Geochemical characteristics and spectrometric prospecting in the muscovite-bearing pegmatites and granites, southeastern Aswan, Egypt

Rare metal mineralization of Sn, Nb-Ta and W is encountered in the Gebel Dihmit area (GDA), south- eastern Aswan, Egypt. The mineralization is related to muscovite granites and their pegmatite derivatives. The peg- matites are divided into three types according to their main mineral assemblages: K-feldspar-muscovite-tourmaline, K-feldspar-albite-muscovite and albite-K-feldspar-lepidolite veins. Petrogenetic studies indicate that Sn and Nb-Ta mineralization extends from the late-magmatic stage to the pegmatite and hydrothermal stages of the (GDA) suite. The albite-K-feldspar-lepidolite granite is composed dominantly of albite, lepidolote, and quartz, with topaz, K-feldspar and amblygonite. The accessory minerals are zircon, monazite, pollucite, columbite-tantalite, microlite and Ta-rich cassiterite. Phenocrysts of quartz, topaz and K-feldspar contain abundant inclusions of albite laths and occasional lepidolite crystals along growth zones (snowball texture), indicating simultaneous crystallization from a subsolvus, residual magma. The origin of the pegmatites is attributed to extreme differentiation by fractional crystal- lization of a granitic magma. The economic potential for rare metals was evaluated in the geochemical discrimination diagrams. Accordingly, some of the pegmatites are not only highly differentiated in terms of alkalis, but also the promising targets for small-scale Ta and, to a less extent, Sn. The pegmatites also provide the first example of Fe-Mn and Nb-Ta fractionation in successive generations of granites to cassiterite-bearing pegmatites, which perfectly ex- hibit similar fractionation trends established for primary columbite-tantalite in the corresponding categories of peg- matites. Uranium and Th of magmatic origin are indicated by the presence of thorite and allanite, whereas evidence of hydrothermal mineralization is the alteration of rock- foring minerals such as feldspar and the formation of sec- ondary minerals such as uranophane..

The enhanced element enrichment in the supercritical states of granite–pegmatite systems

In this paper, we show that supercritical fluids have a greater significance in the generation of pegmatites,and for ore-forming processes related to granites than is usually assumed. We show that the supercritical melt or fluid is a silicate phase in which volatiles; principally H_2O are completely miscible in all proportions at magmatic temperatures and pressures. This phase evolves from felsic melts and changes into hydrothermal fluids, and its unique properties are particularly important in sequestering and concentrating low abundance elements, such as metals. In our past research, we have focused on processes observed at upper crustal levels, however extensive work by us and other researchers have demonstrated that supercritical melt/fluids should be abundant in melting zones at deep-crustal levels too. We propose that these fluids may provide a connecting link between lower and upper crustal magmas,and a highly efficient transport mechanism for usually melt incompatible elements. In this paper, we explore the unique features of this fluid which allow the partitioning of variouselements and compounds, potentially up to extreme levels,and may explain various features both of mineralization and the magmas that produced them.

Timing of granite pegmatite-type high-purity quartz deposit in the Eastern Qinling,China:constraints from in-situ LA-ICP-MS trace analyses of quartz and monazite U–Pb dating

Eastern Qinling,China is one of the important rare metal metallogenic provinces with extensively distributed granite pegmatite dikes.The No.5 granite pegmatite intruded into the granitic gneiss of the Qinling Group,and the major minerals are quartz(39.8%),K-feldspar(18.8%),albite(36.3%),muscovite(3.4%),and garnet(1.1%).Monazite U–Pb isotopic dating indicates that the No.5 pegmatite from the Eastern Qinling was emplaced at ca.420.2±2.2 Ma,which confirms that highpurity quartz mineralization probably formed during the Early Devonian.In-situ laser ablation inductively coupled plasma mass spectrometry analysis of quartz show that quartz samples from Eastern Qinling have total trace element concentrations(Al,Ti,Sc,Li,B,Cr,Mn,and Fe)ranging from 23.2 to 52.8 ppm,slightly higher than the quartz(impurity element content from 13.4 to 25.9 ppm)of the Spruce Pine high-purity quartz deposit in western North Carolina.The No.5 pegmatite of Eastern Qinling could be defined as one high-purity quartz deposit of China.

