Tomtor Massif Research Articles

RELATION BETWEEN δ13С, δ18О AND REE CONTENT IN CARBONATITES OF THE TOMTOR COMPLEX, SAKHA REPUBLIC (YAKUTIA)

The paper reports the comprehensive study of phosphorus-rare metal (polymineral) carbonatites (I) and rare metal (ankerite) carbonatites (II) of the Tomtor massif based on ICP-MS, XRF, XRF-SI, SEM methods and isotope determination of C, O and 86Sr/87Sr. With a similar mineral composition, the REE+Y content in carbonatites (I) averages 0.38 wt. %, and in carbonatites (II) it is 1.3 wt. %. The δ18О-δ13С diagram provides the C and O isotopic compositions of carbonatites (I) and (II) as two intersecting trends: (I) carbonates from wells 4041, 6151, 115-117 represent the secondary generation of carbonates derived with the deuterium fluid involved; (II) depicts transformation of carbonate by low-T fluid, with fluid/rock ratio = 5. The study identified an increase in the REE and δ18O contents in carbonatites as the temperature of their formation decreases and enrichment of rocks with REE minerals, associated with REE mobility reduction in the fluid while the temperature is decreasing.

PROSPECTS AND PROBLEMS OF DEVELOPMENT OF THE RAW MATERIAL BASE OF SUFFICIENT STRATEGIC TYPES OF SOLID MINERAL RESOURCES OF SIBERIA

The analysis of the state of the mineral resource base of strategic types of solid minerals in Russia in general and in Siberia in particular has been carried out. Particular attention is paid to the prospects for the development of the resource base of lithium, rare earth metals, ordinary and impact diamonds in Siberia. The characteristics of a number of deposits and options for their development were assessed, taking into account the quality of ores, geographical location, the state of the infrastructure and the level of development of technologies for ore dressing and obtaining end products. The prospects for the development of the raw material base of niobium and rare earth metals within the Tomtor massif and the territory of the Udzha uplift as a whole are assessed. Summary results of long-term regional field and laboratory studies of the distribution and compositional variations of Cr-pyrope garnet, the most informative of the set of indicator minerals for determining the potential diamond content of kimberlites, selected from uneven-aged intermediate reservoirs of the Siberian Platform, are presented. Based on these results, areas within the platform were identified with signs of the presence of new fields of potentially diamond-bearing kimberlites of the Middle Paleozoic age. A mineralogical description and assessment of the technological characteristics of impact diamonds from the Popigai astrobleme and from the ejection zone in its frame is given. The prospects of creating a new large area of the extractive industry on the raw material base of strategic materials in the territory of the Lena-Khatanga interfluve are substantiated

Mineralogical and Geochemical Evidence of Paragenetic Unity of Igneous Silicate and Carbonatite Rocks of the Tomtor Massif in the North-East of the Siberian Platform

The Tomtor massif is a polychronous ring zonal complex of alkaline ultramafic and carbonatite rocks containing unique Nb and REE deposits. Mineralogical and geochemical studies of minerals from different types of silicate rocks and carbonatites of the Tomtor massif were performed. For excluding traces of the interaction between silicate and carbonatite melts, we limited ourselves to the study of independent small secant bodies located in the immediate vicinity of the massif itself. The presence of through mineral series in various silicate igneous rocks and carbonatite ores of high-titanium chromium spinels, rare-metal, ore and other exotic phases with similar compositional trends was defined. Such studies will help reveal the mineralogical criteria for the genetic relationship between silicate melts and associated carbonatite derivatives, which can form rich rare elements mineralization. Also, such studies help to improve the petrochemical and mineralogical criteria for dividing potentially diamond-bearing magmatites (typical kimberlites) from non-diamond-bearing kimberlites, alpicrites and other non-diamond-bearing rocks convergent to kimberlites, which are formed under different physicochemical conditions. The existence of polychronous complex ore–magmatic ring complexes, such as the Tomtor massif, indicates the existence of large deep intraplate magma-generating chambers in the lithospheric mantle.

