Geochemical features of rare-earth elements in surface and subsurface waters in the field of the Albynskoe Gold-Bearing Placer,Amur oblast

The distribution and fractionation of rare-earth elements (REE) are studied in the surface and subsurface waters and rocks of the Albynskoe Gold-Bearing Placer. The obtained data show the rocks of the placer to be enriched with rare-earth elements and to feature the predominance of light lanthanides over heavy ones. Groundwater show an equality between the groups of light and heavy lanthanides, while in the surface waters the concentration of light REE is much higher than that of heavy ones, thus reflecting the composition of the drained ore rocks. The leaching of rare-earth elements from rocks by atmospheric water is intensified by agents produced by microorganisms in their vital activity.     

Rare-earth abundances in indian kimberlite

Abundances of some rare-earth elements (REE), together with Hf, Ta, Th, and Ba have been determined by neutron activation analyses in twelve kimberlite samples from Peninsular India. The kimberlites have fractionated REE patterns with enrichment of light rare earths; La/Yb ratio varies from 39 to 166. A systematic relationship exists between the total rare-earth abundances and the petrochemistry of the rocks. The rare-earth abundances observed in the kimberlites are consistent with their derivation by partial melting of a hydrous garnet peridotite mantle and subsequent fractional crystallization of the melt.     

Geochemistry and chronology of the Jiehekou Group metamorphic basic volcanic rocks in the Lüliang Mountain area,Shanxi, China

Samples were systematically collected from metamorphic basic volcanic rocks in the Jiehekou and Xiyupi areas on both sides of the Lüliang Mountains, Shanxi Province and analyzed for their major elements, trace elements and rare earth elements (REE). The geochemical characteristics of their major, trace and rare-earth elements indicated that the metamorphic basic volcanic rocks in this area were emplaced in the tectonic environment like a modern continental rift. Sm-Nd and Rb-Sr isotope chronological studies demonstrated that the Jiehekou Group metamorphic basic volcanic rocks were formed during the 2600-Ma crust/mantle differentiation event, and were transformed by granulite facies metamorphism during the late Neo-Archaean period (2500 Ma ±), making the Sm-Nd systematics of the rocks reset. During the late Paleoproterozoic period (1800 Ma ±) the Rb-Sr systematics of the rocks were disturbed again in response to the Lüliang movement. Since the extent of disturbance was so weak that the Sm-Nd systematics was not affected, the age of 1600 Ma ± obtained from this area seems to be related to local magmatic activities within the craton. Research results lend no support to the idea that the Lüliang Group was formed during the Archaean. Instead, it should be formed during the Proterozoic.     

Major and trace element zoning in plagioclase from Kizimen Volcano (Kamchatka): Insights into magma-chamber processes

The data on the geochemistry of the rocks of Kizimen Volcano and results of microprobe studies of major and trace elements in plagioclase grains from acid lavas and basalt inclusions are presented. The characteristics of the Kizimen Volcano are the following: (1) basalt inclusions are abundant in acid lavas; (2) banded, mixed lavas occur; (3) the distribution curves of rare-earth elements of acidic lavas and basalt inclusions intersect; (4) Sr-Nd isotope systematics of the rocks and inclusions do not indicate mixture with crustal material; (5) plagioclase phenocrysts are of direct and reverse zonation; (6) olivine and hornblende, as well as acid and mafic plagioclases, coexist in the rocks. The studies revealed that the rocks are of a hybrid nature and originated in the course of repeated mixture of acid and mafic melts either with chemical and thermal interaction of melts or exclusively thermal ones. Study of the major- and trace-element distribution in zonal minerals provides an informative tool for understanding the history of the generation and evolution of melts in a magma chamber.     

