一种特殊类型的云英岩:湘南香花岭地区癞子岭云英岩成岩成矿特征

癞子岭岩体具有极好的垂向分带性,从下部到顶部包括了花岗岩、云英岩和伟晶岩,其中云英岩以其厚度巨大,云母类型属于铁锂云母,黄玉含量高,W-Sn-Nb-Ta含量高,而区别于其他地区云英岩。通过对癞子岭云英岩进行岩石学、地球化学和矿物学的研究,本文得出:癞子岭云英岩是高硅的强过铝质岩石类型,全碱含量低(3~4.3 wt%),富集挥发组分,全岩Zr/Hf(~8)和Nb/Ta(~1.7)比值低。造岩矿物铁锂云母中Nb(~74×10~(-6))、Ta(~66×10~(-6))、W(~23×10~(-6))、Sn(~75×10~(-6))等成矿元素含量较高。副矿物锆石自形且成分均一,含有HfO_2约10 wt%,Zr/Hf比值最低为5,与云英岩下部的癞子岭钠长花岗岩中的锆石成分有连续过渡的关系。这些特征与南岭地区高演化稀有金属花岗岩或伟晶岩相当,体现了相近的演化程度。癞子岭云英岩中有明显的Nb-Ta-W-Sn成矿作用发生,主要形成铌铁矿族矿物、锡石和黑钨矿,成分和结构均具有岩浆成因特征。花岗质熔体中含有大量挥发组分Li和F,结晶出黄玉和Li-F云母,F在稀有金属的成矿作用和云英岩的成岩过程中发挥了非常重要的作用,成矿作用发生在岩浆演化的晚期并伴随有流体作用。因此,云英岩可能是钠长花岗岩高度分异演化之后的特殊产物,这为研究花岗岩岩浆-热液体系成岩成矿过程提供了新的窗口。     

湖南香花岭地区花岗岩中锂对成岩成矿的制约

锂（Li）是一种战略关键金属,岩浆阶段主要在花岗质岩石中得到富集和结晶。由于具有不相容和富挥发性等性质,锂对花岗岩的成岩成矿具有重要的制约。文章利用电子探针、LA-ICP-MS 等分析手段,对湖南香花岭地区癞子岭和尖峰岭花岗岩进行系统岩相学、主微量和矿物学研究,结果表明：（1）花岗质岩浆结晶分异过程中,Li 含量逐渐升高,大幅度降低了熔体粘度,增大了结晶温度区间,花岗质岩浆得到充分结晶分异,导致花岗岩的垂直分带;（2）花岗岩中Li 与稀有金属含量呈正相关关系,Li 与Ta、Nb、Sn 等稀有金属具有协同成矿作用;（3）花岗岩中云母类矿物具有向富Li 演化的趋势,以铁锂云母为主,随着铁锂云母的结晶,Nb、Ta、Sn 等稀有金属相继析出,导致晚期云母中Ta、Nb 等含量降低。熔体中H2O、F 等对花岗质岩浆的性质和结晶分异有较大影响,但不足以致使花岗岩呈垂直分带。     

In situ analyses of micas in the Yashan granite,South China: Constraints on magmatic and hydrothermal evolutions of W and Ta–Nb bearing granites

