probably of 4). The existence of a denudation-period before contemporary age. Their present position above

l) Refers to locality number in text and in Fig. 2. the quartz-porphyry is the result of folding fol- SANDSTONE, PHYLLlfE

m KURRAVAARA AN0 m SYENITE-PORPHYRY m BASAL QUARTS- PORPHYRY ( KERATOPHYRE) m GREENSTONE. SPI LITE WlTH SEOIMENTS VlSCARlA COPPER-ORE GREENSTONE WlTH ULTRABASITS

gfO NUMBERS REFER TO EXCUR5lON LOCAL1 TI ES a CROSS-SECTIONS

CROSS SECTION A-@ CROSS SECTION C- b

Fig. 2. Geological map and cross-sections of the Kirunn district...... ,:. ..:..7+:..:. . rI .: ...... ,.....::.. ~odulsrsyeniteporphyry /r/ Drift

Fig. 3. Beds of nodular syenite-porphyry in foot-wall porphyry. Kiirum- vaara (Dh = Drill holes).

Fig. 4. Tkre Luossavaara-ore and ore-veins in the footwall. lowed by over-thrusting. This interpretation cross-bedding structures indicate a reworking of implies that the quartz-bearing porphyry is the volcanic material. The Hauki Hematite (8,9) younger than the Lower Hauki-series. is lady developrd as quartz-banded haatite- The R&or Porphyry (8, 9) is a product of a ores (Fig. 7). potassium-dominant volcadsm that differs from The Hauki Conglomerate (10) shows a strong that which formed the sodium-ricb country- similarity to the Kurravaara Conglomerate and rocks of the main ores. Locally bedding and is therefore considered to be of contemporary Fig. 5. Pebbles of nodular syenite-porphyry in a matrix of magnetite in the foot-wall contact in the Kiirunavaara ore. Photo B. Ronnberg.

1-1 1-1 P-rsch ore m-4 P- PO.. ore

Fig. 6. Distribution of P-rich and P-poor ore in the Kiirunavaara ore. Fig. 7. Photo showing the continuous transition from pure quartz to pure hematite.

age, i.e. younger than the syenite-porphyries and The metamorphic grade of the area is low older than the ores. (greenschist facies), and primary structures such The phyllites and the sandstones (7) of Vakko- as graded bedding, slumping, stylolites, oolites, type represent the youngest sedimentary cycle. distinct layering and pillows are extremely well Intraformational conglomerates are common in preserved. Major folds and boudinage in the the sandstone. limestone, and pinch and swell structures in the The Lina Granites of this area are considered albitite are also common. The rocks show to be the youngest plutonic rocks (about 1500 distinct bedding and some are mineralized with Ma old). The quartz-porphyry-dykes that inter- chalcopyrite (Fig. 8). sect the southern part of the Kiirunavaara ore, The copper mineralization which is mainly as well as its country-rocks, are of a similar age. bound to the limestone and graphite-schist, The Tuolluvaara area is dominantly underlain appears as rich impregnations and also as more by quartz-porphyries identical to the basal por- distinct bands in the limestone which is locally phyries east of the Kurravaara Conglomerate. bordered by zones of massive ore (1 cm-l m). The Tuolluvaara iron ore is thus older than the The copper mineralization is also found as Kiruna ores. distinct stratabound bands, lenses and fracture Cross-section through the Viscaria ore (stop 1-1, fillings in the graphite-schist. Magnetite is found locality 1). Kiruna Greenstone with sediments as rich impregnations in the limestone, as thin and copper mineralization. layers in the tuffs and also as distinct, several The Kiruna Greenstone comprise a series of metres-thick beds. Rhytmic banding with slump NE-trending spilitic lavas intercalated with thick structures between magnetite and chalcopyrite sedimentary beds. The dip of the rocks is 80" to layers can be seen locally. There is always a the east. The sedimentary beds consists of tuff, positive correlation between copper and mag- partly fine-grained and partly coarser (up to netite. Pyrrhotite is the most common sul- lapilli size), graphite-schists, albitites (chert) and phide mineral throughout the greenstone series; limestones. pyrite is only rarely found. Apart from chalco- GRAPHITE- 1 WITH \ALBITITE GRAPHITE- .*.....-..*- SCHIST

