Uranium Occurrences Research Articles

Calcrete uranium deposits in the Southern High Plains, USA

The Southern High Plains (SHP) is a new and emerging U.S. uranium province. Here, uranyl vanadates form deposits in Pliocene to Pleistocene sandstone, dolomite, and limestone. Fifteen calcrete uranium occurrences are identified; two of these, the Buzzard Draw and Sulfur Springs Draw deposits, have combined in-place resources estimated at about 4 million pounds of U3O8. Ore minerals carnotite and finchite are hosted in dolomite at the Sulfur Springs Draw deposit, with accessory fluorite, celestine, smectite/illite, autunite, and strontium carbonate. Host carbonate at the Sulfur Springs Draw deposit is ∼190 ka and mineralization mobilized as recently as 3.8 ka. Ash collected near the deposit is 631 ka and erupted from the Yellowstone caldera complex. The Triassic Dockum Group that contains sandstone-hosted uranium deposits throughout the region and underlies the SHP is a potential source for uranium and vanadium. Regional uplift and dissection reintroduced oxygenated groundwater into the Dockum Group, mobilizing uranium. Additional uranium may have been contributed to groundwater by weathering of volcanic ash in Pliocene and Pleistocene host rocks. The locations of the uranium occurrences are mostly in modern drainage systems in the southeast portion of the SHP. Modelling of modern groundwater in the SHP carried out in a parallel study shows that a single fluid could form carnotite through evaporation, and that fluids of the requisite composition are more prevalent in the southern portion of the SHP. The southeastern portion of the SHP hosts more uranium occurrences due to a variety of factors including (1) upward transport of groundwater and connectivity between source and host rock, (2) higher uranium and vanadium content of groundwater, (3) higher rates of groundwater recharge in this region to drive the mineralizing system, and (4) shallower groundwater facilitating surface evaporation. Ongoing erosion of host rocks challenges preservation of deposits and may limit their size.

The Mineral Chemistry of Chlorites and Its Relationship with Uranium Mineralization from Huangsha Uranium Mining Area in the Middle Nanling Range, SE China

The Huangsha uranium mining area is located in the Qingzhangshan uranium-bearing complex granite of the Middle Nanling Range, Southeast China. This uranium mining area contains three uranium deposits (Liangsanzhai, Egongtang, and Shangjiao) and multiple uranium occurrences, showing favorable mineralization conditions and prospecting potential for uranium mineral resources. Chloritization is one of the most important alteration types and prospecting indicators in this mining area. This study aims to unravel the formation environment of chlorites and the relationship between chloritization and uranium mineralization, based on detailed field work and petrographic studies of the wallrock and ore samples from the Huangsha uranium mining area. An electron probe microanalyzer (EPMA) was used in this study to analyze the paragenetic association, morphology, and chemical compositions of chlorite, to classify chemical types and to calculate formation temperatures and n(Al)/n(Al + Mg + Fe) values of chlorite. The formation mechanism and the relationship with uranium mineralization of the uranium mining area are presented. Some conclusions from this study are: (1) There are five types of chlorites, including the chlorite formed by the alteration of biotite (type-I), by the metasomatism of feldspar with Fe–Mg hydrothermal fluids (type-II), chlorite vein/veinlet filling in fissures (type-III), chlorite closely associated with uranium minerals (type-IV), and chlorite transformed from clay minerals by adsorbing Mg- and Fe-components (type-V). (2) The chlorite in the Huangsha uranium mining area belongs to iron-rich chlorite and is mainly composed of chamosite, partly clinochlore, which are the products of multiple stages of hydrothermal action. The original rocks are derived from argillite, and their formation temperatures vary from 195.7 °C to 283.0 °C, with an average of 233.2 °C, suggesting they formed under a medium to low temperature conditions. (3) The chlorites were formed under reducing conditions with low oxygen fugacity and relatively high sulfur fugacity through two formation mechanisms: dissolution–precipitation and dissolution–migration–precipitation; (4) The chloritization provided the required environment for uranium mineralization, and promoted the activation, migration, and deposition of uranium.