Petrological and mineralogical characteristics of younger granites and pegmatites in the Wadi Haleifiya area, southeastern Sinai, Egypt

This study is concerned with the radioactivity and mineralogy of the younger granites and pegmatites in the Wadi Haleifiya area, southeastern Sinai Peninsula, Egypt. The area is occupied by metasediments, migmatites, older and younger granites. Most of these rocks, especially granites, are dissected by mafic and felsic dykes as well as pegmatites. The younger granites are represented by three main varieties: monzogranites, syenogranites and alkali feldspar granites. The monzogranite consists essentially of quartz, plagioclase, potash feldspar and biotite with minor musco-vite. Iron oxide, titanite, zircon and allanite are the main accessory minerals. Syenogranite is massive, medium- to coarse-grained and commonly exhibits equigranular and hypidiomorphic textures. It is made up essentially of potash feldspar, quartz, plagioclase and biotite. Iron oxides, allanite, epidote, titanite, and zircon are accessory minerals. The alkali feldspar granite consists mainly of perthite, quartz, alkali amphibole (arfvedsonite and riebekite), biotite, sub-ordinate plagioclase and aegirine. Iron oxide, zircon and apatite are accessory minerals, whereas chlorite and sas-surite are secondary minerals. The altered monzogranite and pegmatite recorded high radioelement contents. The eU reaches up to 120 (av.=82×10-6) in the altered monzogranite and up to 55 (av.=27×10-6) in the pegmatites. The high radioactivity in the altered monzogranite is due to the presence of thorite, uranothorite and metamict zircon. In the pegmatites, it is re-lated to the presence of uranophane, uranothorite, thorite, zircon, samarskite, monazite, xenotime, magnetite, ilmen-ite, hematite and rutile.

Fluid Characteristics and Evolution of the Zhawulong Granitic Pegmatite Lithium Deposit in the Ganzi-Songpan Region, Southwestern China

The Zhawulong granitic pegmatite lithium deposit is located in the Ganzi-Songpan orogenic belt.Fluid inclusions in spodumene and coexisting quartz were studied to understand the cooling path and evolution of fluid within albite–spodumene pegmatite.There are three distinguishable types of fluid inclusions:crystal-rich,CO2–NaCl–H2 O,and NaCl–H2 O.At more than 500°C and 350~480 MPa,crystal-rich fluid inclusions were captured during the pegmatitic magma-hydrothermal transition stage,characterized by a dense hydrous alkali borosilicate fluid with a carbonate component.Between 412°C and 278°C,CO2–Na Cl–H2 Ofluid inclusions developed in spodumene(I)and quartz(II)with a low salinity(3.3–11.9 wt%NaCl equivalent)and a high volatile content,which represent the boundary between the transition stage and the hydrothermal stage.The subsequentNaCl–H2 Ofluid inclusions from the hydrothermal stage,between 189°C and 302°C,have a low salinity(1.1–13.9 wt%NaCl equivalent).The various types of fluid inclusions reveal the P–T conditions of pegmatite formation,which marks the transition process from magmatic to hydrothermal.The oreforming fluids from the Zhawulong deposit have many of the same characteristics as those from the Jiajika lithium deposit.The ore-forming fluid provided not only materials for crystallization of rare metal minerals,such as spodumene and beryl,but also the ideal conditions forthe growth of ore minerals.Therefore,this area has favorable conditions for lithium enrichment and excellent prospecting potential.

Geochemistry of the uranium-thurium-bearing granitic rocks and pegmatites of Wadi Haleifiya area,Southeastern Sinai,Egypt

