Rare earths in Precambrian sediments

Thirty-six samples of well-preserved Precambrian sedimentary rocks have been analyzed for rare-earth elements (REE) as one test of the proposition that the present relative REE abundances at the Earth's surface have developed gradually with time. Except for Eu, the average relative abundances of the REE appear to be the same for the Precambrian sediments as in a composite of Paleozoic shales (taken as representative of younger sedimentary rocks). Abundances of Eu relative to the other REE in all except two of the Precambrian sedimente are significantly higher than in the younger sediments. The extent of enrichment of the Precambrian sediments in Eu over the composite of younger sediments ranges from 0.7 to 3.0. The average abundance of Eu relative to the other REE for all the Precambrian sedimente is the same as that in chondritic meteorites. Several of the oldest Precambrian sedimente have relative abundances of Eu that exceed that of chondrites. Large-scale separations of Eu from the other REE as a result of igneous, metamorphic, or sedimentary processes are considered. Present information does not convincingly support any of the proposed mechanisms.     

Iron in Precambrian rocks: implications for the global oxygen budget of the ancient Earth

Banded iron formations (BIF) are prominent in sediments older than 2 Ga. However, little is known about the absolute abundance of BIF in Archean and Early Proterozoic sediments, and the source of the Fe is still somewhat uncertain. Also unknown is the role that Fe may have played in the maintenance of low oxygen pressures in the Archean and Early Proterozoic atmosphere. An analysis of the chemical composition of Precambrian rocks provides some insight into the role of Fe in Precambrian geochemical cycles. The Fe content of igneous rocks is well correlated with their Ti content. Plots of Fe vs. Ti in Precambrian sandstones and graywackes fall very close to the igneous rock trend. Plots of Fe vs. Ti in Precambrian shales also follow this trend but show a definite scatter toward an excess of Fe. Phanerozoic shales and sandstones lie essentially on the igneous rock trend and show surprisingly little scatter. Mn/Ti relations show a stronger indication of Precambrian Mn loss, perhaps due to weathering under a less oxidizing early atmosphere. These data show that Fe was neither substantially added to nor significantly redistributed in Archean and early Proterozoic sediments. Enough hydrothermal Fe was added to these sediments to increase the average Fe content of shales by at most a factor of 2. This enrichment would probably not have greatly affected the near-surface redox cycle or atmospheric oxygen levels. Continued redistribution of Fe and mixing with weathered igneous rocks during the recycling of Precambrian sediments account for the excellent correlation of Fe with Ti in Phanerozoic shales and for the similarity between their Fe/Ti ratio and that of igneous rocks.     

Rare earth element geochemistry of Archean metasedimentary rocks from Kambalda,Western Australia

Archean sedimentary rocks of very limited lateral extent from horizons within basaltic and ultramafic volcanic sequences at Kambalda, Western Australia, are extremely variable in major elements, LIL and ferromagnesian trace element compositions. The REE patterns are uniform and do not have negative Eu anomalies. Two samples have very low total REE abundances and positive Eu anomalies attributed to a very much greater proportion of chemically deposited siliceous material. Apart from these two samples, the Kambalda data are similar to REE abundances and patterns from Archean sedimentary rocks from Kalgoorlie, Western Australia and to average Archean sedimentary rock REE patterns. These show a fundamental distinction from post-Archean sedimentary rock REE patterns which have higher $\text{La}\text{Yb}$ ratios and a distinct negative Eu anomaly.     

