东天山马头滩金矿金赋存状态及矿物特征

论述了东天山马头滩金矿矿石的物质组成、矿石中金的成色、赋存状态及粒度,并提出合理选矿方法.对区域金矿评价和开发利用具重要意义.     

东昆仑可支塔格蛇绿混杂岩的地质地球化学特征

东昆仑可支塔格蛇绿混杂岩属于木孜塔格-鲸鱼湖大断裂的西延部分,主要由辉橄岩、辉长岩、闪长岩、斜长花岗岩、辉绿岩、玄武岩及硅质岩等组成,形成时代为早石炭世。为构造强烈破坏的蛇绿混杂岩,形成于俯冲带环境,属SSZ型蛇绿岩。其中辉橄岩以相对低SiO2、TiO2、Al2O3和CaO、高MgO为特征,贫有色金属成矿元素,富集相容元素Cr、Ni、Co。稀土总量低,接近于球粒陨石稀土元素总量,以LREE略富集为特征。闪长岩SiO2、K2O含量较低,MgO、CaO、Na2O较高,稀土总量高,∑REE为90.95μg/g,LREE富集。斜长花岗岩SiO269.8%,Na2O>K2O,K2O/Na2O为0.78,A/CNK为1.68,具有大洋斜长花岗岩的岩石化学特征。闪长岩、斜长花岗岩的微量元素特征相似,表现为大离子亲石元素K、Sr、Rb、Ba相对富集,高场强元素Nb、Ta、Zr、Hf相对亏损。研究表明,辉橄岩来源于亏损的地幔岩,接近于强烈亏损的方辉橄榄岩,而明显不同于结晶分异作用成因的超镁铁质岩石。闪长岩、斜长花岗岩为蛇绿混杂岩的浅色岩组分,是地幔岩浆结晶分异的产物。     

三江造山带玉峰寺深埋隧道岩爆危险性综合评价

深埋隧道的岩爆机理和岩爆预报预测一直是工程地质和岩石力学的热点和难点问题,已成为困扰地下工程发展的瓶颈之一。以滇藏铁路穿越三江造山带玉龙雪山南段的玉峰寺深埋隧道方案为例,在野外工程地质调查的基础上,对影响隧道岩爆的相关因素进行了系统分析。根据岩石力学试验、地应力分析和数值模拟计算结果,采用多种判据对玉峰寺隧道岩爆危险性进行了分析预测和综合评价。研究结果对于地质构造复杂区深埋隧道规划设计和岩爆灾害防治具有一定指导意义。     

东昆仑古特提斯后碰撞阶段伸展作用:来自晚三叠世岩浆岩的证据

通过对东昆仑造山带晚三叠世岩浆岩的岩石类型、形成时代、岩石地球化学和同位素地球化学资料综合分析,对岩浆岩的岩石组合、分布特征和岩石成因进行研究,探讨东昆仑造山带晚三叠世构造演化的地球动力学背景。东昆仑造山带晚三叠世是古特提斯演化过程中重要的构造转换期,岩浆岩岩石类型多样,主要包括辉长岩、花岗闪长岩、二长花岗岩和正长花岗岩,并且广泛出露具埃达克质特征的岩浆岩和A型花岗岩。晚三叠世岩浆岩的出露规模与俯冲阶段相比,规模较小,一般以小岩体、岩株和岩脉侵入于早期岩体和地层中。东昆仑晚三叠世岩浆岩主体为准铝-弱过铝质高钾钙碱性-钾玄岩系列,轻重稀土元素具有一定分异,富集大离子亲石元素,亏损高场强元素,岩石类型不同时分异程度、富集和亏损程度有一定差异。大部分晚三叠世花岗质岩浆岩的同位素特征与晚二叠世-三叠纪镁铁质岩浆岩近似,部分具有更高的εNd(t)和εHf(t)值。镁铁质岩浆岩、普通花岗岩、埃达克质岩浆岩在东昆仑各个构造带皆有分布,A型花岗岩主要分布在祁漫塔格构造带(东昆北)的阿牙克库木湖-香日德断裂附近。东昆仑晚三叠世镁铁质岩浆岩具有弧岩浆岩特征,为俯冲流体交代的地幔楔部分熔融产物。普通花岗岩和埃达克质岩浆岩多为新生下地壳部分熔融产物,少量埃达克质岩浆岩由于与地幔的交代作用,具有幔源特征。A型花岗岩为残留下地壳部分熔融的产物。部分普通花岗岩、埃达克质岩浆岩和A型花岗岩由于岩浆混合作用,具幔源特征。构造环境研究表明,东昆仑在晚三叠世进入古特提斯演化的后碰撞阶段。巴颜喀拉地块同东昆仑地块的持续碰撞导致地壳加厚,密度增大,使岩石圈重力不稳定发生拆沉作用,引发岩石圈地幔减压熔融,产生大量的镁铁质岩浆岩;镁铁质岩浆底侵不同类型地壳熔融及拆沉地壳部分熔融而形成的岩浆交代地幔,以及岩浆混合和岩浆后期演化,形成了东昆仑造山带晚三叠世丰富多样的岩浆岩。     

