Ore Occurrences Research Articles

Formation and formation-fracture oxidation in Carbon-Permian sediments and ancient weathering crust of Western Yakutia and related scandium ore occurrences

Formation and formation-fracture oxidation in Carbon-Permian sediments and ancient weathering crust of Western Yakutia and related scandium ore occurrences

First Data on Gold–Copper Mineralization of the Kontorskoe Ore Occurrence (Ariadnoe Ultramafic Intrusion, Primorye)

First Data on Gold–Copper Mineralization of the Kontorskoe Ore Occurrence (Ariadnoe Ultramafic Intrusion, Primorye)

Gold–Sulfide Mineralization in the Manitanyrd Region, Polar Urals, Russia

This article describes the characteristics of gold–sulfide–quartz and gold–sulfide (gold–arsenic) ore occurrences in the Manitanyrd region of the Polar Urals. Ore occurrences are confined to NE-trending shear zones and have the common features of a geological structure. The host rocks are metamorphosed volcanic and volcanic–sedimentary rocks. We analyzed the mineral and chemical composition of the ore mineralization in all studied ore occurrences, showing that they belong to the same mineral type—pyrite–arsenopyrite, with a variable ratio of the main minerals. Arsenic pyrite is present in all ore occurrences. Two stages of ore formation were distinguished: early gold–pyrite–arsenopyrite with finely dispersed gold and late gold–galena–chalcopyrite–sphalerite with coarse gold, fahlore, and sulfosalts Pb, Cu, Bi, Sb. Native gold of the first generation, finely dispersed in arsenopyrite and pyrite, had an average to high fineness (800‰–1000‰) with a relatively low dispersion. Native gold of the second generation was larger, and its fineness in ore occurrences varied; in one of them, it varied from 300‰ to 950‰, while in others, it varied from 800‰ to 950‰. The isotope composition of sulfur in sulfides (δ34S) ranged between −0.2‰ and −8.0‰. δ34S values of sulfides in the range of −0.2‰ to −3.5‰ were similar to meteorite, indicating the participation of a single deep magmatic source of sulfur in the ore formation. According to the study of fluid inclusions, the formation of ore quartz veins occurs in the temperature range of 467–109 °C. The similarity of the geological–structural, mineralogical–geochemical, and isotope–geochemical features of the gold–sulfide–quartz and gold–sulfide occurrences in the area suggest their formation in a single hydrothermal system.

AGE OF ORE-BEARING IRON-MAGNEZIAN METASOMATITES OF THE CENTRAL PART OF THE ALDAN SHIELD: RESULTS OF U–PB (ID-TIMS) GEOCHRONOLOGICAL STUDIES OF GARNET

U–Pb (ID-TIMS) geochronological studies of garnet from iron-magnesian metasomatites of the ore occurrence of the Kurung-Hoonku River area (Legliera group of deposits, West Aldan megablock) were carried out. The results obtained (1901 ± 5 MA) are first age determination of formation ore-bearing iron-magnesian metasomatites on the Aldan shield. It show their connection with the final stages of the Early Proterozoic tectonic-magmatic evolution of the Aldan geoblock.

Redox conditions of formation of the Priiskovy massif rock and their metallogenic consequences (South Sikhote-Alin, Primorye)

The same Cenomanian (96.91 ± 0.88 and 96.5 ± 1.2 Ma) age of amphibole granodiorites of the magnetite and ilmenite series in the southern part of the Priiskovy massif has been established. Among the relatively homogeneous central ilmenite zone of the Sikhote-Alin orogenic belt, the local occurrence of magnetite rocks of the Priiskovy massif explains the distribution of deposits and ore occurrences of the studied site. All deposits and ore occurrences of tin within the boundaries of the Priiskovy massif are located in the zone of distribution of rocks of the ilmenite series (reducing conditions), and deposits and placers of gold and manifestations of polymetallic mineralization are located in the zone of rocks of the magnetite series (oxidizing conditions)