There are two main granitic rocks cropping out in the study area:1) the syn-orogenic granites are moderately weathered,jointed,exfoliated and characterized by low relief.These rocks are subdivided into tonalite and granodiorite.They are essentially composed of plagioclase,quartz,biotite,hornblende and potash feldspar;and 2) the post-orogenic granites,characterized by high relief terrain and represented by monzogranite,syenogranite and alkali granite.The monzogranites suffered hydrothermal alteration in particular along joints,faults,shear zones and fractures,which recorded the highest values of radioactivity,reflecting the role of post-magmatic alteration processes in the enhancement of radioactivity.The hydrothermal alteration(desilicification and hematitization) resulted in the formation of mineralized(altered) granites.The altered granites are enriched in TiO 2,Al 2 O 3,FeO T,MnO,MgO,Na 2 O,Rb,Sr,Y,Zr,Zn,Ga and Co and depleted in SiO 2,CaO,P 2 O 5,Nb,Pb,Cu,Ni and Cr relative to the fresh monzogranite.The investigated granites contain basic xenoliths as well as pockets of pegmatites.Perthites,quartz,plagioclase and sometimes biotite,represent the essential constituents.Some accessory minerals like zircon are metamicted reflecting their radiogenic nature.The alkali granites are characterized by the presence of aegirine,rebeckite and arfvedsonite.Both syn-and post-orogenic granites show some variations in their bulk chemical compositions.The older granitoids are metaluminous and exhibit characteristics of I-type granites and possess an arc tectonic environment.On the other hand,the younger granites are peraluminous and exhibit the characteristics of post-collisional granites.It is interpreted that radioactivity of the studied rocks is mainly controlled by both magmatic and post-magmatic activities.Frequently,the post-orogenic granites host zoned and unzoned pegmatite pockets.Some of these pockets anomalously attain high radioactivity.The syenogranites and the pegmatites are characterized by high contents of SiO 2 and K 2 O and low CaO and MgO.They have transitional characters from highly fractionated calc-alkaline to alkaline.The alkali granites related to A2-subtype of A-type granites.The post-orogenic granites were originated from magma of dominant crustal source materials and related to post-collisional setting under extensional environment.

Petrogenetic and Metallogenetic Characteristics of the Xikeng Granitic Pegmatites, Fujian Province

The Xikeng pegmatite field lies on the eastern margin of the south China fold system in Fujian Province,and it is located at the junction of three major tectonic units. The distribution of pegmatites is obviously controlled by the fold system.There exists apparent in jectionrelationship between the pegmatites and the surrounding Sinian schist and granulitite.The granitoidsextensively distributed in the field belong either to the Variscan or to the Yenshanian cycle,and it is evidentthat the pegmatites are genetically related to Variscan migmatitic granites. The pegmatites can be grouped into four types:muscovite-orthoclase-albite pegmatite（I）.muscovitedlbite-orthoclase pegmatite（Ⅱ）,muscovite-orthoclase-albite pegmatite（Ⅲ）,and muscovite-albitespodumene pegmatite（IV）.Owing to strong metasomatism and multi-stage emplacement of pegmatitic meltsolution,the sequence of interior assemblage zones in the pegmatites does not always represent the sequenceof original crystallization. The mineral composition of the pegmatites is extremely complicated.81 kinds of minerals have so farbeen found、From type I to type IV,the mineral assemblage tend to get increasingly complex.together withthe synchronous intensification of rare-metal and Sn mineralizations.Most of the type-IV pegmatites are ofeconomic value The features of fluid inclusions in the minerals are significantly different not only in different typos ofpegmatite,but also in different parts of a single pegmatite vein.Theδ18O values of migmatitic granite andpegmatites are comparatively low（9.3-10.4‰）,and those of rock-forming fluids are higher than 9.5‰ Isotopic ages of the pegmatites brangs from 235 to 328 Ma with initial 87Sr/86Sr ratios being ”.715-0.746. According to the temporal and spatial relationships between the pegmatites and the migmatitic granitecombined with the features of the pegmatites themselves,it can be concluded that the Xikeng pegmatites arethe product of differentiation closely related to the migmatitic granite.

