Evaluating the Variability of Geothermal Heat
Production Potential from the Radiogenic Granites of
Scotland
by
Thomas Harley 0800517
Overall Results
Aims
• Gather radiogenic isotope data and calculate heat productions
of granite plutons within the eastern Highlands of Scotland in
order to identify potential for CHP geothermal plants.
70
Robust Regression Mean
4.83 ± 0.41 mWm-3
• Compare the calculated values with previous data,
commenting on and accounting for any discrepancies.
Th-U Ranges
for each Pluton
40
30
20
10
Granite plutons within the eastern Highlands were chosen for
investigation based on selection criteria including accessibility,
exposure and proximity to population and infrastructure.
The six chosen plutons are
depicted to the right where
(A) Monadhliath, (B) Cairngorm,
(C) Lochnagar, (D) Ballater,
(E) Grantown & (F) Strathspey
Monadhliath
Cairngorm
Grantown
Ross of Mull
Strathspey
Lochnagar
Ballater
0
0
-6
-2
2
6
10
14
18
22
0
5
10
15
Pluton
K (wt%)
20
25
30
35
40
45
50
U (ppm)
Heat Production (mWm-3)
Approach
Th/U = 2
50
Th (ppm)
Number
Relative probability
10
5
Th/U = 4
60
n=130
15
• Evaluate handheld gamma ray spectrometers as a field
instrument for the determination of heat productions.
Th/U = 6
Heat Production for all Plutons
20
U (ppm)
Th (ppm)
Th/U
Heat Production
(mWm-3)
Dosage Rate
(nGy/h)
Monadhliath granite (n=22)
4.6 ± 0.8
6.1 ± 3.2
32.4 ± 9.8
5.4 ± 3.1
4.3 ± 1.5
175 ± 47
average and stdev1
Cairngorm granite (n=37)
average and stdev
4.2 ± 0.6
11.8 ± 8.1
31.2 ± 11.6
3.4 ± 1.9
5.7 ± 2.6
200 ± 70
Lochnagar granite (n=35)
average and stdev
4.6 ± 0.6
8.3 ± 3.1
24.7 ± 4.9
3.0 ± 1.6
4.4 ± 1.0
169 ± 30
Ballater granite (n=19)
average and stdev
4.9 ± 0.8
18.0 ± 4.8
42.7 ± 8.3
2.4 ± 1.7
8.2 ± 1.5
272 ± 37
Grantown granite (n=6)
average and stdev
3.6 ± 0.8
2.5 ± 1.9
10.9 ± 9.9
4.4 ± 5.2
1.7 ± 1.2
86 ± 37
Strathspey granite (n=4)
average and stdev
3.6 ± 0.7
2.1 ± 1.5
5.7 ± 0.7
2.7 ± 0.5
1.2 ± 0.4
70 ± 13
All Data Combined (n=123)
global average
4.4 ± 0.8
9.6 ± 6.8
28.2 ± 12.8
3.9 ± 2.4
5.1 ± 2.4
182 ± 69
note 1: averages and standard deviations are derived from the point-by-point measurements of K, U and Th without incorporating associated
measurement uncertainties.
Conclusions
Granites typically have high concentrations of the unstable
isotopes of uranium, thorium and potassium which decay and
produce radiogenic heat.
• Handheld gamma ray spectrometers are a viable field
instrument for radiogenic isotope data gathering but require
prior geological knowledge of the investigated site.
The decay of these radionuclides produces gamma radiation
which was measured in the field using the handheld Gamma
Surveyor II (right). This gamma ray spectrometer
used the direct proportionality between the energy
of an incoming gamma ray and the pulse amplitude
at the output of the detector to determine element
concentrations.
.
By determining the concentrations of these elements, the heat
production of granite plutons was estimated by the following
calculation:
𝑨 𝛍𝐖/𝐦³ = 𝟎. 𝟎𝟐𝟕(𝟗. 𝟕𝑪𝑼 (𝒑𝒑𝒎) + 𝟐. 𝟔𝑪𝑻𝒉 (𝒑𝒑𝒎) + 𝟑. 𝟓𝑪𝑲 (%))
• This study found the Cairngorm suite of granite plutons to
have variable heat productions, averaging at 5.1 ± 2.4µWm-3.
This is slightly lower than the 6.0 ± 2.2µWm-3 estimated by
previous studies and may be due to the methodology
employed in gathering data.
Ballater Example
Histogram (left) and GIS
(right) showing calculated
heat productions at specific
coordinates upon the pluton.
7
Ballater Pluton
6
Acknowledgements
I would like to thank Prof Paul Younger, Prof
Simon Harley, Dr Andrew Bell and Alastair McCay
for making this study possible.
References
• YOUNGER P.L., GLUYAS, J. AND STEPHENS, W.E. (2012).
Development of deep geothermal energy resources in the
UK. Energy. 165 (1), p19-32.
n=19
4
Robust Regression Mean
8.12 ± 0.69 mWm-3
3
2
Relative probability
5
Number
• Within the suite, the Ballater pluton exhibited the highest
geothermal potential with estimated heat productions in
excess of 8µWm-3 and hence should be considered for further
investigation.
1
0
3
5
7
9
11
13
15
-3
Heat Production (mWm )
University of Glasgow, charity number SC004401
• INTERNATIONAL ATOMIC ENERGY AGENCY. (2003).
Guidelines for radioelement mapping using gamma ray
spectrometry data. International Journal of Earth Sciences.
1363 (1), p1-179.