活化断层对加拿大阿萨巴斯卡盆地不整合型铀矿的控制

先存断层的活化对许多热液矿床的形成起到至关重要的作用。加拿大阿萨巴斯卡盆地的不整合型铀矿是一个受活化断层控制矿床的典型例子。该铀矿产于基底与盆地砂岩之间的不整合面附近,并与根植于基底的断层密切相关。这些控矿基底断层切穿并错动了盆地的不整合面。一系列证据表明这些基底断层以韧性的方式形成于盆地之前,但在盆地形成之后又发生脆性活化,而正是这种断层活化作用控制铀矿的产出。先存断层作为完整岩石中的薄弱位置,在后期构造运动中,其活化比产生新断层更容易发生。数值模拟表明在后期挤压构造运动中,有先存基底断层的不整合面被显著错动,而无先存断层的不整合面并没有错动。基底断层的脆性活化,不仅在活化过程中为流体提供了驱动力,而且由于活化导致岩石渗透率的提高,为后期的流体流动提供了通道以及容矿场所,形成阿萨巴斯卡盆地的不整合型铀矿。     

巴音戈壁盆地砂岩型铀矿找矿新发现与意义

砂岩型铀矿是全球最重要的铀矿类型之一,一般以表生流体的氧化还原成矿作用为主。虽然在勘查中发现部分砂岩型铀矿中存在热液流体活动的痕迹,但热液流体与铀成矿之间的关系仍不明确。本研究以巴音戈壁盆地下白垩统巴音戈壁组下段底部砂质砾岩中新发现的铀矿化为研究对象,通过镜下鉴定、电子探针(EPMA)、铀含量、铀价态和微量元素分析等手段,研究了铀矿石的岩石学、矿物学和地球化学特征。结果显示,铀矿化产出于巴音戈壁组下段的紫红色砂岩中,与不整合界面及次级断层有关;铀呈分散状态分布在胶磷矿中,并伴生有方铅矿、闪锌矿等金属硫化物;微量元素分析显示矿石中Sr、Y、Mo、W和REE等显著富集,指示其形成与深部流体密切相关。研究认为,苏红图组玄武岩喷发形成的火山热液在上升过程中与地表大气降水混合形成弱酸性氧化流体,流体沿不整合和断层向上运移并不断萃取地层中的U和P,当其遇到上覆巴音戈壁组砂砾岩中的菱铁矿等还原物质时,形成酸碱度和氧化还原接触界面,进而诱发铀、磷的沉淀。本次在新层位发现的铀矿化拓宽了巴音戈壁盆地铀矿勘查的找矿空间和方向。     

Chemical brecciation processes in the Sue unconformity-type uranium deposits, Eastern Athabasca Basin (Canada)

Chemical brecciation in sandstone is common in many unconformity-type uranium deposits of the Athabasca Basin, and is expressed in some of them as ball zone breccia. Ball zones are composed of rounded argillized sandstone fragments, varying in size from several centimeters to 1 m, wrapped in a clay matrix. The Sue C open pit provided a unique opportunity to map and to study such ball zones. Here, they were up to 5 m wide with a 20–30 m vertical extension. They were mainly observed along a reverse fault controlling the Sue A and B uranium deposits, and were well developed at intersections with dextral NE-trending structures. Their maturity, characterized by the matrix percentage, increased toward the unconformity and at fault intersections. They are characterized by massive quartz dissolution, hematite leaching, (Ca,Sr,LREE)Al-phosphates crystallization and replacement of dickite by illite. Illite composition indicates formation temperatures of 240–280 °C, close to peak diagenesis conditions in the basin. Mass balance calculations show that V, K, Rb, B, LREE, Mg, Cr, Sr, U and Y were added and Si and Fe leached out with up to 85% volume loss.Ball zones were initiated by tectonic fracturing in sandstone during reverse faulting. Consecutive permeability increase induced basement fluid circulation in the sandstone with quartz dissolution along fractures. With a silica saturation of the fluid of 90%, a minimum fluid/rock ratio of 38,000 is obtained. The rounded morphologies of the breccia fragments are attributed to a diffusion-limited regime of dissolution. The resulting increase of clay content led to self-sealing of the hydrothermal system. Seismic reactivation may have been periodically rejuvenated the permeability. These processes seem to be coeval with the formation of structurally controlled high-grade unconformity-type uranium mineralization. Formation of the ball zones required probably more than 1 million years.     