Typomorphic features of magnetite from tomtor massif camaphorites

Background. The paper presents new data on the material composition and formation conditions of apatite-magnetite rocks (phoscorite and camaphorites) from the Onkuchakh deposit within the Tomtor massif drawing on the study into the typomorphic features of magnetite.Aim. To study the morphology, chemical composition, and relations of magnetite with associated minerals in apatite-magnetite rocks from the Onkuchakh deposit (Tomtor massif).Materials and methods. The study employed core samples measuring 177 m in total length (borehole No. 801, Onkuchakh field, Tomtor massif). In order to determine the composition of recovered minerals, the following instruments were used: JEOL JXA-8230 Electron Probe Microanalyzer (ALROSA, Mirny, Russia); TESCAN MIRA 3 LMU field emission scanning electron microscope equipped with an Oxford Instruments INCA Energy 450+ energy dispersive spectrometer with an XMax-80 detector (ALROSA, Mirny; V. S. Sobolev Institute of Geology and Mineralogy, SB RAS). The measurements were performed according to a standard procedure: accelerating voltage — 20 kV; current — 1 nA; counting time — from 60 s; probe size — 2 μm. Instrument calibration was carried out using a set of characterized artificial compounds and natural minerals; instrument stability was confirmed by measuring Co line intensity.Results. The authors identified the textural and structural features of magnetite ores, as well as ascertaining their relations with the areas of camaphorites characterized by different material composition and host rocks. The impact of superimposed hydrothermal processes was determined. In addition, a detailed morphological characterization was provided for magnetite found to comprise two generations: primary magmatic magnetite and that transformed under the influence of superimposed processes. Finally, representative data on the chemical composition of magnetite were obtained.Conclusion. It is concluded that magnetite is formed through a magmatic process involving crystallization differentiation. The occurrence of noble metal is shown to be related to hydrothermal processes superimposed on magnetite ores. The role of apatite-magnetite ores in the formation of the supergene complex — ferrous phosphate lateritic weathering crusts of the Tomtor massif — is confirmed. It is recommended to consider camaphorites from the Tomtor massif as naturally alloyed iron ores potentially extracted along with a number of valuable components.

Mineralogical Criteria for Genetic Relationship of Igneous and Carbonatite Rocks of the Tomtor Massif (Siberian Platform)

The Tomtor massif, located in the north-east of the Siberian Platform, is a polychronous zonal-ring complex of alkaline ultrabasic rocks and carbonatites containing a unique deposit of Nb and REE. A comparative analysis of the typomorphic features of minerals of different types of silicate rocks and carbonatites of the Tomtor massif is given in order to establish their convergent features. In order to exclude the mutual influence of rocks formed at different times on each other, samples were taken from different dispersed independent pipe-like bodies of melteigites, a sheet body of alkaline picrites and a transverse dike of carbonatite located south of the Tomtor massif, as well as from alkaline syenites from the southern margin of the massif. It is shown that interesting convergent features are identified in the rock-forming and accessory minerals, including rare-metal ore minerals of different silicate igneous rocks and carbonatite formations. Rock-forming minerals - pyroxenes, micas, feldspars, feldspathopids, garnets, as well as basic and rare carbonates, oxide ore minerals, including Cr-containing spinelides, and sulfide and other exotic phases have such features. The confirmation of the convergence of a group of obvious high-temperature early magmatic elements-MgO, Cr, and Ni - with a group of CaO, CO2, H2O, P2O5, and Y components forming carbonatite derivatives was the most interesting nuance in this regard. Existence of such polychromous complicated ore-magmatic ring complexes as Tomtor massif indicates occurrence of intraplate deep large magma-generating hearths in lithosphere mantle. Such easily fusible hearths, conserved in lithosphere mantle of residual melts of kimberlite, alkali-picrites, carbonatite compositions, under the subsequent favorable geodynamic settings, are subject to rapid flotation, undergoing decompression melting and forming concentric-zonal platform complexes of alkali ultrabasic rocks with carbonatites

Convergent mineralogical features of silicate igneous and carbonatite rocks of the Tomtor massif in the northeast of the Siberian platform