COPPER - 0 RE

HIGH-GRADE ORE ---I

Fig. 8. Generalized profile through the A-zone of the Viscaria copper ore. pyrite there also exists subordinate amounts of alternating. The pebble material can be traced sphalerite. to the porphyries, jaspilitic rocks, magnetite ore The estimated reserves known today are 30 and to the greenstones. million tons of ore of about 1.1 % Cu bound to West of the beneficiation plant (stop 1-3, locality three separate beds. These are named A, B and 3). Syenite (3 a). Quartz-porphyry-dyke (grano- D horizons and have a length of 3.5, 1.8 and phyre) (3 b). The open pit: syenite-porphyry (3 c) 1.0 km, respectively and a grade of 1.4 %, 1.0 % with tuff-intercalation (3 d). and 1.0 % Cu. The thickness varies between 5 m 3 a. The syenite is red to grey, often greenish- and 25 m and the depth between 150 m and coloured by epidote. The transition between the 400 m. the syenite and the syenite-porphyry is gra- Valkeasiipivaara (stop 1-2, locality 2). Pillow- dational. The mineralogical composition of the lava (2a). Kurravaara Conglomerate (2 b). syenite is similar to that of the syenite-porphyry, 2a: The main part of the Kiruna Greenstone consisting of Na-rich, perthitic feldspar, pyr- lava consists of a medium-grained, commonly oxene, epidote, magnetite, sphene, apatite, and scapolitized, homogeneous rock of spilitic to occasionally quartz. basaltic composition. It is only at the highest 3 b: The quartz-porphyry-dyke is of a similar levels of the greenstone series (above known age as the Lina Granite and usually rather mineralizations) that pillow-structures have been strongly deformed. found in beds up to 80 m thick. The pillows are 3 c-3 d: Along the bench in the foot-wall comparatively small, 5-50 cm in diameter. different types of the syenite-porphyry can be Pillow exteriors are composed of devitrified glass studied as well as minor intercalations of banded which enclose a zone of radially oriented nodules; tuff. the central parts of the pillows are fine-grained. The Kiirunavaara ore, undergro~nd (stop 1---4 2 b: The Kurravaara Conglomerate rests un- locality 4). A cross-section from footwall to conformably on the Kiruna Greenstones. The hanging-wall. Ore and contacts between the ore Conglomerate is polymictic, and commonly and the syenite-porphyry (foot-wall) and the cross-bedded; pebble-free and pebble-rich layers quartz-bearing porphyry (hanging-wall). Second day ding and cross-bedding. Intraformational con- glomerate-beds are common. A few pebbles of The smmit of Luossavaara Mountain (stop 2-1, of rocks from the Lower Hauki-series were locality 5). ))Ore-dykes,) in the syenite-porphyry recorded by T. Pardk but normally only quartz- (5)- bearing porphyry-pebbles are found which 5. These ore-veins (Fig. 4) have been regarded implies that the Lower Hauki-rocks were largely as an indication of an intrusive emplacement of covered by quartz-bearing porphyry at the the ore. However, as much other data suggest a time of the deposition of the Vakko Sand- volcanic-sedimentary origin of the ores, a more stone. likely interpretation is that these ore-veins are The central part of the open pit of the Rektor ore precipitates formed in connection with the (stop 24, locality 8). >,Rektor-porphyry>>, extrusion of the syenite-porphyry lava. Major Hauki Hematite (8 a) and Hauki-ore with a differences are found between the trace element ))slaty cleavage,, (8 a). The Rektor Porphyry distribution in magnetites from the >)oredykes)) commonly forms the hanging-wall to the apatite- and that in magnetite from the main ore body. magnetite ore. The hanging-wall (east) side of the Luossavaara 8a. The Rektor Porphyry is a somewhat in- ore (stop 2-2, locality 6). Xenoliths of ore and adequate name for a group of mostly red rocks porphyry in the quartz-bearing porphyry (6 a). comprising lava, tuff and their reworked material. Agglomerates (6 b). In the banded varieties one locally finds cross- 6 a. Xenoliths and fragments of magnetite-ore bedding. are rather common in the quartz-bearing por- The Hauki Hematite, a quartz-hematite-ore, phyry. The ore-inclusions are of the same fine- sometimes developed as a quartz-banded ore grained apatite-magnetite type that exists in the (Fig. 7), shows a more or less gradational con- main ores. Fragments of syenite-porphyry are tact zone to the Rektor Porphyry. also rather common. The ore-inclusions support 8 b. The ore of the ~ektordeposit at this the concept that the quartz-bearing porphyry is locality displays a unique schistosity resembling younger than the main ores. slaty cleavage. Pardk (1975 a) also reported fragments of The sodern part of the open pit of the Rektor ore rock-types similar to those of the Lower Hauki- (stop 2-5, locality 9). Banded, folded apatite-ore serie, which suggests that the quartz-bearing (9 a). ),Agglomerate)> (9 b). Normal apatite- porphyry is younger than the Lower Hauki magnetite ore with intersecting pegmatitic dykes rocks. (9 c). Rektor Porphyry and Hauki Hematite (9 d). 6 b. Agglomeratic and sometimes conglom- Syenite-porphyry of Hauki-type (9 e). eratic intercalations are common in the quartz- 9a. In the western wall of the open pit there bearing porphyry. is a banded apatite-hematite rock exhibiting Nakutusvaara (stop 2-3, locality 7). Lower minor folding. Similar apatite-rich ores are Hauki-ore with banded apatite-magnetite ore characteristic of the contact-zone between nor- (7 a). Upper Hauki-sediments: Vakko Sandstone mal Hauki-ores and the quartz-bearing porphyry. (7 b). 9 b. The same type of banded apatite-rock 7a. The banded, apatite-rich ore is typical of forms the matrix in a rock with large ,fragments), the apatite-rich ores both here and in the main of schistose, quartz-bearing porphyry. The shape ore body. Recrystallization of the apatite has of the pebbles perhaps indicates a pyroclastic commonly segregated the apatite and magnetite. origin. 7 b. The Vakko Sandstone is a red to grey-red 9 c. The apatite-magnetite ore displays large feldspar-quartzite, commonly with distinct bed- veins and irregular areas, where a mobilization of the apatite has produced veins and irregular less-deformed rocks resemble the syenite-por- bodies of almost pure apatite. The intersecting phyries in the foot-wall of the main ores. pegmatite dykes consist of quartz, calcite, Dokfornr &lie (east of the Rektor ore) (stop hematite, albite and rarely tourmaline. 2-6, locality 10). Hauki Conglomerate (10.) 9d. The great variation of the Rektor por- 10. The pebbles of the conglomerate, where it phyry and the Hauki Hematite is well exposed is less schistose than at this locality, can be at this locality. In the eastern part of the open observed to consist of quartz-porphyry and pit there is a Hauki Hematite-rock with por- hematite. The porphyry-pebbles here mostly phyroblasts of potash-feldspar. resemble grey schists. Jaspilite, quartz and green- 9e. The syenite-porphyry of the Hauki-type stone are other more rare pebble components. is normally a schistose rock consisting of albite, In other parts of the Lower Hauki series the quartz, muscovite, sericite, biotite and hematite. conglomerate is subordinate to fine-grained Orthite, zircon, tourmaline and apatite are also sediments of greywacke-character. The similarity found. Locally it is possible to determine the to the Kurravaara Conglomerate has already original character of the rock. The structurally been pointed out.

