Major (EPMA) and trace (SIMS) element geochemistry in the silicate minerals (olivine, pyroxene and plagioclase) of Kunashak equilibrated ordinary chondrite (L6) is described. No variations in the major element concentrations of the silicate minerals have been found, which is characteristic of equilibrated chondrites of petrological type VI. Low-Са pyroxene and plagioclase from the radiated olivine-pyroxene chondrule of Kunashak Meteorite contain an abundance of trace elements (Yb, Cr, Nb and Ti – pyroxene; Sr, Y, Ti and Zr – plagioclase), which is not characteristic of minerals from the porphyritic olivine and olivine-pyroxene chondrules of the meteorite. The porphyritic olivine-pyroxene chondrule of the Kunashak Meteorite has high trace element concentrations in olivine, in particular, the highest Yb concentration (0.12 ppm on the average) relative to porphyritic and radiated olivine-pyroxene chondrules (0.02 ppm). High trace element concentrations indicate rapid crystallization of a radiated chondrule in a nebula and show no traces of trace element homogenization upon thermal metamorphism. The trace element composition of silicate minerals from Kunashak Meteorite has retained the individual melting pattern of the chondrules and remained unaffected by thermal metamorphism on the parent bodies of the chondrules. Similar results, obtained in the study of Bushkhov Meteorite (L6), indicate that trace elements in olivine and low-Са pyroxene are resistant to thermal metamorphism. The persistence of the individual pattern of the chondrules enables us to use equilibrated ordinary chondrites for the study of processes at early stages in the formation of the Solar System and to better understand chondrule and planet formation mechanisms.
Major (EPMA) and trace (SIMS) element geochemistry in olivine, low-Са pyroxene and mesostasis from porphyritic and barred chondrules, as well as the pyroxene-olivine aggregate and matrix of equilibrated ordinary Borodino chondrite (Н5) is discussed. No differences in major element concentrations in the silicate minerals of the chondrules and matrix of the meteorite were found. The minerals of porphyritic olivine-pyroxene and barred chondrules display elevated trace element concentrations, indicating the rapid cooling of chondrule melt in a nebula, and are consistent with experimental data. The trace element composition of low-Са pyroxene is dependent on the position of a pyroxene grain inside a chondrule (centre, rim, matrix) and the composition of mesostasis is controlled by the type of the object (porphyritic and barred chondrules, pyroxene-olivine aggregate). The depletion in trace elements of low-Са pyroxene from the rims of chondrules in comparison with those from the centre and matrix of the meteorite was revealed. The chondrule rim is affected by interaction with surrounding gas in a nebula, possibly resulting in the exchange of moderately volatile trace elements in low-Са pyroxene and depletion in these elements relative to pyroxene from the centre of the chondrule or matrix of the meteorite. The mesostasis of barred and porphyritic olivine-pyroxene chondrules contains more trace elements than that of porphyritic olivine chondrule and pyroxene-olivine aggregate, suggesting the rapid cooling of these objects or their high liability to thermal metamorphism, which results in the recrystallization of chondrule glass into plagioclase. However, no traces of the elevated effect of thermal metamorphism on the above objects have been revealed. The results obtained indicate no traces of the equilibration of the trace element composition of silicate minerals in equilibrated chondrites.
The paper discusses the geochemistry of major (EPMA) and trace (SIMS) elements in olivine of porphyritic, nonporphyritic chondrules, and the matrix of equilibrated ordinary chondrite Saratov (L4). Olivine corresponds to forsterite and is rather heterogeneous (Fo 73-77). No differences in the content of the major elements in the olivine of the chondrule and the matrix of the meteorite were found. However, the content of major and trace elements in olivine within chondrules varies considerably; high values found in olivine from barred chondrules. Olivine from porphyritic chondrules and the matrix of the Saratov meteorite have similar concentrations of trace elements. High concentrations of refractory (Zr, Y, Al) and moderately volatile (Sr and Ba) trace elements in barred olivine chondrule indicate the chondrule melt formation due to the melting of precursor minerals and its rapid cooling in the protoplanetary disk, which is consistent with the experimental data. The olivine of the chondrules center of the Saratov meteorite differs from the olivine of the chondrules rims and meteorite matrix by the increased values of the Yb/La ratio. No relict grains and magnesian cores of olivine were found in meteorite chondrules. Individual grains in the chondrules are distinguished by their enrichment in trace elements relative to the rest of the olivine grains in the chondrule.
It has been attempted to expand existing understanding of accessory mineralization evolution of rare metal-granite series at post-magmatic stage of their development and formation of associated hydrothermal deposits. Composition and distribution of rare elements of Verkhneurmiysk ore cluster have been examined from the position of mineralogy: the study focused on accessory and ore minerals Sn, W, Nb, Ta, Bi, Y, rare earth elements in rare metal Li-F granites and associated metasomatites. It has been discovered that accessory magmatic and hydrothermal mineral complexes share the same geochemical features, are formed under the leading role of abovementioned elements and consistently follow each other over time. It has been traced how mineral forms of accumulation of Sn, W, Nb, Ta, Y and rare earth elements evolve in the processes of magmatic crystallization and post-magmatic metasomatism in the time series: rare metal granites → zwitters → tourmalinites → chloritites. Mineral rocks of each stage were noted to inherit mineralogical and geochemical distinctions from the rocks of the previous stage. A significant number of minerals, forming in the course of two-three stages, have been discovered, as well as omnipresent magmagene-hydrothermal minerals. For a number of accessory minerals of rare metal granites post-magmatic generations have been identified. Special diversity among accessories of rare metal granites and zwitters was observed in tungsten, tin and bismuth minerals. Composition of Verkhneurmiysk ore cluster mineralization is in many aspects similar to the one of metasomatic accessory minerals of rare metal granites. Tungsten-tin deposits of Verkhneurmiysk ore cluster are polyformational and combine mineralogical features of cassiterite-quartz and cassiterite-silicate formations. Evolution of mineral forms of the key rare elements (Sn, W, Bi, Nb, Ta, rare earth elements) points to a genetic link between tungsten-tin mineralization of zwitter-tourmalinite formation and rare metal Li-F granites of the region. The evidence of that is a specific genetic category of accessory materials, formed as a result of pseudomorphism of protominerals, – transformational minerals or metasomatic accessory minerals. The list of metasomatic accessories includes exactly those minerals which are considered indicators of ore generation capacity of Far Eastern leucogranites: cassiterite, wolframite, scheelite, a number of sulphides. Similar qualitative composition of magmatic and post-magmatic minerals demonstrates metallogenic specialization of parent granite magma. Predicted mineragenic significance of research in the field of mineral forms evolution of rare elements accumulation in ore-bearing granites and metasomatites is associated with possibilities to assess metallogenic specialization of parent granite magma. Understanding of accessory paragenesis evolution should serve as a base for exploration geo-technologies in the Far East metallogenic province.
