V. I. Alekseev

Wolframoixiolite and niobian ferberite from zinnwaldite granitic rocks of the Chukchi Peninsula

The finding of wolframoixiolite with inclusions of niobian ferberite is described from zinnwaldite granite and ongonite of the Severny pluton of the Chukchi Peninsula. The optical, morphological, and chemical properties of minerals are characterized and compared with their analogues from other regions. The petrologic and mineragenic index implications of the minerals are discussed with allowance for our contemporary mineralogical knowledge on W-bearing Ta-Nb minerals.

Accessory mineralization of rocks from Late Cretaceous intrusive series with Li–F granites in the Far East

Accessory mineralization of the Late Cretaceous intrusive series in the Far East was investigated on the basis of published data and the author’s original evidence. The composition of accessory minerals from leucogranite, monzonitoid rocks, and Li–F granites has been established. The trend in the evolution of Late Cretaceous granitoids is characterized by an increase in the mineral-forming role of iron and rare elements. Diverse accessory minerals and their typomorphic assemblages have been identified for Li–F granites and ongonites. The regional specificity of accessory mineralization in rare-metal granites consists in the leading role of the minerals W, Ta, Nb, Bi, Y, REE, and As. The uniformity of mineral species and mineral assemblages and the typomorphism and evolution of accessory minerals are inherent to the Far East belt of Li–F granites.

Evolution of zircons from postorogenic intrusive series with Li-F granites, Russian Far East

The paper discusses the morphology, anatomy, and geochemistry of zircons from granitic rocks of postorogenic intrusive series with Li-F granites in the Russian Far East. The multiphase Upper Urmi pluton in the Amur region and the Severny pluton in the Chukchi Peninsula have been chosen as reference objects. The directed variations of zircon morphology and geochemistry in the history of Pacific postorogenic granitic magmatism reflect decrease in depth of magma generation and crystallization temperature along with an increase in alkalinity, fluid saturation, and rare-metal potential of granitic melts.

Composition and evolution of accessory mineralization of Li–F granites in the Far East as indicators of their ore potential

The ore potential of Pacific Li–F granites is considered on the basis of original and published data on composition of these granites and related metasomatic rocks in the Badzhal (Amur region) and Kuiviveem–Pyrkakai (Chukchi Peninsula) ore districts. The accessory mineralization in rare-metal granites is compared with that in W–Sn deposits. The main features in evolution of magmatic and hydrothermal mineralization are pointed out. A conclusion on the similarity between mineralization of the zwitter–tourmalinite type and accessory minerals in Li–F granites is drawn. It is established that magmatic and hydrothermal types of mineralization belong to the same evolutionary sequence. Genetic links between Li–F granites and the large ore deposits in the East Asian tungsten–tin zone are suggested.

U-Pb age of zircon and the history of impact transformations of the Chelyabinsk meteorite

586 The fall of the Chelyabinsk meteorite LL5 (Febru ary 15, 2013), the largest in the past century, caused a wide resonance in the scientific world and initiated the complex investigation of meteorite material. The results of such study have been reported in many pub lications ([1, 2] and others). In discussing the results of the isotope–geochemical study of this meteorite, we should primarily mention the local U–Pb dating of apatite in situ, which was performed independently by X. H. Li in Beijing, China (4452 ± 21 Ma [2]) and by K. Terada in Hiroshima, Japan (4433 ± 110 Ma [3]). Both ages are consistent within the error and, in opin ion of the authors [2, 3], correspond to the largest impact event which was registered by apatite in other meteorites as well (e.g., Novato L6 [4]) and highly likely this impact event was connected with the forma tion of the Moon. The older age (4538 ± 2 Ma) obtained by A. Bouvier [5] who used the isochron method for leached meteorite glass is correlated by the author with the impact event, rather than with cooling of the parental body of the meteorite after its forma tion. Based on the results of the study of rock forming minerals (olivine, orthopyroxene, and troilite) of the Chelyabinsk meteorite, the Sm–Nd isochron with an age of 3733 ± 110 Ma was plotted [6]. This is the age of an impact event, which resulted in melting of meteor ite material and re equilibration of the Sm–Nd iso tope system. Independent dating of the meteorite by the Sm–Nd method at the Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sci ences, was not performed for monomineral samples and did not provide a precise isochronous depen dence. A linear trend (“geochron”) corresponding to an age of ~290 Ma was obtained [1]. The age of frag mentation of the parental body of the Chelyabinsk meteorite (the age of exposure) was estimated by the concentration of cosmogenic nuclides as ~1.2 Ma [7].

