The results of Sr-chemostratigraphic study of carbonates of the Staraya Rechka and Nemakit-Daldyn formations which make up the upper part of the Precambrian cover of the Anabar Uplift in Northern Siberia are presented. A Pb–Pb age of the Staraya Rechka Formation dolostone has been obtained (549 ± 25 Ma, MSWD = 1.4) for the first time. An improved stepwise dissolution procedure was used to determine the 87Sr/86Sr, 206Pb/204Pb and 207Pb/204Pb isotopic ratios in carbonates rocks. The methodology for studying the Rb–Sr systematics included the chemical removal of about a third of the crushed sample [fraction L(Rb–Sr)1] by preliminary acid leaching in 0.2N CH3COOH and subsequent partial dissolution [fraction L(Rb–Sr)2] of the remaining part of the sample in CH3COOH of the same concentration. The Pb–Pb isotopic systematics of dolostones was studied by six to nine-step dissolution in 0.5N HBr. Chemical procedures resulted in the removal of secondary epigenetic carbonate material, which improved the quality of Sr-chemostratigraphic and U–Pb geochronological information. The initial 87Sr/86Sr ratios in the least altered carbonate material [fraction L(Rb–Sr)2] of the Staraya Rechka Formation dolostone are 0.70822‒0.70836, and in the Nemakit-Daldyn Formation limestone, 0.70854–0.70856. The Pb–Pb age of early diagenesis of dolostones of the Staraya Rechka Formation (549 ± 25 Ma) was calculated from fractions [L(U–Pb)2–L(U–Pb)n], where n for different samples varied in the range from 6 to 9. Epigenetic carbonate fractions L(U–Pb)1 are characterized by a Pb–Pb age of 360 ± 190 Ma (MSWD = 0.8). The obtained results prove that the Staraya Rechka Formation of the Anabar Uplift belong to the Late Vendian (Late Ediacaran), allowing them to be confidently correlated with the carbonate rocks of the upper part of the Yudoma Group of the Uchur-Maya region and to include the named strata into a single Yudoma Complex of Siberia.

Complex gold-iridium-osmium placer deposits associated with the Guli massif of ultramafic, alkaline rocks and carbonatites are located within the Maimecha-Kotui province in the northern part of the Siberian Platform. Unlike natural Os-Ir alloys, which are genetically related to ultramafic rocks, the bedrock source of gold remains controversial. We report, for the first time, morphological and compositional features of gold mineralization from calcite-dolomite carbonatite of the Guli massif. Gold minerals are represented by natural Au-Ag alloys containing gold (69.64–88.57 wt

The Kotuy intrusive complex was identified from the geological survey of the western slope of the Anabar Massif in the middle reaches of the Kotuy River. It is represented by dolerite–gabbrodolerite sills and dikes of Vendian age (556 ± 28 Ma). A number of sills are characterized by 30–80 m thickness, and dikes often have a length of a few dozen kilometers. The distribution area of the complex is a few hundred square kilometers. However, the geodynamic evidence for the formation of extensive intrusive bodies in the northern part of Siberia in the Vendian is not clear. We present new geochronological, geochemical, and paleomagnetic data indicating that at least part of the Kotuy magmatic complex intrusions in the middle reaches of the Kotuy River should be attributed to the 1500 Ma Kengede magmatic complex (Kuonamka large igneous province). In this light, the very existence of Vendian intrusive magmatism on the western slope of the Anabar massif appears questionable.

This paper presents new age estimates and results obtained by the chemostratigraphic study of dolostones of the Billyakh Group, which consists of the Kotuikan and the Yusmastakh formations. The Billyakh Group forms the upper part of the Riphean section of the Anabar uplift in northern Siberia. The stepwise dissolution technique was used for the first time to determine the 87Sr/86Sr, 206Pb/204Pb, and 207Pb/204Pb isotopic ratios in dolostones. The Rb‒Sr systematics was studied by the chemical removal of about a third of the crushed sample (fraction L1) by the preliminary acid leaching in 0.2 N CH3COOH and the subsequent partial dissolution (fraction L2) of the remaining part of the sample in CH3COOH with the same concentration. The Pb‒Pb isotope systematics of dolostones was studied by the six-step dissolution of crushed samples in 0.5 N HBr. These procedures led to the removal of secondary carbonate material and greatly improved the quality of Sr chemostratigraphic and geochronological information. The initial 87Sr/86Sr ratios of the least altered carbonate material (fraction L2) of the Billyakh Group dolostones are 0.70502 ± 0.00029 in the Kotuikan Formation, 0.70519 ± 0.00026 in the lower subformation of the Yusmastakh Formation, and 0.70511 ± 0.00018 in the upper subformation of the Yusmastakh Formation. The Pb‒Pb age of early diagenesis of Kotuikan and Yusmastakh dolostones (1519 ± 18 Ma at MSWD = 1.8) was calculated from the results obtained for carbonate fractions L3–L6. Secondary carbonate fractions L1‒L2 are characterized by a Pb‒Pb age of 1466 ± 54 Ma at MSWD = 0.6. The δ13C values vary from ‒1 to ‒0.4‰ in dolostones of the Kotuikan Formation and from ‒0.4 to +0.8‰ in those of the Yusmastakh Formation (from ‒0.1 to +0.4‰ in the lower subformation and from ‒0.4 to +0.8‰ in the upper subformation). Comparison of these variations, as well as variations in the initial 87Sr/86Sr ratios in dolostones of the Kotuikan Formation and the Lower and Upper Yusmastakh subformations (0.70460‒0.70499, 0.70450‒0.70525, and 0.70462‒0.70523, respectively), does not make it possible to distinguish these units on the basis of chemostratigraphic characteristics.

