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

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.