Report of Investigation 219 - Geologian tutkimuskeskus

GEOLOGICAL SURVEY OF FINLAND

Report of Investigation 219 2015

Discovery potential of hi-tech metals and critical minerals in Finland Sarapää, O., Lauri, L. S., Ahtola, T., Al-Ani, T., Grönholm, S., Kärkkäinen, N., Lintinen, P., Torppa, A. & Turunen, P.

GEOLOGIAN TUTKIMUSKESKUS

GEOLOGICAL SURVEY OF FINLAND

Tutkimusraportti 219

Report of Investigation 219

Sarapää, O., Lauri, L. S., Ahtola, T., Al-Ani, T., Grönholm, S., Kärkkäinen, N., Lintinen, P., Torppa, A. & Turunen, P.

Discovery potential of hi-tech metals and critical minerals in Finland

Front cover: Trenching and sampling of the Mäkärä Au-REE target in northern Lapland. Photo: Helena Hulkki, GTK Unless otherwise indicated, the figures have been prepared by the authors of the publication. ISBN 978-952-217-338-6 (pdf) ISSN 0781-4240 Layout: Elvi Turtiainen Oy

Espoo 2015

Sarapää, O., Lauri, L. S., Ahtola, T., Al-Ani, T., Grönholm, S., Kärkkäinen, N., Lintinen, P., Torppa, A. & Turunen, P. 2015. Discovery potential of hi-tech metals and critical minerals in Finland. Geological Survey of Finland, Report of Investigation 219, 54 pages, 27 figures and 3 tables. The economy of Finland and the whole European Union is heavily dependent on imported mineral raw materials. An ad hoc working group was established by the European Commission to estimate the most critical raw materials for the EU. These include antimony, beryllium, borates, chromium, cobalt, coking coal, fluorite, gallium, germanium, graphite, indium, magnesite, magnesium, niobium, phosphate rock, platinum group metals (PGM), rare earth elements (REE), silicon metal, tantalum, and tungsten. GTK has undertaken several projects to establish the discovery potential of the critical commodities in the bedrock of Finland. The Hi-tech Metals project (2009–2012) evaluated the exploration potential of Li, Ti, Ga, Ge, Nb, In, Ta, and REEs in Finland. The Li and Ti (ilmenite) exploration potential was also investigated in the industrial mineral projects of GTK in 1998–2010. The Critical Minerals project (2013–2015) has continued the work of the Hi-tech Metals project, mostly concentrating on the REE and P potential in Finland. The investigations have mainly focused on the following REE, P-REE and P targets: (1) the fenite zone of the Sokli carbonatite intrusion, (2) the Panjavaara carbonatite dykes, (3) the Tana Belt (Mäkärä and Vaulo) in northern Finland, (4) the Lamujärvi alkaline rocks in central Finland, (5) the Kovela monazite-bearing granite in southern Finland, (6) the Iivaara alkaline intrusion, (7) the Kortejärvi and Laivajoki carbonatites and (8) the Lehmikari, Vanttaus, and Suhuvaara appinite intrusions. Titanium ores are mainly found in mafic (gabbroic or gabbronoritic) intrusions, such as the ilmenite deposits of Koivusaarenneva, Peräneva, and Kairineva in western Finland, which may also have significant phosphorus potential due to their apatite content. Based on investigations by GTK, the areas with highest Li potential are the Kaustinen and Somero–Tammela provinces, which both host LCT-type pegmatites. The exploration potential of other critical commodities was evaluated based on literature and published data. Keywords (GeoRef Thesaurus, AGI): mineral exploration, high-tech metals, rare earths, rare-earth deposits, phosphate deposits, raw materials, potential deposits, Finland Olli Sarapää Geological Survey of Finland P.O. Box 77 FI-96101 ROVANIEMI FINLAND E-mail: [email protected]

