Review of Rare Earths and Fluid-Rock Interaction

As demonstrated by a great amount of geologic and experimental evidences, RE of rock systems may be mobilized during fluid-rock interaction when solutions are rich in F -, Cl -, CO 3 2-, HCO 3 -, CO 2, HPO 4 2-, HS -, S 2-, SO 4 2-, though little has been known about the mobilizing mechanism of these anions or ligands. The fractionation of RE resulted from hydrothermal alterations, i. e., fluid-rock interactions, are distinctive. One set of field data implies the preferential mobility of the LRE, while another set of field observations demonstrates the dominant mobilization of the HRE, and some theoretical prediction is not consistent with the field evidence. The Eu anomalies caused by fluid-rock interaction are complex and compelling explanation is not available due to inadequate experimental approaches. To know the exact behavior of RE during fluid-rock interaction and to solve the contradiction between some theoretical predictions and field observations, the following works remain to be done: (1) experimental investigations of RE mobility and fractionation as a function of fluid chemistry, e.g., the activity of F -, Cl -, CO 3 2-, HCO 3 -, CO 2, HPO 4 2-, HS -, S 2-, SO 4 2-, etc.; (2) experimental determination of RE mobility and fractionation as a function of T, P, pH, E h and water/rock ratios; (3) investigation of the mechanism and the controlling factors of RE partitioning between hydrothermal minerals and fluids. It was demonstrated that RE mobility is a potentially useful method for exploration.

Enrichment and Release of Rare Earth Elements during Weathering of Sedimentary Rocks in Wujiang Catchments

Thirteen weathering profiles of sedimentary rocks such as limestone, dolomitic limestone, dolomite, silicalite, black shale and purple sandrock from Wujiang catchments were selected for study on enrichment and release behavior of rare earth elements （REE） during weathering, and in its impact on plant growth and riverine REE distribution in the catchments with methods of hierachical cluster analysis and mass balance calculation in order to set a basis for riverine material source research and agricultural production. The results show that the enrichment degree of REE in calcareous soils from the Wujiang catchments is much higher than that of limestone, yellow soil, upper continental crust （UCC）,

Rare Earths of Magmatic Rocks in Yanshanian Stage in Adjacent Region of Anhui and Jiangxi Provinces, Jiangnan Uplift

The geochemical characteristics of rare earth elements of magmatic rocks of Yanshanian stage were studied in the south of Anhui Province and northeast of Jiangxi Province, Jiangnan Uplift. The result shows that the magmatic rocks of Yanshanian stage in the south of Anhui Province are the typical crust source type and those in the northeast of Jiangxi Province have the characteristics of mantle source type. So the polymetal deposits having relation to the magmatic rocks of Yanshanian stage in the northeast of Jiangxi Province were developed better than those in the south of Anhui Province. The research results of the rare earth elements are confirmed by the studies of geophysics,tectonic setting and stable isotope at the same time. It also indicates that the rare earth elements are the effective approach to tracing the material sources of magmatic rocks.

Rare Earths, Trace Element Characteristics of High-Mg Volcanic Rocks of Yixian Formation in Sihetun West Liaoning Province and Its Apocalypse

The high-Mg volcanic rocks of the Yixian Formation in the Sihetun area have the obvious characteristics of mantie-derived lava in rare earth, trace element characteristics with high Mg # （62 - 70） and high content of compatible elements. In the meantime, the volcanic rocks also have the obvious characteristics of Crust-source material in rare earth, trace element characteristics with high ∑ REE （ 158.78 × 10^-6 - 359.66 × 10^-6 ）, high （La/Yb） N （ 14.61 - 29.60）, high La/Nb（2.37 - 7.52） and high Ba/Nb （67.58- 205.96）, obvious positive anomaly of Pb and negative anomaly of Nb, Ta in trace element spider-gram. In Sr-Nd-Pb isotope the （^87Sr/^86Sr）i ratio is higher than 0.706 and the εNd（ t ） ratio is from - 3.4 to - 13, both reflect enriched Mantle characteristics. The characteristics above of the volcanic rocks combined with the content of Sr, Ba, Y, Yb and the ratio of Sr/Y show that the volcanic rocks have the property of the Sanukite rocks in Setouchi Japan beside subduction zone, and illuminate that the Sanukite rocks can be formed not only in island-arc near subduction zone but also in intro-plate. The analysis indicates that the high-Mg volcanic rocks in the Sihetun area result from the collective function of mantle-derived lava and crust-source materials. The result illuminates that the West Liaoning region is very special in tectonic geochemical background in Cretaceous in East China, and is an ideal region for us to further study the characteristics of magmatic activity as well as the process of Crust-Mantle interaction in Eastern China.

