scholarly journals Typomorphism of Placer Gold and Prerequisites for the Discovery of Gold Ore Occurrences in the Southern Part of the Lena-Anabar Trough (North-East of The Siberian Platform)

2021 ◽  
Vol 906 (1) ◽  
pp. 012081
Author(s):  
Boris Gerasimov
Keyword(s):  
Siberian Platform ◽  
Primary Source ◽  
Potassium Feldspar ◽  
Primary Sources ◽  
Gold Content ◽  
High Grade ◽  
Alluvial Deposits ◽  
Placer Gold ◽  
North East ◽  
The North

Abstract The article examines the results of exploratory work carried out in the southern part of the Lena-Anabar trough in the north-eastern part of the Siberian platform. Alluvial deposits of the Polovinnaya river, which belongs to the Uele-Udzhinsky placer cluster, were sampled for predictive assessment of commercial prospects for placer occurrences of gold. The mineralogical-geochemical features of the placer gold were studied in order to identify potential primary sources. It is proved that the Mesozoic and Cenozoic deposits are the main sources of gold. Its typomorphic features are small size (-0.5 mm), toroidal and flake shape, shagreen surface with casts of pressing of the minerals, and high fineness (950-999 %). The internal structures of gold particles are represented by thick high-grade shells, translation lines and high-grade intergranular veinlets. Along with this, the discovery of the autochtonous gold of ore habit in the studied gold area suggested the presence of an additional primary source. Very small size (-0.2 mm) and angular-lumpy shapes of the individuals, almost unrounded surface and low fineness are typical features of slightly altered gold. The discovery of small (3-4mm) fragments of hydrothermal-metasomatic rocks in the alluvium of the Polovinnaya river confirms the above assumption. The epigenetic mineral composition of these fragments is represented by pyrite, potassium feldspar, fluorapatite, and quartz. Micro-X-ray spectral analysis determined the smallest (first microns) mineral phases of native gold, argentite, galena, sphalerite and greenockite in them. It is worth noting that the described fragments are quite fragile, and they are destroyed with a slight impact with a steel needle. The fragility of these fragments indicates the close proximity of the rewashed ore occurrences. In addition, increased gold content in small classes of heavy concentrate material of small-volume samples was determined according to atomic absorption analysis. All this together is a prerequisite for the discovery of ore occurrences with finely-dispersed and fine gold. It is assumed that the ore occurrences can be localized in the Anabar-Eekit fault zone, which extends parallel to the Pronchishchev ridge, through the Anabar-Olenek trough, to the Sololiy uplift of the Olenek arch. In the area of the Olenek arch, this zone is associated with superimposed gold-bearing low-temperature hydrothermal mineralization, expressed by K-feldspathization and sulfidization of the Permian deposits.

scholarly journals The Internal Structure of Placer Gold of the North-East of the Siberian Platform as a Reliable Search Sign of Primary Sources

2021 ◽  
Vol 906 (1) ◽  
pp. 012082
Author(s):  
Boris Gerasimov
Keyword(s):  
Internal Structure ◽  
Siberian Platform ◽  
Native Gold ◽  
Primary Source ◽  
Primary Sources ◽  
Placer Gold ◽  
North East ◽  
The North ◽  
History Of ◽  
Gold Sulfide

Abstract Typomorphic features of placer gold are carriers of the most important information necessary for the reconstruction of the history of the formation of placer and ore occurrences of gold and can be used as mineralogical criteria in the search for primary sources of placers. The study of these features is relevant for placer areas with unidentified gold sources, which include the territory of the north-east of the Siberian Platform. The internal structure of native gold is one of the most informative typomorphic features is. We studied the internal gold structures of modern placers and conglomerates of the Early Permian age in the north-east of the Siberian Platform. The purpose of the work: to identify the features of the internal structure of placer gold, depending on the chemical composition and the degree of its transformations, as well as the possibility of their use as a prospecting indicator. Structural etching of native gold was performed using the reagent: HCl + HNO3 + FeCl3 × 6H2O + CrO3 + thiurea + water. As a result of the research, it was found that the well-rounded high-grade gold of modern placers has undergone repeated redeposition through intermediate sources. The discovery of slightly rounded gold with an internal structure without signs of exogenous transformation indicates that it entered the modern alluvium from a nearby primary source. This was a prerequisite for setting up ore gold exploration, resulting in identification of apocarbonate hydrothermal-metasomatic formations with disseminated gold-sulfide mineralization were identified. Thus, the features of the internal structures of placer gold in combination with other typomorphic features are additional indications of determining the sources of formation of gold-bearing placers.