Petrogenetic relationships of acid and basic rocks in iceland: Sr-isotopes and rare-earth elements in late and postglacial volcanics

Strontium isotope ratios and rare-earth element abundances have been measured in acid, intermediate and basic rocks from three late to postglacial volcanic complexes, and several other postglacial basalts in Iceland. Late and postglacial basalts in Iceland have been generated from a source region which is essentially homogeneous with respect to⁸⁷Sr/⁸⁶Sr. The mean⁸⁷Sr/⁸⁶Sr ratio for the basalts analysed is 0.70328 and the range is from 0.70317 ± 6to0.70334 ± 5 (2σ).Acid rocks from the Kerlinganfjöll and Namafjall volcanic complexes have⁸⁷Sr/⁸⁶Sr ratios which are indistinguishable from analysed basalts from the same complexes. However, intermediate and acid rocks from the Torfajökull complex have significantly higher⁸⁷Sr/⁸⁶Sr ratios and could not have been derived by fractional crystallization from basaltic magmas similar to those found in the same complex. These latter rocks have most probably been produced by remelting of Tertiary gabbroic rocks in Layer 3. Most of the basalts analysed have higher total rare-earth element abundances than typical dredged ocean-ridge tholeiites, and show less light rare-earth depletion. Intermediate and acid compositions show overall higher abundances and light rare-earth enrichments. The measured rare-earth abundances are compared with abundances generated by differential partial melting of various model source regions.It is shown that both the tholeiitic and alkali basalt compositions could be generated from the same source material by different degrees of partial melting. Variable partial melting of gabbroic material may account for the rare-earth element abundances of both the rhyolitic rocks (small degrees of melting) and the intermediate rocks (more extensive melting).     

Rare-earth data on monzonoritic rocks related to anorthosites and their bearing on the nature of the parental magma of the anorthositic series

Major and trace elements have been determined in monzonoritic rocks (hypersthene-monzodiorite or jotunite) from two intrusions belonging to the South Rogaland anorthositic complex (Norway). The rare-earth abundance pattern reveals no Eu anomaly, or only a very small one. This fact together with field observations suggest that these rocks represent the parental magma of the anorthositic suite. High Ti and P abundances, low Si content, high Fe/Mg and K₂O/SiO₂ ratios are characteristics of the major element geochemistry. Absolute amounts of some trace elements abundances vary distinctly between the two intrusions. K/Rb ratios as high as 1700 are observed. Partial fusion of upper mantle kaersutite is proposed as a possible mechanism of magma generation. Partition coefficients between plagioclase phenocrysts and liquid are determined.     

Provenance for the Chang 6 and Chang 8 Member of the Yanchang Formation in the Xifeng area and in the periphery Ordos Basin: Evidence from petrologic geochemistry

Study indicates that the major paleocurrent and source direction for the Chang 8 Member of the Yangchang Formation, Upper Triassic in the Xifeng area of the southwestern Ordos Basin derived from the southwest direction with the southeast source as the subordinate one. While the Chang 6 Member was influenced not only by the same source as that of the Chang 8 Member from the southwest and the southeast direction, but also affected by the northeast and the east provenance around the Ordos Basin, based upon measurement of paleocurrents on outcrops located in the periphery Ordos Basin, analysis of framework grains and heavy minerals in sandstones of the Chang 6 and Chang 8 Members and their spatial distribution in the study area, combined with characteristics of trace elements and rare-earth elements of mudstones and of a small amount of sandstones in the Xifeng area and outcrops in margin of the Ordos Basin. The Yuole-Xuanma-Gucheng-Heshui-Ningxia region located in the northeastern and the eastern Xifeng area was the mixed source area where the southwest, southeast, northeast and the east sources were convergent till the Chang 6 Member was deposited. The rare earth elements of the Chang 6 and Chang 8 Members are characterized by slight light rare earth-elements (LREE) enrichment and are slightly depleted in heavy rare earth-elements (HREE) with weak to moderate negative abnormal Eu, resulting in a right inclined REE pattern, which implies that the source rocks are closely related with better differential crust material. Analysis on geochemical characteristics of the mudstones and sandstones, features of parent rocks in provenance terranes and tectonic settings shows that source rocks for the Chang 8 Member mainly came from metamorphic and sedimentary rocks in transitional continental and basement uplift terranes with a small amount of rocks including metamorphic, sedimentary and igneous rocks coming from mixed recycle orogenic belt located in the southwest margin of the Ordos basin. Rocks in the crystalline basement and the overlying sedimentary cover in a basement uplift setting in the northeast periphery of the basin also contributed a part of the sources for the Chang 6 Member, in addition to the sources deriving from transitional continental and basement uplift terranes in the southwest margin of the basin. Parent rocks of the provenance terrane in the northeast margin of the Ordos Basin are characterized by having more felsic rocks.     