Layered Intrusions of Paleoproterozoic Age in the Kola and Karelian Regions

Large-scale layered intrusions of a peridotite–pyroxenite–gabbronorite complex, to which Cr, Ni, Cu, and PGE deposits and ore occurrences are confined, were emplaced into the Baltic paleocontinent 2.50–2.45 Ga. Layered intrusions in the Monchegorsk Ore District, including the Monchepluton and Imandra–Umbarechka Complex, as well as the gabbro-anorthosite complex of the Main Ridge, were analyzed earlier geochemically and isotopically. In the present paper, the authors analyze layered intrusions in the Kola region (Mount Generalskaya) and Karelia (Kivakka, Kovdozero, and the Burakovsky Pluton). The primary composition of mantle magmas for the layered intrusions is assumed to be identical to that of the komatiitic basalts making up the volcanogenic units of the Vetreny Belt and the Imandra–Varzuga zone. A general model for the formation of layered intrusions includes superplume uplift in the early Paleoproterozoic, the generation of mantle magmas and their injection into the lower portion of the earth crust, the formation of deep-seated and intermediate magma chambers, and the intense contamination of the granulite–metamorphic complex followed by the generation of magma chambers provoked by single or multiple injections.

PETROCHEMICAL AND STRUCTURAL CHARACTERISTICS OF PORPHYRY COPPER MINERALIZATION IN THE ASTANEH ORE DEPOSIT, MIDDLE PART OF THE URUMIEH-DOKHTAR MAGMATIC ARC (IRAN)

Within the Urumieh-Dokhtar Magmatic Arc in the central part of Iran, the formation of which is associated with the Neotethys closure, there are many porphyry copper deposits and ore occurrences. One of them is the Astaneh porphyry copper ore deposit, located in the central part of the Saveh-Ardestan ore region southeast of Ardestan city. The purpose of this study is to investigate the petrochemical characteristics of rocks and to determine the relationship between the distribution of porphyry copper mineralization and tectonic position of faults within the study area. To achieve the goal, there were used the structural and geological data obtained in the fieldwork, as well as the results of mineralogical and geochemical analyses. The obtained results show that rocks of different composition of the Astaneh ore deposit (andesite, andesite-basalt, basalt, trachybasalt) were formed in the suprasubduction zone, and probably in the environment prior to the collision of the of continental plates. Paragenetic relationships and mineralogical analysis show that the evolution of mineralization of the Astaneh ore deposit can be divided into three stages: pre-ore, hypogene and supergene mineralization. Geochemical research based on the study of the content of the major chemical elements in the rocks of the region shows that igneous rocks belong to calc-alkaline basalts and geodynamically can be attributed to the products of magmatism of the ensial island arc. The results concluded that the main stages of the formation of a porphyry copper ore deposit in the study area attain maximum spatio-temporal similarity with the tectonomagmatic phases of the development of the Neotethys Ocean. In addition, the Southern Ardestan fault, running through the study area and intersecting the basement structures, forms wide permeable zones favorable for the formation of porphyry copper deposits therein.

Pd,Hg-Rich Gold and Compounds of the Au-Pd-Hg System at the Itchayvayam Mafic-Ultramafic Complex (Kamchatka, Russia) and Other Localities

The unique minerals of the Au-Pd-Hg system in gold grains from heavy concentrates of the Itchayvayam placers and watercourses draining and ore samples of the Barany outcrop at the Itchayvayam mafic–ultramafic complex (Kamchatka, Russia) were investigated. Gold grains from watercourses draining and heavy concentrates of the Itchayvayam placers contain substitution structures formed by Pd,Hg-rich low-fineness gold (Au0.59–0.52Pd0.24–0.25Hg0.17–0.23, 580‰–660‰) and Pd,Hg-poor high-fineness gold (Au0.94–0.90Pd0.02–0.04Hg0.03, 910‰–960‰). Potarite (PdHg) without and with impurities (Au < 7.9, Cu < 3.5, Ag < 1.2 wt.%), Ag-poor high-fineness gold (Au0.91Ag0.09, 950‰), Ag,Pd,Hg-bearing middle-fineness gold (Au0.75Ag0.08Pd0.09Hg0.08—Au0.88Ag0.09Pd0.02Hg0.01, 820‰–930‰), and Pd,Hg-rich low-fineness gold with minor contents Ag and Cd (Au0.51–0.55Pd0.25–0.22Hg0.21–0.16Ag0.03–0.06Cd0.01, fineness 580‰–630‰) were observed as individual microinclusions in the ore samples of the Barany outcrop. XRD and EBSD study results show that the Pd,Hg-rich low-fineness gold is isotypic to gold and has the same structure type, but different cell dimensions. According to data obtained for the Itchayvayam and some deposits and ore occurrences with Pd,Hg-bearing gold, the stable ternary phases and solid solutions of the following compositions in the Au-Pd-Hg system have been identified: Pd,Hg-poor gold (Au0.94–0.90Pd0.02–0.04Hg0.03), Pd,Hg-rich gold (Au0.59–0.52Pd0.24–0.25Hg0.17–0.23), Au-potarite (PdHg0.62Au0.38—Pd1.04Hg0.96—Au0.80Pd0.68Hg0.52), and Au,Hg-bearing palladium (Pd0.7Au0.3Hg0.1). The genesis of Pd,Hg-rich gold is insufficiently studied. We supposed that the meteoric waters or low-temperature hydrotherms rich in Pd and Hg could lead to the replacement Pd,Hg-poor gold by Pd,Hg-rich gold. High concentrations of Pd in Pd,Hg-bearing gold indicate a genetic relationship with mafic–ultramafic rocks.