scholarly journals ABOUT ANCIENT SOURCES OF DIAMONDS PLACERS

2018 ◽  
pp. 44-54
Author(s):  
N. N. ZINCHUK
Keyword(s):  
Siberian Platform ◽  
Primary Sources ◽  
Complex Investigation ◽  
North East ◽  
The North ◽  
Upper Paleozoic ◽  
Middle Paleozoic ◽  
History Of ◽  
Recent Sediments ◽  
Thick Layers

Basing on generalization of large actual material on complex investigation of diamond, its characteristic in Upper Paleozoic and  Mesozoic sedimentary thick layers of the Siberian platform has been  provided. It has allowed receiving new data on composition features  and distribution of diamond in recent sediments of main  diamondiferous regions of Lena-Anabar, Central-Siberian and  Tungusskaya sub-provinces. On the north-east of Siberian platform,  the region of Kyutyungdinsky graben and nearby territories,  perspective for the discovery of rich kimberlite bodies with specific  dia- monds, are of the most interest. Special attention has been paid to the Central-Siberian sub-province, where it has been convincingly  shown that the area of development of individual diamond macro- associations is limited by a specific diamondiferous region, within  which complexes of different in age terrigenous and coastal Upper  Paleozoic and Mesozoic sediments are developed. The complex of  features of diamonds from placers of the described platform testifies  by morphology, coloration, hard inclusions, internal structure,  photoluminescence and admixture composition about plurality of  primary sources and availability of still undiscovered kimberlite  bodies within many diamondiferous regions. Application of  typomorphic features of crystals for restoration of exogenous history of diamonds on the path from primary sources to the sites of modern allocation in placers, as well as for paleogeographical reconstructions of distribution of ancient productive thick layers and clarification of  diamondiferous material drift direction, has a significant importance.  Proximity of typomorphic features of diamonds in sedimentary thick  layers of these ages, identified in some diamondiferous regions,  testifies about formation of these collectors due to washout of more  ancient productive layers or Middle Paleozoic primary sources.  Polygeny of mineralogical associations of diamonds from different in age placers within some diamondiferous regions has been noted,  which may be successfully used when forecasting and prospecting primary sources of the mineral.

scholarly journals Mineralogical and Geochemical Features of Native Gold From Placers of the Evota Gold-Bearing Region (Russia, Aldan Shield)

2021 ◽  
Vol 906 (1) ◽  
pp. 012116
Author(s):  
Anatolii Zhuravlev ◽  
Zinaida Nikiforova ◽  
Aleksey Ivanov ◽  
Michil Ivanov
Keyword(s):  
Native Gold ◽  
Aldan Shield ◽  
Potassium Feldspar ◽  
Primary Sources ◽  
Alkaline Magmatism ◽  
High Grade ◽  
Alluvial Deposits ◽  
Ore Mineralization ◽  
Very High ◽  
Gold Bearing

Abstract Evota gold-bearing region is located in south of Republic Sakha (Yakutia) within the Nimnyr terrane of Aldan shield. A large numbers of gold-bearing placers are known on studied territory, but the primary sources for them have not been established. In this work, based on the study of the mineralogical and geochemical features of gold from alluvial deposits of the Evota gold-bearing region, possible genetic types of primary sources are considered. Obtained data showed that native gold in the studied objects has a very high, high and medium fineness. The roundness of gold is different. Almost ore crystals with sharp edges and well-rounded individuals with polished faces were found. The fineness of the studied gold grains was determined by microprobe analyzer Cameca Camebax-micro and varies in the range from 812 to 1000 %⁰. A thin (up to 20 μm) high-grade rim was found in two grains (cr. Zolotoy). The central part of one of them has a fineness of 865 %o, and in the edge part it reaches 1000 %⁰, which indicates that this gold was in the hypergenesis zone. Admixture elements determined as traces and are presented Cu, Pd, Fe, Ni. Minerals-microinclusions - quartz, potassium feldspar, pyroxene, staurolite, maldonite, bismuthite revealed in gold grains. In some watercourses, for example, in the creek Sukhoi, only very high fineness gold (993-1000 %⁰) was found. The presence of high-grade gold (cr. Sukhoi), intergrowths of gold with bismuthite (cr. Zolotoy), as well as inclusions of maldonite (cr. Yagodny) gives opportunity for assuming that primary sources could be basic ores such presented in the P. Pinigin deposit. At the sites (cr. Elovyi, r. Evota), both medium-grade and very high-grade gold were found, the fineness range varied from 827 to 998 %⁰. The presence of gold with medium fineness and good roundness in studied watercourses probably indicates an additional supply of gold from primary sources formed as a result of the alkaline magmatism development of the Mesozoic age. Thus, for gold with high and very high fineness by admixture-elements, chemical composition and microinclusions, a genetic relationship with primary sources similar to the P. Pinigin deposit was found; for gold grains with medium fineness, formation in gold-ore mineralization characterized for the Mesozoic stage ore development such in deposits of Central-Aldan ore region is assumed.

