REE Abundance and REE Minerals in Granitic Rocks in the Nanling Range,Jiangxi Province,Southern China,and Generation of the REE‐rich Weathered Crust Deposits

Studies of Mesozoic granites associated with rare earth element (REE)‐rich weathered crust deposits in southernmost Jiangxi Province indicate that they have high‐K to shoshonite compositions and belong to ilmenite‐series I‐type granites. Of the studied rocks at 59–292 ppm of bulk REE content, the highest are seen in the biotite granites of Dingnan (358, 429 ppm) and mafic biotite granite of the Wuliting Granite (344 ppm) near the Dajishan tungsten mine, both areas where weathered‐crust REE deposits occur. REE‐bearing accessory minerals in these granites are mainly zircon, apatite and allanite, and REE‐fluorocarbonates are common. REE enrichment occurs in the rims of apatite crystals, and in fluorocarbonates that occur along grain boundaries of and cracks in major silicate minerals, and in fluorocarbonates that replaced altered biotite. It is therefore thought that a major part of the REE content of these granites was concentrated during deuteric activity, rather than during magmatic crystallization. The crack‐filling REE‐fluorocarbonates could subsequently have been easily leached out and deposited in weathered crust developed during a long period of exposure.     

Rare Earth Elements in Hydrothermally Altered Granitic Rocks in the Ranong and Takua Pa Tin‐Field,Southern Thailand

Geochemical studies were conducted on the hydrothermally altered granitic rocks in the Ranong and Takua Pa tin‐fields in southern Thailand in order to investigate the mode of occurrence of REE (rare earth elements), with emphasis placed on a potential REE resource associated with granitic rocks in the Southeast Asian Tin Belt. The total REE (ΣREE) content of altered granitic rocks ranges from 130 to 350 ppm at Haad Son Paen (which is presently mined for kaolin clay) in the Ranong tin‐field, and that of altered granitic rocks and kaolinite veinlets reaches up to 424 ppm and 872 ppm, respectively, at Nok Hook in the Takua Pa tin‐field. Rare earth elements in the altered granitic rocks and kaolinite veinlets show a relatively flat chondrite‐normalized pattern, thus enriched in heavy REE compared with the original granitic rocks and their weathered crusts. At Nok Hook (Takua Pa), the ΣREE content of kaolinite separated from an altered granitic rock by elutriation is 1313 ppm, a ΣREE amount about four times higher than that of whole‐rock composition of the altered granitic rock. Chondrite‐normalized REE patterns of the elutriated kaolinite and of the altered granite are relatively flat. Sequential extraction experiments suggest that 41 and 85 percent of REE are present as ion exchangeable‐form in the altered granitic rock, and in the kaolinite veinlets, respectively. In addition, more than 90% of REE in the kaolinite veinlets are present as the acid‐soluble state. On the other hand, the ΣREE content of kaolinite veinlets and of the kaolinite concentrated by elutriation from an altered granitic rock at Haad Som Paen (Ranong) is 70 ppm and 75 ppm, respectively, thus enrichment of REE in kaolinite was not confirmed. In addition, by the sequential extraction experiments, 23% and 4% of REE were extracted from the altered granitic rock and the kaolinite veinlets at Haad Som Paen. In the altered granitic rocks at Haad Som Paen, REE are present as refractory phases, and REE in the acid‐soluble states had been leached by hydrothermal fluid.     

