赣北石门寺钨多金属矿床成矿流体演化过程：白钨矿微区成分限定

大湖塘钨矿地处江南造山带中段,为一大型钨-钼-铜多金属矿田,由4个矿床组成,其中石门寺矿床规模最大.文章利用LA-ICP-MS对石门寺矿床石英脉型钨矿中的白钨矿进行单矿物原位微区分析,以揭示成矿流体演化过程.研究表明,石英脉中的白钨矿可划分为2期,其中,早期白钨矿与黑钨矿、黑云母及石英共生,而晚期白钨矿在石英大脉中仅与石英共生.前者表现为右倾型稀土元素配分模式,而后者则显示平坦型稀土元素配分模式,两者均具Eu正异常.此外,早期白钨矿较晚期白钨矿具有较高的ΣREE、Mo、Sn、Nb、Ta、Y含量,但Sr含量较低.早期白钨矿表现出LREE富集型和较高的ΣREE、Nb、Ta含量,说明成矿流体来源于岩浆热液,从早期到晚期成矿流体中Eu由Eu2+为主转变为Eu3+为主,表明流体演化过程中氧逸度升高,暗示成矿晚期有氧化性大气降水加入.早期高LREE、Sn、Nb、Ta含量的白钨矿的沉淀以及辉钼矿结晶显著改变成矿流体的组成,导致晚期白钨矿具平坦型REE配分模式和低Mo、Sn、Nb、Ta的特征.此外,在流体演化过程中,新元古代花岗闪长岩中斜长石因为蚀变分解持续为成矿热液提供Eu和Sr,造成白钨矿Eu正异常和晚期白钨矿中Sr含量的升高.     

云母矿物对仁里稀有金属伟晶岩矿床岩浆-热液演化过程的指示

仁里5号伟晶岩脉是湖南仁里超大型铌钽多金属矿床中含矿性最好且分带完整的一条含铌钽矿脉,云母作为其中的贯通性矿物出现于各分带中,由外部带至内部带表现出不同的成分和结构特征。文章通过对5号脉各带中的云母矿物进行详细的电子探针(EPMA)分析,查明了不同分带中云母矿物的演化规律:自外向内云母类型从白云母→锂云母的方向变化,Ⅰ带→Ⅲ带主要为白云母,Ⅳ带起出现富锂云母类型,并开始发育多种不平衡和交代结构;Ⅰ带→Ⅳ带云母的Li、Rb、Cs、F、Mg、Ti含量逐渐升高,K/Rb和K/Cs比值逐渐降低,从Ⅳ带→Ⅴ带,Mg、Ti降低、Li、Rb、Cs、F含量出现突增,其中,w(F)最高可达11.8%、w(Li_2O)可达8.33%,w(Cs_2O)为4.00%,而铯多硅锂云母中的w(Cs_2O)可达18.0%。这些证据均表明,5号脉具有极高的分异演化程度,从外部带向核部演化程度逐渐增高;Ⅳ带云母的突变很可能暗示其经历了岩浆-热液过渡过程,而Ⅴ带主要发育于热液阶段,此时的流体性质有利于Nb、Ta尤其是Ta元素的富集再沉淀。仁里矿床经历了岩浆-热液2阶段成矿作用,并且稀有金属的成矿很可能持续至热液阶段,这也是造就它特殊性(高品位)的重要原因。     

内蒙古乌努格吐山斑岩铜钼矿床成矿流体演化——基于短波红外光谱、云母成分和石英流体包裹体研究SCIEI北大核心CSCD

内蒙古乌努格吐山斑岩铜钼矿床是中国东北地区最大的斑岩矿床之一,发育显著的石英-绢云母化蚀变,对早期的钾硅化蚀变有强烈的叠加改造,模糊了各蚀变的分带特征和不同矿化之间的关系,复杂的流体改造阻碍了精细热液演化过程的重建。本文以白云母为研究对象,在细致的显微镜、扫描电镜分析确定云母的形态特征以及矿物共生组合等基础上,利用电子探针(EPMA)、激光剥蚀电感耦合等离子体质谱(LA-ICP-MS)以及短波红外光谱(SWIR)分析手段,详细揭示不同阶段、不同产状白云母的成分差异,探讨了其对矿床热液演化以及成矿机制的指示意义。结果显示,乌山斑岩矿床的白云母由白云母端员及少量钠云母、绿鳞石、伊利石端员组成。与辉钼矿有关的云母更富集Al、K、Sr、Ba,且Al-OH特征波长在2197~2203nm之间。与黄铜矿有关的云母具有更高的Si、Ti、Fe、Mn、Mg、Cu、Zn、Sn、W等元素含量,Al-OH特征波长在2200~2206nm之间。氧化环境下形成的云母更富集Sc、V、W。乌山斑岩矿床的白云母在2200nm处吸收峰位置的波长偏移与距离成矿中心的远近及矿化类型有关,特征波长<2203nm则指示钼矿化,并且靠近成矿中心,因此可以利用SWIR特征圈定热液活动区域,确定矿化类型,指导找矿勘查工作。石英流体包裹体测温证据、白云母成分等信息,暗示铜沉淀阶段存在其他流体补充注入。综上所述,白云母作为常见的蚀变、热液矿物,对研究成矿流体演化及矿床勘查评价具有重要的科学意义。     