Sarapää, O., Lauri, L. S., Ahtola, T., Al-Ani, T., Grönholm, S., Kärkkäinen, N., Lintinen, P., Torppa, A. & Turunen, P. 2015. Discovery potential of hi-tech metals and critical minerals in Finland. Geologian tutkimuskeskus. Tutkimusraportti 219, 54 sivua, 27 kuvaa ja 3 taulukkoa. Suomen ja Euroopan unionin talous on vahvasti riippuvainen mineraalisten raakaaineiden tuonnista. Euroopan komission perustama työryhmä määritteli teollisuuden kannalta kriittisten raaka-aineiden listan, johon kuuluvat antimoni, beryllium, boraatit, kromi, koboltti, koksi, fluoriitti, gallium, germanium, grafiitti, indium, magnesiitti, magnesiummetalli, niobi, fosfaattikivi, platinaryhmän metallit (PGM), harvinaiset maametallit (REE), metallinen pii, tantaali ja volframi. Useiden näiden raaka-aineiden esiintymispotentiaalia Suomen kallioperässä on tutkittu GTK:n hankkeissa. Hi-tech-metallit -hanke (2009–2012) keskittyi litiumin, titaanin, galliumin, germaniumin, niobin, indiumin, tantaalin ja harvinaisten maametallien esiintymiseen. Litium- ja titaaniesiintymiä on tutkittu myös useissa teollisuusmineraalihankkeissa vuosina 1998–2010. Kriittiset mineraalit -hankkeessa (2013–2015) on jatkettu erityisesti harvinaisten maametallien ja fosforiesiintymien tutkimusta. Tärkeimmät tutkimuskohteet ovat: (1) Soklin karbonatiitti-intruusion feniittikehä, (2) Panjavaaran karbonatiittijuonet, (3) Tana-vyöhyke (Mäkärä ja Vaulo) PohjoisSuomessa, (4) Lamujärven alkalikivet Keski-Suomessa, (5) Kovelan monatsiittigraniitti Etelä-Suomessa, (6) Iivaaran alkalikivi-intruusio, (7) Kortejärven ja Laivajoen karbonatiitti-intruusiot sekä (8) Lehmikarin, Vanttauksen ja Suhuvaaran appiniitti-intruusiot. Potentiaalisimpia titaanimalminetsintäkohteita ovat koostumukseltaan mafiset (gabroidiset tai gabronoriittiset) intruusiot, joissa esiintyy korkeita ilmeniittipitoisuuksia erityisesti Länsi-Suomessa Koivusaarennevan, Peränevan ja Kairinevan alueilla. Ilmeniittipitoisissa gabroissa saattaa esiintyä myös merkittäviä määriä apatiittia, mikä tekee niistä potentiaalisia fosforimalmikohteita. Korkein litiumpotentiaali on GTK:n tutkimusten perusteella Kaustisilla ja Someron–Tammelan alueilla, missä esiintyy LCT-tyypin graniittipegmatiittijuonia. Muiden tässä raportissa käsiteltyjen kriittisten raaka-aineiden etsintäpotentiaalin arviointi perustuu olemassaolevaan aineistoon ja kirjallisuuteen. Asiasanat (Geosanasto, GTK): malminetsintä, hi-tech-metallit, harvinaiset maametallit, harvinaisten maametallien esiintymät, fosfaattiesiintymät, raaka-aineet, potentiaaliset esiintymät, Suomi Olli Sarapää Geologian tutkimuskeskus PL 77 96101 ROVANIEMI Sähköposti: [email protected]

Geologian tutkimuskeskus, Tutkimusraportti 219 – Geological Survey of Finland, Report of Investigation 219, 2015 Sarapää, O., Lauri, L. S., Ahtola, T., Al-Ani, T., Grönholm, S., Kärkkäinen, N., Lintinen, P., Torppa, A. & Turunen, P.

CONTENTS

1 INTRODUCTION.................................................................................................................................... 5 2 RARE EARTH ELEMENTS (REE)........................................................................................................ 7 2.1 Field investigations and mineralogical studies on REE and P-REE targets............................. 8 2.2 Sokli carbonatite P-REE-Nb........................................................................................................ 15 2.3 Panjavaara REE-rich carbonatite dykes...................................................................................... 22 2.4 Tana Belt Au-REE targets............................................................................................................. 22 2.5 Lamujärvi syenites......................................................................................................................... 27 2.6 Kovela monazite-granite............................................................................................................... 27 2.7 Korsnäs Pb-REE deposit............................................................................................................... 27 2.8 Katajakangas and Kontioaho Nb-REE deposit.......................................................................... 30 2.9 Virtasalmi kaolin deposits............................................................................................................ 31 2.10 Rapakivi granites........................................................................................................................... 31 2.11 Rautalampi ferrogabbro................................................................................................................ 32 3 PHOSPHORUS........................................................................................................................................ 32 3.1 Siilinjärvi carbonatite.................................................................................................................... 32 3.2 Kortejärvi–Laivajoki carbonatites............................................................................................... 32 3.3 Iivaara alkaline intrusion ............................................................................................................. 35 3.4 Appinitic intrusions...................................................................................................................... 38 4 LITHIUM................................................................................................................................................. 41 4.1 Kaustinen Li-pegmatite province................................................................................................ 41 4.2 Somero–Tammela Li-pegmatite province.................................................................................. 41 4.3 Other Li pegmatites....................................................................................................................... 43 5 TITANIUM.............................................................................................................................................. 43 5.1 Koivusaarenneva Ti deposits....................................................................................................... 43 5.2 Otanmäki Fe-Ti-V deposit........................................................................................................... 44 5.3 Karhujupukka Fe-Ti-V deposit................................................................................................... 44 5.4 Kauhajoki Ti-P-Fe deposits.......................................................................................................... 44 6 GRAPHITE.............................................................................................................................................. 45 7 OTHER HI-TECH/CRITICAL METALS AND MINERALS.......................................................... 45 7.1 Platinum group metals (PGM).................................................................................................... 45 7.2 Antimony........................................................................................................................................ 45 7.3 Beryllium, niobium and tantalum in granitic pegmatites....................................................... 46 7.4 Cobalt.............................................................................................................................................. 46 7.5 Tungsten......................................................................................................................................... 46 7.6 Chromium...................................................................................................................................... 47 8 CONCLUSIONS...................................................................................................................................... 47 REFERENCES.............................................................................................................................................. 48

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Geologian tutkimuskeskus, Tutkimusraportti 219 – Geological Survey of Finland, Report of Investigation 219, 2015 Discovery potential of hi-tech metals and critical minerals in Finland