Geochemistry of Archean shales from the Pilbara Supergroup,Western Australia

Archean clastic sedimentary rocks are well exposed in the Pilbara Block of Western Australia. Shales from turbidites in the Gorge Creek Group (ca. 3.4 Ae) and shales from the Whim Creek Group (ca. 2.7 Ae) have been examined. The Gorge Creek Group samples, characterized by muscovite-quartzchlorite mineralogy, are enriched in incompatible elements (K, Th, U, LREE) by factors of about two, when compared to younger Archean shales from the Yilgarn Block. Alkali and alkaline earth elements are depleted in a systematic fashion, according to size, when compared with an estimate of Archean upper crust abundances. This depletion is less notable in the Whim Creek Group. Such a pattern indicates the source of these rocks underwent a rather severe episode of weathering. The Gorge Creek Group also has fairly high B content (85 ± 29 ppm) which may indicate normal marine conditions during deposition.Rare earth element (REE) patterns for the Pilbara samples are characterized by light REE enrichment ($\text{La}{}_{\mathrm{N}}\text{Yb}{}_{\mathrm{N}}\text{≥ 7.5}$) and no or very slight Eu depletion ($\text{Eu}\text{Eu}{}^1\text{= 0.82 – 0.99}$). A source comprised of about 80% felsic igneous rocks without large negative Eu-anomalies (felsic volcanics, tonalites, trondhjemites) and 20% mafic-ultramafic volcanics is indicated by the trace element data. Very high abundances of Cr and Ni cannot be explained by any reasonable provenance model and a secondary enrichment process is called for.     

Trace-element geochemistry of archean greenstone belts

Progressive alteration, diagenesis, and low-grade metamorphism of Archean greenstone belts often leads to redistribution of alkali and related trace elements. Transition metals and rare earths are relatively resistant to these processes and hence are most useful in evaluating petrologic problems.Depleted Archean tholeiite (DAT) exhibits flat REE distributions and low LIL-element contents while enriched Archean tholeiite (EAT) exhibits slightly enriched REE patterns and moderate LIL-element contents. DAT is grossly similar to modern rise and are tholeiites and EAT to cale-alkaline and oceanic island tholeiites. Archean and esites fall into three categories: depleted Archean andesite (DAA) exhibits flat REE patterns, negative Eu anomalies and low LIL-element contents; low-alkali Archean andesite (LAA) shows minor light REE enrichment and low LIL-element contents; and high-alkali Archean andesite (HAA) shows light REE enrichment and high LIL-element contents. LAA is grossly similar to modern cale-alkaline andesites, but DAA and HAA do not have modern analogues. Archean depleted siliceous volcanics (DSV) exhibit depletion in heavy REE and Y compared to modern siliceous volcanics whereas undepleted varieties (USV) are similar to modern ones. Almost all Archean volcanic rocks, regardless of composition, are enriched in transition metals compared to modern varieties. Archean graywackes are similar in composition to Phanerozoic graywackes. Rock associations in Archean greenstones suggest the existence of two tectonic settings.Magma model studies indicate that partial melting has left the strongest imprint on trace-element distributions in greenstone volcanics. Three magma source rocks are necessary (listed in order of decreasing importance): ultramafic rock, eclogite, and siliceous granulite. Trace-element studies of Archean graywackes indicate a mixed volcanic—granitic provenance with minor ultramafic contributions.Alkali and related trace-element contents of Archean volcanics have been interpreted in terms of both undepleted and depleted upper mantle sources. Preferential enrichment of transition metals in Archean volcanics may have resulted from upward movement of immiscible liquid sulfide droplets with Archean magmas, depleting the source area in these elements. Initial Sr isotope distributions in Archean volcanics indicate the upper mantle during the Archean was heterogeneous in terms of its Rb/Sr ratio.     

Excess europium content in precambrian sedimentary rocks and continental evolution

We propose that the europium excess in Precambrian sedimentary rocks, relative to those of younger age is derived from volcanic rocks of ancient island arcs, which were the source materials for the sediments. Precambrian sedimentary rocks and present-day volcanic rocks of island arcs have similar REE patterns, total REE abundances and excess Eu, relative to the North American shale composite. The present upper crustal REE pattern, as exemplified by that of sediments, is depleted in Eu, relative to chondrites. This depletion is considered to be a consequence of development of a grandioritic upper crust by partial melting in the lower crust, which selectively retains europium.     

Anomalies in rare earth distributions in seawater: Gd and Tb

We have measured profiles of the rare earth elements (REE) in Atlantic and Pacific Ocean waters. The data, normalized versus shales, exhibit a pronounced anomaly in Gd relative to its neighbors Eu and Tb in the REE series such that the Gd concentrations are high by 30–50%. Closer inspection reveals that the anomaly is made up of both elevated Gd and depressed Tb concentrations, likely associated with solution chemistry shifts in the transition from an exactly half filled 4f electron shell. Anomalies in Gd and Tb solution complexation are also indicated by the Turner-Whitfield-Dickson speciation model. The overall trend of heavy REE(III) enrichment in seawater and the $\text{Gd}\text{Tb}$ anomaly described here tend to support scavenging as an important removal mechanism for the REE from seawater.     