Integrated image processing and GIS-based techniques using knowledge-driven approaches to produce potential radioactivity map for the uraniferous granite of Egypt

ABSTRACTInterpretation of remote sensing data for allocating of lithologic units and for mapping of radioactive zones, supplies a valuable utility to produce Potential Radioactivity Map for the uraniferous granite. The study applied a digital image processing technique including interpretation and manipulation of Geophysical Airborne gamma-ray spectrometry data and The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) sensor image data of Terra satellite over a case study well-known radioactive area of El-Missikat, El-Eridya and Kab Amiri areas in the Central Eastern Desert, Egypt. The possible forms of digital image manipulation are categorised into the following procedures: Minimum Noise Fraction (MNF) rotation, colour composite, band ratios, Principle Component Analysis (PCA), decorrelation stretching and Iterative Self-Organising Data Analysis Technique Algorithm (Isodata) unsupervised classification. Matched Filter (MF) classification was performed on the data to map a chosen well- known alteration mineral association with the uranium occurrences from USGS library. Each of these constructed images with the surveyed Airborne spectrometry data (equivalent uranium) has been given a suitable weight to be integrated using Geographic Information System (GIS) tools to delineate the most promising potential radioactive zones. Moreover, the other comparatively and quantitatively goal of the study was to evaluate the performance of various knowledge-driven mineral probability modelling.

Geochemical evidence for K-metasomatism related to uranium enrichment in Daejeon granitic rocks near the central Ogcheon Metamorphic Belt, Korea

A new type of uranium occurrence in Korea was identified in pegmatitic and hydrothermally altered granite in the Daejeon area. The U-bearing parts typically include muscovite, pink-feldspar and sericite as alteration minerals. In this study, the geochemical characteristics and alteration age of the granitic rocks were examined to provide evidence for hydrothermally-enriched uranium. The K-Ar ages of muscovite coexisting with U-bearing minerals were determined as 123 and 128 Ma. The U-bearing rocks have relatively low (CaO + Na2O), high K2O contents, and high alteration index values by major element geochemistry. The trace element geochemistry shows that the uraniferous rocks have significantly low Th/U ratios and strongly differentiated features. The rare earth element patterns indicate that the uraniferous rocks have a low total REE and LREE contents with depletion of Eu. Considering the geochemical variation of the granitic rock major, trace and rare earth elements, it can be concluded that uranium enrichment in pegmatites and altered granite should be genetically related to post-magmatic hydrothermal alteration of K-metasomatism after emplacement of the two-mica granite. This is the first report for geochemical characteristics of Mesozoic granite-related U-occurrences in South Korea. This study will help further research for uranium deposits with similarities in geological setting, mineralogy and age data between South China and Korea, and can also be expected to help solve the source problems related to high uranium concentrations in some groundwater occurring in the granitic terrane.

Mechanism of uranium release from uranium mill tailings under long-term exposure to simulated acid rain: Geochemical evidence and environmental implication

To date, there is not sufficient knowledge to fully understand the occurrence, transport and fate of residual uranium (U) from uranium mill tailings (UMT). Herein this study investigated different U release behaviors from natural UMT (without grinding) under four simulated acid rain (pH = 2.0–5.0) compared with controlled scenario (pH = 6.0) for 25 weeks. The results showed that the most notable U release was observed from UMTpH2.0, followed by UMTpH3.0 whereas a nonlinear relationship between pH and U release was observed from UMTpH4.0–6.0. The divergence of U release behaviors was attributed to the presence of minerals such as calcite and clinochlore. Autunite, a secondary mineral formed after leaching, might regulate U release in UMTpH3.0–6.0. Fick theory model revealed the shift of U release mechanism from surface dissolution to diffusion transport for UMTpH2.0, UMTpH3.0 and UMTpH5.0 at varied stage, whereas UMTpH4.0 and UMTpH6.0 displayed univocal dissolution and diffusion mechanism, respectively. This study highlights the necessity of performing long-term leaching tests to detect the “shift event” of leaching kinetics and to better understand the mechanism of U release influenced by mineralogy of the natural UMT under simulated acid rain conditions, which is conducive to developing UMT management strategies to minimize the risk of U release and exposure.

