PORTABLE XRF: AN ADVANCED ON-SITE ANALYSIS …tupa.gtk.fi/julkaisu/specialpaper/sp_057_pages_063_086.pdf · METHOD IN TILL GEOCHEMICAL EXPLORATION ... site analysis method in till

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PORTABLE XRF: AN ADVANCED ON-SITE ANALYSIS METHOD IN TILL GEOCHEMICAL EXPLORATION

Novel technologies for greenfield explorationEdited by Pertti SaralaGeological Survey of Finland, Special Paper 57, 63–86, 2015

byPertti Sarala, Anne Taivalkoski and Jorma Valkama

Sarala, P., Taivalkoski, A. & Valkama, J. 2015. Portable XRF: An advanced on-site analysis method in till geochemical exploration. Geological Survey of Finland, Special Paper 57, 63−86, 8 figures and 4 tables.

The application of the portable XRF method (pXRF) in mineral exploration us-ing till was developed and tested in the Savukoski-Pelkosenniemi area, northern Finland. The research was a part of the Tekes-funded project ‘Novel technologies for greenfield exploration’ realized in 2012–2014. Till samples from the basal till layer (1–2 m above the bedrock surface) were collected using test pits and deep soil drilling. The use of pXRF was tested for 100 basal till samples of the following sample types: 1) natural (wet), 2) natural (dried) and 3) pulverised and briquetted. A comparison was carried out with laboratory XRF and conventional aqua regia-based geochemistry. The correlation between the results from the tested methods was excellent or good for most of the main and basic elements, particularly for base metals. pXRF analyses also correlated well with aqua regia-digested till geochem-istry. The results demonstrate that pXRF provides a rapid and practical method for obtaining a reliable view of the geochemical characteristics of till, and can be used in mineral exploration and lithological mapping.

Keywords (GeoRef Thesaurus, AGI): X-ray fluorescence, mineral exploration, till, geochemistry, Savukoski, Pelkosenniemi, Finland

Geological Survey of Finland, P.O. Box 77, FI-96101 Rovaniemi, Finland

E-mail: [email protected]

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Geological Survey of Finland, Special Paper 57Pertti Sarala, Anne Taivalkoski and Jorma Valkama

INTRODUCTION

X-ray fluorescence (XRF) is a total chemical analy-sis method that has been used as a standard meth-od in laboratories for decades (cf. Potts & Webb 1992, Beckhoff et al. 2006). With XRF, the concen-trations of the main elements and metals, as well as several precious elements can be determined. Modern portable XRF (pXRF) analysers have been effectively developed during the last decade (Cok-er 2010). The main advance in the development of mobile applications has been the lightweight equipment set-up and the detection limits, which are low enough (ppm scale) for a large group of elements. Furthermore, analysers are easy to take into the field and do not require laboratory con-ditions. These portable (i.e. hand-held) analysers have commonly been used in metal recycling and industry, and also for the analysis of rock and bed-rock samples, but have rarely been applied for soil samples. Furthermore, analysers have been exten-sively tested in mineral exploration and lithologi-cal research in arid and semi-arid conditions and at mine sites (Bowell et al. 2012, Gazley et al. 2014, Le Vaillant et al. 2014), but recently also by GTK for glacial till (Sarala & Mäkikyrö 2012, Sarala 2013, 2014).

An aim in this task of the project ‘Novel tech-nologies for greenfield exploration’ (NovTecEx) was to study and evaluate the applicability of pXRF in mineral exploration using till as a sam-ple material. Conventional surficial geological and geochemical methods have long been used in ex-ploration in glaciated terrains. Till sampling with variable sampling densities and patterns such as grids, lines or scattered sampling points have been carried out. Till samples are usually taken by per-cussion drilling, from tractor-excavated test pits or from small, hand-made sampling pits (Hirvas & Nenonen 1990). Hundreds or even thousands of

till samples or bedrock samples are collected from the surface of fresh bedrock or sometimes pre-gla-cial weathered bedrock, and after chemical labo-ratory analysis the potential for the explored ore deposit type is estimated. For till samples (the fine till fraction <0.06 mm), aqua regia digestion, i.e. partial leaching, is commonly used. At best, geo-chemical anomalies directly show mineralization in the bedrock.

Although till geochemical research is often the most useful method in the exploration of glaciated terrains, conventional till sampling with geochem-ical analyses is a time-consuming and expensive part of the exploration. Numerous till samples must be collected and analysed in the laboratory. For pre-control and qualification, the till stratig-raphy of the study area must be carefully exam-ined before geochemical interpretation (Sarala & Ojala 2008). In particular, in terrains with a com-plex till stratigraphy, till samples should be taken from separate till units, which means an increase in the number of collected samples. If a whole set of samples should be analysed in the laboratory, the analysis costs increase. Furthermore, sample pre-processing and powder pellet preparation for laboratory XRF are time-consuming and raise costs even further.

Although pXRF analysers are widely used in ex-ploration and in mining using rock samples, the use of pXRF in till geochemical exploration has been poorly tested and reported. In this study, the applicability and reliability of pXRF in till geo-chemical exploration was investigated, including an estimation of the need for sample preparation and assay process development for field and/or laboratory conditions. A comparison with conven-tional till geochemical methods was also carried out.

STUDY AREA AND GEOLOGICAL SETTINGS

The study area is located in the Savukoski-Pelko-senniemi area in eastern Lapland (Fig. 1). The total study area is about 980 km2, of which the new till sampling covered about 850 km2. Only the Akan-

vaara claim area in the southeast and the Sakkala-aapa mire area in the west had to be excluded from till sampling during the project.

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Geological Survey of Finland, Special Paper 57Portable XRF: An advanced on-site analysis method in till geochemical exploration

Fig. 1. Location and the bedrock of the Pelkosenniemi-Savukoski study area in northeastern Finland. Till and bedrock sampling points (157) are also indicated on the map. Bedrock map (Bedrock of Finland – DigiKP). Contains data from the National Land Survey of Finland Topographic Database 03/2013.