新疆巴里坤小加山钨矿地质特征与成因

小加山钨矿区位于东准噶尔成矿区中部南缘,处于博格达-哈尔里克构造带上。构造位置上矿区处于哈尔里克复式背斜中,构造线方向以EW向为主。矿区出露地层主要为中泥盆统大南湖组第一亚组第一段(D_2d_1~1)、和第二段(D_2d_1~2)。主要岩浆岩有石英闪长岩、黑云母二长花岗岩、钾长花岗岩及少量中酸性花岗闪长岩脉。矿体赋存于邻近海西晚期花岗岩侵入体附近的中泥盆统大南湖组第一亚组第二段(D_2d_1~2)的变质晶屑凝灰岩中。矿石类型为石英脉型黑钨矿石,有用金属主要为黑钨矿,黑钨矿石英脉分为灰色含钨石英脉和白色含钨石英脉2种。四极质谱分析法测得矿床流体包裹体气相成分以H_2O、CO_2为主,次为N_2、CH_4,此外还含有少量的Ar、C_2H_6,液相成分以Cl~-、Na~+为主,次为Ca~(2+),表明成矿流体主要为H_2O-CO_2-NaCl体系。矿床成因类型属于高温热液石英脉型黑钨矿床,矿体主要位于围岩裂隙构造。钨主要由侵入围岩地层中的地幔热液迁移富集而来,W元素迁移过程中,含钨络合物成矿流体分解进而沉淀成矿。     

塔吾尔别克-阿庇因迪斑岩型金矿特征

矿床的形成与矿区二长斑岩岩体有关.岩体内发育4组原生节理或裂隙带,这些节理或裂隙带控制了矿体的分布,特别是它们的交汇部位是成矿的良好部位.矿体形态为脉状、网脉状和透镜体状.有4种矿石类型:黄铁矿石英脉型;黄铁矿硅酸盐石英脉型;黄铁绢英岩型和细脉浸染型.矿床可以划分为2个成矿期:内生成矿期和表生成矿期.内生成矿期划分3个成矿阶段,第2成矿阶段是金矿主成矿阶段.矿物组合为黄铁矿、自然金、银金矿、石英、绿泥石、方解石、白云石、绢云母、白云母和重晶石.矿体的围岩蚀变主要为硅化、绢云母化、黄铁绢英岩化、绿泥石化、硅酸盐化.氢氧同位素、硫同位素以及流体包裹体的研究表明,成矿热液为岩浆热液和大气降水的混合体.成矿热液温度为130℃,成矿压力为22MPa,盐度1.03%,氧逸度-36.7~-38.8,pH=5.8~8.8.成矿流体早期显酸性,晚期显碱性.认为该矿床为浅成低温、低盐度流体成矿,属于次火山斑岩型金矿.     

福建行洛坑钨矿床黑钨矿LA-ICP-MS U-Pb年龄和微量元素地球化学特征北大核心CSCD

为精确厘定福建行洛坑钨矿床成矿时代和揭示其成矿流体演化特征,利用LA-ICP-MS对矿床中的浸染状石英细脉和大脉中的黑钨矿进行了U-Pb年代学和微量元素地球化学研究。结果表明,石英细脉和大脉中黑钨矿的原位U-Pb年龄分别为(151.3±5.8)Ma和(150.5±8.1)Ma。钨成矿时代与南岭地区钨矿化幕次相吻合,表明华南晚侏罗世大规模钨成矿作用可能从南岭地区向东延伸至武夷山成矿带。细脉黑钨矿较大脉黑钨矿具有更低的δEu值,但Nb、Ta含量更高,暗示早期的浸染状石英细脉形成于相对还原环境,晚期可能由于大气降水的增加使氧逸度升高。此外,黑钨矿Y/Ho、Zr/Hf值的非CHARAC行为及其稀土模式四分组效应暗示钨成矿过程中氟对钨等元素的迁移、富集起着重要作用。黑钨矿稀土总量和稀土配分曲线与南岭地区石英脉型钨矿相似,均为重稀土富集型。研究表明行洛坑钨矿属于石英脉型钨矿而非以往认为的斑岩型钨矿。     

