Gold-Bearing Rodingites of the Agardag Ultramafic Massif (South Tuva,Russia) and Problems of Their Genesis

Geology of Ore Deposits - The limited literature data on gold-bearing albite–pyroxene rodingites are summarized for the Agardag ultramafic massif in southern Tuva. These data are supplemented...     

The Ore Mineralogy of the Kedrovskoe Gold Deposit (the Muya Region,the Republic of Buryatia,Russia)

The ore mineralogy of the largest quartz vein, Osinovaya, at the Kedrovskoe gold deposit has been studied. Three stages of mineral formation, namely, marcasite–pyrrhotite–pyrite, gold–polysulfide, and hypergenic stages are identified. Native gold is attributed to the gold–polysulfide stage and is represented by two generations. The earlier high fineness generation (600–870, 780–820 prevails) cements the fragments of pyrite grains or forms inclusions in pyrite, and the later low fineness generation (520–580, 540–580 prevails) is associated with sphalerite–chalcopyrite–galena veinlets in pyrite. The disappearance of arsenious pyrite, the increase in iron content of sphalerite, and the change in pyrite to pyrrhotite with depth is recorded.     

Geophysical investigations on Por-Bajin island in the Republic of Tuva

Complex geophysical research was carried out to examine the safety of the Por-Bajin Fortress archaeological monument that is located at a height of 1300 m on an island in the middle of Lake Tere-Khol in the south-eastern area of Tuva. It was established that the monument is constructed on permafrost rocks that are subjected to the warming effect of the lake. The electrical soundings in the area of the lake showed that previously the island was a part of the land adjoining the southern shore of the lake together with other sections. Using deep electrical soundings, it was established that the depth of the Tere-Khol depression exceeds 400 m and the lower boundary of the permafrost lies at the depth of about 170 m.     

Minerals of Bauxites and Residues: Problems of Processing and Enrichment (Russia)

The complex of mineralogical methods was developed to obtain reliable data about mineral composition of bauxites and new crystal-chemical information (the whole cycle of used chemical elements, methods of residue utilization, position of residue tails in dump pits). Natural and technogenic structures were studied as sources of necessary chemical elements and useful properties.     

Belogubite,a New Mineral of the Chalcanthite Group from the Gaiskoe Deposit,South Urals,Russia

Geology of Ore Deposits - Belogubite CuZn(SO4)2 ⋅ 10H2O, a new mineral of the chalcanthite group, is found in the Gai (Gaiskoe) massive sulfide deposit, South Urals, Russia. This mineral...     

Geology and Genesis of the Natalka Gold Deposit,Northeast Russia

The Natalka lode gold deposit, also known as the Matrosov mine, is located in the Magadan region of northeastern Russia at 61° 39′ N, 147° 50′ E. The deposit was discovered in 1943 and production started in 1945. The mine has produced more than 75 metric tons of gold, with an average grade 4 g/metric ton (mt), and has reserves of about 450 mt.

The Natalka deposit occurs along the southwestern flank of the Yana-Kolyma metallogenic belt and is confined to the major, NW-trending Tenka fault. The deposit is hosted by Upper Permian carbonaceous sediments, subjected to greenschist metamorphism. The ore zones occur along a Z-shaped, strike-slip fault zone that extends for about 12 to 13 km. In plan view, the ore zones are about 5 km long and 100 to 200 m wide in the northwest portion, 350 to 400 m wide in the central portion, and 600 m wide in the southeast portion of the deposit.

The main ore minerals are arsenopyrite and pyrite, which comprise about 95% of the sulfides, along with subordinate pyrrhotite, Co-Ni sulfarsenides, sphalerite, chalcopyrite, galena, native gold, ilmenite, and rutile. Scheelite, tetrahedrite, bournonite, boulangerite, and stibnite occur locally. The major gangue mineral is quartz, with subordinate carbonates, feldspars, chlorite, sericite, kaolinite, montmorillonite, and barite. The total sulfide content of the ore zones ranges from 1 to 3%, and in places up to 5%. Native gold occurs as large individual grains ranging from 0.1 to 2.0 mm in diameter, or as fine disseminations in arsenopyrite. The average gold fineness is 750 to 790.