Using spatial statistics to identify the uranium hotspot in groundwater in the mid-eastern Gangetic plain, India

The occurrence of uranium in groundwater is of particular interest due to its toxicological and radiological properties. It has been considered as a relevant contaminant for drinking water even at a low concentration. Uranium is a ubiquitously occurring radionuclide in the environment. Four hundred and fifty-six (456) groundwater samples from different locations of five districts of South Bihar (SB) were collected and concentrations of uranium (U) were analyzed using a light-emitting diode (LED) fluorimetric technique. Uranium concentrations in groundwater samples varied from 0.1 µg l−1 to 238.2 µg l−1 with an average value of 12.3 µg l−1 in five districts of Bihar in the mid-eastern Gangetic plain. This study used hot spot spatial statistics to identify the distribution of elevated uranium concentration in groundwater. The hypothesis whether spatial distribution of high value and low value of U is more likely spatially clustered due to random process near a uranium hotspot in groundwater was tested based on z score and Getis-Ord Gi* statistics. The method implemented in this study, can be utilized in the field of risk assessment and decision making to locate potential areas of contamination.

Hydrogeochemistry and Occurrences of Uranium and Radon in Groundwater of in Chungwon, Korea

Hydrogeochemistry and Occurrences of Uranium and Radon in Groundwater of in Chungwon, Korea

C-O Isotope Analysis of Dolostone of Vempalle Formation in Dhone-Gudipadu-Korivipalle Sector, Western Part of Papaghni Sub-basin, Andhra Pradesh and Its Impact on Uranium Mineralization

ABSTRACT Cuddapah basin is an important uranium province, wherein unconformity related uranium deposit occur in Srisailam sub-basin in northern part and the dolostone hosted strata bound uranium deposit in Vempalle dolostone in southern part. The latter host the low-grade, large-tonnage uranium deposit. Vempalle Formation in Dhone-Gudipadu-Korivipalle (DGK) sector, along western part of the Papaghni sub-basin consists of three major units viz. (a) lower dolostone, (b) middle purple shale and (c) upper cherty dolostone. The lower dolostone has lot of detritus, represented mainly by quartz, feldspar, mica and clay. The upper cherty dolostone has chert as layers, nodules, rip-up clasts and at places do have conspicuous reddish brown shale bands with <2mm size siliceous oolite layers. They exhibit shallowing-upward carbonate depositional system with tidal flat environment. A number of uranium occurrences in Gudipadu-Korivipalle sector are hosted by the lower dolostone unit, especially at its lower stratigraphic level, i.e. 15-42m above the Gulcheru-Vempalle (GV) contact. Micro-stylolites are indicative of comparatively more burial pressure. Presence of fenestral voids filled with recrystallised fibrous calcite and thin mud drapes in the dolostone is indicative of precipitation in a shallow marine-tidal flat environment with late burial dolomitisation. Depletion of heavier C and O isotopes [13C: (-2.31 to 1.32%) and 18O: (-6.21 to -17.3%)] in the lower dolostone indicate mixing of fresh water with sea water in the depositional environment of tidal flat regime

Uranium potentiality mapping of G-V occurrence at Gabal Gattar area, North Eastern Desert, Egypt, using GIS approach

