Duality and genetic significance of REE speciation in tourmaline from tin deposits of the Far East

The distribution of REEs and some minor elements in tourmalines of different associations and deposits of the Russian Far East is studied by the methods of ICP-MS, ICP-MS with laser ablation and scanning electron microscopy. The duality of REE speciation in tourmaline is established: in high-temperature varieties, most REEs (mainly HREEs) are incorporated in rare minerals (monazite, xenotime, zircon, and F–Ce–Y carbonate), whereas hydrothermal ores are characterized by isomorphic incorporation of LREEs in the mineral structure, as well as by a fine admixture of zircon at the expense of detrital clasts in flyschoid rocks with the zones of tourmalinization.     

REE geochemistry in groundwater of the Sikhote Alin fold region (Russian Far East)

Analysis of the distribution and fractionation of rare earth elements in the groundwater of the Sikhote Alin fold region reveals that their concentrations, geochemistry, and fractionation ability vary in different groundwater types depending on many factors, including the pH–Eh parameters and mineralization of the solutions and the composition of the host rocks. The results of monitoring of changes in the REE concentrations in the groundwater of the region over ten years provides the opportunity to establish the range of their variations. Inorganic forms of REE migration are rated for all geochemical types of water in the meteoric–surface–ground water system.     

Diatom characteristics of the Far East siliceous organogenic deposits

Three Far East diatomites, Puzanov (Kunashir Island, Kuril Islands), Sergeevskii, and Terekhovka (Southern Primorye) are characterized in detail. Rock-forming taxa are identified (Puzanov—Aulacoseira subarctica (O. Mull.) Hawort and Stephanodiscus niagarae var. pusanovae Genkal et Cherepanova; Sergeevskii—Staurosira construens var. venter (Ehr.) Gran., Aulacoseira italica (Ehr.) Sim., and representatives of the genus Cymbella with large valves (up to 175 Jim in length); Terekhovka—Aulacoseira praegranulata var. praeislandica f. praeislandica (Sim.) Moiss.). Morphometric analysis of valves of the dominant taxa showed a low variability of valve parameters for the Puzanov diatomite and a high one for the Sergeevskii and Terekhovka diatomites. The lake environments of the diatoms forming the diatomites were reconstructed based on the elemental composition of diatom valves and the ecological structure of diatom paleocommunities. The high oxygen and low silicon concentrations in valves of the Puzanov diatomite, most likely, indicate that the diatoms were part of plankton communities formed in a large deep freshwater lake. Significant concentrations of silicon in valves of the Terekhovka diatomite, in contrast, suggest that the diatoms occurred in benthic ecotopes in a shallow lake. The age of the deposits was refined by detailed studies of Aulacoseira valves, using light and scanning electron microscopes. For example, the presence of Aulacoseira taxa of the “prae” group in the Terekhovka diatomite confirms its Pliocene age, and the presence of valves of the present species A. italica in the Sergeevskii diatomite points to its Late Pliocene age. The identified features of the diatomites permit their use in practice.     

Buchia faunas and biostratigraphy of the Jurassic-Cretaceous boundary deposits in the Komsomolsk section (Russian Far East)

Abundant Buchiidae (Bivalvia) from the Upper Volgian-Lower Valanginian sediments of the Northern Sikhote-Alin (Russian Far East) were studied in the key section at right bank of the Amur River opposite to Komsomolsk-on Amur. The analysis of the Buchiidae stratigraphic distribution in the section allowed us to reveal the sequence of Buchia-bearing beds: this is well correlated with the Buchia zonal scales of many Arctic regions. Here, from the base upward, there have been recognized the following: beds with Buchia terebratuloides, beds with B. unschensis and B. terebratuloides, beds with B. volgensis, and beds with B. inflata and B. keyserlingi. The beds with B. unschensis and B. terebratuloides also yielded the Berriasian ammonite Pseudosubplanites? sp. of Tethyan affinity. The obtained paleontological data confirm the occurrence of a large syncline in the studied section. The data also permit one to refine the age spans of the local stratigraphic units.     

