STUDIA UNIVERSITATIS BABEŞ-BOLYAI, PHYSICA, SPECIAL ISSUE, 2003
RESULTS OF THE APPLICATION OF STABLE ISOTOPES OF LIGHT
ELEMENTS IN GEOLOGY AND HYDROLOGY
Jovan Zoto
Institute of Nuclear Physics, Tirana, Albania
ABSTRACT
Stable isotopes of light elements there are using for study of many
problems of different fields; the extended of their application and
improvement of the analytical methods there are the objections of
scientists. Geology, agriculture, hydrogeology, hydrology, precipitation,
geology of petroleum there are the fields of application of stable isotopes
in our country. Follow there are some results of application in geology and
hydrology.
A - Determination of absolute geological age it is very important for
geological studies. There are known some methods of determination, but,
for some specific analytical problems we have used the pothasium - argon
method; the formula of the determination of the geological age there is :
t = 1 /  x ln ( / k x 40Ar / 40K + 1 )
where :  = k +  ;
The 40K content of the monomineral geological sample is calculated by
the content of K of the sample which is determinated by the
flamephotometer, but the 40Ar content is determinated by the mass
spectrometer ZhH-1301. The results of our determination there are
between 23.6 x 106 milion years and 446.2 x 106 years, and, generally,
there are in good correlation with the geological evaluations and in good
agreement with the determinations of other laboratories.
B - The stable isotopes of hydrogen and oxygen there are used in the study
of many problems of the hydrology in our country, but, more interesting
there is the study of underground connection between Prespa and Ohrid
lakes. Prespa and Ohrid lakes there are in the east part of Albania and the
bordery between Albania - Greece - Fyr. of Makedonia. The altitude of
Prespa and Ohrid lakes there are respectively 850 m. and 690 m. asl. and
between lakes there are Mali i Thate and Galitcica mountains. At the lake
side of Ohrid there are two big springs, Tushemishti in Albania territory
and Sveti Naum in Fyr. of Makedonia territory. Refering the our data of
18O and 2H, the underground connection exist between Prespa lake and
big springs at the lake side of Ohrid.
Introduction
The development of the science and economy it is attendanted with the
using of the new methods of the studies. The method of mass spectrometry
analysis it is very important in the frame of physico - chemical methods; the high
JOVAN ZOTO
sensitivity, the high accuracy, quick analyse and small quantity of samples for
analyse there are some advantages of mass spectrometry method.
A - The determination of absolute geological age, as is known, it is an
important problem of the geology. The radioactivity disintegration it is a process
that ocurred with the constant speed, so, it is used as unit of time. The base of
radioactivity dating there is the low of radioactivity disintegration N = N o x e-t,
where  is the constant of the process [2]. There are some radioactivity methods
of geological dating, but, for some reasons of the analytical techniques we have
used the pothasium - argon method, which is based on the radioactivity
transformation of the 40K to the 40Ar by the “k” capture reaction. The melt of the
mineral samples and the cleaning of the argon gas from the other gases there are
made in the quatz - glass vacuum system and the calculation of the argon gas there
is made by the volumetric method. The isotope ratio of Argon there is made by the
mass spectrometer ZhH-1301, while the K content of the samples there is made by
the flamephotometer. The our experimental data of the geological ages there are in
good agreement with the geological considerations.
B - The isotopic compositions of elements with low atomic numbers are
variable because their isotopes are fractionated in the course of certain chemical
and physical processes ocurring in the nature. The most important elements in
which natural variations of the isotopic composition have been observed include
hydrogen, carbon, nitrogen, oxygen and sulfur. Isotope ratios, defined by the
expression : R = abundance of rare isotope / abundance of abundant isotope,
generally, there are not reported as absolute numbers [6]. Therefore, an isotope
abundance is expressed as a deviation of the isotope ratio of a sample “s” relative
to that of a reference or standard “r”, as below :
s/r = Rs - Rr / Rr ;
[8]
The  has a dimensionless value and their values are expressed in per mille (‰)
because its are very small; the  values are expressed with respect to SMOW.
For the determination of 2H and 18O of the water samples of the Prespa - Ohrid
lakes system have used the SIRA 10 mass spectrometer, the ISOPREP 18 system
for the equilibration method of water with CO2 and the line preparation of the H2
by the reduction of water with Zinc. The experimental data of  concerning the
underground connection between Prespa and Ohrid lakes there are interesting.
