A plutonic association of the axial zone of the Mid-Atlantic Ridge (MAR) composed of peridotite, gabbro, and trondhjemite is typical for geodynamically crucial components of the lithosphere section of slow-spreading mid-oceanic ridges indicated in modern publications as oceanic core complexes (OCCs). According to the existing ideas, OCCs are represented by blocks of deep rocks moved to the surface of the oceanic bottom by the system of low-angle detachment faults (for example, [1, 2]). During the last 15 years, a huge volume of petrological and geochemical data on rocks composing OCCs has been accumulated and petrogenetic schemes of their formation have been suggested [1–4]. In addition, the data on the age and duration of OCC formation are still scarce and have been discussed in a limited number of publications (for example, [5, 6]). The Ashadze hydrothermal field is located in the axial zone of the MAR and is related to a large cluster of active hydrothermal fields: Ashadze–Semenov–Logachev discovered during the expeditions of the Russian R/V Professor Logachev. These fields occur in blocks of deep rocks moved to the oceanic bottom surface and mainly represented by peridotite and gabbro. As a result of investigation of the petrological peculiarities of rocks from the OCC hosting the Anshadze field, it was established that hydrothermal alteration of rocks of the gabbro–peridotite association resulted not only in mobilization of ore material, but in the formation of veins of acid rocks (trondhjemite) as well .