A. I. Khanchuk

First results of zircon LA-ICP-MS U-Pb dating of the rocks from the Granulite complex of Khanka massif in the Primorye region

This work is dedicated to the first results of zircon LA–ICP–MS U–Pb dating of the rocks from the granulite complex of the Khanka Massif in the Pri� morye region. Similar to the Khingan–Bureya (Rus� sia) and Jiamusi (China) terranes, the Khanka Massif (terrane) represents one of the principal structural ele�

Cenozoic volcanism of the eastern Sikhote Alin: Petrological studies and outlooks

Based on geological and isotope geochemical data obtained during the past decade, the eastern Sikhote Alin volcanic belt can be considered as a polygenic structure with spatially superimposed magmatic complexes of different geodynamic stages. Only Late Cretaceous intermediate and silicic volcanics enriched in LILE and depleted in HFSE can be interpreted as typical subduction complexes. Cenozoic lavas of mainly basic composition were formed after the termination of active subduction under complex dynamic conditions of the rearrangement of eastern Eurasia owing to the collision with the Indian plate. The eruption of Eocene-Oligocene-early Miocene basalts corresponded to the transform continental margin environment, rupture of an ancient subducted slab, and upwelling of hot depleted oceanic asthenosphere of the Pacific MORB-type into the Asian subcontinental lithosphere with EMII-like isotopic characteristics. The late Miocene-Pliocene magmatic activity of the eastern Sikhote Alin showed an intraplate character, but the composition of erupted magmas was strongly affected by previous tectonomagmatic events: subduction of different ages and opening of the Sea of Japan Basin. The distinct EMI isotopic signature of low-potassium plateau basalts, which is not observed in the lavas of earlier stages of volcanic belt evolution, suggests that the continental asthenosphere contributed to magma formation, and the direction of mantle flows changed owing to the formation of a new subduction zone.

First finds of platinoids in black-shale sequences of the Bureya Massif (Khabarovsk Region and Jewish Autonomous Okrug)

The problem of the platinum-metal potential in black-shale sequences has recently attracted the attention of geologists [1‐5], since highly carbonaceous rocks of different origins are considered to represent the most probable future nontraditional natural source of gold and platinoids. Black shales with high carbon contents are widespread in the Bureya Massif. Single chemical analyses revealed in them elevated concentrations of platinoids ranging from 0.0 n to n g/t [6]. The forms of platinoids occurring in these rocks remain, however, unknown, which hampers the assessment of their recoverable reserves and development of technologies for their extraction. In this connection, the purpose of this work is the study of the composition, morphology, and grain-size of platinoids in these rocks. Using the method of the scanning electron microscopy with an energy-dispersion analyzer (SEM-EDA), we found and first studied platinoids in black shales of the Sutyr and Kimkan sequences in the eastern Bureya Massif. These sequences represent constituents of the Upper Riphean‐Lower Cambrian Khingan Group. They are subjected to greenschist metamorphism, structurally uniform, and characterized by elevated carbon contents. The Sutyr Sequence ( PR 1 st ) constitutes an extended (75 × 5 km) tectonic block in the Khingan deep-seated fault zone. It is largely composed of carbonaceous shales, phillites, and metasiltstones with C org concentrations of 1 to 22%. Shales are sulfidized to different extents and enclose locally thin quartz stringers. Sulfides (pyrite and subordinate pyrrhotite, chalcopyrite, arsenopyrite, covelite, and marcasite) form fine-grained (up to 1 mm) impregnation, rare stringers, and lenses up to 0.5‐2.0 cm long. Carbonaceous material consists of fine dispersed amorphous matter and fine graphite scales sized 0.01‐0.03 mm. The semiquantitative analyses revealed gold, platinum, and palladium (up to 0.1, 0.04, and 0.01 g/t, respectively) in rocks of the sequence. Based on the lithological features, the Kimkan

Noble metals in graphitized rocks of the Khanka terrain (Primorye): Evidence from analytical results based on decomposition by the fluoroxidizing method

