Abstract <p>The evolution of interrelated processes within the geological history of magmatic complexes in the Argun Block, which includes southeastern Transbaikalia, China, and Mongolia, as well as their metallogenic specialization, are studied in the context of changes in geodynamic regimes during the Neoproterozoic, Caledonian, Hercynian, Early Mesozoic, and Late Mesozoic tectonic–magmatic cycles. The results of a comparative cross-border analysis of the petrogeochemical features of volcanoplutonic complexes, enclosing different-aged ore mineralization and various ore-accompanying hydrothermal–metasomatic alterations, are presented for the first time. Two trends of development of magmatic and ore-forming processes and, accordingly, two types of hydrothermal mineralization were identified within the Argun block territory during the Late Mesozoic cycle. One of these trends, manifested in permeable zones with a residual regime of collision, is associated with postorogenic magmatism of the oxidized (or magnetite) type. Within ore deposits, it is possible to observe the entire sequence of altered rocks, from the high-temperature skarns and K-feldspar halos of porphyry intrusions to low-temperature varieties of argillisites (excluding greisens). The other trend is manifested in stable blocks of the Earth’s crust and rift zones. Here, anorogenic rare-metal granites were predominant and a more limited range of syn-ore metasomatic rocks is presented, including greisens with subordinate development of beresitization and argillization. The fluid-magmatic systems of the two identified trends of the development are characterized by their metallogenic specialization: Pb, Zn, Au, Cu, Mo, U, Ag, and fluorite deposits are associated with the oxidized-type system, while Ta, Nb, W, Sn, Be, and fluorite deposits are associated with the reduced type system (rare-metal granites).</p>