Near-field high temperature transport: evidence from the genesis of the Osamu Utsumi uranium mine, Poços de Caldas alkaline complex, Brazil

The chemical, isotopic and mineralogical alteration which occurred during primary uranium ore deposition at the breccia pipe-hosted Osamu Utsumi mine, Poços de Caldas, Brazil was studied as a natural analogue for near field radionuclide migration. Chemical and isotopic alteration models were combined with finite difference models of the convective cooling of caldera intrusives. The modeling indicates that the intense chemical, isotopic, and mineralogical alteration of the Osamu Utsumi breccia pipe requires the circulation of > 10⁵ kg/cm² of boiling hydrothermal fluid > 200°C through each square centimeter cross-section of the pipe. This circulation could be driven by heat from a 6 km diameter intrusive extending to 10 km depth. Even with this large amount of circulation concentrated in the permeable breccia pipe, uranium solubilities must be orders of magnitude greater than indicated in the most recent experiments (and more in line with previous estimates) to produce the primary uranium mineralization at the Osamu Utsumi mine.The same models applied to a hypothetical high temperature waste repository show that heat from radioactive decay will produce a hydrothermal circulation system remarkably similar to that studied at the natural analogue site at Poços de Caldas. The depth of fluid convection induced by the hypothetical repository would be 5 to 10 km, the maximum temperature would be 300°C, the lifetime of the high temperature phase would be a few thousand years, and boiling would occur and cause most of the alteration within the hypothetical waste repository. This physical analysis emphasizes the importance of permeability on a 10 × 10 × 10 km scale in controlling the potential amount of circulation through the hypothetical repository.Application of the chemical models successfully used to interpret mineralization and alteration at the Poços de Caldas Osamu Utsumi mine to the hypothetical waste repository shows that even in a worst case scenario (waste implaced in a permeable host rock with no measures taken to inhibit flow though the repository) the amount of hydrothermal alteration in the hypothetical repository will be 0.1% of that in the breccia pipe at Osamu Utsumi. Assuming no barriers to uranium mobility, uranium precipitation above the hypothetical repository would be 0.04 ppm (rather than 40 ppm), hydrothermal alteration 0.03 wt% (rather than 30 wt%), etc.Our analysis indicates that modeled mineralogical alteration is sensitive to the thermodynamic data base used. Prediction of mineralogical alteration (which may be necessary to predict the migration of radionuclides other than uranium, for example) probably cannot be based directly on even very carefully collected laboratory thermodynamic data. Mineralogical complexities of the system, as well as data base uncertainties will require calibration of the thermodynamic framework against mineralogical alteration observed in the laboratory or field.     

The Thermal History of the Huangmeijian Granite Intrusion in Anhiii and Its Relation to Mineralization: Isotopic Evidence

Abstract Whole—rock Rb—Sr, zircon U—Pb and hornblende, biotite and K—feldspar K—Ar ages are used to reconstruct the cooling history of the Huangmeijian intrusion in the Anqing—Lujiang quartz—syenite belt in Anhui. Oxygen isotope geothermometry of mineral pairs demonstrates that diffusion is a dominant factor controlling the closure of isotopic systems. Assuming the cooling of the intrusion is synchronous with a dicrease in local geothermal gradients, an emplacement depth of about 8 km and the magma crystallization temperature of 800 ± 50°C are estimated. The Huangmeijian intrusion experienced a rapid cooling process and uplifted after its emplacement and crystallization at 133 Ma B.P. with a cooling rate of 34.5°C / Ma and an uplifting rate of 0.35 mm/ a. The intrusion was rising until it rested at a depth of 3 km at a temperature of 300 ± 50°C about 14 Ma later. Then the intrusion was in slow cooling and uplifting with a cooling rate of 4.4°C / Ma and an uplifting rate of 0.04 mm/ a. U—Pb dating of pitchblende is done for the hydrothermal uranium deposit formed in the contact zone of the Huangmeijian intrusion. The result shows that the mineralization age is close to the closing time of the K—Ar system in biotite. The fluid inclusion thermometry indicates that the mineralization temperature is in agreement with the closure temperature of the biotite K—Ar system. This suggests a close relationship between the slow cooling of the intrusion and the hydrothermal uranium mineralization process.     

