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Native sulfur deposits on fumarolic fields at Ebeko volcano (Northern Kuriles, Russia) are enriched in chalcophile elements (As-Sb-Se-Te-Hg-Cu) and contain rare heavy metal sulfides (Ag2S, HgS, and CuS), native metal alloys (Au2Pd), and some other low-solubility minerals (CaWO4, BaSO4). Sulfur incrustations are impregnated with numerous particles of fresh and altered andesite groundmass and phenocrysts (pyroxene, magnetite) as well as secondary minerals, such as opal, alunite, and abundant octahedral pyrite crystals. The comparison of elemental abundances in sulfur and unaltered rocks (andesite) demonstrated that rock-forming elements (Ca, K, Fe, Mn, and Ti) and other lithophile and chalcophile elements are mainly transported by fumarolic gas as aerosol particles, whereas semimetals (As, Sb, Se, and Te), halogens (Br and I), and Hg are likely transported as volatile species, even at temperatures slightly above 100°C. The presence of rare sulfides (Ag2S, CuS, and HgS) together with abundant FeS2 in low-temperature fumarolic environments can be explained by the hydrochloric leaching of rock particles followed by the precipitation of low-solubility sulfides induced by the reaction of acid solutions with H2S at ambient temperatures. The elemental composition of native sulfur can be used to qualitatively estimate elemental abundances in low-temperature fumarolic gases. [ABSTRACT FROM AUTHOR]

Hyperspectral cathodoluminescence (CL) mapping, combined with electron probe microanalysis (EPMA) and Fourier transform infrared spectroscopy, was used for the reconstruction of crystallization conditions of quartz from porphyry environments. Quartz eyes from the two porphyry deposits Rio Blanco (Chile) and Climax (U.S.A.) were studied. Three peaks are found to be responsible for the total CL emission: 1.93, 2.05, and 2.72 eV. The first two peaks are assigned to O-M (with M being an alkali ion) and oxygen vacancies, respectively. The 2.72 eV peak shows a linear correlation with the Ti concentration determined by EPMA point measurements. In addition, a negative correlation between the 1.93 eV emission and the Al concentration was observed.Quartz grains often form clusters in which adjacent grains show identical CL patterns, indicating that they crystallized attached to each other and were not disturbed later. Quartz cores display sector zoning and enrichment in Li, OH, and sometimes Al, which points to rapid crystallization from an extremely evolved melt. Quartz rims show high Ti, and low Li and OH contents, indicating crystallization from a less evolved melt either at higher temperatures or at higher titanium activities. The Al and Ti distribution patterns are frequently not correlated and both show uneven distribution indicating fast growth from inhomogeneous melts. Only Ti displays sharp transitions and fine oscillatory zoning, which can be explained by the higher mobility of Al in the quartz lattice.The quartz eyes crystallized after magma emplacement under non-equilibrium conditions. It is likely that the crystallization occurred from the melt enriched in Al, Li, and OH and probably other metals and/or volatiles on the brink of fluid exsolution. Subsequent fluid exsolution brought about disequilibrium to the system, resulting in dissolution of quartz and redistribution of elements between the melt and the fluid. The OH, Li, and other alkali metals and volatiles partitioned into the fluid, whereas Ti and Al remained in the melt. Resorption of quartz caused by the fluid exsolution continued until equilibrium was reached again, after which crystallization of quartz rims began from the water-, alkali-, and volatile-poor melt with higher Ti activity. Further accumulation of Al and Ti in the residual melt led to crystallization of extremely Al- and Ti-rich quartz. [ABSTRACT FROM AUTHOR]

Alaskan-type platinum-bearing plutons and potassium-enriched mafic to ultramafic volcanic rocks are temporally and spatially associated within the Late Cretaceous–Paleocene Achaivayam–Valaginskii intra-oceanic palaeo-arc system, allochthonously present in the Koryak Highland and Kamchatka Peninsula (Far East Russia). The compositions of the parental magmas to the Alaskan-type complexes are estimated using the Galmoenan plutonic complex as an example. This complex, composed of dunites, pyroxenites and minor gabbros, is the largest (∼20 km3) in the system and the best studied owing to associated platinum placer deposits. The compositions of the principal mineral phases in the Galmoenan intrusive rocks [olivine (Fo79–92), clinopyroxene (1–3·5 wt % Al2O3, 0·1–0·5 wt % TiO2), and Cr-spinel (5–15 wt % Al2O3 and 0·3–0·7 wt % TiO2)] are typical of liquidus assemblages in primitive island-arc magmas in intra-oceanic settings, and closely resemble the mineral compositions in the Achaivayam–Valaginskii ultramafic volcanic rocks. The temporal and spatial association of intrusive and extrusive units, and the similarity of their mineral compositions, suggest that both suites were formed from similar parental magmas. The composition of the parental magma for the Galmoenan plutonic rocks is estimated using previously reported data for the Achaivayam–Valaginskii ultramafic volcanic rocks and phenocryst-hosted melt inclusions. Quantitative simulation of crystallization of the parental magma in the Galmoenan magma chamber shows that the compositions of the cumulate units are best modelled by fractional crystallization with periodic magma replenishment. The model calculations reproduce well the observed mineral assemblages and the trace element abundances in clinopyroxene. Based upon the estimated composition of the parental magmas and their mantle source, we consider that fluxing of a highly refractory mantle wedge (similar to the source of boninites) by chlorine-rich aqueous fluids is primarily responsible for both high degrees of partial melting and the geochemical characteristics of the magmas, including their enrichment in platinum-group elements. [ABSTRACT FROM AUTHOR]

Thick dolerite sills show a range of vertical geochemical variation trends attributable to various processes during slow crystallization. We have identified chemical parameters in a 169-m-thick sill from the Karoo igneous province in South Africa that define three different lower crossover levels (maximum or minimum concentrations) creating S-shaped variation trends. The crossover level for wholerock MgO is at 20 m height (due to mechanical sorting of olivine); the anorthite content of plagioclase is at 52 m (due to addition of primitive magma); and that of the incompatible trace elements is at 75 m (due to different proportions of early formed grains to trapped liquid). Each process can operate independently and concurrently, leading to their maximum effects occurring at different levels in the intrusion. The independence of these processes and the triple S-shaped geochemical profiles have not been recognized before in any mafic-ultramafic sills. [ABSTRACT FROM AUTHOR]