Fluid inclusion studies reveal homogenization temperatures of 150° to 360° C, with mainly liquid and as much as 5% vapor. Two temperature peaks of 280° to 320° C and 180° to 240° C occur in many samples. The δ³⁴S composition of sulfides in orebodies ranges from ?6.3 to ?2.4 per mil and approximates that of sedimentary rock-hosted pyrite. The δ³⁴S values of the ore solutions are interpreted as having been close to that of the sulfide minerals. The δ¹⁸O composition of ore quartz ranges from 13.9 to 14.1 per mil. The calculated δ¹⁸O composition for the ore fluid ranges from 7.1 to 7.3 per mil at 300° C. The δ¹⁸O values of oxygen indicate a quite homogeneous fluid of metamorphic origin.

The sulfur, arsenic, and gold in the ore deposit were mobilized during metamorphism that included transformation of pyrite to pyrrhotite. The PT conditions for this reaction are estimated at about 400°C and 2.5 kbar, approximately at the biotite isograd. Associated decarbonatization and dehydration reactions produced much of the ore fluid. The interaction of ore-fluid sulfur with Fe-bearing silicate and oxide minerals probably caused deposition of sulfide minerals and gold.     

A New Model of a Unique Schlema-Alberoda Five-Element Deposit,Federal Republic of Germany

Geology of Ore Deposits - The paper completes a series of works about the unique Schlema-Alberoda deposit. The data on sources of vein and ore minerals and their relation to the processes of...     

Chironomid record of Late Quaternary climatic and environmental changes from two sites in Central Asia (Tuva Republic,Russia)—local,regional or global causes?

Sediment cores from two mountain lakes (Lake Grusha at 2413 m a.s.l. and Ak-Khol at 2204 m a.s.l.) situated in the Tuva Republic (southern Siberia, Russia), just north of Mongolia, were studied for chironomid fossils in order to infer post-glacial climatic changes and to investigate responses of the lake ecosystems to these changes. The results show that chironomids are responding both to temperature and to changing lake depth, which is regarded as a sensitive proxy of regional effective moisture. The post-glacial history of this mountain region in Central Asia can be divided into seven successive climatic phases: the progressive warming during the last glacial–interglacial transition (ca 15.8–14.6 cal kyr BP), the warm and moist Bølling-Allerød-like interval (ca 14.6–13.1 cal kyr BP), the cool and dry Younger Dryas-like event (ca 13.1–12.1 cal kyr BP), warmer and wetter conditions during ca 12.1–8.5 cal kyr BP, a warm and dry phase ca 8.5–5.9 cal kyr BP, cold and wet conditions during ca 5.9–1.8 cal kyr BP, as well as cold and dry climate within the last 1800 years. The chironomid records reveal patterns of climatic variability during the Late-glacial and Holocene, which can be correlated with abrupt climatic events in the North Atlantic and the Asian monsoon-dominated regimes. Apparently, the water balance of the studied lakes is controlled by the interrelation between the dominant westerly system and the changing influence of the summer monsoon, as well as the influence of alpine glacier meltwater supply. It is possible that monsoon tracks could have reached the southwest Tuva, resulting in an increase in precipitation at ca 14.6–13.1 and ca 12.1–8.5 cal kyr BP, whereas cyclonic westerlies from the North Atlantic were likely responsible for considerable moisture transport accompanying the global Neoglacial cooling at ca 5.9–1.8 cal kyr BP. These events suggest the changes of the regional pattern of atmospheric circulation, which could be in turn induced by the global climatic shifts. Some discrepancies compared with other reconstructions from Central Asia may be associated with regional (spatial) differences between the changing predominant circulation mechanisms and with local differences in uplift and descent of air masses within the complicated mountain landscape. In this paper, we also discuss the possibilities and perspectives for using chironomids in reconstructions of past temperatures and climate-induced changes in water depth of lakes in Central Asia.     

The Dzhalinda Deposit in the Amur Region,Russia: Genesis and position in the classification of tin deposits

The Dzhalinda wood tin deposit is located at the eastern margin of the Bureya Massif and, according to the Russian classification of tin deposits, is referred to the rhyolite-hosted type. The Dzhalinda deposit is compared with the deposits located in the southwestern United States and in northern Mexico. In spite of some similar features, the Dzhalinda deposit differs significantly from the American deposits in the composition of ore-bearing rhyolite and the type and composition of host rocks. It is suggested that the ore-bearing rhyolitic melt at the Dzhalinda deposit evolved with the formation of a highly silicic residual melt depleted in P and Li and enriched in Sn, being opposed in this respect to the ongonite model typical of such deposits. The drastic change in the physicochemical parameters of the system caused by the evolution of the melt under near-surface conditions of a volcanic vent led to the separation of Si-Sn complexes, which broke down into various silica modifications and oolite-like wood tin.     

