Rare Earth Deposits of North America

Rare earth elements (REE) have been mined in North America since 1885, when placer monazite was produced in the southeast USA. Since the 1960s, however, most North American REE have come from a carbonatite deposit at Mountain Pass, California, and most of the world’s REE came from this source between 1965 and 1995. After 1998, Mountain Pass REE sales declined substantially due to competition from China and to environmental constraints. REE are presently not mined at Mountain Pass, and shipments were made from stockpiles in recent years. Chevron Mining, however, restarted extraction of selected REE at Mountain Pass in 2007. In 1987, Mountain Pass reserves were calculated at 29 Mt of ore with 8.9% rare earth oxide based on a 5% cut‐off grade. Current reserves are in excess of 20 Mt at similar grade. The ore mineral is bastnasite, and the ore has high light REE/heavy REE (LREE/HREE). The carbonatite is a moderately dipping, tabular 1.4‐Ga intrusive body associated with ultrapotassic alkaline plutons of similar age. The chemistry and ultrapotassic alkaline association of the Mountain Pass deposit suggest a different source than that of most other carbonatites. Elsewhere in the western USA, carbonatites have been proposed as possible REE sources. Large but low‐grade LREE resources are in carbonatite in Colorado and Wyoming. Carbonatite complexes in Canada contain only minor REE resources. Other types of hard‐rock REE deposits in the USA include small iron‐REE deposits in Missouri and New York, and vein deposits in Idaho. Phosphorite and fluorite deposits in the USA also contain minor REE resources. The most recently discovered REE deposit in North America is the Hoidas Lake vein deposit, Saskatchewan, a small but incompletely evaluated resource. Neogene North American placer monazite resources, both marine and continental, are small or in environmentally sensitive areas, and thus unlikely to be mined. Paleoplacer deposits also contain minor resources. Possible future uranium mining of Precambrian conglomerates in the Elliott Lake–Blind River district, Canada, could yield by‐product HREE and Y. REE deposits occur in peralkaline syenitic and granitic rocks in several places in North America. These deposits are typically enriched in HREE, Y, and Zr. Some also have associated Be, Nb, and Ta. The largest such deposits are at Thor Lake and Strange Lake in Canada. A eudialyte syenite deposit at Pajarito Mountain in New Mexico is also probably large, but of lower grade. Similar deposits occur at Kipawa Lake and Lackner Lake in Canada. Future uses of some REE commodities are expected to increase, and growth is likely for REE in new technologies. World reserves, however, are probably sufficient to meet international demand for most REE commodities well into the 21st century. Recent experience shows that Chinese producers are capable of large amounts of REE production, keeping prices low. Most refined REE prices are now at approximately 50% of the 1980s price levels, but there has been recent upward price movement for some REE compounds following Chinese restriction of exports. Because of its grade, size, and relatively simple metallurgy, the Mountain Pass deposit remains North America’s best source of LREE. The future of REE production at Mountain Pass is mostly dependent on REE price levels and on domestic REE marketing potential. The development of new REE deposits in North America is unlikely in the near future. Undeveloped deposits with the most potential are probably large, low‐grade deposits in peralkaline igneous rocks. Competition with established Chinese HREE and Y sources and a developing Australian deposit will be a factor.     

P507负载泡塑反相色层富集岩石中的稀土元素

研究了Ｐ５０７负载泡塑萃取柱色谱分离富集稀土元素的条件,并与Ｐ５０７萃淋树脂柱进行了对比;拟定了Ｐ５０７负载泡塑反相色属富集岩石中稀土元素的方法。在ｐＨ２．５介质中ＲＥＥ上柱率９８％,用５０ｍｌ２．５ｍｏｌ／ＬＨＮＯ３作洗脱液,ＲＥＥ总回收率达９６．１％,干扰测定的Ｔｈ,Ｕ,Ｔｉ,Ｚｒ,Ｈｆ等均被除法。方法用于标样分析验证,结果与推荐值相符。     

与碱性花岗岩有关的稀有稀土矿床

概述了含矿碱性花岗岩产出的地质背景，含矿岩体的主要特征。根据岩石中暗色矿物与主要成矿元素的关系，将碱性花岗岩矿床划分为３种矿化类型：含Ｎｂ（Ｓｎ）黑云母花岗岩；含Ｎｂ（Ｓｎ）、ＨＲＥＥ钠铁闪石－钠闪石花岗岩；含ＬＲＥＥ霓石花岗岩，并指出，碱性花岗岩矿床在我国北部边区和攀西裂谷带具有良好的成矿前景。     

Rare earth elements in waters from the albitite-bearing granodiorites of Central Sardinia, Italy

