The Dal’negorsk borosilicate skarn deposit,primorye, Russia: Composition of ore-bearing solutions and boron sources

The Dal’negorsk borosilicate skarn deposit (44° 34′ N and 135° 37′ E), located in the center of the ore field bearing the same name, is referred to the category of giant deposits. The currently predominant genetic concept assumes that ore mineralization at this deposit is related to a mantle source and that boron and ore-bearing alkaline fluids are derivatives of a juvenile source as well. The alternative model considered in this paper suggests that sedimentary sequences, probably, evaporites of a local basin, were immediate boron sources and hot subsurface water served as an agent of ore deposition. The authors’ conclusions are based on (1) mineralogical and geochemical features of alteration of premineral dikes as evidence for the composition of percolating ore-bearing fluids, (2) results of fluid inclusion study, and (3) boron and oxygen isotopic compositions of datolite.The latite bodies immediately predating deposition of economic datolite ore do not show mineralogical or geochemical attributes of their belonging to alkaline rock series. According to our data, these bodies are composed of Paleogene premineral basalts that intruded into the future borosilicate deposit close to the central channel of ore-bearing fluid, served as fluid conduits, and were altered to ultrapotassic rocks under the effect of such fluid. It is suggested that hot aqueous ore-bearing fluid was enriched in highly soluble compounds of Ba, K, and B and extremely depleted in poorly soluble compounds of Zr, Nb, Ta, La, and Ce. This suggestion does not contradict the properties and composition of primary and pseudosecondary two-phase fluid inclusions in danburite, datolite, quartz, and fluorite from orebodies. Judging from the boron isotopic composition of datolite (δ¹¹B = ?9 to ?31 ‰), the main amount of boron was extracted from metasedimentary rocks of the Mesozoic basement. The oxygen isotopic composition of datolite from the Dal’negorsk deposit (δ¹⁸O_SMOW = ?1.64 to ?2.97 and less frequently up to ?5‰) indicates a significant contribution of subsurface water to the transport of boron. A model of multistage accumulation of boron in ore of the Dal’negorsk borosilicate skarn deposit is proposed.     

Genesis of the boron potential of the Taukha metallogenic zone,Sikhote Alin,and boron sources during formation of the Dal’negorsk boron deposit

It is shown that the formation of borosilicate skarn in the Taukha metallogenic zone completes a series of successive stages of the formation and transformation of the folded sequences of the Taukha accretionary wedge. The Early Cretaceous sedimentary stage, including accumulation of detrital tourmaline-rich sedimentary rocks, was implemented in the marginal sea of the Paleopacific Sino-Korean segment. In the Turonian–Campanian, the boron-bearing folded sequences of the accretionary wedge were involved in anatexis to generate siliceous S-type boron-bearing melts. The thus-formed magmatic chambers were emptied during catastrophic volcanic eruptions. At the final Middle Campanian volcanic stage, fluid-magmatic differentiation of the melt in the residual chambers generated fluid flow. The infiltration interaction of the fluids, which inherited enrichment in boron, with limestones of the olistostrome sequence resulted in the formation of a giant zone of grossular–wollastonite skarns and danburite lodes. The boron potential of the Taukha boron–lead–zinc metallogenic zone may be considered as a reproduction of the Precambrian boron metallogeny of the eastern Eurasian margin, which was implemented in the Late Mesozoic during recycling of the continental crust.     

Sulfur Isotopic Composition of Sulfides in Skarn and Vein Mineralization of the Dal’negorsk Ore Region (Primorye)

The S isotopic composition in the ore-forming minerals galena and sphalerite was studied in different Ag–Pb–Zn deposits of the region. It was pointed out that the δ³⁴S modal values range from–1.2 to +6.7‰ in the minerals with a positive value for the skarn mineralization. In the flyschoid formation, the vein-type mineralization is characterized by negative and positive values. The narrow range of δ³⁴S values indicates the marginal-continental type of the mineralization and the multiple origins of its sources.     