Complex mineralization at large ore deposits in the Russian Far East

Genetic and mineralogical features of large deposits with complex Sn, W, and Mo mineralization in the Sikhote-Alin and Amur-Khingan metallogenic provinces are considered, as well as those of raremetal, rare earth, and uranium deposits in the Aldan-Stanovoi province. The spatiotemporal, geological, and mineralogical attributes of large deposits are set forth, and their geodynamic settings are determined. These attributes are exemplified in the large Tigriny Sn-W greisen-type deposit. The variation of regional tectonic settings and their spatial superposition are the main factor controlling formation of large deposits. Such a variation gives rise to multiple reactivation of the ore-magmatic system and long-term, multistage formation of deposits. Pulsatory mineralogical zoning with telescoped mineral assemblages related to different stages results in the formation of complex ores. The highest-grade zones of mass discharge of hydrothermal solutions are formed at the deposits. The promising greisen-type mineralization with complex Sn-W-Mo ore is suggested to be an additional source of tungsten and molybdenum. The Tigriny, Pravourminsky, and Arsen’evsky deposits, as well as deposits of the Komsomol’sk and Khingan-Olonoi ore districts are examples. Large and superlarge U, Ta, Nb, Be, and REE deposits are localized in the southeastern Aldan-Stanovoi Shield. The Ulkan and Arbarastakh ore districts attract special attention. The confirmed prospects of new large deposits with Sn, W, Mo, Ta, Nb, Be, REE, and U mineralization in the south of the Russian Far East assure expediency of further geological exploration in this territory.     

Noble metal-bearing ferromanganese deposits in the Kimkan basin,Russian Far East

It has been established that large ferromanganese deposits enriched in noble metals, Co, U, V, and REE in the Kimkan sedimentary basin are confined to Vendian–Cambrian black shales. Lithostratigraphy plays an important role in the localization of such deposits and promising ore-bearing fields. Deposits and occurrences of complex iron and ferromanganese ores are polygenous and polychronous, because they underwent intense hydrothermal alterations with the superposition of noble metal and uranium mineralization in the Cretaceous. Efficient utilization of complex iron ores in the Kimkan open pit needs the construction of a metallurgical plant.     

Rare earth elements in tourmaline and chlorite from tin-bearing assemblages: Factors controlling fractionation of REE in hydrothermal systems

The REE distribution in minerals from tin-bearing ore-magmatic systems of the Russian Far East, including the Komsomolsk, Khingan, and Badzhal districts in the Amur region and the Kavalerovo, Lesozavodsk, Voznesenka, Furmanovo, and other districts in Primorsky krai, has been studied. The main attention was focused on tourmaline and chlorite; in addition, associated biotite, feldspar, apatite, fluorite, and carbonates were examined. The major factors affecting the REE distribution in the studied minerals are the temperature, Eh, and pH of the mineral-forming medium; crystal chemistry; partition coefficients of REE between fluid and minerals; and complexation that disturbs the coherent behavior of REE. Fluid evolution at different stages is characterized.     

Paleogeography of the Bureya Foredeep (in the Far East) in the Jurassic

Using the standard methods of paleogeographic analysis, small-scale paleogeographic sketch maps of the Verkhnyaya Bureya and Gudzhik depressions of the Bureya Foredeep are compiled for the Pliensbachian, Bajocian-Bathonian, Callovian, and Tithonian ages of the Jurassic. Marine sedimentation settings that existed during the Late Triassic and the major part of the Jurassic are characterized.     

Factors determining origination of gold ore systems in the Russian Far East

Relationships of gold mineralization to deep-seated low-density domains of granitization are considered. The gold mineralization originates in the zones of interaction of these domains with femic rocks established from the results of regional magnetic survey or with thick folded sequences of carbonaceous clay rocks and intercalated members of femic volcanics. The intensity of granitization decreases from continent to ocean, and the ore-forming centers and mineralization are rejuvenated in this direction from the Jurassic-Cretaceous to the Pleistocene, while the productivity of the ore-forming process remains unchanged.     