Delineation and evaluation of mineral resources are major exploration parameters required for investment decisions. Identifying the best probable sites for uranium mineralization in terrains of lack subsurface penetrations is a challenging task. In northern part of Egyptian Eastern Desert, the uranium occurrences of Gabal Gattar area are among the most important source of uranium mineralization. Gattar-V (G-V) uranium occurrence considered as the most important uranium locality in the northern parts of Gabal Gattar area. The well-known uranium mineralization in this occurrence is restricted to the geological contact zone between the Hammamat sedimentary rocks and the G. Gattar Alkali feldspar granite. The lithological units and their alteration zones that are associated with the uranium mineralization and the ground spectrometric measurements data are identified and delineated throughout the field work of the geological investigation. In addition to the delineation of visible uranium mineralized zones, useful aid for the location of uranium promising zones is provided. Uranium potential (UP) mapping is a systematic tools that considers the main controlling factors which influence the localization of uranium mineralization within their host rocks. The present study aims to highlight, identify, model and map uranium promising zones in G-V uranium occurrence by using Geographic Information System (GIS) to construct multiple geological thematic maps such as different kind of alteration, contact zone, radiometric measurement and secondary zones of uranium mineralization. The constructed thematic maps of the different controlling factors of U-mineralization are assigned with a fixed score, weight, and calculated using a linear equation approach. Each weighted thematic map is statistically calculated to produce a uranium potential levels map of the investigated area. The uranium potential areas thus obtained were classified into four classes of potentiality (very high, high, moderate and low). The obtained an integrated uranium potential map of the investigated area will be a useful guide in the mining planning activity and create a good decision for better planning and management of uranium resource.

210Pb numa região anômala de Pocinhos-Paraíba

From 1979 to 1982, the extinct company NUCLEBRAS carried out studies on the occurrence of uranium in Pocinhos, a city located in the harsh region of the State of Paraiba, where dairy farms currently exist. 210 Pb, descending from the 238 U radioactive series, is deposited in soil and plants, mainly due to the natural fallout of 222 Rn. Once present in the plants, the 210 Pb can be ingested by dairy cows, and then transferred to the milk. Thus, milk consumption may constitute an important route of 210 Pb intake by man. In the human body, 210 Pb is rapidly transferred to the bones, which can induce the onset of leukemia. In this context, the objective of the present work was to determine the concentrations of 210 Pb in soil samples and forage palm ( Opuntia spp .) From farms located in the uranium anomaly of the city of Pocinhos. For that, the ion exchange resin technique was used. The concentrations of 210 Pb in the soil samples ranged from 7 to 5,098 Bq.kg -1 . For the forage palm samples, the concentrations varied from 4 to 178 Bq.kg -1 in the dry matter. The results showed a high availability of 210 Pb for the cattle feed chain of the farms studied.

Radioactivity recorded by clay minerals in the Shea Creek area, Athabasca Basin (Canada): Implications for uranium transfers and exploration

The understanding of uranium mobility in the geosphere is a prerequisite for the modelling of high-level nuclear waste repositories and economic uranium deposit genesis. To complement more classical geochemical and mineralogical approaches, this understanding can be improved by measuring the record of past cumulative radioactivity as stable radiation-induced defects in clay mineral structure. This study focuses on world-class unconformity-related uranium deposits of the Athabasca Basin (Canada) for which the source, timing, and paths of the uranium-bearing fluids are still matters of debate. A set of 46 samples collected from the Athabasca Group sandstones in the Shea Creek area of the western Athabasca Basin, up to 634 m above either the unconformity (barren drill hole) or uranium mineralization, was selected in order to locate the paleo-occurrences of radioelements. A relevant three-dimensional view is shown by plotting (i) the concentrations of radiation-induced defects (RID's) in clay minerals, (ii) the present dose rate, and (iii) the distance to the mineralization or unconformity. The results clearly reveal different cases, such as geochemical background, equilibrated dose rate, late accumulations of radioelements, and/or records of their past temporary occurrence. Noticeable paleo-occurrences, now leached away, are revealed within 100 m of the structures hosting present-day mineralized bodies, which is in line with a recent model of long range lateral paleofluid flow in a basinal permeable formation, and may be useful for exploration, albeit within a proximal range. Such results rely on the detection of RID's in clay minerals, as chemical analysis or gamma counting alone detect only the present concentration of radioelements and are unable to distinguish between accumulations, equilibration of transfers, or temporary occurrences of uranium. This study represents a first step toward spatial 3D quantitative reconstruction of U transfers, which will require time constraints and artificial dosimetry to improve models of genesis of high-grade unconformity-related deposits and to identify paleo-pathways of U migration.