Rare earth elements in Huronian (Lower Proterozoic) sedimentary rocks: Composition and evolution of the post-Kenoran upper crust

The Huronian sequence (Lower Proterozoicl. north of Lake Huron, contains tillites and abundant fine-grained sedimentary rocks. Analyses of rare earth elements (REE) in the matrix of tillite samples from the Gowganda Formation (~ 2.3 Gal is considered to be a reasonable estimate of upper crustal REE abundances for the region north of Lake Huron at the time of Gowganda deposition. The average is characterized by a moderately steep pattern (σLREEσHREE = 9.1) and a slight negative europium anomaly ($\text{Eu}\text{Eu1}\text{= 0.89}$). This pattern is similar to estimates of the composition of the surface of the Canadian Shield and is intermediate between estimates of typical Archean and post-Archean sedimentary rocks. REE patterns for framework granitoid clasts from the tillite suggest that K-rich granites, which were apparently unimportant in the formation of Archean sedimentary rocks, were abundant in the source regions of the Gowganda Formation. This may explain the intermediate nature of the Gowganda pattern.Comparison of the tillites and associated Gowganda mudstones suggests that previous estimates of upper crustal REE abundances, which were based on the analyses of fine-grained sedimentary rocks, may be systematically high. Relative distributions, however, are the same.Analyses of mudstones from the McKim. Pecors. Serpent Gowganda Lorrain and Gordon Lake Formations suggest rapid evolution in the composition of the exposed upper crust at the close of the Kenoran orogeny. REE patterns at the base of the Huronian are similar to typical Archean sedimentary rocks. REE characteristics change up section: patterns at the top resemble typical post-Archean sedimentary rocks.It is inferred that an essentially episodic change from an early exposed upper crust dominated by a tonalite-greenstone suite to one approximating granodioritic composition is recorded in Huronian sedimentary rocks. A deviation from the evolutionary trend of the Huronian, documented in the Gowganda Formation, may be related to the glacial origin of the Gowganda.     

煤系高岭岩的地球化学判别标志

本文主要研究了煤系高岭岩的微量、稀土、氧同位素地球化学特征。根据高岭岩产出层序、岩石学、矿物学、地球化学特征的研究，将煤系高岭岩分为两类：（１）铝土质高岭岩，微量元素含量、稀土总量，氧同位素值高，稀土配分模式与典型北美页岩相似，Ｅｕ负异常，反映其源岩为风化壳化学风化作用产物。（２）夹矸高岭岩，微量元素含量，稀土总量，氧同位素值低，稀土配分模式部分与典型北美页岩相似，反映其源岩与铝土质高岭岩类似；部     

Rare earth element patterns and crustal evolution—II. Archean sedimentary rocks from Kalgoorlie,Australia

REE data, with major element and other trace element data are reported for a suite of Archean sedimentary rocks (2800 million years old) from Kalgoorlie, Western Australia. The REE patterns fall into two groups with ?LREE/?HREE ratios of 6 and 15, respectively. The first group have either no Eu anomaly relative to chondrites, or a positive Eu anomaly, in contrast to the pronounced Eu depletion (Eu/Eu ~ 0.67) shown by younger (Post-Archean) sedimentary rocks.The problem of positive Eu enrichment relative to chondritic patterns, is examined by analysing a suite of Devonian greywackes, derived from calc-alkaline volcanic rocks. Some of these samples also show positive Eu anomalies, attributable to local accumulation of feldspar. This explanation is preferred to models involving an early anorthositic crust. The group of samples showing heavy REE depletion patterns (complementary to those observed in garnet) appear to be derived from adjacent Na-rich granites which display identical REE patterns. Locally abundant K-rich granites do not appear to have made any contribution to the Archean sedimentary rocks.The majority of the sedimentary rocks have REE patterns indistinguishable from those of recent island arc calc-alkaline rocks, and so could constitute evidence that the Archean crust was principally formed by processes analogous to present day island-arc type volcanism. However, similar REE patterns may be produced by an appropriate mixture of the common bimodal tholeiitic-felsic igneous suite commonly observed in Archean terrains. The REE data presented here do not distinguish between these two models.     