Regional soil-gas helium distribution of the Ely and Delta 1° × 2° quadrangles, Basin and Range Province

A reconnaissance soil-gas helium survey was made in the Ely, Nevada and Delta, Utah 1° × 2° quadrangles in the Basin and Range Province. Helium concentrations in 510 samples ranged from −147 to 441 ppb He with respect to ambient air. The median helium value for the study area was 36 ppb. Concentrations of more than 100 ppb He and less than −20 ppb He occur more commonly in the Ely quadrangle and are especially numerous in the western one-half of this quadrangle. Interpretation of the data reveals that the helium concentrations reflect the rock type, particularly the silicic volcanic occurrences, and the geological structure of the area created by crustal extension. The regional soil-gas helium distribution is important information to consider when interpreting anomalies from detailed surveys.     

Geochemical evidence for a brooks range mineral belt, Alaska

Geochemical studies in the central Brooks Range, Alaska, delineate a regional, structurally controlled mineral belt in east—west-trending metamorphic rocks and adjacent metasedimentary rocks. The mineral belt extends eastward from the Ambler River quadrangle to the Chandalar and Philip Smith quadrangles, Alaska, from 147° to 156°W. longitude, a distance of more than 375 km, and spans a width from 67° to 69°N. latitude, a distance of more than 222 km. Within this belt are several occurrences of copper and molybdenum mineralization associated with meta-igneous, metasedimentary, and metavolcanic rocks; the geochemical study delineates target areas for additional occurrences.A total of 4677 stream-sediment and 2286 panned-concentrate samples were collected in the central Brooks Range, Alaska, from 1975 to 1979. The −80 mesh (< 177 μm) stream sediment and the heavy (specific gravity > 2.86) nonmagnetic fraction of the panned concentrates from stream sediment were analyzed by semiquantitative spectrographic methods.Two geochemical suites were recognized in this investigation; a base-metal suite of copper-lead-zinc and a molybdenum suite of molybdenum-tin-tungsten. These suites suggest several types of mineralization within the metamorphic belt. Anomalies in molybdenum with associated Cu and W suggest a potential porphyry molybdenum system associated with meta-igneous rocks. This regional study indicates that areas of metaigneous rocks in the central metamorphic belt are target areas for potential mineralized porphyry systems and that areas of metavolcanic rocks are target areas for potential massive sulfide mineralization.     

Integrated interpretation of satellite imagery, aeromagnetic, aeroradiometric and ground exploration data-sets to delineate favorable target zones for unconformity related uranium mineralization, Khariar basin, Central India

The Mesoproterozoic Khariar basin, to the SE of Chhattisgarh basin, comprises 1000 m thick arenaceous-argillaceous sediments. For the first time, a multidisciplinary approach has been made to the integrate interpreted satellite imagery, aero-magnetic and aero-radiometric data with available ground exploration data sets with an objective to understand structural fabric and to establish various parameters for unconformity related uranium mineralization in the environs of Khariar basin. Total Magnetic Intensity (TMI) anomaly image has been useful to mark major faults (ENE-WSW), magnetic bodies and overall basement characteristics. Combination of first vertical derivative (1^VD) and tilt derivative magnetic images brought out presence of NW-SE magnetic linear (dominant) with minor ENE-WSW and NNE-SSW trends. Basic dykes and quartz veins are the surface manifestations of NW-SE trend in basement. Radially averaged power spectrum indicates the approximate basement configuration. Enhanced Thematic Mapper satellite imagery (Landsat ETM⁺) interpretation has shown lineaments along NW-SE, NNE-SSW, ENE-WSW and ENW-WSE directions. These observations are corroborated by interpreted results of magnetic data. Analysis of both results indicate NW-SE and ENE-WSW trends as post depositional. Aero-radiometric images (U, Th, K and ternary U-Th-K) show overall radio-elemental distribution for various litho-units. Besides, Th and K images along with interpreted ETM⁺ satellite imagery (RGB: 432/752/751) are useful to map small outliers and to modify basement-sediment contact. Geochemical data from basement rocks around Khariar basin suggests the younger Bundeli granitoids and its equivalents are good source of uranium in the western margin. Presence of labile uranium is inferred from higher concentration of uranium in water samples. The Airborne gamma-ray spectrometry (AGRS) and hydro-geochemical anomalies fall along fault zones and intersection of fault zones. The western and southern margin of Khariar basin are also characterized by presence of paleosol at unconformity, which are favorable factors for unconformity type uranium mineralization. Based on the present study, part of western and southern margin emerge as potential target areas for further exploration of uranium.     

