АННОТАЦИЯ: Для Джимидонского жильного полиметаллического месторождения (Северная Осетия, Россия), сформированного в среднеюрское время, по характеру распределения редкоземельных элементов в жилах и породах установлено, что источники РЗЭ и рудных компонентов являлись комбинацией различных по составу вмещающих пород (PR3-PZ1, PZ3) и сменялись во времени

Data on the distribution of elements across the Pb-Zn section of the Gatsyrovskaya vein (Upper Zgid, North Ossetia, Russia) showed that during the formation of the vein significant changes in the spectra of rare-earth elements (REE) occur in ore samples. The sharp growth of ratios La N /Yb N , La N /Nd N , Gd N /Ho N , and Gd N /Yb N is confined to the vein intervals, where the maximum amount of ore components is deposited. A comparison of the REE spectra of ores with the characteristics of the spectra of the near-vein and host rocks suggests that the deposition of the vein material occurred from solutions whose compositions with respect to the REE varied with time. REE fractionation occurred due to the mobilization of components by hydrothermal solutions during their reaction with the host Paleozoic granites.

A possibility of the direct determination of palladium in dissolved samples of platinum sulfide ores by high-resolution electrothermal atomic absorption spectrometry with a continuous light source without preconcentration and separation from the matrix components is investigated. The conditions of analysis are selected and a procedure for the determination of palladium is developed. The results of determination well agree with the data obtained using extraction separation and traditional atomic absorption spectrometry with selective line spectrum sources. The accuracy of the results was estimated by the added–found method.

The distribution of elements and their correlations were analyzed throughout the section of the Kivakka intrusion to formulate the geochemical tendencies in the behavior of elements of different groups during formation of layered basic-ultrabasic complexes. (1) It was shown that the distribution of trace elements in the layered series is controlled by their ability or inability to enter isomorphically the cumulus minerals. The distribution of trace elements that occur as isomorphic admixtures in cumulus minerals (Cr, Mn, Zn, Co, Ni, and Ti), regardless of their geochemical type, is correlated with the crystallization order and distribution of minerals in the silicate matrix of the rocks. Elements that practically are not involved into silicates (S, Cu, Ag) show no any systematic variations; i.e., they are not controlled by fractionation of major rock-forming mineral. Their behavior is driven by the appearance of individual phase—sulfide melt, whose localization, formation time, and scales of fractionation are determined by saturation of parental melt in sulfide sulfur and general degree of its fractionation. (2) The comparison of cross-section variations of elements that isomorphically substitute for major elements in the Fe-Mg silicates, but differ in chalcophile affinity (in order of increase of chalcophile affinity: Mn → Zn → Co → Ni) reflects the contribution of unmixing and fractionation of sulfide melt during intrusion solidification. This is quantitatively defined primarily by partitioning coefficients of elements between cumulus silicates and magmatic melt, on the one hand, and between magmatic and sulfide melts, on the other hand. (3) The absence of simple correlation between local sulfide-rich horizons and silicate matrix of the rocks and signs of independent fractionation of sulfide melt prevent any attempts to predict the localization and scales of local sulfide mineralization within the layered series on the basis of petrochemical and related criteria. Only tendencies in the distribution of ore elements and sulfur across the section can be used for these purposes.

A variety of geological, petrological, and geochemical techniques were used in examining the internal structure of the Kivakka layered intrusion, whose thickness attains 2000 m. The following zones were distinguished in the vertical section of the intrusion: the Upper and the Lower Contact zones and the Layered Series. The Layered Series is composed of a succession of cumulates (listed in order from bottom to top): olivine, bronzite-plagioclase, bronzite-plagioclase-augite, and plagioclase-augite-pigeonite. The section is characterized by analyses (for major and trace elements) of 87 rock samples. Based on cumulative mineral assemblages, the Layered Series was subdivided into four zones: Olivinite, Norite, Gabbronorite, and Gabbronorite with pigeonite as a low-Ca pyroxene. The distribution of major oxides was used to distinguish six megarhythms. The boundaries between the lower four megarhythms are accompanied by horizons of low-sulfide mineralization with elevated concentrations of precious metals. The outlines of the intrusion suggests that its original shape was a vertical inverted cone with an apex angle of approximately 80 degrees and a height of approximately 3.9 km. Later, the intrusion was inclined to the northwest at an angle of 36 degrees and partly eroded. The weighted-average composition of the intrusion is close to the mean composition of the contact-facies rocks and is approximated by basalts of the marianite-boninite series. The vertical succession of cumulative mineral assemblages (which is typical of the crystallization of boninitic magma) and the trends in the trace-element concentrations of the rocks testify that the development of the intrusive layering was controlled predominantly by crystallization differentiation. Our data will be utilized in the computer simulation of the development of the intrusion with the use of the COMAGMAT program package.