Material and method
A - The isotop 40K there is radioactive and its radioactive transformations
there are :  disintegration (about 88.4 %) and k - capture (about 11.6 %). The
constant of disintegrations there are known and respectively there are = 4.7 x 1010
years-1 and k = 5.8 x 10-11 years-1. The scheme of disintegration of 40K there is:
40
K
40
Ca
40
Ar
THE APPLICATION OF STABLE ISOTOPES OF LIGHT ELEMENTS IN GEOLOGY AND HYDROLOGY
The mean content of the Pothassium to the earth’s crust is evaluated at the
2.6 % and it is mixture of three isotopes 39K, 40K and 41K and with relatively
content, respectively 93.08 %, 0.0119 %, 6.91 %; while, the mean content of the
Argon at the air is about 0.9 - 1 % and there is mixture of stable isotopes 36Ar,
38
Ar, 40Ar and with relatively content respectively 0.337 %, 0.063 % and 99.6%
[3]. Exsperimentaly there is observated the increase of the Argon at the air as a
result of formation of radiogenic 40Ar and its coming out in the air.
The fundamental relations of the absolute age determination by the
pothassium argon method there are :
d40K
d40Ar
 = - x 40K
and
 = k x 40K
dt
dt
but, the formula of the age determination there is :
40
1

Ar
t =  x ln (  x  + 1 )
40

k
K
[2]
The determination of the 40K of the monomineral geological sample is
made by the relation of 40K and total Pothassium of the sample (40K / 39K + 40K +
41
K = 0.0122 % weight), while for the determination of the total Pothassium it is
used the flamephotometer method after the treatment of the geological sample with
HNO3, H2SO4, HF etc. The Pothassium content of the geological samples of our
determinations there is between 2.4 % to 8 % [5].
The treatment of the monomineral geological samples for the extraction of
the Argon and its cleaning from other gases of the samples is made at the quartz glass vacuum system. The geological samples there are melted at the temperature
between 1100oC and 1300oC and the argon it is cleaning from the gases as CO,
CO2, H2, H2O, N2, O2, Kr etc. by the different absorbents incorporated at the
vacuum system such as CuO, Ti, active Carbon etc.; the temperature of the
absorbents there are different (high temperature for the CuO, Ti and very low
temperature for the Carbon). The quantity of the cleaning Argon it is measured by
the Mak Leod mannometer incorporated at the vacuum system.
The cleaning Argon of the geological samples it is analysed for the
isotopic ratio using mass spectrometer ZhH-1301 and by the following formula it
is calculated the radigenic 40Ar of the samples.
40
40
Arrad
36
Ar
Ar
= [ 1 - ( )air x (  )samp ] x Q
36
40
Ar
Ar
[2]
where Q is the total quantity of the argon of the sample ( Q = 40Ar + Arnonrad).
At the Table No.1 there are results of the geological age for some samples :
JOVAN ZOTO
Table 1
Results of the geological age for some samples
Sample
Age
Kersantit
269.2 x 106  12 %;
Sericit
446.2 x 106  16.5 %;
Ortofir
373.1 x 106  13.6 %;
Glaukonit
23.7 x 106  15 %;
[5]
The our results of the geological age by the pothassium - argon method, generaly,
there are in good agreement with the geological considerations. We have compared
the our result of the age determination with the result of foreign laboratory for the
same sample; the used method of the age determination is the same (pothassium argon method ) but, the used method of the treatment of the geological sample and
cleaning of the argon there is different. The taken results for the sample Biotit
0190 there are : t = (179  26 ) x 106 years of our laboratory and t1 = ( 188  6 ) x
106 years of the foreign laboratory [4].
B - The isotopic compositions of elements having low atomic numbers are
variable because their isotopes are fractionated in the course of certain chemical
and physical processes ocurring in nature. Isotope fractionation there is a
consequence of the fact that certain thermodynamic properties of molecules
depend on the masses of the atoms of which they are composed. The major
changes in the isotopic composition of natural waters occur in the atmospheric part
of the water cycle and in surface waters which are exposed to the atmosphere [6].
The different isotopes of the Hydrogen and Oxygen and their isotopic
compositions in the water molecules we have used for the study of underground
communication between Prespa and Ohrid lakes.