“寨背式”离子吸附型稀土矿床多类型稀土矿化及其成因

赣南寨背离子吸附型稀土矿床产于寨背复式花岗岩体的风化壳中,自20世纪80年代发现以来一直以轻稀土型开采,近年在轻稀土型花岗岩风化壳中发现了重稀土矿。为了探讨轻稀土型花岗岩风化过程中重稀土元素的迁移、分馏和富集机制,本文选择了区内三个具有代表性的风化壳钻孔(ZK1、ZK2和ZK4)对其进行了全相和离子交换相稀土元素地球化学研究。结果显示：钻孔ZK4中离子交换相稀土含量介于14.90×10^-6～835.8×10^-6之间,并富集轻稀土(LREE/HREE=2.28～10.78);钻孔ZK1中离子交换相稀土含量达1470×10^-6(9件样品均值),具有从轻稀土型向重稀土型过渡的配分特征(LREE/HREE=1.30～1.65),并且剖面自上而下显示轻、重稀土逐渐富集的趋势;钻孔ZK2中离子交换相稀土含量为492.4×10^-6(8件样品均值),自上而下稀土配分类型从轻稀土型过渡至重稀土型(LREE/HREE=0.43～2.25),且轻稀土富集在全风化层上部而重稀土则富集在下部。三个钻孔的Nb/Ta和Zr/Hf...     

Geology and rare-earth element geochemistry of highly evolved, molybdenite-bearing granitic plutons, Southeastern Desert, Egypt

The field relations, mineralogy, and major and trace elements (including REE analyses of whole-rock samples and minerals) of granites and their associated molybdenite uranium mineralized aplites in Southeastern Desert, Egypt, have been studied. The granites are leucocratic and mostly peraluminous in nature with muscovite increasing at the expense of biotite. The chemical and mineralogical characteristics of the granitic rocks indicate that their melts originated from the LILE-enriched mantle wedge by partial melting and are contaminated by crustal melts, followed by thermogravitational processes. Leucogranites with higher Na2O/K2O ratios from Um Dargag and Um Maiat crystallized under H2O-saturated equilibrium conditions in which the exsolved vapor continuously migrated away. The REE patterns of the granites studied are characterized by LREE enrichments and negative Eu anomalies. In comparison, the potassic aplites and the more sodic leucogranites are depleted in LREE, enriched in HREE and show more remarkable negative Eu anomalies. Allanite and monazite are the most important REE carriers in the granites. These minerals are strongly enriched in LREE, whereas fluorite and xenotime, which are more abundant in the aplites, are enriched in HREE. The average Lu/Ce ratio represents the fractionation trend with respect to HREE. It is 0.71 for radioactive fluorite, and it increases to 1.22 for non-radioactive fluorite. The high REE contents of molybdenite represent re-deposition of the mobilized Mo and REE. Due to the strong control of accessory minerals, the REEs are of limited use in petrogenetic modelling of highly evolved granitic systems.     

Geochemical and mineralogical characteristics of recent clastic sediments from lower Godavari river: Implications of source rock weathering

The major, trace and rare earth elements geochemistry and clay mineral compositions in the river bed sediments from lower reaches of Godavari river suggest that they are derived from weathering of felsic rocks. Trace and rare earth elemental compositions indicate evidence of sedimentary sorting during transportation and deposition. Lower concentrations of transition elements, such as V, Ni and Cr imply enrichment of felsic minerals in these bed sediments. The REE pattern in lower Godavari sediments is influenced by the degree of source rock weathering. The light rare earth elements (LREE) content are indicating greater fractionation compared to the heavy rare earth elements (HREE). A striking relationship is observed between TiO₂ and gZREE content suggesting a strong control by LREE-enriched titaniferous minerals on REE chemistry. Shale-normalized REE pattern demonstrate a positive Eu anomaly, suggesting weathering of feldspar and their secondary products, which are enriched in Eu. Chondrite-normalised REE pattern is characteristic of felsic volcanic, granites and gnessic source rocks. Trace elemental compositions in sediments located near urban areas suggest influence of anthropogenic activity. Chemical Index of Alteration (CIA) is high (avg. 65.76), suggesting a moderate chemical weathering environment. X-ray diffraction analysis of clay fraction shows predominance of clay minerals that are formed because of the chemical weathering of felsic rocks.     

