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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.

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Yukonite, a rare arsenic-bearing hydrous mineral, the crystal symmetry and variety in chemical composition of which have so far been insufficiently studied, has been found in the modern deposit of Nalychevskie hot springs in Central Kamchatka, Russia. This is the first finding of yukonite in Eastern Eurasia and Siberia. Yukonite specimens from Nalychevskie hot springs and from Venus Mine in Yukon Territory, Canada, have been investigated using an analytical transmission electron microscope (TEM). Yukonite is a crystalline substance with extremely thin (∼5 nm) platy morphology. Yukonite from Venus Mine forms brittle aggregates in which grains are irregularly bent and randomly distributed. At Nalychevskie hot springs, yukonite occurs as single plates, coexisting with some amorphous material of similar composition. Intensity distributions in electron diffraction indicate that most plates of yukonite at Nalychevskie hot springs have orthorhombic symmetry, but some are hexagonal with ahex = 11.3 Å. The orthorhombic cell is C-centred with aorth = √3ahex, borth= ahex. High-resolution images of edge-on mounts indicate that the periodicity normal to the planes is d001=11.2 Å. Yukonite from Nalychevskie hot springs contains anomalously high Si relative to that in yukonite from Venus Mine and that reported previously. Strong negative correlation between As and Si indicates that Si substitutes for As in the structure.

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. The Mutnovskoe deposit located in the Porozhisto‐Asachinskaya metallogenic province of South Kamchatka, Russia, is a polymetallic vein and Au‐Ag quartz vein associated type of hydrothermal deposit. The Mutnovskoe deposit is located inside a paleo‐caldera structure at the center of the Mutnovsko‐Asachinskaya geothermal field of Pliocene ‐ Quaternary age, where active gold deposition is identified in hot spring precipitate. The Mutnovskoe deposit is subdivided into the north flank, the central flank and the south flank based on the vein distributions and mineral parageneses. The mineralized vein system is oriented N‐S hosted in diorite ‐ gabbroic diorite stock, volcanic rocks and sedimentary rocks of Miocene ‐ Pleistocene age. The mineralization stage I (polymetallic vein) mainly in the central and the south flanks is Zn‐Pb‐Cu‐Au‐Ag contained in sphalerite, galena and tetrahedrite‐tennantite group mineral. The stage II (Au‐Ag quartz vein) occurs in the north and the central flanks. The stage III (Mn‐sulfide and Mn‐Ca‐carbonate vein) occurs in the whole deposit area. Stage II is the typical Au‐Ag quartz‐adularia vein of low‐sulfidation type. Stage III is alabandite‐rhodochrosite‐quartz‐calcite vein. The K‐Ar ages are 1.3±0.1 Ma for stage I sericite in alteration zone, and 0.7±0.1 Ma for the stage II adularia in mineralized vein. Based on the fluid inclusion study, range of ore forming temperature of the Mutnovskoe deposit is 200 to 260d̀C (av. 230d̀C). Salinities of fluid inclusions indicate 2.2 to 5.7 wt% NaCl in sphalerite and 0.8 to 3.3 wt% NaCl in quartz for the stage I. Mineral paragenesis of the polymetallic vein (stage I) is characterized by a district zoning of tennantite and Cd‐rich sphalerite in the south flank and tetrahedrite and Mn‐rich sphalerite in the central flank, which is due to the fractional crystallizations of ore‐forming fluid. Depositional condition of the low sulfidation state is inferred for the Mutnovskoe deposit, where the polymetallic vein of the south flank is in relatively higher sulfidation state than the central flank.

Abstract:The new mineral novograblenovite, (NH 4 ,: 3.330 (100) (2 2 0), 2.976 (45) ( ̅ ), 2.353 (29) ( ̅ ), 3.825 (26) (2 0 2), 1.997 (25) ( ̅̅̅̅̅ 2). The density calculated from the empirical formula and the X-ray data is 1.504 g·cm -3 . The mineral is biaxial (+) with α = 1.469(2), β = 1.479(2), γ = 1.496(2) (λ = 589 nm); 2V (meas.) = 80(10) º and 2V (calc.) = 75.7º. The crystal structure (solved and refined using single-crystal X-ray diffraction data, R1 = 0.0423) is based on the perovskite-like network of (NH 4 ,K)Cl 6 -octahedra sharing chlorine vertices, and comprises [Mg(H 2 O) 6 ] 2+ groups in framework channels. The positions of all independent H atoms were obtained by difference Fourier techniques and refined isotropically. All oxygen, nitrogen and chlorine atoms are involved in the system of hydrogen bonding, acting as donors or acceptors. The formula resulting from the structure refinement is [(NH 4 ) 0.7 K 0.3 ]MgCl 3 ·6H 2 O. The mineral is named after Prokopiy Trifonovich Novograblenov, one of the researchers of Kamchatka Peninsula, a teacher, naturalist, geographer and geologist.

The Asachinskoe epithermal Au-Ag deposit is a representative low-sulfi dation type of deposit in Kamchatka, Russia. In the Asachinskoe deposit there are approximately 40 mineralized veins mainly hosted by daciteandesite stock intrusions of Miocene -Pliocene age. The veins are emplaced in tensional cracks with a north orientation. Wall-rock alteration at the bonanza level (170 -200 m a.s.l.) consists of the mineral assemblage of quartz, pyrite, albite, illite and trace amounts of smectite. Mineralized veins are well banded with quartz, adularia and minor illite. Mineralization stages in the main zone are divided into stages I -IV. Stage I is relatively barren quartz -adularia association formed at 4.7 ± 0.2 Ma (K-Ar age). Stage II consists of abundant illite, Cu-bearing cryptomelane and other manganese oxides and hydroxides, electrum, argentite, quartz, adularia and minor rhodochrosite and calcite. Stage III, the main stage of gold mineralization (4.5 -4.4 ± 0.1 -3.1 ± 0.1 Ma, K-Ar age), consists of a large amount of electrum, naumannite and Se-bearing polybasite with quartz -adularia association. Stage IV is characterized by hydrothermal breccia, where electrum, tetrahedrite and secondary covellite occur with quartz, adularia and illite. The concentration of Au+Ag in ores has a positive correlation with the content of K 2 O + Al 2 O 3 , which is controlled by the presence of adularia and minor illite, and both Hg and Au also have positive correlations with the light rare-earth elements. Fluid inclusion studies indicate a salinity of 1.0 -2.6 wt% NaCl equivalent for the whole deposit, and ore-forming temperatures are estimated as approximately 160 -190°C in stage III of the present 218 m a.s.l . and 170 -180°C in stage IV of 200 m a.s.l. The depth of ore formation is estimated to be 90 -400 m from the paleo-water table for stage IV of 200 m a.s.l., if a hydrostatic condition is assumed. An increase of salinity ( ⌬ C NaCl ≈ 0.2 wt%) and decrease of temperature ( ⌬ T ≈ 30°C) within a 115-m vertical interval for the ascending hydrothermal solution is calculated, which is interpreted as due to steam loss during fl uid boiling. Ranges of selenium and sulfur fugacities are estimated to be log f Se 2 = −17 to −14.5 and log f S 2 = −15 to −12 for the ore-forming solution that was responsible for Au-Ag-Se precipitation in stage III of 200 m a.s.l. Separation of Se from S-Se complex in the solution and its partition into selenides could be due to a relatively oxidizing condition. The precipitation of Au-Ag-Se was caused by boiling in stage III, and the precipitation of Au-Ag-Cu was caused by sudden decompression and boiling in stage IV.