The Slyudyanogorsk muscovite deposit in the Middle Ural

The Slyudyanogorsk muscovite deposit of the central Urals has been known since 1884, but little geologic data are available in the literature. The muscovite occurrences are restricted to pegmatites found near the contact of the Late Precambrian Slyudyanogorsk Formation and the unconformably overlying Kurta Formation of Ordovician age. The country rock is dominantly metasedimentary in origin. Migmatization of schists is common and migmatites may be traced into pegmatites. The pegmatites may be classified on the basis of form into lens- and net-like veins and pipes that may be concordant or discordant to schistosity. Conformable pegmatites usually have higher mica contents and are distinctive in their extension to great depths. Transverse cutting types of pegmatites taper rapidly downward and are usually mica-free. On the basis Of composition, pegmatites may be divided into plagioclase (albite-oligoclase) and microcline varieties. Commercial muscovite occurrences are restricted to plagioclase pegmatites, as are the accessory ore minerals (molybdenite, chalcopyrite, pyrrhotite). The mica-bearing pegmatites usually have a more complex structure (zonal, cellular) than the massive mica-free pegmatites. The character and structure of the mica-bearing pegrnatites, the relicts of biotite within sheet muscovite and muscovite aggregates, the enlargement and replacement of biotite by muscovite in the surrounding wall rock, and the high iron content of the muscovite .suggest that muscovite is metasomatic after biotite in pegmatites that have formed from the wall rock by migmatization, recrystallization, and metasomatism. — R. D. DeRudder.     

Ore mineralization of the Amur stratiform zinc deposit (Southern Urals)

This paper deals with the geological structure of the Amur zinc deposit. The host shaly-carbonaceous flysch sediments are evaluated from the point of view of their precious metal, tungsten, and molybdenum potential. It is shown that the rare-metal mineralization is superimposed on a primarily sedimentary precious-metal mineralization and stratiform zinc ores. The discussed data permit us to look at these carbonaceous sediments as highly prospective for rare metal and precious metal mineralization.     

New data on mineralogy and geochemistry of rare-metal mineralization of the Gremiakha-Vyrmes Massif

Doklady Earth Sciences -     

喜马拉雅稀有金属成矿作用研究的新突破

喜马拉雅地区淡色花岗岩广泛分布,但相关的稀有金属成矿问题长期被学术界忽略,因为传统观点认为,这些花岗岩是高喜马拉雅变质岩系原地部分熔融而成。但自提出该地区淡色花岗岩高度结晶分异成因模式后,与这些花岗岩演化相关的稀有金属成矿问题引起各方重视,并在铍和铌钽的矿化研究方面取得显著进展。尽管如此,锂的成矿作用研究和资源寻找并没有取得大的突破。本期《岩石学报》报道的喜马拉雅中部琼嘉岗和热曲锂辉石伟晶岩及珠峰前进沟锂电气石-锂云母伟晶岩的发现,充分说明喜马拉雅地区锂资源前景广阔,表明喜马拉雅有望在近期内成为我国稀有金属资源的大型接替基地。根据目前的进展,喜马拉雅地区未来稀有金属成矿作用应加强如下方面的研究：1）加大区内淡色花岗岩岩石学与岩石成因研究力度,厘定它们岩浆结晶分异的程度与成矿潜力;2）对北喜马拉雅穹窿和岩体开展接触变质与围岩蚀变研究,以寻找热液交代型稀有金属矿床;3）加强高喜马拉雅地区藏南拆离系与花岗岩侵位关系的研究,以判断分异岩浆及成矿伟晶岩的赋存部位。近期应集中力量围绕普士拉一带的藏南拆离系、韧性变形的肉切村群地层和淡色花岗岩-伟晶岩等开展联合攻关研究,以期在锂资源上取得更大的突破。

     

