Research subject. The Zhaman-Koitass granite-leucogranite massif of the Borovsk complex in Northern Kazakhstan. In the platform cover of the West Siberian plate, overlying granite-leucogranites, a large uranium deposit Semizbai of sandstone type is localized. Materials and methods . Geochemical, mineralogical, and geochronological studies of granite-leucogranites were conducted by X-ray fluorescence analysis, ICP-MS, electron probe microanalysis, scanning electron microscopy, and LA-ICP-MS (Analytical Center for multi-elemental and isotope research SB RAS). Results and conclusions . The Zhaman-Koitass massif is composed by A-type subalkaline leucogranites (SiO 2 = 72.8–75.4 wt %, Na 2 O + K 2 O = 7.5–8.8 wt %, K 2 O/Na 2 O = 1.11–1.25, ∑REE = 120–231 ppm, (La/Yb)n = 10–22, Eu/Eu* = 0.2–0.4), which are characterized by titanite-ilmenite-magnetite accessory specialization. U-Pb isotope dating confirms the silurian age of the Zhaman-Koitass granite-leucogranites (426–420 Ma). The obtained geochronological data, along with the similarity of the chemical composition of the rocks, confirm that the granite-leucogranites of the Zhaman-Koitass massif belong to the Borovsk complex. The significant age interval between the ordovician granitoids of the krykkuduk complex (448 ± 2 Ma) and the silurian granite-leucogranites of the karabulak and borovsk complexes considered in the article (431–426 Ma) suggests a change in the geodynamic situation from suprasubduction to transform marginal-continental.

The study is focused on metapelitic granulites of Cape Kaltygei (Western Baikal region) that contain a diagnostic mineral assemblage of ultrahigh temperature (UHT) metamorphic rocks (orthopyroxene+sillimanite+quartz). The pseudosection-based thermobarometry yields peak metamorphic temperature and pressure values (T=950 °C, P=~9 kbar) and suggests near-isobaric cooling (IBC) conditions during the retrograde evolution of the granulites. The U/Pb zircon age estimates for metamorphism (~1.87 Ga) support the data published by other researchers. The SHRIMP-II U-Pb dating of zircon cores yields a minimum protolith age of 1.94–1.91 Ga. Biotites and amphiboles from granulites of Cape Kaltygei show the 40Ar/39Ar isotopic ages that are close to the Early Paleozoic accretion-collision system of the Western Baikal region.

The oceanic stage in the history of the South Urals completed in the Ordovician – Early Silurian. The Ordovician through Devonian events in the region included the formation of an island arc in the East Ural zone from the Middle Ordovician to Silurian; westward motion of the subduction zone in the Late Silurian – Early Devonian and the origin of a trench along the Main Ural Fault and the Uraltau Uplift; volcanic eruptions and intrusions in the Magnitogorsk island arc system in the Devonian. The Middle-Late Paleozoic geodynamic evolution of uralides and altaides consisted in successive alternation of subduction and collisional settings at the continent-ocean transition. The greatest portion of volcanism in the major Magnitogorsk zone was associated with subduction and correlated in age and patterns of massive sulfide mineralization (VMS) with Early – Middle Devonian ore-forming events in Rudny Altai. Within-plate volcanism at the onset of volcanic cycles records the Early (D 1 e 2 ) and Middle (D 2 ef 2 ) Devonian slab break off. The volcanic cycles produced, respectively, the Buribay and Upper Tanalyk complexes with VMS mineralization in the Late Emsian; the Karamalytash complex and its age equivalents in the Late Eifelian – Early Givetian, as well as the lower Ulutau Formation in the Givetian. Slab break off in the Late Devonian – Early Carboniferous obstructed the Magnitogorsk island arc and supported asthenospheric diapirism. A new subduction zone dipping westward and the Aleksandrovka island arc formed in the Late Devonian – Early Carboniferous. The Early Carboniferous collision and another event of obstructed subduction led to a transform margin setting corresponding to postcollisional relative sliding of plates that produced another slab tear. Postcollisional magmatism appears as alkaline gabbro-granitic intrusives with related rich Ti-magnetite mineralization (C 1 ). Transform faulting persisted in the Middle Carboniferous through Permian, when the continent of Eurasia completed its consolidation. The respective metallogenic events included formation of Cu-Ni picritic dolerites (C 2–3 ), as well as large-scale gold and Mo-W deposits in granites (P 1–2 ).