Sources of stream sediments in the granulite terrain of the Walawe Ganga Basin,Sri Lanka,indicated by rare earth element geochemistry

Thirty-eight samples of stream sediments draining high-grade metamorphic rocks in the Walawe Ganga (river) Basin, Sri Lanka, were analysed for their REE contents, together with samples of metamorphic suites from the source region. The metamorphic rocks are enriched in light REE (LREE) compared to heavy REE (HREE) and are characterised by high La/Lu ratios and negative Eu anomalies. The chondrite-normalised patterns for these granulite-grade rocks are similar to that of the average post-Archaean upper crust, but they are slightly enriched with La and Ce. The REE contents of the <63-μm fraction of the stream sediments are similar to the probable source rocks, but the other grain size fractions show more enriched patterns. The <63-μm stream sediments fraction contains lower total REE, more pronouncd negative Eu anomalies, higher Eu_N/Sm_N and lower La _N/Lu_N ratios relative to other fractions. The lower La _N/Lu_N ratio is related to the depletion of heavy minerals in the <63-μm fraction. The 63–125-μm and 125–177-μm grain size fractions of sediments are particularly enriched in LREE (average ΣLREE=2990 μg/g and 3410 μg/g, respectively). The total HREE contents are surprisingly uniform in all size fractions. However, the REE contents in the Walawe Ganga sediments are not comparable with those of the granulite-grade rocks from the source region of the sediments. The enrichment of REE is accounted for by the presence of REE containing accessory mineral phases such as zircon, monazite, apatite and garnet. These minerals are derived from an unknown source, presumably from scattered bodies of granitic pegmatites.     

华南印支期花岗岩类的岩石特征、成因类型及其构造动力学背景探讨

华南地区印支期花岗岩按照成因类型可分两类,第一类属强过铝质S型花岗岩,富含过铝质矿物,富SiO2、Al2O3和P2O5,高A/CNK值,微量元素原始地幔标准化分布型式图中富集Rb、U、Ta、Zr、Hf,亏损Ba、Sr、Nb、Ti;稀土元素球粒陨石标准化分布型式图中具显著的负Eu异常,稀土元素总量偏低(ΣREE<80×10-6);第二类属准铝质I型花岗岩,含角闪石等镁铁质矿物,富SiO2、Na2O。总体来说,这两类花岗岩具有高的(87Sr/86Sr)i值(0.710490～0.742118)和低εNd(t)值(-14.42～-4.1),Nd模式年龄(2.09～1.63Ga)指示印支期花岗岩为典型的壳源型花岗岩。CaO/(MgO+FeOT)-Al2O3/(MgO+FeOT)(摩尔比)图解表明这些花岗岩主要来源于变质杂砂岩和变质泥岩的部分熔融,夹杂了少量变质玄武岩和变质英云闪长岩。华南印支期花岗岩形成于挤压加厚的地壳发生局部伸展-减薄时期,推断印支期发生了多期次的岩石圈挤压和拉张,花岗岩侵位于大规模岩石圈挤压后局部减压-伸展的构造环境中。     

REE Geochemistry in the Weathered Crust of Granites, Longnan Area,Jiangxi Province

Warm and humid climate and gentle hilly topography have provided favourable conditions for the devel-opment of the weathering crust of the granite intrusions in the Longnan area, Jiangxi Province. REE is mostlyconcentrated in an adsorption state in clay in the wholly weathered zone. The rare-earth minerals enriched inthe parent rocks provided the source material for the REE enrichment. Exchangeable REE accounts for48-86%. Extraction experiments and stable isotopic study of clay minerals suggest that the downward infiltra-tion of meteoric water and increasing gradient of pH values have played an important role in the enrichment ofREE during the progressive weathering. Slight fractionation of individual REE can not change their distribu-tion patterns in the profiles. which are inherited from the parent rocks.     

