GEOLOGICAL SURVEY OF FINLAND
Report of Investigation 207
2014
Current Research:
2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014
Edited by Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P.
GEOLOGIAN TUTKIMUSKESKUS GEOLOGICAL SURVEY OF FINLAND
Tutkimusraportti 207
Report of Investigation 207
Current Research: 2nd GTK Mineral Potential Workshop,
Kuopio, Finland, May 2014
Edited by
Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P.
Unless otherwise indicated, the figures have been prepared by the authors of the publication.
Front cover: Kylylahti Cu-Au-Zn ore in mine tunnel, length of the hammer is ca. 60 cm.
Photo: Esko Koistinen, GTK.
Layout: Elvi Turtiainen Oy
Espoo 2014
Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds) 2014.
Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, 6–7 May 2014. Geological Survey of Finland, Report of Investigation 207, 161 pages, 71 figures and 4 tables.
The Mineral Potential research programme of the Geological Survey of Finland (GTK) mainly
concentrates on assessing the reserves and discovery potential of metal ores and industrial mineral deposits and developing exploration innovations for their delineation. Other important tasks
within the programme include the study of ores, including structures and formations that have
ore potential, and the modelling of tectonic and metallogenic evolution of the Fennoscandian
Shield. Evaluating the sufficiency, life cycle and total environmental impact of raw materials is
also within the scope of the programme. Mineral potential assessment and research comprises all
aspects of a mineral deposit. Seismic reflection and other geophysical techniques help to improve
our knowledge of deep structures and their ore potential. Thus, we can model in more detail
the evolution of Precambrian bedrock and the geological processes involved. This may help in
identifying locations of probable and possible reserves, including discovery potential as deep as
1-5 kilometres. Beneficiaries of the results provided by the programme include exploration companies, mining and refining industries, officials responsible for permitting and land-use planning,
governmental institutes, research institutes and universities.
A large amount of geologists and geophysicists in all the offices of GTK are working within
the scope of the Mineral Potential research programme. The 2nd Mineral Potential Workshop held
in Kuopio on 6–7 May 2014 gathered together the researchers to discuss on their work, give new
ideas and network within GTK. The abstracts for the oral and poster presentations are published
in this volume of the Report of Investigation series of GTK. They provide an up-to-date view of
the multidisciplinary activities taking place within the scope of the Mineral Potential research
programme. The organizing committee of the workshop, also responsible for the editing of the
abstract volume, included Laura S. Lauri, Esa Heilimo, Hanna Leväniemi, Mari Tuusjärvi, Raimo
Lahtinen and Pentti Hölttä. Esa Heilimo and Anne Hukkanen handled the practical issues of the
meeting. English language of the abstracts was proof-read by Roy Siddal.
Keywords (Georef Thesaurus, AGI): economic geology, potential deposits, symposia, Finland
Laura S. Lauri, Geological Survey of Finland, P.O. Box 77, FI-96101 Rovaniemi, Finland
E-mail: [email protected]
Esa Heilimo, Geological Survey of Finland, P.O. Box 1237, FI-72101 Kuopio, Finland
E-mail: [email protected]
Hanna Leväniemi, Mari Tuusjärvi, Raimo Lahtinen, Pentti Hölttä
Geological Survey of Finland, P.O. Box 96, FI-02151 Espoo, Finland
E-mail: [email protected], [email protected], [email protected],
[email protected]
ISBN 978-952-217-283-9 (pdf)
ISSN 0781-4240
Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (toim.) 2014.
Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, 6–7 May 2014. Geologian tutkimuskeskus, Tutkimusraportti 207, 161 sivua, 71 kuvaa ja 4 taulukkoa.
Geologian tutkimuskeskuksen (GTK) mineraalipotentiaali-tutkimusohjelma tuottaa tutkimustietoa Suomen hyötymineraalivarojen sijainnista ja löytymispotentiaalista. Mineraalipotentiaalisten muodostumien syntyprosesseista, syvyysulottuvuudesta ja malmipotentiaalista tuotetaan yhä tarkentuvaa tietoa Fennoskandian kilven laajuudelta. Raaka-aineiden riittävyys, elinkaari
ja ympäristövaikutusten arviointi kuuluvat myös tutkimusohjelman piiriin. Geologisten prosessien ymmärtäminen ja sen perusteella laaditut laaja-alaiset kallioperän kehitysmallit luovat
perustan luonnonvarojen etsinnälle ja moninaiselle maankamaran hyödyntämiselle. Tutkimusohjelmassa tuotetaan uutta tietoa todennäköisten ja mahdollisten mineraalivarojen sijainnista ja
löytymispotentiaalista aina 1-5 km:n syvyyteen asti. Tuloksia hyödyntävät malminetsintäyritykset,
kaivos- ja jatkojalostusteollisuus, rakennusaineteollisuus ja kalliorakentajat, päätöksentekijät (lupaviranomaiset) sekä tutkimuslaitokset ja tiedeyhteisö (yliopistot).
Mineraalipotentiaali-tutkimusohjelmassa työskentelee suuri määrä geologeja ja geofyysikoita kaikissa GTK:n toimipaikoissa. Kuopiossa toukokuussa 2014 järjestettävät toiset mineraalipotentiaali-tutkimusohjelman tutkijapäivät kokoavat yhteen eri yksiköiden tutkijat keskustelemaan tutkimusaiheista, luomaan ideoita ja verkottumaan GTK:n sisällä. Esitelmien ja postereiden
lyhennelmät, jotka tarjoavat ajankohtaisen poikkileikkauksen tutkimusohjelman sisällä tehtävästä tutkimuksesta, julkaistaan tässä GTK:n tutkimusraportissa. Järjestelytoimikuntaan kuuluivat
Laura S. Lauri, Esa Heilimo, Hanna Leväniemi, Mari Tuusjärvi, Raimo Lahtinen ja Pentti Hölttä,
jotka myös toimittivat julkaisun. Esa Heilimo ja Anneli Hukkanen vastasivat tutkijapäivien
käytännön järjestelyistä ja englannin kielen tarkastajana toimi Roy Siddal.
Asiasanat (Geosanasto, GTK): malmigeologia, potentiaaliset esiintymät, symposiot, Suomi
Laura S. Lauri, Geologian tutkimuskeskus, PL 77, 96101 Rovaniemi
S-posti: [email protected]
Esa Heilimo, Geologian tutkimuskeskus, PL 1237, 72101 Kuopio
S-posti: [email protected]
Hanna Leväniemi, Mari Tuusjärvi, Raimo Lahtinen, Pentti Hölttä
Geologian tutkimuskeskus, PL 96, 02151 Espoo
S-posti: [email protected], [email protected], [email protected], [email protected]
Geologian tutkimuskeskus, Tutkimusraportti 207 – Geological Survey of Finland, Report of Investigation 207, 2014
Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
CONTENTS
Preface.............................................................................................................................................................. 8
Laura S. Lauri, Esa Heilimo, Hanna Leväniemi, Mari Tuusjärvi, Raimo Lahtinen and Pentti Hölttä
Developing deep exploration methods in the Outokumpu mining camp area..................................... 9
Soile Aatos, Esko Koistinen, Asko Kontinen, Peter Sorjonen-Ward, Johanna Torppa, Jarkko Jokinen,
Juha Korhonen, Arto Korpisalo, Maija Kurimo, Eevaliisa Laine, Hanna Leväniemi and
Ilkka Lahti
Prospectivity modelling of the lithium pegmatites in the Somero–Tammela RE pegmatite region.12
Timo Ahtola and Hanna Leväniemi
Preliminary observations on the lithology of the southeastern corner of the Central Finland
Granitoid Complex...................................................................................................................................... 15
Marjaana Ahven, Esa Heilimo, Perttu Mikkola, Jouni Luukas and Jukka Kousa
Potential field data featuring crustal structures........................................................................................ 18
Meri-Liisa Airo
Mineralogical and geochemical study on carbonatites and fenites from the Kaulus drill cores,
Sokli complex, NE Finland.......................................................................................................................... 22
Thair Al-Ani and Olli Sarapää
Hyperspectral analysis of drill cores from the Kedonojankulma Cu-Au deposit................................ 26
Hilkka Arkimaa, Viljo Kuosmanen, Markku Tiainen and Rainer Bärs
Stakeholder engagement practiced by the Geological Survey of Finland in mineral potential
mapping in southern Finland..................................................................................................................... 28
Toni Eerola, Niilo Kärkkäinen and Markku Tiainen
Some geochemical constraints on the Siilinjärvi carbonatite-glimmerite complex............................ 30
Esa Heilimo, Jouni Luukas, Perttu Mikkola and Pasi Heino
Seismically reflective volcanic stratigraphy in Pyhäsalmi and Vihanti massive sulphide mining
camps............................................................................................................................................................ 33
Suvi Heinonen, Jouni Luukas and Jukka Kousa
The Korpela Cu-Zn mineralization, a new VMS potential target in the Palaeoproterozoic
Viholanniemi volcanic suite in Joroinen, southeastern Finland............................................................ 35
Janne Hokka, Sami Niemi and Jukka Kousa
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Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014
Mineral resource estimation for the Kiviniemi Sc-Zr-Y-deposit........................................................... 39
Janne Hokka and Tapio Halkoaho
Isotope geology and crustal genesis in Finland........................................................................................ 42
Hannu Huhma, Yann Lahaye, Irmeli Mänttäri and Hugh O’Brien
Geochemical anomalies reflecting ore-forming processes in the Svecofennian Häme Belt,
southern Finland.......................................................................................................................................... 45
Pekka Huhta, Niilo Kärkkäinen, Markku Tiainen and Erkki Herola
Stream sediment survey as a mineral exploration technique in the Vähäkurkkio area,
Enontekiö...................................................................................................................................................... 48
Helena Hulkki and Anne Taivalkoski
Proterozoic metamorphism in the Archaean Tuntsa suite, NW Finland............................................. 51
Pentti Hölttä, Hannu Huhma and Tiia Kivisaari
VMS deposits in the Häme volcanic belt: petrophysical data to supplement geophysical
modelling....................................................................................................................................................... 55
Fredrik Karell and Hanna Leväniemi
4D model of the Hietakero area, northern Finland................................................................................. 56
Tuomo Karinen, Ilkka Lahti, Tero Niiranen and Jukka Konnunaho
Geological and mineralogical challenges related to the beneficiation of REE deposits...................... 59
Risto Kaukonen, Jukka Laukkanen and Neea Heino
Digitizing an old geological 3D interpretation of the Miihkali area..................................................... 62
Esko Koistinen and Soile Aatos
PGE ore potential in the southwestern granulite belt of northern Finland.......................................... 64
Kari Kojonen
The problem with the age of the Central Puolanka Group keeps fighting us...................................... 68
Asko Kontinen, Hannu Huhma, Yann Lahaye and Hugh O’Brien
Talvivaara biotite has stories to tell............................................................................................................ 72
Asko Kontinen, Bo Johanson, Lassi Pakkanen and Mia Tiljander
Geochemical surveys in northern Uganda............................................................................................... 75
Esko Korkiakoski
ZTEM survey in Outokumpu..................................................................................................................... 78
Maija Kurimo, Hanna Leväniemi and Ilkka Lahti
Preliminary results of U-Pb age determinations from the Pampalo gold mine and
the Hosko gold deposit, Hattu Schist Belt, eastern Finland.................................................................... 82
Asko Käpyaho, Ferenc Molnár, Irmeli Mänttäri, Martin Whitehouse and Grigorios Sakellaris
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Geologian tutkimuskeskus, Tutkimusraportti 207 – Geological Survey of Finland, Report of Investigation 207, 2014
Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
Further insight into ore-forming processes using in situ Pb, S and Sr isotopic analysis on
thin sections by LA-MCICPMS.................................................................................................................. 85
Yann Lahaye, Hugh O’Brien, Ferenc Molnár, Shenghong Yang, Kirsi Luolavirta and
Wolfgang Maier
Coupled oroclines in the central part of the composite Svecofennian orogen: from linear
orogen to equidimensional continental crust........................................................................................... 87
Raimo Lahtinen, Mikko Nironen and Stephen T. Johnston
3D modelling of the Sola serpentinite usind old geological maps and 3D magnetic inversion........ 88
Eevaliisa Laine and Hanna Leväniemi
Age constraints for the appinites of the Central Lapland Granitoid Complex, Finland..................... 90
Laura S. Lauri and Hannu Huhma
New Li potential based on till geochemistry in the Kaustinen area, western Finland........................ 94
Heidi Laxström, Olavi Kontoniemi, Henrik Wik and Hannu Lahtinen
Geophysical indications of VMS deposits in the Häme volcanic belt................................................... 97
Hanna Leväniemi and Fredrik Karell
Preliminary results from new drillings and geochemical studies on the apatite deposits in
the Kortejärvi and Petäikkö–Suvantovaara carbonatites, Pudasjärvi–Posio district,
northern Finland........................................................................................................................................ 100
Panu Lintinen
Partition coefficient for nickel between sulphide and silicate liquid: observations and
applications................................................................................................................................................. 104
Hannu V. Makkonen
Petrophysical properties characterizing the formations of the Hattu Schist Belt.............................. 106
Satu Mertanen and Fredrik Karell
Possible ore potential of the Jyväskylä–Kangasniemi area................................................................... 109
Perttu Mikkola, Aimo Hartikainen and Sami Niemi
Observations on occurrences of awaruite in Lapland........................................................................... 111
Ferenc Molnár, Pekka Nurmi, Tuomo Törmänen and Jukka Laukkanen
Boron and sulphur isotopes reveal the role of magmatic fluids in the formation of
orogenic gold deposits in the Archaean Hattu Schist Belt, eastern Finland....................................... 114
Ferenc Molnár, Irmeli Mänttäri, Asko Käpyaho, Hugh O’Brien, Yann Lahaye,
Peter Sorjonen-Ward, Martin Whitehouse and Grigorios Sakellaris
Layman’s sample practice.......................................................................................................................... 118
Jari Nenonen and Satu Hietala
Revision of stratigraphic units in northern Finland.............................................................................. 121
Mikko Nironen, Raimo Lahtinen, Hannu Huhma, Jouni Luukas and Tuomo Manninen
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Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014
Biogeochemical signatures in common juniper: gold and REE exploration in Finnish Lapland.... 123
Paavo Närhi, Maarit Middleton and Raimo Sutinen
Finland geosciences laboratory (SGL) – analytical facilities update................................................... 125
Hugh O’Brien, Yann Lahaye and Bo Johanson
Quantitative assessment of Cu-Zn resources in VMS deposits in Finland........................................ 129
Kalevi Rasilainen, Pasi Eilu, Pekka Sipilä, Markku Tiainen, Jukka Kousa, Jouni Luukas,
Jarmo Nikander, Peter Sorjonen-Ward, Kaj Västi, Antero Karvinen and Tuomo Törmänen
Comparison of the portable XRF with conventional methods in till geochemical mineral
exploration.................................................................................................................................................. 132
Pertti Sarala
New low-impact geochemical sampling and exploration methods – application of
the green mining concept for greenfield exploration in Finland......................................................... 135
Pertti Sarala
Critical mineral exploration and potential in northern Finland......................................................... 137
Olli Sarapää, Panu Lintinen and Thair Al-Ani
The use of high resolution X-ray computed micro-tomography in metamorphic
fabric analyses: a virtual method of studying foliations and porphyroblasts in 3D.......................... 140
Mohammad Sayab, Jussi-Petteri Suuronen, Pentti Hölttä, Aki Petteri Kallonen,
Raimo Lahtinen, Domingo Aerden and Ritva Serimaa
Modernised bedrock map of the Häme Belt........................................................................................... 143
Pekka Sipilä
Magnetic susceptibility effects on the GTK airborne electromagnetic data – modelling and
interpretation example............................................................................................................................... 145
Ilkka Suppala
Mineral potential mapping in southern Finland.................................................................................... 147
Markku Tiainen, Niilo Kärkkäinen, Timo Ahtola, Sari Grönholm, Pekka Huhta,
Hanna Leväniemi, Pekka Sipilä and Esko Koistinen
Comparison of prospectivity mapping techniques for central Lapland orogenic gold..................... 150
Johanna Torppa
On the depth structure of the Iivaara pipe.............................................................................................. 152
Pertti Turunen, Ilkka Lahti and Olli Sarapää
Temporal changes in the amount of mineral resources in Finland..................................................... 156
Mari Tuusjärvi and Raili Aumo
New type of low-sulphide PGE-reef of the Sotkavaara pyroxenite intrusion, Rovaniemi,
northern Finland........................................................................................................................................ 158
Tuomo Törmänen, Irmeli Huovinen and Jukka Konnunaho
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
preface
The Geological Survey of Finland (GTK) promotes the sustainable use of rock
and mineral resources at the national and EU levels and provides society and
industry with state-of-the-art geological knowledge. The Mineral Potential research programme is tasked with identifying and studying prospective terrains
for all types of raw materials, ranging from metals to industrial minerals, and
through these activities to assist explorers in finding economically viable mineral
resources.
The biannual Mineral Potential Workshop brings together researchers working within the Mineral Potential research programme in all the branch offices of
GTK to discuss the current activities and develop new ideas. The workshop held
in Kuopio on 6–7 May 2014 is the second such event. The session themes include
bedrock and ore geology, exploration methods, geological and geophysical modelling, mineral potential and resource estimations, and database systems. Altogether, 53 extended abstracts were submitted for the workshop and are published
in this volume, providing the reader with an up-to-date view of the multidisciplinary activities taking place within the scope of the Mineral Potential research
programme.
Laura S. Lauri, Esa Heilimo, Hanna Leväniemi, Mari Tuusjärvi, Raimo Lahtinen
and Pentti Hölttä
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Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014
developing deep exploration methods in the
Outokumpu mining camp area
by
Soile Aatos1, Esko Koistinen1, Asko Kontinen1, Peter Sorjonen-Ward1, Johanna
Torppa1, Jarkko Jokinen2, Juha Korhonen2, Arto Korpisalo2, Maija Kurimo2,
Eevaliisa Laine2, Hanna Leväniemi2 and Ilkka Lahti3
1 Geological
Survey of Finland, P.O. Box 1237, FI-70211 Kuopio, Finland
Survey of Finland, P.O. Box 96, FI-02151, Espoo, Finland
3 Geological Survey of Finland, P.O. Box 77, FI-96101 Rovaniemi, Finland
E-mail: [email protected]
2 Geological
Introduction
Exploration and mining companies increasingly require more systematic and efficient exploration concepts and techniques in both mature, brownfields exploration as well as in greenfields targeting. While the near-surface environment may
be relatively well explored in brownfields terrains, there is a recognized need for
developing and improving deep exploration (DEX) methods. The demand for
more efficient allocation of resources to ore potential mapping makes the integration of 3D geophysical measurements and geological knowledge through Common Earth Modelling (CEM) and 3D GIS interpretations an attractive strategic
option in both exploration and mining, compared to more traditional empirical
exploration and targeting methods.
DEX concepts and technologies are currently being developed in collaboration
with the Institute of Seismology and Department of Physics of the University of
Helsinki in the Outokumpu brownfield mining camp area in eastern Finland.
Research at the Geological Survey of Finland (GTK) has been divided into two
separate but linked projects (Aatos et al. 2013), within the Mineral Potential Research Program of GTK, which is designed to implement Finnish governmental
policies concerning mineral resources. In addition to the scientific deliverables,
the results of these projects are expected to help focus GTK strategies on new
opportunities for regional mineral potential investigations, as well as enhancing
capabilities in modelling methods.
The project results will also benefit mining, exploration and consulting companies, in addition to research and development in geoscience agencies and universities. Generating future exploration targets regionally (and throughout Finland) will be another anticipated outcome of the Outokumpu DEX technological
development projects.
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
Research and development
The main goals of the project are DEX method development and CEM building
of the Outokumpu brownfield mining camp and surrounding areas to a depth of
2 km, or in optimal cases, to 5 km. One of the main aims of the Outokumpu CEM
approach is to integrate several different types of deep geophysical model data,
acquired at different scales, together with the relatively good regional geological
understanding of the area, into a number of common interpretations, enabling
an updated understanding of the deep geology and ore potential of the research
area. Similar regional- or camp-scale CEMs in 3D have previously been developed elsewhere, e.g. in Australia (Barnett & Williams 2006, Greenfields Prospectivity Unit 2013) and Canada (Martin et al. 2007).
The geophysical methods being used or developed by GTK are audiomagnetotellurics (AMT), deep magnetic, potential field and new electromagnetic (EM)
field methods. The recently acquired regional Z-axis tipper electromagnetic
(ZTEM) data (Aatos et al. 2013, Kurimo et al. 2014) will also be an essential part
of CEM development. In addition, GTK will reprocess and remodel previous geophysical data from the area (e.g. Laine & Leväniemi 2014).
The data in these projects are mainly acquired and provided by GTK. We will
also use existing exploration and geo-data from the area in GTK archives as background data. The geophysical data will be either acquired from existing GTK databases or measured in the field, in demonstrating and developing new methods
(AMT, EM) or as complementary data acquisition (deep magnetic, gravimetry,
geology) for further processing and modelling. The existing 3D model data will
also be used or acknowledged in the development work (e.g. Koistinen & Aatos
2014).
CEM data and 3D application platform drafting has been going on, e.g. in GIS
and high-resolution visualization tools in 3D vision environments, in addition to
data-specific computational and 3D software for modelling and interpretation.
Development of the CEM process for the Outokumpu mining camp area will
be benchmarked via collaboration with project research associates in Canada,
Sweden and Greece and research colleagues or subcontractors in other European
countries or elsewhere.
References
Aatos, S., Heikkinen, P., Kukkonen, I. & Kurimo, M. 2013. Developing Deep Exploration Concepts and Technologies in Outokumpu Mining Camp Area. Abstract. Green Mining Poster
Exhibition by Tekes. 29–31 October. 9th Fennoscandian Exploration and Mining (FEM) 2013,
Levi, Finland.
Barnett, C. T. & Williams, P. M. 2006. Mineral exploration using modern data mining
techniques. Mining Geoscience. Special Topic. First Break, vol. 24, 43-55 [Accessed 3 February 2014]. Available at: <http://www.bwmining.com/papers/Spectopic1_mineralexploration_
July06.pdf>.
Greenfields Prospectivity Unit 2013. North Queensland Gold and Strategic Metals Study. Regional Studies. Prospectivity assessments [Accessed 3 February 2014]. Available at: <http://
mines.industry.qld.gov.au/geoscience/prospectivity-assessments.htm>.
Koistinen, E. & Aatos, S. 2014. Digitizing an old geological 3D interpretation of the Miihkali
area. In: Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014.
Geological Survey of Finland, Report of Investigation 207. (this volume)
Kurimo, M., Leväniemi, H. & Lahti, I. 2014. ZTEM survey in Outokumpu. In: Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds) Current Research: 2nd
GTK Mineral Potential Workshop, Kuopio, Finland, May 2014. Geological Survey of Finland,
Report of Investigation 207. (this volume)
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Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014
Laine, E. & Leväniemi, H. 2014. 3D modelling of the Sola serpentinite using old geological maps
and 3D magnetic inversion. In: Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds) Current Research: 2nd GTK Mineral Potential Workshop, Kuopio,
Finland, May 2014. Geological Survey of Finland, Report of Investigation 207. (this volume)
Martin, L., Perron, G. & Masson, M. 2007. Discovery from 3D Visualization and Quantitative
Modelling. Paper 37. Advances in 3D Visualization and Data Integration, 543−550, [Accessed
3 February 2014]. Available at: <http://www.mirageoscience.com/solutions/Noranda_camp_
targeting_case_study.pdf>.
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Prospectivity Modelling of the Lithium
Pegmatites in the Somero-Tammela
re pegmatite region
by
Timo Ahtola and Hanna Leväniemi
Geological Survey of Finland, P.O. Box 96, FI-02151, Espoo, Finland
E-mail: [email protected]
Introduction
The Somero-Tammela rare element (RE) pegmatite region (Fig. 1) is located in
the Häme belt, between the town of Somero and the municipality of Tammela in SW Finland. The Häme belt mainly consists of volcanic rocks intercalated
with greywackes and metapelites. The succession is intruded by gabbros, diorites,
granodiorites, tonalites and the youngest magmatic rocks, K-granites as well as
pegmatites. A regional-scale prospectivity modelling study was carried out in the
Somero-Tammela RE (lithium) pegmatite province (Leväniemi 2013). The purpose of the study was to investigate the suitability of various regional datasets and
to construct and validate a prospectivity map for the region.
Somero-Tammela Li pegmatites
The Somero-Tammela region contains 56 known RE pegmatites (Fig. 1). Of these,
at least nine contain lithium minerals. According to Alviola (2003), the lithium
pegmatites belong to the LCT (Li, Cs, Ta) family of Černý (1998). The two most
significant lithium pegmatite deposits are called Hirvikallio and Kietyönmäki.
Hirvikallio, the largest known petalite (LiAlSiO4O10) pegmatite in Finland, is 170
m long and 5–25 m wide. It contains 200 kt @ 1.78 wt% Li2O to the depth of 50 m.
The Kietyönmäki dyke swarm is composed of half a dozen Li-bearing pegmatites,
of which the largest is 200 m long and 10 m wide (Alviola 1989). It contains 300 kt
@ 1.5 wt% Li2O. In Kietyönmäki, most of the petalites are altered to spodumene
(LiAlSi2O6) + quartz, and only one dyke contains magmatic petalite. It is probable
that there are still several undiscovered RE pegmatites in the Somero-Tammela
region.
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Lithium Pegmatite Prospectivity Modelling
in THE Somero region
As the lithium pegmatites are relatively small in size, their resolution in regional
datasets is low, and due to their physical properties, the deposits are difficult to
trace in geophysical datasets (e.g. Černy & Trueman 1982). Therefore, an empirical modelling method called weights of evidence (Bonham-Carter 1994) was selected for the prospectivity modelling. The method merges the regional datasets
(evidence layers), such as aerogeophysical or till geochemistry data, and known
deposits (training points) into a Bayesian stastistics-based probability model in
such a way that the model highlights areas where the evidence suggests a high
probability for a deposit occurrence.
Several regional evidence layers that were tested for the model were either of
too coarse a resolution or did not have a sufficient statistical relationship with the
training point distribution, and as such could not be be included in the model.
The final modelling (Fig. 2) was carried out using only four evidence layers (a
derivative of the aeromagnetic dataset, the airborne electromagnetic in-phase to
quadrature ratio, the radiometric uranium-to-thorium ratio and a derivative of
the digital elevation model dataset) and with 70% of the known deposits as training points. Despite the small number of input layers, the validation parameters
confirm the model to perform reasonably well when validated against the remaining known deposits. If more suitable datasets become available in the future,
the model could be updated and improved.
The applied empirical modelling method proved suitable for this study area,
where the correlations between the deposits and the regional datasets were expected to be ambiguous. The modelling, once completed, will also provide useful insights into the relationships between the various regional datasets and the
known deposits. To further study the model performance, a number of selected
locations highlighted by the model are due to be checked in the field during 2014.
References
Alviola, R. 2003. Pegmatiittien malmipotentiaalista Suomessa. Geological Survey of Finland,
archive report M10/03/85. 5 p. (in Finnish)
Alviola, R. 1989. The granitic pegmatites of the Somero-Tammela area. In: Symposium Precambrian granitoids. Petrogenesis, geochemistry and metallogeny, August 14–17, 1989, Helsinki,
Finland. Excursion C 1: Lateorogenic and synorogenic Svecofennian granitoids and associated
pegmatites of southern Finland. Geological Survey of Finland, Guide 26, 16–25.
Bonham-Carter, G. F. 1994. Geographic Information Systems for Geoscientists – modelling with
GIS. New York: Pergamin. 398 p.
Bedrock of Finland − DigiKP. Digital map database [Electronic resource]. Espoo: Geological
Survey of Finland [referred 05.02.2014]. Version 1.0.
Černý, P. 1998. Magmatic vs. metamorphic derivation of rare-element granitic pegmatites.
Krystalinikum 24, 7–36.
Černy, P. & Trueman, D. L. 1982. Exploration For Rare-element Granitic Pegmatites. In: Černy, P.
(ed.) Short Course In Granitic Pegmatites In Science And Industry. Mineralogical Association
of Canada, Short Course Handbook 8, 463–493.
Leväniemi, H. 2013. Lithium Pegmatite Prospectivity Modelling in Somero-Tammela Area,
Southern Finland. Geological Survey of Finland, archive report 151/2013. 15 p.
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
Fig. 1. Bedrock (Bedrock of Finland – DigiKP) and location of the RE pegmatites in the SomeroTammela region. Those with the name are lithium bearing. Contains data from the National Land
Survey of Finland Topographic Database 08/2012.
Fig. 2. A detailed view of the model at the center of the area with known lithium pegmatite dyke
locations shown also in Figure 1. Contains data from the National Land Survey of Finland Topographic Database 08/2012.
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Geologian tutkimuskeskus, Tutkimusraportti 207 – Geological Survey of Finland, Report of Investigation 207, 2014
Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014
PRELIMINARY OBSERVATIONS ON THE LITHOLOGY OF
THE SOUTHEASTERN CORNER OF
THE CENTRAL FINLAND GRANITOID COMPLEX
by
Marjaana Ahven, Esa Heilimo, Perttu Mikkola, Jouni Luukas and Jukka Kousa
Geological Survey of Finland, P.O. Box 1237, FI-70211 Kuopio, Finland
E-mail: [email protected]
The southeastern Central Finland Granitoid Complex (CFGC) consists of various
granitic to dioritic igneous intrusions enclosing the NE–SW-oriented Tammijärvi-Makkola-Halttula supracrustal sequence (Fig. 1). Systematic mapping was
conducted in the area a century ago (Frosterus 1903), and updated to a wider
context by Nironen (2003). An MSc thesis on the Makkola sequence (Ikävalko
1981) and target-scale ore potential studies have been carried out in the area. A
systematic mineral potential project was initiated in 2013 by the Geological Survey of Finland to specify the lithological boundaries and the continuations of the
geological units in the area between Jyväskylä, Pieksämäki and Joutsa. The connections of the Tammijärvi, Makkola and Halttula sequences with the Häme and
Tampere Belts are especially under evaluation.
Supracrustal rocks of the study area
The largest continuous volcanogenic rock-dominated supracrustal sequences at
Tammijärvi, Makkola, Halttula, Kauppila, Toivakanlehto and Vitikkala display
a similar assemblage of porphyries and tuffaceous rocks, while interbeds of volcanic breccias have only been observed in Makkola, Halttula and Toivakanlehto.
Southeast of the Makkola and east of the Halttula sequences lie variably sized
areas of migmatitic paragneiss with garnet, sillimanite, andalusite, and cordierite
porphyroblasts.
The texture of continuous supracrustal sequences is relatively well preserved.
Volcanic breccias include rounded elongated fragments of porphyritic rocks
(uralite and plagioclase), felsic blocks, and epidote chunks 5–15 cm in diameter (Fig. 2a). Uralite porphyrites (Fig. 2b) and plagioclase porphyries are found
as interlocking sills in mafic to felsic tuff and tuffite layers. Some basaltic lapilli
tuffs are found in the southwestern part of the Makkola sequence. Felsic tuffaceous sandstone in the northwestern Makkola shows cross bedding and graded
bedding, while laminar graded bedding and slumping of plagioclase porphyry
blocks into intermediate tuffite can be seen in the Toivakanlehto sequence. Felsic
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
tuffaceous rocks may contain garnet and sillimanite porphyroblasts. Quartz veins
(max. 10 cm thick) are common, especially in the Makkola sequence.
The dykes, volcanic, and volcanogenic sedimentary rocks in the Makkola,
Halttula and Kauppila sequences display subalkaline compositions from basaltic
to rhyolitic. Compositions are mostly calc-alkaline, although some mafic rocks
show tholeiitic affinities. Based on diagrams of log-transformed ratios of the immobile elements Ti, Zr, Nb, Y and V (Verma & Agrawal 2006), all mafic samples
categorize as island arc basalts. While the work is still in progress, some similarities with the Tampere and Häme Belts, and especially with the Forssa volcanic
suite were observed.
Igneous rocks of the southeastern CFGC
According to Nironen (2003), the igneous rocks from the study area can be divided into synkinematic (1890−1870 Ma) and postkinematic (1880−1860 Ma)
groups. The synkinematic rocks are porphyritic and even-grained granites, granodiorites, tonalites, quartz diorites and quartz monzodiorites. Contacts between
porphyritic and even-grained igneous rocks are either sharp or gradual over a
distance of a few metres. Minor intrusions of gabbros, diorites and monzodiorites are generally even-grained, orthopyroxene-bearing and locally brecciated.
In places, local deformation can be seen as gneiss banding and mylonitic shear
zones in granodiorites, granites and quartz diorites.
Postkinematic rocks are often quartz-poor and cryst-supported (term by
Nironen 2003), and the amount of groundmass appears to increase in relation to
the amount of plagioclase. In addition to the large, well-studied Puula intrusion,
several small quartz monzonite bodies are known from the area. Dykes, both
mafic and felsic, are abundant near the supracrustal sequences. They often display either uralite or plagioclase porphyritic texture, depending on their composition. Small migmatitic paragneiss and intermediate volcanic rock xenoliths can
be found throughout the study area. The youngest magmatic event is represented
by leucogranite veins sharply cross-cutting all the other rock types.
References
Frosterus, B. 1903. Mikkeli. General Geological Map of Finland 1:400 000. Explanation to the
Map of Rocks, Sheet C2. Geological Survey of Finland. 102 p.
Ikävalko, O. 1981. Makkolan-Kokonkylän suprakrustinen vyöhyke. Unpublished M.Sc. thesis,
University of Helsinki, Department of geology and mineralogy. 119 p. (in Finnish)
Nironen, M. 2003. Keski-Suomen granitoidikompleksi, karttaselitys. Summary: Central Finland
Granitoid Complex – Explanation to a map. Geological Survey of Finland, Report of Investigation 157. 45 p., 1 app.
Verma, S. P. & Agrawal S. 2006. New tectonic discrimination diagrams for basic and ultrabasic
volcanic rocks through log-transformed ratios of high field strength elements and implications
for petrogenetic processes. Revista Mexicana de Ciencias Geológicas 28 (1), 24–44.
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Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014
Fig. 1. Contemporary geological map showing the volcanogenic supracrustal sequences of the study
area. Contains data from the National Land Survey of Finland Topographic Database 08/2012.
a)
b)
Fig. 2. (a) Volcanic breccia with rounded felsic and epidote-rich fragments in Makkola (observation site KK4$-2012-806); (b) Massive mafic uralite porphyrite, Makkola. The changes between
phenocryst-rich and phenocryst-poor phases can be sharp. A cross-cutting quartz vein is visible in
the upper left corner (observation site MAAH-2012-7). The length of the lighter is 6 cm.
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
POTENTIAL FIELD DATA FEATURING
CRUSTAL STRUCTURES
by
Meri-Liisa Airo
Geological Survey of Finland, P.O. Box 96, FI-02151 Espoo, Finland
E-mail: [email protected]
INTRODUCTION AND METHODS
Potential fields – the Earth’s magnetic and gravitational fields – give information
on the lateral variation in the physical properties of rocks (magnetization and
density, respectively) and provide a better understanding of the subsurface geology. Discontinuities in magnetization or density form underground sub-planar
intersection surfaces between crustal blocks with contrasting properties. Their
surface expressions are indicated by continuous regional magnetic and gravity
close-to-linear features, i.e. lineaments. For mineral potential, these boundaries
have importance, because mineral deposits are often spatially related to major
lineament systems. To investigate this relationship, regional geophysical data over
Finland (Airo et al. 2011) were visually analyzed in terms of the regional magnetic and gravity lineaments.
Common practices for enhancing potential field data in lineament mapping
include various derivative-based transformation methods or special edge detection tools. Visual interpretation was complemented by applying a semi-automatic method for the detection of the zones of gravity minima. Bouguer anomaly
data over Finland were analysed for curvature minima by using a raster analysis
method implemented by the US Geological Survey for Oasis Montaj (Phillips
2007). The method determines the existence of local gravity minima points of
features showing directional continuity with their associated strike directions,
and the result can be vectorized in ArcGIS. Comparison of the visual and the
semi-automatically detected lineaments over Finland was presented in Korja &
Kosonen (2013).
RESULTS
The major tectonic boundaries, formed during the Archaean and Proterozoic
evolution of the Fennoscandian shield, are associated with regional magnetic and
gravity lineaments. Some of these lineaments traverse throughout the Fennoscandian shield and segment the lithosphere into crustal blocks – sub-vertically
and sub-horizontally. The old continental basement in Finland is made up of
blocks bound by vertical and horizontal slip surfaces that may have either moved
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Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014
together or independently at different times. Because of their straightness and
great length – reaching up to hundreds of kilometres – some of these surfaces can
be assumed to cut down through the whole lithosphere.
The main geophysical lineament zones are formed by clusters of parallel or
sub-parallel small-scale lineaments with corresponding trends. North–southtrending, northeasterly-trending and northwesterly-trending lineaments are
displayed by blue, red and green polylines, respectively, to visualize the network
(Fig. 1). Each trend shows angle variation within a window of 30–40 degrees.
Mineral deposits (Eilu 2012, FODD 2013) tend to cluster along the main zones.