Third day

GEOLOGY AND ORES OF THE SVAPPAVAARA AREA - by Rudyard Frietsch

Geological setting belong to mainly the Greenstone and the Por- The Svappavaara area, which is one of the phyry groups. The Schist-conglomerate group oldest mining districts in the county of Norr- covers only a small area. botten, contains iron and sulphide ores (Frietsch The Greenstone group is dominated by tuffites 1966). The copper ore at Gruvberget was in which the original material is of basic volcanic discovered 1654 and mined to the end of the origin. These rocks, which are partly banded, 1670's. The copper deposits at Sarkivaara (dis- consist of tremolite-actinolite, albite and biotite. covered 1714) and Kiilavaara (discovered 1751) In the tuffites occur intercalations of graphite- were mined to a limited extent in the middle of bearing schists, biotite-rich quartzites, marls, the 18th century. The apatite-bearing ore at amphibole schists and limestones, all of which Gruvberget, which was found at the same time have a sedimentary origin. The marls, whichare as the copper ore, underwent small scale exploita- well banded, contain scapolite, diopside, tre- tion at the beginning of the 18th century. The molite-actinolite and biotite. The amphibole other iron ores of the area (Leveaniemi and Tan- schists, dominantly of tremolite-actinolite, are sari of the apatite-bearing type and Alpha, interpreted as silica-rich, calcareous sediments. Kiilavaara and Kulleri of the skarn ore type) Amphibole and pyroxene skarns, which in part were all discovered at the end of the 19th century. contain thin intercalations of chert, occur on a The Leveaniemi ore has been mined since 1964. small scale in association with the limestones. Supracrustal rocks and intrusive rocks have The Greenstone group is in the east overlain approximately the same aerial extent in the by a quartzitic sandstone, partly limited by fault- Svappavaara area (Fig. 9). The supracrustals ing, belonging to the Schist-conglomerate group. Fig. 9. Geological map of the Svappavaara area. After Grip and Erietsch (1973). The main part of the Porphyry group is com- the eastern massif the gabbro contains bodies of posed of trachytes which are fine-grained equi- microcline-plagiodase-bearing syenite and gran- granular rocks consisting of plagioclase (albite- ite which probably belong to the same magmatic oligoclase, more rarely oligoclase or andesine), suite. The age of the intrusives is not known. microcline, quartz and biotite. Locally the rocks The tectonic conditions in the Svappavaara are porphyritic with phenocrysts of albite or area are difficult to interpret. The Greenstone microcline. Within the trachytes are intercala- group shows a complicated folding fabric with tions of basic volcanics containing biotite and moderate to steep folding axes. The rocks adja- subordinate amounts of microcline, albite-oligo- cent to the Porphyry group are delineated by clase, chlorite and tremolite-actinolite. Towards NW-SE and NE-SW faults. The Porphyry group the northwest a large area is covered by albite is also folded; the trachytes occur in synforms porphyrites which consist of plagioclase (albite, with fold axes trending (moderately) N or NE. rarely oligoclase or andesine), biotite, and locally Albitites or so called leucodiabases are found also amphibole. The chemical composition is in the basic volcanics within the Porphyry group, similar to a trachyte although the occasional Greenstone group and to a small extent in presence of Ca-rich feldspar and the high am- andesite porphyrite, and gabbro. Mostly the phibole content suggest that the albite porphyri- albitites, which occur as elongated bodies parallel tes might originally have been basic lavas but to tectonic disturbances, are fine-grained, red- later altered to their present composition. dish leucocratic rocks which consist of albite In the trachytes west of the iron ore at LeveH- (An,-,J and small amounts of amphibole and niemi occurs an intercalation of mar1 with some carbonate. The albite often forms irregular laths limestone; narrow limestone bands are also found arranged in a pseudo-ophitic texture. kccording in the trachytes to the NNE of the deposit. to adman (1957) the albitites are of magmatic These calcareous rocks are similar to those in origin. Padget (1959) and Frietsch (1966) con- the Greenstone group. sidered them to have been formed by meta- Syn-kinematic intrusions occur concordant to somatic alteration of basic rocks in the neigh- the layering within the supracrustals. In the bourhood of faults and fracture zones. Active in Greenstone group and the Porphyry group small this process were solutions rich in sodium and intrusions of andesite porphyrite are found con- containing some carbon dioxide; in the basic sisting of andesine, hornblende, biotite and less rocks successive change in the mineral composi- commonly diopside. The quartzitic sandstone of tion commonly occurred with the breaking down the Schist-conglomerate group is intruded by a of the dark minerals and a bleaching of the rocks. granodiorite possibly belonging to the older With the