A multivariate statistical and geostatistical study on the geochemistry of allochtonous karst bauxite deposits in Hungary     

Bárdossy  George  Kovács  Ó. 《Natural Resources Research》1995,4(2):138-153

A geochemical evaluation of the Szc-Halimba-Kisld area, Hungary, covering an area of more than 200 km² is presented using different statistical and geostatistical methods. The study area is a representative example of allochtonous karst bauxite accumulation. The three groups of deposits studied here have been explored and mined since 1950. Several thousand boreholes have been drilled, and bauxite cores were analyzed for the five main chemical components. A total of 80,000 pleces of analytical data were processed, followed by a geological examination of borehole logs and of mining excavations.The quantitative geochemical evaluation of the data set led to both geochemical and practical results: The geochemical behavior of the allochtonous, clastic karst bauxite deposits differs essentially from that of the autochtonous and parautochtonous ones, as well as that of the lateritic bauxite deposits. The deposits of the study area can be split into several subsequent geochemical-sedimentological units, each representing an event of bauxite transport and accumulation. Clear regional patterns can be revealed in the composition of these units. The geostatistically measured chemical variability of the geochemical units is rather different, the lowest units showing the smallest variability. The interrelations of the main chemical components are weaker and more irregular in the studied deposits than in the autochtonous lateritic bauxite deposits. Additional local genetic features, such as transport routes, can be delineated by the methods applied. Within each deposit, local changes of chemical composition and of its variability can be determined more precisely. These results can be used in bauxite prospecting and exploration, because areas of high or low bauxite quality can be predicted.  相似文献   

Fluid salinities obtained by infrared microthermometry of opaque minerals: Implications for ore deposit modeling — A note of caution     

Robert Moritz   《Journal of Geochemical Exploration》2006,89(1-3):284

Infrared microthermometry of opaque minerals has revealed that temperatures of phase changes vary with the infrared light source intensity, resulting in an overestimate of fluid salinities and an underestimate of homogenization temperatures. Failing to recognize this analytical artifact during infrared microthermometry may result in meaningless geological models. A fluid inclusion investigation on enargite from a high-sulfidation epithermal deposit is used as an example to document this. Fluid salinities obtained during an early investigation ranged between 6.3 and 20.4 wt.% NaCl, which were interpreted as intense boiling or as evidence for the involvement of a magmatic brine during ore formation. Fluid inclusion salinities obtained with improved analytical settings, i.e. low light intensities, fall between 1.1 and 1.7 wt.% NaCl and are in better agreement with fluid salinities obtained in quartz from similar deposits, and recent modeling suggesting vapor transport of Au and Cu from deep porphyry-Cu environments to shallower high-sulfidation epithermal deposits.  相似文献   

High-resolution sedimentary record of lead in the coastal mud of the East China Sea in the past one hundred and fifty years     

Yunchao HAO Zhigang GUO Dejiang FAN 《中国地球化学学报》2006,25(B08):13-13

In the East China Sea （ECS）, there are some mud areas, including the south coastal mud area, the north coastal mud area, and the mud area to the southwest of Cheju Island. X-ray fluorescence （XRF） techniques and Thermal Ionization Mass Spectrometry （TIMS） were used to study the high-resolution sedimentary record of Pb concentrations and Pb stable isotopic compositions in the past one hundred and fifty years in the coastal mud of the ECS. Pb concentrations of a ^210Pb dating S5 core in the study area have increased rapidly since 1980, and reached the maximal value with 65.08 μg/g in 2000, corresponding to the fast economic development of China since the implementation of the ＂Reform and Open Policy＂ in 1978; ^206Pb/^207Pb ratios generally had stabilized at 1.195 from 1860 to 1966, and decreased gradually from 1966 to 2000, indicating that the anthropogenic source Pb contribution to the ECS has increased gradually since 1966, especially since 1980. Pb concentrations decreased distinctly from 2000 to 2003 and ^206Pb/^207Pb ratios increased from 2001 to 2003, corresponding closely to the ban of lead gasoline from 2000 in China. From 1950 to 2003, there occurred four distinct decrease events of ^206Pb/^207Pb, possibly responding to the Changjiang River （Yangtze River） catastrophic floods in 1998, 1991, 1981 and 1954; from 1860 to 1966, there were two decrease periods of ^206Pb/^207Pb, which may respond to the catastrophic floods of Changjiang River in 1931 and 1935, and 1870. As a result of the erosion and drowning by the catastrophic floods, the anthropogenic lead accumulated in soil and water environments over a long period of time was brought into the Changjiang River, then part of them was finally transported into the ECS, which leads to changes in Pb stable isotopic composition.  相似文献   

Molar tooth structures of the Neoarchean Monteville Formation, Transvaal Supergroup, South Africa. I: Constraints on microcrystalline CaCO₃ precipitation     

