De Caldas Plateau Research Articles

Sampling and Homogenization Studies of Uranium Mining Waste Rocks Using Normal and Large-Sample INAA

Uranium mining activities at Pocos de Caldas plateau, Brazil, generated huge amounts of sulfidic waste rocks which were dumped into piles around the mine pit, requiring control measures to minimize the environmental impact. In this work, the sampling and the homogenization of these waste rocks are studied and their elemental analysis by instrumental neutron activation analysis (INAA) using normal (about 200 mg) and large (about 2 kg) samples. The results obtained allowed us to conclude that the waste rocks are extremely heterogeneous requiring even larger quantities of sample for its characterization.

Evaluation of Dose due to Ingestion of Natural Radionuclides of the Uranium Series in Spring Waters

The concentrations of uranium isotopes and their decay products 226Ra, 222Rn, 210Pb and 210po have been analyzed in the mineral spring waters of a highly radioactive region of Brazil: Aguas da Prata. This region is located in the Poços de Caldas Plateau, one of the largest weathered alkaline intrusions in the world. Dose calculations were performed to evaluate the relative importance of these radionuclides in the exposure of the local population to radiation. Based upon concentrations measured in all the springs available, effective doses per year varying from 1.4 x 10(-4) mSv year(-1) for 238U to 5.1 x 10(-2) mSv year(-1) for 222Rn were observed. The doses from the ingestion of 222Rn, 210Po and 210Pb are of the same order of magnitude, and therefore these radionuclides are the most critical as far as the consumption of these waters is concerned.

Implications of groundwater weathered profile interactions to the mobilization of radionuclides

This study reports the nature and extent of open-system interaction between groundwater and a weathered profile developed in the high grade thorium and REE ore body in Morro do Ferro, Poços de Caldas plateau. The radioelement mobility in the shallow oxidizing environment was considered by using chemical data in conjunction with 234U/ 238U, 226Ra/ 230Th, 230Th/ 234U, 228Th/ 232Th, 228Ra/ 232Th and 230Th/ 228Ra activity ratios (AR’s) for borehole spoil and groundwater samples. Recharging groundwater from the studied borehole has low salinity values, with total dissolved solids content of 14.7 mg/l and total ionic strength of 0.00018. The ratio of the weight of dissolved radioelement per unit volume of solution to the weight of radioelement in solid phase per unit weight of solid phase showed that the radioelement solubility in the studied waters varied according to the following order: radium>uranium>thorium. 234U/ 238U AR’s less than 1 were measured in solid phase and can justify the enhancement of 234U in solution. 226Ra/ 230Th AR’s greater than 1 and 230Th/ 234U AR’s less than 1 were evaluated between 20 and 27 m in depth, where a 2.1-m thick magnetite dike was intersected. These ratios could be justified by deposition of U and Ra associated with Fe-Mn oxides and kaolinite, where mineral saturation indices evaluated from the available data confirm this possibility. Covariations among disequilibria involving 228Th/ 228 Ra and 228Ra/ 232Th AR’s showed the preferential removal of 228Ra relative to Th isotopes, 228Th and 232Th. The recent deposition of radium within the timescale of at least the last 35 years also is suggested.

Integration, manipulation and spatial analysis of data in mineral research, through empiric prospecting models: case study in the Pocos de Caldas Plateau: R. Almeida Filho, Revista Brasileira de Geofisica, 13(2), 1995, pp 127–142

Integration, manipulation and spatial analysis of data in mineral research, through empiric prospecting models: case study in the Pocos de Caldas Plateau: R. Almeida Filho, Revista Brasileira de Geofisica, 13(2), 1995, pp 127–142

The Radiological Impact of Agricultural Activities in an Area of High Natural Radioactivity

The Pocos de Caldas Plateau, Brazil, with 70 radioactive anomalies is used for cattle, pigs and poultry production and for raising crops like potatoes, corn, brown beans and carrots. Data on the radioactivity concentration of natural radionuclides in air, soil, animal products, vegetables, water, sediment, external dose rates, and outdoor and indoor radon were used together with socio-economical information to estimate the radiological exposure from these agricultural activities in this high natural radioactivity area for the local rural and remote populations. For the local population agricultural products from the plateau contribute only relatively little (ca. 0.14–0.24 mSv.y-1) to the high radiation exposure (ca. 6–16 mSv.y-1) from external exposure and inhalation of radon and thoron daughters. However, the agricultural products carry a significant annual collective dose (ca. 14 man.Sv.y-1) to remote populations.

