The Vuoriyarvi Paleozoic alkaline–ultramafic complex with carbonatites is made up of a great diversity of rocks with various ore mineralization. The paper presents data on the geochemistry of pyroxenites, phoscorites, and carbonatites from the Neskevara deposit of rare metals. The pyroxenites of the rare-metal deposit are significantly enriched in Nb, Ta, and Th relative to the primitive mantle and the primary alkaline–ultramafic melt composition calculated for the Kola alkaline province and are characterized by high Nb/Ta, Zr/Hf, and Th/U ratios of 29, 35, and 14, respectively. HFSE are maximally enriched in the phoscorites and carbonatites of stages II and III, with the highest concentrations of Nb (16 000 ppm), Th (2800 ppm), and Zr (4000 ppm) found in the calcite–tetraferriphlogopite phoscorites, in which pyrochlore crystallization on the liquidus was identified. The rocks of the carbonatite series are strongly enriched in LREE relative to carbonaceous chondrite. The calcite–dolomite carbonatites of the late magmatic–carbothermal stage show REE enrichment up to 25 800 ppm. The chondrite-normalized REE patterns and (La/Yb) N ratio indicate that REE were systematically more strongly fractionated in the sequence pyroxenite (70)—phoscorite (90)—calcite (540) and dolomite (3790) carbonatites The crystallization sequence of minerals in the rare-metal phoscorites and carbonatites of intermediate stages indicates that magnetite and pyrochlore crystallized nearly simultaneously. The crystallization temperatures of such associations are, according to data of the magnetite–ilmenite thermometer, lower than 500–600°C, at ∆NNO = –0.3 and + 1.5 and corresponded to the temperature at which the rare-metal ore mineralization of the main stage was formed.

The paper presents newly acquired geochemical and mineralogical data on carbonatites and fluorapatite of the Newania intrusive complex, India. A magmatic−metamorphic hypothesis is proposed to explain the origin of this complex. The Newania carbonatites are comparable to the average composition of ferro- and magnesiocarbonatites worldwide in terms of Ca, Fe, Mg, Mn, Na, K, Al, Ti, P, and Sr contents but is depleted in Ba, Ta, Zr, Th, and REE. Fluorapatite and monazite-(Ce) are the main P, Sr, Th, and REE concentrators in the rocks, whereas U is concentrated mostly in U-rich pyrochlore. The major chemical changes in the fluorapatite can be described in a generalized form by the following reaction: REE3+ + Na+ ↔ 2Ca2+. The fluorapatite is relatively poor in radioactive elements and contains no more than 0.2 wt

In this work, mineralogical and geochemical data are presented for sulfide-rich phoscorites and carbonatites in the Kovdor massif. The PGE and Ag-bearing mineralization of bornite–chalcopyrite and Ag‑bearing mineralization of pyrrhotite–chalcopyrite associations were investigated. In carbonatite stage formation of massif, the noble metal minerals occurred during evolution of alkaline–ultrabasic melt and after separation of primary sulfide melt enriched in PGE, Au and Ag. According to the observed relationships, the minerals of PGE, Au, and Ag in bornite–chalcopyrite association are crystallized sequentially from magmatic to hydrothermal stages. Crystallization of Os, Ir, Pt and Pd minerals (erlichmanite, rustenburgite, isoferroplatinum, mertieite–II, etc.) occurred at temperature close to 480°С, while further decrease in the temperature and an increase in the Cu and Fe activity in the melt leads to the crystallization of Sb, Pb, As, Bi and Te-bearing minerals (sperrylite, tatyanaite, moncheite, stumpflite, etc.). Formation of Au and Ag-bearing minerals (electrum, silver, stromeyerite, lenaite, etc.) occurred at temperatures below 300 °C with relatively low sulfur activity. In carbonatites and phoscorites of the middle and late magmatic stages enriched with magnetite, pyrrhotite–chalcopyrite association with silver-bearing minerals was formed at temperatures below 300°C. Ag-bearing minerals were produced during hydrothermal recrystallization of Cu–Fe–Ni sulfides at temperature close to 150°C.

