NOVEL TECHNOLOGIES FOR INDICATOR MINERAL-BASED EXPLORATIONtupa.gtk.fi/julkaisu/specialpaper/sp_057_pages_023_062.pdf · Novel technologies for indicator mineral-based exploration

23

NOVEL TECHNOLOGIES FOR INDICATOR MINERAL-BASED EXPLORATION

byMarja Lehtonen1*), Yann Lahaye1, Hugh O’Brien1), Sari Lukkari1),

Jukka Marmo1) and Pertti Sarala2)

Lehtonen, M., Lahaye, Y., O’Brien, H., Lukkari, S., Marmo, J. & Sarala, P. 2015. Novel technologies for indicator mineral-based exploration. Geological Survey of Finland, Special Paper 57, 23−62, 9 figures, 6 tables and 4 appendices.

New mineralogical and geochemical methods for till sampling-based exploration were developed at the Geological Survey of Finland (GTK) during the TEKES-funded project “Novel technologies for greenfield exploration (NovTecEx)”. The techniques are based on recently installed analytical instruments at the Finnish Geosciences Research Laboratory (SGL), a high-resolution single collector induc-tively coupled mass spectrometer for trace element analysis (HR-SC-ICPMS) and field emission SEM for automated electron optics (FE-SEM-EDS). The sample ma-terial comprised till samples collected in the Savukoski-Pelkossenniemi study area in eastern Lapland during another NovTecEx subproject in which different drill-ing techniques were tested for sampling. The heavy mineral concentrates of the till samples were produced by optimizing conventional processing methods to meet the requirements of modern research instruments. The fully digested concentrates were analysed by HR-SC-ICPMS to detect interesting trace element concentrations and screen the samples for detailed FE-SEM-EDS. The resulting processing and analytical protocols can be applied in the exploration of various types of deposits. The results demonstrate that the use of modern research instruments can reduce the sample size needed for indicator mineral studies. The mineralogical and geo-chemical results from the eastern Lapland samples reflect the large and diversified provenance area.

Keywords (GeoRef Thesaurus, AGI): till, sampling, mineralogy, geochemistry, methods, analysis, indicator minerals, mineral exploration, Savukoski, Pelkosen-niemi, Finland

1) Geological Survey of Finland, P.O. Box 96, FI-02151 Espoo, Finland2) Geological Survey of Finland, P.O. Box 77, FI-96101 Rovaniemi, Finland*) corresponding author, e-mail: [email protected]

Novel technologies for greenfield explorationEdited by Pertti SaralaGeological Survey of Finland, Special Paper 57, 23–62, 2015

mailto:[email protected]

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Geological Survey of Finland, Special Paper 57Marja Lehtonen, Yann Lahaye, Hugh O’Brien, Sari Lukkari, Jukka Marmo and Pertti Sarala

INTRODUCTION

The basis of this study was a TEKES-funded 3-year (2012–2014) project, “Novel technologies for greenfield exploration”, or “NovTecEx” in short. The Research Laboratory of the Geological Survey of Finland (GTK) was responsible for NovTecEx subproject 2, entitled “Mineralogical study of till”. The international collaborative partner in this pro-ject was the Geological Survey of Canada (GSC).

The aim of the subproject was to develop new, cost- and time-efficient methods for processing exploration till samples and investigating their mineralogical composition for ore potential. The goal was to be able to detect extremely small quantities of indicator minerals from a range of mineralization types and to subsequently quanti-tatively analyse them by a combination of mod-ern geochemical and electron optical methods. The most commonly used indicator minerals are listed in Table 1. The development relied on re-cently (2013) installed analytical facilities at the Finnish Geosciences Research Laboratory (SGL), a high-resolution single collector inductively cou-pled mass spectrometer for trace element analysis (HR-SC-ICPMS) and a field emission scanning electron microscope for automated electron optics (FE-SEM-EDS).

The sample material consisted of till samples collected in eastern Lapland (Fig. 1). For this pro-ject, the main focus was on processing and analysis of the fine fraction of till (<63 μm), because this is

the most likely material to contain indicator min-erals relevant to the exploration area (e.g. gold, platinum group minerals and REE minerals; Table 1). This is due to the exponentially higher num-ber of individual mineral grains in the fine frac-tion relative to the coarse fraction, and also due to the expected grain size of indicators from this area. For these reasons, the till fine fraction has also conventionally been used as a sample medium for geochemical investigations (e.g. Koljonen et al. 1992, and references therein).

The majority of the indicator minerals have significantly higher densities (Table 1) than the minerals that make up the vast majority of till materials (e.g. quartz and feldspar), and they can consequently be concentrated using gravity-based methods. The indicator mineral method as such is a long-established and conventionally used ex-ploration method (cf. Peuraniemi 1990, Stendal & Theobald 1996). An important aspect in this study was the establishment of a processing protocol to effectively concentrate even the finest heavy min-eral fraction without significant indicator grain loss. The next step was to develop a cost- and time-efficient method to analyse the trace element chemistry of the concentrates in order to identify samples of interest. Finally, the indicator minerals were to be identified and analysed from these se-lected samples using automated electron optics.

SAMPLING AREA AND GEOLOGICAL SETTING

The NovTecEx study area is located in the Savukos-ki-Pelkosenniemi district in eastern Lapland (Fig. 1) and covers about 980 km2 in total. The heavy

mineral samples were collected in an 850 km2 area, since sampling was not possible in the Akanvaara claim and the Sakkala-aapa mire areas.

Bedrock geology

Lithologically, the Savukoski-Pelkosenniemi study area is divided into two main domains: Archaean and Palaeoproterozoic. The bedrock in the east-ern part of the area is composed of granite gneiss with greenstones of the Archaean basement. In the west, the bedrock consists of metasedimen-tary rocks with narrow mafic volcanic and diabase veins of the Palaeoproterozoic Central Lapland Greenstone Belt (Lehtonen et al. 1998). The main domains are separated by a N–S-oriented chain of

komatiite and graphite sulphide schists. The Akan-vaara layered intrusion with a known chromite-PGE mineralization is located in the SE part of the study area (Mutanen 1997). There is no knowl-edge of other economically significant mineraliza-tions in the area, but there is potential for various types of deposits, including gold, base metals and so-called high-tech metals (e.g. Nb, Ta and REE) (e.g. Sarapää et al. 2013).

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Geological Survey of Finland, Special Paper 57Novel technologies for indicator mineral-based exploration

Commodity / Deposit

Indicator minerals

Chemical composition

Average density (gcm-3)

Typical size range (mm)

Diamond1 Cr-pyrope garnet (Mg,Fe)3(Al,Cr)2(SiO4)3 3.7 0.25-0.5

Eclogitic garnet (Fe++,Mg)3Al2(SiO4)3 4.0 0.25-0.5

Mg-ilmenite (Fe++,Mg)TiO34.7 0.25-0.5

Cr-diopside CaMg(Fe,Cr)Si2O6 3.3 0.25-0.5

Chromite (Fe++, Mg)(Cr,Al)2O4 4.8 0.25-0.5

Forsteritic olivine (Mg,Fe)2SiO4 3.3 0.25-0.5

Diamond C 3.5 0.25-0.5Gold2 Gold Au 17.6 0.01-0.25

Scheelite CaWO4 6.0 0.01-0.25

Rutile TiO2 4.3 0.01-0.25

Sulphides >4.0 0.01-0.25

Magmatic Ni-Cu-PGE3 Cr-diopside CaMg(Fe,Cr)Si2O6 3.3 0.25-2.0

Forsteritic olivine (Mg,Fe)2SiO4 3.3 0.25-2.0

Enstatite (Mg,Fe)2Si2O6 3.2 0.25-2.0

Chromite (Fe++, Mg)(Cr,Al)2O4 4.8 0.25-2.0

Pentlandite (Fe,Ni)9S8 4.8 0.01-0.25

Pyrrhotite Fe(1-x)S (x=0-0.17) 4.6 0.01-0.25

Chalcopyrite CuFeS2 4.2 0.01-0.25

Pyrite FeS2 5.0 0.01-0.25Platinum group minerals (PGM)

>8.0 0.001-0.1

VMS deposits4 Chalcopyrite CuFeS2 4.2 0.01-0.25

Galena PbS 7.4 0.01-0.25

Sphalerite (Zn,Fe)S 4.1 0.01-0.25

Pyrrhotite Fe(1-x)S (x=0-0.17) 4.6 0.01-0.25

Pyrite FeS2 5.0 0.01-0.25

Gahnite (Zn,Fe)Al2O4 4.3 0.25-2.0

Spessartine (Mn++,Fe)3Al2(SiO4)3 4.2 0.25-2.0

Staurolite (Fe++,Mg)2Al9(Si,Al)4O20(O,OH)4 3.7 0.25-2.0

Pb-Zn deposits5 Galena PbS 7.4 0.01-2.0

(Mississippi Valley type) Sphalerite (Zn,Fe)S 4.1 0.01-2.0

Porphyry Cu deposits6 Sulphides > 4.0 0.25-2.0

Andradite Ca3Fe+++2(SiO4)3 3.9 0.25-2.0

Diaspore AlO(OH) 3.4 0.25-2.0

Barite BaSO4 4.5 0.25-2.0

Alunite KAl3(SO4)2(OH)6 2.7 0.25-2.0

Dravite NaMg3Al6(BO3)3Si6O18(OH)4 3.1 0.25-2.0

Apatite Ca5(PO4)3(OH,F,Cl) 3.2 0.25-2.0

W-Mo deposits7 Scheelite CaWO4 6.0 0.01-0.25

Wolframite (Fe,Mn)WO4 7.3 0.01-0.25

Sulphides >4.0 0.01-0.25

Bi minerals >6.0 0.01-0.25

”High tech metals” Pyrochlore (Na,Ca)2Nb2O6(OH,F) 5.3 0.01-0.25

e.g. Nb, Ta, REE Columbite Fe++Nb2O6 6.3 0.01-0.25Ta-minerals >8.0 0.01-0.25

Allanite (Ce,Ca,Y)2(Al,Fe+++)3(SiO4)3(OH) 3.75 0.01-0.25

References:1. McClenaghan & Kjarsgaard (2007) 2. McClenaghan & Cabri (2011) 3 and 6. Averill (2011) 4. Averill (2001) 5. Oviatt et al. (2013) 7. McClenaghan et al. (2013)

Table 1. The most commonly used indicator minerals. Modified from McClenaghan (2013).

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Fig. 1. The Savukoski-Pelkossenniemi study area in eastern Lapland, where the NovTecEx till samples were collected. Contains data from the National Land Survey of Finland Topographic Database 03/2013.

Surficial geology

Northern Finland was at the centre of the latest continental glaciations by the Scandinavian ice sheet (Johansson et al. 2011). The central Lapland area belongs to the latest ice-divide zone of the Late Weichselian glaciation, where the glacier has had only a low erosional effect on the bedrock (Hirvas 1991, Johansson et al. 2011). Earlier knowledge of the surficial deposits and the glaciogenic for-mations in the study area is mainly based on re-search carried out during the 1970s by Hirvas et al. (1977) and the 1990s by Johansson (1995). During

these investigations, it was established that in the Savukoski-Pelkosenniemi area the till units were formed during three glacial phases, with a north-ern ice-flow direction during the oldest phase and northwestern and western directions during the middle and younger phases, respectively. The ice flow directions reflect the glacial transport and thus the possible provenance area for till.

Based on new observations during this project, glacial overburden is dominant in the study area (Sarala 2015). Sandy, matrix-dominant till is the

27


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 greater than in the other areas due to a bedrock shear or weakness zone underlying the river. The basal parts of the valley deposits are glaciogenic in origin, but the uppermost sediments have been deposited during post-glacial fluvial processes. The deepest thick-ness of the overburden based on drilling is more

than 50 m in the northern part of the study area. The sediments in the deepest drill hole were most-ly composed of sand and gravel, but layers of till were also observed. Under the Quaternary depos-its, the bedrock surface is commonly weathered, ranging from some centimetres up to several tens of metres, being mainly of the saprock type (frac-tured and partly weathered) and rarely saprolite (profoundly weathered) (cf. Sarala & Ojala 2008).

METHODS

Sampling

Heavy mineral samples were collected using test pit excavations and soil drilling using variable drilling techniques (soil drilling with a core diam-eter of 7–8 cm, soil drilling with ship sampling and reverse circulation (RC) drilling). The number of sampling sites was 157 (71 test pits + 86 drilling sites), resulting in a sampling density of about 1 sample per 5.5 km2.

The sampling strategy was to take the till sam-ples from the basal part of the till cover, about 1–2 m above the bedrock surface. This layer was thought to generally represent the same type of glacial deposition and transport history through-out the study area. At the same time, it allowed the

direct influence of the underlying bedrock sur-face on the samples to be avoided, i.e. the sampled till had been transported some distance from its source, representing a larger bedrock area.