The Ore-forming Mechanism of the Jiajika Pegmatite-Type Rare Metal Deposit in Western Sichuan Province:Evidence from Isotope Dating

Granitic pegmatites are commonly thought to form by fractional crystallization or by liquid immiscibility of granitic magma; however, these proposals are based mainly on analyses of fluid and melt inclusions. Here, we use the Jiajika pegmatite deposit, the largest spodumene deposit in Asia, as a case study to investigate ore forming processes using isotope dating. Dating of a single granite sample from the Jiajika deposit using multiple methods gave a zircon U-Pb SHRIMP age of 208.4 ~ 3.9 Ma, an 4~Ar/39Ar age for muscovite of 182.9 ~ 1.7 Ma, and an 4~Ar/39Ar age for biotite of 169.9 ＋ 1.6 Ma. Based on these dating results and the 4~Ar/39Ar age of muscovite from the Jiajika pegmatite, a temperature-time cooling track for the Jiajika granite was constructed using closure temperatures of the different isotope systems. This track indicates that the granite cooled over ^-40 m. y., with segregation of the pegmatite fluid from the granitic magma at a temperature of ~700~C. This result suggests that the Jiajika pegmatite formed not by fractional crystallization, but by segregation of an immiscible liquid from the granitic magma. When compared with fractional crystallization, the relatively early timing of segregation of an immiscible liquid from a granitic magma can prevent the precipitation of ore-forming elements during crystallization, and suggests that liquid immiscibility could be an important ore-forming process for rare metal pegmatities. We also conclude that isotope dating is a method that can potentially be used to determine the dominant ore-forming processes that occurred during the formation of granite-related ore deposits, and suggest that this method can be employed to determine the formation history of the W-Sn ore deposits found elsewhere within the Nanling Metallogenic Belt.

Geochemistry and Petrogenesis of Late Ediacaran Rare-metal Albite Granites of the Arabian-Nubian Shield

The Abu Dabbab albite granite(ADAG),in the central Eastern Desert of Egypt,hosts the most significant rare metal ore deposit in the northern part of the Neoproterozoic Arabian-Nubian Shield.Here,we report detailed field,petrographic,mineralogical and geochemical investigation of the ADAG,an isolated stock-like granitic body with sharp intrusive contacts against metamorphic country rocks,probably emplaced at about 600 Ma.The fine-grained porphyritic upper unit is a preserved remnant of the shallowly-emplaced apex of the magma chamber,whereas the medium-grained lower unit crystallized at deeper levels under subvolcanic conditions.The peraluminous leucocratic ADAG shares common geochemical characteristics with post-collisional intraplate A-type magmas.In addition to the conspicuous enrichment in Na2O,the ADAG is remarkable for its anomalous concentrations of Ta,Nb,Li,Hf,Ga,Sn,Zn and heavy rare-earth elements.Nb-Ta minerals in the ADAG are mixed with Fe-Mn oxides,forming black patches that increase in abundance toward of the base of the intrusion.Columbite-tantalite,cassiterite and wolframite are the most important ore minerals.Pronounced negative Eu anomalies(Eu/Eu*=0.10–0.24)reflect extreme magmatic fractionation and perhaps the effects of late fluid-rock interaction.The ADAG was most likely generated by partial melting of the juvenile middle crust of the ANS as the geotherm was elevated by erosional uplift following lithospheric delamination and it was emplaced at the intersection of lineations of structural weakness.Although formation of the ADAG and its primary enrichment in rare metals are essentially due to magmatic processes,late-stage metasomatism caused limited redistribution of rare metals.Fluid-driven subsolidus modification was limited to the apex of the magma chamber and drove development of greisen,amazonite,and quartz veins along fracture systems.

新疆瓦石峡南锂铍矿地质特征以及磷灰石对成矿的指示

新疆阿尔金地区近几年在稀有金属找矿方面取得了重大突破,新发现了瓦石峡南、阿亚克、吐格曼、稀长沟等多个稀有金属矿床。瓦石峡南锂铍矿位于阿尔金成矿带的西段,由新疆地质矿产局第三地质大队于2020年发现,共圈定伟晶岩脉20余条,含稀有金属花岗伟晶岩脉9条,现阶段勘查和研究程度较低。本文以矿区ρ9号脉含锂花岗伟晶岩脉中的磷灰石为研究对象,通过开展矿物学和地球化学特征分析,探讨其对花岗伟晶岩成矿的指示作用。显微镜和背散射图像观察显示,磷灰石可分为岩浆期和热液期两个期次。电子探针和LA-ICP-MS分析表明矿脉中磷灰石主要为氟-羟基磷灰石,地球化学特征指示ρ9号脉含锂花岗伟晶岩源于地壳物质部分熔融,是具有S型花岗岩特征的富磷花岗伟晶岩(平均P2O5>0.42%的高分异过铝质花岗岩),形成于低氧逸度的还原环境。通过探讨矿区花岗质岩浆的来源、成岩环境以及磷灰石对成矿的指示,推测瓦石峡南ρ9号脉含锂花岗伟晶岩的富磷特征是因为富磷过铝质岩浆体系对稀有金属的富集起到了促进作用。