Convergent mineralogical features of silicate igneous and carbonatite rocks of the Tomtor massif in the northeast of the Siberian platform

Petrochemical features of the association of ultrabasic alkali rocks and carbonatites of the Tomtor massif and interpretationof possible trends of their evolution

Petrochemical features of the association of ultrabasic alkali rocks and carbonatites of the Tomtor massif and interpretationof possible trends of their evolution

U-Pb age of sphene grains, petrochemical, mineralogical and geochemical features of alkaline rocks of the Bogdo complex (Arctic Siberia)

In the north of the Siberian Platform, east of the Anabar Shield, several identified massifs of alkaline rocks with carbonatites are known: Tomtorsky, Bogdo, Promezhutochniy, as well as Bualkalakh, Chuempe, Uele, which are projected according to geophysical data and forming a large alkaline-carbonatite province. The first data on the composition of alkaline rocks of the Bogdo massif were obtained, which correspond to a group of feldspathic rocks of the main composition: rischorrites, biotite-aegirine libenerite syenites, carbonatized, with symplectites and nepheline-feldspar aggregates, pseudo-leucite nepheline syenites. Sphenes were extracted from various types of rocks of the Bogdo massif and their U-Pb age was determined using the SHRIMP-II secondary-ion microprobe. The calculated U-Pb age corresponds to 394,4 3,2 Ma, which is close to the age stage established for the Tomtor massif and the age of the rocks of the Kola alkaline province. One of the reasons for the manifestation of alkaline plume magmatism in this territory may be the influence of the peripheral zone Africa Large Low Shear Velocity Province (Tuzo) in the Baltic and Siberia during the Devonian era.

U‒Pb Age of Sphene and the Petrochemical, Mineralogical, and Geochemical Features of Alkaline Rocks of the Bogdo Complex (Arctic Siberia)

In the northern part of the Siberian Platform, east of the Anabar Shield, several massifs of alkaline rocks with carbonatites identified (Tomtor, Bogdo, Promezhutochnyi) and projected according to geophysical data (Bualkalakh, Chuempe, Uele) form a large alkaline–carbonatite province. The first data on the composition of alkaline rocks of the Bogdo massif indicate that the latter belong to a group of feldspathoid rocks of basic composition: rischorrites, biotite–aegirine liebenerite syenites, carbonatized pseudo-leucite nepheline syenites with symplectites, and nepheline–feldspar aggregates. Sphene grains were extracted from various rocks of the Bogdo massif, and their U‒Pb age was determined using the SHRIMP-II secondary-ion microprobe. The calculated U‒Pb age is 394.4 ± 3.2 Ma, which is similar to the age of the Tomtor massif and the age of the rocks of the Kola alkaline province. One of the reasons for the manifestation of alkaline plume magmatism on this territory may be the effect of the peripheral zone of the African Large Low Shear Velocity Province (“Tuzo”) on the Baltic area and Siberia during the Devonian age.

Mineralogical, geochemical and isotopic (C, O, Sr) features of the unique high-grade REE-Nb ores from the Tomtor deposit (Arctic Siberia, Russia)

The mineralogy (SEM), geochemistry (LA-ICP-MS) and isotopic composition of C, O and Sr in carbonates from uniquely high-grade REE-Nb ores of the Tomtor massif is presented. Testing of the formation conditions for uniquely high-grade ores from the Tomtor deposit was conducted.

Trace Elements in Alkaline Lamprophyres, Clinopyroxene, and Amphibole of the Tomtor Massif and the Ore Potential of the Melts

