Till geochemistry in Arctic exploration Pertti Sarala Research Professor, PhD, EurGeol Geological Survey of Finland GTK / Oulu Mining School, University of Oulu Photo P. Sarala
Till geochemistry in Arctic
exploration
Pertti Sarala
Research Professor, PhD, EurGeol
Geological Survey of Finland GTK /
Oulu Mining School, University of Oulu
Photo P. Sarala
Background
7.9.2017Pertti Sarala - Oulu Mining Summit 20172
• Large areas in the Northern
Hemisphere were glaciated several
times during the Quaternary period
• Glaciers eroded the bedrock surface,
transported material and formed the
soils and morphologies which are
typical for example in Finland,
• Surficial deposits are composed mainly
of till and glaciofluvial/fluvial sand and
gravel deposits
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Background
• Surficial geochemical sampling and
analytical methods are largely used in
mineral exploration in glaciated
terrains
• Tens of glaciations during Quaternary
• Glaciogenic sediments dominate
• Geochemical methods have been
widely applied for mineral potential
mapping and exploration in the
glaciated areas for more than 50
years
• Supported by the surficial boulder
and indicator mineral methods
Cu anomaly in till at Outokumpu
Kauranne 1959
p
K
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Till geochemical exploration in glaciated terrain• Soils and till are traditional sample mediums in exploration
• Till is a representative medium for exploration (secondary dispersion)
• Sampling is usually easy and effective
• Till geochemistry (< 0.06 mm) and heavy mineral studies are most used methods
• Soil horizons were also used in exploration together with environmental research
• IMPORTANT! Till stratigraphy and glacial deposition mechanisms must be well-known to succeed in till sampling and data interpretation!
Photo by J. Valkama
Geological background
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• Arctic areas have good potential for new mineral discoveries
• Bedrock formed mainly crystalline of Archean (>2,500 milj. year) and Proterozoic (2,500-542 milj. year) rocks
• Main metallogenic zones have strong lithological control
• Nowadays, the focus is in deeper ore deposits and in critical minerals
• ”Easy”, exposed ore deposits are more or less found
• However, large areas still remain under-explored
• Physical and chemical weathering has produced deeply weathered bedrock surface of which remains are still found in many places
Luukkonen & Sorjonen-Ward 1998
Occurrences of the Archean bedrock in the world
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Pre-glacial
weathered bedrock
• Saprolite and saprock common
particularly in the central part of
the glaciated terrains;
like in northern Finland
• Weathering processes,
composition of weathered rocks
and their influence to the till
geochemistry is important in
mineral exploration
=> can cause false anomalies
• Weathered bedrock itself is
a potential source for many
elements such as Au and REEs
Photo by P. Sarala
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Till geochemical maps and data analysis
• Small-scale till geochemical datasets (e.g. 1 sample /4 km2) are used for identifying regional geochemical characteristic
• Increased density needed for target-scale research
• Deep analysis and interpretation together with available geological and geophysical data
Salminen 1995
Till, Density ¼
km2
Foregs
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Prospectivity mapping and SOM
Nykänen & Salmirinne 2006
Torppa et al. 2015
• Regional till geochemical datasets are effective for spatial
modelling; used for example in prospectivity and self-
organising mappings
Prospectivity mapping for Au in central Finnish Lapland
Self-organising map study
in eastern Finnish Lapland
Critical metals and minerals
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Cri
tic
alR
aw
Mate
ria
ls
Gallium
Magnesite
Silicon MetalCoking coalFluorsparGermaniumIndium
Chromium
Tungsten
AntimonyBerylliumBorateCobaltMagnesiumNatural Graphite
Niobium
PGMs
Phosphate Rock
REEs (Heavy)
REEs (Light)
EU
Supply >20% <20% <10% <3% <1%
No
n-C
riti
ca
lR
aw
Mate
ria
ls
Clays (& Kaolin)
Diatomite
Feldspar
Hafnium
Limestone
Perlite
Sawn Softwood
Silica sand
Tellurium
Bentonite
Gypsum
Potash
Pulpwood
Selenium
Talc
Aluminium
Copper
Rhenium
SilverZinc
Barytes
Bauxite Iron
Lithium
Nickel
Gold
Manganese
Molybdenum
Natural Rubber
Scandium
Tantalum
Tin Titanium
Vanadium
There is a need to increase self-production and reserves of the critical, high
technology metals and minerals (incl. REE) in EU (EU’s mineral strategy).
