Crustal Structure of the Baltic Shield Along the Pechenga–Kostomuksha–Lovisa Geotraverse

Results of geologic and geophysical modeling are presented, based on detailed seismic studies along two profiles—Pechenga-Kostomuksha and Lieksa-Lovisa. Density, geothermal, magnetic, and geoelectric models were obtained from the interpretations of various geophysical fields and correlated with the reference seismic sections. All the models were combined in order to compile a geologic-geophysical crustal section. The crustal thickness along the Pechenga-Kostomuksha-Lovisa geotraverse varies from 38 to 65 km. Two anomalous structures have been observed that are referred to as the Belomorian-Karelian and Ladoga-Bothnian zones. These zones are characterized by enhanced values of magnetic fields, presence of seismic foci and wave attenuation, and variation of the depth and magnitude of modern crustal movements. These zones are distinguished by the discontinuity M reconstruction, an increase in transitional layer thickness (to 25 km) at the base of the crust, and an increase in depth down to the discontinuity M (50 to 65 km). On average, the crust is thinner (40 km) in the ancient part of the shield than in the younger Svecofennian province (45 km). The velocity differences also are important: for example, the crust of the ancient shield is characterized by lower velocities and the transitional high-velocity layer is absent or thinner. The Karelian granite-greenstone area (a fragment of the Archean craton) has the most simple and balanced deep structure. Within the Karelian area, the layers are nearly horizontal and their thickness is rather constant. The northeastern part of a fragment of the Murmansk block has similar crustal characteristics within the Kola area, where it has undergone Early Proterozoic deformation. Geological and geophysical data for the Pechenga-Varzuga zone suggests that there was intracontinental rifting and a subsequent construction regime during the Svecofennian orogeny that involved a considerable part of the shield. The deep-crustal structure is more complicated to the south. An increase in volume of material with the properties of granulites and basic rocks is observed in the upper crust. The rocks form an inclined alternation of high-density and high-velocity plates and lenses. The packet of tectonic clustering of supracrustal rocks is most conspicuous in the Lapland-Kolvitsa granulite belt. The packet thickness does not exceed 13 km.     

Low-temperature thermodynamic model for the system Na2CO3−MgCO3−CaCO3−H2O

A comprehensive low-temperature thermodynamic model for the geochemically important Na₂CO₃−MgCO₃−CaCO₃−H₂O system is presented. The model is based on calorimetrically determined Δ_fH°₂₉₈ values, S°₂₉₈ values and C°_p(T) functions taken from the literature as well as on μ°₂₉₈ values of solids derived in this work from solubility measurements obtained in our laboratories or by others. When these thermodynamic quantities were combined with temperature-dependent Pitzer parameters taken from the literature, solubilities calculated for a wide range of conditions agree well with experimental data. The results for several subsystems were summarized by depicting the respective phase diagrams. For the MgO−CO₂−H₂O subsystem, it was found that the commonly believed stability relations must be revised, i.e., in the temperature range covered, nesquehonite never becomes more stable than hydromagnesite at p_CO2 ≤ 1 atm. Although the recommended set of thermodynamic data on sparingly soluble solids was derived from experimental results on mainly NaClO₄ systems, it can be incorporated in databanks containing additional Pitzer parameters for modeling more complex fresh- or seawater systems.     

The Geology,Mineral Associations,and Composition of Native Gold in the Mineral Deposits of the Taimyr–Severnaya Zemlya Orogen

Doklady Earth Sciences - The variety of sizes and morphology of grains and chemical composition of native Au, and the diversity of mineral productive associations in the new ore occurrences of the...     

The order–disorder potential of the crystal structure of monohydrocalcite,CaCO3·H2O

Mineralogy and Petrology - Monohydrocalcite, CaCO3·H2O, forms a P31 structure composed of composite rods in which a spiral arrangement of Ca ions is accompanied by spiral arrangements of CO3...     

Evolution of the Processes of Mineral Formation in Early Vendian Terrigenous Rocks of the Nepa–Botuoba Anteclise

Lithology and Mineral Resources - Main regularities in the manifestation of epigenetic processes in Lower Vendian terrigenous rocks of the Nepa–Botuoba anteclise are established. Evolution of...     

Mineral Indicators of Provenances for Rare-Metal–Titanium Placers of the Stavropol Arch: Zircon

Geology of Ore Deposits - A comprehensive study of the indicator properties of zircon from rare-metal–titanium placers of the Stavropol Arch (using the example of the most-explored...     

Raman study of MgCO3–FeCO3 carbonate solid solution at high pressures up to 55 GPa

Magnesite, siderite and ferromagnesites Mg_1?x Fe _x CO₃ (x = 0.05, 0.09, 0.2, 0.4) were characterized using in situ Raman spectroscopy at high pressures up to 55 GPa. For the Mg–Fe-carbonates, the Raman peak positions of six modes (T, L, ν₄, ν₁, ν₃ and 2ν₂) in the dependence of iron content in the carbonates at ambient conditions are presented. High-pressure Raman spectroscopy shows that siderite undergoes a spin transition at ~40 GPa. The examination of the solid solutions with compositions Mg_0.6Fe_0.4CO₃, Mg_0.8Fe_0.2CO₃, Mg_0.91Fe_0.09CO₃ and Mg_0.95Fe_0.05CO₃ indicates that with increase in the amount of the Fe spin transition pressure increases up to ~45 GPa.     