Nature of ore-forming fluids of the Dal’negorsk deposit: Isotopic and geochemical parameters of the altered host rocks

Oxygen isotopic composition was studied in the altered host rocks of the Dal’negorsk borosilicate deposit in order to establish a boron source and the origin of ore-forming fluids responsible for deposition of economic borosilicate ore. The relationships between oxygen isotopic composition and geochemistry of the altered igneous rocks occupying various structural and temporal positions in the ore zone were studied, including premineral high-potassium minor intrusions located in the zones of datolite mineralization; alkali basalt, gabbro, and breccia from the sedimentary framework of the deposit; and postmineral basaltic andesite, basalt, and dolerite dikes. It was suggested that interaction of aqueous fluid with host rocks brought about not only variation in oxygen isotopic composition but also shifts in geochemistry of these rocks, especially as concerns the chemical elements contained in ore-forming fluid. The disturbance of oxygen isotopic system is typical of all studied rocks: δ¹⁸O values sharply decrease indicating interaction with aqueous fluid at elevated temperatures. The lowest δ¹⁸O (from −2.9 to +0.1‰) is characteristic of the premineral high-potassium and ultrapotassium minor intrusions from skarn-datolite zone. Igneous rocks from the sedimentary framework of the deposit have δ¹⁸O of +2 to −0.9‰ The δ¹⁸O of postmineral basaltic andesite, basalt, and dolerite dikes varies from 0 to +7‰ with increasing distance from the ore zone. The oxygen isotopic composition of aqueous fluid evidences its exogenic origin. The geochemical and isotopic characteristics of ore-forming fluid show that it could have been deep-seated subsurface water similar to the contemporary water of the Alpine fold zone, which contain up to 700–1000 mg/l B and is distinguished by high K, Li, Rb, Cs contents and high K/Na ratio. Similar geochemistry is characteristic of the fluid inclusions in quartz from ore zones. It cannot be ruled out that continental evaporites were a source of boron as well. The relationships between δ¹⁸O, K-Ar age, and geochemical parameters of premineral and postmineral altered intrusive bodies allow us to suggest that the subsurface B-bearing water discharged through narrow channels controlled by premineral basaltic bodies. The discharge was probably initiated by emplacement of basalt and dolerite dikes.     

On the nature of ore-bearing fluids on the Dal’negorskoe borosilicate deposit (Primor’e)

Doklady Earth Sciences -     

Malinovka deposit—A new type of gold mineralization in Primorye,Russia: Geology,mineralogy, and genesis

Original data on the ore composition are obtained by studying samples from mining workings. In terms of mineral composition, gold-productive veinlets are subdivided into three types: sulfide–quartz, sulfide–carbonate–quartz, and sulfide. The wall-rock metasomatites and typomorphic features of the minerals are studied and the genetic problems of the ores and deposit are discussed. It is established that the Malinovka deposit is ascribed to the gold–tourmaline type (gold–quartz formation), which is identified for the first time in Primorye. In terms of many parameters, the ores of this type are close to those of the large deposits from the Transbaikalian and Amur regions (Klyuchevsky, Kariy, Kirov, Darasun, and others), which are genetically related to granitoid magmatism.     

Dal’negosrk skarn deposit,Sikhote-Alin: Stages and sources of matter for borosilicate ores

The danburite orebody at the northeastern wall of the open pit of the Dal’negorsk borosilicate deposit is studied. The comparative mineralogical-, isotopic-, and thermobarogeochemical analyses of danburite from the Levoberezhnyi area and datolite of the late skarn stage from the Tsentral’nyi open pit confirms that danburite is a result of the early borosilicate stage of formation of the deposit. Combined with previously published data, it is concluded that marine sedimentary rocks or Early Cretaceous arkose sandstones from the matrix of the Taukhin accretionary prism could be the source of boron.     

Model for the development of rhythmically banded wollastonite-hedenbergite skarns at the Dal’negorsk deposit,southern Russian Far East

Skarns at the Dal’negorsk boron deposit belong to the infiltration type. In their outer contact zone (bounded by limestone and consisting of wollastonite + hedenbergite), rhythmically banded textures developed, with alternating wollastonite and hedenbergite bands. The petrological study and modeling of the process that produced them led us to propose a mechanism for the genesis of such textures. They are thought to form as a consequence of a dissipative structure in the infiltrating solution and its interaction with the rock. The dissipative structure itself resulted from the instability of the equilibrium state of the skarn-solution system and the development of pervasive spatial oscillations in the redox potential of the solution. The progressive development of the banded texture was associated with a change in the dissipative structure because of the existence of feedback (mutual influence) between the structure of the solution and the texture of the rock. The rhythms generated thereby are of several orders (as follows from their thicknesses and the distances between them), which is an indication of a large-scale invariance of the developing texture. The simulation of the process involved the analysis of a system of kinetic equations, the stability of the equilibrium, and the conditions of the stability of spatial oscillations in the concentrations of major components in the solution. A necessary condition of the stability of the dissipative structure is a low velocity of fluid filtration, which should be no higher than a critical value, with the latter controlled by kinetic parameters of the system. The proposed model can be modified and adapted for rhythmically banded skarns of other composition and for banded hydrothermal mineralized veins with the aim of constraining the petrogenetic conditions and elucidating the role of banded textures as precipitators of ore and minor components of the solution.     