东天山镜儿泉花岗伟晶岩型锂铍矿中石榴子石的地球化学特征:岩浆过程和稀有金属矿化的指示

石榴子石是花岗岩和花岗伟晶岩中的常见副矿物之一,能够保留岩浆演化和稀有金属矿化等重要信息。镜儿泉稀有金属矿床是东天山最为典型的花岗伟晶岩型锂铍矿床,其岩浆演化过程及Li-Be-Nb-Ta等稀有金属富集成矿动力学背景仍不清楚。对该矿床的白云母花岗岩和锂辉石伟晶岩中的石榴子石开展了电子探针(EPMA)及激光剥蚀电感耦合等离子质谱(LA-ICP-MS)仪原位微区主量、微量元素分析。结果表明:镜儿泉白云母花岗岩和锂辉石伟晶岩中的石榴子石主要以锰铝-铁铝榴石的固溶体形式产出,两端元组分总和超过95%,表现为富Mn、贫Ca的特征;白云母花岗岩中石榴子石富集重稀土元素(HREE)、亏损轻稀土元素(LREE)并具有Eu负异常,而锂辉石伟晶岩中石榴子石则以重稀土元素亏损和Eu负异常显著为特征,且Y、Sc、HREE含量在伟晶岩阶段有下降的趋势。综上所述,镜儿泉锂辉石伟晶岩中的石榴子石为典型的岩浆成因,石榴子石中Li、Na、Y、REE等元素具有耦合替代现象,随着岩浆分异程度增加,REE和Y含量呈递减趋势。此外,富锂伟晶岩中石榴子石具有较高的Nb、Ta含量,对伟晶岩铌钽矿化具有重要的指示意义。

Proterozoic Granitization of the Archaean Gneisses in the Central Zone of the Precambrian Limpopo High-grade Terrain

Our research covers the granitization and charnockitization processes that affected the metapelitic gneisses in the Central Zone of the Precambrian Limpopo high-grade terrain,South Africa.Precambrian granulite facies terrains underwent two regional high-grade events,of which the first one occurred

中国花岗岩型锂矿床:重要特征、成矿条件及形成机制

随着新能源汽车产业的快速发展和可控核聚变技术的不断革新,锂产业已成为各国竞相发展的新兴朝阳产业,全球锂资源争夺态势愈发激烈。中国是全球拥有花岗岩型锂矿床数量最多的国家,目前该类型锂矿占全国锂总供应量的1/4,进一步加强对该类型锂矿的研究和勘查对提升我国锂资源的自给能力至关重要。通过对全国40个主要花岗岩型锂矿床的时空分布、岩石序列、矿物演变、地球化学和锂独立矿物等特征的梳理,发现该类矿床主要形成于中生代晚侏罗世-早白垩世期间,主要集中在华南地区尤以华南腹地的南岭地区最为密集;近1/3的成矿岩体隐伏于地下,出露的岩体面积普遍较小,为0.07~5.7km^(2);花岗岩体垂直方向从下至上逐渐从黑云母二长花岗岩演变为锂云母钠长石花岗岩,其上通常发育云英岩和伟晶岩;锂及其他稀有元素(铷铯铍铌钽钨锡)一般在强钠长石花岗岩和云英岩中高度富集;黑云母二长花岗岩→含锂云母钠长花岗岩→云英岩,岩浆分异程度逐步增加且逐渐从熔体过渡到熔体-流体共存体系,全岩SiO_(2)含量、Nb/Ta和Zr/Hf比值、A/CNK和δEu值发生规律性变化;多数情况下岩体伴生煌斑岩脉、辉长岩脉、辉绿岩脉、花岗斑岩脉、细晶岩脉、霏细岩脉等各类脉体。总结规律提出:(1)伟晶岩壳是较早进入岩浆房内的岩浆与上覆围岩接触而冷却固结的产物,其构成岩浆房与外界的隔绝屏障,使Li、F、P、H_(2)O等易挥发组分无法逃逸;(2)较晚进入岩浆房的岩浆经历了长时间晶粥体与残留熔体的分凝过程,锂等稀有金属元素愈来愈富集于残余熔体中,最终形成富锂花岗岩和云英岩;(3)各类岩脉是岩浆房底部有持续热补给从而使残留含矿熔体能够逐步抽离上升的证据:基性岩脉来源于下伏高温地幔岩浆,不含矿中酸性斑岩脉是岩浆房底部堆晶体重熔的产物,含矿酸性斑岩脉和细粒岩脉来自岩浆房顶部富矿熔体-流体,三者沿地壳裂隙快速上升至地壳浅部就位。正是由于上覆伟晶岩壳形成的封闭体系和下伏幔源岩浆提供的充足热量,才使得岩浆房在热驱动机制下长期保持原地分异状态,最终形成花岗岩型锂矿床。