Most rare-metal granites in South China host major W deposits with few or without Ta–Nb mineralization. However, the Yashan granitic pluton, located in the Yichun area of western Jiangxi province, South China, hosts a major Nb–Ta deposit with minor W mineralization. It is thus important for understanding the diversity of W and Nb–Ta mineralization associated with rare-metal granites. The Yashan pluton consists of multi-stage intrusive units, including the protolithionite (-muscovite) granite, Li-mica granite and topaz–lepidolite granite from the early to late stages. Bulk-rock REE contents and La/Yb ratios decrease from protolithionite granite to Li-mica granite to topaz–lepidolite granite, suggesting the dominant plagioclase fractionation. This variation, together with increasing Li, Rb, Cs and Ta but decreasing Nb/Ta and Zr/Hf ratios, is consistent with the magmatic evolution. In the Yashan pluton, micas are protolithionite, muscovite, Li-mica and lepidolite, and zircons show wide concentration ranges of ZrO₂, HfO₂, UO₂, ThO₂, Y₂O₃ and P₂O₅. Compositional variations of minerals, such as increasing F, Rb and Li in mica and increasing Hf, U and P in zircon are also in concert with the magmatic evolution from protolithionite granite to Li-mica granite to topaz–lepidolite granite. The most evolved topaz–lepidolite granite has the highest bulk-rock Li, Rb, Cs, F and P contents, consistent with the highest contents of these elements and the lowest Nb/Ta ratio in mica and the lowest Zr/Hf ratio in zircon. Ta–Nb enrichment was closely related to the enrichment of volatile elements (i.e. Li, F and P) in the melt during magmatic evolution, which raised the proportion of non-bridging oxygens (NBOs) in the melt. The rims of zoned micas in the Li-mica and topaz–lepidolite granites contain lower Rb, Cs, Nb and Ta and much lower F and W than the cores and/or mantles, indicating an exotic aqueous fluid during hydrothermal evolution. Some columbite-group minerals may have formed from exotic aqueous fluids which were originally depleted in F, Rb, Cs, Nb, Ta and W, but such fluids were not responsible for Ta–Nb enrichment in the Yashan granite. The interaction of hydrothermal fluids with previously existing micas may have played an important role in leaching, concentrating and transporting W, Fe and Ti. Ta–Nb enrichment was associated with highly evolved magmas, but W mineralization is closely related to hydrothermal fluid. Thus these magmatic and hydrothermal processes explain the diversity of W and Ta–Nb mineralizations in the rare-metal granites.     

川西可尔因锂矿田云母矿物化学及稀有金属成矿和 找矿指示

为明确可尔因矿田岩浆演化过程中锂的迁移与富集,指明稀有金属矿床的找矿方向,文章通过野外地质观察、室内岩矿鉴定及云母LA-ICP-MS原位测试,发现随着岩浆分异程度的增强,云母由镁铁质黑云母演化为硅铝白云母,以云母Mg~#/n(Li)值作为岩体分异程度指示,显示其与亲铁元素组合(V、Cr、Co、Ni)、稀碱金属(Li、Rb、Cs)、稀有金属(Nb、Ta、Sn)及稀散元素(Ga)和指示岩浆演化的元素对(Nb/Ta、K/Rb)均存在显著的相关性。根据岩体结晶环境、源区类型及云母结晶时对应熔(流)体中的Li含量,将可尔因矿田岩浆-热液活动划分为3期次7阶段,进而指出矿田内第三期次一、二阶段岩浆热液活动为Li迁移与富集的主要阶段。该过程中深源Li成矿元素和热量持续供给、早阶段岩体黑云母分解、三叠系围岩混染和上侵流体圈闭促成了富Li熔(流)体的形成与就位,表明矿田内及外围寻找岩浆型锂矿和三叠系层控富锂矿体的潜力。结合Li和其他稀有金属的相关性,指明了Sn、Nb、Ta等稀有金属元素的找矿方向。     

芙蓉锡矿方解石稀土元素地球化学特征及其对成矿流体来源的指示

方解石是芙蓉锡矿田重要的脉石矿物。根据芙蓉矿田白蜡水矿区和狗头岭矿区不同产状(云英岩型、蚀变岩体型和构造蚀变带-矽卡岩型)矿石中方解石稀土元素地球化学特征研究表明:两矿区成矿期热液方解石具有两种稀土模式,LREE(轻稀土元素)富集型和相对平坦型。其中,蚀变岩体型方解石所具有的相对平坦型稀土模式代表了LREE带出后残余热液的稀土模式特征,而云英岩型和构造蚀变带—矽卡岩型方解石的LREE富集型稀土模式与骑田岭新鲜花岗岩类似,表明成矿过程中没有LREE明显带出的迹象,残余热液继承了岩浆期后热液的特征。成矿流体来源于骑田岭花岗岩岩浆期后热液。     

Tracking magmatic and hydrothermal Nb–Ta–W–Sn fractionation using mineral textures and composition: A case study from the late Cretaceous Jiepailing ore district in the Nanling Range in South China

