Stable isotope compositions are examined for brucite marble and Mg-skarn that occur in the southern part of the Tazheran massif, Olkhon region, Russia. Brucite marble exhibits a narrow range in δ
18
...O of +23.3 to +26.2 ‰ and shows carbon isotope depletion of −1.9 to −4.4 ‰) as compared with the country dolomite isotope compositions (+2.0 to +2.4 ‰) which is explained by both decarbonation processes and participation of fluids depleted in
13
C. The emplacement of brucite marble was accompanied by the formation of endo- and exoskarn at the contact between syenite and brucite marble. δ
18
O profiles across the contact show a typical decrease towards the syenite side interpreted as the result of fluid/rock interaction and influx of magmatic fluids. Finally, we discuss the mechanisms of brucite marble emplacement and consider three possible ways of producing these rocks: (1) injection of dolomite with subsequent transformation to periclase marble and then to brucite marble; (2) injection of periclase marble with a following replacement of periclase by brucite or injection of brucite marble; (3) crustal water-rich carbonate melt. We favor models 2 and 3 and discuss their strengths and weaknesses.
Research subject
. This paper presents the results of a study of minerals of the apatite group from aillikites of the Zima alkaline-ultramafic carbonatite complex.
Aim
. To determine the composition ...of apatites to characterize the studied rocks and to elucidate the patterns of element distribution in the magma of aillikites in the late crystallization stages.
Materials and Methods
. Minerals of the apatite group from 6 samples (4 from dikes of the Bol'shetagninsky massif, 1 from the Bushkanai dike, 1 from the Beloziminskaya pipe) were studied. The samples showed similar textural-structural features, differing in the mineral composition of the groundmass.
Results
. Minerals of the apatite group are widespread in the groundmass of all the studied rocks. They are characterized by idiomorphic, subidiomorphic crystals of homogeneous composition, 10-100 microns in size. Minerals of the apatite group were identified as fluorapatite and hydroxyapatite characterized by a significant SiO
2
content (up to 5 wt %), low SrO content (up to 1.5 wt %) and REE
2
O
3
(up to 2 wt %). The studied apatites also include MgO, FeO, Na
2
O, SO
4
, and CO
3
. Fluorapatites from dyke aillikites are characterized by a higher silicon content as compared to apatites from the Beloziminskiy pipe. Apatites from fresh aillikites of the Bushkanai dyke have a relatively higher content of Sr, REE, and F than minerals from serpentinized samples.
Conclusions
. The composition of the studied apatites has a lower Sr and Ba content than orangeite and lamproite apatites. In terms of Sr, Si and REE contents, the studied apatites are similar to kimberlite and ailikite apatites. Such a difference allows minerals of the apatite group to be used as an indicator mineral for classification of kimberlites and related rocks, but only in combination with petrography and composition of other minerals of the groundmass.
Aluminium phosphate and aluminium phosphate-sulphate (APS) minerals occur as disseminated crystals and fine-grained aggregates in kyanite schists near Ichetuyskoye, in the Dzhida basin (West ...Transbaikal region, Russia). Petrographical, mineralogical and geochemical data suggest a metamorphic evolution through prograde and retrograde stages. Lazulite-scorzalite and trolleite in association with kyanite, quartz, muscovite, paragonite, topaz, rutile, magnetite and hematite formed during the prograde stage. More than 25 minerals identified in schists are genetically related to the retrograde stage. Some phosphates and all of the APS minerals belong to the alunite, beudantite and plumbogummite groups. Electron-microprobe data reveal the presence of wide compositional variations and complex solid-solution series among the members. The main crystal-chemical variations of the APS solid-solution series in the alunite supergroup concern the relative proportions of svanbergite, woodhouseite, goyazite, crandallite, florencite-(Ce) and natroalunite. Chemical analyses of APS minerals indicate extremely high amounts of LREE, Sr, Ba, Ca and Na. In some cases, APS minerals have compositions of Ba and Ca,Ba phosphates– sulphates.
