A new Cu-rich variety of lyonsite from fumarolic sublimates of the Tolbachik volcano (Kamchatka, Russia) and its crystal structure

A new Cu-rich variety of lyonsite has been found from fumarolic sublimates of the Tolbachik volcano (Kamchatka, Russia). The empirical formula is Cu_4.33Fe _2.37 ³⁺ Ti_0.26Al_0.26Zn_0.07(V_5.85As_0.07Mo_0.07P_0.01S_0.01)O₂₄. The crystal structure was studied on single crystal using synchrotron radiation, R = 0.0514. The mineral is orthorhombic, Pnma, a = 5.1736(7), b =10.8929(12), c = 18.220(2) Å, V = 1026.8(2) ų, and Z = 2. The structural formula is (Cu_0.6Ti_0.3Al_0.3Fe _0.2 ³⁺ □_0.6)_Σ2Cu₂(Fe _2.2 ³⁺ Cu_1.8)_Σ4(V_5.8As_0.1Mo_0.1)_Σ6O₂₄. It is proposed to recast the simplified formula of lyonsite as Cu_3+x (Fe _4?2x ³⁺ Cu_2x )(VO₄)₆, where 0 ≤ x ≤ 1.     

High‐temperature gold‐copper extraction with chloride flux in lava tubes of Tolbachik volcano (Kamchatka)

Subvolcanic environments in supra‐subduction zones are renowned for hosting epithermal deposits that often contain electrum and native gold, including bonanza examples. This study examined mineral assemblages and processes occurring in shallow‐crust volcanic settings using recent eruption (2012–2013) of the basaltic Tolbachik volcano in the Kamchatka arc. The Tolbachik eruptive system is characterized by an extensive system of lava tubes. After cessation of magma input, the tubes maintained the flow of hot oxidized gases that episodically interacted with the lava surfaces and sulphate‐chloride precipitates from volcanic gases on these surfaces. The gas‐rock interaction had strong pyrometamorphic effects that resulted in the formation of molten salt, oxidized (tenorite, hematite, Cu‐rich magnesioferrite) and skarn‐like silicate mineral assemblages. By analogy with experimental studies, we propose that a combination of these processes was responsible for extraction of metals from the basaltic wall rocks and deposition of Cu‐, Fe‐ and Cu‐Fe‐oxides and native gold.     

Arcanite from Fumarole Exhalations of the Tolbachik Volcano (Kamchatka,Russia) and Its Crystal Structure

The crystal structure (R = 0.0194) of arcanite β-K₂SO₄ was studied on a single crystal from exhalations of the Arsenatnaya fumarole, Tolbachik Volcano (Kamchatka, Russia). The mineral crystallizes at a temperature of ≥350–430°C and associates with langbeinite, aphthitalite, hematite, tenorite, johillerite, and others. Arcanite is orthorhombic, Pnma, a = 7.4763(2) Å, b = 5.77262(16) Å, c = 10.0630(3) Å, V = 434.30(2) ų, Z = 4. Its structure contains isolated SO₄ tetrahedra, whereas K cations center ten- and nine-fold polyhedra.     

Ludwigite and Yuanfuliite from Fumarolic Exhalations of the Tolbachik Volcano,Kamchatka, Russia

Geology of Ore Deposits - This paper in focused on the data for ludwigite and yuanfuliite of the new fumarolic genetic type. These ferric–magnesian borates (oxoborates) have been found in...     

New data on the composition of ophiolites from the Kumroch-Valagin segment of the Achayvayam-Valagin paleoarc (Eastern Kamchatka)

This study presents new data on the geochemistry and mineral chemistry of ultramafic and mafic rocks in ophiolits from the base of the Kumroch segment of the Achayvayam-Valagin paleoarc. The new data enabled us to consider peridotites and the associated diabases and gabbros enclosed as separated blocks into a serpentinite mélange as a single ophiolite complex formed in a supra-subduction setting and subsequently disintegrated as a result of nappe formation. The variations identified in the geochemistry and compositions of rock-forming minerals are shown to be characteristic of the other study ophiolite complexes of Eastern Kamchatka. This is suggested to reflect spatial-temporal heterogeneity of partial melting during evolution of the Achayvayam-Valagin island arc.     