Hydrothermal alteration of monazite in the Precambrian crystalline basement of the Athabasca Basin (Saskatchewan, Canada): implications for the formation of unconformity-related uranium deposits

Microanalytical studies of basement rocks below the Athabasca sandstone basin indicate that monazite is the dominant uranium-bearing mineral in the study area. Drill core samples of hydrothermally altered basement show that monazite is commonly altered to a Th–silicate phase, and uranium has been significantly mobilized. On average, 75% of the uranium bound to monazite is leached out during monazite alteration. In contrast, no substantial mobilization of uranium from detrital minerals (e.g. zircon) has yet been observed in the Athabasca sandstones. It is suggested that hydrothermal alteration of granitic rocks (especially potassic pegmatoids and potassic orthogneisses) of the sub-Athabasca basement, represents the most important uranium source for the unconformity-type deposits. Received: 3 December 1999 / Accepted: 24 May 2000     

二连盆地可地浸砂岩型铀成矿的再认识

笔者从铀成矿条件入手 ,分析了二连盆地在基底演化期、含矿建造形成期以及后生改造成矿期各阶段对可地浸砂岩型铀矿的控制作用 ,认为二连盆地在含矿建造形成期是由众多分割性强的 ,构造演化和沉积变迁自成体系 ,并具有多物源、近物源特点的小凹陷所组成。同时 ,综合其他控制砂岩型铀矿的因素 ,确定了二连盆地是以发育潜水 层间氧化带砂岩型铀矿为其主要成矿类型 ,且矿床规模以中、小型为主 ,具有成群成带产出的特点。     

Role of hydrodynamic factors in controlling the formation and location of unconformity-related uranium deposits: insights from reactive-flow modeling

The role of hydrodynamic factors in controlling the formation and location of unconformity-related uranium (URU) deposits in sedimentary basins during tectonically quiet periods is investigated. A number of reactive-flow modeling experiments at the deposit scale were carried out by assigning different dip angles and directions to a fault and various permeabilities to hydrostratigraphic units). The results show that the fault dip angle and direction, and permeability of the hydrostratigraphic units govern the convection pattern, temperature distribution, and uranium mineralization. A vertical fault results in uranium mineralization at the bottom of the fault within the basement, while a dipping fault leads to precipitation of uraninite below the unconformity either away from or along the plane of the fault, depending on the fault permeability. A more permeable fault causes uraninite precipitates along the fault plane, whereas a less permeable one gives rise to the precipitation of uraninite away from it. No economic ore mineralization can form when either very low or very high permeabilities are assigned to the sandstone or basement suggesting that these units seem to have an optimal window of permeability for the formation of uranium deposits. Physicochemical parameters also exert an additional control in both the location and grade of URU deposits. These results indicate that the difference in size and grade of different URU deposits may result from variation in fluid flow pattern and physicochemical conditions, caused by the change in structural features and hydraulic properties of the stratigraphic units involved.     