Petrological and geochemical characteristics of Zhaibei granites in Nanling region,Southeast China: Implications for REE mineralization

Mineralization with ion adsorption rare earth elements (REEs) in the weathering profile of granitoid rocks from Nanling region of Southeast China is an important REE resource, especially for heavy REE (HREE) and Y. However, the Jurassic granites in Zhaibei which host the ion adsorption light REE (LREE) ores are rare. It is of peraluminous and high K calc-alkaline composition, which has similar geochemical features of high K₂O + Na₂O and Zr + Nb + Ce + Y contents and Ga/Al ratio to A-type granite. Based on the chemical discrimination criteria of Eby [Geology 20 (1992) 641], the Zhaibei granite belongs to A1-type and has similar source to ocean island basalts. The rock is enriched in LREE and contains abundant REE minerals including LREE-phosphates and halides. Minor LREE was also determined in the feldspar and biotite, which shows negligible and negative Eu anomalies, respectively. This indicates that the Zhaibei granite was generated by extreme differentiation of basaltic parent magmas. In contrast, granites associated with ion adsorption HREE ores contain amounts of HREE minerals, and show similar geochemical characteristics with fractionated felsic granites. Note that most Jurassic granitoids in the Nanling region contain no REE minerals and cannot produce REE mineralization. They belong to unfractionated M-, I- and S-type granites. Therefore, accumulation of REE in the weathering profile is controlled by primary REE mineral compositions in the granitoids. Intense fractional crystallization plays a role on REE enrichment in the Nanling granitoid rocks.     

Chemical Evolution of Zircons in the Paleogene Naegi Granite,Central Japan

The chemical composition of zircons from S‐ and I‐type ilmenite‐series granitic rocks in the Chubu district is summarized based upon recent electron probe microanalysis. Zircons in S‐type Busetsu granite of the Ryoke Metamorphic Belt have a homogeneous composition with minimum impurities, whereas those of I‐type Naegi granite in the non‐metamorphic Sanyo Belt are enriched in Hf, Y, REE, Th and U along the crystal rims. Similar enrichment has been observed in a variety of zircon called Naegite. These minor components are concentrated in the F‐rich fluid phase of residual melts of the Naegi granite magma, and are crystallized in pegmatites during the latest magmatic stage. High values of Nb and Ta in some Naegite reported previously are attributed to micro‐inclusion of fergusonite.     

Evolution in the provenance of a tectonically controlled Plio–Pleistocene alluvial system between the Variscan Iberian Massif and the Atlantic margin, Portugal

Geochemical and mineralogical data from a Pliocene to Pleistocene alluvial sequence are integrated to access the factors that control rare earth elements (REE) geochemistry and the evolution and spatial differences in provenance. The studied alluvial system is situated in a tectonic active setting at the contact between the Variscan Massif, with several Paleozoic and Precambrian units that support a coastal range, and the Atlantic margin. REE and HREE abundances are generally higher in swamp-lake than in floodplain sediments. The majority of the REE in floodplain sediments is hosted by Y and Th-bearing minerals and illite; in swamp-lake sediments is also probable an association with organic matter. The high Gd/Yb, Eu/Eu* and kaolinite content in older sediments suggest that during the earlier phases provenance was mainly from the hinterland (weathered granitic rocks and its sediment cover). The subsequent illite (Mg-rich) clay assemblages and REE patterns indicate mainly lateral input from the eastern basin edge (Palaeozoic and Precambrian metapelitic rocks). These sediments tend to have lower Gd/Yb and La/Sm than their source rocks. The analysis of the chemical index of alteration (CIA) indicates that although a north-directed fluvial axis existed at that time the “mature” basin edge units found to the south (Silurian) had a limited role in supplying sediments. This shift in provenance is attributed to the uplift of the coastal range. Afterwards, the contribution of recycled Cretaceous and Cenozoic sedimentary units increased progressively. This is demonstrated by the increase is SiO₂/TiO₂, CIA and kaolinite/illite when the climatic conditions are expected to have become less chemically aggressive.     

