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Origin of abundant alkaline and related lamproite massifs and dykes in Aldan shield have no explanation and the geochemistry of rocks and their xenocrysts is used for the explanation. Bulk-rock geochemistry, mineral chemistry data of the Kayla lamproites of Russia and mineral chemical data (trace and rare elements) of the mantle xenocrysts found in these lamproites was studied using ICP MS and electron microprobe analyses (EPMA). The trace element spectrum of Kayla tuffs and breccias show the similarity with the olivine lamproites and belong to the orogenic type according to Th–U–Nb systematics. Primitive mantle normalized trace element (TRE) spider diagrams show right-leaning patterns with the peaks in large ion lithophile elements Sr, Pb, U, and troughs in Ta, Nb suggesting melting of original peridotites mixed with the ancient EMI (according to Nd, Sr isotopes) source probably belonging to eclogites or lower crust. The age of the emplacement is 132–134 Ma, similar to the Chompolo lamprophyres and many other alkaline Aldan complexes. Thermo-barometric estimation from Cr-diopsides and chromites xenocrysts suggest the origin from the spinel-garnet transition in the lithospheric mantle region. The P–T estimates derived from low-Cr-clinopyroxene xenocrysts, and related to lamproites show a high heat flow of 90 mW/m2 due to interaction with the plume-related magma. The Cr-diopsides and chromites give 45 mW/m2 geotherm similar to regional heat flow. The chondrite normalized rare earth element (REE) pattern for chrome-diopsides is steeper, compared to the low-chrome varieties. Primitive mantle normalized spidergram of Cr-diopsides displays peaks for Sr, U, and Th, and deep troughs of Nd, Nb, Ta. REE. The trace element spider diagrams of both types of xenocrysts show that they were equilibrated with the lamproitic melts and reconstructed parental melts of low-Cr-clinopyroxene coincides with the lamproite spectrums. [ABSTRACT FROM AUTHOR]

• Some Fe-oxide grains crystallized from silicate melt were incorporated into downward percolated sulfide liquid. • Fe-oxide in massive ores crystallized from the sulfide liquid pool mingled with the downward percolated sulfide liquid. • Downward percolation of sulfide liquid is crucial in the formation of the net-textured and massive ores. The mineralogy and chemical composition of magnetite and chromite series (simplified as magnetite) can provide valuable insights into the formation processes of magmatic Ni-Cu-(PGE) sulfide deposits. Previous studies mainly focus on magnetite in disseminated ores and massive ores, but very little is known about the magnetite in net-textured ores. In this study, magnetite in net-textured ores (type 1 magnetite) and massive ores (type 2 magnetite) from the Zhdanov Ni-Cu-(PGE) deposit in the Pechenga ore field, were recognized and analyzed using scanning electron microscope (SEM), electron probe microanalysis (EPMA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Both the type 1 and type 2 magnetite grains show zoned textures with Cr concentration decreasing from the core to the rim. Type 1 magnetite has higher Al and Mg concentrations than type 2 magnetite. These observations indicate that type 1 and type 2 magnetite crystallized from and record the solidification process of silicate melt and sulfide liquid, respectively. Type 1 magnetite within sulfides of net-textured ores has identical chemical composition to that within silicates, which suggests that the chemical composition of magnetite is not significantly affected by sub-solidus re-equilibrium with sulfide minerals. It also suggests that the type 1 magnetite within sulfides was incorporated into sulfide liquid later during the downward percolation of sulfide liquid through the magnetite-bearing olivine crystal mush. On the other hand, type 2 magnetite has comparable concentrations of W, Sc, Ga, Cr, Mo, and Mn to the type 1 magnetite. Such compositional similarity can be explained by the crystallization of type 2 magnetite from the sulfide liquid pool that have been mingled with the downward percolated sulfide liquid. Accordingly, the downward percolation of sulfide liquid plays an important role in the formation of net-textured ores and massive ores in the Zhdanov deposit. [ABSTRACT FROM AUTHOR]

The paper presents petrochemical, geochemical, and mineralogical data on rocks of the phoscorite–carbonatite complex in the Kovdor alkaline–ultramafic massif, Kola Peninsula, Russia. In contrast to what is usually thought, trace elements were determined to be concentrated not in the carbonatites themselves but in the related phoscorites. The paper presents data on the evolution of the compositions and zoning of minerals in successive generations of both rock types as a result of the fractional crystallization of their parental magmas, and data on general trends in the concentrations of trace elements. The Fe-rich phosphate–carbonate melt seems to have separated from the primitive alkaline–ultramafic silicate melt during its advanced differentiation. The Fe-rich phosphate–carbonate magma was parental for the phoscorite–carbonatite complex. The possibility of its splitting into immiscible Fe-rich phosphate and carbonatite melts is discussed. [ABSTRACT FROM AUTHOR]

The article presents a study which focuses on the genesis of ultramafite rock complexes in the basement of West Siberian Platform. The study was conducted to the complexes of the ultramafite which is divided into two groups, wherein the first group is characterized by complete serpentinization and the second group which is represented by peridotites that contains chromites, olivines, and orthopyroxenes. The study used chromium (Cr)/ aluminum (Al) ratios in chromespinelides to determine the depletion degree of ultramafites. Results of the study show that there are two types of ultramafite complexes in the area.

• Complex Zr-Hf-Nb-Ta-REE-Ga mineralization in coals of the Kuznetsk Basin (Russia). • Oxides of Fe, Ti, Nb, Zr, Ta, carbonates, and phosphates represent the ore matter. • Ore is associated with volcanogenic pyroclastics of pantellerite composition. The research describes the detailed mineralogical and geochemical characteristics of rare-metal Nb-Ta-Zr-Hf-Y-REE-Ga ores found in Permian coals in the layer XI in the south of the Kuznetsk Basin. The concentrations and distribution of ore, and related elements, were studied in the coal seam section and along the seam strike. Spatial and genetic relationships of the mineralization in the coal were found to be related to the presence of an altered volcanogenic pyroclastic horizon of REE-enriched pantellerite composition. The highest concentrations of basic ore elements in the coal are associated with the contact zones above and below the volcanogenic horizon. The ore matter is mainly concentrated in the fine mineral phases, composed mainly of Zr-Nb-Ti-Fe oxides, fine zircons, rare-earth carbonates (bastnesite) and phosphates (monazite, xenotime, goyacite). Resource estimates are made of the rare metals. Confirmation of the connection between the complex rare-metal mineralization and the alkaline volcanogenic pyroclastics significantly expands the prospects of revealing further such mineralization in the coals of East and Central Asia. [ABSTRACT FROM AUTHOR]