An iron-rich deposit from the Northeast Pacific

An iron-rich deposit dredged from the upper flank of Dellwood Seamount in the Northeast Pacific has been analyzed for major and trace elements, rare-earth contents and uranium isotopic composition. In terms of mineralogy and overall chemical composition, the deposit resembles other iron-rich deposits variously attributed to volcanic hydrothermal activity. Both the relative concentrations of the rare-earth elements and the isotopic composition of uranium rule out seawater as the sole source of elements in this deposit. The rare-earth element pattern indicates that these elements were derived from the underlying basalt. The²³⁴U/²³⁸U ratio is significantly higher than in seawater and can best be explained by preferential leaching of²³⁴U generated by decay from its parent²³⁸U in the underlying rock and subsequent redeposition of the excess²³⁴U together with the Fe and minor metals. These data are consistent with a model for the origin of submarine metal-rich solutions involving mobilization of elements from the interior of slowly cooling basalts by circulating seawater.     

Assessment of the Uvod Reservoir pollution with heavy metals

Concentrations of heavy metals (Cu, Ni, Cd, Pb, Cr, and Zn) in bottom sediments, water, snow, and biota of the Uvod Reservoir, as well as of rare-earth elements (Ce, Dy, Er, Eu, Gd, Ho, La, Lu, Nd, Pr, Sm, Tb, Y, and Yb) in its water are assessed. Geochemical studies of concentrations of Cu, Ni, Cd, Pb, Cr, and Zn in soils, water, and snow allow us to state that the metals enter the reservoir mostly from natural sources; however, some part of them are of anthropogenic origin. The sum of concentrations of light rare-earth elements (La, Ce, and Nd) make almost the total of all rare-earth elements in the reservoir—from 70 to 97%, depending on the sampling site. The highest concentrations of metals (and the highest percentage of their labile forms) are recorded in the Priplotinnyi and Kolbaskinskii (in macrophite deposits) pools and at the site of water inflow from the Volga-Uvod canal. There is also reason to suppose a secondary entry of the elements under study into the water mass. The largest variations in metals’ concentrations are observed during the periods of spring and autumn floods, when a great quantity of terrigenous suspended matter enters the water body. The distribution of the above metals and rare-earth elements in water is uneven; their highest concentrations are observed in the site of water inflow from the canal and in the Uvod River (the latter is likely to be due to the effect of the settlement of Pistsovo). The analysis of biota (fennel-leaved pondweed and zooplankton) has shown that the Uvod Reservoir is polluted with heavy metals.     

Trace element characteristics of the fluid liberated from amphibolite-facies slab: Inference from the metamorphic sole beneath the Oman ophiolite and implication for boninite genesis

Major and trace element compositions of amphibolites and quartzose rocks in the 230-m-thick metamorphic sole underlying the mantle section of the Oman ophiolite in Wadi Tayin area were determined to investigate the chemical characteristics of the hydrous fluid released from subducted amphiboltie-facies slab. The fluid-immobile element compositions indicate that protoliths of these rocks are mid-ocean ridge basalt-like tholeiite and deep-sea chert, which is consistent with the idea that these rocks represent Tethyan oceanic crust overridden during the early, intraoceanic thrusting stage of the Oman ophiolite emplacement. The rare-earth element (REE) and high field-strength element concentrations of the amphibolites show limited variations, within a factor of two except for a few evolved samples, throughout transect of the sole. On the other hand, concentrations of fluid-mobile elements, especially B, Rb, K and Ba, in amphibolites are highly elevated in upper 30 m of the sole (> 600 °C in peak metamorphic temperature), suggesting the equilibration with evolved, B-Rb-K-Ba-rich fluids during prograde metamorphism. The comparison with amphibolites in the lower 150 m (500 to 550 °C) demonstrates that the trace element spectra of the fluids equilibrated with the high-level amphibolites may vary as a function of metamorphic temperature. The fluids are characterized by striking enrichments of B, Rb, K and Ba and moderate to minor enrichments of Sr, Li, Be and Pb. At higher temperature (up to 700 °C), the fluids become considerably enriched in light REE and Nb in addition to the above elements. The estimated trace element spectra of the fluids do not coincide with the compositions of basalts from matured intra-oceanic arcs, but satisfactorily explain the characteristics of the low-Pb andesites and boninites found in the Oman ophiolite. Compositional similarity between the boninites of Oman and other localities suggests that the fluids estimated here well represent the amphibolite-derived fluids involved in the magmatism of immatured, hot, shallow subduction zones.     