Isotopic geochemical characterization of selected nepheline syenites and phonolites from the Poços de Caldas alkaline complex, Minas Gerais, Brazil

This paper presents and discusses the isotopic data from the hydrothermal studies of the Poços de Caldas Natural Analogue Project. The purpose of these studies was to elucidate the mass transport of relevant elements and isotopes associated with hydrothermal mineralization and alteration at the Osamu Utsumi uranium mine, as applicable to high-temperature radwaste isolation (particularly in the U.S. nuclear waste program). Research efforts were focused on studying the thermal, chemical and hydrologic nature of the palaeohydrothermal regime associated with a breccia pipe at the Osamu Utsumi mine, and related to the geochemical, geochronological and petrological characterization studies of unaltered regional nepheline syenite and phonolite. The regional rocks studies have a vertically elongated δD, δ 18O pattern, which possibly indicates meteoric water/rock interaction. Regression of RbSr whole-rock isotopic data for the regional nepheline syenite and phonolite samples did not produce isochrons. An internal, mineral-separate isochron regression from a nepheline syenite sample, considered representative of unaltered nepheline syenite of the Poços de Caldas plateau, yields an age of 78 Ma, and an initial 87S 86Sr ratio of approximately 0.7051. The initial 87Sr 86Sr ratios of the regional nepheline syenites are possibly indicative of a mantle source for the alkaline magmatism, with some incorporation of old, high Rb/Sr crustal material. The greater-than-mantle values of δ 18O, if not due solely to surficial processes, also appear to require some assimilation of crustal material. SmNd isotopic data for the regional rocks do not define any isochrons, although the nepheline syenite samples conform very well to a calculated reference isochron for 78 Ma and a fixed initial 143Nd/ 144Nd of 0.512359. The regional phonolite samples lie markedly off this isochron. This is probably due to the phonolite samples having different initial 143Nd/ 144Nd values. All regional samples lie within the “Mantle Array” trend. Their location within ϵ Nd–ϵ Sr space indicates as asthenospheric Mid Ocean Ridge Basalt (MORB)-type source magma also contaminated by continental igneous and metamorphic rocks (e.g. the Precambrian gneiss surrounding the Poços de Caldas plateau). The rocks studied at the Osamu Utsumi mine from the F4 drillcore have experienced varying degrees of hydrothermal mineralization and metasomatism, and deep weathering. The hydrothermally altered rocks have a quite pronounced δD shift, with only a slight δ 18O shift. The δD-δ 18O trend of the hydrothermally altered F4 samples most likely reflects the variability of temperature, hydrologic flow, mineralogical alteration and, therefore, water/rock interaction and isotopic exchange in the palaeohydrothermal regime. Regression of RbSr whole-rock isotopic data for subsamples from a nepheline syenite xenolith sample yields an age of 76 Ma and an initial 87Sr 86Sr ratio of approximately 0.7053. Due to the marked hydrothermal alteration and metasomatism of this sample, the RbSr isotopic system is interpreted as being re-equilibrated and thus the regressed age is the age of the hydrothermal event. Using a ( 87Sr 86Sr) 1 versus 1/Sr mixing diagram, distinct trends are seen for hydrothermal alteration, mineralization and weathering. Again, the F4 nepheline syenite samples do not define an SmNd isochron, but conform very well to a calculated model isochron for 78 Ma and an initial 143Nd/ 144Nd of 0.512365. The SmNd isotopic data also exhibit a possible disturbance by the hydrothermal, metasomatic alteration. A lamproite dyke which crosscuts the hydrothermal alteration in the Osamu Utsumi mine gives an age of 76 Ma, which is essentially the same as the RbSr age of the hydrothermally altered nepheline syenite subsamples.

