www.geologicacarpathica.com
GEOLOGICA CARPATHICA
, JUNE 2016, 67, 3, 289–299
doi: 10.1515/geoca-2016-0019
In-situ ground gamma spectrometry — an effective tool for
geological mapping (the Malé Karpaty Mts., Slovakia)
ANDREJ MOJZEŠ
1
and BARBARA PORUBČANOVÁ
2
1
Comenius University in Bratislava, Faculty of Natural Sciences, Department of Applied and Environmental Geophysics, Mlynská dolina,
Ilkovičova 6, 842 15 Bratislava, Slovak Republic; mojzes@fns.uniba.sk
2
Slovak Academy of Sciences, Earth Science Institute, Dúbravská cesta 9, 840 05 Bratislava, Slovak Republic; geofbapo@savba.sk
(Manuscript received September 14, 2015; accepted in revised form March 10, 2016)
Abstract: This contribution presents the results of profile in-situ gamma spectrometry measurements that sought to
determine the content of natural radionuclides
40
K,
238
U and
232
Th in a near surface horizon of rocks, their weathering
cover and soils in the area of the Malé Karpaty Mts. It is widely established that the exploration of radioactivity of
bedrocks and cover rocks can be a very effective and useful tool for both geological mapping, for identifying deposits
of mineral resources, and even addressing the issues of structural and tectonic geology. This assertion is equally con-
firmed by the ground gamma spectrometry measurements carried out as part of this case study on larger scales, seeking
more detailed geological structure solutions. The results obtained provide a welcome addition to an already existing
database, which monitors the content of naturally occurring radionuclides individually for every rock lithotype of the
Western Carpathians, by elaborating on the data collected by previous research and by updating this database for any
future needs. The presented results confirmed the low to medium radioactivity levels of rocks and soils in the studied
area. The highest values were detected in granitoids and metamorfic phyllitic rocks of the Malé Karpaty Mts. core; the
lowest values were detected in carbonates, arenaceous sediments and, above all, amphibolite bodies. In this way, the
presented results of the interpreted profile (P5) confirm the model of local geological structure as represented on the
most up-to-date edition of the geological map of the Malé Karpaty Mts. (Polák et al. 2011).
Key words: Western Carpathians, Malé Karpaty Mts., geological mapping, geophysical exploration, in-situ ground
gamma spectrometry, concentration of
40
K,
238
U and
232
Th in rock.
Introduction
Radiometric survey methods used in applied geophysics,
which typically include radiometry as well as more sophis-
ticated gamma spectrometry (in all of their airborne, car-
borne, ground and well log modifications) and soil
emanometry, represent the primary techniques of surveying
and evaluating the natural radioactive resources and
their geological mapping based on nuclear radiation detec-
tion. Employing gamma spectrometry for the purposes of
geological mapping is made possible by the very existence
of measurable differences in contents of natural radionu-
clides
40
K,
238
U and
232
Th in rocks, their weathering cover
and soils. Knowledge of the geochemical and mineralogical
structures and processes that determine their distribution
and mobility in bedrocks, cover rocks and soils plays a de-
cisive role in interpretation of the results of gamma spec-
trometry measurements, preferably in combination with
information provided by other geophysical survey methods
(electrical, magnetic, electromagnetic, seismic, gravime-
try), satellite images, geological and soil maps and accurate
positional GIS data. As the largest proportion of detected
gamma rays originate in the depth horizon of 30 cm at maxi-
mum (which comprises the weathering and/or soil cover of
bedrock), gamma spectrometry is considered a near surface
mapping method. Therefore, it is essential to understand
the relationship between the bedrock and its weathering and
soil cover, which is influenced by weathering processes
themselves, such as disequilibrium of radioactivity in the
uranium decay series or the impact of soil moisture and
vegetation cover on measured data. The most important
factors of successful mapping of lithological units by gam-
maspectrometry survey are: 1) the contrasts in radioelement
content between lithological assemblages, 2) the extent of
bedrock exposure and soil cover, 3) the relative distribution
of transported and in-situ soils, 4) the nature and type of
weathering, 5) the soil moisture content and 6) the vegeta-
tion cover (IAEA-TECDOC-1363 2003).
The results of ground profile gamma spectrometry with
GPS positional data from stations in the studied area of the
Pezinské Malé Karpaty Mts. were processed and analysed
with regard to the general geological map of Slovakia on the
scale of 1:200,000 (Bezák et al. 2008) and to the last edition
of the geological map of the Malé Karpaty Mts. on the scale
of 1:50,000 (Polák et al. 2011). The lithological units in
question were attributed values of rock radioactivity with the
results being contrasted with the findings of previous sur-
veys in the region. Conclusions reached in doing so were
used to determine the effectiveness of the applied survey
gamma spectrometry method for the purposes of describing
the spatial distribution of the individual lithological units and
setting up the boundaries between them.