New Data on the Geochemistry of Mississippi-Type Ores at the Sardana Deposit (Northeastern Russia)

New data obtained using a modern analytical technique on the geochemistry and conditions of the formation of Mississippi-type ores at the Sardana deposit are presented. Comparative analysis related to other deposits of the same type was carried out. The geochemical data point to a considerable role of metamorphism of the enclosing carbonate–terrigenous masses in ore formation at the deposit.     

Glauconite Deposits in Russia: Geological Position,Formation Conditions,and Development Perspectives

Lithology and Mineral Resources - The article is devoted to analysis of the glauconite resource base in Russia. The geotectonic and lithological-paleogeographic positions of deposits and large...     

Geological Structure and Ore Mineralogy of the Juliette Gold-Silver Deposit,Northeast Russia

Julietta is a rich epithermal gold-silver deposit of the low-sulfidation, adularia-sericite type, located in the Cretaceous Okhotsk-Chukchi volcanic-plutonic belt 250 km northeast of Magadan. The deposit was discovered in 1989 by a regional soil geochemical survey in an area previously considered barren on the basis of a regional stream-sediment survey. The deposit has not been completely explored, but presently is in the feasibility stage; proven reserves are 26 metric tons of Au (grades averaging 23 g/t) and the Au/Ag ratio is about 1:10.

The deposit occurs on the periphery of a large volcanic-tectonic depression. Host andesite, andesite-basalt lava, corresponding subvolcanic bodies, and tuff are cut by Early Cretaceous quartz diorite stocks. Six vein zones occur in tensional and compression fissures. Ore shoots and smaller bonanzas comprising most of the gold reserves are located in flexures of the ore-host fissures. Ore mineralization was preceded by intense voluminous propylitization and linear sericitization (sericite + quartz + pyrite + ankerite). Orebodies occur within the low-temperature propylite (pyrite + calcite + quartz + chlorite + hydromica). Colloform-crustiform banded textures are commonly observed in the ore. Most of the ore minerals occur within thin, cyclically repeated, fine-grained bands of a hydromica-carbonate-adularia-quartz aggregate. Ore-bearing, fine-grained bands probably formed by periodic fracturing of the veins, whereas barren bands were deposited in relatively quiet conditions. “Micro-stalactites” and other gravitational textures demonstrate that minerals grew in open spaces. Ore-host structures gradually opened during mineralization.

Gangue minerals are primarily quartz, various carbonates (calcite, dolomite, Fe-dolomite [Mg:Fe>2:1], parankerite [Mg: Fe = 2:1], ankerite [Mg: Fe = 1:1], and mesitite [Mg: Fe = 1:1]), and minor hydromica and adularia. Major ore minerals include pyrite, sphalerite, chalcopyrite, galena, tetrahedrite, silver sulfosalts, native gold, and custelite (Au: Ag = 9: 1). Ore mineralization occurred in two stages-an early, post-volcanic stage and a late, post-granitoid stage. The early stage contains most of the precious metals and includes two substages-(1) gold-polymetallic (200 to 260° C) and (2) gold-silver-sulfosalt (90 to 200° C). The late stage also includes two substages-(1) carbonate-rhodonite-quartz (260 to 380° C) and (2) postore quartz-carbonate. Fluid-inclusion homogenization temperatures demonstrate complex temperature zoning. Fluid composition was mainly aqueous, with Cl^?, HCO₃?, Na⁺, K⁺, Ca₂ ⁺, and a salinity less than 4 to 9%. The isotopic age of the deposit is 136 ± 3 Ma by the Rb-Sr method on adularia. The ⁸⁷Sr/⁸⁶Sr ratio is about 0.7075 ± 0.0005, indicating a mixed crust-mantle source of the vein matter. Chloride complexes transported gold and silver. The gas composition of the fluid suggests a near-surface, “closed” paleohydrothermal system. A major ore-forming factor could have been high seismic activity related to intrusion of the subvolcanic bodies. Breccias and multiphase veinlets may be related to relatively large-magnitude earthquakes, whereas cyclically banded ores may reflect local pH variations caused by smaller earthquakes.     