Critical metals and minerals in Finland
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• Finland has a good
potential for high
technology mineral
deposits, and
particularly in northern
Finland where there
occur large pre-glacial
weathered bedrock
areas (saprolite/saprock)
• Weathering reach
c. 100 m depth
• Some elements (e.g. La,
Y, Ce) in till and
lithogeochemistry are
very good indicators of
both LREE and HREE
mineralization
HREELREE
Sarapää et al. 2013 JGE; Sarapää & Sarala 2013 GEEA,
Al-Ani & Sarapää 2013 GEEA
Exploration challenges
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• Exploration is challenging in the northern and/or Arctic regions by
the complex glacial deposits, large peat bog and tundra areas as
well as pre-glacial weathered bedrock in places
=> Indication and indicators of mineralization are hard to recognize
• Logistical problems, (large) conservation areas and political issues
restrict sampling and research
Photo by M. Moilanen
P. Sarala
Different techniques for till sampling
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• Light-way sampling by hand
• Easy but not effective, only surface samples, thick organic deposits problematic; practically no traces and nature impact
• In some places usable, if supported by for example stream sediment and water sampling and biogeochemistry
• Percussion drilling for basal till sampling
• Effective in till geochemistry although sample size small
• Benefit: samples from different depths and weathered bedrock, small traces and low nature impact
• Soil drilling for basal till and bedrock sampling
• Effective in till and bedrock geochemistry; lithology, mineralogy and stratigraphy; indicator mineral research for big sample size
• Benefit: big and representative samples => sparse sampling grid needed
• Nature impact and traces bigger than in other techniques; can be diminished using good planning and advanced methods such as Sonic Drilling
P. Sarala
P. Sarala
7.9.2017Pertti Sarala - Oulu Mining Summit 201713
Development of exploration techniques
• Development has been very active in recent years
• E.g. Green Mining projects (NovTecEx and UltraLIM)for greenfield exploration
• New on-site, real-time analyse methods (e.g. pXRF)
• Sampling and analysis based on weak/selective leachingtechniques beside the conventional till geochemical analyses => top mineral soil, organic layer, vegetation and snow
• New chemical analyse and indicator mineral research techniques, such as HR-ICP-MS and automated FE-SEM-EDS and MLA
• Data processing (like SOM-mapping) and spatial data modelling give advanced ways to analyse geochemical datasets and create prospectivity maps
87.604
0mean=1.5037std=0.6448
mean=0.5588std=0.4959
87.187
0
0 10 205 km
a b
c d
clusters: 24
clusters: 22
P. Sarala
Torppa et al. 2015
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Advanced, low-impact
geochemical methods• Many light-weigth and effective methods
available
• Sampling for selective/weak leach
analyses (Ammonium acetate, Bioleach,
MMI, Ionic leach, Entzyme leach, Soil Gas
Hydrogen etc.)
• Biogeochemistry
(plants and peat)
• Snow geochemistry
• Stream sediment and
water geochemistry
• On-site
methods,
like pXRF, pXRD
Photo by P. Sarala
Photo by J. ValkamaPhoto by P. Sarala
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Theoretical background for mobile ions• Mobile metal ion processes move ions through the soil (and upper bedrock)
into upper part of mineral or organic soil horizons, where ions accumulate on
surface of mineral and organic particles – many known processes
• Furthermore, soil gasses produced by bacteria on top soil horizons
accumulate into the bottom layer of snow. Certain hydrocarbons indicate
indirectly metal-ions’ composition in soil giving a signature of the underlying
buried mineralization
Modified after
Heberlain 2013
Snow
Mineral soil
21.4.2016
Indika Project
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• Automated indicator mineral identification methods for the critical mineral exploration (Indika)
• ERDF funded (EAKR) project (2016-2018)
• Partners: GTK, Lapin AMK and University of Oulu
• Financiers: Oxford Instruments, Suomen Kaivosyrittäjät ry and Lapin Kullankaivajain Liitto
• Project focuses on the development of critical minerals’ exploration concept by developing cost-effective methods for the indicator mineral concentration techniques and the automated indicator minerals identification methods and by using new on-site geochemical and mineralogical analysis techniques
• New, indicator mineral based concept for the critical minerals exploration will be developed by increasing co-operation between research organizations, mineralogical lab facilities and companies in northern Finland
P. Sarala
P. SaralaP. Saralawww.olympus.com
Available:
http://tupa.gtk.fi/julkaisu/specialpaper/sp
_057.pdf
• Sarala, P. (ed), 2015. Novel technologies for greenfield exploration.
Geological Survey of Finland, Special Paper 57, 196 p.
• Sarala, P. (toim.), Karinen, T., Lahti, I., Lehtonen, M., Middleton, M.,
Pirttijärvi, M., Salmirinne, H., Taivalkoski, A., Torppa, J., Valkama, J.
& Nykänen, V. 2015. NovTecEx – Uusia malminetsintämenetelmiä
herkille pohjoisille alueille: Loppuraportti; NovTecEx – Novel
technologies for greenfield exploration: Final report. Geologian
tutkimuskeskus, Raportti 37/2015, 57 p.
• Sarala, P. 2016. Comparison of different portable XRF methods for
determining till geochemistry. Geochemistry, Exploration,
Environment, Analysis 16, 181-192.
• Middleton, M. et al. 2017. Ultra low impact geochemical exploration
methods in the sub-arctic. Geological Survey of Finland, Report of
Investigation. (In prep)
Publications
Pertti Sarala - Oulu Mining Summit 2017
Photo P. Sarala
7.9.201718