宁芜盆地大岭岗金铜矿床地质特征及找矿前景

宁芜盆地发育一系列与火山—岩浆侵入作用有关的热液脉型金铜矿床(点),大岭岗金铜矿床属区内该类矿床。矿体主要赋存于NNW向张扭性断裂带中,呈脉状、复脉状、透镜状产出。大岭岗金铜矿床的蚀变和矿化划分为三个阶段：早期石英阶段、中期石英碳酸盐硫化物阶段和晚期石英碳酸盐重晶石阶段。大岭岗金铜矿床与燕山晚期岩浆活动有着密切的联系,岩浆发展的晚期阶段,从次火山岩(闪长玢岩)中分离出来的富含S、Cu、Fe、Co、Au等元素热液沿着断裂带及其派生的次生裂隙流向各方,与安山质火山岩中的水溶液或下渗的大气水混合,萃取地层成矿物质,使之活化转移,在有利的环境中富集成矿。大岭岗金铜矿床属次火山岩中低温热液脉型金铜矿床。大岭岗金铜矿区成矿地质背景良好,成矿条件优越,通过攻深找盲,寻找新的工业矿体的潜力巨大。     

赣西大港花岗岩型锂矿床锂赋存状态及成岩成矿年代学

大港锂矿床是赣西地区近年来新探明的超大型花岗岩型锂矿之一,成矿与白云母花岗岩密切相关.研究开展了云母矿物学特征及电子探针分析确定锂赋存状态,并利用锆石和锡石LA-ICPMS U-Pb定年法对白云母花岗岩进行了系统的年代学研究,精确厘定成岩成矿时代.年代学结果显示I型热液锆石Tera-Wasserburg U-Pb下交点年龄为129±2 Ma,而颜色较暗的II型锆石下交点年龄为100±4 Ma.锡石核部和边部Tera-Wasserburg U-Pb下交点年龄分别为125±3 Ma和108±7 Ma,同期结果与锆石年龄在误差范围内一致.这些年龄数据显示大港锂矿呈多期次成矿特点.成矿作用均形成于早白垩世,与江南造山带中段燕山期大规模稀有金属成矿时限一致.大港锂矿床中云母主要为富锂白云母、铁锂云母和锂云母,且云母具有明显环带特征,边部较核部富Si、Li和F等元素.云母微观结构及矿物化学特征表明大港高演化花岗岩型锂矿床经历了早期岩浆分异和晚期热液交代两个阶段.晚期富氟富锂热液对白云母花岗岩进行了强烈的交代改造,使锂元素在云母边部高度富集,从而形成富锂矿物.九岭南缘高演化花岗岩型锂矿床的厘定指示了...     

论岩浆热液矿床的成矿期——以南岭地区燕山期钨矿为例

中国岩浆热液型钨矿主要赋存在南岭地区的燕山期花岗岩体内部或周围。目前,尚无法精准地测定此类钨矿的成矿年龄,统计上,得出了两期钨成矿作用：150?160 Ma（主成矿期）和130?140 Ma（次成矿期）,然而,这困扰了对南岭钨矿成矿作用及其与花岗岩关系的理解。本文将综合分析各种最新资料,对成矿母岩、深部岩浆房和成矿机制开展系统的讨论,从而针对南岭钨矿的成矿模式给出明确的判断：（1）燕山早期呈岩基、岩株状的黑云母二长花岗岩不是南岭钨矿的成矿母岩,150?160 Ma的年龄值不是钨成矿作用的年龄值;（2）燕山晚期呈岩株、岩瘤、岩脉状的二云母/白云母碱长花岗岩是潜在的钨源载体,但其体积太小,也无法满足成矿母岩要求;（3）当组合燕山早期主体花岗岩（黑云母二长花岗岩）、燕山晚期补体花岗岩（二云母/白云母碱长花岗岩）和燕山晚期钨矿三者为一体时,一种新颖的成矿模式被构建起来：一个长期存活的深部岩浆房可以分异出富含成矿物质的残余岩浆;当这种岩浆沿着张性断裂快速侵位时,将发生流体–熔体之间的溶离作用,碱性硅质流体形成含黑钨矿的石英脉,而强硅铝质熔体固结为二云母/白云母碱长花岗岩;（4）130?140 Ma的二云母/白云母碱长花岗岩与黑钨矿石英脉是一对同源分体,两者的同步出现充分展示了成矿物质“源–运–储”的完整过程。该认识不仅可以合理地解释与岩浆热液矿床有关的多种地质现象（如“小岩体成大矿”）,而且更新了岩浆热液成矿作用理论,更加重要的是为找矿勘探提供了确切的指导方向。     