Geochemistry of Archean metasedimentary rocks from West Greenland

Archean metasedimentary rocks occur as components of the Isua supracrustals, Akilia association and Malene supracrustals of southern West Greenland. Primary structures in these rocks have been destroyed by metamorphism and deformation. Their chemistry and mineralogy is consistent with a sedimentary origin, but other possible parents (e.g. acid volcanics, altered pyroclastic rocks) cannot be excluded for some of them. There is little difference in the composition of metasedimentary rocks from the early Archean Isua supracrustals and probable correlative Akilia association. Both have a wide range in rare earth element (REE) patterns with $\text{La}{}_{\mathrm{<mtext>N</mtext>}}\text{Yb}{}_{\mathrm{<mtext>N</mtext>}}$ ranging from 0.61?5.8. The REE pattern of one Akilia sample, with low $\text{La}{}_{\mathrm{<mtext>N</mtext>}}\text{Yb}{}_{\mathrm{<mtext>N</mtext>}}$, compares favourably with that of associated tholeiites and it is likely that such samples were derived almost exclusively from basaltic sources. Other samples with very steep REE patterns are similar to felsic volcanic boulders found in a conglomeratic unit in the Isua supracrustals. Samples with intermediate REE patterns are best explained by mixing of basaltic and felsic end members. Metasedimentary rocks from the Malene supracrustals can be divided into low silica (≤55% SiO₂) and high silica (>77% SiO₂) varieties. These rocks also show much variation in $\text{La}{}_{\mathrm{<mtext>N</mtext>}}\text{Yb}{}_{\mathrm{<mtext>N</mtext>}}$ (0.46?14.0) and their origin is explained by derivation from a mixture of mafic volcanics and felsic igneous rocks. The wide range in trace element characteristics of these metasedimentary rocks argues for inefficient mixing of the various source lithologies during sedimentation. Accordingly, these data do not rigorously test models of early Archean crustal composition and evolution. The systematic variability in trace element geochemistry provides evidence for the bimodal nature of the early Archean crust.     

Geochemistry of Archean shales from the Witwatersrand Supergroup,South Africa: Source-area weathering and provenance

With a few exceptions, shales from the Archean Witwatersrand Supergroup (~2800 Ma) in South Africa are depleted in Na, Ca, LILE, REE and HFSE compared to Phanerozoic shales. Cr, Co and Ni are enriched in all Witwatersrand shales and Fe and Mg are high in shales from the West Rand Groups (WRG) and lower Central Rand Group (CRG). Shales from the CRG and uppermost WRG are enriched in Na, Al, LILE, REE, HFSE and transition metals relative to shales from the lower WRG. Chondrite-normalized REE patterns for all Witwatersrand shales are enriched in light-REE and exhibit small to moderate negative Eu anomalies. A positive correlation of REE and Al₂O₃ contents in the shales suggests that REE are contained principally in clay minerals.Relative to shales from the CRG, shales from the WRG exhibit depletions of Na, Ca and Sr, a feature probably reflecting intense chemical weathering of their source rocks. CIA indices in Witwatersrand shales are variable (chiefly 70–98), even within the same shale unit. Such variations reflect chiefly variable climatic zones or rates of tectonic uplift in source areas with perhaps some contribution from provenance and element remobilization during metamorphism.Compared to present-day upper continental crust, all but the Orange Grove, Roodepoort, and K8 shales appear to have been derived from continental sources depleted in LILE, REE, and HFSE and enriched in transition metals. Computer mixing models based on six relatively immobile elements (Th, Hf, Yb, La, Sc, Co) and four source rocks indicate that the relative proportions of granite, basalt and komatiite increased with time in sediment source areas at the expense of tonalite. The contributions of basalt and komatiite appear to reach a maximum during deposition of the Booysens shale, and granite during deposition of the K8 shales and possibly during deposition of the Orange Grove shales.     

