We present results of new mineralogical, geochemical, geochronological, and isotope (Sm-Nd, Rb-Sr, and O) studies of the volcanic rocks of the Tyya complex in the Olokit trough. These are normal tholeiitic basalts and scarcer basaltic andesites forming a fractionated series with mg# = 45-65, medium TiO2 contents (0.73-1.62 wt.%), low P2O5 contents (0.04-0.25 wL%), and a significant domination of Na over K (Na2O/K2O = 2.1-50.0). The rocks are metamorphosed to greenschists, which are composed of chlorite, actinolite, epidote, and albite with quartz, titanite, ilmenite, and magnetite impurity. The metabasalts have is an age of 915 +/- 5 Ma (zircon U-Pb dating) and are characterized by wide variations in epsilon(Nd) (T) (-3.5 to -11.9) and Sr-87/Sr-86 (0.70602-0.70732) and high delta O-18 values (9.0-15.2960) as compared to the mantle ones. According to the isotope-geochemical characteristics, the studied metabasalts have features of both IAB and E-MORB. The Tyya metabasalts might have resulted from the melting of the lithospheric mantle with a subductional component. Comparison of the studied rocks with volcanic rocks of recent geodynamic settings shows their similarity to basalts of back-arc basins. The Tyya metabasalts might belong to a back-arc basin of the late Mesoproterozoic Nyurundukan island arc system.

В работе приведены результаты новых минералогических, петрогеохимических, геохронологических и изотопных (Sm-Nd, Rb-Sr, O) исследований вулканических пород тыйского вулканогенного комплекса Олокитского рифтогенного прогиба (Байкало-Муйский пояс). Вулканиты имеют возраст 915±5 млн лет (U-Pb метод, циркон), представлены низкои нормальнощелочными толеитовыми базальтами, реже пикробазальтами, образуют фракционированный ряд с вариацией значений магнезиальности (mg#) в интервале 45-65, с умеренными содержаниями TiO2 (0.75-1.54 мас. %), низкими P2O5 (0.04-0.25 мас. %) и существенным преобладанием содержаний натрия над калием (Na2O/K2O = 2.1-50.0). В результате метаморфизма превращены в зеленые сланцы. Для них характерны пониженные содержания Nb, повышенные Th и легких РЗЭ, а также отрицательные Nb-Ta, P и Ti аномалии на мультиэлементных спектрах, что свойственно островодужным базальтам. Установленные низкие отрицательные значения Nd(T) (-3.7 -12.1), ɛ аномально высокие 87Sr/86Sr (0.70737 0.70799) и δ18O (+9.0 – +15.2 ‰) указывают на древние коровые источники магматизма. Об этом же свидетельствует Nd модельный возраст протолитов (ТNd(DM) = 2.1-до 2.8 млрд лет), что сближает их по возрасту с протолитами Нюрундуканской островной дуги. Анализ полученных данных позволил сделать вывод о том, что происхождение мезопротерозойских тыйских метабазальтов связано с частичным плавлением литосферного обогащенного мантийного источника, содержащего субдукционный компонент древней океанической коры. Показано, что Олокитский рифтогенный прогиб сформировался в задуговой области Нюрундуканской островной дуги. Таким образом, изотопно-геохимические особенности тыйских метавулканитов обладают чертами двойственности, заключающейся

The structures and conditions of fluorite ore formation of the Egitinsky deposit in Trans-Baikalia were examined through the geological and mineralogical evidences and fluid inclusion study. The fluorite ores were formed due to the filling of fractures and cavities and, to a lesser degree, by replacing the Ca-bearing host rocks. The productive assemblage consisted of 3 ore types and included the same minerals in different proportions. The main ores of the Egitinsky deposit were formed at temperatures ranging from 400 to 300 °C due to Na-K-Mg-chloride fluids with the involvement of metamorphic and magmatic fluids.