赣北大湖塘矿床的含铌钽与含钨花岗岩成岩成矿特征对比研究

大湖塘钨多金属矿床位于江西北部三县（武宁、修水、靖安）交界处,是近年来发现的一个超大型钨矿床,与燕山期含钨花岗质岩浆活动密切相关。本次研究发现该区还存在含铌钽花岗斑岩,利用全岩地球化学特征、矿物的结构和主微量元素成分、以及锆石和铌铁矿族矿物U- Pb同位素年代学,对比含铌钽花岗斑岩和含钨似斑状花岗岩成岩成矿特征,以探讨两类不同成矿花岗岩的成因及成矿联系。研究得出： WingdingsAB@ 含铌钽花岗斑岩的U- Pb LA- ICP- MS锆石和铌铁矿族矿物同位素年龄分别为146±2 Ma和144±5 Ma,与含钨似斑状花岗岩的成岩成矿年龄（150~140Ma）接近;②含铌钽花岗斑岩全岩的Nb/Ta和Zr/Hf比值分别为1.7和13,云母为含锂白云母,Li2O和F含量最高可达2.1%和3.8%,K2O/Rb2O比值24,而含钨似斑状花岗岩中具有相对较高的Nb/Ta（~4.8）和Zr/Hf（~30）比值,云母也以白云母为主,含有0.32% Li2O和1.5% F,K2O/Rb2O比值88,表明含铌钽花岗斑岩的演化程度比含钨似斑状花岗岩更高;③两类花岗岩中的成矿指示性矿物有明显差异,含铌钽花岗斑岩中包括具有岩浆成因特征的铌铁矿族矿物、钨铌锰矿、锡锰钽矿、含铌钽黑钨矿、含铌钽金红石和富集稀有金属元素的含锂白云母;而含钨似斑状花岗岩中主要体现为热液期形成的黑钨矿、白钨矿、金红石和锡石。本次研究认为,含铌钽花岗斑岩的原始岩浆中富含铌钽钨等元素,高挥发组分和岩浆流体的作用有利于岩浆期稀有金属成矿作用的发生;而含钨似斑状花岗岩中钨成矿作用发生在岩浆作用的后期,与后期流体作用相关性更大,这些信息也验证了大湖塘矿床发生了多期多阶段钨锡稀有金属成矿作用。     

A combined EMPA and LA-ICP-MS study of Li-bearing mica and Sn–Ti oxide minerals from the Qiguling topaz rhyolite (Qitianling District,China): The role of fluorine in origin of tin mineralization

The Sn-rich Qiguling topaz rhyolite dike intrudes the Qitianling biotite granite of the Nanling Range in southern China; the granite hosts the large Furong Sn deposit. The rhyolite dike is typically peraluminous, volatile-enriched, and highly evolved. Whole-rock F and Sn concentrations attain 1.9 wt.% and 2700 ppm, respectively. The rhyolite consists of a fine-grained matrix formed by quartz, feldspar, mica and topaz, enclosing phenocrysts of quartz, feldspar and mica; it is locally crosscut by quartz veinlets. Lithium-bearing micas in both phenocrysts and the groundmass can be classified as primary zinnwaldite, “Mus-Ann” (intermediate member between annite and muscovite), and secondary Fe-rich muscovite. Topaz is present in the groundmass only; common fluorite occurs in the groundmass and also in a specific cassiterite, rutile and fluorite (Sn–Ti–F) assemblage. Cassiterite and rutile are the only Sn and Ti minerals; both cassiterite and Nb-rich rutile are commonly included in the phenocrysts. The Sn–Ti–F assemblage is pervasive, and contains spongy cassiterite in some cases; cassiterite also occurs in quartz veinlets which cut the groundmass. Electron microprobe and LA-ICP-MS compositions were used to study the magmatic and hydrothermal processes and the role of F in Sn mineralization. The presence of zinnwaldite and “Mus-Ann”, which are respectively representative of early and late mica crystallization during magma differentiation, also suggests a significant decrease in f(HF)/f(H₂O) of the system. Cassiterite included in the zinnwaldite phenocrysts is suggested to have crystallized from the primary magma at high temperature. Within the Sn–Ti–F aggregates, rutile crystallized as the earliest mineral, followed by fluorite and cassiterite. Spongy cassiterite containing inclusions of the groundmass minerals indicate a low viscosity of the late fluid. The cassiterite in the quartz veinlets crystallized from low-temperature hydrothermal fluids, which possibly mixed with meteoric water. In general, cassiterite precipitated during both magmatic and hydrothermal stages, and over a range of temperatures. The original fluorine and tin enrichments, f(HF)/f(H₂O) change in the residual magma, formation of Ca,Sn,F-rich immiscible fluid, decrease of the f(HF) during groundmass crystallization, and mixing of magma-derived fluids with low-saline meteoric water during the late hydrothermal stage, are all factors independently or together responsible for the Sn mineralization in the Qiguling rhyolite.     