exception of syenite and granite the group of intrusives. rocks of the Svappavaara area are more or less In the southern part of the Svappavaara area scapolitized. The scapolite is a dipyr (Ma,,-,,), microdine-plagioclase-beariag granites and as- exceptionally a mizzonite. In the Greenstone sociated pegmatites occur peripherally against group the scapolite has been formed in those the supracrustals. These late-kinematic intrusions rocks which contain carbonate and day minerals, belong to the younger intrusive group. In the such as marls and calcareous-rich graphite- granite are found biotite-quartz-oligoclase gneis- bearing schists. This explains the intimate, but ses of unknown origln; they might either be irregular distribution of scapolite-rich and derived from the Greenstone group, or, less scapolite-poor or scapolite-free rocks in the probable, from the Porphyry group. Greenstone group. The content of scapolite is A gabbro forms the eastern and partly also here a measure of the original content of car- the western border of the supracrustal rocks. In bonate and day minerals. The scapolitization is a regional process of The northern part of the ore body consists of a relatively young age. According to Geijer magnetite with small amounts of hematite. The (1931 a) and Odman (1957) it is genetically gangue is composed of apatite, calcite and some related to the younger group of granitoids. An actinolite. To the south the magnetite ore passes addition of solutions rich in chlorine (and other transitionally into hematite ore. The hematite, elements such as sodium) is considered as pre- often associated with apatite, calcite and andra- requisite. According to Frietsch (1966) all the dite, has been formed from magnetite through necessary components, except chlorine, could oxidation. The northern part of the hematite have been present in the marly and calcareous ores is separated from the wall rock by a skarn sediments in the Greenstone group, so that the consisting of andradite, actinolite and epidote. formation of scapolite is thus mainly a result of In the hanging wall part of the hematite ore a internal redistribution caused by regional there is a fragment-bearing zone about 400 m metamorphism. long and up to 20 m wide. This fragmentary ore type, which contains angular to sub-angular fragments of hematite and sericite schist in a Ore deposits matrix of hematite, chlorite and some quartz and In the Svappavaara area both apatite iron ores calcite, is tectonically derived and is probably and skarn iron ores are found. The apatite- related to a crush-zone which borders the hanging bearing ore exemplified at Gruvberget, Levea- wall of the ore body. The tectonization is of a niemi and Tansari, occur within trachytes be- relatively young age; this is shown by the presence longing to the Porphyry group in the central of fragments of coarse microcline derived from part of synforms. The skarn iron ores which the pegmatites belonging to the Lina granite. are of limited extent and importance, include Within the fragment-bearing ore extending Alpha, Kiilavaara and Kulleri in the Greenstone northwards, the hematite at the hanging wall has group, and Koivujarvi which lies within a biotite been subject to weathering to a depth of at least gneiss. Some unimportant sulphide mineraliza- 200 m (Frietsch 1960). The trachyte in the hang- tions are also present, for example, at Gruv- ing wall has been kaolinized. The alteration of berget disseminations and veins of copper both the ore and the trachyte is caused by the sulphides occur in scapolitized trachytes of the action of percolating surface water. The altera- Porphyry group. Syngenetic sulphide assem- tion seems to be restricted to the same zone of blages consisting mainly of pyrite, pyrrhotite tectonization as the fragment-bearing hematite; and subordinate chalcopyrite are found in the the fracturing of the hematite and the trachyte rocks of the Greenstone group; at Isovainio in has probably facilitated the percolation of the a skarn-bearing limestone and at Kiilavaara in a solutions. In the soft ore all minerals except graphite-bearing schist. In the latter deposit some hematite were leached out. The age of this galena and sphalerite appear as fissure-fillings. process is older than the latest glaciation. The Grtlvberget iron and copper ore (stop 3-1). The age relations between the fragment-bearing and Gruvberget iron ore, situated 3 km to the west soft ore types are not further known; possibly of the Svappavaara village, is in the form of a the superficial weathering is much younger. tabular body about 1300 m long, 6 to 65 m In the foot wall, adjacent to the main ore body, across and an outcrop area of about 44 000 m2 an nore breccia),, up to 70 m across, is encoun- (Fig. 10). The body strikes about N-S and dips tered containing veinlets of magnetite and 50-75" eastwards; to the north the body is hematite. In addition small ore bodies and miner- dislocated by NE-SW, or less commonly WNW- alization~are scattered throughout the volcanics ESE, faults. up to 500 m west of the ore body. Magnetite ore Trachyte

