International Symposium on Uranium Raw Material for the Nuclear Fuel Cycle: Exploration, Mining, Production, Supply and Demand, Economics and Environmental Issues (URAM-2018)

DETERMINATION OF URANIUM-BEARING SAMPLES IN TERMS OF POSSIBLE CONTAMINATION, ARIKLI URANIUM REGION, CANAKKALE, TURKEY

27 Jun 2018, 17:00

1h

Vienna

POSTER Track 4. Advances in exploration Poster Session

Speaker

Ms Gülcan Top Top (ITU Eurasia Institute of Earth Sciences/Istanbul/Turkey)

Description

INTRODUCTION Radioactive mineralisation sites and related exploration activities threaten the living ecosystems of surrounding areas which is a current concern in many countries [1,2]. Natural and artificial factors provoke the dispersion of radioactive isotopes from the sites and increase the contamination in the impacted area [3,4]. It is observed that the isotopes may be liberated, transported and precipitated under certain oxidation conditions and can accumulate in different regions and this process even may lead to secondary mineralization under appropriate conditions. Over time, these accumulation and transport environments may act as secondary sources and damage human and environmental health [5,6,7]. Radioisotope distribution continuously vary among landscape components (e.g. rock, soil, groundwater and surface water) [3,8,9]. As an example, groundwater interacts with background rock, leaches radioisotopes and then influences the chemical composition of the surface water and soil [10] Sampling strategy is one of the most important issues in contamination research. Methods which are suitable for one environment may be quite inappropriate for another one. For example, the mechanisms of the formation of uranium deposits vary widely and hence the geochemical makeup of the deposits also vary [3]. Therefore, careful measurements and analyses are needed to understand the geological and physical structure of the area before cost-effective analyses. Generally, for the determination of the radioactive element distribution originating from an exploration site, the easiest and cheapest step is to carry out outdoor absorbed gamma dose measurements (OAGD). The distance between the measurement points should be adjusted according to the detector range and integration time. Based on the gamma measurement values, the target area can be restricted. Especially, if erosion is dominant in the area, drawing the borders along the hilltops, gives the advantage to understand the flow of elements. Primarily the catchments of the exploration sites should be investigated, but measurements should also be performed at neighbouring catchments in terms of comparisons of the results and possible contamination risk. For sampling design, the next step is geochemical analysis. Geochemical parameters such as pH, EC (electric conductivity), organic matter, carbonate and clay content, and oxidation state help to evaluate the migration characteristics. Proper GIS operations using all the multisource predictor maps such as lithology, topography, soil type, land cover, erosion, hydrology, flow accumulation, run-off etc. can significantly reduce the sample number. Statistical analyses such as homogeneity test of univariate distributions, bivariate scatter plots, and multivariate cluster analysis (CA) and, principal component analysis (PCA) are used to separate populations in the dataset that possibly indicate various geochemical processes. The case study reported in the present work develops an integrated methodology including geochemical, radiometric and GIS-based landscape analysis for the determination of uranium-bearing samples to assess the possible uranium-related contamination at Arıklı uranium mineralisation region. DESCRIPTION The restricted study area, after the OAGDR orientation measurements, is covering Arıklı (Turkey/Çanakkale/Ayvacık) uranium mineralisation site (Ayvacık-Çanakkale/Turkey) and its surroundings. Turkey General Directorate of Mineral Research and Exploration (MTA) Office determined radioactive anomalies by an airborne survey in 1959 in the area. In 1967 the field was surveyed by the help of exploration ditches and between 1968-1982 a total 56 uranium exploration drillings were carried out [11]. Although it had been reported that the area contained uranium-favourable regions, the last drilling programme (1982) was finalized due to the decision of the government about uneconomical reserves [12]. According to the geochemical analyses applied to the samples taken from rock dumps and exploration ditches, phosphate-uranium relationship and in some samples, thorium enrichment was detected. Although, based on these analyses, the area was considered to be a phosphate-favourable area, after detailed analyses, it was abandoned due to insufficient economic reserves, as well. Later on, as stated in the report of Gök (1978), magnesite lenses and radioactive minerals were also found in some parts of volcanic tuff levels in samples taken from the vicinities of Arıklı village and in 1980, MTA took two samples from the region and 1050 mg/kg and 1300 mg/kg uranium was detected by TAEK (Turkish Atomic Energy) laboratories [13, 14] By the help of the phosphate related studies on Arıklı tuffs (ignimbrite) performed by Çelik et al. (1999), Günaydın and Çolak (2009) and Günaydın (2017) it was concluded that uranium and phosphate enrichments were formed by the help of hydrothermal fluids and they were accumulated at fragmented fault zones [15,16,11]. Bayleyite [Mg2(UO2)(CO3)3.18H2O] and ningyoite [(U,Ca,Ce)2(PO4)2.1−2H2O] were defined as minerals of uranium in the area. During the studies, 1:5000 scale geological maps were prepared [11]. Based on the restrictions after outdoor gamma measurements, the final study area covers approximately 12 km2 at the south-east of Ayvacık town in Ayvalık İ17-d4 pedestal. The population of Arıklı village was is about 256 in 2000. Livestock, poultry and beekeeping are common in the village. The region is also very important for olive production. The region has own private drinking water source transferred from the Kaz mountains, but groundwater is also used as drinking water. Additionally, groundwater is also used for agriculture and animal husbandry in the region. Streams flow into the Edremit Gulf, but their water flows are intermittent during the year. The area contains deep valleys and narrow plains. Kocakaya Hill is the highest peak in the region with 742 m height. Olive trees