Ore composition and native gold characteristics of an ore occurrence in Eastern Transbaikalia

The article deals with the characteristics of the ores of an ore occurrence of the Munginsky cluster located on the western flank of one of the commercial fields of Eastern Transbaikalia. The ores of this promising ore occurrence are underexplored, especially in the technological aspect, which served the basis for studying their composition and characterizing native gold as their main commercial component. The composition of ores and altered rocks was studied by the following methods: atomic emission spectral quantitative analysis, X-ray fluorescence, as well as phase atomic absorption and atomic emission analysis with inductively coupled plasma ICP-AES. The mass fraction of total and organic carbon was determined in the Central Fire Assay Laboratory of JSC Pokrovsky Rudnik, Blagoveshchensk. The proportion of carbonate carbon dioxide was determined by the method of titrimetric determination of carbon dioxide. The content of gold was given according to the data of assay melting, the content of silver – according to the data of atomic absorption analysis. Petrographic and mineragraphic studies were carried out using an optical microscope Olympus BX-51. The mineral composition of the ore sample was also estimated based on the results of X-ray diffraction analysis. The quantitative mineral composition was studied on the crushed material of the original ore with a particle size of -2 mm using the microscopic study data of transparent and polished thin sections on a microscope Nikon Eclipse LV 100 POL. The content of iron hydroxides was determined from the weight difference after the sample was treated with a 10 % oxalic acid solution in a water bath. Comparison of the results obtained on the ore occurrence with the materials on the ore composition of the closest deposit located in 30 km demonstrates that on the one hand they are similar and uniform, and on the other hand they feature some differences. Their common parameters include a rather high degree of sulfide content of ores and similar chemical and mineral composition with the predominance of arsenopyrite, an increased role of bismuth as well as the predominance of fine gold and its similar morphological characteristics. This fact allows to consider the ore occurrence under investigation as an integral part of a single ore system of the closest deposit.

Uranium in Lake Sediments of Humid Zone: A Case Study in the Southeast Fennoscandia (Karelia, Russia)

The article presents data on the analysis of U accumulation in recent sediments of lakes in the territory of the Southeast Fennoscandia. The research was carried out in the study area of the Republic of Karelia. It has been established that the content of U in sediments varies from 0.1 to 42.3 mg/kg (median is 0.91 mg/kg). In general, the studied sediments of the region had low concentrations of U in comparison with the average content of this element in the upper part of the Earth’s crust. In some areas associated with deposits or ore occurrences of U, an increased content of U in lake sediments was revealed. The highest U accumulation level was found in the lake sediments, which are under the influence of the North Onega ore-geochemical region, where V deposits and ore occurrences that contain U, Fe, Mo and Cu are widespread. In the sediments of some studied lakes, Th anomalies were found, which often accompany U in ore geological formations. The analysis of uranium fractions in the sediments of some lakes in Karelia revealed the key role of the mineral (insoluble) phase in the accumulation of U, up to 64–68% of the total U content. The share of the organic fraction in the accumulation of U in the studied sediments of the lakes is small and ranges from 7 to 15% with respect to the total concentration of the metal.