scholarly journals Early Ordovician trilobites and molluscs from the Poulsen Cliff Formation, Washington Land, western North Greenland

1990 ◽  
Vol 38 ◽  
pp. 11-32
Author(s):  
R. A. Fortey ◽  
]. S. Peel
Keyword(s):  
Shallow Water ◽  
Siberian Platform ◽  
Gastropod Species ◽  
Early Ordovician ◽  
North East ◽  
The North ◽  
Close Relationship ◽  
North Greenland ◽  
Subjective Synonym

A well-preserved, shallow water bathyurid trilobite fauna of early Ordovician age, and associated gastropods and an undetermined hyolith are described from the Poulsen Cliff Formation of Washington Land, western North Greenland. Two new bathyurid species, Licnocephala sminue and Pe/tabellia elegans, and a new gastropod species, Plethospira(?) floweri, are described. Biolgina Maximova is considered a junior subjective synonym of Peltabellia Whittington. The distribution of the genus is an example of close relationship between shallow water trilobite faunas of Laurentia and the North-east Siberian platform in the early Ordovician.

Prospects of primary gold potential in southern Siberian platform based on study results for placer gold morphological and geochemical features

2021 ◽  
pp. 97-114
Author(s):  
Ivan Chetvertakov ◽  
Alexey Ivanov ◽  
Ekaterina Mikheeva ◽  
Tatyana Chikisheva ◽  
Tamara Yakich
Keyword(s):  
Siberian Platform ◽  
Geological Structure ◽  
Gold Deposits ◽  
Primary Sources ◽  
Placer Gold ◽  
Genetic Types ◽  
Study Results ◽  
Geochemical Property ◽  
Geochemical Studies ◽  
Primary Gold

Data on geological structure and minerals of the southern Siberian platform are presented. Placer and primary gold occurrences widespread in this region are briefly characterized. Based on placer gold morphological and geochemical property studies using electron microscopy, its four types are revealed. Conclusions are made about potential primary sources of various placer gold types. Using retrospective data and based on the authors’ placer gold morphological and geochemical studies, Ust-Ilimskaya, Chernorechinskaya and Buraevskaya gold areas are characterized, their prospects for discovering primary gold deposits of various genetic types are determined.

Deformation at the southern boundary of the late Archaean Atâ tonalite and the extent of Proterozoic reworking of the Disko terrane, West Greenland

1999 ◽  
pp. 155-169 ◽  
Author(s):  
John Grocott ◽  
Steven C. Davies
Keyword(s):  
Large Scale ◽  
Hanging Wall ◽  
Shear Zones ◽  
High Grade ◽  
Southern Boundary ◽  
Late Archaean ◽  
West Greenland ◽  
North West ◽  
North East ◽  
The North

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Grocott, J., & Davies, S. C. (1999). Deformation at the southern boundary of the late Archaean Atâ tonalite and the extent of Proterozoic reworking of the Disko terrane, West Greenland. Geology of Greenland Survey Bulletin, 181, 155-169. https://doi.org/10.34194/ggub.v181.5123 _______________ The c. 2800 Ma old Atâ tonalite in the area north-east of Disko Bugt, West Greenland has largely escaped both Archaean and Proterozoic regional deformation and metamorphism. At its southern margin the tonalite is in contact with migmatitic quartz-feldspar-biotite gneiss and to the south both are progressively deformed in a high-grade gneiss terrain. The main deformation in the high grade gneisses involved hanging wall north-west displacements on a system of low-angle ductile shear zones that structurally underlie the Atâ tonalite. This shear zone system is folded by a large-scale, steeply inclined and north-west-trending antiform defined by the change in dip of planar fabrics. Minor folds related to the antiform are present and there is some evidence that folding was synkinematic with emplacement of a suite of c. 1750 Ma old ultramafic lamprophyre dykes. In much of the north-east Disko Bugt area it remains difficult to separate Archaean from Proterozoic structures and hence the extent of the Archaean terrane that has escaped intense Proterozoic reworking remains uncertain.

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