2011

Тезисы международной конференции

Рудный потенциал щелочного, кимберлитового

 и карбонатитового магматизма

Abstracts of International conference

Ore potential of alkaline, kimberlite

and carbonatite magmatism

Possibilities of mass-spectrometry ICP-MS method (ЕLAN 9000) in studying rocks and minerals of alkaline and mafic magmatism

Еlizarova, I.R.*, Bayanova, T.B.**

* I.V.Tananaev Institute of Chemistry and Technology of Rare Elements and Mineral Raw Materials, Kola Science Center, RAS, Apatity, Russia.

** Geological Institute, Kola Science Center, RAS, Apatity, Russia

elizarir@chemy.kolasc.net.ru

The development of the mineral resources on the Kola Peninsula, solution of fundamental geological tasks, improvement of raw material treatment methods are facilitated by introducing mass-spectrometry into the practice of analytical support to operations from exploration and mining of deposits to treatment of raw material down to end product. If earlier it was enough to measure content of rare-earth elements (REE) at a level of 10^-3 to 10^-4 %, now it is necessary to know low content limits at a level of 10^-5 to 10^-7 %. To solve this intricatea issue, one needs to minutely work out methods and procedures for mass-spectrometric analysis of complex geological REE-bearing units.

This study was aimed at establishing possibilities of ICP-MS method for mass-spectrometric REE measurement in samples of alkaline and magic igneous rocks and derivatives using quadruple mass-spectrometer ELAN 9000 DRC-e (Perkin Elmer, USA). In order to ultimately cover REE concentrations in the geological samples, for the analysis, loparite concentrate of the Lovozero intrusion (tens percents of REEs), apatite ore of the Khibiny intrusion (thousands ppm), and pyrite from Finland (Penikat intrusion; some, or fractions of ppm) were taken. The first results of working-out the methods and procedures were published in [1 - 4].

Two loparite concentrate acid opening regimes were tested for the purpose of comparison, one in open carbon-glass cups, the other in fluoroplastic pressure tank using a microwave opening system BERGHOF MWS -3+ (Germany) with the use of distilled HF, HNO₃, HCl, and, to increase temperature of opening and more complete passing REE into solution, H₂SO₄ or HPO₃ was added.

The loparite concentrate in the Lovozero deposit contains, in accordance with the data from the Lovozero Mining and Processing Plant, ≥ 94.9 per cent of loparite, where the total of REE trioxides varies from 30.5 to 36.0 %. The analysis has demonstrated total TR₂O₃ of 34.15±1.02. The complete REE elements analysis was made for the loparite concentrate, which corresponds to rough data provided by the producer [5] and well correlates with the data reported in [6].

In the Murmansk region, North-Western Phosphorus Company, JSC, exploits two deposits in the Khibiny Mountains: Partomchorr and Oleny Ruchey. The apatite-nepheline ore of these deposits are planned to yield both phosphorus concentrate, and rare-earth element concentrates [7]. Within the framework of contracts with this company, about two hundred REE samples were analyzed. Passing these samples into solution was easier than that of loparite concentrate, and did not require usage of microwave opening in pressure tanks, sulphuric and phosphoric acids.

To compare samples and confirm the accuracy of the analytical results, parallel to the investigation of samples, the composition of the reference samples was analyzed: apatite concentrate GSO 2462 and 2463, apatite ore ST SEV 5750, nepheline syenite NS-1 (Khibiny General'naya), and chalcopyrite of the Talnakh deposit. The accuracy of the pyrite (primary mineral of the PGE ores) samples analysis was tested in accordance with the results of REE measurements in the sulphide of the Talnakh deposit with the data presented in [8], and with the analysis of the comparison solutions derived from multielement reference solutions by Perkin Elmer (Multi-element ICP-MS Calibration Std). The same solutions were used as calibration ones. The linearity of the approximating dependencies for the elements to measure was at least 99.99 %.

The adjustment and optimization of mass-spectrometer operation modes was made in spraying reference solution by Perkin Elmer (10 ppb Mg, Ce, In, Ba, U, each) into the plasma to gain necessary analytical figures. The sensitivity of the device in our investigations was maintained at a high level; the strength of the analytical signal for Indium, for example, was as high as 400 000 - 500 000 cps, with the level of CeO / Ce, and Ва⁺⁺ / Ва⁺ being ≤ 0.03. The power of plasma (1300 – 1350 W), spraying gas flow (high-purity Ar, at least 99.995 %) varied within 0.75 – 1.0 l × min^-1. The voltage at the ion lens was 6.5 to 10 V on average to serve as an indirect evidence of the ion optics purity. The level of the total REE content in the blank sample was within 0.1 ppb, demonstrating the analytical level of experimental integrity and detection limit for elements.

The spectral impositions were taken into account using the software for ELAN 9000, and application of the adjustment equations into the analytical program established with due regard of REE isotopes abundance in nature.