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MOJZEŠ and PORUBČANOVÁ
GEOLOGICA CARPATHICA
, 2016, 67, 3, 289–299
The study area and its geological structure
The studied area of the Malé Karpaty Mts. lies in the
southwestern part of Slovakia, extending more than 100 km
from Bratislava to Nové Mesto nad Váhom in the SW–NE
direction (Fig. 1) with their largest part — the Pezinské Malé
Karpaty Mts. — starting at the Lamač Gate in the SW and
ending at Buková Village in the NE (Vass et al. 1988).
The Malé Karpaty Mts. form the SW edge of an extensive
Carpathian belt of more than 2000 km spreading across
Slovakia, West Ukraine and Romania.
The Malé Karpaty Mts. are an integral part of the Western
Carpathian orogeny. They represent a horst structure tectoni-
cally extensively confined by faults with a SE–NW direction
(Császár et al. 2000, 2001; Bezák et al. 2008; Vozár et al.
2014). The studied area of the Pezinské Malé Karpaty Mts.
belongs geologically to the Pezinok-Hainburg Zone of the
Tatra-Fatra Belt of core mountains of the Western Car-
pathians (Plašienka et al. 2007 in Kellerová 2011; Vozár et
al. 2014). The Pezinok-Hainburg Zone is predominantly
formed by the Tatricum Superunit as the NE continuation of
the Central Alpine Unit (correlated with the Lower Austro-
Alpine units) (Császár et al. 2000; Vozár et al. 2014) and by
a large allochthonous unit — the Bratislava Nappe. The Ta-
tricum Superunit comprises two partial subautochthonous
units — the Borinka Unit and the Orešany Unit. The Borin
-
ka Unit (Infratatricum) stretches along the NW slopes and
foothill belt of the Pezinské Malé Karpaty Mts. from Lamač
and Záhorská Bystrica villages to the NE, but mainly in
a wide belt that exists between Borinka and Pernek villages
Fig. 1. Tectonic sketch of the Western Carpathians (Biely et al. 1996) with the Malé Karpaty Mts. position and the geological map of the
study area with localization of profile measurements.
291
GROUND GAMMA SPECTROMETRY IN GEOLOGICAL MAPPING (MALÉ KARPATY MTS)
GEOLOGICA CARPATHICA
, 2016, 67, 3, 289–299
(Fig. 1). The Borinka Succession consists mostly of clastic
to coarse-clastic Jurassic sediments that can be divided into
five main formations: the Korenec, Marianka, Slepý, Pre-
padlé and Somár formations. The Orešany Unit (Tatricum)
represents the NE tip of the Pezinské Malé Karpaty Mts. be-
tween Píla–Červený Kameň and the Horné Orešany villages
(Fig. 1). Similarly to the Borinka Unit, it is in a subauto-
chthonous position to the Bratislava Nappe, but they differ in
filling: in the case of the latter, it consists of complexes of
pre-Alpine crystalline basement of the Tatricum and from its
Late Permian–Mesozoic sedimentary cover affected by an-
chizonal metamorphosis. The pre-Alpine basement (the so-
called Doľany crystalline basement) is to be found on the SE
slopes between Častá and Dolné Orešany villages and it is
formed by lithologically monotonous, formerly clayey-sandy
Early Palaeozoic sediments changed by Variscan low- to
medium-grade metamorphosis to chlorite-biotite phyllites to
siliceous and micaceous biotite-garnet gneisses. The cover
sequence begins with sparse arkose sandstones of the Late
Permian Devín Formation followed by quartzites of the
Lúžna Formation and the Middle Triassic Ramsau dolomites
of the Werfen Formation followed by the Jurassic–Creta-
ceous Orešany Succession, which consists of the Slepý,
Lučivná, Solírov and Poruba formations. The Bratislava
Nappe (Tatricum) covers the largest part of the Pezinské
Malé Karpaty Mts. (Fig. 1) and is composed of fairly varie-
gated complexes of both the pre-Alpine basement and its
Mesozoic sedimentary cover. The Early Palaeozoic crystal-
line basement consisting of medium- to low-grade metamor-
phites and bodies of Variscan deep-seated rocks is divided
into the Pezinok Unit (Group) formed by a monotonous
Silurian–Devonian complex of formerly flysch-sandy and
clayey sediments converted to quartzite mica schist gneisses
and biotite phyllites, and the Pernek Unit (Group), which
represents a Devonian–Lower Carboniferous volcanic-sedi-
mentary succession metamorphosed into green shales facies
during the Variscan orogeny. Two large granitoid massifs
were placed into the Early Palaeozoic metamorphic mantle
during the Variscan orogeny (Fig. 1): the Bratislava and
the Modra Massifs. In its southern part, the Bratislava Mas-
sif penetrates the rocks of the Pezinok Succession and is
made up of leucocratic S-type granites and monzogranites
rich in pegmatite and aplite veins. The younger Modra Mas-
sif in the northern part of the Pezinské Malé Karpaty Mts. is
formed by granodiorites to tonalites that intruded into higher
structural levels than those of the Bratislava Massif, princi-
pally in the rocks of the Pernek Succession. The Tatric sedi-
mentary cover sequences are preserved in the Bratislava
Nappe in several, partly separated places, and differ substan-
tially. Late Palaeozoic sediments in the Pezinské Malé Kar-
paty Mts. have their origin most likely in the premature local
Upper Permian terrestrial clastics of the Devín Formation.
