Evidence of uranium biomineralization in sandstone-hosted roll-front uranium deposits, northwestern China

We show evidence that the primary uranium minerals, uraninite and coffinite, from high-grade ore samples (U₃O₈>0.3%) in the Wuyiyi, Wuyier, and Wuyisan sandstone-hosted roll-front uranium deposits, Xinjiang, northwestern China were biogenically precipitated and psuedomorphically replace fungi and bacteria. Uranium (VI), which was the sole electron acceptor, was likely to have been enzymically reduced. Post-mortem accumulation of uranium may have also occurred through physio-chemical interaction between uranium and negatively-charged cellular sites, and inorganic adsorption or precipitation reactions. These results suggest that microorganisms may have played a key role in formation of the sandstone- or roll-type uranium deposits, which are among the most economically significant uranium deposits in the world.     

A Surface-Layer Study of the Transport and Dissipation of Turbulent Kinetic Energy and the Variances of Temperature,Humidity and CO$$_$$

We discuss scalar similarities and dissimilarities based on analysis of the dissipation terms in the variance budget equations, considering the turbulent kinetic energy and the variances of temperature, specific humidity and specific CO\(_2\) content. For this purpose, 124 high-frequency sampled segments are selected from the Boundary Layer Late Afternoon and Sunset Turbulence experiment. The consequences of dissipation similarity in the variance transport are also discussed and quantified. The results show that, for the convective atmospheric surface layer, the non-dimensional dissipation terms can be expressed in the framework of Monin–Obukhov similarity theory and are independent of whether the variable is temperature or moisture. The scalar similarity in the dissipation term implies that the characteristic scales of the atmospheric surface layer can be estimated from the respective rate of variance dissipation, the characteristic scale of temperature, and the dissipation rate of temperature variance.     

Geotechnical and Environmental Hazards in Desert New Cities: A Case Study of El Minia El Gedida Site,Egypt

The plateau east of the Nile Valley at El Minia, Egypt, has been chosen for the siting of El Minia El Gedida city. Problems of underground caves suggested the need for integral geological, geotechnical and environmental hazard studies to examine the suitability of the area as a building site.Geologically, the area is formed of a thick sequence of Middle Eocene fossiliferous limestones and chalk with some layers of sandy, cherty and marly limestones. These rocks have heterogeneous physical and mechanical properties and fall within the weak to very weak range of limestones. Their mode of failure is almost of the brittle type developing extension, wedge and single shear type fractures. The mechanical properties are controlled by their physical, geological and mineralogical properties. They increase with density and dolomite content and decrease with porosity and calcite content. Empirical equations for some of these relations as well as the relation between field measures of rebound index and compressive strength are presented.Both regional and detailed structural analyses revealed the presence of major and minor normal faults and fractures trending in NW and NE directions. The NW faults are dominant. They define the topographic escarpments in the area. Most of the caves are aligned along major faults of this trend. Faults, fracture distribution and structural hazard maps of the area are presented. Paleostress tectonic analysis of these fractures suggests that the NW and NE faults are extensional due to tectonic stress which changes from normal to parallel to the Red Sea at different geologic times starting in post Middle Eocene. The similarity of this paleotectonic setting to present Red Sea tectonics points out the possibility of future rejuvenation of these faults.Topographically, the area lies in shallow surface drainage basins. The topographical risk is increased by fracturing and it should be considered if the area is subjected to a long period of heavy rainfall. Radiometrically, El Minia El Gedida city represents one of the lowest natural radioactivity areas within the safe limits recommended by the International Commission on Radiological Protection (ICRP).     

Local site effects estimated from ambient vibration measurements at the Nubian habitations area in Kurkur,Aswan, Egypt

The Egyptian government proposed a general plan, aiming to construct new settlements for Nubians in south Aswan in different places around Nasser’s Lake, one of these settlements in Kurkur area. This area are affecting by near distance earthquakes from Kalabsha faults system. These earthquakes generated great site effects on the sedimentary layers that in turn significantly influenced earthquake ground motions in the area. The main objective of the current study is to estimate the effect of local geology on seismic motion in terms of fundamental resonance frequency (f₀) and the corresponding H/V amplitude values (A₀) using the Nakamura technique. Ambient vibration measurements were carried out at 40 sites that are representative for the different geological units beneath the area. The recorded signals were processed using the horizontal-to-vertical (H/V) spectral ratio Nakamura’s technique. Analysis of spatial distribution of the fundamental frequencies (f₀) and the corresponding H/V amplitudes (A₀) showed that the f₀ value varies from 0.98 to 2.74 Hz, while A₀ varies from 2.2 to 6.6 within the study area. Output of this study is very important for solving the problems, which associated with the construction of various civil engineering purposes, for land-use planning and for earthquakes resistant structure design.     

Study the feasibility of using PPP for establishing CORS network

Nowadays many continuously operating reference stations (CORS) network were established in Middle East to improve the surveying tasks. Establishing such geodetic control networks can be a costly business where multiple stations should be occupied simultaneously and post-processed with scientific software. Recently, precise point positioning (PPP) provides precise positioning values that may be an alternative to precise relative processing. The current research aims to investigate that PPP has a potential as a reliable absolute positioning technique operational simplicity as well as to investigate the capability of PPP approach to be a low cost alternative to the conventional positioning methods used in position determination of core networks stations. In comparison with common relative GPS techniques, the costs are reduced; because no base stations and no simultaneous observations are necessary, no need for control network maintenance which could be the most defective factors that Egypt HARN network suffered from. To see the feasibility study of using PPP for precise determination of the CORS, 14 days of GNSS data for the 14 Kuwait integrated with 27 IGS stations were processed by Bernese software to calculate the precise coordinates of Kuwaiti CORS network in the latest terrestrial geodetic frame. Three days of these data were processed by Trimble business center software and using PPP approach to calculate the precise coordinates of Kuwait network. In the current research, a comparable investigation was carried out between the coordinates obtained from Bernese software, Trimble business center, and PPP approach. The comparison proved high level of agreement between the coordinates which confirm that PPP approach can be applied for establishment of CORS network.     