The Jiepailing mining district in the Nanling range in South China is well-known for its granite-related Sn–Be–F-mineralization. Recently, drill holes have exposed an Nb–Ta–W–Sn mineralized granitic porphyry and topaz-bearing granite–greisen at depth, which we have studied here, using mineral (columbite, rutile, wolframite, cassiterite, zircon, and mica) major- and trace-element compositional data, mineral textures, and zircon and columbite U–Pb geochronology. Our age data shows that the porphyry and the granite and their mineralization formed at ~ 91–89 ± 1 Ma in the late-Cretaceous, and thus subsequent to the main ore-forming events of the region. Continuous mineral compositional trends indicate that the studied granitoids are related by progressive fractionation. We propose that: (1) subhedral–euhedral, low-Ta columbite crystallized from melt; (2) euhedral–subhedral rutile and wolframite and subhedral and subhedral cassiterite up to ~ 30 μm in size formed at the magmatic–hydrothermal transition of the system; and (3) high-Ta columbite and subhedral cassiterite up to ~ 10 μm in size formed from subsolidus hydrothermal fluids. In combination with the Nb, Ta, W, and Sn compositions of zircon and mica, their textures and compositional variation allow us to track the magmatic to hydrothermal rare-metal fractionation (concentration, mobilization, and deposition) of the system in detail, despite our limited access to it through only two exploration drill cores. Using the Nb, Ta, W, and Sn concentrations in zircon (refractory, early-crystallized) and in micas (late equilibrated), respectively, was particularly useful for tracing the partial loss of Sn and W ore components from the intrusion, and to constrain the information which is crucial for any rigorous ore exploration.     

Mineralogy and geochemistry of indium-bearing polymetallic veins in the Sarvlaxviken area,Lovisa, Finland

A number of polymetallic vein mineralizations of different styles and metal associations, including base, alloy, noble and critical metals, have been discovered around the Sarvlaxviken bay in the westernmost parts of the Mesoproterozoic Wiborg Batholith, south-eastern Finland. The veins occur in two rapakivi granite varieties: coarse-grained wiborgite; and medium-grained Marviken granite. The veins are divided into five groups based on the dominant metal associations.The Li–As–W–Zn–Mn, Pb–Zn and Cu–As–In associations are hosted by wiborgite, and are strongly controlled by a NNW-trending tectonic pattern that evolved in two main stages. The Li–As–W–Zn–Mn association (generation 1) formed in a typical greisen environment with Li-bearing mica in significant alteration halos around a narrow quartz vein. This greisenization was accompanied by silicification, followed by sericitization and chloritization. The Pb–Zn association occurs in a similar vein type but without typical high-temperature minerals and is considered to have formed at a higher crustal level. Generations 2a and 2b formed under more brittle conditions leading to fracturing, quartz veining and metal precipitation of ore minerals. This metal association is characterized by very high contents of Cu, As and up to 1490 ppm In but with ≤ 0.4% Zn, which leads to very high In/Zn ratios (up to 8400) enabling formation of abundant roquesite.The As–Sn–Cu and Mo–Bi–Be associations are hosted by alteration zones without hydrothermal quartz in the Marviken granite. Mineralization with moderately high contents of As, Sn and Cu is associated with greisenization while mineralization with spectacular contents of Be as well as high contents of Mo and Bi is associated with sericitization, chloritization and berylification.The internal age relations between the wiborgite-hosted, NNW-trending veins show a clear evolution from a typical greisen type environment (the Li–As–W–Zn–Mn and Pb–Zn associations of generation 1) to cooler and more brittle conditions governing quartz veining and precipitation of ore minerals belonging to the Cu–As–In association (generations 2a and 2b). The age relations between these wiborgite-hosted veins and the veins in the Marviken granite are more uncertain but the presence of a NS-trending granitic dyke on the eastern side of the Sarvlaxviken bay, with similar ore-fertile geochemical composition as the Marviken granite, indicates that the tectonically controlled veins formed simultaneously with the emplacement of the Marviken granite and associated hydrothermal activity.The polymetallic veins in the Sarvlaxviken bay are unique for the Fennoscandian Shield, not the least for the locally high indium grades and spectacular roquesite grains. There is an obvious exploration potential for similar veins (and hence a number of base, alloy, noble and critical metals) also elsewhere in the entire Wiborg Batholith.     

Magmatic control on the contrasting Sn feritility of different granite plutons in the giant Gejiu orefield.SCIEI北大核心CSCD

