Listvenite-related gold deposits of the South Urals (Russia): A review

The Urals is a complex fold belt, which underwent long geological evolution. The formation of most gold deposits in the Urals is related to the collision stage. In this paper, we review some relatively small listvenite-related gold deposits, which are confined to the large Main Uralian fault zone and some smaller faults within the Magnitogorsk zone. The Mechnikovskoe, Altyn-Tash, and Ganeevskoe deposits are studied in detail in this contribution. They comprise the ore clusters along with other numerous small gold deposits, and constituted the sources for the gold placers exploited in historical time. The gold is hosted by metasomatites (listvenites, beresites) and quartz veins with economic gold grades (up to 20 g/t Au). Listvenites are developed after serpentinites and composed of quartz, fuchsite, and carbonates (magnesite, dolomite) ± albite. Volcanic and volcanoclastic rocks are altered to beresites, consisting of sericite, carbonates (dolomite, ankerite), quartz and albite. Pyrite and chalcopyrite are major ore minerals associated with gold; pyrrhotite, Ni sulfides, galena, sphalerite, arsenopyrite and Au-Ag tellurides are subordinate and rare. Gold in these deposits is mostly high-fineness (>900‰). The lower fineness (∼800‰) is typical of gold in assemblage with polymetallic sulfides and tellurides. The ores have been formed from the NaCl–CO₂–H₂O ± CH₄ fluids of low (∼2 wt% NaCl-equiv.) to moderate (8–16 wt% NaCl-equiv.) salinity at temperatures of 210–330 °C. The oxygen isotopic composition of quartz (δ¹⁸O) varies from 14.7 to 15.4‰ (Mechnikovskoe deposit), 13.2 to 13.6‰ (Altyn-Tash deposit) and 12.0 to 12.7‰ (Ganeevskoe deposit). The oxygen isotopic composition of albite from altered rocks of the Ganeevskoe deposit is 10.1‰. The calculated δ¹⁸O_H2O values of the fluid in equilibrium with quartz are in a range of 5.7–6.3, 4.2–4.6 and 6.3–6.7‰ respectively, and most likely indicate a magmatic fluid source.     

北方前寒武纪长城系常州沟组的宇宙尘

河北滦县、蓟县、北京十三陵三个地方的常州沟组宇宙尘是在人工重砂的重矿物中发现的,产在古老沉积岩地层中的砾岩和砂岩里,大部分是铁质宇宙尘,形态各异,表面构造多种多样,内部构造各有不同,具Fe—Ni金属,核与壳的化学元素分布不匀匀,化学成分与深海宇宙尘相似。     

Supergene sulphides and related minerals in the supergene profiles of VHMS deposits from the South Urals

The mineralogy and structure of the supergene profile in recently-exploited volcaniс hosted massive sulphide (VHMS) deposits of Cyprus, Uralian and Kuroko type in the South Urals, Russia, have been studied. Specific subzones enriched in secondary sulphides and associated minerals have been distinguished in residual pyrite and quartz–pyrite sands at the Gayskoye, Zapadno-Ozernoye, Dzhusinskoye and Alexandrinskoye deposits. Besides minerals which are common to the cementation subzones (covellite, chalcocite and acanthite), non-stoichiometric colloform and framboidal pyrite, pyrite–dzharkenite, pyrrhotite-like and jordanite-like minerals, metacinnabar, sphalerite, selenium-enriched tetrahedrite and unidentified As-, Sb sulphosalts of Pb or Hg and Ag, sulphur-bearing clausthalite, naumannite and tiemannite were also found. Secondary sulphide minerals in VHMS deposits of the South Urals region are characterized by light sulphur isotope compositions (− 8.1 to − 17.2‰). Superposition of the advanced oxidation of colloform pyrite, an enrichment in impurities (sphalerite, galena, and tennantite) from the primary ores, stagnant water conditions, an elevation of the water table during oxidation, and bacterial activity led to supergene concentrations of the base metals as sulphide, selenides or sulphosalts.     

Late Carboniferous lycopsids of the Karantrav locality (the Southern Urals)

Numerous plant remains as the imprints of lycopsid strobili and stems and the sporadic imprints of articulate stems were first found in the Upper Carboniferous deposits from the Western Slope of the Southern Urals (Karantrav Settlement area). The brief stratigraphic characteristic of the studied locality is given. The studied plant assemblage is represented by Lepidodendron ophiurus Brongniart, L. vaselgense Anikeeva et O. Orlova, sp. nov., Lepidodendron sp., Lepidostrobus tevelevii O. Orlova, Mamontov et Anikeeva, sp. nov., L. ronnaensis Bek et Oplustil, Knorria sp., Calamites sp., and Mesocalamites ramifer (Stur) Hirmer. In-situ microspores of the Lycospora type were discovered in the sporangia of some strobili of the genus Lepidostrobus. Four lycopsid species (two are new) were described.     