Geomorphological and hydrogeological features of the Poços de Caldas caldera analogue study sites

The Osamu Utsumi mine and Morro do Ferro analogue study sites lie within the Poços de Caldas plateau in Brazil, which is the eroded remnant of a caldera formed from an 80 million year old intrusion. Geomorphologically, both sites occupy watershed areas adjacent to small streams in the centre of the plateau. The climate of the area has a marked wet season from November to April and is dry the rest of the year. The streams are ephemeral in their upper reaches, tending to dry up in the dry season as they are fed by a declining base flow. In the wet season they exhibit flash floods fed by intense rainfall causing overland flow. The wet season also provides recharge to groundwater. The plateau is a stable feature and its surface has been eroding at an average rate of 12 m per million years over the last 50 million years. The hydrogeological conditions at the mine have been significantly changed by localised quarrying involving the removal of rock below the natural water table and destruction of interfluves. This has modified natural groundwater flow patterns and disturbed the movement of oxidising and reducing waters. Flow velocities have increased five-fold close to the quarry and flow paths have shortened. Morro do Ferro is a similar site accompanied by more intense weathering (laterite/clay) and by magnetite breccia dykes but the groundwater conditions remain in a natural state. Simplified numerical models of the two sites are used to estimate groundwater flow rates and the effects of mining activity. The hydraulic conductivity of the Osamu Utsumi mine model was calibrated to observed mine pumping rates and results indicate that Darcy flow rates of 2 mm day −1 or more may be expected. Residence and interaction times are probably quite short.

Uranium Isotopes as Radioactive Pollutants in Groundwaters of the Morro do Ferro Thorium Deposit, Brazil

Groundwater and surface water samples were collected at Morro do Ferro, a thorium and rare earth deposit located on the Poços de Caldas Plateau, Minas Gerais State, Brazil, to evaluate if the mechanisms related to the migration of 238U and 234U isotopes can generate concentrations greater than the grossalpha activity contaminant limit. The 238U content range was 0.003-0.24 pCi/l and the 234U content range was 0.004-0.25 pCi/l, showing that the studied hydrologie environment doesn't indicate pollution by radioactivity due to these nuclides. However, 226Ra and 228Ra isotopes can be considered as radioactive pollutants in groundwaters but not in surface waters of the Morro do Ferro.

Th, U, Ra and rare earth element distribution in farm animal tissues from an elevated natural radiation background environment

A field study was conducted in an area of elevated natural background radioactivity (the Pocos de Caldas plateau, Brazil) to assess tissue concentrations and the comparative bioavailability of isotopic Th (IV), U (IV, VI), Ra (II) and light rare earth elements (REE), i.e. La (III) and Ce (III, IV) in adult steers, pigs and chickens. Among animals, analyses are limited primarily to bone and muscle since they represent the major loci for deposition/retention and transport to man, respectively. The assessment of comparative bioavailability was aided by normalizing tissue concentrations to local soil concentrations, i.e. by calculating soil-to-tissue concentration ratios (CRs). Mean CRs (for muscle/soil) in these animals were very similar for U, La and Th which, as a group, decreased among the farm animals sampled as (all × 10 −4): chicken (1)/>- steer(0·7) />- pig (0·4). For 226Ra, CRs in muscle decreased in the same order among animals although mean values were 3–5 times greater than those quoted. Much greater values and greater differences among the elements are noted for bone/soil CRs, which for all animals decreased as: Ra >> U > La = Th, indicating the order of elemental bioavailability (assuming bone to be the major retention compartment). Isotopic ratios in farm animal tissue are shown to resemble closely those in soils over which the animals forage, with few exceptions, indicating the importance of the soil component in the transfer of these elements to tissues.