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Bedrock

Lithologically, the Savukoski-Pelkosenniemi study area is divided into two main rock domains: Ar-chaean and Palaeoproterozoic. The bedrock in the eastern part is composed of granite gneisses and greenstones of the Archaean basement. In the west, the bedrock consists of metasedimentary rocks with narrow mafic volcanic rock ribbons and diabase dykes that are assigned to the Palaeoprote-rozoic Central Lapland Greenstone Belt (Lehtonen

et al. 1998). The two rock domains are separated by a north–south-oriented chain of komatiite and graphite sulphide schists. In the southeastern part of the study area occurs the Akanvaara layered in-trusion with known chromite-PGE mineralization (Mutanen 1997). No other observations of eco-nomically significant mineral deposits have been made in the area.

Surficial geology

The study area is located in central Lapland, which is situated in the central part of the last continen-tal glaciations of the Scandinavian ice sheet. It is located close to the latest ice-divide zone of the Late Weichselian glaciation (Hirvas 1991, Johans-son et al. 2011). A generally typical feature for the central part of the glaciated terrain is a thin gla-ciogenic overburden together with a weak glacial erosion rate and distant transport. However, thick glaciogenic deposits with multiple till units were also found in the Savukoski-Pelkosenniemi area (Johansson 1995).

Earlier knowledge of the surficial deposits and the glaciogenic formation in the study area is mainly based on research conducted during the 1970s by Hirvas et al. (1977) and the 1990s by Johansson (1995). Based on those investigations, the till units of three different glacial phases can be found in the Savukoski-Pelkosenniemi area, representing a northern ice-flow direction in the older phase and a northwestern and western direc-tion during younger phases. These give some esti-mation of glacial transportation and the possible source areas for till material.

Based on new observations during this pro-ject, glacial overburden dominates the study area, although post-glacial, fluvial sediments are also dominant as the upper sediments in modern river valleys (Sarala 2015). Sandy, matrix-dominant till is the main sediment type, having a thickness of 2–5 m in the higher ground and 5–15 m in the lowland areas. In the Kemijoki River valley, the thickness of sediment deposits is usually higher than in other areas due to the location of the river in a shear or weakness zone. The basal parts of the valley deposits are glaciogenic in origin, but the uppermost sediments were deposited during post-glacial fluvial processes. The deepest soil thick-ness based on soil drilling is more than 50 m in the northern part of the study area. The sediments in that drill hole were mostly composed of sands and gravels, but layers of till were also observed. Under the overburden, the surface of the bedrock is commonly weathered from some centimetres up to several tens of metres, being mainly saprock in type and rarely saprolite (cf. Sarala & Ojala 2008).

METHODS

Sampling and sample processing

Till samples were collected from test pits and soil drilling cores representing the same sample mate-rial as conventional till geochemical samples and heavy mineral samples. The number of sampling sites was 157 (71 test pits + 86 drilling sites), with the sampling density being about 1 sample per 5.5 km2. Till samples were collected from the bottom part of the glaciogenic overburden (1–2 m above

the bedrock surface), representing as exactly as possible the same type of glacial transport mecha-nism and transport distances throughout the study area.

The pXRF analyses were carried out following a four-step analysis programme. At first, natural, unprocessed, moist samples were analysed using pXRF directly in the field or field camp. In the

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Fig. 2. The benefit of the pXRF analyser in exploration is its easy and fast usability in the field. Element contents can be rapidly analysed, even using natural till. The photos demonstrate the use of the Delta 6000 pXRF analyser for till geochemical analysis from a sample bag (left) and directly from the fresh till surface (right). A thin plastic film (<10 µm) between the analyser head and the samples was normally used to avoid contamination and protect the detector window. Photos: P. Sarala, GTK.

second phase, the same unprocessed till samples were dried (c. 40 °C) before analysis. To avoid con-tamination and protect the detector window, a thin plastic film (<10 µm) was used between the ana-lyser head and the natural samples (both wet and dried; Fig. 2). In the third phase, the samples were sent to the laboratory of Labtium, where the dried

samples were first pulverised and then pressed into briquettes before laboratory XRF analysis. Final-ly, the briquettes were analysed using pXRF. As a comparison, a batch of the samples was sent for geochemical analysis using aqua regia digestion and ICP-OES and ICP-MS (Labtium code 515PM) for the <0.06 mm till size fraction.

Portable XRF analyses

An Olympus Innov-X Delta 6000 pXRF analyser was used for testing and developing the tech-nique described in this paper (Fig. 2). The Delta 6000 has a four-watt X-ray tube with an Rh an-ode, 8–40 keV, 5–200 μA, and a high resolution, thermo-electrically cooled Si PIN diode detector. Two different modes were used in the measure-ment procedure: the Soil mode with three beams and MiningPlus mode with two beams. The time for a single measurement was set as 40 seconds for both assay modes: 10+15+15 seconds for beams 1–3 in the Soil mode and 20+20 seconds for the two beams of the MiningPlus mode. Each meas-urement was repeated three times per sample, and

the average values were determined and used for analysis.

The element list for the Soil mode is Ag, As, Bi, Ca, Cd, Cl, Co, Cr, Cu, Fe, Hg, K, Mn, Mo, Ni, P, Pb, Rb, S, Sb, Se, Sn, Sr, Th, Ti, U, V, W and Zn, and for the MiningPlus mode Ag, Al, As, Bi, Ca, Cd, Cl, Co, Cr, Cu, Fe, K, Mg, Mn, Mo, Ni, P, Pb, Sb, S, Sn, Si, Ti, V, W, Zn and Zr. When the same element was measured with both assay modes, the values from the Soil mode were used in analysis. Detection limits are not constant in the case of pXRF. Instead, the pXRF analyser gives too low or unreliable contents signalled as <LOD, indicating undetected values.

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Laboratory XRF analyses

After pXRF measurements, the same till samples were analysed using laboratory XRF methods in the laboratory of Labtium. The analyses were con-ducted on pressed powder pellets that were pre-pared from homogenised subsamples after fine

grinding (<10 μm). The list of the analysed ele-ments is: Al, As, Ba, Bi, Ca, Ce, Cl, Cr, Cu, Fe, Ga, K, La, Mg, Mn, Mo, Na, Nb, Ni, P, Pb, Rb, S, Sb, Sc, Si, Sn, Sr, Th, Ti, U, V, Y, Zn and Zr.

