During cruise 41 of the R/V Professor Logachev in 2019, two new ore fields were discovered within the Russian exploration area of the Mid-Atlantic Ridge. The Korallovoe ore field is located in the middle part of the rift valley ridge and lies on a gentle slope in the depth range of 2800–2850 m. The Molodezhnoe ore field is located approximately 5 km northeast of the Korallovoe field and lies on a less steeper section of the slope at depths of 3500–3550 m. The Korallovoe and Molodezhnoe fields are confined to an outcrop of a gabbro–peridotite massif on the western side of the Mid-Atlantic Rift valley. The total number of discovered ore fields in the Russian exploration area has increased to 14.

During cruise 41 of the R/V Professor Logachev in 2019, two new ore fields were discovered within the Russian exploration area of the Mid-Atlantic Ridge. The Korallovoe ore field is located in the middle part of the rift valley ridge and lies on a gentle slope in the depth range of 2800-2850 m. The Molodezhnoe ore field is located approximately 5 km northeast of the Korallovoe field and lies on a less steeper section of the slope at depths of 3500-3550 m. The Korallovoe and Molodezhnoe fields are confined to an outcrop of a gabbro-peridotite massif on the western side of the Mid-Atlantic Rift valley. The total number of discovered ore fields in the Russian exploration area has increased to 14.

An overview of Russian studies of deep-sea polymetallic sulfides (PМS) in the axial zone of the Mid-Atlantic Ridge (MAR) at the Russian Exploration Area (REA‒PMS) is presented. A brief geological description of the axial zone of the MAR and PMS sites discovered and studied for almost forty years before and after the signing of an exploration contract with the International Seabed Authority in 2012 is given. Information on methods for conducting searches and exploration of PMS, technical equipment, as well as on metallurgical processing of raw materials is presented.

The results of 230 Th/U dating and mineralogical–geochemical studies of sulfide ores from the Irinovskoe hydrothermal field and the Severo-Zapadnoe ore occurrence (Mid-Atlantic Ridge) are presented. Sulfides are represented primarily by copper–sulfide ores with 12–30% Cu content; sulfur- and zinc-sulfide ores are distributed less frequently. The analysis of a change in the composition of sulfides over time has made it possible to identify three stages of formation. Each stage assumes that mineral associations are changed from high-temperature (sulfur and copper sulfide) to medium temperature (Zn–Cu and Zn-sulfide) sulfide ores. The whole age range of formation of the hydrothermal deposits falls within the time interval of about 58000–8000 for the Irinovskoe field and 69000–11000 years ago for the Severo-Zapadnoe ore occurrence.

Two new sulfide fields (Yubileinoe, 20°09′ N, and Surprise, 20°45.4′ N) were discovered between 20°01′ and 20°54′ N within the Russian Application Area of the Mid-Atlantic Ridge (MAR). The Yubileinoe field is located at a depth of 2300–2550 m in the near-top area of the first rift ridge, which is a boundary of the western wall of the rift valley. This new field and the Zenith-Victory field, which was previously discovered in the eastern wall, occur symmetrically relative to the rift valley of this MAR segment. The Surprise field at a depth of 2800–2850 m is situated in the eastern wall of the rift valley, on the slope of the volcanic uplift. After the discovery of these inactive sulfide fields, the number of hydrothermal fields within the Russian Application Area reached ten.

The optimal set of prospecting methods, including geophysical (geoelectrical), geological (mineralogical-geochemical), and hydrological observations, was developed during the long-term investigations of the sulfide mineralization in the northern equatorial zone of the Mid-Atlantic Ridge. The application of these methods made it possible to discover six massive sulfide deposits and considerably extend the boundaries of another two ore objects. The ores associated with ultramafic rocks are characterized by elevated Cu, Au, and Co concentrations. It is established that the ore formation was a multistage process that resulted in the accumulation of large deposits (over 10 million tons).

Comparative studies of the composition and distribution of the dispersed organic matter (DOM) were performed for the bottom sediments from active areas of the Ashadze hydrothermal field (the Mid-Atlantic Ridge, 13° N) and for background sediments from the area treated (sampled during the cruises of R/V Professor Logachev in 2003 and 2007). The content of hydrocarbons (HCs) in the hydrothermal samples is about 20 times as high as the background values. The HCs composition includes both low-transformed (isoprenoids, hopenes, ββ-hopanes, and ααα27R-steranes) and geologically mature chemofossils (C16-C35 n-alkanes, geohopanes, moretanes, and polyaromatic hydrocarbons). The polyaromatic hydrocarbons (PAHs) are mainly represented by phenanthrene and its alkyl homologues, i.e., by possible products of the diagenetic transformation of biogenic precursors. The results obtained point to the mixed genesis of the hydrothermal DOM, which is caused first by the diversity of the biota composition in the considered region, as well as by the specificity of the processes of the DOM’s maturing under the extreme environmental conditions.