Sedimentary formations of the Cretaceous Sakhalin Basin (Far East Asia)

The marine sedimentary formations of the Middle Albian to Maastrichtian in the Cretaceous Sakhalin Basin (CSB) were investigated. These successions of strata consist of interbedded sandy, clayey and calcareous rocks which are underlain by heterogeneous metamorphosed (up to greenschist facies) Paleozoic to Mesozoic (pre-Aptian) rocks. The studied sections display several different facies reflecting geological settings ranging from an inner shelf to a continental slope. Three depositional complexes bound by regional subaerial unconformities are recognized within the marine successions. Since the Albian, the CSB has been a rapidly subsiding marginal part of the Okhotsk Sea plate. The Naiba Valley succession, corresponding to a sublittoral zone, shows extremely high sedimentation rates up to 190 m/Ma. The stratigraphic distribution of lithofacies indicates that the CSB became shallower from the Middle Albian to the Maastrichtian.     

Mesozoic paleogeography of the Northwestern Sikhote-Alin fold system (Far East)

Paleogeographic schemes (Late Triassic; Early, Middle, and Late Jurassic; and Cretaceous) were constructed for the northwestern part of the Sikhote-Alin fold system. The paleoenvironmental reconstructions require more detailed and comprehensive schemes of the tectonic zoning, which will provide a basis for the reconstruction of the Late Jurassic-Cretaceous events at the convergent plate boundary along the east Eurasian margin.     

Main geologic-genetic types of bedrock gold deposits of the Transbaikal region and the Russian Far East

Tens of gold deposits of different genetic classes (endogenous and exogenous), groups, and types were recognized in cratons, orogenic belts and magmatic arcs of the Transbaikal region and Russian Far East (T and RFE), evaluated to different extents, explored, and prepared (or are being prepared) for exploitation. The formation of the noble-metal mineralization of the region was related to the activity of different genetic types of ore systems, which were responsible for the magmatogenic- and metamorphogenic-hydrothermal, hydrothermal-sedimentary-metamorphogenic, and hydrogenic deposits. The concepts of geologic-genetic and economic types of gold deposits serve as the basis for such fundamental notions of metallogenic analysis as ore formations and geologic-economic types of mineralization. In recent years, the researchers of gold deposits (especially large ones) arrived at conclusions of their polygenous and polychronous formation, which is confirmed sometimes by the sufficiently long-term (up to hundreds of millions of years) conjugate development of ore formations, sedimentation, metamorphism, and magmatism of diverse geodynamic natures. The polygenous nature and significant duration of the formation of the gold deposits affect their economic significance and should be taken into account in the metallogenic forecasting and assessment of the potentially ore-bearing areas.     

Alkaline granites and Be (Phenakite-bertrandite) mineralization: An example of the Orot and Ermakovka deposits

The Orot (Or) and Ermakovka (Er) intrusions of aegirine granites with various resources of accompanying Be mineralization in Transbaikalia were studied to reproduce Be behavior during the crystallization and degassing of alkaline granite magma. Data on the petrography and geochemistry of the rocks and the microthermomety and microprobe analysis of fluid and melt inclusions in them indicate that the intrusions were formed by discrete magma portions derived from a single magmatic source during successive stages of its differentiation. The intrusions crystallized at temperatures higher than 1030–1070°C (Or) and 840–640°C (Er), and the melts contained elevated concentrations of H₂O and F: from 2.1 to 3.5% F and from <1 to 1% H₂O for the former intrusion and from 3.9 to 6.7% F and from <2.6 to 4.1% H₂O for the latter. Fluids were released from the magma during a late crystallization stage for the Orot intrusion and an intermediate stage for the Ermakovka intrusion. Early in the course of this process, the fluids were halide-sulfate brines with the Cl: F ratio higher for the Orot intrusion and lower for the Ermakovka intrusion. A temperature decrease resulted in the exsolution of the fluids into two immiscible phases, one of which contained low and the other high concentrations of salts. The magmatic brines and low-salinity solutions of both intrusions were enriched in Be (up to 1.1 g/kg), which is comparable with the concentration of this element in the emanations of Be-bearing pegmatites in the Pamirs and is manyfold higher than C _Be in magmatic fluids related to granite intrusions with W-Sn mineralization. The Be ore mineralization of the Orot and Ermakovka deposits was produced by solutions whose composition and Be concentrations were analogous to those in the low-salinity phase of the corresponding magmatic fluids. The brines of the Ermakovka intrusion were enriched in Mo (up to 17 g/kg) and, to a lesser extent, Mn, Ce, and La and produced uneconomic monazite-molybdenite ore mineralization. Based on available data and results of our calculations, we arrived at the conclusion that the very high alkali concentrations in the melts of both intrusions (ASI < 1), their high F concentrations (up to 4.1%), and the absence of magmatic Be-bearing minerals facilitated Be selective extraction by the separated fluids in the form of its most soluble F-complexes. The high oxidation of the melt predetermined the predominance of hexavalent S and Mo compounds, which could be efficiently extracted by the fluid phase in the form of sulfates and molybdates of alkali metals. The differences in the ore potentials of the Orot and Ermakovka intrusions were caused by the different H₂O, F, and perhaps, also Be concentrations in the parental melts, which was, in turn, caused by their different degrees of differentiation during the preintrusive stages of their magmatic evolution.     