花岗伟晶岩分异演化与含矿性评价——从造岩矿物组构视角

高演化稀有金属伟晶岩的成矿过程是复杂和苛刻的,涉及到岩浆-热液过程热历史、岩浆迁移路径与成矿空间、侵位环境的过冷程度以及岩浆组分中稀有金属元素的初始富集等条件。而伟晶岩的分带特征是其形成过程的一种综合体现,不论是伟晶岩区域分带还是伟晶岩内部结构分带,都反映了伟晶岩岩浆结晶分异过程中岩浆的性质与形成环境,而这同时也赋予了造岩矿物在组构上的特殊性,形成遗传代码,对其进行解密,从而能够用于示踪与评估花岗伟晶岩的演化程度与成矿潜力。对于区域伟晶岩群的成矿潜力评估,由于含矿熔体在组分上的跨度较大,随着远离母体花岗岩体距离的增大,伟晶岩群演化程度增加,熔体中铁镁质组分以及Ca、Ba、Sr等碱土金属含量迅速降低,而挥发分、助熔剂组分、碱金属含量在残余熔体中逐渐增加,长石、云母与石英在类别和组构上产生显著变化;其中长石向钾-钠端元演化,且钠长石相对钾长石占据主导地位,云母由黑云母向白云母以及锂白云母转变,石英阴极发光特征与晶体结构及微量元素成分也表现出规律性的变化。受矿物晶格的限制,长石的K/Rb、K/Cs以及云母的K/Rb、K/Cs、Nb/Ta等比值特征能有效区分不同矿化潜力的伟晶岩群。石英的阴极发光特征能够揭示其生长环境与历史,石英的Li、Al、Ti、Ge等微量元素组成可以用来区分不同类型的伟晶岩矿床,并提供关于岩浆演化和成矿过程的重要线索。伟晶岩内部分带的形成主要受成矿熔体规模、过冷度以及成矿空间的封闭性等因素的控制,但在初始熔体成分上可以具有较大的变化。其中强分带型稀有金属伟晶岩记录了完整的岩浆-热液演化过程,不同阶段石英、长石和云母在晶体形态、微观结构以及微量元素组成上都具有显著变化。弱分带型稀有金属伟晶岩(钠长石-锂辉石伟晶岩)的造岩矿物组分在伟晶岩内部变化不大,其受构造控制明显,在空间上与贫矿伟晶岩之间可具有较大的矿物组成差异,表明二者之间存在流动分异过程。而长距离(以更厚的地壳或大型拆离断层为标志)的熔体迁移正是形成超大型伟晶岩稀有金属矿床的有利要素。

