geological importance of sulfur isotope.

1. STABLE ISOTOPES- SULFUR
PRESENTED BY;
VINAY C
M.SC GEOLOGY,
DOS IN EARTH SCIENCE
UNIVERSITY OF MYSORE
UNIVERSITY OF MYSORE
Department of Studies in Earth Science
GUIDE;
DR. K. N. PRAKASH NARASIMHA
PROFESSOR,
DOS IN EARTH SCIENCE,
UNIVERSITY OF MYSORE.

2. contents
1. INTRODUCTION
2. STABLE ISOTOPES
3. STANDARDS
4. SULFUR
5. MEASUREMENT OF ISOTOPE EFFECTS
6. SULFUR ISOTOPE COMPOSITIONS OF SOME GEOLOGICALLY IMPORTANT RESERVOIRS
7. VARIATIONS OF STABLE ISOTOPE RATIOS IN NATURE
8. SIGNIFICANCE OF SULFUR ISOTOPES
9. CONCLUSION
10. REFERENCE

3. INTRODUCTION
Isotopes means an atom of the same atomic number but different atomic
weights.
And also is known as an atom have the same proton number(Z) but different
values of neutron number(N).
 Isotopes are atoms of the same chemical elements. They have very similar
chemical properties and differ only in their masses.
 Isotopes occupy the same position in the periodic table.
Eg : Oxygen, hydrogen etc

4. Cont.…..
 Isotopes can be divided in to Stable and Unstable(radioactive)
 Unstable – isotopes that continuously and spontaneously break
down/decay in other lower atomic weight isotopes.
 Stable – isotopes that do not naturally decay but can exist in
natural materials in differing proportions.

5. STABLE ISOTOPES
Stable isotopes are chemical isotopes that are not radioactive, i.e. they do
not decay spontaneously.
 Many isotopes that are classed as stable (i.e. no radioactivity has been
observed for them) are predicted to have extremely long half-lives.
 Stable isotopes of an element differ in mass, but have essentially identical
chemical reactivity.
 Isotopes also show abundance variations in the earth as a result of decay
from long-lived radioactive nuclides.

6. Cont.…..
 There are 253 known stable nuclides of the 80 elements which have one or
more stable isotopes.
 e.g.- Oxygen (16O, 17O, 18O )

7. Sulfur
 Sulfur is an abundant element in nature.
 Sulfur has four stable isotopes (32S,33S, 34S, 36S) whose percentage abundances are
approximately 95.0, 0.75, 4.20, and 0.017 respectively.
 It may be a major component in ore deposits, where sulfur is the dominant nonmetal,
and as sulfates in evaporites.
 It occurs as a minor component in igneous and metamorphic rocks, throughout the
biosphere in organic substances, in marine waters and sediments as both sulfide and
sulfate.
 These occurrences cover the whole temperature range of geological interest.
 Measurements of sulfur isotope ratios is carried out by separating the sulphur bearing
mineral from a rock, converting the material to sulphur dioxide, and analysing the gas
in a mass spectrometer .

8. MEASUREMENT OF ISOTOPE EFfECTS
 Isotope abundance variations are generally considered in terms of the
abundance ratio 34S/32S of the two principal isotopes.
 Isotope effects are generally small and this makes it convenient to refer to
fractional differences in isotope ratios ('del' values (8) of samples relative to a
standard, and to express these differences in parts per thousand (per mil):
 The isotopic composition of sulfur is expressed in terms of the delta notation
 The generally accepted standard is troilite from the Canyon Diablo meteorite
for which 34S/32S is assigned the value 1/22.22.

9. Cont.…..
 For many years the reference standard commonly referred to is sulfur from
troilite of the Canyon Diablo iron meteorite (CDT).
 As Beaudoin et al. (1994) have pointed out, CDT is not homogeneous and
may display variations in 34S up to 0.4‰.
 Therefore a new reference scale, Vienna-CDT or V-CDT has been
introduced by an advisory committee of IAEA in 1993.
 Recommending an artificially prepared Ag2S (IAEA-S-1) with a δ34SVCDT of
−0.3‰ as the new international standard reference material.

10. sulfur isotope compositions of some
geologically important reservoirs

11. Variations of stable isotope ratios in
nature
Extra Terrestrial Materials- Chondrites
 Hydrogen-D/H ratios in carbonaceous chondrites may hint on the origin of
water on Earth. Robert (2001) suggested that since the contribution of
cometary water to terrestrial water should be less than 10%, most of the water
on Earth should derive from a meteoritic source.
 Sulfur-There are many sulfur components in meteorites which may occur in all
possible valence states (−2 to +6).
 Troilite is the most abundant sulfur compound of iron meteorites and has a
relatively constant S-isotope composition .
 Carbonaceous chondrites contain sulfur of all valence states: sulfates, sulfides,
elemental sulfur, and complex organic sulfur containing molecules.

12. SIGNIFICANCE OF SULFUR ISOTOPE
 Sulfur occurs in a variety of forms in the mantle, the major sulfur phase is
monosulfide solid solution between Fe, Ni, and Cu.
 Recent ion microprobe measurements on sulfide inclusions from megacrysts
and pyroxenite xenoliths from alkali basalts and kimberlites and in diamonds
gave δ34S-values from −11 to +14‰ .
 Sulfur isotopes are used in hydrology to trace natural and anthropogenic
sources of sulfur, in particular to study
 The cycling of sulfur in agricultural watersheds,
 The sources of salinity in coastal aquifers or sedimentary strata,
 Groundwater contamination by landfill leachate plumes, and acid mine dr

13. conclusion
 Stable isotopes are chemical isotopes that are not radioactive, i.e. they do not
decay spontaneously
 Sulfur has four stable isotopes (32S, 33S, 34S, 3oS whose percentage
abundances are approximately 95.0, 0.75, 4.20, and 0.017 respectively.
 It may be a major component in ore deposits, where sulfur is the dominant
nonmetal, and as sulfates in evaporites.
 It occurs as a minor component in igneous and metamorphic rocks, throughout
the biosphere in organic substances, in marine waters and sediments as both
sulfide and sulfate.

14. reference
1. Jochen Hoefs(2009), Stable isotope geochemistry, 6th edition, Springer, Berlin,
pp-36-38, 71-73, 93-94.
2. C.S.Pichamuthu (1985),Archaean geology, Oxford & IBH publishing
co,Pages:93-95.
3. http://web.sahra.arizona.edu/programs/isotopes/hydrogen.html
4. http://web.sahra.arizona.edu/programs/isotopes/sulfur.html
5. http://en.wikipedia.org/wiki/Isotopes_of_sulfur/hydrogen

15. THANK YOU