Geochemistry of cassiterite and wolframite from tin and tungsten quartz veins in Portugal

Cassiterite and wolframite compositions from Sn > W- and W > Sn-bearing quartz veins in Northern and Central Portugal are compared to provide evidence on fluid compositions. In Sn > W-bearing quartz veins, euhedral cassiterite shows sequences of alternating parallel darker and lighter zones. The darker zones are pleochroic, oscillatory zoned, exhibit exsolutions of columbite and ixiolite and are richer in Nb, Ta and Fe than the lighter zones which consist of nearly pure SnO₂. Cassiterite from W > Sn-bearing quartz veins is usually zoned, with homogeneous and slightly pleochroic darker zones, which are chemically similar to lighter zones. Both zones have inclusions of rutile and rare ilmenite. The darker zones of cassiterite from the former veins are richer in Nb, Ta and Fe contents and poorer in Ti than the darker and lighter zones of cassiterite from the latter veins. This is attributed to differences in the composition of magmatic hydrothermal fluids.Wolframite compositions from Sn > W- and W > Sn-bearing quartz veins do not show any significant distinction, because they precipitate from relatively similar magmatic hydrothermal fluids. In some deposits, most wolframite crystals are homogeneous, but others are heterogeneous. Inner patches, rich in a hübnerite component, rarely occur in crystals from the Filharoso and Panasqueira deposits. Zoned crystals, showing an increase in Fe and a decrease in Mn from core to rim, were found in the Vale das Gatas deposit. Complex oscillatory zoned crystals occur. In the Carris deposit, later wolframite contains inclusions of scheelite, partially replaces it and is richer in Fe and poorer in Mn than earlier wolframite. Wolframite from Sn > W-bearing quartz veins in the Argozelo deposit and W > Sn-bearing quartz veins from Vale das Gatas and Panasqueira deposits has significant Nb content. This does not depend on the Fe and Mn content of the wolframite, but W content is negatively correlated with Nb content. Only very rare single crystals of wolframite show an increase in W and a decrease in Nb from core to rim. Sn > W-bearing quartz veins contain wolframite poorer in Nb than the darker zones of cassiterite, which exsolved columbite and ixiolite. In W > Sn-bearing quartz veins from Panasqueira and Vale das Gatas, the wolframite has a higher Nb content than the cassiterite, which contains rutile inclusions enriched in Nb, because cassiterite and wolframite are derived from two distinct magmatic hydrothermal fluids of different age. The fluid responsible for wolframite precipitation will have a similar composition to that resulting from the evolution of the fluid responsible for cassiterite precipitation in the Sn > W-bearing quartz veins.     