The composition of melt and fluid inclusions in spinel of peridotite xenoliths from Avacha volcano (Kamchatka)

This work considers the studies of melt and fluid inclusions in spinel of ultramafic rocks in the mantle wedge beneath Avacha volcano (Kamchatka). The generations of spinel were identified: 1 is spinel (Sp-I) of the “primary” peridotites, has the highest magnesium number (#0.69–0.71), highest contents of Al₂O₃ and lowest contents of Cr₂O₃ (26.2–27.1 and 37.5–38.5 wt %, respectively), and the absence in it of any fluid and melt inclusions; 2 is spinel (Sp-II) of the recrystallized peridotites, has lower magnesium number (Mg# 0.64–0.61) and the content of Al₂O₃ (18–19 wt %), a higher content of Cr₂O₃ (45.4–47.2 wt %) and the presence of primary fluid inclusions; 3 is spinel (Sp-III) that is characterized by the highest content of Cr₂O₃ (50.2–55.4 wt %), the lowest content of Al₂O₃ (13.6–16.6 wt %), and the presence of various types of primary melt inclusions. The data obtained indicate that metasomatic processing of “primary” peridotites occurred under the influence of high concentrated fluids of mainly carbonate-water-chloride composition with influx of the following petrogenic elements: Si, Al, Fe, Ca, Na, K, S, F, etc. This process was often accompanied by a local melting of the metasomatized substrate at a temperature above 1050°C with the formation of melts close to andesitic.     

Physicochemical parameters of crystallization of melts in intermediate suprasubduction chambers (by the example of Tolbachik and Ichinskii Volcanoes,Kamchatka Peninsula)

In study of plagioclases, amphiboles, and melt inclusions, we have determined the physicochemical parameters of crystallization of melts in the intermediate suprasubduction chambers of volcanoes representing different types of subduction magmatism on the Kamchatka Peninsula: the young basaltic systems of Tolbachik Volcano (Klyuchevskaya group) and ancient Ichinskii Volcano (Sredinnyi Ridge) with alternating basaltic and felsic eruptions. For Tolbachik Volcano, we have found that plagioclase lapilli formed from basaltic melts at 1075-1115 °C and low (< 1 kbar) pressures at depths of 2-3 km. Andesite minerals crystallized within a wider range of temperatures and pressures (1220-1020 °C and 3.3-1.6 kbar) in an intermediate chamber at depths of < 10 km. The melts were generated in basaltic magma chambers (detected well by geophysical methods at depths of 18-20 km) with minimum temperatures of ~ 1290 °C. For Ichinskii Volcano, three levels of intermediate chambers are distinguished. Andesites formed at depths of < 23 km at < 1225 °C. Dacitic melts were generated from an intermediate chamber (14 km) at 1135-1045 °C as a result of differentiation of andesitic magmas. Dacites formed in the uppermost horizons (9-3 km) at 1130-1030 °C. Despite the similarity between differentiation processes in the intermediate chambers of the Kamchatka volcanoes, each volcano is characterized by specific magmatism. The lavas of basaltic volcanoes (Tolbachik) and those of andesitic volcanoes (Ichinskii) differ in genesis and differentiation.     

Insights into the origin of primitive silica-undersaturated arc magmas of Aoba volcano (Vanuatu arc)

Aoba picrites in Vanuatu arc (Southwestern Pacific) offer the opportunity to address the question of the origin of Si-undersaturated arc magmas, through the geochemical study of their olivine-hosted melt inclusions. These latter delineate a differentiation trend of calc-alkaline silica-undersaturated basalts, with typical trace-element patterns of arc magmas. The most primitive melt inclusions, preserved in olivines with Fo ≥ 89, have normative nepheline compositions with CaO/Al₂O₃ > 0.8, but belong to three distinct populations differing in their enrichment or depletion in LILE, Cl, and alkalis (Rb, K). The dominant population is characterized by medium-LILE concentrations (La/Yb ~ 7–8) and represents the parental magma of the Aoba lavas. The two others (La/Yb ~ 20 and 2) are either significantly enriched or extremely depleted in LILE, Cl, and alkalis. This compositional variability of primitive magma batches requires the multi-stage mixing between melts generated by partial melting of both peridotite and clinopyroxene-rich lithologies. Medium-LILE magma derives from the mixing between peridotite- and clinopyroxenite-derived melts, whereas the high- and low-LILE melts involve amphibole-bearing and amphibole-free clinopyroxenite sources, respectively.     