Geochemistry of the Archean Yellowknife Supergroup

The Archean Yellowknife Supergroup (Slave Structural Province. Canada) is composed of a thick sequence of supracrustal rocks, which differs from most Archean greenstone belts in that it contains a large proportion ( ~ 80%) of sedimentary rocks. Felsic volcanics of the Banting Formation are characterized by HREE depletion without Eu-anomalies, indicating an origin by small degrees of partial melting of a mafic source, with minor garnet in the residua. Granitic rocks include synkinematic granites [HREE-depleted; low (${}^{87}\text{Sr}{}^{86}\text{Sr}$)_I], post-kinematic granites [negative Eu-anomalies, high (${}^{87}\text{Sr}{}^{86}\text{Sr}$)_I] and granitic gneisses with REE patterns similar to the post-kinematic granites. Sedimentary rocks (turbidites) of the Burwash and Walsh Formations have similar chemical compositions and were derived from 20% mafic-intermediate volcanics, 55% felsic volcanics and 25% granitic rocks. Jackson Lake Formation lithic wackes can be divided into two groups with Group A derived from 50% mafic-intermediate volcanics and 50% felsic volcanics and Group B, characterized by HREE depletion, derived almost exclusively from felsic volcanics.REE patterns of Yellowknife sedimentary rocks are similar to other Archean sedimentary REE patterns, although they have higher $\text{La}{}_{\mathrm{N}}\text{Yb}{}_{\mathrm{N}}$. These patterns differ significantly from typical post-Archean sedimentary REE patterns, supporting the idea that Archean exposed crust had a different composition than the present day exposed crust.     

Rare earth element studies of surficial sediments from the southwestern Carlsberg Ridge,Indian Ocean

The rare earth element (REE) contents of sixteen surficial calcareous sediments from the southwestern Carlsberg Ridge, Indian Ocean, have been determined. The total REE vary from 35 ppm to 126 ppm and are inversely related to the calcium carbonate content. REEs show a strong positive correlation with Al + Fe + K + Mg + Na (r ²= 0.98) and Mn + Fe + Cu + Ni (r ²= 0.86) suggesting that the REE is associated with a combined phase of clays (mainly illite) and Mn-Fe oxyhydroxides. The aeolian input into these sediments is suggested from the weak positive Eu/Eu* anomaly. Shale-normalized (NASC) pattern along with La_(n)/Yb_(n) ratio suggest enrichment of heavy REE (HREE) relative to the light REE (LREE) with a negative Ce/Ce* anomaly implying retention of a bottom water REE pattern. An erratum to this article is available at .     

Geochemical characteristics of precious metal-bearing carbonaceous sequences from the eastern Bureya Massif

This paper reports the geochemical characteristics of PGE- and Au-bearing carbonaceous shales of the Sutyr and Kimkan sequences from the eastern Bureya Massif in the Russian Far East. The weakly altered shales are chemically close to the average upper crustal shale (NASC) but differ in the lower contents of iron, manganese, magnesium, phosphorus, calcium, and REE. According to the discrminant diagrams, these sediments are similar to the modern sediments accumulated under the influence of the continental terrigenous runoff, suprasubduction volcanism, and seawaters, which suggest their relation either with the deep-water trench near the active continental margin or with the central part of the marginal sea. The iron-rich sedimentary rocks of the Kimkan Sequence, including the Kimkan iron ore, are characterized by a positive Eu anomaly, which probably indicates their rift origin. The superimposed hydrothermal alterations of the Sutyr Sequence, including sericitization, sulfidization, and formation of quartz veinlets, were accompanied by the removal of silica and the input of potassium, LREE, and MREE with the formation of a well expressed Eu anomaly. The rocks from the weakly altered to metalliferous sediments of the Kimkan Sequence show a decrease in alkalis and especially in potassium. The carbon isotope composition of the Sutyr shales corresponds to that of the biogenic carbon (δ¹³C_VPDB from ?20.7 to ?23.7‰). The shales of the Kimkan Sequence have a heavier carbon isotope composition (δ¹³C_VPDB from ?15.6 to ?19.1‰), which may indicate either partial carbon influx from an endogenous source or its formation during decarbonatization in the presence of iron.     