The western part of the boundary of the Karelian Province is composed of two
prevailing main trends: firstly, in the direction (north–northwest) following the
Savo-Lapland orogeny (Lahtinen et al. 2011), and secondly, in the direction of the
Skellefte belt – Knaften (northwest). Figure 2 illustrates the northern edge of the
“Keitele” block of Lahtinen et al. and the northwest trends between two north–
south-trending major zones (“Main faults_NS” in Figures 1 and 2). In this case,
many of the ore deposits, in particular the gold deposits, appear to follow the
related, intersecting shear zones connected to the major north–south-trending
zones. Many of the zinc deposits are related to the northwest trends.
References
Airo, M.-L., Hautaniemi, H., Korhonen, J. V., Kurimo, M. & Leväniemi, H. 2011. Airborne
geophysical data management and interpretation. In: Nenonen, K. & Nurmi, P. A. (eds) 2011.
Geoscience for Society: 125th Anniversary Volume. Geological Survey of Finland, Special
Paper 49, 349–358.
Eilu, P. (ed.) 2012. Mineral deposits and metallogeny of Fennoscandia. Geological Survey of
Finland, Special Paper 53.
FODD 2013. Fennoscandian Ore Deposit Database [Electronic resource]. Geological Survey of
Finland (GTK), Geological Survey of Norway (NGU), Geological Survey of Russia (VSEGEI),
Geological Survey of Sweden (SGU), SC Mineral [referred 20.3.2013]. Available at: http://
en.gtk.fi/informationservices/databases/fodd/index.html
Korja, A. & Kosonen, E. (eds) 2013. Seismotectonic framework and models in the northern part
of the Fennoscandian shield – Evaluating seismic hazard for the Pyhäjoki nuclear power plant,
Part 2. Report S-61, Institute of Seismology, University of Helsinki. 237 p.
Lahtinen, R., Hölttä, P., Kontinen, A., Niiranen, T., Nironen, M., Saalmann, K. & SorjonenWard, P. 2011. Tectonic and metallogenic evolution of the Fennoscandian shield: key questions with emphasis on Finland. In: Nenonen, K. and Nurmi, P. A. (eds) 2011. Geoscience for
Society: 125th Anniversary Volume. Geological Survey of Finland, Special Paper 49, 23–33.
Phillips, J. D. 2007. Geosoft eXecutables (GX’s) developed by the U.S. Geological Survey, version 2.0, with notes on GX development from Fortran code. U.S. Geological Survey, Open-File
Report 2007-1355. 111 p.
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
Fig. 1. Geophysical lineaments inferred from potential field data (magnetic and gravity). Different
directional trends are enhanced by characteristic colours. Major north–south-trending geophysical lineaments are indicated as thick blue lines and the northwesterly trending deformation zones
between them as thick light green lines. Ore deposits from the FODD database (FODD 2013).
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Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014
Fig. 2. Major north–south-trending geophysical lineaments (thick blue lines) and the northwesterly trending deformation zones between them (thick light green lines) displayed on the aeromagnetic map (GTK). Selected ore deposits (FODD 2013) tend to cluster along these zones.
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
Mineralogical and geochemical study on
carbonatites and fenites from the Kaulus
drill cores, Sokli Complex, NE Finland
by
Thair Al-Ani1 and Olli Sarapää2
1 Geological
Survey of Finland, P.O. Box 96, FI-02151 Espoo, Finland
Survey of Finland, P.O. Box 77, FI-96101 Rovaniemi, Finland
E-mail: [email protected]
2 Geological
Introduction
In 2012, sixteen diamond drill holes were drilled in two profiles across the fenite
zone of the Kaulus P-REE-prospect, in the southern part of the Sokli carbonatite
complex. The locations of the drill holes are shown in Figure 1. A mineralogical
study was performed on samples selected from the drill cores by using X-ray
diffraction (XRD) and MLA, optical microscopy, scanning electron microscopy
(SEM) and electron probe microanalysis (EPMA). Rock types were classified
according to whole rock XRF analysis.
Results
Most rock types are varieties of carbonatite that range in composition from silicocarbonatite in drillholes R6 and R11 to ferro- and calcio-carbonatite in drillholes
R12, R13 and R14 (Al-Ani & Sarapää 2013a). Accessory silicate minerals in carbonatites include Na-Ca amphibole, Mn-bearing ilmenite, magnetite, richterite,
phlogopite and clay minerals (Fig. 2). P-rich phoscorite, weathered down to 70
metres, occurs in R6.
The REE minerals that occur in the Kaulus carbonatite dykes are almost entirely LREE-dominated minerals such as ancylite-(Ce), calcioancylite-(Ce),
monazite, allanite and bastnäsite-(Ce). Ancylite-(Ce) is the most common and
occurs as coarse-grained phenocrysts with an average diameter of 300 μm. Calcioancylite-(Ce) is commonly associated with baryte, strontianite and pyrite (Fig.
3). Monazite-(Ce) occurs most commonly in the form of microcrystalline, sporadic, isolated equidimensional crystals and is mainly associated with apatite. The
crystal habit of bastnäsite and allanite in the studied carbonatites appears to be
acicular or needle-shaped, forming either radial accumulations or intricate crosscutting grids within a variety of minerals such as albite and dolomite. Apatite
in late carbonatite veins contains significant amounts of RE2O3, which indicates
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Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014
that the REE could perhaps be a by-product of phosphate production in the Sokli
area. This shows potential for further exploration in apatite carrying RE2O3 in the
future (Al-Ani & Sarapää 2013b).
Hydrothermal solutions, metasomatism and weathering have changed the
original mineralogy and caused the remobilization of REEs. The final precipitation of fluids carried REEs in fractures and vugs. Petrographic study of the REE
mineral assemblage reveals a close association of baryte, strontianite and calcite
along with REE minerals.
References
Al-Ani, T. & Sarapää, O. 2013a. Mineralogical and geochemical study on carbonatites and fenites
from the Kaulus drill cores, southern side of the Sokli Complex, NE Finland. Geological Survey
of Finland, archive report 145/2013. 66 p.
Al-Ani, T. & Sarapää, O. 2013b. Geochemistry and mineral phases of REE in Jammi carbonatite
veins and fenites, southern end of the Sokli complex, NE Finland. Geochemistry: Exploration,
Environment, Analysis 13, 217–224.
Woolley, A. R. & Kempe, D. R. C. 1989. Carbonatites: nomenclature, average chemical compositions, and element distribution. In: Bell, K. (ed.) Carbonatites: Genesis and Evolution. London:
Unwin Hyman, 1–14.
Fig. 1. Location of the Kaulus drill holes in a high-density aeromagnetic map of the Sokli carbonatite complex.
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
Fig. 2. Ternary diagrams of major-element concentration data from Kaulus samples. Note the
distinctive difference between samples from different parts of the complex. Field boundaries of
silico-, ferro-, calcio-, and magnesio-carbonatite after Woolley & Kempe (1989).
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Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014
Fig. 3. BSE images from carbonate minerals in silico-carbonatite and carbonatite. (a) Clustering
of barite, strontianite and ancylite within calcite; (b) ancylite aggregates associated with prismatic
pyrite crystals; (c) monazite in contact with needle-like goethite and granular apatite (lower left
corner); (d) a large Ba-pyrochlore grain with zoning structure.
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Geologian tutkimuskeskus, Tutkimusraportti 207 – Geological Survey of Finland, Report of Investigation 207, 2014
Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
Hyperspectral analysis of drill cores from
the Kedonojankulma Cu-Au deposit
by
Hilkka Arkimaa1, Viljo Kuosmanen1, Markku Tiainen1 and Rainer Bärs2
1 Geological
Survey of Finland, P.O. Box 96, FI-02151 Espoo, Finland
Spectral Imaging Ltd, Teknologiantie 18 A, FI-90590 Oulu, Finland
E-mail: [email protected]
2 SPECIM,
INTRODUCTION
Hyperspectral analysis involves measuring and studying light and nearby electromagnetic radiation reflected or emitted from a target at varying wavelengths,
preferably from 0.3 microns to 20 microns (300 to 20 000 nanometres). The variety of absorption processes and their wavelength dependence allows us to obtain information on the abundances of minerals. Due to the varying molecular
structure of different minerals, their reflectance/emittance characteristics are expressed by the respective wavelengths of electromagnetic radiation.
SisuROCK (SisuROCK Hyperspectral Core Imaging Station), the hyperspectral imaging instrument developed by Specim, is a fully automated device for
the high speed scanning of drill cores. Depending on the application, SisuROCK
contains one or more of the following spectral imaging modes: VNIR (400–1000
nm), SWIR (970–2500 nm), combined VNIR+SWIR (380–2500 nm), TIR (8–12
µm) and a high-resolution RGB camera. SisuROCK collects spectral and spatial
information on drill cores as the core box is automatically moved through the
system. The spectral performance of SisuROCK VSWIR reflectance in mineral
quantification has been shown to be comparable to that of a FieldSpecFR portable
spectrometer (Kuosmanen et al. 2009).
DATA FROM KEDONOJANKULMA CU-AU DEPOSIT
The Kedonojankulma Cu-Au deposit (Tiainen et al. 2013) is located in the volcanic-intrusive Häme Belt. The ore formation is related to the strong hydrothermal
alteration of the northern part of the intrusion. The most distinct alterations are
silicification, sericitization, carbonatization, epidotization, and less distinctively
defined oxidation (reddish alteration) in an area wider than the ore formation.
Silicification has taken place in several phases. SisuRock measurements were carried out using the combined VNIR+SWIR (380–2500 nm) imaging mode from
twenty drill core boxes. Approximately 120 m of core representing two separate
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Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014
drill holes from the Cu-Au occurrence were imaged. The resulting total imagery
comprises 6.3 million pixels (size 1.2 mm x 1.2 mm), each of which contains a
continuous VNIR+SWIR reflectance spectrum built up of 256 channels.
INTERPRETATION OF THE SISUROCK DATA
By using so-called unmixing methods, it is possible to determine the relative
abundances of different materials in the measured spectrum. If not all end members (materials) are known or if the aim is to map a few endmembers, the socalled partial unmixing methods, such as Matched filtering (MT) and Mixture
Turned Matched Filtering (MTMF), can be used.
User-defined endmember spectra in the interpretation of SisuROCK data were
collected from the mean spectra of regions of interest (ROIs) chosen by the exploration geologist. The results estimate the relative degree of match with the reference spectrum and the approximate subpixel abundance. The mineral contents of
chosen model targets (ROIs, endmembers) were also determined by mineral liberation analysis (MLA). The abundances of alteration minerals were interpreted
from SisuROCK data by subpixel unmixing and calibration. The quantities were
validated using MLA.
CONCLUSIONS
The results demonstrated that it is possible to distinguish between several mineralogical features, which is crucial for the evaluation of the mineral potential:
• Unaltered rocks can be separated from altered ones;
• Sericitization shows up and correlates with an increased copper content;
• Carbonatization is clearly indicated;
• Abundant quartz is clearly indicated. However, the classification of
silicification types needs further studies, preferably using
the SisuROCK LWIR option.
References
Kuosmanen, V., Laitinen, J. & Bärs, R. 2009. Comparison of quantitative assessment of
mineral powder components using SisuROCK hyperspectral scanner and FieldSpec portable
spectrometer [Electronic resource]. In: Ben-Dor, E. (ed.) Proceedings of 6th EARSeL Imaging Spectroscopy SIG Workshop: innovative tool for scientific and commercial environmental
applications, Tel Aviv, Israel, March 16−18, 2009. Available at: http://www.earsel.org/workshops/IS_Tel-Aviv_2009/PROCEEDINGS.htm
SisuROCK Hyperspectral Core Imaging Station. [WWW document]. SPECIM, Spectral
Imaging Ltd. [Referred 19.02.2014] Available at: http://specim.fi/index.php/products/geology/
sisurock.
Tiainen, M., Molnár, F., Kärkkäinen, N. and Koistinen, E. 2013. The Forssa-Jokioinen Cu-AuZn Province, with special emphasis on the Kedonojankulma Cu deposit. Geological Survey of
Finland, Report of Investigation 198, 179–184.
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
STAKEHOLDER ENGAGEMENT PRACTICED BY THE
GEOLOGICAL SURVEY OF FINLAND IN MINERAL
POTENTIAL MAPPING IN SOUTHERN FINLAND
by
Toni Eerola, Niilo Kärkkäinen and Markku Tiainen
Geological Survey of Finland, P.O. Box 96, FI-02151 Espoo, Finland
E-mail: [email protected]
INTRODUCTION
A good company–community relationship is important in order to earn a social
license to operate (SLO) in mining. To secure the building of good relationships,
it is important to start communication and stakeholder engagement at the very
beginning of mineral exploration. A model for stakeholder engagement in mineral exploration was recently developed by the Mining Academy. Here, we present
a methodology for stakeholder engagement that has been used by the Geological
Survey of Finland (GTK) in mineral potential mapping in Southern Finland.
GTK’S MINERAL POTENTIAL MAPPING
A fundamental and traditional task of GTK is to collect, investigate, store and disseminate national geological information, including data on ore deposits. GTK’s
field activities in mineral potential research and mapping are very similar to those
performed by private companies in mineral exploration, involving geological
mapping, sampling, trenching and drilling. However, GTK generally operates in
areas not in the focus of private mineral exploration companies.
STAKEHOLDER ENGAGEMENT IN GTK’S MINERAL POTENTIAL
MAPPING
As mineral exploration performed by private companies has caused resistance by
locals in some areas of the country, GTK has adopted systematic local stakeholder
engagement in its mineral potential mapping operations.
Southern Finland is the most densely populated part of the country, so avoiding encounters with the locals, even in the countryside, is difficult. Sharing information on who is operating, how and why on private lands and in the region
helps to prevent possible conflicts.
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Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014
The considered stakeholder groups of local communities in Southern Finland
are local landowners, residents, media, schools and the municipality representatives. Direct contacts in the field, press releases and conferences, as well as open
and public meetings and lectures are the approaches used to engage with these
groups. Before activities are started, leaflets informing about the fieldwork and
contact information are left in mailboxes. The leaflet explains why and how the
investigations are being conducted. Landowners are also informed by letter attached to the leaflet about when the systematic geophysical measurements will
be carried out in the area. In addition to the regulations of the Mining Act, the
exploration operations have often been discussed with landowners to avoid dispensable harm. Drillings outside exploration permit areas are always carried out
with written consent from the landowners.
Stakeholder engagement is performed by geologists working in the region.
GTK’s stakeholder engagement has been practiced and developed since the early
2000s. At present, GTK is performing mineral potential mapping in the Häme
region between Forssa and Hämeenlinna in Southern Finland, where little or no
opposition has been encountered.
Similar stakeholder engagement methods are widely used around the world,
and GTK mainly follows those suggested in the literature, and a model created by
the Mining Academy for Finland. However, there are also some differences: GTK
has produced an information leaflet, and it has not considered NGOs in its set of
local stakeholder groups.
FURTHER DEVELOPMENTS
The stakeholder engagement performed by GTK in mineral potential mapping
has not been a systematic nor standardized activity. It has largely been a polite and
respectful approach towards the local communities. However, as the new Mining
Act requires the informing of landowners, and public resistance towards mining
activities is growing in Finland, such approaches and methodologies should be
surveyed, developed, systematized and standardized in the updating of GTK’s
mineral potential mapping strategy. This should be carried out by reflecting on
the local conditions and stakeholder groups, and considering different contexts in
northern and southern Finland (such as the Sámi people and reindeer herders).
These contexts might impose some specificity in stakeholder engagement in
different regions that should be taken into account.
OPPORTUNITY FOR CROSS-DISCIPLINARY COOPERATION
There are several on-going social science projects studying, developing and promoting socially sustainable mining in Finland in which GTK is participating.
This opens possibilities for multidisciplinary cooperation between geologists and
social scientists within the projects dealing with the SLO and CSR of mineral
potential mapping. This cooperation could have a role by examining the effectiveness, impacts and impressions of local people related to GTK’s stakeholder engagement in order to provide feedback to develop and improve its social
performance in mineral potential mapping and research.
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Geologian tutkimuskeskus, Tutkimusraportti 207 – Geological Survey of Finland, Report of Investigation 207, 2014
Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
Some Geochemical constraints on
THE SiilinjärVI carbonatite-Glimmerite
complex
by
Esa Heilimo1, Jouni Luukas1, Perttu Mikkola1 and Pasi Heino2
1 Geological
Survey of Finland, P.O. Box 1237, FI-70211 Kuopio, Finland
Finland Ltd., FI-71840 Siilinjärvi, Finland
E-mail: [email protected]
2 Yara
Introduction
Carbonatites are relatively rare rocks with a unique low silica composition. The
oldest known examples are 2.8 Ga old and their number has continued increasing to the present day (Woolley 1989). The ca. 2.6 Ga Siilinjärvi carbonatiteglimmerite complex in Finland is located in the Archaean Karelia Province near
the boundary of the Palaeoproterozoic Svecofennian domain. The geology of this
complex was first described by Puustinen (1969). The complex forms a roughly
N–S-oriented, 16-km-long and 1.7-km-wide elongated body (Fig. 1). Carbonatite-glimmerites are intrusive to Archaean igneous rocks, which have been fenitized to a variable degree, although the width of fenitization is difficult to estimate.
The complex is intruded by several diabase dykes and ca. 1.8 Ga dioritic-tonalitic
rocks.
The carbonatite-glimmerite complex was formed by at least three separate
phases. The first phase was mainly hydrothermal and fenitized the country rocks,
while glimmerites were emplaced in the second, magmatic phase, and the third
phase formed the sharply cross-cutting carbonatite veins. The dominant carbonate mineral is calcite, and dolomite is present in accessory amounts. Tetraferriphlogopite is the major mineral in glimmerites. The carbonatite-glimmerite
complex has undergone two intense Palaeoproterozoic deformation stages. The
older folding stage has produced open to tight fold structures with almost horizontal N- and S-trending fold axes. The second deformation stage has caused
intense vertical shearing in incompetent glimmerite ore, producing small-scale
left- and right-handed shear folds with vertical fold axes (Fig. 2). These structural
features have been observed in both the Archaean carbonatite complex and the
Palaeoprotetozoic dykes cross-cutting the complex.
The high content of apatite makes the Siilinjärvi carbonatite-glimmerite complex economically important for fertilizer production, and it is the largest phosphorus resource in Western Europe, with an average in situ grade of 4.3 wt% P2O5.
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Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014
Geochemical constraints with implications
FOR petrogenesis
In collaboration with Yara Finland Ltd., the company operating the Siilinjärvi
mine, we have collected samples for a detailed description of the geochemistry of
the complex. The carbonatite veins are calciocarbonatitic in composition, whereas glimmerite and different variants between pure glimmerite and carbonatite
show a relatively unfractionated magnesiocarbonatite composition.
The major elements show gradual variation between carbonatite and glimmerite end-members. The P2O5 concentration varies between 2.0 and 7.0 wt% in carbonatite and related rocks, excluding a group of pure calciocarbonatite veinlets,
which contain practically no apatite at all. The rare earth element (REE) concentrations are not high enough to be economically intresting. The average REE
concentrations rise between magmatic phases from fenite (REE(tot) = 230 ppm)
to glimmerite (REE(tot) = 360 ppm), and from glimmerite to carbonatite (REE(tot)
= 760 ppm). A similar trend is evident in Sr, Ba, and Y concentrations, which
gradually increase from fenite to carbonatite. The carbonatite and glimmerite
have high Mg#, typically up to 0.8. This indicates that the parental magmas of
carbonatite could have been in equilibrium with mantle peridotite. The regional
geology and available geochronological data support an anorogenic setting at the
time of emplacement of the complex, possibily in a rift setting.
References
Bedrock of Finland − DigiKP. Digital map database [Electronic resource]. Espoo: Geological Survey of Finland [referred 21.02.2014]. Version 1.0.
Puustinen, K. 1969. Geology of the Siilinjärvi carbonatite complex, eastern Finland. Bulletin de la
Commission Géologique de Finlande 249. 43 p. + 1 app. map.
Woolley, A. R. 1989. The spatial and temporal distribution of carbonates. In: Bell, K. (ed.) Carbonatites: genesis and evolution. London: Unwin Hyman, 15–37.
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
Fig. 1. Geological map of the Siilinjärvi carbonatite-glimmerite complex based on the Digital bedrock database of Finland (Bedrock of Finland − DigiKP).
Fig. 2. Intensive vertical N–S shearing of the second deformation stage causing small-scale lefthanded shear folds with an N-fold axis on carbonatite-glimmerite. The length of the compass is
11 cm.
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Geologian tutkimuskeskus, Tutkimusraportti 207 – Geological Survey of Finland, Report of Investigation 207, 2014
Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014
seismically reflective volcanic stratigraphy
in Pyhäsalmi and Vihanti massive sulPHide
mining camps
by
Suvi Heinonen1, Jouni Luukas2 and Jukka Kousa2
1 Geological
Survey of Finland, P.O. Box 96, FI-02151 Espoo, Finland
Survey of Finland, P.O. Box 1237, FI-70211 Kuopio, Finland
E-mail: [email protected]
2 Geological
INTRODUCTION
A network of seismic reflection profiles was acquired in the Pyhäsalmi and Vihanti massive sulphide mining areas in central Finland during the HIRE (HIgh
REsolution reflection seismics for ore exploration 2007–2010) project by the
Geological Survey of Finland. The multiphase deformation history of the study
areas is demonstrated by folding, faulting and shearing, which cause the complex subsurface reflectivity patters observed in the seismic data. These data enable
thorough discussion on the applicability of reflection seismic profiling to massive
sulphide exploration in a geological environment that is highly deformed and
metamorphosed.
SEISMIC PROCESSING AND INTERPRETATION
The quality of seismic images can be improved and tailored to the needs of geological interpretation by careful re-processing of the data (Heinonen et al. 2013).
Careful static corrections and velocity analysis are the most important processing steps when reflections from the physically similar or steeply dipping rock
contacts typical for hardrock seismic data need to be restored. Steeply dipping
structures are also common in Pyhäsalmi and Vihanti, and proper stacking of
these features requires the use of unrealistically high NMO velocities. Steep and
horizontal structures are best interpreted from separate stacks using 3D visualization and modelling software, such as Paradigm GoCad.
The difference in the acoustic impedance of the rocks defines the strength of
a reflection originating from a rock contact. Geophysical drill hole logging indicates that in addition to the massive sulphides, the hosting rock sequences are also
strongly reflective in Vihanti and Pyhäsalmi (Heinonen et al. 2013 and Heinonen
et al. 2012, respectively). Reflective hosting lithology enables the determination
of favourable exploration environments. In Pyhäsalmi, the known massive sulphide deposit could not be reliably identified from the seismic section because
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Geologian tutkimuskeskus, Tutkimusraportti 207 – Geological Survey of Finland, Report of Investigation 207, 2014
Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
of the crooked acquisition lines, the noise caused by the functioning mine and
the lithologically heterogeneous and strongly three-dimensional geological background of the deposit.
Knowledge of the structural geology of the study area is essential for seismic
interpretation. In Pyhäsalmi, only hinges of the sub-vertical folds are clearly visible in seismic profiles, while steep limbs could not be directly imaged by seismic
profiling. Gentle open folding is typical for the Vihanti region and was shown
as undulating reflectivity in the seismic profiles. Prominent reverse faults were
interpreted in the Vihanti area, where strong reflectors are cut by faults. Seismic
reflection data provide an insight into the deep continuation of the fault zones
that might have acted as pathways for fluids carrying sulphide minerals during
deformation.
CONCLUSIONS
Results from the HIRE seismic soundings in the Vihanti and Pyhäsalmi mining
camps encourage the use of seismic reflection profiling for deep ore exploration.
Geophysical drill hole logging data confirm that the volcanic stratigraphy is reflective in the Pyhäsalmi and Vihanti areas, and a network of seismic reflection
profiles creates the framework on which geological 3D models of reflective subsurface structures can be constructed. The direct detection of massive sulphide
deposits remains challenging within the resolution of HIRE seismic reflection
profiles, but reflection seismic profiling combined with geological 3D modeling
enables the strategic planning of exploration and facilitates decisions on expensive deep drill holes.
References
Heinonen, S., Imaña, M., Snyder, D. B., Kukkonen, I. T. & Heikkinen, P. J. 2012. Seismic reflection profiling of the Pyhäsalmi VHMS-deposit: A complementary approach to the deep base
metal exploration in Finland. Geophysics 77, WC15-WC23.
Heinonen, S., Heikkinen, P. J., Kousa, J., Kukkonen, I. T. & Snyder, D. B. 2013. Enhancing
hardrock seismic images: reprocessing of high resolution seismic reflection data from Vihanti,
Finland. Journal of Applied Geophysics 93, 1–11.
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Geologian tutkimuskeskus, Tutkimusraportti 207 – Geological Survey of Finland, Report of Investigation 207, 2014
Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014
THE KORPELA CU-ZN MINERALIZATION, A NEW VMS
POTENTIAL TARGET IN THE PALAEOPROTEROZOIC
VIHOLANNIEMI VOLCANIC SUITE IN JOROINEN,
SOUTHEASTERN FINLAND
by
Janne Hokka, Sami Niemi and Jukka Kousa
Geological Survey of Finland, P.O. Box 1237, FI-70211 Kuopio, Finland
E-mail: [email protected]
The Viholanniemi area is situated in the municipality of Joroinen, 20 km south of
the city of Varkaus. It belongs to the southeastern part of the Svecofennian RaaheLadoga structural zone. The (1.91 Ga) Viholanniemi volcanic suite covers an area
of ca. 10 km2 and hosts the Viholanniemi Zn-Ag-Au deposit (Fig. 1).
A geophysical survey and ore potential mapping in the Viholanniemi volcanic
suite have led to a new and interesting Cu-Zn anomaly target area named as Korpela, about 2 km south of the known Zn-Ag-Au deposit. The surface projection
is approximately 50 x 800 m in size, forming a north–south-trending zone. Interpretation of the in-house Sampo survey has revealed several deep electromagnetic (EM) conductors at a depth of 150–200 m. At the surface, several copperpyrite-magnetite-bearing altered volcanic rock units have been found (including
0.9 wt% copper). The volcanic package is mainly dipping at 65–70 degrees to the
SW. The host rock lithologies include felsic to intermediate volcaniclastic rocks
(lapilli tuffs/tuff breccias) with intermediate to mafic volcanic layers (Fig. 2a). The
on-going drilling programme has produced four holes with a total length of 648
m. The drill holes have mainly been targeted at testing the geophysical anomalies
(magnetic, induced polarization) and vertical extensions of mineralized surface
outcrops. Some of the geophysical anomalies probably originated from iron sulphides. The first three drill holes (N5122013R6-N5122013R8) intersected only a
few narrow mineralized veins, including 0.35 m, grading 1.3 wt% zinc, 788 ppm
copper and 156 ppb gold, and 0.20 m, grading 0.49 wt% copper and 0.3 wt% zinc.
The alteration mainly results from a quartz-garnet-pyrite assemblage. Drill hole
N5122013R9 intersected an altered zone starting at a depth of 160 m (down-hole
direction), which is highly aluminous and strongly calcium and sodium depleted.
It is strongly to pervasively sericite altered, together with increasing sulphide (pyrite ± pyrrhotite ± magnetite ± chalcopyrite) abundance. At a depth of 200 m,
the aluminium content increases, and produces an andalusite-muscovite-quartz
assemblage. Mineral assemblages range from a biotite-staurolite assemblage to a
quartz-muscovite-andalusite assemblage (Fig. 2b).
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
The Viholanniemi area is potential for hosting a new volcanogenic massive sulphide (VMS) deposit. The high aluminous alteration zone might be an equivalent
of an advanced argillic alteration assemblage common to metamorphosed highsulphidation deposits. EM conductors have not yet been tested with drilling.
The priority for future exploration is to conduct a geophysical transient electromagnetic (TEM) survey as a comparison with the in-house Sampo instrument
and to obtain a better 3D estimation of the location of conductors and their properties. A magnetic survey using GTK’s walking magnetometers will be carried
out with a station spacing of less than one metre and a line spacing of 50 metres.
Magnetic data will be used to construct a 3D susceptibility model of the Korpela
area. Altered and fresh assemblages from the Korpela area will be further studied
to gain a better understanding the ore forming processes.
References
Bedrock of Finland − DigiKP. Digital map database [Electronic resource]. Espoo: Geological
Survey of Finland [referred 31.1.2014]. Version 1.0.
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Geologian tutkimuskeskus, Tutkimusraportti 207 – Geological Survey of Finland, Report of Investigation 207, 2014
Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014
Fig. 1. Lithology of the Viholanniemi volcanic suite area (modified after Bedrock of Finland–
DigiKP). The photo of chalcopyrite bearing anthophyllite garnet altered intermediate pyroclastic
rock from Korpela target. Contains data from the National Land Survey of Finland Topographic
Database 08/2012.
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
Fig. 2. (a) Unaltered felsic to intermediate volcaniclastic rock from drillhole N5122013R9. The
clasts are mostly lapilli size, rounded/anglular in shape and tectonically flattened. The composition
is felsic dominated with occasional mafic clasts. (b) Altered drillcore samples from N5122013R9
that contains mainly pyrite dissemination (± pyrrhotite ± magnetite ± chalcopyrite). The bottom
sample represents quartz-muscovite-andalusite assemblage. The andalusite porfyroblasts are up to
1.5 cm in diameter.
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Geologian tutkimuskeskus, Tutkimusraportti 207 – Geological Survey of Finland, Report of Investigation 207, 2014
Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014
MINERAL RESOURCE ESTIMATION FOR
THE KIVINIEMI SC-ZR-Y- DEPOSIT
by
Janne Hokka and Tapio Halkoaho
Geological Survey of Finland, P.O. Box 1237, FI-70211 Kuopio, Finland
E-mail: [email protected]
The Kiviniemi intrusion is located in the municipality of Rautalampi, Central
Finland, about 70 km SW of the city of Kuopio and about 350 km NNE of Helsinki. GTK commenced two diamond drilling programmes on the Kiviniemi property during 2008–2009 and 2010, totalling 1251.8 m (Ahven 2012, Halkoaho et al.
2013a, 2013b). Drill holes P433_2010_R1–P433_2010_R4 were used in a mineral
estimation study, and the distance between the drill hole profiles was between
100–200 m (see Fig. 1).
The Kiviniemi intrusion was divided into domains that were used to construct
the Kiviniemi block model (Fig. 2). The block model is made up of parent cells of
size 20 m (X) x 20 m (Y) x 20 m (Z), and was sub-celled into blocks of 5 m (X) x
5 m (Y) x 5 m (Z) at the domain boundaries. Due to the sparse drilling (Fig. 2A),
the grade continuity of mineralisation resulted in poor variograms. The blocks
inside the wireframes were estimated using the inverse distance method. The
mean sample length was 1.3 m and assay data were composited to the nearest half
metre. All elements (Sc, Zr and Y) were estimated in the same estimation round.
The average specific gravity of three samples taken from fayalite ferrogabbro, 3.16
g/cm3, was assigned to all mineralised rocks and used in resource estimation.
Several basic validation methods were performed to check the quality of the
model, such as visual checks (Fig. 2B) and primary data versus model data comparison. Due to the scattered sample grid, the resource estimation is categorised
as an inferred mineral resource class and the global estimation as a prospective
mineral resource (Table 1). Although the host rock lithology appears to be fairly
homogeneous with a rather continuous scandium grade distribution, it is only a
rough estimate and more drilling is required to obtain the level of confidence to
allow the grade and geological continuity to be considered as confirmed.
The criteria for the domains are as follows:
1. The global domain consists of an interpretation of the total volume of the intrusion. Wireframe was modelled to envelope all scandium-bearing samples and
honouring the intrusion boundaries from available surface mapping and drill
hole data. The individual domains were included in the model.
2. Individual domains consist of three domains (codes: 101, 201, 301) and three
sub-domains (codes: 102, 103, 202). Lenses were modelled by using lithology
and scandium grade to distinguish the main populations and classify them into
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
high-grade, low-grade and medium-grade domains. High-grade and low-grade
domains included several lenses that were subdivided into sub-domains.
References
Ahven, M. 2012. Petrology and geochronology of the Kiviniemi garnet-bearing fayalite ferrogabbro, Rautalampi. Unpublished M.Sc. Thesis, University of Helsinki, Department of Geosciences and Geography. 62 p.
Halkoaho, T., Ahven, M. & Rämö, O. T. 2013a. A New Type of Magmatic Sc-Zr Occurrence
Located in the Kiviniemi Area, Rautalampi, Central Finland. In: Erik Jonsson et al. (eds) Mineral deposit research for a high-tech world. 12th Biennial SGA Meeting, 12–15 August 2013,
Uppsala, Sweden, Vol. 4, 1717−1719.
Halkoaho, T., Johanson, B. & Niskanen, M. 2013b. A new type of Sc-Zr occurrence located in
the Kiviniemi Area, Rautalampi, central Finland. In: Hölttä, P. (ed.) Current Research: GTK
Mineral Potential Workshop, Rauhalahti/Kuopio, May 2012. Geological Survey of Finland,
Report of Investigation 198, 33−35.
Fig. 1. The Kiviniemi intrusion is subdivided into two intrusion blocks (wireframes). The surface
extension of the main intrusion is circa 2.5 hectares and it extends to a vertical depth of at least 70
m below the surface. The smaller block is situated approximately 100 m NE of the main intrusion
and is also exposed in surface outcrops. The Kiviniemi intrusion consists of five rock types: coarsegrained (garnet-bearing) fayalite ferrogabro, leucocratic ferrogabbro, medium- and fine-grained
ferrogabbro, and granite. The main host rock for enriched scandium, zirconium and yttrium is the
coarse-grained fayalite ferrogabbro.
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Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014
Fig. 2. (a) The wireframe model of the main intrusion and smaller NE block. Red areas represent
drill-hole intersections with good confidence and brown areas are interpretations. (b) Visual validation of the block model from section P433_2010_R1- P433_2010_R3. The colour coding represents different scandium (g/t) values. No grade top-cutting was applied in the model. (c) A block
model of all individual domains at different cut-off grades. The average scandium grade is 142.15
g/t, so distinct tonnage loss does not start to appear until cut-off levels of 100–150 g/t.
Table 1. Estimated tonnages (Mt) and grades (g/t) of the Kiviniemi deposit at cut-off grades of
40 g/t Sc and 100 g/t Sc. The global domain is only an indication of the exploration potential and
should be treated as having a low level of confidence.
Kiviniemi Sc-Zr-Y deposit
Method: Inverse distance
Individual domains total
Cut-off (Sc g/t)
Tonnage (Mt)
Scandium (Sc)
Zirconium (Zr)
Yttrium (Y)
40
3.7
150.1
1751.3
83
100
3.2
166.1
1787.5
80.3
Global domain total
Cut-off (Sc g/t)
Tonnage (Mt)
Scandium (Sc)
Zirconium (Zr)
Yttrium (Y)
40
13.4
162.8
1726.2
81
100
12.5
170.9
1743.6
80.3
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Geologian tutkimuskeskus, Tutkimusraportti 207 – Geological Survey of Finland, Report of Investigation 207, 2014
Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
ISOTOPE GEOLOGY AND CRUSTAL GENESIS IN
FINLAND
by
Hannu Huhma, Yann Lahaye, Irmeli Mänttäri and Hugh O’Brien
Geological Survey of Finland, P.O. Box 96, FI-02151, Espoo, Finland
E-mail: [email protected]
Introduction
Since the early 1960s, the isotope laboratory at GTK has provided key parameters
for modelling the age and genesis of the Fennoscandian Shield. The principal
dating method has been U-Pb thermal ionization mass spectrometry (TIMS) on
zircon, monazite and titanite. Essential genetic information has been obtained by
Pb-Pb and Sm-Nd methods. However, conventional multi-grain TIMS data have
yielded only average ages, which may lead to biased interpretations. Together
with secondary ion mass spectrometry (SIMS), recent years have seen the very
successful application of spot analyses with laser multiple-collector inductively
coupled plasma mass spectrometry (LA-MC-ICPMS). According to the register
of the laboratory, U-Pb data are currently available on ca. 1800 samples from Finland (TIMS ~1500, SIMS ~300, LA-MCICPMS ~300). Sm-Nd isotope data have
been obtained since the early 1980s on more than 2000 samples. The main picture
of the isotope results was briefly summarized in Huhma et al. (2011), and for the
Archaean crust in more detail by Huhma et al. (2012a,b).
Results
The recent fruitful isotope research on crustal genesis has largely been in co-operation with ca. 50 geologists at GTK and universities. The new results, mostly
from LA-MC-ICPMS, are outstanding and in some cases confirm the old estimates using TIMS (some examples in Huhma et al. 2012a), but also frequently
provide a completely new picture on the complex crustal history. Nevertheless,
some cases remain problematic (Fig. 1). Many questions had already earlier
been solved by SIMS, but now the powerful capacity of MC-ICPMS has really made it possible to focus, for instance, on sedimentary rocks with complex
detrital zircon populations.
A few selected examples of the recent results include the following. The 3.5 Ga
Siurua gneisses are still the oldest rocks in Finland (Mutanen & Huhma 2003),
but evidence of 3.5–3.6 Ga has been obtained from several sedimentary samples.