新疆阿尔金西段瓦石峡南锂铍稀有金属矿成矿背景与勘查进展

锂、铍等稀有金属矿产是重要的战略矿产资源。近年来,在阿尔金地区发现了多处稀有金属伟晶岩型矿床,已成为我国一处新的稀有金属成矿带,但调查研究水平总体较低。通过对阿尔金造山带的成矿动力背景的讨论,得出阿尔金造山带的稀有金属成矿作用涵盖了多个不同的造山运动构造演化阶段,证明该区域具备良好的稀有金属成矿条件,并具有巨大的找矿潜力。通过对位于阿尔金西段的瓦石峡南锂铍稀有金属矿进行勘查评价,发现其具有大型远景:瓦石峡南锂铍稀有金属矿体主要赋存于绿片岩相-角闪岩相变质岩系中的伟晶岩脉中,矿床类型为花岗伟晶岩型稀有金属矿床;已有勘查成果显示此矿床目前推断的稀有金属资源量达到中型以上矿床规模,并且随着勘查工作的进行,在深部及外围还有极大增储空间。研究成果对在阿尔金造山带内寻找同类型矿床具有借鉴意义。

新疆和田大红柳滩矿田稀有金属矿床的成矿机制

大红柳滩稀有金属矿田位于西昆仑中段,是松潘-甘孜-西昆仑花岗伟晶岩型稀有金属成矿带的重要组成部分,已发现白龙山、509道班西、大红柳滩东、507锂矿等大中型花岗伟晶岩型锂矿床7处,探获Li_(2)O储量达到1Mt以上,成矿潜力巨大。本文梳理了前人对大红柳滩稀有金属矿田的成矿特征及成矿作用研究,得出以下认识:(1)花岗伟晶岩与大红柳滩复式岩体形成于晚三叠世,两者空间关系密切,自岩体向远端可分成微斜长石型(矿物组合为微斜长石、石英和白云母)、锂辉石型(矿物组合为锂辉石、钠长石、石英和白云母)的分带规律,锂辉石伟晶岩多数分布在岩体外接触带1~2km范围内;(2)石英闪长岩、黑云母二长花岗岩和二云母二长花岗岩具有不同的地球化学特征以及ε_(Hf)(t)、ε_(Nd)(t)和δ^(7)Li值,是晚三叠世同碰撞构造背景下不同源区熔融的产物;(3)花岗伟晶岩与二云母二长花岗岩形成时代基本一致,具有相似的Hf、Li同位素特征,反映其源于相同的源区,形成于富白云母矿物的变沉积岩通过白云母脱水熔融;(4)初始熔体富助熔元素P、B、F和碱金属,能够增加H_(2)O在熔体中的溶解度,有利于Na、Li碱金属元素的富集,形成初始富锂熔体;(5)二云母二长花岗岩和花岗伟晶岩的空间关系、地球化学和Li同位素特征与岩浆分离结晶模型不同,与花岗岩浆的不混溶作用有关。综上所述,富挥发分、碱金属元素的初始富锂熔体上升过程中的熔体-流体分离作用可能是稀有金属元素超常富集的主要机制。大红柳滩复式岩体的外围,特别是二云母二长花岗岩的外接触带1~2km范围是寻找锂辉石伟晶岩的有利地区。

阿尔金锂铍花岗岩-伟晶岩成矿规律与资源潜力

阿尔金是原特提斯构造带,曾是锂铍金属成矿研究与找矿的空白区。通过科学分析,研究团队认为阿尔金锂铍研究空白区有找锂铍金属矿床的潜力,并于2018年率先进入阿尔金山无人区开展锂铍成矿作用的调查与研究、并发现多个花岗伟晶岩型锂铍矿床。本文对阿尔金中段地区花岗伟晶岩型锂铍矿床的成矿规律进行了梳理与总结,结果显示:(1)锂铍等稀有金属花岗伟晶岩类型多样,不同类型伟晶岩脉空间上分带,部分伟晶岩脉内部发育丰富的分带结构;(2)锂铍等稀有金属伟晶岩为花岗岩演化的产物,区域上发育有从黑云母花岗岩到二云母花岗岩、白云母花岗岩、钠长花岗岩及电气石伟晶岩、绿柱石伟晶岩、锡石伟晶岩、锂辉石伟晶岩、锂云母伟晶岩与铯沸石伟晶岩的分带结构;(3)花岗岩-伟晶岩成因于变泥砂岩在麻粒岩相变质过程中的黑云母脱水熔融形成的花岗岩浆的结晶分异,是区域构造演化的产物。吐格曼地区的锂铍矿床形成于阿南陆块与阿中陆块的拼贴-碰撞,而位于塔特布拉克花岗岩基两侧的瓦石峡南与塔木切锂铍矿集区的锂铍花岗伟晶岩则形成于三个微陆块的最终碰撞阶段。阿尔金中段地区早古生代花岗岩-伟晶岩发育,成矿条件优越,成矿潜力大,有望成为我国大型锂资源基地。