The REE measurement could have been significantly problem by Ba 135, 136, 137, 138 isotopes due to spectral folding of monovalent oxide and hydroxide and Sm and Eu isotopes. The Eu content was measured on Eu 151 isotope, and the Sm content on Sm 152 isotope. The REE analysis preceded the analysis of samples for Ba content. It is found that the Ba concentration has not distorted the results of REE measurements. It is accounted for by a low content of oxide ions in the plasma within 3 % (controlled variable in adjusting operation of the spectrometer). Moreover, the REE measurements were positively affected by presence of Si, Fe, Al, Mg, Ca, Na, K, Ti ions in the sample that are highly affinal to oxygen to reduce possible formation of REE monovalent oxides in the plasma, and mass discrimination. To level possible impositions, the REE calibration solutions were added with GSO 7107-9 solution of such a Ba ion composition that Ba concentration would exceed REE concentration 500 times to simulate their ratio in a geological sample.

In order to prove stability of analysis, and absence of ions precipitated at different parts of the mass-spectrometer, and their reiterated ionization, the data on measurement results reproducibility were obtained each 5.5 minutes for In, Ba, Pb, Ln (10 µg/l) along with spraying a solution with Li background concentration of 100 mg/l continuously during 4 hours. No intensity drift during 4 hours of measurement was confirmed by registration of analytical signal for all REE when analyzing samples of apatite concentrate GSO 2462, 2463, and ST SEV 5750.

For the first time, the investigations carried out to study REE distribution in the rock-forming and sulphide minerals from the deposits of the Lovozero and Khibiny tundras, as well as the Penikat PGE deposits in Finland using ICP-MS (ELAN 9000) method, have shown a possibility to identify rare-earth elements composition in alkaline and mafic rocks within a wide range of REE concentrations, i.e. from portions of ppm without preliminary procedures of separation and concentration.

The investigations were supported by RFBR grants 09-05-00058, 11-05-00570, and Division of Earth Sciences RAS, Program 4.

References:

1.      Elizarova, I.R., Bayanova, T.B., Mitrofanov, F.P., Kalinnikov, V.T. Procedures of mass-spectrometer (ELAN 9000) rare-earth elements measurement in reference geological samples // Proceedings of the III All-Russian Conference with International Participation "Mass-spectrometry and applied issues", 18-22 May 2009, Moscow, NU-8. P. 110 (in Russian).

2.      Ekimova, N.A., Serov, P.A., Elizarova, I.R., Bayanova, T.B. Mass-spectrometric REE measurement in sulphides, and Sm-Nd dating of sulphide-bearing rocks in mafic intrusions // Proceedings of the All-Russian Conference "Precambrian Mineral Genesis". Petrozavodsk, 11-13 November 2009. Pp. 77-81 (in Russian).

3.      Elizarova, I.R., Bayanova, T.B. Mass-spectrometric (ELAN 9000) measurement of rare-earth elements in geological samples // Investigations and developments in chemistry and technology of functional materials. All-Russian Conference with International Participation, 2010. Apatity. Pp. 203 - 206 (in Russian).

4.      Ekimova, N.A., Serov, P.A., Bayanova, T.B., Elizarova, I.R., Mitrofanov, F.P. REE distribution in sulphide minerals and Sm-Nd ore genesis dating of layered mafic intrusions // DAN, V. 436. No. 1. 2011. Pp. 75 – 78 (in Russian).

5.      http://www.lovgok.ru

6.      Kogarko L.N., Williams C.T., Woolley A.R.  Chemical evolution and petrogenetic implications of loparite in the layered, agpaitic Lovozero complex, Kola Peninsula, Russia. // Mineralogy and Petrology. 2002. Vol. 74. Pp. 1-24.

7.      Information and analytical center "Mineral", http://www.mineral.ru

8.      Dubinin, A.V. Geochemistry of rare-earth elements. Moscow: Nauka. 2006. 360 p. (in Russian)

Реферат

Определены возможности ICP-MS метода масс-спектрометрического определения REE в пробах щелочных и базитовых магматических пород и продуктах их переработки при использовании в анализе квадрупольного масс-спектрометра ELAN 9000 DRC-e (Perkin Elmer, США). Для анализа выбраны лопаритовый концентрат Ловозерского массива, апатитовая руда Хибинского массива, пирит (интрузия Пеникат, Финляндя). Опробованы в сравнении два режима кислотного вскрытия лопаритового концентрата: открытое в стеклоуглеродных тиглях и во фторопластовых автоклавах в микроволновой системе вскрытия. В качестве образцов сравнения и для подтверждения правильности анализа проведен анализ стандартных образцов состава: апатитового концентрата ГСО 2462 и 2463, апатитовой руды СТ СЭВ 5750, НС-1 нефелинового сиенита «Хибины Генеральная», халькопирита месторождения Талнах. Получены данные по воспроизводимости результатов определения и  подтверждено отсутствие дрейфа интенсивности в течение 4 часов измерений.