The Lukkulaisvaara intrusion (U–Pb age: 2442 ± 1.9 Ma), in northern Karelia, Russia, belongs to the Oulanka plutonic group. The intrusion cuts rocks of the Archean granite – migmatite – gneiss basement and is disconformably overlain by Proterozoic metavolcanic rocks. The layered body does not exceed 4600 m in thickness; data obtained on the structural profile of the intrus ion suggest a complete section. Its weighted-mean composition is equivalent to a magma of the marianite–boninite series, but whethe r or not this composition corresponds to the parental magma is uncertain owing to possible multiphase features of the intrusion. It is quite possible that large and small lenticular bodies of fine-grained gabbronorite whose texture suggests rapid crystallizat ion are associated with injections of fresh magma. Crystallization to fine-grained gabbronorite in the process of magma chilling is related, in turn, to decompression. Chilling would be equally feasible in the case of the injection of residual melts, squeezed from lower horizons and already carrying cumulus minerals in the process of compaction. Structures in which fine-grained rocks occur do not differ from “potholes” in morphology and structural setting. Two genetic types of sulfides are distinguished: (a) sulfid es of magmatic stage are present in fresh rocks, commonly with magmatic quartz and biotite; (b) a metasomatic sulfide assemblage contains the richest sulfide and platinum mineralization and is related to potholes. Amounts of sulfide in the metasomatic rock s are very variable (1–30 vol.%). Forty platinum-group minerals have been documented in sulfide-bearing metasomatic rocks; the concentration of noble metals (Pt + Pd) covers a wide range (0.3–10 ppm Pt, 0.42–66 ppm Pd). Sulfides in the cumulates and iron bearing magmatic minerals altered by metasomatism are considered to be the source of the ore-bearing metasomatic assemblages. These assemblages were formed under the action of a reducing hydrothermal fluid. A high content of chlorine was observed in biotite (up to 0.55 wt%), amphibole (up to 2.5 wt%), chlorite (up to 0.1 wt%), and scapolite (up to 2.3 wt%). Examination of th e metasomatic quartz reveals the presence of different types of micro-inclusions. Some are filled with liquid only, others are ga s– liquid, aqueous – salt inclusions with a gas bubble, and hydrocarbon inclusions with various amounts of liquid. The highest T h recorded is 370°C at a pressure of 1.5 kbar, as estimated using aqueous – salt inclusions. These data agree well with thermobarometric results calculated using estimated equilibration states. Nd and Sr isotopic data suggest that the metasomatic assemblages formed simultaneously with the layered intrusion (2442 Ma) during an autometasomatic process due to reworking of intrusive rocks by a mantle-derived fluid with an Nd of +2.1 and an initial 87 Sr/ 86 Sr value of 0.7028.

PGE mineralization of the Lukkulaisvaara massif belongs to the low-sulfide type. The most considerable deposits are confined to the "pothole" structures of the gabbro-norite-I and norite-II zones and have a metasomatic genesis. The sulfide and PGE mineralization is restricted to (1) the pothole bottom or underlying rocks, (2) the contacts with fine-grained norites and gabbro-norites, and (3) veined facies of the mineralized pyroxenites and gabbro-norites typical of large microgabbro-norite bodies. According to the assemblage of secondary silicate minerals, talc-anthophyllite-tremolite metasomatites I and amphibole-clinozoisite-chlorite-quartz metasomatites II are distinguished. The former are characteristic of the veined facies of the ore-bearing rocks. The richest PGE mineralization was discovered in the metasomatized veined facies of the mineralized pyroxenites and gabbro-norites (metasomatites I), as well as in the metasomatites after leucocratic gabbronorite-anorthosites developed on contact with microgabbro-norites (metasomatites II). These rocks contain more than 40 PGE minerals the Pt + Pd contents in the rocks are as high as 70 ppm. Data on gas-liquid and aqueous inclusions, together with the paragenetic analysis of the secondary minerals indicate that the most active rock alteration occurred at 320-450 degrees C and 1.5-2.0 kbar in a reduced environment of high salinity. The Sm-Nd mineral age of the metasomatites is 2423+/-180 Ma, which is consistent with the massif age within the analytical error. However, the distinct initial Nd isotope composition of the metasomatites and layered-series rocks (epsilon Nd=+0.9 for metasomatites compared to -2.1 for the weakly altered rocks) may indicate that the metasomatic fluids were derived from different sources: one of them being isotopically similar to and the other different from the source of the rocks.