Hematite ore m]Kaalinired trachyte

m . . , . . . Fragment-bearing hemotite ore

Soft hemat i te ore

- Sericite schist ''---yt \ "Ore breccia" p1-- L'Jm Fig. 10. The iron ore at Gruvberget. After Grip and Frietsch (1973). The average grade of the magnetite ore is Probably the alteration is facilitated by NE-SW 56.5 % Fe and 1.1 P. The hematite ore and faults acting as channelways in this part of the the fragment-bearing hematite ore contain 55.4 deposit. In the south where no faults are known, % Fe and 0.86 % P. The soft hematite ore con- the scapolitization is missing. tains 66.6 % Fe and 0.02 % P. To a depth Within the scapolitized trachyte a sporadic 1 somewhat greater than 300 m the amount of ore copper mineralization is found. The main part (including adjacent parts of the nore breccia))) of the mineralization, which was discovered in with an average of 40.9 % Fe and 0.65 P, 1654 and exploited to the end of the 167OYs, is about 74 million tons. lies to the west of the iron ore body. The pri- The wall rock is composed of an equigranular mary copper minerals are chalcopyrite and trachyte with plagioclase (albite-oligoclase, more bornite from which secondary chalcocite, covel- rarely oligoclase or andesine), microcline, quartz lite, malachite and azurite are formed by super- and biotite. Locally the rock is porphyritic with ficial weathering. Exceptionally and in very phenocrysts of albite. West of the ore body minor amounts, pyrite, arsenopyrite, crythrite, there are up to 200 m wide intercalations of a molybdenite, gold and native copper are encoun- biotite-rich basaltic lava. tered. The mineralization appears in the scapolite- The ore and the volcanics are cut by a series altered trachyte in secondary schlieren and joints, NW-SE trending dykes (up to 10 m wide) of which besides scapolite contain tremolite-actino- metabasites composed of scapolite, biotite and lite, stilbite, chabazite and calcite. The minerali- and hornblende. zed zones are up to a few metres wide and con- Locally the volcanics have been metasomati- tain around 0.5 % Cu. cally altered with the formation of sericite, quartz Kiilavaara iron ore (stop 3-2). The skarn iron and some chlorite. The alteration is closely ore at Kiilavaara, situated about 1 km to the associated with tectonic zones; evidenced by the east of the Svappavaara village, occurs in associa- occurrence of altered sericite-quartz breccias. tion with a limestone in the Greenstone group. These altered rocks are cut by the Lina granite The ore body has a known length of some and its pegmatite. From the nearby iron ore at hundred metres and is about 20 m across. The Leveaniemi, it is possible to show that the ore which strikes N-S and dips steeply towards metabasites that intersect the volcanics and the east, is surrounded by and contains a skarn ore, are also younger than the sericitization. consisting of tremolite-actinolite or less com- According to Frietsch (1967 b), the alteration monly of phlogopite with some diopside, pyrite is intimately connected with the ore forming and chalcopyrite. The skarn forms separate process, representing a late hydrothermal phase layers some metres wide or occurs within the in the differentiation. The same solutions are ore as a mm-wide banding or uniformly distrib- considered to have caused the alteration of uted. Small amounts of pyrite and occasionally magnetite to hematite. some chalcopyrite belong to the association. The On both sides of the iron ore body, mainly ore contains 30-35 % Fe, 0.02-0.05 % P and around the northern part and to a less extent the 1-2 % S. middle part, the trachyte is scapolitized over The immediate wall rock of the ore is a skarn- relatively large areas. The altered rock contains bearing limestone surrounded by basic tuffites scapolite with subordinate amounts of tremolite- and graphite-bearing schists. On both sides of actinolite, epidote and minor quartz, calcite, the ore an albitite is encountered which has stilbite, chabazite and copper sulphides. The possibly a N-S extension and follows in the secondary minerals occur as schlieren, vein fil- main a small fault visible in the terrain as a lings and evely distributed within the trachyte. bog-filled depression. SAIVO IRON ORE - by Rudyard Frietsch

