EGU23-3560, updated on 22 Feb 2023
https://doi.org/10.5194/egusphere-egu23-3560
EGU General Assembly 2023
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Mineralogical and geochemical characteristics of lamproite minerals of the Murunsky massif.

Igor Ashchepkov1, Nikolai Vladykin2, Irina Sotnikova2, Nikolai Medvedev3, Nikolai Karmanov1, and Natalia Alymova2
Igor Ashchepkov et al.
  • 1Institute of Geology and Mineralogy SB RAS, Geology, Novosibirsk, Russian Federation (igor.ashchepkov@igm.nsc.ru)
  • 2Institute of Geochemistry SB RAS, Geology, Irkutsk, Russian Federation
  • 3Nikolaev Institute of Inorganic Chemistry SB RAS, Novosibirsk, Russian Federation

Minerals from leucite lamproites of the Murunsky alkaline massif (Vladykin, 2000; 2005; Vladykin, 2009) were analyzed by electron microscopy in the sections of 700 grains of minerals (IGM SB RAS) and LA ICP MS (IIC SB RAS) - 40 grains. Pyroxenes, amphiboles, various micas including varieties of the Ba type, leucites and nephelines, Ba and K feldspars, eudialyte, barite, stroztianite, ilmenites, Cr- spinelides, Ti magnetites, apatites, tourmaline, and various carbonates and sulfides: pyrrhotite, petlandite, chalcopyrite, murunite, smithsonite, galena.

 

Pyroxenes are divided into 3 groups from diopsides to augites and aegirines, revealing a continuous series of compositions according to MgO (Fig. 1). Amphiboles K-richterites and arfversonites, and Ca-Fe ackermanites. Complete ranges from phlogopites to biotites have been established among micas. The proportion of Ba micas is significant. In the diagram  genetic digram (Minchell, 1995 )(Fig. 2) falls into the field of ailikites or orangeites,  and lamproites. Leucites and nephelines occurs  friquiently. Numerous apatites are characterized by Ca-Sr substitution and noticeable F contents (to 3%). K-type eudialytes and a mineral close to priderite were found.

 

In the TRE diagrams (Fig.3), pyroxenes are characterized by La-enriched ~200-250 weakly inclined spectra of La/Ybn (2-3) that spread out in the HREE wing. Amphiboles of the K-Na-Ca are characterized show inclined spectra with Ho-Tm depression,  LILE peaks elevated Zr, Hf, Y and Ta-Nb minima. The more alkaline amphiboles are characterized by reduced REE concentrations, more  elevated Zr-Hf. Ultra-alkaline amphiboles (richterite and arfvedsonite) have higher REE contentswith characteristic U-shaped spectra, very high LILE contents high peaks of Sr, Zr, Hf. Phlogopites have oblique U-shaped spectra with a sharp peak Eu interference Ti. Very high LILE with a peak at Va, Sr, Y, Pb are typical.

Low REE and especially LREE with a peak of Eu are characteristic of leucites. U, Sr, Pb peaks are also characteristic, and HFSE vary. The REE spectra of K-Ba feldspars are similar to those of phlogopite. High peaks of LILE, Sr, Pb, Y are expressed on spiderdiagrams

Judging by the peculiarities of mineral trends, lamproites are the result of low degrees melting  under the influence of plume melts of a mantle deeply metasomatized by subduction processes. Pyroxenes are end–to-end minerals, at an early stage their compositions were controlled by fractionation of olivine and then saturated SiO2 silicates. Further fractionation led to enrichment with rare elements P, Sr, F. In amphiboles, the growth of REE was accompanied by the accumulation of Zr, Hf, while Nb, Ta were removed during the deposition of T-magnetite. Grant RBRF 19-05-00788.

How to cite: Ashchepkov, I., Vladykin, N., Sotnikova, I., Medvedev, N., Karmanov, N., and Alymova, N.: Mineralogical and geochemical characteristics of lamproite minerals of the Murunsky massif., EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-3560, https://doi.org/10.5194/egusphere-egu23-3560, 2023.

Supplementary materials

Supplementary material file