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.     

Calcareous nannoplankton in the Jurassic deposits of the Dobrudja foredeep (Ukraine and Moldova)

The paper is concerned with Jurassic calcareous nannoplankton from the Dobrudja foredeep. The regional Jurassic stratigraphy based on nannoplankton is considered. The NJ10/Stephanolithion speciosum, NJ11/Pseudoconus enigma, NJ14/Stephanolithion bigotii maximum, and NJ15/Cyclagelosphaera margerelii Zones, consistent with the International Nannoplankton Zonation Scheme, have been recognized in the deposits of the Dobrudja foredeep.     

Dolomitization of the Waulsortian Limestone (Lower Carboniferous) in the Irish Midlands

The Waulsortian Limestone (Lower Carboniferous) of the southern Irish Midlands is dolomitized pervasively over a much larger region than previous studies have documented. This study indicates a complex, multistage, multiple fluid history for regional dolomitization. Partially and completely dolomitized sections of Waulsortian Limestones are characterized by finely crystalline (0·01–0·3 mm) planar dolomite. Planar replacive dolomite is commonly followed by coarse (≥0·5 mm) nonplanar replacive dolomite, and pervasive void‐filling saddle dolomite cement is frequently associated with Zn–Pb mineralization. Planar dolomite has average δ¹⁸O and δ¹³C values (‰ PDB) of –4·8 and 3·9 respectively. These are lower oxygen and slightly higher carbon isotope values than averages for marine limestones in the Waulsortian (δ¹⁸O=–2·2, δ¹³C=3·7). Mean C and O isotope values of planar replacive dolomite are also distinct from those of nonplanar and saddle dolomite cement (–7·0 and 3·3; –7·4 and 2·4 respectively). Fluid inclusions indicate a complex history involving at least three chemically and thermally distinct fluids during dolomite cementation. The petrography and geochemistry of planar dolomites are consistent with an early diagenetic origin, possibly in equilibrium with modified Carboniferous sea water. Where the Waulsortian was exposed to hydrothermal fluids (70–280 °C), planar dolomite underwent a neomorphic recrystallization to a coarser crystalline, planar and nonplanar dolomite characterized by lower δ¹⁸O values. Void‐filling dolomite cement is isotopically similar to nonplanar, replacive dolomite and reflects a similar origin from hydrothermal fluids. This history of multiple stages of dolomitization is significantly more complex than earlier models proposed for the Irish Midlands and provides a framework upon which to test competing models of regional vs. localized fluid flow.     

喜马拉雅北缘石炭系纳兴组事件沉积的发现及意义

石炭系纳兴组事件沉积的发育对明确喜马拉雅北缘盆地属性和构造背景具有重要指示意义。通过野外地质调查在石炭系纳兴组下部识别出典型深水重力流沉积,并新发现大量软沉积物变形构造。深水重力流主要包括滑塌沉积和砂质碎屑流沉积,浊流沉积发育有限。负载构造、火焰构造、液化砂岩脉和液化角砾岩的发育指示地震触发软沉积物变形构造特征。综合区域地质背景,纳兴组深水重力流和软沉积物变形构造特征表明石炭纪喜马拉雅北缘处于被动陆缘裂谷环境。     

西秦岭武山杨河-礼县固城地区石炭纪地层的发现及其意义

通过区域地质调查,在西秦岭天水地区武山杨河-礼县固城一带原划上泥盆统大草滩群和中泥盆统舒家坝群中解体出一套石炭纪沉积地层。根据所发现的牙形刺、珊瑚、非篮有孔虫化石,确定其地质时代为早石炭世。     