Two types of samples were collected. The first were approximately five-litre till samples that rep-resented a one-metre soil drill core (core diam-eter 7–8 cm) or were collected from the test pits as one-metre-thick vertical profiles imitating the drilled samples (Fig. 2). The second sample type was a more conventional type of till sample with a volume of 12 litres and approximately 20–25 kg in weight. These were used as a reference for the equal-sized exploration samples.

Fig. 2. Sampling strategy for the till samples using soil drilling and test pit excavations.

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Sample processing and laboratory protocols

Prior to working on real samples, a large 200-kg sample of basal till was excavated in the Ilomantsi area, Eastern Finland, to obtain test material for process development. The chemical and mineral-ogical composition of basal till in the area is well known because of GTK’s previous heavy mineral surveys (Lehtonen et al. 2011). Testing of preconcentration methods

The starting point for establishing the sample pro-cessing protocol for the NovTecEx till samples was to reassess GTK’s routinely used processing meth-ods in order to meet the requirements of modern mineralogical research instruments. The tradi-tional processing methods were developed dur-ing a time when the main mineralogical research method was optical microscopy, which is rarely quantitatively possible for grain sizes below 0.25 mm. There are only a small number of exceptions, including the rare ultra heavy minerals such as gold and PGM, which can be effectively concen-trated and manually picked out even from grain sizes down to 15–20 microns. Presently, however, scanning electron microscopes and microprobes can automatically analyse the entire range of min-eralogy, even down to the submicron scale.

Testing was carried out on the Ilomantsi test sample employing the two preconcentration meth-ods most often used by GTK, the Knelson concen-trator and the shaking table (Wilfley table). The Knelson concentrator has been used at GTK for over two decades to process diamond and gold ex-ploration samples, in particular. The concentrator has been modified with add-ons to ensure better recovery of diamond indicator minerals (0.25–0.5 mm) (Chernet et al. 1999). The advantages of the method are efficiency, the standardized procedure, the minimal contamination risk and the standard size of the concentrate. The disadvantages include the large original sample size (10 kg), breakage of fragile mineral grains during processing, problems in concentrating sorted sediments lacking a clay fraction, and the recovery of fine-grained (<100 µm) moderately heavy minerals (density ~ 3.5–4.0 g·cm-3). The advantage of the shaking table is the user-specific procedure, which allows a skilled op-erator to influence the size and density of the pre-concentrate. During the tabling, there is also less breakage of fragile mineral grains. A disadvantage

is the overflow of flaky and platy heavy minerals, such as baddelyite. The preconcentration results for the Ilomantsi sample (Table 2) clearly dem-onstrated that the shaking table more efficiently recovers fine-grained heavy minerals, which was a crucial aspect in the project and the reason for choosing this method for the NovTecEx samples.

Separation methods

Subsequent laboratory methods involved standard heavy media separation (HMS) using methylene-di-iodide (3.3 g·cm-3), sieving and low intensity magnetic separation (LIMS). HMS was carried out using a centrifuge in order to intensify the sepa-ration of fine mineral grains (<250 µm). Table 3 presents the mineralogical composition of heavy and light mineral fractions of the test material, representing three different grain-size classes. The results for each grain size are combined from ten individual subsamples, and their mineralogy was determined by an automated SEM-EDS technique (see section Analytical methods). The mineral species of the light and heavy density fractions are highlighted in Table 3, and indicate that the sepa-ration process is very effective.

Nevertheless, there are some problems that are particularly related to separating the finest grained heavy minerals. Figures 3a and 3b are backscat-tered electron images (BSE) of <63 µm light and heavy mineral fractions. In Figure 3b there are sev-eral bright grains, mostly Fe and Fe-Ti oxides that are less than 10 µm in diameter. Based on their spe-cific gravity, they should have been included with the heavy mineral concentrate, but as they are so small they had been trapped by larger light mineral grains. When compared with the total amount of heavy minerals in the entire sample, these trapped grains constitute only 5–10%, but they selectively represent the finest grained portion of the heav-ies. This may be significant for minerals that ex-clusively occur in the very fine-grained fraction. Consequently, it is important to regularly monitor the process by also analysing light mineral frac-tions and unprocessed samples.

Based on the tests performed on the Ilomantsi reference material, a processing flow sheet for the NovTecEx samples was generated, as presented in Figure 4.

29


Tabl

e 2.

Pre

conc

entr

atio

n re

sults

for t

he Il

oman

tsi t

est s

ampl

e.

Sam

ple

_ID

Met

hod

Init

ial

wei

ght

(kg

)G

rain

siz

eP

reco

ncen

trat

eC

onc

entr

ate

d>

3.3

gcm

-3Fi

ne f

ract

ion

in c

onc

entr

ate

(mm

)W

eig

ht (g

)w

t%

init

ial w

eig

htW

eig

ht (g

)w

t%

init

ial w

eig

ht<

0.10

mm

(g)

<0.

10 m

m (w

t%)

3”K

nels

on45

.1<

1 m

m

426/

12-P

OH

D

rive

1_R

ound

131

1.4

0.7

25.2

8.1

8.6

34.1

426/

12-P

OH

D

rive

1_R

ound

235

9.1

0.8

55.1

15.3

9.9

18.0

426/

12-P

OH

D

rive

1_R

ound

332

7.7

0.7

16.6

5.1

6.5

39.2

426/

12-P

OH

D

rive

329

3.8

0.7

6.3

2.2

2.9

45.1

426/

12-P

OH

D

rive

425

2.1

0.6

6.3

2.5

2.8

45.0

426/

12-P

OH

D

rive

531

6.4

0.7

7.7

2.4

3.2

41.6

Tota

l18

60.5

4.1

117.

36.

333

.928

.9

Sha

king

tab

le25

0.9

< 1

mm

426/

12-P

OH

R

ound

118

79.0

0.7

1024

.854

.540

9.1

39.9

426/

12-P

OH

R

ound

218

08.2

0.7

348.

519

.318

9.3

54.3

Tota

l36

87.2

1.5

1373

.337

.259

8.4

43.6

30


Tabl

e 3.

Min

eral

ogic

al co

mpo

sitio

n of

hea

vy li

quid

sepa

rate

d an

d ce

ntrif

uged

test

till

sam

ples

.

grai

n si

ze 1

00-2

50 µ

m63

-100

µm

-63

µm

den

sity

gcm

-3d

<3.

3d

>3.

3d

<3.

3d

>3.

3d

<3.

3d

>3.

3

wt%

of s

amp

le90

-95.

50.

5-10

95-9

91-

598

-99

1-2

% t

ota

l fea

ture

s%

to

tal f

eatu

res

% t

ota

l fea

ture

s%

to

tal f

eatu

res

% t

ota

l fea

ture

s%

to

tal f

eatu

res

Pla

gioc

lase

22.6

0.5

25.2

0.5

23.6

0.0

K-f

eld

spar

16.7

0.2

16.7

0.3

16.3

0.2

Qua

rtz

45.4

0.8

40.0

1.6

46.2

0.1

Mic

a11

.517

.412

.612

.58.

35.

2

Chl

orite

1.6

2.7

1.9

2.4

2.2

1.5

Am

phi

bol

e1.

010

.31.

18.

71.

013

.8

Pyr

oxen

e0.

00.

80.

01.

00.

12.

9

Gar

net

0.1

13.0

0.5

10.7

0.1

14.8

Ep

idot

e0.

26.

00.

510

.40.

510

.8

Sp

hene

0.1

4.7

0.2

7.1

0.3

9.3

Tour

mal

ine

0.1

0.5

0.2

0.3

0.2

0.1

Zirc

on0.

00.

80.

02.

60.

02.

0

Fe-o

x0.

238

.00.

536

.00.

231

.6

Ilmen

ite0.

03.

50.

03.

80.

05.

0

Ti-O

x0.

00.

50.

01.

30.

01.

5

Ap

atite

0.1

0.2

0.2

0.3

0.3

0.4

Mon

azite

0.0

0.1

0.0

0.3

0.0

0.5

Cal

cite

0.2

0.0

0.3

0.0

0.5

0.0

Sul

phi

des

0.0

0.0

0.0

0.0

0.0

0.1

Gyp

sum

0.0

0.1

0.0

0.1

0.0

0.0

TOTA

L10

0.0

100.

010

0.0

100.

010

0.0

100.

0

Ana

lyze

d g

rain

s8

139

8 25

98

439

10 1

358

450

8 38

6

min

eral

col

our

cod

esd

ensi

ty <

3.3

gcm

-3d

ensi

ty ±

3.3

gcm

-3d

ensi

ty >

3.3

gcm

-3

31


Fig. 3. a) Heavy mineral concentrate, d >3.3 g·cm-3, grain size <63 μm, non-magnetic fraction. Sample HAH1-2013-1.1 9-10.1m. BSE. Jeol JSM-5900LV. b) Light mineral fraction, d <3.3 g·cm-3, grain size <63 μm. Sample HAH1-2013-1.1 9-10.1m. BSE. Jeol JSM-5900LV.

Fig. 4. A simplified sample processing flowsheet for the NovTecEx samples. The green boxes indicate optional processing steps that were only carried out on a subset of samples.

Preconcentrate Screening 0.063, 0.1, 0.25, 0.5 mm

<0.063, 0.063-‐0.1mm heavy liquid separa�on

d =3.3 gcm-‐3 centrifuge

0.1-‐0.25, 0-‐25-‐0.5, 0.5-‐1.0 mm heavy liquid separa�on

d=3.3 gcm-‐3

funnel

d>3.3 gcm-‐3

-‐0.063 mm magne�c separa�on

d>3.3 gcm-‐3 0.063-‐0.1mm

magne�c separa�on

d>3.3 gcm-‐3 magne�c separa�on

<1.0 mm Shaking table

Wet screening 1.0 mm

Trace element geochemistry SC-‐ICPMS

I Electron op�cal analysis LV-‐SEM Main mineralogy

II Electron op�cal analysis FE-‐SEM Detailed mineralogy

Till sample Drilled (mean 5 l/8 kg)

Excavated (mean 12 l/18 kg)

d<3.3 gcm-‐3

archived d<3.3 gcm-‐3

archived

>1.0mm archived

magne�c frac�on

archived

d>3.3 gcm-‐3

-‐0.063 mm magne�c frac�on

d>3.3 gcm-‐3

-‐0.063 mm non-‐magne�c frac�on

d>3.3 gcm-‐3

0.063-‐0.1 mm non-‐magne�c frac�on

Division into three subsamples

magne�c frac�on

archived

0.1-‐0.25 mm non-‐magne�c

frac�on archived 0.25-‐0.5, 0.5-‐1.0 mm non-‐magne�c frac�on

op�cal microscopy

Subsample 100g

Screening 0.063 mm

<0.063 mm

>0.063 mm archived

32


Sample processing at the ODM Laboratory

In order to obtain independent reference data for sample processing, a set of NovTecEx samples was sent to Overburden Drilling Management Ltd in Ottawa (ODM). The samples consisted of ten 12-l original till samples and ten heavy mineral con-centrates of their duplicate samples processed at GTK. The ODM laboratory provides sample-pro-cessing services for indicator mineral work relat-ed, for instance, to gold, diamond and base metal

exploration. The laboratory is routinely used by the Geological Survey of Canada for sample pro-cessing in various types of research projects.

The ODM processing protocol for till samples is quite similar to that used at GTK for this pro-ject (Averill & Huneault 2006). Preconcentration is carried out using a shaking table, followed by heavy liquid and magnetic separations. Gold and PGM grains are separately concentrated by micro-panning.

Analytical methods

LV-SEM-EDS for main mineralogy

The heavy mineral concentrate of the Ilomantsi test sample was studied using an automated SEM attached to an EDS system. The aim was to estab-lish a practical and rapid method to examine the main mineralogy of the NovTecEx samples by an-alysing a few thousand mineral grains from each concentrate. Basic knowledge of the mineralogy was considered important in designing the chemi-cal analysis method for the concentrates, and also in interpreting the results. Finding indicator min-eral grains during this preliminary SEM investiga-tion was not anticipated due to the low number of analysed grains. Detailed mineralogical studies for indicator minerals were only intended to be car-ried out for selected samples based on the chemi-cal analysis results.

Two different types of preparation methods were investigated using the test sample: grain mounts and polished epoxy mounts. The grain mounts were prepared by simply scattering sample material on adhesive carbon discs, meaning they were much faster and cheaper to produce than polished mounts. The disadvantage, however, was that the analysis quality was not as good as from the polished surface. The SEM-EDS results of the test runs are presented in Figure 5, diagrams A-F, both as numbers of analysed mineral grains and as their measured areas. The results indicate that the main mineralogical composition is quite similar, regardless of the sample preparation type. Thus, the grain mounts were considered adequate when focusing on the bulk mineralogy. For detailed mineralogical analysis, polished epoxy mounts were exclusively used.