The ultramafic-rock-hosted and active Ashadze submarine hydrothermal field, located at a depth of 4100-4200 m at 13 degrees N along the Mid-Atlantic Ridge, was discovered and sampled by dredge and grab sampler at four stations in 2003, on the 22(nd) cruise of RV "Professor Logatchev". Recovered material included fragments of sulfide chimneys, massive and veinlet-disseminated ore assemblages, sulfide breccia and mineralized peridotite. Preliminary investigations of the field suggested a zonal structure, which was confirmed by further laboratory investigations. A mineralogical Study was carried out, using EMPA and SEM/ EMD (280 analyses). Data on the morphology and composition of the principal sulfides indicate non-equilibrium conditions of submarine formation of the minerals. The following main characteristics of the massive sulfides in the Ashadze field were established: 1) varied morphologies of the main sulfide minerals (pyrrhotite, sphalerite, chalcopyrite, isocubanite, pyrite and chalcocite). 2) Variations occur in the composition of the main sulfide minerals. Concentrations of minor elements are much higher than the amounts estimated experimentally in corresponding systems under equilibrium conditions, but may also depend on mineral associations. 3) Temporal and spatial transformations of minerals were observed and are reflected by pseudomorphs (most commonly after pyrrhotite grains) and exsolution phenomena in various solid-solutions. For the first time, an exsolution texture was found in phase Y (Cu2FeS5) along with that in isocubanite and bornite. The latter transformations occur as a result of microfacies zoning of chimney walls.

The composition of ore minerals in MAR sulfide occurrences related to ultramafic rocks was studied using methods of mineragraphy, electron microscopy, microprobe analysis, and X-ray analysis. The objects are located at various levels of the maturity of sulfide mounds owing to differences in age, duration, and degree of activity of the following hydrothermal systems: generally inactive Logatchev-1 field ( up to 66.5 ka old), inactive Logatchev-2 field (3.9 ka), and generally active Rainbow field ( up to 23 ka). Relative to MAR submarine ore occurrences in the basalt substrate, mineralization in the hydrothermal fields mentioned above is characterized by high contents of Au, Cd, Co, and Ni, along with the presence of accessory minerals of Co and Ni. The studied mounds differ in quantitative ratios of major minerals and structural - textural features of ores that suggest their transformation. Ores in the Logatchev-1 field are characterized by the highest Cu content and the development of a wide range of multistage contrast exsolution structures of isocubanite and bornite. In the Logatchev-2 field, sphalerite - chalcopyrite and gold - arsenic exsolution structures are present, but isocubanite exsolution structures are less diverse and contrast. The Rainbow field is marked by the presence of homogenous isocubanite and the subordinate development of exsolution structures. We have identified four new phases in the Cu - Fe - S system. Phases X and Y ( close to chalcopyrite and isocubanite, respectively) make up lamellae among isocubanite exsolution products in Logatchev-1 and Logatchev-2. Phase Y includes homogenous zones in zonal chimneys of the Rainbow field. Phases A and B are formed in the orange bornite domain at low-temperature alteration of chalcopyrite in the Logatchev-1 field. Mineral assemblages of the Cu - S system are most abundant and diverse in the Logatchev-1 field, but their development is minimal in the Logatchev-2 field where mainly Cu-poor sulfides of the geerite - covellite series have been identified. Specific features of mineral assemblages mentioned above reflect the maturity grade of sulfide mounds and can serve as indicators of maturity.

Дается сравнительный анализ минералого-геохимических особенностей медно-цинковых сульфидных руд полей Логачев-2 и Рейнбоу Срединно-Атлантического хребта (САХ), приуроченных к протрузии серпентинитов. Установлено, что Zn(Fe)- и CuFe(Zn)-сульфиды отлагались в трубах черных курильщиков практически одновременно из пульсирующих разнотемпературных неравновесных растворов, обедненных H 2S. Изотопный состав свинца подтверждает, что источником свинца являются глубинные участки океанской коры. В рудах поля Рейнбоу содержится в 20 раз больше Со, чем в рудах, приуроченных к базальтам, и наблюдается высокое отношение Со/Ni = 46. Руды поля Рейнбоу обогащены тяжелым изотопом 34S (δ 34S средн. = 10‰) за счет постоянного подтока холодной морской воды в близповерхностную зону гидротермальной системы. Руды поля Логачев-2 обогащены золотом в 8 раз по сравнению с другими районами САХ. По обогащенности полезными компонентами (Zn, Cd, Co и Au) сульфидные руды полей Рейнбоу и Логачев-2 не имеют аналогов среди рудопроявлений САХ.