四川扎乌龙伟晶岩型稀有金属矿床的成矿机制及找矿标志

扎乌龙稀有金属矿床位于松潘-甘孜造山带,属于伟晶岩型锂辉石矿床,同时伴生铍和铌钽矿化。本文总结了扎乌龙矿床地球化学和矿物学特征,初步梳理了矿床成矿模式,并指出含矿性评价与找矿标志。扎乌龙伟晶岩脉在空间上围绕白云母花岗岩分布,具有类似的稀土元素和微量元素配分模式,但其稀土元素含量明显低于白云母花岗岩,表明伟晶岩脉为白云母花岗熔体分异演化的产物。扎乌龙白云母花岗岩岩石地球化学组分呈现高Rb/Sr和Rb/Ba、低CaO/Na_(2)O壳源特征,具有接近地壳的Sr-Nd-Hf同位素组成,表明其来源于松潘-甘孜大规模造山运动导致的西康群变泥质岩的深部重熔。矿物学和流体包裹体特征显示,扎乌龙伟晶岩脉的形成可划分为岩浆阶段和热液阶段。岩浆阶段主要结晶稀有金属矿物,如锂辉石、绿柱石和铌钽铁矿族矿物;热液阶段主要为原生矿物与流体发生再平衡,如原生锂辉石发生蚀变形成云母等矿物,原生绿柱石边部和内部缝隙产出相对富Cs_(2)O或Na_(2)O的次生绿柱石。锂矿物主要沉淀于相对封闭、高压(350MPa)的伟晶岩岩浆阶段。氢、氧同位素组成表明成矿流体主要来源于岩浆水,晚期流体来源于伟晶岩熔体的自身分异演化。扎乌龙锂辉石伟晶岩熔体分异程度属于中等,远低于高分异的新疆可可托海三号伟晶岩脉,而高于低分异的南爱尔兰Leinster伟晶岩脉。地质背景条件、围岩标志、断裂构造条件、矿物标型、物化探异常标志、遥感图像可作为扎乌龙重要找矿标志。

若羌塔什达坂锂矿床矿物分带特征及找矿意义

塔什达坂锂矿床位于阿尔金稀有金属成矿带的东段,锂矿体赋存于花岗质伟晶岩中,已圈定23条含锂花岗伟晶岩脉,含锂矿物主要为锂辉石、锂云母和锂电气石,伟晶岩脉主要为含锂电气石伟晶岩、锂辉石伟晶岩、锂云母伟晶岩及不含矿黑色电气石伟晶岩,矿物分带明显,其中ρ52号脉特征矿物变化最典型。塔什达坂锂矿床一区南部ρ52~ρ59、ρ58~ρ70之间的区域存在隐伏矿体,通过矿床地质特征及矿物分带研究,为区域锂矿的勘查评价提供找矿方向。

某花岗伟晶岩锂矿石中铷矿物的性质及含铷云母的回收

西昆仑509道班西花岗伟晶岩型锂多金属矿石中主要含铷矿物为白云母和微斜长石,为了在不影响主金属矿物锂辉石回收的情况下优先高效回收铷,开展了含铷矿物的矿物学研究及白云母浮选试验。研究表明:矿石中长石矿物种类较多,且以钠长石为主,微斜长石与之分离困难,因此,白云母是矿石中可回收的载铷矿物;白云母嵌布粒度粗细不均、以细粒居多,与钠长石等脉石矿物嵌布关系密切,宜在充分磨矿的情况下采用浮选工艺回收,但应避免较强的碱性环境,确保不影响后续浮锂;在以碳酸钠调浆、磨矿细度-0.074 mm占71.5%的情况下,以GYMN为抑制剂,GYR-3为捕收剂,采用1粗2精2扫闭路浮选流程处理,可获得Rb_(2)O品位0.65%的白云母精矿,白云母中的铷回收率达81.83%,云母的浮出为后续浮锂辉石创造了有利条件。