The Behaviour of Rare—Earth Elements（REE） During Weathering of Granites in Southern Guangxi,China

The behaviour of the rare-earth elements(REE)during the weathering of granites was studied in southern Guangxi,China.Based on the study of the weathering profiles,the soil,weathered and sub-weatereb zones are identified with different REE geochemical behaviours throug the weathering profiles of granite.The Ce anomalies of the weathering profiles cover a large range of values with most falling between 1.02 and 1.43in the soil zone and 0.16and 0.40in the weathered and sub-weathered zones.Light rare-earth elements(LREE) and heavy rare-earth elements(HREE)are enriched to varying degree in the weathering profiles as compared to host granites.In the soil zone,more HREEs are leached than LREEs,and HREEs are more enriched than LREE in the weathered and sub-weathered zones.It is considered that infiltration and adsorption on clays are two processes controlling the enrichment and formation of REE deposits in the weathering profiles of granite.     

Evolution of Pan African A- and I-Type Granites from Southeastern Egypt: Inferences from Geology,Geochemistry, and Mineralization

Field study of granitic rocks in the Gebel Abu Brush-Dahis (ABD) area, Southeastern Desert, Egypt, shows that they comprise two granitic groups, namely A- and I-type suites. The A type is distinguished mineralogically by abundant orthoclase and sodic plagioclase, ferrohornblende, monazite, and allanite. In contrast, the I type has more hornblende and biotite, which are more magnesian in composition, and less feldspar. The parental magmas of both suites have many similar geochemical characteristics, although the A type has slightly higher alkalis, Zr, Hf, Zn, and LREE, and lower CaO, MgO, Sr, Ni, and Fe⁺². The geochemical properties characteristic of leucocratic A-type granites-such as high Ga/Al ratios, Nb, Y, HREE, and F contents-are only manifest in the more felsic members of the A-type suite. These features were produced by 70% fractional crystallization of feldspar, hornblende, quartz, and biotite. Geotectonically, the study revealed that the A-and I-type granites are typical of an arc setting, but the more felsic members of the A-type suite plot in a within-plate regime. Geochemically, the granites are subalkaline and peraluminous to metaluminous. The granodiorites/adamellites (I-type suite) have fractionated LREE and slightly fractionated or nearly flat HREE, with small or no Eu anomalies. The alkali-feldspar granites (A-type suite) have flat REE with large Eu anomalies, except for one sample, which shows increasing LREE and decreasing HREE with large Eu anomalies; the quartz-monzonites have fractionated LREE and nearly flat HREE with no Eu anomaly. The flat HREE and/or HREE enrichment is attributed to involvement of garnet and/or zircon in melt generation at the source.

The uranium and thorium contents in the granitic rocks are present in the accessory minerals—particulary in monazite, titanite, zircon, allanite, fluorite, apatite, and opaques. Anomalous high radioactivity in the bostonite (alkaline) dike as well as uranium mineralization are largely confined to contacts and fracture zones. Uranophane is the characteristic uranium mineral in the oxidation zone. An XRD study of the high anomalies in pegmatite and bostonite reveals that the uranium mineralizations produced uranophane (Usilicate), thorianite, soddyite, zippeite, and becquerelite.     

Differential Fractionation of Rare Earth Elements in Oxidized and Reduced Granitic Rocks: Implication for Heavy Rare Earth Enriched Ion Adsorption Mineralization

