From: Radiological survey on radon entry path in an underground mine and implementation of an optimized mitigation system
Rock type
U-238 (Bq kg−1)
Ra-226 (Bq kg−1)
Carbonate ore
1–3 (1.6)
15 & 18 (16)
Black shale
5
9–18 (13)
limestone
1–2 (1.6)
2–6 (3)
Marlstone
1 & 4
3–6 (4)