Geochemical zoning around the McClean uranium deposits, Saskatchewan, Canada

Some 3400 drill core samples of the Athabasca Group and underlying regolith have been obtained by sampling 8-m sections from 55 diamond drill holes in the McClean Lake Area, Saskatchewan. Forty eight holes are from sections over six areas known to contain uranium mineralization and 7 are from unmineralized areas. The uranium zones are covered by 30 to 180 m of Athabasca sandstones and conglomerates.The uranium mineralization of the McClean deposits can be described as belonging to two different facies; a more reduced sulphide-arsenide facies and a more oxidized hematite-“bleached” facies, superimposed on any one of three host rocks.The sulphide-arsenide facies is probably older and, except in one deposit, it forms a patchy distribution of relicts. The principal pattern is an upwards increase in sulphur/arsenic ratio. The hematite-“bleached” facies appears to be younger and may represent a reworking of the earlier sulphide-arsenide facies mineralization under more oxidizing conditions.The trace metals can be grouped according to their redox behaviour. Vanadium, Mo and U, occurring as oxides, form one group while Ni, Co, Zn, Cu and As, occurring as sulphides and/or arsenides, form intermediate and most reduced groups, respectively. Iron is concentrated in the most oxidized facies as hematite or goethite and in the most reduced facies as pyritebravoite, siderite and chlorite. Manganese follows the distribution of siderite.The ratio of oxidized to reduced minerals can be represented by the ratio of U/Ni. This ratio can be used to estimate the variation of redox potential in the deposit at the time of deposition or alteration. The principal pattern is one of systematic increase in U/Ni ratio or oxidation potential both upward and to the northeast in each of the hematite and bleached facies.A generalized Eh-pH diagram is used to qualitatively describe the significance of each mineral facies.The U/Ni ratio of the transition between the hematite and “bleached” facies increases upwards. The phase diagram suggests that a possible cause is an upward decrease in pH and increase in Eh.The overall distribution is compatible with the origin of the deposits due to reduction at the interface between a plume of reductant emanating from fractures in the sub-Athabasca basement and an oxidizing aquifer moving southwestward in the sandstone. This model does not accurately predict the distribution of elements among the seven McClean Lake pods. However, it explains the overall pattern. Local variations in metal ratios in solution either in time or reflecting local provenance could be adduced to explain local deviations from the overall pattern.Clay alteration, apparently largely contemporaneous with the earliest mineralization, is largely illitic but with sporadic occurrences of xenotime and goyazite. Thus K and to some extent P, Y and light REE's are also enriched to some degree in the deposits.Uranium analysis of the drill core shows that there is little movement of U into the overlying sandstones from basement rocks and regolith that contain no uranium deposits. Uranium in the Athabasca sandstone from these areas averages less than 1 ppm. However, where uranium zones have been found in the basement rocks, regolith and lower Athabasca sandstone, U values greater than 2–3 ppm consistently occur in the overlying sandstones at or near surface.There appear to be two types of U anomalies, those that flank the deposits and those that directly overlie them. Both types exhibit vertical and lateral continuity. They are associated with vertical to steeply dipping fracture systems that traverse the Athabasca sandstone from basement to surface. The fractures are thought to be related to diagenetic processes from compaction of the sedimentary rocks over basement irregularities as well as tectonic processes (i.e. re-adjustment along old basement structures).These results suggest that target areas containing deeply buried uranium deposits could be defined by U analyses of the Athabasca sandstone from quite widely spaced holes of limited depth. This conclusion can be compared to XRD and chemical studies of clay mineral distribution within the Athabasca sandstone about the deposits.     

不整合面控制内生金属成矿的新实例:山东沂南金铜铁矿床

山东沂南矽卡岩—热液型金铜铁矿床产于燕山期中酸性杂岩体的接触带及其外侧围岩中。近年来,在太古宇与新元古界之间不整合面及其上覆的新元古界地层中新发现了两层矿体,同时在不整合面以下局部地段的太古宇花岗片麻岩中也见有金铜矿化。受控于不整合面的矿体多呈层状、似层状,埋藏深度大(一般介于430~650 m),产状平缓,侧向延伸连续且稳定。作为一种容易失稳的构造薄弱带,不整合面及其上下机械性质不同的岩层之间极易产生层间破碎、滑脱,导致岩浆及其所分泌的含矿气水热液顺层贯入,并通过交代—充填作用成矿。同时,不整合面又是一个地球化学性质的转换带或地球化学屏障,盖层(含砾砂岩、砂岩、页岩夹泥灰岩)与基底岩石(花岗片麻岩、斜长角闪岩)化学成分和性质的显著差异,也是控制不整合面成矿的重要因素之一。不整合面以下太古宇花岗片麻岩中细脉浸染状金铜矿化,则可能与沿不整合面的拆离断裂活动引发的基底张性裂隙有关。该矿床中不整合面附近矿体的发现,对矿山深部、外围乃至整个鲁西地区的成矿规律研究和找矿勘探工作,具有重要的理论和实际意义。     