Werfenian clastics consist of the sandstone Lúžna Formation
and shale Werfenian Formation. The Jurassic–Early Creta-
ceous sequences appear along the north-western border of
the Bratislava fundament in 4 successions: Devín, Kuchyňa,
Kadluby and Solírov.
From the overburdens of the Malé Karpaty Mts. horst,
mostly the relics of Middle Miocene sediments are preserved
on up-lifted edges and piedmonts of the mountains. From the
morphological point of view, the Pezinské Malé Karpaty
Mts. are low expressive mountains, as is indicated by local
types of Quaternary cover sediments: for the most part, they
include relatively thick eluvial weathering covers, slope de-
luvia and alluvial sediments of flood plains. In some places,
widespread proluvial fans originated at openings of valleys
into the surrounding basins. Finally, a small proportion of
eolian loesses and sands are also present in the area (Plašienka
et al. 2007 in Kellerová 2011).
Methods applied and methodology of work
Numerous surveys, aimed at surface mapping of the dis-
tribution of individual rock units in various locations, were
realized in the area of the Pezinské Malé Karpaty Mts. be-
tween 2010 and 2014 (see Fig. 1). These included especially
the following four transverse profiles of 2010: Rača–Stupava
(profile P1), Svätý Jur–Lozorno (P2), Pezinok–Pernek (P3)
and Modra (Harmónia)–Kuchyňa (P4) selected for the pur-
pose of regional geological mapping. In 2011, measurements
were carried out along the P5 profile situated between the al-
titude quotes of Starý kopec (528 m a.s.l.) and Skalnatá
(704 m a.s.l.) exploring the presence of amphibolite bodies
in the region of Modra-Piesok. A complex geological and
geophysical survey was realized in 2012 near Orešany vil-
lage in the area of the altitude quote of Krč (409 m a.s.l.), lo-
cated in the karst region Komberek; with the aim of locating
and exploring karstic structures — sinkholes, pits and caves
(Putiška et al. 2013, 2014). The 2013 geophysical survey
near Svätý Jur village sought to locate pegmatite veins in-de-
tail and finally, another detailed geophysical survey of an ar-
chaeological site at Molpír in Smolenice village in 2014
attempted to detect archaeological artefacts. The results of
the five above-mentioned research projects, which admittedly
dealt with a wide range of issues, can be used for evaluation
of the mapping potential of the employed in-situ ground
gamma spectrometry method.
Nuclear geophysical properties of the rock and soil envi-
ronment were determined by using the survey method of
in-situ ground gamma spectrometry. Measurements were
carried out along profiles, with the step of stations ranging
from 1 to 50 m depending on the focus of each task. This
method allows us to measure three values at each measure-
ment point (station), based on gamma rays detection in the
near surface horizon of soil, weathering cover and rock:
mass concentrations of
40
K [%K],
238
U [ppm eU] and
232
Th
[ppm eTh]. As the determination of
238
U and
232
Th is indi-
rect, by detection of gamma radiation of their daughter
products (
214
Bi, resp.
208
Tl), the determined values of
238
U
and
232
Th concentrations are valid under condition of radio-
active equilibrium in their disintegration series. In addition,
the total gamma activity eU
t
[Ur] (Ur is the unit of radioele-
ment concentration; 1 Ur~1 ppm eU) was calculated by the
equation (Regulation of the Ministry of Environment
No. 1/2000-3)
eU
t
[Ur]=2.79 K [%]+eU [ppm]+0.48 eTh [ppm] (Eq. 1)
292
MOJZEŠ and PORUBČANOVÁ
GEOLOGICA CARPATHICA
, 2016, 67, 3, 289–299
The field measurements were realized by portable gamma
spectrometer GS-256 (manufactured by former state company
Geofyzika Brno, Czechoslovakia) with scintillation detector
NaI(Tl) 76×76 mm and 256-channel analyser. All measure-
ments were carried out in surface 2π geometry (not in holes)
following the traditional procedure: first, grass, leaves and
a thin upper humus layer of soil were removed and the sur-
face was levelled in a 1–1.5 m radius on every measurement
point. The duration of measurement was 2 minutes for each
point. The points were placed without exception in a natural
environment, never in landfills that could form part of fields,
forest roads or waste disposal sites. Moreover, the measure-
ments were scheduled in summer and autumn periods with
stable, dry weather in order to avoid the results being
influenced by changes in soil moisture. Consistency of the
data measured by the instrument was regularly checked by
repeating the measurements on the same point in the field, as
well as in laboratory conditions. The precision and repeatabili-
ty of instrument readings based on repeated measurements at
several stations were evaluated by calculation of the average
quadratic error (σ) and the relative average quadratic error (p)
by equations (Čížek et al. 1993)
σ
=±[Σ(x
i
–y
i
)
2
/2N]
1/2
; p=200Nσ/[Σ(x
i
+y
i
)] [%] (Eq. 2)
where N — number of stations with repeated measure-
ments,
x — first measurement,
y — second (repeated) measurement at the same
station.