A rock fragment within Archaean TTG gneiss in the Lahnasjärvi complex close
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Geologian tutkimuskeskus, Tutkimusraportti 207 – Geological Survey of Finland, Report of Investigation 207, 2014
Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014
to Talvivaara turned out to be ca. 3.4 Ga. The oldest volcanic rocks, at ca. 2.94 Ga,
have been obtained from the Suomussalmi belt (Huhma et al. 2012), and now also
confirmed from Sarvisoaivi, NW Lapland. Further evidence of 2.88 Ga volcanics
has been found from the Kovero belt. A large amount of data from detrital zircons in several Palaeoproterozoic metasediments indicates that the early findings
(Huhma et al. 1991, Lahtinen et al. 2002) of a broadly bimodal distribution are
very typical. In particular, the abundance of ca. 2 Ga material is significant in
many samples from both Svecofennian and Karelian domains. The felsic crustal
source of that age is enigmatic, although 2 Ga granites have recently been found
in W Lapland. The complexity of Proterozoic granitoid magmatism in Lapland
has become more evident, since reliable ages include 2.48 Ga, 2.38 Ga, 2.13–2.11
Ga, 2.00 Ga, 1.91 Ga, 1.89–1.85 Ga and 1.81–1.77 Ga. The U-Pb data on detrital
zircons have been successfully applied to constrain the age of deposition, but the
lack of Proterozoic populations, particularly in the Vuojärvi and Central Puolanka Group rocks, as well as in many Jatulian quartzites, leaves the problem still
open (Kontinen et al., this volume). We have also been able to more precisely
date many gabbroic rocks, which may be of interest in terms of mineral potential.
Examples of recent results will be discussed.
Acknowledgements
We acknowledge the fruitful co-operation with geologists at GTK and universities, which has provided the basis for high-quality research and interpretation.
References
Huhma, H., Claesson, S., Kinny, P. & Williams, I. 1991. The growth of early Proterozoic crust: new
evidence from Svecofennian detrital zircons. Terra Nova 3, 175–179.
Huhma, H., O’Brien, H., Lahaye, Y. & Mänttäri, I. 2011. Isotope geology and Fennoscandian lithosphere evolution. In: Nenonen, K. & Nurmi, P. A. (eds) 2011. Geoscience for Society: 125th
Anniversary Volume. Geological Survey of Finland, Special Paper 49, 35–48.
Huhma, H., Mänttäri, I., Peltonen, P., Kontinen, A., Halkoaho, T., Hanski, E., Hokkanen, T.,
Hölttä, P., Juopperi, H., Konnunaho, J., Lahaye, Y., Luukkonen, E., Pietikäinen. K., Pulkkinen, A., Sorjonen-Ward, P., Vaasjoki, M. & Whitehouse, M. 2012a. The age of the Archaean
greenstone belts in Finland. In: Hölttä P. (ed.) The Archaean of the Karelia Province in Finland.
Geological Survey of Finland, Special Paper 54, 74–175.
Huhma, H., Kontinen, A., Mikkola, P., Halkoaho, T., Hokkanen, T., Hölttä, P., Juopperi, H.,
Konnunaho, J., Luukkonen, E., Mutanen, T., Peltonen, P., Pietikäinen, K. & Pulkkinen, A.
2012b. Nd isotopic evidence for Archaean crustal growth in Finland. In: Hölttä P. (ed.) The
Archaean of the Karelia Province in Finland. Geological Survey of Finland, Special Paper 54,
176–213.
Kontinen, A., Huhma, H., Lahaye, Y. & O’Brien, H. 2014. The problem with the age of the Central Puolanka Group keeps fighting us. In: Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi,
M., Lahtinen, R. & Hölttä, P. (eds) Current Research: 2nd GTK Mineral Potential Workshop,
Kuopio, Finland, May 2014. Geological Survey of Finland, Report of Investigation 207. (This
volume)
Lahtinen, R., Huhma, H. & Kousa, J. 2002. Contrasting source components of the Paleoproterozoic Svecofennian metasediments: Detrital zircon U-Pb, Sm-Nd and geochemical data.
Precambrian Research 116, 81–109.
Mutanen, T. & Huhma, H. 2003. The 3.5 Ga Siurua trondhjemite gneiss in the Archaean Pudasjärvi Granulite Belt, northern Finland. Bulletin of the Geological Society of Finland 75, 51–68.
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
A1291 Kaivanto trondhjemite
0.7
data-point error ellipses are 2s
A1291-1b
3000
0.6
A1291-1a
2800
206
Pb
238
U
2600
0.5
A1291-4a
A1291-1c
2400
A1291-4b
TIMS
2200
0.4
2000
A1291-4c
1800
0.3
4
8
12
207
Pb/
235
A454 Siikakämä gabbro
20
data-point error ellipses are 2s
Range of Pb/Pb ages from 2.43 Ga to 1.8 Ga
19 analyses on five grains
0.5
2500
U
2300
0.4
2100
Pb/
238
U
16
206
1900
1700
0.3
1500
TIMS
1300
0.2
2
4
6
207
Pb/
235
8
U
10
12
Fig. 1. Laser MC-ICPMS data on zircon explain the old heterogeneous TIMS results. A1291: Old
cores up to 3 Ga, mantle mostly ca. 2.6 Ga, age of rock? A454: The best-preserved domains register primary igneous ages at ca. 2.43 Ga, and strong metamorphic effects are evident in altered
domains.
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Geologian tutkimuskeskus, Tutkimusraportti 207 – Geological Survey of Finland, Report of Investigation 207, 2014
Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014
Geochemical anomalies reFLECTING
ore-forming processes in THE Svecofennian
Häme Belt, southern Finland
by
Pekka Huhta, Niilo Kärkkäinen, Markku Tiainen and Erkki Herola
Geological Survey of Finland, P.O. Box 96, FI-02151, Espoo, Finland
E-mail: [email protected]
Introduction
A till geochemical survey has been used to recognize possible regional ore-forming processes and direct indications of mineralization in the Häme Belt, southern
Finland. The results include versatile data on the overburden, element distribution, soil depth, and in most cases, the local rock type. The study was carried out
during 2004–2007 and 2010–2013 in GTK projects assessing the ore potential
of the Häme Belt. The area is about 600 km2 and the sampling grid was 500 m,
producing about 4000 samples. The samples were taken from basal till from a
depth of 1–4 m, or deeper if the till was located under locally common glacial
clay deposits. There are gaps in sampling sites, especially due to eskers, protected
areas or towns.
The sampling points were selected within till-dominated areas by using maps
of Quaternary deposits. The bedrock was reached in about 30% of sampling
points. In these cases, the till sample represented the bottom of the basal till. In
most of these cases, a tiny bedrock fragment was also obtained, and the rock type
could be determined. Otherwise, the sampling stopped in till due to excessively
compressed material or large boulders. Locally, the only material in the drilling
site was sand or clay. The mean depth of points was about 4 m and deepest points
were over 15 m.
Geochemical anomalies
Some preliminary results can be discussed in this paper. Sampling was completed
in late 2012, but many samples are still waiting to be analysed. Analyses are based
on partial (aqua regia) leach from the fine fraction (<0.06 mm) of till, the traditional method in geochemistry in glaciated terrains.
In nationwide geochemical maps, one of the major features was a regional
Te anomaly in the Forssa area. According to our study, Te forms separate clear
anomaly fields (Fig. 1), one of which with As, Sb, Cu, and Au was the first sign of
the recently discovered Kedonojankulma porphyry-type Au-Cu mineralization
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Geologian tutkimuskeskus, Tutkimusraportti 207 – Geological Survey of Finland, Report of Investigation 207, 2014
Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
north of Forssa (Tiainen et al. 2011). Elevated Te in till is also met in Zn-critical
areas of Kiipu and Kuuma, as well as around the Liesjärvi Au-Cu deposit east of
Kedonojankulma. Unknown Te anomalies occur in a roughly east–west-oriented
zone along the northern part of the sampling area, close to terrain border against
the Pirkanmaa Belt, as well as in some other localities east of Liesjärvi.
In addition to tellurium, most pronounced anomalies in the Häme Belt are related to trace metals such as arsenic, bismuth and antimony, which most obviously are enriched in hydrothermal processes. Cu, Zn, and Mo also show anomalies,
some of which are possibly related to mineralization. The partial leach method restricts the usability of the analyses. However, local or regional anomalies of some
other elements also need more precise consideration. These include lithium (because spodumene and complex pegmatites occur in the area), sulphur (sulphide
schists are rare) and iron (secondary surficial processes).
Conclusions
Trace elements usually related to ore-forming hydrothermal processes make
up anomalies in the new geochemical survey of the Häme Belt. A multielement As-Au-Cu-Sb-Te-Zn anomaly north of Forssa resulted in the discovery of
the porphyry-type Kedonojankulma Au-Cu deposit, and Zn mineralization of
Kuuma. There are several other anomalies, related either to a group of elements
or a single metal, that need closer examination. Some of these anomalies may be
related to variation in lithology, but some may be the first indication of hidden
deposits.
References
Bedrock of Finland − DigiKP. Digital map database [Electronic resource]. Espoo: Geological Survey of Finland [21.01.2014]. Version 1.0.
Kärkkäinen, N., Huhta, P., Lehto, T., Tiainen, M., Vuori, S. & Pelkkala, M. 2012. New geochemical data for gold exploration in southern Finland. In: Grönholm, S. & Kärkkäinen, N. (eds)
Gold in Southern Finland: results of GTK studies 1998–2011. Geological Survey of Finland,
Special Paper 52, 23–46.
Tiainen, M., Molnár, F. & Koistinen, E. 2013. The Cu-Mo-Au mineralization of the Paleoproterozoic Kedonojankulma intrusion, Häme Belt, Southern Finland. Proceedings of the 12th
Biennial SGA Meeting, 12–15 August 2013, Uppsala, Sweden, vol. 2., 892–895.
46
Geologian tutkimuskeskus, Tutkimusraportti 207 – Geological Survey of Finland, Report of Investigation 207, 2014
Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014
Fig. 1. Geochemical tellurium anomaly map of Häme Belt lithologies based on the digital bedrock
database of Finland (Bedrock of Finland − DigiKP). Contains data from the National Land Survey
of Finland Topographic Database 08/2012.
47
Geologian tutkimuskeskus, Tutkimusraportti 207 – Geological Survey of Finland, Report of Investigation 207, 2014
Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
stream sediment SURVEY as A MINERAL
EXPLORATION technique in tHE vÄHÄKURKKIO
AREA, eNONTEKIÖ
by
Helena Hulkki and Anne Taivalkoski
Geological Survey of Finland, P.O. Box 96, FI-96101 Rovaniemi, Finland
E-mail: [email protected]
Introduction
During the recent years, environmental issues have also been raised in mineral
exploration, raising the need for exploration techniques with a minimum impact
on the environment. Thus, the development of new, more sensitive methods for
mineral exploration has been started. However, old methods can also be useful
if they are updated to present day requirements. A few decades ago, organic and
inorganic stream sediments were used as sampling media in geochemical surveys
both in reconnaissance and on a detailed scale (Bølviken et al. 1986, Lahermo et
al. 1996, Isomaa 1988). Nowadays, stream sediments as a sampling medium are
mainly used in environment surveys, but less in mineral exploration in Finland.
Stream sediment sampling is, however, a convenient way to take samples, because
it does not leave any marks in the environment. In recent years, analytical methods have improved, giving results with very low detection limits. In addition, the
processing techniques for heavy mineral samples are under development. However, only a few heavy mineral surveys appear to have been performed in streams
in Finland. These were the reasons why inorganic stream sediments and heavy
minerals from stream bottoms were tested as sampling media in mineral exploration. The Vähäkurkkio area in the municipality of Enontekiö, about 300 km north
from the Arctic Circle, was selected as a testing site.
The study area is situated in the northern part of the Fennoscandian Shield,
in the Lätäseno Greenstone belt. The greenstone belt is mainly composed of
Palaeoproterozoic mafic metavolcanic and metasedimentary rocks with minor
ultramafic and felsic rocks, pegmatitic granitoids and metadiabases. The major
structural feature in Vähäkurkkio is a fold structure whose contact on the eastern side in the Lätäseno River is interpreted to be tectonic (Inkinen 1975), but
its existence and real character are still questionable. This fold structure is best
seen on geophysical maps as a highly magnetic zone (Fig. 1), which is caused
by magnetite-rich mafic tuffs and tuffites. The Geological Survey of Finland performed preliminary diamond drilling in the Vähäkurkkio area in 2011–2012,
and as a consequence an iron oxide-copper-gold type (IOCG) of mineralization
was localized in the northern part and on the western limb of the fold structure.
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Geologian tutkimuskeskus, Tutkimusraportti 207 – Geological Survey of Finland, Report of Investigation 207, 2014
Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014
The mineralized parts consist of malachite-rich skarn breccias and chalcopyritebornite-magnetite-bearing carbonate-rich breccias surrounded by skarns with
disseminated metallic copper. The main alteration is a skarn formation, and disseminated chalcopyrite occurs widely in the host rocks.
The stream sediment sampling survey was carried out in summer 2013. It comprised 38 sampling sites along the Lätäseno and Piippujoki Rivers. Three types of
samples were taken: mineral stream sediment, heavy minerals and water. Both of
the mineral samples were collected from 3–6 points along a 20–50-m-long stream
stretch.
Results
The geochemistry of drill cores revealed that in addition to Cu, Fe and Au, elevated levels of Bi, Te, U, S and Co and in some cases also Se, Ba and Ca are related to
the mineralized zones. The preliminary results from the stream sediments show
an almost 2.5-km-long Cu-Co-S±Au anomaly along the Lätäseno River (Fig. 2).
This anomalous zone also includes patch-like elevated Bi, Te and Ba contents.
The significant Cu-Co-S anomaly reflects the widespread feature of the sulphide
disseminated host rocks of the area. Bi and Te are probably more closely related
to mineralization and thus produce only patch-like anomalies. At this point, the
results from the heavy minerals are pending.
References
Bølviken, B., Bergström, J., Björklund, A., Kontio, M., Lehmuspelto, P., Lindholm, T., Magnusson, J., Ottesen, R.-T., Steenfelt, A. & Volden, T. 1986. Geochemical Atlas of Northern
Fennoscandia 1:4 000 000. Uppsala: Geological Survey of Sweden, Espoo: Geological Survey of
Finland, Trondheim: Geological Survey of Norway. 19 p. + 155 app. maps.
Inkinen, O. 1975. Yhteenvetoraportti - Enontekiö, Vähäkurkkio (1834 04). Outokummun aineistot, 001/1834 04/OI/1975. 10 p. (in Finnish)
Isomaa, J. 1988. Tutkimustyöselostus Enontekiön Ruossakeron nikkelimineralisaation tutkimuksista. Geological Survey of Finland, archive report M19/1834/-88/1/10. 29 p. (in Finnish)
Lahermo, P., Väänänen, P., Tarvainen, T. & Salminen, R. 1996. Geochemical Atlas of Finland.
Part 3: Environmental geochemistry − stream waters and sediments. Geological Survey of
Finland. 149 p.
49
Geologian tutkimuskeskus, Tutkimusraportti 207 – Geological Survey of Finland, Report of Investigation 207, 2014
Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
Fig. 1. Location of the Vähäkurkkio study area (inset), sampling sites and drill holes presented
on an aeromagnetic map. Contains data from the National Land Survey of Finland Topographic
Database 08/2012.
Fig. 2. Cu content in mineral stream sediment presented on an aeromagnetic map. Contains data
from the National Land Survey of Finland Topographic Database 08/2012.
50
Geologian tutkimuskeskus, Tutkimusraportti 207 – Geological Survey of Finland, Report of Investigation 207, 2014
Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014
Proterozoic metamorphism in the Archaean
tuntsa SUITE, nw finland
by
Pentti Hölttä1, Hannu Huhma1 and Tiia Kivisaari2
1 Geological
Survey of Finland, P.O. Box 96, FI-02151, Espoo, Finland
of Geosciences & Geography, FI-00014 University of Helsinki,
2 Department
Finland
Present address: Northland Mines Oy, Asematie 4, FI-95900 Kolari, Finland
E-mail: [email protected]
The Tuntsa suite in NE Finland forms the northwesternmost part of the Archaean Belomorian Province of the Fennoscandian Shield. The Tuntsa suite mainly
consists of TTGs and metasedimentary quartz-feldspar and mica gneisses, which
are often migmatized. Metasedimentary rocks in Tuntsa are strongly foliated and
banded medium-grained gneisses, often with porphyroblasts of Al minerals. The
primary sedimentary textures have normally been destroyed by penetrative foliation. Metasedimentary rocks are commonly migmatitic, indicative of partial
melting. A typical mineral assemblage in the Tuntsa metasediments is staurolitebiotite-quartz-plagioclase ± garnet ± kyanite ± chlorite ± cordierite ± muscovite.
During the field mapping, andalusite was found in two localities and sillimanite
in four outcrops, both minerals in the eastern part of the suite. All three Al2SiO5
polymorphs were found together in one sample. Cordierite and andalusite were
late crystallization products, andalusite evidently representing cooling related
with the clockwise PT path. In the eastern parts of the Tuntsa suite, the temperature reached the sillimanite field during decompression.
Most analysed garnet grains have a composition where XCa (Ca/Fe+Mn+Mg+Ca)
and XMn decrease and XMg increases from the core to the rim. XCa is quite high
in the cores of many garnet grains, up to 0.14–0.19, and XMg increases in zoned
grains from ca. 0.06–0.08 in the core to 0.15–0.16 in the rims. Figure 1 presents
a pseudosection with garnet composition isopleths, constructed using Perple_X
software (Connolly & Petrini 2002, Connolly 2009) with the thermodynamic data
of Holland & Powell (1998) and with the XRF whole rock composition of the
sample TTKI-2005-14.2. The isopleths show that during the crystallization of the
high Ca, low Mg and high Mn garnet core, the P and T have been at around 7.5
kbar and 550 oC. The low Ca, high Mg and low Mn garnet rim grew at P and T of
ca. 4.5 kbars and 590 oC, which is in accordance with the presence of cordierite
in this specimen.
For U-Pb age determinations on zircon and monazite, samples were taken
from a staurolite- and kyanite-bearing metasediment (A1843) and a several tens
of centimetres thick felsic leucosome vein (A1844) from the same exposure.
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Geologian tutkimuskeskus, Tutkimusraportti 207 – Geological Survey of Finland, Report of Investigation 207, 2014
Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
Because most zircon grains in the metasediment are obviously detrital, the age
determinations were expected to constrain the maximum age of sedimentation
and also the age of metamorphism in the case of monazite, and possible metamorphic zircon growth, especially in the leucosome, where zircon is expected to
crystallize from melt. Monazite was not obtained from sample A1843. A small
amount of monazite was obtained from leucosome sample A1844, which provided no zircon.
The Nordsim ion microprobe results for the concordant zircon grains fall into
two groups, the older grains being ca. 2.84–2.80 Ga and the younger ones mostly
2.69–2.67 Ga. In the latter group, zircon is generally low in Th and has a low Th/U
ratio, indicating a metamorphic origin. The TIMS U-Pb analysis of monazite is
concordant within error and provides an age of 1786 ± 2 Ma. The detrital zircon
in the metasediments seems to have been derived from the 2.83–2.80 Ga granitoids because of the lack of 2.75–2.70 Ga zircon grains. Obviously, the sedimentation took place between 2.80–2.75 Ga, and the younger granitoids of 2.75–2.70
Ga then intruded the sediments, which explains the lack of 2.75–2.70 Ga zircon
grains in the metasediment. After this, the belt was metamorphosed at least in
upper amphibolites facies, producing migmatites in partial melting. As shown by
the metamorphic zircon population in the A1843 metasediment sample, this may
have taken place at 2.69–2.67 Ga, which is a strong thermal and melting event in
the Karelia Province, recorded by the abundance of granite-granodiorite-monzogranite intrusions and metamorphic zircon in granulites and in leucosomes
of migmatites (Hölttä et al. 2000, 2014, Mänttäri & Hölttä 2002, Käpyaho et al.
2007, Mikkola et al. 2011, Lauri et al. 2011). Another possibility is that all zircon
grains are detrital, being inherited from upper amphibolite facies or granulite
facies rocks, which would explain the zircon population with low Th and low
Th/U ratios. In this case, sedimentation would have been younger than 2.67 Ga.
However, a titanite from Tuntsa also gives an age of 2.68 Ga, which supports the
2.69–2.67 Ga metamorphism (Juopperi & Vaasjoki 2001).
If the 2.69–2.67 Ga zircon population in sample A1843 represents metamorphism in situ, the abundance of zircon grains of this age and the presence of
migmatites is not in accordance with the garnet compositions and metamorphic
mineral assemblages. These represent mid-amphibolite facies, where little metamorphic zircon is expected to grow and melting should not occur (Fig. 1). Garnet
compositions do not indicate that they were crystallized in high temperatures.
On the contrary, they show that garnet started to grow at around 550 oC. The
presence of sillimanite and of kyanite together with staurolite suggests that the
maximum temperatures could have been at around 650 oC, but the abundance of
staurolite indicates that the maximum temperatures were below those of melting.
Therefore, most porphyroblasts in metasediments may not be Archaean at all, but
Palaeoproterozoic, and the Archaean high-grade metamorphism is represented
by the leucosomes and metamorphic zircon grains.
Flat-lying nappe or overthrust structures are common in both Tuntsa and Proterozoic formations in eastern Lapland (Evins & Laajoki 2002, Hölttä et al. 2007),
and assemblages bearing kyanite and staurolite are commonly found in Proterozoic metasediments west of the Tuntsa suite (Niemelä 1976, Mielikäinen 1979,
Hanski 2002, Hölttä et al. 2007), so that there is no clear change in metamorphic grade or type when coming across the Archaean-Proterozoic boundary. The
clockwise PT path, indicated by mineral reactions and garnet zoning of the Tuntsa rocks, is typical for tectonically thickened crust. It is possible that the Tuntsa
suite metasediments were penetratively deformed in the Proterozoic thickening
52
Geologian tutkimuskeskus, Tutkimusraportti 207 – Geological Survey of Finland, Report of Investigation 207, 2014
Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014
that produced nappe structures, and the Archaean mineral assemblages were destroyed and totally recrystallized, now recording only the Proterozoic PT path.
This took place at around 1.79–1.84 Ga, which was a time of intensive deformation, metamorphism and granitoid genesis in Proterozoic Central Lapland (e.g.
Ahtonen et al. 2007) and in the Archaean Belomorian Province.
References
Ahtonen, N., Hölttä, P. & Huhma, H. 2007. Intracratonic Palaeoproterozoic granitoids in northern Finland: prolonged and episodic crustal melting events revealed by Nd isotopes and U-Pb
ages on zircon. Bulletin of the Geological Society of Finland 79, 143–174.
Connolly, J. A. D. 2009. The geodynamic equation of state: what and how. Geochemistry,
Geophysics, Geosystems 10, Q10014 DOI:10.1029/2009GC002540.
Connolly, J. A. D. & Petrini, K. 2002. An automated strategy for calculation of phase diagram
sections and retrieval of rock properties as a function of physical conditions. Journal of Metamorphic Petrology 20, 697–708.
Evins, P. M. & Laajoki, K. 2002. Early Proterozoic nappe formation: an example from Sodankylä,
Finland, northern Baltic Shield. Geological Magazine 139 (1), 73-87.
Hanski, E. 2002. Vikajärvi. Geological Map of Finland 1:100 000, Pre-Quaternary Rocks, Sheet
3614. Espoo: Geological Survey of Finland.
Holland, T. J. B. & Powell, R. 1998. An internally consistent thermodynamic data set for phases
of petrological interest. Journal of Metamorphic Geology 16, 309–343.
Hölttä, P., Huhma, H., Mänttäri, I. & Paavola, J. 2000. P-T-t development of Archaean granulites
in Varpaisjärvi, central Finland. II. Dating of high-grade metamorphism with the U-Pb and
Sm-Nd methods. Lithos 50 (1–3), 121–136.
Hölttä, P., Väisänen, M., Väänänen, J. & Manninen, T. 2007. Paleoproterozoic metamorphism
and deformation in central Lapland, Finland. In: Ojala, V. J. (ed.) Gold in the Central Lapland
Greenstone Belt. Geological Survey of Finland, Special Paper 44, 7–56.
Hölttä, P., Heilimo, E., Huhma, H., Kontinen, A., Mertanen, S., Mikkola, P., Paavola, J., Peltonen, P., Semprich, J. Slabunov, A. & Sorjonen-Ward, P. 2014. The Archaean Karelia and
Belomorian Provinces, Fennoscandian Shield. In: Dilek, Y. & Furnes, H. (eds) Evolution of
Archean crust and early life. Modern Approaches in Solid Earth Sciences 7. Dordrecht: Springer, 55–102.
Juopperi, H. & Vaasjoki, M. 2001. U-Pb mineral age determinations from Archean rocks in eastern Lapland. In: Vaasjoki, M. (ed.) Radiometric age determinations from Finnish Lapland and
their bearing on the timing of Precambrian volcano-sedimentary sequences. Geological Survey of Finland, Special Paper 33, 209–207.
Käpyaho, A., Hölttä, P. & Whitehouse, M. J. 2007. U-Pb zircon geochronology of selected
Archaean migmatites in eastern Finland. Bulletin of the Geological Society of Finland 79 (1),
95–115.
Lauri, L. S., Andersen, T., Hölttä, P., Huhma, H. & Graham, S. 2011. Evolution of the Archaean
Karelian Province in the Fennoscandian Shield in the light of U-Pb zircon ages and Sm-Nd and
Lu-Hf isotope systematics. Journal of the Geological Society 168 (1), 201–218.
Mänttäri, I. & Hölttä, P. 2002. U-Pb dating of zircons and monazites from Archean granulites in
Varpaisjärvi, central Finland: evidence for multiple metamorphism and Neoarchean terrane
accretion. Precambrian Research 118, 101–131.
Mielikäinen, P. 1979. Pelkosenniemi. Geological Map of Finland 1:100 000, Pre-Quaternary
Rocks, Sheet 3642. Espoo: Geological Survey of Finland.
Mikkola, P., Huhma, H., Heilimo, E. & Whitehouse, M. 2011. Archean crustal evolution of the
Suomussalmi district as part of the Kianta Complex, Karelia: constraints from geochemistry
and isotopes of granitoids. Lithos 125 (1), 287–307.
Niemelä, M. 1976. Pelkosenniemen alumiinirikkaat kiillegneissit. Unpublished MSc thesis.
Department of Geology and Mineralogy, University of Turku. (in Finnish)
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
Fig. 1. Pseudosections showing the composition isopleths of the garnet core (left) and garnet rim
(right) in sample TTKI-2005-14. The possible PT path of the Tuntsa suite is shown by the stippled
arrow in the left-hand figure.
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Geologian tutkimuskeskus, Tutkimusraportti 207 – Geological Survey of Finland, Report of Investigation 207, 2014
Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014
VMS deposits in the häme volcanic belt:
petrophysical data to supplement
geophysical modelling
by
Fredrik Karell and Hanna Leväniemi
Geological Survey of Finland, P.O. Box 96, FI-02151 Espoo, Finland
E-mail: [email protected]
The aim of our recent study regarding volcanogenic massive sulphide (VMS) ore
deposits within the Häme belt (Leväniemi & Karell 2013) was to re-assess the
available geophysical data on the Häme belt in order to better understand the
geophysical properties and signatures of the known sulphide mineralizations in
the study area and to locate new targets for follow-up investigations.
Petrophysical data provide essential information on the target properties and
together with geological information can be used in estimating the target’s suitability for various geophysical exploration methods. In particular, petrophysical
information is needed for accurate and reliable geophysical models, but also to
give additional information for geological interpretations (Airo & Säävuori 2013).
As part of the Häme belt VMS study, we collected new samples from drillcores
of known deposits to complement existing petrophysical log data from the late
Outokumpu Oy archives. Known Zn/Cu deposits from the Häme belt were resampled and measured for their density and magnetic and electric properties.
There are some uncertainties related to the samples, mostly as the drill cores are
old, the most interesting samples are partly missing and the depth markings are
not always reliable. However, the petrophysical data indicate that in most cases,
the ore properties do show a contrast to those of the host rock, suggesting that
sufficiently massive polymetallic (VMS) deposits could be detected with applicable geophysical survey methods.
With realistic and informative petrophysical data, we can develop successful
multidisciplinary joint models that can be applied not only to existing targets, but
also in locating new potential deposits.
REFERENCES
Airo, M-L. & Säävuori, H. 2013. Petrophysical characteristics of Finnish bedrock: Concise handbook on the physical parameters of bedrock. Geological Survey of Finland, Report of Investigation 205. 33 p.
Leväniemi, H. & Karell, F. 2013. Geophysical Indications of VMS Deposits in the Häme Volcanic
Belt. Geological Survey of Finland, archive report 152/2013. 64 p.
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
4D model of the Hietakero area,
NORTHERN FINLAND
by
Tuomo Karinen, Ilkka Lahti, Tero Niiranen and Jukka Konnunaho
Geological Survey of Finland, P.O. Box 77, FI-96101 Rovaniemi, Finland
E-mail: [email protected]
During the past years, the Enontekiö area has been a target area for projects carried out by the Geological Survey of Finland (GTK). The focus of these projects
has been to create target- and regional-scale geological models to promote mineral exploration in northern Finland. Here, we describe the 3D geological model
of the Hietakero area and discuss the geological evolution of the area, from its
initial geometry to the present form. This type of modelling, which considers the
3D history of a certain area, is referred to as 4D modelling.
The Hietakero area includes metamorphosed mafic volcanic rocks, minor felsic volcanites, gabbros, quartzites and sulphide-bearing schists. These rocks have
been multiply folded, as suggested by their complex interference pattern. The sulphidic schist and mafic igneous rocks make the area potential for orthomagmatic
mineral deposits such as Ni-Cu and PGE deposits (Fig. 1).
In 4D modelling, the challenge lies in the testing of past geological processes
that would logically explain the present features in bedrock. However, many of
these features are indirect, because in areas such as northern Finland, the glacial
till cover and weathering of the uppermost basement limit the possibilities for direct field observations. Furthermore, although diamond drillings provide direct
information from the bedrock, the scale of these drillings is relatively small in
comparison to large regional-scale models such as the Hietakero model. Therefore, geophysical surveys are the most important methods to gain information for
these models. In addition to national airborne measurements, a regional airborne
SkyTEM survey was carried out in summer 2012. 3D inversions of ground gravity
and airborne magnetic measurements were carried out to model magnetic and
density variations. The SkyTEM inversion results were used to map conductive
horizons in 3D. In the Hietakero area, the rocks can be characterized by their geophysical features, because the mafic metavolcanic rocks show high susceptibilities
and sulphide-bearing schists display high conductive zones. Figure 2 presents the
geophysical models (susceptibility and conductivity) and lithological model of
the Hietakero area.
The geological evolution of the Hietakero area began with sedimentation of
quartzites and eruption of volcanic rocks. This was followed by a tilting episode
during which the gabbroic intrusion was emplaced. Subsequent folding episodes
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resulted in the distinct fold interference pattern of the area. These folding episodes
occurred in roughly orthogonal N–S- and E–W-directed folding stages (Fig. 3).
References
Bedrock of Finland − DigiKP. Digital map database [Electronic resource]. Espoo: Geological
Survey of Finland [referred 30.01.2014]. Version 1.0.
Fig. 1. Simplified lithological map of the Hietakero area showing the 3D modelled area by red line.
The lithological map is redrawn after the digital bedrock database of Finland (Bedrock of Finland
– DigiKP).
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
Fig. 2. 3D models of the Hietakero area: (a) Aeromagnetic inversion model, (b) Electromagnetic
conductivity model and (c) Lithological model of the Hietakero area. Modelling area is shown
in Fig. 1, vertical dimension of the model is 2500 meters. (In aeromagnetic inversion model low
values are indicated by red and high values by white. In electromagnetic conductivity model low
values are indicated by green and high values by red.)
Fig. 3. Schematic diagram showing the structural evolution of the Hietakero area.
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Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014
Geological and Mineralogical Challenges
Related to THE Beneficiation of REE deposits
by
Risto Kaukonen, Jukka Laukkanen and Neea Heino
Geological Survey of Finland, Mintec, Tutkijankatu 1, FI-83500 Outokumpu,
Finland
E-mail: [email protected]
Introduction
Rare earth elements (REE) are playing an important role in limiting greenhouse
gas emissions, because they are used in a number of significant green energy technologies, such as hybrid and electric vehicles and wind power generators (BGS/
NERC 2011). Almost every electronic device contains some REE. Hence, modern
life cannot be without REE. This has led to increased demand and thus also to
increased exploration for REE in the recent years.
The European Union has classified REE as critical metals (European Commission 2010). From a geological perspective, Finland is one of the most promising
places in Europe to carry out exploration for them, because the bedrock of Finland contains similar rock types to those known to contain REE deposits elsewhere in the world, such as alkaline intrusions and carbonatites. GTK has several
research projects targeting REE, and a number of foreign mining and exploration
companies are also searching for them in Finland. GTK Mintec is actively developing new beneficiation techniques for REE ores by participating in national and
international collaboration projects, as well as through customer-funded research
projects.
Geological background
Rare earth elements (REE) occur in a wide variety of host rocks in very different
geological settings. These include alkaline igneous rocks (e.g. Lovozero and Khibina massifs in Russia; Illimaussaq in Greenland), carbonatites (Bayan Obo and
Saima in China; Mountain Pass in the USA), hydrothermal deposits unrelated to
alkaline igneous rocks (Karonge in Burundi), ion-adsorption clays (Longnan and
Xunwu in China), iron-oxide-copper-gold deposits (Olympic Dam in Australia),
lateritic deposits (Mount Weld in Australia; Araxá in Brazil), marine placers including coastal dune deposits (Chavara in India) and many other types (Long et
al. 2010, BGS/NERC 2011). From a mineralogical perspective, this wide variety
in the mode of occurrence directly translates into the minerals in which the REE
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
occur. The mineralogy of REE has a significant impact on the ease and financial
viability of their beneficiation.
Beneficiation challenges derived from geological and
mineralogical features
From the beneficiation perspective, a change in ore type often means that the ore
minerals change. This, in turn, may trigger the need to redesign the entire beneficiation process, including adjustments to grinding and flotation chemicals. In
some cases, the REE minerals may be the same but the gangue minerals are different. In such a case, it is again likely that the entire beneficiation process will need
to be redesigned. Of course, even within the same deposit there can be changes
in the grain sizes and textures of both the ore and the gangue minerals, and these
can have a major impact on the efficiency of the beneficiation process. Most REE
minerals carry several different REE, and the proportions of each REE in the ore
mineral can vary to the extent that they have a significant effect on the physical
and chemical properties of the mineral itself, such as density, hardness and solubility. In such a case, at best only some minor adjustments may be needed to the
flotation chemicals, but at worst this may necessitate a complete process redesign.
Finally, there is the added problem of potential radioactivity. In addition to the
many radioactive isotopes of the REE themselves, many REE minerals may also
carry uranium and thorium, which render the minerals radioactive, and this is
another problem that needs to be addressed in the beneficiation process.
More than 200 different minerals are known to bear essential or significant
REE concentrations. They include carbonates, phosphates, oxides, silicates and
halides, or mixtures of these (BGS/NERC 2011). In many cases, a few or even
several different REE-bearing minerals occur in the ore and they all need to be
recovered. This may be possible when the REE minerals are of the same group,
for example they are all carbonates or all are phosphates. However, when the REE
occur in more than one mineral group in the same ore, problems are bound to
occur, as each mineral group requires specific flotation chemicals, not to mention
that to date there are no effective flotation chemicals for some potentially important REE-bearing minerals, such as allanite.
Another factor that has a direct impact on the potential success of beneficiation and which is directly derived from the geological environment and processes
that generated the ore is zoning within the ore minerals or their solid-solution
series. An example of such a solid-solution series is apatite-britholite (Pasero et
al. 2010). Extreme effects of zoning within a given solid-solution series can result
in the core of a mineral grain having a vastly different chemical composition from
the rim (Fig. 1). This may have a significant impact on the surface chemistry of
crushed mineral grains, as their surfaces would be mostly mixtures of two minerals in varying proportions. This would probably affect the overall flotation behaviour of the crushed ore feed, potentially resulting in a poor quality concentrate.
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References
British Geological Survey (BGS), Natural Environment Research Council (NERC) 2011. Rare
Earth Elements Profile. Available at: http://www.bgs.ac.uk/mineralsuk/statistics/mineralProfiles.html.
European Commission 2010. Critical raw materials for the EU, Report of the Ad-hoc Working
Group on defining critical raw materials. 84 p.
Long, K. R., Van Gosen, B. S., Foley, N. K. & Cordier D. 2010. The Principal Rare Earth Elements
Deposits of the United States – A Summary of Domestic Deposits and a Global Perspective.
USGS Scientific Investigations Report 2010-5220.
Pasero, M., Kampf, A. R., Ferraris, C., Pekov, I. V., Rakovan, J. & White, T. J. 2010. Nomenclature of the apatite supergroup minerals. European Journal of Mineralogy 22, 163–179.
Fig. 1. An example of extreme zoning: A back-scattered electron image of REE-bearing apatitebritholite solid-solution series where the REE-bearing apatite core is rimmed with REE-bearing
britholite. The overall REE concentration increases towards the rim. The numbers in the picture
refer to zones of distinctly different chemical composition.