The Use of Typomorphic Features of Placer Gold of the Anabar Region for Determining Its Sources

Typomorphic features of placer gold of the Anabar region were studied as predictive-exploration criteria. The target of the study was to determine the typomorphic features of placer gold related to the intermediate sources (paleo-placers) and the supposed nearby primary ore occurrences. Two varieties of placer gold were identified. The first variety is well-rounded high-fineness lamellar gold with a highly modified internal structure. This native gold is associated with intermediate sources, Neogene–Quaternary watershed pebble beds. The second type includes slightly rounded gold with a wide variation in fineness (494‰–999‰). Its indicator is a block heterophase internal structure. The set of typomorphic features of this variety of placer gold indicates the vicinity of the primary source, what was the prerequisite for constructing prospecting traverses in order to find ore occurrences. As a result of these studies, hydrothermal-metasomatic formations with gold-sulfide mineralization were identified. The main primary substrate for them is fractured near-fault carbonate rocks of the Cambrian and Vendian–Cambrian age. Along with this, hydrothermalites developed on slightly cemented fine-pebble quartz conglomerates of the Middle Permian age were found in the core of exploration wells. Two types of metasomatic rocks are identified: quartz-potassium feldspar and jasperoid. The main ore minerals were galena and pyrite, different ratios by sites were revealed. Gold was identified in the form of small particles in the carbonate and siliceous substrate of hydrothermal-metasomatic formations. The lithological factor was one of the leading favorable factors for the ore formation due to the presence of near-fault highly permeable fractured carbonate and slightly cemented terrigenous rocks. The structural control of the studied ore occurrences is determined by their localization in the Mayat–Logoy and Dogoy–Kuoy faults of the Molodo–Popigay system of discontinuous faults. We assume a two-stage formation of the gold ore occurrences: during the first stage, the ore components in the form of primary hydrothermal-sedimentary ores in the near-gault zones were formed. The second stage was related to the processes of the Mesozoic tectonic-magmatic activation, when the intrusion of basite dikes initiated the mobilization of ore components the gold-sulfide occurrences were formed in the near-fault zone as a result of silicic-potassic metasomatosis of the carbonate and terrigenous rocks.

Геохимические особенности Ag-Au рудопроявления Кыплатап (центральная Чукотка)

The article considers the geochemical features of unconventional mineralization in secondary quartzite’s of the Kyplatap ore occurrence, located on the southeastern flank of the volcanic dome structure (VDS) of the same name, complicating the Palyavaam-Pykarvaam volcanotectonic depression (VTD) in the Chaun zone of the Central Chukotka sector of the Okhotsk-Chukotka volcanic Belt (OChVB). The Kyplatap VDS was formed due to the intrusion into the Late Cretaceous Alkaquun volcanites of a large laccolith-like subvolcanic body composed of rhyolite-trachyriolite-trachydacites. Based on the geochemical studies of the Kyplatap ore occurrence, the authors compiled a representative database of geochemical data, including the results of analyses of express-RFA, PKSA and XSA with coordinates and composition of ores and rocks. Correlation analysis of the database showed a positive relationship between Au and Ag, as well as Sb for ore mineralization, and a negative correlation of these elements with the association of the rock group of elements (Ti, Y, Zr, Nb and Yb) that were removed during ore formation. The authors also distinguished the second rock group of elements (K, Ga, Sn, Ba, V, W, Pb, Sc, La and B), characterized by medium and weak correlation of the first group of elements. They calculated the coefficients of enrichment and deficiency of ore-forming elements for the samples taken within the ore zones of the Kyplatap ore occurrence. The extreme enrichment group includes elements Au, Ag, Sb, Bi, As, the average contents of which are 100 times or more, and the minimum concentrations are at least 2-10 times higher than the average contents in the upper crust. The normal enrichment group includes elements S, Sn, Cu, Zn, Mn, Mo and Pb, the average contents of which are 2-10 times, and the maximum concentrations are 5-100 times higher than the average concentrations of the upper crust. The obtained values of the enrichment coefficients indicate a sufficiently intensive metensomatoses and ore formation within the Kyplatap ore occurrence.