云南个旧锡矿是全球最大的锡多金属矿床之一,但矿区内同时代花岗岩成锡矿潜力差异显著,其控制因素仍不清楚。本文选取贫矿的龙岔河似斑状花岗岩和成锡矿的老厂-卡房(后文简称老-卡)花岗岩为研究对象,通过全岩地球化学成分和黑云母成分分析,系统研究个旧矿区不同花岗岩成锡矿潜力差异的控制因素。测试结果表明,龙岔河花岗岩和老-卡花岗岩具有相似的、以表壳物质为主的岩浆源区以及较高的初始熔融温度,表明岩浆源区和熔融条件不是控制二者成矿潜力差异的主要原因。黑云母成分显示老-卡花岗岩和龙岔河花岗岩均具有较低的氧逸度,岩浆演化过程中锡为不相容元素,有利于锡在残余熔体中富集,表明氧逸度条件也不是导致成矿潜力差异的关键因素。龙岔河花岗岩发育角闪石、榍石、黑云母,而老-卡花岗岩发育岩浆白云母,指示后者分异程度更高。此外,与龙岔河花岗岩相比,老-卡花岗岩具有富硅,贫钛、铁、镁、钙和稀土元素特征,稀土元素呈现“海鸥式”配分模式,并且具有较低的Nb/Ta、Zr/Hf、K/Rb和较高的Rb/Sr比值,同样指示老-卡花岗岩具有更高的结晶分异程度。并且相比于龙岔河花岗岩为准铝质的特征,老-卡花岗岩的过铝质特征有利于锡分配进入岩浆出溶的流体相中富集成矿。因此,岩浆性质和演化程度是导致个旧地区不同花岗岩成矿潜力差异的主要原因,龙岔河花岗岩形成锡矿化的潜力较小。     

Chemistry of Micas in Rare-Metal Granitoids and Associated Rocks,Eastern Desert,Egypt

Paragenetic, textural, and chemical characteristics of micas from 10 rare-metal granitic stocks and the associated greisens were examined in order to identify the metallogenetic processes of the host granitoids. The investigated granitoids and type occurrences can be categorized as: (1) metaluminous, Nb + Zr + Y-enriched alkali granite (e.g., Hawashia, Ineigi, and a stock northwest of Um Naggat); (2) peraluminous, Ta > Nb + Sn ± W + Be-enriched Li-albite granites (e.g., Nuweibi, Igla, and Abu Dabbab); and (3) metasomatized, Nb » Ta + Sn + Zr + Y + U ± Be ± W-enriched apogranites (e.g., Um Ara, Abu Rusheid, Mueilha, and Homr Akarem).

Mica of the alkali granite is of the annite-siderophyllite series, and is characterized by an average FeO? of 28.14, low MgO of 0.05, a mean Fe?/(Fe? + Mg)_atom. value of 0.996, TiO₂ of 0.69, enhanced Al₂O₃ of 14.91, MnO of 0.58, Li₂O of 0.26, and moderate to low F of 0.86. These characteristics are representative of the relatively highly evolved nature of the annite-siderophyllite-bearing magmas. The micas closely resemble those of the anorogenic pegmatites and A-type granites.

Primary mica of the Li-albite granites is compositionally constrained between zinnwaldite in the lower zones, and white mica in the apical, more evolved zone, and is associated with columbite-tantalite, topaz, and fluorite. The occurrence of zinnwaldite with high contents of Mn and F indicates its stabilization at rather low temperatures in Li- and F-rich sodic melts. The restriction of white mica with lower Mn, F, and Li contents to the apical zones can be attributed to either volatile degassing or to the beginning of topaz crystallization. These two factors brought about an evolutionary trend for micas, which contrasts with the documented trends of Li-micas in other Li-granites (i.e., from Li-siderophyllite or Li-muscovite to lepidolite).

Micas range in composition between white mica in the lower unaltered zones of the apogranites and Li-siderophyllite-zinnwaldite in the apical microclinized and albitized zones; this systematic compositional change appears to reflect roofward increasing in μ_KF and μ_LiF of the exsolved fluids. Columbite, cassiterite, zircon, xenotime, beryl, and fluorite are common associates of the zinnwaldites. However, white micas from the greisenized apogranite and endogreisen veins have diminishing Li contents. The subsolidus formation of zinnwaldite and Li-siderophyllite in the apogranites, and white mica in the associated greisens, represent transitions from magmatic to hydrothermal environments under the influence of decreasing P, T, salinity, and alkalinity of the exsolved fluids.     