Abstract Pyrochlore-group minerals are common accessory rare-metal bearing minerals in the calcite and ankerite carbonatites of the Amba Dongar complex (India). Pyrochlore from the Amba Dongar carbonatites differs from that in other Indian complexes in Ta, Zr, Ti, rare earth element (REE) and Pb contents, but is similar with respect to Ca, Ba and Sr abundances. The evolution of pyrochlore composition was studied to understand the alteration processes and the formation of late-stage pyrochlores enriched in REE and Pb. The early magmatic pyrochlore are calcio- and niobium-dominant types and were replaced by secondary cation-deficient varieties as a consequence of the action of hydrothermal fluids and supergene weathering. These processes produce changes mainly at the A site, rarely at the B site, and the original F is replaced by OH– groups. Calcium and Na can be extracted from the structure at the alteration stage and charge balance is achieved by the introduction of REE, Th, U, Ba or Sr. At the latest supergene stages, marginal and fractured zones of pyrochlore grains are altered to Pb-rich, Si-rich and cation-deficient hydrated varieties. The magmatic pyrochlore was crystallised in a highly alkaline environment at a high activity of Ca and at temperatures near 600°C, the alteration of pyrochlore began in a hydrothermal environment at temperatures below 350°C. The major compositional changes that are associated with the alteration are summarised by the following reactions: Ca2+ + Nb5+→ REE3+ + Ti4+; Nb5+ + Fe3+ → Ti4+ + Zr4+; and 2Nb5+ + Ca2+ → Ti4+ + Si4+ + U4+.

We report the first combined investigation (neutron activation, X-ray fluorescence, and electron microprobe analysis) of mineral forms of Au and Ag and noble metal distribution in the sulfide-bearing phoscorites and carbonatites of the Guli alkaline ultrabasic massif (Polar Siberia) and magnetite and sulfide separates from these rocks. The highest noble metal contents were observed in the sulfide separates from the carbonatites: up to 2.93 Pt, 61.6 Au, and 3.61 ppm Ag. Pyrrhotite, djerfisherite, chalcopyrite, and pyrite are the most abundant sulfides and the main hosts for Au and Ag. The latest assemblage of chalcopyrite, Ag-rich djerfisherite, lenaite, sternbergite, and native silver shows significant Ag concentrations. The wide occurrence of K sulfides and presence of multiphase inclusions in pyrrhotite consisting of rasvumite, K‒Na–Ca carbonate, carbocernaite, strontianite, galena, chalcopyrite, sternbergite, lenaite, and native silver suggest that the sulfides were formed at high activities of K, Na, Sr, LREE, F, Cl, and S. Chlorine shows high complex-forming capacity to Ag and could be an agent of noble metal transport in the carbonatites. Crystallization of the early djerfisherite–pyrrhotite assemblages of the phoscorites and carbonatites began at a temperature not lower than 500°C and continued up to the formation of late Ag-bearing sulfides at temperatures not higher than 150°C. The carbonatite-series rocks could be enriched in Au and Ag during late low-temperature stages and serve as a source for Au placers.

Впервые на примере щелочно-ультраосновного Гулинского массива (Полярная Сибирь) в сульфидсодержащих фоскоритах и карбонатитах, выделенных из них магнетитовых и сульфидных концентратов, проведено комплексное исследование (нейтронно-активационный, рентгенофлуоресцентный и рентгеноспектральный зондовый анализы) минеральных форм нахождения Au и Ag и распределения благородных металлов. Установлено, что сульфидные концентраты карбонатитов являются наиболее обогащенными в отношении благородных металлов ― до 2.93 ppm Pt, 61.6 ppm Au и 3.61 ppm Ag. Пирротин, джерфишерит, халькопирит и пирит — наиболее распространенные сульфиды и главные концентраторы Au и Ag. Самый поздний парагенезис, представленный халькопиритом, Ag-обогащенным джерфишеритом, ленаитом, штернбергитом и самородным серебром, содержит значимые концентрации Ag. Согласно широкому распространению калиевых сульфидов и выявленным в пирротине полифазным включениям расвумита, K-Na-Ca карбоната, карбоцернаита, стронцианита, галенита, халькопирита, штернбергита, ленаита и самородного серебра, сульфиды формировались в условиях повышенной активности K, Na, Sr, LREE, F, Cl и S. Хлор, обладающий высокой способностью к комплексообразованию с серебром, мог быть агентом переноса благородных металлов в карбонатитах. Кристаллизация ранних джерфишерит-пирротиновых ассоциаций фоскоритов и карбонатитов начиналась при температуре не менее 500°С и продолжалась до образования поздних Ag-содержащих сульфидов при температуре не более 150°C. Породы карбонатитовой серии на поздних низкотемпературных стадиях могут обогащаться Au и Ag и являться одним из источников при образовании золотоносных россыпей.