The relevance of the research is caused by the need to expand mineral resources base, including gold-bearing ores. Large alkaline provinces, like Aldan-Stanovoy shield, are of interest because ...gold-bearing ores usually related to alkaline rock. They may form large and even giant deposits. Verkhneamginskiy massif is located in Verkhneamginskiy ore field in Aldan-Stanovoy shield. Verkhneamginskiy ore field is the part of large Charo-Aldan metallogenic zone, its length is more than 700 km from west to east. A characteristic feature of the Verkhneamginskiy ore region is its association with the Amginsky submeridional structural zone of the tectonic melange separating the Central Aldan compound terrain in the East from the West Aldan and Tynda composite terrains in the West and South, respectively. The main aim of the research is to detect the main rock types of Verkhneamginskiy massif, to study the features of structure and composition and to identify the age of massif crystallization as well as to compare the results with the available geochronological data on Mesozoic magmatism of the Aldan shield. Methods: petrographic study and 40Ar/39Ar dating by the step heating method by phlogopite monofractions. Results. The main phases of Mesozoic alkaline magmatism are leucocratic syenites and mesocratic lamprophyres. Using the 40Ar/39Ar dating of phlogopite monofraction the authors have determined two discrete impulses: (1) 129,1.5±2,5 Ma emplacement of syenites; (2) 117,7±3,4 Ma emplacement of lamprophyre dikes. Mesozoic magmatism, manifested in Verkhneamginskiy area, demonstrates similar age boundaries with magmatic processes shown in the Aldan shield in the Mesozoic era.
40Ar/39Ar ВОЗРАСТ ЩЕЛОЧНЫХ ПОРОД ВЕРХНЕАМГИНCКОГО МАССИВА (АЛДАНСКИЙ ЩИТ, ЮЖНАЯ ЯКУТИЯ) (Anton V. Ponomarchuk), Пономарчук Антон Викторович; (Ilya R. Prokopyev), Прокопьев Илья Романович; (Anna G. Doroshkevich), Дорошкевич Анна Геннадьевна ...
Izvestiâ Tomskogo politehničeskogo universiteta. Inžiniring georesursov,
03/2019, Letnik:
330, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Актуальность исследования обусловлена необходимостью расширения ресурсной базы полезных ископаемых, в том числе и золота. Крупные ареалы щелочного магматизма, такие как Алдано-Становой щит, ...представляют особый интерес, так как часто со щелочными породами ассоциируют золоторудные месторождения, в том числе крупные и гигантские. Верхнеамгинский массив расположен в Верхнеамгинском рудном районе Алдано-Станового щита, который, в свою очередь, входит в состав Чаро-Алданской металогенетической зоны, протянувшейся более чем на 700 км с запада на восток. Характерной особенностью Верхнеамгинкого рудного района является его приуроченность к Амгинской субмеридиональной структурной зоне тектонического меланжа, отделяющей Центрально-Алданский составной террейн с востока от расположенных к западу и югу от нее соответственно Западно-Алданского и Тындинского составных террейнов. Цели: определить основные типы магматических пород Верхнеамгинского массива, изучить особенности строения и состава и выяснить время внедрения различных фаз массива; сравнить полученные результаты с имеющимися геохронологическими данными по мезозойскому магматизму Алданского щита. Методы: петрографические исследования и 40Ar/39Ar датирование методом ступенчатого прогрева по монофракциям флогопитов. Результаты. В результате петрографических исследований показано, что основные фазы мезозойского щелочного магматизма в пределах Верхнеамгинского массива представлены лейкократовыми сиенитами и дайками мезократовых лампрофиров (минетт). Результаты 40Ar/39Ar датирования показали, что образование массива происходило в несколько этапов: (1) 129,1±2,5 млн лет внедрение сиенитов; (2) 117,7±3,4 млн лет внедрение даек лампрофиров. Мезозойский магматизм, проявленный в Верхнеамгинском районе показывает сходные возрастные рубежи с магматическими процессами, проявленными на Алданском щите в мезозойскую эпоху.
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