The relevance of the study is in the need to expand the mineral resource base of Russia. Eastern Transbaikalia is one of the oldest gold mining regions of the country. Nevertheless, even in such a well-studied region, the issue of search and discovery of new ore deposits is acute. For the successful completion of such a task, the data are needed from a detailed study of already known ore deposits, which can be used to develop scientifically based criteria for search for ore deposits and mineralization forecast. Such data include determination of sources of ore-bearing magmatic melts, age and conditions for gold mineralization formation of the Alexandrovskoe gold deposit. The aim of the study was to prove participation in formation of several magma chambers with different characteristics, using the results of studying the distribution of rare-earth elements in igneous rocks and ores, the isotopic composition of oxygen of ore-bearing quartz and sulfur sulfide, as well physicochemical conditions for formation of mineralization by studying fluid inclusions in minerals. Objects of researches is igneous rocks and ores of the Alexandrovskoe gold deposit, located in the Eastern Transbaikalia. Methods. To determine the elemental composition of the rocks, we used the X-ray fluorescence method and standard chemical analysis, the concentrations of rare-earth elements were measured using the method of sorption-atomic emission analysis with inductively coupled plasma (GIN SB RAS, Ulan-Ude). The study of isotopic composition of sulfur sulfides, Au and Ag contents, and isotopic age (40Ar/39Ar) was carried out at the multicomponent and isotopic research center of the Siberian Branch of the Russian Academy of Sciences (Novosibirsk). Fluid inclusions in quartz of ore veins were studied by traditional methods of thermobarogeochemistry and Raman spectroscopy. Results. The age (40Ar/39Ar) of synrudic sericite (162 +/- 2,3 Ma) was determined, which corresponds to the age of intrusions of the Amujikan-Shakhtaminsky complex. It was established that variations in isotopic composition of oxygen in ore-bearing quartz and isotopes of sulfur sulfides correspond to a fluid of magmatic nature. An analysis of distribution of rare and rare earth elements indicates that the sources of mineralization were deep-seated, differentially differentiated magma chambers that functioned both in the upper and lower continental crust. According to the study of fluid inclusions in quartz of ore veins, crystallization of mineral paragenesis of ore deposits occurred in the temperature range from 150 to 402 degrees C. A productive mineral association was formed at 402-360 degrees C. The paper indicated the participation of ore-forming fluids that differ in salt composition in ore formation. This indicates different conditions for generation and nature of ore-forming fluids. A distinctive feature of the deposit is ore formation due to various depth different degrees differentiated orebearing magmatic sources. The relevance of the study is in the need to expand the mineral resource base of Russia. Eastern Transbaikalia is one of the oldest gold mining regions of the country. Nevertheless, even in such a well-studied region, the issue of search and discovery of new ore deposits is acute. For the successful completion of such a task, the data are needed from a detailed study of already known ore deposits, which can be used to develop scientifically based criteria for search for ore deposits and mineralization forecast. Such data include determination of sources of ore-bearing magmatic melts, age and conditions for gold mineralization formation of the Alexandrovskoe gold deposit. The aim of the study was to prove participation in formation of several magma chambers with different characteristics, using the results of studying the distribution of rare-earth elements in igneous rocks and ores, the isotopic composition of oxygen of ore-bearing quartz and sulfur sulfide, as well physicochemical conditions for formation of mineralization by studying fluid inclusions in minerals. Objects of researches is igneous rocks and ores of the Alexandrovskoe gold deposit, located in the Eastern Transbaikalia. Methods. To determine the elemental composition of the rocks, we used the X-ray fluorescence method and standard chemical analysis, the concentrations of rare-earth elements were measured using the method of sorption-atomic emission analysis with inductively coupled plasma (GIN SB RAS, Ulan-Ude). The study of isotopic composition of sulfur sulfides, Au and Ag contents, and isotopic age (40Ar/39Ar) was carried out at the multicomponent and isotopic research center of the Siberian Branch of the Russian Academy of Sciences (Novosibirsk). Fluid inclusions in quartz of ore veins were studied by traditional methods of thermobarogeochemistry and Raman spectroscopy. Results. The age (40Ar/39Ar) of synrudic sericite (162 +/- 2,3 Ma) was determined, which corresponds to the age of intrusions of the Amujikan-Shakhtaminsky complex. It was established that variations in isotopic composition of oxygen in ore-bearing quartz and isotopes of sulfur sulfides correspond to a fluid of magmatic nature. An analysis of distribution of rare and rare earth elements indicates that the sources of mineralization were deep-seated, differentially differentiated magma chambers that functioned both in the upper and lower continental crust. According to the study of fluid inclusions in quartz of ore veins, crystallization of mineral paragenesis of ore deposits occurred in the temperature range from 150 to 402 degrees C. A productive mineral association was formed at 402-360 degrees C. The paper indicated the participation of ore-forming fluids that differ in salt composition in ore formation. This indicates different conditions for generation and nature of ore-forming fluids. A distinctive feature of the deposit is ore formation due to various depth different degrees differentiated orebearing magmatic sources. The relevance of the study is in the need to expand the mineral resource base of Russia. Eastern Transbaikalia is one of the oldest gold mining regions of the country. Nevertheless, even in such a well-studied region, the issue of search and discovery of new ore deposits is acute. For the successful completion of such a task, the data are needed from a detailed study of already known ore deposits, which can be used to develop scientifically based criteria for search for ore deposits and mineralization forecast. Such data include determination of sources of ore-bearing magmatic melts, age and conditions for gold mineralization formation of the Alexandrovskoe gold deposit. The aim of the study was to prove participation in formation of several magma chambers with different characteristics, using the results of studying the distribution of rare-earth elements in igneous rocks and ores, the isotopic composition of oxygen of ore-bearing quartz and sulfur sulfide, as well physicochemical conditions for formation of mineralization by studying fluid inclusions in minerals. Objects of researches is igneous rocks and ores of the Alexandrovskoe gold deposit, located in the Eastern Transbaikalia. Methods. To determine the elemental composition of the rocks, we used the X-ray fluorescence method and standard chemical analysis, the concentrations of rare-earth elements were measured using the method of sorption-atomic emission analysis with inductively coupled plasma (GIN SB RAS, Ulan-Ude). The study of isotopic composition of sulfur sulfides, Au and Ag contents, and isotopic age (40Ar/39Ar) was carried out at the multicomponent and isotopic research center of the Siberian Branch of the Russian Academy of Sciences (Novosibirsk). Fluid inclusions in quartz of ore veins were studied by traditional methods of thermobarogeochemistry and Raman spectroscopy. Results. The age (40Ar/39Ar) of synrudic sericite (162 +/- 2,3 Ma) was determined, which corresponds to the age of intrusions of the Amujikan-Shakhtaminsky complex. It was established that variations in isotopic composition of oxygen in ore-bearing quartz and isotopes of sulfur sulfides correspond to a fluid of magmatic nature. An analysis of distribution of rare and rare earth elements indicates that the sources of mineralization were deep-seated, differentially differentiated magma chambers that functioned both in the upper and lower continental crust. According to the study of fluid inclusions in quartz of ore veins, crystallization of mineral paragenesis of ore deposits occurred in the temperature range from 150 to 402 degrees C. A productive mineral association was formed at 402-360 degrees C. The paper indicated the participation of ore-forming fluids that differ in salt composition in ore formation. This indicates different conditions for generation and nature of ore-forming fluids. A distinctive feature of the deposit is ore formation due to various depth different degrees differentiated orebearing magmatic sources. The relevance of the study is in the need to expand the mineral resource base of Russia. Eastern Transbaikalia is one of the oldest gold mining regions of the country. Nevertheless, even in such a well-studied region, the issue of search and discovery of new ore deposits is acute. For the successful completion of such a task, the data are needed from a detailed study of already known ore deposits, which can be used to develop scientifically based criteria for search for ore deposits and mineralization forecast. Such data include determination of sources of ore-bearing magmatic melts, age and conditions for gold mineralization formation of the Alexandrovskoe gold deposit. The aim of the study was to prove participation in formation of several magma chambers with different characteristics, using the results of studying the distribution of rare-earth elements in igneous rocks and ores, the isotopic composition of oxygen of ore-bearing quartz and sulfur sulfide, as well physicochemical conditions for formation of mineralization by studying fluid inclusions in minerals. Objects of researches is igneous rocks and ores of the Alexandrovskoe gold deposit, located in the Eastern Transbaikalia. Methods. To determine the elemental composition of the rocks, we used the X-ray fluorescence method and standard chemical analysis, the concentrations of rare-earth elements were measured using the method of sorption-atomic emission analysis with inductively coupled plasma (GIN SB RAS, Ulan-Ude). The study of isotopic composition of sulfur sulfides, Au and Ag contents, and isotopic age (40Ar/39Ar) was carried out at the multicomponent and isotopic research center of the Siberian Branch of the Russian Academy of Sciences (Novosibirsk). Fluid inclusions in quartz of ore veins were studied by traditional methods of thermobarogeochemistry and Raman spectroscopy. Results. The age (40Ar/39Ar) of synrudic sericite (162 +/- 2,3 Ma) was determined, which corresponds to the age of intrusions of the Amujikan-Shakhtaminsky complex. It was established that variations in isotopic composition of oxygen in ore-bearing quartz and isotopes of sulfur sulfides correspond to a fluid of magmatic nature. An analysis of distribution of rare and rare earth elements indicates that the sources of mineralization were deep-seated, differentially differentiated magma chambers that functioned both in the upper and lower continental crust. According to the study of fluid inclusions in quartz of ore veins, crystallization of mineral paragenesis of ore deposits occurred in the temperature range from 150 to 402 degrees C. A productive mineral association was formed at 402-360 degrees C. The paper indicated the participation of ore-forming fluids that differ in salt composition in ore formation. This indicates different conditions for generation and nature of ore-forming fluids. A distinctive feature of the deposit is ore formation due to various depth different degrees differentiated orebearing magmatic sources. The relevance of the study is in the need to expand the mineral resource base of Russia. Eastern Transbaikalia is one of the oldest gold mining regions of the country. Nevertheless, even in such a well-studied region, the issue of search and discovery of new ore deposits is acute. For the successful completion of such a task, the data are needed from a detailed study of already known ore deposits, which can be used to develop scientifically based criteria for search for ore deposits and mineralization forecast. Such data include determination of sources of ore-bearing magmatic melts, age and conditions for gold mineralization formation of the Alexandrovskoe gold deposit. The aim of the study was to prove participation in formation of several magma chambers with different characteristics, using the results of studying the distribution of rare-earth elements in igneous rocks and ores, the isotopic composition of oxygen of ore-bearing quartz and sulfur sulfide, as well physicochemical conditions for formation of mineralization by studying fluid inclusions in minerals. Objects of researches is igneous rocks and ores of the Alexandrovskoe gold deposit, located in the Eastern Transbaikalia. Methods. To determine the elemental composition of the rocks, we used the X-ray fluorescence method and standard chemical analysis, the concentrations of rare-earth elements were measured using the method of sorption-atomic emission analysis with inductively coupled plasma (GIN SB RAS, Ulan-Ude). The study of isotopic composition of sulfur sulfides, Au and Ag contents, and isotopic age (40Ar/39Ar) was carried out at the multicomponent and isotopic research center of the Siberian Branch of the Russian Academy of Sciences (Novosibirsk). Fluid inclusions in quartz of ore veins were studied by traditional methods of thermobarogeochemistry and Raman spectroscopy. Results. The age (40Ar/39Ar) of synrudic sericite (162 +/- 2,3 Ma) was determined, which corresponds to the age of intrusions of the Amujikan-Shakhtaminsky complex. It was established that variations in isotopic composition of oxygen in ore-bearing quartz and isotopes of sulfur sulfides correspond to a fluid of magmatic nature. An analysis of distribution of rare and rare earth elements indicates that the sources of mineralization were deep-seated, differentially differentiated magma chambers that functioned both in the upper and lower continental crust. According to the study of fluid inclusions in quartz of ore veins, crystallization of mineral paragenesis of ore deposits occurred in the temperature range from 150 to 402 degrees C. A productive mineral association was formed at 402-360 degrees C. The paper indicated the participation of ore-forming fluids that differ in salt composition in ore formation. This indicates different conditions for generation and nature of ore-forming fluids. A distinctive feature of the deposit is ore formation due to various depth different degrees differentiated orebearing magmatic sources.