Regional geochemical prospecting in Calabria, Southern Italy

A governmental regional drainage survey assessed the mineral potential of Calabria in 1974. The Calabria area of southern Italy is a mineralized region in which Penninic and Austro-Alpine nappes, comprising ophiolites, metasedimentary rocks (phyllites, paragneiss, granulites, amphibolites) and granitic and granodiorite plutons, are overthrusting carbonate Apenninic nappes. Pre-Alpine stratabound and vein-type base-metal sulfide mineralization predominate, tectonically redistributed during the Alpine orogeny.A total of 5518 samples of the original 6999 active stream sediments from an area of 10,000 km² were analyzed by X-ray fluorescence and atomic absorption for Cu, Pb, Zn, Hg, Fe, Mn, As, W, Mo, Sn, and Be on the minus 180 μm fraction. Follow-up investigation of a 39-km² area around Bivongi-Ferdinandea using 760 soil samples analyzed for Fe, Mn, Zn, Cu, Pb, K, Mo, and Au, investigated molybdenite and chalcopyrite occurrences associated with granodiorite.A five-factor R-mode factor analysis reflected geological and mineralization features in the reconnaissance data. Factor 1 (Fe-Mn-Cu-Zn) is related to the Fe and Mn distribution in the stream sediments. Factor 2 (Be-Sn) reflects presence of pegmatites within metamorphic and magmatic rocks. Factor 5 (Mo) is essentially a single-element factor. Factor 4 (As-Pb-Zn-Hg-Cu) reflects mineralization. Factor 3 (W-Ba) does not cluster in association with any specific lithological unit. Significant metal associations, recognized from R-mode factor analysis, were used as independent variables and regressed against the original metal concentration of each sample. Residuals of multiple regression analysis, differentiated features representing mineralization from those related either to lithologic or geochemical parameters. New prospecting targets were identified and areas of known mineral occurrences were evident in the distinction of residuals.R-mode factor analysis of data from the follow-up investigation identified three factors. Factor 2 (Mo-K) reflects Mo mineralization and associated hydrothermally altered areas but does not suggest additional target areas.     

Electron paramagnetic resonance (EPR) spectroscopy in massive sulphide exploration, Rosebery mine area, western Tasmania, Australia

Electron paramagnetic resonance (EPR) spectroscopy of hot HNO₃ insoluble residues of rock powders is used as a new exploration technique for the volcanic-hosted massive sulphide (VHMS) deposit in the Rosebery mine area. The EPR signal intensities measured in 326.5±5 mT sweeps are strong in the altered rocks, and show a negative correlation with Ca, Na and Sr, and a positive correlation with K/Na, Rb/Sr and (K × Rb)/(Ca × Na × Sr). The EPR intensities measured in 326.5±100 mT sweeps show high values in the footwall pyroclastics, host rocks and hanging wall pyroclastics near and around the Rosebery deposit, and correlate positively with K, Fe, Mn, Ba, F, Rb, Zn, Pb and Zr. The Rosebery deposit and associated footwall alteration zone are located at the intersection of two elongated paramagnetic halos. The first is characterized by strong intensities of [AlO₄]° signals measured at magnetic flux density sweeps over 326.5±5 mT, trends NE–SW, and passes discordantly from the west to the east the White Spur Formation, altered footwall (footwall alteration zone), host rock of the Rosebery deposit, hanging wall and Mount Black Volcanics. The second, largely stratabound, halo is defined by strong intensities of Mn²⁺ sextets observed at magnetic flux density sweeps over 326.5±100 mT, runs N–S following the stratigraphic trend, and outlines the mineralized host rock and footwall alteration zone. It also extends toward the south into the unaltered footwall and hanging wall rocks. The first type of halo is considered to be related to wall rock alteration due to the VHMS mineralization processes as well to later Devonian metamorphism, and the second is thought to be related to massive sulphide mineralization alone.     