Mechanism of Formation of Premian Volcanic Rocks in Sawu′er Region, Xinjiang, China: Constraints from Rare Earth Elements

A large quantity of Premian volcanic rocks formed in Sawu＇er region of Xinjiang, China. Based on the analysis of the rare earth elements＇ （REEs） geochemical characteristics of the volcanic rocks, the correlativity of REE and major elements, and diagrams of covariant relation of REE, combined with the research results of the regional geological setting, petrology, and petrochemistry characteristics, it is inferred that the mechanism of the formation of Premian basic and intermediate volcanic rocks is mainly attributed to equilibrium partial melting, and the magmatic fractional crystallization is not significant, whereas the rock-forming processes of medium-acidic volcanic rocks is influenced by both partial melting and fractional crystallization. The REE geochemical research provided important evidence for the mechanism of magmatism of the Premian post-collision stage and the geodynamical evolution process.

Behaviors of Rare Earths during Fluid-Rock Interaction and Its Significance of Geochemistry

Rare earths in ores, altered and unaltered sericite phyllite, altered and unaltered dacite porphyry were determined in order to examine behaviors of rare earths in hydrothermal alteration associating with ore-forming processes of Yinshan deposit. It is not sufficient to show the mobility only by the absolute abundance of trace elements changes before and after alteration. This can simply result from dilution or concentration if other elements are added to or removed from the rock. As shown by that in Yinshan deposit, less than 20% of the increment of RE was caused by the 'condensed' of leaching some of major elements (e.g. Si, Na) from the rock. The principal factor which should be responsible for the higher contents of RE in altered rock is the addition of RE into the rock by hydrothermal fluids. Eu is selectively leached from the altered sericite phyllite by a mild acidity and reducing fluid which is characterized by much lower LRE/HRE ratio and a large positive Eu anomaly. A major effect on the RE patterns is the tendency to develop relatively flatter chondrite-normalized patterns. The RE characteristics may be used to distinguish between small and large ore bodies at a later stage of exploration.

Rare Earth Element Geochemistry on Magmatic Rocks and Gold Deposits in Shizishan Ore-Field of Tongling, China

REE geochemical characteristics of the magmatic rocks and gold deposits in Shizishan ore-field of Tongling were studied. Three types of the magmatic rocks have almost the same chondrite-normalized REE patterns, Eu and Ce anomalous values, and ∑REE, ∑LREE/∑HREE regular changes, which indicates that their magmas come from the same source and their digenetic mechanism is fractional crystallization. In three gold deposits, the mineral ores and related altered rocks have similar chondrite-normalized REE patterns and sharp Eu positive anomalous values. The REE contents reduced from the magmatic rocks to skamization or alteration magmatic rocks, skam type ores, sulphide type ores, wall-rocks limestone or marble. The REE geochemical characteristics of the ores and related rocks show that primary fluids originated from magmatic differentiation in lower pressure of shallow crust, ore-forming hydrothermal solutions gained REE and mineralization elements further from leaching the magmatic rocks, then superimposed and reformed the limestones or marbles and deposited ore-forming material.