白云母成分对富锂铍伟晶岩成因的指示：以卡鲁安稀有金属矿田为例

新疆阿尔泰造山带是我国重要的稀有金属矿床矿产资源基地,尤以富Li和富Be伟晶岩型矿床广泛发育为特色。本研究选择阿尔泰造山带卡鲁安-阿祖拜矿田富Li和富Be伟晶岩型矿床开展典型解剖,以贯穿岩浆阶段-伟晶岩阶段的白云母矿物为研究主线,探讨不同矿化类型伟晶岩中云母的成分演化规律、花岗岩与伟晶岩的成因联系。矿物学特征显示富Be伟晶岩中发育大量磷酸盐矿物,而富Li伟晶岩含较多橙色锰铝榴石、锂云母而缺乏典型的Fe-Mn磷酸盐。白云母成分分析显示,从白云母花岗岩→富Be伟晶岩→富Li伟晶岩,白云母总体呈Nb含量和Nb/Ta值降低,指示白云母花岗岩、富Be伟晶岩经历了不同程度的分离结晶作用,也代表了富Li伟晶岩的岩浆分异演化程度更高。尽管利用云母成分变化(尤其是K、Rb、Cs等大离子亲石元素)模拟岩浆结晶演化过程,显示可由初始花岗质岩浆经瑞利分离结晶作用依次形成白云母花岗岩→富Be伟晶岩→富Li伟晶岩的假设。但研究区年代学、矿物学、同位素证据指示富Li伟晶岩和富Be伟晶岩具有不同的熔体性质和形成时代。因此,应用云母成分探讨伟晶岩的成因联系应当建立在花岗岩-伟晶岩系统具有合理的时空分布和其它支持源自同一...     

Age of the Vishnyakovskoe deposit of rare-metal pegmatites (East Sayan): U-Pb geochronological study of manganotantalite

The U-Pb age of the manganotantalite from rare-metal pegmatites of the Vishnyakovskoe deposit (East Sayan Belt) has been assessed at 1838 ± 3 Ma. The acquired data indicate the pegmatites of this deposit and associated granites of the Sayan complex belong to the postcollision South Siberian igneous belt (1.88–1.84 Ga), which stretches along the southwestern frame of the Siberian Craton by more than 2500 km, from the Yenisei Ridge to the Aldan Shield. Formation of this igneous belt is related to joining (starting from about 1.9 Ga BP) of the series of continental microplates and island arcs to the Siberian Craton; this led to final stabilization of the craton at about 1.8 Ga BP.     

珠峰地区热曲锂辉石伟晶岩的发现及对喜马拉雅稀有金属成矿作用研究的启示

目前研究已经显示,喜马拉雅淡色花岗岩具有良好的铍-铌钽-锂等稀有金属成矿潜力。其中珠穆朗玛峰（后文简称珠峰）西侧的普士拉一带,是喜马拉雅地区锂辉石伟晶岩集中的区域。本文报道在普士拉东北的珠峰北侧热曲地区,发现有含锂辉石伟晶岩脉,这些伟晶岩呈透镜体状集中赋存于肉切村群"黄带层"大理岩与北坳组钙质硅酸岩的接触界线部位,同围岩一起经历了强烈的变形,且未出现明显内部分带结构,矿物组成中包含锂辉石、透锂长石、绿柱石、铌钽铁矿、锡石等锂-铍-铌钽-锡稀有金属矿物,其Li2O含量达1.30%~2.15%,显示经历过高程度分异演化的岩浆结晶特征。热曲含锂辉石伟晶岩的发现表明珠峰地区具有锂成矿的良好前景,是未来锂矿产勘查的重点靶区,而藏南拆离系韧性剪切带中的肉切村群"黄带层"下部与北坳组顶部位置,是锂辉石伟晶岩的重要富集层位,值得今后在锂资源寻找过程中予以充分关注。     

Trace elements and REE in the Cevonian clastic complexes of the Magnitogorsk Megazone, Southern Urals

The first data on trace-element geochemistry, REEs included, of the Devonian clastic and volcanosedimentary complexes in the Magnitogorsk Megazone have been obtained with ICP-MS. The correlation links and the character of distribution indicate that many elements, including those readily passing into solutions during weathering, were transferred as mechanical suspensions. Therefore, minerals concentrating these elements were largely preserved, as also were the distribution and concentrations of elements inherent to the source rocks. Both accessory minerals (apatite, zircon, Ti-minerals, and magnetite) and rock-forming minerals (pyroxene, amphibole, biotite, serpentine, chlorite, and plagioclase) were found among mineral concentrators. Clay minerals also seem to have participated in the processes. The typical elements of various complexes were identified. The distribution of trace elements is correlated with the stratigraphic position of rocks and depends on the character of the petrographic provinces.     