The position of all measurement points was determined
using a GPS device in WGS84 coordinates of longitude and
latitude.
Results and discussion
On the whole, the survey in the Pezinské Malé Karpaty
Mts. covered 1816 measurement points: 1039 points placed
on 4 regional profiles P1–P4 (the length of each was
ca. 10 km), 39 points situated on profile P5 in the area of
Modra–Piesok (ca. 1.5 km long), 225 points on 9 profiles in
the Komberek Karst (the length of which varied from 600 to
1000 m), 324 points on 10 profiles in the region near Svätý
Jur village (of length from 15 to 300 m) and 185 points on
3 profiles on the archaeological site Molpír in Smolenice
village (each profile was 60 m long).
Results of repeated measurements calculated by Eq. 2 are
presented in Table 1.
Using its position established using GPS data, every mea-
surement point was located on the general geological map of
Slovakia with the scale 1:200,000 (Bezák et al. 2008) and
the measured value of radioactivity in the form of eU
t
, %K,
ppm eU and ppm eTh was then attributed to each of the cor-
responding geological units. From the point of view of the
survey’s focus on single localities the simplest situation was
those with a detailed survey: on the archaeological site
Molpír in Smolenice village where all measurements were
done within only one lithological unit — the Cretaceous
Poruba Formation of marlstones, shales, sandstones, sandy
limestones and orthoconglomerates and on the pegmatite site
near Svätý Jur village where most of the measurement points
lie on granites and granodiorites rich in pegmatites (the Bratisla-
va type) and only a few on Quaternary deluvial and
fluvial sediments. The geological structure of the other 3 lo-
calities is much more varied and, of course, the most com-
plex is along 4 regional profiles.
The geological units explored (24) and the basic statistical
parameters of their radioactivity (eU
t
, %K, ppm eU
and ppm eTh) are presented in Table 2 and in Fig. 2. Table 3
provides an overview of the lithotypes with the highest and
the lowest values of radioactivity.
The measurements carried out as a part of this gamma
spectrometry survey confirmed that the study area is a region
with medium to low rock radioactivity (Matolín 1976;
Daniel et al. 1996, 1999). The highest values were shown by
igneous rocks, namely medium-grained muscovite granites
to granodiorites of the Bratislava Massif (2.6 %K, 3.3 ppm
eU, 9.7 ppm eTh and 17.3 Ur), fine-grained biotite granites
to granodiorites of the Bratislava Massif (2.6 %K, 2.8 ppm
eU, 9.9 ppm eTh and 16.9 Ur) and coarse-grained granites to
granodiorites of the Bratislava Massif with pegmatites, while
the third group also manifested a lower concentration of tho-
rium (2.2 %K, 3.0 ppm eU, 7.8 ppm eTh and 14.7 Ur). The
lowest values of radioactivity of igneous rocks were detected
in the case of biotite granodiorites and tonalites of the Modra
Massif (1.7 %K, 2.5 ppm eU, 6.3 ppm eTh and 11.4 Ur). In
the category of crystalline rocks, very high values of radioac-
tivity were measured in phyllites and phyllitic slates
(2.1 %K, 4.3 ppm eU, 7.8 ppm eTh and 15.5 Ur), the radio-
activity was lower in the case of gneisses and paragneisses
(1.6 %K, 2.7 ppm eU, 6.9 ppm eTh and 11.8 Ur). Schists and
meta-quartzites tend to belong among rocks with a higher
concentration of uranium and thorium (2.3 %K, 2.7 ppm eU,
7.3 ppm eTh and 14.4 Ur). The lowest radioactivity value in
the category of crystalline rocks was detected in fine-grained
and medium-grained amphibolite bodies (1.3 %K, 2.1 ppm
eU, 4.4 ppm eTh and 8.8 Ur). A common characteristic of
Mesozoic rocks is their low radioactivity value. The Jurassic
limestones (1.4 %K, 2.3 ppm eU, 5.8 ppm eTh and 9.8 Ur)
tend to have lower values than the Triassic ones (1.9 %K,
2.8 ppm eU, 8.9 ppm eTh and 13.5 Ur) (Kellerová 2011).
The values characteristic for the Neogene sandstones, con-
glomerates and gravels are very low (1.6 %K, 2 ppm eU,
5.4 ppm eTh and 10.5 Ur) (Kellerová 2011) except for the
Jakubov Formation (2.4 %K, 2.5 ppm eU, 7.8 ppm eTh
and 14.8 Ur). Finally, the Quaternary deluvial sediments
manifest lower values (1.7 %K, 2.4 ppm eU, 5.9 ppm eTh
Table 1: Evaluation of repeated measurements.