Geochemistry of Rare Earth Elements of Mesozoic-Cenozoic Sandstones in North Margin of Dabie Mountains and Adjacent Areas: Constraints to Source Rocks

Based on the study of REE in Mesozoic-Cenozoic sandstones, the paper indicates that Jurassic Fanghushan and Yuantongshan Formations and Lower Cretaceous Zhougongshan Formation have ∑REE of 157 μg·g^(-1), δ_(Eu) of 0.69 and (La/Yb)_N of 11.1, which are similar to the Foziling and Luzhenguan Groups, and it implies that the latter may be the source rocks of the former. The Sanjianpu and Heishidu Formations have high REE concentrations (∑REE=264.8 μg·g^(-1), 328.2 μg·g^(-1) respectively), high Eu anomaly (δ_(Eu)=0.57, 0.67 respectively) and lower Eu/Sm ratios (0.18～0.19), which differs from existent metamorphic rocks in the Dabie Mountains, so where their source rocks came from remains to be studied. The REE features of the Zhengyangguan Formation can be comparable to the Dabie complex and Luzhenguan Group, which shows that the Dabie complex had suffered unroofing in Neocene and constituted the source rocks. Mesozoic sandstones in Huainan area have lower REE concentrations (∑REE=80.9 μg·g^(-1)), high Eu anomaly (δ_(Eu)=0.66) and (La/Yb)_N of 5.7, and it indicates that their source rocks may not come from the Dabie Mountains.

Enrichment and Release of Rare Earth Elements during Weathering of Sedimentary Rocks in Wujiang Catchments,Southwest China

Thirteen weathering profiles of sedimentary rocks such as limestone, dolomitic limestone, dolomite, sillicalite, black shale and purple sandrock from Wujiang catchments were selected for study on enrichment and release behavior of rare earth elements （REE） during weathering, and its impact on plant growth and riverine REE distribution in the catchments with methods of hierachical cluster analysis and mass balance calculation in order to set a basis for riverine material source research and agricultural production. The results show that the enrichment degree of REE in calcareous soils from the Wujiang catchments is much higher than that of limestone, yellow soil, upper continental crust （UCC）, China soil （CS） and world soil （WS）. The ability of enrichment and release of REE is partly controlled by distribution of REE in bedrocks, contents and adsorption ability of organic matters, clay minerals and Fe-oxides/hydroxides in weathering profiles. The REE released from weathering of carbonate rocks and clastic rocks can be absorbed and utilized by local plants. The results also reveal that release of REE and Fe mainly from weathering of carbonate rocks and partly from clastic rocks exerts an important control on riverine REE distribution.

Study on Mechanism of Formation of Volcanic Rock in North Altay by Using Rare Earths

The characteristics of rare earth elements in the Devonian and Carboniferous volcanic rocks were studied in the north Altay. And the mechanism of formation of volcanic rocks were discussed by using the rare earth elements. The correlativity of rare earth elements and major elements shows that the fractional crystallization is undistinguishable during the formation of Devonian and Carboniferous volcanic rocks, and the mechanism of formation of volcanic rocks may be the partial melting. The further study of the relationship of manifold rare earth elements shows that the mechanism of formation of Devonian and Carboniferous volcanic rocks in the north Altay is the partial melting. And the result also shows that the rare earth elements in the Devonian and Carboniferous volcanic rocks inherited the characteristics of those in its source materiels.

Geochemical Characteristics and Behaviors of Rare Earth Elements in Process of Vertisol Development

Vertisol developed on argillaceous rocks has its special pedogenic processes and properties, and formed some secondary nodules. In study area, contents of rare earth elements (REE) are significantly different in different sedimentary rocks due to varied contents of clay fraction and clay mineral composition, etc. Under the dry and hot climate, REEs were less differentiated than their parent sedimentary rocks. However, REEs in secondary nodules formed in pedogenic process display their specific behaviors. They are more concentrated in iron concretions, the content of heavy REEs increases relatively, and positive Ce-anomaly appears. But, negative Ce-anomaly was found in calcium concretions, while normal Ce content in parent rocks and vertisol.

State of rare earth elements in the rare earth deposits of Northwest Guizhou,China

We studied the states of rare earth elements in ore of the Xianglushan rare earth deposit. Rare earth ore samples were tested and examined by scanning electron microscope, electron probe, and chemical leaching. No independent rare earth minerals were detected by scanning electron microscope. Elements detected by the electronic probe for the in situ micro-zone of the sample included: O,Al, Si, Ca, Mg, Fe, Ti, K, Na, S, Cl, C, Cu, Cr, V, and Pt.Rare earth elements were not detected by electron probe.(NH_4)_2 SO_4,(NH_4)Cl, NaCl, and H_2 SO_4 were used as reagents in chemical leaching experiments that easily leached out rare earth elements under the action of 10%reagent, indicating that the rare earth elements in ore are mainly in the ionic state rather than present as rare earth minerals.

