Metasomatized hazburgite xenoliths from Avacha volcano as fragments of mantle wedge of the Kamchatka arc: Implication for the metasomatic agent

金沢大学理工研究域自然システム学系Abundant peridotite xenoliths have been found in pyroclasitics of Avacha (Avachinsky) volcano, the south Kamchatka arc, Russia. They are mostly refractory harzburgite with or without clinopyroxene: the Fo of olivine and Cr/(Cr+Al) atomic ratio of spinel range from 91 to 92 and from 0.5 to 0.7, respectively. They are metasomatized to various extents, and the metasomatic orthopyroxene has been formed at the expense of olivine. The metasomatic orthopyroxene, free of deformation and exsolution, is characterized by low contents of CaO and Cr2O3. The complicated way of replacement possibly indicates low viscosity of the metasomatic agent, namely hydrous fluids released from the relatively cool slab beneath the south Kamchatka arc. This is a good contrast to the north Kamchatka arc, where the slab has been hot enough to provide slab-derived melts. High content of total orthopyroxene, 40 vol% on average, in metasomatized harzburgite from Avacha suggests silica enrichment of the mantle wedge, and is equivalent to some subcratonic harzburgite. Some subcratonic harzburgites therefore could have been formed by transportation of subarc metasomatized peridotites to a deeper part of the upper mantle

Sulfides of the Modern Kamchatka Hydrothermal Systems

ABSTRACT Sulfides pyrite, melnikovite-pyrite, marcasite, sphalerite, chalcopyrite, galena, cinnabar, coloradoite, metacinnabar are precipitating at the modern geothermal systems of Kamchatka: Kireunsky, Dvukhyurtochny and Apapel'sky in Central Kamchatka, Vilyuchinsky and Mutnovsky in Southern Kamchatka. Ore deposits are spatially associated with hydrothermal springs. Pyrite is the most common mineral precipitated at the discharge of hydrothermal style. It varies in mode of occurrence, size, inner structure, chemical composition and microstructure. Frequently pyrite occurs as framboids, idiomorphic crystals and their aggregates. By chemical composition, two varieties of pyrite are observed: homogeneous and heterogeneous. Heterogeneity of composition is due to impurities of As, Cu, Sb, Hg and Ag. Au as impurity in pyrite was relieved only in pyrite from Voinovsky hot springs in Southern Kamchatka. Cinnabar is the next most common occurring mineral at the modern hydrothermal systems in Kamchatka. Chalcopyrite, galena, sphalerite and gold are rare minerals. The modern hydrothermal systems in Kamchatka provide the opportunity to study sulfide typomorphism and physico-chemical conditions of the deposition mechanism. We suppose that some of them are the elements of the long-life ore generating hydrothermal systems

Heavy metallic concentration in microbial mats found at hydrothermal systems, Kamchatka, Russia

Department of Earth Sciences, Faculty of Science, Kanazawa UniversityInstitute of Volcanology Far Eastern Division of Russian Academy of SciencesDepartment of Earth Sciences, Faculty of Science, Kanazawa UniversityGraduate School of Natural Science and Technology, Kanazawa UniversityGraduate School of Natural Science and Technology, Kanazawa UniversityGraduate School of Natural Science and Technology, Kanazawa UniversityGraduate School of Natural Science and Technology, Kanazawa UniversityGraduate School of Natural Science and Technology, Kanazawa UniversityDepartment of Earth Sciences, Faculty of Science, Kanazawa UniversityThis study described the investigation of microbial mats that are rich in iron, arsenic, and manganese in four hydrothermal systems of Kamchatka, Russia namely Vilyuchinskie, Mutnovskie, Nachikinskie, and Malkinskie. The hydrothermal systems (hot springs) are contributing to the metallic and non-metallic mineral resources of Russia such as oil, gas, coal, copper, nickel, cobalt, tin, mercury, lead, zinc, diamond, platinum, gold, and silver. We observed the biogeochemical activities of microorganisms originating from microbial mats. The structure and elemental composition of microbial mats in these hydrothermal systems were studied with optical microscopy and scanning electron microscopy equipped with energy dispersive X-ray analyzer (EDX), whereas the water quality of these springs was measured by using pack tests. Additionally, portable Y-ray analyzer was employed to determine the kind and quantity of Y-ray in the atmospheric condition of sampling areas. Optical and scanning electron microscopic observations revealed that the microbial mats at these springs were mainly composed of a large number of microorganisms such as bacteria (coccus, bacillus, and filamentous), cyanobacteria, and algae in association with biominerals. Bacterial fluorometric enumeration of the thermal water informed that the total number of bacteria was relatively low, while the fraction of enzymatically active bacteria was high ranging from 27 % to 91 %. Besides that, ƒﾁ-ray observation showed that the predominantly ƒﾁ-ray range was between 320-380 keV dominating in green and black-colored microbial mats at Vilyuchinskie hot springs. Correspondingly, heavy metal and minerals deposits accumulated at all these springs indicating that microorganisms may contribute to binding and formation of the minerals. These activities and heavy mineral encrustation of cyanobacteria, bacteria, and algae may contribute to the growth of the heavy metal deposit (such as iron, manganese, and arsenic) at these springs. Obviously, Kamchatka hot springs provide a model for studying the potential role of prokaryotes and eukaryotes in the origin of heavy metal and minerals formation

Cathodoluminescence and Trace Elements in Quartz : Clues to Metal Precipitation Mechanisms at the Asachinskoe Gold Deposit in Kamchatka

The Asachinskoe epithermal gold deposit in South Kamchatka, Russia, is a low-sulfidation type deposit which consists of Au-Ag bearing quartz-adularia-illite veins. Cathodoluminescence (CL) analysis using optical microscope and scanning electron microscope and trace element analysis of quartz using electron probe micro-analyzer (EPMA) were performed to elucidate the relationships between CL structures, trace element concentrations of different quartz generations, and metal precipitation mechanism of the Asachinskoe deposit. Five sequences of quartz crystallization can be distinguished within the mineralized vein of the bonanza zone. Most distinctive trace elements in quartz are Al (av. 1463 ppm) and K (av. 350 ppm). Colloform and microcrystalline quartz with moderate to dull red-brown CL coexists with electrum (Au-Ag alloy), naumannite-aguilarite (ss) and polybasite-pearceite (ss). The Au-Ag-Se precipitation is related to fluid boiling, and the Se enrichment is attributed to relative oxidizing mineralization conditions. Almost non-luminescent, dark brown luminescent quartz forming the matrix of the hydrothermal breccia coexists with electrum, tetrahedrite-tennantite (ss) and covellite. The Au-Ag-Cu precipitation is associated with rapidly precipitated quartz and adularia, and is due to sudden decompression and fluid boiling related to the hydrothermal brecciation.International Symposium, "The Origin and Evolution of Natural Diversity". 1–5 October 2007. Sapporo, Japan

Rock seismic anisotropy of the low-velocity zone beneath the volcanic front in the mantle wedge

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