与A型花岗岩有关锡矿的云英岩化蚀变矿化地球化学:以新疆卡姆斯特和干梁子矿床为例

新疆准噶尔盆地东部卡拉麦里地区发育我国典型的A型花岗岩型锡矿.通过对该区卡姆斯特和干梁子两个锡矿4个矿化蚀变带的岩相学及地球化学研究,发现矿体和致矿岩体是同源岩浆演化的结果,矿体是岩浆分异演化末期向流体演化过程中形成的.矿床的蚀变分带模式可分为两种:（1）（红色）细粒黑云母花岗岩→云英岩化细粒花岗岩→含锡石英脉;（2）细粒黑云母花岗岩→含锡云英岩→含锡石英脉.其蚀变带中岩石的地球化学组分总体迁移规律为:SiO₂迁入,Na₂O、K₂O迁出,Fe₂O₃总体表现为迁入,Th/U值不断降低,表明硅化和碱交代作用贯穿整个成矿过程,成矿环境由碱性向酸性变化,并伴随氧逸度的升高.F、Cl、W、Cu、Bi、In、Pb、Rb、Nb、Ta等元素与成矿元素Sn的迁移、富集和沉淀密切相关,其中F和Cl是迁移过程中最活跃的组分,是Sn元素最大的"搬运工",Sn元素的富集与W、Cu、Bi、In等元素迁移呈正相关,反映流体作用与Sn成矿密切相伴,而与Pb、Rb、Nb、Ta等元素的迁移呈负相关,反映致矿岩体自身元素的稀释和带出,Sn的富集和成矿是在岩浆向流体演化过程中完成的.      

江西石城海罗岭花岗岩型铌钽矿床岩石地球化学、 年代学特征及其地质意义

稀有金属矿产是江西省优势矿产资源,成矿类型以花岗岩型为主,主要分布于赣西和赣北地区,以宜春414超大型钽铌矿为代表,而花岗岩广泛分布的赣南地区鲜有关于燕山期花岗岩型稀有金属矿床的报道。本文以赣南石城海罗岭铌钽矿床为研究重点,结合详细的野外调查,开展花岗岩的岩石学、岩石地球化学和同位素年代学等研究,厘定了海罗岭的中粒斑状黑云母二长花岗岩- 中细粒黑云母二长花岗岩岩石组合,明确了钠长石化叠加白云母化的中粒斑状黑云母二长花岗岩与铌钽矿密切相关的成矿专属性。海罗岭的成矿作用具两阶段特征,早阶段以蚀变花岗岩型钽铌矿为主,赋存于钠长石化白云母化中粒斑状黑云母二长花岗岩中,晚阶段则以花岗伟晶岩型锂矿为主,赋存于云母锂辉石伟晶岩中。海罗岭的花岗岩主要经历了钠长石化、白云母化、黄玉化、绢云母化、硅化等蚀变作用,呈现碱性长石化→云英岩化的演化过程。海罗岭花岗岩具富硅、富碱、富铝,贫钛、镁的特征,其中钠长石化白云母化中粒斑状黑云母二长花岗岩（富钽花岗岩）中F含量为8330×10-6～13076×10-6,平均为10475×10-6,具极低的Nb/Ta值（0. 34~0. 49）、Zr/Hf值（3. 73~4. 19）、稀土总量低（ΣREE为16. 3×10-6~23. 2×10-6）和“四分组”效应等特征,显示其成矿经历了岩浆- 流体相互作用的过程。研究显示,Li矿化富集程度与F含量呈明显的正相关,与稀土总量、K/Rb值呈负相关;Ta矿化富集程度与F含量呈明显的正相关,与Nb/Ta值、Zr/Hf值呈明显的负相关。中细粒黑云母二长花岗岩锆石U- Pb年龄为141. 9±1. 1 Ma,云母锂辉石伟晶岩和碱性长石伟晶岩独居石U- Pb年龄分别为141. 68±0. 69 Ma和137. 62±0. 73 Ma,均归属于早白垩世。研究表明,赣南地区140 Ma左右可能存在一次与钠长石化叠加白云母化中粒斑状黑云母二长花岗岩相关的独特的铌钽矿成矿事件和与花岗伟晶岩相关的锂成矿事件。这一发现打破了以往华南稀有金属主要赋存于燕山期复式岩体晚期二云母花岗岩- 白云母花岗岩中的认识,拓宽了找矿思路,为赣南乃至华南地区稀有金属找矿提供了新的方向。     

Composition and evolution of accessory mineralization of Li–F granites in the Far East as indicators of their ore potential

The ore potential of Pacific Li–F granites is considered on the basis of original and published data on composition of these granites and related metasomatic rocks in the Badzhal (Amur region) and Kuiviveem–Pyrkakai (Chukchi Peninsula) ore districts. The accessory mineralization in rare-metal granites is compared with that in W–Sn deposits. The main features in evolution of magmatic and hydrothermal mineralization are pointed out. A conclusion on the similarity between mineralization of the zwitter–tourmalinite type and accessory minerals in Li–F granites is drawn. It is established that magmatic and hydrothermal types of mineralization belong to the same evolutionary sequence. Genetic links between Li–F granites and the large ore deposits in the East Asian tungsten–tin zone are suggested.     