Определены концентрации U и Pb и изотопные составы углерода, кислорода и свинца в доломитах билляхской серии (в 6 образцах котуйканской свиты и 15 образцах юсмастахской свиты), слагающей верхнюю часть рифейского разреза Анабарского поднятия Северной Сибири. Величины δ 13 С и δ 18 O в доломитах билляхской серии варьируют от –3.0 до +0.8‰ PDB и от 23.7 до 27.3‰ SMOW соответственно и согласуются с таковыми в карбонатных осадках, отлагавшихся 1600–1400 млн лет назад. На графике в координатах 206 Pb / 204 Pb – 207 Pb / 204 Pb 18 фигуративных точек всех образцов котуйканской и юсмастахской свит располагаются вдоль прямой линии, которая отвечает возрасту 1513 ± 35 млн лет. Полученный Pb – Pb возраст доломитов впервые дает прямую изотопно-геохронологическую характеристику осадочных пород чехла Анабарского поднятия и в сочетании с опубликованным ранее Rb–Sr возрастом глауконита нижележащей усть-ильинской свиты позволяет поместить всю осадочную последовательность билляхской серии в ранний рифей. Эти результаты указывают на относительно быстрое (в пределах ~10 млн лет) накопление терригенно-карбонатных отложений билляхской серии до внедрения долеритов котуйского комплекса и заложения мезопротерозойской куонамской магматической провинции на Сибирском кратоне. Новые данные ставят точку в дискуссиях о возрастном положении рифейских отложений, вскрытых на Анабарском поднятии.

The U and Pb contents and C, O, and Pb isotopic compositions are determined for dolomites of the Billyakh Group (6 and 15 samples of the Kotuikan and Yusmastakh formations, respectively), which composes the upper part of the Riphean section of the Anabar Uplift of North Siberia. The δ13С and δ18O values of dolomites vary from –3.0 to +0.8‰ PDB and from 23.7 to 27.3‰ SMOW, respectively, and are in agreement with those of carbonate sediments 1600–1400 Ma in age. On the 206Pb/204Pb–207Pb/204Pb plot, 18 data points of all samples of both formations occur along a straight line which corresponds to the age of 1513 ± 35 Ma. The Pb–Pb age of dolomites is a first direct geochronological characteristic of sedimentary rocks of the Anabar uplift cover and, along with the previously published Rb–Sr age of glauconite of the underlying Ust’-Il’ya Formation, allows us to ascribe the entire sedimentary sequence of the Billyakh Group to the Lower Riphean. These results indicate relatively fast (~10 m.y.) terrigenous-carbonate sedimentation of this group prior to intrusion of dolerites of the Kotui complex and origination of the Mesoproterozoic Kuonamka igneous province on the Siberian Craton. New data close a discussion on the age position of Riphean sediments of the Anabar Uplift.

New 87Sr/86Sr, δ13C, and δ18О chemostratigraphic data were obtained for carbonate rocks of the Lower Riphean Yusmastakh and the Vendian Starorechenskaya formations. The δ13С values in dolomites of the Yusmastakh Formation varies from–0.6 to–0.1‰ and in dolomites and dolomitic limestones of the Starorechenskaya Formation, from–1.2 to–0.4‰ PDB, and δ18О values, from 24.4 to 26.4‰ and from 25.3 to 27.6‰ SMOW, respectively. The Rb–Sr systematics of carbonate rocks was studied using the refined method of stepwise dissolution of samples in acetic acid, including chemical removal of up to one-third of the ground sample by preliminary acid leaching and subsequent partial dissolution of the rest of the sample. Owing to this procedure, secondary carbonate material is removed, which enables one to improve the quality of the Sr-chemostratigraphic data obtained. The initial 87Sr/86Sr ratios in carbonate rocks of the Yusmastakh (0.70468–0.70519) and Starorechenskaya (0.70832–0.70883) formations evidence the Riphean–Vendian boundary in the Precambrian sequence of the Anabar Uplift.