Prikaz podataka o kategorijama ukupnih (geoloških) rezervi urana u Srbiji u klasama mineralnih resursa iz aktuelne zakonske regulative

Geological data on the results of the research and on the 'determined masses of reserves', i.e. the total (geological) reserves of nuclear mineral resources, uranium and thorium in Serbia, were obtained by research carried out in accordance with the legal regulations of SFR Yugoslavia and of SR Serbia. In this paper, the mentioned data are considered in the light of the newly adopted concepts, mineral resources and reserves from the Law on Mining and Geological Exploration of the Republic of Serbia (Official Gazette of RS No. 101/15). By the moratorium on the construction of nuclear power plants in the SFR Yugoslavia in 1989 and the Law on the Prohibition of the Construction of Nuclear Power Plants in the Federal Republic of Yugoslavia (1995), half-century geological exploration of nuclear mineral raw materials started in 1948/1949 was interrupted. With this interruption, the many uranium occurrences and uranium deposits remained unexplored and unrated, and the separate categories of reserves B + C1 + C2 + D1 + D2 were not balanced, which reflects the low level of their research. Data on the total uranium reserves of categories B + C1 + C2 + D1 + D2 in Serbia, in the amount of 19 651 680 t or 13 537 779 t [14], are (with appropriate correction) shown via the 'established' conversion map (as a Bridging Document) in the classes of superiors , indicated and measured mineral resources (in situ) from the current Serbian law. The position of the author of the paper is to present the existing data on the total (geological) uranium reserves in the newly introduced terms from the current law and as such approximate to the interested users.

Occurrence of Uranium in Groundwater Along the Lithological Contacts in Central Tamilnadu, India: An Isotope Hydrogeochemical Perspective

Groundwater contributes to the highest exposure level of naturally occurring uranium (U) to biosphere, and hence, the source and concentration of uranium in groundwater needs to be monitored periodically. In the present study, groundwaters from different lithologic locations were collected and measured for uranium concentration and major ions in order to establish any possible link with the lithology on the uranium distribution in central parts of Tamil Nadu, South India. About 11% of the samples contain U in excess of the permissible limit of WHO (Guidelines for drinking-water quality, WHO, Geneva, 2011), and the contamination was limited to mostly hard rock terrain, which is granitic in nature. The correlations among U, major ions, and environmental isotopes were studied to understand the mechanism governing uranium dissolution and transport in groundwater of this region. Observations lead us to infer that the older water with near-neutral pH and oxidizing condition contains higher dissolved U compared with relatively young groundwater. The results also reflect the possible health risk to the local population through long-term consumption of uranium-containing groundwater without any pretreatment.

Abundance, Distribution, and Modes of Occurrence of Uranium in Chinese Coals

Due to its environmental and resource impacts, the geochemistry of uranium in coal is of both academic and practical significance. In order to give a comprehensive summary about the geochemistry of uranium in coals, the abundance, distribution, and modes of occurrence of uranium in Chinese coals were reviewed in this paper. Although some coals from southwestern and northwestern China are significantly enriched in uranium, the common Chinese coals are of a comparable uranium concentration to the world coals. The roof and floor rocks, and parting of coalbeds, or coal benches that are close to the surrounding rock are favorable hosts for uranium in one coalbed. The uranium concentrations in coals of different ages decrease in this order, e.g., Paleogene and Neogene > Late Permian > Late Triassic > Late Carboniferous and Early Permian > Late Jurassic and Early Cretaceous > Early and Middle Jurassic. Uranium in Chinese coals is mainly associated with organic matter, and is correspondingly enriched in subbituminous coal and lignite.