新疆伊犁盆地砂岩型铀矿床层间氧化带中粘土矿物特征及与铀矿化关系研究

新疆伊犁盆地砂岩型铀矿床,由于规模大、成矿环境和成矿条件好,在同类型矿床中具有良好的代表性,研究矿床的成矿作用对今后找矿勘查以及开采具有重要理论意义。本文在区域赋铀层位沉积环境研究基础上,以赋矿围岩为研究主体,对伊犁盆地典型铀矿床沉积序列和矿床的控矿层位开展研究,通过对赋矿沉积层位中粘土质对铀矿成矿的控制作用及与铀矿的空间联系和成因分析,开展系统的铀矿床学、能谱测试、显微结构、扫描电镜、地球化学、氢氧同位素等研究,特别是开展了富矿砂体中粘土矿物的种类、成分、结构、同位素、成因等的研究,对粘土质矿物对铀矿成矿的控制作用进行了系统研究。通过研究粘土矿物在伊犁盆地蒙其古尔砂岩型铀矿床成矿过程中的作用及与铀矿的空间联系和成因分析表明:粘土矿物在层间氧化带中分布较为广泛,在主要矿体的氧化还原过渡带中,尤其是部分具有强烈粘土蚀变的砂岩层中铀含量较其他层位要高,反映出粘土矿物与铀成矿是有成因关联的。通过系统的扫描电镜、能谱测试研究,从微观证明粘土矿物与铀成矿有相关关系;粘土矿物的存在导致在近地表含氧含铀水在经过砂岩孔隙时被具有较强吸附能力和巨大表面自由能的粘土矿物所吸附,形成了铀含量较高的片状,团块状的粘土矿物,其在铀成矿作用中起到了吸附和界面的作用,有利于赋矿空间的形成及定位。结合沉积作用、构造活动和后期流体成矿作用等因素,分析了成矿机制和成矿作用,赋矿层位中的粘土矿物、其它成矿条件如岩性(赋矿层和矿源层)、构造(对铀矿化的动力和对地下水径流及铀矿体)等共同控制了铀成矿作用。     

Migration of brines in the basement rocks of the Athabasca Basin through microfracture networks (P-Patch U deposit,Canada)

The unconformity-type uranium deposits of the Athabasca Basin (Saskatchewan, Canada) are hosted near the unconformity between a middle Proterozoic intracratonic sedimentary basin and an Archean to Paleo-Proterozoic metamorphic and plutonic basement. These deposits, which are considered to be the richest U deposits in the world, are the result of massive basinal fluid migrations in the basement rocks.This study shows that basinal brines have strongly penetrated into the basement not only through faults and major pathways but also by way of dense networks of microfractures which favoured the percolation of fluids down to considerable depths (hundred metres below the unconformity) and their chemical modification (salinity increase) by interaction with basement lithologies. These processes are one of the major causes of uranium mobility within the basement rocks and the formation of unconformity-type mineralization.Microfracture networks, which opened during the basinal brine stage (ca. 1600–1400 Ma) are interpreted as sets of mode I cracks corresponding to a specific stage of deformation and occur as fluid inclusion planes after healing. The stress field at that stage (σ₁ = N130–150 °E, subvertical) partly reopened the earlier microcrack networks (σ₁ = N80–110 °E and N130–150 °E, subvertical) issued from the Trans-Hudson Orogeny late retrograde metamorphic stage (ca. 1795–1720 Ma). The circulation of the two types of fluids (carbonic and brines) occurs thus at two distinct events (Trans-Hudson Orogeny late retrograde metamorphism for carbonic fluids and maximal burial diagenesis for brines) but the same main microfissure geometry was used by the fluids. This demonstrates the existence of a similar stress field direction acting before and after the basin formation. Moreover, the brine circulations in the basement acted in a wider volume than the clay-rich alteration halo surrounding the U-ores, generally considered as the main envelope of fluid percolation outside the fault systems. The data on the chemistry of the fluids and on the geometry of their migration at various scales emphasise the fundamental role of the basement in the chemical evolution of highly saline brines linked to unconformity-related uranium mineralization in the Athabasca Basin.     

赣南白面石铀矿田成因再认识

赣南白面石铀矿田经上世纪60~80年代勘查,发现和探明了白面石、龙坑、双坑、马荠塘4个铀矿床和黄泥湖铀矿点,成为中国重要的铀资源基地。该矿田产于EW向南岭铀成矿带东段的白面石沉积-火山盆地内。该盆地的基底为印支期白面石花岗岩体;盖层为中侏罗统菖蒲组。盖层的底部为第一层砂岩,其上由基性-酸性双峰式火山岩组合与5层碎屑岩夹层组成。铀矿主要赋存在盖层底部的第一层砂岩中,其次是产在第一层玄武岩与第一层砂岩的接触带,有少量产在基底花岗岩顶部的风化壳中。关于该铀矿田的成因,有砂岩型沉积说、同生沉积后生富集说、成岩成矿热液叠加说、岩浆热液说,等等。为了厘定矿床成因类型,以确立今后的找矿方向,笔者对该矿田的资料进行了重新整理,应用Minesight软件选择典型的白面石铀矿床建立了三维地质模型,并收集了最新的同位素定年和岩石地球化学分析资料。研究表明,白面石铀矿田存在2次成矿（160~156 Ma和99~86 Ma）,其主成矿作用与第一层玄武岩的覆盖,在空间上相伴（铀矿体主要赋存于第一层砂岩及其与玄武岩的接触带）、时间上相近（成矿时间为160~156 Ma,玄武岩成岩时间为173 Ma）、成生上相关（矿化具有明显的中-低温热液蚀变）,为火山热盖成因类型,后期又有大量脉体活动,在岩脉两侧的砂岩层内又有热液型铀矿化叠加,从而形成了火山热盖及热液叠加的复成因矿床。该矿田的成矿条件是：富铀的基底,砂岩的沉积,洼沟的地形,岩浆的热盖,脉岩的入侵。     