1 INTRODUCTION Hi-tech metals and critical minerals are raw materials that have an essential role in green technology and electronics. The global demand for applications such as solar panels, wind turbines, batteries, and fuel cells for electric vehicles, phosphors, magnets, mobile phones, and computers has rapidly increased in recent years, also increasing the demand for the critical raw materials. The economy of Finland and the whole European Union is heavily dependent on imported mineral raw materials. The Raw Materials Initiative of the EU in 2008 delineated the role of the EU in the global raw material market and the material flows that affect the industry within the EU. An ad hoc working group was established following the RMI to estimate the most critical raw materials for the EU. The report (European Commission 2010) included a list of 14 metals and minerals that were considered as critical; these include antimony, beryllium, cobalt, fluorite, gallium, germanium, graphite, indium, magnesium, niobium, platinum group metals (PGM), rare earth elements (REE), tantalum, and tungsten. The list was updated in 2014 (European Commission 2014) to include borates, coking coal, chromium, magnesite, phosphate, and silicon metal. The REE were divided into light REE (LREE) and heavy REE, and tantalum was removed from the list due to decreased criticality. The critical commodities are listed in Table 1 and a rough estimate of their exploration potential in Finland is included. The Geological Survey of Finland (GTK) has estimated the exploration potential of the critical raw materials in Finland in several projects. The aim of the Hi-tech Metals project (2009–2012) was to map and study the exploration potential of several hi-tech metals, including Li, In, Ga, Ge, Nb, Ta, Ti, and REE, and promote their exploitation in mining and technology industries. The project included the revision of existing data (literature, databases, drill cores) combined with new mineralogical, geochemical, and geophysical surveys

and drilling of several targets (Sarapää et al. 2010, Sarapää et al. 2013a). Cobalt and the platinumgroup metals were left outside the scope of the study, as their exploration potential in Finland had already been established (Rasilainen et al. 2010). The Li and Ti (ilmenite) exploration potential was also investigated in the industrial mineral projects of GTK in 1998–2010 (Sarapää et al. 2003, Ahtola et al. 2007, 2010a). The Critical Minerals project (2013–2015) has continued the work of the Hi-tech Metals project. The goal of the project is to find polymetallic deposits, from which the exploitation of a number of minerals and metals would be possible. Based on targeting studies, the suitable exploration targets include carbonatites and alkaline rocks (P, REE, Nb), the rapakivi granite batholiths (In, REE, Nb) in southern Finland, REE pegmatites and REE skarns, and gabbros (P, Ti, Sc). The apatite potential is being estimated for future fertilizer requirements. Prediction of the flake graphite potential will be based on exploration results and lowaltitude geophysical interpretation from the areas of high-grade metamorphism. The survey results will be reported and published in the GTK archive report series by the end of 2015. The primary target in the field studies in both projects has been the exploration potential of rare earth elements and phosphorus (or apatite). Preliminary field mapping has been performed for graphite exploration. The estimation of titanium and lithium resources has been undertaken in the Industrial Minerals project of GTK. Estimation of the exploration potential for other metals (Fig. 1, Table 1) is based on reports and publications (Finland’s Minerals Strategy 2010, Eilu 2012, Sarapää et al. 2013c, Kihlman et al. 2014). The raw materials with low exploration potential such as borates, coking coal, fluorspar, gallium, germanium, and magnesium are not discussed in this report.

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Fig. 1. The most important hi-tech metal deposits in Finland (modified from Tuusjärvi et al. 2010).

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Table 1. The critical commodities defined by European Commission (2010, 2014) and an estimation of their exploration potential in Finland. Modified from Finland’s Minerals Strategy (2010). Raw material

Exploration potential

Deposits (examples)

Mines

Antimony

Moderate

Kalliosalo, Törnävä

Beryllium

Moderate

Länttä, Rapasaaret, Kymi, Väkkärä

Borates

Low

No deposits

Coking coal

Low

No deposits

Chromium

Good

Koitelainen, Akanvaara

Kemi

Cobalt

Good

Juomasuo, Sivakkaharju, Meurastuksenaho, Hangaslampi, Kouvervaara

Talvivaara, Hitura, Kevitsa, Kylylahti

Graphite

Moderate

Kiihtelysvaara, Juuka, Joutsijärvi

Fluorspar

Low

No deposits

Gallium

Low

No deposits

Germanium

Low

No deposits

Indium

Low

No deposits

Lithium

Fair

Länttä, Rapasaaret, Somero

Magnesite

Moderate

Magnesium

Low

Pehmytkivi, Punasuo, Uutela, Lahnaslampi, Horsmanaho No deposits

Niobium

Fair

Sokli, Katajakangas

PGMs

Good

Suhanko, Penikat, Koillismaa

Kevitsa

Phosphate rock

Good

Sokli, Iivaara, Kortejärvi, Kauhajoki

Siilinjärvi

HREE (Heavy)

Moderate

Sokli, Katajakangas

LREE (Light)

Moderate

Sokli, Korsnäs

Silica (quartz)

