OGC214 Environmental Geochemistry
OGC214 Omgewingsgeochemie
Stable Isotope Tutorial 02 – 20th October 2008
Stabiele Isotoop Tutorial 02
Total Marks = 50
Totale Punte = 50
Dr. Jodie Miller
Dr. Jodie Miller
University of Stellenbosch
Universiteit van Stellenbosch
Introduction to Stable Isotope Geochemistry
Inleiding tot Stabiele Isotoop Geochemie
YOUR NAME:
STUDENT NO:
The following data areD and 18O values obtained on seventeen water samples from three different
reservoirs. Reservoirs 1 and 2 are local spring waters and reservoir 3 is a local mine pit. The pit is a
shallow tailings dam with no shade cover. Also provided is the data over a period of two years for the
local rainwater which is collected at the mine site.
Reservoir
1
1
1
1
1
1
1
2
2
2
2
2
3
3
3
3
3
3
1.
2.
3.
4.
5.
6.

D‰
-32
-15
-31
-2
-36
-10
-5
-27
-18
-30
-26
-15
-2
-12
-8
-4
4
0

18O‰
-6.1
-3.4
-5.7
-1.9
-6.5
-2.7
-2.1
-5.2
-3.5
-5.9
-5
-3
-1.9
-2.9
-2.6
-1.8
-0.4
-1.4
Local Rainwater
D‰
18O‰
-15
-3.4
-35
-5.7
-2
-1.9
-36
-6.5
-10
-2.7
-5
-2.1
-30
-5
-18
-3.5
-30
-5.9
-26
-5
-15
-3
-2
-1.9
-12
-3.4
-8
-2.6
-4
-1.4
4
-0.4
0
-1.4
-20
-3.4
-25
-5
-26
-4.7
Construct a 18O versus D plot and determine what the local meteoric water line is in this area.
You must do this by hand. Computer program print outs will not be accepted.
Do the waters from all three reservoirs plot on the local meteoric water line? If not give some
reasons that might account for why some samples do not plot on the meteoric water line.
What type of climate do you think prevails in this region?
Provide some reasons for the differences in isotopic composition between reservoirs 1 and 2 and
make some comments in general about the interaction of waters from the three reservoirs.
A small stream fed by spring 1 approximately 1 km from the mine is sampled. The four samples
analysed have the following D and 18O isotopic compositions; (1)–6.1‰ and –22‰; (2) -5.8‰
and -20‰; (3) -6.4‰ and -27‰; and (4) -6.1‰ and -25. Account for the isotopic character of the
stream.
What steps do you think the miner should take in light of your answer to question 5?