Uranium in groundwater – A synopsis based on a large hydrogeochemical data set

Most of the knowledge on the occurrence of Uranium (U) in groundwater comes from in-situ manipulation experiments in the field, computational modelling studies or from laboratory analyses where individual processes of U mobilization were studied in isolation. Because of Uranium's vital redox chemistry it interacts, often simultaneously, with many other element cycles (e.g., sulfur, carbon, iron, and manganese) making it difficult to predict U concentrations in natural environments. For the present study a large data set was analyzed to predict the occurrence of U in groundwater from basic hydrochemistry. The data set consists of more than 8000 chemical groundwater analyses (including Uranium concentrations) from more than 2000 sampling locations.A strong relation between U concentrations and electric conductivity as well as alkalinity was observed, suggesting that weathering of geogenic source material and desorption from mineral surfaces is the principle mechanism of U release. Except for aquifers with strongly reducing conditions this process leads to a slow but continuous accumulation of U in groundwater in most cases. Importantly, the occurrence of U is modulated by the prevailing redox conditions in an aquifer. Uranium concentrations were moderate under oxic conditions and highest under manganese and nitrate-reducing conditions (heterotrophic as wells as autotrophic nitrate reduction). Only in iron- and sulfate-reducing groundwater the probability of U concentrations above 1 μg l−1 was virtually zero, as these ground waters act as U sinks.The combination of mineral weathering (especially carbonates) with mobilization of U under manganese and nitrate reducing conditions results in the highest risk of detecting U. In contrast, a low risk is associated with low pH (<7) and low mineralization of groundwater, which is the case in granitic catchments, for example. Our results further provide evidence, that agricultural practices such as liming, use of fertilizers and irrigation influence the occurrence of U in groundwater in multiple ways. Accurate management of aquifers underlying farmland will therefore become more and more important in the future. In summary, we find that the vulnerability of an aquifer to elevated U concentrations cannot be explained by a single factor. This complicates efforts to target elevated U concentrations in groundwaters that are abstracted for drinking water production.

Removing uranium (VI) from aqueous solution with insoluble humic acid derived from leonardite

The occurrence of uranium (U) and depleted uranium (DU)-contaminated wastes from anthropogenic activities is an important environmental problem. Insoluble humic acid derived from leonardite (L-HA) was investigated as a potential adsorbent for immobilizing U in the environment. The effect of initial pH, contact time, U concentration, and temperature on U(VI) adsorption onto L-HA was assessed. The U(VI) adsorption was pH-dependent and achieved equilibrium in 2 h. It could be well described with pseudo-second-order model, indicating that U(VI) adsorption onto L-HA involved chemisorption. The U(VI) adsorption mass increased with increasing temperature with maximum adsorption capacities of 91, 112 and 120 mg g−1 at 298, 308 and 318 K, respectively. The adsorption reaction was spontaneous and endothermic. We explored the processes of U(VI) desorption from the L-HA-U complex through batch desorption experiments in 1 mM NaNO3 and in artificial seawater. The desorption process could be well described by pseudo-first-order model and reached equilibrium in 3 h. L-HA possessed a high propensity to adsorb U(VI). Once adsorbed, the release of U(VI) from L-HA-U complex was minimal in both 1 mM NaNO3and artificial seawater (0.06% and 0.40%, respectively). Being abundant, inexpensive, and safe, L-HA has good potential for use as a U adsorbent from aqueous solution or immobilizing U in soils.