The Zhireken Porphyry Mo-Cu Deposit, Eastern Transbaikalia, Russia: Isotope Geochemistry, Geochronology and Implications for Magma Sources

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Epithermal Gold-Silver Mineralization of the Asachinskoe Deposit in South Kamchatka, Russia

The Asachinskoe epithermal Au‐Ag deposit is a representative low‐sulfidation type of deposit in Kamchatka, Russia. In the Asachinskoe deposit there are approximately 40 mineralized veins mainly hosted by dacite–andesite stock intrusions of Miocene–Pliocene age. The veins are emplaced in tensional cracks with a north orientation. Wall‐rock alteration at the bonanza level (170–200 m a.s.l.) consists of the mineral assemblage of quartz, pyrite, albite, illite and trace amounts of smectite. Mineralized veins are well banded with quartz, adularia and minor illite. Mineralization stages in the main zone are divided into stages I–IV. Stage I is relatively barren quartz–adularia association formed at 4.7 ± 0.2 Ma (K‐Ar age). Stage II consists of abundant illite, Cu‐bearing cryptomelane and other manganese oxides and hydroxides, electrum, argentite, quartz, adularia and minor rhodochrosite and calcite. Stage III, the main stage of gold mineralization (4.5–4.4 ± 0.1–3.1 ± 0.1 Ma, K‐Ar age), consists of a large amount of electrum, naumannite and Se‐bearing polybasite with quartz–adularia association. Stage IV is characterized by hydrothermal breccia, where electrum, tetrahedrite and secondary covellite occur with quartz, adularia and illite. The concentration of Au+Ag in ores has a positive correlation with the content of K₂O + Al₂O₃, which is controlled by the presence of adularia and minor illite, and both Hg and Au also have positive correlations with the light rare‐earth elements. Fluid inclusion studies indicate a salinity of 1.0–2.6 wt% NaCl equivalent for the whole deposit, and ore‐forming temperatures are estimated as approximately 160–190°C in stage III of the present 218 m a.s.l. and 170–180°C in stage IV of 200 m a.s.l. The depth of ore formation is estimated to be 90–400 m from the paleo‐water table for stage IV of 200 m a.s.l., if a hydrostatic condition is assumed. An increase of salinity (>C_NaCl≈ 0.2 wt%) and decrease of temperature (>T ≈ 30°C) within a 115‐m vertical interval for the ascending hydrothermal solution is calculated, which is interpreted as due to steam loss during fluid boiling. Ranges of selenium and sulfur fugacities are estimated to be logfSe2 = ?17 to ?14.5 and logfS2 = ?15 to ?12 for the ore‐forming solution that was responsible for Au‐Ag‐Se precipitation in stage III of 200 m a.s.l. Separation of Se from S‐Se complex in the solution and its partition into selenides could be due to a relatively oxidizing condition. The precipitation of Au‐Ag‐Se was caused by boiling in stage III, and the precipitation of Au‐Ag‐Cu was caused by sudden decompression and boiling in stage IV.     

Polymetallic and Au-Ag Mineralizations at the Mutnovskoe Deposit in South Kamchatka, Russia

Abstract. The Mutnovskoe deposit located in the Porozhisto‐Asachinskaya metallogenic province of South Kamchatka, Russia, is a polymetallic vein and Au‐Ag quartz vein associated type of hydrothermal deposit. The Mutnovskoe deposit is located inside a paleo‐caldera structure at the center of the Mutnovsko‐Asachinskaya geothermal field of Pliocene ‐ Quaternary age, where active gold deposition is identified in hot spring precipitate. The Mutnovskoe deposit is subdivided into the north flank, the central flank and the south flank based on the vein distributions and mineral parageneses. The mineralized vein system is oriented N‐S hosted in diorite ‐ gabbroic diorite stock, volcanic rocks and sedimentary rocks of Miocene ‐ Pleistocene age. The mineralization stage I (polymetallic vein) mainly in the central and the south flanks is Zn‐Pb‐Cu‐Au‐Ag contained in sphalerite, galena and tetrahedrite‐tennantite group mineral. The stage II (Au‐Ag quartz vein) occurs in the north and the central flanks. The stage III (Mn‐sulfide and Mn‐Ca‐carbonate vein) occurs in the whole deposit area. Stage II is the typical Au‐Ag quartz‐adularia vein of low‐sulfidation type. Stage III is alabandite‐rhodochrosite‐quartz‐calcite vein. The K‐Ar ages are 1.3±0.1 Ma for stage I sericite in alteration zone, and 0.7±0.1 Ma for the stage II adularia in mineralized vein. Based on the fluid inclusion study, range of ore forming temperature of the Mutnovskoe deposit is 200 to 260d?C (av. 230d?C). Salinities of fluid inclusions indicate 2.2 to 5.7 wt% NaCl in sphalerite and 0.8 to 3.3 wt% NaCl in quartz for the stage I. Mineral paragenesis of the polymetallic vein (stage I) is characterized by a district zoning of tennantite and Cd‐rich sphalerite in the south flank and tetrahedrite and Mn‐rich sphalerite in the central flank, which is due to the fractional crystallizations of ore‐forming fluid. Depositional condition of the low sulfidation state is inferred for the Mutnovskoe deposit, where the polymetallic vein of the south flank is in relatively higher sulfidation state than the central flank.     