准噶尔盆地东部双井子地区上石炭统泥岩地球化学特征及其地质意义

准噶尔盆地东部石钱滩凹陷石炭系巴塔玛依内山组火山岩之后发育一套连续稳定的碎屑岩沉积。笔者等通过XRD、主微量元素分析等手段针对其中的细粒沉积岩开展元素地球化学研究,其结果对恢复准东地区晚石炭世源区风化特征、古气候、判断其源岩性质及源区构造背景具有重要意义。研究表明,巴山组—石钱滩组泥岩具有低石英含量特点,其中巴山组泥岩黏土含量稍高,而石钱滩组泥岩中长石含量高,两者黏土成份均为蒙脱石（>99%）,反映了干燥、寒冷的气候特征且沉积介质长期为碱性;CIA结果显示巴山组—石钱滩组时期经历了中等—弱化学风化作用,并具有干湿交替气候变化特征;主微量元素及相关判别图解显示巴山组—石钱滩组泥岩的源岩多以偏中性的长英质火山岩为主,少量中基性及少量偏酸性的火山岩物源,并且多数为未分异的弧;泥岩的地球化学特征反映了沉积物源区构造背景主要为大陆岛弧背景,结合石钱滩组碎屑锆石峰值年龄及主要物源区分析认为,野马泉地体与其南部的准噶尔地体东北缘于335 Ma左右开始由俯冲转变为碰撞造山。     

贵州龙里地区早石炭世杜内期铝土矿微地貌及其对铝土矿的控制作用*

贵州龙里地区发育早石炭世杜内期“丰源层”铝土矿。通过收集龙里地区地质钻孔资料,结合实测剖面和踏勘地质点资料,统计含铝岩系厚度、矿体厚度、品位、铝硅比数据,利用Surfer⁸.0成图软件,采用微地貌编图的方法,还原早石炭世杜内期含铝岩系古地貌,发现本区古喀斯特岩溶洼地2处,丰源层铝土矿产于水场—比孟—草原—高坡一带的古喀斯特岩溶洼地中。微地貌进一步研究表明,品位较高的碎屑状、豆鲕状铝土矿位于古喀斯特岩溶洼地的中心部位,品位较低的致密状铝土矿则分布于其中心和边缘。本区古地理研究表明,龙里地区早石炭世杜内期丰源层铝土矿的含矿岩系形成环境为海陆交互相,由北至南依次为发育陆相、古喀斯特岩溶洼地相和海相,古喀斯特岩溶洼相为丰源层铝土矿的形成提供了有利的沉积就位场所。     

Turbidites facies response to the morphological confinement of a foredeep (Cervarola Sandstones Formation,Miocene, northern Apennines,Italy)

The Cervarola Sandstones Formation, Aquitanian–Burdigalian in age, was deposited in an elongate, north‐west stretched foredeep basin formed in front of the growing northern Apennines orogenic wedge. As other Apennine foredeep deposits, such as the Marnoso‐arenacea Formation, the stratigraphic succession of the Cervarola Sandstones Formation records the progressive closure of the basin due to the propagation of thrust fronts towards the north‐east, i.e. towards the outer and shallower foreland ramp. This process produces a complex foredeep that is characterized by syn‐sedimentary structural highs and depocentres that strongly influence lateral and vertical turbidite facies distribution. This work describes and discusses this influence, providing a high‐resolution physical stratigraphy with ‘bed by bed’ correlations of an interval ca 1000 m thick, parallel and perpendicular to the palaeocurrents and to the main structural alignments, on an area of ca 30 km that covers the proximal portion of the Cervarola basin in the northern Apennines. The main aim is to show, for the first time ever, a detailed facies analysis of the Cervarola Sandstones Formation, based on a series of bed types that have proven fundamental to understand the morphology of the basin. The knowledge of the vertical and lateral distribution of these bed types, such as contained‐reflected and slurry (i.e. hybrid) beds, together with other important sedimentary structures, i.e. cross‐bedded bypass facies and delamination structures, is the basis for better understanding of facies processes, as well as for proposing an evolutionary model of the foredeep in relation to the syn‐sedimentary growth of the main tectonic structures. This makes the Cervarola Sandstones, like the Marnoso‐arenacea Formation, a typical example of foredeep evolution.     

Microgeomorphology and its control on the Early Carboniferous Tournaisian bauxite deposits in Longli area of Guizhou Province

In the Longli area of Guizhou,the Early Carboniferous Tournaisian “Fengyuan layer” bauxite was developed. In this paper,based on the geological boreholes,measured profiles and exploration geological point data in study area,the thickness of the aluminous rock series and the ore was calculated. The data of volume thickness,ore grade,and Al/Si ratio were used by Surfer⁸.0 mapping software and the method of microgeomorphology mapping to restore the paleogeomorphology of the Early Carboniferous Tournaisian aluminous rock series. Two paleokarst depressions were found in this area. Fengyuan layer bauxite was produced in paleokarst depressions along the Shuichang-Bimeng-Caoyuan-Gaopo area. Further research on microgeomorphology shows that the high-grade clastic and bean oolitic bauxite is located in the center of paleokarst depressions,while the low-grade dense bauxite is distributed in the center and margin. The paleogeographic research shows that the formation environment of bauxite aluminous rock series in the Fengyuan strata of the Early Carboniferous Tournaisian is a continent-marine transitional facies,including continental facies,paleokarst depression facies and marine facies from north to south. The karst bottomland provides a favorable depositional site for the formation of Fengyuan layer bauxite.     