Exploration rock geochemistry for Pinnacles-type mineralization at Broken Hill, N.S.W., Australia

Geochemical responses in weathered and oxidized surface metasedimentary rocks associated with stratiform lead-zinc mineralization at Stirling Hill (6 km west of Broken Hill) are compared with the geochemical responses in fresh drill core from an equivalent lithostratigraphic section with stratiform lead-zinc mineralization at the Pinnacles Mine (8 km south of Stirling Hill). Mineralization is interpreted as being volcanic exhalative and it lies within highly metamorphosed (sillimanite grade) rocks of the Willyama Supergroup.Surface rocks were classified into groups by discriminant analysis using drill core data from the Pinnacles Mine as the initial training set. The behaviour of elements in surface rocks varies with the rock group but Zn, Pb, Mn, Fe, and Co are leached from all surface rocks relative to fresh drill core.Nothwithstanding the leaching effects of weathering, common geochemical responses to mineralization have been identified in drill core and surface rocks. Coincident positive anomalies for Zn/Ba and Fe/(Na × Ba) ratios and negative anomalies for Na/(Mn × Ca) ratios uniquely define mineralization in both weathered surface rocks and in fresh drill core.The results demonstrate that the pattern of geochemical responses to Pinnacles-type stratiform volcanic-exhalative mineralization in surface rocks has survived the intensive weathering regime in the Broken Hill region.     

Scoresum — A technique for displaying and evaluating multi-element geochemical information, with examples of its use in regional mineral assessment programs

A technique called SCORESUM was developed to display a maximum of multi-element geochemical information on a minimum number of maps for mineral assessment purposes. The technique can be done manually for a small analytical data set or can be done with a computer for a large data set. SCORESUM can be used with highly censored data and can also weight samples so as to minimize the chemical differences of diverse lithologies in different parts of a given study area.The full range of reported analyses for each element of interest in a data set is divided into four categories. Anomaly scores — values of O (background), 1 (weakly anomalous), 2 (moderately anomalous), and 3 (strongly anomalous) — are substituted for all of the analyses falling into each of the four categories. A group of elements based on known or suspected association in altered or mineralized areas is selected for study and the anomaly scores for these elements are summed for each sample site and then plotted on a map. Some of the results of geochemical studies conducted for mineral assessments in two areas are briefly described. The first area, the Mokelumne Wilderness and vicinity, is a relatively small and geologically simple one. The second, the Walker Lake 1° × 2° quadrangle, is a large area that has extremely complex geology and that contains a number of different mineral deposit environments. These two studies provide examples of how the SCORESUM technique has been used (1) to enhance relatively small but anomalous areas and (2) to delineate and rank areas containing geochemical signatures for specific suites of elements related to certain types of alteration or mineralization.     

Metal response in plants to sulfide mineralization in the Longobucco area (Calabria, southern Italy)

The results of a multielemental biogeochemical orientation survey carried out in Calabria, southern Italy, are reported in this paper. Five plant species: three herbaceous species, Oenanthe pimpinelloides, Anthemis triumphetti, and a stonecrop (Sedum tenuifolium), a leguminous shrub, spanish broom (Spartium junceum) and laricio pine (Pinus nigra ssp laricio) were studied to determine which species is the most responsive to sulfide mineralization and which are the best indicator elements. Si, Fe, Ti, Mn, Zn, Mo, Cu, and Pb were determined in ashed material by X-ray fluorescence analysis. All the data were treated statistically and classified into geometrically increasing intervals, in order to discriminate anomalous from background values. In addition, an R-mode factor analysis and a correlation analysis were performed to find out whether any specific metal association that could characterize both the lithology and mineralization existed for each plant species. The herbaceous plants, particularly Oenanthe, were much more effective as indicators of mineralization compared with laricio pine. The elements that gave the best indication of sulfide mineralization were Zn and Pb, confirming the usefulness of biogeochemical methods as an additional prospecting tool in Calabria, where such exploration has never been attempted before. R-mode factor analysis was found to be extremely promising as a supplemental tool in the interpretation of results from this biogeochemical survey. Each plant species is always characterized by a metal association (predominantly Pb-Zn-Mn) whose high factor loading scores constantly show a close relationship with proven sulfide mineralization.     