The SEM-EDS results for the main mineralogy were also compared with conventional chemi-cal analysis by XRF performed in Labtium (code 175X). This was to ensure that the amount of sam-ple used for SEM-EDS analysis was enough to give reliable results. Even though the number of analysed grains can easily reach thousands or tens of thousands, by mass they represent a very small amount of concentrate, usually some tens of mil-ligrams. In contrast, the XRF analysis is performed on a pellet made out of a pulverized sample weigh-ing 7 g at minimum, meaning at least 100 times more material for analysis than with SEM-EDS.

Table 4 presents the mineral composition of the Ilomantsi heavy mineral concentrates deter-mined by SEM-EDS using grain mounts for three grain-size classes. Each result is a combination of three subsamples. The results demonstrate how the mineral compositions vary in relation to grain size. The amounts of amphiboles, epidote, titanite and staurolite clearly decrease as a function of the grain size, whereas the amount of Fe oxides, chro-mite, zircon and monazite increases.

The unclassified mineral class comprises analy-ses that were not identified. In practice, they repre-sent poor quality analytical data resulting from the unpolished grain mounts. The number of unclassi-fied analyses increases in relation to the grain size because the topography of the sample also increas-es. For this reason, grain mounts are best used only for the fine fractions.

When comparing the mineralogy with the XRF analyses, there is a clear correlation between cer-tain minerals and elements. For example, the con-centration of Ca correlates with that of epidote, Ti with ilmenite, Fe with Fe-oxides, Zr with zircon and Ce with monazite. One of the easiest element

33


0

10

20

30

40

% o

f fea

ture

s H1 PM feat (n=1500)

H1 GM feat (n=1500)

H1 PM area (n=1500)

H1 GM area (n=1500)

0

10

20

30

40

% o

f fea

ture

s

H2 PM feat (n=1500)

H2 GM feat (n=1500)

H2 PM area (n=1500)

H2 GM area (n=1500)

0

10

20

30

40

50

% o

f fea

ture

s

H3 PM feat (n=1500)

H3 GM feat (n=1500)

H3 PM area (n=1500)

H3 GM area (n=1500)

0

10

20

30

40

50

60

% o

f fea

ture

s

K2 PM feat (n=1500)

K2 GM feat (n=1500)

K2 PM area (n=1500)

K2 GM area (n=1500)

0

10

20

30

40

% o

f fea

ture

s

K1 PM feat (n=1500)

K1 GM feat (n=1500)

K1 PM area (n=1500)

K1 GM area (n=1500)

0

10

20

30

40

% o

f fea

ture

s

K3 PM feat (n=1500)

K3 GM feat (n=1500)

K3 PM area (n=1500)

K3 GM area (n=1500)

Fig. 5. Mineral composition of six heavy mineral concentrates (a–f) produced from the Ilomantsi sample. Density >3.3 g·cm-3, grain size <0.1 mm, PM = polished epoxy mount, GM = grain preparate, H = <0.1 mm, K = 0.1–0.25 mm. Data: Jeol JSM-5900LV + Oxford Instruments EDS, INCA Feature software.

a)

c)

e)

b)

d)

f)

concentrations to correlate with the mineral dis-tribution is Zr, since it exclusively exists in zircon in the Ilomantsi sample. When Zr concentrations are calculated based on the SEM mineral composi-tion, the results match quite well with Zr measured

by XRF. The same applies to Ce bound in monazite and Cr bound in chromite and Cr-Fe spinel. The results validate the SEM-EDS method for reliable determination of the main mineralogical compo-sitions of the heavy mineral concentrates.

34


Tabl

e 4.

Min

eral

ogic

al (L

V-SE

M-E

DS)

and

chem

ical

(XRF

) com

posit

ion

of th

e Ilo

man

tsi s

ampl

e he

avy

min

eral

conc

entr

ates

. The

XRF

ana

lyse

s wer

e pe

rfor

med

by

Labt

ium

.

TP

R-1

TP

R-1

TP

R-1

TP

R-1

TP

R-1

TP

R-1

Gra

in s

ize

mm

0.1-

0.5

mm

0.06

3-0.

1 m

m<

0.06

3 m

mG

rain

siz

e m

m0.

1-0.

5 m

m0.

063-

0.1

mm

<0.

063

mm

Den

sity

gcm

-3d

>3.

3d

>3.

3d

>3.

3D

ensi

ty g

cm-3

d>

3.3

d>

3.3

d>

3.3

Set

1-3

Set

1-3

Set

1-3

L130

0765

6L1

3005

911

L130

0591

2C

lass

Ave

rag

e d

ensi

tyFe

atur

es%

to

tal

feat

ures

%

mas

sFe

atur

es%

to

tal

feat

ures

%

mas

sFe

atur

es%

to

tal

feat

ures

%

mas

sE

lem

ent

(175

X)

%

%

%

Qua

rtz

2.62

270.

20.

264

0.6

0.4

140.

00.

0E

lem

ent

(175

X)

%

%

%

K-f

sp2.

567

0.1

0.0

60.

10.

01

0.0

0.0

Na2

O0.

251

0.10

30.

079

Alb

ite2.

624

0.0

0.0

180.

20.

10

0.0

0.0

MgO

1.41

00.

630

0.49

2P

lagi

ocla

se2.

656

0.1

0.0

30.

00.

00

0.0

0.0

Al2

O3

12.6

06.

164.

19B

iotit

e3.

4019

0.2

0.2

250.

30.

215

0.1

0.0

SiO

224

.50

12.4

09.

59M

g-b

iotit

e2.

8080

0.7

0.5

290.

30.

221

0.1

0.1

P2O

50.

132

0.14

60.

315

Clin

ochl

ore

2.65

750.

70.

548

0.5

0.3

400.

20.

1K

2O0.

129

0.05

20.

041

Fe-H

ornb

lend

e3.

4794

18.

67.

934

03.

42.

870

52.

92.

2C

aO10

.29

4.30

3.34

Mg-

Hor

nble

nde

3.23

100.

10.

14

0.0

0.0

40.

00.

0Ti

O2

9.60

18.8

020

.11

Act

inol

ite3.

0424

0.2

0.2

60.

10.

012

0.0

0.0

MnO

0.83

1.16

1.02

Cum

min

gton

ite3.

3526

0.2

0.2

160.

20.

18

0.0

0.0

Fe2O

338

.90

52.0

054

.40

Dio

psi

de

3.40

410.

40.

311

0.1

0.1

20.

00.

0S

0.02

00.

035

0.03

2E

pid

ote

3.45

4 02

936

.933

.71

914

19.4

15.8

2 56

510

.78.

0C

l0.

012

0.00

60.

009

Clin

ozoi

site

3.34

158

1.4

1.3

620.

60.

512

0.0

0.0

Sc

0.00

50.

002

0.00

3Ti

tani

te3.

4865

56.

05.

541

14.

23.

454

22.

31.

7V

0.06

10.

080

0.08

5S

chor

l3.

1527

0.2

0.2

170.

20.

129

0.1

0.1

Cr

0.04

90.

093

0.12

5A

pat

ite3.

1915

0.1

0.1

180.

20.

193

0.4

0.3

Ni

0.00

50.

007

0.01

0A

l-si

licat

e3.

610

0.0

0.0

210.

20.

20

0.0

0.0

Cu

0.00

2<

0.00

2<

0.00

2Z

ircon

4.65

730.

70.

837

13.

84.

11

352

5.6

5.7

Zn

0.01

40.

016

0.01

7M

onaz

ite5.

153

0.0

0.0

90.

10.

182

0.3

0.4

Ga

<0.

002

<0.

002

<0.

002

Pyr

ochl

ore

5.30

00.

00.

00

0.0

0.0

10.

00.

0A

s0.

014

0.03

40.

029

Alm

and

ine

4.19

384

3.5

3.9

411

4.2

4.1

514

2.1

1.9

Rb

0.00

30.

005

0.00

6S

pes

sart

ine

4.18

550.

50.

645

0.5

0.5

490.

20.

2S

r0.

088

0.03

20.

024

Sta

urol

ite3.

7162

0.6

0.6

590.

60.

57

0.0

0.0

Y0.

017

0.02

90.

042

Oliv

ine

3.32

40.

00.

00

0.0

0.0

10.

00.

0Z

r0.

565

2.69

53.

991

Hem

atite

5.30

891

8.2

11.5

2 26

122

.928

.78

670

36.1

41.3

Nb

0.00

40.

001

<0.

0007

Goe

thite

3.80

677

6.2

6.2

561

5.7

5.1

713

3.0

2.4

Mo

<0.

001

0.00

90.

017

Ilmen

ite4.

7299

29.

111

.41

812

18.4

20.5

7 12

529

.730

.2S

n0.

005

0.00

60.

005

Fe-T

i ox

5.00

180.

20.

283

0.8

1.0

216

0.9

1.0

Sb

<0.

01<

0.01

<0.

01C

hrom

ite4.

790

0.0

0.0

70.

10.

126

0.1

0.1

Ba

0.02

80.

054

0.05

5C

r-Fe

-sp

inel

5.00

30.

00.

021

0.2

0.3

114

0.5

0.5

La0.

018

0.03

80.

078

Rut

ile_T

i-O

x4.

2563

0.6

0.6

136

1.4

1.4

282

1.2

1.1

Ce

0.04

30.

070

0.15

4G

alen

a7.

400

0.0

0.0

10.

00.

010

0.0

0.1

Pb

0.01

00.

025

0.08

8A

rsen

opyr

ite6.

070

0.0

0.0

20.

00.

00

0.0

0.0

Bi

<0.

003

0.00

30.

006

Sco

rod

ite3.

200

0.0

0.0

30.

00.

00

0.0

0.0

Th0.

015

0.01

60.

026

Gol

d17

.64

00.

00.

00

0.0

0.0

10.

00.

0U

0.00

30.

005

0.00

8U

ncla

ssifi

ed

3.50

1 53

614

.113

.01

064

10.8

8.9

806

3.4

2.5

Tota

l10

905

100.

010

0.0

9 85

910

0.0

100.

024

019

100.

010

0.0

Zr

% (c

alcu

late

d)

0.36

1.78

2.44

Ce

% (c

alcu

late

d)

0.01

0.03

0.11

Cr

% (c

alcu

late

d)

0.01

0.09

0.15

35


LV-SEM-EDS analytical parameters The analyses were performed using GTK’s Jeol JSM-5900LV scanning electron microscope (SEM), which is attached to an energy dispersive spectrometer (EDS) by Oxford Instruments con-trolled by INCA Feature software. The analytical conditions in the SEM were as follows: low vacuum mode (22 Pa), a COMPO back-scattered signal, 20 kV accelerating voltage and 1 nA probe current. The EDS analyses were carried out on the longest chord of the detected mineral grains with 5 µm as the smallest expected feature width. From each sample preparate, 3000–5000 individual mineral grains were analysed. The mineral identification was based on GTK’s internal mineral database.

Microwave digestion and HR-SC-ICPMS analyses for trace elements

The results in Table 4 demonstrate how low the concentrations of interesting minerals can be in till. For example, only a grain of gold and pyro-chlore was discovered among 20 000 analysed grains in the fine fraction (0.063 mm) heavy min-eral concentrate. In some cases, such as in diamond exploration (e.g. Lehtonen et al. 2005), even 100 times lower concentrations of specific indicator minerals can be crucial when exploring for an ore deposit in an area. Detecting such extreme trace element concentrations in heavy mineral concen-trates requires an ultra-sensitive chemical analysis method. Development was carried out on SGL’s recently installed high-resolution single collector inductively coupled mass spectrometer (HR-SC-ICPMS), which provides the means to analyse trace element concentrations well below the ppb level. The aim was to analyse a subsample of each concentrate by HR-SC-ICPMS, and then use the results to select specific samples to mount for de-tailed mineralogical mapping by FE-SEM-EDS. Prior to HR-SC-ICPMS analysis, the concentrates need to be dissolved, and the development of an efficient and time-saving dissolution method was an important step in the process. The dissolution protocol was built around a microwave digestion technique, using a system that had also been newly installed at SGL.

Microwave digestion is a commonly used meth-od for the mostly partial dissolution of environ-mental samples in many commercial laboratories, including Labtium. The method has not been widely applied in the total dissolution of heavy

mineral concentrates. To obtain background in-formation for the process development at GTK, some Ilomantsi heavy mineral concentrates were sent to Labtium for microwave digestion and sub-sequent ICP-MS analysis (Labtium code 310). Nine 100-mg reference samples were subjected to microwave digestion in a mixture of hydrochloric, nitric and hydrofluoric acid, followed by analysis of the resulting solution by ICP-MS. The analysed material was the same as that measured by XRF for major element compositions (Table 4). As ex-pected, the concentrates did not dissolve entirely in the microwave. The remaining undigested ma-terials were analysed by SEM-EDS for mineralogi-cal composition at GTK.