Combined high-resolution aeromagnetic and radiometric mapping of uranium mineralization and tectonic settings in Northeastern Nigeria

Geological lineaments, depths to the basement, uranium concentrations, and remobilization in parts of the Upper Benue Trough, covering about 55 × 55 km2 (longitudes 11°30′–12°00′E and 10°30′–10°30′N), Northeastern Nigeria were investigated using integrated High-Resolution Aeromagnetic Data (HRAD) and radiometric data. This was with a view to identifying the potential zones of uranium occurrence in the area. The HRAD was processed to accentuate anomalies of interest and depths estimate of 150–1941 m were obtained from source parameter imaging technique. The results from the superposition of the horizontal gradient magnitude, analytical signal amplitude, first vertical derivative, and 3D Euler solutions of the HRAD revealed that the study area was dissected by linear structures that trend ENE–WSW, NE–SW, E–W, NNE–SSW, WNW–ESE, and NW–SE; among which the ENE–WSW and NE–SW trends dominated. Analyses of radiometric data showed that uranium ores in the study area were possibly remobilized epigenetically from the granitic rocks, and were later deposited into sedimentary rocks (Bima formation). Burashika group (Bongna hills) and Wawa area of the study area showed vein-type deposits, while the anatectic migmatite in the northeastern region and the uranium rich Bima formation showed both fault/fracture and contact types of deposition. It was also observed the northwesterly and southeasterly, dominant dip direction, dipping faults dip in the same direction as the paleocurrent direction (direction of depositions of sediments), and trend in a direction perpendicular to the hypothetical direction of uranium deposition. The study concluded that the studied area is dissected by several linear structures and the studied area possibly contains deposits of uranium ore, which are likely to be found in: the Bima Sandstones of Wade, Shinga, Bima hill, Wuyo, Teli, Bryel, Dali, Barkan, Gasi, Kunkun, Boragara, Deba, and Gberundi localities; the anatectic migmatite at Kubuku, Whada, and Hyama; and the Bongna hills and agglomerates around Burashika, Kawaba, and Galu.

Magnetic Mapping for Delineating Structures Favorable to Uranium Mineralization in Dhofar Region, Sultanate of Oman

The Proterozoic basement is a potential host for uranium mineralization and therefore the probability of occurrence of uranium is highly likely in the Dhofar region of southern Oman. The crystalline basement of the Salalah area (Dhofar, Sultanate of Oman) is the largest area of Proterozoic basement of the Arabian-Nubian Shield which outcrop in Oman. It is because, the most productive parts of the crust for uranium exploration and production in the world are in similarly aged i,e Proterozoic rocks. Further, the area is heavily faulted and some of these faults have already been identified as the place of uranium enrichment. Also, the fault systems must have acted as fluid conduits for circulating waters scooping up uranium from deeper formations and carrying it to higher levels along the fault plane and also distributing it near the surface. Random sampling of gamma ray spectroscopy has revealed a concentration of uranium as much as 30-35 ppm which was substantiated by XRF analysis near the study area. And therefore, the interest lies in investigating the uranium mineralized subsurface structuers. Accordingly, total magnetic fields along eleven traverses were recorded at an approximate line interval of 20 m with a measurement interval of 10 m in the study area close to Yemen border. The acquired data was subjected to regional residual separation to decipher low frequency signals related to deep anomalies and also residual component to depict high frequency shallow seated small features. The computed amplitude of analytical signal indicates the precise spatial location of subsurface sources. Further, estimated depth to source based on Euler deconvolution (ED) and Fourier spectral analysis are found to be in the range of < 15m - > 60 m. The salient features of the analysis highlighting the outcome are presented.