Total gamma
activity eU
t
Potassium
40
K
Uranium
238
U
Thorium
232
Th
Average quadratic
error σ
0.24 Ur
0.1 %K
0.48 ppm eU 0.79 ppm eTh
Relative everage
quadratic error p
[%]
1.8
4.5
18.7
11.5
No. of repeated
measurements
57
293
GROUND GAMMA SPECTROMETRY IN GEOLOGICAL MAPPING (MALÉ KARPATY MTS)
GEOLOGICA CARPATHICA
, 2016, 67, 3, 289–299
Table 2: Basic statistical parameters of radioactivity of the studied geological units.
Lithotype map index
No. of
stations
Radioactivity variables
Total gamma activity eU
t
[Ur]
Potassium
40
K [%K]
Uranium
238
U [ppm eU]
Thorium
232
Th [ppm eTh]
Mi
Ma
ø
Me
σ
Mi Ma
ø
Me
σ
Mi Ma
ø
Me
σ
Mi Ma
ø
Me
σ
kr147
138 7.6 19.2
11.8
11.3
2.3
0.9 3.2
1.6
1.5
0.5
1.6
5.1
2.7
2.7
0.7
3.1 10.8 6.9
6.8
1.5
kr162
26
2.9 14.4
8.8
10.6
4.2
0.4 2.7
1.3
1.3
0.7
0.5
8.5
2.1
1.9
1.5
0.4
8.8
4.4
5.0
2.3
kr17
16 11.7 21.0 16.9 17.6
2.4
1.4 3.7
2.6
2.6
0.6
1.8
3.4
2.8
2.7
0.5
7.7 12.3 9.9
9.9
1.5
kr26
73
9.2 22.1 17.3 17.5
2.7
1.3 4.3
2.6
2.6
0.5
1.7
5.9
3.3
3.1
0.8
1.5 15.2 9.7
9.8
2.5
kr35
457 7.5 22.7 14.7 14.3
2.1
0.7 4.4
2.2
2.1
0.5
1.6
6.2
3.0
2.9
0.6
2.2 13.6 7.8
7.9
1.8
kr50
36
4.8 18.2
11.4
12.1
3.0
0.6 2.7
1.7
1.8
0.5
1.1
4.3
2.5
2.4
0.7
2.1
9.9
6.3
6.2
1.8
kr94
15
8.6 20.5 15.5 15.0
3.6
0.9 3.1
2.1
2.1
0.8
2.0
8.4
4.3
4.0
2.0
3.0 13.9 7.8
8.3
3.5
kr97
16 12.3 20.0 14.4 13.7
1.9
1.8 3.6
2.3
2.2
0.4
1.7
3.5
2.7
2.6
0.5
4.7
9.3
7.3
7.2
1.3
mj13
8
9.1 14.6
11.7
12.1
2.1
0.9 1.6
1.3
1.3
0.3
1.4
3.2
2.5
2.6
0.6
7.4 12.1 9.4
9.5
1.5
mj25
6
11.0 13.8 12.7 13.1
1.2
1.3 1.9
1.7
1.8
0.2
2.3
3.7
2.8
2.7
0.5
6.9
8.6
7.7
7.7
0.7
mj26
32
8.9 14.6
11.2
11.1
1.3
1.1 2.5
1.5
1.4
0.3
1.2
3.7
2.4
2.3
0.5
5.1
9.7
7.4
7.4
1.2
mj29
3
12.8 14.5 13.6 13.4
0.9
1.6 2.2
1.9
1.9
0.3
2.7
3.0
2.8
2.8
0.1
7.6
9.2
8.5
8.6
0.8
mj61
2
14.2 16.9 15.5 15.5
1.8
2.2 2.5
2.3
2.3
0.3
3.2
3.4
3.3
3.3
0.2
8.3 10.3 9.3
9.3
1.4
mk38
201 3.8 15.8
7.0
6.5
2.5
0.5 2.4
0.9
0.9
0.4
0.3
3.5
1.3
1.2
0.6
2.5 11.4 5.3
5.0
1.6
mt16
108 5.1 20.0 12.5 13.0
3.2
0.6 3.5
1.5
1.5
0.5
0.9
4.3
3.0
3.0
0.7
2.8 13.5 8.8
9.5
2.5
mt22
43
4.1 15.0 12.1 12.9
2.7
0.5 2.0
1.4
1.4
0.3
1.4
4.5
3.1
3.2
0.8
1.7 12.3 8.5
9.3
2.3
mt3
7
8.9 17.1 12.0
11.4
2.8
1.3 3.0
1.9
1.7
0.6
1.4
2.5
1.9
1.9
0.4
4.5 10.6 6.6
5.9
2.1
mt61
15
9.2 15.1 13.2 13.8
1.7
0.9 2.2
1.7
1.8
0.4
1.7
3.9
3.0
3.0
0.6
5.2 10.6 8.5
8.6
1.7
ng12
19 10.7 23.0 14.8 14.8
3.2
1.7 4.1
2.4
2.4
0.6
1.6
3.5
2.5
2.3
0.5
4.5 11.0 7.8
8.2
1.9
q19
13
7.0 11.3
9.4
9.0
1.4
1.2 2.0
1.6
1.6
0.2
1.0
2.7
1.7
1.8
0.6
2.4
7.0
4.5
4.3
1.4
q20
222 5.7 22.7 14.6 14.3
2.7
0.8 4.3
2.2
2.2
0.5
1.0
4.8
2.6
2.6
0.7
1.9 17.3 8.2
8.0
2.3
q24
87
5.3 23.9
11.2
10.8
3.1
0.8 3.5
1.7
1.6
0.5
1.1
6.5
2.4
2.3
0.9
2.2 14.9 5.9
5.7
2.0
q7
240 4.2 19.0
11.5
11.1
2.8
0.6 3.3
1.6
1.5
0.5
0.9
5.3
2.6
2.5
0.7
2.6 13.7 6.4
6.2
1.9
rauhwackes 33
6.5 15.2
11.5
12.4
2.5
0.5 2.1
1.4
1.4
0.4
1.5
4.9
2.9
2.8
0.8
3.3 11.4 7.9
8.6
2.4
Explanations (legend by Bezák et al., 2008, 2009):
Mi – minimum
Ma – maximum
Me – median
ø – arithmetic mean (AVG)
σ – standard deviation (SD)
kr147 – metamorphic rocks with medium to higher metamorphic
grade: biotitic paragneisses with flaky graphite
kr162 – metamorphic rocks with high metamorphic grade: fine- to
medium-grained amphibolites (the Pezinok Succession)
kr17 – leucocratic and vein types of granitoides: leucocratic fine-