— Integrated structural geological, minerogenic, and metallogenic studies with allowance for previous topical surveying, geological mapping and prospecting, and mineral exploration data has revealed that Upper Paleozoic and Early Mesozoic tectonomagmatic structures are widespread in the Selenga ore district. They are associated with the evolution of the transregional Upper Paleozoic Selenga–Vitim rift-related volcanoplutonic belt and the formation of the Early Mesozoic West Transbaikalian region of intraplate magmatism. Late Paleozoic–Mesozoic igneous activity accounts for the bulk of mineable mineral resources in the Selenga ore district concentrated inside and outside the ore clusters (Kunalei, Kizhinga, Cheremshana–Oshurkovo, Tashir, etc.). It is demonstrated that the main mineable metals in the district are molybdenum and beryllium, which determine the minerogenic specificity of the ore district. New compositional characteristics of the Upper Paleozoic and Early Mesozoic intraplate magmatic complexes and the associated mineral deposits (Mo, Be, Ti, quartz, fluorite, and apatite ores), as well as other promising gold, uranium, and REE–Ba–Sr ore occurrences were obtained. The geodynamic settings of their formation and the ages of the main ore-forming processes have been established; the viability of the mining industry in the Selenga ore district and the feasibility of involving its ore potential in the district’s economic modernization program have been assessed.

