1. Faculty of Civil Engineering and Resources Management, AGH University of Science and Technology, Al. Mickiewicza 30, 30-059 Kraków, Poland
2. Department of Geoscience and Petroleum, Faculty of Engineering, Norwegian University of Science and Technology, 7031 Trondheim, Norway
3. Maelgwyn Mineral Services Ltd., Ty Maelgwyn, 1A Gower Road, Cathays, Cardiff CF24 4PA, UK