Rare earth element mobility at constant inter-REE ratios in the alteration zone at the Phelps Dodge massive sulphide deposit,Matagami, Quebec

Rare earth elements (REE) from La to Ho were mobile and enriched in hydrothermally altered rocks below the Archean Phelps Dodge Cu-Zn volcanogenic massive sulphide deposit in northwestern Quebec. Largest net enrichment was in the moderately altered quartz-chlorite zone where La concentration increased six-fold and La_NYb_N steepened from 1.9 to 13.0; the intensely altered chloritite zone had both minor net REE enrichment and depletion. Yb and Lu were immobile throughout both zones. The mobile REE were added and subtracted in constant chondrite-normalized inter-REE proportions: 1.0 La, 0.79 Ce, 0.57 Nd, 0.49 Sm, 0.01 Eu, 0.10 Tb and 0.02 Hb. Small additions of Eu relative to generally larger additions of LREE and Tb produced enhanced negative Eu-anomalies. The REE were mobilized at the hot (>300 C) core of the alteration system and deposited at the cooler periphery. Other sites of intense alteration and water/rock interaction display similar REE changes, indicating that selective REE enrichment at constant inter-REE ratios is a widespread phenomenon.     

松辽盆地白垩系泉头组碎屑沉积岩岩石地球化学特征及其地质意义

松辽盆地庆安地区白垩系泉头组碎屑沉积岩主要由砂岩、泥岩和粉砂岩类组成。通过对白垩系泉头组碎屑沉积岩岩石样品的岩石化学分析表明 :主元素化学分类结果主要为长石砂岩、页岩 ,少量岩屑砂岩和硬砂岩 ;稀土元素分布模式显示其明显富集轻稀土及Eu负异常 ,并与NASC和PAAS稀土分布模式相似 ;碎屑沉积岩与上地壳的微量元素含量比值曲线显示为平坦型 ,这说明沉积岩是在活动性较弱的构造背景下缓慢沉积 ,具有被动大陆边缘和活动大陆边缘沉积物的特点。松辽盆地庆安地区白垩系泉头组碎屑沉积岩物质来源于张广才岭海西期花岗岩 ,后者的物源来自于上地壳。     

北京十三陵地区前寒武纪岩石中稀土矿物的发现及对同位素测年的意义

华北中、新元古代地层的年龄数据很混乱(表1),本文建议将北京十三陵地区新发现的稀土矿物用SHRIMP方法测年,有助于问题的解决。北京十三陵地区保存了新太古代五台群和新—中元古代较完整的地层,电子耦合等离子体分析(即原子收光谱分析)(ICP)的定量分析数据表明,在这些地层中,岩石中所含钾和稀土元素含量都比北美页岩(NASC)、欧洲页岩(ES)和澳大利亚后太古宙页岩(PAAS)高出很多,经电子扫描+能谱仪+波谱仪(SEM+EDS+WDS)分析证明,在岩石中包含独居石(碎屑的和自生-成岩的)和磷钇矿(自生-成岩的),并首次发现钍石-独居石环带状混合矿物(变质的)以及显微脉状稀土硅酸盐矿物(地下流体形成的)等稀土矿物。利用激光拉曼光谱鉴定发现稀土矿物的分布状态包括:1在太古宙五台群的片麻岩中,云母、石英和长石之间有非自形晶独居石,而且在石英单晶里还有独居石的自形晶包裹体;并发现独居石和钍石-独居石环带状混合矿物,这些稀土矿物都是变质成因的;2在新太古代五台群片麻岩的准平原化风化面上,沉积的元古宙常沟组的底砾岩中发现了碎屑的独居石,这些独居石的同位素年龄对于元古宇的底界定年意义重大;3在常州沟组下部压扁-透镜状层理的粉砂岩中,普遍发现碎屑锆石的外缘生长出自生-成岩磷钇矿,磷钇矿的同位素定年对于常州沟组的地层年代有代表性意义;4串岭沟组的粉砂岩中发现了无形晶状自生-成岩独居石和磷钇矿,并且较多出现在显微缝合线内外,可作为SHRIMP测年的对象;5大红峪组粉砂岩中除了发现碎屑独居石外还发现脉状硅-铝稀土矿物,可能与后元古宙热液活动有关。事实上这些自生-成岩的稀土矿物的形成,都是源自太古宙富含稀土元素的变质岩石,其形成机理也与地下流体活动有关。笔者认为北京十三陵以及至华北地区,前寒武系富稀土元素形成的自生-成岩的稀土矿物,有助于用SHRIMP方法对前寒武纪地层的同位素测年研究。     