湖南邵东下石炭统刘家塘组的介形类

湖南邵东下石炭统刘家塘组产丰富的介形类化石，计有１８属３５种（包括６新种），它们绝大多数可与国内外下石炭统介形类对比，其地质时代为早石炭世杜内期，刘家塘组介形类明显地可分成上、下两个不同组合。本文仅描述了刘家塘组介形类６属７种（包括６新种）。     

Platinum group elements zoning and mineralogy of chromitites from the cumulate sequence of the Nurali massif (Southern Urals, Russia)

The Nurali lherzolite massif is one of the dismembered ophiolite bodies associated with the Main Uralian Fault (Southern Urals, Russia). It comprises a mainly lherzolitic mantle section, an ultramafic clinopyroxene-rich cumulate sequence (Transition Zone), and an amphibole gabbro unit.The cumulate section hosts small chromitite bodies at different stratigraphic heights within the sequence. Chromitite bodies from three different levels along a full section of the cumulate sequence and two from other localities were investigated. They differ in the host lithology, chromitite texture and composition, and PGE content and mineralogy. Chromitites at the lowest level, which are hosted by clinopyroxenite, form cm-scale flattened lenses. They have high Cr# and low Mg# chromites and are enriched in Pt and Pd relative to Os and Ir. At a higher, intermediate level, the chromitites are hosted by dunite. They form meter thick lenses, contain low Cr# and high Mg# chromites, have high PGE contents (up to 26,700 ppb), and are enriched in Os, Ir and Ru relative to Pt and Pd, reflecting a mineralogy dominated by laurite–erlichmanite and PGE–Fe alloys. At the highest level are chromitites hosted by olivine–enstatite rocks. These chromitites have high Cr# and relatively low Mg# chromites and very low PGE content, with laurite as the dominant PGE mineral.The platinum group minerals (PGMs) show extreme zoning, with compositions ranging from erlichmanite to almost pure laurite and from Os-rich to Ru-rich alloys, with variable and irregular zoning patterns.Two chromitite bodies up to 6 km from the main sequence can be correlated with the latter based on geochemistry and mineralogy, implying that the variations in chromitite geochemistry are due to processes that operated on the scale of the massif rather than those that operated on the scale of the outcrop.Pertsev et al. [Pertsev, A.N., Spadea, P., Savelieva, G.N., Gaggero, L., 1997. Nature of the transition zone in the Nurali ophiolite, Southern Urals. Tectonophysics 276, 163–180.] propose that the Transition Zone formed by solidification of a series of small magma bodies that partially overlapped in time and space. The magmas formed by successive partial melting of the underlying mantle. We suggest that this process determined the changing PGE geochemistry of the successive batches of magma. The PGE distribution fits a model of selected extraction from the mantle, where monosulphide solid solution–sulphide liquid equilibrium was attained until complete melting of the monosulphide solid solution. Later and localized variations in fS₂ resulted in the formation of different PGMs with complex zoning patterns.     

Carboniferous convergence and subsequent crustal extension in the southern Schwarzwald (SW Germany)

Abstract

Detailed structural analysis in the southwestern part of the Variscan Sehwarzwald Massif (SW Germany) indicates polyphase, synmetamorphic deformation in ductile shear zones. The tectono-melainnrphir evolution is characterized by orogenic crustal shortening and subsequent late- orogenic crustal extension in Carboniferous times. Convergence is responsible for an KSK trending, north dipping thrust zone with intense deformation in orthogneissic S-C type mylonites Superposed on schistose and folded metasediments presumably lower Carboniferous in age. Southeastward thrust-’“g parallel to pervasive stretching lineation, similar to the pre-dominant oblique convergent structures ill the central part of the massif, is related to crustal stacking. Relations of early granite intrusions with the outlasting retrograde tectonics Point to a Lower Carboniferous (Late-Visean) age of shortening.

Subsequent crustal extension is indicated by a broad N-S trending and west dipping ductile shear zone within high grade meetamorphic (I1T7LP) gneisses. Retrograde stretching lineatone marked by sillimanite to chlorite anr consistent with a top-to-the-west shearing on the western flank of a large progressively warping domai structure. Intensely sheared and boudinaged granitic rocks are syn-tectonic and seal the age of extension at about 325 Ma (Lower/ Upper Carboniferous boundary). During progressively cataclastic stages of tectonic denudation the still active detachment controlled formation of an adjacent late Paleozoic (Stephano-Pcrniian) continental basin supersedding high-grade gneiss. As elsewhere in the Varisean belt, the late extensional process in the tectono-”“‘tainorphie evolution of the southern Sehwarzwald is related rapid uplift, exhumation and thinning by a gravitational collaps of a previously thickened crust.     