Data obtained on lamprophyres from the carbonatite–volcanic unit in the lower horizon of the Tomtor Massif indicate that the rocks and zoned diopside and kaersutite phenocrysts in them are enriched in incompatible elements more significantly than is typical of alkaline ultramafic rocks of the Maymecha–Kotui and Kola provinces. The concentrations of these elements and their indicator ratios in the cores and intermediate zones of the diopside and kaersutite phenocrysts significantly vary, and this suggests that the minerals might have crystallized from different melts. This is consistent with the earlier conclusions, which were derived from studying melt inclusions, that the phenocrysts crystallized from mixing alkaline mafic melts of sodic and potassic types and different Mg–number which were enriched in the carbonatite component. The cores of the diopside phenocrysts started to crystallize from sodic mafic magma in a magmatic chamber, while the intermediate and outermost zones of this mineral crystallized from mixed sodic–potassic mafic melts. The carbonatite component was separated from the sodic mafic melt at high temperature (>1150°C) during diopside core crystallization. The bulk compositions of the alkaline lamprophyres and of the diopside and kaersutite phenocrysts contain lower normalized concentrations of HREE than LREE. This led us to conclude that the parental sodic and potassic mafic melts were derived from an enriched mantle source material under garnet–facies parameters, as is typical of continental rifts. It is noteworthy that the potassic mafic melt was derived at greater depths and lower degrees of melting of the mantle source than the sodic melt. The iron–rich sodic melt from which the cores of the diopside phenocrysts started to crystallize was enriched in V, REE, Y, and volatile components (H2O, CO2, F, Cl, and S). The onset of carbonate–silicate liquid immiscibility was marked by the redistribution of REE and Y into the carbonatite melt. The potassic, more Mg–rich mafic melt from which the intermediate and outermost zones of the diopside phenocrysts crystallized was enriched in Ti, Nb, Zr, and REE and always remained homogeneous when this mineral crystallized.

Mineral composition of alkaline lamprophyres of the Tomtor massif as reflection of their genesis

The influence of parental melts on the chemical composition of rock-forming minerals of alkaline lamprophyres (monchiquites) referred to as the volcanic series of porphyritic potassic alkaline-ultrabasic rocks was studied in the Tomtor alkaline-ultrabasic carbonatite massif (Yakutia) hosting a unique deposit of Sc-REE-Y-Nb ores. Previous fluid-melt inclusion study showed that these rocks formed from two mixing alkaline-basic melts of different alkalinity. A detailed study of the chemical composition of minerals revealed a repeated irregular zoning in most of phenocrysts, which reflects the influence of different parental magmas and their mixing. It was established that the cores of diopside phenocrysts (Di I) with inclusions of Na-Fe-rich silicate melts have a low Mg-number and low contents of Ti, Al, and Ca and high contents of Na and Mn. The intermediate zones of phenocrysts (Di II) containing inclusions of K-Mg-rich silicate melts show a high Mg-number and are rich in Ti and Al and poor in Mn and Na. Groundmass grains and rims (and, sometimes, intermediate zones) of diopside phenocrysts often have a mixed Di I-Di II composition with slightly elevated contents of Mg, Ti, and Al. Amphibole phenocrysts, like the diopside ones, have both zones with low Mg contents and high Na/K ratios and Mn contents and zones with high Mg contents, low Na/K ratios, and low Mn and elevated Ti contents. Phlogopites are also of two varieties: highly magnesian, with high contents of Si and K and low content of Mn, and lowly magnesian, with low contents of Si and K and high content of Mn. Ilmenite, titanomagnetite, and fine grains of femic minerals are mostly of mixed varying composition. The chemical composition of rock-forming minerals, especially zoned phenocrysts, evidences that they crystallized with the participation of two alkaline-basic melts: Na-Fe-rich silicate melt enriched in Mn and K-Mg-rich silicate melt enriched in Ti but depleted in Mn.

Phlogopite and phlogopite–amphibole parageneses in the lithospheric mantle of the Birekte terrane (Siberian craton)

Mantle xenoliths containing phlogopite and phlogopite–amphibole mineralization from kimberlites of the Kuoika field have been studied. Such xenoliths were found in two series of rocks: magnesian (Mg) pyroxenite–peridotite and Fe-type phlogopite–ilmenite hyperbasite. The 40Ar/39Ar phlogopite age (1600–1800 Ma) and Re–Os and oxygen isotope data in rocks and minerals of the first series of rocks allow us to suggest that Phl–Amph metasomatism of the lithospheric mantle under the Birekte block and its accretion to the Siberian craton occurred in the subduction zone. The second series of rocks is comagmatic to potassium ultramafites and mafites, finding in the Siberian Platform. The phlogopite ages (870–850 Ma) from Phl–Ilm ultramafites corresponds to the beginning of the breakup of the supercontinent Rodinia and is close to ancient age datings of the alkaline ultramafic-carbonatite Tomtor massif. Phlogopite from xenoliths with garnet is much younger in age (500–600 Ma).