Fluid regime of the amphibolite-facies metamorphism in the Dzhugdzhur-Stanovoy fold area (Far East)

Chromatographic and electrochemical measurements, combined with computer simulation of the natural mineral parageneses and estimation of the stability field of muscovite-bearing assemblages, yielded a consistent model of the fluid regime for the amphibolite-facies metamorphism of the Dzhugdzhur-Stanovoy fold area (DSFA). The model allows the fluid differentiation into “internal” and “external” fluids. The “internal” fluid is formed by the volatiles of the rock, while the “external” fluid arrived from an outer source: the mantle or other reservoir. It is established that the chromatographic and electrochemical measurements refer to the “external” fluid, whereas the redox state estimated from the mineral equilibria is related to the “internal” fluid, whose composition is buffered by the equilibrium mineral assemblage. The “external” fluid trapped by rocks preserves its own redox state only at the regtrograde stage, when the solid-phase reactions slacken and the buffer role of the mineral assemblages is minimized. This aspect explains the contradiction between the wide variations in the oxidation state of the mineral equilibria (log fO₂ from ?15 to ?20), on the one hand, and the persistent oxidation state of the external fluid established by the chromatographic and electrochemical methods, on the other hand. The main reason for the wide development of hornblende-bearing assemblages in the amphibolite-facies metamorphic rocks of the Dzhugdzhur-Stanovoy fold system is the high H₂O pressure in the “external” fluid. According to the obtained data, the composition of the “external” fluid is determined by the conditions $ P_{H_2 O} Chromatographic and electrochemical measurements, combined with computer simulation of the natural mineral parageneses and estimation of the stability field of muscovite-bearing assemblages, yielded a consistent model of the fluid regime for the amphibolite-facies metamorphism of the Dzhugdzhur-Stanovoy fold area (DSFA). The model allows the fluid differentiation into “internal” and “external” fluids. The “internal” fluid is formed by the volatiles of the rock, while the “external” fluid arrived from an outer source: the mantle or other reservoir. It is established that the chromatographic and electrochemical measurements refer to the “external” fluid, whereas the redox state estimated from the mineral equilibria is related to the “internal” fluid, whose composition is buffered by the equilibrium mineral assemblage. The “external” fluid trapped by rocks preserves its own redox state only at the regtrograde stage, when the solid-phase reactions slacken and the buffer role of the mineral assemblages is minimized. This aspect explains the contradiction between the wide variations in the oxidation state of the mineral equilibria (log fO₂ from −15 to −20), on the one hand, and the persistent oxidation state of the external fluid established by the chromatographic and electrochemical methods, on the other hand. The main reason for the wide development of hornblende-bearing assemblages in the amphibolite-facies metamorphic rocks of the Dzhugdzhur-Stanovoy fold system is the high H₂O pressure in the “external” fluid. According to the obtained data, the composition of the “external” fluid is determined by the conditions ≥ 0.7 P_S and = 0.01–0.3. The oxidation potential of the “external” fluid is close to that of the H₂O-C system under carbon-saturated vapor conditions. Original Russian Text ? O.V. Avchenko, I.A. Aleksandrov, V.O. Khudolozhkin, M.A. Mishkin, 2009, published in Tikhookeanskaya Geologiya, 2009, Vol. 28, No. 4, pp. 3–15.     