Tbe Saivo iron ore deposit (stop 3-3), situated schlieren-like remnants of a scapolitized gabbro; about 20 km east of Kiruna and about 400 m in these scapolite, diopside and albite-oligoclase north of lake Sautusjarvi, is economically quite dominate with small amounts of biotite and unimportant but interesting from the genetic tremolite-actinolite. A less altered gabbro is point of view. It differs from the other ore types found 1 km west of the deposit. in Norrbotten. Within the syenite there is an E-W oriented, The ore lies within a large gabbro massif. The about 250 m long and 50-60 m wide skarn immediate wall rock is perthite-syenite, which is body which has the general apperance of a locally porphyritic and granitic in composition fissure filling (Fig. 11). In the gabbro and the (Lehto 1972). The syenite is a red, fine- to syenite there are in addition smaller veins and medium-grained rock with albite-oligoclase and fissure fillings of a similar skarn. In part the perthitic microcline as the main minerals. Sub- skarn contains angular fragments of the syenite ordinate are diopside, tremolite-actinolite, quartz, in breccia-like formations. The main skarn body epidote, magnetite and sphene. The gabbro and is built up of a diopside (the crystals reaching the syenite pass successively into each other with 50 cm or more in length) with subordinate the syenite often containing irregular and magnetite, sphene, ankerite and plagioclase.

b...... E

m Iron ore m Skam U Syenite m Syenite with relicts a Gabbra of gabbro Fig. 11. The Saivo iron ore. After Lehto (1972). Along the skarn-syenite contact, mainly in the to Frietsch (1970) the skarn and magnetite south, accumulations of magnetite occur which represent a late stage in the magmatic activity are between some decimetres and 5-6 m across that gave rise to the gabbro; an interpretation and consist of a coarse magnetite with crystals supported by the high content of titanium in the up to 10-20 cm in length. The magnetite is magnetite. A metasomatic origin of the skarn accompanied by diopside, amphibole and sphene. and ore is, however, also plausible (Lehto 1972); Magnetite occurs also within the skarn together by metasomatic processes the gabbro has been with sphene as coarse crystals or as veins up to altered to syenite and the skarn and ore were some decimetres wide. The magnetite has a high formed by elements released by this process. content of titanium (3 % Ti) which occurs as According to Eriksson and Hallgren (1975) the ilmenite or is sited in the magnetite lattice skarn and ore are connected with the formation (Frietsch 1970). of the perthite-syenite which is considered as a The origin of the magnetite-bearing skarn at normal member of the youngest group of deep- Saivo is uncertain. The order of formation is seated rocks, and thus with an age of about gabbrolsyenitelskarn and magnetite. According 1 535-1 565 Ma.

Fourth dq

MERTAINEN IRON ORE - by Rudyard Frietsch

Tbe Mertainen deposit (stop 4-l), situated Smellie 1979). In addition the trachyte often con- 30 km SE of Kiruna, is an apatite-bearing iron tains impregnations of magnetite, occurring as a ore (of the Kiruna type). The ore-bearing area finely divided matrix material. There are gradual strikes NE-SW and has a length of about 1 200 transitions between ore, ))ore breccian, trachyte m and a width of 200 m (Fig. 12). The dip of with magnetite vesicles and magnetite impregna- the ore is moderately or steeply northwest. The tions. According to Lundberg and Smellie (1979) ore which is composed of magnetite, to a very the magnetite-rich trachytes resulted by an slight degree altered to hematite, appears as assimilation of iron-rich material during their narrow, relatively short bodies or as veinlets formation. The ore is the result of immiscibility forming a net-work ())ore breccia))). The mag- aided by a high content of volatiles. The impor- netite is accompanied by small amounts of tance of the magnetite filled vesicles is empha- actinolite skarn. In the ))breccian there is also sized. This is in accordance with Geijer (1931 a, calcite, partly of secondary nature, and scapolite, 1960): the ores and the vesicles are similar for- which at least partly was formed simultaneously mations, volatiles being active in both. with the magnetite. In spite of many irregularities within the ore The wall rock is a porphyritic trachyte which there is some degree of partition in that the ore in a matrix of quartz and feldspar contains bodies which occur in the south-eastern part of phenocrysts of albite together with secondary the deposit are separated from the underlying biotite and scapolite. Vesicles filled with magnet- almost ore-free porphyry by a narrow zone of a ite and some actinolite, sphene, apatite, biotite, poor ))ore breccia)) containing vesicles and im- quartz and feldspar are common (Lnndberg and pregnations of magnetite. To the north the ore Magnetite ore I/-I Rich "ore breccia" D Poor "ore breccio"

Fig. 12, The Mertainen iron ore. After Gsip and Frietsch (1973). bodies are surrounded by rich sbreccia>>passing there are parts which are relatively rich in transitionally to a poor >)breccia~and finally to a phosphopas (between 0.2 and 0.9 % P). The magnetite-poor trachyte. The ore-bearing area, reserves in the deposit calculated to a depth of often cut by narrow dykes of metabasites, is also 300 m, are about 165 million tons of ore with an dislocated latt~ally by small faults mainly aTeragt af 34 Fe. The ore body in the middle orientated in NW-SE and NNVV-SSE direcrions. part of the deposit has been mined between The apatite content of the ore is low, on an 1956-1958 with 218 900 t~nsof ore and average 0.05 % P although in the northeast 210 000 tons of )>breccia))removed.