The application of lithogeochemistry in the search for unconformity-type uranium deposits, Northern Saskatchewan, Canada

Lithogeochemical-mineralogical haloes around unconformity-type uranium deposits in northern Saskatchewan can expand the size of drill targets up to fifteen times. The deposits are located at or near the unconformity between Aphebian metamorphosed basement rocks in close proximity to Archean granitoids and overlying unmetamorphosed sandstones of the Helikian Athabasca Group. Deposits studied include Key Lake (Deilmann), Midwest Lake and Eagle Point.Unconformity-type deposits are associated with broad alteration haloes in the overlying sandstones and more restricted haloes in the basement rocks. The haloes in the sandstone are localized around steeply dipping fault structures and are characterized by zones of intense leaching of specular hematite and detrital heavy mineral layers and by changes in chemistry related to clay mineral alteration and tourmalinization.Clay mineral alteration haloes are common in the sandstone and basement host rocks. Interstitial clays consist mainly of kaolinite and illite with lesser amounts of chlorite. The ratio K₂O/AI₂O₃ proved useful in delineating illite-kaolinite patterns in the sandstone and in the uppermost portions of the paleoweathering profile in basement rocks. The Midwest deposit is characterized by a broad bell-shaped zone (500 m across strike) of high K₂O/AI₂O₃ ratios (>0.18) in which illite is the dominant clay mineral. The sandstone above the Deilmann deposit, on the other hand, is characterized by silicification and kaolinitization with low K₂O/AI₂O₃ ratios (<0.04). This kaolinite cap overprints a preexisting illite zone.Anomalously high boron values are characteristic of the three deposits considered in this study. Boron anomalies are similar in extent to the anomalous clay mineral alteration haloes. Altered sandstones commonly contain aggregates of radiating magnesium-rich dravite needles within the clay matrix. The interpretation of boron patterns is problema tical however, mainly because of the detrital tourmaline component in sandstones and metamorphic tourmalines present in the Aphebian metasediments.Trace elements such as U, Ni, As and Co are generally of limited use in expanding targets in sandstone because their haloes are restricted to a few tens of metres horizon-anomalies along the steeply dipping zones of mineralization related to fault structures. Uranium (>3 ppm) does form an anomaly more than 200 metres laterally across the Midwest deposit. At the Deilmano deposit anomalous uranium dispersion is restricted to within a few metres of high grade ore.In the basement rocks, the various layers of the paleoweathering profile are geochemically overprinted up to 250 m from mineralization. Bleaching related to illitization and chloritization is associated with enrichment in K₂O, MgO, B, S, U, As, Ni and P₂O₃. The ratio Fe₂O₃/MgO is useful in delineating chloritization in the upper portion of the paleo weathering profile.Deposits with large root extensions in the Aphebian metasediments such as Eagle Point, have intense dravite-chlorite-illite alteration zones which are restricted to within a few metres of mineralization across strike. ‘Quartzite” units are alteration related. The complexity of the basement lithology inhibits the use of individual elements as alteration guides other than in the intensely altered zone. The application of multivariant techniques, element ratios and clay mineralogical work prove useful in identifying the mineralogical changes at Eagle Point.     