Specific Features in the Formation of the Mine Water Microelement Composition during Ore Mining

High concentrations of rare, trace, and rare-earth elements, which cannot exist outside the sphere of long-term active technogenesis, have been determined in the highly transformed anthropogenic water of the sulfide (ore) and sulfidized (coal and ore) deposits characterized by the sulfuric acid environment. It has been established that many deposits of the traditional raw materials can be considered rare metal water pools (liquid ore accumulations) because of high rare-earth element (REE) concentrations in water in the case of a sulfuric hydrolysis and stable anthropogenic water flow rates. The environment-controlling systems of anthropogenic solutions have been substantiated, the boundaries of the inorganic forms of element transportation have been determined, and the degrees of hydration of these elements and the geoenvironmental consequences have been studied.     

Epithermal mineralization in the Kedon Paleozoic volcano-plutonic belt,Northeast Russia: Geochemical studies of Au–Ag mineralization

This paper is concerned with the geochemical features and conditions of generation for Paleozoic Au–Ag mineralization in the pre-accretionary Kedon (D_2-3) volcano-plutonic belt (KVB), which is situated within the Omolon cratonic terrane (Northeast Russia). We present new data on the compositions and concentrations of trace elements and rare-earth elements (REEs) in the host rocks and volcanogenic ores of epithermal Au–Ag fields. The ores are found to be enriched in a wide range of trace elements. The general features of the ores under study include a low level of REE concentrations, an obvious enrichment in light REEs, and considerable variations in europium anomalies, ranging from low negative to low- and strongly positive. Fluid inclusions were studied to show that the ore-forming solutions were hydrocarbonate potassium in composition. The mineral content of the fluid increases toward later, low-temperature phases of the mineralization. We found a tendency of potassium increasing from the earlier oreless quartz to productive quartz going to great depth, as well as a slow decrease in the concentrations of Na⁺, Ca⁺⁺, and Cl^–. The productive quartz shows direct correlation in Ag–K and a reverse correlation in Ag–Na. The results indicate andesite magmas and meteoric water as the most likely sources of the fluids that have formed epithermal Au–Ag ores in the KVB deposits.     

腾冲火山岩稀土和微量元素地球化学研究

本通过腾冲火山岩稀土和微量元素丰度的测试与分析,结合前人部分资料探讨了该区火山岩的稀土和微量元素地球化学特征：各喷发期火山岩均富集ＬＲＥＥ和Ｒｂ、Ｓｒ、Ｂａ、Ｕ、Ｔｈ等不相容元素;均具极为相似的稀土分配型式和微量元素地球化学模式,这可能反映了各其火山岩初始岩浆的同源性。     

The Geochemistry of Volcanogenic Mineralization in the Northwestern Segment of the Pacific Ore Belt: Northeast Russia