Chemical analyses

For the chemical analyses, duplicate till samples were used. The analyses were conducted in the laboratory of Labtium (accreditation SFS-EN ISO/IEC 17025, T025). The till samples were first dried at 70 °C and then sieved to the <0.06 mm fraction before a partial leach using aqua regia at 90 °C. Inductively coupled plasma atomic emission spec-trometry (ICP-OES) was used for the analysis of 28 elements (Al, As, B, Ba, Ca, Cd, Co, Cr, Cu, Fe,

K, La, Li, Mg, Mn, Na, Ni, P, Pb, Rb, S, Sc, Sr, Ti, V, Y, Zn, Zr) in the 0.15-g subsamples and inductive-ly coupled plasma mass spectrometry (ICP-MS) for the analysis of Ag, Be, Bi, Ce, In, Mo, Sb, Se, Te, Th, U, W and Yb (Labtium method PM515). Gold and Pd were analysed using graphite furnace atomic absorption spectrometry (GFAAS) with Hg co-precipitation using a 5-g subsample (Lab-tium method 521U).

Quality control

Quality control was carried out for the Delta pXRF analyses by randomly measuring six natural till samples twice in the field. The measurement pro-cedure was the same for both samples and the av-erage values were used to compare the results. A comparison of the duplicate field analyses is pre-sented in Tables 1 and 2. The analysis data indicate very good similarity between the original and du-plicate measurements in both the MiningPlus and Soil modes. Some differences were also seen due to the heterogeneous nature of till. This was more clearly evident if the first and second measure-ments were not carried out from exactly the same place.

After drying the natural till samples, two types of references were used in the sample set meas-ured by pXRF. The first was an older till laboratory XRF pellet (LO8007205) that has been measured at 20–25-sample intervals using pXRF. Another reference was GTK’s in-house, arsenic-bearing, natural till sample (c. 100 kg) collected from the

Häme region of southern Finland in 2008. Af-ter removing bigger stones (>1–2 cm), this large sample was first dried and homogenised and then stored as subsamples in 500-g sample bags. Four of these were randomly added to the original till sample set and processed in the same way as the original samples in the laboratory, i.e. first dried and measured three times by pXRF and then sent to the laboratory of Labtium for pulverising, bri-quetting and measurement using the laboratory XRF analyser (Table 3).

For the conventional till geochemistry (<0.06 mm and aqua regia digestion), 5% of the duplicate samples was taken for QA. Furthermore, the labo-ratory, as a part of its own quality control system, estimated the reliability of analyses during leach-ing and other analysis step by inserting 10% of the samples in random order as duplicates. The labora-tory also used certified reference samples that were added within the analytical batches in the labora-tory following the ILAC-MRA Arrangement.

Data processing

ArcMap 10.1 software was used for the map pro-cessing. In the data processing and calculations of the conventional till geochemistry (for aqua regia-

based analyses), a value of half the detection limit was assigned for elements with contents lower than the detection limit.

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Table 1. Comparison of the pXRF results (Soil mode) for the six till samples measured twice in a random order within the analysis batches. Duplicate measurement is marked as R, +/- indicates a standard deviation calculated by pXRF.

Sample_ID POS$-2012- POS$-2012- POS$-2012- AMPE-2012- AMPE-2012- AMPE-2012-

49.1 49.1 R 56.2 56.2 R 79.2 79.2 R 41.2 41.2 R 49.2 49.2 R 54.2 54.2 R

Depth 1.0 1.0 3.0 3.0 3.0 3.0 0.2 0.2 0.2 0.2 0.2 0.2

Unit PPM PPM PPM PPM PPM PPM PPM PPM PPM PPM PPM PPM

K 9483 8999 10921 11503 10129 11314 11706 11901 7216 5348 8327 8586

K +/- 227 215 225 236 223 236 249 244 170 128 196 198

Ca 20126 19674 15069 15242 11448 12610 12974 12298 8470 6388 10975 10907

Ca +/- 319 308 234 239 199 211 222 208 152 116 191 189

Ti 2224 2163 1640 1644 1301 1385 2660 2658 1572 1990 2263 2938

Ti +/- 46 44 34 35 31 32 50 49 33 56 43 51

V 49 44 40 40 26 39 54 51 34 54 38 41

V +/- 5 5 4 4 4 4 5 5 4 10 5 5

Cr 197 189 59 69 51 62 46 52 66 87 88 108

Cr +/- 9 9 6 6 6 6 7 7 6 13 7 7

Mn 302 300 185 200 167 173 194 189 136 132 150 156

Mn +/- 10 9 7 7 7 7 8 7 6 9 7 7

Fe 26565 25378 18006 16984 18815 17771 24884 25186 18946 19864 17729 18148

Fe +/- 174 167 121 117 127 121 161 159 122 130 120 121

Co 10.2 9.8 7.8 7 7.1 8.3 8.2 6.6 7.3 6.3 7.7 6.4

Co +/- 0.9 0.9 0.7 0.7 0.7 0.7 0.9 0.9 0.7 0.8 0.7 0.7

Ni 76 74 <LOD <LOD <LOD <LOD <LOD <LOD <LOD <LOD 29 <LOD

Ni +/- 10 10 26 26 26 26 27 26 25 25 9 25

Cu 34 31 <LOD 13 17 16 <LOD <LOD <LOD <LOD <LOD <LOD

Cu +/- 5 5 12 4 4 4 13 13 12 12 12 12

Zn 31 31 17 17 19 20 35 37 13.2 13 16 14

Zn +/- 3 3 2 2 2 2 3 3 2 2 2 2

Rb 36.4 36.5 44.5 46.7 39.9 43.1 48.5 45.9 30.5 31.1 31.5 36.2

Rb +/- 1.4 1.3 1.4 1.4 1.3 1.4 1.5 1.4 1.2 1.2 1.2 1.3

Sr 227 222 210 211 170 169 296 286 118 120 115 110

Sr +/- 7 7 6 6 6 6 9 8 4 4 4 4

Zr 177 170 197 201 152 170 190 206 169 158 204 200

Zr +/- 6 6 6 6 5 6 7 7 5 5 6 6

Pb 6.4 6.6 6.2 9.3 7.3 5.9 12.1 11.6 5 <LOD 5.1 5.2

Pb +/- 1.9 1.9 1.7 1.8 1.8 1.7 2 2 1.6 5 1.7 1.7

Under detection limit Ag, As, Bi, Cd, Cl, Hg, Mo, P, S, Sb, Se, Sn, Th, U, WNot measured Al, Hf, Mg, Si, Ta

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Sample_ID POS$-2012- POS$-2012- POS$-2012- AMPE-2012- AMPE-2012- AMPE-2012-

