SGEM SGEM 2021. 21st International Multidisciplinary Scientific GeoConference. Volume 21. Science and Technologies in Geology, Exploration and Mining : conference proceedings of selected papers. Albena, Bulgaria, 16 - 22 August, 2021 Issue 1.1 Geology, Hydrogeology, Engineering Geology and Geotechnics, Exploration and Mining, Mineral Processing, Applied and environmental Geophysics, Oil and Gas Exploration. -- 1. vyd. -- Sofia : STEF 92 Technology, 2021. -- 1038 s. -- ISBN : 978-619-7603-20-0. -- 978-619-7603-21-7 (DVD). -- ISSN : 1314-2704. -- 10.5593/sgem2021/1.1.