This book describes for the first time the complexity of the Northeastern Transbaikalia province of Russia. This province is one of the largest Early Proterozoic metallogenic provinces on Earth. It comprises three extra large deposits: Cu-sandstones Udokan, Fe-Ti-V and Cu-PGE Chiney, and REE Katugin. This book is a research study and includes geological, mineralogical, and geochemical data obtained by the authors from 30 field trips in the region, using XRF, ICP-MS, La-ICP-MS, EPMA, and the study of Sr, Nd, U-Pb isotopes in rocks and minerals. It demonstrates the complicated origin of Cu deposits comprising 50 Mt copper concentrated in sedimentary and magmatic rocks in this area.