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
digitizing an old geological
3D interpretation of the miihkali area
by
Esko Koistinen and Soile Aatos
Geological Survey of Finland, P.O. Box 1237, FI-70211 Kuopio, Finland
E-mail: [email protected]
Fortunately, some of the hand-drawn geological 3D interpretations of well-explored regions have been preserved from the times before sophisticated modelling software and computers. A large amount of scientific and practical experience may be summarized in such maps and drawings. It is highly valuable to
digitize the well-reported and geologically still relevant drawn models to be used
and reworked in modern computerized 3D modelling.
As part of the ongoing deep exporation method development in the Outokumpu mining camp area (Aatos et al. 2013, 2014), an old, hand-drawn block
model of the geology of the Miihkali area (Fig. 1) was digitized. In the original
perspective drawing at the scale of 1:100 000, the Miihkali area is cut into seven
separated blocks. The length of the modeled area is about 60 km (SE–NW) and
width of the area about 40 km (SW–NE). The model depth is approximately 3 km
in the perspective drawing.
To make the digitizing task more realistic, the original nine rocktypes of the
drawing were simplified to five main rock classes: Archaean basement, mica
schist, serpentinites, black schist and Karelian rocks. First, every single horizontal
and vertical surface of the scanned drawing was cut into an individual Joint Photographic Experts Group formatted (JPEG, .jpg) file using Adobe® Photoshop®
Elements 9 software. The individual surfaces were georeferenced and the outlines
of the rock types were digitized in Geovia GEMSTM software. Finally, solid models of the rock elements were derived, connecting the outlinings (Fig. 2). Outlines
of the rock elements and the solids can be exported to commonly used modelling
software to be used in 3D with other modelling data.
The aim of digitizing old geological maps and drawings is to save and convert
the geological knowledge into today’s workable formats. The digitized 3D model
of the Miihkali area will act as a development base for updating the digital geological 3D interpretations of Miihkali as part of the construction of a Common Earth
Model (CEM) of the Outokumpu mining camp area (Aatos et al. 2013, 2014).
References
Aatos, S., Heikkinen, P., Kukkonen, I. & Kurimo, M. 2013. Developing Deep Exploration Concepts and Technologies in Outokumpu Mining Camp Area. List of posters of Green Mining
Poster Exhibition/9th Fennoscandian Exploration and Mining - FEM 2013, 29–31 October
2013, Levi, Finland. Green Mining – Tekes. 11 p.
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Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014
Aatos, S., Jokinen, J., Koistinen, E., Kontinen, A., Korhonen, J., Korpisalo, J., Kurimo, M.,
Lahti, I., Laine, E., Leväniemi, H., Sorjonen-Ward, P. & Torppa, J. 2014. Developing
deep exploration methods in the Outokumpu Mining Camp area. In: Lauri, L. S., Heilimo,
E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds) Current Research: 2nd GTK
Mineral Potential Workshop, Kuopio, Finland, May 2014. Geological Survey of Finland,
Report of Investigation 207. (this volume)
Ruotoistenmäki, T. & Koistinen, E. 2012. Three-Dimensional Modeling of the Outokumpu
Nappe Area, SE Finland. In: Laine, E. (ed.) 3D modeling of polydeformed and metamorphosed
rocks: the old Outokumpu Cu-Co-Zn mine area as a case study. Geological Survey of Finland,
Report of Investigation 195, 67–75.
Saastamoinen, J. 1972. Miihkalin jakson tutkimukset vuosina 1966–1972. Outokumpu Oy,
archive report 001/4311, 4313/JyS/72. 27 p, 7 app. reports. (in Finnish)
Fig. 1. The original block model of the geological 3D interpretation of the Miihkali area (Saastamoinen 1972).
Fig. 2. An example of the digitized Miihkali 3D model: Archaean basement (beige), serpentinite
solids (green) and the draped drawing of Section VS_3. The northern parts of the Outokumpu
Nappe model (Ruotoistenmäki & Koistinen 2012) are presented in the same view (red).
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
PGE ore potential in the southwestern
granulite belt of Northern Finland
by
Kari Kojonen
Geological Survey of Finland, P.O. Box 96, FI-02151 Espoo, Finland
E-mail: [email protected]
Platinum group minerals (PGM) have been discovered in gold placers during
the prospecting and mining of the Ivalojoki and Lemmenjoki Au-bearing tills
and river banks. Placer gold washing started in the Ivalojoki area in 1868 and
in the Lemmenjoki area in 1945 (Stigzelius 1986). PGM have been discovered
from the Ivalojoki area since 1875 and in Lemmenjoki area since 1951 (Ervamaa
1975, Saarinen 1984). Modern mineralogical research on PGM was started in the
1980s by Mr Yrjö Vuorelainen and Dr Ragnar Törnroos (Törnroos & Vuorelainen
1987), and later continued by Törnroos et al. (1996), Kojonen (2005), Törnroos et
al. (2006), Kojonen (2007), Kojonen et al. (2007), Kojonen (2008), Törnroos et al.
(2008) and Kojonen et al. (2010). Tens of thousands of grains were analysed with
modern electron beam methods using automatic feature analysis software, EDS
and WDS analyses with the electron microscope and microprobe. The distribution of PGM placer minerals is quite common in the tributaries of Lemmenjoki
and Miessijoki in northern Lapland and in the Ivalojoki tributary ca. 50 km WSW.
Observations of PGM further east in Lauttaoja, Tankavaara, Vuotso and Kiilopää
area have not been as common (Ervamaa 1975). The bedrock in the area is mainly
leucocratic granulite that has been conformably intruded by hypersthene-bearing
norites/enderbites. The enderbite intrusions can be followed ca. 200 km in lowaltitude aeromagnetic maps crossing from Lemmenjoki in the northwest over to
Ivalojoki 50 km WSW, and further to Vuotso village in Sodankylä and the Korvatunturi fell on the eastern Russian border (Fig. 1).
Dating of five homogeneous zircon grains gave a concordant age of 1906 ± 4
Ma, suggesting enderbite intrusion at that time (Tuisku & Huhma 2006). The
granulites were deposited after 1950 Ma and were later intruded by the mantlederived hypersthene gabbros and norites. The first hints of the source rocks of
PGM were found in Ängesneva, 15 km south of Miessijoki, in a till and bedrock
surface geochemical study (Nurmi et al. 1991), where Pt, Pd, Te and Au anomalies were discovered from two low-altitude aeromagnetic anomalies consisting of
diorite-gabbro-olivine pyroxenite intrusions.
Twenty years later, the author received a heavy mineral black sand sample from
a gold miner at Kaarreoja, 15 km NNE of the Ängesneva magnetic and geochemical anomalies. This sample contained soft PGE selenides, tellurides and antimo-
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Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014
nides that had exceptionally well preserved crystal forms, and thus had not been
moved far from their host rock. In summer 2011, the author visited the Kaarreoja
gold miners and mapped the area north to Miessijoki and south to Puskujärvi
and west of the Vasarovat hills. A contact of leucocratic granulite and underlying
gabbro was discovered in Kaarreoja and numerous banded gabbro outcrops were
discovered on the borders of the swamps west of Vasarovat, south of Kaarreoja
and in the lower Miessijoki River banks and bottom, which had been excavated
by gold miners. It was obvious that a cover of only a few tens of metres of leucocratic granulite was laying on the layered gabbro-norite intrusions, and this cover
had been removed by erosion in the Miessijoki and Kaarreoja river valleys. The
dip of the gabbro intrusions in the Kaarreoja is 20–25⁰ NE, and the gabbro was
partially weathered in situ to soft sandy material that still had the original rock
texture, magmatic layering and chemical composition. In other locations nearby,
the gabbro shows a fresh and unweathered layered outlook (Fig. 2).
PGE mineral grains studied (Kojonen 2007) from Ivalojoki and its tributaries
(Sotajoki, Louhioja, Moberginoja and Laanila) totalling 471 grains consisted of
62.2% isoferroplatinum, 28.5% sperrylite, 2.7% native OsIrRu alloy, 1.1% cooperite-braggite, 0.8% hongshiite, 0.7% Pt7Cu and other PGM. The grains of isoferroplatinum contain inclusions of laurite, irarsite, erlichmanite, cuproiridsite and
sperrylite. Single grains of isomertieite, mertieite, arsenopalladinite, rustenburgite, luberorite and undefined PtTe-selenide have been encountered in the Ivalojoki tributaries. A total of 12 022 PGM grains calculated from the tributaries of
Lemmenjoki and Miessijoki (Kojonen 2008) consist of 95.13% sperrylite, 1.37%
isomertieite and related minerals, 1.08% braggite and cooperite, 1.04% isoferroplatinum, 0.89% native Pd-Pt-Au-Cu-Fe alloys, 0.13% stillwaterite, 0.05% arsenopalladinite, and 0.06% comprising small amounts of atokite, moncheite, kotulskite, keithconnite, miessiite and törnroosite. Inclusions of laurite, erlichmanite,
osmium and iridium occur in the isoferroplatinum. OsIrRh-alloy also occurs as
single grains. Some of the PGM discovered have been formed as secondary products in the oxidation and weathering, e.g. Pt oxide, native Pt and Pd-Cu-Fe alloys.
A small amount of PGE in the ppb range have been analysed in the bedrock at
Kaarreoja and Pehkosenkuru and in the erratic pyroxenite boulders.
The PGM paragenesis of the placers indicates a magmatic origin of high temperatures with a further hydrothermal phase and secondary formation of oxides
and PGE alloys through oxidation. The findings of mafic-ultramafic intrusion
in the Naukussuo low-altitude airborne anomalies, some PGE analytical results
of the mafic bedrock and erratic pyroxenitic boulders suggest that the gabbronoritic layered intrusions and associated olivine pyroxenitic intrusions could be
the source of the PGM in the Ivalojoki and Lemmenjoki areas, as well as further
east of the Ivalojoki area.
References
Ervamaa, P. 1975. Selostus Tankavaaran ja Morgamin alueen sekahipuista tehdystä alustavasta tutkimuksesta. Geological Survey of Finland, archive report M17/Sdk/Ira/52/2. 5 p. (in
Finnish)
Kojonen, K. 2005. Platinamineraaleja Ivalojoelta ja Lemmenjoelta. Prospäkkäri 1, 16–25. (in
Finnish)
Kojonen, K. 2007. Ivalojoen alueen platinamineraaleista. Prospäkkäri 2, 28–33. (in Finnish)
Kojonen, K. 2008. Lemmenjoen platinamineraaleista ja uusi mineraali, miessiitti. Prospäkkäri 2,
28–37. (in Finnish)
Kojonen, K., Tarkian, M, Knauf, V. V., Törnroos, R. & Heidrich S. 2006. Placer platinum-group
minerals from Ivalojoki and Lemmenjoki rivers, Finnish Lapland. 19th General Meeting of the
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
International Mineralogical Association, Kobe, Japan, July 23-28, 2006, Program and Abstract,
p. 196.
Kojonen, K., Tarkian, M., Roberts, A. C. & Heidrich, S. 2007. Miessiite, Pd11Te2 Se2, a new mineral species from Miessijoki, Finnish Lapland, Finland. Canadian Mineralogist 45, 1221–1227.
Kojonen, K., MacDonald, A., Stanley, C. & Johanson, B. 2010. Törnroosite, Pd11 As2Te2, a new
mineral species from Miessijoki, Finnish Lapland, Finland. Canadian Mineralogist 49, 1643–
1651.
Nurmi, P. A., Huhta, P & Hakala, P. 1991. Rapakallio- ja moreeninäytteenoton jalometallitulokset Inarin Naukussuon alueella vuonna 1991. Geological Survey of Finland, archive
report M19/3812/-91/1. 16 p. 22 attachments. (in Finnish)
Saarinen, V. 1984. Platinalöydöistä Lapissa. Geological Survey of Finland, archive report 3058. 6
p. (in Finnish)
Stigzelius, H. 1986. Kultakuume. Lapin kullan historia, Suomen matkailuliitto. 251 p. (in Finnish)
Tuisku, P. & Huhma, H. 2006. Evolution of migmatitic granulite complexes: Implications from
Lapland granulite belt, Part II: isotopic dating. Bulletin of Geological Society of Finland 78,
143–175.
Törnroos, R. & Vuorelainen, Y. 1987. Platinum-group metals and their alloys in nuggets from
alluvial deposits in Finnish Lapland. Lithos 20, 491–500.
Törnroos, R., Johanson, B. & Kojonen, K. 1996. Alluvial nuggets of platinum-group minerals
and alloys from Finnish Lapland. IGCP Project 336 Symposium, Rovaniemi, Finland, August
1996, Program and Abstracts, 85–86.
Törnroos, R., Kojonen, K., Tarkian, M. & Kivioja, E. 2006. A review of the native Au and PGM
nuggets in the Ivalojoki and Lemmenjoki tributaries, Finnish Lapland. The 27th Nordic Geological Winter Meeting, Abstract volume. Bulletin of the Geological Society of Finland, Special
Issue 1, 165.
Törnroos, R., Kojonen, K. & Johanson, B. 2008. Alluvial nuggets of PG mineral and alloys of
Finnish Lapland. In: Wahl, N. A. (ed.) 28th Geological Winter Meeting, January 7-10, 2008,
Aalborg, Denmark: abstract volume, p. 9.
Fig. 1. Low-altitude airborne magnetic map of Northern Lapland, Finland. Contains data from the
National Land Survey of Finland Topographic Database 08/2012.
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Fig. 2. Layered fresh gabbro on the river bank of the lower Miessi River, Hepo-oja.
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
The problem with the age of the Central
Puolanka Group KEEPS fighting us
by
Asko Kontinen1, Hannu Huhma2, Yann Lahaye2 and Hugh O’Brien2
1 Geological
Survey of Finland, P.O. Box 1237, FI-70211 Kuopio, Finland
Survey of Finland, P.O. Box 96, FI-02151 Espoo, Finland
E-mail: [email protected]
2 Geological
The Central Puolanka Group (CPG) along the western margin of the Palaeoproterozoic Kainuu schist belt presents an unresolved problem in terms of its age of
deposition, being inferred either as early Proterozoic 2.35–2.20 Ga (Laajoki 2005)
or late Archean >2.70 Ga (Kontinen et al. 1996, Huhma et al. 2000). This state of
affairs is badly hampering the modelling of the Archaean to Proterozoic tectonic
transition in Kainuu and southern Lapland (cf. Laajoki 2005). The reason is that
the CPG lacks easily datable syngenetic magmatic rocks.
Our efforts to address the problem include U-Pb dating of detrital zircon grains
from all the main units (from oldest to youngest: Puolankajärvi, Akanvaara and
Pärekangas Fms) of the CPG within the Oikarila structure in the western-central part of the KSB (Fig. 1). The studied samples contain only Archaean zircons,
in most cases dominated by ca. 2.70 Ga grains, which in several cases form the
youngest, clearly detrital population. This also concerns samples from the rocks
previously interpreted (Huhma et al. 2000) as ca. 2.70 Ga sodic rhyodacitic tuffs
(Fig. 2) in the Pärekangas Fm, as these rocks also carry a wide scpectrum of grains
from 2.7 Ga up to 3.7 Ga (Fig. 3). The heterogeneous zircon in the tuffs in fact
supports their alternative interpretation (Laajoki & Wanke 2002) as albitized epiclastic silts. However, given the occurrence of unmistakable mafic-intermediate
lavas and lapilli tuffs in the Pärekangas stratigraphy below the sodic tuffs/silts, it
is nevertheless possible that these rocks mix syngenetic 2.7 Ga volcanic with similarly aged and older epiclastic materials. Whether the mafic lavas and lapilli tuffs
are indeed 2.7 Ga, as this option would require, remains an issue to be resolved.
Recent mapping and exploration drilling within the Oikarila structure has revealed some useful new constraints. A 150-m-thick unexposed gabbro–wehrlite
sill has been drill-intersected in the Pärekangas Fm within the Kaunisjoki valley. The distinct “Karjalite” character of the sill defines the host Pärekangas lavas,
lapilli tuffs, sands and pelites as at least ca. 2.22 Ga in age (cf. Hanski et al. 2010).
In the Varislahti area within the SE part of the Oikarila structure (Fig. 1), the
granophyre of the 2.44 Ga (Fig. 3) Junttilanniemi layered gabbro intersects a sequence of felsic and mafic metavolcanic rocks (Pitkälika rhyodacites and basalts),
which is overlain by a thin layer of conglomerate-wacke (Soidensuu wacke).
The wacke, which contains granophyre clasts and ca. 2.4 Ga zircons, both most
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probably derived from the Junttilanniemi gabbro-granophyre, which is in turn
overlain by a >500-m-thick sequence of pillowed and massive amygdaloidal metabasalts (Varislahti basalts) that we find physically and chemically similar to the
Greenstone 1 and correlative metabasalts in the Kuusamo and Koillismaa areas
(Laajoki 2005 and references). Now, considering the tectonic-stratigraphic situation within the Oikarila structure, it seems most likely that the Pitkälika and CPG
rocks represent the framework into which the 2.44 Ga old Junttilanniemi gabbro
intruded, and on which the Varislahti basalts extruded after an intervening period of erosion. Consequently, a >2.44 Ga age for the CPG is strongly indicated.
It is notable here that the chemical compositions of the Pärekangas and Pitkälika basalts are close enough to allow a common magmatic lineage, whereas the
Varislahti basalts seem distinct.
The CPG schists in the Oikarila structure are in the west in an abrupt fault
contact with the quartzitic, pelitic and mafic gneisses of the Kalpio Complex/
Oulunjärvi shear zone. Just west of the separating Raappana Fault, the gneisses
include a <100-m-wide and >700-m-long body of quartz-albite gneiss (Fig. 1)
with a similar sodic rhyodacite composition to the Pärekangas albite-rich felsites.
The Petäjäniemi gneiss body, although faulted-mylonitic for its contacts, appears
to represent a dyke into the host mafic and metasedimentary gneisses. As the
dyke contains a rather homogeneous, apparently magmatic zircon population
dated at ca. 2.70 Ga (Huhma et al. 2000), it appears to define the host Kalpio
gneisses as correspondingly older. In the light of the Petäjäniemi evidence and
Laajoki’s (2005) view of the Kalpio gneisses as lithodemic derivatives of schists in
lower parts of the CPG, this would mean that the latter rocks should also be older
than ca. 2.70 Ga.
In a summary of the presently available evidence, we feel comfortable in only
proposing that the CPG was most probably deposited somewhere between 2.72
and 2.45 Ga. Although this represents some progress, the keys to full resolution
of the problem are still missing.
References
Hanski, E., Huhma, H. & Vuollo, J. 2010. SIMS zircon ages and Nd isotope systematics of the
2.2 Ga mafic intrusions in northern and eastern Finland. Bulletin of the Geological Society of
Finland 82, 31–62.
Huhma, H., Kontinen, A. & Laajoki, K. 2000. Age of the metavolcanic-sedimentary units of the
central Puolanka Group, Kainuu schist belt, Finland. In: Eide, E. (ed.) 24. Nordiske Geologiske
Vintermøte, Trondheim 6.–9 Januar 2000. Geonytt 1, 87–88.
Kontinen A., Huhma, H. & Laajoki, K. 1996. Sm/Nd isotope data on the Central Puolanka Group,
Kainuu Scist Belt, Finland; constraints for provenance and age of deposition. In: Kohonen, T.
& Lindberg, B. (eds) The 22nd Nordic Geological Winter Meeting, Turku – Åbo, 8–11 January
1995. Abstracts, p. 95.
Laajoki, K. 2005. Karelian supracrustal rocks. In: Lehtinen, M., Nurmi, P.A., Rämö, O.T. (eds)
Precambrian Geology of Finland − Key to the Evolution of the Fennoscandian Shield. Amsterdam: Elsevier B.V., 279–342.
Laajoki, K. & Wanke, A. 2002. Kainuu Belt. In: Laajoki, K. & Wanke, A. (eds) Stratigraphy and
sedimentology of the Palaeoproterozoic Kainuu, Kuusamo and Peräpohja belts, northern
Finland. Res Terrae A22, 18–73.
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
Fig. 1. Simplified geological map of the western central part of the Kainuu schist belt with locations
of the Oikarila structure (black quadrangle) and lithostratigraphic units discussed in the text. AR
Archaean rocks, mainly TTG gneisses, PjF Puolankajärvi Fm, AvF Akanvaara Fm, PkF Pärekangas
Fm (Kalpio mica and quartzite gneisses with the same colour as PjF and AvF, respectively), Nsp
Nuottasaari serpentinite. JAT Jatuli rocks, MJAT Marine Jatuli rocks. LKA Lower Kaleva rocks,
UKA Upper Kaleva rocks, JOC Jormua Ophiolite Complex, Kajaani Gr c. 1.8 Ga pegmatite-granite.
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Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014
Fig. 2. Photographs of typical Pärekangas sodium-rich felsic (SiO2 63–69 wt%, Na2O 5–9 wt%) tuffs
or silts. (Left) Field photograph of sample HAQ-157, for which detrital zircon age data are presented
below in Fig. 3. (Right) Scanned image of a diamond-sawn slab (height ca. 7 cm) from sample 14AATK-90 (chemically nearly identical with HAQ-157). The main minerals in both these near micafree rocks are actinolitic amphibole, quartz and albite.
Fig. 3. Concordia diagrams for zircon U-Pb data. (Left) LA-MC-ICPMS analyses of zircons from
Pärekangas sodic tuff or silt (photo of the sampled rock in Fig. 2) at Haapalanmäki. The youngest cluster of 22 technically good grains gives an intercept age of 2716 ± 8 Ma. (Right) SHRIMPII
analyses of zircons from the Junttilanniemi granophyre. The older data points give the magmatic
crystallization age of 2444 ± 4 Ma. The one close to 1.7 Ga is from a metamorphic grain domain.
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Geologian tutkimuskeskus, Tutkimusraportti 207 – Geological Survey of Finland, Report of Investigation 207, 2014
Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
TaLvivaara Biotite has stories to tell
by
Asko Kontinen1, Bo Johanson2, Lassi Pakkanen2 and Mia Tiljander2
1 Geological
Survey of Finland, P.O. Box 1237, FI-70211 Kuopio, Finland
Survey of Finland, P.O. Box 96, FI-02151, Espoo, Finland
E-mail: [email protected]
2 Geological
The sulphide-rich black schists forming the Talvivaara (TV) Ni-Zn-Cu deposit
contain 5–30 vol% biotite as their only significant ferromagnesian silicate phase.
We have performed 104 electron microprobe analyses from biotites in 11 samples
representing all the main structural-textural types of the deposit. These data show
that biotite has a remarkably uniform composition throughout the deposit, with
22.26 ± 1.53 wt% MgO and only 1.49 ± 0.48 wt% FeO (Table 1). However, the
biotite is not pure Mg-phlogopite, as it contains a large (>50%) eastonite (aluminous phlogopite) component. Biotites from flanking sulphide-rich but base
metal-poor black schists have a similar Fe-poor mean composition to the ore
biotites, whereas those in flanking sulphide-poor (with low S/Fe) graphitic schists
are much richer in Fe (Table 1).
Given that biotite in the sulphide-rich TV black schists is the only non-sulphide mineral that contains (a little) Fe, it is clear that a near total relocation
of original detrital Fe in these rocks (5 to 95% of the present total Fe) into the
sulphide phase must have taken place at the latest during peak metamorphism.
Most probably, this was primarily through the reaction of diagenetic±syngenetic
pyrite with ferrous Fe in detrital silicate±oxide minerals to form pyrrhotite, and
involved carbon to balance the reaction, which can be schematically expressed as:
2 FeO (in silicate±oxide minerals) + 2 FeS2 + C (in graphitic material) --> 4 FeS
+ CO2 (Ferry 1981). In the light of mass-balance considerations, it is possible that
most pyrrhotite in TV rocks was generated by this mechanism.
It is must be recalled that Ferry (1981), in his classic study on pyrite to pyrrhotite conversion in the sulphidic black schists of south-central Maine, rejected
the silicate Fe plus pyrite reaction pathway. He instead considered desulphidation
of pyrite to be more likely, in spite of the similarly Fe-poor biotite in Maine as
in TV rocks, being the only significant Fe nonsulphide. One of his main arguments against the silicate sulphidation pathway was the lack of supporting textural evidence, as is also the case in TV rocks. However, we consider this as an
expected situation considering the much higher tendency of pyrite and micas to
form finite euhedral shapes compared to pyrrhotite, which is also a mechanically
very weak and easily recrystallizing phase at temperatures >300 °C (Marshall &
Gilligan 1987). Therefore, and as Ferry’s (1981) study shows, pyrite to pyrrhotite
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Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014
conversion already starts in greenschist facies conditions, and we do not expect
to see any related textures preserved in the multiply deformed amphibolite facies
TV black schists.
Our deductions above have serious consequences for the interpretation of such
features as the degree of pyritization and Fe and S isotopes in TV rocks. As for an
actual example, the metamorphic origin of the TV pyrrhotite, as inferred above,
means that the minor mass-anomalous fractionations of S-isotopes recently reported by Young et al. (2013) from TV pyrrhotites (Δ33S from -0.55 to 1.25‰)
and pyrites (Δ33S from -0.25 to 0.57‰) are most likely of metamorphic origin,
caused by some as yet undiscovered thermochemical mechanism(s) related to the
pyrite to pyrrhotite conversion. It should be noted here that pure pyrrhotite and
pyrite were not analysed by Young et al. (2013). However, we can assume that pyrrhotite and pyrite were the main components in their acid-volatile sulphide and
chromium-reducible sulphide fractions, respectively.
Finally, we note that biotites in TV ore-grade black schists contain on average
0.54 wt% V2O3 and 0.12 wt% Cr2O3. These values are high enough to indicate that
biotite is presently the principal mineral host of the whole-rock Cr (mean 130
ppm) and V (mean 590 ppm). This is a significant observation given that there is
a large authigenic component (60–85%) in whole-rock V contents of these black
schists. Obviously, if the introduced authigenic V was principally scavenged by
defunct organic matter from the water column, as we believe, it was relocated into
phyllosilicates at the latest with early metamorphism.
References
Ferry, J. M. 1981. Petrology of graphitic sulfide-rich schists from south-central Maine: an
example of desulfidation during prograde regional metamorphism. American Mineralogist 66,
908–930.
Marshall, B. & Gilligan, L. B. 1987. An introduction to remobilization: information from orebody geometry and experimental considerations. Ore Geology Reviews 2, 87–131.
Young, S. A., Loukola-Ruskeeniemi, K. & Pratt, L. M. 2013. Reactions of hydrothermal solutions
with organic matter in Paleoproterozoic black shales at Talvivaara, Finland: Evidence from
multiple sulfur isotopes. Earth and Planetary Science Letters 367, 1–14.
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
Table 1. Mean compositions of Talvivaara biotites.
SiO2 (wt%)
TiO2
Al2O3
Cr2O3
V2O3
FeO
MnO
MgO
CaO
Na2O
K 2O
SrO
BaO
NiO
ZnO
SO2
P2O5
F
Cl
Total
TV-Ni
Mean
Std
n = 11/104
TV-loNi
Mean
Std
n = 5/63
TV-loS
Mean
n = 2/8
40.35
1.14
18.01
0.12
0.54
1.49
1.10
22.26
0.07
0.01
9.76
0.00
0.00
0.01
0.15
0.01
0.01
0.45
0.01
95.49
40.33
0.93
18.09
0.09
0.31
2.00
0.43
22.67
0.02
0.08
9.90
0.01
0.03
0.01
0.16
0.01
0.03
0.72
0.01
95.82
36.86
1.86
18.83
0.05
0.08
14.25
0.15
13.47
0.01
0.16
9.25
0.00
0.07
0.01
0.17
0.01
0.00
0.33
0.02
95.58
0.99
0.15
1.36
0.04
0.18
0.48
0.27
1.53
0.13
0.02
0.73
0.01
0.00
0.01
0.13
0.01
0.04
0.17
0.01
0.63
0.23
1.04
0.04
0.21
0.45
0.19
1.04
0.02
0.09
0.34
0.01
0.03
0.01
0.12
0.01
0.06
0.22
0.01
Std
0.61
0.25
0.24
0.02
0.03
2.05
0.03
1.61
0.01
0.03
0.15
0.01
0.02
0.01
0.04
0.01
0.00
0.06
0.02
Maine
Mean
n = 7
Std
41.54
0.95
18.68
0.92
0.51
0.58
2.63
0.36
21.89
0.00
0.08
9.77
2.00
0.24
1.90
0.00
0.04
0.16
95.91
TV-Ni: mean and standard deviation (std) of 104 electron microprobe analyses (duplicate points included)
from 11 samples of sulphide-rich (S/Fe > 0.5) and mineralized (Ni > 0.1 wt%) black schists. TV-loNi: mean
of 63 electron microprobe analyses from 5 samples of sulphide-rich (S/Fe > 0.5) and non-mineralized
(Ni < 0.1 wt%) black schists. TV-loS: mean of 8 electron microprobe analyses from 2 sulphide-poor
(S/Fe < 0.5) and non-mineralized (Ni < 0.1 wt%) black schists. Maine: for comparison, mean composition of
biotite analyses from sulphidic black schists in south-central Maine from Ferry (1981) are also presented
(one sample with exceptionally high FeO excluded from the mean).
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Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014
Geochemical surveyS In northern uganda
by
Esko Korkiakoski
Geological Survey of Finland, P.O. Box 1237, FI-70211 Kuopio, Finland
E-mail: [email protected]
BACKGROUND AND IMPLEMENTATION
Geochemical Surveys of Northern Uganda were implemented by the GTK Consortium (GTK with a local partner) as part of the Geological and Mineral Deposit Mapping Project in 2009–2011. The mapping project was a component of
the broader Sustainable Management of Mineral Resources Project (SMMRP) and
financed by the Nordic Development Fund (NDF Credit No. 427).
Targets for regional stream sediment surveys and more detailed soil surveys
were selected in co-operation with the geochemists of the Department of Geological Survey and Mines (DGSM) of Uganda (Fig. 1). The design of the geochemical surveys was based on new findings from geological mapping and airborne
geophysics, carried out as part of the SMMRP, and complemented with earlier
geochemical data and company reports. Sampling was performed by the DGSM
field team under the supervision of GTK experts.
Regional stream sediment surveys were carried out at six selected mineral potential targets, including West Nile, Hoima, Karuma Falls, Kaliro, Icheme and
Barr, totalling 1025 samples. The overall survey areas covered nearly 8000 km2,
the average sampling density being 7.5 km2 per sample.
Soil sampling included ten different targets. Due to time constraints and logistical reasons, not all soil sampling targets were defined for follow-up study using
the preceding results of the new stream sediment surveys, but were selected on a
geological basis (i.e. new maps) or using earlier exploration data.
The stream sediment samples were analysed for major and minor elements by
Acme Analytical Laboratories (Vancouver) Ltd. Canada by ICP-MS, while soil
samples were analysed by XRF at the CGS laboratory in Pretoria, South Africa.
The precious metals Au, Pt and Pd were also determined by ICP-MS. All samples were sieved before analysis into the <150 μm fraction at the DGSM mineral
laboratory.
OUTCOME OF THE SURVEY
For overall processing of the stream sediment and soil surveys, analytical
results were combined into a spatial database using ArcGIS. For interpretation, the
analytical results were integrated with new geological maps and processed
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
geophysical data, both prepared as part of the main mapping project. Based on
the results of the stream sediment and soil geochemical surveys, complemented
with data integration and geological analogs from other places, several ore potential targets were identified in the NDF geochemical study areas for further
exploration:
1) The southern West Nile area, where Au and Cu anomalies are related to mafic metavolcanic rocks associated with (fuchsitic) quartzites and tremoliteactinolite schists, all belonging to the War group.
2)The Hoima area, where Cu-Zn-Fe anomalies are related to Proterozoic
Bunyoro fine-grained sediments and their NW contact zone.
3) The Karuma Falls area, with superimposed high Ni-Cr and geophysical anomalies possibly indicating an occurrence of a hidden mafic-ultramafic body.
4) The Kafu River West, with high and well-defined Au anomalies.
5) The northern central West Nile area, where REE (La, Ce and Y) and associated
Nb-Ta anomalies are related to the highly-metamorphic rocks of the Watian
series.
References
Korkiakoski, E., Salminen, R., Eklund, M. & Backman, B. 2012. Provisional exploration programme – Geochemistry – on short, medium and long term – a summary report. Geological Mapping, Geochemical Surveys and Mineral Resources Assessment in Selected Areas of
Uganda. Sustainable Management of Mineral Resources project. NDF Credit No. 427. 39 p.
(unpublished report)
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Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014
Fig. 1. The location of the geochemical stream sediment and soil sampling targets in the NDF
survey area, northern Uganda. Stream sediment areas are delineated by red lines and soil targets
by black dots. Base map; 1:1.5 M scale geological map; symbols of the main geological units are
indicated by text.
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
ZTEM survey in outokumpu
by
Maija Kurimo1, Hanna Leväniemi1 and Ilkka Lahti2
1 Geological
Survey of Finland, P.O. Box 96, FI-02151, Espoo, Finland
Survey of Finland, P.O. Box 77, FI-96101 Rovaniemi, Finland
E-mail: [email protected]
2 Geological
Introduction
GTK supported the Tekes-funded project “Developing Mine Camp Exploration
Concepts and Technologies - ‘Brownfield exploration’” (Aatos et al. 2014) by acquiring a systematic helicopter Z-axis tipper electromagnetic (ZTEM) survey
over the target area in Outokumpu, eastern Finland (Fig. 1). The survey was an
essential part of GTK’s deep exploration development work. The airborne survey
was carried out by Geotech Airborne Ltd. in June 2013, and the contractor also
calculated the 2D and 3D inversions of the results (Geotech Ltd. 2013).
ZTEM Method
The Z-axis tipper system measures naturally occurring magnetic fields in the
earth in a similar manner to the magnetotelluric (MT) technique (Condor Consulting Inc. 2012). From a geological point of view, the ZTEM responds best to
conductivity contrasts associated with large-scale geological features. The system
measures the vertical magnetotelluric field (Hz), whereas the horizontal components (Hx, Hy) are measured at a base station inside the survey area (Fig. 2).
The processed data (tipper components) comprise the ratios of Hz/Hy and Hz/
Hx, commonly referred to as the tipper ratios Tzx and Tzy. The data consist of 24
parameters in total: in-phase and quadrature parts of the tipper transfer functions
derived from the in-line (Tzx) and the cross-line (Tzy) components of six frequencies (25, 37, 75, 150, 300 and 600 Hz) (Fig. 3). The skin depth of the system
is commonly approximately 0.5–2 km.
The tipper components produce crossover-type anomalies: maxima or minima
are not above the conductors (Fig. 3). Additional processing steps are applied to
convert the components into local maxima for easier interpretation (total divergence DT and phase rotation TPR).
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Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014
The helicopter survey
The survey was carried out in the Outokumpu region in June 2013. The line spacings were 500 m, 1 km or 2 km, which was a compromise between the budget and
the coverage (Fig. 1). The terrain clearance of the electromagnetic bird (receiver
coil) was approximately 90 m and the sampling interval along the line was ca. 10
m. The original processed survey data were delivered in August 2013. Both 2D
inversions along survey lines and a full 3D inversion of the whole survey area
were delivered during the winter of 2013–2014.
Discussion
Preliminary analysis of the results indicates that the ZTEM depth penetration
is rather deep, being up to 1 km in the Outokumpu area. The system is sensitive
to power-line noise, but fortunately not too much; more good-quality data were
gathered than expected, despite the fact that there are many power lines in the
survey area. The first impression is that the interpreted models do not appear
very detailed, especially at greater depths, but still correlate with existing 3D information. Comparisons with the results of the FIRE and HIRE reflection seismic
surveys, as well as ground magnetotelluric, drill hole, magnetic and gravity data
will be carried out and published by the Outokumpu project in 2014–2015.
References
Aatos, S., Koistinen, E., Kontinen, A., Sorjonen-Ward, P., Torppa, J., Jokinen, J., Korhonen, J., Korpisalo, A., Kurimo, M., Laine, E. & Leväniemi, H. 2014. Developing
deep exploration methods in Outokumpu mining camp area. In: Lauri, L. S., Heilimo,
E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds) Current Research: 2nd GTK
Mineral Potential Workshop, Kuopio, Finland, May 2014. Geological Survey of Finland,
Report of Investigation 207. (this volume)
Condor Consulting Inc. 2012. THE ZTEM PRIMER. Rev 3. Available at: http://www.condorconsult.com/downloads/ZTEM%20Primer_March%202012.pdf
Geotech Ltd. 2013. Report on a helicopter-borne Z-axis tipper electromagnetic (ZTEM) and aeromagnetic geophysical survey, Outokumpu Mining Camp Area, Finland. Project AB130076.
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
Fig. 1. The survey lines drawn on the GTK 3 kHz airborne electromagnetic in-phase (real)
component map.
Fig. 2. Principle of ZTEM (Condor Consulting Inc. 2012). Black horizontal arrows show the magnetotelluric field passing through the earth, green lines on the right show the secondary magnetic
field. Different colours represent resistivity variation in the earth.