Аннотация.Установлен полистадийный генезис пирохлоровых кальцит-доломитовых карбонатитов массива Вуориярви.Эволюция состава минералов гр.пирохлора проходит с накоплением Nb и уменьшением U, Pb, согласно схемам изоморфизма: 2Ti 4+ + U 4+ ↔ 2Nb 5+ + Ca 2+ и U 4+ + вакансия ↔ 2Ca 2+ .Вторичные разновидности обогащены Ba, Sr, Th, LREE.Краевые и измененные зоны кристаллов представлены катиондефицитным и Si-обогащенным пирохлором.Обнаружены многочисленные включения фторапатита, кальцита, доломита, Sr-Ca-Ba карбонатов, бадделеита, цирконолита, ниобиевго рутила, ильменита, а также замещение цирконом и хошелагоитом.U-Pb датировки единичных зерен пирохлора из карбонатитов (SIMS, SHRIMP-II) показали дисперсию возраста от 410 до 350 млн.лет и менее, связанную с нарушением Th/U отношения в минерале за счет катионнообменных процессов и вторичных преобразований матрицы минерала.

The paper discusses specifics of gas separation techniques by means of sample crushing in vacuum, and, in particular, the stepwise crushing method for studying the sources and evolution of the fluid phase of rocks and minerals. The data on the Seblyavr massif, Kola Peninsula, are employed to demonstrate that, if the age of the minerals is old enough and they contain elevated concentrations of parental elements (U, Th, and K), in situ produced noble gas components can strongly distort the composition of the initially entrapped gases and thus result in misinterpretations of the analytical data. The application of stepwise crushing technique, as well as an individualized approach to data interpretation for each of the samples, makes it possible to solve the problem.

The first data on the composition and inner structure of zircon, one of the main ore minerals of the rare-metal metasomatites of the Gremyakha–Vyrmes alkaline-ultramafic massif, are reported. Early zircon generations are enriched in Y and REE and contain numerous inclusions of rock-forming and accessory minerals of metasomatites, as well as syngenetic fluid inclusions of calcite, thorite and thorianite. Late generations differ in the elevated Hf content and contain no inclusions. The elevated concentrations of Ca and Th in the central zones of crystals are related to the presence of numerous micron-sized inclusions of calcite and thorium phases. All zircon varieties have extremely low U and Pb contents. Concentrations and distribution patterns of incompatible and rare-earth elements in zircon from the metasomatites of the Gremyakha–Vyrmes Massif are similar to those of syenite pegmatites and magmatic carbonatites around the world. Mineral from these associations shows a positive Ce anomaly and elevated HREE contents. According to the compositions of zircon and thorite inclusion in it and experimental data on the simultaneous synthesis of these minerals, the crystallization temperature of zircon was 700–750°С. Using Ti-in-zircon temperature dependence, late zurcon was formed at temperature of 700–750°С. The rare-metal metasomatites are formed at the final stages of the massif formation, presumably after foidolites. Carbonatites could initiate metasomatic reworking of foidolites and accumulation of trace metals in them. The evolution of the primary alkaline–ultramafic melt toward the enrichment in trace elements was mainly controlled by crystallization differentiation.