Lamprophyres of the Tomtor Massif: A result of mixing between potassic and sodic alkaline mafic magmas

The paper presents data on inclusions in minerals of the least modified potassic lamprophyres in a series of strongly carbonatized potassic alkaline ultramafic porphyritic rocks. The rocks consist of diopside, kaersutite, analcime, apatite, and rare phlogopite and titanite phenocrysts and a groundmass, which is made up, along with these minerals, of potassic feldspar and calcite. The diopside and kaersutite phenocrysts display unsystematic multiple zoning. Chemically and mineralogically, the rock is ultramafic foidite and most likely corresponds to monchiquite. Primary and secondary melt inclusions were found in diopside, kaersutite, apatite, and titanite phenocrysts and are classified into three types: sodic silicate inclusions with analcime, potassic silicate inclusions with potassic feldspar, and carbonate inclusions, which are dominated by calcite. Heating and homogenization of the inclusions show that the potassic lamprophyres crystallized from a heterogeneous magma, with consisted of mixing mafic sodic and potassic alkaline magmas enriched in a carbonatite component. The composition of the magmas was close to nepheline and leucite melanephelinite. The minerals crystallized at 1150–1090°C from the sodic melts and at 1200–1250°C from the potassic ones. The sodic mafic melts were richer in Fe than the potassic ones, were the richest in Al, Mn, SO3, Cl, and H2O and poorer in Ti and P. The potassic mafic melts were not lamproitic, as follows from the presence of albite in the crystallized primary potassic melt inclusions. The diopside, the first mineral to crystallize in the rock, started to crystallize in the magmatic chamber from sodic mafic melt and ended to crystallize from mixed sodic–potassic melts. The potassic mafic melts were multiply replenished in the chamber in relation to tectonic motions. The ascent of the melts to the surface and rapidly varying P–T parameters of the magma were favorable for multiple separations of carbonatite melts from the alkaline mafic ones and their mixing and mingling.

Main minerals of abnormally high-grade ores of the Tomtor deposit (Arctic Siberia)

The Tomtor massif of Paleozoic ultramafic alkaline rocks and carbonatites is located in the northern part of the Sakha Republic (Yakutia). The massif (its total area is ~250 km2) is ~20 km in diameter, with a rounded shape and a concentrically zoned structure. The core of the massif consists of carbonatites surrounded by a discontinuous ring of ultramafic rocks and foidolites. The outer part is composed of alkali and nepheline syenites. All rocks are weathered and covered with eluvium, which is the thickest after carbonatites enriched in phosphates and REE. The weathering profile consists of four layers, from the top: kaolinite-crandallite, siderite, goethite, and francolite. The highest-grade ores are observed in the bedded deposit which fills depressions in “sagging” eluvium. The ores are laminated and cryptogranular, with high Nb, Y, Sc, and REE contents (on average, 4.5% Nb2O5, 7-10% REE2O3, 0.75% Y2O3, and 0.06% Sc2O3). The highest-grade ores are natural Nb and REE concentrates. The total REE content in some layers is >10%. The morphologic features of the highest-grade phosphate ores from the northern part of the Burannyi site were studied. The ore-forming minerals belong to the pyrochlore group, crandallite group (goyazite), and monazite-Ce. The pyrochlore group minerals occur mainly as crystals that were completely replaced by barium-strontium pyrochlore and/or plumbopyrochlore but retained the original faces; also, they occur as numerous conchoidal fragments. The grains of the pyrochlore group minerals sometimes have a zonal structure, with an unaltered pyrochlore core and a reaction rim. Goyazite occurs predominantly as colloform grains. According to SEM and TEM data, monazite occurs in the ores as ~50 nm particles, which cover the outer part of halloysite tubes (800–3000 nm long and 300 nm in diameter) as a dense layer and make up peculiar biomorphic aggregates. The mineralogical data, the occurrence of biomorphic aggregates, and the close association of organic remains with ore minerals suggest that the high-grade ores of the Tomtor deposit, including the Burannyi site, resulted from a hydrothermal-sedimentary process with a presumably important role of bioaccumulation of REE phosphates.