The significance of europium anomalies in the REE spectra of granites and pegmatites,Mont Laurier,Quebec

Negative Eu anomalies in the REE spectra of granitic rocks are usually interpreted as evidence of earlier separation of a mineral phase such as plagioclase. Our study of the behaviour of the REE, and of U and Th, during late stage alteration of granites and the formation of pegmatites, suggests an alternative means for producing Eu anomalies. Albitization of earlier-formed plagioclase has depleted the granites in Eu and enriched the pegmatites in this element. This process is linked to the mobilization of U in the granites which is dependent on the oxidation state of the fluids. A systematic correlation between the ratios $\text{Eu}\text{Ce}$ and $\text{U}\text{Th}$ leads us to suggest a similar explanation for irregularities in the abundances of Ce and other rare-earths in the REE spectra of these rocks.We suggest that anomalous behavior of Eu in other environments or processes such as the alteration of basalt and the formation of certain ore deposit types may be caused partly by this mechanism.     

REE and their relevance to the development of the Kupferschiefer copper deposit in Poland

Over one hundred samples, representing mainly clayey-organic- and carbonate-rich shales (Kupferschiefer) but also other members of different ore sections, including hangingwall dolomites (Z1 Werra) and footwall Weissliegend sandstone (Lower Permian), have been collected in different mines of the Lubin–Głogów mining district, mainly near the contact (transitional zone) between the copper-mineralized zone and secondarily oxidized (Rote Fäule = RF) zone. In general, the Polish Kupferschiefer shales are enriched in MREE in comparison to NASC. In a typical copper-rich ore section the REE amounts and patterns depend on lithologies, being generally similar in shales and dolomite. ∑REE vary among sandstones, shales and dolomites (average 73, 143 and 85 ppm, respectively), probably reflecting mainly their clay contents. Sandstones have strongly convex REE patterns with positive Eu and negative Gd anomalies and depletion in LREE and enrichment in MREE relative to HREE. The REE patterns of shale and dolomite are similar to one another and rather flat, with strong negative Eu anomalies, and a small positive Gd anomaly in the case of shales.The REE patterns of shales from the mineralized Cu-zone are generally convex (MREE enriched) and have negative Eu anomalies. However, in a section with Cu-, Zn- and Pb-shales the REE pattern of Pb-bearing shales shows a positive Eu anomaly, in contrast to other shales and overlying dolomite. More oxidizing conditions of deposition can be assumed for Pb-shales.No significant differences between REE distributions in transitional and oxidized zones have been observed. Their REE patterns are more convex and are much higher (av. 247 ppm) than those in the mineralized zone and they do not show Eu anomalies. The strongly convex pattern may suggest either enrichment in MREE or relative depletion in LREE due to localized precipitation of light REE minerals, both in shales and in the uppermost part of the sandstones.Two unique sections, one Cu-rich and one Cu-lean (partly oxidized), comprising three shale beds interbedded with dolomites have been compared. Generally ∑REE contents are similar in these two sections. Also similar are changes in contents of REE between beds in both sections, which decrease significantly upwards (from 157–171 ppm to 54–60 ppm). The REE patterns of the lowermost beds (directly overlying sandstones) are ramp-like, with LREE enrichments. The upper beds have concave REE patterns. Comparison between sections shows generally stronger negative Eu and positive Gd anomalies in the highly-mineralized section.There is a highly significant positive relationship between Cu and ∑ REE contents in Cu-rich shales and slightly less significant negative relationship for their concentration in oxidized and transitional shales. There is a moderate significant positive correlation between P₂O₅ and ∑ REE contents in Cu-rich shales.The observed differences in REE contents cannot be provenance dependent but have been caused by diagenetic processes, possibly related to mineralization and oxidation processes. Europium anomalies, generally reflecting different Eh conditions in the deposit, can be eliminated by the prolonged oxidation. Strong enrichment of the RF zones in REE may result from their desorption from large volumes of oxidizing, including mineralizing, solutions which probably emerged from the underlying molasse lithologies into the Rote Fäule areas. Higher contents of REE in the lowermost shales suggest upward movement of solutions from the underlying sandstones also far away from the RF areas.