Cooling and exhumation of the oldest Sanqiliu uranium ore system in Motianling district,South China Block

The Sanqiliu uranium deposit belongs to a uranium ore system in Motianling district. It is the oldest uranium deposit in South China. Primary uranium mineralization occurred almost simultaneously with the emplacement of the host granites and subsequent dykes, and it has a relatively high grade of uranium (0.421%). We clarify the age of mineralization and investigate the cooling history through new pitchblende U–Pb and apatite fission‐track thermochronology. The pitchblende U–Pb results indicate that uranium mineralization occurred at ~801–759 Ma. Fractionation of uranium and lead at ~374–295 Ma is interpreted as remobilization and resetting of the original uranium. The Motianling area has apatite fission‐track ages of 57 to 18 Ma. By combining our results with previous work, we conclude that the deposit cooled slowly and was exposed at the surface during the Cenozoic. The timing and depth of exhumation helped to preserve and avoid erosion of the uranium deposit, and highlight the potential for regional uranium exploration.     

东秦岭—大别山铀钍钾空间分布与铀矿化

本文在综合分析东秦岭—大别山航空伽玛能谱资料的基础上,结合区域地质特征,探讨本区铀、钍、钾元素的空间分布与铀矿化的关系。     

Temporal relationship between granite cooling and hydrothermal uranium mineralization at Dalongshan in China: a combined radiometric and oxygen isotopic study

A combined study using multi-radiometric dating and oxygen isotopic geothermometry was carried out for Mesozoic quartz syenite, alkali-feldspar granite and associated hydrothermal uranium mineralization at Dalongshan in the Middle-Lower Yangtze valley of east-central China. Radiometric dating of the quartz syenite yields a whole-rock Rb–Sr isochron age of 135.6±4.3 Ma, a zircon U–Pb isochron age of 132.9±2.2 Ma, and K–Ar ages of 126±2, 118±3 and 94±4 Ma for hornblende, biotite and orthoclase, respectively. The alkali-feldspar granite yields a whole-rock Rb–Sr isochron age of 117.3±3.3 Ma, a zircon U–Pb isochron age of 114.7±2.1 Ma, and K–Ar ages of 112±2, 109±3 and 88±4 Ma for hornblende, biotite and orthoclase, respectively. Oxygen isotope thermometry for both granites gives temperatures of 685 to 720, 555 to 580, 435 to 460 and 320 to 330 °C, for hornblende, magnetite, biotite and orthoclase respectively, when paired with quartz. The systematic differences among the ages by the different techniques on the different minerals are used to reconstruct the cooling history of the granite. The results yield rapid cooling rates of 27.4 to 58.6 °C/Ma from 800 to 300 °C in the early stage, but slow cooling rates of 6.3 to 7.2 °C/Ma from 300 to 150 °C in the late stage. The regular sequence of oxygen isotope temperatures for the different quartz–mineral pairs demonstrates that diffusion is a dominant factor controlling the closure of both radiometric and O isotopic systems during granite cooling. Pitchblende U–Pb isochron dating yields an uranium mineralization age of 106.4±2.9 Ma, which is younger than the age of the granite emplacement and thus considerably postdates the time of magma crystallization, but is close to the closure time of the K–Ar system in the biotite. This points to a close relationship between granite cooling and ore-forming process. It appears that hydrothermal mineralization took place in the stage of slow cooling of the granite, whereas the rapid cooling of the granite was concurrent with the migration of hydrothermal fluids along fault structures. Therefore, the activity of the ore-forming hydrothermal system is temporally dictated by the cooling rates of the granite and may lag about 25 to 30 Ma behind the crystallization timing of associated granite.     