На основе комплексных структурно-геологических, минерагенических и металлогенических исследований, с учетом раннее проведенных тематических, поисково-съемочных, геолого-разведочных работ установлено, что в пределах рудного района широко развиты верхнепалеозойские и раннемезозойские тектоно-магматические структуры. Они связаны с развитием трансрегионального верхнепалеозойского Селенгино-Витимского вулкано-плутонического пояса рифтогенного типа, а также с формированием раннемезозойской Западно-Забайкальской области внутриплитного магматизма. С магматической деятельностью позднепалеозойско-мезозойского этапа связаны основные промышленно-значимые ресурсы минерального сырья Селенгинского рудного района, которые сосредоточены в рудных узлах (Куналейском, Кижингинском, Черемшано-Ошурковском, Таширском и др.), а также за их пределами. Показано, что основными рудными полезными ископаемыми в пределах района являются молибден и бериллий, определяющие минерагенический облик исследованного рудного района. Получены новые вещественные характеристики верхнепалеозойских и раннемезозойских внутриплитных магматических комплексов и связанных с ними месторождений минерального сырья (Mo, Be, Ti, кварцевое, флюоритовое и апатитовое сырье), а также других перспективных объектов золотого, уранового и редкоземельно-барий-стронциевого оруденения. Выявлены геодинамические условия их формирования и главные возрастные рубежи проявления рудообразующих процессов, оценены перспективность добычи полезных ископаемых в Селенгинском рудном районе и вовлечения этого рудного потенциала в программу модернизации экономики региона.