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Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014
Fig. 3. Results of one ZTEM survey line compared to the GTK 3 kHz airborne electromagnetic inphase (real) component, RE_GTK (ppm). The ZTEM components are measured along the line (X)
and cross-line (Y), both having in-phase (IP) and quadrature (QD) components at each frequency
(25, 37, 75, 150, 300 and 600 Hz) as Tipper transfer function units. The total length of the profile is
approximately 20 km; the units are artificial.
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
Preliminary results of U-Pb Age
determinations from the Pampalo gold mine
and the Hosko gold deposit, Hattu schist belt,
eastern Finland
by
Asko Käpyaho1, Ferenc Molnár1, Irmeli Mänttäri1, Martin Whitehouse2 and
Grigorios Sakellaris3
1 Geological
Survey of Finland, P.O. Box 96, FI-02151 Espoo, Finland
Museum of Natural History, Box 50007, SE-10405 Stockholm, Sweden
3 Endomines Oy, Pampalontie 11, FI-82967 Hattu, Finland
E-mail: [email protected]
2 Swedish
The Late Archaean Hattu schist belt, located in eastern Finland, is a N–S-trending
belt with epiclastic and felsic to mafic volcanic rocks and it is known to host several gold deposits (Eilu et al. 2012) (Fig. 1). The linear belt of gold deposits and
ore occurrences is referred to as the Karelian Gold Line. An upper constraint for
the age of gold mineralization in Kuittila is set by a U-Pb concordia age of 2741 ±
9 Ma for the Kuittila pluton (Heilimo et al. 2011), which hosts a quartz vein system containing Au and Mo (Fig. 1). The age is coeval with an earlier TIMS dating
by Vaasjoki et al. (1993) from the same sample. Trace lead from gold combined
with Pb analyses on galena from the Pampalo deposit have produced a rough
two-point age estimate of 1.73 ± 0.1 Ga, but its significance has been difficult to
interpret (Vaasjoki et al. 1993).
With an aim to obtain a new age constraint for the Au mineralisation event(s),
zircon and titanite separated from host rock samples of gold ore from the Pampalo mine and Hosko deposit were analysed using the secondary ion mass spectrometer U-Pb method in the Nordsim laboratory, Stockholm. Three samples
that were taken from schistosity parallel dyke- and boudin-like felsic units within
the high-grade ore zones of the Pampalo mine contain structurally and texturally
complex zircon grains. U-Pb data from these samples are often discordant and
the concordant data are difficult to interpret, revealing the complex history of the
rocks associated with the Au mineralization. One of the reasons for the observed
behaviour is probably related to the intense K-feldspar alteration that also affects
zircon crystals.
Results of U-Pb dating on zircon grains from an auriferous quartz-feldspar
rock sample show inheritance from a >2.8 Ga source and a population clustering around ca. 2.71 Ga. This population either records an igneous event resulting
in emplacement of the quartz feldspar rock or a hydrothermal event. Later Archaean event(s) were also observed. U-Pb analyses on zircon grains from another
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felsic boudin revealed clustering of concordant U-Pb data on zircons at around
ca. 2.73–2.69 Ga, whereas a titanite analysis, with large analytical error, pointed to
a Palaeoproterozoic age. The third sample from a boudinaged vein-like felsic unit
provided mostly discordant U-Pb data on zircons: only two analyses were concordant, pointing to late Archaean ages. Titanite analyses from the same sample,
although having low 206Pb/204Pb (53-135), produced concordant Palaeoproterozoic ages after the common lead correction.
On the basis of these results, our preliminary conclusion is that the zircon population with an age of 2.71 Ga sets the upper limit for the formation of the gold
deposit of the Pampalo mine. In the light of the results, it is also likely that the ore
was remobilised by Palaeoproterozoic events.
Three samples were taken from the Hosko deposit for U-Pb dating: mica schist
containing microscopic gold associated with arsenopyrite, mica schist hosting a
complex quartz-tourmaline vein system with gold, and a pegmatite vein crosscutting the mica schist. Samples from the mica schists revealed similar age distributions of detrital zircon grains. Based on the youngest detrital zircon grains, the
formation of the Hosko gold deposit is younger than 2.72 Ga. The emplacement
age of the pegmatite could not be determined.
References
Eilu, P., Ahtola, T., Äikäs, O., Halkoaho, T., Heikura, P., Hulkki, H., Iljina, M., Juopperi, H.,
Karinen, T., Kärkkäinen, N., Konnunaho, J., Kontinen, A., Kontoniemi, O., Korkiakoski,
E., Korsakova, M., Kuivasaari, T., Kyläkoski, M., Makkonen, H., Niiranen, T., Nikander, J.,
Nykänen, V., Perdahl, J.-A., Pohjolainen, E., Räsänen, J., Sorjonen-Ward, P., Tiainen, M.,
Tontti, M., Torppa, A. & Västi, K. 2012. Metallogenic areas in Finland. In: Eilu, Pasi (ed.)
Mineral deposits and metallogeny of Fennoscandia. Geological Survey of Finland, Special Paper 53, 207–342.
Heilimo, E., Halla, J. & Huhma, H. 2011. Single-grain zircon U–Pb age constraints of the western
and eastern sanukitoid zones in the Finnish part of the Karelian Province. Lithos 121, 87–99.
Vaasjoki, M., Sorjonen-Ward, P. & Lavikainen, S. 1993. U-Pb age determinations and sulfide
Pb-Pb characteristics from the late Archaean Hattu schist belt, Ilomantsi, eastern Finland. In:
Nurmi, P. A. & Sorjonen-Ward, P. (eds) Geological development, gold mineralization and exploration methods in the late Archean Hattu schist belt, Ilomantsi, eastern Finland. Geological
Survey of Finland, Special Paper 17, 103–132.
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
Fig. 1. Map showing the orogenic gold occurrences (after Eilu et al. 2012) in the Archaean Hattu
schist belt, eastern Finland.
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Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014
Further insight into ore-forming processes
using in situ Pb, S and Sr isotopic analysis on
thin sections by LA-MCICPMS
by
Yann Lahaye1, Hugh O’Brien1, Ferenc Molnár1, Shenghong Yang2,
Kirsi Luolavirta2 and Wolfgang Maier3
1 Geological
Survey of Finland, P.O. Box 96, FI-02151, Espoo, Finland
of Geosciences, University of Oulu, FI-90014 Oulu, Finland
3 School of Earth and Ocean Sciences, Cardiff University, UK
E-mail: [email protected]
2 Department
Sulphur, strontium and lead isotopic systems have been used for more than half a
century to decipher ore deposits. The behaviour of these isotopic systems in geological systems and the compositions of their end members is well constrained.
The formation of ore deposits in layered intrusions and hydrothermal systems
is the result of complex dynamic processes, and the primary ores are generally
overprinted and modified by multiple episodes of metamorphism in Precambrian terrains. The recent development of an in situ analytical technique allows us
to see through the geological complexity by analysing individual minerals in thin
section, thereby maintaining textural control. When compared to bulk chemical analysis, high spatial resolution isotopic analysis targeting pristine domains
within single crystals, clearly linked to the mineralization, provides a much more
powerful tool to understand the processes leading to the formation and modification of ore deposits.
We present the results and analytical problems related to laser ablation multicollector inductively plasma mass spectrometer (LA-MCICPMS) in situ analysis
of the radiogenic (Sr) and stable (Pb, S) isotope geochemistry of specific minerals
co-genetic with ore mineralization in magmatic sulphides from layered intrusions and in hydrothermal gold deposits. It is well known that (1) Sr isotopic
compositions have great potential for deciphering the petrogenesis of magmatic
rocks and (2) evaluating melt-country rock interactions and their relationship
with ore deposits, and that (3) the stable Pb isotopic composition of Pb-bearing
minerals and S isotopic variations in sulphide phases can be used to trace the
sources of metals and fluids in ores.
Samples from layered intrusions such as the Bushveld magmatic complex may
show considerable Sr isotopic variation among the various mineral phases and
within individual grains in the same thin section, indicating the mixing of crystals from more than one magma source, a process that may be linked to a mineralization event (Yang et al. 2013). The combined use of Sr and S isotopes together
with trace element data also appeared to indicate the involvement of crustal con85
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
tamination in the genesis of the Ni-Cu sulphide-hosted mafic-ultramafic rocks
from the Mesoproterozoic Fraser Zone in Western Australia (Maier et al. 2014),
as well as in the Kevitsa intrusion in Finland (Luolavirta et al. 2014). The precision and accuracy of measurements of the 87Sr/86Sr ratio strongly depend on the
Ca/Sr ratio and the beam diameter (200 to 110 μm spot).
In samples from the Pampalo gold mine in eastern Finland, measurements of
Pb isotopes with spatial resolution capabilities of up to 150 micrometres on hydrothermal K-feldspar and down to a few micrometres wide galena rims or thin
altaite plates (3 x 50 μm lines) indicate several episodes of hydrothermal activity. The Pb isotopic compositions of Pb-rich phases are slightly less precise, but
sometimes more accurate than solution analysis due to the preferential leaching
of labile radiogenic Pb.
Sulphur isotopic data (δ34S) on pyrite and chalcopyrite from the Pampalo mine
in the Hattu schist belt vary within 10‰ (from +1 to -9‰), suggesting the mixing
of sulphur from two reservoirs (Molnár et al. 2013, 2014). The main limitation
to the accuracy of S isotopes is the lack of certified international standards and
plasma interferences. However, the variation in data among individual spots is
less than 1‰ in homogeneous sulphide grains, i.e., much less than the variation
among samples from different geological settings.
LA-MCICPMS is capable of generating a large amount of data (hundreds of
analyses in a day) on thin (200 μm) sections that require minimum sample preparation and careful optical observation. A specific Pb-Pb age on a micrometric
Pb-rich phase or a specific crustal isotopic signature from a plagioclase or sulphide could be used to identify vectors toward the location of an ore deposit in
geochemical exploration.
References
Luolavirta K., Hanski, E., Maier, W., O'Brien, H., Lahaye, Y., Santaguida, F. & Voipio, T. 2014.
Petrology and in situ Strontium isotope investigation of the Ni-Cu-(PGE) ore bearing Kevitsa
intrusion, northern Finland. Abstract Volume, 31st Nordic Geological Winter Meeting, Lund,
Sweden, January 8–10, 2014, p. 56.
Maier, W. D., Smithies R. H., Spaggiari C. V., Yang, S. & Lahaye, Y. 2014. Petrogenesis and NiCu sulphide potential of mafic-ultramafic rocks in the Mesoproterozoic Fraser Zone, Albany
Fraser Orogen, Western Australia. MDSG meeting, Oxford.
Molnár, F., O'Brien, H., Lahaye, Y., Käpyaho, A. & Sakellaris, G. 2013. Signatures of overprinting mineralisation processes in the orogenic gold deposit of the Pampalo mine, Hattu schist
belt, eastern Finland. Abstract Volume, 12th Biennial SGA Meeting, 12–15 August 2013, Uppsala, Sweden, 1160–1163.
Molnár, F., Mänttäri, I., O'Brien, H., Lahaye, Y., Käpyaho, A., Sorjonen-Ward, P., Whitehouse,
M. & Sakellaris, G. 2014. Boron and sulphur isotopes reveal the role of magmatic fluids in
the formation of orogenic gold deposits in the Archaean Hattu Schist Belt, eastern Finland. In:
Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds) Current
Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014. Geological Survey of Finland, Report of Investigation 207. (this volume)
Yang, S., Maier, W. D., Lahaye, Y. & O’Brien, H. 2013. Strontium isotope disequilibrium of plagioclase in the Upper Critical Zone of the Bushveld Complex: evidence for mixing of crystal
slurries. Contribution to Mineralogy and Petrology 166, 959–974.
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Coupled oroclines in the central part of the
composite Svecofennian orogen: From linear
orogen to equidimensional continental
crust
by
Raimo Lahtinen1, Mikko Nironen1 and Stephen T. Johnston2
1 Geological
Survey of Finland, P.O. Box 96, FI-02151, Espoo, Finland
of Earth and Ocean Sciences, University of Victoria, Bob Wright Centre, P.O. Box 3065 STN CSC, Victoria, BC V8W 3V6, Canada
E-mail: [email protected]
2 School
The composite Svecofennian orogen (SO) forms the largest piece of Palaeoproterozoic crust in Fennoscandia. The central part of the SO shows some linear
features, such as the Tampere magmatic arc, but as a whole it is equidimensional.
One approach to make equidimensional crustal blocks out of elongate, narrow
magmatic arcs and orogens is to shorten these into equidimensional continental
domains by buckling of the linear systems about the vertical axes of rotation into
one or more coupled oroclines or ‘terrane wrecks’.
The central part of the SO is characterized by two continuous large arcuate
structures: a southerly convex to the west bend that is continuous into a northerly
convex to the east bend. We propose that these arcuate structures constitute a
pair of coupled oroclines. A test of the orocline model is to determine whether
tectonic vectors (TVs) change as a function of strike around the arcuate structures. TVs established in the SO include structural vergence, metamorphic gradient, the direction oceanward as indicated by the distribution of subaerial vs submarine volcanic rocks, the component of older radiogenic crust as indicated by
epsilon-Nd values, and the crustal conductivity gradient. We have demonstrated
that TVs vary as a function of structural strike around both bends of the SO. In
addition, a number of geological belts, including MORB/EMORB volcanic rocks
and Ni-bearing intrusions, are continuous around both bends. These observations are consistent with the geometry of the SO being the result of oroclinal
buckling of an originally linear orogen. Palinspastic restoration of the central SO
to an originally linear geometry yields a 1000-km-long orogen, restores the TVs
to a common orientation, explains the continuity of geological belts around the
bends, and shows that the orogen consists of a SW-facing arc that was shortened
prior to oroclinal buckling along NE-verging thrusts.
The possibility of a continuation of this oroclinal buckling via the Uusimaa belt
in southern Finland to the Bergslagen area in Sweden and the effects of younger
orogenic events on the oroclines are being considered. The coupled Bothnian
oroclines imply that the rapid construction of large areas of stable and equidimensional continental lithosphere in the Palaeoproterozoic was possibly facilitated by terrane wrecks.
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
3D modelling of the sola serpentinite
using old geological maps and 3D magnetic
inversion
by
Eevaliisa Laine and Hanna Leväniemi
Geological Survey of Finland, P.O. Box 96, FI-02151, Espoo, Finland
E-mail: [email protected]
The Outokumpu mining district hosts a Palaeoproterozoic sulphide deposit characterized by an unusual lithological association (Fig. 1). It is located in the North
Karelia Schist Belt, which was thrust on the late Archaean gneissic–granitoid
basement of the Karelian craton during the early stages of the Svecofennian Orogeny between 1.92 and 1.87 Ga (Koistinen 1981). Two major tectono-stratigraphic
units can be distinguished: (1) a lower, parautochthonous ‘Lower Kaleva’ unit
and (2) an upper, allochthonous ‘upper Kaleva’ unit or ‘Outokumpu allochthon’.
The latter consists of tightly-folded deep marine turbiditic mica schists and metagraywackes containing intercalations of black schist, and the Outokumpu assemblage, which comprises ca. 1950 Ma old, serpentinized peridotites surrounded by
carbonate-calc-silicate (‘skarn’)-quartz rocks.
At Sola and Horsmanaho the Outokumpu assemblage rocks are roundish bodies slightly elongated in the SW–NE direction. The aim of the present study was
to model the geometry of the Sola serpentinite and its relation to the Sola shear
zone. As a starting point, there were three different 3D models and visualization
of the Sola serpentinite:
1) visualized by two geological sections (Gaál et al. 1975),
2) a 3D model of the serpentinite and black schist constructed using Surpac (Laine et al. 2012), and
3) a 3D model of the boundary surface between serpentinite and associated black schists constructed using Geomodeller by Intrepid (Laine et al. 2012).
The final 3D model was built by constraining it based on tectonic observations
extracted from old geological maps using Geomodeller (Intrepid). The 3D stochastic inversion of the magnetic data was used to improve this final model. In
order to separate different lithologies (serpentinite, calc-silicate rocks and black
schists), the Sola serpentinite was modelled as a voxet by geostatistical simulation
using lithology as a categorical variable. Both models will be used in building the
regional 3D model of the whole Outokumpu area (Outokumpu Mining Camp
project, TEKES, GTK; described by Aatos et al. this volume).
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References
Aatos, S., Koistinen, E., Kontinen, A., Sorjonen-Ward, P., Torppa, J., Jokinen, J., Korhonen, J., Korpisalo, A., Kurimo, M., Laine, E., Leväniemi, H. & Lahti, I. 2014. Developing
deep exploration methods in the Outokumpu mining camp area. In: Lauri, L. S., Heilimo,
E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds) Current Research: 2nd GTK
Mineral Potential Workshop, Kuopio, Finland, May 2014. Geological Survey of Finland,
Report of Investigation 207. (this volume)
Gaál, G., Koistinen, T., & Mattila, E. 1975. Tectonics and stratigraphy of the vicinity of Outokumpu, North Karelia, Finland: including a structural analysis of the Outokumpu ore deposit.
Geological Survey of Finland, Bulletin 271. 67 p.
Koistinen, T. J. 1981. Structural evolution of an early Proterozoic stratabound Cu-Co-Zn deposit,
Outokumpu, Finland. Trans. Royal Soc. Edinb., Earth Sciences 72(2), 115–158.
Korsman, K., Koistinen, T., Kohonen, J., Wennerström, M., Ekdahl, E., Honkamo, M., Idman,
H. & Pekkala, Y. (eds) 1997. Suomen kallioperäkartta = Berggrundskarta över Finland = Bedrock map of Finland 1:1 000 000. Espoo: Geological Survey of Finland.
Laine, E., Koistinen, E., Saalmann, K., Coirrioux, G., Diaz, R., Salminen, N. & Tervo, T. 2012.
3D modeling of polydeformed and metamorphosed rocks at different scales using geological
and geophysical data from Outokumpu area. In: Laine, E. (ed.) 3D modeling of polydeformed
and metamorphosed rocks: the old Outokumpu Cu-Co-Zn mine area as a case study. Geological Survey of Finland, Report of Investigation 195. 77 p.
C
Fig. 1. (a) Location of the Outokumpu area, (b) Regional geology drawn by Kerstin Saalmann
after Korsman et al. (1997), (c) Study area.
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
age constraints for the Appinites of
the Central lapland granitoid complex,
finland
by
Laura S. Lauri1 and Hannu Huhma2
1 Geological
Survey of Finland, P.O. Box 77, FI-96101 Rovaniemi, Finland
Survey of Finland, P.O. Box 96, FI-02151, Espoo, Finland
E-mail: [email protected]
2 Geological
Introduction
Appinites, first described from Scotland (e.g. Bowes & McArthur 1976), are a
suite of mantle-derived, alkali-rich, dioritic to syenitic igneous rocks, which are
characterized by high amounts of Mg, Ba, Sr, P and LREE. The appinites have
plagioclase, hornblende, biotite and magnetite as the main minerals. Syenites are
rich in K-feldspar and commonly contain quartz that may be secondary. Accessory phases include apatite, ilmenite, titanite, zircon, sulphides, monazite, allanite
and baryte.
Palaeoproterozoic appinitic intrusions are widespread within the Central Lapland Granitoid Complex (CLGC) in northern Finland (Mutanen 2011). They
form numerous small stocks, dykes and some large intrusions, which are clearly
discernible on the aeromagnetic map due to abundant magnetite (Fig. 1). Appinites are generally post-kinematic to the tectonic movements in the CLGC and are
commonly associated with presumably coeval granites, forming possible magma
mixing/mingling systems.
Geochronology of the CLGC appinites
Several published age determinations indicate that the appinites of the CLGC
were emplaced at ca. 1.79 Ga. Both the Tainio gabbro (1796 ± 4 Ma; Väänänen
2004) and the Jääskö monzonite (1796 ± 3 Ma; Ahtonen et al. 2007) in the central part of the complex have compatible thermal ionization mass spectrometry
(TIMS) zircon U-Pb ages. Several other samples from different appinite intrusions have been taken in the course of the studies of the CLGC between 2003
and 2012 and presented here. The analytical methods include multigrain TIMS/
chemical abrasion (CA)-TIMS analyses (samples A1855 Peittoselkä and A1955
Uusijänkkä), and single crystal zircon analyses using a sensitive high-resolution
ion microprobe (SHRIMP; sample A1854 Lehmilehto) and laser ablation multicollector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS;
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samples A2183 Hormuoja diorite, A2184 Vanttauskoski diorite, and A2185 Vanttauskoski syenite).
Samples A1854 Lehmilehto and A1855 Peittoselkä were taken from cores
drilled from the dykes of the Kierinki dyke swarm, which is discernible as a
roughly E–W-trending magnetic anomaly cross-cutting the structures in the N
part of the CLGC. The Kierinki dykes vary in composition from mafic to felsic,
and show mixing and mingling textures. Both samples were taken from felsic
parts of the dykes. The SHRIMP analyses of zircons in sample A1854 Lehmilehto
(Fig. 2a) yielded an age of 1785 ± 20 Ma (MSWD = 0.85, n = 8). TIMS analyses
of sample A1855 Peittoselkä were somewhat discordant (Fig. 2b). However, the
results are compatible with data from sample A1854 Lehmilehto, and 1785 ± 20
Ma may be considered as the best estimate for the age of the Kierinki dyke swarm.
Sample A1955 Uusijänkkä is syenitic in composition. Out of the three zircon fractions analysed with TIMS, two were concordant and yielded an age of
1796 ± 2 Ma (Fig. 2c). The concordia age may be considered as the intrusion age
for sample A1955 Uusijänkkä.
Sample A2183 Hormuoja was taken from medium-grained, grey diorite that
forms a major part of the Hormuoja intrusion in the E part of CLGC. The Hormuoja intrusion is not outcropping, but it was drilled by Polar Mining Inc. in 2009.
The 12 zircons analysed from sample A2183 gave a concordant age of 1795 ± 5
Ma, which may be considered as the intrusion age for the diorite (Fig. 2d).
The Vanttaus appinite intrusion forms a large (20 km x 30 km) multiple intrusion complex that was emplaced within the metasupracrustal rocks of the
Palaeoproterozoic Peräpohja Belt. The intrusion is very poorly outcropping, and
samples A2184 and A2185 were thus collected from a drill core. Sample A2184
is dark grey, fine-grained quartz diorite with spots of dark minerals that consist
of both biotite and amphibole (hornblende). Sample A2185 is grey, fine-grained
quartz monzodiorite that shows a weak fabric. Both samples yield concordant
zircon ages. However, the age for sample A2184 is 1784 ± 5 Ma (Fig. 2e), whereas
the age for sample A2185 is 1794 ± 5 Ma (Fig. 2f). In the drill core, the quartz
monzodioritic type seems to be somewhat older based on cross-cutting relations.
The observations are compatible with the dating results, suggesting that the Vanttauskoski complex was formed by multiple intrusion phases of different appinitic
magma types.
The appinites of the CLGC appear to have intruded in a temporally tightly constrained pulse between 1796 Ma and 1784 Ma. They form a geochemically unique
intrusion type within the CLGC and seem to represent a phase when tectonic
movements were minimal within the area, based on the virtually undeformed appearance of the appinitic rocks within the CLGC. The appinite suite of the CLGC
was followed by voluminous granite plutonism between 1.79–1.76 Ga (Ahtonen
et al. 2007, Lauri et al. 2012, Ranta 2012). However, the younger event does not
seem to have markedly affected the appinite intrusions.
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References
Ahtonen, N., Hölttä, P. & Huhma, H. 2007. Intracratonic Palaeoproterozoic granitoids in northern Finland: prolonged and episodic crustal melting events revealed by Nd isotopes and U-Pb
ages on zircon. Bulletin of the Geological Society of Finland 79, 143–174.
Bowes, D. R. & McArthur, A. C. 1976. Nature and genesis of the appinite suite. Kristalinikum 12,
31–46.
Lauri, L. S., Andersen, T., Räsänen, J. & Juopperi, H. 2012. Temporal and Hf isotope geochemical evolution of southern Finnish Lapland from 2.77 Ga to 1.76 Ga. Bulletin of the Geological
Society of Finland 84, 121–140.
Mutanen, T. 2011. Alkalikiviä ja appiniitteja. Raportti hankkeen ”Magmatismi ja malminmuodostus II” toiminnasta 2002−2005. Geological Survey of Finland, archive report 9/2011. (in
Finnish)
Ranta, J. 2012. Peräpohjan liuskealueen pohjoisosan yksiköiden zirkoniajoitus U-Pb-menetelmällä. University of Oulu, unpubl. M.Sc. Thesis, 77 p. (in Finnish)
Väänänen, J. 2004. Sieppijärven ja Pasmajärven kartta-alueiden kallioperä. Summary: Pre-Quaternary rocks of the Sieppijärvi and Pasmajärvi map-sheet areas. Geological map of Finland,
1:100 000, Explanation to the maps of Pre-Quaternary rocks, sheets 2624 and 2642. Geological
Survey of Finland. 55 p.
Fig. 1. Aeromagnetic grey-scale map of the CLGC with appinite intrusions marked as stars.
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Fig. 2. Concordia diagrams of samples analysed: (a) A1854 Lehmilehto, (b) 1855 Peittoselkä, (c)
A1955 Uusijänkkä, (d) A2183 Hormuoja, (e) A2184 Vanttauskoski diorite and (f) A2185 Vanttauskoski quartz monzodiorite.
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
New Li potential BASED ON till geochemistry in
the Kaustinen area, Western Finland
by
Heidi Laxström, Olavi Kontoniemi, Henrik Wik and Hannu Lahtinen
Geological Survey of Finland, P.O. Box 97, FI-67101 Kokkola, Finland
E-mail: [email protected]
Introduction
The Kaustinen region of Central Ostrobothnia in Western Finland has long been
known for its potential for high-tech metals, and lithium in particular. The area
has been subject to exploration by several private companies during the past decades. The Geological Survey of Finland (GTK) has been exploring the area during
the past 10 years. Three lithium deposits have been reported to the Ministry of
Employment and Economy (MEE): Leviäkangas and Syväjärvi in 2010 and Rapasaaret in 2012. The exploration by GTK in the area mainly comprises boulder
mapping, diamond drilling, geophysical ground surveys and re-assaying of old
till sample material, which is the main focus of this abstract.
Regional geology
The Kaustinen Li province is located in the Pohjanmaa schist belt, between the
Central Finland Granitoid Complex in the east and the Vaasa Migmatite Complex in the west (Fig. 1). According to Alviola et al. (2001), the lithium pegmatites
in the Kaustinen area belong to the albite-spodumene subgroup of the LCT (Li,
Cs, Ta) pegmatite family of Černý & Ercit (2005). These Palaeoproterozoic, 1.79
Ga old (Alviola et al. 2001) pegmatites cross-cut the Svecofennian supracrustal
rocks, clearly postdating the 1.89–1.88 Ga peak of regional low to high amphibolite facies metamorphism (Mäkitie et al. 2001).
Today, there are 7 known deposits in the Kaustinen area, with a combined geological in situ resource (not JORC compliant) of 12 Mt and an average grade of
approximately 1.0% Li2O (Lovén & Meriläinen 2011, Ahtola & Kuusela 2013).
Li potential based on till geochemistry
During the latter half of the 1970s, GTK collected more than 10 000 till samples in
the Kaustinen area as a part of a regional till sampling programme. Samples were
collected along lines with an interval of 500–2000 m between lines and 100–400
m between sample sites. Sampling lines were planned to be perpendicular to the
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direction of glacial ice drift. The average sample depth was about 2 m. No assays
for Li were performed at the time, but the sample material was kept in storage at
GTK’s facility in Kuopio for almost 40 years.
In 2010, GTK’s KaLi project (Li resources of the Kaustinen area), partly supported by ERDF, re-assayed old till sample material to map out the regional-scale
Li potential. A test batch of 542 till samples consisting of the 0.06–0.5 mm fraction
was submitted to the laboratory of Labtium Oy for analysis using a sodium peroxide fusion technique with ICP finish (code 720P of Labtium Oy). The results were
encouraging and the investigation was subsequently continued in a GTK project
during 2011 and 2012. For the investigation, the K fraction (0.06–0.5 mm) of till
was used and the minimum depth of samples was 10 dm. The average depth of
all samples was about 24 dm. Sample preparation included pulverizing the whole
sample in a carbon steel bowl (method 40/Labtium Oy) and sub-sampling 0.2 g
for assays.
A total of 9658 samples from the Kaustinen area were assayed using the technique described above, and an additional multi-element (41 elements) analysis
package was carried out for most of the samples (8979 samples) with aqua regia
digestion and ICP-MS and ICP-OAS finish (code 515PM). The results have been
published in GTK archive reports (Kontoniemi 2011, 2012 and 2013).
A regional distribution map of Li in till is presented in Figure 1. Principally, some of the known Li deposits (Leviäkangas, Rapasaaret, Jänislampi, and
Emmes) are reflected very well in the till geochemistry, while the Outovesi, Syväjärvi and Länttä deposits are poorly reflected in till. There are many areas outside the known lithium province (Länttä-Emmes area) with high Li contents in
till. The largest anomalous area is located NW of the Jänislampi-Emmes area. The
Kaitfors-Rasmus region (area 1 in Fig. 1) and the area around Rita village (2), in
particular, have high potential. The same areas also have some high Be contents
in till. In the area of Alikylä-Emmes (3), Tunkkari-Kortjärvi (4) and Liedes (5),
there are inhomogeneous Li anomalies in till, which might have an unknown
source deposit.
As a whole, this investigation has revealed new Li anomalies and potential areas for follow-up investigations. In the future, new Li pegmatites might also be
discovered and the area of the historical Li province might be extended.
References
Alviola, R., Mänttäri, I., Mäkitie, H. & Vaasjoki, M. 2001. Svecofennian rare-element granitic
pegmatites of the Ostrobothnia region, western Finland; their metamorphic environment and
time of intrusion. In: Mäkitie, H. (ed.) Svecofennian granitic pegmatites (1.86–1.79 Ga) and
quartz monzonite (1.87 Ga), and their metamorphic environment in the Seinäjoki region,
western Finland. Geological Survey of Finland, Special Paper 30, 9–29.
Černý, P. & Ercit, T. S. 2005. The classification of granitic pegmatites revisited. The Canadian
Mineralogist 43, 2005–2026.
Kontoniemi, O. 2011. Kaustisen seudun litium-varannot-hankkeen (KaLi) tutkimukset vuosina
2010–2011. Geological Survey of Finland, archive report 35/2011. 12 p. (in Finnish)
Kontoniemi, O. 2012. Kaustisen alueen Li-potentiaali − vanhojen moreeninäytteiden uudelleenanalysointi. Geological Survey of Finland, archive report 68/2012. 12 p. (in Finnish)
Kontoniemi, O. 2013. Kaustisen alueen Li-potentiaali – vanhojen moreeninäytteiden uudelleenanalysointi, vaihe 2. Geological Survey of Finland, archive report 52/2013. 17 p. (in Finnish)
Korsman, K., Koistinen, T., Kohonen, J., Wennerström, M., Ekdahl, E., Honkamo, M., Idman,
H. & Pekkala, Y. 1997. Bedrock map of Finland 1:1 000 000. Geological Survey of Finland.
Lovén, P. & Meriläinen, M. 2011. Mineral resource and ore reserve estimation of the Länttä and
Outovesi lithium deposits. Outotec OY. Available at: http://www.keliber.no/getfile.php/Keliber-/Keliber%20Mineral%20Resource%20Reserve%20Statements%20Final.pdf.
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
Mäkitie, H., Kärkkäinen, N., Lahti, S. I. & Alviola, R. 2001. Compositional variation of granitic
pegmatites in relation to regional metamorphism in the Seinäjoki region, Western Finland.
In: Mäkitie, Hannu (ed.) 2001. Svecofennian granitic pegmatites (1.86-1.79 Ga) and quartz
monzonite (1.87 Ga), and their metamorphic environment in the Seinäjoki region, western
Finland. Geological Survey of Finland, Special Paper 30, 31–59.
Fig. 1. Li content in till. Values below the detection limit (10 ppm) have been assigned to 5 ppm.
Black rectangles denote Li-potential areas described in the text. The known Li deposits of the
Kaustinen area are also marked. Contains data from the National Land Survey of Finland Topographic Database 08/2012.
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Geophysical Indications of VMS Deposits In
the Häme Volcanic Belt
by
Hanna Leväniemi and Fredrik Karell
Geological Survey of Finland, P.O. Box 96, FI- 02151, Espoo, Finland
E-mail: [email protected]
Introduction
The 1.9–1.8 Ga Häme volcanic belt in southwestern Finland hosts several ZnCu mineralizations in the Hämeenlinna-Somero region (Fig. 1). Although all of
them are currently estimated to be subeconomic, the sulphide-enriched region
can be considered a suitable environment for possible larger volcanogenic massive sulphide (VMS) deposits. Examples from, for instance, the Penokean belt in
Wisconsin, USA (Babcock 1996) that are analogous in many ways to the Häme
volcanic belt, show that geophysical methods can be successfully used in direct
exploration for massive sulphide ores. The purpose of the recent Häme belt VMS
study (Leväniemi & Karell 2013) was to re-assess the available geophysical data
on the Häme belt in order to better understand the geophysical properties and
signatures of the known sulphide mineralizations and to locate possible new targets in the study area.
Role of Geophysics in VMS Exploration
VMS deposits are considered as syngenetic, stratabound formations comprising
massive to semi-massive concordant sulphide lenses and an underlying stringer
zone enveloped in an alteration zone (e.g. Gibson et al. 2007). The theoretical
geophysical approach suggests that the petrophysical properties of the massive
sulphide formations contrast significantly with the host rock, and the formation
should thus be detectable by a variety of geophysical survey methods (e.g. Morgan 2012). However, the true response and exploration success depends on several factors such as the mineral composition of the ore, the petrophysical properties of the hosting environment, the overburden thickness and properties and the
deposit dimensions and depth. Thus, re-analysing the available geophysical datasets for known deposits as well as geophysical forward modelling are beneficial
methods for defining the possibilities and constrains of new target prospecting.
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
Study Methodology and Results
Six of the known Zn/Cu deposits in the Häme belt were re-evaluated for their
petrophysical and geophysical signatures. The available data comprised GTK
low-altitude airborne data in addition to legacy ground geophysical survey data,
and in parts the petrophysical drill-hole logs from the archives of Outokumpu
Inc. Petrophysical data provide essential information on the target properties and
together with geological information can be used in estimating the suitability of
the target for various geophysical exploration methods. Consequently, some new
samples were taken from the drill cores of the deposits for complementary petrophysical measurements as part of the study (for further information, see Karell &
Leväniemi 2014).
For many of these deposits, although not all, petrophysical sampling indicated
that the ore properties do contrast with those of the host rock, suggesting that a
sufficiently massive metal deposit could be detected with applicable geophysical survey methods. However, interpretation of the survey data on the currently
known mineralization suffers in many cases from the characteristically thick
overburden of the region, and this, in combination with weak grades and small
dimensions, made the deposits challenging to detect with the geophysical methods employed.
The regional re-evaluation concentrated on the available one-frequency airborne electromagnetic (AEM) data and aeromagnetic data. AEM forward modelling indicated that in order to detect a conductive ore, the deposit would need
to be a rather massive conductor and also located at shallow depths with little
or no conductive overburden. Additionally, the aeroradiometric dataset ratio of
potassium to thorium was inspected mainly in the vicinity of the known mineralizations, as high values might relate to surficial hydrothermal alteration, which
is possibly related to mineralization (Dickson & Scott 1997). As a result of the
regional data re-evaluation, approximately a dozen new targets were identified
and prioritized. A few of them are currently being investigated with follow-up
surveys.
References
Babcock, R. C. 1996. History of exploration for volcanogenic massive sulfides in Wisconsin. In:
LaBerge, G. L. (ed.) Volcanogenic massive sulfide deposits of northern Wisconsin: A commemorative volume. Institute on Lake Superior Geology Proceedings, 42nd Annual Meeting
42 (2), 1–15.
Dickson, B. L. & Scott, K. M. 1997. Interpretation of aerial gamma-ray surveys – adding the geochemical factor. AGSO Journal of Australian Geology & Geophysics 17(2), 187–200.
Gibson, H. L., Allen, R. L., Riverin, G. & Lane, T. E. 2007. The VMS Model: Advances and
Application to Exploration Targeting. In: Milkereit, B. (ed.) Proceedings of Exploration
07: Fifth Decennial International Conference on Mining Exploration, 713–750.
Karell, F. & Leväniemi, H. 2014. VMS Deposits in the Häme Volcanic Belt – Petrophysical Data
to Supplement Geophysical Modelling. In: Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi,
M., Lahtinen, R. & Hölttä, P. (eds) Current Research: 2nd GTK Mineral Potential Workshop,
Kuopio, Finland, May 2014. Geological Survey of Finland, Report of Investigation 207. (this
volume)
Leväniemi, H. & Karell, F. 2013. Geophysical Indications of VMS Deposits in the Häme Volcanic
Belt. Geological Survey of Finland, archive report 152/2013. 64 p.
Morgan, L. A. 2012. Geophysical characteristics of volcanogenic massive sulphide deposits in volcanogenic massive sulphide occurrence model. U.S. Geological Survey Scientific Investigations
Report 2010-5070-C, chap. 7. 16 p.
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Fig. 1. The locations of known Zn-Cu mineralizations indicated on a topographic map of the Häme
region. Contains data from the National Land Survey of Finland Topographic Database 08/2012.