二连盆地苏尼特右旗地区HFU-39、40异常特征及找矿意义

为查明二连盆地苏尼特右旗地区HFU-39、HFU-40航放异常的铀成矿情况,本文在分析异常区区域地质资料基础上,采用地质剖面测量、地面伽玛总量测量、伽玛能谱剖面测量、土壤氡剖面测量及岩石化探取样分析综合方法,对HFU-39、HFU-40两个异常进行查证及评价。查证结果显示异常呈团块状展布,地面伽玛能谱测量铀含量最高达w（U）=135×10^-6,岩石化学分析铀含量最高达w（U）=256×10^-6,该区域氡异常突出;综合异常查证结果和对二连盆地泥岩型铀矿化的形成环境分析,指出了该区的下一步铀找矿方向。     

Global 1° × 1° thermal model TC1 for the continental lithosphere: Implications for lithosphere secular evolution

This paper reports a new 1° × 1° global thermal model for the continental lithosphere (TC1). Geotherms for continental terranes of different ages (> 3.6 Ga to present) constrained by reliable data on borehole heat flow measurements (Artemieva, I.M., Mooney, W.D. 2001. Thermal structure and evolution of Precambrian lithosphere: a global study. J. Geophys. Res 106, 16387–16414.), are statistically analyzed as a function of age and are used to estimate lithospheric temperatures in continental regions with no or low-quality heat flow data (ca. 60% of the continents). These data are supplemented by cratonic geotherms based on electromagnetic and xenolith data; the latter indicate the existence of Archean cratons with two characteristic thicknesses, ca. 200 and > 250 km. A map of tectono-thermal ages of lithospheric terranes complied for the continents on a 1° × 1° grid and combined with the statistical age relationship of continental geotherms (z = 0.04  t + 93.6, where z is lithospheric thermal thickness in km and t is age in Ma) formed the basis for a new global thermal model of the continental lithosphere (TC1). The TC1 model is presented by a set of maps, which show significant thermal heterogeneity within continental upper mantle, with the strongest lateral temperature variations (as large as 800 °C) in the shallow mantle. A map of the depth to a 550 °C isotherm (Curie isotherm for magnetite) in continental upper mantle is presented as a proxy to the thickness of the magnetic crust; the same map provides a rough estimate of elastic thickness of old (> 200 Ma) continental lithosphere, in which flexural rigidity is dominated by olivine rheology of the mantle.Statistical analysis of continental geotherms reveals that thick (> 250 km) lithosphere is restricted solely to young Archean terranes (3.0–2.6 Ga), while in old Archean cratons (3.6–3.0 Ga) lithospheric roots do not extend deeper than 200–220 km. It is proposed that the former were formed by tectonic stacking and underplating during paleocollision of continental nuclei; it is likely that such exceptionally thick lithospheric roots have a limited lateral extent and are restricted to paleoterrane boundaries. This conclusion is supported by an analysis of the growth rate of the lithosphere since the Archean, which does not reveal a peak in lithospheric volume at 2.7–2.6 Ga as expected from growth curves for juvenile crust.A pronounced peak in the rate of lithospheric growth (10–18 km³/year) at 2.1–1.7 Ga (as compared to 5–8 km³/year in the Archean) well correlates with a peak in the growth of juvenile crust and with a consequent global extraction of massif-type anorthosites. It is proposed that large-scale variations in lithospheric thickness at cratonic margins and at paleoterrane boundaries controlled anorogenic magmatism. In particular, mid-Proterozoic anorogenic magmatism at the cratonic margins was caused by edge-driven convection triggered by a fast growth of the lithospheric mantle at 2.1–1.7 Ga. Belts of anorogenic magmatism within cratonic interiors can be caused by a deflection of mantle heat by a locally thickened lithosphere at paleosutures and, thus, can be surface manifestations of exceptionally thick lithospheric roots. The present volume of continental lithosphere as estimated from the new global map of lithospheric thermal thickness is 27.8 (± 7.0) × 10⁹ km³ (excluding submerged terranes with continental crust); preserved continental crust comprises ca. 7.7 × 10⁹ km³. About 50% of the present continental lithosphere existed by 1.8 Ga.     

Critical review of some multivariate procedures in the analysis of geochemical data

Simulation experiments have been conducted to examine the potential usefulness of R-mode and Q-mode factor methods in the analysis and interpretation of geochemical data. The R-mode factor analysis experiment consisted of constructing a factor model, using the model to generate a correlation matrix, and attempting to recover the model by R-mode techniques. The techniques were successful in determining the number of factors in the model, but the factor loadings could not be estimated even approximately on the basis of mathematical procedures alone. Q-mode factor methods were successful in recovering all of the properties of a model used to generate hypothetical chemicaldata on olivinesamples, but it was necessary to use a correction previously regarded as unimportant.Publication approved by Director, U.S. Geological Survey.     