This article presents new geochronological and isotope-geochemical data on ultramafic–mafic rocks of the banded complex of the Dzhida zone of the Caledonides ophiolite association.

Based on complex structural, rheological, and metallogenic studies, taking into account the results of earlier subject-specific, prospecting, mapping, and exploration works, it has been established that the geological structure of the district was caused by the ensimatic evolution of the Vendian–Early Paleozoic Dzhida island-arc system, in which oceanic and island-arc complexes served as a melanocratic basement for Late Paleozoic–Mesozoic active within-plate (riftogenic) processes, which gave rise to the formation of ore deposits and occurrences of strategic mineral commodities (Mo, W, Au, Pt, Ag, and rare elements, including REE). Mantle plumes and flows of deep-seated transmagmatic solutions (ore-forming fluids) played a critical role in these processes, the significance of which increases in upper crustal swarms of dikes and fault systems. The forecasts and development prospects of the Dzhida ore district envisage the expansion of geological prospecting and exploration, scientific research, and technological testing of ore for insight into strategic mineral commodities, as well as reanimation of mining within the areas of the Dzhida’s large territorial and industrial complex (TIC) in eastern Siberia.

Object . The results of geochronological and isotope-geochemical studies of the Arsentyevsky titaniferous gabbro-syenite massif of the Western Transbaikalia, which previously referred to the gabbro-syenite series of a two-phase structure are presented. The rocks of the massif contain an increased concentration of titanomagnetite, ilmenite, magnetite and in some cases apatite and are considered as complex iron-titanium ores. Methods. The studies were performed by silicate analysis me­thods, XRF and ICP-MS; age determination for zircons was carried out by LA-ICP-MS and SHRIMP-II methods. The composition of minerals on the X-ray microarray analyzer MAP-3 and electron microscope LEO-1430 was studied. Results. In the basites, a standard trend is observed for the evolution of compositions from melanocratic to terminal leucocratic differen­ces with an increase in the content of silica, alumina, and sodium, and a decrease in magnesium and calcium. Syenites differ from anorthosites in the content of impurity elements including rubidium, niobium, strontium and REE The geochronological studies of rocks of Arsent’evsky gabbro-syenite massif, showed a significant time gap in the formation of gabbroids rela­tive to syenites. The U-Pb age of the gabbroids was 279.5 ± 2.0 Ma, alkali feldspar syenites have age 229.4 ± 2.8 Ma, and biotite syenites - 226 ± 2.4 Ma. Conclusion. The obtained results by age and data on the geochemical features of the rocks made it possible to conclude that there was no genetic relationship between basites and syenites. Petrochemical and geochemical features of biotite and alkali-feldspar syenites proved to be close to the rocks of the Mesozoic Kunaleisky complex.

