Disseminated Gold–Sulfide Mineralization in Metasomatites of the Khangalas Deposit, Yana–Kolyma Metallogenic Belt (Northeast Russia): Analysis of the Texture, Geochemistry, and S Isotopic Composition of Pyrite and Arsenopyrite

At the orogenic gold deposits of the Yana–Kolyma metallogenic belt (northeast Russia) both Au–quartz-sulfide mineralization with native gold and disseminated sulfide mineralization with invisible Au developed. The textural and mineralogical-geochemical features, isotope-geochemical characteristics of gold-bearing sulfides from proximal metasomatites, and possible forms of Au occurrence in pyrite and arsenopyrite have been studied using electron microprobe, atomic absorption, LA-ICP-MS trace element, isotope analysis, and computed microtomography. Four generations of pyrite (Py1, diagenetic; Py2, metamorphic; Py3, metasomatic; Py4, veined) and two generations of arsenopyrite (Apy1, metasomatic; Apy2, veined) have been identified at the Khangalas deposit. In the proximal metasomatites, the most common are Py3 and Apy1. Studying their chemical composition makes it possible to identify the features of the distribution patterns of typochemical trace elements in pyrite and arsenopyrite, and to establish the nature of the relationship between Au and these elements. In Py3 and Apy1, structurally bound (solid solution) Au+ prevails, isomorphically entering the crystal lattice or its defects. Isotope characteristics of hydrothermal sulfides (d34S = –2.0 to –0.6‰) indicate that mantle/magmatic sulfur was involved in the formation of the deposit, though the participation of sulfur from the host rocks of the Verkhoyansk clastic complex cannot be ruled out. The Khangalas deposit has much in common with other gold deposits of the Yana–Kolyma metallogenic belt, and from this point of view, the results obtained will help to better reveal their gold potential and understand their origin.

AGE OF GOLD MINERALIZATION IN THE YANA-KOLYMA METALLOGENIC BELT, NORTHEAST RUSSIA: FIRST DATA OF RE-OS ISOTOPE GEOCRONOLOGY OF NATIVE GOLD

Presented are the first results of studying the Re-Os isotope system of native gold from the orogenic Malo-Taryny, Khangalas, and Bazovsky deposits located in the central part of the Yana-Kolyma metallogenic belt. Re concentration in the sampled gold varies from 0.168 to 6.997 mg/t while that of Os changes from 0.068 to 1.443 mg/t. The data obtained enabled calculation of the isochrone age which is consistent, within the limits of error, with 40Ar-39Ar and К-Аr dates of sericite from the above deposits. The results obtained indicate that gold deposits under study were formed in the interv of 147.8–137.1 Ma synchronously with Late Jurassic – Early Cretaceous orogenic processes in the Yana-Kolyma metallogenic belt and the eastern margin of the Siberian continent. The initial Os isotope ratios ((187Os/188Os)i= 0.1844–0.2475) in the studied samples and fractions of gold from the Malo-Tarynsky, Khangalas and Bazovsky deposits suggest a significant role of a non-radiogenic component, normally associated with mantle sources.

THE FIRST U-PB SHRIMP DATING OF ZIRCONS FROM CAPITANIAN (MIDDLE PERMIAN) DEPOSITS OF THE OMOLON MASSIF (NORTHEAST RUSSIA)

U-Pb dating of zircons from two samples of stratotype sections of the Gizhiga Formation of the Middle Permian of the Omolon Massif was first performed. Weighted average ages are 266 ± 2 and 265 ± 3 Ma taking into account the error, are consistent with Capitanian age previously established by paleontological determination. The presence of a detrital zircon population made it possible to identify several sources in the Omolon Basin. Pre–permian zircons are associated with erosion of basement deposits of the Omolon Massif, and the Middle Paleozoic volcanic rocks of the Kedon series and Permian population of zircons linked with volcanic activity of the Okhotsk-Taigonos volcanic arc.

Three new and one little-known species of Hypogastruridae (Collembola) from Russia’s northeast

Three new species, Hypogastrura variatasp. nov., Xenylla aculeatasp. nov., and X. arneisp. nov., are described based on material from coastal communities of the Sea of Okhotsk, northeast Russia. Taxonomic remarks concerning a little-known species, H. yosii Stach, 1964, found in coastal wrack sediments on Kunashir Island, Kuriles are also given. COI sequences of the above species are analysed, thus allowing for their species statuses to be confirmed.