49.1 49.1 R 56.2 56.2 R 79.2 79.2 R 41.2 41.2 R 49.2 49.2 R 54.2 54.2 R

Depth 1.0 1.0 3.0 3.0 3.0 3.0 0.2 0.2 0.2 0.2 0.2 0.2

Unit PPM PPM PPM PPM PPM PPM PPM PPM PPM PPM PPM PPM

Al 42738.6 36524.9 39003.7 39007.1 33439.6 31838.0 56051.4 55589.2 40922.5 39900.3 33531.1 30678.6

Al +/- 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1

Si 227615.2 212158.6 244197.6 241280.6 228840.2 228608.7 211490.2 202287.2 196399.9 197363.0 210924.4 187720.9

Si +/- 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1

P 176.2 162.8 113.0 <LOD <LOD 194.8 909.8 989.9 351.8 285.9 <LOD <LOD

P +/- 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

K 6875.4 7109.2 8949.8 9381.2 9352.9 9226.0 8978.4 9228.6 5819.1 5653.7 6342.1 6025.1

K +/- 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Ca 15428.0 15892.4 12649.9 12757.1 9836.5 9649.3 9497.8 9554.3 7305.3 7204.5 7769.9 8705.6

Ca +/- 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Ti 3403.1 3152.2 3486.0 3365.8 2705.4 2744.0 3869.6 3403.2 2501.4 3245.8 3788.5 3672.4

Ti +/- 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

V 213.2 166.6 90.8 146.1 204.9 85.7 94.2 114.5 78.0 81.3 93.3 232.3

V +/- 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Cr 352.2 380.6 215.7 111.1 109.9 171.7 50.7 147.6 156.1 114.6 202.0 216.1

Cr +/- 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Mn 499.7 401.2 359.6 347.0 304.1 264.7 279.1 274.4 209.2 180.6 225.0 299.6

Mn +/- 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Fe 29967.4 28327.9 21331.0 20324.6 22621.7 21714.5 27494.0 28084.3 24900.4 22375.9 22204.7 25803.8

Fe +/- 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Mg 1743.2 <LOD <LOD <LOD <LOD <LOD <LOD <LOD 4069.5 3254.5 <LOD <LOD

Mg +/- 0.3 0.7 0.6 0.7 0.7 0.7 0.6 0.7 0.3 0.3 0.7 0.8

Co <LOD <LOD <LOD 93.3 <LOD <LOD <LOD <LOD <LOD <LOD <LOD <LOD

Co +/- 0.1 0.1 0.0 0.0 0.1 0.1 0.1 0.1 0.1 0.1 0.0 0.1

Ni 181.6 136.2 96.3 68.7 65.7 43.3 79.0 57.4 43.5 53.0 81.9 85.1

Ni +/- 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Cu 54.8 20.8 <LOD <LOD <LOD <LOD <LOD <LOD <LOD <LOD <LOD <LOD

Cu +/- 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Zr 155.5 157.3 172.6 155.1 132.2 127.2 139.1 169.5 118.3 123.2 144.3 125.2

Zr +/- 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Cd 263.3 227.1 252.1 240.8 238.9 237.6 233.6 242.7 208.6 222.4 209.8 257.2

Cd +/- 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Pb <LOD <LOD 8.4 5.1 <LOD <LOD <LOD <LOD <LOD <LOD <LOD <LOD

Pb +/- 0.018 0.017 0 0 0.018 0.017 0.017 0.018 0.017 0.016 0.017 0.015

Sn 308.9 264.7 289.9 309.7 305.1 281.1 269.5 298.1 277.1 252.1 233.6 300.0

Sn +/- 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Sb 376.7 343.7 377.0 385.6 368.0 348.5 340.8 365.6 333.6 321.1 306.8 393.9

Sb +/- 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

LE 669647.0 694574.0 668415.0 672026.2 691474.9 694465.1 680214.4 689188.2 716305.8 719368.1 713942.6 735484.1

LE +/- 0.7 0.7 0.7 0.7 0.7 0.7 0.7 0.7 0.7 0.7 0.7 0.7

Under detection limit Ag, As, Bi, Cl, Mo, S, W, ZnNot measured Hf, Hg, Rb, Se, Sr, Ta, Th, U

Table 2. Comparison of the pXRF results (MiningPlus mode) for the six till samples measured twice in a random order within the analysis batches. Duplicate measurement is marked as R, +/- indicates a standard deviation calculated by pXRF.

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Sample_ID Mg_%_175X Mg_%_pXRF* Al_%_175X Al_%_pXRF* Si_%_175X Si_%_pXRF* P_%_175X P_%_pXRF

POS$-2012-41.10 0.95 <LOD 7.95 6.6 32.7 35.7 0.075 <LOD

POS$-2012-70.10 1.04 <LOD 8.01 6 32.4 31.9 0.072 <LOD

POS$-2012-92.10 1.07 <LOD 8.04 6.3 32.3 34.6 0.072 <LOD

POS$-2012-102.10 1.02 <LOD 8.08 6.3 32.2 33.7 0.075 <LOD

Sample_ID K_%_175X K_%_pXRF Ca_%_175X Ca_%_pXRF Ti_%_175X Ti_%_pXRF Mn_ppm_175X Mn_ppm_pXRF

POS$-2012-41.10 2.18 2.28 1.65 1.48 0.312 0.3 372 420

POS$-2012-70.10 2.18 2.26 1.67 1.48 0.336 0.31 411 432

POS$-2012-92.10 2.25 2.36 1.62 1.43 0.336 0.32 418 419

POS$-2012-102.10 2.18 2.27 1.67 1.52 0.336 0.32 411 453

Sample_ID Fe_%_175X Fe_%_pXRF* S_%_175X S_%_pXRF Cl_%_175X Cl_%_pXRF V_ppm_175X V_ppm_pXRF

POS$-2012-41.10 3.10 2.96 0.028 <LOD 0.008 <LOD 70 78

POS$-2012-70.10 3.41 2.95 0.026 <LOD 0.009 <LOD 70 75

POS$-2012-92.10 3.40 3.2 0.035 <LOD 0.011 <LOD 75 75

POS$-2012-102.10 3.38 3.04 0.029 <LOD 0.009 <LOD 74 74

Sample_ID Cr_ppm_175X Cr_ppm_pXRF Ni_%_175X Ni_ppm_pXRF* Cu_ppm_175X Cu_ppm_pXRF Zn_ppm_175X Zn_ppm_pXRF