AITIK COPPER ORE - by Hans Zweifel

Introduction The area is covered by extensive swamps dissected by moraine ridge*. Outcrops are rare The Aitik wr is the glacial overburden has a thickness of about 15 km E of Gallivare, Norrbomn County, 5-15 m. Several small deposits are known to the at lat. 67'07'N and long. 21" E. About 5 km N of Ai& (Liikavaara, Nautanen a.s.0.). E of Aitik a similar but smaller mineralization Glacial boulders with disseminated chalco- occurs called Liikavaara E. pyrite were found in the area by the Boliden Company in 1930. Geological investigations in crushing, autogenous and pebble grinding. The 1932 resultated in the discovery of a small miner- fine product from the hydrocyclons in the A- alized outcrop at the place where the Aitik mine and B-sections is mixed together and pumbed to has subsequently been developed. EM-survey bulk flotation series. In the A-section the bulk with the Swedish two-frame method at that time concentrate is floated in two parallel flotation resulted in the localization of the Aitik zone and series, each consisting of 28 BFR-300 flotation Liikavaara E zone, 5 km east of Aitik. Drilling cells. In the B-section the bulk flotation consists took place in 1933 and 1936. As the grade of of three flotation series with 40 BFR-300 cells mineralization was not attractive at that time, in each. there was a period of inactivity until 1948. Be- The Cu-grade of the feed ore is 0.4 X,the tween 1948 and 1956 loop frame (slingram) concentrate 28.0 and the tailings 0.04 X. The surveys and minor geochemical investigations dried concentrate is collected in containers with were carried out. In 1957 a new period of 11 tons net weight and then transported 18 kilo- activity started including geological mapping, meters (12 miles) with lorries to the railway airborne electromagnetic and magnetic surveys station in Gallivare, where the containers are and later diamond drilling, especially on the loaded over to railway cars for further transport deeper levels of the mineralizations. Resistivity 400 kilometers (250 miles) to the company's surveys which were carried out between 1960 smelting plant in Ronnskar situated on the coast. and 1962 showed that this method was superior to the EM-methods to indicate the disseminated Geological Setting mineralization in the Aitik zone. By 1963 the drilling had outlined so extensive an area of low The rock units of the area are of Precambrian grade mineralizations that a feasibility study for age and consist of metamorphosed sediments an open pit mine was started, which later showed occurring in a zone 40 km long, parallel to the that the project was economically reasonable. general N 20°W strike and with an average The development work started in 1965 and ore width of about 5 km (Zweifel 1972, 1976). This production in 1967. zone of metasediments is surrounded by the Project Aitik No. 1 was to develop the mine younger Lina granite and gabbro (see Figs. 13 for a 2 million tonlyear open pit operation with and 14). The Lina granite, which is obviously an average grade of 0.5 Cu and a cut-off younger than the metasediments, has been shown grade of 0.37 % Cu down to 50 m below the by the Rb/Sr-method to be 1 565&35 million surface. In project No. 2, 1970-1972, the mine years old (Welin et al. 1971). was developed for a 5 million tonslyear output According to the geological structures and the with an average grade of 0.4 % Cu. At present type of country rock a distinction can be made the mine produces 6.5-7 million tonslyear with between the eastern and western part of the an average grade of 0.4 Cu. Future plans are to Aitik-Liikavaara zone. Tectonically the eastern design the mine for a production of 11.3 million part is a syncline, with a SSE dipping axis, tonslyear by open pit operation down to a depth slightly overturned to the east with both limbs of 370 m. The stripping ratio is 0.7 : 1. dipping steeply west. This syncline can be The ore handling from the primary crushing recognized from the magnetic map and way-up to the bulk flotation consists of two parallel determinations based on cross-bedding observa- sections, the A- and B-section. The A-section tions. The rocks of the eastern part, the Liika- is built in a conventional way with primary vaara group, consist mainly of meta-arenites; in crushing, secondary crushing, rod- and pebble the higher parts intercalations with amphibolitic grinding. The B-section consists of primary layers occur. The sedimentary clastic origin of Aitik Region Geological map H. Zweifel 1971 l 1 Z km 4

A;t;k group Liikovooro group

[IIIIIII B8ot;te- omph;bole gneisses mMetooren;tes with amphibolat~clayers 0~;t;ktormotion Metooren;tes Skornbonded layer lA;ti k Syncline ahongnng wall 1 W more m Anticline I\(\ Gneasses with skorn-schlieren aNoulonen f ormotion