На основе реконструкции термической эволюции гнейсогранитного массива Шонгчай (Северный Вьетнам) обосновано длительное существование гранитоидной магмы на глубинных уровнях земной коры ( H = 15-20 км, Δ t ~ 20÷50 млн лет). Геодинамический анализ и математическое моделирование истории консолидации и остывания гранитоидного батолита показывает, что эта магматическая камера представляла собой термоловушку на нижнем уровне земной коры, длительное время сохранявшую остаточный гранитный расплав. Выведение этой термоловушки из квазистационарного состояния происходит в зонах трансформного скольжения литосферных плит и сопровождается тектоническим экспонированием крупных сегментов земной коры. В конечном итоге это приводит к трансформации батолитов в комплекс метаморфического ядра кордильерского типа, внедрению остаточных расплавов и, как следствие - к формированию промышленных редкометалльных месторождений.

Research subject. The Novo-Akhmirovskoe lithium-bearing deposit in the East Kazakhstan region, which is represented by an intrusive layer of topaz-zinnwaldite granites, is located within of the Kalba-Narym-Koktogai lithium-tantalum raremetal-granite belt. Being part of the Altai collision system, this belt is considered unique in terms of its length (more than 1000 km). Ores in the Novo-Akhmirovskoe deposit are represented by massive to low porphyry leucocratic granites composed of quartz (30–40%), albite (25–40%), microcline (15–35%), lithium mica varying in composition from zinnwal dite to lepidolite (up to 10%) and topaz (up to 5%). According preliminary estimates, the Novo-Akhmirov deposit is factually a poor lithium deposit with the Li2O content of 0.2–0.4 wt % and the estimated Li2O reserves of 110 thousand tones. Despite the favourable infrastructure and close proximity of this stock to Ust-Kamenogorsk mining and chemical-metallurgical enterprises, its ore-generating potential has not been sufficiently studied.Materials and Methods. In this research, we obtained new data on the geological structure, age, mineral composition and formation conditions of topaz-zinnwaldite granites in the Novo-Akhmirovskoe deposit. In addition, a comparative analysis of these ores with the topaz-biotite granites of the Black Sopka massif (0.6–0.7 wt % Li2O in protolitionite) and spodumene granite porphyries of the Alakha stock (Li2O = 0.9–1.1 wt %) was conducted. Results and Discussion. It is concluded that the development of this unique nonpegmatite lithium-bearing deposit requires deep exploratory drilling, mineralogical and technological research of core samples and reconsideration of economic efficiency parameters.

—The Kalguty Mo–W ore-magmatic system (OMS) is a granite batholith (S = 70 km2, V = 12,800 km3 at the recent denudation level, according to geological and geophysical data). This batholith is cut by the East Kalguty belt of rare-metal ongonite–elvan dikes spatially and temporally associated with the East Kalguty quartz-vein–greisen Mo–W deposit. Geological and petrogenetic studies along with published and our new results of geochronological (U/Pb zircon, Re/Os molybdenite, and 40Ar/39Ar biotite and muscovite) dating made it possible to reconstruct the thermochronological history of the Kalguty OMS. Five stages have been recognized: I (215 ± 1 Ma)—formation of granites of major intrusive phase and of Mo-rich mineralization, which is an orebody called the Molybdenum stock; II (206 ± 1 Ma)—formation of leucogranite and intragranitic-pegmatite stocks in the granites of major intrusive phase; III (202 ± 1 Ma)—formation of most of ongonite–elvan dikes composing a dike belt; IV (195 ± 1 Ma)—formation of long ultrarare-metal ongonite–elvan dikes in the central part of the dike belt, which is spatially associated with the W-rich veins of the deposit; and V (181 ± 1 Ma)—formation of thin ongonite–elvan dikes on the periphery of the dike belt. The recognized age stages of the Kalguty Mo–W ore-magmatic system were mathematically tested based on the model of crystallization differentiation and the dynamics of heat and mass transfer in the magma chamber corresponding to the Kalguty granite batholith. The results obtained show that the formation of a granite batholith (215 ± 1 Ma) and a later ongonite–elvan dike complex with Mo–W-rich mineralization (195 ± 1 Ma) can be explained only by a two-level ore-magmatic system with the “upper” granite batholith at a depth of 5–15 km and the “lower” granite chamber at a depth of 20–31 km. The total duration of ore-magmatic processes is 20 Myr (ore production stage) or 30 Myr, if we take into account occasional elvan dikes with poor quartz–fluorite–barite–ferberite mineralization (181 ± 1 Ma) on the periphery of the Kalguty deposit.

