till geochemistry in arctic exploration · 2017-09-19 · • till geochemistry (< 0.06 mm) and...

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

http://en.wikipedia.org/wiki/File:Iceage_north-intergl_glac_hg.png

http://en.wikipedia.org/wiki/File:Iceage_north-intergl_glac_hg.png


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


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


• 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


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


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


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


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


• 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

7.9.201711 Pertti Sarala - Oulu Mining Summit 2017

• 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


• 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


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


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


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


• 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

till geochemistry in arctic exploration · 2017-09-19 · • till geochemistry (< 0.06 mm) and...

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