中国磷块岩型稀土矿资源前景分析

磷块岩中通常伴生有稀土元素富集,是一种潜在、具有很高开发利用价值的稀土资源。我国磷块岩型稀土矿分布广、稀土含量高、具有综合回收价值,是仅次于独立稀土矿床的伴生稀土资源。通过统计全球及中国磷矿时空分布规律,总结中国典型磷块岩型稀土矿床的矿床成因、地质背景、沉积环境、岩石组合、REE地球化学特征。在此基础上,结合P_2O_5与ΣREE、δCe、δEu、MREE/ΣREE和MREE/LREE在各时代之间的对比及耦合关系,讨论各时代稀土配分模式,讨论磷块岩中稀土富集机制与控制因素问题,讨论中国典型磷块岩型稀土矿资源储量。同时总结国内对磷块岩中稀土高效、环保的提取技术,对工业化开发利用磷块岩中稀土资源具有良好的可行性。因此,从磷矿中提炼稀土资源可以获得很好的社会价值和经济效益,能有效缓解我国南方离子吸附型稀土开采带来的环境污染、生态破坏,为日益枯竭稀土资源提供新的资源途径。     

The regularities of formation of noble- and rare-metal mineralization in Cenozoic coaliferous deposits in the southern Far East

We performed system studies of age parageneses and lateral conjugation of peat and gold accumulation areas as well as the regularities of formation of noble- and rare-metal mineralization in Cenozoic coaliferous deposits in the south of the Russian Far East. The migration properties of noble metals (NMs) and their behavior in different media are considered. Based on literature data and results of experimental studies, we performed analysis and selection of the most optimal methods for the quantitative determination of NMs and trace and rare-earth elements. The experiments have confirmed the NB fugacity and have shown for the first time the scales of transportation of NMs as ultrafine particles during coal combustion. The obtained results significantly expand the notions of the migration properties of NMs and serve as the key to the solution of the problem of NM extraction in analytical and technological processes. Also, areas promising for noble- and rare-metal mineralization have been revealed in coal basins.     

Inhomogeneous distribution of REE in scheelite and dynamics of Archaean hydrothermal systems (Mt. Charlotte and Drysdale gold deposits, Western Australia)

Scheelite is a widespread accessory mineral in hydrothermal gold deposits, and its rare earth element (REE) patterns and Nd and Sr isotopic compositions can be used to constrain the path and origin of the mineralising fluids and the age of the hydrothermal activity. Micro-analyses by laser ablation high resolution inductively coupled mass spectroscopy and cathodoluminescence imaging reveal a very inhomogeneous distribution of the REE in single scheelite grains from the Mt. Charlotte and Drysdale Archaean gold deposits in Western Australia. Two end-member REE patterns are distinguished: type I is middle REE (MREE)-enriched, with no or minor positive Eu-anomaly, whereas type II is flat or MREE-depleted with a strong positive Eu-anomaly. The chemical inhomogeneity of these scheelites is related to oscillatory zoning involving type I and type II patterns, with zone widths varying from below 1 to 200 μm. Intra-sectorial growth discontinuities, syn-crystallisation brittle deformation, and variations in the relative growth velocities of crystallographically equivalent faces suggest a complex crystallisation history under dynamic hydraulic conditions. The co-existence of MREE-enriched and MREE-depleted patterns within single scheelite crystals can be explained by the precipitation of a mineral which strongly partitions MREE relative to light and heavy REE. Scheelite itself has such characteristics, as does fluorapatite, which is locally abundant and has REE contents similar to that of scheelite. In this context, the systematic increase of the Eu-anomaly between type I and type II patterns is produced by the difference between the partition coefficients of Eu²⁺ and Eu³⁺, and not by fluid mixing or redox reactions. Consequently, the high positive Eu-anomaly typical of scheelite from gold ores may not necessarily be inherited from the hydrothermal fluid, but may reflect processes occurring during ore deposition. This case study demonstrates that in hydrothermal systems characterised by low REE concentrations in the fluid, and by the precipitation of a REE-rich mineral which strongly fractionates the REE, the REE patterns of such a mineral will be highly sensitive to the dynamics of the hydrothermal system. Received: 1 November 1999 / Accepted: 4 February 2000