Ion adsorption rare earth element (REE) deposits in southern China are the exclusive source of heavy REEs (HREEs) in the world, and this HREE‐enriched character of the deposits is inherited from the REE compositions of the underlying granitic rocks. Such HREE‐enriched rocks form from heavy fractionation of reduced granitic magmas. We explore why reduced granitic magmas are enriched in HREEs during the fractionation, based on the REE geochemistry of granitic rocks and abundance of REEs in their constituent minerals in the southwestern Japan arc of Cretaceous to Paleogene age. The compilation of the whole rock geochemistry and REE compositions of the granitic rocks of the Sanin (oxidized), Sanyo (reduced) and Ryoke (reduced) belts in the southwestern Japan arc indicates that: (i) light REEs (LREEs) decease with fractionation of the granitoids in the Sanin belt but this trend is not clear in the granitoids in the Sanyo belt and LREEs rather increase in the Ryoke granitoids; (ii) Eu decreases with fractionation in all the belts; and (iii) HREEs slightly, but steadily decrease in the Sanin belt but enrich significantly in the Sanyo and Ryoke belts with fractionation. Analytical results of REE concentrations by scanning electron microscope with energy dispersive X‐ray spectroscope and laser ablation‐inductively coupled plasma mass spectrometer in the constituent minerals in a granodiorite sample from the Sanin belt show a moderate concentration of REEs in hornblende (577 ppm) in addition to high concentrations in allanite (~20 %), britholite (~30 %), primary titanite (8922 ppm), apatite (4062 ppm), and zircon (1693 ppm). Because primary titanite and allanite are commonly present in the oxidized granitoids but not in the reduced ones, the REE depletion in the fractionated, oxidized granites is attributed to the crystallization of these minerals. In contrast, scarcity of these minerals in the reduced granitoids enriches REEs, in particular HREEs in the fractionated magmas, which finally precipitate REEs in the granites and pegmatites. Both positive, but different correlation ratios between the Nb and Dy concentrations in the granitoids of the Sanin and Sanyo‐Ryoke belts suggest that columbite–pyrochlore‐group and fergusonite‐group minerals are the major HREE host in the oxidized and reduced granites, respectively.     

Geochemical and mineralogical characteristics of ion-adsorption type REE mineralization in Phuket, Thailand

Geochemical and mineralogical studies were conducted on the 12-m-thick weathering profile of the Kata Beach granite in Phuket, Thailand, in order to reveal the transport and adsorption of rare earth elements (REE) related to the ion-adsorption type mineralization. The parent rock is ilmenite-series biotite granite with transitional characteristics from I type to S type, abundant in REE (592 ppm). REE are contained dominantly in fluorocarbonate as well as in allanite, titanite, apatite, and zircon. The chondrite-normalized REE pattern of the parent granite indicates enrichment of LREE relative to HREE and no significant Ce anomaly. The upper part of the weathering profile from the surface to 4.5 m depth is mostly characterized by positive Ce anomaly, showing lower REE contents ranging from 174 to 548 ppm and lower percentages of adsorbed REE from 34% to 68% compared with the parent granite. In contrast, the lower part of the profile from 4.5 to 12 m depth is characterized by negative Ce anomaly, showing higher REE contents ranging from 578 to 1,084 ppm and higher percentages from 53% to 85%. The negative Ce anomaly and enrichment of REE in the lower part of the profile suggest that acidic soil water in an oxidizing condition in the upper part mostly immobilized Ce⁴⁺ as CeO₂ and transported REE³⁺ downward to the lower part of the profile. The transported REE³⁺ were adsorbed onto weathering products or distributed to secondary minerals such as rhabdophane. The immobilization of REE results from the increase of pH due to the contact with higher pH groundwater. Since the majority of REE in the weathered granite are present in the ion-adsorption fraction with negative Ce anomaly, the percentages of adsorbed REE are positively correlated with the whole-rock negative Ce anomaly. The result of this study suggests that the ion-adsorption type REE mineralization is identified by the occurrence of easily soluble REE fluorocarbonate and whole-rock negative Ce anomaly of weathered granite. Although fractionation of REE in weathered granite is controlled by the occurrence of REE-bearing minerals and adsorption by weathering products, the ion-adsorption fraction tends to be enriched in LREE relative to weathered granite.     