Planktonic foraminifera and calcareous nannofossils record in the upper Campanian-Maastrichtian pelagic deposits of the Malatya Basin in the Hekimhan area (NW Malatya,eastern Anatolia)

The uppermost Cretaceous (upper Campanian-Maastrichtian) pelagic successions from the Malatya Basin (NW Malatya, eastern Anatolia) were studied by 688 samples, which were collected from five stratigraphic sections in the Hekimhan area. The pelagic deposits conformably overlie rudist bearing shallow-water limestones and are overlain conformably by Maastrichtian dolomites and unconformably by Paleocene-Eocene deposits, respectively.The pelagic successions in the Hekimhan area comprise the Kösehasan Formation at the base and the Zorbehan Formation at the top and reach up to 1100 m in thickness. The Kösehasan Formation rests over the neritic rudist-bearing limestones of the Güzelyurt Formation along a sharp contact and consists mainly of flysch-type sandstone-mudstone alternation with complete and partial Bouma sequences. The carbonate content of abundant planktonic foraminifera and nannoplankton-bearing 980-m-thick succession increases upwards and the formation passes gradually to the clayey limestones and marlstones of the Zorbehan Formation to the top. Occurrences of nannoplankton Lithraphidites quadratus Bramlette and Martini and Micula praemurus (Bukry) in the first beds of the Kösehasan Formation indicate that the age of the Kösehasan Formation and overlying Zorbehan Formation is of late Maasthrichtian. Another late Maastrichtian taxa Cribrosphaerella daniae Perch-Nielsen and Arkhangelskiella maastrichtiana Burnett are observed from the lowermost part of the succession. Maastrichtian planktonic foraminifera such as Contusotruncana walfischensis (Todd) and Globotruncanita pettersi (Gandolfi) were recorded through the successions. Although planktonic foraminifera are diverse and abundant particularly in the Kösehesan Formation, index late Maasthrichtian species were not encountered. Campanian and Santonian-Campanian planktonic foraminifera, e.g. Radotruncana calcarata (Cushman) and Globotruncanita elevata (Brotzen), obtained particularly from the lower part of the succession and calcareous nannofossils such as Broinsonia parca parca Bukry, Reinhardtites anthophorus (Deflanre) and Eiffellithus eximius (Stover) are interpreted as reworked from older strata. Trace fossils are common throughout the succession.Rareness of planktonic foraminifera and nannoplankton in the uppermost part of the succession (Zorbehan Formation) indicates maximum shallowing of the latest Maastrichtian sea in this part of the basin. Rare echinoids, bivalves and ammonites are observed in that part of the sequence.The obtained data indicate that sediment accumulation rate of the pelagic deposits is rather high and about 27.5 cm/ky for this part of the basin. Changes in thickness of the formations along short distances in the five stratigraphic sections analysed in this study should be related to the diachroneity of the depositional and erosional events.     