赣中聚源大型石英脉型白钨矿床含铀富钨矿物初步研究

聚源钨矿是华南地区为数不多的大型石英脉型白钨矿矿床之一。在详细的野外地质调查基础上,本文利用α径迹蚀刻、电子显微镜、扫描电镜以及电子探针等实验手段,对该矿床含钨和含铀矿物开展了精细矿物学的研究工作,探讨了成矿过程中钨和铀的富集规律。研究显示,该矿床钨铀矿物的形成可分为四个阶段:第一阶段,钨铀主要进入富含Nb、Ti的氧化物矿物,形成铌铁矿、钇易解石等富钨矿物,另有极少量的钨进入黑钨矿和早阶段白钨矿;第二阶段,铌铁矿与钇易解石被后期流体交代,形成含钨富铀的骑田岭矿、铌锰矿以及钛-钇易解石;第三阶段,钨进入中阶段白钨矿,这一阶段也是钨最主要的矿化阶段;第四阶段,钨进入晚阶段白钨矿。最后两阶段白钨矿中铀含量不高。骑田岭矿(WO_3 26.74%～29.68%),是聚源钨矿中除白钨矿和黑钨矿之外钨含量最高的含钨矿物。该矿易解石族矿物WO_3最高可达9.80%,极度富钨,是目前有文可查的钨含量最高的易解石。聚源钨矿中的含钨矿物大多数为白钨矿,但绝大多数的白钨矿却在骑田岭矿、易解石族矿物、铌铁矿族矿物、黑钨矿之后形成,说明成矿流体在演化过程中,绝大多数W首先进入富含Nb、Ti的含铀矿物和少量黑钨矿,之后才是白钨矿的大量结晶。     

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.     

柿竹园钨锡多金属矿床矽卡岩中碱交代脉研究

柿竹园钨锡多金属矿床地处南岭中段,矿种多、规模大、共生组分丰富,是世界罕见的超大型钨锡钼铋多金属矿床。区内发育有大量不同类型的脉体,包括酸性岩浆岩脉、云英岩脉、碱交代脉等,其中发育于矽卡岩中的碱交代脉是矿区规模最大、分布最广的矿体。本文通过详实的野外地质调研、显微镜下岩相学鉴定以及电子探针测试分析,发现大部分碱交代脉中以钾长石、斜长石、石英、萤石为主,白云母含量较少,一般小于3%,含少量黄玉、电气石等矿物,并非前人所称的"云英岩脉"或"云英岩网脉",脉体外侧发育较多的石榴子石、透辉石等矽卡岩类矿物,脉体及其两侧含有较多的白钨矿、磁铁矿等氧化物。从矿物组合和矿化特点上分析,碱交代脉总体碱质成分含量较高,发生了较强的碱交代作用,脉体的形成与矽卡岩演化关系密切,可进一步分为:早期阶段碱交代脉,富斜长石、黑钨矿,形成矽卡岩,对应矽卡岩演化的矽卡岩阶段,是黑钨矿的主成矿期;晚期阶段碱交代脉,富钾长石、白钨矿、磁铁矿,表现为交代矽卡岩,对应矽卡岩演化的退变质阶段,是白钨矿的主成矿期。综上,柿竹园矿床矽卡岩中碱交代脉,制约和影响着矽卡岩的形成与成矿,贯穿矽卡岩演化过程的矽卡岩阶段和退变质阶段,其形成的矿体为矽卡岩型矿体。     

西昆仑塔什库尔干地区赞坎铁矿床磁铁矿元素地球化学特征及其对成矿的制约

赞坎铁矿床是塔什库尔干地区一个典型的沉积变质型铁矿,具有多阶段成矿的特征,是塔什库尔干地区铁矿成矿作用演化的典型代表。文章将赞坎铁矿床主要矿石矿物磁铁矿的形成划分为3个世代,分别为条带状磁铁矿、浸染状磁铁矿和粗晶脉状或块状磁铁矿,分别代表3个成矿阶段的产物。电子探针和LAICP-MS原位分析表明,赞坎铁矿从条带状磁铁矿到粗晶块状磁铁矿随着磁铁矿的成矿演化主量元素中Al元素有减少的趋势,而Ti、Mn、Mg、V元素均具有增加的趋势;微量元素中Co、Nb、Hf、Ta等具有减少的趋势,Sc、Ga、Zr、Sn等元素具有增加的趋势。根据以上各成矿阶段中磁铁矿成分变化,并结合前人的研究成果发现,赞坎铁矿早期条带状磁铁矿与火山沉积作用有关,成矿后期特别是在粗晶块状和脉状磁铁矿阶段受岩浆热液影响明显,富铁矿有岩浆热液的参与。     

Hydrothermal processes and shifting element association patterns in the W—Sn enriched granite of Regoufe, Portugal