The Labtium results are presented in Appendix I. When comparing the ICP-MS analyses of the partially digested samples with the corresponding XRF analyses, it can be seen that the concentra-tions of certain elements (Zr, Y, La, Ce, Ba, Cr) are systematically lower in the former. The SEM-EDS analyses of the undigested residual mate-rial confirmed that especially the finest fractions contained abundant chemically resistant miner-als such as zircon, xenotime, monazite, barite and chromite, which are also the main carriers of the elements that gave low results in the ICP-MS data.

The Labtium results demonstrated which min-erals, in particular, are the most difficult ones to dissolve. The resulting dissolution protocol and analytical methods are explained below.

Sample dissolutionSamples (500 mg) were dissolved in Teflon PFA pressure vessels using an Ethos 1 microwave diges-tion system from Milestone Inc. The samples were first dissolved with a mixture of 4 ml HCl 6N and 4 ml HNO3 6.5 N at 220 °C for 45 min. The superna-tant of the first dissolution step was extracted and stored in a separate beaker. The residue of the first dissolution was again attacked using with a mix-ture of 3 ml HCl with 4 ml HNO3 and 2 ml HF at 230 °C for 45 min. The resulting fluoride salts were converted to nitrates by drying down after adding 2 ml of concentrated HNO3. The supernatant of the first dissolution step was mixed with the fully dissolved sample from the second dissolution step. The sample was diluted 5000 times in 250 ml of 2% HNO3 with traces of HF (to stop Zr and Hf pre-cipitation) and spiked with 1 ppb In as the internal standard.

36


Method of analysisSamples were analysed using a Nu AttoM HR-SC-ICPMS (Nu Instruments Ltd., Wrexham, UK). The analytical strategy was that developed by Cheatham et al. (1993). This technique uses a matrix-matched external standardization method and non-linear response drift corrections. A series of well-characterized USGS internal standards, BIR-1, BHVO and BCR2, were used. A blank was measured before each sample and standard. The standard BHVO was used to monitor instrument drift and was analysed every 10 positions.

Operating parametersThe normal parameters of operation of the ICP-MS include the use of an autosampler, peristaltic pump and Meinhard nebulizer. Analyses were per-formed in peak jumping mode using 10 sweeps of 50 cycles. A typical element menu consisted of 97 isotopes from 65 elements. Several non-isobaric isotopes of the same elements were used in order to correct for potential interferences. The wash time between samples was 180 s, and a further 60 s of sample uptake was allowed before measurement started. Blank nitric acid aliquots were run before each sample and the resulting values were used to blank-subtract the standard and sample data.

Data reductionThe results were calculated using an in-house Ex-cel data reduction program. After the blank sub-traction and overall drift correction based on the internal standard indium, a polynomial curve was

fitted to the BHVO standard data for each isotope, allowing a specific drift correction for each isotope to be applied. A calibration curve for each isotope forced to the origin and based on three USGS standards was used to calculate concentrations.

FE-SEM-EDS for detailed mineralogical mapping

Selected samples were analysed at GTK using a JEOL JSM 7100F field emission scanning electron microscope attached to an Oxford Instruments EDS. The FE-SEM-EDS system was operated by INCA and Aztec software. The samples for analysis were selected based on the preliminary LV-SEM-EDS mapping for major mineralogy and the HR-SC-ICPMS analyses for trace element concentra-tions. Analyses were performed on polished epoxy mounts made from <63-µm fractions of till. From each mount, approximately 150 000–250 000 indi-vidual mineral grains were automatically scanned, and the BSE signal strength (i.e. mean atomic num-ber) was used to target certain mineral phases for analysis. Elemental distribution mapping was also used for detailed mineralogy. The mineral identifi-cation was based on GTK’s own mineral database.

The analytical conditions in the SEM were as follows: high vacuum mode, a COMPO back-scattered signal, 20 kV accelerating voltage and 1 nA probe current. The EDS spectra were generated from the entire surface areas of the detected min-eral grains, with 2.5 µm as the smallest expected feature width.

RESULTS

ODM optical microscopy results

The optical microscopy results for the grain size fraction of 0.25–1.0 mm are reported in Appendix II. The mineralogy of the ODM- and GTK-pro-cessed samples compared well with each other, in-dicating that the processing systems worked simi-larly. During the micro-panning at ODM, gold and PGM grains were recovered from most of the samples. The number of gold grains varied from 5 to 50 grains per sample, and PGM grains from

0 to 4 (Appendix III). The smallest recovered gold grains were 15 x 15 x 3 µm in size, and the largest 250 x 450 x 150 µm. The combined weights of the gold grains were converted to estimated Au con-tents of the concentrates, which varied between 2–1200 ppb. The detected PGM grains were all un-der 50 µm in diameter and too few to allow PGE concentration calculations.

37


GTK results: new sample processing and analytical protocol

The NovTecEx preconcentrates weighed 400 g on average (range 100–1000 g) and comprised ap-proximately 5% of the <63 μm fine fraction (range 0.3–21%). The fine fraction had already been con-centrated during tabling, and consequently con-sisted of more than 60% heavy minerals with a density of over 3.3 g·cm-3. Approximately half of this portion was magnetite.

The sample processing and analysis followed the new protocol developed for the project, as follows.

Stage 1: Main mineralogy by LV-SEM-EDS

In total, 68 NovTecEx heavy mineral concentrates were analysed by LV-SEM-EDS for mineralogical composition. Both non-magnetic and magnetic (>0.1 T) fractions were analysed from the grain size fraction <0.063 mm. The results are published in Lehtonen et al. (2014).

The mineralogy of the non-magnetic fractions varies greatly, as expected based on the large and diverse sampling area (Fig. 1). The most abundant heavy minerals include ilmenite, Fe-oxides (most-ly hematite and goethite in non-magnetic frac-tions), titanite, zircon, Fe-hornblende and epidote. Rutile, monazite, almandine, apatite and chromite are also common. The graph in Figure 6 illustrates the compositional variation of the concentrates. In the diagram, the abundances of selected minerals are expressed as numbers of grains per 1000 ana-lysed grains.

The magnetic fractions are dominated by mag-netite and ilmenite (ilmenomagnetite). They also contain approximately 10–20% of mineral grains that should have been separated into the non-magnetic fractions, such as rutile, chromite, zircon and monazite, meaning that the magnetic separa-tion was not entirely accurate.

Observations of indicator minerals are listed in Table 5. The results are combined from both mag-netic and non-magnetic fractions. No gold or PGE grains were detected in the heavy mineral concen-trates during this step of the analysis. This is prob-ably due to the relatively low number of analysed grains (max. 5000) per sample. Based on the mi-cro-panning results of ODM, discovering a gold or PGE grain in this small amount of sample would have been purely accidental.

Despite the relatively low detection limits for minor phases in this step using the LV-SEM, some

contamination was detected. Most commonly, this consisted of chips of stainless steel and cupro-nickel, and sometimes solder. Most probably the contamination occurred during the sampling or preconcentration stages of the process.

Stage 2: Trace element geochemistry by HR-SC-ICPMS

The HR-SC-ICPMS data are presented in Appen-dix IV. As expected, the trace element contents of the samples show broad variation. An interesting set of analyses are labelled as 1–5 (a,b,c). They are reference samples representing different splits of the same starting fine fractions (<0.063 mm) of till. (1) The a samples are unprocessed other than

screening; (2) the b samples are concentrates separated by

heavy liquid; (3) the c samples are tabled and heavy liquid sepa-

rated concentrates.

The main difference between the b and c samples is the size of the original volume of till they are derived from; this is less than 0.5 l for the b sam-ples and from 5 to 12 l for the c samples. The HR-SC-ICPMS data show a clear correlation of certain elements with the sample type, meaning either en-richment of or a decrease in specific minerals as a function of processing. Elements such as REE, Nb, Y, Th, U, Pb, Bi, W, Au and PGE, which are exclu-sively bound to heavy minerals, are concentrated in the c samples. Contrastingly, elements such as Li, Be and Rb follow the opposite trend, as they mostly occur in lighter minerals. Many elements (e.g. Cr, Ni, Cu, Co) do not appear to show any particular discernible patterns.

When the results are studied in the context of the main mineralogy by LV-SEM-EDS (Table 5 and Lehtonen et al. 2014), some matches can be de-tected. Sample RM_HAH1-2013-1.1 (number 17 in Appendix IV), which is the only one containing pentlandite, is clearly enriched in Ni compared to the other concentrates (>5000 ppm). Sample RM_POSS-2012-38.1 (number 7), on the other hand, contains over 1% of chromite, which is reflected by its Cr concentration of over 6000 ppm. Another chromite-rich sample, RM_JOVS-2012-2.1 (16), has more than 5000 ppm of Cr, which is well above the average of the concentrates. The monazite-rich

38


0

100

200

300

400

500

600

700

800

900

1000

HAH1 1.1 HAH1 5.1

HAH1 500.1 HAH1 501.1 HAH1 502.3 HAH1 504.1 HAH1 505.1 HAH1 507.1 HAH1 509.1 HAH1 511.1 HAH1 512.1

JOV$ 1.1 JOV$ 2.1 JOV$ 3.1 JOV$ 4.1 JOV$ 9.1

JOV$ 11.2 JOV$ 15.2 JOV$ 21.2 JOV$ 25.2 JOV$ 32.1 POS$ 32.1 POS$ 33.3 POS$ 36.2 POS$ 38.1 POS$ 41.2 POS$ 42.2 POS$ 43.3 POS$ 45.2 POS$ 46.2 POS$ 46.4 POS$ 47.1 POS$ 48.2 POS$ 50.2 POS$ 51.2 POS$ 53.2 POS$ 55.2 POS$ 56.2 POS$ 57.3 POS$ 61.2 POS$ 63.2 POS$ 64.2 POS$ 65.2 POS$ 66.1 POS$ 66.2 POS$ 68.2 POS$ 69.2 POS$ 71.2 POS$ 72.2 POS$ 73.2 POS$ 75.2 POS$ 77.2 POS$ 77.6 POS$ 83.2 POS$ 84.2 POS$ 85.2 POS$ 86.2 POS$ 88.2 POS$ 89.2 POS$ 89.4 POS$ 89.5 POS$ 90.1 POS$ 90.2 POS$ 90.4 POS$ 92.4 POS$ 93.4 POS$ 97.2

POS$ 102.2

Features / 100

0 an

alyzed

grains

Zirc

on

Sphe

ne

Epid

ote

Chlo

rite

Fe

-‐Hor

nble

nde

Fe-‐o

x (g

oeth

ite/l

imon

ite)

Fe-‐o

x (h

ema�

te)

Ilmen

ite

Fig.

6. Th

e m

ain

min

eral

pha

ses o

f the

Nov

TecE

x he

avy

min

eral

con

cent

rate

s. G

rain

size

<0.

063

mm

, non

-mag

netic

frac

tions

. Dat

a: Je

ol JS

M-5

900L

V +

Oxf

ord

Inst

rum

ents

ED

S, IN

CA

Fe

atur

e so

ftwar

e.

39


Table 5. Indicator minerals detected during mineralogical mapping by LV-SEM-EDS. Data: Jeol JSM-5900LV + Oxford Instru-ments EDS, INCA Feature software.

Sample ID grain size density (gcm-3) indicator minerals

RM_HAH1-2013-1.1 <63 µm >3.3 pentlandite, pyrite, pyrrhotite

RM_HAH1-2013-5.1 <63 µm >3.3 pyrite, pyrrhotite, chalcopyrite

RM_HAH1-2012-500.1 <63 µm >3.3 pyrite

RM_HAH1-2012-502.3 <63 µm >3.3 pyrite

RM_HAH1-2012-504.1 <63 µm >3.3 chalcopyrite, pyrite

RM_HAH1-2012-505.1 <63 µm >3.3 pyrite

RM_HAH1-2012-509.1 <63 µm >3.3 gahnite, Nb-Ta-mineral

RM_JOV$-2012-2.1 <63 µm >3.3 pyrite

RM_JOV$-2012-3.1 <63 µm >3.3 pyrite

RM_JOV$-2012-9.1 <63 µm >3.3 pyrite, pyrrhotite

RM_JOV$-2012-32.1 <63 µm >3.3 pyrite

RM_POS$-2012-33.3 <63 µm >3.3 pyrite

RM_POS$-2012-43.3 <63 µm >3.3 gahnite

RM_POS$-2012-46.4 <63 µm >3.3 gahnite

RM_POS$-2012-47.1 <63 µm >3.3 gahnite, Nb-Ta-mineral

RM_POS$-2012-51.2 <63 µm >3.3 pyrite

RM_POS$-2012-56.2 <63 µm >3.3 gahnite

RM_POS$-2012-66.1 <63 µm >3.3 pyrite

RM_POS$-2012-83.2 <63 µm >3.3 pyrite

RM_POS$-2012-85.2 <63 µm >3.3 Ni-mineral (awaruite?)

(1–5%) samples are also easy to identify based on their REE concentrations, with La and Ce exceed-ing the limits of calibration.