New data on geology of the Shatak Complex (western slope of the Southern Urals)

The comprehensive study of sections of the Shatak Complex has revealed that conglomerates at the base of Middle Riphean rocks are not basal but intraformational rocks. Previously described angular unconformities between shales of the Sukhin Subformation (Yusha Formation, R₁) and conglomerates of the Kuz”elga Subformation (Mashak Formation, R₂) are related to late tectonic movements. Magmatic rocks developed at the base of the Middle Riphean section are represented by sheet intrusions formed in the course of emplacement of a fluid-saturated magmatic melt into partially or completely lithified terrigenous rocks at the graben formation stage during the origination of synkinematic faults that served as magma conduits. It is inferred that distribution of provenances of clastic materials and sedimentation basins in the Burzyanian and Yurmatian should be scrutinized in the study region, because the normal regressive sequence of rocks from the uppermost Yusha Formation to the lowermost Mashak Formation, which was established in the Shatak Ridge, eliminates a clear boundary distinguished between them at present. The idea about an older age of the Mashak conglomerates is substantiated.     

Distribution patterns of rare-metal pegmatites in the Hindu Kush (Afghanistan)

In the Hindu Kush system of ranges, rare-metal pegmatites are spatially and genetically associated with granitoids of the Laghman complex, which form gigantic massifs in the Karakorum - South Pamir late Cimmerian fold region. Age of the granitoids and pegmatites is Early Cretaceous - Paleogene. Fields of rare-metal pegmatites occur in the roof of the massifs of biotite and two-mica granites in quartz-muscovite-biotite schists with garnet and staurolite, and in a lesser degree, these pegmatites are distributed among gabbro-diorites, gneisses, limestones, and amphibolites. The fields of rare-metal pegmatites on the largest scale and of practical importance are located in graben-synclines of the upper structural stage, where only the apical crests of massifs of the parent granites crop out. The pegmatite fields in Afganistan have been grouped into clearly defined belts extending for hundreds of kilometers. The principal belts of rare-metal pegmatites (Nuristan, Hindu Kush, and Badakhshan) are located in the surroundings of the rises in the Precambrian basement. —Authors.     

川西甲基卡锂矿床伟晶岩结构分带及多期岩浆成矿作用

LCT(lithium- cesium- tantalum)伟晶岩的分带有两种形式,一种是单个伟晶岩脉的内部结构分带,这种伟晶岩脉通常体积巨大,内部结构显示出成分分带的特征,单一脉体中不同结构带中可能发育不同的稀有金属矿化带,例如新疆可可托海3号伟晶岩脉;另一种分带性表现为伟晶岩和成矿系统的区域分带,通常以高分异的过铝质花岗岩为中心,围绕花岗岩数以百计的伟晶岩脉显示出不同的伟晶岩类型和矿化类型,越向外围,伟晶岩的演化程度越高。区域分带内的伟晶岩单个脉体的规模不大、内部分带性差、含矿性各不相同,甲基卡锂矿就是这一类伟晶岩矿床的典型代表。对甲基卡矿区伟晶岩的野外观察发现,含Be的9号脉、含Li的133号脉和含Nb、Ta的528号脉具有相对较好的内部结构分带性,而含Li的104号脉和308号脉的内部分带性则相对较差,推测与脉体内部多期岩浆- 热液活动有关。甲基卡矿区伟晶岩脉的相互穿插现象说明,矿区存在多期次的岩浆与成矿作用。科学钻探在JSD- 2和JSD- 3两个钻孔中均发现含锂辉石的伟晶岩脉和细晶岩脉侵入在不含矿的马颈子花岗岩中,佐证了多期岩浆与成矿事件的存在。伟晶岩中不同矿物U- Pb定年结果表明,全区伟晶岩的形成至少有两期,分别发生在213~206 Ma和199~191 Ma。依据钻孔JSD- 1的研究表明,岩浆由深至浅逐步向高分异方向演化。从下向上,花岗岩与伟晶岩同步演化,花岗岩依次出现黑云母花岗岩、含白云母的黑云母花岗岩、二云母花岗岩、白云母花岗岩和钠长石花岗岩,伟晶岩依次出现微斜长石型伟晶岩、微斜长石- 钠长石型伟晶岩、钠长石型伟晶岩和钠长石- 锂辉石型伟晶岩。根据不同深度伟晶岩的矿化特点,矿床的垂向分带大致划分如下：0~105 m的Li- Be- Nb- Ta矿化带;0~860 m的Be- Nb- Ta矿化带;0~1730 m的第一期Nb- Ta矿化带;1730~3170 m的无矿伟晶岩带;3170~3211 m的第二期Nb- Ta矿化带。     

青海查查香卡矿床铀、稀土元素矿化特征及成矿潜力分析

通过野外地质调查及实验室分析,探讨了查查香卡矿床含矿岩石岩性特征、铀矿化特征及稀土元素的富集,并对其成矿潜力进行了评价。     

Distribution of REE,Y, Sc,and Th in the unique complex rare-metal ores of the Tomtor deposit