Rare Earth Elements Compositions and Genesis of Xinhua Large-Scale Phosphorite Deposit in Western Guizhou, China

Zhijin County in Western Guizhou is one of the most important production areas of phosphorites in China. In order to investigate genesis of the phosphorites, their REE compositions were analyzed by using inductively coupled plasma emission mass spectrometry (ICP-MS) method. For comparison, phosphorites from the Lower Cambrian black rock series in Southern China, such as Zunyi in Guizhou and Zhangjiajie in Hunan Province, were also analyzed. The analytical data show that: (1) Xinhua phosphorites possess a quite high and greatly varied total rare earth elements (ΣREE), which varying between 164.23×10-6 and 1395.01×10-6 with average of 642.54×10-6, remarkable differentiation between light (LREE) and heavy rare earth elements (HREE), and the ΣLREE/ΣHREE ratios varying between 5.04 and 6.52. The ΣREE and ΣLREE/ΣHREE ratios of the Zunyi and Zhangjiajie phosphorites are 156.69×10-6～637.41×10-6 with average of 431 75×10-6 and 3.17～6.95 with average of 4.37 respectively; (2) All the phosphorites from Xinhua, Zunyi and Zhangjiajie show remarkable negative Ce anomalies. Besides, the Xinhua phosphorites possess lower δCe, which varying between 0.26 and 0.53 with average of 0.35, while δCe of the Zunyi and Zhangjiajie phosphorites are 0.30～0.66 with average of 0.47, suggesting that all of the phosphorites are typical marine sediments deposited mainly in ancient peri-continental seas, and the depositional position of the Xinhua phosphorite might be deeper; (3) Most phosphorites from Xinhua, Zunyi and Zhangjiajie possess unremarkable positive Eu anomaly, and only a few of samples show obvious ones. The δEu varies between 0.98 and 2.4, suggesting that hot (>200 ℃) and strong reductive hydrothermal fluids might have been involved in genesis of the phosphorites; (4) The Xinhua phosphorite is relatively depleted in HREE, and LaN/NdN and δY of most samples are >1 and >1.5 respectively. Besides, there exists no correlation between δY and δCe, suggesting that the phosphorite was subjected to quite strong weathering and leaching processes, and catagenesis do not greatly modify its REE compositions.

Characteristics of Rare Earth and Trace Element Patterns in Bedded Cherts from the Bottom of the Lower Cambrian in the Northern Tarim Basin, Northwest China and Their Genetic Significance