The Prespa and Ohrid lakes there are in the east part of Albania and in the
border between Greece and Fyr. of Makedonia. The altitude of Ohrid lake there is
695 m. asl., while the altitude of Prespa lakes (Big Prespa and Small Prespa) there
is about 850 m. asl. The three lakes constitute a common hydraulic system. A
natural surface communication exists between two Prespa lakes and water flows
from Small to Big Prespa lake. Between Prespa and Ohrid lakes there are situated
Mali i Thate mountain in Albania territory and Galichitsa mountain in the Fyr. of
Makedonia territory. The mountains there are composed of carbonate karstic rocks.
At the western part of Mali i Thate and Galichitsa mountains there are some big
springs (Tushemishti and Saint Naum, the average discharge, respectively, is about
2.5 m3 /s-1 and 5.58 m3 /s-1) and some small springs at the lakeside of Ohrid lake
[9].
The sampling net of the water of the lakes, springs and rivers there was
created; every two months was the frequency of the sampling process for a period
of two years. The determination of 2H and 18O of the water samples it is realised
using mass spectrometer SIRA 10, which in principle is derived from the Nier’s
THE APPLICATION OF STABLE ISOTOPES OF LIGHT ELEMENTS IN GEOLOGY AND HYDROLOGY
mass spectrometer [1]. The mass spectrometer, essentialy, consists of a tube in
which high vacuum is maintained, with an ion source placed at one end and ion
collectors at the other end. The middle part of the tube is curved and immersed in a
magnetic field normal to the curvature plane. The vacuum in the mass
spectrometer SIRA 10, is in order (1 - 2) E-09 torr; it is realised by two rotary
pumps and two diffussion pumps and it is measured by two Pirani gauges and by
means of ionization gauge.
The determination of 18O in the water samples it is made using CO2 gas in
the isotopic equilibrium with the water samples; the ISOPREP 18 system of the
isotopic equilibration of the water and gas CO2 is used and it is based to the
Roether method. The 5 ml. of water is introduced in a glass container, which is
then coupled to a stopcock and connected to the line by means of ground joints;
the air is pumping through a capillary tube and the pressure drops to a few tens of
torrs for a short time; the water loss is too small. After eliminating the air, the
carbon dioxide is introduced in the samples containers which are in the
thermostatic bath at the temperature 25oC. The isotopic equilibrium it is reaches
after 5 hours shaking the samples; the isotopic exchange reaction is :
C16O2 + H218O  C16O18O + H216O
[8]
The ISOPREP 18 is connected online with mass spectrometer.
For the determination of the 2H of the water samples it is used the hydrogen gas
getting by the reduction of water samples with granulated Zinc at the high
temperature and vacuum conditions. The reaction which occur is :
H2O + Zn  ZnO + H2
[6]
The preparation of the H2 gas samples it is made in the separated line from the
mass spectrometer. The 2H and 18O are normalized with respect to SMOW.
Refering the exsperimental data of 2H and 18O for the sampling points
at the region of Prespa - Ohrid lakes, the respective correlation function of the
precipitation there is :
2H = 8 x 18O + 13.8
[9]
For the sampling points at the Prespa lakes and big springs Tushemishti and Saint
Naum the slope of the correlation there is 5.2 that is attributed to waters with a
significant rate of evaporation relative to input. The isotopic composition of the
above springs is constituted by mixing in different proportions of precipitations
and Prespa lake waters.
JOVAN ZOTO
References
[1] - Mass Spectrometry, Edited by C. A. McDowell, 1963;
[2] - I . E. Star ik : Jadernaja geohronologija, 1961;
[3] - O. Schaefer , I . Zahr inger : Potassium Argon dating, 1966;
[4] - B io tite Alb anese , Pisa - Italy, 1985, personal communication;
[5] - J . Zo to , E. Millo na : Disa rezultate te moshes absolute gjeologjike te marra me
metoda te ndryshme, Punime te Institutit te Fizikes Berthamore, Nr. 5, 1987;
[6] - Stable Isotope Hydrology, IAEA, Technical Reports No. 210, 1981;
[7] - G. Faur e : Oxygen and Hydrogen in the hydrosphere and the atmosphere (Principles
of Isotope Geology), 1977;
[8] - J . R. Gat : Variability of the isotopic composition of precipitation, IAEA, 1987;
[9] - R. Eftimi, J . Zo to : Isotope study of the connection of Ohrid and Prespa lakes,
PPNEA, 1997.