The variations in the chemical composition of lamprophyllite-group minerals from a peralkaline dyke of the Mokhnatye Roga area (Kandalaksha region, Kola Peninsula), which are crystallized during the entire period of dyke formation and form several generations, have been investigated. The early generations differ in a steadily high fluorine content, while the later ones exhibit reduced amount of fluorine, impurity elements, and sodium, with a simultaneous increase in the potassium content. The crystal structure of fluorine- rich barytolamprophyllite (potentially a new representative of the lamprophyllite group, differing by the predominance of fluorine in the anion X site) has been analyzed by single crystal X-ray diffraction. This mineral is found to have a monoclinic unit cell with the following parameters: a = 19.5219(8) Å, b = 7.0915(2) Å, c = 5.3925(2) Å, β = 96.628(3)°, and sp. gr. C2/m. The structure is refined to R = 5.73% in the anisotropic approximation of the atomic displacement parameters using 3668I > 2σ(I). The idealized formula (Z = 2) is (Ba,Sr)2[Na(Na,Fe)2(Ti,Mg)F2][Ti2(Si2O7)2O2].

1125 Alkaline magmatism has been widely abundant on the territory of the Kola Peninsula with the maximal activity in the Paleozoic, when most of the alkaline– ultrabasic complexes, alkaline intrusions of the agpaitic series, and rocks of the dyke series were formed [1–3]. Paleozoic dykes of alkaline rocks were registered (1) in the Khibiny and Lovozero agpaitic massifs and their frames; (2) in the massifs of alka� line–ultrabasic rocks with carbonatite (Kovdor, Turii Mys, Vuorijarvi, Afrikanda, Kandaguba, etc.); (3) in autonomous swarms, which are not spatially related to alkaline intrusions (dykes on the coast of the Kan� dalaksha Bay, swarms of pipes and dykes of kimberlite and melilitite of the Tersk coast, etc.) [3]. A new occurrence of alkaline dyke magmatism was discovered in 2010 during the geological works per� formed by the Murmansk Geological Prospecting Expedition in the “Mokhnatye Roga” area located 55 km to the southeast of the Kovdor massif ( 67°15′ N, 31°30′ E) (Fig. 1). The “Mokhnatye Roga” area is located in the Ensk segment of the northwestern part of the Belomorian mobile belt. We performed a complete petrological and geochemical description of the sections in Holes 19 and 24, which reveal one of the largest dykes in the area. The dyke, with a length of ≈4 km and a width of ≈160 m, has an eastern orientation with steep dipping (60°–90°) to the north. The thickness of Quaternary deposits ranges from 0.8 to 4.0 m; alkaline rocks occur in the range of 4.0–93.9 m being followed by host amphibole–biotite gneiss with interbeds of plagioam� phibolite (AR2 mt) along the section. The contacts with host rocks are sharp, secant, magmatic; there are no

Carbonatites and related pyroxenites from the Seblyavr alkaline-ultramafic massif were analyzed for isotopic composition and concentrations of carbon (in carbon dioxide), nitrogen, and noble gases using the stepwise crushing technique. The C isotopic composition in crushing steps of calcite from the carbonatite varies from −6.6 to −15.0‰ (PDB) with average values from −8.5 to −10.5‰, which is lower than the mantle range for \(\delta ^{13} C_{(CO_2 )} \) (from −3 to −5‰) and can likely be explained by long-term isotopic exchange between the carbon of CO2 in inclusions and their host Ca carbonate. The 40Ar/36Ar ratios in the crushing extractions of the calcites vary from the atmospheric value of 296 to 3200. Diopside from the pyroxenite has these ratios as high as 26000–33000 (such high values for pyroxenite in the Kola alkaline-ultramafic province have been obtained for the first time), which corresponds to the values obtained for MORB chilled glasses. Nitrogen in the samples is isotopically heavy, δ15N from +1 to +2 on average, which is consistent with earlier data on carbonatite massifs in the Kola alkaline province (Dauphas and Marty, 1999) and carbonatites of the Guli Massif (Buikin et al., 2011). The N2 content in the crushing extractions is correlated with the 36Ar concentration, which is an indicator of atmospheric contamination and suggests the dominance of the crustal N component in the samples, likely as a result of subduction or penetration of the ancient meteoric water into the magma chamber or a metasomatic source. The variations in the isotopic and elemental composition of the gas components between crushing steps suggest that the investigated samples contain inclusions of at least two populations.