POS$-2012-41.10 48 76 <20 16 30 26 53 41

POS$-2012-70.10 58 82 <20 <LOD 30 29 55 41

POS$-2012-92.10 57 81 22 <LOD 44 36 66 50

POS$-2012-102.10 56 87 <20 29 30 40 66 38

Sample_ID As_ppm_175X As_ppm_pXRF Rb_ppm_175X Rb_ppm_pXRF Sr_ppm_175X Sr_ppm_pXRF Y_ppm_175X Y_ppm_pXRF

POS$-2012-41.10 20 37 96 79.6 229 185 18 15

POS$-2012-70.10 21 28 97 71.9 236 172 26 11

POS$-2012-92.10 25 33 100 83.8 232 199 21 16

POS$-2012-102.10 <20 38 100 76.8 238 195 26 13

Sample_ID Zr_ppm_175X Zr_ppm_pXRF Mo_%_175X Mo_%_pXRF Sn_%_175X Sn_%_pXRF Sb_%_175X Sb_%_pXRF

POS$-2012-41.10 198 225 <0.001 <LOD <0.002 <LOD <0.01 <LOD

POS$-2012-70.10 187 198 <0.001 <LOD <0.002 <LOD <0.01 <LOD

POS$-2012-92.10 193 223 <0.001 <LOD <0.002 <LOD <0.01 <LOD

POS$-2012-102.10 191 219 <0.001 <LOD <0.002 <LOD <0.01 <LOD

Sample_ID Pb_ppm_175X Pb_ppm_pXRF Bi_ppm_175X Bi_ppm_pXRF Th_%_175X Th_%_pXRF U_%_175X U_%_pXRF

POS$-2012-41.10 <20 10 <30 <LOD 0.001 <LOD <0.001 <LOD

POS$-2012-70.10 24 10 <30 30 0.001 <LOD <0.001 <LOD

POS$-2012-92.10 21 13 <30 <LOD <0.001 <LOD <0.001 <LOD

POS$-2012-102.10 <20 8 <30 <LOD 0.001 <LOD <0.001 <LOD

* Contents measured by the MiningPlus mode.

Detected only by the laboratory XRF

Sample_ID Ba_%_175X Na_%_175X Sc_%_175X Ga_%_175X Nb_%_175X La_%_175X Ce_%_175X

POS$-2012-41.10 0.058 2.30 <0.002 <0.002 <0.0007 <0.003 0.006

POS$-2012-70.10 0.058 2.26 <0.002 <0.002 <0.0007 <0.003 0.007

POS$-2012-92.10 0.061 2.28 <0.002 0.002 <0.0007 <0.003 0.006

POS$-2012-102.10 0.060 2.23 <0.002 0.002 <0.0007 <0.003 0.007

Detected only by pXRF

Sample_ID Se_ppm_pXRF Ag_ppm_pXRF Cd_ppm_pXRF Hg_ppm_pXRF W_ppm_pXRF

POS$-2012-41.10 15 <LOD <LOD <LOD 2468

POS$-2012-70.10 9.7 <LOD <LOD <LOD 1491

POS$-2012-92.10 11 <LOD <LOD <LOD 1672

POS$-2012-102.10 20 <LOD <LOD <LOD 2611

Table 3. Comparison of the pXRF and laboratory XRF (175X) results for the four reference till samples randomly measured using the Soil mode (or in some cases with the MiningPlus mode as indicated by *) within analysis batches.

72


RESULTS

Portable XRF analyser data

The statistical parameters of the measured data are presented in Table 4, in which all five different data-sets are compared for those elements that could be found in all data types with a sufficient number of detections (i.e. values over the detection limits) for statistical calculations. Based on the statistics, the main elements in all datasets, such as Al, Ca and K, behave the same way; the mean and me-dian values only slightly differ between the sample types and analysis methods. The contents are high-est in the pellet samples for both laboratory XRF and pXRF; this, however, is generally expectable because homogenised (pulverised and pressed) pellets are optimal for XRF. By comparison, for the main elements, aqua regia-based ICP-OES results are usually much lower than in the case of the dif-ferent XRF methods. This is understandable due to difference between the analytical methodologies; XRF measures total values, while aqua regia is a partial leaching method.

In the case of As and metals such as Co, Cr, Cu, Fe, Mn, Ni, V and Zn, the contents of the elements are at the same level for all XRF methods. This is a very important result and demonstrates that even natural and wet, unprocessed till samples analysed by pXRF can be used in mineral exploration. It is also notable that the base metal contents are most-ly at the same level and hence comparable to con-ventional, aqua regia-based analysis results for till fines (<0.06 mm).

The spatial distribution of the elements is simi-lar for all XRF analysis methods if they are plotted on a map. In fact, the patterns of the anomalies can be considered almost identical. The distribution of Ca is shown as an example of the main elements in Figure 3. It can clearly be seen that although the concentrations differ between the XRF methods, the distribution patterns are mainly the same; only

minor differences are seen. Only the results from conventional till geochemistry significantly di-verge from the other methods. On the other hand, all analysis results from till samples differ consid-erably from bedrock geochemical assays. This very strongly suggests that the till samples collected 1–2 m above the bedrock surface indicate a wider source area and longer glacial transportation, which has diluted the original geochemical signatures of the bedrock. In the case of metals, of which Cr is an example (Fig. 4), both XRF and conventional till geochemistry result in the same distribution pat-terns. Furthermore, for the base metals, there is a strong lithological control, indicating higher con-tents in the metamorphosed volcanic rocks and komatiites than in the surrounding rocks in the central part of the study area. This lithological con-trol is also seen for As and several base metals such as Co, Cu and Ni. Elevated arsenic and base metal contents follow the north–south-oriented series of volcanic rocks in central parts of the study area, indicating the presence of mineralized, most prob-ably sulphide-bearing rocks in the bedrock. High sulphide contents are typical, for example, of black schists, which are common in relation to metavol-canic rocks in the area.

One of the interesting features to investigate in this area is the potential for so-called critical min-erals such as REEs (cf. Sarapää et al. 2013). It has been noted that Y in till can be used as an indica-tor for these minerals in Finland (e.g. Sarapää and Sarala 2013). The distribution of Y is presented in Figure 5. However, the observed Y contents and the great difference between the distribution pat-terns for different analysis methods do not give any clear indication of previously unknown areas with potential for REEs.