Explosion breccias of the Vysokogorskoe tin–porphyry deposit: Genesis and role in ore formation (Kavalerovo ore district,Primorye)

Detailed geological observations and analytical studies make it possible to distinguish two groups of fluid-explosion breccias (FEB) in the Vysokogorskoe tin deposit of the Kavalerovo ore district. These breccias are assumed to be related to different stages of geological (geodynamic) evolution and played different roles in ore formation. The earlier breccias (79–69 Ma), which were altered by boron metasomatism and subsequent main tin mineralization, were most probably formed at the Cretaceous subduction stage. The later breccias (55–51 Ma) are syngenetic to the dacite (rhyolite) porphyry dikes of the Paleocene–Eocene transform stage. They were formed after precipitation of the majority of the cassiterite, but prior to the latest quartz–fluorite–carbonate stage of ore formation. According to the Sillitoe classification, the explosion breccias of the Vysokogorskoe deposit correspond to a magmatic–hydrothermal genetic type. They are characterized by multiple brecciation and intersection by small bodies of porphyritic rhyolites.     

Peculiarities of ore formation at the N’yavlenga Au-Ag epithermal deposit,Northeast Russia

Thermobarogeochemical studies have revealed the relatively high-temperature ore-bearing fluid of the N’yavlenga deposit. The dependence between the homogenization temperatures of the fluid inclusions and salinity of the fluid and the bimodal distribution of salinity values indicates mixing of two different fluids in the ore-bearing system. These facts are related to the thermal metamorphism of ores from the N’yavlenga deposit and indicate the complex relations of the early Au-Ag epithermal and late Au-Cu-Mo porphyry mineral complexes in orebodies of the deposit.     

The Guelb Moghrein Cu–Au deposit: Neoarchaean hydrothermal sulfide mineralization in carbonate-facies iron formation

The Guelb Moghrein copper–gold deposit in the Islamic Republic of Mauritania reopened in 2006 and has produced copper concentrate and gold since then. The deposit is hosted in Neoarchaean–Palaeoproterozoic Fe–Mg carbonate-dominated metamorphic rocks interpreted as carbonate-facies iron formation. It forms tabular orebodies controlled by shear zones in the hanging wall and footwall of this meta-iron formation. Copper and gold are hosted in a complex sulfide ore in tectonic breccia replacing Fe–Mg carbonate and magnetite. Hydrothermal monazite dates the mineralization at 2492 ± 9 Ma. Two types of aqueous fluid inclusions suggest fluid mixing at 0.75–1.80 kbar and ~ 410 °C as the mineralization and precipitation mechanism, which is temporally coincident with regional retrograde metamorphism at 410 ± 30 °C (garnet-biotite). Distal alteration zones are enriched in K, Rb and Cu, whereas orebodies are depleted in K, Rb, Sr and Ba. The copper–gold mineralization at Guelb Moghrein formed during retrograde shearing in metamorphic rocks and contemporaneous hydrothermal alteration. The stable isotope signature of alteration and ore minerals suggest an external crustal fluid source. Fluids were focused in the reactive and competent meta-iron formation. Potassium alteration, magnetite and copper–gold mineralization suggest an IOCG mineral system akin similar deposits in Australia and Brazil.     

Ra’s Abdah of the north Eastern Desert of Egypt: the role of granitic dykes in the formation of radioactive mineralization,evidenced by zircon morphology and chemistry

Syenogranitic dykes in the north of Egypt’s Eastern Desert are of geological and economic interest because of the presence of magmatic and supergene enrichment of radioactive mineralization. Zircon crystal morphology within the syenogranitic dykes allows precise definition of sub-alkaline series granites and crystallized at mean temperature of about 637 °C. The growth pattern of the zircons suggest magmatic and hydrothermal origins of radioactive mineralization. Hydrothermal processes are responsible for the formation of significant zircon overgrowth; high U-zircon margins might have occurred contemporaneously with the emplacement of syenogranitic dykes which show anomalous uranium (eU) and thorium (eTh) contents of up to 1386 and 7330 ppm, respectively. Zircon chemistry revealed a relative increase of Hf consistent with decreasing Zr content, suggesting the replacement of Zr by Hf during hydrothermal activity. Visible uranium mineralization is present and recognized by the presence of uranophane and autunite.     