grow at the southern coastline, pine forests on the north side and some short trees and bushes can also be found there. Significant faults developed in NE-SW and NW-SE directions. [17]. The study area consists of four main rock groups. These are Upper Cretaceous aged ophiolitic base rocks, volcanic units, lacustrine sediments and alluvial sediments; The Çetmi ophiolitic melange which is a complex rock group of split-volcanic lavas, pyroclastic rocks, limestone blocks shale and greywacke form the basement of the study area and are covered by volcanic and lacustrine sediments [18]. Neogene-aged lacustrine sediments are called Küçükkuyu formation [19]. The formation contains volcanic intercalations with conglomerate, sandstone, siltstone, claystone and marl. These levels are transverse to each other in lateral and vertical directions [20,21]. In the study area, the main unit is Arıklı tuff which consists of andesite/andesitic tuffs and andesitic agglomerates. Based on its SiO2 content, it has an acidic-moderate character and in terms of their chemical characteristics, they are rhyolite and rhyodacite [11]. Inside the tuffs, there are silicic and altered nodules of 2-7 cm radius, some of which have rings of iron-oxide bands. Uranium enrichment developed via Ca+2-U+4 ion exchange in the phosphate nodules found in the Arıklı volcanic [21]. MATERIALS AND METHODS Taking into consideration the studies made by MTA, at first OAGDR (Outdoor Absorbed Gamma Dose Rate) orientation measurements were performed in the presented survey covering Arıklı, Nusratlı, Ahmetçe, Hüseyinfakı, Demirciköy and Kayalar villages, approximately 50 km2. For the measurements, portable ESP-2 Na(I) probed Eberline gamma detector was used at 1 m above the ground level during 100 s for each measurement [22]. The measurements were planned according to the lithological units. The map of the OAGDR data was prepared by kriging geostatistical interpolation method applying with the Arc-GIS software. As a result, the study area was restricted into a 2,63 x 4,25 km rectangle (~11 km2) which includes the catchment area of Arıklı mineralisation site and the Arıklı village. The restricted area first was split into 500x500m grids then inside the catchment, they were minimised to 250x250m. From the corners of each square, OAGDR measurements were taken. Open exploration ditches were identified and their OAGDR measurements were taken, either. From the measurement points soil samples were collected. Before collecting the soil samples, the sampling points were cleared off from vegetation, root and stones then 250 g of material from the first 10 cm of the topsoil was packaged. Beach sediments were homogenised and representative 250 g samples were collected in plastic bags. All the samples were dried to remove the moisture under sunlight and then transported to laboratory. The samples were sieved in 1-mm mesh, packaged and labelled. For pH measurement 6 g sample was mixed with 15 mL distilled water and after 12 h waiting, measurements were taken. For calibration of the pH meter (Multi 340i and pH/Cond 340i Handheld Multimeter) pH 4.00, 7.00 and 9.00 buffer solutions were used. The same solution at the same time and with the same device but different probe was used for EC measurements with the same device [23]. For carbonate analysis, 3-10 g soil was mixed with 0.1 M HCL solution. The probe of the Scheibler calcimeter was filled with the HCL solution and after fixing into the polyethylene wide-mouth 250 ml tube, the solution was mixed into the samples and were shaken by magnetic stirrer. CO2 pressure was measured by the Scheibler calcimeter chamber filled with 0.1 M Sodium hydroxide solution. The results of the gas volume were converted to CaCO3% by calculations [24]. Barium chlorite method was used for cation exchange capacity analysis (CEC). 4 g sample was mixed 0.1 M BaCl2 solution and buffered up to pH 8.0 with tetraethyl ammonium (TEA). After stirring by shaker 2 hours at 480 rpm the solution was filtered into centrifuge tubes and centrifuged. Finally, Ba2+ content is measured by ICP-OES [25]. On account of topographic analyses, run-off, slope-break and watershed models were derived from Digital Elevation Model (DEM) for 5x5m grid cells (Jordan, 2011). Drainage map and land cover map derived from topographic map using Arc-GIS software. All the multisource predictor maps were superimposed by using GIS operations using Surfer Software Homogeneity test of univariate distributions, bivariate scatter plots, and multivariate cluster analysis (CA) and, principal component analysis (PCA) were used for statistical analysis. RESULTS In the area, the highest outdoor gamma levels were detected at Karakisla region. In the study area, other anomalous measurement levels were found in the exploration ditches on Feyzullah Hill. At both sites, the ditches were still open and the maximal depth reached even 5 m. It is advised to close the ditches and check the radon emission of the sites. Since the area was under the effect of slope driven soil erosion, the OAGDR measurements were more correlating with topographical units than with the lithological units. The gamma levels at the alluvial accumulating flat bottoms of valleys were also higher than the background level due to the erosion effect and hills acted as physical barriers to prevent the dispersion of the radioactive contaminants from the catchment. According to the results of soil chemical analyses, higher values of EC and CEC measurements were driven by topographical and hydrologic barriers. For example, in the alluvial accumulative bottoms of valleys and along the meanders of stream branches, where water flow is slower, deposition took place providing higher values of EC and CEC. Regarding pH and carbonate measurements, their results correlated to each other and had the highest values in the beach sample. CONCLUSION Although there are numerous in situ geogenic radioactivity determination studies, this interdisciplinary developed methodology helps to analyse the behaviour of uranium distribution originating from Arıklı mineralisation site. It determines the geochemical, topographic units and proves their control mechanisms on the distribution. REFERENCES [1] INTERNATIONAL ATOMIC ENERGY AGENCY, Management of Radioactive Waste from the Mining and Milling of Ores, Safety Standard Series No. WS-G, IAEA, Vienna (2002). 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