Allanite-(Y) in areas of ongonite magmatism in the Far East: Isomorphism and petrogenetic implications

The research history of allanite-(Y) has been considered. The composition and genesis of this mineral is discussed with allowance for new findings in Li-F granites of the Russian Far East. Compositional anomalies in allanite-(Y) reflect the metastable character of its structure. Types of zoning and trends in the chemical substitution of major components are described. Two crystal chemical modes of allanite-(Y) formation and the two-step isomorphism of its components are suggested. The main tendencies in the chemical evolution of allanite-(Ce) and allanite-(Y) in granitic rocks of the Far East are pointed out. Allanite-(Y) is formed in the anomalous geochemical setting that characterizes crystallization of fluid-saturated subalkaline granitic melt and is regarded as an index mineral of rare-metal ongonite magmatism completing the Late Cretaceous Pacific Orogeny.

First data on chemical composition of zircon from lithium-fluorine granite of the Severnyi pluton, Chukchi Peninsula

The chemical composition of zircons from lithium-fluorine granite of the Severny pluton in the Chaun region, Chukchi Peninsula, has been studied. The magmatic origin of zircons has been established. Elevated LREE, Li, and Nb contents; moderate enrichment in Hf; and deep Eu anomalies are characteristic of zircons from rare-metal granite. The contents and distribution of chemical elements in studied zircons differ from those of biotite granite. Zircons from lithium-fluorine granite of the Severny pluton also differ from the worldwide analogs in moderate Hf, Y, and REE concentrations and extremely low contents of U, Th, and other incompatible elements.

Structural and chemical heterogeneity of natural crystals and microgeochemical line of research in ontogeny of minerals

A review of the current state of genetic mineralogy in the field of the chemical heterogeneity of mineral individuals is presented. Due to advances in the local analysis of matter, the ontogenetic approach is now being focused on the chemical anatomy of minerals. A new line of research, microgeochemistry, deals with the migration of chemical elements in natural crystals caused by defects in the crystal lattice. It becomes evident that structural and chemical heterogeneity is an intrinsic property of mineral individuals. Phenomenological laws of this heterogeneity and the interaction of atoms with lattice defects are stated.

Zircon geochemistry and U–Pb age at rare metal deposits of syenite in the Ukrainian Shield

The distribution of rare and rare earth elements in zircon at the Yastrebets, Azov (Zr–REE–Y), and Perzhan (Be) rare metal deposits of the Ukrainian Shield was studied. Additional evidence for magmatic genesis of these deposits is obtained: unaltered zircon is characterized by a magmatic REE distribution spectrum with a somewhat higher δ18O value than that of the mantle (6.6‰ on average). The final formation stage of the deposit was marked by predominance of fluids enriched in Y, REE, Nb, and heavy oxygen, resulting in anomalous geochemical characteristics of zircon rims and alteration zones (up to 81500 Y ppm, over 10300 ppm Nb, and 13.9‰ δ18O). The age of zircon formed in ore-bearing Yastrebets and Azov nonnepheline syenite deposits was estimated at ~1770 Ma (U–Pb, SHRIMP-II).

Pegmatoid schlieren with tourmaline in granitoids of eastern russia as an attribute of intrusive series completed by ore-bearing Li-F granites

Tourmaline schlieren in pegmatoids and host granites are widespread in Cretaceous granitoid plutons occurring in tin districts of eastern Russia. These schlieren were formed under the action of fluoricboron fluids, which are considered to be forerunners of rare-metal granite magmatism. The tourmaline schlieren in adamellites, biotite, and two-mica granites are reliable attributes of intrusive series completed by emplacement of ore-bearing Li-F granites.