This paper considers the geochemistry of volcanogenic mineralization in the northeastern segment of the Pacific Ore Belt (Northeast Russia). We give new evidence for the compositions and concentrations of trace and rare-earth elements (REE) in the ores of volcanogenic fields: Au-Ag epithermal (of various types and ages), Cu-Mo-Au porphyritic, Au-Bi related to granitoidal intrusions, Sn-Ag subvolcanic and kies polymetallic enriched in Au and Ag, as well as REEs in alkaline volcanic rocks. Geochemical signatures have been compiled for 17 formation types of volcanogenic fields. It was found that the ore-forming fluids in most fields belonged to an NaCl-H₂O hydrothermal system that was enriched in Cl relative to F; the values of Y/Ho in the ores of nearly all types correspond with the interval of ratios characteristic for present-day hydrothermal fluids in backarc basins; most of the ores that we studied had near-chondrite spectra with configurations similar to those of the REE spectra in volcanic rock sequences of the andesite-diorite series. Comparative analysis of REE spectra in the distribution of trace elements over classes of gold concentration shows synchronous enrichment of ores in similar sets of trace elements. The high Co/Ni ratio in volcanogenic ores probably reflects the superposition of a later magmatic fluid upon an earlier mineralization. Samples from ores of volcanogenic fields, except for Kuroko, show δCe and δEu varying from negative to mildly positive values, thus indicating low-oxidizing conditions during deposition. It was found for Au-Ag epithermal ores that they are enriched in a wide range of trace elements; they have low concentrations of REEs, the light REEs are more abundant than the heavy ones, and the Eu anomalies vary considerably from small negative to low and high positive values. The results provide evidence of an exhalation hydrothermal origin of the Khotoidokh field. It has been shown that the REEs in the ores of the Bol’shoe field are of the type that is most valuable to industry. The results can be used to deal with practical problems: determining the formation type and evaluating the industrial value of a field; detecting accessory components in ores; and discriminating between the types of geochemical anomalies (in rocks or in soil) and stray fluxes as to the potential of a field.     

East pacific ridge (2°S–19°S) versus nazca intraplate volcanism: Rare-earth evidence

Basalts from seamounts within the Nazca Plate representing intraplate volcanism, and the East Pacific Ridge between 19°S and 2°N have similar light rare earth depleted abundance patterns. Both intraplate and ridge basalts appear to have been derived from the low-velocity layer apparently depleted in large lithophile elements (DLVL). Nepheline-normative basalts and ferrobasalts occasionally occurring on the East Pacific Rise are shown to have also been derived from the same DLVL source. Furthermore, the rare-earth pattern similarity of nepheline-normative and tholeiitic basalts from the East Pacific Rise is best explained by distinct, pressure induced, conditions of partial melting of the DLVL source; whereas total rare-earth pattern enrichment and relative europium depletion of the ferrobasalts are consistent with shallow depth fractional crystallization during ascent.     

Origin of volcanic rocks from Stromboli (Italy)

Quaternary volcanic rocks of Stromboli (Italy) can be divided into older calc-alkaline and younger shoshonitic series. The SiO₂ contents of the rocks range from 50% to 61% but the majority of them are basalts. The rocks show systematic variations in chemical composition which correlate with the volcanic stratigraphy, such that, at a given SiO₂ content, K and other incompatible elements such as REE increase with decreasing age. In addition, the La/Yb ratio increases while the K/Rb, K/Ba, Zr/Ce and Zr/Nb ratios decrease towards the top of the volcanic pile. On the other hand, the abundances of transition elements, V, Co, Sc and Zn, like most major elements are broadly similar in comparable rocks of different ages. It is suggested that the parent magmas were derived by partial melting from upper mantle peridotite enriched in incompatible elements by fluids released from the descending oceanic lithosphere. The temporal chemical variations may probably be related to the lengths of time during which fluids were in contact with the upper mantle source.     