关于花岗岩与成矿作用若干基本概念的再认识

借着对张旗先生两篇文章提出进一步质疑的机会,文章阐述了与花岗岩有关成矿作用的若干基本概念、基础知识以及国内外矿床学界对某些相关问题的研究成果。认为花岗岩浆从形成起到最后固结成岩,必然经历了一定的演化过程,花岗岩浆的分异演化,可以形成富含水和其他挥发组分的残余岩浆,出现晶体、熔体、流体三相共存的"岩浆-热液过渡阶段",并最终分泌出热液(岩浆水)。中国华南尤其是南岭地区钨锡铋钼锂铍铌钽等稀有金属的大规模成矿作用正是与该地区大规模花岗岩浆活动及其演化密切相关的。文章强调了花岗岩类与钨锡等成矿作用之间存在着密切的成因关系,并重申了"成矿母岩"、"含矿岩体"等术语在矿床学研究及指导找矿勘查等方面的积极意义。指出"金铜和钨锡可以伴生"是大量矿床所反映的、因此也是必须尊重的基本地质事实,而不是依据了什么理论。文章最后认为,关于成矿作用问题的任何讨论和争鸣都必须建立在尊重地质事实、尊重矿床学基本概念和尊重矿床学领域前人研究成果的基础之上。     

The late stages of evolution of the Kwandonkaya A-type granite complex,Nigeria, as deduced from mafic minerals

In the Kwandonkaya Complex, an A-type metaluminous to peraluminous granite complex in northern Nigeria, the presence of Fe²⁺-rich ferromagnesian phases (fayalite, hedenbergite and amphibole) at the initial and annite at final stages of crystallisation indicates relatively reduced melts throughout (⪯QFM). Annite and associated species in the biotite granites provide the best indication as to the nature of volatile loss, albitisation and greisen formation.From the mica chemistry, it is inferred that degassing was accompanied by preferential loss of Cl in the roof zones and margins of the plutonic rocks, with the resulting enrichment of F and inferred Li in mica from the drusy facies. During albitisation, the mica composition was rockbuffered with respect to major constituents like Fe. However, the F±(Li, REE, Y, Nb, Ta, Sn) contents were enhanced during albitisation to produce F-rich mica associated with disseminated-type typaz-columbite-cassiterite mineralisation. Greisen formation was accompanied by the buildup of Si, Al, Ti, F and possibly Li, which is in agreement with enhanced normative quartz and corundum, and increases in modal mica, quartz, topaz and fluorite. The mafic minerals and their alteration assemblages indicate that volatile loss, incipient subsolidus modifications, albitisation and greisen formation were associated with increases in f_HF and f_H2O). Both oxidation and preferential Cl loss promoted the deposition of cassiterite at post-magmatic stages.     

Geochemical Exploration on the Stream Sediments of Gabal El Mueilha Area, Central Eastern Desert, Egypt: An Overview on the Rare Metals

Abstract: El Mueilha area consists of post-collision granitic rocks intruding Pan-African metasediments, metavolcanics and granodiorites. Tin mineralization in Gabal El Mueilha is either of vein type or disseminated in the greisenized and albitized parts of the granitic rocks. Cassiterite and wolframite-bearing quartz veins also characterize a small intrusion of muscovite granite at El Mueilha tin mine area. Detailed geochemical prospecting for the rare metals Sn, Nb, Be, Li, U, Th and some other trace elements was carried out at Gabal El Mueilha area using stream sediments survey. Sixty-seven stream sediment samples were collected from the main drainage patterns of the study area. Statistical parameters were calculated for the analyzed elements. The sought elements Sn, Nb, Be and Li have relatively high background values in the studied sediments. This may reflect the role of the pathfinder elements (Nb, Be and Li) during secondary dispersion survey for Sn mineralization.
Geochemical maps were constructed to delineate anomalous areas with abnormally high rare metal contents. The anomalous Sn, Nb and Be areas are mainly encountered in the main stream draining the mineralized zones of El Mueilha tin mine and near the SW albitized parts of the post-collision granite. Correlation coefficient matrices show significant positive relation between Sn and the rare metals group (Nb, Rb and Li) at 99 % significant level. R-mode factor analysis for the concerned elements yields five factor–model.     