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
Preliminary results from new drillings and
geochemical studies oN the apatite deposits
in the Kortejärvi and Petäikkö-Suvantovaara
carbonatites, Pudasjärvi–Posio district,
Northern Finland
by
Panu Lintinen
Geological Survey of Finland, P.O. Box 96, FI-96101 Rovaniemi, Finland
E-mail: [email protected]
The Early Proterozoic Kortejärvi, Petäikkö-Suvantovaara and Laivajoki carbonatites are situated in the Pudasjärvi and Posio municipalities of northern Finland
(Fig. 1), where they intrude early Palaeoproterozoic mafic volcanic rocks along
a crustal-scale fault zone. The ca. 2.0 Ga carbonatites are strongly magnetic and
form highly strained bodies that are 20–60 m wide and 2–4 km long, according
to previous estimates from airborne magnetic data (Nykänen 1993, Nykänen et
al. 1997, Karhu et al. 2001, Sarapää et al. 2013).
The Kortejärvi and Laivajoki carbonatites were discovered and drilled in 1971–
1972 by Rautaruukki Co. The magnetic anomaly at Petäikkö-Suvantovaara between the Kortejärvi and Laivajoki intrusions was acknowledged at that time as a
probable carbonatite, but it was not tested by drilling (Nykänen et al. 1997). Since
2010, the Geological Survey of Finland (GTK) has investigated the carbonatites
and their surroundings with magnetic ground surveys and diamond drilling. The
aim of the investigations has been to locate new carbonatite intrusions within
the shear zone and to estimate the mineral (mainly P, REE and Zr) potential of
the carbonatites. The investigations have so far focused on the Kortejärvi and
Petäikkö-Suvantovaara intrusions. The existence of carbonatite in Petäikkö-Suvantovaara has been confirmed by diamond drilling.
The Kortejärvi carbonatite has been intersected with three new drilling profiles, and two additional profiles are scheduled to be drilled in February–March
2014 (Fig. 2). According to the new drill-core data, the Kortejärvi carbonatite is
30–35 m thick in the northern part and over 120 m thick in the central part of the
intrusion. The northern section consists of uniform and homogeneous carbonatite, but the thicker central section turned out to be more heterogeneous, with
abundant inclusions of mafic volcanic rocks and granitoid dykes. The carbonatite
in the Petäikkö-Suvantovaara intrusion was tectonically fragmented, generally
occurring as a system of 1–3-m-thick carbonatite dykes within the mafic volcanic
rocks, where the maximum thickness of the individual carbonatite dykes was
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<10 m. Alkaline rocks have not been detected in either of the intrusions and the
mafic volcanic country rocks are not fenitized.
According to whole-rock geochemistry, the Kortejärvi and Petäikkö-Suvantovaara carbonatites are magnesiocarbonatites, although a few samples are chemically very close to calciocarbonatites. Previous mineralogical studies have shown
that calcite carbonatites occur in Kortejärvi (Nykänen 1993). However, because
of the high magnetite contents, these rocks fall into the ferrocarbonatite group.
Some samples are classified as silicocarbonatites (SiO2 >20%), but this is either
due to inclusions of mafic volcanic material or bands of phlogopite rock, glimmerite, in the carbonatite.
Both the Kortejärvi and Petäikkö-Suvantovaara carbonatites are rich in apatite.
The average P2O5 content of all analysed samples from the Kortejärvi carbonatite
is 3.6%, and for the apatite-rich carbonatite (>2% P2O5, >70% of all carbonatite)
4.9%, with maximum contents of 8.1%. In Petäikkö-Suvantovaara, the average
P2O5 content of carbonatite is 4.7%, with a maximum of 9%. The P2O5 contents
of 5% and 9% correspond to apatite contents of 12% and 21%, respectively. An
enrichment test for apatite is currently under way at GTK Mintek. The total REE
contents of Kortejärvi and Petäikkö-Suvantovaara carbonatites are quite low, being on average 850 ppm (max 1400 ppm) in Kortejärvi and 1075 ppm (max 2000
ppm) in Petäikkö-Suvantovaara. Mineralogical studies have shown that the dominant REE minerals are monazite and allanite (Al-Ani & Sarapää 2012).
In early 2014, the two remaining profiles in the southern part of the intrusion
will be drilled, and after core logging, analysis and the enrichment tests, an evaluation of the apatite ore potential with resource estimation for the Kortejärvi carbonatite will be reported. In addition, more detailed petrological, petrographic
and ore geological features will be presented when all the required material and
data are available.
References
Al-Ani, T. & Sarapää, O. 2012. REE-rich accessory minerals in carbonatitic, alkaline, appinitic
and metasomatic-hydrothermal rocks, Central and Northern Finland. Geological Survey of
Finland, Report of Investigation 198, 17–21.
Bedrock of Finland − DigiKP. Digital map database [Electronic resource]. Espoo: Geological
Survey of Finland [accessed 30.01.2014]. Version 1.0.
Karhu, J. A. Mänttäri, I. & Huhma, H. 2001. Radiometric ages and isotope systematics of some
Finnish carbonatites. In: Gehör, S., Wall, F. & Liferovich, R. (eds) Formation, exploration and
exploitation of economic deposits associated with mantle carbon. EuroCarb Finland workshop. Programme and abstracts, vol 19, p 8.
Nykänen, J. 1993. Pudasjärven Kortejärven ja Posion Laivajoen proterotsooisten karbonatiittien
geologia, mineralogia ja geokemia. Unpublished M. Sc. Thesis, University of Oulu, Department of Geology, 60 pp. (in Finnish)
Nykänen, J., Laajoki, K. & Karhu, J. 1997. Geology and geochemistry of the early Proterozoic
Kortejarvi and Laivajoki carbonatites, central Fennoscandian Shield, Finland. Bulletin of the
Geological Society of Finland 69 (1−2), 5–30.
Sarapää, O., Al-Ani, T., Lahti, S. I., Lauri, L. S., Sarala, P., Torppa, A. & Kontinen, A. 2013. Rare
earth exploration potential in Finland. Journal of Geochemical Exploration 133, 25–41.
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
Fig. 1. Location of the Kortejärvi, Petäikkö-Suvantovaara and Laivajoki carbonatites. Geology after the Bedrock of Finland − DigiKP base (accessed 30.1.2014). Aeromagnetic grey-scale map in
the background. Contains data from the National Land Survey of Finland Topographic Database
08/2012.
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Fig. 2. Magnetic ground survey map of the Kortejärvi carbonatite intrusion showing the location
of the drill holes. The cross-sections of drilled holes are presented with lithologies. Note the scale
differences in the cross-sections. Contains data from the National Land Survey of Finland Topographic Database 08/2012.
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
Partition coefficient for nickel between
sulphide and silicate liquid: observations and
applications
by
Hannu V. Makkonen
Geological Survey of Finland, P.O. Box 1237, FI-70211 Kuopio, Finland
E-mail: [email protected]
INTRODUCTION
The partitioning of a trace or minor element between two phases can be described
by the Nernst partition coefficient. The Nernst Distribution Law determines the
relative distribution of a component that is soluble in two liquids, these liquids
being immiscible or miscible to a limited extent. Referring to the equilibria between sulphide melts and silicate melts, the Nernst partition coefficient Di for a
metal i is defined as (e.g. Naldrett 1989, 2011):
Di (sulphide melt/silicate melt) = isulphide melt/isilicate melt (wt%)
Nickel, copper, (cobalt) and PGE are highly chalcophile elements and will strongly partition into the sulphide melt segregating from silicate magma. The D value
can be experimentally determined by chilling crystallizing magmas and analysing
the composition of phenocrysts and host magmatic glass. Determination of the D
value can also be based on empirical observations. Metal contents in sulphides
and in their fresh host, e.g. in volcanic glass, are often used for D value determinations. Furthermore, in a magmatic sulphide ore, the ratio of the concentration of
a chalcophile element in the sulphide fraction to that in the silicate melt indicates
the D value (assuming that equilibrium existed between the sulphide and silicate
melts).
Experimental and observed
values for basaltic to andesitic magmas
vary between 231–1300 (compilation by Naldrett, 2011). Recently, Patten et al.
(2013) reported the D value to be 776 ± 98 from sulphide droplets and their
host, fresh mid-ocean-ridge basalt (MORB) glasses. Estimates for
in
komatiitic magma (after Naldrett 1989) were 175 at an MgO content of 19 wt%
and 100 at an MgO content of 27 wt%.
Extensive data have been collected from the Svecofennian nickel ores in Finland (e.g. Makkonen et al. 2003, Lamberg 2005), also enabling the determination
of D values. This study focused on observed
values from nickel deposits
within the Kotalahti Ni Belt and the use of the D values in ore modelling (e.g.
mass balance calculations). The
values were calculated from those nickelbearing intrusions for which sufficient data were available on both the nickel ore
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and the parental magma. A range of D values from 323 to 986 was obtained in 14
separate nickel deposits with an MgO content of 7.3 to 10.4 wt% in the parental
magma, when the arithmetic averages of the olivine composition (Fo, Ni) in each
deposit were used. Using the median values for the olivine composition, the D
values ranged from 310 to 1078. The results are within the range of experimental
and observed values from other studies. A negative correlation with the MgO
content of the parental magma was observed, consistently with the experimental
results, and could be described by a preliminary equation. An additional review
is, however, still needed to verify the correlation.
values are needed when comparing the nickel content of the sulphide
fraction of a magmatic nickel ore with the nickel content of the related parental
magma. The results of mass balance calculations by R factor modelling (Campbell
& Naldrett 1979) also largely depend on the D value used.
References
Campbell, I. H. & Naldrett, A. J. 1979. The influence of silicate:sulphide ratios on the geochemistry of magmatic sulphides. Economic Geology, 74, 1503–1505.
Lamberg, P. 2005. From genetic concepts to practice − lithogeochemical identification of Ni-Cu
mineralised intrusions and localisation of the ore. Geological Survey of Finland, Bulletin 402.
264 p.
Makkonen, H., Kontoniemi, O., Lempiäinen, R., Lestinen, P., Mursu, J. & Mäkinen, J. 2003.
Raahe-Laatokka-vyöhyke, nikkelin ja kullan etsintä-hankkeen (2108001) toiminta vuosina
1999-2003. Geological Survey of Finland, archive report M10.4/2003/5/10. 90 p. (in Finnish)
Naldrett, A. J. 1989. Magmatic sulphide deposits. Oxford monographs on geology and geophysics,
no. 14. New York: Oxford University Press. 186 p.
Naldrett, A. J. 2011. Fundamentals of Magmatic Sulphide Deposits. In: Li, C. & Ripley, E. M. (eds)
Magmatic Ni-Cu and PGE deposits: Geology, Geochemistry, and Genesis. Society of Economic Geologists, Reviews in Economic Geology v. 17, 1–50.
Patten, C., Barnes, S.-J., Mathetz, E. A. & Jenner, F. E. 2013. Partition coefficients of chalcophile
elements between sulphide and silicate melts and the early crystallisation history of sulphide
liquid: LA-ICP-MS analysis of MORB sulphide droplets. Chemical Geology 358, 170–188.
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petrophysical properties characterizing
the formations of the hattu schist belt
by
Satu Mertanen and Fredrik Karell
Geological Survey of Finland, P.O. Box 96, FI-02151 Espoo, Finland
E-mail: [email protected]
PURPOSE OF INVESTIGATION AND METHODS
Petrophysical studies in the Archaean Hattu schist belt, focusing on the Pampalo
deposit, have been carried out in the geophysical laboratory of GTK in Espoo in
order to delineate physical differences between altered felsic feldspar porphyry
and unaltered tonalite. Oriented samples were taken from several sites and rock
types in the Pampalo deposit, roughly following a profile from altered felsic felspar porphyry to unaltered tonalite and to mafic schists and greenstones. In addition to the Pampalo deposit, samples were taken from the Kuittila and Viluvaara
tonalite and from the Kartitsa granodiorite (Fig. 1). The measured petrophysical
parameters were density, magnetic susceptibility and its anisotropy (AMS) and
remanent magnetization, coupled with rock magnetic studies. Palaeomagnetic
multicomponent analysis was also carried out in order to determine whether
Proterozoic overprinting on Archaean remanent magnetization can be isolated.
These studies were, however, restricted due to the lack of GTK’s SQUID magnetometer, and only small proportion of the samples was therefore measured at
the University of Helsinki.
RESULTS
The hydrothermal alteration of rock is typically seen as lowered magnetization
values when primary ferromagnetic minerals alter to less magnetic or paramagnetic minerals. In this process, the density may also decrease. In the Pampalo deposit, the alteration is most clearly seen as much lower susceptibility values of the
felsic feldspar porphyry compared with the unaltered tonalite. Densities are about
the same in both rock types. In both formations, the main magnetic mineral is
magnetite. The altered feldspar porphyry and unaltered tonalite are separated by
a zone of skarn and talc-chlorite schist, thought to have formed due to fluid flow
related to a strong shearing. In the tonalite close to the skarn, the susceptibility values have clearly increased. Likewise, the altered feldspar porphyry close
to the skarn contains mainly pyrrhotite instead of magnetite, both suggesting
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that shearing and fluid flow postdate the emplacement of tonalite and the earlier
alteration of feldspar porphyry.
The overall magnetizations (susceptibility and remanence) of the unaltered tonalite increase towards the Pampalo open pit, where the rock types vary from
mafic schist to greenstone and strongly deformed tonalite. In these rocks, the
magnetizations are relatively low, suggesting later alteration when pyrrhotite has
formed at the expense of magnetite.
The Kuittila tonalite has similar petrophysical properties to the Pampalo altered felsic feldspar porphyry. The Viluvaara tonalite and the Kartitsa granodiorite also have low paramagnetic susceptibilities, as in the Pampalo felsic feldspar porphyry, suggesting that these formations have experienced corresponding
alteration.
AMS data from the Pampalo deposit reveal that the linear and planar magnetic
fabric elements are generally parallel to the rock fabric elements. The shapes of
the AMS ellipsoids of all samples are predominantly oblate, which indicates a
stronger planar fabric throughout the study area. The anisotropy degree of mafic
schists and greenstones is generally lower than in the tonalite and feldspar porphyry, which have anisotropy degrees typical of deformed rocks.
The strong shearing of the Hattu schist belt has most probably destroyed the
original ca. 2.7 Ga primary remanent magnetization. Likewise, because there are
no signs of a steep upwards-pointing Archaean remanence that was previously
isolated in the Koitere granitoids, slightly NW from the present study area (Mertanen and Korhonen 2011), this remanence was also destroyed in later shearing
and deformation. In some of the most highly magnetized samples from Kartitsa,
Viluvaara and Kuittila granitoids, remanence of a Svecofennian age (ca. 1.9–1.8
Ga) was isolated.
References
Mertanen, S. & Korhonen, F. 2011. Paleomagnetic constraints on an Archean-Paleoproterozoic
Superior-Karelia connection: new evidence from Archean Karelia. Precambrian Research 186
(1–4), 193–204.
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
Fig. 1. Generalized geological map of the Hattu schist belt (black square in the inset map) showing
the locations of study areas.
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Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014
POSSIBLE ORE POTENTIAL OF
THE JYVÄSKYLÄ−KANGASNIEMI AREA
by
Perttu Mikkola, Aimo Hartikainen and Sami Niemi
Geological Survey of Finland, P.O. Box 1237, FI-70211 Kuopio, Finland
E-mail: [email protected]
The southeastern corner of the Central Finland Granitoid Complex has traditionally been regarded as having an uninteresting ore potential. However, even in preexisting data, several indications were evident. For example, a closer examination
of the areal till geochemistry revealed anomalous gold concentrations from the
Makkola area (Fig. 1). Additional geological sampling confirmed their existence
and also the presence of alteration processes, such as sericitization within the
known volcanic sequence. Diamond drilling, mainly carried out to update lithological information, revealed high concentrations of iron sulphides in practically
all drilled holes, and anomalous gold concentrations and variably intense chlorite
and sericite alteration of intermediate volcanic rocks in two profiles. Although
the highest measured gold concentrations were <150 ppb and as such do not warrant immediate further studies, together with the observed rock types and their
alterations they indicate that the existence of gold mineralization(s) in the Makkola area cannot be regarded as impossible.
Hiekkapohja, situated northeast of Jyväskylä in a granitoid-dominated area,
hosts several high-grade boulders and small mineralizations with variable combinations of Zn, Cu, Pb, Ag, Au and Mo. These indications were briefly investigated
by the Geological Survey of Finland at the beginning of the 1980s. An interesting feature of these known indications is their close spatial correlation with an
intrusion phase that is characterized by a negative magnetic anomaly and a weak
positive gravity anomaly (Fig. 2). Although even the basic fieldwork within this 8
x 4 km area is still very much in progress, the known mineralized samples appear
to form a concentric structure: Mo±Cu+W+Ag, Ag+Zn+Pb, As±Au, and Au+Te
from the centre outwards. Such a combination of clustered mineralized samples,
a negative magnetic anomaly and a positive gravity anomaly is so far unknown
from other parts of the Central Finland Granitoid Complex. Drilling in Huikko
(inset in Fig. 1) encountered a 3 x 1 km gabbro resembling the Ni-critical gabbros
of the Kotalahti and Vammala belts. As basic bedrock mapping carried out in the
surrounding area has demonstrated the presence of a potential external sulphur
source, i.e. migmatized paragneisses, the potential area for liquid immiscibility
type Ni mineralizations has widened.
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
Fig. 1. Geological map of the Makkola area and locations of samples with anomalous gold concentrations (e.g. >10 ppb). Bedrock map modified from the national digital bedrock map. Contains
data from the National Land Survey of Finland Topographic Database 08/2012.
Fig. 2. Ore mineralized outcrops, mineralization zones and glacial boulders from the Hiekkapohja
area on an aeromagnetic map. Contains data from the National Land Survey of Finland Topographic Database 08/2012.
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observations on Occurrences of awaruite in
Lapland
by
Ferenc Molnár1, Pekka Nurmi1, Tuomo Törmänen2 and Jukka Laukkanen3
1 Geological
Survey of Finland, P.O. Box 96, FI-02151, Espoo, Finland
Survey of Finland, P.O. Box 77, FI-96101 Rovaniemi, Finland
3 Geological Survey of Finland, Tutkijankatu 1, FI-83500 Outokumpu, Finland
E-mail: [email protected]
2 Geological
Awaruite is a naturally occurring stainless steel nickel-iron alloy with an average
Ni content of 72.4 wt%. Most commonly, it is found as an accessory mineral in
serpentinized cumulate units of ophiolite complexes (Filippidis 1985). Awaruite
is a cubic mineral with saturation magnetization of 120 Am2/kg at room temperature (magnetite: 90–92 Am2/kg). The density of awaruite is between 7.8 and
8.2 g/cm3. Awaruite shows a silver white colour with higher reflectance than pyrite in polished sections and it is a relatively soft mineral with Mohs hardness
between 5 and 6 and Vickers hardness from 265 to 380 kg/mm2. Occurrences of
awaruite had been considered as mineralogical curiosities until the discovery of
potentially mineable awaruite enrichments in serpentinized harzburgite, dunite
and peridotite of obducted ophiolite complexes of Palaeozoic and Mesozoic age
in British Columbia, Canada (Lovén & Meriläinen 2011). The economic interest
in this mineral is that a substantial reduction in the environmental impact and
cost of stainless steel production can be achieved by the direct use of awaruite
concentrate in steel mills.
Occurrences of awaruite in Lapland are reported in Papunen and Idman (1982).
However, details of exact localities are not mentioned. The database of Papunen’s
original report on the nickel potential of Lapland (Papunen 1976) lists occurrences of awaruite at the following localities: Tarpomapää, Allivuotso-Ivalon Matti
and Kuusi-Lomavaara. Our SEM-EDS-supported petrographic work confirmed
the occurrence of awaruite as an early product of alteration of Ni-bearing olivine
to magnetite and serpentine minerals at the Kuusi-Lomavaara locality (Fig. 1A):
the texture and paragenesis correspond to the most common type of awaruite
formation process (Klein & Bach 2009). Pentlandite partially replaces the early
magnetite-awaruite association, suggesting that a weak sulphurization overprinted awaruite formation at the Kuusi-Lomavaara locality (Fig. 1a).
Taking into account the characteristics of the awaruite-bearing rocks at KuusiLomavaara and other localities worldwide, we selected further samples of serpentinite from Lapland to check for the presence of awaruite according to the
following criteria: no carbonate-talc-chlorite alteration, a sulphur content of less
than 0.1 wt%, a relatively high (>0.05 wt%) nickel content and relatively high
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(>4000) magnetic susceptibility values. Polished thin sections of samples from
ten serpentinite occurrences of Lapland, which were available from the work reported in Papunen (1976) and from other Ni(-Cu-PGE) exploration projects of
GTK, were subjected to SEM-EDS-supported petrography and MLA studies. Our
work resulted in the recognition of two localities where the presence of awaruite
was detected in more than 10% of thin sections that were subjected to detailed
studies.
Serpentinite forms several small lensoid bodies in the host gneiss in an approximately 700-m-long NE–SW-oriented zone at Pahtajärvi in northern Lapland
(Marmo 1960). The serpentinite bodies are locally altered to soapstone and also
contain 1–2-cm-thick subparallel magnetite-antigorite veinlets in some places.
The major mass of serpentinite without carbonate-talk alteration and magnetite
veining consists of antigorite and chrysotile, with a few needles of tremolite and
remnants of olivine. Awaruite partially or almost completely replaces round-irregular grains of millerite, which are randomly disseminated in serpentine minerals. Ni-rich magnetite replaces awaruite along grain boundaries (Fig. 1b). Millerite also encloses inclusions of pentlandite, heazlewoodite and gersdorffite. The
most typical grain size of awaruite is between 10 and 50 microns, but its grain size
is less than 10 microns in sections with low awaruite contents.
The Värriöjoki intrusion forms a large ellipsoid body of approximately 4 km x 2
km in an Archaean gneiss-amphibole-chlorite schist complex in eastern Lapland.
The major mass of the intrusion consists of relatively fresh dunite with a serpentinized peridotite and pyroxenite zone a few tens of metres thick along its contacts
with the country rocks. Awaruite mostly occurs in an approximately 1000-mlong narrow zone of metaperidote along the southern margin of the intrusion.
Awaruite exclusively forms thin rims along the perimeters of 50–100-micron
composite pentlandite–Ni-rich magnetite aggregates (Fig. 1c). Awaruite rims occasionally also contain millerite and nickeline grains (Fig. 1d). The textural and
mineralogical characteristics of awaruite occurrences are consistent with the formation of awaruite by desulphurization of primary rock, forming pentlandite and
hydrothermal millerite at Värriöjoki and Pahtajärvi, respectively.
The preliminary results presented here are insufficient for outlining the economic potential of awaruite in Lapland. However, our observations suggest that
awaruite is not an uncommon mineral in some serpentinite bodies in Lapland,
and it is expected that new occurrences will be discovered by refinement of targeting criteria on the basis of further mineralogical-textural, geochemical and
petrophysical studies.
References
Filippidis, A. 1985. Formation of awaruite in the system Ni-Fe-Mg-Si-O-H-S and olivine hydration with NaOH solutions, an experimental study. Economic Geology, 80, 1974–1980.
Klein, F. & Bach, W. 2009. Fe-Ni-Co-O-S phase relations in peridotite-seawater interactions.
Journal of Petrology 50, 37–59.
Lovén, P. & Meriläinen, M. 2011. Mineral resource and ore reserve estimation of the Länttä and
Outovesi lithium deposits. Outotec OY. Unpublished report.
Marmo, V. 1960. Serpentinite of Pahta-autsi, Finnish Lapland. Geologinen Tutkimuslaitos,
Bulletin de la Commission Géologique de Finlande 188, 67–76.
Papunen, H. 1976. Lapin nikkeliprojekti. Department of Geology and Mineralogy, University
of Turku, Report PMST-P11/2-1976. (in Finnish)
Papunen, H. & Idman, H. 1982. Ultramafic rocks and related ore minerals of Lapland, northern
Finland. In: Amstutz, G. C. and others (eds) Ore genesis the state of the art. Berlin: SpringerVerlag, p. 374–386.
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Fig. 1. Textural varieties of awaruite occurrences in serpentinites in Lapland. Mineral abbreviations: Awr – awaruite; Pn – pentlandite; Mlr – millerite; Nk – nickeline; Mag – magnetite; Srp
– serpentine mineral. (a) Awaruite corroded by magnetite and pentlandite, Kuusi-Lomavaara locality. (b) Awaruite replacing millerite and a magnetite rim on awaruite, Pahtajärvi locality; (c)
Awaruite rims on a pentlandite-magnetite aggregate, Värriöjoki locality. (d) Millerite and awaruite
replacing a pentlandite-magnetite aggregate and nickeline in the awaruite rim, Värriöjoki locality.
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
Boron and sulPHur isotopes reveal THE role
OF magmatic fluids in THE formation of
orogenic gold deposits in the Archaean
Hattu schist Belt, eastern Finland
by
Ferenc Molnár1, Irmeli Mänttäri1, Asko Käpyaho1, Hugh O´Brien1, Yann Lahaye1,
Peter Sorjonen-Ward2, Martin Whitehouse3 and Grigorios Sakellaris4
1 Geological
Survey of Finland, P.O. Box 96, FI-02151, Espoo, Finland
Survey of Finland, P.O. Box 1237, FI-70211 Kuopio, Finland
3 NORDSIM, Natural History Museum, Stockholm, Sweden
4 Endomines Oy, Pampalontie 11, FI-82967 Hattu, Finland
E-mail: [email protected]
2 Geological
The sources of fluids and metals, as well as the role of magmatic processes in the
formation of orogenic gold deposits are highly debated questions of ore geology
research. These geological features are critical in defining models for mineral
systems with orogenic gold deposits, and thus highly influence concepts and
parameters applied to the evaluation of mineral potential in greenstone belts.
In situ secondary ion mass spectrometer (SIMS) and laser ablation multicollector inductively coupled mass spectrometer (LA-MC-ICPMS) analyses of boron
and sulphur isotope ratios in minerals provide powerful approaches to study
the sources of fluids in orogenic gold deposits, because these isotopes highly
fractionate during geological processes and the high spatial resolution of spot
analyses supports the recognition of local variations in the origin and composition of fluids.
The Hattu schist belt (HSB) consists of felsic, locally mafic and ultramafic volcanic as well as epiclastic units of around 2.75 Ga in age. These units are aligned
between tonalite-trondhjemite-granodiorite (TTG) and leucogranite intrusions
of similar ages (2.75–2.70 Ga; Sorjonen-Ward & Korsakova 2012). Lower amphibolite facies metamorphism at pressures of 4–6 kbars and temperatures of 500–
600 °C affected rocks of the HSB between ca. 2.74–2.63 Ga (O’Brien et al. 1993).
Emplacement of NW-trending gabbroic dykes took place from 2.3 to 2.0 Ga in
relation to the Palaeoproterozoic rifting of the Archaean craton. Between ca. 1.85
and 1.7 Ga, tectonothermal processes affected the region due to overthrusting
of an up to 5–6-km-thick Svecofennian nappe complex (Kontinen et al. 1992,
O’Brien et al. 1993, Käpyaho et al. 2014). The nappe complex was completely
eroded away during the Neoproterozoic exhumation of the Archaean basement.
In the HSB, several orogenic gold deposits occur along N–S and NE–SW-trending shear zones that cross-cut folded epiclastic and volcanogenic units (Sorjonen-
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Ward 1993). The general characteristics of gold deposits in the HSB are largely
comparable with orogenic gold systems formed on several Archaean cratons at
around 2.7 Ga. However, it appears that their formation in the HSB took place
under peak metamorphic conditions (Sorjonen-Ward 1993).
Tourmaline (TUR) is a rock forming mineral in the Naarva leucogranite
and common mineral in magmatic-hydrothermal quartz veins of the Kuittila
pluton. In the felsic dykes, as well as in the volcanoclastic host rocks of the
gold deposits, TUR occurs in deformed quartz veins and in disseminations.
In pelitic bands of turbiditic metasediments, it forms fine-grained masses. All
types of TUR belong to the alkali and hydroxy group with variable, but usually low Ca contents and low X-site vacancies with transitional compositions
between schorl/dravite and uvite. Compositional data also suggest more oxidative conditions for the crystallization of TUR in felsic dykes and some volcanoclastic host rocks units in comparison to metasedimentary units. δ11BTUR
data (mean ± stdev.) for samples from leucogranite, magmatic-hydrothermal
veins and felsic dykes are between -12 and -17.4‰ (Fig. 1), suggesting a δ11Bfluid
between -10 and -15‰ (500 ºC, 200 MPa; Meyer et al. 2008), which is typical
for granite-related magmatic fluids. δ11BTUR data from the volcanoclastic and
metasedimentary host rocks of gold deposits range from -16.2 to -22.1‰ (Fig.
1), corresponding to δ11Bfluid between -13 and -20‰ (400–500 ºC, 200 MPa).
This observation suggests that a fluid with a light boron isotope composition
admixed with the magmatic fluids in the volcanoclastic and metasedimentary
host rock of gold deposits.
There is a positive correlation between sulphide δ34S and δ11BTUR data according to the host rock lithology in the Pampalo mine (Fig. 2). δ34S data for Py and
Cpy are between 0 and -4‰ in most samples from felsic dykes (but two samples
have δ34S at round -6‰), whereas these minerals provided δ34S values of -3 to
-8‰ in samples from the volcanoclastic host rocks. The lighter δ34S values may
suggest more oxidative or lower temperature conditions in the volcanoclastic
host rocks in comparison to felsic dykes, but this is not supported by the mineral
assemblages and mineral chemistry of tourmaline. Thus, we suggest that the observed differences in sulphur isotope compositions reflect mixing of fluids from
two different sources: dominant magmatic fluids related to the igneous activity
producing the felsic dykes and fluids with a lighter sulphur isotope composition
related to the volcanoclastic host rock units.
References
Käpyaho, A., Molnár, F., Mänttäri, I. & Whitehouse, M. 2014. Preliminary results of
U-Pb age determinations from the Pampalo gold mine and the Hosko gold deposit, Hattu Schist Belt, eastern Finland In: Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds) Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014. Geological Survey of Finland, Report of
Investigation 207. (this volume)
Kontinen, A., Paavola, J. & Lukkarinen, H. 1992. K-Ar ages of hornblende and biotite from
late Archean rocks of eastern Finland – interpretation and discussion of tectonic implications.
Geological Survey of Finland, Bulletin 365, p. 31.
Meyer, C., Wunder, B., Meixner, A., Romer, R. L. & Heinrich, W. 2008. Boron-isotope fractionation between tourmaline and fluid: an experimental re-investigation. Mineralium Deposita
156, 259–267.
O’Brien, H. E., Huhma, H. & Sorjonen-Ward, P. 1993. Petrogenesis of the late Archean Hattu
schist belt, Ilomantsi, eastern Finland. In: Nurmi, P. A. & Sorjonen-Ward, P. (eds) Geological
development, gold mineralization and exploration methods in the late Archean Hattu schist
belt, Ilomantsi, eastern Finland. Geological Survey of Finland, Special Paper 17, 133–146.
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
Sorjonen-Ward, P. 1993. An overview of structural evolution and lithic units within and intruding the late Archean Hattu schist belt, Ilomantsi, eastern Finland. In: Nurmi, P. A. & SorjonenWard, P. (eds) Geological development, gold mineralization and exploration methods in
the late Archean Hattu schist belt, Ilomantsi, eastern Finland. Geological Survey of Finland,
Special Paper 17, 193–232.
Sorjonen-Ward, P. & Korsakova, M. 2012. Ilomantsi Au, Mo. In: Eilu, P. (ed.) Mineral deposits
and metallogeny of Fennoscandia. Geological Survey of Finland, Special Paper 53, 255–260.
Fig. 1. Boron isotope data for tourmaline from different host rocks in the Hattu schist belt.
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Fig. 2. Boron isotope data for tourmaline (TUR) and sulphur isotope data for pyrite (Py) and chalcopyrite (Cpy) from the Pampalo mine, Hattu schist belt.
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
Layman’s sample practice
by
Jari Nenonen and Satu Hietala
Geological Survey of Finland, P.O. Box 1237, FI-70211 Kuopio, Finland
E-mail: [email protected]
The Geological Survey of Finland (GTK) has a unique method for collecting information from its bedrock: a layman’s sample practise. The method is used to
collect valuable information on ore potential areas, industrial minerals and dimensional stone deposits. Even most of the lapidary material and gemstones have
been found by layman prospectors.
The layman’s sample practice already started in the 1700s and has continued
until this day. Most of the ore mines in Finland were originally discovered on account of a layman’s sample (Fig. 1). Five of these mines are currently operating.
For example, the Outokumpu copper mother lode and the massive Kemi chromite deposit were discovered by curious amateurs.
GTK invites amateur prospectors to deliver mineral, soil and rock samples.
There is no postal charge for sending a sample, and in return, senders receive a
copy of GTK’s sample analysis. Information about the sender and sample data are
recorded in GTK’s databases.
If the sample is promising, the person automatically participates in GTK’s national ore exploration contest. Personal prizes for finding the most promising
samples run as high as €4,000. Each year, prospectors find samples that lead to
further investigations.
The Layman’s Sample Office at GTK receives nearly 6,500 rock samples per
year. About 30% of these samples are subjected to further analysis and about 150
samples result in on-site investigations (Figs. 2 and 3). Of these, one sample in ten
leads to drilling investigations (Hietala & Nenonen 2012, 2014).
Rock samples sent by amateur prospectors provide GTK with valuable geological information, and at the same time the sender’s knowledge of rocks and
minerals increases. Each sample sent promotes the socially important work of
raw material exploration. In the best case, a layman’s sample may even lead to new
industry and jobs.
The Layman’s Sample Office also answers geology-related questions from the
general public and provides competent and up-to-date information on the importance of raw materials to society and our everyday lives.
Searching for and collecting rocks and minerals is an excellent outdoor hobby. It is possible to get to know the mineral kingdom through various types of
outdoor activities. Rocks and natural geological formations are great themes for
nature excursions for all age groups.
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References
Hietala, S. & Nenonen, J. 2012. Kansannäytetoiminnan raportti 2011. Geological Survey of
Finland, archive report 72/2012. 34 p. (in Finnish)
Hietala, S. & Nenonen, J. 2014. Kansannäytetoiminnan raportti 2012–2013. Geological Survey of
Finland, archive report 42/2014. 91 p. (in Finnish)
Fig. 1. Twenty-seven of the ore mines in Finland were discovered on account of a layman’s sample.
Currently, five of these mines are still operating.
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
Fig. 2. Working in the Layman’s Sample Office at GTK.
Fig. 3. Checking an analysed rock sample in the field.
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revision of stratigraphic units in northern
finland
by
Mikko Nironen1, Raimo Lahtinen1, Hannu Huhma1, Jouni Luukas2 and
Tuomo Manninen3
1 Geological
Survey of Finland, P.O. Box 96, FI-02151 Espoo, Finland
Survey of Finland, P.O Box 1237, FI-70211 Kuopio, Finland
3 Geological Survey of Finland, P.O. Box 77, FI-96101 Rovaniemi, Finland
E-mail: [email protected]
2 Geological
Background
Stratigraphic units in the GTK Geodatabase for northern Finland are mainly
based on Lehtonen et al. (1998). They divided the Proterozoic supracrustal rocks
in central Lapland into lithostratigraphic units, whereas the Archaean gneisses
and plutonic rocks were divided into lithodemic units. Although the appended
map includes thrusts and faults, an explanation for these structures is missing.
Metamorphic mapping of central Lapland (Hölttä et al. 2007) revealed abrupt
lateral changes in the degree of metamorphism. These changes, as well as the interpretation of the reflection seismic FIRE 4 profile (Patison et al. 2006) indicate
important tectonic breaks in central Lapland.
Planning of the GTK Geodatabase included the storing of bedrock geological
data in a scale-less database (Bedrock of Finland − DigiKP), as well as the production of databases at the scales 1:200 000 (DigiKP200) and 1:1 000 000 (1:1M;
DigiKP1M). As a consequence, a structural layer, mainly based on low altitude
aerogeophysical data, was made over Finland at the scale 1:1M. An interpretation
of structural evolution in central Lapland attempted to take into account the tectonic breaks in central Lapland indicated by metamorphic and seismic studies, as
well a structural study that invoked large lateral displacements (Evins & Laajoki
2002).
The two other areas in northern Finland dominated by supracrustal rocks,
the Kuusamo and Peräpohja belts, have also been divided into lithostratigraphic
units by Silvennoinen (1972) and Perttunen (1985), respectively. Interpretation of
structural evolution was carried out for these two areas.
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
Need for reinterpretation of stratigraphic units in
northern Finland
In addition to the units presented by Lehtonen et al. (1998), new stratigraphic
units were defined in the first version of the GTK Geodatabase, some of these ad
hoc. Interpretation of the tectonic setting based on geochemical data (Hanski &
Huhma 2005), structural interpretation and unpublished age data led to a need
to re-evaluate the distribution of units in central Lapland, and to assess whether
some of the present lithostratigraphic units should rather be considered as lithodemic.
