Abstract <p>A variant of possible epigenetic endogenic formation of some large pyrite deposits at depths of hundreds of meters and more than 1&#xa0;km below the seabed with the active thermal participation of subvolcanic bodies with acidic composition or their groups in basaltoid belts of submarine spreading zones is considered. Based on data available in the literature, geological setting of the localization of ten well-studied deposits in the South Ural and Gorno-Altai ore provinces are specifically analyzed. According to the authors, these deposits were formed in thermal fields of subvolcanic (porphyritic) intrusions from deep metal-bearing fluids during their ascent along deep faults and near-intrusion thermal convection in reservoirs. The factors that favored the formation of large pyrite deposits are discussed: positive bends of overlying volcanogenic-sedimentary strata, sealing of structures, dynamic development of combined magma and fluid conductors, high permeability of rocks replaced by sulfides—fluid reservoirs, additional thermal potential of subvolcanic bodies, and mineralization zoning. The complexity of ores and the specificity of the formation of such deposits require their separation into an individual genetic group of subvolcanic deposits that are highly promising for industrial development. For these purposes, it is necessary to study the conditions of their formation in more detail and to develop specific criteria for predicting and searching for new large deposits of complex ores in developed ore regions and provinces. The concept of the oresphere is refined to include not only the upper part of the lithosphere but also parts of the hydrosphere and biosphere.</p>