Combined research in geochemistry and mineral chemistry of the hydrothermally altered W-Sn specialized granite of Regoufe and its derivatives in Portugal was undertaken to gain insight in the mineralogical changes associated with hydrothermal processes within a single granite cupola. Over 1000 unpolished rock sections were analyzed by automated X-ray fluorescence spectrometry (XRF). On the basis of the XRF data, a small number of these same sections was selected for investigation by electron probe microanalysis. The study focuses on fourteen elements of interest that are measurable with the chosen techniques. Major pervasive alteration within the Regoufe granite is virtually contemporaneous with mineralization in the form of Sn- or W-bearing quartz veins. Two phases of hydrothermal activity are discerned, characterized by different element associations. Fluids of the first phase were especially rich in Sn, Cs and F, whereas the second phase was marked by a W-Ta-Nb-Rb association and presumably carried less F. Phosphorus probably was an important fluid component in both phases. The fluids are inferred to have fractionated from a related granitic magma at depth.Tin, W, Nb and Ta are mainly found as substitutions or inclusions in biotite in the least altered part of the Regoufe granite. Tantalo-niobian rutile is an important control for the distribution of Nb. Tin occurs in rutile and rarely as cassiterite. Muscovitization caused leaching of Ti and Zr from the granite. Tin, supplied or mobilized by the hydrothermal fluids, behaves differently from W, Nb and Ta. In the most altered rocks, muscovite hosts significant amounts of Sn. Whereas Sn is still related to Cs and Ti, elements that probably represent altered biotite, W, Ta and Nb are related to newly formed Rb-rich muscovite. Columbitetantalite was detected embedded in late muscovite. In contrast to Sn, the fluid-supplied W was predominantly deposited as wolframite in quartz veins and the altered granite is not enriched in W compared to the relatively unaltered rocks. Strontium is preferentially hosted by K-feldspar in the least altered granite; Ca in this rock is still partly contained in albite. With increasing albitization and muscovitization, Sr and Ca were released and are partly bound in newly formed apatite. The primary magmatic apatites have near-ideal formula compositions, but mobilization of P during hydrothermal activity resulted in the formation of Mn-rich apatite in all parts of the granite, and Sr- and probably Li-rich varieties in the most altered rocks. Eosphorite, and scorodite as the oxidation product of arsenopyrite, were also formed as a result of P mobilization. In the least altered rocks, Cs is mainly contained in biotite. In the most altered granite and aplitic rocks, enrichment of Cs and Rb is evenly distributed over K-feldspar and micas. The processes that lead to increased Rb are partly independent of Cs enrichment, and apparently related to the W-Nb-Ta mineralization event, separate from the preceding Sn mineralization.     

Mineralogy, fluid inclusion, and oxygen isotope constraints on the genesis of the Lalla Zahra W-(Cu) deposit, Alouana district, northeastern Morocco

The Lalla Zahra W-(Cu) prospect of northeastern Morocco is hosted in a Devonian volcaniclastic and metasedimentary sequence composed of graywacke, siltstone, pelite, and shale interlayered with minor tuff and mudstone. Intrusion of the 284?±?7 Ma Alouana concentrically zoned, two micas, calc-alkaline, and post-collisional Alouana granitoid pluton has contact metamorphosed the host rocks, giving rise to a metamorphic assemblage of quartz, plagioclase, biotite, muscovite, chlorite, and alusite, and cordierite. The mineralization occurs in and along subvertical, 20 to 40 cm thick, and structurally controlled tensional veins composed of quartz accompanied by molybdenite, wolframite, scheelite, base metal sulphides, carbonates, barite, and fluorite. Three main stages of mineralization (I, II, and III), each characterized by a specific mineral assemblage and/or texture, are recognized. Quartz dominates in all the veins and commonly displays multiple stages of vein filling and brecciation, and a variety of textures. The early tungsten-bearing stage consists of quartz-1, tourmaline, muscovite, wolframite, scheelite, and molybdenite. With advancing paragenetic sequence, the mineralogy of the veins shifted from stage I tungsten-bearing mineralization through stage II, dominated by base metal sulphides, to stage III with late barren carbonates and barite?±?fluorite mineral assemblages. Pervasive hydrothermal alteration affected, to varying degrees, the Alouana intrusion, resulting in microclinization, albitization, episyenitization, and greisenization of all the granitic units. Fluid inclusion data yield homogenization temperatures ranging from 124°C to 447°C for calculated salinity estimates in the range of 0.4 to ~60 wt% NaCl equiv. Similarly, the δ¹⁸O values for the three generations of quartz range from 11.7‰ to 13.9‰ V-SMOW. Calculated δ¹⁸O values of the parent fluid in the range between ?3‰ and +9‰ V-SMOW are consistent either with a mixture of water of different origins, including magmatic water, or an origin from seawater or meteoric water that probably exchanged oxygen with rocks at elevated temperatures. The coexistence of CO₂-rich and H₂O-rich fluid inclusions reflect the presence of a boiling fluid associated with the deposition of the early tungsten-bearing stage mineralization at relatively high temperature. The general temperature and salinity decrease with advancing paragenetic sequence suggest that the early high temperature, magmatic, highly saline, and boiling fluid mixed with meteoric non-boiling fluid results in the precipitation of base metal sulphide and carbonate–barite stage mineral assemblages, respectively.     