Statistical analysis of stream sediment data from the Ife-Ilesha area of Southwest Nigeria

Statistical treatment of geochemical exploration data in the Ife-Ilesha area has not been fully utilized as a tool in their interpretation. The results of 176 stream sediment samples from an area of 1800 km² analyzed for Cu, Zn, Mn, Ni, Co and Cr after hot extraction were treated with both simple and sophisticated (R-mode factor) statistical analytical methods. All the elements were found to have density distributions closely approaching lognormal or a mixture of two lognormal populations.They all show strong positive correlations with correlation coefficient values ranging from 0.5 between Mn and Ni to 0.84 between Mn and Co, all considered to be real at 5% level of significance.R-mode factor analysis produced a three-factor model which accounts for 82.0% of the total variance in the data. Factor 1 (Cu-Co-Ni) correlates spatially with the area underlain by the amphibolite complex, thus reflecting the parent rock as dominant influencing factor. Factor 2 (Mn-Co) and the strong positive correlation between Mn and Co are interpreted as resulting from the influence of Co-adsorption by Mn-oxides. Factor 3 (Zn) is probably a mineralization factor.     

The Vale de Abrutiga uranium phosphates mine, central Portugal

A brief summary about the composition and origins of the U deposit is present. The mineralization is composed by secondary uranium phosphates (saleeite and meta-saleeite). The precipitation was probably the main responsible factor for U retention within the quartz veins leading to the uranium phosphate mineralization of Vale de Abrutiga.     

Chemical and Sr isotopic characterization of North America uranium ores: Nuclear forensic applications

This study reports major, minor, and trace element data and Sr isotope ratios for 11 uranium ore (uraninite, UO_2+x) samples and one processed uranium ore concentrate (UOC) from various U.S. deposits. The uraninite investigated represent ores formed via different modes of mineralization (e.g., high- and low-temperature) and within various geological contexts, which include magmatic pegmatites, metamorphic rocks, sandstone-hosted, and roll front deposits. In situ trace element data obtained by laser ablation-ICP-MS and bulk sample Sr isotopic ratios for uraninite samples investigated here indicate distinct signatures that are highly dependent on the mode of mineralization and host rock geology. Relative to their high-temperature counterparts, low-temperature uranium ores record high U/Th ratios (>1000), low total rare earth element (REE) abundances (<1 wt%), high contents (>300 ppm) of first row transition metals (Sc, Ti, V, Cr, Mn, Co, Ni), and radiogenic ⁸⁷Sr/⁸⁶Sr ratios (>0.7200). Comparison of chondrite normalized REE patterns between uraninite and corresponding processed UOC from the same locality indicates identical patterns at different absolute concentrations. This result ultimately confirms the importance of establishing geochemical signatures of raw, uranium ore materials for attribution purposes in the forensic analysis of intercepted nuclear materials.     

内蒙古新城子盆地铀及多金属矿产勘查遥感应用

内蒙古新城子盆地位于大兴安岭南端及扎兰屯火山岩型铀成矿远景带南端,盆地内中生代火山活动频繁且强烈,区域断裂构造发育,主要发育火山岩型铀矿化,目前已发现小型火山岩型铀矿床1处、铀矿点2处、矿化异常点20余处,成矿潜力较大。研究区基岩出露较好,利于开展遥感铀矿勘查工作。笔者利用遥感数据对研究区进行了构造解译及蚀变信息提取,依据高分一号数据,初步厘定了研究区以NE、NW、近EW、近NS向4组线性构造为构造格架的特征;根据Landsat ETM数据提取了铁染、羟基等蚀变信息,缩小找矿范围,并开展铀矿地质调查及钻探查证工作;最后依据多源地学信息进行成矿预测,圈定胡斯台北、巴彦尔灯、五间房以及任家营子东4处成矿远景区。钻探揭露胡斯台北远景区多金属工业孔1个、五间房远景区铀工业孔2个。