Fair

Siiselkä, Virtasalmi

Tantalum

Moderate

Kemiö, Sokli

Titanium

Fair

Koivusaari, Otanmäki

Tungsten

Moderate

Ahvenlammi, Hieronmäki

Nilsiä

2. RARE EARTH ELEMENTS (REE) Rare earth elements (REE) include 15 lanthanides, from La to Lu, and Y and Sc. They are commonly present in the crust in minor quantities, with the average total concentration of REE varying from 150 ppm to 220 ppm, but mineable REE deposits are rare (Long et al. 2010). High REE concentrations are mostly found within carbonatites and peralkaline igneous rocks (Castor & Hedrick 2006), ion-adsorption type deposits in weathered rocks (Chi & Tian 2008), niobium-yttrium & REEfluorine (NYF) type granitic pegmatites (Černy & Ercit 2005), heavy mineral placer deposits, iron oxide-copper-gold (IOCG) type deposits and marine phosphates, which generally contain low grades of REE (Long et al. 2010). Light REE (LREE, La to Sm) are commonly present in carbonatites and the more valuable heavy REE (HREE, Eu to Lu)

concentrate in alkaline rocks, fractionated granites and pegmatites, and ion-adsorption deposits. The tonnages and grades of the currently exploited REE deposits are quite variable. The largest exploited REE deposit in Bayan Obo, China, has a resource of 48 Mt of ore grading 6 wt% REO (Wu 2008). The recently re-opened Mountain Pass in USA has 16.7 Mt of ore grading 7.98 wt% REO (Castor 2008, Mariano & Mariano 2012). The HREE-dominated ion-adsorption clays of southern China have 0.05–0.20 wt% REO (Chi & Tian 2008). Currently, only bastnäsite, monazite, and loparite, and the ion adsorption clays are considered as economic source minerals of rare earths. Other ore minerals with potentially economic REE concentrations include xenotime, fergusonite, and apatite. 7


2.1 Field investigations and mineralogical studies on REE and P-REE targets The REE targets investigated have been grouped into four classes (deposit, prospect, occurrence and showing) based on the amount of data available. The deposit class includes targets that have a resource estimate or that have been mined. Prospects are targets that are or have been under active exploration. An occurrence is a target located from the bedrock either by grab sampling or drilling. A showing is an indirect indication of the presence of mineralization (e.g., an anomalous area delimited by till geochemistry, erratic ore boulders). The geochemical and mineralogical studies and new drilling results during the current projects (HiTech Metals and Critical Minerals projects) were mainly focused on the following REE, P-REE, and

P targets: (1) the fenite zone of the Sokli carbonatite intrusion, (2) the Panjavaara carbonatite dykes, (3) the Tana Belt (Mäkärä and Vaulo) in northern Finland, (4) the Lamujärvi alkaline rocks in central Finland, (5) the Kovela monazite-bearing granite in southern Finland, (6) the Iivaara alkaline intrusion, (7) the Kortejärvi and Laivajoki carbonatites, and (8) the Lehmikari, Vanttaus, and Suhuvaara appinite intrusions (Fig. 2). The description of previously known deposits or showings is mostly based on earlier studies supported with new mineralogical and geochemical analyses of existing drill cores (Table 2, Fig. 2). Most of these show up as potential REE exploration targets in regional till and bedrock geochemistry (Fig. 3).

Table 2. The dominant REE minerals, REE-bearing minerals and apatite in the REE and P-REE targets studied. Locality, category

Host rock type

Dominant mineral phases

References

Jammi and Kaulus, Sokli, P-REE prospect

Carbonatite dykes

Fluorapatite, Sr-apatite, monazite, bastnäsite, ancylite, strontianite, baryte

Panjavaara REE prospect

Carbonatite dykes

Korsnäs Pb-REE deposit (closed mine)

Carbonatite dyke

Bastnäsite, ancylite, Ba-REE carbonates, baryte, apatite, strontianite Apatite, monazite, carbocernaite, calcio-ancylite, bastnäsite, barytocalcite

Al-Ani & Sarapää 2009a, 2010c, 2013a,b,c, 2014, Al-Ani & Pakkanen 2013, Al-Ani et al. 2011 Sotka 1984

Katajakangas REE-Nb deposit

Alkaline gneiss

Fergusonite-(Y), allanite, bastnäsite-(Ce), columbite

Lamujärvi REE prospect

Syenite

Allanite, monazite

Kovela REE-Th prospect

Monazite granite

Monazite, thorite, REE carbonate

Al-Ani & Grönholm 2011, Al-Ani & Pakkanen 2013

Iivaara P prospect

Nepheline syenite

Apatite, allanite

Kortejärvi P(-REE) prospect

Carbonatite dyke

Apatite, allanite, monazite, bastnäsite, columbite

Laivajoki P(-REE) prospect

Silicocarbonatite dyke

Apatite, monazite, allanite, bastnäsite

Mäkärä-Vaulo Au-REE prospect

Arkosic gneiss, saprolite

Monazite, rhabdophane, bastnäsite, allanite, xenotime

Al-Ani & Sarapää 2010c, 2013a, Al-Ani et al. 2010a, Al-Ani & Pakkanen 2013 Al-Ani & Sarapää 2010c, 2013a, Al-Ani et al. 2010b, Al-Ani & Pakkanen 2013 Al-Ani & Sarapää 2010c, 2013a, Al-Ani et al. 2010b, Al-Ani & Pakkanen 2013 Al-Ani & Sarapää 2010a,b,c, 2012, 2013a, Al-Ani 2012, Al-Ani & Pakkanen 2013

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Al-Ani & Sarapää 2010c, 2013a, Al-Ani et al. 2010a, Al-Ani & Pakkanen 2013 Al-Ani & Sarapää 2010c, 2013a, Al-Ani et al. 2010a, Al-Ani & Torppa 2011, Al-Ani & Pakkanen 2013 Al-Ani & Torppa 2011, Al-Ani & Pakkanen 2013