Similarly, a recent stratigraphic study (Kyläkoski et al. 2012) and structural interpretation, as well as new published (Hanski et al. 2005) and unpublished age
data on the Peräpohja belt led to the reorganization and renaming of lithostratigraphic units. These units are correlated with units in the central Lapland, Kuusamo and Kainuu belts.
References
Bedrock of Finland − DigiKP. Digital map database [Electronic resource]. Espoo: Geological
Survey of Finland [referred 30.01.2014]. Version 1.0.
Evins, P. M. & Laajoki, K. 2002. Early Proterozoic nappe formation: an example from Sodankylä,
Finland, Northern Baltic Shield. Geological Magazine 139, 73–87.
Hanski, E. & Huhma, H. 2005. Central Lapland greenstone belt. In: Lehtinen, M., Nurmi, P. A. &
Rämö, O. T. (eds) Precambrian Geology of Finland – Key to the Evolution of the Fennoscandian Shield. Amsterdam: Elsevier, 139–194.
Hanski, E., Huhma, H. & Perttunen, V. 2005. SIMS U-Pb, Sm-Nd isotope and geochemical study
of an arkosite-amphibolite suite, Peräpohja Schist Belt: evidence for ca. 1.98 Ga A-type felsic
magmatism in northern Finland. Bulletin of the Geological Society of Finland 77, 5–29.
Hölttä, P., Väisänen, M., Väänänen, J. & Manninen, T. 2007. Paleoproterozoic metamorphism and
deformation in Central Lapland, Finland. In: Ojala, V. J. (ed.) Gold in the Central Lapland Greenstone Belt, Finland. Geological Survey of Finland, Special Paper 44, 7–56.
Kyläkoski, M., Hanski, E. & Huhma, H. 2012. The Petäjäskoski Formation, a new lithostratigraphic
unit in the Paleoproterozoic Peräpohja Belt, northern Finland. Bulletin of the Geological Society
of Finland 84, 85–120.
Lehtonen, M., Airo, M-L., Eilu, P., Hanski, E., Kortelainen, V., Lanne, E., Manninen, T., Rastas, P.,
Räsänen J. & Virransalo, P. 1998. Kittilän vihreäkivialueen geologia. Lapin vulkaniittiprojektin
raportti. Summary: The stratigraphy, petrology and geochemistry of the Kittilä greenstone area,
northern Finland. A report of the Lapland Volcanite Project. Geological Survey of Finland, Report of Investigation 140. 144 p. (in Finnish)
Patison, N. L., Korja, A., Lahtinen, R., Ojala, V. J. & FIRE Working Group 2006. FIRE seismic
reflection profiles 4, 4A and 4B: insights into the crustal structure of northern Finland from
Ranua to Näätämö. In: Kukkonen, I. T. & Lahtinen, R. (eds) Finnish Reflection Experiment
FIRE 2001−2005. Geological Survey of Finland, Special Paper 43, 161–222.
Perttunen, V. 1985. On the Proterozoic stratigraphy and exogenic evolution of the Peräpohja area,
Finland. Geological Survey of Finland, Bulletin 331, 131–142.
Silvennoinen, A. 1972. On the stratigraphic and structural geology of the Rukatunturi area,
northeastern Finland. Geological Survey of Finland, Bulletin 257. 48 p.
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Biogeochemical signatures in common
juniper: gold and REE exploration in Finnish
Lapland
by
Paavo Närhi, Maarit Middleton and Raimo Sutinen
Geological Survey of Finland, P.O. Box 77, FI-96101 Rovaniemi, Finland
E-mail: [email protected]
Biogeochemical exploration involves chemical analyses of soil organic matter and
plant species, and has been extensively used in Canada, Russia, and more recently
in Australia (e.g. Lintern et al. 2013). In Finland, a few plant species have been
investigated for rare earth element (REE) and Au concentrations (Erämetsä and
Yliruokanen 1971, Yliruokanen 1975, Pulkkinen et al. 1989, Närhi et al. 2013).
Plant roots penetrate soil horizons, have access to weathered or fractured bedrock
and associated groundwater, and accumulate elements in their organs. Therefore,
plants containing anomalous concentrations of certain elements can be used as
indicators of mineralization. In trees and shrubs, metals exceeding the metabolic
needs are transported to bark, leaves and twigs.
The Mäkärärova study site is located in the Tanaelv Complex, in the municipality of Sodankylä, Finland. The main bedrock structure is a NNW-trending shear
zone that comprises parallel non-continuous hydrothermal Au-rich hematitequartz veins in conjunction with deeply weathered zones (Sarapää & Sarala
2013). Sampling transects of 270 sites were conducted across the shear zone.
Along transects, common juniper (Juniperus communis) twigs including needles,
B-horizon soil and saprolite were sampled, soil dielectric permittivity, electrical
conductivity and pH were measured, and coverages of plant species were estimated. Samples were digested with aqua regia and HF-HClO4 and element concentrations determined with ICP-MS. Au concentrations were determined with
GFAAS after aqua regia digestion and preconcentration with Hg.
The maximum Au concentrations in common juniper twigs (5 ppb) at
Mäkärärova were low compared to those (70 ppb) observed by Pulkkinen et al.
(1989) in the area of the present Pahtavaara gold mine, and those (54 ppb) obtained by Närhi et al. (2013) in the Suurikuusikko shear zone. However, the highest gold concentrations in the common juniper twigs spatially coincide with Aurich hematite-quartz veins in the bedrock, indicating that the chemical analysis of
common juniper is a feasible biogeochemical exploration method for gold.
Concentrations of REEs in common juniper twigs were high in the area where
juniper growth was restricted, as evidenced by low tissue nutrient concentrations,
and did not spatially coincide with the saprolite REE anomalies. The restricted
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annual growth indicates that REE-rich twigs represented more years of growth
compared to other same-sized twig samples. The results suggest that common
juniper accumulates REEs over years, and in biogeochemical sampling the twig
age (instead of size) should therefore be kept constant.
References
Erämetsä, O. & Yliruokanen, I. 1971. The rare earths in lichens and mosses. Suomen Kemistilehti
B44, 121–128.
Lintern, M., Anand, R., Ryan, C. & Paterson, D. 2013. Natural gold particles in Eucalyptus leaves
and their relevance to exploration for buried gold deposits. [Electronic resource] Nature Communications 4. Available at: http://www.nature.com/ncomms/2013/131022/ncomms3614/full/
ncomms3614.html
Närhi, P., Middleton, M. & Sutinen, R. 2013. Gold prospectivity of common juniper and Norway
spruce in Suurikuusikko shear zone, Finnish Lapland. Journal of Geochemical Exploration
128, 80–87.
Pulkkinen, E., Räisänen, M.-L. & Ukonmaanaho, L. 1989. Geobotanical and biogeochemical
exploration for gold in the Sattasvaara volcanic complex, Finnish Lapland. Journal of Geochemical Exploration 32, 223–230.
Sarapää, O. & Sarala, P. 2013. Rare earth element and gold exploration in glaciated terrain: example from the Mäkärä area, northern Finland. Geochemistry: Exploration, Environment,
Analysis 13, 131–143.
Yliruokanen, I. 1975. Uranium, thorium, lead, lanthanoids and yttrium in some plants growing
on granitic and radioactive rocks. Bulletin of the Geological Society of Finland 47, 71–78.
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Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014
Finland Geosciences Laboratory (SGL)
– Analytical Facilities Update
by
Hugh O’Brien, Yann Lahaye and Bo Johanson
Geological Survey of Finland, P.O. Box 96, FI-02151, Espoo, Finland
E-mail: [email protected]
The original SIGL (Suomen isotooppigeotieteen laboratorio), housed at the Research Laboratory in the GTK Espoo office, was commissioned in early 2008, and
consisted of a Nu InstrumentsTM multi-collector ICPMS equipped with a New
Wave solid state deep UV (193 nm wavelength) laser (for analysis of isotopic
systems in solids) and a desolvating nebulizer (for analysis of isotopic systems in
liquids). In December 2011, an additional and more robust and powerful deep
UV excimer laser built by Photon MachinesTM was added to the facility. Reported here are the changes at the end of 2013, when the facility was significantly
expanded by the addition of an FE-SEM and an HR-ICPMS. The facility now
provides the capabilities for researchers in Finland to image and analyse very
fine particles down to a few nanometres in size and to analyse elemental concentrations down to ppq levels (solutions) and ppt levels (solids). As a consequence
of these new capabilities, and with the limitation for only isotope work removed,
the laboratory has been renamed SGL (Suomen geotieteen laboratorio) to better
reflect present capabilities that span the needs for nearly all the geosciences. SGL
continues to play an important role in driving collaboration between the geology
departments of Finnish universities and GTK.
The Nu InstrumentsTM AttoM High Resolution ICP-MS (Fig. 1) can be run at
resolutions from 300 to over 10,000. However, for most applications, the AttoM
will be run at the lower end of the resolution range, where it produces flat-topped
peaks (Fig. 2). This allows for greater accuracy during peak jumping mode, which
is necessary, for example, to properly analyse transient signals produced by laser
ablation. Along with two new analytical software packages, Iolite and Glitter, the
AttoM will generate new fields of applications by its ability to perform trace element fingerprinting and elemental mapping by laser ablation, particularly useful
for mineral exploration. Additionally, we are currently working on moving all
laser ablation U-Pb analytical work (zircon, monazite, titanite, perovskite) to the
AttoM, thereby freeing more time on the multicollector for such analytical jobs as
Cu, Pb, S, Sr isotopes in minerals by laser (Lahaye et al. this volume), isotope hydrogeology studies and U-series work on solutions and solids. For solution work,
the AttoM’s limits of detection (LOD) for most elements are two or more orders
of magnitude better relative to a typical quadrupole ICPMS, and this lack of sensitivity has previously been a limitation for a number of environmental studies.
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The AttoM has LOD in solution mode for elements ranging across the periodic
table that include: lithium < 500 ppq, indium < 100 ppq, palladium < 10 ppq and
uranium < 1.2 ppq (Fig. 3). For a number of troublesome elements that are low
in concentration and yet have significant ICP-induced mass interferences, (e.g.,
56Fe = 40Ar + 16O), the analytical method can be shifted to use a higher resolution
(e.g., 3800), which, although degrading the peak shape to pointy tops, allows true
discrimination of baselines for proper analysis.
The other new instrument SGL has purchased is a JEOLTM JSM-7100F Field
Emission Scanning Electron Microscope (Fig. 4; FE = field emission because of
the gun type, which has charged plates rather than a wire filament). By combining
large beam currents with a small probe size at any accelerating voltage, the JEOL
JSM-7100F dramatically increases analytical resolution to the sub-100 nm scale.
This SEM is therefore ideal for both imaging and analysis of nanostructures, and
determining the chemical composition of the sample through X-ray spectroscopy. Included in this system is the low vacuum (LV) option, a capability that
supports operation in a low chamber vacuum (from 10 to 300 Pa) for the imaging and microanalysis of non-conductive samples. The system is equipped with
an Oxford Instruments EDS system, including the software package for semiquantitative compositional analysis, and Feature, the rapid mineral and particle
search, identification and classification software from Oxford Instruments.
The real strength of the newly extended SGL laboratory facilities is the ability to
combine the versatile instrumentation to be able to use multiple methods to solve
problems, and to be able to carry out this work in situ. For example, we can now
image zoning in major elements in grains on thin sections or mounts in the FESEM, for which we also obtain x and y locations. Coordinate transfer is facilitated
by adding copper TEM grids to the thin sections or polished mounts, providing
permanent reference points. The thin sections or mounts are then placed in the
laser with coordinates of the desired grains recalculated automatically using the
reference points, usually to within a few micrometres. Analysis then proceeds for
spot trace element information (AttoM) or spot isotopic information (multicollector), or both, depending on the nature of the problem. These new powerful
tools are now available for the SGL consortium researchers, but methodology
development should be a shared task and more involvement by SGL researchers
in this area is highly desirable.
References
Lahaye, Y., O’Brien, H., Molnár, F., Yang, S., Luolavirta, K. & Maier, W. 2014. Further insight
into ore forming processes using in situ Pb, S and Sr isotopic analysis on thin sections by
LA-MCICPMS. In: Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. &
Hölttä, P. (eds) Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland,
May 2014. Geological Survey of Finland, Report of Investigation 207. (this volume)
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Fig. 1. Newly installed Nu Instruments AttoM HR-ICPMS at GTK, Espoo
Fig. 2. Configuration on the Nu Instruments AttoM for measurement of U-Pb with one peak mass
(218.6) and fast scanning using ion beam deflectors over flat peaks.
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Fig. 3. Table of LOD for solution analyses using the Nu Instruments AttoM.
Fig. 4. Newly installed JEOLTM JSM-7100F Field Emission Scanning Electron Microscope at GTK,
Espoo.
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Quantitative Assessment of CU-ZN resources in
VMS deposits in Finland
by
Kalevi Rasilainen1, Pasi Eilu1, Pekka Sipilä1, Markku Tiainen1, Jukka Kousa2,
Jouni Luukas2, Jarmo Nikander2 , Peter Sorjonen-Ward2, Kaj Västi2,
Antero Karvinen3 and Tuomo Törmänen3
1 Geological
Survey of Finland, P.O. Box 96, FI-02151, Espoo, Finland
Survey of Finland, P.O. Box 1237, FI-70211 Kuopio, Finland
3 Geological Survey of Finland, P.O. Box 77, FI-96101 Rovaniemi, Finland
E-mail: [email protected]
2 Geological
Introduction
The undiscovered resources of important metals in the Finnish bedrock have been
systematically assessed by the Geological Survey of Finland using the three-part
quantitative mineral resource assessment method (Singer 1993, Singer & Menzie
2010). This includes the selection or construction of deposit models for the relevant mineral deposit types, the delineation of areas where geology permits the
existence of the deposit types (permissive tracts), the estimation of the number of
undiscovered deposits within the permissive tracts, and the calculation of metal
tonnages for the undiscovered deposits at various levels of probability.
Here, we describe the results from the assessment of copper, zinc, lead, gold
and silver resources in volcanogenic massive sulphide (VMS) deposits down to
the depth of one kilometre in the bedrock of Finland.
VMS deposits have historically been the most important source of zinc in Finland, and the second most important source of copper after the Outokumpu deposits. By the end of 2012, VMS deposits had produced about 0.66 Mt Cu and 2.8
Mt Zn in Finland. However, the remaining known VMS resources were only 0.34
Mt Cu and 0.74 Mt Zn, which are small compared to the total known resources of
4.6 Mt of Cu and 11 Mt of Zn in Finland.
Deposit models
Descriptive and grade-tonnage models specifically developed for the three-part
assessment method were recently published for VMS deposits (Mosier et al.
2009, Shanks & Thurston 2012). The existing descriptive model for VMS deposits
(Shanks & Thurston 2012) was considered to adequately characterise the Finnish
VMS deposits.
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Representative grade-tonnage data on well-known VMS deposits within the
Fennoscandian shield were gathered from the FINCOPPER (Västi 2009), FINZINC (Eilu & Västi 2009) and FODD (FODD 2012) databases. Our dataset contains grade-tonnage information on 134 well-known, totally delineated VMS deposits from Finland (20), Norway (38) and Sweden (76). Statistical tests indicate
that there are significant differences in ore tonnage and metal grades between the
Fennoscandian and global (Mosier et al. 2009) deposits. The final grade-tonnage
models were created for the Fennoscandian felsic, bimodal-mafic and mafic VMS
deposit types.
Permissive tracts and number of undiscovered deposits
In total, 31 permissive tracts were delineated for VMS deposits. The tracts are
controlled by lithology, but the existence of known VMS deposits, occurrences
and other indications of VM-type mineralization, as well as the exploration history of areas, were used as criteria for delineating and subdividing the tracts. The
tracts cover approximately 41,600 km2, which is 12% of the total land area of
Finland.
The number of possibly existing undiscovered VMS deposits was estimated for
each permissive tract in a series of workshops. The mean estimate of the number
of undiscovered VMS deposits within the topmost one kilometre of the bedrock
in Finland is 45 deposits, of which 18 belong to the felsic type, 10 to the bimodalmafic type and 17 to the mafic type.
Metal resources in undiscovered deposits
The assessment of metal tonnages in the undiscovered deposits was performed
by Monte Carlo simulation using data from the grade-tonnage models and the
estimated numbers of undiscovered deposits. Metal tonnages were estimated separately for each permissive tract. Summary values were estimated for the felsic,
bimodal-mafic and mafic tracts, and a grand total was estimated for all the VMS
tracts in Finland.
The median estimated undiscovered resources in VMS deposits in Finland are
730,000 t Cu, 1.6 Mt Zn, 150,000 t Pb, 1,100 t Ag and 16 t Au (Table 1). For copper, the largest part of the undiscovered resources resides in mafic-type deposits,
whereas for zinc, lead, silver and gold, the majority are contained in felsic-type
deposits.
Comparison of the known remaining and undiscovered resources of copper
and zinc in VMS deposits within the topmost one kilometre of the Finnish bedrock indicate that at least 68% of their total remaining resources are in poorly
known and explored or in totally undiscovered deposits.
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References
Eilu, P. & Västi, K. 2009. FINZINC - a public database on zinc deposits in Finland. Version 1.1
[Electronic resource]. Espoo: Geological Survey of Finland. Optical disc (CD-ROM)
FODD 2012. Fennoscandian Ore Deposit Database. Geological Survey of Finland (GTK), Geological Survey of Norway (NGU), Geological Survey of Russia (VSEGEI), Geological Survey of
Sweden (SGU), SC mineral. Online database, available at: http://en.gtk.fi/ExplorationFinland/
fodd. Last accessed 10 July 2012.
Mosier, D. L., Berger, V. I. & Singer, D. A. 2009. Volcanogenic massive sulfide deposits of the
world; database and grade and tonnage models. U.S. Geological Survey, Open-File Report
2009-1034. 28p.
Shanks, W. C. P. III & Thurston, R. (eds) 2012. Volcanogenic massive sulfide occurrence model.
U.S. Geological Survey, Scientific Investigations Report 2010–5070–C. 345 p.
Singer, D. A. 1993. Basic concepts in three-part quantitative assessments of undiscovered mineral
resources. Nonrenewable Resources 2, 69−81.
Singer, D. A. & Menzie, W. D. 2010. Quantitative mineral resource assessments: An integrated
approach. New York: Oxford University Press. 219 p.
Västi, K. 2009. FINCOPPER - a public database on copper deposits in Finland. Version 1. 1 [Electronic resource]. Espoo: Geological Survey of Finland. Optical disc (CD-ROM)
Table 1. Summary of the estimated amounts of metal and ore in undiscovered VMS deposits in Finland.
Mean
At least the indicated amount at the probability of
0.95
0.90
0.50
0.10
0.05
Probability of
Mean or None
greater
Cu (t)
Zn (t)
Pb (t)
Au (t)
Ag (t)
Ore (Mt)
4,200
14,000
750
0.19
8.0
0.65
2,500,000
5,800,000
1,000,000
68
5,000
250
0.24
0.22
0.16
0.20
0.20
0.26
35,000
88,000
6,000
1.1
56
4.4
730,000
1,600,000
150,000
16
1,100
76
6,400,000
15,000,000
1,900,000
150
12,000
750
11,000,000
27,000,000
4,000,000
280
23,000
1,200
0.04
0.04
0.04
0.04
0.04
0.04
Ore: Mineralised rock containing the metals.
The estimated amounts of metal and ore are rounded to two significant digits.
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Comparison of the portable XRF with
conventional methods in till geochemical
mineral exploration
by
Pertti Sarala
Geological Survey of Finland, P.O. Box 77, FI-96101 Rovaniemi, Finland
E-mail: [email protected]
Surficial geology, till geochemistry and heavy mineral studies have been used as
practical exploration tools in glaciated terrains for nearly one hundred years. Till
as a sampling medium is very useful due to its glaciogenic nature and being a
mixture of fresh bedrock, pre-glacial weathered bedrock and older sediments.
The lithological and geochemical characteristics of secondary dispersed till are an
effective way to estimate the transport distances and deposition processes of mineralised material in glaciogenic formations. Heavy mineral investigations support
till geochemical studies.
New sampling techniques and analytical methods for till geochemical and
heavy mineralogical exploration are being investigated at the Geological Survey
of Finland (GTK). The purpose is to identify new applications for regional and/or
target-scale exploration by finding new solutions for surficial exploration and by
developing effective but environmentally-friendly sampling techniques and analysis methods in the environmentally sensitive glaciogenic terrains. The aim is to
minimize the environmental impacts of mineral exploration in areas with a thick
glaciogenic overburden, peat-cover and/or reservation. At the same time, the focus is on reducing the analytical costs and increasing the sample efficiency of till
geochemical methods. One of the tested methods is a portable X-ray fluorescence
(pXRF) system supported by laboratory XRF and conventional till geochemistry
based on partial leaching followed by ICP-AES and ICP-MS analysis.
The development of modern pXRF analysers has been effective during the last
decade. One of the notable achievements in the development of mobile applications has been that their detection limits are low enough (ppm scale) for a large
group of elements. Furthermore, analysers are easy to take into the field and do
not need clean laboratory conditions. There are two types of equipment, portable
(i.e. hand-held) and car-supported, and both types have been tested at GTK.
The portable equipment is lightweight and easy to take into the field (Fig. 2).
The equipment (known also as a pistol) includes a central unit for receiving and
analysing measurement data and processing the spectrum of reflected energies.
Based on the energy spectra, the contents of elements are determined. Due to
the small size, the measuring length is only one to two centimetres, which gives
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an area of measurement of typically Ø 2–3 mm and a depth of penetration into
sample of only about one millimetre.
The XRF analyser can also be mobilized using car-supported systems, such as
ScanMobile®. A low-energy X-ray tube is used for measurements, but due to the
long measuring length (about 20 cm), the area on the surface of the sample is
larger than in the case of pXRF. ScanMobile includes an automatic measurement
system optimized for drill core boxes. The same boxes with slight modification
were also used in till sample testing (Fig. 1).
Several exploration examples from northern Finland have demonstrated that
the methods are suitable and effective for exploration purposes in glaciated terrains. Correlations between different pXRF analysers, laboratory XRF and even
ICP-AES (based on aqua regia leaching) analyses are mostly good or moderate
for the large group of elements, proving the usefulness of pXRF (Fig. 2). The relative values and trends are mostly worth considering (seen, for example, for Zn
in Figure 2), but the absolute values are also often equal to the results of conventional analytical methods.
Fig. 1. Till sample measurements using Delta pXRF and ScanMobile® XRF.
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Fig. 2. Correlation between Delta pXRF and ICP-AES analyses for Cu, Mn, Fe and Zn.
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Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014
New low-impact geochemical sampling and
exploration methods – application of
the Green Mining concept for greenfield
exploration in Finland
by
Pertti Sarala
Geological Survey of Finland, P.O. Box 77, FI-96101 Rovaniemi, Finland
E-mail: [email protected]
The Green Mining Programme of the Finnish Funding Agency for Technology
and Innovation (Tekes) was launched in 2011 in Finland. A focus is on promoting
the development of a low-impact and sustainable mineral industry and increasing the number of small and medium-sized enterprises in the mineral cluster
in Finland. The Geological Survey of Finland (GTK) has several ongoing projects within this programme, and two of these concern new methodologies for
sampling, analysis and the interpretation of multiple geological, geochemical and
geophysical datasets in environmentally sensitive Arctic and Sub-Arctic areas.
The projects are Novel technologies for greenfield exploration (NovTecEx; 20122014) and Ultra low-impact exploration methods in the subarctic (UltraLIM;
2013-2015).
These projects aim to minimize the environmental impact of mineral exploration, reduce analytical costs, and increase sampling and data interpretation efficiency. In the NovTecEx project, new sampling techniques and analytical methods for till geochemistry and indicator minerals are being investigated together
with advanced data mining methods and interpretation tools for geophysical
data. The UltraLIM project is focused on the study and comparison of several
geochemical techniques to determine the best practices for exploration of various
ore types. The three tasks included in the UltraLIM project are: 1) selective/weak
leach techniques, 2) biogeochemistry and 3) snow geochemistry.
Both projects include a strong development component for geochemical sampling and analytical methods. In particular, methods for surficial geochemical
sampling and analysis are important factors and widely used in mineral exploration in Finland. The reason for this is that Finland is located in the central part
of the last glaciated area and glaciogenic sediments cover almost 97% of the land
area. Furthermore, mineral exploration is challenging due to the thick glaciogenic overburden, large peatland areas and dense vegetation in the nutrient-rich
areas. In addition, in many parts of the country, various types of nature reserves
and conservation areas cover a significant part of the land area. There is increasing demand for the development of new applications for regional and target-scale
exploration.
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Different types of drilling equipment have been tested for the deep till geochemical and heavy mineralogical sampling in the NovTecEx Project. One aim
is to obtain more representative and stratigraphically better controlled samples
from till layers, and from weathered bedrock and/or fresh bedrock at the same
location. In addition to conventional geochemical assays, the samples should
also be collected for heavy mineral (e.g. indicator mineral) studies. This means
a minimum sample size of 5 to 10 litres, i.e. 10 to 20 kg, to obtain representative
samples and a high enough sampling accuracy. Considering the glacial transport
and deposition mechanisms, an ideal sampling layer for a regional till geochemical survey is usually the lowest till bed. By focusing the sampling on this till layer
throughout the sampling area, the samples will be comparable with each other. In
the NovTecEx Project, several types of deep drilling equipment and test pits have
been tested for till sampling. One of these is the sonic drilling method, which uses
high-frequency resonant vibration technology. It provides good penetration, even
into stony till, and enables the collection of continuous sediment and bedrock
sample cores (Fig. 1) to support the stratigraphical work during the sampling.
Another focus in the methodological development is on finding the best possible methods for topsoil sampling and analysis (analyses are based on selective
and/or weak leaching) for mineral sediments. This is one of the tasks of the UltraLIM Project. In order to test and compare different shallow sampling depths
and leaching methods, several target areas in northern Finland have been chosen.
These include different types of mineralization and have variable thickness of the
glacigenic overburden. For comparison, conventional geochemical methods, biogeochemistry and snow geochemistry will be used as a reference.
As a result, practical knowledge concerning the application of different methods for mineral exploration will be gained, enabling an estimation of the suitability of the sampling methods for the sensitive Arctic and Sub-Arctic environments.
Fig. 1. Photo of the full, 13-m-long till, varved silt and weathered bedrock sample core (top on the
upper left and bottom on the lower right) from eastern Rovaniemi as an example of methodological testing for the deep till sampling within the NovTecEx project. The sample core was obtained
using the sonic drilling method. The length of the core box is one metre. Photo: P. Sarala, GTK.
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Critical mineral exploration and potential
in Northern finland
by
Olli Sarapää1, Panu Lintinen1 and Thair Al-Ani2
1 Geological
Survey of Finland, P.O. Box 77, FI-96101 Rovaniemi, Finland
Survey of Finland, P.O. Box 96, FI-02151 Espoo, Finland
E-mail: [email protected]
2 Geological
Introduction
An exploration project on critical minerals (2013–2015) by the Geological Survey of Finland (GTK) is focused on evaluating the potential for new phosphate
(P) rocks (apatite), rare earth elements (REEs) and graphite deposits in northern
Finland. The list of critical raw materials at the EU level (European Commission
2010) does not include phosphorus. However, there are no substitutes for phosphorus in agriculture, and the growing need for food and biofuels may lead to the
depletion of phosphate rock resources and increase prices in the future. In Finland, carbonatites, alkaline rocks, ilmenite-magnetite gabbros and appinites have
the highest potential for apatite ores. At present, the main P prospects of GTK are
the Sokli (Kaulus) and Kortejärvi carbonatites and Iivaara alkaline rocks. REEs
play a particularly critical role in numerous hi-tech applications and environmentally friendly energy technologies, but the problem is that their production
is mainly controlled by China. At present, the main global sources of REEs are in
carbonatites and alkaline rocks, placer deposits and ion-adsorption clays. Currently, the REE-rich veins of Kaulus and Jammi at Sokli are the most promising
prospects in northern Finland.
Graphite is the major component in Li-ion batteries and fuel cells. Sales of
batteries are expected to increase rapidly when electronic vehicles become more
common. China dominates graphite production and restricts export. In Finland,
graphite is common in most schist belts, but high-quality flake graphite deposits
are presently not known. The highest potential to find them is restricted to the
areas of the high-grade metamorphic, granulite facies terrains.
Results
The Sokli carbonate complex in northeastern Finland (Fig. 1) belongs to the Kola
Alkaline province (Kramm et al. 1993), and contains the most important deposits
of phosphate rock, REE and Nb in the Fennoscandian Shield. At Sokli, a deeply
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weathered carbonatite with regolithic phosphorus ores has remained to this day
due to the evasion of glacial erosion (Vartiainen 1980).
The P-REE exploration prospects at Sokli (Jammi and Kaulus) are located in
the fenite zone, outside the main phosphorus deposit (Sarapää et al. 2013). The
first indications of the prospects were high La (0.1–1%) and Zn (0.81%) contents
in drill cores from Jammi. More detailed mineralogical and chemical analyses
from the drill cores revealed that the cross-cutting late carbonatite veins in the
fenite zone were enriched in both apatite (up to 19.9 wt% P2O5) and REE minerals
(0.5–1.8 wt% REE) such as ancylite-(Ce), bastnäsite-(Ce), Sr-apatite, monazite,
strontianite, baryte and brabantite; all these are enriched in LREE, P, F, Sr and Ba
(Al-Ani & Sarapää 2013).
The Kaulus prospect, 6 km2 in size, is located partly in the fenite zone and
partly in the metasomatite zone of the Sokli deposit. After geochemical and weak
leaching geochemical studies on till and weathered bedrock, diamond drilling
for apatite exploration was focused on carbonatite ring dykes, visible as magnetic
highs on the aeromagnetic maps, and for REE exploration on aeroradiometric
Th anomalies. The apatite deposit associated with the ring dykes at Kaulus can be
followed for at least 2.5 km. Two dikes are several tens of metres wide and include
both soft (down to 70 m below ground) and hard apatite ores. The average P2O5
content is 7 wt% (cut-off 4 wt%). In some drill holes, the apatite residue contains
10–20 wt% P2O4 and 10–55 wt% Fe2O3 (Fig. 2). The late magmatic REE carbonatite veins in fenites at Kaulus have similar REE mineralogy to the Jammi veins.
These veins contain 0.7–1.7 wt% REE. According to the mineralogical study, ancylite is the dominant REE mineral (Al-Ani & Sarapää 2013).
The Iivaara alkaline complex, also a part of the Kola Alkaline Province (Kramm
et al. 1993), has similarities with the REE-rich Lovozero alkaline massive. The
Iivaara central massive consists of nepheline-clinopyroxene urtites, ijolites, and
melteigites surrounded by a fenite zone. Studies by GTK have included bedrock
mapping, weak leaching geochemistry, till and weathered rock geochemistry and
geophysical measurements. Drill hole R1 intersected phosphorus ore with 33 m
@ 5.5 wt% P2O5 (up to 10%), and the whole section of 166 m averaged 3.5 wt%
P2O5. Processing tests at Mintek gave good apatite and magnetite concentrates
from apatite-magnetite-rich melteigite. The REE content is low, but geophysical
interpretation has revealed ring structures around the Iivaara massif that could
be potential REE targets.
One of the most promising apatite prospects in Finland is the Palaeoproterozoic Kortejärvi carbonatite intrusion (Lintinen, this volume). The Kortejärvi
apatite-rich carbonatite contains 5 wt% P2O5, and has a maximum thickness of
over 100 m. In both the Kortejärvi and Iivaara intrusions, the dominant REE
minerals are monazite and allanite.
References
Al-Ani, T. & Sarapää, O. 2013. Mineralogical and geochemical study on carbonatites and fenites
from the Kaulus drill cores, southern side of the Sokli Complex, NE Finland. Geological Survey
of Finland, archive report 145/2013. 66 p.
European Commission 2010. Critical raw materials for the EU. Annex V. 220 p. Available at:
http://ec.europa.eu/enterprise/policies/raw-materials/files/docs/annex-v-b_en.pdf
Lintinen, P. 2014. Preliminary results from new drillings and geochemical studies of the apatite
deposits in the Kortejärvi and Petäikkö-Suvantovaara carbonatites, Pudasjärvi–Posio district,
Northern Finland. In: Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. &
Hölttä, P. (eds) Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland,
May 2014. Geological Survey of Finland, Report of Investigation 207. (this volume)
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Sarapää, O., Al Ani, T., Lahti, S. I., Lauri, L. S., Sarala, P., Torppa, A. & Kontinen, A. 2013. Rare
earth exploration potential in Finland. Journal of Geochemical Exploration 133, 25–41.
Fig. 1. On the left, GTK drill holes from 2012–2013 on a high-density aeromagnetic map of Sokli;
on the right, a plan view of the drilling results on the magnetic map showing P and La contents.
Fig. 2. Drill core R10 penetrates weathered apatite-rich phoscorite (up to 20 wt% P2O5). The La
content has a good correlation with the P2O5 content.
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
The use of high resolution X-ray computed
micro-tomography in metamorphic fabric
analyses: A virtual method of studying
foliations and porphyroblasts in 3D
by
Mohammad Sayab1, Jussi-Petteri Suuronen2, Pentti Hölttä1, Aki Petteri Kallonen2,
Raimo Lahtinen1, Domingo Aerden3 and Ritva Serimaa2
1 Geological
Survey of Finland, P.O. Box 96, FI-02151 Espoo, Finland
of Physics, University of Helsinki, P.O. Box 64, FI-00014 Helsinki, 2 Department
Finland
3 Departmento de Geodinámica, Universidad de Granada, Campus de Fuente nueva s/n, 18071 Granada, Spain
E-mail: [email protected]
Much of our knowledge about the inter-relationships between deformation and
metamorphism has been gained through the study of porphyroblastic microstructures in thin sections. Until 1990, however, the majority of workers studied
thin sections that were not precisely oriented relative to geographic coordinates
and cut perpendicular and/or parallel to the dominant matrix fabrics (see review
in Vernon 2004, Passchier & Trouw 2005). This approach changed when Hayward
(1990) introduced a technique for determining the orientation of crenulation
axes preserved within porphyroblasts and matrix from radial sets of vertical thin
sections of single samples. The method was further refined by Bell et al. (1995),
and its subsequent application has helped to clarify the tectono-metamorphic
histories of numerous mountain belts in unprecedented detail. A closely related
computer technique was developed by Aerden (2003), allowing the calculation
of preferred orientations of internal foliations (inclusion trails) from pitch and
strike measurements collected in sets of differently oriented thin sections. More
recently, high-resolution X-ray computed tomography has been applied for direct
imaging of porphyroblasts and their inclusion trail patterns in 3D (e.g. Huddlestone-Homes & Ketcham 2010). This technique is non-destructive and provides
detailed spatial imagery of the interior of the rock by measuring the attenuation
of X-rays as they pass through minerals. Minerals such as quartz, feldspar, andalusite and mica have lower X-ray linear attenuation coefficients than garnet,
whereas oxides are significantly more attenuating.
We have taken this visualization technique one step further by applying it to a
sample of oriented drill core (diameter 2.5 cm) from Orijärvi, Finland, precisely
where 100 years ago Eskola (1914) developed the concept of metamorphic facies.
The sample was drilled vertically from andalusite-cordierite mica schist. While
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still in situ, the drill core was marked with a N–S-oriented groove so that it could
be easily reoriented in the X-ray scanner. The acquired 3D image composed of
two thousand horizontal slices, with a voxel size of 14×14×14 μm. After segmentation of data from several horizontal slices and subsequent interpolation, 3D
renderings (Fig. 1a–c) were produced showing the shape, orientation (relative
to true North) and spatial distribution of different mineral phases, as well as the
geometry of tectonic fabrics. In addition to 3D spatial images, oriented crosssections can be obtained through any part of the drill core as a new kind of virtual
petrographic section (Fig. 1d–f).
For the studied sample, the technique revealed: (1) the tabular shapes of porphyroblasts and their orientation; (2) the distribution of porphyroblasts versus
oxides (possibly sulphides) in separate layers, probably reflecting compositional
differences between the layers or deformation partitioning; (3) the orientations of
the main matrix foliation and matrix crenulations; and (4) the geometry and orientation of inclusion trails hosted by the porphyroblasts, as well as crenulationor foliation-intersection axes (FIA) defined by them. Geometric orientations
of inclusion trails in different porphyroblasts indicate that they did not rotate
significantly relative to each other.
References
Aerden, D. G. A. M. 2003. Preferred orientation of planar microstructures determined via statistical best-fit of measured intersection-lines: the ‘FitPitch’ computer program. Journal of Structural Geology 25, 923–934.
Bell, T. H., Forde, A. & Wang, J. 1995. A new indicator of movement direction during orogenesis:
measurement technique and application to the Alps. Terra Nova 7, 500–508.
Eskola, P. 1914. On the petrology on the Orijärvi region in southwestern Finland. Bulletin de la
Commission Géologique de Finlande 40, 1–279.
Hayward, N. 1990. Determination of early fold axis orientation in multiply deformed rocks using
porphyroblast inclusion trails. Tectonophysics 179, 353–369.
Huddlestone-Holmes, C. R. & Ketcham, R. A. 2010. An X-ray computed tomography study of
inclusion trail orientation in multiple porphyroblasts from a single sample. Tectonophysics
480, 305–320.