High-K basaltic trachyandesite xenoliths in pyroclastic deposits from the Bezymianny volcano (Kamchatka)

Bezymianny is an active andesitic volcano of the Klyuchevskaya group, and its eruptive products are xenolith- and enclave-bearing basaltic andesites and dacites. Here we report the first occurrence of clinopyroxene-plagioclase high-potassium basaltic trachyandesite xenoliths (51.84-53.00 wt.% SiO₂, 0.45-1.95 wt.% K₂O) crystallized in the temperature range 1120-840 °C in products of modern eruptions (2007, 2011, 2012). Basaltic trachyandesite differ systematically in petrologic and geochemical characteristics from all previously studied rocks from the Bezymianny volcano. They correspond to the clinopyroxene-plagioclase porphyry rocks from the foot of the Tolbachik volcanoes.     

First data on composition of the volcanic rocks of the IVS 50th anniversary Fissure Tolbachik eruption (Kamchatka)

First data on major, minor and trace element (XRF. 1CP-MS) concentrations in the volcanic rocks of the IVS 50th anniversary Fissure Tolbachik eruption are reported for the period from 27.11.2012 to 25.01.2013; scheme of lava flows distribution by March 2013 is made. The volcanic rocks of the new eruption are substantially different from the other studied volcanic rocks of Tolbachinsky Dol by their higher alkalis and incompatible elements content. The rocks of the first three days of eruption (Menyailov Vent) have higher silica and alkalis content than all previously reported volcanic rocks of Tolbachinsky Dol. Volcanic rocks of the Naboko Vent, at silica content similar to high-Al basalts of Tolbachinsky Dol, have different concentrations of trace elements and some major elements (K₂O, CaO, TiO₂, P₂O₅). REE and other incompatible element concentrations in the rocks of the Menyailov Vent are higher than in the rocks of the Naboko Vent at the same element ratios. The differences of the volcanic rocks of the two vents of the new eruption may be caused by the fact that the erupted lavas came from the different levels of the same magma chamber.     

Specific features of the mineral composition and petromagnetic properties of rocks from the Minami-Khiosi submarine volcano (Mariana island arc)

Complex studies of the mineral composition and petromagnetic properties of the rocks which compose an edifice of the Minami–Khiosi submarine volcano located in the Mariana island arc are carried out for the first time. The Minami–Khiosi Volcano is a part of the Khiosi volcanic complex within the alkaline province of the Idzu–Bonin and Mariana island arcs. All of the rocks analyzed are enriched in K₂O (1.34–3.30%), Ba (370–806 ppm), and Sr (204–748 ppm). The basalt has a porhyric texture and contains mosTy olivine phenocrysts as individual crystals and growths with a size up to 2 cm; the groundmass is finecrystalline. The samples studied contain at least three Fe-bearing oxide minerals. These are predominant magnetite and less abundant ilmenite and Fe hydroxides. It is established that the samples studied are magnetically isotropic and have high values of natural remanent magnetization and Königsberger ratio. Similarly to the other island-arc Late Cenozoic submarine volcanoes in the western part of the Pacific Ocean, the samples studied are strongly differentiated by the value of natural remanent magnetization and magnetic susceptibility. The low-coercivity magnetic minerals (titanomagnetite and magnetite) of the pseudo-single-domain structure, as well as high-coercivity minerals (hematite) are the main carriers of magnetization. The high values of natural remanent magnetization are explained by the pseudo-single-domain structure of the titanomagnetite grains, whereas the high values of magnetic susceptibility result from the high concentration of ferromagnetic grains.     