PHYSICO-CHEMICAL CONDITIONS FOR THE FORMATION OF PRODUCTIVE MINERAL ASSOCIATIONS OF GOLD DEPOSITS OF THE TAIMYR-NORTH EARTH ORGEN

For the first time, based on the data of the study of fluid inclusions, the PTX parameters of the formation of gold mineralization of the Taimyr-Severozemelsky orogen were established. The temperature of formation of gold ores covers the range from 310 to 105°C, the pressure was not lower than 110–96 MPa. The ore-forming fluids were characterized by NaCl + KCl + H2O + CO2 + CH4 + N2 composition and salinity up to 9.7 wt. % in equiv. NaCl. The composition of native gold (fineness varies from 960 to 550‰) and minerals of productive mineral associations has been determined. Ore-forming fluids of gold-sulfide-quartz ore occurrences of the accretionary Schrenk-Fadeevskaya zone (Yasnenskoye and Malinovskoye in North-East Taimyr) are more oxidized and less saline compared to the gold-quartz occurrences of the orogenic type of the Mininsko-Bolshevitskaya myogeoclinal zone (Nizhnelitkenskoye, Vidimoe, Nerpichye).

Justification of geotechnology for nonuniform geomechanical medium of Dzhamgyr gold ore deposit

The uncertain discontinuity and concentration of the mineralization at Dzhamgyr deposit govern the errors in the appraisal of the commercial ore reserves and in the choice of the optimal mining system parameters. In particular, the ore occurrence discontinuity is different when determined using the ore content coefficient in exploration blocks (observations along the block perimeter at a step of 3.5 m along the dip and strike) or the operational exploration data at a regular grid 3.5×(4–5) m. The accomplished research substantiates the geotechnology based on the geological medium discreteness. It is shown that the extraction-purpose delineation of ore and no-ore and generation of pillars allows using the mixed-type stoping flow chart in enlarged extraction panels. Feasibility of lumpiness-conditioned grading, screening and sensor-based calibration of gold-andquartz ore makes it possible to increase the minimum stoping thickness to 2.5–3 m at the high ore dilution of 70%. This enables using mechanized stoping in larger extraction panels (160×(120–160 m) in combination with shrinkage stoping and /or overhand stoping slicing of very rich (bonanza) ore. With the proposed geotechnology introduced, it is possible to implement planning of investment and economic development of production at the doubled mining output and annual ore extraction of 60 thousand tons at the reduced cost of stoping.The authors appreciate contribution of the Geotechnical Engineering Department Head E. A. Babkin, Vertex Gold Company, to preparation of this article.

Three-dimensional geoelectrical model of the central part of the Zvizdal-Zaliska and Brusyliv fault zones of the Ukrainian Shield

To study the deep structure of the geoelectrically complex junction zone of three megablocks of the western part of the Ukrainian Shield (Volyn', Podil, and Ros'), a three-dimensional model of the central part of the Zvizdal-Zaliska and Brusyliv fault zones was created. It is based on modern experimental observations of the Earth's natural low-frequency electromagnetic field in a wide range of periods. Synchronous experimental data of deep magnetotelluric sounding and magnetovariational profiling, obtained by the Institutes of the National Academy of Sciences of Ukraine in 2009—2019, were analyzed. The main issues of the geoelectrical modeling methodology using the Mtd3fwd software complex were considered, such as model elements, stages, alternative models, examples of calculations and comparison of observations, errors, etc. The constructed model analysis showed that of the large number of near-surface anomalies with low resistivity (5 to 100 Ohm · m), most sink to 500 m and only a few reach a depth of 1 km and are followed up to 11 km. It was established that there are connections between conductivity and structural features of the Zvizdal-Zaliska, Brusyliv, Nemyriv fault zones, the Samgorod fault and the Kocheriv synclinorium. Most of the isolated conductors appear in a mosaic pattern along the extended fault zones and form interspersed chains of high and low resistivity. Regional anomalies were confirmed and detailed both in the deep part of the crust and in the upper mantle; part of the Zvizdal-Zaliska fault zone appeared at depths of 15—30 km as a contact zone of abnormally high and low resistivities. Anomalies are confined to elongated zones of metasomatization and graphitized rock areas, some of the surface anomalies correspond to areas of the weathering crust. Most of the anomalies coincide with ore occurrences, ore-bearing fields and mineral deposits. The conducted geological-geoelectrical analysis of the model made it possible for the first time to identify two promising areas for further study that meet the geoelectrical criteria for the mineral search: along the Zvizdal-Zaliska fault zone between the Samgorod and Unava faults; along the Samgorod fault in the area of its intersection with the Kocheriv and Taboriv faults.