The Palaeozoic tectono-metallogenic evolution of the northern Tasman Fold Belt System, Australia: Interplay of subduction rollback and accretion

The Tasman Fold Belt System in eastern Australia provides a record of the Palaeozoic geological history and growth of the Australian continent along the proto-Pacific margin of Gondwana inboard of an extensive and long-lived subduction system. The Hodgkinson and Broken River provinces represent prominent geological elements of this system and together form the northern Tasman Fold Belt System. Geochronological age dating of the timing of gold formation in the Amanda Bel Goldfield in the Broken River Province and the Hodgkinson Goldfield in the Hodgkinson Province provides constraints on the occurrence of a deformation and mineralisation episode in the Late Devonian–Early Carboniferous. Integration of these newly-obtained data with petrogenetic constraints and a time–space evaluation of the geological evolution of the Hodgkinson and Broken River provinces, as well as other terranes in the northern Tasman Fold Belt System, allows for the development of a geodynamic model for the Palaeozoic evolution of the northern Tasman Fold Belt System. Our model indicates that three cycles of extension–contraction occurred during the Palaeozoic evolution of the northern Tasman Fold Belt System. Episodes of extension were controlled by rollback of the subduction system along the proto-Pacific margin of Gondwana, whereas episodes of contraction resulted from accretion following the arrival of positively buoyant segments (i.e., micro-continental blocks/oceanic plateaus) at the subducting trench.Our composite interpretative model on the geodynamic evolution of the northern Tasman Fold Belt System integrates the timing of the development of mineral deposits throughout this part of the system and provides a significant advancement in the understanding of Palaeozoic geodynamics along the margin of Gondwana in northeast Australia and allows comparison with the southern part of the Tasman Fold Belt System.     

西秦岭晚新生代构造变形的几何图像、运动学特征及其动力机制

西秦岭位于东西向展布的秦岭-大别-苏鲁中央造山带与南北向展布的贺兰山-龙门山-川滇地震带构成的巨型"十字"构造区的交汇点,是中国大陆中部"西秦岭-松潘构造结"的重要组成部分.西秦岭晚新生代的构造变形与青藏高原的侧向扩展过程密切相关.该区构造变形的几何图像、运动特征及其深部动力学机制对于揭示青藏高原东北部的动力过程及强震...     

Infiltration Metasomatism of Cumulates by Intrusive Magma Replenishment: the Wavy Horizon, Isle of Rum, Scotland

The Eastern Layered Intrusion of the Rum Layered Suite comprisespaired peridotite and allivalite (troctolite and gabbro) layersforming 16 macro-rhythmic units. Whereas the majority of thesemacro-units are believed to have formed by a process of crystal–liquiddifferentiation involving successive accumulation of crystalsfrom multiple picritic replenishments of the chamber, the Unit9 peridotite is interpreted as a layer-parallel picrite intrusion.Closely correlated with this discontinuous peridotite body isa distinctive feature generally known as the Wavy Horizon, whichdivides the overlying allivalite into a lower troctolite andan upper gabbro along a well-defined undulating contact. Wepropose that the Wavy Horizon is a metasomatic feature formedconsequent to the removal of clinopyroxene from an originalgabbroic mush. Foundering of the mush into the picritic sillresulted in the replacement of the original interstitial liquidby one saturated only in olivine (± plagioclase). Progressivethrough-flow of this liquid resulted in the stripping out ofclinopyroxene from the lower parts of the allivalite. We interpretthe Wavy Horizon as a reaction front, representing the pointat which the invading liquid became saturated in clinopyroxene.The distinctive pyroxene-enriched zone immediately above theWavy Horizon could have formed when mixing of the interstitialliquids on either side of the reaction front formed a supercooledliquid oversaturated in pyroxene, as a result of the curvatureof the olivine–plagioclase–clinopyroxene cotectic.The presence of many such approximately layer-parallel features,defined by differences in pyroxene content, in the Eastern LayeredIntrusion of Rum suggests that such an infiltration–reactionprocess was not unique to Unit 9. KEY WORDS: cumulate; infiltration metasomatism; Rum; Eastern Layered Intrusion     

Petrology and Geochronology of Granulites from the McKaskle Hills, Eastern Amery Ice Shelf, Antarctica, and Implications for the Evolution of the Prydz Belt