Melt evolution in subarc mantle: evidence from heating experiments on spinel-hosted melt inclusions in peridotite xenoliths from the andesitic Avacha volcano (Kamchatka,Russia)

Glass-bearing inclusions hosted by Cr-spinel in harzburgite xenoliths from Avacha are grouped based on homogenization temperatures and daughter minerals into high-T (1,200°C; opx + cpx), intermediate (900–1,100°C; cpx ± amph), and low-T (900°C; amph) and are commonly accompanied by larger “melt pockets”. Unlike previous work on unheated inclusions and interstitial glass in xenoliths from Kamchatka, the homogenized glass compositions in this study are not affected by low-pressure melt fractionation during transport and cooling or by interaction with host magma. Primary melt compositions constrained for each inclusion type differ in major and trace element abundances and were formed by different events, but all are silica saturated, Ca-rich, and K-poor, with enrichments in LREE, Sr, Rb, and Ba and negative Nb anomalies. These melts are inferred to have been formed with participation of fluids produced by dehydration of slab materials. The high-T inclusions trapped liquids produced by ancient high-degree, fluid-induced melting in the mantle wedge. The low-T inclusions are related to percolation of low-T melts or hydrous fluids in arc mantle lithosphere. Melt pockets arise from localized heating and fluid-assisted melting induced by rising magmas shortly before the entrapment of the xenoliths. The “high-T” melt inclusions in Avacha xenoliths are unique in preserving evidence of ancient, high-T melting events in arc mantle, whereas the published data appear to characterize pre-eruption enrichment events.     

Initial H2O content and conditions of parent magma origin for Gorely volcano (Southern Kamchatka) estimated by trace element thermobarometry

Doklady Earth Sciences - The formation conditions of the parental magmas of Gorely volcano, which is located behind a volcanic front in Southern Kamchatka, have been evaluated using the modern...     

The origin and evolution of the parental magmas of frontal volcanoes in Kamchatka: Evidence from magmatic inclusions in olivine from Zhupanovsky volcano

The paper presents data on naturally quenched melt inclusions in olivine (Fo 69–84) from Late Pleistocene pyroclastic rocks of Zhupanovsky volcano in the frontal zone of the Eastern Volcanic Belt of Kamchatka. The composition of the melt inclusions provides insight into the latest crystallization stages (∼70% crystallization) of the parental melt (∼46.4 wt % SiO₂, ∼2.5 wt % H₂O, ∼0.3 wt % S), which proceeded at decompression and started at a depth of approximately 10 km from the surface. The crystallization temperature was estimated at 1100 ± 20°C at an oxygen fugacity of ΔFMQ = 0.9–1.7. The melts evolved due to the simultaneous crystallization of olivine, plagioclase, pyroxene, chromite, and magnetite (Ol: Pl: Cpx: (Crt-Mt) ∼ 13: 54: 24: 4) along the tholeiite evolutionary trend and became progressively enriched in FeO, SiO₂, Na₂O, and K₂O and depleted in MgO, CaO, and Al₂O₃. Melt crystallization was associated with the segregation of fluid rich in S-bearing compounds and, to a lesser extent, in H₂O and Cl. The primary melt of Zhupanovsky volcano (whose composition was estimated from data on the most primitive melt inclusions) had a composition of low-Si (∼45 wt % SiO₂) picrobasalt (∼14 wt % MgO), as is typical of parental melts in Kamchatka and other island arcs, and was different from MORB. This primary melt could be derived by ∼8% melting of mantle peridotite of composition close to the MORB source, under pressures of 1.5 ± 0.2 GPa and temperatures 20–30°C lower than the solidus temperature of “dry” peridotite (1230–1240°C). Melting was induced by the interaction of the hot peridotite with a hydrous component that was brought to the mantle from the subducted slab and was also responsible for the enrichment of the Zhupanovsky magmas in LREE, LILE, B, Cl, Th, U, and Pb. The hydrous component in the magma source of Zhupanovsky volcano was produced by the partial slab melting under water-saturated conditions at temperatures of 760–810°C and pressures of ∼3.5 GPa. As the depth of the subducted slab beneath Kamchatkan volcanoes varies from 100 to 125 km, the composition of the hydrous component drastically changes from relatively low-temperature H₂O-rich fluid to higher temperature H₂O-bearing melt. The geothermal gradient at the surface of the slab within the depth range of 100–125 km beneath Kamchatka was estimated at 4°C/km.     