Comparison of pXRF results with conventional methods

One of the aims of this study was to investigate whether the results from the pXRF analyser are comparable with conventional methods, i.e. labo-ratory XRF and aqua regia-based till geochemistry. In Figures 6 and 7, the results are compared as box-plot diagrams. The lowest values for all elements were measured from the natural, wet till samples

analysed by pXRF. This makes sense, because even a low water content reduces the penetration of X-ray fluorescence into the sample material. How-ever, it is significant that even the results of wet samples are comparable with all other datasets for the base metals. However, pXRF results from the dried samples correlate better with the laboratory

73


pX

RF,

wet

(p

pm

)p

XR

F, d

ry

(pp

m)

Lab

XR

F, b

riq

(p

pm

)p

XR

F b

riq

(p

pm

)A

R, I

CP

-OE

S

(pp

m)*

pX

RF,

wet

(p

pm

)p

XR

F, d

ry

(pp

m)

Lab

XR

F, b

riq

(p

pm

)p

XR

F b

riq

(p

pm

)A

R, I

CP

-OE

S

(pp

m)*

Al

x40

446

4882

765

771

5355

611

657

Mn

x23

7.8

365.

042

1.8

464.

417

2.7

md

4023

848

029

6495

053

332

1005

0m

d21

8.0

340.

538

3.4

429.

013

9.0

s10

066

8379

7767

6359

5981

s10

1.6

151.

717

9.5

195.

694

.1m

in91

8529

868

3740

029

819

4200

min

56.0

76.0

92.9

129.

071

.9m

ax69

148

8247

591

800

6898

136

000

max

938.

013

35.0

1619

.017

99.0

590.

0N

9298

9898

98N

9398

9898

98

P

x20

9.6

249.

430

3.6

-39

5.1

Fe

x23

926

2624

934

146

2733

820

621

md

196.

218

4.1

279.

3-

361.

0m

d22

530

2433

932

415

2525

118

050

s15

2.9

128.

611

5.9

-14

5.8

s92

3498

0810

470

1069

583

37m

in67

.514

4.8

113.

5-

166.

0m

in44

4555

9111

330

8302

1040

0m

ax76

5.0

442.

710

30.0

-10

30.0

max

6719

865

328

8113

083

531

5190

0N

475

98-

98N

9398

9898

98

K

x10

897

1321

712

769

1355

321

40

Co

x9.

412

.0-

29.9

10.1

md

1050

012

322

1208

012

677

1225

md

8.7

11.1

-29

.97.

8s

2789

3640

3461

3467

2491

s3.

54.

2-

4.9

6.0

min

4233

8120

3346

5251

281

min

1.8

2.5

-19

.73.

4m

ax19

087

2734

528

560

3159

613

200

max

26.0

26.0

-47

.037

.6N

9398

9897

98N

9393

-98

98

Ca

x15

058

1834

121

011

2026

124

73

Ni

x75

.666

.760

.110

2.8

42.9

md

1482

818

366

2026

518

796

2400

md

76.7

53.5

42.0

55.5

25.0

s48

4959

9362

6790

2175

4s

38.4

49.2

67.8

95.9

48.1

min

2993

4388

4360

3034

1250

min

17.4

27.0

10.0

32.0

13.0

max

4772

656

552

6254

085

600

5950

max

267.

031

9.0

408.

033

2.0

272.

0N

9398

9897

98N

9098

9822

98

Ti

x19

7431

6235

9834

5593

7

Cu

x31

.227

.325

.433

.433

.5m

d20

4731

8936

5734

4983

8m

d21

.018

.021

.027

.016

.6s

514

789

860

960

363

s27

.622

.622

.517

.136

.3m

in49

611

0110

6191

551

1m

in13

.010

.010

.017

.05.

6m

ax30

8551

5058

7566

6824

00m

ax17

2.0

122.

011

3.0

101.

017

9.0

N93

9898

9898

N70

9098

6798

V

x46

.962

.885

.667

.850

.0

Zn

x25

.827

.239

.231

.723

.6m

d45

.055

.581

.065

.044

.2m

d21

.023

.034

.526

.516

.8s

12.7

35.6

30.1

15.7

20.8

s14

.316

.118

.115

.624

.3m

in13

.018

.015

.024

.026

.7m

in10

.610

.010

.017

.06.

7m

ax94

.027

9.2

213.

013

8.0

140.

0m

ax10

2.0

125.

014

0.0

97.0

165.

0N

9398

9895

98N

9296

9886

98

Cr

x10

7.4

155.

018

8.9

189.

610

8.8

md

90.0

139.

015

9.5

162.

078

.2s

75.4

83.8

136.

312

2.8

99.4

min

28.0

36.0

37.0

62.0

40.8

max

508.

058

2.0

835.

087

5.0

683.

0

N93

9898

9798

Tabl

e 4. S

tatis

tical

par

amet

ers o

f the

diff

eren

t bat

ches

ana

lyse

d by

pX

RF, l

abor

ator

y X

RF a

nd IC

P-O

ES. p

XRF

, wet

= n

atur

al, w

et ti

ll sa

mpl

es a

naly

sed

by p

XRF

; pX

RF, d

ry =

nat

ural

, dry

till

sam

ples

anal

ysed

by

pXRF

; Lab

XRF

, briq

= ti

ll pe

llets

(pul

veriz

ed an

d br

ique

tted)

anal

ysed

by

labo

rato

ry X

RF; p

XRF

briq

= ti

ll pe

llets

anal

ysed

by

pXRF

; AR,

ICP-

OES

= <

0.06

mm

till

size

frac

tion

anal

ysed

after

pul

veriz

ing

and

aqua

regi

a di

gest

ion

by IC

P-O

ES. C

o co

nten

ts n

ot d

etec

ted

with

labo

rato

ry X

RF. x

= av

erag

e, m

d =

med

ian,

s =

stan

dard

dev

iatio

n, m

in =

min

imum

, m

ax =

max

imum

and

N =

num

ber o

f sam

ples

.