The sedimentary sequence of the Lower Cambrian is a key interval to reveal the early evolution history of the Earth and there occur widespread cherts worldwide. These cherts possibly carry important information to decipher the breakup process of the Rodinia Continent. Black rock series at the bottom of the Lower Cambrian in the Northern Tarim Basin, China, is composed of black shales interbedded with thin-bedded cherts. Ten chert samples were systematically collected from two outcrops at Xiaoerbulak and Sogatbulak, 8.8 and 7.5 m thick respectively. The cherts were crushed, and were analyzed for trace element and rare earth concentrations. Trace elements such as V, Cu, Zn, U, Pb, Ba, Cd, Ag, Mo, As and Sb are highly enriched, and others such as Rb, Zr, Cs, Hf, Ta, W, Tl, Bi and Th are highly depleted in the cherts. These trace element patterns suggest that the cherts may be of deep crustal origin. The low ratios of Th/U and Rb/Sr further suggest that the cherts are of earth interior sources or received hydrothermal input during their deposition. Chondrite- normalized Eu/Eu* value markedly decreases upward in the section from 5.54 at the lowermost to 0.73 at the top, and NASC-normalized Eu/Eu* value decreases from 8.05 to 1.03. The relatively high Eu/Eu* ratio for the cherts from the northern Tarim Basin is most likely due to a hydrothermal input (e.g., Eu/Eu* ~10). The systematic decrease of Eu/Eu* ratio from the bottom to the top of the section reflects that the hydrothermal input is the largest in the lowermost portion of the section and gradually decreases upward. The chondrite-normalized Ce/Ce* ratio ranges from 0.42 to 0.83, with an average of 0.60. North American Shale Composite (NASC)-normalized Ce/Ce* ratio ranges from 0.42 to 0.79, with an average of 0.57. Negative Ce anomalies are distinct. ΣREEs in the cherts generally increase from 10.50 ppm at the bottom to 35.97 ppm at the top of the sampled section. NASC-normalized (La/Lu) N ratio decreases from 2.72 at the bottom to 0.67 at the top. NASC-normalized (La/Ce) N ratio increases from 1.36 at the bottom to 3.13 at the top. These REE patterns are very similar to those for the cherts deposited in the pelagic ocean-basin floor in the Franciscan Complex exposed at Marin Headlands, California (F-MH chert) (Murray et al., 1991). These geochemical signatures are inconsistent with our previous sedimentological data, which suggests a continental shelf setting. Based on multiple lines of evidence including high TOC content in the concomitant black shales, phosphorite at the bottom of black rock series, regional rise of sea level, and beginning of the southern Tianshan Ocean geotectonic cycle, the authors infer that the hydrothermal fluid was carried to the continental shelf by upwelling from a divergent pelagic ocean floor setting.

Genetic Relationship of Minerals and Carbonate Units of Stratigraphy Sequence in the Ahmadabad Deposit (NE of Bafq) Using Data Related to Rare Earth Elements

Ahmadabad Pb-Zn ore deposit is located in the mineral area of Bahabad in Central Iran Zone. This ore deposit like other metallogenic areas in Bahabad is found in Triassic carbonate rocks. Carbonate rocks in Shotori formation have the highest frequency in the regional sequence stratigraphy. This formation is composed of TRSh1, TRSh2, TRSh3 and TRSh4 units. The TRSh3 unit hosts minerals in ore deposit Ahmadabad. Microcrystalline particles are the main constituent of these rocks. The most important minerals in this ore deposit include calamine Celestine, Cerussite and Wulfenite. The comparison of normalized ore patterns and carbonate sequence indicates that they have a specified genetic relationship. Here the TRSh2 unit is more similar to minerals.

Geochemical Characteristics of Rare Earth Elements of Guidong Granitic Complex and Their Relationship with Uranium Mineralization

The Guidong granitic complex is constituted by Luxi pluton, Xiazhuang pluton, Maofeng pluton, Sundong pluton, Aizi pluton and Siqian pluton, which intruded in Indosinian and early Yanshanian Periods. These plutons varies from each other not only in major element content, aluminium saturation index, but also in ∑REE, δEu, and LREE/HREE, （La/Yb）N, （La/Sm） N and （Gd/Yb） N ratios. Uranium mineralization is mainly hosted by strong peraluminous granites, which has undergone intense fluid-rock interaction, and their REE compositions are characterised by M-type tetrad effects and lower ∑REE, δEu value, LREE/HREE, （La/Yb） N, （La/Sm） N and （Gd/Yb） N ratios.

Geochemical Characteristics of Rare Earth Elements of Guidong Granitic Complex and Relationship with Uranium Mineralization

Guidong granitic complex is constituted by Luxi intrusion, Xiazhuang intrusion, Maofeng intrusion, Sundong intrusion, Aizi intrusion and Siqian intrusion, which emplaced in Indosinian and early Yanshanian Periods. These intrusions varied from each other not only in major element content, aluminium saturation index, but also in values of ∑REE, δEu, and LREE/HREE, (La/Yb)N, (La/Sm)N and (Gd/Yb)N. The Maofeng intrusion, which has the closest relationship with uranium mineralization, belongs to strong peraluminous granites. Having undergone much intense fluid-rock interaction, it is characterized by typical M-type tetrad effects and lowest values of ∑REE, δEu, LREE/HREE, (La/Yb)N, (La/Sm)N and (Gd/Yb)N ratios than other studied intrusions.