Physicochemical Conditions of Formation of Productive Mineral Assemblages of Gold Deposits in the Taimyr–Severnaya Zemlya Orogen

Doklady Earth Sciences - The PTX parameters of the formation of gold mineralization in the Taimyr–Severnaya Zemlya orogen were established for the first time based on data from studies of...     

Mineral Phases of the Pd–Bi–Se System in the Ores at the Chudnoe Au–Pd Deposit (Subpolar Urals,Russia)

Doklady Earth Sciences - In the Pd–Bi–Se system, the only known mineral containing all three elements is padmaite PdBiSe. Three compounds with different element ratios have been found...     

Quantitative Zoning Assessment of Crustal Stability Along the Yunnan–Tibet Railway Line, Western China

The planned Yunnan–Tibet railway goes through the northwest of Yunnan Province and the southeast of the Tibet Autonomous Region. Because of its location near the collision belt of the Eurasian and Indian plates, complex engineering geological conditions and difficult engineering geological problems are encountered. The study is aimed at making the zoning assessment of crustal stability along the railway line so as to provide a better base for its construction, especially its line selection. For this purpose, the following seven influencing factors of crustal stability were selected and quantified by grading and scoring: active fault, seismic activity, geo-stress field, geo-strain field, geothermal field, geo-hazard, and lithologic character. Of these factors, the active fault, seismic activity and geo-hazard are the three most prominent factors influencing the railway construction. Along the railway line there are 1731703 calculation units to be divided. The zoning assessment calculation was completed by ArcGIS-based information fusion method. The assessment results aid railway line selection and show that there are 10 stable sectors, 28 relatively stable sectors, 23 relatively unstable sectors, and 20 unstable sectors along the Yunnan–Tibet railway line.     

Rare-Earth Elements from Modern Mineral–Organic Associations in the Zone of Sulfide Ore Hypergenesis

The REE composition of modern mineral–organic associations in the sulfide ore hypergenesis zone of the Berezitovoe deposit in the Russian Far East was studied for the first time. It is shown that the mineral–organic associations widely abundant in the valley of Konstantinovskii Creek and represented by bright brown crusts on the surface of deluvial deposits were formed at the expense of the influence of acid highly mineralized mine waters from the Berezitovoe deposit. The mineral–organic associations found in the Creek valley may be considered as a new indicator for evaluation of the geoecological state of modern technogenic landscapes.     

Mineral Deposit Model of Cu–Fe–Au Skarn System in the Edongnan Region,Eastern China

Cu and Fe skarns are the world’s most abundant and largest skarn type deposits, especially in China, and Au-rich skarn deposits have received much attention in the past two decades and yet there are few papers focused on schematic mineral deposit models of Cu–Fe–Au skarn systems. Three types of Au-rich deposits are recognized in the Edongnan region, Middle–Lower Yangtze River metallogenic belt: ～140 Ma Cu–Au and Au–Cu skarn deposits and distal Au–Tl deposits. 137–148 Ma Cu–Fe and 130–133 Ma Fe s...     

Relationship of the Extent of Antarctic and Arctic Ice with Temperature Changes, 1979–2020

Doklady Earth Sciences - Quantitative estimates of the relationship between interannual variations in the extent of Antarctic and Arctic sea ice and changes in the surface air temperature in the...     

Mineral Associations and Mo–W Ore Types of the Slepaya Zalezh’ Orebody at the Tyrnyauz Deposit

Geology of Ore Deposits - Slepaya Zalezh’, the largest orebody of the Tyrnyauz Mo–W deposit, is considered a first-priority object should mining operations at the deposit be resumed....     

The First Finding of Sapphirine in Granulites of the Angara–Kan Block: Evidence of Ultra-High–Temperature Metamorphism in the SW Siberian Craton

This work reports the first discovery of sapphirine-bearing mineral parageneses in granulites of the Angara–Kan block, information on the mineral assemblage of rocks, and the mineral composition. Based on mineral geothermometers utilizing alumina content in orthopyroxene, reconstruction of the composition of ternary feldspar, and the titanium content in zircon, it was revealed that the peak temperatures of metamorphism reached 1100°C, after which the rocks underwent cooling under sub-isobaric conditions. It is assumed that the pulse of ultra-high-temperature metamorphism correlates with processes of extension and intraplate magmatism during the age interval of 1.78–1.75 Ga.     

The Ni–Antimonide Mineral Assemblage: A Product of Recrystallization of Sn–Pb–Zn Ores of the Yuzhnoe Deposit,Sikhote-Alin,Russia

Doklady Earth Sciences - A mineral assemblage with nisbite NiSb2 and breithauptite NiSb unique for a Mesozoic (Sn)–Pb–Zn vein deposit is found during mineralogical–geochemical...     

Genesis,Features of Mineral Composition,and Problems of the Development of Rare Metal–Titanium Placers in the West Siberian Megaprovince

Lithology and Mineral Resources - The coastal-marine rare metal–titanium placers of the West Siberian megaprovince were formed in a relatively short Eocene–Late Oligocene interval. A...