grained biotite and two-mica granites to granodiorites
kr26 – granites to granitoides: medium-grained leucocratic
muscovite and two-mica granites, granodiorites (the Bratislava type)
kr35 – granites to granitoides: coarse-grained muscovite, muscovite-
biotite granites, granodiorites enriched in pegmatites (the Bratislava
type)
kr50 – granodiorites to tonalites: biotite granodiorites to tonalites
(the Modra type)
kr94 – metamorphic rocks with lower metamorphic grade: graph-
ite-sericite phyllites, graphite metasandstones
kr97 – metamorphic rocks with lower metamorphic grade: phyllites,
micaceous shales, metapelites of biotite-garnet zone
mj13 – the Jaseniny Formation: light-grey, pink, low-marly thin
bedded to slab-like limestones
mj25 – the Prepadlé Formation: grey, massive or thick bedded,
textureles fine-grained limestones with lithoclasts of the Triassic
carbonates, bioclastic limestones, sandstones
mj26 – the Korenec Formation: dark-grey sandy claystones,
sandstones with beds of sandy limestones
mj29 – the Somár Formation: polymict, non-stratificated breccia
mj61 – the Trlenská dolina Formation: light-grey to pink, sandy-
crinoidal limestones
mk38 – the Poruba Formation: marlstones, clayey-sandy shales,
sandstones, sandy limestones, ortoconglomerates
mt16 – the Gutenstein limestones: dark-grey and black, thick bedded,
stratified, vermiform limestones
mt22 – the Ramsau dolomites: grey stratified dolomites
mt3 – the Lúžna Formation: light-grey, pink, red quartzites, quartz
sandstones, arkose sandstones, conglomerates
mt61 – the Carpathian Keuper: quartz sandstones, arkose,
conglomerates, clayey shales, dolomites
ng12 – the Jakubov Formation: the Devínska Nová Ves Formation:
conglomerates, sands
q19 – deluvial-polygenetic sediments: loamy-clayey and sandy slope
loams
q20 – deluvial sediments: mostly loamy-rocky (less sandy-rocky)
slope sediments and debris
q24 – deluvial sediments in all: litofacially unsorted slope sediments
and debris
q7 – fluvial sediments: lithofacially unsorted plain loams or sandy to
gravelly loams of valley alluvial plains and plains of ravine streams
rauhwackes – tectonically derived from the Gutenstein limestones
(Putiška et al., 2014)Mi – minimum
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Fig. 2: Selected statistical parameters of the studied lithological units (range, AVG ± SD, median).
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and 11.2 Ur) when compared with fluvial sediments
(1.6 %K, 2.6 ppm eU, 6.4 ppm eTh and 11.5 Ur).
The presented results clearly show that the lithological unit
with the highest total gamma activity is represented by the
medium-grained granitoids of the Bratislava type (kr26).
These are closely followed by fine-grained biotite granitoids
(kr17), low-grade metamorphosed graphite-sericite phyllites
(kr94), the Neogene Jakubov Formation (ng12) and coarse-
grained granitoids with pegmatites (the Bratislava type)
(kr35). The other extremity of the spectrum is constituted by
rocks with the lowest total values of gamma activity in the
studied area, namely the flysh Poruba Formation (mk38) fol-
lowed by high-grade metamorphosed amphibolites (kr162)
and Quaternary deluvial loamy-clayey and sandy slope
loams (q19/q24) (Table 3).