Immiscibilty between silicate magma and aqueous fluids in Egyptian rare-metal granites: melt and fluid inclusions study

Rare-metal granites of Nuweibi and Abu Dabbab, central Eastern Desert of Egypt, have mineralogical and geochemical specialization. These granites are acidic, slightly peraluminous to metaaluminous, Li–F–Na-rich, and Sn–Nb–Ta-mineralized. Snowball textures, homogenous distribution of rock-forming accessory minerals, disseminated mineralization, and melt inclusions in quartz phenocrysts are typical features indicative of their petrographic specialization. Geochemical characterizations are consistent with low-P-rare metal granite derived from highly evolved I-type magma in the late stage of crystallization. Melt and fluid inclusions were studied in granites, mineralized veins, and greisen. The study revealed that at least two stages of liquid immiscibility played an important role in the evolution of magma–hydrothermal transition as well as mineral deposition. The early stage is melt/fluid case. This stage is represented by the coexistence of type-B melt and aqueous-CO₂ inclusions in association with topaz, columbite–tantalite, as well as cassiterite mineral inclusions. This stage seems to have taken place at the late magmatic stage at temperatures between 450 °C and 550 °C. The late magmatic to early hydrothermal stage is represented by vapor-rich H₂O and CO₂ inclusions, sometimes with small crystallized silicic melt in greisen and the outer margins of the mineralized veins. These inclusions are associated with beryl, topaz, and cassiterite mineralization and probably trapped at 400 °C. The last stage of immiscibility is fluid–fluid and represented by the coexisting H₂O-rich and CO₂-rich inclusions. Cassiterite, wolframite ± chalcopyrite, and fluorite are the main mineral assemblage in this stage. The trapping temperature was estimated between 200 °C and 350 °C. The latest phase of fluid is low-saline, low-temperature (100–180 °C), and liquid-rich aqueous fluid.     

Lithium-mica composition as pathfinder and recorder of Grenvillian-age greisenization,Rondonia Tin Province,Brazil

The tin-greisens of the Rondonia Tin Province, Brazil, are related with the intrusion of a 995−975 Ma evolved rapakivi granite suite interpreted as post-collisional with respect to the Grenvillian orogeny during assembly of Rodinia. Lithium-iron mica (‘zinnwaldite’) is the main mineral in late- to post-magmatic and ore stages of such greisens, and has the potential of being a recorder of the mineralization processes. We provide bulk rock geochemistry of granite, greisen, and greisenized granite, coupled with in-situ major and trace element analyses in mica. Trace element and Li contents in mica were assessed via LA-ICP-MS analysis to avoid interference from ore-mineral inclusions. There is a large-scale zoning (hundreds of meters) of the composition of magmatic mica within the massif. Within 200 m of greisen zones, the mica composition in granite becomes similar to hydrothermal greisen mica, i.e. mica composition is suggested as a proximity indicator for greisen. Mica records the evolution of the system from magmatic to hydrothermal. Early-magmatic mica is Li, Rb and F poor and Mg, Ti and Fe rich, as opposed to greisen mica. Rare metals (e.g. Sn, Ta, W) display complex behavior, as their content in mica increases from magmatic to transitional stages, but decreases from transitional to ore (greisen and vein) stages. This can be explained by a complex interaction between enrichment of metals in the fluid, crystallization order of HFSE-bearing minerals, a decrease in the acceptance of HFSE in mica due to Ti depletion, and a change in the system from melt-dominated to fluid-dominated. Depletion of rare metals in mica can be an important factor for mineralization, since binding these metals to silicates reduces the amount of ore minerals. In granite, up to 86 % of Sn is bound to mica, while in greisen, up to 95 % of it is available to form cassiterite. Niobium behaves differently than other rare metals, likely due to its very high initial partition coefficient in mica and its lower solubility in fluids when compared to Sn and Ta. As such, changes in the Nb/Sn ratio in mica can be used as a proxy for the rock/fluid ratios. Mica pseudomorphs after feldspar in greisenized granite have anomalously high Sr contents inherited from their albite precursor.