Based on reconstruction of the thermal evolution of the Song-Chai gneiss–granite massif (Northern Vietnam), the long-term occurrence of granitoid magma at deep levels of the Earth’s crust (H = 15–20 km, Δt ~ 20–50 Ma) is established. The geodynamic analysis and mathematical modeling of the history of consolidation and cooling of the granitoid batholith shows that the magmatic chamber was a thermal trap at the lower level of the Earth’s crust, preserving the residual granite melt for a long time. The removal of this thermal trap from the quasi-stationary state occurs in the zones of transform sliding of lithospheric plates and is accompanied by tectonic exposure of large segments of the Earth’s crust. Ultimately, this leads to transformation of the batholiths into a metamorphic core complex of the Cordilleran-type, to emplacement of residual melts, and, consequently, to the formation of commercial rare-metal deposits.

This paper is a review of the saline endorheic lakes of the Northern Kazakhstan, with the provided data on chemical composition of their waters and sediments, diversity/uniformity, mineral precipitation sequences and brine evolution. Study saline lakes are located in the Ishim steppe geographical unit of the southern Western Siberia and are ancient closed basins. The lakes are of Cl-Na and Cl-Na-Mg chemical types (the most saline Zhalauly lake (428 g/L) is Cl-Mg type), their pH values vary from 6.0 (Kalibek lake) to 9.1 (Shureksor Lake). The common trend for the lakes chemical state is a low calcium concentration with high values of sodium, i.e. calcium < magnesium < sodium (with three exceptions). The Na/Cl, Cl/SO4 and Mg/Ca ratios were calculated for the solutions from the lakes in order to reveal their primary trends of geochemical evolution. The geochemical indexes of enrichment and pollution (EF and I-geo) of the bottom sediments show that enrichment is low or absent in comparison with the geochemical background for the lakes of Western Siberia. We imply four main stages of lake evolution indicated by precipitation of different secondary minerals: calcite and Mg-carbonates, gypsum, halite, thenardite and bischofite. We suggest the onset of crystallization of each mineral as a tipping point of the water evolution that resulted in the complete removal of a certain chemical element consistent with the solubility constant of corresponding mineral.

The article presents an event correlation of the Permian‐Triassic granites of the Altai collision system, which are associated with industrial ore deposits and occurrences (Mo‐W, Sn‐W, Li‐Ta‐Be). The multi‐system and multi‐mineral isotope datings of igneous rocks and ore bodies (U/Pb, Re/Os, Rb/Sr, Ar/Ar‐methods) suggest the postcollisional (intraplate) formation of ore‐magmatic systems (OMS), the duration of which depended on the crustmantle interaction and the rates of tectonic exposure of geoblocks to the upper crustal levels.Two cases of the OMS thermal history are described: (1) Kalguty Mo‐W deposit associated with rare‐metal granite‐leucogranites and ongonite‐ elvan dykes, and (2) Novo‐Akhmirov Li‐Ta deposit represented by topaz‐zinnwaldite granites and the contemporary lamprophyre and ongonit‐elvan dykes. For these geological objects, numerical modeling was carried out. The proposed models show thermal cooling of the deep magmatic chambers of granite composition, resulting in the residual foci of rare‐metal‐granite melts, which are known as the petrological indicators of industrial ore deposits (Mo‐W, Sn‐W, Li‐Ta‐Be). According to the simulation results concerning the framework of a closed magmatic system with a complex multistage development history, the magmatic chamber has a lower underlying observable massif and a reservoir associated with it. A long‐term magmatic differentiation of the parental melt (a source of rare‐metal‐granite melts and ore hydrothermal fluids) takes place in this reservoir.

We consider two examples of systems in which imposed external constraints push the underlying stochastic process to a very improbable large deviations possessing the anomalous statistics. In the first example we consider the fluctuations of a two-dimensional random walk above a semicircle or a triangle in a special regime of elongated trajectories. The second example deals with a two-dimensional biased random walk along a channel with inaccessible voids of circular and triangular shapes. In both cases, the typical span of the stochastic trajectory above the tip of the semicircle shares the Kardar-Parisi-Zhang scaling with the critical exponent $nu=frac{1}{3}$, while is constant above the triangle. We provide simple scaling arguments justified by the conformal approach. For practical purposes, our results demonstrate that the geometry has a crucial impact on the width of the boundary layer in which the diffusive mixing of laminar flow lines takes place.