The data obtained corresponds relatively well with the re-
sults of previous measurements that provided an outline of
the radioactive character of the rocks in this area. It should
be pointed out, however, that the data collected in previous
surveys are less detailed (Daniel et al. 1996, 1999) but also
confirm the low radioactivity values of rocks of the Malé
Karpaty Mts.
An example of the possible uses of in-situ ground gamma
spectrometry for purposes of rock mapping in geology is il-
lustrated using the results of measurements carried out on the
P5 profile (Fig. 1). Figure 3 shows the geological structure of
the P5 profile area in more detail on the general geological
map of Slovakia with the scale 1:200,000 (Bezák et al. 2008)
and Figure 4 shows the same on the newest edition of the
geological map of the Malé Karpaty Mts. with the scale
1:50,000 (Polák et al. 2011). Figure 5 presents the course of
the total gamma activity eU
t
values along the P5 profile.
Cross section 1 under the eU
t
curve on Fig. 5 documents
the boundaries of geological lithotypes as observed on the
geological map by Bezák et al. (2008) (Fig. 3). Cross section
2 on Fig. 5 represents the boundaries of geological lithotypes
as observed on the geological map by Polák et al. (2011)
(Fig. 4). Cross section 3 on Fig. 5 represents an interpretation
of these boundaries based on measured data and the values of
total gamma activity eU
t
.
It appears relatively simple to iden-
tify certain lithotypes bearing in mind eU
t
values characteris-
tic of them: this is the case of amphibolites (kr162/193a),
associated with the minimum values on the eU
t
curve; grano-
diorites and tonalites (kr50/188), graphite-sericite phyllites
(kr94/196b) and biotite paragneisses (kr147/199a) that typi-
cally demonstrate slightly elevated values of eU
t
grouping
close to the typical averages (Tables 2 and 3). To some ex-
tent, it is also possible to determine the location of both flu-
vial and deluvial Quaternary (q/20).
Certain segments of the eU
t
curve (Fig. 5) are characterized
by a greater scatter of values and can therefore point to zones
of transition where individual lithotypes overlap. This is
Table 3: Lithotypes with the highest and the lowest values of radioactivity (based on AVG).
Sequence No.
Sequence of rocks by average (AVG) value of single radioactivity variable:
by total gamma activity eU
t
[Ur]
by potassium
40
K content
[%K]
by uranium
238
U content
[ppm eU]
by thorium
232
Th content
[ppm eTh]
1.
kr26 (17.3)
kr26 (2.6)
kr94 (4.3)
kr17 (9.9)
2.
kr17 (16.9)
kr17 (2.6)
mj61 (3.3)
kr26 (9.7)
3.
mj61 (15.5)
ng12 (2.4)
kr26 (3.3)
mj13 (9.4)
4.
kr94 (15.5)
mj61 (2.3)
mt22 (3.1)
mj61 (9.3)
5.
ng12 (14.8)
kr97 (2.3)
kr35 (3.0)
mt16 (8.8)
6.
kr35 (14.7)
q20 (2.2)
mt61 (3.0)
mt22 (8.5)
7.
q20 (14.6)
kr35 (2.2)
mt16 (3.0)
mt61 (8.5)
8.
kr97 (14.4)
kr94 (2.1)
rauhwackes (2.9)
mj29 (8.5)
9.
mj29 (13.6)
mt3 (1.9)
mj25 (2.8)
q20 (8.4)
10.
mt61 (13.2)
mj29 (1.9)
mj29 (2.8)
rauhwackes (7.9)
11.
mj25 (12.7)
q24 (1.7)
kr17 (2.8)
kr94 (7.8)
12.
mt16 (12.5)
mt61 (1.7)
kr97 (2.7)
ng12 (7.8)
13.
mt22 (12.1)
kr50 (1.7)
kr147 (2.7)
kr35 (7.8)
14.
mt3 (12.0)
mj25 (1.7)
q20 (2.6)
mj25 (7.7)
15.
kr147 (11.8)
q7 (1.6)
q7 (2.6)
mj26 (7.4)
16.
mj13 (11.7)
kr147 (1.6)
kr50 (2.5)
kr97 (7.3)
17.
rauhwackes (11.5)
q19 (1.6)
mj13 (2.5)
kr147 (6.9)
18.
q7 (11.5)
mt16 (1.5)
ng12 (2.5)
mt3 (6.6)
19.
kr50 (11.4)
mj26 (1.5)
q24 (2.4)
q7 (6.4)
20.
q24 (11.2)
mt22 (1.4)
mj26 (2.4)
kr50 (6.3)
21.
mj26 (11.2)
rauhwackes (1.4)
kr162 (2.1)
q24 (5.9)
22.
q19 (9.4)
kr162 (1.3)
mt3 (1.9)
mk38 (5.3)
23.
kr162 (8.8)
mj13 (1.3)
q19 (1.7)
q19 (4.5)
24.