Development of the geology, geochemistry, and analytical chemistry of noble metals (NM) in the past 30 years has provided new insights into the nature of unconventional complex gold and platinum group metal (PGM) deposits. In particular, such deposits confined to black shales were discovered in Caledonides of the Central Asian orogenic belt, such as the well-known Muruntau, Kumtor, Zun-Kholba, Irokinda, Sukhoi Log, Nezhdaninskoe, Natalka, and others. In the past 10‐15 years, commercial PGM concentrations were detected in ores of these deposits [1‐4 and others]. The PGMs in these deposits are traditionally assigned to the carbonaceous matter (CM) of rocks. However, it turned out that they are likely (and primarily) associated with sulfides. Geochemical aspects of PGM concentration in rocks (and ores) and issues of their reliable determination have attracted the main attention in discussions devoted to the problem of PGM occurrence in black shales in the recent period of more than 20 years [4, 5, and others]. The Khankai massif is located at the center of the Central Asian orogenic belt in the Russian Far East. The NM mineralization (Au + PGM) was recently discovered in graphitized rocks [6] of the well-known graphite deposits in the Lesozavodsk region of Primorye [7]. Relative to the typical black shales mentioned above, these rocks are almost devoid of sulfides [8]. However, this interesting feature is provoked apparently by technical difficulties in the analysis of PGMs. For example, analysis of Au and Pt by glow discharge ion mass spectrometry (GDI MS) [9] yielded 3‐30 and 4‐52 g/t, respectively. Duplicate analysis of the same samples by atomic coupled plasma atomic emission spectrometry (ICP AES) and atomic absorption spectrometry by thermoelectric atomization with prior extract concentration (EC TEA) yielded, on average, two orders of lower Au concentrations, while the presence of Pt was not confirmed at all [10]. However, such contradictory results are common for the analysis of black shales due to both poor representativeness of the samples analyzed and losses of the NM during the chemical preparation of samples and their transfer to solutions, as was demonstrated for the Natalka deposit [5, 11, and others].

Platinum- and gold-bearing rodingites of the ust'-dep ophiolite block (middle amur region)

The Ust’-Dep ophiolite block, a part of the Selemdzha‐Zeya Belt, occupies an area of 350 km 2 and incorporates apoharzburgite serpentinite massifs intruded by numerous (>60) dikes of diabases and granitoids up to 100 m thick and more than 1 km long. Ophiolitic outcrops of this block make up a SW- to NW-trending band extending from the right bank of the Zeya River to the Gar River basin. Only small fragments of ophiolite massifs are preserved in spurs of the Tukuringr Ridge (Fig. 1). The Ust’-Dep and Gar protrusions in this area include dislocation zones with superimposed metasomatic alterations (development of listvenites and rodingites with gold mineralization). The majority of rodingite and listvenite occurrences are confined to outcrops of Lower Paleozoic‐Middle Cretaceous granitoid intrusions and dikes. Listvenites usually considered the source of placer gold are scrutinized in [1, 2]. However, data on the gold potential of rodingites in the Ust’-Dep block are lacking, although they are similar to rodingites in the Zolotaya Gora deposit (southern Urals) that was previously proposed as a holotype of the gold‐rodingite association [3]. Their similarity is manifested in the development of rodingites among listvenitized serpentinites. Therefore, the gold mineralization of Uralian rodingites is attributed to a younger process of listvenitization [4].

Ferromanganese crusts from submarine volcanoes of backarc basins as a new genetic type of gallium deposits

Study of the material composition of Fe-Mn crusts from submarine rises in the central part of the Sea of Japan, with modern precision methods applied, has yielded a high (up to 854 g/t) concentration of gallium contained in sorbed form. The new data obtained have allowed a new genetic type of gallium deposits—hydrothermal-sedimentary—to be distinguished.

Discoveries of nanostructures of natural mercury-bearing gold at the surface of ilmenite crystals from the Fadeevskii ore-and-placer cluster (Primor’ye)

1310 Recently, the volume of publications dedicated to the nanomineralogy of gold has increased significantly in the geological literature [1, 2]. Although there is wide coverage of the problem as a whole, we note that there is a lack of information on the natural nano structures of gold. Investigations of ultrasmall amounts of rock material sampled from the occur rences of rocks and deluvial sediments of the Fadeevskii ore and placer cluster (Fig. 1) located at the boundary between the Khankayskii and Laoelin Grodekovskii territories [3] may make up for this lack of information. In the lower part of the stratified section of the investigated area, basalt–siliceous–tuffaceous, sili ceous–clayey, argilliferous, and tuffaceous–sandstone sediments (S1–2) occur. They are overlapped by volca nogenic–sedimentary strata of Permian age (P1–2) and acid effusive rocks (P2). The rocks of the volcano genic–terrigenous complex, including black shales, are intruded in the south by large massifs of granitoids. In the north they are intruded by small bodies of gab broids and syenites [4]. Silver bearing gold, minerals of platinum group metals (first of all, isoferroplatinum) as well as sulfides (pyrite, arsenopyrite, sphalerite, galenite, molibden ite), kassiterite, volframite, and minerals of bismuth were found among the minerals of heavy crop schlichs of loose sediments of the Faddevka (watershed system of Razdol’naya River) and Zolotaya (basin of the Nes terovka River) rivers draining granitoids and black shale stratum in the southern and northern parts of the area, respectively. A significant part of black schlich consists of ilmenite, magnetite, chromespinellides, garnets, rutile, and sphene. The presence of the unique association of natural mercury bearing gold, cinnabar, native metals, and carbides is a unique fea ture of northern placers [5].