JAMES W. BISHOP  DAWN Y. SUMNER 《Sedimentology》2006,53(5):1049-1068

Molar tooth (MT) structures are enigmatic, contorted millimetre‐ to decimetre‐long veins and spheroids of microcrystalline calcite that formed during very early diagenesis in Precambrian sediments. MT structures in the ca 2·6 Ga Monteville Formation are 600–800 Myr older than previously reported occurrences and establish that conditions necessary for MT genesis were met locally throughout much of the Precambrian. In the Monteville Formation, MT structures were formed shallow subtidally, extending to depths near storm wave base, in shale host sediments intercalated with storm‐generated carbonate sand lenses. They are filled with microcrystalline calcite and rare pyrite. Microcrystalline calcite identical to that in MT structures fills other pore space, including porosity between grains in carbonate sand lenses, moldic porosity in sand grains, sheet cracks in columnar stromatolites, and shallow cracks on sandy bedding planes. Relationships in the Monteville Formation demonstrate that microcrystalline CaCO₃ precipitated in fluid‐filled cracks and pores; microcrystalline calcite characteristics, as well as the paucity of carbonate mud in host rocks, are inconsistent with injection of lime mud as the origin of MT structures. Locally, MT cracks were filled by detrital sediment before or during precipitation. Precipitation occurred in stages, and MT CaCO₃ evolved from granular cores to a rigid mass of cores with overgrowths – allowing both plastic and brittle deformation of MT structures, as well as reworking of eroded MT structures as rigid clasts and lime mud. Crystal size distributions and morphology suggest that cores precipitated through nucleation, Ostwald ripening and size‐dependent crystal growth, whereas overgrowths formed during size‐independent crystal growth.  相似文献   

Stratigraphic evolution of a fluvial–eolian succession: The example of the Upper Jurassic—Lower Cretaceous Guará and Botucatu formations, Paraná Basin, Southernmost Brazil     

Claiton M.S. Scherer  Ernesto L.C. Lavina 《Gondwana Research》2006,9(4):475-484

The Guará and Botucatu formations comprise an 80 to 120 m thick continental succession that crops out on the western portion of the Rio Grande do Sul State (Southernmost Brazil). The Guará Formation (Upper Jurassic) displays a well-defined facies shift along its outcrop belt. On its northern portion it is characterised by coarse-grained to conglomeratic sandstones with trough and planar cross-bedding, as well as low-angle lamination, which are interpreted to represent braided river deposits. Southwards these fluvial facies thin out and interfinger with fine- to medium-grained sandstones with large-scale cross-stratification and horizontal lamination, interpreted as eolian dune and eolian sand sheets deposits, respectively. The Botucatu Formation is characterised by large-scale cross-strata formed by successive climbing of eolian dunes, without interdune and/or fluvial accumulation (dry eolian system). The contact between the Guará and the Botucatu formations is delineated by a basin-wide deflation surface (supersurface). The abrupt change in the depositional conditions that took place across this supersurface suggests a major climate change, from semi-arid (Upper Jurassic) to hyper-arid (Lower Cretaceous) conditions. A rearrangement of the Paraná Basin depocenters is contemporaneous to this climate change, which seems to have changed from a more restrict accumulation area in the Guará Formation to a wider sedimentary context in the Botucatu Formation.  相似文献   

Origin of fluids in iron oxide–copper–gold deposits: constraints from δ 37Cl, 87Sr/86Sri and Cl/Br     

Massimo Chiaradia  Dave Banks  Robert Cliff  Robert Marschik  Antoine de Haller 《Mineralium Deposita》2006,41(6):565-573

The origin of the hypersaline fluids (magmatic or basinal brine?), associated with iron oxide (Cu–U–Au–REE) deposits, is controversial. We report the first chlorine and strontium isotope data combined with Cl/Br ratios of fluid inclusions from selected iron oxide–copper–gold (IOCG) deposits (Candelaria, Raúl–Condestable, Sossego), a deposit considered to represent a magmatic end member of the IOCG class of deposit (Gameleira), and a magnetite–apatite deposit (El Romeral) from South America. Our data indicate mixing of a high δ ³⁷Cl magmatic fluid with near 0‰ δ ³⁷Cl basinal brines in the Candelaria, Raúl–Condestable, and Sossego IOCG deposits and leaching of a few weight percent of evaporites by magmatic-hydrothermal (?) fluids at Gameleira and El Romeral. The Sr isotopic composition of the inclusion fluids of Candelaria, Raúl–Condestable, and El Romeral confirms the presence of a non-magmatic fluid component in these deposits. The heavy chlorine isotope signatures of fluids from the IOCG deposits (Candelaria, Raúl–Condestable, Sossego), reflecting the magmatic-hydrothermal component of these fluids, contrast with the near 0‰ δ ³⁷Cl values of porphyry copper fluids known from the literature. The heavy chlorine isotope compositions of fluids of the investigated IOCG deposits may indicate a prevailing mantle Cl component in contrast to porphyry copper fluids, an argument also supported by Os isotopes, or could result from differential Cl isotope fractionation processes (e.g. phase separation) in fluids of IOCG and porphyry Cu deposits.  相似文献   