New data on palynostratigraphy of the Lipovtsy formation in the Razdol’naya coal Basin (Southern Primorye)

Palynological samples, plant megafossils, and fossil wood taken from the upper Lipovtsy Subformation (Porechye open-pit coal mine in the Il’ichevka coalfield, Razdol’naya River Basin, southern Primorye), as well as coal samples for determining coal-forming plants from dispersed cuticles are analyzed. The taxonomic composition of the identified palynomorphs from the coals and interstratal clastic sediments indicates the Aptian age of host deposits. The palynological spectra from the lower humic–rhabdopissite coal seam are dominated by Gleicheniaceae and Cyatheaceae accompanied by Dicksoniaceae and Ginkgocycadophytus. In the palynological spectra from the upper coal seam, the share of Gleicheniaceae substantially decreases, though they remain dominant; simultaneously, single angiosperm pollen grains appear in them. The spectra from the clastic rocks are dominated by Polypodiaceae and Cyatheaceae. The taxonomical composition of the gymnosperms is relatively diverse, although their abundance is low. The share of angiosperms increases with respect to both their diversity and abundance. The angiosperm pollen, found for the first time in the Aptian deposits of the Razdol’naya River Basin, provides grounds to assume that these pants appeared earlier than previously thought (early Albian). The coal-forming plants of the Il’ichevka coalfield are determined.     

The Role of Forests in the Implementation of Russia’s Low-Carbon Development Strategy

Doklady Earth Sciences - The potential role of forests in achieving carbon neutrality in the Russian Federation by 2060 is analyzed. It is shown that the key rate in the Strategy for the...     

The theory of magnetic hole formation in the vicinity of the Earth’s magnetoshere

Doklady Earth Sciences -     

The Ural–Herirud transcontinental postcollisional strike-slip fault and its role in the formation of the Earth’s crust

The paper considers the morphology, deep structure, and geodynamic features of the Ural–Herirud postorogenic strike-slip fault (UH fault), along which the Moho (the “M”) shifts along the entire axial zone of the Ural Orogen, then further to the south across the Scythian–Turan Plate to the Herirud sublatitudinal fault in Afghanistan. The postcollisional character of dextral displacements along the Ural–Herirud fault and its Triassic–Jurassic age are proven. We have estimated the scale of displacements and made an attempt to make a paleoreconstruction, illustrating the relationship between the Variscides of the Urals and the Tien Shan before tectonic displacements. The analysis of new data includes the latest generation of 1: 200000 geological maps and the regional seismic profiling data obtained in the most elevated part of the Urals (from the seismic profile of the Middle Urals in the north to the Uralseis seismic profile in the south), as well as within the sedimentary cover of the Turan Plate, from Mugodzhary to the southern boundaries of the former water area of the Aral Sea. General typomorphic signs of transcontinental strike-slip fault systems are considered and the structural model of the Ural–Herirud postcollisional strike-slip fault is presented.     

Rubidium mineralization in rare-element granitic pegmatites of the Voron’i tundras,Kola Peninsula,Russia

Rare-element pegmatites in the Voron’i tundras, Kola Peninsula, Russia, contain late abundant Rb mineralization. Individual Rb minerals are Rb-dominant feldspars and micas that form continuous solid solution series with K analoques. The feldspars contain from 17 to 86 mol % RbAlSi₃O₈ (5.5–25 wt % Rb₂O) and 1–5 mol % CsAlSi₃O₈, and the muscovite contains 2.6–9.4 wt % Rb₂O. The Li micas are members of the lepidolite-polylithionite series and their Rb-dominant analogues. They form a continuous series of solid solutions with the Rb concentrations varying from 0.09 to 0.54 apfu., K concentrations varying from 0.82 to 0.33 apfu, and Cs concentrations varying from 0.02 to 0.18 apfu The maximum Rb₂O concentration in the newly found mineral voloshinite, an Rb analogue of lepidolite, is 12.2 wt %. The Rb-rich feldspars and micas sometimes crystallized directly or were formed via cation exchange with the young fluid. The Rb minerals are spatially and genetically closely associated with pollucite. It is supposed that initially Rb was contained in a high-temperature pollucite solid solution and was released from it at decreasing temperature as a result of a reaction with the aqueous fluid and notably enriched the latter. It is shown that Rb mineralization is generally typical of pollucite-bearing pegmatites.