* <

0.0

6 m

m fr

actio

n

* <

0.0

6 m

m fr

actio

n

74


Fig. 3. Spatial distribution of Ca in bedrock and till from sampling sites in the Pelkosenniemi-Savukoski study area. a) Bedrock samples analysed by ICP-OES, b) aqua regia-leached till geochemistry (<0.06 mm; aqua regia digestion and ICP-OES), c) natu-ral, wet till samples analysed by pXRF, d) natural, dry till samples analysed by pXRF, e) till pellets (pulverised and briquetted) analysed by laboratory XRF and f) till pellets analysed by pXRF. A geological map is presented in the background (see legend in Fig. 1). Bedrock map (Bedrock of Finland – DigiKP). Contains data from the National Land Survey of Finland Topographic Database 03/2013.

a)

b)

75


c)

d)

76


e)

f)

77


Fig. 4. Spatial distribution of Cr in bedrock and till from sampling sites in the Pelkosenniemi-Savukoski study area. a) Bedrock samples analysed by ICP-OES, b) aqua regia-leached till geochemistry (<0.06 mm; aqua regia digestion and ICP-OES), c) natu-ral, wet till samples analysed by pXRF, d) natural, dry till samples analysed by pXRF, e) till pellets (pulverised and briquetted) analysed by laboratory XRF and f) till pellets analysed by pXRF. A geological map is presented in the background (see legend in Fig. 1). Bedrock map (Bedrock of Finland – DigiKP). Contains data from the National Land Survey of Finland Topographic Database 03/2013.

a)

b)

78


c)

d)

79


e)

f)

80


Fig. 5. Spatial distribution of Y in bedrock and till from sampling sites in the Pelkosenniemi-Savukoski study area. a) Bedrock samples analysed by ICP-OES, b) aqua regia-leached till geochemistry (<0.06 mm; aqua regia digestion and ICP-OES), c) till pellets (pulverised and briquetted) analysed by laboratory XRF and d) natural, dry till samples analysed by pXRF. A geological map is presented in the background (see legend in Fig. 1). Bedrock map (Bedrock of Finland – DigiKP). Contains data from the National Land Survey of Finland Topographic Database 03/2013.

a)

b)

81


c)

d)

82


Fig. 6. Comparison of the distribution of different sample/analyser datasets for Cu, Zn, Cr and Fe (pXRF, wet = nat-ural, wet till samples analysed by pXRF; pXRF, dry = natural, dry till samples analysed by pXRF; Lab XRF, briq = till pellets (pulverised and briquetted) analysed by laboratory XRF; pXRF briq = till pellets analysed by pXRF; AR, ICP-OES = <0.06 mm till size fraction analysed after aqua regia digestion by ICP-OES.

XRF and pXRF analyses conducted on pellets. In the case of dried samples, accuracy was particu-larly found to increase for the main elements (Fig. 7). Thus, based on the results, it is possible to state that all pXRF datasets are very compatible for lab-oratory XRF and aqua regia-based analyses. This is also demonstrated by the XY plots for pXRF and

laboratory XRF results from the pellets for several elements presented in Figure 8. A general feature is that most of the elements have good or excel-lent correlations for the base metals and main ele-ments, although the contents, especially for Al, K, Ca, Mn and Ti, are lower in aqua regia-based com-pared with other results.

Fig. 7. Comparison of the distribution of different sample/analyser datasets for Al, K, Ca and Mn (pXRF, wet = nat-ural, wet till samples analysed by pXRF; pXRF, dry = natural, dry till samples analysed by pXRF; Lab XRF, briq = till pellets (pulverised and briquetted) ana-lysed by laboratory XRF; pXRF briq = till pellets analysed by pXRF; AR, ICP-OES = <0.06 mm till size fraction ana-lysed after pulverizing and aqua regia digestion by ICP-OES.

83


Fig. 8. Scatter diagrams with fitted reference lines for the pXRF (x-axis) and laboratory XRF (y-axis) analysis of till pellets (<2 mm fraction, pulverised and briquetted) for Al, Ca, K, Cr, Cu, Fe, Mn, Ni, Ti, V and Zn.

84


DISCUSSION

In this research, natural till samples, i.e. not dried or sieved, were analysed to estimate the usability of pXRF analysers directly in the field in mineral exploration, applying till as a sample media. By us-ing natural till samples, genuine field conditions were simulated and extra sample processing was avoided (to minimize costs) prior to analyses. A thin plastic film (<10 µm) between the analyser head and the samples was also used to avoid con-tamination and protect the detector window.

In this study, XRF data were compared with conventional aqua regia-based analytical results from the <0.06 mm size fraction of till. According to the results, natural till (i.e. wet or dry) is a usable sample medium for pXRF analysis in exploration, as till comprises a mixture of different size frac-tions. An additional advantage is that natural till not only represents a single source in the bedrock, but stores information from a much larger source area by forming a secondary halo for the miner-als and the elements in the direction of ice move-ment. Furthermore, till includes commonly ho-mogenised, fine-grained debris that is composed

of particles ranging from clay to fine sand. This debris forms a basic matrix that generally covers rock fragments and the space between them. For this reason, after pebbles are removed, even natu-ral, raw till material can be used for pXRF analy-sis. The indication of the pXRF spectrum mostly arises from the till fines, which is seen in the very good correlation with the conventional method (aqua regia) for the <0.06 mm till size fraction. At the same time, good or excellent correlations (in Fig. 8) indicate that coarse rock fragments, such as cobbles and pebbles, have a minor influence on the overall outcome.

In this research, the till samples were collected using different drilling methods and test pits from the lowest part of the glacial overburden. The till layer about 1–2 m above the bedrock surface was thought to represent the most uniform till layer that is transported and deposited by glaciers. The results demonstrate that the basal till is very usable in exploration and support earlier observations of a short glacial transportation distance for basal till in the region (cf. Sarala & Ojala 2008).

CONCLUSIONS

The use of a portable XRF analyser (Delta 6000) was tested for basal till samples gathered using soil drilling and test pit surveys in the Savukoski-Pelkosenniemi study area, northeastern Finland. pXRF datasets were compared with laboratory XRF and conventional (<0.06 mm fraction of till) aqua regia-based geochemistry. The comparison yielded usually good or excellent correlations be-tween different elements and assay procedures. The study proved that till is an excellent medium for pXRF due to the homogenised matrix and gla-ciogenic distribution. Even natural, wet, unpro-cessed samples can be used, but dried, sieved sam-ples or pulverized and compressed pellets increase accuracy. The results demonstrate that pXRF is a usable, practical and effective tool in both mineral

exploration using till and also in geological map-ping.