We report data on the geology, mineralogy, petrography, and chemistry of 733 Ma gabbro-peridotite sills from the Late Riphean Dovyren plutonic complex. Thick sills were differentiated into plagiolherzolite to olivine gabbronorite compositions by fractional crystallization of the K-Na series high-Mg low-alkali low-Ti picritic parental magma. The magma already contained up to 5% of intratelluric olivine crystals when entering the reservoir. The sills emplaced before the whole complex, judging by the presence of their fragments as plagiolherzolite xenoliths in the gabbro zone of the Yoko-Dovyren layered pluton. The gabbro-peridotite sills are products of high-temperature within-plate magmatism. High heat flow during the generation of the magma, evident from its high-Mg composition, was likely maintained by the activity of a mantle plume associated with the Neoproterozoic Franklin large igneous province. (C) 2018, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.

New data are presented on the geologic structure, age, petrogeochemical composition, and conditions of formation of the Late Proterozoic Meteshikha ultramafic-mafic pluton of the Ikat complex. Mafic rocks are the main rocks of the massif, whereas ultramafic rocks are secondary; both of them correspond to two intrusive phases. The first phase includes a layered rock series enriched in intercumulus amphibole, which varies in composition from olivine gabbro to leucocratic gabbro-anorthosite; the second is composed of wehrlite, plagiowehrlite, and olivine clinopyroxenite. Mineralogical, petrographic, geochemical, and isotope studies show that the rocks of both phases crystallized from the same mantle melt; note that the PT-conditions of their formation were considerably different. We suppose that they were separated in the intermediate chamber during fractional crystallization and the accumulation of early minerals (olivine and, probably, clinopyroxene) in the lower part of the chamber. Using the COMAGMAT software, we have found the composition of the parental melt for the rocks of the first phase-normal tholeiitic basalt with 0.2-0.5 wt.% water, which might have crystallized at 3.0-3.5 kbar and the oxygen activity controlled by the QFM buffer. The differentiated series is characterized by gradual depletion with Cr and Ni and enrichment with Sr, Ti, Cu, and REE during the evolution of melt. The REE patterns for the massif rocks have a similar low-fractionation trend with domination of light lanthanides over heavy ones and (La/Yb) N = 1.25-2.75. Multielement spectra are characterized by negative anomalies of K, Th, Nb, and Zr and positive anomalies of Ba, U, Sm, and Sr. The geochemical characteristics of the rocks are similar to those of the tholeiitic basalts of present-day island arcs. Studies show that the Meteshikha massif formed in the subduction setting of the active margin of the Siberian continent in the Late Riphean (809 Ma). (C) 2015, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.

The studied massifs in Western Transbaikalia (Arsentyev and Orongoi) are composed of pyroxenites, high-Ti subalkalic gabbro, gabbro-diorites, monzodiorites, anorthosites, and syenites. The Orongoi massif also includes small olivinite and plagioperidotite bodies. The gabbroids have high contents of Sr, Ba, Nb, Ta, Zr, and Hf, which is typical of intraplate basites. The REE pattern shows the rock enrichment in LREE (La/YbN = 5.35–25.82). The 87Sr/86Sr values vary from 0.7050 to 0.7054, and εNd, from 1.44 to –1.18. The presence of radiogenic Nd in the gabbroids and their enrichment in 87Sr suggest their formation as a result of the melting of the EM-II-type lithospheric mantle.

The study of endogenic titanomagnetite-ilmenite ores are of interest as they present a number of petrologic problems. One such problem is determining their genetic connection with alkalimafic and mafic complexes and associated phosphorus enrichment. The Arsentyev gabbro-syenite massif is representative of these systems and provides an ideal situation in which a detailed study allows further understanding of interrelated magmatic and ore-formation processes. It is shown that an oxide-ore liquid separated from a parental silicate melt during early stages of subalkaline mafic magma crystallization.