江西龙南-定南-全南地区泥盆系与钨铋多金属矿的关系探讨

赣南素有“世界钨都”之称,而龙南-定南-全南（简称“三南”）地区是世界钨都中的重要钨铋成矿区,钨铋成矿与三南地区广布的泥盆纪地层密不可分;由此本文通过对三南地区的泥盆系的微量元素的分布及其丰度、以及W、Bi等成矿元素在不同岩性中的丰度等进行了初步分析与讨论,认为W成矿元素在泥盆系中丰度仅次于寒武纪地层,高于其它地层,并高出地壳克拉克值的2～4倍,而Bi元素则高达几十倍。在细碎屑岩石中含量最高,与钨铋成矿关系最为密切。     

Geochemical variation with time in the Cenezoic volcanic rocks of southwest Hokkaido, Japan

Abundances of major and trace elements were determined for the Tertiary volcanic rocks from SW Hokkaido. The Late Miocene to Pliocene volcanic rocks of this region show geochemical features similar to those of the Quaternary rocks, that is, K/Si, Th/Si and LREE/HREE ratios increasing across the arc, east to west, from the Pacific to the Japan Sea side. In contrast, the Early Miocene volcanic rocks, which are geographically restricted to the Japan Sea coast, are distinct from all later volcanics and show “within-plate” characteristics — in particular, high concentrations of HFS elements. The Quaternary basalts have low Hf/Yb ratios and Hf contents, whereas the Early Miocene basalts are high in Hf/Yb and Hf, similar to Hawaiian alkali basalts. The compositional variation with time may result from the progressive depletion of incompatible HFS elements in the mantle source. Th/Yb ratios increase from Early Miocene to Quaternary, possibly reflecting increase in the LIL element contribution to the mantle source during that time.     

Petrology and geochemistry of clastic sedimentary rocks as evidences for provenance of the Late Palaeozoic Madzaringwe Formation,Tshipise-Pafuri Basin,South Africa

Petrography and geochemistry(major, trace and rare earth elements) of clastic rocks from the Late Palaeozoic Madzaringwe Formation, in the Tshipise-Pafuri Basin, Northern South Africa, have been investigated to understand their provenance. Sandstone petrography and detrital modes indicates that the Late Palaeozoic succession was derived from craton interior and recycled orogen provenance. Sandstones in the Madzaringwe Formation are sub-arkosic to sub-litharenite. The sediments may represent a recycled to craton interior provenance. The geochemical data of major elements show that sandstone and shales have the same source. The study of paleoweathering conditions based on modal composition, chemical index of alteration(CIA) and A-CN-K(Al2O3-Ca O+Na2O-K2O) relationships indicate that probably chemical weathering in the source area and recycling processes have been more important in shale and sandstone rocks. The relatively high CIA values(70–90%) indicates moderate to high weathering conditions of the samples and the paleoclimate of the source area was warm. K2O/Na2 O versus Si O2 and Na2O-Ca O-K2 O tectonic setting discrimination plots, suggest a passive continental margin. In the study of trace elements, triangular Th-Sc-Zr/10 and La-Th-Sc plots both suggest a passive margin setting of the basin. Petrographic and geochemical results of the samples suggest uplifted basement source areas dominated by sedimentary rocks and/or granite-gneiss rocks. The source rocks might have been the recycled pre-Soutpansberg Karoo Supergroup rocks and the metasedimentary rocks of the Soutpansberg Group. Other source rocks may have been the pre-Beit-Bridge basement rocks(granites and gneisses).     

The Karymskii Volcanic Center: Volcanic rock geochemistry

This paper is concerned with the petrology and geochemistry of rocks found in the Karymskii Volcanic Center (KVC), which is the largest volcanic center in the Eastern volcanic belt of Kamchatka. The KVC has been built in a rhythmic manner since the Late Pliocene, forming successive differentiated rock complexes. The pattern of variation for major and minor elements in the KVC volcanic rocks can be explained by the fractionation of mineral phases from the parent melt. The process involved enrichment of the residual melts with alkalis and lithophile elements (Rb, Ba, Sr, Pb, Th, U, REE), as well as depletion in coherent elements (Ni, Cr, Sc, Ti). A geochemical study of the KVC volcanic rocks shows that these are typical island arc formations. The relationships between incompatible elements suggest a two-component magma generation system: a depleted mantle source (N-MORB) and suprasubduction fluids (an island arc component). The melt may have been contaminated by a metasomatically altered substratum in the top of the intermediate chamber with added crystalline cumulus phases (and melts) of the earlier magma generation phases in the KVC.