However, the LV-SEM-EDS results do not ex-plain the mineralogy behind the most interesting observations. A few specific samples stand out from the bulk with unusual elemental concentra-tions, such as RM_POSS-2012-44.2 and 47.2 (1c and 2c), with over 2000 ppm of Y, 200 ppm of Bi, 100 ppm of W and 5 ppm of Au. Sample RM_POSS-2012-43.3 (10) also has over 2000 ppm of Y, which is also well above the average.

When the HR-SC-ICPMS data are compared with the calculated concentrations of Au by ODM based on the visually observed gold grains, the HR-SC-ICPMS analyses nearly always show sys-tematically higher levels of Au. This is probably due to the limitations in the visual identification of gold. The grains below 15–20 µm in diam-eter cannot be identified, meaning that the finer-grained gold is excluded from the calculations. On the other hand, the calculated Au concentra-tion of sample RM_POS$-2012-41.1 is extremely high, 1200 ppb, compared to the 140 ppb meas-

ured by HR-SC-ICPMS from its reference sample RM_POS$-2012-41.2 (9). The calculated concen-tration, however, is in practice entirely based on one single larger gold nugget with dimensions 120 x 250 x 450 µm (Appendix III). Thus, the seeming discrepancy in the results can be explained in this case by an obvious nugget effect.

Stage 3: Detailed mineralogy by FE-SEM-EDS

Detailed mineralogical investigations were car-ried out by FE-SEM-EDS on selected samples that had been analysed by HR-SC-ICPMS for trace elements. Figures 7a and 7b present mineralogi-cal maps created by INCA MinLib software for the heavy mineral concentrates. The figures dem-onstrate that the material in the <63 µm fraction mostly consists of individual mineral grains with some bimineralic grains and rock fragments. Min-eral inclusions and alteration products can also be detected.

Trace mineral searches were conducted for min-eral phases with a BSE grey-scale at the level of or higher than that of monazite, i.e. a setting to ignore

40


Fig. 7. Mineral distribution maps (a–b) over a heavy mineral concentrate. Sample RM_POS$-2012-82.1. Grain size <0.063 mm. Jeol TM JSM-7100F. Oxford Instruments INCAMineral.

41


all but the densest portion of the heavy mineral concentrates. The aim was to detect gold and PGM that had already been recovered at ODM, and also to find mineralogical explanations for Y-, Bi- and W-rich concentrates.

The results are presented in Table 6. The amount of heavies varies greatly in the concentrates, from 0.1% to over 13% by area. The dominant heavy mineral is monazite, making up 70% to 99% of analysed grains, and representing up to 6% of all scanned mineral grains. The next most common mineral is xenotime, with maximum concentra-tions of 27% of heavies and 0.6% of all scanned minerals. Other heavy minerals, such as pyro-chlore, scheelite, gold, and Pt and Bi minerals, are extremely rare.

The mineralogy of the variably processed refer-ence till samples (1–5, as in Appendix IV) demon-strates that the tabled and separated concentrates (type c) have a systematically higher and more ver-satile content of heavy minerals than their merely HMS-separated counterparts (type b). This ob-servation correlates well with the HR-SC-ICPMS analyses.

The trace element data are also supported by other mineralogical findings. Scheelite and Bi

minerals (mostly Bi oxides) are most commonly found in samples with elevated levels of W and Bi (GK_POS$-2012-44.1 and RM_POS$-2012-44.2) and xenotime in Y-rich samples (e.g. RM_POS$-2012-44.2). The extremely rare findings of gold also coincide with the most Au-rich samples (e.g. RM_POS$-2012-44.2). The largest detected gold grains are 20–30 µm in diameter, but most are micron to sub-micron scale (Fig. 8). The smallest detected gold particles exist as inclusions in other mineral grains, mostly goethite. Within the larger grains, some compositional variation can be de-tected by element distribution mapping, as seen in Figure 9, where a ~200 nm vein of pure gold cuts across a silver-bearing gold grain.

Pt minerals were only detected as inclusions in other minerals, except for one individual grain of sperrylite in sample RM_POS$-2012-97.2 (Fig. 8). The inclusions are submicron scale and too small for reliable mineral identifications. Importantly, the rare Pt-mineral findings match with the elevat-ed Pt concentrations measured by HR-SC-ICPMS, such as in samples RM_POS$-2012-36.2 (900 ppb) and RM_POS$-2012-43.3 (600 ppb).

42


GK

_PO

S$-

2012

-44.

11b

RM

_PO

S$-

2012

-44.

21c

Cla

ssFe

atur

es%

ana

lyze

d

feat

ures

% t

ota

l fe

atur

es

(est

.)

Feat

ure

area

(s

q. µ

m)

% a

naly

zed

fe

atur

es a

rea

%

tota

l ar

eaFe

atur

es%

ana

lyze

d

feat

ures

% t

ota

l fe

atur

es

(est

.)

Feat

ure

area

(s

q. µ

m)

% a

naly

zed

fe

atur

es

area

%

tota

l ar

eaM

onaz

ite5

313

97.3

32.

661.

30E

+6

99.2

80.

4613

139

89.8

55.

716.

34E

+6

97.4

31.

57X

enot

ime

122

2.23

0.06

3.60

E+

30.

270.

001

369

9.36

0.60

1.41

E+

52.

170.

03S

chee

lite

100.

180.

013.

25E

+3

0.25

0.00

130.

090.

014.

66E

+3

0.07

0.00

Bi-

min

eral

80.

150.

001.

38E

+3

0.11

0.00

320.

220.

011.

44E

+4

0.22

0.00

Gol

d1

0.02

0.00

2.28

E+

10.

000.

003

0.02

0.00

2.95

E+

20.

000.

00P

yroc

hlor

e2

0.04

0.00

8.06

E+

20.

060.

0049

0.34

0.02

5.55

E+

30.

090.

00N

b-T

a-m

iner

al1

0.02

0.00

1.23

E+

20.

010.

0014

0.10

0.01

3.52

E+

20.

010.

00Th

-min

eral

10.

020.

002.

12E

+2

0.02

0.00

20.

010.

001.

09E

+3

0.02

0.00

Gal

ena

10.

020.

004.

64E

+1

0.00

0.00

10.

010.

004.

92E

+0

0.00

0.00

Pb

-oxi

de

Pt-

min

eral

U-m

iner

al2

0.01

0.00

5.27

E+

00.

000.

00To

tal

5 45

910

0.00

2.73

1.31

E+

610

0.00

0.47

14 6

2410

0.00

6.36

6.51

E+

610

0.00

1.61

Tota

l fea

ture

s (e

stim

ate)

200

000

230

000

Tota

l sca

nned

are

a

(sq

. µm

)2.

81E

+8

4.04

E+

8

SC

-IC

PM

S d

ata

Y p

pm

1 19

02

332

Bi p

pm

6221

1W

pp

m24

526

1N

b p

pm

558

652

Au

pp

b

1 89

55

015

Pt

pp

b15

638

8

OD

M r

esul

ts

Gol

d (g

rain

s)

no d

ata

no d

ata

Pt

(gra

ins)

Sp

erry

lite

(gra

ins)

Au

pp

b c

alcu

late

d

Tabl

e 6.

Res

ults

of h

eavy

min

eral

map

ping

by

FE-S

EM-E

DS.

Jeol

TM

JSM

-710

0F. I

NC

A F

eatu

re. S

C-I

CPM

S da

ta (A

ppen

dix

IV),

OD

M re

sults

(App

endi

x II

I).

43


GK

_PO

S$-

2012

-47.

22b

RM

_PO

S$-

2012

-47.

22c

Cla

ssFe

atur

es%

an

alyz

ed

feat

ures

% t

ota

l fe

atur

es

(est

.)

Feat

ure

area

(s

q. µ

m)

% a

naly

zed

fe

atur

es a

rea

%

tota

l ar

ea

Feat

ures

%

anal

yzed

fe

atur

es

% t

ota

l fe

atur

es

(est

.)

Feat

ure

area

(s

q. µ

m)

% a

naly

zed

fe

atur

es a

rea

%

tota

l ar

ea

Mon

azite

7 02

187

.07

3.51

2.29

E+

692

.45

0.80

4 67

493

.52

3.90

3.31

E+

695

.33

1.53

Xen

otim

e1

034

12.8

20.

521.

85E

+5

7.47

0.06

313

6.26

0.26

1.57

E+

54.

520.

07S

chee

lite

Bi-

min

eral

50.

060.

001.

37E

+3

0.06

0.00

80.

160.

014.

10E

+3

0.12

0.00

Gol

dP

yroc

hlor

e1

0.02

0.00

4.12

E+

20.

010.

00N

b-T

a-m

iner

alTh

-min

eral

20.

020.

003.

35E

+2

0.01

0.00

Gal

ena

10.

010.

001.

69E

+1

0.00

0.00

Pb

-oxi

de

10.

010.

002.

32E

+2

0.01

0.00

10.

020.

001.

13E

+2

0.00

0.00

Pt-

min

eral

U-m

iner

al1

0.02

0.00

4.12

E+

20.

010.

00To

tal

8 06

410

0.00

4.03

2.48

E+

610

0.00

0.86

4 99

810

0.00

4.17

3.47

E+

610

0.00

1.60

Tota

l fea

ture

s (e

stim

ate)

200

000

120

000

Tota

l sca

nned

are

a

(sq

. µm

)2.

88E

+8

2.17

E+

8

SC

-IC

PM

S d

ata

Y p

pm

734

2 07

4B

i pp

m59

224

W p

pm

6710

7N

b p

pm

468

650

Au

pp

b

108

237

Pt

pp

b86

268

OD

M r

esul

ts

Gol

d (g

rain

s)

Pt

(gra

ins)

Sp

erry

lite

(gra

ins)

Au

pp

b c

alcu

late

d

Tabl

e 6.

Con

t.

44


GK

_PO

S$-

2012

-82.

13b

RM

_PO

S$-

2012

-82.

13c

Cla

ss

Feat

ures

%

anal

yzed

fe

atur

es

% t

ota

l fe

atur

es

(est

.)

Feat

ure

area

(s

q. µ

m)

% a

naly

zed

fe

atur

es

area

% t

ota

l ar

eaFe

atur

es

%

anal

yzed

fe

atur

es

% t

ota

l fe

atur

es

(est

.)

Feat

ure

area

(s

q. µ

m)

% a

naly

zed

fe

atur

es

area

%

tota

l ar

eaM

onaz

ite36

978

.68

0.18

9.64

E+

492

.24

0.03

795

88.5

30.

505.

60E

+5

94.2

70.

20X

enot

ime

100

21.3

20.

058.

11E

+3

7.76

0.00

100

11.1

40.

063.

29E

+4

5.54

0.01

Sch

eelit

eB

i-m

iner

alG

old

Pyr

ochl

ore

20.

220.

001.

11E

+3

0.19

0.00

Nb

-Ta-

min

eral

Th-m

iner

al1

0.11

0.00

1.12

E+

10.

000.

00G

alen

aP

b-o

xid

eP

t-m

iner

alU

-min

eral

Tota

l46

910

0.00

0.23

1.05

E+

510

0.00

0.04

898

100.

000.

565.

94E

+5

100.

000.

21

Tota

l fea

ture

s (e

stim

ate)

200

000

160

000

Tota

l sca

nned

are

a

(sq

. µm

)2.

83E

+8

2.79

E+

8

SC

-IC

PM

S d

ata

Y p

pm

310

289

Bi p

pm

21

W p

pm

1311

Nb

pp

m25

626

5A

u p

pb

50

73P

t p

pb

2714

3

OD

M r

esul

ts

Gol

d (g

rain

s)22

Pt

(gra

ins)

Sp

erry

lite

(gra

ins)

Au

pp

b c

alcu

late

d48

Tabl

e 6.

Con

t.

45


GK

_PO

S$-

2012

-83.

44b

RM

_PO

S$-

2012

-83.

2 4c

Cla

ssFe

atur

es%

an

alyz

ed

feat

ures

% t

ota

l fe

atur

es

(est

.)

Feat

ure

area

(s

q. µ

m)

% a

naly

zed

fe

atur

es

area

% t

ota

l ar

eaFe

atur

es%

an

alyz

ed

feat

ures

% t

ota

l fe

atur

es

(est

.)

Feat

ure

area

(s

q. µ

m)

% a

naly

zed

fe

atur

es

area

%

tota

l ar

ea

Mon

azite

700

88.8

30.

351.

98E

+5

93.4

90.

071

137

95.3

10.

761.

26E

+6

97.0

50.

47X

enot

ime

789.

900.

041.

11E

+4

5.24

0.00

534.

440.

043.

36E

+4

2.59

0.01

Sch

eelit

eB

i-m

iner

alG

old

Pyr

ochl

ore

20.

250.

008.

71E

+1

0.04

0.00

20.

170.

003.