Based on this study, the use of pXRF can be sum-marized on the element level as follows:– Excellent for base metals (Co, Cr, Cu, Fe, Mn,

Ni, V, Zn);– Excellent/good for several main elements (Al,

Ca, K);– Good/moderate for some elements (Bi, Pb, Rb,

Sb, Sr, Ti); – Poor/moderate for a few elements (Mg, P); – Questionable/no experience in this study for

Ag, As, Cd, Hg, Mo, S, Se, Sn, W, Th and U.

85


ACKNOWLEDGEMENTS

This research was carried out within the NovTecEx project funded by the Tekes Green Mining Pro-gramme and GTK. The authors thank Hannu Hir-vasniemi for field assistance and Hannu Panttila

for data preprocessing. Marko Holma and Timo Tarvainen are thanked for their criticism and con-structive comments on the manuscript.

REFERENCES

Beckhoff, B., Kanngießer, B., Langhoff, N., Wedell, R. & Wolff, H. (eds) 2006. Handbook of Practical X-Ray Fluo-rescence Analysis. New York: Springer.

Bedrock of Finland – DigiKP. Digital map database [Electronic resource]. Espoo: Geological Survey of Finland[accessed 31.3.2014]. Version 1.0. Available at: http://www.geo.fi/en/bedrock.html

Bowell, R. J., Egorova, L., Gurevick, D., Sedov, V., Holwell, D.A., Mikhailov, A. & Kordi, P. 2012. Grass roots ex-ploration in remote areas: An example from the Kuene region, Namibia. CIM Journal, 3, 33–46.

Coker, W. B. 2010. Future research directions in exploration geochemistry. Geochemistry: Exploration, Environment, Analysis 10 (1), 75−80.

Gazley, M. F., Tutt, C. T., Brisbout, L. I., Fisher, L. A. & Duclaux, G. 2014. Application of portable X-ray fluores-cence analysis to characterize dolerite dykes at the Pluto-nic Gold Mine, Western Australia. Geochemistry: Explo-ration, Environment, Analysis 14, 223−231.

Hirvas, H. 1991. Pleistocene stratigraphy of Finnish Lap-land. Geological Survey of Finland, Bulletin 354. 123 p.

Hirvas, H., Alfthan, A., Pulkkinen, E., Puranen, R. & Tyn-ni, R. 1977. Raportti malminetsintää palvelevasta maa-perätutkimuksesta Pohjois-Suomessa vuosina 1972-1976. Summary: A report on glacial drift investigations for ore prospecting purposes in northern Finland 1972-1976. Geological Survey of Finland, Report of Investigation 19. 54 p.

Hirvas, H. & Nenonen, K. 1990. Field methods for glacial indicator tracing. In: Kujansuu, R. & Saarnisto, M. (eds) Glacial indicator tracing. Rotterdam: A. A. Balkema, 217−248.

Johansson, P. W. 1995. The deglaciation of the eastern part of the Weichselian ice divide in Finnish Lapland. Geological Survey of Finland, Bulletin 383. 72 p.

Johansson, P., Lunkka, J. P. & Sarala, P. 2011. The Glaciation of Finland. In: Ehlers, J., Gibbard, P. L. & Hughes, P. D. (eds) Quaternary Glaciations – Extent and Chronology – A closer look. Elsevier B.V., Developments in Quaternary Sciences, vol 15, chapter 9, 105−116.

Lehtonen, M. I., Airo, M. L., Eilu, P., Hanski, E., Kortelai-nen, V., Lanne, E., Manninen, T., Rastas, P., Räsänen, J. & Virransalo, P. 1998. Kittilän vihreäkivialueen geologia. Lapin vulkaniittiprojektin raportti. Summary: The strati-graphy, petrology and geochemistry of the Kittilä greens-tone area, northern Finland. A report of the Lapland Vol-canite Project. Geological Survey of Finland, Report of Investigation 140. 144 p.

Le Vaillant, M., Barnes, S. J., Fisher, L., Fiorentini, M. L. & Caruso, S. 2014. Use and calibration of portable X-Ray fluorescence analysers: application to lithogeochemical exploration for komatiite-hosted nickel sulphide depo-sits. Geochemistry: Exploration, Environment, Analysis 14, 199−209.

Mutanen, T. 1997. Geology and ore petrology of the Akan-vaara and Koitelainen mafic layered intrusions and the Keivitsa-Satovaara layered complex, northern Finland. Geological Survey of Finland, Bulletin 395. 233 p.

Potts, P. J. & Webb, P. C. 1992. X-ray fluorescence spectro-metry. Journal of Geochemical Exploration 44 (1−3), 251−296.

Sarala, P. 2013. Portable XRF methods in till geochemical exploration – examples from Finland. In: Jonsson, E. et al. (eds) Proceedings of the 12th Biennial SGA Meeting, 12–15 August 2013, Uppsala, Sweden. 437−439.

Sarala, P. 2014. Comparison of the portable XRF with con-ventional methods in till geochemical mineral explorati-on. 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 Investiga-tion 207, 132−134.

Sarala, P. 2015. Comparison of different techniques for ba-sal till sampling in mineral exploration.In: Sarala, P. (ed.) Novel technologies for greenfield exploration. Geological Survey of Finland, Special Paper 57, 11–22. (this journal)

Sarala, P. & Ojala, V. J. 2008. Implications of Complex Gla-cial Deposits for Till Geochemical exploration: Examples from the central Fennoscandian ice sheet. In: Stefánsson, Ó. (ed.) Geochemistry Research Advances, Chapter 1. New York: Nova Publishers, 1−29.

Sarala, P. & Mäkikyrö, M. 2012. Mobile XRF methods in mineral exploration in glaciated terrain – examples from northern Finland. In: 34th International Geology Cong-ress, Brisbane, Australia, 5-10 Aug 2012. Optical disc (CD-ROM).

Sarapää, O. & Sarala, P. 2013. Rare earth element and gold exploration in glaciated terrain – example from the Mä-kärä area, Northern Finland. Geochemistry, Exploration, Environment, Analysis 13, 131−143.

Sarapää, O., Al Ani, T., Lahti, S. I., Lauri, L. S., Sarala, P. & Torppa, A. 2013. Rare earth element occurrences and exploration potential in Finland. Journal of Geochemical Exploration 133, 25−41.

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