内蒙古那仁乌拉埃达克质花岗岩的发现、成因、锆石U-Pb年龄及其构造意义

在中亚造山带东段华北克拉通北缘,识别出一套晚古生代那仁乌拉黑云母花岗岩。其LA-ICP-MS锆石U-Pb年龄为267.2Ma±1.4 Ma(MSWD=1.3,n=21)和捕获锆石年龄为296.3Ma～296.1Ma、278.8Ma～277.4 Ma;岩石为低钾(拉斑)到高钾钙碱性,弱准铝质到过铝质I型;ΣREE较低,轻重稀土分馏较强(LaN/YbN:15.59～32.36)。在稀土元素配分模式图上,都表现为轻稀土富集,重稀土亏损的右倾散开式。弱到正的铕负异常(δEu:0.79～1.08);在微量元素蛛网图上,相对富集LREE(La,Ce),LILE(K,Rb)和HFSE(Zr,Hf),元素Nb,Ta,P,Ti,Y,Yb,Lu亏损程度较大,元素U,Th,Sr由相对亏损到富集。岩石整体具有埃达克质岩的亲合性,形成于弧向同碰撞过渡的构造环境;锆石εHf(t)值(0.95～4.05)显示具有弱亏损的幔源组分特性,与主量元素、微量元素及REE一致,变化范围都较大,共同暗示其源岩的壳幔混源性。较年轻的锆石Hf模式年龄(1 030.9Ma～1 226.8Ma)与兴蒙造山带范围一致;那仁乌拉花岗岩与西部乌拉特中旗克布岩体,东部吉林大玉山岩体共同组成一条华北克拉通北缘埃达克质岩浆带,其都为与古亚洲洋俯冲碰撞引起的具有弧岩浆性质的年轻的基性玄武质下地壳部分熔融有关的C型埃达克岩。这条埃达克质岩浆带与稍晚期的华北克拉通北缘碱性岩浆带相对应,都具有西部形成早于东部的特征,可能暗示古亚洲洋自西向东逐渐闭合的规律。     

The Stream Sediment Geochemistry of the Walawe Ganga Basin of Sri Lanka - Implications for Gondwana Mineralization

A regional geochemical and mineralogical study aimed at investigating the mineralization in the western-part of the Walawe Ganga (river) Basin in Sri Lanka is represented in this paper. The river basin is the 3^rd largest in the country and has within it a boundary zone between two geologically different crustal blocks, which are marked by granulitic grade rocks and amphibolite grade rocks. Size fractions of stream sediments (< 63 μm; 63–125 μm; 125–177 μm and 177–250 μm) developed on the granulite-grade metamorphic terrain have been analysed at their source for their mineralogical and selected element compositions. Thirty-eight (38) sediment samples and 15 representative probable parent rock samples were chemically analysed giving special emphasis to the High Field Strength trace Elements (HFSE) including the Rare Earth Elements (REE). The granulite grade rocks in the study area is geochemically similar to that of post Archean upper crust. However the stream sediments developed from the high-grade rocks during the intense weathering, are markedly enriched with HFSE and REE. The enrichment of HFSE and LREE is accounted for by the presence of HFSE- and REE- rich accessory mineral phases such as zircon, monazite, apatite, garnet and rutile in the sediments. In some samples, the content of heavy minerals contributes as much as 50 wt. %. These minerals act as a source of elements in the sediments. However, extreme hydraulic sorting of HFSE- and REE-bearing minerals during the sediment deposition cannot be expected within a short distance from near the sources except from a mineralized occurrence. Therefore, the higher enrichment of these elements presumably indicates occurrences of scattered mineral sources such as highly differentiated granites and associated pegmatites within the Walawe Ganga drainage basin. These granitic pegmatites are probably intruded during or soon after the main granulite-facies metamorphic event and similar events are seen in other terrains of East-Gondwana.     