On the ore-formational affiliation of gold deposits of the Beltau-Kuramin volcano-plutonic belt in Eastern Uzbekistan (according to thermobarogeochemical data)


 
 
 Gold deposits in the Beltau-Kuramin volcano-plutonic belt (Eastern Uzbekistan) are traditionally considered mineral products of the volcanogenic-hydrothermal class of shallow formations. However, geological, geochemical, isotope-geochemical and precise thermo- barogeochemical studies of the physical and chemical conditions of their formation give reason to question their shallow nature. Comparison of the thermobaric conditions of ore-genesis, the chemical composition of the fluid’s aqueous and gas phases, the value of the paleotemperature gradient (ΔT/100 m) of the hydrothermal solutions of the Kochbulak and Kyzil-Alma deposits with those belonging to the medium-depth formation of the plutonic-hydrothermal class (Lyahov, 1988; Lyahov, Pavlun, Piznyur, Popivnyak, 1995) shows that there are much more similarities than differences with genotypic deposits of medium depths. Signs that call into question the shallow nature of gold deposits in the Beltau-Kuramin volcanic-plutonic belt include the following: interspersion of gold ore process and dike magmatism; high-medium temperature level of hydrothermal processes (> 390–200 °С); relatively high pressure in the mineral formation system (from 40 to > 58 MPa); a high content of Na+ and Cl– ions in solutions of fluid inclusions according to the data of triple water extractions and a significant predominance of Na+ over K+ (by two to five times); high and predominant content in the gas phase of the productive stage solutions of CO2 (up to 97 %) and CH4 (up to 45%); the presence in fluid inclusions at room temperature of a liquid phase of CO2 of relatively high density (up to 0.560 g/cm3); high purity of native gold of early generations; exclusively electronic electrical conductivity of galena; relatively insignificant paleotemperature gradient (ΔТ/100 m) in ore bodies of different morphology (15–20 °С/100 m for vein structures and 9–12 °С/100 m for ore-explosive ones). Geological data indicate a large erosion section of ore-conjugated morphostructures, which is at least 2000–2500 m, depending on the depression or domed nature of the volcanic morphostructures. At shallow depths of the formation of the syn-ore paleosurface, the gold deposits would have been completely eroded, while in the modern erosion section there is a large scale of vertical mineralization. Ore-formation correlation of gold deposits in Eastern Uzbekistan increases the prospect of deep horizons of these deposits, as well as gold-bearing areas and ore occurrences, where prospecting and evaluation work will be carried out.
 
 

Paragenetic Association of Platinum and Gold Minerals in Placers of the Anabar River in the Northeast of the Siberian Platform

Areal placers of diamond and precious metals (platinum and gold) of unknown origin are widespread in the Anabar River basin on the northeastern part of the Siberian Platform. This article discusses the typomorphic features of palladium gold (porpezite) and ferroan platinum, which, in addition to fragmented individual grains, sometimes form close growths, which indicates their obvious genetic relationship. This can be used to delimit the primary sources of commercial components of complex placers by their genetic types. The composition of minerals was determined on a Camebax-Micro (Cameca, France) microprobe analyzer, and their microstructural relationships were studied using the scanning microscope JSM-6480LV JEOL. Determination of the structure and parameters of elementary lattices of minerals was carried out on the D8 Discover diffractometer. According to microprobe analysis, the Pd content in porpezite ranges from 0.73% to 12.83%, Ag does not exceed 2.75% and Cu reaches 3–4%. Considering the composition, such a gold–platinum mineral association from placers of the Anabar river is close to precious metals from placers of the Gulinsky massif, as well as Au–PGE ore occurrences related to ultramafic–mafic intrusions of other regions of the world. Complex gold–platinum-metal mineralizations are usually closely related to parent rocks and are often observed in sulfide and chromite ores of layered ultramafic–mafic intrusions with complex metasomatic and hydrothermal transformations. It is shown that in such cases gold and platinum form a magmatogenic paragenesis of minerals that coexist until the separation of hydrothermal solutions from magma, which, as a rule, transports Au and Ag with a small fraction of PGE from the fluid-ore-magmatic system in accordance with the model of the formation of gold–porphyry deposits. Within the Anabar diamond-bearing region, according to modern geophysical data, a significant number of local gravimagnetic anomalies associated with the presence of intrusive massifs of basic and alkaline-ultrabasic rocks in the cover and within the basement have been identified. This allows us to assume that the buried parent rocks of the Anabar Au–Pt placers may be located in both the Precambrian and Phanerozoic strata.