The paper presents new original data and a review of previous studies on the Late Carboniferous - Early Permian granitoids of the Kunush and Kalguty intrusive complexes from the Kalba fold belt (East Kazakhstan). These rocks formed at the initial post-collisional stage of the Irtish-Zaisan orogen in the western Central Asian Orogenic Belt (CAOB). The granitoids form isometric or NW linear intrusions inside the Late Devonian - Early Carboniferous metasediments which overlap the accretionary lithology of the Kalba fold belt in front of the Altai active margin of the Siberian continent. These granitoids contain zircon grains with U-Pb ages of ca.308-291 Ma, synchronous with the peak post-orogenic magmatic event at similar to 300 Ma in the CAOB. The Kunush high-Na granitoids, with high SiO2 (67-72%) and Al2O3 (15-18%) contents and the Na2O/K2O ratio (1.94-6.43), and low HREEs (Yb = 0.22-0.93 ppm) but moderate Sr/Y ratios (47-179), Mg# (35-55) and Ni, Cr, are generally common to high-Al TTG-series with non-subduction geochemical signatures. The Kalguty granitoids mostly belong to calc-alkalic to subalkalic high-K series, have non-corundum CIPW-norm compositions and mainly weakly peraluminous (ASI = 0.97-1.09) characteristics. Their Fe* = 0.7-1 at 62-74 wt.% SiO2 and relatively high Y/Nb (2-4) and Rb/Nb (9-18) ratios are similar to transitional compositions reported for fractionated I- and A(z)-type post-orogenic granites worldwide. The Kunush high-Na and Kalguty high-K granitoids formed at different depths in the crust and the parent melts were derived from metabasaltic (MORB; P = 10-15 kbar) and metagranitic (TTG-like; P < 10 kbar) protoliths, respectively. We propose that relaxation of tangential compression after oblique collision and the following thermal impact of mafic magma that acted simultaneously at different crustal depths, along with decompressional partial melting, may be a basic petrological scenario for synchronous formation of geochemically different granitoids.

Forms of occurrence of platinum (sperrilite, moncheite) and palladium (Sb-michenerite, Pd–Bi phase) minerals in intrusive rocks of the Khudolaz differentiated complex have been studied. Platinum minerals were identified in disseminated Cu–Ni sulfide ores from ultramafic olivine–hornblende rocks of the Khudolaz complex, whereas palladium minerals were found in ores from olivine–hornblende gabbroids. The structural arrangement of grains as inclusions in sulfides of the primary magmatic association testifies that they were formed as a result of segregation of platinum group elements, which partitioned into the composition of sulfides during low-temperature mineral formation process at the late-magmatic stage.

Hydrochemical analysis of the high-salinity lakes in the Ishim Plain (>250–300 g/L) located at the border with the Northern Kazakhstan uranium ore province is performed. The studies have shown that the main factor of concentration and redistribution of uranium in the lake basins of the Ishim Plain are the processes of intense salt deflation causing sanding of lakes and uranium depletion in the near-surface layer of the bottom deposits. The correlation between the hydroxide forms of uranium binding in the bottom lacustrine deposits of the Ishim Plain and the coffinite composition of the Semizbai deposit makes it possible to consider this province to be promising for the discovery of hydromineral uranium deposits.

Overall petrologic and geochemical data indicate that the early Paleozoic magmatism in the Olkhon area of the Baikal Region exhibits diverse types of granitoids, whose time of formation is estimated at a narrow age interval of 500-465 Ma. This magmatism was responsible for the formation of both autochthonous gneiss-migmatite-granitoid suites (Sharanur complex) and multiphase intrusions (Aya complex) emplaced into the upper horizons of the continental crust. In major-element chemistry, K2O/Na2O values, and rare-element composition the migmatite-plagiogranites and calc-alkaline and subalkalime granitoids of the Sharanur complex are similar to the host gneisses and schists, as they were likely derived from melting of the ancient metamorphic substratum of the Olkhon series. In new isotope-geochemical characteristics (ICP MS method) the Sharanur granitoids are close to the first-phase biotite granites of the Aya massif, whose further geochemical evolution was governed mainly by intrachamber magmatic differentiation leading to the production of second-phase leucogranites enriched in HREE and HFSE (in particular, Ta and Nb) and depleted in Sr, Ba, Eu, Li, and LREE. The origin of the autochthonous and intrusive granitoids is related to early Paleozoic collision events within the Olkhon metamorphic terrane, while the formation of syncollisional granitoids is best explained by both melting of the crust protolith (Sharanur complex) and magmatic differentiation (multiphase Aya intrusion). All mineralogical and geochemical characteristics indicate that these granitoids are distinguished from rare-metal pegmatoid granites and Li-F and Rb-Be-Nb pegmatites, whose vein bodies crosscut the granitoids, and are regarded as middle Paleozoic rocks, which mark the transition to within-plate magmatism in the Baikal Region. (C) 2018, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All right reserved.