Table 2. Cont. Locality, category

Host rock type

Dominant mineral phases

References

Virtasalmi REE occurrence

Kaolin deposit

Monazite, zircon, kaolinite

Eurajoki REE-Sn-Be occurrence

Rapakivi granite

Bastnäsite, monazite, xenotime, thorite, zircon

Al-Ani & Sarapää 2009b, 2011c, Al-Ani et al. 2009, Al-Ani & Pakkanen 2013 Al-Ani & Sarapää 2011b, Al-Ani & Pakkanen 2013

Suhuvaara P(-REE) prospect

Appinitic diorite

Apatite, monazite, allanite

Vanttaus P prospect

Appinitic diorite

Lehmikari P prospect

Appinitic diorite

Uuniniemi REE occurrence

Carbonatite and albitite

Honkilehto Au-Co-REE occurrence

Carbonate-sericiteschist

Palovaara REE occurrence

Albite-carbonate rock

Palkiskuru U-REE occurrence

Albitite

Karhukoski REE occurrence

Garnet-cordieritemica gneiss, granite veins

Al-Ani & Sarapää 2010c,d, 2013a, Al-Ani & Pakkanen 2013 Apatite, allanite, titanite, Al-Ani & Sarapää zircon 2010b,c, 2013a, Al-Ani & Sarapää 2011a, Al-Ani & Pakkanen 2013 Apatite, monazite, allanite, Al-Ani 2010, Al-Ani & ancylite, thorite, zircon, Sarapää 2010c, 2013a, baryte Al-Ani & Pakkanen 2013 Euxenite, Fe-columbite, Al-Ani & Sarapää Fe-thorite 2010b,c, 2013a, Al-Ani & Pakkanen 2013 Bastnäsite, allanite, davidite Al-Ani & Sarapää 2010c, 2013a, Al-Ani et al. 2010b, Al-Ani & Pakkanen 2013 Allanite, ancylite, bastnäsite, Al-Ani & Sarapää 2010c, xenotime 2013c, Al-Ani et al. 2010b, Al-Ani & Pakkanen 2013 Bastnäsite, allanite, monazite, Al-Ani & Sarapää 2010c, ancylite, davidite 2013a, Al-Ani et al. 2010b, Al-Ani & Pakkanen 2013 Monazite, bastnäsite, zircon, Pohjolainen 2012, Al-Ani rutile & Pakkanen 2013

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Fig. 2. REE and P-REE targets investigated during the Hi-tech Metals (2009–2012) and Critical Metals (2013–2015) projects of GTK. Targets are classified according to the host rock type. The base map is the 1:5 000 000 bedrock map of GTK.

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Caledonian tectonic units Mainly Neo- and Mesoproterozoic sediments Mesoproterozoic rapakivi granites Paleoproterozoic igneous rocks Paleoproterozoic schists Archean rocks

Finland Norway

Sweden

Estonia

Russian Federation

Denmark Latvia Lithuania Germany

Poland

Belarus

Rock Lanthanum La ppm 75 - 110 111 - 171 172 - 358

Till Lanthanum La ppm 75 - 128 129 - 296 297 - 920

100 km

Fig. 3. Regional lanthanum anomalies in the geochemical till and bedrock data of the GTK indicate areas with high exploration potential for REE. The base map is the 1:5 000 000 bedrock map of GTK.

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Polished thin sections from drill cores and grab samples from outcrops were prepared for petrographic studies and REE-mineral identification by scanning electron microscopy (SEM), mineral liberation analyses (MLA), and electron microprobe analysis (EPMA). The mineralogy of weathered samples was studied using a combination of X-ray diffraction (XRD) and MLA. The methods and results for targets listed in Table 2 are presented in more detail in the archive reports and publications of GTK. The most important REE minerals recognized in the carbonatite dykes of the Sokli complex (Jammi and Kaulus) are ancylite-(Ce), monazite-(Ce), and bastnäsite-(Ce). They are strongly enriched in LREE, P, F, Sr, and Ba. Apatite occurs as large, elongated grains closely associated with monazite (AlAni & Sarapää 2009a, 2013a,b,c, 2014, Al-Ani et al. 2011). During late-stage processes, apatite and carbonate minerals were replaced by various assemblages of REE–Sr–Ba minerals in the carbonatite (Al-Ani & Sarapää 2014, Figs 4–5). Allanite-(Ce) and fergusonite-(Y) are the most abundant and widespread REE-bearing minerals in the Katajakangas alkali gneiss and alkaline rocks of Lamujärvi (Al-Ani & Torppa 2011). New mineralogical data from the Katajakangas deposit indicate that LREE reside in monazite, ancylite(Ce), bastnäsite-(Ce), and parisite-(Ce), whereas Y is predominantly included in fergusonite-(Y), euxenite-(Y), and yttroclumbite. Nb is present in columbite-tantalite and pyrochlore. In addition to allanite-(Ce) and fergusonite-(Y), the accessory REE minerals observed in the Lamujärvi samples include monazite-(Ce), ancylite-(Ce), bastnäsite(Ce), titanite hydrate, columbite, and pyrochlore. Allanite contains the highest atomic percentage of total LREE (~50 at%) and total iron as Fe2O3 (2.5 at%) and the lowest Al2O3 (5.9 at%), as well as some radioactive elements such as Th (3 at%) and U. REE minerals in the Korsnäs Pb-REE deposit include REE-bearing apatite, monazite, calcio-ancylite, and bastnäsite (Al-Ani et al. 2010a). Monazite forms either anhedral grains or larger grain