77E

+3

0.29

0.00

Nb

-Ta-

min

eral

Th-m

iner

al4

0.51

0.00

2.46

E+

31.

160.

00G

alen

aP

b-o

xid

e4

0.51

0.00

1.29

E+

20.

060.

00P

t-m

iner

alU

-min

eral

10.

080.

009.

77E

+2

0.08

0.00

Tota

l78

810

0.00

0.39

2.12

E+

510

0.00

0.08

1 19

310

0.00

0.80

1.30

E+

610

0.00

0.48

Tota

l fea

ture

s (e

stim

ate)

200

000

150

000

Tota

l sca

nned

are

a

(sq

. µm

)2.

82E

+8

2.69

E+

8

SC

-IC

PM

S d

ata

Y p

pm

368

607

Bi p

pm

21

W p

pm

1617

Nb

pp

m41

131

7A

u p

pb

35

113

6P

t p

pb

5824

3

OD

M r

esul

ts

Gol

d (g

rain

s)

Pt

(gra

ins)

Sp

erry

lite

(gra

ins)

Au

pp

b c

alcu

late

d

Tabl

e 6.

Con

t.

46


GK

_PO

S$-

2012

-97.

35b

RM

_PO

S$-

2012

-97.

25c

Cla

ssFe

atur

es%

an

alyz

ed

feat

ures

% t

ota

l fe

atur

es

(est

.)

Feat

ure

area

(s

q. µ

m)

% a

naly

zed

fe

atur

es

area

%

tota

l ar

ea

Feat

ures

%

anal

yzed

fe

atur

es

% t

ota

l fe

atur

es

(est

.)

Feat

ure

area

(s

q. µ

m)

% a

naly

zed

fe

atur

es

area

%

tota

l ar

ea

Mon

azite

586

83.4

80.

291.

39E

+5

89.2

60.

051

027

70.9

70.

412.

68E

+5

91.2

80.

06X

enot

ime

110

15.6

70.

061.

44E

+4

9.25

0.01

401

27.7

10.

162.

31E

+4

7.87

0.01

Sch

eelit

eB

i-m

iner

alG

old

40

0.00

6.67

E+

00.

000.

00P

yroc

hlor

e5

00.

008.

01E

+2

0.27

0.00

Nb

-Ta-

min

eral

10.

140.

005.

88E

+2

0.38

0.00

10

0.00

6.79

E+

20.

230.

00Th

-min

eral

50.

710.

001.

74E

+3

1.12

0.00

50

0.00

9.88

E+

20.

340.

00G

alen

a1

00.

004.

22E

+0

0.00

0.00

Pb

-oxi

de

20

0.00

1.55

E+

10.

010.

00P

t-m

iner

al1

00.

002.

46E

+0

0.00

0.00

U-m

iner

alTo

tal

702

100.

000.

351.

56E

+5

100.

000.

061

447

100.

000.

582.

94E

+5

100.

000.

07

Tota

l fea

ture

s (e

stim

ate)

200

000

250

000

Tota

l sca

nned

are

a

(sq

. µm

)2.

77E

+8

4.48

E+

8

SC

-IC

PM

S d

ata

Y p

pm

334

222

Bi p

pm

11

W p

pm

1710

Nb

pp

m30

615

6A

u p

pb

65

50P

t p

pb

3663

OD

M r

esul

ts

Gol

d (g

rain

s)49

Pt

(gra

ins)

Sp

erry

lite

(gra

ins)

1A

u p

pb

cal

cula

ted

43

Tabl

e 6.

Con

t.

47


RM

_PO

S$-

2012

-36.

26

RM

_PO

S$-

2012

-39.

18

Cla

ssFe

atur

es%

an

alyz

ed

feat

ures

% t

ota

l fe

atur

es

(est

.)

Feat

ure

area

(s

q. µ

m)

% a

naly

zed

fe

atur

es

area

% t

ota

l ar

eaFe

atur

es%

an

alyz

ed

feat

ures

% t

ota

l fe

atur

es

(est

.)

Feat

ure

area

(s

q. µ

m)

% a

naly

zed

fe

atur

es

area

%

tota

l ar

ea

Mon

azite

2 99

183

.13

1.20

2.95

E+

695

.13

0.67

3 29

093

.04

1.57

2.20

E+

695

.62

0.59

Xen

otim

e52

914

.70

0.21

1.47

E+

54.

740.

0323

46.

620.

119.

57E

+4

4.16

0.03

Sch

eelit

eB

i-m

iner

al1

0.03

0.00

4.22

E+

00.

000.

00G

old

40.

110.

009.

84E

+0

0.00

0.00

Pyr

ochl

ore

391.

080.

022.

40E

+3

0.08

0.00

60.

170.

001.

58E

+3

0.07

0.00

Nb

-Ta-

min

eral

20.

060.

001.

42E

+3

0.06

0.00

Th-m

iner

al8

0.22

0.00

1.56

E+

30.

050.

001

0.03

0.00

2.15

E+

30.

090.

00G

alen

a4

0.11

0.00

1.55

E+

10.

000.

001

0.03

0.00

1.26

E+

10.

000.

00P

b-o

xid

e16

0.44

0.01

9.87

E+

10.

000.

002

0.06

0.00

2.53

E+

10.

000.

00P

t-m

iner

al4

0.11

0.00

1.23

E+

10.

000.

00U

-min

eral

20.

060.

004.

92E

+0

0.00

0.00

Tota

l3

598

100.

001.

443.

10E

+6

100.

000.

713

536

100.

001.

682.

30E

+6

100.

000.

61

Tota

l fea

ture

s (e

stim

ate)

250

000

210

000

Tota

l sca

nned

are

a

(sq

. µm

)4.

38E

+8

3.75

E+

8

SC

-IC

PM

S d

ata

Y p

pm

277

525

Bi p

pm

22

W p

pm

129

Nb

pp

m28

427

2A

u p

pb

12

710

1P

t p

pb

902

574

OD

M r

esul

ts

Gol

d (g

rain

s)18

5

Pt

(gra

ins)

11

Sp

erry

lite

(gra

ins)

3A

u p

pb

cal

cula

ted

133

2

Tabl

e 6.

Con

t.

48


RM

_PO

S$-

2012

-41.

29

RM

_PO

S$-

2012

-43.

310

Cla

ssFe

atur

es%

an

alyz

ed

feat

ures

% t

ota

l fe

atur

es

(est

.)

Feat

ure

area

(s

q. µ

m)

% a

naly

zed

fe

atur

es

area

%

tota

l ar

ea

Feat

ures

%

anal

yzed

fe

atur

es

% t

ota

l fe

atur

es

(est

.)

Feat

ure

area

(s

q. µ

m)

% a

naly

zed

fe

atur

es

area

%

tota

l ar

ea

Mon

azite

4 13

186

.53

1.65

4.25

E+

694

.85

0.95

21 1

4299

.63

8.81

9.38

E+

610

0.00

2.26

Xen

otim

e62

713

.13

0.25

2.22

E+

54.

950.

0564

0.30

0.03

1.57

E+

20.

000.

00S

chee

lite

10.

000.

007.

38E

+0

0.00

0.00

Bi-

min

eral

20.

040.

009.

78E

+2

0.02

0.00

20.

010.

009.

48E

+0

0.00

0.00

Gol

d1

0.00

0.00

1.76

E+

00.

000.

00P

yroc

hlor

e5

0.10

0.00

3.79

E+

30.

080.

00N

b-T

a-m

iner

al2

0.04

0.00

2.70

E+

30.

060.

00Th

-min

eral

40.

080.

003.

68E

+2

0.01

0.00

20.

010.

009.

48E

+0

0.00

0.00

Gal

ena

10.

000.

003.

16E

+0

0.00

0.00

Pb

-oxi

de

10.

020.

001.

83E

+1

0.00

0.00

70.

030.

004.

57E

+1

0.00

0.00

Pt-

min

eral

10.

000.

001.

76E

+0

0.00

0.00

U-m

iner

al2

0.04

0.00

8.97

E+

20.

020.

00To

tal

4 77

410

0.00

1.91

4.48

E+

610

0.00

1.00

21 2

2110

0.00

8.84

9.38

E+

610

0.00

2.26

Tota

l fea

ture

s (e

stim

ate)

250

000

240

000

Tota

l sca

nned

are

a

(sq

. µm

)4.

48E

+8

4.15

E+

8

SC

-IC

PM

S d

ata

Y p

pm

999

2 15

2B

i pp

m64

5W

pp

m21

58N

b p

pm

357

416

Au

pp

b

140

146

Pt

pp

b62

960

8

OD

M r

esul

ts

Gol

d (g

rain

s)9

13

Pt

(gra

ins)

Sp

erry

lite

(gra

ins)

2A

u p

pb

cal

cula

ted

1200

40

Tabl

e 6.

Con

t.

49


RM

_PO

S$-

2012

-48.

211

RM

_PO

S$-

2012

-55.

212

Cla

ssFe

atur

es%

an

alyz

ed

feat

ures

% t

ota

l fe

atur

es

(est

.)

Feat

ure

area

(s

q. µ

m)

% a

naly

zed

fe

atur

es

area

%

tota

l ar

ea

Feat

ures

%

anal

yzed

fe

atur

es

% t

ota

l fe

atur

es

(est

.)

Feat

ure

area

(s

q. µ

m)

% a

naly

zed

fe

atur

es

area

%

tota

l ar

ea

Mon

azite

2 55

095

.26

1.02

1.95

E+

699

.30

0.44

1 13

487

.30

0.52

1.27

E+

697

.17

0.32

Xen

otim

e10

63.

960.

043.

64E

+3

0.19

0.00

145

11.1

60.

073.

16E

+4

2.42

0.01

Sch

eelit

eB

i-m

iner

al2

0.07

0.00

8.98

E+

20.

050.

001

0.08

0.00

4.88

E+

10.

000.

00G

old

Pyr

ochl

ore

70.

260.

002.

59E

+3

0.13

0.00

10.

080.

009.

84E

+2

0.08

0.00

Nb

-Ta-

min

eral

30.

110.

002.

68E

+2

0.01

0.00

Th-m

iner

al3

0.11

0.00

4.44

E+

30.

230.

008

0.62

0.00

3.13

E+

30.

240.

00G

alen

aP

b-o

xid

e4

0.15

0.00

5.60

E+

20.

030.

009

0.69

0.00

1.84

E+

20.

010.

00P

t-m

iner

alU

-min

eral

20.

070.

001.

44E

+3

0.07

0.00

10.

080.

009.

84E

+2

0.08

0.00

Tota

l2

677

100.

001.

071.

96E

+6

100.

000.

441

299

100.

000.

591.

31E

+6

100.

000.

33

Tota

l fea

ture

s (e

stim

ate)

250

000

220

000

Tota

l sca

nned

are

a

(sq

. µm

)4.

45E

+8

3.92

E+

8

SC

-IC

PM

S d

ata

Y p

pm

602

498

Bi p

pm

32

W p

pm

1915

Nb

pp

m36

633

7A

u p

pb

12

212

6P

t p

pb

469

434

OD

M r

esul

ts

Gol

d (g

rain

s)23

9

Pt

(gra

ins)

Sp

erry

lite

(gra

ins)

2A

u p

pb

cal

cula

ted

3530

Tabl

e 6.

Con

t.

50


RM

_PO

S$-

2012

-66.

113

RM

_PO

S$-

2012

-77.

214

Cla

ssFe

atur

es%

an

alyz

ed

feat

ures

% t

ota

l fe

atur

es

(est

.)

Feat

ure

area

(s

q. µ

m)

% a

naly

zed

fe

atur

es

area

%

tota

l ar

ea

Feat

ures

%

anal

yzed

fe

atur

es

% t

ota

l fe

atur

es

(est

.)

Feat

ure

area

(s

q. µ

m)

% a

naly

zed

fe

atur

es

area

%

tota

l ar

ea

Mon

azite

2 88

498

.94

0.93

6.40

E+

599

.82

0.11

1 66

480

.58

0.67

1.58

E+

696

.37

0.35

Xen

otim

e25

0.86

0.01

7.81

E+

20.

120.

0039

319

.03

0.16

5.40

E+

43.

290.

01S

chee

lite

20.

070.

008.

75E

+1

0.01

0.00

Bi-

min

eral

Gol

dP

yroc

hlor

e1

0.03

0.00

4.46

E+

10.

010.

003

0.15

0.00

3.33

E+

30.

200.

00N

b-T

a-m

iner

al1

0.03

0.00

4.29

E+

10.

010.

001

0.05

0.00

4.35

E+

20.

030.

00Th

-min

eral

20.

070.

001.

88E

+2

0.03

0.00

20.

100.

001.

20E

+3

0.07

0.00

Gal

ena

Pb

-oxi

de

10.

050.

001.

72E

+1

0.00

0.00

Pt-

min

eral

U-m

iner

al1

0.05

0.00

5.21

E+

20.

030.