Fig. 13. Geological map and cross-section of the Aitik region. m Skarn-banded rocks m hmphibolite 0Somewhat banded biotite gneisses between and Pegmatite W of skarn-banded rocks 0Ore boundary (0.4% Cu average) m Sericite schists and gneisses d Drillholes outside of the ore 0Fin?-grained biotite quartzites, gneisses and sch~stspartly with garnet J Fold axes (small scale) - - Gneisses with skarn veinlets and schlieren m partly amphibolite -r Strike IS) generally foliation Coarse-grained gneisses with porphyroblasttc feldspar 7 Contact, dip Pig. 14. The Aitik copper ore. these rocks can easily be recognized from con- The average S-content is about 1.5 %, BaO glomerates and other sedimentary features, e.g. 1.0 % and P20, 0.18 %; the magnetite content cross- and graded bedding. The copper deposit is around 3 % and the average Au content is Liikavaara East occurs on the eastern side of the 0.4 g/t and Ag 4 g/t. Other metallic elements syndine. occur in traces only. The western part of the zone is tectonically At present the ore is mined at an average grade interpreted as an antiform and dome structure. of 0.4 % Cu. Ore reserves (open pit) down to The antiform has been established by observa- the 300 m level are about 300 million tons with tions of folding axes, change of dip and inter- an average content of 0.45 % Cu and a 0.22 % pretation of the magnetic map. The rocks here Cu cut-off. are collectively referred to as the Aitik group, Mineralogj. The only mineral of economic and are divided into the older Aitik formation importance is chalcopyrite, which occurs to- and an overlying formation of biotite and gether with pyrite, magnetite and pyrrhotite. biotite-amphibole gneisses. The main rock types Bornite, chalcocite and malachite also occur but of the Aitik formation are skarnbanded gneisses, are without economic importance. fine grained biotite gneisses, partly with garnet Molybdenite, sphalerite, galena and arseno- or amphiboles, sometimes changing to mica- pyrite have only been observed occasionally schists or quartzites, gneisses with skarn-schlie- within the mineralization. Pegmatites (post- ren, amphibolites and coarse grained biotite mineralization) contain occasionally isolated gneisses. Scapolitization, tourmalinization and grains of molybdenite, scheelite and uraninite. microcline infiltration have partly changed the Barite occurs generally as veinlets and fluorspar original composition of the rocks. Sericitization has also been observed. occurs mainly within the ore zone. Mode of occurrence. The mineralized zone occurs Pegmatites occur between the Lina granite in on the western flank of an antiform structure the west and the Aitik ore zone. Their frequence and is almost 3 km long and 400 m wide. and thickness diminishes from W to E, and with Towards the hanging (west side) wall the increasing depth. mineraked zone has a sharp contact, marked by the skarnbanded gneisses. To the east, along the The Ore footwall, the mineralization gradually fades out, Area andgrade. The mineralized zone is almost with no sharp boundary. The general dip of the 3 km long and 400 m wide. Within this the ore ore and the mineralized zone is 45' W and the has a length of about 2 km and a width of up strike N 10-20°E. The dip of the footwall to 200 m. The known ore areas on the different (grade limit) is generally somewhat steeper than levels are as follows; the 300 and 600 m levels the dip of the hanging wall. In the deeper parts, are at present only known in the northern part the hanging wall flattens to about 35'W. The of the ore zone. ore is probably situated in a minor anticlinal Surface structure on the west side of the larger antiform. (040 m) 300 m 600 m Average % Cu 0.68 0.65 0.7 The plunge of the economic mineralization is Cut-off % Cu 0.5 0.5 0.5 25-30" toward N 20°E in the northern part of Area mz 100 000 92 000 14 000 the ore, parallel to observed fold axes. In the Average % Cu 0.5 0.54 0.52 centre of the ore the fold axes are almost hori- Cut-off % Cu 0.32 0.4 0.4 l;ontal and in the southern part they dip 20" Area m% 220 000 205 000 97 000 toward S 20°W. The plunge of the ore (> 0.4 % Average % Cu 0.4 0.42 0.38 Cu) does not follow the fold axes in the south Cut-off y, Cu 0.22 0.22 0.22 part, but the mineralization, if we include the Area m2 380 000 480 000 270 000 pyrite, seems to do so. Tjjes of mineralization: The sericite schists occur mainly towards the hanging wall, where pyrite is also dominant in 1 1. Disseminations and stringers of chakopyrite relation to other parts of the ore. There exists a (and some pyrite) in fine grained biotite- certain zoning between pyrite and chalcopyrite. l gneiss, -schist or -quartzite. The grade of the mineralization varies both in 1 2. Disseminated chalcopyrite and pyrite (or the small and large scales. Zones from dm to stringers) in sericite-schist or quartzite. 10'th of metres wide with Cu-contents of more 3. Chalcopyrite and pyrite in skarn-schlieren and than 1 % alternate with low grade mineralized -veinlets. parts. The hanging wall is composed of a layer of typical skarnbanded gneisses, and the miner- 4. Chalcopyrite and pyrite in quartz-veinlets and alization never penetrates this layer. The bound- -veins (partly with some bornite and chalco- aries of the economic ore are just grade limits. cite). The genesis of the Aitik ore is explained by 5. 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