Apport de la gravimétrie à l'étude de la structure du bassin des Triffa (Maroc nord-oriental) : implications hydrogéologiques

Various techniques (horizontal and vertical derivatives, upward continuation, Euler deconvolution) have been applied to the gravity data from the Triffa's plain and the north flank of the Beni-Snassen massif to delineate various major geological structures such as faults and basins. These results allow the production of a structural map showing the fault systems for the survey area. This map forms the basis for planning future hydrogeological research in this region. To cite this article: D. Khattach et al., C. R. Geoscience 336 (2004).     

开鲁盆地砂岩型铀矿中黄铁矿与铀矿化成因关系探讨

开鲁盆地位于松辽盆地西南部,是中国北方砂岩型铀矿勘查的重点地区,自钱家店铀矿床发现以来,盆地内上白垩统姚家组目的层中相继发现了一些具有工业价值的铀矿床.为查明该层位中黄铁矿成因及其形成机制,探讨其与铀矿化之间的关系,本研究对含矿层砂岩中黄铁矿与铀矿物矿物学特征、黄铁矿S同位素开展细致研究.研究表明:(1)开鲁盆地姚家组砂岩中铀主要以独立铀矿物及吸附铀形式存在,独立铀矿物以沥青铀矿为主,含少量的钛铀矿及部分铀石,多数沿黄铁矿周边生长.吸附态的铀与黏土矿物密切相关.(2)姚家组砂岩中黄铁矿主要以草莓状、胶状及粒状产出,多与沥青铀矿共生,其中黄铁矿S同位素(d34S=–55.6‰～23.2‰),平均值–20.87‰,变化范围很大,说明硫的分馏程度较高,硫的来源范围较广.(3)分析表明黄铁矿具有细菌硫酸盐还原作用及热化学硫酸盐还原作用两种成因,并探讨了这2种成因黄铁矿的形成机制.综合前人研究,结合研究区成矿地质背景,认为黄铁矿为铀成矿作用提供了发生还原反应所需要的还原剂,且黄铁矿及铀矿物的形成与区内热流体存在紧密联系.     

Multistage mineralization in the Haoyaoerhudong gold deposit,Central Asian Orogenic Belt:Constraints from the sedimentary-diagenetic and hydrothermal sulfides and gold

The Central Asian Orogenic Belt,as one of world-class gold economic belts,preserves a number of giant,large black shale-hosted gold deposits,while it is still debated for origin of sulfides and gold mainly due to lack of identification for multiple stages of sulfides.The Haoyaoerhudong gold deposit is hosted in a sequence of Mesoproterozoic carbonaceous and pyritic slate,phyllite,and schist that form a tight syncline along the north margin of the North China Craton.Detailed petrography of the host rocks and mineralization have defined five stages of pyrites.The earliest form of pyrite(Py₁)occurs as fine-grained dispersed pyrite in black carbonaceous slate and medium-to coarse-grained disseminated pyrite in pyrite-rich layers,contains relative low gold and high arsenic content,indicating a syn-sedimentary or diagenetic in origin.Stage Ⅱ pyrite(Py₂)occurs with garnet and quartz inclusions and Py₃ occurs as pyrite veins,contains higher gold and lower As content,and are interpreted to have formed from the dissolution-reprecipitation of Py₁ during the peak metamorphism or post-peak metamorphism.Stage Ⅳ pyrite(Py₄)from the pyrite-quartz veins crosscut the metamorphic garnet,contains the highest gold concentrations and other trace elements,and is considered to have formed post-peak metamorphism.Abundant native gold,electrum,and maldonite occur as inclusions within Py₄ and monazite and in fractures that crosscut garnet.While,Py₅ with typical remobilized feature is thought to be a product of melting of former pyrites(Py₁ to Py₄)triggered by the large-scale Hercynian magmatism.The sedimentary/diagenetic Py₁ have δ³⁴S values that range from +12.4‰to +16.2‰.Later generations of sulfides,including Py₂ to Py₅,and Ccp₂ to Ccp₃,have δ³⁴S values from +9.5‰to +12.7‰.Monazite with maldonite inclusions from quartz-pyrite veins yielded an intercept age of 341.3±6.6 Ma,while coarse grained monazite associated biotite along fractures in the reefs yielded an intercept age of 254.6±8.2 Ma.The paragenetic,textural,chemical,and isotopic data suggest three distinct gold producing episodes at Haoyaoerhudong gold deposit.Gold and arsenic were clearly initially concentrated in organic muds,and enriched along the structures of diagenetic arsenic-rich pyrite.Subsequently,accompanying metamorphism and deformation,gold was liberated from the dissolution of diagenetic pyrites to form the pyrite veins.Finally,accompanying transformation of pyrite into pyrrhotite,gold was released into the metamorphic fluids to become concentrated as native gold,electrum,and maldonite in pyrite-quart veins.Monazite with age of 341 Ma from quartz-pyrite veins suggests that the third major gold mineralizing event in Haoyaoerhudong occurred before the Hercynian magmatism,suggesting that the Haoyaoerhudong deposit is a typical orogenic gold deposit rather than intrusion-related deposit.