Kankan diamonds (Guinea) III: δ13C and nitrogen characteristics of deep diamonds

Diamonds from the Kankan area in Guinea formed over a large depth profile beginning within the cratonic mantle lithosphere and extending through the asthenosphere and transition zone into the lower mantle. The carbon isotopic composition, the concentration of nitrogen impurities and the nitrogen aggregation level of diamonds representing this entire depth range have been determined. Peridotitic and eclogitic diamonds of lithospheric origin from Kankan have carbon isotopic compositions ('¹³C: peridotitic -5.4 to -2.2‰; eclogitic -19.7 to -0.7‰) and nitrogen characteristics (N: peridotitic 17-648 atomic ppm; eclogitic 0-1,313 atomic ppm; aggregation from IaA to IaB) which are generally typical for diamonds of these two suites worldwide. Geothermobarometry of peridotitic and eclogitic inclusion parageneses (worldwide sources) indicates that both suites formed under very similar conditions within the cratonic lithosphere, which is not consistent with a derivation of diamonds with light carbon isotopic composition from subducted organic matter within subducting oceanic slabs. Diamonds containing majorite garnet inclusions fall to the isotopically heavy side ('¹³C: -3.1‰ to +0.9‰) of the worldwide diamond population. Nitrogen contents are low (0-126 atomic ppm) and one of the two nitrogen-bearing diamonds shows such a low level of nitrogen aggregation (30% B-centre) that it cannot have been exposed to ambient temperatures of the transition zone (̿,400 °C) for more than 0.2 Ma. This suggests rapid upward transport and formation of some Kankan diamonds pene-contemporaneous to Cretaceous kimberlite activity. Similar to these diamonds from the asthenosphere and the transition zone, lower mantle diamonds show a small shift towards isotopic heavy compositions (-6.6 to -0.5‰, mode at -3.5‰). As already observed for other mines, the nitrogen contents of lower mantle diamonds were below detection (using FTIRS). The mutual shift of sublithospheric diamonds towards isotopic heavier compositions suggests a common carbon source, which may have inherited an isotopic heavy composition from a component consisting of subducted carbonates.     

Typomorphic characteristics of the Ural diamonds (from FTIR spectroscopy data)

Natural diamonds from the Ural alluvial deposits have been studied by FTIR spectroscopy. It is shown that these diamonds are similar in some typomorphic features, such as nitrogen content and aggregation state, to the diamonds of the Coromandel (Brazil) and Verkhnee Molodo (Lena region, Yakutia) placers and to the diamonds from kimberlites of the Arkhangel’sk Region but differ significantly in lower contents of hydrogen and higher contents of platelets. The high contents of hydrogen (5–20 cm–1) determined in some diamonds are due to the specific formation of their internal structure and to the presence of inclusions. The nonuniform distribution of nitrogen A- and B-centers throughout the crystal testifies to the zonal structure of diamonds. The temperature conditions of formation of the Ural diamonds have been estimated.     

Kankan diamonds (Guinea) I: from the lithosphere down to the transition zone

Peridotitic inclusions in alluvial diamonds from the Kankan region of Guinea in West Africa are mainly of lherzolitic paragenesis. Nevertheless, extreme Cr₂O₃ contents (max. 17 wt%) in some of the exclusively lherzolitic garnets document that the diamond source experienced a previous stage of melt extraction in the spinel stability field. This initial depletion was followed by at least two metasomatic stages: (1) enrichment of LREE and Sr and (2) introduction mainly of MREE–HREE and other HFSE (Ti, Y, Zr, Hf). The Ti- and HFSE-poor character of stage (1) points towards a CHO-rich fluid or carbonatitic melt, the high HFSE in stage (2) favour silicate melts as enriching agent. Eclogitic inclusions are derived from a large depth interval ranging from the lithosphere through the asthenosphere into the transition zone. The occurrence of negative Eu anomalies in garnet and clinopyroxene from both lithosphere and transition zone suggests a possible relationship to subducted oceanic crust. Lithospheric eclogitic inclusions are derived from heterogeneous sources, that may broadly be divided into a low-Ca group with LREE depleted trace element patterns and a high-Ca group representing a source with negative LREE–HREE slope that is moderately enriched in incompatible elements relative to primitive mantle. High-Ca inclusions of majoritic paragenesis are significantly more enriched in incompatible elements, such as in Sr and LREE. Calculated whole rock compositions require metasomatic enrichment even if a derivation from MORB is assumed. Received: 26 January 2000 / Accepted: 18 May 2000