Petrology and mass-balance constraints on major-, trace-, and rare-earth-element mobility in porphyry-greisen alteration associated with the epizonal True Hill granite, southwestern New Brunswick, Canada

Endogreisen and exogreisen weakly mineralized with Bi, Sn, and Mo are associated with two of three granite porphyry (granite) cupolas hosted in Silurian metasedimentary rocks at True Hill, southwestern New Brunswick. The epizonal, weakly peraluminous and compositionally evolved True Hill granite is quartz and K-feldspar porphyritic; groundmass textures, such as granophyric patches, miarolitic cavities, and pegmatite pods, are indicative of rapid cooling and vapor saturation.The greisen mineralization in cupolas B and C is overprinted by various types of alteration, reflecting multi-stage devolatilization of the magma. The most intense topaz-bearing greisen is confined mainly to the apical parts of the granite. In places, fluorite is associated with silicification, sericitization, and chloritization, which is common to greisen-type alteration. The alteration types reflect the physical and chemical changes in the hydrothermal fluid that was derived principally by second boiling of the magma. Al-normalized, mass-balanced geochemical data supported by petrographic observations show that in the greisenized True Hill granite, Fe, Mn and Mg enrichment corresponds to chlorite and/or Fe-muscovite alteration and are coincident with leaching of Na and K and deposition of SiO₂. Ca was remobilized in the greisen environment, but erratically deposited as fluorite. Minor P and LREE enrichment are reflected by the presence of monazite in the greisen. The HFSE are mobile to a minor degree, based on correlations with elements known to be hydrothermally mobile. The base metals correlate with S and other ore-forming elements. The distribution of many of the trace elements is related to alteration, including the leaching of alkalis, which leads to the stabilization of aluminosilicates, principally muscovite and topaz. The distribution of trace elements reflects their relative mobility during greisenization, with high-field-strength elements (Zr and Ti) the most immobile and the lithophile and chalcophile elements the most mobile. Breccias and greisen alteration in cupola C at True Hill are similar to those at the base of the W-Mo-Bi porphyry-greisen in the Fire Tower zone above the Mount Pleasant fine-grained granite.     

Geochemistry of lepidolitic granitoids from the Mungutiyn Tsagaan Durulj occurrence (central Mongolia)

We studied the geologic position, geodynamic setting, petrology, and geochemistry of veined lepidolitic granitoids from the Mungutiyn Tsagaan Durulj (MTD) occurrence (central Mongolia), found within the area of Mesozoic intraplate rare-metal magmatism. It has been established that their trace-element enrichment resulted from the intense effect of fluids rich in F, K, Li, Rb, Cs, Sn, Be, and W, which arrived from a deep magma chamber of rare-metal granitic melts, on leucogranites with originally weak rare-metal mineralization. Very high contents of F, rare alkali metals, Sn, Be, and W, characteristic of MTD granitoids, are close only to those in greisens of rare-metal granites and topaz-lepidolite-albitic pegmatites. The difference from the greisens in each case might be due to the features of the original rocks. The difference between the greisenized MTD leucogranites and the topaz-lepidolite-albitic pegmatites is more radical: Along with evident petrographic distinctions, it includes an evolution trend toward the albite norm decrease, not typical of Li–F igneous rocks; rock shearing and gneissosity, which must have contributed to their chemical transformation according to this trend; and stably lower contents of Nb and Ta (trace elements which usually accumulate during crystallization fractionation of F–Li granitic melts and are poorly soluble in magmatic fluids). The greisenized MTD granitoids are not only high-grade rare-metal ores of Li, Rb, F, and Sn but are also regarded as an indicator of a deep concealed pluton of rare-metal granites.     

Main types of rare-metal mineralization in Karelia

Rare-metal mineralization in Karelia is represented by V, Be, U deposits and In, Re, Nb, Ta, Li, Ce, La, and Y occurrences, which are combined into 17 types of magmatic, pegmatite, albitite–greisen, hydrothermal–metasomatic, sedimentary, and epigenetic groups. The main vanadium resources are localized in the Onega ore district. These are deposits of the Padma group (556 kt) and the Pudozhgorsky complex (1.5 Mt). The REE occurrences are primarily characterized by Ce–La specialization. The perspective of HREE is related to the Eletozero–Tiksheozero alkaline and Salmi anorthosite–rapakivi granite complexes. Rare-metal pegmatites bear complex mineralization with insignificant low-grade resources. The Lobash and Jalonvaara porphyry Cu–Mo deposits are potential sources of rhenium: Re contents in molybdenite are 20–70 and 50–246 ppm and hypothetical resources are 12 and 7.5 t, respectively. The high-grade (～100 ppm) and metallogenic potential of indium (～2400 t) make the deposits of the Pitkäranta ore district leading in the category of Russian ore objects most prospective for indium. Despite the diverse rare-metal mineralization known in Karelia, the current state of this kind of mineral commodities at the world market leaves real metallogenic perspective only for V, U, Re, In, and Nb.     