Metasomatic and magmatic processes in the mantle lithosphere of the Birekte terrain of the Siberian craton and their effect on the lithosphere evolution

Metasomatic and magmatic processes in the mantle lithosphere of the Birekte terrain of the Siberian craton and their effect on the lithosphere evolution

Tomtor, the world's largest Sc-REE-Y-Nb-deposit

The Tomtor Massif, which is exposed over an area of more than 250 km 2 , belongs to the class of giant carbonatite-nepheline syenite massifs within the alkaline ultramafic association. The spatial restriction of the Tomtor Massif to a junction zone between mantle convective cells led us to suggest the existence of a giant long-lived mantle plume. Such plume could bring mantle matter rich in different trace elements related to different metasomatic processes at different depths. The uniqueness of the Tomtor Sc-REE-Y-Nb deposit, which jointly contains both Nb and REE ore mineralisations, can be explained by the genetic relation of the complex to a K-Ca parent mantle magma.

The discovery of the Tomtor Massif in the northern part of the Siberian Platform - Comparison with the Khibina Massif on Kola Peninsula and its potential in REE and Nb

The discovery of the Tomtor Massif in the northern part of the Siberian Platform - Comparison with the Khibina Massif on Kola Peninsula and its potential in REE and Nb

The Tomtor alkaline ultrabasic massif and related REE-Nb deposits, northern Siberia

Nb-REE ore deposits related to weathered carbonatite within the Tomtor massif, northern Siberia, contain the world9s largest carbonatite-related concentrations of Nb and REE. Despite its remote location, economic exploitation of the deposit was made possible by the discovery of rich Sc-REE-Y-Nb ore, The 300-km 2 Tomtor massif is a ring complex in which the Nb-REE deposits are situated within and above a central carbonatite stock. The deposits include: (1) pyrochlore-bearing carbonatite, (2) a lower ore horizon, and (3) an upper ore horizon. The average concentration of niobium increases from a few tenths of a percent in the carbonatite, to a few percent in the lower ore horizon, and up to 12 percent in the upper ore horizon. BEE contents range from 0.5 to 0.7 percent in carbonatite, 4 to 6 percent in the lower ore horizon, and 11 to 30 percent in the upper ore horizon. In a plot of 19) O vs. delta 3 C, the Tomtor carbonates plot along a trend from the Oka box for magmatic carbonates to the field of sedimentary carbonates. The Tomtor carbonatites have initial 87 Sr/ 86 Sr ratios ranging from 0.70346 to 0.70374, a range consistent with mantle derivation for the magmas. The lower ore horizon, which is up to 300 m thick, consists of niobium (Nb 2 O 5 content 1-2%) and phosphorus ores that occur in a variety of original rock types (carbonatites, volcanics, picritic dikes, and country rocks) which have undergone several types of alteration including weathering, hydrothermal alteration, and low-temperature sideritization. 87 Sr/ 86 Sr ratios of the lower ore horizon range from 0.70421 to 0.70374 and suggest a dominantly mantle source for Sr with a very minor addition of crustal Sr. The upper ore horizon is a placer deposit 3 to 25 m thick which has been partly affected by hydrothermal alteration. Rich ores of the upper ore horizon are composed mainly of pyrochlore, phosphates and alumophosphates of REE, Sr and Ba (florencite, monazite, gorceixite, goyazite), rutile, and pyrite. Nb in the Tomtor deposits occurs principally in pyrochlore, columbite, rutile, and ilmenorutile. REE and Y occur in florencite, monazite, rhabdophane, xenotime, and bastnaesite, and Sc occurs in monazite, rhabdophane (0.55-0.95%), minerals of the crandallite group (0.017-.0030%), rutile, and as a thin film of Sc(OH) 3 on phosphates.