Radon finds uranium under 18 meters of sandstone
but you have to measure thoron as well.

  • An orientation survey of radon in soil gas at Mora 6, in the Karoo Formation, Folakara, Madagascar, by IAEA and OMNIS.
  • Uranium mineralization buried under up to 18 meters of sandstone.
  • Previously drilled by the French Atomic Energy Authority.
  • 139 soil-gas samples taken from 30-cm deep holes at 10-meter spacing.
  • Anomalies confirmed on different days.
  • Higher radon values, and higher ratios of radon to thoron over mineralization as deep as 18 meters. Gamma survey does not respond to this depth, nor does radium and uranium geochemistry of termite hills.
  • False radon highs have high thoron (low Rn/Tn ratios). Similar high values of both isotopes occur on a small sand ridge south of Midwest Lake, removed from the mineralization. Higher levels of both radon isotopes in the absence of uranium mineralization is because greater soil permeability releases larger amounts of both gases into the sample hole.
  • Measuring radon is not enough: we also have to measure thoron to check for these false "permeability" anomalies.
  • A similar survey at Mora 13, where the section overlying the mineralization includes shale layers, gave negative results. Shale is impermeable and blocks upward migration of radon.

INSTRUMENTS Robert H. Morse, Ph.D., P.Eng.
January 25, 2009
LEGEND: radon counts per minute / ratio of radon to thoron

ANOMALY DEFINITIONS
Based on radon counts per minute and ratio of radon to thoron
Strong: Rn>75 and ratio>0.9 or Rn>50 and ratio>3
Marginal: Rn>37 and ratio>0.6
Background:Rn<38 or ratio<0.7
False:Rn>100 and ratio<0.7
17 strong radon anomalies
with high Rn/Tn ratios
all overlying uranium mineralization
165/3
117/5
147/10
352/10
90/3
101/2
97/1.1
71/4
80/3.5
*147/1.0
*86/1.1
112/6
102/1.5
111/1.6
92/1.5
134/2
76/1.0
*buried 18m
3 false radon anomalies
with low Rn/Tn ratios
not overlying known uranium mineralization


112/0.5
103/0.3
142/0.2

We use low radon:thoron ratios to weed out false anomalies.
17 marginal radon anomalies
overlying uranium mineralization
41/1.9
70/0.7
59/0.7
94/0.8
86/0.7
41/0.7
51/1.1
56/1.7
72/1.2
58/0.7
50/0.8
81/0.7
38/0.9
85/0.9
42/0.8
218/0.8
234/0.9
Only 3 marginal radon anomalies
not overlying known uranium mineralization


137/0.7
39/13
72/1.8
21 background values
overlying uranium mineralization

0
39/0.2
30/1.1
63/0.3
32/0.5
0
0
21/0.2
21/0.4
0
23/0.4
14/0.2
0
41/0.5
30/0.4
37/0.6
28/0.5
42/0.6
0
0
0
Some background values over mineralization.
Geochemistry requires large numbers of samples.
78 background values
not overlying known uranium mineralization

34/0.8
13/4
16/0.6
0
21/0.7
0
13/0.5
13/3
29/1.2
24/0.5
70/0.4
15/0.1
0
0
0
0
10/0.1
18/6
18/0.4
11/0.5
0
0
57/0.4
10/10
0
11/0.7
0
0
0
34/0.3
69/0.3
57/0.6
37/2
15/0.3
39/0.3
15/0.9
0
13/1.0
0
15/0.1
33/0.3
45/0.3
0
60/0.1
71/0.2
23/0.2
35/0.2
14/0.2
0
0
36/0.3
0
37/0.3
0
24/0.5
27/1.3
0
23/1.6
0
62/0.6
0
22/0.6
0
11/0.5
35/0.4
10/0.1
23/0.2
0
0
55/0.6
0
50/0.6
0
21/0.3
54/0.6
0
0
0
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