A combined petrological and geochronological study was carriedout on mafic granulites and associated felsic gneisses fromthe McKaskle Hills, eastern Amery Ice Shelf, East Antarctica.Garnet-bearing mafic granulites exhibit reaction textures andexsolution textures that indicate two-stage metamorphic evolution.Thermobarometric estimates from matrix and symplectite assemblagesyield peak and retrograde P–T conditions of 9·0–9·5kbar and 880–950°C and 6·6–7·2kbar and 700–750°C, respectively. Similar but slightlyscattered peak P–T estimates of 7·9–10·1kbar and 820–980°C are obtained from the core compositionsof minerals from felsic para- and orthogneisses. Evidence forthe prograde history is provided by muscovite inclusions ingarnet from a paragneiss. Sensitive high-resolution ion microprobeU–Pb zircon dating reveals an evolutionary history forthe granulites, including a mafic and felsic igneous intrusionat 1174–1019 Ma, sedimentation after 932–916 Ma,and a high-grade metamorphism at 533–529 Ma. In contrast,Sm–Nd mineral–whole-rock dating mainly yields asingle age population at 500 Ma. This suggests that the McKaskleHills form part of the Prydz Belt, and that the relatively highpeak P–T conditions and a decompression-dominated P–Tpath for the rocks resulted from a single Cambrian metamorphiccycle, rather than two distinct metamorphic events as formerlyinferred for the granulites from Prydz Bay. The age data alsoindicate that the Precambrian history of the McKaskle Hillsis not only distinct from that of the early Neoproterozoic terranein the northern Prince Charles Mountains, but also differentfrom that of other parts of the Prydz Belt. The existence ofmultiple basement terranes, together with considerable crustalthickening followed by tectonic uplift and unroofing indicatedby the clockwise P–T–t evolution, suggests thatthe Prydz Belt may represent a collisional orogen that resultedin the assembly of Gondwana during the Cambrian period. KEY WORDS: Mesoproterozoic basement; Cambrian metamorphism; P–T path; Prydz Belt; East Antarctica     

新疆东准噶尔顿巴斯套金矿地质特征及矿床成因

新疆东准噶尔地区自北向南发育额尔齐斯、阿尔曼太、卡拉麦里三条大型构造带,南北两条构造带已发现大量造山型金矿,而阿尔曼太构造带与南北构造带具有相似的成矿地质背景,却未见造山型金矿的报道。因此,笔者等选取了该构造带最重要的金矿床——顿巴斯套金矿,开展了详细的岩相学、矿相学研究以及构造解析。研究表明,该矿床具有区域性断裂的次级断裂控矿、脆—韧性剪切带控矿、背斜核部控矿“三位一体”的控矿特征,其中,NW—SE向脆—韧性剪切带是最重要的控矿构造,金矿化显著晚于矿区赋矿岩浆岩——石英闪长玢岩,且该矿床与相邻构造带典型的造山型金矿地质地球化学特征相似。结合成矿流体具有中低温、富CO2的特征,综合认为顿巴斯套金矿是典型的造山型金矿。将该矿床成矿过程划分为3期：① 以产出草莓状黄铁矿为典型特征的沉积期;② 以黄铁矿压实、结核、重结晶为特征的成岩期;③ 以产出热液脉和金的矿化为典型特征的热液期。热液期进一步划分为两个阶段：以脆—韧性变形为主的铁白云石—石英—黄铁矿阶段和由脆—韧性变形向脆性变形转变的石英—钠长石—方解石阶段。黄铁矿可划分为6个世代、毒砂可划分为3个世代：① Py1为沉积成因的黄铁矿,具有草莓状、胶状等特殊结构;② Py2为成岩作用形成的黄铁矿,具有顺层分布、呈结核状等特征;③ 热液期毒砂Apy1,粒度20~50 μm,自形、半自形,常与金共生;④ 热液期毒砂Apy2,自形,粒度80~200 μm;⑤ 热液期黄铁矿Py3,他形—自形,粒度50~150 μm,以内部包体多、孔洞多为显著特征;⑥热液期黄铁矿Py4,半自形—自形,粒度100~250 μm,以包体多,孔洞少,发育压力影为特征;⑦ 热液期Py5,以背散射下亮度高、显著富As为特征;⑧ 热液期毒砂Apy3：以颗粒粗大、自形、内部包体少、发育碎裂结构和压力影为特征;⑨ 热液期黄铁Py6：以颗粒粗大、半自形到自形、内部包体少、发育碎裂结构和压力影为特征。随着脆—韧性变形作用进行,黄铁矿、毒砂的粒度有序递增,自形程度逐渐升高,而品位逐渐降低,金的沉淀主要发生在脆—韧性变形阶段,脆性变形阶段无金矿化。主成矿阶段标志性的铁白云石化蚀变、微细浸染状的黄铁矿化、毒砂化蚀变可以作为找矿标志。