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Metamorphism of carbonatite is exemplified in the Vesely occurrence. According to available data, the age of the carbonatite
is 596 ± 3.5Ma, whereas metamorphism is dated at 550 ± 14 Ma. The rocks at the Vesely occurrence were metamorphosed under
conditions of greenschist facies (epidote-muscovite-chlorite subfacies) under elevated pressure. Microthermometry of fluid
inclusions in minerals indicates that the temperature of metamorphism is 377−450°C and the pressure estimated from phengite
geobarometer is 6−8 kbar. The low-grade metamorphism led to the partial recrystallization of carbonates and apatite with removal
of trace elements. This process resulted in a change of the oxygen isotopic composition of the studied minerals. Metamorphism
was accompanied by formation of talc, phengite, chlorite, quartz, tremolite-actinolite, and anthophyllite, which are not typical
of carbonatite. The data obtained show that the metamorphism exerted an effect on the mineralogical, isotopic, geochemical,
and technological properties of the carbonatite. The effect of metamorphism should be taken into account in determination
of the nature of ore mineralization and estimation of ore quality and perspective of the occurrence. 相似文献
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G. S. Ripp I. A. Izbrodin A. G. Doroshkevich E. I. Lastochkin M. O. Rampilov S. A. Sergeev A. V. Travin V. F. Posokhov 《Petrology》2013,21(4):375-392
This paper reports the results of Rb-Sr, 40Ar-39Ar, and U-Pb geochronological investigations for igneous and metamorphic rocks from the regions of the Oshurkovo basic massif. It was shown that the gabbro-syenite-granite complex that was formed there is similar to the bimodal basalt-rhyolite series of volcanic associations. Three major stages of magmatic activity were recognized: syenite-granite (132–127 Ma), basic (126–117 Ma), and granite (121–112 Ma). The silicic igneous rocks were formed owing to anatexis under the influence of heat released from the parent chamber of alkaline gabbroids. 相似文献
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G. S. Ripp A. G. Doroshkevich N. S. Karmanov S. V. Kanakin 《Geology of Ore Deposits》2009,51(8):812-821
The Khaluta carbonatite deposit located in the western Transbaikal region was formed during the Late Mesozoic rifting in the
southern framework of the Siberian Craton. Carbonatite is associated with shonkinite and syenite and is accompanied by fenitization.
The composition of mica in more than 160 samples of country rocks, carbonatites, silicate rocks, and fenites was studied.
The Fe3+ and Fe2+ contents, as well as oxygen isotopic composition, were determined. The Mg and Fe contents increase, whereas the Ti and Al
contents decrease in micas when passing from silicate rocks and fenites to carbonatites. Micas from carbonatites are depleted
in Al, enriched in Fe3+, and distinguished by high Si and F contents. According to our calculations, in some cases Al replaces Si in the tetrahedral
site instead of replacement of Fe3+ as is characteristic of tetraferriphlogopite. Formally, the mica from carbonatites falls within the tetraferriphlogopite
field, but typical inverse pleochroism is not always observable. The δ18O values of micas from carbonatite, shonkinite, syenite, and fenite are similar to those of mantle-derived silicate minerals.
The δ18O values in the minerals coexisting with phlogopite testify to their isotopic equilibrium and make it possible to calculate
the crystallization temperature of carbonatite. 相似文献
15.
The phosphate and sulfate-phosphate minerals in the sillimanite-bearing rocks of the Kyakhta deposit are considered. The mineral
assemblages of the high-Al rocks were formed during prograde and retrograde stages of metamorphism. The first stage is characterized
by the formation of sillimanite, corundum, muscovite, quartz, rutile, titanohematite, magnetite, feldspar, biotite, lazulite,
and wagnerite. The muscovite composition showed that sillimanite paragenesis was formed at temperatures above 510–600°C. According
to oxygen isotope thermometry, the minimum metamorphic temperature for quartz and titanohematite is 690°C. Andalusite, diaspore,
quartz, pyrophyllite, muscovite, and a wide range of phosphates and sulfate-phosphates crystallized during the retrograde
stage. The decrease in temperature and increase in the water content led to the following sequence of mineral formation: Mg-Fe-Al-Ca-REE-rich
phosphates (lazulite, scorzalite, augelite, apatite, and monazite) → Ca-Sr sulfate-phosphates (woodhouseite and svanbergite)
→ sulfate (barite) → Sr-Ca-Ba aluminophosphates (goyazite, crandallite, and gorceixite). The chemical compositions of phosphates
and sulfate-phosphates minerals and their formation conditions are discussed. 相似文献
16.