准噶尔盆地卡姆斯特地区侏罗系铀成矿模式研究

本文对卡姆斯特地区中侏罗统头屯河组、西山窑组层间氧化带及铀矿化特征进行了归纳与总结,运用层间氧化带砂岩型铀矿成矿理论,重建了该区铀成矿模式,初步认为铀矿化、异常符合层间氧化带控矿理论,受层间氧化带及不整合面控制,总体上遵循层间氧化带砂岩型铀成矿规律。指出区内铀矿找矿目的层主要为中侏罗统头屯河组,次为西山窑组,主要找矿类型为层间氧化带砂岩型,次为不整合面砂岩型、煤岩型,明确了今后该地区找矿方向,可为准噶尔盆地今后铀矿资源勘查工作提供参考。     

K-Ar dating of episodic Mesozoic fluid migrations along the fault system of Gernsbach between the Moldanubian and Saxothuringian (Northern Black Forest,Germany)

Along the SW-NE trending fault zone of Gernsbach (northern Black Forest), over a distance of about 45 km between Baden-Baden and Pforzheim, basal series of the sedimentary cover are extensively altered by hydrothermal solutions. The fluids were conveyed in the fault zone and because of favourable permeabilities they spread out along the unconformity between the basement and sedimentary cover. K-Ar dates on authigenic white micas (illites) and hydrothermally altered detrital micas point to the occurrence of two major episodes of fluid migration. The extensive alteration along the entire fault system occurred about 150 Ma ago during the Jurassic. In relation to these hydrothermal activities, the epigenetic strata-bound uranium deposit of Müllenbach originated in Upper Carboniferous sediments near the fault and the fluorite-quartz vein-type mineralization of Käfersteige was formed along the fault about 100 Ma ago during the Cretaceous. The results indicate various geological processes of the fault system of Gernsbach, which is located between the Saxothuringian and Moldanubian zone. The mobilization of the fluids and the formation of the ore deposits were probably caused by and connected with tectonic activities in mid-Europe.     

湖南前震旦系铀矿化成因探讨

湖南前震旦系冷家溪群和板溪群是一套浅变质沉积岩,主要由各种板岩、变质砂岩、凝灰质板岩组成,夹有基性、中-酸性火山熔岩、火山碎屑岩及碳酸盐岩。现已落实铀矿床3个、矿(化)点14个。铀成矿年龄为85—50Ma,最晚者16Ma。稳定同位素研究结果表明,前震旦系铀矿化属岩浆岩源及沉积(变质)岩源中-新生代大气降水热液成因;铀矿化受断裂构造控制;凝灰质板岩、砂质板岩及角岩等是矿化有利的围岩。     

正向构造对层间氧化带砂岩型铀矿成矿和定位的控制

正向构造指的是与铀矿带或铀矿床产出位置相关的背斜、隆起、上升断块等矿床地质构造。伊犁盆地南缘、吐哈盆地西南缘、酒东盆地东北缘等砂岩型铀矿成矿带的产出特征表明,层间氧化带砂岩型铀矿床、矿段和矿点总是选择性地就位于正向构造之中。其原因在于层间氧化带砂岩型铀矿的成矿机理所决定。即正向构造抬升了容矿层位,使其出露或接近地表,容易接受补给区含氧含铀水的渗入,造成主砂岩层的层间氧化,铀在主砂岩层中迁移,并在氧化还原界面还原成矿。因此,正向构造对氧化带砂岩型铀矿成矿和定位的作用应引起足够重视,它可以作为产铀盆地砂岩型铀矿带成矿远景区段识别和预测的一项重要判据。     

Sedimentary basin formation associated with a silicic large igneous province: stratigraphy and provenance of the Mesoproterozoic Roopena Basin,Gawler Range Volcanics

The Mesoproterozoic Gawler Silicic Large Igneous Province (SLIP) in the Gawler Craton and Curnamona Province, southern Australia, comprises extensive felsic and lesser mafic volcanic sequences, with only limited sedimentary successions. The Roopena Basin is a rare example of a synvolcanic sedimentary basin that formed within the Gawler SLIP in the eastern Gawler Craton. It is a north–south-trending basin with a preserved area of 75 km², bound by the Roopena and Wizzo Well faults, and contains three units of the lower Gawler Range Volcanics; the Angle Dam Dacite, Fresh Well Formation and Roopena Basalt. The Angle Dam Dacite is a porphyritic lava and the oldest part of the volcanic succession, directly overlying basement. The Fresh Well Formation overlies the Angle Dam Dacite or basement, comprises three coarsening-upwards volcaniclastic packages of claystone, siltstone, fine-grained to coarse-grained lithic sandstone and conglomerate deposited in a fluvio-lacustrine setting, and contains three tuff members. The Roopena Basalt is interlayered with the Fresh Well Formation, and comprises auto-brecciated lavas that exhibit only local interaction with water or wet sediment. Sharp basal contacts of the prograding packages within the Fresh Well Formation provide evidence of rapid flooding events within the basin. New detrital zircon geochronology of a sandstone within the Fresh Well Formation yielded a maximum depositional age of ca 1580 Ma, with provenance dominated by felsic volcanic units of the 1635–1605 Ma St Peter Suite. Sedimentation in the Gawler SLIP appears to have occurred in isolated basins with limited areal extent. It was largely restricted to the eastern Gawler Craton, and as well as the Roopena Basin, and includes similar basins at the Olympic Dam and Prominent Hill iron oxide–copper–gold ± uranium (IOCG ± U) deposits. The coincidence of sedimentation and mafic volcanism in the eastern Gawler Craton suggests that this region underwent extension at this time, although high-temperature metamorphism and compressional deformation occurred in some parts of the Gawler Craton and Curnamona Province synchronous with the Gawler SLIP. The Roopena Basin sedimentary rocks and underlying basement contain hematite–chlorite–sericite–white mica assemblages, permissive of hematite-style IOCG mineral deposits; however, no significant ore deposit has yet been discovered in the Roopena Basin.     