Geochronology of granite and associated Sn mineralization in the Shuangyuanchong Sn deposit and its implication for Sn-W prospecting potential in the Shizhuyuan-Hehuaping area,the Nanling region,South ChinaSCIEI北大核心CSCD

南岭成矿带是全球最重要的钨锡成矿带之一,区内钨锡成矿条件优渥,是开展钨锡找矿勘查的重要目标区。然而如何开展钨锡找矿工作,尤其是在已有矿床周缘圈定成矿远景区,是钨锡成矿作用研究以及找矿勘查工作关注的重要科学问题。双园冲矿床位于南岭成矿带中西段,处于荷花坪与柿竹园两个大型锡钨多金属矿田中间,并与两个矿田处于同一构造体系,但目前对该矿床的研究程度较低,由此也制约了其矿床成因研究及该区的找矿部署。本次研究获得双园冲云英岩化花岗岩的锆石和独居石原位LA-ICP-MS U-Pb年龄分别为161.2±2.5Ma和157.1±1.8Ma,与云英岩型矿石中锡石原位LA-ICP-MS U-Pb年龄(158.9±2.9Ma)一致,二者均形成于晚侏罗世,表明其具有密切的成因关系,这一年龄也与南岭成矿带钨锡成矿大爆发时代(150-160Ma)一致。综合对比双园冲锡矿及与其空间相邻的柿竹园和荷花坪锡多金属矿田特征显示,三者成岩成矿时代一致,岩体侵位和矿体分布均受NE向断裂控制,矿体也均赋存于中-上泥盆统碳酸盐岩地层中,并且成矿花岗岩具有相似的岩石学特征和岩浆源区。综合以上信息,本文提出三个矿床可能形成于同一次岩浆热液活动,成矿岩体可能来自地壳深部同一个大岩浆房,柿竹园和荷花坪之间的区域具有发育晚侏罗世花岗岩体及相关钨锡矿的较大潜力。根据双园冲锡矿及其周缘大型锡钨矿床浅部脉状Pb-Zn-Fe-Mn矿化和深部矽卡岩-云英岩型Sn-W矿化的特征,提出研究区乃至整个南岭地区浅部脉状Pb-Zn-Fe-Mn矿化是深部Sn-W找矿勘查的有利部位。     

Tin-bearing minerals at the Furong tin deposit,South China: Implications for tin mineralization

It remains poorly constrained whether remobilization of Sn from granites and prograde skarns plays an essential role in forming economic (skarn-type) tin mineralization. Using both electron probe microanalysis and laser ablation–inductively coupled plasma–mass spectrometry methods, in-situ Sn contents, as well as major elements, were analyzed for numerous silicates and magnetite from fresh granite, altered granite, and skarn at the large Furong Sn deposit (530,000 t Sn @ 0.8% Sn) in the Nanling Range, South China. Hornblende and biotite in fresh granite are the main Sn-bearing phases (Sn = 44–321 ppm), while plagioclase and K-feldspar are poor in Sn (< 5 ppm). In altered granite, tin is hosted mainly by hydrothermal muscovite (299–583 ppm) replacing plagioclase, but rarely by chlorite (mostly <10 ppm) replacing hornblende and biotite. In contrast, most silicates (garnet, diopside, vesuvianite, pargasite and epidote) and magnetite from tin skarn are Sn-rich (47–44,241 ppm), except for Sn-poor phlogopite and scapolite (< 10 ppm). In particular, garnet, pargasite, and epidote reach tin concentrations in the percent range. Tin generally enters the stannous silicates and magnetite through substitutions for octahedral Al^vi and Fe³⁺. Comparisons of Sn contents between magmatic and hydrothermal minerals in granite, prograde and retrograde minerals related to tin skarn indicate that remobilization of Sn from granite and prograde skarn is not a pre-requisite to form tin mineralization.