G. S. Ripp E. V. Khodyreva I. A. Izbrodin M. O. Rampilov E. I. Lastochkin V. F. Posokhov 《Geology of Ore Deposits》2017,59(5):407-420
The paper gives a mineralogical and geochemical characterization of the North Gurvunur deposit, which was discovered in the Eravna ore district. The ore is composed of apatite–magnetite paragenesis. Apatite is distinguished by elevated LREE concentrations; some of them are contained in emulsion-type impregnation of monazite. Hematitization, carbonate, quartz, and pyrite veinlets formed at the postore stage, and gypsum–anhydrite mineralization is widespread in the supraore sequence. Two groups of endogenic minerals are distinguished by oxygen isotopic composition. One of them comprises magnetite and apatite, which are characterized by a homogeneous composition throughout the section of the ore lode and are close to the mantle source. The oxygen–isotope temperature calculated for the apatite–magnetite couple (620–800°C) provides evidence for magmatic origin of ore. The δ18O of fluid in equilibrium with hematite is 8.0–8.5‰ and shows a certain enrichment in crustal component; carbonates of postore veinlets reveal participation of meteoric water. The study has made it possible to refer the North Gurvunur deposit to the Kiruna type. 相似文献
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Lithology and Mineral Resources - 相似文献
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A.G. Doroshkevich I.A. Izbrodin M.O. Rampilov G.S. Ripp E.I. Lastochkin V.B. Khubanov 《Russian Geology and Geophysics》2018,59(9):1061-1077
We present results of geochronological (40Ar-39Ar, U-Pb SHRIMP-II, and LA-ICP-MS) and geochemical studies of alkaline rocks of the Amalat, Sirikta, Tsipa, Pravyi Uligli, and Verkhnii Uligli massifs in the Vitim plateau (western Transbaikalia). The formation of the alkaline rocks and the accompanying albitization are dated at 261-242 Ma. The isotope inhomogeneity (?Nd(T) = + 8.4 to -1.7) of the alkaline rocks indicates the heterogeneous composition of the source of their material, having a depleted component, an enriched juvenile metasomatic fluid, and a crustal substrate. 相似文献
19.
The paper reports Ar-Ar, Rb-Sr, and U-Pb (SHRIMP II) geochronologic data on carbonatites in Transbaikalia, related metasomatically altered rocks, and comagmatic silicate alkaline rocks. Metamorphic processes at two carbonatite occurrences were dated at 550–559 Ma (U-Pb and Rb-Sr methods). Geochronologic data make it possible to distinguish two major epochs when carbonatite were formed: Late Mesozoic in southwestern Transbaikalia and Late Riphean-Vendian in northern Transbaikalia. Small carbonatite occurrences are also known in the Vitim and Baikal alkaline provinces, which were formed in the Middle-Late Paleozoic. The Late Mesozoic carbonatite-forming epoch is definitely correlated with the development of the Western Transbaikalia rift structure and the Late Riphean-Vendian epoch, with the breakup of Laurasia in the Late Riphean. 相似文献
20.
This paper reports the results of isotopic investigations of the rocks of the Khalyuta carbonatite complex (carbonatites,
comagmatic silicate rocks, fenites, and hydrothermal rocks) and host limestones and granites. Pyroxene, amphibole, magnetite,
potassium feldspar, apatite, phlogopite, calcite, dolomite, strontianite, celestite, and barite were investigated. The isotopic
compositions of C, O, Sr, and S were analyzed. The character of the distribution of oxygen isotopic composition in minerals
(carbonates, silicates, phosphates, and oxides) suggests their equilibrium formation. It was supposed that the evolutionary
trend of C and O isotopic compositions is mainly related to the processes of differentiation in the melt-fluid system and
indicates the absence of significant contamination by carbon and oxygen from a crustal source during rock formation from the
magmatic stage to the hydrothermal stage. The isotopic compositions of S and Sr did not change. 相似文献