Typomorphic features of placer gold of the Sololi River basin (northeast of the Siberian platform)

Mineralogical features of placer gold and gold-sulfide ore occurrences of the Sololi river basin from the Sololi uplift of the Olenek arch have been studied. According to the typomorphic indicators, two types of gold are distinguished. The first type is gold of a tabular and lumpy shape, often with mineral indentation imprints. The inner structure is represented by granulation, and recrystallization, high-grade intergranular veins, and high-grade shells typical of the gold of intermediate reservoirs. This type of gold is characterized by a high fineness. The sources of this type of gold were gold-bearing intermediate reservoirs of the Permian and Riphean widely developed in the studied area. The second type of gold includes subrounded and poorly rounded gold, ore gold of hooked, tabular, crystalline and angular-lumpy shapes with a pitted-bumpy or flat surface, as well as large growths of gold with quartz. The fineness of this type of gold varies from low to very high. Its primary sources were probably quartz veins genetically related to the metamorphic rocks of the Eekit series and Precambrian rhyolites. Ore occurrence formed by the Late Permian clastic rocks during the processes of the Mesozoic tectonomagmatic activation is considered as an additional source of feeding. Establishment of indicators of low–temperature hydrothermal processes as mineral parageneses, such as mercury gold, cinnabar and barite, suggests shallow and low-temperature formation conditions of this ore occurrence.

MINERALOGICAL AND GEOCHEMICAL CHARACTERISTICS OF THE HURIVKA COMPLEX P-U-TR ORE OCCURRENCE, INHUL MEGABLOCK, UKRAINIAN SHIELD

The article presents the results of the study of the Hurivka apatite-uranium-rare earth ore occurrence, which is confined to the contact of the southern part of the Hurivka granitoid massif with metasedimentary rocks of the Inhul-Inhulets series. Argillizites, which host the productive mineralization, are represented by two zones: the lower montmorillonite-chlorite zone and the upper kaolinite-chlorite zone with hydromica. The concentrator minerals of rare earths (∑TR=0.05-0.5 %) in the bedrock are xenotime and monazite, while only xenotime was detected in argillizites. At the same time, minor impurities of yttrium and lanthanides were detected in apatite, chlorite and clay minerals. Xenotime and monazite also contain insignificant concentrations of uranium. The maximum uranium content in xenotime is 4.94% UO2, and in argillizites it can reach 0.86%. No native uranium minerals were detected in the studied ore. It is assumed that the most common form of its occurrence in argillizites is adhesion to the surface of clay and mica minerals due to sorption and adsorption processes. Anomalous high phosphorus content within the ore occurrence is associated with apatite mineralization. In bedrock, apatite is confined to skarns. In argillizites, its concentration in some intervals reaches 5%. The complex apatite-uranium-rare earth mineralization of the Hurivka ore deposit was formed in the course of complex long-term processes, which was expressed in the hydrothermal-metasomatic transformation of high carbonated rocks in contact with the granitoid massif and their subsequent argillization by low-temperature hydrotherms of endogenous and exogenous origin.

New data on sulfosalts from the hydrothermal siderite-type veins in the Spišsko-gemerské rudohorie Mts. (eastern Slovakia): 5. Minerals of the kobellite-tintinaite series from the Majerská dolina ore occurrence near Čučma

A new occurrence of minerals of the kobellite-tintinaite series was recently discovered at the Majerská dolina siderite-type hydrothermal ore occurrence near Čučma, Spišsko-gemerské rudohorie Mts., Rožňava Co., Košice Region, Slovakia. Minerals of the kobellite-tintinaite series occur in quartz gangue as acicular to prismatic crystals up 5 mm long, associated together with arsenopyrite, pyrite and chalcopyrite. The calculated value of N for studied samples is ranging from 1.91 to 2.00 and the Sb/(Sb+Bi) atomic ratio in three studied samples varies between 0.41 and 0.52, hence corresponding mostly to Sb-rich kobellite, with a few analyses representing Bi-rich tintinaite.