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clusters that occur as inclusions within apatite phenocrysts. The Kortejärvi carbonatite is enriched in apatite and also contains monazite and allanite. The Laivajoki carbonatite has abundant apatite with associated REE minerals, especially allanite and monazite (Al-Ani et al. 2010b). The carbonate-rich rocks in Uuniniemi, Kuusamo, are also highly enriched in apatite and REE minerals such as monazite-(Ce), columbite-(Fe), euxenite-(Y), and zircon (Al-Ani & Sarapää 2010b). Backscatter electron (BSE) imaging shows high contents of monazite, which is characterized by large grain sizes with significant porosity and fractures. The Mäkärä Au-REE target in Sodankylä is characterized by many varieties of radioactive minerals such as columbite, monazite, and euxenite (Al-Ani & Sarapää 2010a, Al-Ani 2012). Appinitic intrusions are widespread within the central Lapland granitoid complex and the Lapland granulite belt. They form numerous small stocks or dykes and some larger intrusions, such as Vanttaus (Al-Ani & Sarapää 2011a) and Lehmikari (Al-Ani 2010) in south-central Lapland and Suhuvaara in the Lapland granulite belt (Al-Ani & Sarapää 2010d). The appinitic rocks have high amounts of P- and REE-bearing minerals such as allanite and monazite (Al-Ani 2010, Al-Ani & Sarapää 2010b,c,d). The albitites in Palkiskuru, Enontekiö, are characterized by a wide variety of REE-rich minerals, mainly bastnäsite, monazite, allanite, and xenotime. U-rich minerals such as davidite, masuyite, and/or sayrite are also found in samples analyzed from the target (Al-Ani et al. 2010b). In the Honkilehto Au-Co-mineralization in Kuusamo, the U-rich minerals are mainly associated with bastnäsite and allanite. The evolution of REE, Y, U, Th and Nb mineralization in the studied areas was a complex, multi-stage process, and in most cases involved both primary magmatic crystallization and late-stage hydrothermal alteration.


Fig. 4. BSE images of REE-bearing minerals in the samples studied (modified from Al-Ani & Sarapää 2013b). (a) Sr-poor apatite (core of the grain) has been altered to the Sr-rich variety (rim of the grain) (Jammi R301 197.15 m), (b) apatite (dark grey) enclosed by Sr-rich apatite (light grey) and monazite (bright rosettes) (Jammi R301 204.9 m), (c) an apatite grain completely replaced by monazite (Jammi R301 197.15 m), (d) strongly zoned ancylite crystals, (e) acicular or needle-shaped bastnäsite (Sokli R194 153.73 m), (f) allanite forming radial accumulations or intricate cross-cutting grids within albite and dolomite (Sokli R200 155.45 m).

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Fig. 5. BSE images of REE-bearing minerals in the samples studied. (a) Ancylite filling fractures and cavities within a rim of calcite and dolomite (Kaulus R14 30 m), (b) euhedral bastnäsite grains filling the vugs and fractures in K-feldspar (Vaulo V434-2011-R28 113.3 m), (c) large grain of Fe-columbite (in gray colours) with patches of lighter-coloured fergusonite-(Y) (Otanmäki 46-ATK-10), (d) two large allanite crystals (centre and right) and bastnäsite-(Ce) mixed with zircon grains (left) (Otanmäki 46-ATK-10), (e) apatite with exsolution-induced domains of monazite (Korsnäs SÖ-66 22.8 m), (f) euhedral bastnäsite overgrown by ancylite (Korsnäs SÖ-66 13.6 m).

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2.2 Sokli carbonatite P-REE-Nb The Sokli carbonatite intrusion in northeastern Finland (Figs 1–2) belongs to the Devonian (ca. 360–380 Ma) Kola alkaline province, which hosts most known REE deposits in the Fennoscandian Shield (Kramm et al. 1993). The Sokli complex is a funnel-shaped, multistage pluton ca. 5 km in diameter that intrudes the local Archean crust. The intrusive complex (Fig. 6) consists of a magmatic carbonatite core surrounded by metacarbonatite, metasomatite, and a wide fenite aureole (Vartiainen 1980, 2001, O’Brien et al. 2005). The Sokli intrusion hosts unexploited phosphate, Nb-Ta-U, and vermiculite deposits (Korsakova et al. 2012). The Sokli carbonatite complex is estimated to contain in total 190.6 Mt of P ore grading 11.2 wt% P2O5. The ore comprises lateritic P ore (36.7 Mt @ 18.7 wt% P2O5), silicate-apatite P ore (19.3 Mt @ 11.0 wt% P2O5), weathered crust P ore (53.1 Mt @ 14.1 wt% P2O5), and hard rock ore (75 Mt @ 5.6 wt% P2O5, 0.2 wt% Nb2O3 and 1.9 Mt Nb-Ta ore @ 1.9 wt% P2O5, 0.6 wt% Nb2O3) (Pöyry Environment Oy 2009). The main phosphate ore is situated in the ~26-m-thick laterite capping the intrusion. In addition to apatite, the Sokli complex contains niobium (2100 ppm), tantalum (50 ppm), and zirconium (0.13 wt%), which are mostly found within the hard rock ore (Hugg & Heiskanen 1983). The so far unexploited phosphate deposit is currently under a mining license held by Yara Oy. In 2010, GTK applied for six exploration permits in the SW part of the Sokli complex. The exploration efforts have been concentrated on the late-stage carbonatite dykes that occur as ring dykes and cross-cutting dykes in the metacarbonatite, metasomatite, and fenite zones in the Jammi and Kaulus claim areas (Sarapää et al. 2013b,c). No outcrops are known from the study area and the bedrock is locally deeply weathered. 2.2.1 Jammi REE prospect The Jammi fenite area is located 4 km south from the core of the Sokli carbonatite complex. The bedrock consists of albite-fenitized Archean mafic