Petrography, geochemistry and Alteration Studies of Kanawa Uranium Occurrences, Wuyo-Gubrunde Horst, Northeastern Nigeria

The Kanawa uranium occurrence is situated along a northerly fault zone at Gubrunde horst, underlain by migmatitesgneiss, syntectonic S-type granites and minor volcanic rock. The sheared zoned is highly altered. The alteration products are sericite, chlorite, and hematite. The uranium occurrences are epigentic derived by remobilization from the host rock to the sheared zones, probably through metasomatic process where feldspars has been replaced by U-Fe-Mg in an oxidized conditions, the mineralizing fluids may be sourced from the numerous volcanic bodies around the area. The host rock showed enrichment of uranium>5, could serve as the potential source of the mineralization. The mineralized mylonite is a product of the granitic host. The Fe-Mg-Ca-P-Sr-Zr-V-Co-U may reflect mineralization fluid composition.

Evaluasi Sistem Pengendapan Uranium Pada Batuan Sedimen Formasi Sibolga, Tapanuli Tengah

ABSTRAKUranium di alam dapat terbentuk dalam berbagai tipe cebakan, sesuai dengan sumber, proses, dan lingkungan pengendapannya. Keterdapatan uranium di Sibolga pada batuan sedimen Formasi Sibolga merupakan suatu potensi yang layak untuk dikembangkan tetapi hingga saat ini belum diketahui pola pengendapan dan proses mineralisasi uranium tersebut. Penelitian bertujuan untuk mengetahui pola sebaran batuan dan keterdapatan anomali kadar uranium berdasarkan data geologi, radiometri permukaan, dan data log bor untuk mengetahui proses pengendapan batuan dan mineralisasi uranium. Keterdapatan mineralisasi berdasarkan data log bor tersebar dari satuan konglomerat alas (Kgl 1), satuan batupasir 1 (Bp 1), satuan konglomerat 2 (Kgl 2), dan satuan batupasir 2 (Bp 2) dengan ketebalan dan sebaran semakin ke atas semakin menipis. Sebaran mineralisasi pada bagian timur pada satuan batuan konglomerat 1 lebih didominasi oleh mineral detrital hasil pengendapan epigenetik berupa monasit yang terbentuk pada saat pembentukan granit sebagai batuan sumber. Pada satuan batuan di atasnya mineralisasi berbentuk pola alur (channel) yang berarah timur laut-barat daya, yang terbentuk secara syn-genetic dengan mineral berupa uraninite, carnotite, dan coffinite. Pengendapan batuan Formasi Sibolga berasal dari timur ke arah barat dan pengendapan uranium terjadi akibat perbedaan kondisi lingkungan pengendapan dari oksidasi di bagian timur menjadi lebih reduktif di bagian barat daya. Peningkatan kandungan material organik yang cukup tinggi pada lingkungan pengendapan bagian barat daya menyebabkan lingkungan pengendapan dalam kondisi reduksi.ABSTRACTUranium in nature formed in various deposit type, depends on its sources, process, and depositional environments. Uranium occurrence in Sibolga, hosted in sedimentary rocks of Sibolga Formation, is properly potential to develop; nevertheless, the depositional pattern and uranium mineralization process so far had not been recognized. The research aim is to determine the rock distribution patterns and the existence of uranium grade anomalies based on surface geology and borehole log data. Mineralization occurrences from borehole log data distributed from basalt conglomerate unit (Kgl 1), sandstone 1 unit (Bp 1), conglomerate 2 unit (Kgl 2), and sandstone 2 unit (Bp 2) with their distribution and thickness are thinning to the top. Mineralization distribution in the eastern area, mainly on Kgl 1 unit, dominated by detritus materials from epi-genetic depositional in the form of monazite which is formed along with the formation of granite as its source rock. Meanwhile, mineralization on the upper rocks units formed a channel pattern trending northeast-southwest, which formed in syn-genetic process consist of uraninite, carnotite, and coffinite. Sibolga Formation deposition originated from east to west and uranium deposit formed because of the differences of depositional environment from oxidation in the east to the more reductive in the southwest. The increasing of organic materials in southwest basin caused the reduction condition of depositional environment.