Behaviour of rare-earth elements in highly evolved granitic systems: Evidence from Proterozoic molybdenite mineralized aplites and associated granites in northern Sweden

Field relations, mineralogy, major- and trace-element contents (including REE analyses of whole-rock samples and minerals) of three Proterozoic granites and their associated molybdenite mineralized aplites have been studied at Allebuoda, Munka and Kåtaberget in northern Sweden. The granites crystallized from melts that were not saturated with water. The mineralized potassic aplites formed by quenching of residual melts caused by sudden pressure drop, H₂O saturation and vapour escape during tectonic rupturing. Leucogranites with higher Na₂O/K₂O ratios from Allebuoda and Munka crystallized during H₂O-saturated equilibrium conditions in which the exsolved vapour could continuously migrate away. The pressure was probably 3 kbar at Munka, and somewhat lower at Allebuoda.

The granites have REE patterns characterized by LREE enrichments and negative Eu anomalies. In comparison, the potassic aplites and the more sodic leucogranites are depleted in LREE, enriched in HREE and have larger negative Eu anomalies. Allanite and monazite are the most important REE carriers in the granites. These minerals are strongly enriched in LREE, whereas fluorite and xenotime, which are more abundant in the aplites, are most enriched in HREE. Due to the strong control of accessory minerals on the REE balance, REE are of limited use in petrogenetic modelling of highly evolved granitic systems.     

重庆南川-武隆铝土矿含矿岩系稀土元素特征及其地质意义

重庆市南川武隆铝土矿是黔中渝南铝土矿成矿带的重要组成部分。为初步查明重庆地区铝土矿稀土元素的地质意义,弥补重庆铝土矿成因研究的不足,笔者以重庆南川武隆铝土矿含矿岩系为研究对象,分析稀土元素(REE)的地球化学特征。通过研究发现,稀土元素总量较高,多数样品轻稀土富集,重稀土不同程度亏损。由于含矿岩系中的REE含量在沉积后只有极微弱的变化,因此利用稀土元素的特征及有关参数对铝土矿含矿岩系的形成环境及其物质来源进行了初步判断:Eu中等负异常,含矿岩系以陆相沉积为主,部分为海相沉积;从含矿岩系样品稀土元素总和、Ce异常、Eu 异常情况来看,含矿岩系形成的古水介质呈弱酸性,含矿岩系主要形成于氧化环境中,氧化能力增强时有利于铝土矿的形成;含矿岩系物质来源具有多样性,志留系韩家店组粉砂质页岩与石炭系黄龙组灰岩均可能为物质来源。     

东天山哈尔里克地区早石炭世A型花岗岩年代学、地球化学及地质意义

A型花岗岩对研究天山造山带壳幔相互作用和构造演化具有重要意义.对东天山哈尔里克地区的碱长花岗岩和正长花岗岩进行了详细的岩石学、地球化学和年代学研究,旨在阐明其成因及构造意义.其中碱长花岗岩的LA-ICP-MS锆石U-Pb年龄为350.7±2.0 Ma和351.8±2.0 Ma,表明该花岗岩体形成于早石炭世早期.岩石含大量碱性长石,暗色矿物以黑云母为主,见钠铁闪石等碱性暗色矿物.岩石高硅、富碱、贫钙镁,富集Rb、Th、K等大离子亲石元素和Zr、Hf等高场强元素,而强烈亏损元素Ba、Sr、Eu,具弱右倾“Ⅴ”字型的稀土分配曲线（（La/Yb）_N=3.23~5.55,δEu=0.19~0.28）.这些矿物学和地球化学特征表明哈尔里克早石炭世花岗岩属高钾准铝质-弱过铝质花岗岩,为典型的A型花岗岩.花岗岩正的ε_Nd（t）值（+4.2~+4.8）和新元古代的二阶段Nd模式年龄（t_DM2=0.71~0.75 Ga）,表明其源区可能为新生年轻地壳,源岩可能是亏损地幔来源的下地壳中基性岩和少量大洋沉积物.结合前人对东天山岩浆活动和构造环境的研究,认为早石炭世哈尔里克与博格达处于同一构造背景下,早石炭世早期A型花岗岩可能形成于博格达弧后裂谷的伸展早期阶段.