00To

tal

2 91

510

0.00

0.94

6.41

E+

510

0.00

0.11

2 06

510

0.00

0.83

1.64

E+

610

0.00

0.37

Tota

l fea

ture

s (e

stim

ate)

310

000

250

000

Tota

l sca

nned

are

a

(sq

. µm

)5.

58E

+8

4.48

E+

8

SC

-IC

PM

S d

ata

Y p

pm

439

440

Bi p

pm

21

W p

pm

1013

Nb

pp

m21

037

6A

u p

pb

15

312

2P

t p

pb

463

276

OD

M r

esul

ts

Gol

d (g

rain

s)20

14

Pt

(gra

ins)

Sp

erry

lite

(gra

ins)

1A

u p

pb

cal

cula

ted

7419

Tabl

e 6.

Con

t.

51


Fig. 8. Gold and sperrylite grains detected in the NovTecEx heavy mineral concentrates. a–b) gold grains in sample RM_POS$-2012-44.2 c–d) gold as inclusions in goethite in sample RM_POS$-36.2 e) submicron-scale gold particle in sample RM_POS$-2012-43.3, and f) sperrylite grain in sample RM_POS$-97.2. BSE images. Jeol TM JSM-7100F.

52


Fig. 9. BSE image (a) of a silver-bearing gold grain in sample RM_POS$-2012-44.1 showing a lighter-coloured vein that is composed of pure gold (b, c). Jeol TM JSM-7100F. AZtec.

53


DISCUSSION

As ore deposits become increasingly difficult to discover, traditional methods of exploration need to be enhanced through the addition of modern technologies. In this project, conventional sample processing protocols were tuned to meet the needs of modern analytical research instruments. The results demonstrate that, for example, panning combined with optical microscopy is probably still the most efficient method for recovering gold and PGM grains over 10 to 20 µm in size from till. However, a significant proportion of these miner-als exist in even finer grain sizes and, importantly, as inclusions in other mineral grains, which cannot be detected without scanning electron microsco-py. In addition, a considerable variety of indicator minerals (Table 1) cannot be concentrated as effec-tively as gold and PGM and also exist as silt-sized grains, or are otherwise difficult to recognize un-der the optical microscope. A modern automated SEM provides a means to efficiently identify and analyse these types of grains. However, a reliable screening method is needed to select the samples for detailed SEM work.

The conventional elemental analysis of the till matrix is performed on the unprocessed fine frac-tion (<63 µm), which is dominated by quartz, feld-spars and other light “bulk” minerals. These min-erals exist in such high concentrations that they prevent ultra-low concentration (ppb level and beyond) indicator minerals from being detected by chemical analysis. Following the conventional method, the samples are digested prior to analy-sis using aqua regia (3:1 mixture of concentrated hydrochloric acid and concentrated nitric acid), which produces only partial dissolution for many elements. When these two factors are combined, it is clear that conventional till geochemistry cannot be used as a screening method for detailed indica-tor work.

In this project, the heavy mineral concentrates were fully digested by a microwave system and subsequently analysed by HR-SC-ICPMS to detect interesting trace element concentrations, and ul-timately screen the samples for detailed FE-SEM-EDS work. The sample size for digestion was 500 mg, which represented on average 20–25% of the

NovTecEx fine fraction heavy mineral concen-trates after magnetite had been removed. Based on the results, the digested sample size appears to have been adequate for the trace element work. Moreover, since only some tens of milligrams of material are needed for the SEM studies, even smaller original samples might have produced enough fine-fraction heavy minerals for analysis.

The possibility to use a small original sample size is particularly important in projects where the till samples are collected by drilling, and obtaining a larger sample would require a substantial amount of effort. The methodology is also useful when re-analysing previously collected exploration samples for novel purposes when only a restricted amount of pristine sample material is available. In particu-lar, a smaller original sample size is significant re-garding the overall context of the project, where all the actions have aimed at minimizing the use of energy, labour and time spent on sampling, sam-ple processing and analysis, and ultimately on the impact of the exploration activities on the environ-ment.

One of the major challenges in this development project was the delay in the installation of the HR-SC-ICPMS and FE-SEM-EDS laboratories. When the project started in 2012, the new analytical fa-cilities were due to be delivered by the end of the year. In practice, they were finally delivered over a year behind the original schedule, during late No-vember in 2013. The delay meant that not all of the designed experiments could be carried out dur-ing the time frame of the project. These planned aspects included more detailed geochemical and mineralogical investigations on sample material at different stages of processing, and also experi-ments on the effect of using variable grain sizes of the concentrates to achieve statistically meaning ful results. The objective would have been to op-timize the original sample size and detect possible short cuts in the processing line for certain target minerals and metals. Importantly, the methodol-ogy for these tests has now been established and abundant sample material collected during the NovTecEx project also remains available for pos-sible future work.

54


CONCLUSIONS

The sample processing protocol designed for the NovTecEx samples turned out to be effective. It was based on a combination of traditional and mod-ern methodologies. Fine-grained heavy minerals were reliably recovered from till, and their over-all mineralogy could be rapidly determined from grain mounts using automated LV-SEM-EDS. As a result, a new dataset was formed on the heavy mineral distribution in till over the Savukoski-Pelkosenniemi sampling area. The most demand-ing aspect of the project was the development of a methodology to completely digest the heavy mineral concentrates for trace element analysis by HR-SC-ICPMS. The resulting protocol is based on microwave digestion and it is far less time-con-suming and laborious than conventional dissolu-tion methods. The analytical capability of HR-SC-ICPMS enables the trace element concentrations to be measured below 1 ppb levels. The detailed mineralogical investigations by FE-SEM-EDS re-

vealed that even submicron-scale indicator min-eral grains could be detected either as individual grains or as inclusions in other minerals.

The results of this project demonstrate that the use of modern research instruments can signifi-cantly reduce the sample size needed for exploring mineralizations in an area. In this study, the aver-age sample size was relatively small (5 l) to begin with, but in most cases processing even half of that would probably have been enough. A smaller sam-ple size obviously means less effort during sam-pling and sample processing, and above all, less impact on the environment. Further tests should still be carried out to determine the optimal sam-ple size for different types of investigations, and also more experiments to detect possible shortcuts in the sample processing protocol. The remaining unprocessed NovTecEx samples provide good test material for future development.

ACKNOWLEDGEMENTS

Beth McClenaghan and Isabelle McMartin from the Geological Survey of Canada are thanked for collaborating on the project, and organizing the sample processing at the ODM Laboratory. Har-vey Thorleifson and Vesa Peuraniemi are appre-

ciated for revising the manuscript and providing valuable suggestions for improvements. Technical and laboratory staff of the Research Laboratory are acknowledged for their efforts.

REFERENCES

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56


Appe

ndix

I. L

abtiu

m d

ata.

Lab

tium

ID

GT

K ID

gra

in s

ize

(µm

)

den

sity

(gcm

-3)

met

hod

L130

0765

6L1

3005

923

L130

0592

4L1

3005

925

L130

0591

1L1

3005

917

L130

0591

8L1

3005

918U

L130

0591

9L1

3005

912

L130

0591

4L1

3005

915

L130

0591

5UL1

3005

916

TPR

-1

TPR

-1TP

R-1

Ø 1

00-5

00 µ

m

Ø 6

3-10

0 µm

Ø

<63

µm

d

>3.

3d

>3.

3d

>3.

3

175X

310M

310M

310M

175X

310M

310M

310M

310M

175X

310M

310M

310M

310M

Na2

O%

0.25

10.

103

0.07

9

MgO

%1.

410

0.63

00.

492

Al2

O3

%12

.60

6.16

4.19

SiO

2%

24.5

012

.40

9.59

P2O

5%

0.13

20.

146

0.31

5

K2O

%0.

129

0.05

20.

041

CaO

%10

.29

4.30

3.34

TiO

2%

9.60

11.4

612

.79

11.8

818

.80

23.3

524

.19

27.5

222

.02

20.1

123

.85

25.1

923

.02

26.0

2

MnO

%0.

831.

171.

160.

921.

161.

541.

521.

811.

471.

021.

361.

391.

381.

37

Fe2O

3%

38.9

052

.00

54.4

0

S%

0.02

0<

0.24

<0.

24<

0.24

0.03

5<

0.24

<0.

24<

0.24

<0.

240.

032

<0.

24<

0.24

<0.

24<

0.24

Cl

%0.

012

0.00

60.

009

Sc

%0.

005

0.00

60.

006

0.00

60.

002

0.00

60.

006

0.00

60.

005

0.00

30.

006

0.00

70.

005

0.00

6

V%

0.06

10.

080

0.08

5

Cr

%0.

049

<0.

040

<0.

040

<0.

040

0.09

30.

083

0.07

80.

080

0.06

60.

125

0.10

40.

121

0.11

00.

111

Ni

%0.

005

0.00

40.

004

0.00

40.

007

0.00

70.

007

0.00

80.

007

0.01

00.

008

0.00

90.

009

0.00

9

Cu

%0.

002

0.00

60.

007

0.00

6<

0.00

20.

010

0.00

90.

011

0.00

9<

0.00

20.

010

0.01

10.

010

0.01

0

Zn

%0.

014

0.01

70.

019

0.01

70.

016

0.02

80.

027

0.03

60.

028

0.01

70.

027

0.02

90.

031

0.03

1

Ga

%<

0.00

2<

0.00

2<

0.00

2

As

%0.

014

<0.

020

<0.

020

<0.

020

0.03

4<

0.02

00.

028

0.03

6<

0.02

00.

029

<0.

020

<0.

020

0.02

50.

022

Rb

%0.

003

<0.

0005

0.00

10.

001

0.00

5<

0.00

05<

0.00

05<

0.00

05<

0.00

050.

006

<0.

0005

<0.

0005

<0.

0005

<0.

0005

Sr

%0.

088

0.07

00.

077

0.07

80.

032

0.02

60.

032

0.02

90.

029

0.02

40.

024

0.02

40.

023

0.02

2

Y%

0.01

70.

002

0.00

20.

002

0.02

90.

003

0.00

30.

006

0.00

40.

042

0.00

50.

003

0.00

30.

004

Zr

%0.

565

0.42

90.

673

0.37

42.

695

2.19

02.

440

2.47

02.

010

3.99

12.

740

3.21

02.

890

3.38

0

Nb

%0.

004

0.01

00.

011

0.00

80.

001

0.01

40.

014

0.01

40.

013

<0.

0007

0.01

30.

015

0.01

30.

015

Mo

%<

0.00

10.

009

0.01

7

Sn

%0.

005

0.00

10.

001

0.00

10.

006

0.00

10.

001

0.00

10.

001

0.00

50.

001

0.00

10.

001

0.00

1

Sb

%<

0.01

0.00

0<

0.00

01<

0.00

01<

0.01

0.00

10.

000

0.00

1<

0.00

01<

0.01

0.00

10.

003

0.00

30.

003

Ba

%0.

028

<0.

005

<0.

005

<0.

005

0.05

4<

0.00

50.

006

<0.

005

<0.

005

0.05

5<

0.00

5<

0.00

5<

0.00

5<

0.00

5

La%

0.01

80.

001

0.00

10.

001

0.03

8<

0.00

1<

0.00

1<

0.00

1<

0.00

10.

078

0.00

1<

0.00

1<

0.00

1<

0.00

1

Ce

%0.

043

0.00

50.

005

0.00

50.

070

0.00

50.

005

0.00

60.

006

0.15

40.

007

0.00

50.

005

0.00

5

Pb

%0.

010

0.02

80.

013

0.00

50.

025

0.03

50.

028

0.03

90.

026

0.08

80.

081

0.11

10.

104

0.13

2

Bi

%<

0.00

3<

0.00

05<

0.00

05<

0.00

050.

003

<0.

0005

<0.

0005

<0.

0005

<0.

0005

0.00

6<

0.00

05<

0.00

050.

002

0.00

3

Th%

0.01

5<

0.00

050.

001

<0.

0005

0.01

6<

0.00

05<

0.00

050.

001

0.00

10.

026

0.00

10.

001

<0.

0005

0.00

1

U%

0.00

30.

003

0.00

50.

002

0.00

50.

007

0.00

80.

008

0.00

60.

008

0.01

00.

011

0.01

00.

010

57


Appe

ndix

II.

Opt

ical

mic

rosc

opy

resu

lts o

f OD

M a

nd G

TK p

roce

ssed

hea

vy m

iner

al co

ncen

trat

es.

The

num

bers

of a

cces

ory

min

eral

s are

nor

mal

ized

to 1

0 kg

of p

roce

ssed

till.

D

ata:

Ove

rbur

den

Dril

ling

Man

agem

ent L

td.

GT

K p

roce

ssed

Wei

ght

<

1 m

m t

able

fe

ed (k

g)

Mic

rosc

op

y 0.