volcanic rocks and tonalitic gneisses, and crosscutting carbonatite dykes, which are composed of calcite, dolomite, aegirine, albite, apatite, and phlogopite in variable amounts (Fig. 4). In 2006, GTK reported carbonatite dykes with high La (0.1–1.0 wt%) and Zn (0.81 wt%) contents in drill cores R301 and R302 from Jammi (Kontio & Pankka 2006). More detailed studies on these drill cores, including mineralogical and chemical analyses, showed that the carbonatite dykes are rich in P2O5 (max 19.9 wt%), Sr (1.9 wt%), Ba (6.8 wt%), and Zn (0.3 wt%), and they have a high total REE content of 0.50–1.83 wt%, including 0.11–1.81 wt% LREE and 0.01–0.041 wt% HREE (Al-Ani & Sarapää 2009a, 2013a,b). REE-bearing minerals in the Jammi carbonatite dykes are predominantly REE carbonates such as ancylite-(Ce) and bastnäsite-(Ce), Sr-apatite, monazite, strontianite, baryte, and brabantite, which are enriched in LREE, P, F, Sr, and Ba (Fig. 5). Mineralogical and chemical evidence suggests that hydrothermal processes were responsible for the REE mineralization in the Jammi carbonatite dykes. During late-stage processes, apatite and carbonate minerals have been replaced by various assemblages of REE-Sr-Ba minerals (Al-Ani & Sarapää 2013b). In summer 2014, test trench R33 at Jammi revealed deeply weathered black to brown ferrocarbonatite below a one-meter-thick till bed (Fig. 7). Samples from the trench along a length of 35 meters contained, on average, 2.34 wt% LREE (max 5.3 wt%), 0.15 wt% HREE (max 0.3 wt%), 10.8 wt% P2O5 (max 18.2 wt%), 0.3 wt% Nb (max 1.7 wt%), 20.3 wt% Fe2O3 (max 29.4 wt%), 0.5 wt% Zn (max 1.0 wt%), and 1.9 wt% Mn (Table 3). The high REE contents are caused by enrichment of less soluble elements such as P, Nb, Fe, Mn, and REE in the crust during weathering processes, when the more soluble elements were washed out. The ferrocarbonatite contains montmorillonite, goethite, aegirine, mica (tainiolite and/or phlogopite), K-feldspar, and possibly strontianite and quartz based on XRD and MLA analyses performed at GTK.

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Fig. 6. Geological map of the Sokli complex. The surrounding rocks are Archean tonalitic migmatites and mafic and ultramafic volcanic rocks (modified from Vartiainen (1980) and Bedrock of Finland – DigiKP database of the GTK). The drilling locations and trenches of the GTK are numbered in the lower panel, which shows the Kaulus target.

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Fig. 7. Black, weathered, Fe-Mn-Zn-Nb-REE-P-rich carbonatite under one-meter-thick till cover in trench R33 in Jammi at Sokli. Photo: Juuso Pynttäri.

2.2.2 Kaulus P-REE prospect The Kaulus prospect covers an area of 6.5 km2 in the SE part of the Sokli complex. The bedrock comprises metacarbonatites, metasomatites, and fenite zones (Fig. 6). A mobile metal ion (MMI) weak leaching profile over the Sokli carbonatite massive and the fenite zone indicated good REE potential for the Kaulus area (Fig. 8a,b). This is also implied by the results of geochemical till and weathered bedrock sampling from 360 holes in a 200-m grid. The weathered bedrock samples, comprising both carbonatites and fenites derived from granitoids and mafic metavolcanic rocks, contain up to

4.7 wt% P, 1290 ppm La, 173 ppm Y, 1290 ppm Zn, 200 ppm Li, and 136 ppb Au. The fine fraction (100 km2 centered on Panjavaara, Juuka, eastern Finland (Fig. 2). The observed carbonatite dykes range from 5 to 60 cm in width and show high enrichment in REE, with TREO contents between 10–15 wt% (Torppa & Karhu 2007), and the smallest amphibole-carbonate veinlets show 1–2 wt% levels of total REE. The rocks studied display elevated LREE to HREE ratios, with bastnäsite, ancylite, and monazite as the most important REE carriers. In addition, a large number of different REE-bearing carbonate minerals have been observed in the dykes and veins. The Panjavaara dyke swarm is exposed at discrete outcrops in a fairly large area, mostly covered by forests and wetlands. During 2012–2014, GTK carried out an exploration program including bedrock mapping, geochemical sampling, geophysical measurements, and diamond drilling. Geochemical sampling revealed spots having very high concentrations of Sr, Ba, and La in ablation till, with values of 550,

2360, and 2320 ppm, respectively, and several carbonatite dykes were discovered near these places by diamond drilling. Unfortunately, geophysical data did not prove very useful for prospecting at Panjavaara, partly because of the small sizes of the dykes, but also because their electromagnetic properties do not markedly differ from the background. This is, at least to some extent, a consequence of ubiquitous hematization of magnetite commonly observed in the rocks studied. Gravimetric measurements could be useful for revealing larger volumes of the carbonatite, due to their abundant heavy mineral contents, but such volumes were not discovered during the present exploration activities. In the light of the present study, the most potential exploration area is located south of the Panjavaara ridge, extending some 5 km upstream in the River Petäisjoki from Lake Petäinen towards the northwest; however, the largest REE-carbonatite dyke so far observed in the area has only been 60 cm thick.