Y/Ho Ratios in the Late Cenozoic Basalts from the Eastern Tuva, Russia: An ICP-MS Study with Enhanced Data Quality

A set of forty seven Late Cenozoic basaltic rocks from the Eastern Tuva (southern Siberia, Russia) have been studied by ICP-MS using In as an internal standard. Yttrium and Ho concentrations, determined along with other trace elements, varied systematically from one analytical run to another and covered the entire charge-and-radius-controlled field within the range 24 < Y/Ho < 34, so obscuring any geochemical interpretation. A correction procedure was therefore developed in which the Y/Ho ratios were recalculated using concentrations of these elements determined in international and in-house reference materials (BHVO-1, AGV-1, BIR-1 and U-94-5). Statistical analysis of the recalculated data set revealed two groups of samples not related by their genesis but rather by their respective analytical runs. Fourteen samples originally analysed in five different runs were then re-measured by the same instrument in peak-hopping mode using only specific mass peaks (m/z = 89, 115 and 165). All of these samples yielded Y/Ho ratios in a narrow range between 29 and 31, thus illustrating how analytical problems in the determination of Y and Ho by routine ICP-MS procedures can be overcome. Finally, a mean value of Y/Ho = 30.3 ± 1.1 (1s) was derived for the basaltic rocks of the Eastern Tuva. This is close to the value of 28.8 accepted for chondrites and for ocean island basalts. Despite the uniform Y/Ho ratio, the element concentrations in basaltic rocks from the Eastern Tuva show systematic enrichment in heavy rare earth elements and yttrium from the Miocene to the Quaternary.     

Genetic Aspects of the Noble-Metal Mineralization at the Poperechnoe Deposit,Lesser Khingan,Russia

Bodies of cryptovolcanic rocks (fluidolites) play a significant role in the structure of the Poperechnoe ferromanganese deposit, Lesser Khingan, Russia. Fe-Mn ores in association with fluidolites are localized in ancient carbonate rocks. PGM, gold, and silver minerals up to tenths of a millimeter in size are established in the rocks and ores of the deposit. Characteristic admixtures in the platinum are iron (9-11%), with less common copper, iridium, and osmium. An intergrowth of isoferroplatinum polycrystal with forsterite is observed. There are also individual grains of Os-Ir-Ru-Rh intermetallides. The gold grains (up to 93% Au) are characterized by dendritic and clumpy morphology, frequently showing faceting elements. The grains are frequently rounded and sometimes have an almost perfect spherical shape. Native silver is distributed among the dolomites, as well as in the dolomitic fragments from the fluidolites. Ubiquitous admixtures in the silver are copper, iron, and more rarely zinc; single grains contain admixtures of molybdenum, nickel, gold, and palladium. PGM and high-fineness gold are related to the fluidolites, which are the only magmatic rocks in the studied range of the deposit. Silver, its minerals, low-fineness gold, and sulfides are confined to the rocks and ores subjected to the regional dolomitization, low-temperature hydrothermal reworking, and silicification. Samples contain up to 11.3 g/t platinum, 2.35 g/t gold, 296.2 g/t silver, which allows us to consider the studied object as economically promising for noble metals.     

Trace Element Distributions in Sulphides: Progress, Problems and Perspectives

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火山岩型铀矿床成矿构造控制特征--以俄罗斯Streltsovka火山岩型铀矿床与中国相山火山岩型铀矿床为例

本文通过对俄罗斯Streltsovka火山岩型铀矿床和中国相山火山岩型铀矿床的对比研究,发现两矿床具有相似的成矿构造控制特征：走滑挤压至拉张伸展的构造转化是矿床形成的有利构造机制;盆地格网状断裂构造对铀的成矿起着导矿、控矿和容矿的作用;多次构造叠加形成的独特的盆地二元结构是成矿的有利因素.根据对这些构造控制特征的分析,提出了火山岩型铀矿床找矿勘探的几点建议.