25-1

.0 m

m:

min

eral

ass

emb

lag

eM

icro

sco

py

0.25

-1.0

m

m: a

cces

sori

es

Chal

co-

pyrit

ePy

rite

Low

Cr

-di

opsi

de

Ruby

Co

run-

dum

Sapp

hire

Co

run-

dum

Mn

ep

idot

eGa

hnite

Red

Rutil

eCh

rom

ite%

Go

ethi

te%

Ky

anite

%

Silli

ma-

nite

%

Tour

-m

alin

e

%

Stau

rolit

e%

Sp

es-

sarti

ne

%

Faya

lite

% O

px%

Ap

atite

%

Mon

azite

RM

_PO

S$-

2012

-36.

210

.9A

lman

din

e-ilm

enite

/sta

urol

ite-e

pid

ote

11

30

00

055

550

10Tr

Tr70

Tr0

Tr0

Tr

RM

_PO

S$-

2012

-39.

118

.5A

lman

din

e/ep

idot

e-st

auro

lite-

kyan

ite0

01

00

00

2210

80

15Tr

030

Tr0

0Tr

Tr

RM

_PO

S$-

2012

-41.

28.

3A

lman

din

e-ilm

enite

/ep

idot

e-st

auro

lite

10

00

00

048

720

8Tr

030

Tr0

00

0

RM

_PO

S$-

2012

-43.

38.

4A

lman

din

e/st

auro

lite-

epid

ote

00

00

00

3136

360

3Tr

050

Tr0

10

0

RM

_PO

S$-

2012

-48.

211

Alm

and

ine-

ilmen

ite/s

taur

olite

-ep

idot

e0

01

00

01

3673

05

Tr0

60Tr

0Tr

00

RM

_PO

S$-

2012

-55.

27.

5A

lman

din

e-ilm

enite

-hor

nble

nde/

ep

idot

e- s

taur

olite

01

00

00

053

53Tr

3Tr

020

Tr0

Tr0

0

RM

_PO

S$-

2012

-66.

119

.7H

emat

ite-a

lman

din

e-ilm

enite

/ st

auro

lite-

ep

idot

e-ky

anite

00

00

00

020

9Tr

20Tr

040

Tr0

Tr0

0

RM

_PO

S$-

2012

-77.

29.

5A

lman

din

e-ilm

enite

-hem

atite

/ep

idot

e- s

taur

olite

-kya

nite

00

00

00

063

32Tr

20Tr

040

Tr0

Tr0

0

RM

_PO

S$-

2012

-82.

122

.2A

lman

din

e-he

mat

ite-i

lmen

ite/

epid

ote-

sta

urol

ite0

00

00

00

2768

Tr8

Tr0

30Tr

0Tr

00

RM

_PO

S$-

2012

-97.

211

.6A

lman

din

e-he

mat

ite/

epid

ote-

stau

rolit

e0

00

00

00

3434

Tr5

Tr0

40Tr

0Tr

00

OD

M p

roce

ssed

Wei

ght

<

2 m

m t

able

fe

ed (k

g)

Mic

rosc

op

y 0.

25-2

.0 m

m:

min

eral

ass

emb

lag

eM

icro

sco

py

0.25

-1.0

mm

: acc

esso

ries

Chal

co-

pyrit

ePy

rite

Low

Cr

-di

opsi

de

Ruby

Co

run-

dum

Sapp

hire

Co

run-

dum

Mn

epid

ote

Gahn

iteRe

d Ru

tile

Chro

mite

%

Goet

hite

%

Kyan

ite%

Si

llim

a-ni

te

%

Tour

-m

alin

e

%

Stau

rolit

e%

Spe

s-sa

rtine

%

Faya

lite

%

Opx

%

Apat

ite%

M

onaz

ite

RM

_PO

S$-

2012

-36.

119

.2A

lman

din

e-ilm

enite

/sta

urol

ite-e

pid

ote

01

00

00

031

420

123

070

Tr0

Tr0

Tr

RM

_PO

S$-

2012

-39.

416

Alm

and

ine/

epid

ote-

stau

rolit

e0

01

00

00

3894

Tr4

Tr0

15Tr

0Tr

00

RM

_PO

S$-

2012

-41.

117

.1A

lman

din

e/ep

idot

e-st

auro

lite

01

20

00

158

88Tr

10Tr

Tr15

Tr0

Tr0

Tr

RM

_PO

S$-

2012

-43.

211

.8A

lman

din

e/st

auro

lite-

epid

ote

03

00

00

4225

19Tr

5Tr

Tr60

Tr0

Tr0

0

RM

_PO

S$-

2012

-48.

111

.3A

lman

din

e-ilm

enite

/sta

urol

ite-e

pid

ote

01

00

00

688

106

Tr6

10

50Tr

Tr

(400

gr)

Tr0

Tr

RM

_PO

S$-

2012

-55.

113

.7A

lman

din

e-ilm

enite

-hor

nble

nde/

ep

idot

e- s

taur

olite

00

10

00

129

44Tr

TrTr

Tr30

Tr0

Tr0

0

RM

_PO

S$-

2012

-66.

414

.6A

lman

din

e-he

mat

ite-i

lmen

ite-

horn

ble

nde/

sta

urol

ite-e

pid

ote-

kyan

ite0

00

00

00

6834

Tr25

TrTr

40Tr

0Tr

0Tr

RM

_PO

S$-

2012

-77.

4R17

.3A

lman

din

e-ilm

enite

/ ep

idot

e-st

auro

lite-

kya

nite

00

21

00

029

35Tr

15Tr

Tr40

Tr0

Tr0

0

RM

_PO

S$-

2012

-82.

416

.6A

lman

din

e-ho

rnb

lend

e-he

mat

ite-

ilmen

ite/

epid

ote-

stau

rolit

e0

01

00

00

3615

1Tr

31

020

Tr0

Tr0

0

RM

_PO

S$-

2012

-97.

121

.5H

emat

ite-a

lman

din

e/st

auro

lite-

epid

ote

00

10

00

028

28Tr

10Tr

Tr70

Tr0

Tr0

0

58


Appendix III. Gold and PGM.

OVERBURDEN DRILLING MANAGEMENT LIMITEDSample Number Panned

Yes/NoDimensions (microns) Number of Visible Gold Grains -0.25 mm

Nonmag HMC

Weight

Calculated V.G. Assay in 0.25 mm

HMC

Metallic Minerals in Pan Concentrate

Thickness (M*/C**) Width Length Reshaped Modified Pristine Total (g) (ppb)

RM_POS$-2012-36.1 Yes 3 C 15 15 2 1 3

5 C 25 25 4 4

8 C 25 50 5 1 6 1 native platinum (50µm).

10 C 25 75 1 1 3 sperrylite (15-50µm).

10 C 50 50 2 2

20 C 100 100 1 1

50 M 200 250 1 1

18 162.4 133

RM_POS$-2012-39.4 Yes 3 C 15 15 2 2

5 C 25 25 1 1

10 C 25 75 1 1 1 native platinum (50µm).

13 C 50 75 1 1

5 352.8 2

RM_POS$-2012-41.1 Yes 3 C 15 15 1 1

8 C 25 50 1 1 2 grains sperrylite (25µm).

10 C 25 75 1 1

10 C 50 50 1 1 2

13 C 50 75 3 3

150 M 250 450 1 1

9 116.3 1200

RM_POS$-2012-43.2 Yes 3 C 15 15 1 1 2

5 C 25 25 2 2

8 C 25 50 4 4

13 C 25 100 1 1

10 C 50 50 1 1

13 C 50 75 2 2

15 C 75 75 1 1

13 58.2 40

RM_POS$-2012-48.1 Yes 3 C 15 15 2 1 3

5 C 25 25 5 1 6 2 grains sperrylite (15-25µm).

8 C 25 50 6 6

10 C 50 50 5 5

13 C 50 75 1 1

15 C 50 100 2 2

23 92.5 35

RM_POS$-2012-55.1 Yes 3 C 15 15 1 1

5 C 25 25 4 4

10 C 50 50 2 2

15 C 50 100 1 1

20 C 75 125 1 1

9 87.3 30

59


Sample Number Panned Yes/No

Dimensions (microns) Number of Visible Gold Grains -0.25 mm Nonmag

HMC Weight

Calculated V.G. Assay in 0.25 mm

HMC

Metallic Minerals in Pan Concentrate

Thickness (M*/C**) Width Length Reshaped Modified Pristine Total (g) (ppb)

5 C 25 25 4 4

8 C 25 50 2 2 1 sperrylite (25µm)

10 C 50 50 3 3

13 C 50 75 1 1

18 C 50 125 1 1

18 C 75 100 1 1

20 C 75 125 2 2

20 84.9 74

RM_POS$-2012-77.4R Yes 5 C 25 25 6 6

8 C 25 50 3 3

10 C 50 50 2 2

13 C 50 75 1 1

15 C 75 75 1 1

20 C 100 100 1 1

14 169.1 19

RM_POS$-2012-82.4 Yes 3 C 15 15 2 1 3

5 C 25 25 6 2 8

8 C 25 50 2 2

10 C 50 50 3 3

13 C 50 75 3 1 4

15 C 75 75 1 1

25 C 125 125 1 1

22 123.6 48

RM_POS$-2012-97.1 Yes 3 C 15 15 12 12

5 C 25 25 11 11 1 grain sperrylite (25µm).

8 C 25 50 9 9

10 C 25 75 2 2

10 C 50 50 6 1 7

13 C 50 75 1 1

15 C 50 100 2 2

20 C 50 150 1 1

18 C 75 100 3 3

20 C 100 100 1 1

49 244.7 43

*) M = Actual measured thickness of grain (microns)

**) C = Thickness of grain (microns) calculated from measured width and length

Appendix III. Cont.

60


Appe

ndix

IV.

HR-

SC-I

CPM

S da

ta.

pp

mp

pm

pp

mp

pm

pp

mp

pm

pp

mp

pm

pp

mp

pm

pp

mp

pm

pp

mp

pm

pp

mp

pm

pp

mp

pm

pp

m

ID#

Sam

ple

co

de

Sam

ple

typ

eLi

Be

Sc

VC

rC

oN

iC

uZ

nG

aA

sR

bS

rY

Nb

Mo

Ru

Pd

Ag

1aG

K_P

OS

$-20

12-4

4.1

till <

0.06

3 m

m35

55.

246

428

752

9537

726

336

273

5.4

175

396

4323

3.26

0.00

10.

003

0.4

2aG

K_P

OS

$-20

12-4

7.2

till <

0.06

3 m

m11

33.

430

306

587

4921

013

724

755

5.7

9046

028

171.

650.

000

0.00

30.

3

3aG

K_P

OS

$-20

12-8

2.1

till <

0.06

3 m

m10

3.1

2433

572

345

167

3296

381.

127

352

3019

0.46

0.00

00.

003

0.2

4aG

K_P

OS

$-20

12-8

3.4

till <

0.06

3 m

m50

3.7

3749

663

856

207

162

8974

2.6

216

142

5018

1.13

0.00

00.

004

0.2

5aG

K_P

OS

$-20

12-9

7.3

till <

0.06

3 m

m17

3.5

3036

160

544

158

3590

451.

238

309

3224

0.43

0.00

00.

003

0.2

1bG

K_P

OS

$-20

12-4

4.1

HM

till,

HM

S, <

0.06

3 m

m89

2.8

209

865

2239

8914

516

764

920

331

17.0

440

1190

558

9.93

0.00

10.

073

14.8

2bG

K_P

OS

$-20

12-4

7.2

HM

till,

HM

S, <

0.06

3 m

m14

22.

016

412

4939

6110

720

911

510

5422

230

5.8

733

734

468

6.15

0.00

10.

059

8.4

3bG

K_P

OS

$-20

12-8

2.1

HM

til

l, H

MS

, <0.

063

mm

224.

212

117

3171

6010

335

070

486

867

8.3

801

310

256

3.07

0.00

10.

021

2.9

4bG

K_P

OS

$-20

12-8

3.4

HM

till,

HM

S, <

0.06

3 m

m26

1.8

122

1925

5052

7921

998

420

788

21.2

520

368

411

3.97

0.00

10.

024

6.5

5bG

K_P

OS

$-20

12-9

7.3

HM

till,

HM

S, <

0.06

3 m

m33

2.2

110

1989

4627

8419

678

397

817

10.2

656

334

306

3.42

0.00

10.

023

4.2

1cR

M_P

OS

$-20

12-4

4.2

till,

pre

con,

HM

S, <

0.06

3 m

m73

3.7

244

630

1320

7683

139

579

443

6614

.534

023

3265

28.

970.

000

0.14

538

.5

2cR

M_P

OS

$-20

12-4

7.2

till,

pre

con,

HM

S, <

0.06

3 m

m10

42.

219

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NOVEL TECHNOLOGIES FOR INDICATOR MINERAL-BASED EXPLORATIONtupa.gtk.fi/julkaisu/specialpaper/sp_057_pages_023_062.pdf · Novel technologies for indicator mineral-based exploration