With the aim of contributing to the knowledge of the geochemical behaviour and mobility of the rare earth element (REE) in the natural water systems, the ground and surface waters of the Ottana-Orani area (Central Sardinia, Italy) were sampled. The study area consists of albititic bodies included in Hercynian granodiorites. The waters have pH in the range of 6.0-8.6, total dissolved solid (TDS) of between 0.1 and 0.6 g/l, and major cation composition dominated by Ca and Na, whereas predominant anions are Cl and/or HCO₃.The pH and the major-element composition of the waters are the factors affecting the concentration of REE in solution. The concentrations of ∑REE+Y in the samples filtered at 0.4 μm vary between 140 and 1600 ng/l, with La of between 14 and 314 ng/l, and Yb of between <6 and 12 ng/l. A negative Ce anomaly, especially marked at high pH, is observed in the groundwaters. The surface waters show lower REE concentrations, which are independent of pH, and negligible Ce anomaly.Speciation calculations, carried out with the EQ3NR computer program, showed that the complexes with the CO₃²⁻ ligand are the dominant REE species at pH in the range of 6.7-8.6. The REE³⁺ ions dominate the speciation at pH <6.7 and only in the light REE (LREE).The relative concentrations of REE in water roughly reflect those in the aquifer host rocks. However, when concentrations of REE in water are normalised relative to the parent rocks, a preferential fractionation of heavy REE (HREE) into the water phase can be observed, suggesting the greater mobility and stability of HREE in aqueous solution.     

Polymetamorphism, zircon growth and retention of early assemblages through the dynamic evolution of a continental arc in Fiordland, New Zealand

The Marguerite Amphibolite and associated rocks in northern Fiordland, New Zealand, contain evidence for retention of Carboniferous metamorphic assemblages through Cretaceous collision of an arc, emplacement of large volumes of mafic magma, high‐P metamorphism and then extensional exhumation. The amphibolite occurs as five dismembered aluminous meta‐gabbroic xenoliths up to 2 km wide that are enclosed within meta‐leucotonalite of the Lake Hankinson Complex. A first metamorphic event (M1) is manifest in the amphibolite as a pervasively lineated pargasite–anorthite–kyanite or corundum ± rutile assemblage, and as diffusion‐zoned garnet in pelitic schist xenoliths within the amphibolite. Thin zones of metasomatically Al‐enriched leucotonalite directly at the margins of each amphibolite xenolith indicate element redistribution during M1 and equilibration at 6.6 ± 0.8 kbar and 618 ± 25 °C. A second phase of recrystallization (M2) formed patchy and static margarite ± kyanite–staurolite–chlorite–plagioclase–epidote assemblages in the amphibolite, pseudomorphs of coronas in gabbronorite, and thin high‐grossular garnet rims in the pelitic schists. Conditions of M2, 8.8 ± 0.6 kbar and 643 ± 27 °C, are recorded from the rims of garnet in the pelitic schists. Cathodoluminescence imaging and simultaneous acquisition of U‐Th‐Pb isotopes and trace elements by depth‐profiling zircon grains from one pelitic schist reveals four stages of growth, two of which are metamorphic. The first metamorphic stage, dated as 340.2 ± 2.2 Ma, is correlated with M1 on the basis that the unusual zircon trace element compositions indicate growth from a metasomatic fluid derived from the surrounding amphibolite during penetrative deformation. A second phase of zircon overgrowth coupled with crosscutting relationships date M2 to between 119 and 117 Ma. The Early Carboniferous event has not previously been recognized in northern Fiordland, whereas the latter event, which has been identified in Early Cretaceous batholiths, their xenoliths, and rocks directly at batholith margins, is here shown to have also affected the country rock. However, the effects of M2 are fragmentary due to limited element mobility, lack of deformation, distance from a heat source and short residence time in the lower crust during peak P and T. It is possible that many parts of the Fiordland continental arc achieved high‐P conditions in the Early Cretaceous but retain earlier metamorphic or igneous assemblages.     

稀土元素指标δCe－ΣREE对沉积相的指示研究

通过对内蒙古额济纳盆地小狐山剖面沉积物中酸溶组分稀土元素含量及其相关指标、分布模式的分析,讨论了剖面中稀土元素指标δCe－ΣREE与沉积相、沉积环境之间的关系。分析结果表明剖面沉积物酸溶组分中稀土元素丰度均值为7.24μg/g(不包括Y),其中LREE含量占稀土总量的88.67%; 且各层的稀土分布模式均为轻稀土适度富集缓右倾斜型、Eu呈负异常模式,但各相位地层的LREE富集程度与分配模式存在差异。由于小狐山剖面中沉积地层的自身岩性、沉积粒径、矿物结构组成以及气候环境变化等因素均可能会引起REE分异。因此,通过δCe－ΣREE图并结合三次回归曲线,可以很好地将不同沉积相得物质有效的区分开来。小狐山剖面除极少数的几个样品(水下沉积砂)之外,其余的均落在三次多项式回归曲线上部; 而风成砂层则几乎全部落在回归曲线之下; 此外,对于风沙－河流作用下的混合样品也有较好识别,河流过渡相的样品则分布在曲线上或与之相邻近。此研究结果得到了柴达木贝壳堤沉积物的REE数据的验证,运用此方法可以为直观的判别剖面中的不同沉积相,并为定量化划分地层提供依据。     

REE-HFSE distribution/partitioning between garnetiferous restites and TTG from Nademavinapura area,Western Dharwar craton