Early Cretaceous U–Pb zircon ages for the Copiapó plutonic complex and implications for the IOCG mineralization at Candelaria, Atacama Region, Chile     

Robert Marschik  Frank Söllner 《Mineralium Deposita》2006,41(8):785-801

Four of the major plutons in the vicinity of the Candelaria mine (470 Mt at 0.95% Cu, 0.22 g/t Au, 3.1 g/t Ag) and a dike–sill system exposed in the Candelaria open pit have been dated with the U–Pb zircon method. The new geochronological data indicate that dacite magmatism around 123 Ma preceded the crystallization of hornblende diorite (Khd) at 118 ± 1 Ma, quartz–monzonite porphyry (Kqm) at 116.3 ± 0.4 Ma, monzodiorite (Kmd) at 115.5 ± 0.4 Ma, and tonalite (Kt) at 110.7 ± 0.4 Ma. The new ages of the plutons are consistent with field relationships regarding the relative timing of emplacement. Plutonism temporally overlaps with the iron oxide Cu–Au mineralization (Re–Os molybdenite ages at ∼115 Ma) and silicate alteration (ages mainly from 114 to 116 and 110 to 112 Ma) in the Candelaria–Punta del Cobre district. The dated dacite porphyry and hornblende diorite intrusions preceded the ore formation. A genetic link of the metallic mineralization with the quartz–monzonite porphyry and/or the monzodiorite is likely. Both of these metaluminous, shoshonitic (high-K) intrusions could have provided energy and contributed fluids, metals, and sulfur to the hydrothermal system that caused the iron oxide Cu–Au mineralization. The age of the tonalite at 110.7 Ma falls in the same range as the late alteration at 110 to 112 Ma. Tonalite emplacement may have sustained existing or driven newly developed hydrothermal cells that caused this late alteration or modified ⁴⁰Ar/³⁹Ar and K/Ar systematic in some areas.  相似文献   

鄂尔多斯盆地北部底河道砂岩型铀矿地质特征   总被引：3，自引：0，他引：3  

吴仁贵  祝民强  余达淦  周万蓬 《华东地质学院学报》2006,29(1):1-6

鄂尔多斯盆地北部直罗组中的铀矿,是典型的产于河道中的砂岩铀矿,该矿床发育较好的卷状矿体。通过对该铀矿地质特征的研究,认识到发育卷状矿体的底河道砂岩型铀矿必须具备两大条件:其一是成矿砂体条件,即砂体要有较好的成层性、连通性和渗透性;其二是地层结构条件,即砂体必须存在较好的上、下隔水岩层。就砂体而言,河流相辫状沉积砂体是形成卷状矿体的主要砂体,并且以具有从辫状河向曲流河完整演化的辫状沉积砂体较好。砂体的上、下隔水岩层则有多种表现形式:下隔水层可由不透水的基岩或湖相沉积泥岩等构成;上隔水层由不透水的湖相泥岩、曲流沉积地层或岩浆岩等构成。在层间氧化作用过程上,存在纵横两个方向的氧化,即存在与河道方向一致的纵向氧化和与河道垂直的横向氧化,两种氧化作用成矿常叠加形成复杂的矿体类型;在矿化赋存的部位上,铀砂体通常发育在基底之上或不同建造之间;在古气候演变上,成矿作用发生在干旱气候条件下,或由潮湿向干旱的气候转变阶段。  相似文献   

地下水中硝基苯污染的防控技术—泥浆回灌法构筑阻截墙     

李绪谦  马莉  蒋惠忠  宗芳  李爽  刘利 《吉林大学学报(地球科学版)》2006,(Z1)

硝基苯污染可使地下水环境质量急剧恶化。利用阻截墙控制地下水中的硝基苯污染范围的扩大,是控制地下水环境继续恶化的经济、有效方法之一。以粘土、沸石、铁粉、硫酸钙等与水调配成泥浆,利用压力向井中回灌,将泥浆注入到含水层中,可有效地阻截地下水中硝基苯的扩散。  相似文献   

陆相油藏中砂泥岩互层时移地震遮掩效应及其对时移地震资料解释的影响     

WANG Da-wei 《现代地质》2006,(4)

从差异波形特征的角度出发,分析时移地震差异波形特征与砂泥岩互层油藏中油层速度变化的关系。通过建立由5层地层组成的楔形地质模型,运用褶积公式及时移地震求差公式,得到泥岩速度为2 400 m/s和砂岩速度为2 700m/s条件下,互层中砂岩速度变化±150 m/s的时移地震响应。研究结果表明:砂泥岩互层的差异波形是一个多峰复合波,泥岩夹层的厚度是决定差异波形特征的一个主要因素,并且存在一个临界值,即四分之一主波长;如果泥岩夹层的厚度小于这一临界值,就会发生遮掩效应,即顶部油层的时移地震响应可以掩盖中、下部油层的时移地震响应。  相似文献