mk38 (7.0)
mk38 (0.9)
mk38 (1.3)
kr162 (4.4)
Explanations:
kr26 (17.3) – lithotype map index of rock and the value of radiaoctivity in brackets
List of lithotype map indexes as in Tab. 2 explanations
AVG – arithmetic mean
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illustrated primarily by the segment A, which represents
a transition zone between granodiorites (kr50) and biotite
paragneisses (kr147) by Bezák et al. (2008) or a transition
zone between gneisses (199a) and phyllites (196b) by Polák
et al. (2011), and the segment E pointing to a transition zone
between amphibolites (kr162) and graphite-sericite phyllites
(kr94) by Bezák et al. (2008) or a transition zone from am-
phibolites (193a) through phyllites (196b) and gneisses
(199a) to granodiorites (188) by Polák et al. (2011). Since its
eU
t
values are higher when compared with the kr162/193a
segments, the B segment (stations of 680, 720 and 760 m)
could indicate the presence of material of the black schists
body with ore mineralization (191) mixed into an environ-
ment consisting primarily of amphibolite bodies (see Fig. 4
by Polák et al. 2011). The whole wide section between 540
and 1380 m might be interpreted as an extensive amphibolite
Fig. 3. Section of geological map of the studied area by Bezák et al. (2008) with localization of the P5 profile.
body, which is intersected approximately at the 1100 m
point, situated in a geomorphological depression, by a tec-
tonic zone oriented in a northwest-southeast direction. The
weathering processes that take place in the amphibolite body
disrupted by the tectonic zone result in elevated values of eU
t
in segments D and C while these are contrasted with low values
of eU
t
in peripheral pluton zones, which form the geomor-
phological elevations, where amphibolite material remains
intact. The eU
t
curve further shows that the granodiorite
body (kr50) documented on the geological map of Bezák et
al. (2008) in Fig. 3 in section 900–1060 m (cross-section 1 in
Fig. 5) is absent from the interpreted cross-section 3 or might
not be crossed by the P5 profile (Fig. 5). On the other hand,
the increased value of eU
t
at the 1080 m station (Fig. 5) could
be the result of granodiorite material from the nearby grano-
diorite body (188) (Fig. 4, by Polák et al. 2011).
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GROUND GAMMA SPECTROMETRY IN GEOLOGICAL MAPPING (MALÉ KARPATY MTS)
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Fig. 4. Section of geological map of the studied area by Polák et al. (2011) with localization of the P5 profile.
In this sense, it is possible to conclude that the results of
the gamma spectrometry measurements carried out on the P5
profile correspond better with the data on the new edition of
the geological map of the Malé Karpaty Mts. in Fig. 4 (Polák
et al. 2011) than with the older edition of the map in Fig. 3
(Bezák et al. 2008).
Conclusions
The profile in-situ gamma spectrometry measurements of
the content of natural radionuclides
40
K,
238
U and
232
Th in
rocks and their weathering and soil cover in the Malé Kar-
paty Mts., which were the subject of the present geophysical
survey, confirmed their effective application in dealing with
issues that arise in geological mapping of distribution of rock
lithotypes. Interpretation of the results of such measurements
combined with a detailed analysis and revision of field and
meteorological conditions during measurement as well as
a thorough knowledge of the geological principles that govern
rock distribution, their weathering processes and geomor-
phological conditions, can significantly contribute to defi-
ning geological boundaries and providing more accurate
characterization of already identified rock lithotypes and any
changes in their properties.
In conformity with previous research, the measurements
confirmed the low and medium level of rock radioactivity in
the studied area. The highest values of radioactivity charac-
terized the granites, granodiorites and metamorphosed phyl-
lites. The lowest values were measured in Jurassic
limestones, arenaceous sediments and mainly amphibolites.
The interpreted results along the profile P5 correspond to
298
MOJZEŠ and PORUBČANOVÁ
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, 2016, 67, 3, 289–299
Fig. 5. Curve of total gamma activity eU
t
along the P5 profile with map and interpreted cross sections.
information about the local geological structure presented on
the up-to-date geological map by Polák et al. (2011).
The fact that the results obtained represent yet another
valuable contribution to the overall database of rock radioac-
tivity and thus permits us to increase its statistical reliability
so that it can continue to provide a solid base with which all
new measurements can be contrasted appears to be no less
important. Both the measurements and the interpretation of
results confirm that an active cooperation between experts in
exploration geophysics and other disciplines concerned with
geological mapping is both inevitable and desirable conside-
ring its indisputable effectiveness.
Acknowledgements: This contribution is the result of im-
plementation of the projects: APVV-0194-10, APVV-0099-
11, APVV-0129-12, VEGA 1/0131/14, VEGA 1/0141/15
and VEGA 1/0462/16. The authors are thankful to the Slo-
vak Research and Development Agency for support.
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GROUND GAMMA SPECTROMETRY IN GEOLOGICAL MAPPING (MALÉ KARPATY MTS)
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, 2016, 67, 3, 289–299
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