2.4 Tana Belt Au-REE targets The Tana Belt, located on the southern side of the Lapland Granulite Belt, northern Finland, is characterized by prominent REE anomalies in regional till geochemical and lithogeochemical data (Salminen 1995, Rasilainen et al. 2008, Sarapää & Sarala 2013, Salmirinne et al. 2013). These data show high La and Y concentrations in both till and bedrock in arkose gneisses in an area 200 km long (Fig. 3). The strongly deformed Tana Belt comprises amphibolites, garnet-biotite-gneisses, and arkose gneisses. It was thrusted together with the Lapland Granulite Belt onto the Central Lapland Greenstone Belt at ca. 1.9 Ga (Tuisku & Huhma 2006, Cagnard et al. 2011). The area is located in the latest ice divide zone of the last (late Weichselian) glaciation. Subglacial erosion has been weak and the till transport distance is short. Bedrock is covered by 5–30-mthick kaolinitic saprolite and the overlying till, usually clay-rich, has a thickness of 0.5–15 m. Weathering in shear zones can reach down to the depth of over 100 meters. The selection of Mäkärä and Vaulo (15 and 25 km northwest of the village of Vuotso, respectively) as exploration targets was based on regional Y anomalies in till and bedrock and existing geological data from earlier studies of 22

the Mäkärä Au target, which pointed to the possibility for an ionic adsorption-type HREE deposit in saprolite and the potential exploitation of REE as a by-product of gold. Earlier studies performed in the area suggest that the hydrothermal Au-bearing quartz-hematite-pyrite veins at Mäkärä are generally narrow (1 mm to 2 m) and within tensional fractures (Härkönen 1987). The recent study included the revision of old drill cores, trenching of till and saprolite, a till stratigraphic study, geophysical measurements, systematic geochemical sampling by a percussion drill (200 m x 200 m grid, 30 km2), weak leaching geochemistry, stream sediment geochemistry, diamond drilling, and mineralogical and chemical analyses of samples (Sarapää & Sarala 2011a,b). At the Mäkärä target, one 100-m-long trench excavated on an electromagnetic anomaly revealed a 13-m-wide, conformable, red hematite-quartz vein in altered hematite-goethite-kaolinite saprolite. The vein contains on average 3.3 ppm Au (1.1– 8.5 ppm Au, fire assay) and 400 ppm REE (Fig. 12, Sarapää & Sarala 2013). The vein is bordered by kaolinitic saprolites, originally representing


a)

b)

Fig. 12. (a) The 13-meter-wide Au-bearing hematite vein at Mäkärä discovered by trenching and penetrated by drill hole R318, which contains deeply weathered hematite rock (max. 8 ppm Au), sericite quartzite, arkosic gneiss, mica gneiss, and amphibolite, (b) in transect A–B of the trench the channel samples from the Au-bearing hematite vein have higher Fe, Bi, As, and LREE (Ce and Eu) contents than the arkosic gneiss (modified from Sarapää and Sarala 2013).

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Fig. 13. (a) Concentrations of Y and Au in till in the Mäkärä area. Geology based on the DigiKP digital bedrock map (GTK internal map database). The black line shows the Au-bearing hematite vein intersected by drill hole R318 (modified from Sarapää & Sarala 2013).

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Fig. 13. (b) Au contents in till and weathered bedrock correlate with slingram imaginary anomalies (GTK internal data) to some extent.

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sericite-quartzites and arkose gneisses, and it does not extend to amphibolite. Drill hole R318 penetrates the same vein, and the measured gold and REE contents in core samples are at the same level as in the trench (Fig. 12). Till geochemistry (fine fraction, ICP-MS and ICP-OES, aqua regia digestion) of samples from the same trench indicate that the deposit in the Mäkärä area can be traced only to a few tens of meters from the mother lode (Fig. 13). The thickness of the till bed in the trench is only 0.5–1.5 meters and its clay content is high. The red color in till and weathered bedrock is a good marker of the gold potential in the target. Further drilling and trenching programs have detected four parallel gold-bearing veins, which are connected to the positive electromagnetic anomalies caused by the weathered sulfide-bearing bedrock (Fig. 13). Hematite prospectivity analyses based on geophysics are a proxy for the areas, where the gold potential is high. Systematic till geochemistry in a 200-me-

ter grid shows that the Au content correlates well with highest hematite contents. On the other hand, the highest La and Y contents correlate well with the Th maxima in aeroradiometric datasets (Fig. 14). The average REE content in saprolite at Mäkärä is 0.05 wt% (max 0.14 wt%) and at Vaulo up to 0.4 wt%, which is nearly at the same level as in the ionic adsorption clays in China (see Chi & Tian 2008). Illite and kaolinite are the dominant mineral phases in the