Evolution of Yizhou aulacogen in Guangxi during Late Paleozoic and distribution of manganese deposits in Early Carboniferous

The palaeogeographic configuration of the shallow water carbonate platform and deep water siliceous basin formed in the Yunnan-Guizhou-Guangxi region during the Late Paleozoic,which developed on the rifting of fold basement and differential subsidence during the Caledonian period. Yizhou-Liuzhou in Guangxi is an important sedimentary boundary in the southern Upper Yangtze carbonate platform. It is also the stratigraphic boundary of Late Paleozoic between middle and northern Guangxi,and it is the tectonic boundary between the southern Xuefengshan and central Guangxi depression during Paleozoic and Mesozoic. In this paper,the evolution of sedimentary basin located at Yishan-Liuzhou region during the Late Paleozoic is reconstructed through the regional stratigraphic correlation and genetic analysis.The elongate Yizhou rifting belt develops from the Nandan-Hechi fault from the west,and extends along Longtou,Beiya,Yizhou,and to Liuzhou. The rifting started at the eastern and western ends of the narrow rifting belt during the Middle Devonian and it developed into the rifting basin during the Early Carboniferous. Due to massive terrestrial siliciclastic filling derived from the Jiangnan Uplift to north,the rifting basin presented the asymmetrical feature and it was eventually filled up at late Early Carboniferous. Many magnesium deposits of Early Carboniferous are found in the rifting basin of Yizhou. The distribution of ore-bearing strata,the depositional succession and sedimentary environment are obviously related with the evolution of rifting basin. They are the evidences of basin evolution,implying the characteristics of rifting aulacogen in central Guangxi,which should be paid more attention in the manganese ore genesis study.     

石炭纪Listracanthus和Petrodus(软骨鱼类)在中国的发现

记述了在宁夏中卫晚石炭世地层中发现的软骨鱼类两个器官属Listracanthus和Petrodus。相似的化石曾在欧洲和北美的石炭纪黑色页岩中出现，但在中国是第一次记述。生物地层学分析表明，这2个器官属的共生出现，可以作为判断晚石炭世地层时代的一个依据。     

The fenestrate bryozoan Septopora carbonaria (Etheridge Jun. 1873a) from the Carboniferous of Great Britain

The Carboniferous fenestrate bryozoan Synocladia carbonaria Etheridge Jun. (1873a) is redescribed. Originally assigned to Synocladia and subsequently diagnosed as a variety of Synocladia biserialis Swallow by Etheridge Jun. (1873b), S. carbonaria is here considered to be a distinct species. Synocladia(?) scotica Young and Young (1878) is conspecific with S. carbonaria, as suggested by Graham (1975). Graham (1975) established the new genus Lanarkopora, naming S. carbonaria and S.(?) scotica in synonomy, with S. carbonaria, the senior synonym, being selected as the type species. Re-examination of the type material of S. carbonaria and S.(?) scotica has shown that they are referable to the genus Septopora Meek, and Lanarkopora is herein designated a junior synonym of Septopora.     

柴达木盆地北缘东段石炭系残留分布及控制因素

柴达木盆地北缘东段石炭系是侏罗系之外的另一套有利生烃层系,针对前人“石炭系为广泛分布于柴达木盆地各残留凹陷”的普遍认识与实际钻探不相符的矛盾,笔者充分利用野外地质调查、钻井、地震、电法等成果资料,通过露头引层、钻井标定、地震相与速度谱识别等方法手段,进行了石炭系顶底界面的追踪解释,重新厘定了柴北缘东段石炭系残留地层分布,并通过平衡剖面恢复分析了自古生代以来的构造演化特征及其对石炭系残留分布的控制作用。结果表明,柴达木盆地东部石炭系平面上残留分布于西段的尕丘凹陷和东段的欧南、霍布逊、德令哈等凹陷,发育尕丘、欧南、霍布逊等多个厚度中心;西段尕西-鱼卡凹陷、马海大红沟凸起、大柴旦凹陷、红山-小柴旦凹陷等基本无石炭系残留;印支末期构造运动造成不同构造单元的差异隆升剥蚀是控制石炭系残留分布及其厚度差异的主要因素,燕山晚期和喜山晚期构造运动造成残留分布的分隔性较强。