The major part of the Peninsular Gneiss in Dharwar craton is made up of Trondjhemite-Tonalite-Granodiorite (TTG) emplaced at different periods ranging from 3.60 to 2.50 Ga. The sodic-silicic magma precursors of these rocks have geochemical features characteristic of partial melting of hydrated basalt. In these TTGs, enclaves of amphibolites (± garnet) are abundant. These restites are considered to be the residue of a basaltic crust after its partial melting. A detailed study of these (residue) enclaves reveals textures formed due to the process of partial melting. Major, trace and REE analysis of these residue enclaves and the melt TTGs and microprobe analysis of the coexisting minerals show partitioning of REE and HFSE between the precursor melt of TTGs and the upper amphibolite facies residues. Formation of garnetiferous amphibolites with biotite, Cpx and plagioclase consequent to melting, has squeezed the original MORB type of basaltic crust and given rise to the TTGs, depleted in Y, Yb, K₂O, MgO, FeO, TiO₂ and enriched in La, Th, U, Zr and Hf. Coevally during the process of melting, the hydrated basalt was depleted in Na₂O, Al₂O₃, LREE, Th, U and enriched in K₂O, MgO, Nb, Ti, Yb, Y, Sc, Ni, Cr and Co. Mineral chemistry of co-existing garnet-biotite and amphibole-plagioclase in these amphibolitic (restite) enclaves indicates an average temperature of 700 ± 50° C and pressure of 5 ± 1 Kbar. These data are inferred to indicate that during the garnet stability field metamorphism, effective fractionation of HREE and HFSE has taken place between the restites having Fe-Mg silicates, ilmenites and the extracted melt generated from the MORB type of hydrated basalt. These results are strongly substantiated by the reported melting experiments on hydrated basalts.     

山东龙宝山岩体稀土元素特征及矿源研究

龙宝山岩体是燕山期多阶段岩浆活动形成的中偏碱性杂岩体,其稀土元素特征为:wΣREE为地壳丰度的2.5倍,wLREE/wHREE为地壳的近9倍,轻稀土强烈富集,δEu、δCe均呈弱负异常,各期侵入岩及含金石英脉的稀土元素分布型式基本相似,呈向右陡倾斜线,但石英脉中稀土总量更高、轻稀土更为富集。研究结果表明:岩浆和成矿物质最初可能均来源于上地幔的同一岩浆房,并在岩浆上侵过程中不同程度地同化混染了地壳物质。     

东秦岭钼矿带内碳酸岩脉型钼（铅）矿床地质 地球化学特征、成矿机制及成矿构造背景

东秦岭钼矿带位于华北板块南缘,NW-NWW向的固始―栾川深断裂带控制着钼矿床的空间分布.黄水庵碳酸岩脉型钼(铅)矿床的确定,为本矿带内已有碳酸岩脉型钼(铅)矿床(黄龙铺地区的大石沟、石家湾和桃园等)增添了又一新成员.本矿带不仅钼金属储量居世界已知单个钼矿带之首,而且碳酸岩脉和花岗斑岩两个成矿体系并存,亦是本区钼矿带的一大特色.业已查明,黄水庵和黄龙铺(大石沟)等碳酸岩脉型钼(铅)矿床的δ~(13)C=-5.3‰～-7.0‰,~(87)Sr/~(86)Sr=0.7049～0.7065.同时,方解石富含轻稀土(LREE/HREE=1.8～2.9).辉钼矿以富含Re(平均为110×10~(-6)～244×10~(-6))为特征.基于含矿碳酸岩脉方解石的Sr、Nd、Pb同位素比值(~(87)Sr/~(86)Sr对~(206)Pb/~(204)Pb、~(207)Pb/~(204)Pb对~(206)Pb/~(204)Pb和~(143)Nd/~(144)Nd对~(87)Sr/~(86)Sr)的关系图,我们初步判断本矿带区域陆壳之下可能存在有EMI(富集地幔Ⅰ),这些含矿碳酸岩脉是源于EMI的碱性硅酸盐-碳酸盐熔体-溶液结晶分异的产物,成矿金属Mo、Pb主要来自EMI.根据黄水庵和黄龙铺(大石沟)钼(铅)矿床的成矿年龄(Re-Os年龄分别为209.5 Ma和221 Ma),我们推断,碳酸岩脉型钼(铅)矿床形成于华北和扬子两大板块三叠纪碰撞造山后伸展阶段的晚三叠世时期,而在侏罗纪陆内造山晚期的伸展阶段,形成了晚侏罗-早白垩世的斑岩型和斑岩-矽卡岩型钼矿床(Re-Os年龄介于147～116 Ma).     

川南沐川地区宣威组底部铌-稀土多金属富集层富集规律、沉积环境与成矿模式

云南、贵州地区对晚二叠世宣威组底部Nb-REE多金属富集层的研究取得了重要进展,但其成因还有较大争议.为厘清沐川地区宣威组底部Nb-REE多金属富集层成因机制及富集规律,本研究开展了野外实地调查、矿物学、岩相古地理与岩石地球化学等系统性研究,探讨其物源、富集规律,建立了成矿模式.结果 表明,川南沐川地区宣威组底部Nb-...