中、新生代陆相沉积盆地砂岩型铀矿床流体作用研究

通过对中、新生代陆相沉积盆地典型砂岩型铀矿床实例分析,本文阐述了砂岩型铀矿床的分类特征及其与盆地流体演化的关系,以及盆地流体演化史分析在砂岩型铀矿床找矿中的重要性,同时对铀在流体中活化、迁移、沉淀机制及砂岩型铀矿床流体作用研究方法进行了探讨。     

Geochronology of unconformity-related uranium deposits in the Athabasca Basin,Saskatchewan, Canada and their integration in the evolution of the basin

The importance of geochronology in the study of mineral deposits in general, and of unconformity-type uranium deposits in particular, resides in the possibility to situate the critical ore-related processes in the context of the evolution of the physical and chemical conditions in the studied area. The present paper gives the results of laser step heating ⁴⁰Ar/³⁹Ar dating of metamorphic host-rock minerals, pre-ore and syn-ore alteration clay minerals, and laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) U/Pb dating of uraninite from a number of basement- and sediment-hosted unconformity-related deposits in the Athabasca Basin, Canada. Post-peak metamorphic cooling during the Trans-Hudson Orogen of rocks from the basement occurred at ca 1,750 Ma and gives a maximum age for the formation of the overlying Athabasca Basin. Pre-ore alteration occurred simultaneously in both basement- and sandstone-hosted mineralizations at ca 1,675 Ma, as indicated by the ⁴⁰Ar/³⁹Ar dating of pre-ore alteration illite and chlorite. The uranium mineralization age is ca 1,590 Ma, given by LA-ICP-MS U/Pb dating of uraninite and ⁴⁰Ar/³⁹Ar dating of syn-ore illite, and is the same throughout the basin and in both basement- and sandstone-hosted deposits. The mineralization event, older than previously proposed, as well as several fluid circulation events that subsequently affected all minerals studied probably correspond to far-field, continent-wide tectonic events such as the metamorphic events in Wyoming and the Mazatzal Orogeny (ca 1.6 to 1.5 Ga), the Berthoud Orogeny (ca 1.4 Ga), the emplacement of the McKenzie mafic dyke swarms (ca 1.27 Ga), the Grenville Orogeny (ca 1.15 to 1 Ga), and the assemblage and break-up of Rodinia (ca 1 to 0.85 Ga). The results of the present work underline the importance of basin evolution between ca 1.75 Ga (basin formation) and ca 1.59 Ga (ore deposition) for understanding the conditions necessary for the formation of unconformity-type uranium deposits. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Uranium Provinces in China

Three uranium provinces are recognized in China, the Southeast China uranium province, the Northeast China-Inner Mongolia uranium province and the Northwest China (Xinjiang) uranium province. The latter two promise good potential for uranium resources and are major exploration target areas in recent years. There are two major types of uranium deposits: the Phanerozoic hydrothermal type (vein type) and the Meso-Cenozoic sandstone type in different proportions in the three uranium provinces. The most important reason or prerequisite for the formation of these uranium provinces is that Precambrian uranium-enriched old basement or its broken parts (median massifs) exists or once existed in these regions, and underwent strong tectonomagmatic activation during Phanerozoic time. Uranium was mobilized from the old basement and migrated upwards to the upper structural level together with the acidic magma originating from anatexis and the primary fluids, which were then mixed with meteoric water and resulted in t