Passchier, C. W. & Trouw, R. A. J. 2005. Micro-tectonics. Springer. 353 p.
Vernon, R. H. 2004. A practical guide to rock microstructure. Cambridge University Press. 579 p.
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Fig. 1. (a–c). 3D rendering of high-resolution X-ray computed tomographic data after segmenting
the 3D volume. Different colours have been chosen to differentiate the shape and size of porphyroblasts, as most of them are andalusite porphyroblasts. (d) Horizontal oriented slice, (e) E–W
vertical section, (f) N–S vertical section. The single barbed arrow in (b–c) and (e–f) indicates the
strike and way up.
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MODERNISED BEDROCK MAP OF THE HÄME BELT
by
Pekka Sipilä
Geological Survey of Finland, P.O. Box 96, FI-02151 Espoo, Finland
E-mail: [email protected]
Bedrock mapping of the Häme Belt was carried out during 2011–2013 in Tammela and Kalvola as part of the Geological Survey of Finland (GTK) project “Mineral
potential in Southern Finland”. The purpose was to amend the geological data
that were regionally mapped about 60 years ago. This area was chosen as a target
of the project because the mineral potential of the region was estimated to be high
based on a till geochemical survey conducted by the project.
All available old bedrock data have been utilised, including reports and target
maps of exploration and mining companies, and the recently completed GTK
Geodatabase. New mapping was carried out during 2008–2009, when the terrain
border between Häme and Pirkanmaa Belts was mapped by GTK. The modernized bedrock map of the Häme Belt will be included in GTK’s DigiKP-map database, and it will include hierarchic classification of the rock units based on the
FINSTRATI system.
The Häme Belt is divided into different suites (Fig. 1) based on lithologies and
the geochemistry of volcanic rocks. The Forssa volcanic suite comprises volcanic
rocks in the Forssa and Somero areas and extends to the east of the Forssa gabbro.
Volcanic rocks around large gabbros in the Kärkölä-Hyvinkää area also belong
to this suite. These volcanic rocks are calc-alkaline, and the composition varies
from basaltic to rhyolitic. Andesitic rocks are most abundant in the Forssa and
Somero areas, whereas basalts are predominant to the east of the Forssa gabbro.
In geochemical spidergrams, these rocks show a clear Ta-Nb minimum, a relatively steeply sloping Zr-Y trend, and they are strongly enriched in the LREE elements, all of these being features typical for arc-type magmatism.
The Häme volcanic suite is located at the northeastern end of the Häme Belt.
The basement is a pelite-psammite unit about one kilometre thick, which includes layers of volcanic ash. This unit is covered by at most 200-m-thick unit
of volcanic conglomerates, iron formations, intermediate and mafic tuffs, and at
top, felsic tuffs. This unit is followed by an approximately 2-km-thick section of
mafic and intermediate pyroclastic rocks and lavas. The northernmost, approximately 1-km-thick unit is mainly composed of intermediated tuffs and tuff breccias, which are characterized by an extensive and strong hydrothermal alteration
that is probably related to granitic intrusions. Basaltic veins and sills with uraliteporphyric texture occur throughout the suite. Mafic volcanic rocks of the Häme
suite show only a minor, if any, Ta-Nb minimum, a very gently sloping or flat
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Zr-Nb trend and much lower enrichment of LREE than in the rocks of the Forssa
suite. In addition, the geochemical composition corresponds to tholeiitic or transitional magma. The age difference between the Forssa and Häme volcanic suites
is not considerable, suggesting that the volcanic activity may have been partly
simultaneous. Many similar features observed in the volcanic rocks of the Forssa
and Häme suites support this theory.
The western part of the Häme Belt is called the Häme migmatite suite. Most of
the mafic volcanic rocks in this area have metamorphosed to amphibolites without any primary textures remaining. However, the chemical composition of these
amphibolites corresponds to calc-alkaline volcanic rocks, and is clearly different
from the volcanic rocks in the Turku region, situated to the west of the migmatite
suite.
A 40-km-long east–west-oriented zone between Kärkölä and Hyvinkää includes several rather large layered gabbro intrusions referred to here as the Southern Finland layered intrusion suite. The most important intrusions are the Hyvinkää, Karkkila and Vähävesi gabbros, all of which were recently studied in the
Hyvinkää-Mäntsälä project of the University of Helsinki. Forssa gabbro, situated
farther north, is compared to these gabbros and classified within this same suite,
even though its chemical composition is different. Forssa gabbro is calc-alkaline,
whereas all gabbros in the Kärkölä-Hyvinkää are tholeiitic.
Fig. 1. Suites of the Häme Belt. Contains data from the National Land Survey of Finland Topographic Database 08/2012.
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MAGNETIC SUSCEPTIBILITY effects in
THE GTK airborne ElectroMagnetic data
– ModelLing and interpretation example
by
Ilkka Suppala
Geological Survey of Finland, P.O. Box 96, FI-02151 Espoo, Finland
E-mail: [email protected]
INTRODUCTION
Airborne electromagnetic (AEM) surveys are used to delineate the subsurface
electrical conductivity σ in bedrock mapping and mineral exploration, but frequency-domain AEM methods are also sensitive to anomalous magnetic susceptibility χ. Using the GTK’s Twin Otter EM system (Leväniemi et al. 2009), the
conducting ground causes positive in-phase and quadrature responses, while the
response caused by the magnetically permeable ground is opposite (negative) in
the in-phase component. As the primary field is caused by a magnetic dipole
rather than by the geomagnetic field, the footprint (the volume from which the
measured information comes) is local, and for susceptibility it is smaller with
AEM measurements than with total magnetic intensity (TMI) data measured in
magnetic surveys.
TMI depicts the anomalous magnetic field caused by induced and remanent
magnetization. The induced part is caused by the susceptibility of the ground. The
effect of remanent magnetization is often unknown due to lack of petrophysical
measurements. Usually, assuming no remanence exists, only the effective susceptibility has been inverted from the magnetic data. By comparing the modelled
TMI using inverted susceptibility from AEM data and the observed TMI, the
near-surface remanently magnetized formations can be revealed. Evidently, AEM
and magnetic measurements complement each other.
NUMERICAL MODELLING ON LOCAL MESHES
In this study, the theoretical effects of anomalous conductivity and susceptibility
have been calculated using EH3D, software that calculates the EM fields in the 3D
domain. In the program, the system of partial differential equations is discretized
using a finite-volume scheme on a staggered grid (Haber & Ascher 2001). The
sparse linear system of equations is solved using a preconditioned iterative solver.
Loki/LokiAir software developed in the CSIRO / AMIRA P223 project would be
faster than EH3D, but it cannot calculate the effect of susceptibility.
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In the model, a set of non-overlapping layers and tabular bodies has been used
to represent the conductivity and susceptibility structure of the survey area, and
a local ‘optimized’ mesh for each AEM measurement at each frequency is used
for the calculation. The local mesh uses fine cells near the transmitter and receiver and coarse cells far away, and the volume of the mesh should be larger than
the footprint at the used frequency. The material averaging (upscaling) scheme
to map the materials σ and χ from the model to local meshes is explained in
Commer and Newman (2008).
RESULTS
Calculated synthetic AEM measurements demonstrate different types of couplings to tabular σ and χ bodies. The footprints of the Twin Otter EM system are
different in shape and volume to conductivity and susceptibility. Some theoretical Slingram results also characterize the difference between EM induction and
magnetic induction.
The 2D and 3D model-based interpretations have been tested in the western
part of the Kellojärvi ultramafic complex (see e.g. Halkoaho & Niskanen 2012).
The area was measured with 100 m line spacing using the Twin Otter system at
3113 Hz. The magnetized formation is clearly outlined from aeromagnetic and
AEM in-phase data. The bedrock model has been interpreted from the AEM data
using homogeneous σ and χ bodies below Lake Kellojärvi and estimated overburden. The lake bathymetry has been taken into account. Comparison of measured
TMI values and the modelled TMI calculated using the interpreted susceptibility
model shows the strong effect of the remanent magnetization. In the formation,
the ratio of the remanent to the induced magnetization should be two or more,
which is in agreement with petrophysical measurements from drilled serpentinite in the study area. The modelled susceptibilities are also in agreement, at least
qualitatively, with measurements from the drill core samples. In the Kellojärvi
case, both conductivity and susceptibility should be used in the inversion of AEM
data.
The measured TMI values are caused by near-surface magnetic sources, as well
as by the deeper buried regional sources. The susceptibility model from AEM only
depicts shallow sources (at a depth of less than 100 m). To reduce the nonuniqueness in the inversion of the TMI data, this near-surface information is valuable.
References
Commer, M. & Newman, G. A. 2008. New advances in three-dimensional controlled-source electromagnetic inversion. Geophysical Journal International 172, 513–535.
Haber, E. & Ascher, U. 2001. Fast finite volume simulation of 3D electromagnetic problems with
highly discontinuous coefficients. SIAM Journal of Scientific Computations 22, 1943–1961.
Halkoaho, T. & Niskanen, M. 2012. Tutkimustyöselostus Kuhmon kaupungin Kellojärven Pärsämänsuo 1 valtausalueella (kaivosrekisterinumero 8344/1) suoritetuista nikkelimalmitutkimuksista vuosina 2007−2011. Geological Survey of Finland, archive report 64/2012. 18 p, 29
app. (in Finnish)
Leväniemi, H., Beamish, D., Hautaniemi, H., Kurimo, M., Suppala, I., Vironmäki, J., Cuss, R.
J., Lahti, M. & Tartaras, E. 2009. The JAC airborne EM system AEM-05. Journal of Applied
Geophysics 67, 219–233.
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MIneral Potential mapping in
southern finland
by
Markku Tiainen1, Niilo Kärkkäinen1, Timo Ahtola1, Sari Grönholm1,
Pekka Huhta1, Hanna Leväniemi1, Pekka Sipilä1 and Esko Koistinen2
1 Geological
Survey of Finland, P.O. Box 96, FI-02151, Espoo, Finland
Survey of Finland, P.O. Box 1237, FI-70211 Kuopio, Finland
E-mail: [email protected]
2 Geological
INTRODUCTION
The aim of the mineral potential mapping project in Southern Finland is to map
ore potential areas and identify new mineralized subareas in the Palaeoproterozoic Svecofennian domain of southern Finland. The focus area is the poorly
explored Häme Belt, where understanding of the geology was mainly based on
old and sparse mapping data. However, the geological setting of the Häme belt,
a volcanic arc, is typically favourable for different types of mineralizations and
there are also numerous showings of mineralizations, especially of base metals,
gold and RE pegmatites (Fig. 1).
REGIONAL MAPPING
In 2004, the regional geodata coverage of the Häme belt was based on old mapping, and some data sets, such as regional gravity data (APV), were entirely missing. The first task of the project was to update the level of the mapping data.
Regional till geochemical mapping, covering the area from Somero and Huittinen to Kalvola, was mainly carried out during the winters of 2004–2014, comprising 4000 basal till samples taken in a 500-m grid. The airborne geophysical
data were updated in 2006–2007 with high-resolution data using the line spacing
of 50–75 m. The measured area of 400 km2 covers the central part of the Häme
belt (Humppila-Nuutajärvi-Tammela). Updating of the geological map database
(DigiKP) was carried out by utilizing the available project maps of the exploration
companies and by conducting new fieldwork at selected targets in 2008–2013.
The collection of new gravity data, planned to follow the seismic FIRE profile
through the Häme belt, was started in 2013 and will be available during 2014.
Based on regional mapping, the volcanic rocks of the Häme Belt have been
divided into three main units: the Häme volcanic suite, the Forssa volcanic suite
and the Häme migmatite suite. Mafic intrusions of the Häme Belt belong to the
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Southern Finland Layered Intrusion suite (Fig. 1). No granitoid classification is so
far available, but it is obvious that there are several types of granitoids in the area.
Regional till geochemical mapping has produced several interesting anomalies
of base metals, gold and lithium, and anomalies related to ore forming hydrothermal processes in general. The results of till geochemistry have been utilized in the
project as soon as the data has become available.
A new approach to the ore potential mapping of the Häme belt is the prospectivity mapping method, which has been applied to select new exploration targets
for VMS type deposits, gold deposits and lithium pegmatites (Leväniemi 2013,
Leväniemi & Karell 2013).
TARGET SCALE MAPPING
Several mineral deposits were already known and partly explored before this project, such as the Zn occurrences of Tupala, Kiipu, Leteensuo and Katumajärvi,
the Cu occurrence of Kotka, the Au occurrences of Satulinmäki and Riukka, the
Ni-Cu occurrence of Särkisuo and the Li deposits of Somero and Tammela. GTK
has developed the Satulinmäki deposit and is now exploring the Kotka Cu occurrence, the Särkisuo Ni-Cu occurrence and the Somero RE-pegmatites (Fig. 1).
The new regional mapping data have produced several new exploration targets,
including the Kedonojankulma-Cu, Arolanmäki-Liesjärvi-Au, Kuuma-Zn, Uunimäki-Au, Pirttikoski-Cu-Au, Kokkojoki Cu-W-Bi and Lempää Cu-PGE targets.
Detailed studies on selected exploration targets will provide new information on
the ore forming processes.
CONCLUSION
Mineral potential mapping of the Häme belt has produced new regional mapping data and comprehensively improved understanding of the geology of the
Häme belt. Modern regional geophysical data together with updated geological
maps and structural geological interpretation form the basis for the interpretation of the first 3D profiles through the Häme Belt and the subsequent regional
3D interpretation of the belt. Target-oriented studies have provided new data for
scientific research on ore geological processes, as well as new exploration targets
for the mining industry.
References
Bedrock of Finland − DigiKP. Digital map database [Electronic resource]. Espoo: Geological
Survey of Finland [referred 30.01.2014]. Version 1.0.
FODD 2013. Fennoscandian Ore Deposit Database [Electronic resource]. Geological Survey of
Finland (GTK), Geological Survey of Norway (NGU), Geological Survey of Russia (VSEGEI),
Geological Survey of Sweden (SGU), SC Mineral [accessed 26.3.2013]. Available at: http://
en.gtk.fi/ExplorationFinland/fodd/
Huhta, P., Kärkkäinen N., Tiainen, M. & Herola, E. 2014. Geochemical anomalies reflecting ore
forming processes in the Svecofennian Häme Belt, Southern Finland. In: Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds) Current Research: 2nd
GTK Mineral Potential Workshop, Kuopio, Finland, May 2014. Geological Survey of Finland,
Report of Investigation 207. (this volume)
Leväniemi, H. 2013. Lithium Pegmatite Prospectivity Modelling in Somero-Tammela Area,
Southern Finland. Geological Survey of Finland, archive report 151/2013. 15p.
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Leväniemi, H. & Karell F. 2013. Geophysical Indications of VMS Deposits in the Häme Volcanic
Belt. Geological Survey of Finland, archive report 152/2013. 64 p.
Sipilä, P. 2014. Modernized bedrock map of the Häme Belt. In: Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds) Current Research: 2nd GTK Mineral
Potential Workshop, Kuopio, Finland, May 2014. Geological Survey of Finland, Report of Investigation 207. (this volume)
Fig. 1. Mineral deposits and occurrences in the Häme belt according to FODD (2013) and the
present project. Geological map according to the GTK Geodatabase/scaleless bedrock database
Bedrock of Finland – DigiKP) and Sipila (this volume).
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Comparison of prospectivity mapping
techniques for central lapland
orogenic gold
by
Johanna Torppa
Geological Survey of Finland, P.O. Box 1237, FI-70211 Kuopio, Finland
E-mail: [email protected]
INTRODUCTION
The extensive geophysical and geochemical data across Finland provide excellent grounds to carry out regional prospectivity mapping using data-miningbased techniques. Airborne frequency-domain electromagnetic, magnetic and
radiometric measurements, till geochemical analysis and field gravity measurements are available for the entire country. In addition, airborne gravimetric and
time-domain electromagnetic measurements have been carried out in regions of
special interest. The applicability of these data has been shown to be promising
for evaluating the regional prospectivity in northern Finland. In this study, the
Central Lapland Greenstone Belt (CLGB) in northern Finland has been used as
a test bed for comparing the prospectivity information on orogenic gold provided by the self-organizing maps method (SOM, Kohonen 2001) with the results
obtained earlier by Nykänen and Salmirinne (2007) and Nykänen et al. (2008).
These authors demonstrated the applicability of data-mining-based regional prospectivity mapping with weights of evidence, fuzzy logic and binary logistic regression methods using airborne geophysics, regional gravity measurements, till
geochemistry and geological mapping. The optimal approach to preprocess the
data is also being reconsidered.
METHODS AND DATA
We have used the self-organizing maps method (SOM) to study the distribution
of a multidimensional geophysical and geochemical dataset of central Lapland.
SOM is an unsupervised data-driven data-mining technique that clusters data in
the data space in groups that are as homogeneous as possible and represents the
data distribution in reduced dimensions; most often a 2-dimensional representation is used for efficient visualization. SOM is a neural-network-type method in
the sense that the model neurons (called best-matching unit vectors or BMUs)
are iteratively taught to obtain the final value. The learning procedure in SOM
is based on the stochastic gradient decent method for minimizing the difference
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between the model, i.e., the BMU vector, and the data. The size of the SOM, i.e.,
the number of output clusters, is defined by the desired outcome. A large SOM
map can be used as a data reduction technique for getting rid of erroneous data
values, for searching for anomalous data values and for reducing the size of the
data set. A somewhat similar approach would be to use object-based image analysis techniques to form spatially connected areas with approximately constant data
properties. SOM differs from the image analysis approach in the sense that it also
clusters similar data points that are not spatially connected. If a small number of
clusters is more useful, SOM can be run hierarchically, i.e., multiple times, while
reducing the map size at each iteration. Another alternative to obtain a moderate number of clusters is to use some other unsupervised clustering method, e.g.,
k-means, to cluster the values of the initial, larger SOM. Clusters obtained with
unsupervised methods such as SOM do not directly have a physical meaning,
and auxiliary information must be used to identify which clusters represent, for
instance, interesting spatial areas. Then again, since SOM only uses data to find
patterns and involves no expert input, it is independent of subjective opinions, for
instance on selecting the data values that are or are not favourable for a ‘prospective’ situation.
We will compare the results obtained using SOM with those obtained earlier
using the fuzzy logic (FL), weights of evidence (WofE) and binary logistic regression (BLR) methods. These methods, unlike SOM, directly provide information
on the prospectivity level of each data point, but require a priori information on
the study area, either in the form of an evidence data set or as expert knowledge.
WofE and BLR assume that the data values represent two possible classes, referring in the case of prospectivity modelling to ‘prospective’ (P) and ‘non-prospective’ (nP). FL uses also intermediate values, i.e., the P–nP range is divided into a
certain number of sub-ranges representing the probability of being P. While SOM
uses the original data values, WofE, FL and BLR require discretizing of the data
ranges of each data component and defining of the value of P or nP, or in the case
of FL the probability of being P, for each sub-range.
We will use the same data sources as in the earlier studies, i.e., airborne magnetic and electromagnetic measurements, gravimetric data, till geochemistry
(Au, As, Cu, Fe, Ni, Te) and structural data. A somewhat different approach to
using the datasets will be taken, however: in the previous study, all data were interpolated. However, since the spatial resolution of the geophysical data is much
larger than that of the geochemical data, only the airborne geophysics will be
interpolated in this study, while geochemical data will be treated as points and
structural data as line elements.
References
Kohonen, T. 2001. Self-Organizing Maps. Third Extended Edition, Springer Series in Information
Sciences 30. 502 p.
Nykänen, V. & Salmirinne, H. 2007. Prospectivity analysis of gold using regional geophysical
and geochemical data from the Central Lapland Greenstone Belt, Finland. In: Ojala, V. J. (ed.)
Gold in the Central Lapland Greenstone Belt. Geological Survey of Finland, Special Paper 44,
251–269.
Nykänen, V., Groves, D., Ojala, V. & Gardoll, S. 2008. Combined conceptual/empirical prospectivity mapping for orogenic gold in the northern Fennoscandian Shield, Finland. Australian
Journal of Earth Sciences 55, 39–59.
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
on the depth structure of the iivaara pipe
by
Pertti Turunen, Ilkka Lahti and Olli Sarapää
Geological Survey of Finland, P.O. Box 77, FI-96101 Rovaniemi, Finland
E-mail: [email protected]
INTRODUCTION
The Iivaara alkaline complex in Kuusamo is an oval intrusion with an area of 8.8
km2. It is divided into a 1000-m-wide fenite zone, a transition zone and the central massif. The central massif consists of urtite, ijolite and melteigite, and with
the age of 373–363 Ma, Iivaara is the westernmost intrusion in the Kola alkaline
rock province. The carbonatites and alkaline rocks of the province are rich in
phosphorus, niobium, tantalum, REE and vermiculite occurrences.
GTK has investigated the intrusion of the Iivaara alkaline complex in order to
establish its phosphorus and REE potential. Of the two drilled holes, R1 met 33 m
of rock with 5.5% P2O5 (max 10%), and the mean P2O5 content of the 166-m-long
rock section was 3.5%.
The depth structure of the Iivaara pipe is not known below the 200-m-deep
drillhole bottoms. On the magnetic airborne map (Fig. 1), viewed from the NE,
the intrusion is visible as an isolated anomaly with a diameter of 3 km and maximum amplitude of 7000 nT. The magnetic method was considered unreliable in
depth structure determination due to unknown orientation of remanent magnetization. The gravimetric method does not suffer from such problems, and its
depth of exploration is better. In the following, the interpretation of the depth
structure is primarily based on gravity and additionally on magnetics.
GEOPHYSICAL SURVEYS
Geophysical airborne mapping at Iivaara was completed in 1988. The magnetic
and electromagnetic data quality is good, and magnetics can be used in structural
modelling. The isolated anomaly is surrounded by a very restful magnetic field,
where the regional data level can be reliably determined. This is of great significance in the depth structure interpretation.
In 2012–2013, ground magnetic surveys covering an area of 6.3 km2 were completed. The mapped area is situated on the top and slopes of Iivaara hill, but the
data only have meaning in shallow structure modelling. For deep structure modelling, two crossing gravity profiles with a total length of 20 km were surveyed.
Two drill holes, both 200 m deep, were drilled near the centre of the intrusion.
The bedrock was weathered to a depth of 30 m. Density, magnetic susceptibility
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and intensity of remanent magnetization were measured in the laboratory with
one-metre intervals. The medians of the physical property values are presented
in Table 1.
MODELLING
The magnetic anomaly in Figure 1 has no deep minima to the north or in any
other direction from the maximum. This may be taken to mean that the causative body is deep. It appears that it dips very steeply towards the north or a little
west of north. Another option is that the body extent grows larger as it plunges
deeper. Half of the total magnetization is remanent. If the direction of remanence
is parallel to the induced magnetization, no problems arise, but if the two magnetizations fail to parallel each other, the anomaly structure changes, which will
inevitably lead to the wrong outcome.
The gravity anomaly was interpreted with elliptic cylinder model bodies. Figure 2 presents the models as partly perspective blocks: the green models are not
projected as real perspective figures. The density of the models is 2975 kg/m3,
in accordance with Table 1. The deeper model explains the bulk of the anomaly,
whereas the surficial model is needed to explain the topography variation and
other near surface effects. The correct definition of the regional gravity level is of
utmost importance, especially in depth interpretation, but the long survey profiles build confidence in the modelling. The selected level gives the model depth
its minimum value, 2700 m. If the diameter of the pipe increases with depth, a
less deep model is sufficient to explain the anomaly, but if the diameter becomes
smaller, a deeper-reaching model is needed.
The gravimetric model explains the magnetic airborne anomaly intensity if the
value of 0.35 (SI) is used for total susceptibility, but the exterior features of the
anomaly require changes in the orientation of remanence. If the orientation of the
remanence is not known, problems will arise in magnetic anomaly interpretation.
As another approach, the magnetic airborne data were processed by Intrepid
WormE software, which produces so-called ‘worms’, curved features that are the
maxima of the horizontal gradients of the upward continued field (Archibald et
al., 1999). The internal heterogeneity of the intrusion and contacts of the anomaly source are enhanced in the process. Figure 3 illustrates the worms from the
magnetic field continued up to 2000 m. The results suggest that the pipe plunges
steeply towards the north.
CONCLUSIONS
The gravity model plunges steeply towards the SSW, while the magnetic model
and worming suggest the plunge to occur in a NNW direction. The gravity model
is at least 2700 m deep. The pipe diameter either grows with depth, or the vertical
extent of the body is deeper than 2700 m. The volume of the model is 20 km3 and
its total mass is 60 Gt. More gravity data are needed to be able to draw reliable
conclusions.
References
Archibald, N., Gow, P. & Boschetti F. 1999. Multiscale edge analysis of potential field data. Exploration Geophysics, 30, 38–44.
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Table 1. Medians of physical properties of drill core samples.
Rock sample
All rocks
Urtite
Ijolite
Melteigite
Boug (mGal)
Number
334
26
301
7
Density (kg/m3)
2975
2893
2981
3034
Susceptibility (SI)
0.133
0.086
0.136
0.268
Q ratio
1.23
1.20
1.22
1.50
Boug (mGal)
-10
-8
-10
-12
-15
-14
-20
-16
-18
TMI (nT)
-20
58000
-22
-24
56000
TMI (nT)
59500
54000
58500
52000
57500
56500
55500
54500
53500
52500
51500
Fig. 1. The Iivaara gravity Bouguer anomaly map on the top, and airborne total magnetic intensity
map on the bottom.
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Bouguer (mGal)
Fig. 2. Gravity model of Iivaara.
-25
-23
-21
-19
-17
-15
-13
-11
-9
-7
Fig. 3. Magnetic worms suggest a steep plunge towards NNW.
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Lauri, L. S., Heilimo, E., Leväniemi, H., Tuusjärvi, M., Lahtinen, R. & Hölttä, P. (eds)
Temporal changes in the amount of mineral
resources in finland
by
Mari Tuusjärvi and Raili Aumo
Geological Survey of Finland, P.O. Box 96, FI-02151 Espoo, Finland
E-mail: [email protected]
INTRODUCTION
Information on known mineral resources (including ore reserves) is continuously updated and published by the Geological Survey of Finland (FODD 2013).
Information on the intensity of use (ore mining) is also published annually (e.g.
Kananoja et al. 2013). However, there is lack of information on annual changes
in the amount of mineral resources and ore reserves. The collection of this information would provide a more comprehensive understanding of the adequacy
of ore reserves, and also the amount of mineral resources in different classes of
the mineral resource classification (Fig. 1). Extraction, price and cost changes affect ore reserves, and exploration affects both resources and reserves. In addition,
changes in the reporting styles of companies can affect both. In this study, the
goal is to measure the annual changes in resources and reserves, and also the level
of effect of the different factors on these changes.
METHODOLOGY
We have now studied 12 operating metal ore mines, their resources, reserves and
production during a three-year period from 2010–2012. The data were mainly
gathered from the annual reports of mining companies. We collected data on
proven and probable reserves, measured, indicated and inferred resources in
tonnes, and their metal grades and metal content (tonnes). Depending on the
company, reserves can be either included in or excluded from resources. Therefore, the data on some mines were converted to be comparable with others. Later,
information on exploration targets will also be included.
PRELIMINARY RESULTS
Preliminary results indicate that despite continuous mining, the amount of ore
reserves has not markedly decreased during the studied period. In addition,
the amount of mineral resources, especially inferred resources, has markedly
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increased. Of the metals, particularly the amount of gold in reserves increased,
most probably reflecting the intensive exploration for gold during the studied period. According to the preliminary results, it appears that the amounts of reserves
and resources vary annually, reflecting the intensity of mining and exploration,
but possibly also the prices and operating costs. More specific analysis of the dataset will hopefully provide more specific observations on these dynamics.
References
FODD 2013. Fennoscandian Ore Deposit Database [Electronic resource]. Geological Survey of
Finland (GTK), Geological Survey of Norway (NGU), Geological Survey of Russia (VSEGEI),
Geological Survey of Sweden (SGU), SC Mineral [referred 26.3.2013]. Available at: http://
en.gtk.fi/informationservices/databases/fodd/index.html
JORC 2012. Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore
Reserves (The JORC Code) [Electronic resource]. The Joint Ore Reserves Committee of The
Australasian Institute of Mining and Metallurgy, Australian Institute of Geoscientists and
Minerals Council of Australia. Available at: http://www.jorc.org
Kananoja, T., Pokki, J., Ahtola, T., Hyvärinen, J., Kallio, J., Kinnunen, K., Luodes, H., Sarapää, O., Tuusjärvi, M., Törmänen, T. & Virtanen, K. 2013. Geologisten luonnonvarojen hyödyntäminen Suomessa vuonna 2011. Summary: Geological resources in Finland, production
data and annual report 2011. Geological Survey of Finland, Report of Investigation 203. (in
Finnish)
Fig. 1. General relationship between exploration results, mineral resources and ore reserves according to JORC (2012). Reprinted with the permission of the Australasian Institute of Mining
and Metallurgy.
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NEW TYPE OF LOW-SULphIDE pge-REEF OF
THE SOTKAVAARA PYROXENITE INTRUSION,
rOVANIEMI, NORTHERN FINLaND
by
Tuomo Törmänen, Irmeli Huovinen and Jukka Konnunaho
Geological Survey of Finland, P.O. Box 77, FI-96101 Rovaniemi, Finland
E-mail: [email protected]
The pyroxenitic Sotkavaara intrusion is located 25 km E-SE of Rovaniemi, in the
so-called Kuluskaira area of the Peräpohja schist belt. The 1.5 x 2.5 km pyroxenite
body was intruded into the mica schists/gneisses of the Pöyliövaara formation
(Paakkola group). Quartzites and amphibolites belonging to the Oikaraisenvaara
formation (Kivalo group) occur nearby to the south and west. The Pöyliövaara
formation additionally contains some black schists, which are visible as minor
conductors on aerogeophysical maps, and also occur close to the intrusion. The
presence of a relatively unknown mafic-ultramafic body intruding black schistbearing country rocks prompted further investigations, which began in 2007 with
outcrop sampling, followed by ground geophysical surveys (magnetic, VLF-R
and two gravity measurement lines) in 2008.
First models of the intrusion, based on gravity data, indicated the possible
presence of more dense rock types (i.e. peridotites) at depth, and a total thickness
of 600–700 m. As the intrusion was considered to have potential for Cu-Ni-PGE
mineralization, it was decided to drill two holes (R398-R399) through the intrusion in 2009. These drillings revealed that the pyroxentic part of the intrusion is
only ca. 300 m thick, followed by an up to 100-m-thick gabbro-amphibolite zone,
and finally quartz-feldspar and mica schist of the Peräpohja schist belt.
Pyroxenite in the Sotkavaara intrusion is small to medium-grained and mostly
composed of clinopyroxene and amphibole. Pyroxenite commonly contains ca.
1-mm spots composed of orthopyroxene ± olivine ± plagioclase. Locally, there
are 1–5-m-thick dunite-peridotite layers/dykes altered to serpentinite. Pyroxenites have low Al2O3 (2–4 wt%), moderate contents of MgO (16–20 wt%), TiO2
(0.4–0.6 wt%) and Cr (0.1–0.2 wt%), and low contents of sulphur (100–600 ppm)
and nickel (300–500 ppm). The rocks in the gabbro-amphibolite zone can be classified into three groups: low-TiO2 gabbros, high-TiO2 gabbros and amphibolites.
The low-TiO2 gabbros also have lower Fe2O3 and V compared to the high-TiO2
gabbros. However, both gabbro types have nearly identical chondrite-normalized
REE patterns, with a flat LREE and sloping MREE to HREE, which also resemble
the REE patterns of the pyroxenites.
Due to low whole-rock S contents, visible sulphides are very rare in the pyroxenites, whereas the gabbros locally contain sparse disseminated sulphides (R399:
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31.5m @ 0.1% Cu). However, the second hole drilled in 2009 (R399) intercepted
a ca. 25-cm-thick massive sulphide vein containing 2.1% Ni, 0.47% Cu, 0.26% Co
and trace amounts of PGEs (79 ppb Pd).
To investigate the presence of additional massive sulphides, 7 holes (1272 m)
were drilled in 2012 in the central and marginal parts of the intrusion. These failed
to detect any additional massive (or disseminated) sulphides. Trace amounts of
sulphides were detected during core logging, closely associated with unusual,
‘mottled’ textured pyroxenite. A 3-m interval (drill hole R6) was submitted for
analysis and was found to contain elevated precious metals (Au+Pd+Pt between
0.86–1.16 ppm, 1-m intervals) with very low S and base metal values (ca. 400 ppm
S, 65 ppm Cu and 150 ppm Ni).
Additional analyses revealed a thick PGE anomalous zone with a very sharp
lower ‘contact’ where PGEs drop from 1 ppm to some tens of ppbs over a onemetre interval. Upwards, the PGE values gradually diminish to anomalous levels
(>100 ppb) (see Figure 3). So far, this reef-type PGE occurrence has been located
from three drill holes: R6, R12 and R398. The best intersection is from hole R6
with 6m @ 0.99ppm Au+2PGE, with additional 7m @ 0.51ppm. The Pt/Pd ratio
varies across the mineralization, with a very low ratio (<0.1–0.5) at the highest
grade intervals. Upwards, the Pd values decline rapidly and the Pt/Pd ratio increases to ca. 5 and moderate 2PGE values, and then decreases again to values
between 1 and 3, as the PGE contents drop to below 150–200 ppb.
The age of the Sotkavaara intrusion is unknown. Age data for the Pöyliövaara
formation indicate a maximum deposition age of ca. 1.98 Ga (Hanski et al. 2005).
Thus, Sotkavaara represents a relatively young mafic intrusive phase in northern
Finland. Mafic intrusive rocks within the Peräpohja schist belt are relatively rare.
Diabase dykes and sills in the central parts of the belt belong to 2.2 Ga and 2.1
Ga age groups (Perttunen & Vaasjoki 2001). Small ultramafic and gabbroic intrusions in the Liakka area near Tornio have similar ages to the Haaparanta suite,
i.e. ca. 1.88 Ga. Mafic intrusive rocks younger than 2.0 Ga are also rare in other
parts of northern Finland. The Jalokoski intrusion on the Swedish-Finnish border
belongs to the Haaparanta suite age group (1.87 Ga), and the Kulkujärvi gabbro
in Kittilä has an age of 1.96 Ga (Rastas et al. 2001, Väänänen & Lehtonen 2001).
The only known host rock for reef-type PGE mineralization in northern Finland is represented by the 2.44 Ga layered intrusions. Although the Liakka-type
intrusions are known to host minor Ni-Cu deposits, their PGE contents are unknown. It is possible that Sotkavaara represents a new type of mafic intrusionhosted PGE mineralization type with extremely low S contents, with an age of
<1.98Ga.
References
Hanski, E., Huhma, H. & Perttunen, V. 2005. SIMS U-Pb, Sm-Nd isotope and geochemical study
of an arkosite-amphibolite suite, Peräpohja Schist Belt: Evidence for ca. 198 Ga A-type felsic
magmatism in northern Finland. Bulletin of the Geological Society of Finland 77, 5–29.
Perttunen, V & Vaasjoki, M. 2001. U-Pb geochronology of the Peräpohja Schist Belt, northwestern Finland. In: Vaasjoki, M. (ed.) Radiometric age determinations from Finnish Lapland
and their bearing on the timing of Precambrian volcano-sedimentary sequences. Geological
Survey of Finland, Special Paper 33, 45–84.
Rastas, P., Huhma, H., Hanski, E., Lehtonen, M. I., Härkönen, I., Kortelainen, V., Mänttäri,
I. & Paakkola, J. 2001. U-Pb isotopic studies on the Kittilä Greenstone area, central Lapland,
Finland. In: Vaasjoki, M. (ed.) Radiometric age determinations from Finnish Lapland and their
bearing on the timing of Precambrian volcano-sedimentary sequences. Geological Survey of
Finland, Special Paper 33, 95–142.
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Väänänen, J. & Lehtonen, M. I. 2001. U-Pb isotopic age determinations from the Kolari-Muonio area, western Finnish Lapland. In: Vaasjoki, M. (ed.) Radiometric age determinations
from Finnish Lapland and their bearing on the timing of Precambrian volcano-sedimentary
sequences. Geological Survey of Finland, Special Paper 33, 85–94.
Fig. 1. Ground magnetic map of the Sotkavaara intrusion superimposed on the digital bedrock
map. Contains data from the National Land Survey of Finland Topographic Database 08/2012.
Fig. 2. 3D presentation with drill holes, lower contact of pyroxenite (grey drape) and PGE reef (red
bars) indicated. The top layer is the same ground magnetic map as in Figure 1.
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Fig. 3. Chalcophile element and sulphur profiles across the PGE reef from two Sotkavaara drill
holes.
161
www.gtk.fi
[email protected]
The GTK Mineral Potential research programme is wide in
scope and multidisciplinary in nature. To provide overviews
of current research activities within the programme, the 2nd
Mineral Potential Workshop was held at Hotel Rauhalahti,
Kuopio, Finland, from 6−7 May 2014. The abstracts of the
presentations and posters are published in this volume of the
GTK’s Report of Investigation series.
ISBN 978-952-217-283-9 (pdf)
ISSN 0781-4240