The REE (Ln), Y, Sc, and Th distribution in the unique complex rare-metal ores of the Tomtor deposit is considered. Significant variability of these components and REE composition is revealed. Ore blocks with elevated Y and HREE contents are identified among prevailing LREE-enriched ores. It is established that the REE variations in the ores are correlated with evolution of REE carriers during epigenetic transformations of the carbonatite weathering products, in particular, with a replacement of Ce-bearing minerals (monazite and florencite) by Y-bearing mineral, xenotime. It is found that LREE and HREE exhibit different behavior during formation of the Tomtor ores, which is expressed in the inert behavior and residual accumulation of Ce-group REE at essential introduction of Y, HREE, Sc, and Th during epigenetic transformation of weathering products of carbonatites, which represent one of the main factors of the formation of the unique rare-metal ores of the Tomtor deposit.     

Triclinicity and barium content of potassium feldspars from muscovite pegmatites

Potassium feldspars in pegmatites of the Mama district are microclines and orthoclases. In granitoid pegmatites and undifferentiated vein pegmatites, unaffected by postmagmatic processes, the feldspars are represented by orthoclase with the X-ray triclinism (△p) as 0.0-0.4. Wherever postmagmatic solutions were active, in granitoid pegmatitic fields or zonal bodies of vein pegmatites, the feldspars are represented by microcline with △p as 0.5-1.0. At that, the ultimate microcline is recorded only in micaceous zones. There is a connection between △p and Ba content of the feldspars High concentrations of Ba interfere with order in the feldspar crystal structures. There is a definite inverse relationship between △p and Ba in feldspars containing 0.9-2.6% Ba. In feldspars which are low in Ba, △p may vary at one and the same concentration of Ba. Such state of the crystal structure of feldspars is metastable. The magnitude of △p depends upon conditions of the original crystallization and on factors conducive to orderliness in the crystal structure, as well as the interferences, specifically the effect of the admixture elements. — Authors.     

玲珑金矿田破头青断裂带稀土和矿化元素特征分析

破头青断裂为玲珑金矿田一级控矿构造带,是重要的导矿、容矿构造;其构造蚀变分带从下盘到上盘为:钾长石化带、绢云母化带和硅化黄铁矿化带。绢英岩及其附近的钾化花岗岩、正常花岗岩的矿化元素、稀土元素分析结果表明,破头青断裂带REE配分模式表现为LREE富集型,轻、重稀土分异明显,La/Lu=8.37-65.03,具有Eu异常,δEu=0.67～1.46,Ce无明显异常;Au与Ag、As、Cu、Mo等矿化元素具有相对较高的相关性,是同一成矿作用的结果。     

New data on Sr-and C-isotopic chemostratigraphy of the Upper Riphean type section (Southern Urals)

New data on Sr-and C-isotopic systematics of carbonate rocks from the Upper Riphean stratotype (Karatau Group of the southern Urals) are obtained for several southwestern sections of the Bashkirian meganticlinorium, which have not been studied before. The results obtained supplement the Sr-and C-isotopic information for the group upper horizons thus detailing chemostratigraphic characterization of the entire succession. Limestone and dolostone samples used to analyze the Sr isotope composition satisfy strict geochemical criteria of the isotopic system retentivity and have been subjected to preliminary treatment in ammonium acetate to remove secondary carbonate phases. Data on 255 samples of carbonate rocks (171 studied for the first time) show that δ¹³C value varies in the Karatau Group succession from ?2.8 to +5.9 ‰ V-PDB with several in-phase excursions from the general trend in all the sections studied in the area 90 × 130 km. The δ¹³C variation trend demarcates several levels in the carbonate succession of the Karatau Group suitable for objectives of regional stratigraphy and for C-isotope chemostratigraphic subdivision of the Upper Riphean. The results of Sr isotopic analysis of 121 samples (51 unstudied before) from the Karatau Group imply that rocks in its lower part (the Katav Formation and basal horizon of the Inzer Formation) experienced considerable secondary alterations, while limestones and dolostones of the overlying interval of the group are frequently unaltered. In the “best” samples satisfying geochemical criteria of the isotopic system retentivity, the ⁸⁷Sr/⁸⁶Sr initial ratio increases from 0.70521–0.70532 in the lower Inzer deposits to 0.70611 in the upper Min’yar carbonates, decreasing to <0.70600 near the top of the latter. Above the regional hiatus separating the Min’yar and Uk formation, this ratio grows from 0.70533 to 0.70605–0.70609 in the limestone succession of the last formation.