云南金沙厂铅锌矿床地球化学特征及其指示意义

位于扬子地块西南缘的“川滇黔铅锌矿集区”是我国西南大面积低温成矿域的重要组成部分,金沙厂铅锌矿床是其中典型矿床之一,前人针对金沙厂矿床的成矿物质来源和成矿流体特征开展了大量研究,但围岩对成矿的贡献和矿床成因仍不明确。针对这一问题,本文系统分析了金沙厂闪锌矿及围岩的微量元素组成,结合围岩和萤石的稀土元素特征,探讨了围岩对成矿的贡献,厘定了矿床成因。研究表明,闪锌矿以富集Cd、Ge、Cu、Ga,贫Fe、Mn、In、Co、Ni为特征,这些元素多以类质同象的形式赋存在闪锌矿中,个别元素如Cu、Ge等含量变化范围较大,可能与低温流体有关。矿床中闪锌矿存在多种颜色的原因可能是Cu、Ge等多种元素共同作用的结果。近矿端的围岩明显富集Zn、Pb、As、Cd等元素,而闪锌矿中同样富集这些元素,说明围岩为成矿提供了部分金属元素。萤石继承了围岩的Eu、Ce负异常,并受到了具有较高Ce负异常的成矿流体影响。萤石较围岩具有较高的Y/Ho比值,说明萤石中的部分Y来源于围岩,从而导致萤石具有较高的Y/Ho值。总体上,该矿床中闪锌矿微量元素组成与MVT矿床基本一致,明显有别于喷流沉积型、岩浆热液型和远端夕卡岩型矿床,其成矿温度属于低温范围,结合其矿床地质地球化学特征,本文认为金沙厂铅锌矿床属于MVT铅锌矿床。

陕北典型矿区烧变岩岩石学及地球化学特征

烧变岩的基础研究对烧变岩水害的防治具有至关重要的作用。为了掌握烧变岩的岩石学及地球化学特征,以陕北榆神矿区张家峁井田为例,通过野外调查、钻孔岩心取样及分析测试,对该区烧变岩的主量元素、微量元素及稀土元素进行了详细的测定分析。结果表明:岩体上部、下部、邻近岩层分别属于板状烧烤岩、烧熔岩、层状烧烤岩,不同类型的烧变岩岩性、颜色、孔隙发育等特征随烧烤程度的不同而呈现较大的差异性。岩石地区化学结果表明:烧变岩主要化学成分为SiO_(2),其次为Al_(2)O_(3)。岩样主要为硅铝质,镁铁组分含量相对较少,TFe_(2)O_(3)+MgO质量百分比平均值为4.76%,而原岩与烧变岩差异性小,与烧熔岩样亦相差不大。烧变岩亲石元素Rb、Ba含量高于原岩,Sr含量低,Cs、Eu相对亏损。高场强元素中Zr含量在所有样品中普遍较高,不同类型岩样均具有Y、Zr、Pb富集的特征,高场强元素在烧变作用下变化不显著。样品的稀土元素丰度趋势曲线出现差异化分布,标准沉积岩与上地壳平均值相较球粒陨石相似性更高。研究结果将为研究烧变岩的成因及形成环境提供基础支撑。

电感耦合等离子体质谱法测定岩石样品中15种稀土元素含量不确定度的评估

【研究目的】稀土元素在地球化学中占有重要的地位,其加和意义也很突出,堪称地球化学指示剂。敞口酸溶-电感耦合等离子体质谱法是测定岩石样品中稀土元素含量的常用方法。为提高岩石中稀土元素检测的准确性,实验从各分量进行测量不确定度的分析与评定。【研究方法】本文通过敞口酸溶-电感耦合等离子体质谱法测定岩石样品中稀土元素含量的不确定度来源,建立逐层分析和最后的评估。【研究结果】此方法的合成相对标准不确定度在0.0049~0.0091之间。【结论】该方法的不确定度主要来自样品的标准溶液,其中标准曲线拟合的贡献值最大,这与实验室中的实际测试情况是一致的。