Radionuclide transport by pocos de caldas plateau rivers, Brazil

Abstract Mass balance of Ra‐226 and U‐238 was used to assess the pollutant discharge from uranium mining and milling and to identify the main physical and chemical processes involved in radionuclide transport. The load value remains unchanged along the rivers although a decrease of radionuclide concentration was observed. Seasonal load variations are influenced by mobilization of sediments during wet periods. Soluble load is the principal form of radionuclide transport at Pocos de Caldas Plateau.

Accumulation of 210Po in foodstuffs cultivated in farms around the Brazilian mining and milling facilities on Poços de Caldas plateau

Several sample types from the environment of the uranium mining and milling facilities of Poços de Caldas plateau (CIPC) in Minas Gerais state, Brazil have been assayed for their concentrations of uranium and its daughters. This paper presents the data for 210Po in food, soils and fertilizers in the CIPC region and, for comparison, the corresponding results from a vegetable garden in a control region in Joinville, in the state of Santa Catarina. The results show that vegetables from two gardens near the CIPC region have no significant differences in Po content, despite the closeness of one of the sites to a uranium mine. For some species of vegetables, however, nearsite values were twice those in the control region. Superphosphate fertilizers influence the accumulation of 210Po by plants, as well as the concentrations in soils, and their contribution is more evident than that of local deposition. The major concentration in the leaf and stem suggests that the accumulation of 210Po in vegetables is due chiefly to its deposition on and absorption by their leaves.

The behavior of dissolved uranium in groundwaters of the Morro do Ferro thorium deposit, Brazil

Groundwater samples were collected for several months in boreholes drilled at Morro do Ferro, a thorium and rare earth deposit located on the Poços de Caldas Plateau, Minas Gerais State, Brazil. An aquifer system has developed in the weathered mantle due to in situ intense alteration. The weathered zone includes a thick argillaceous laterite greater than 100 m thick. The U content and 324U/ 238U activity ratio were measured in the groundwater samples and in spoil samples of a borehole drilled in the ore body. Some possible mechanisms related to the mobilization of uranium are considered such as complexation with humic substances and adsorption by clays.

Transfer of 226Ra and 210Pb to Forage and Milk in a Brazilian High Natural Radioactivity Region

Abstract The Pocos de Caldas plateau, where the Brazilian uranium mine and mill facilities are located, is a natural high radioactivity region. A study has been carried out in order to assess the environmental transport of the natural radionuclides in the region. The present work is concerned with the transfer of 226Ra and 210Pb to forage and milk. Similar concentrations for both radionuclides were found in soil samples. In forage 210Pb concentrations are one order of magnitude higher than those of 226Ra, however, the milk samples presented higher values for 226Ra concentrations. The average forage to milk concentration factors are of the order of 10-4 d.l-1 for 226Ra and 10-5 d.l-1 for 210Pb. Regarding transfer mechanisms, the results suggest the foliar deposition as the main pathway for 210Pb uptake by the forage. In contrast, for 226Ra the root uptake appears as the main transfer pathway.

Colloid Investigations in the ‘Pocos De Caldas” Natural Analogue Project

ABSTRACTPreliminary data are presented on colloids in groundwaters from two radioactive ore deposits (C-09 mine and Morro do Ferro) situated in the Pocos de Caldas plateau in the state of Minas Gerais, Brazil. Ultrafiltration with flat membranes of different nominal MW cutt-off limits (450 nm to 1, 000 dalton) was used to prepare colloid concentrates from 40 to 50 1 water samples. The colloidal retentates as well as the original groundwaters were analysed for relevant ‘major’ and trace element concentrations and for DOC. Distribution characteristics of elements like Si, Fe, Mn, DOC, U, Th and rare earths between colloidal phases and ‘solution’ as result of different groundwater chemistry will be discussed.

Uptake of 226Ra and 210Pb by food crops cultivated in a region of high natural radioactivity in Brazil

The Poços de Caldas Plateau is a deeply weathered alkaline igneous intrusion of about 35 km diameter, in which several radioactive anomalies exist. The first Brazilian uranium mine and mill are located in this region. A study is in progress to assess the edible vegetable uptake of the most abundant natural radionuclides in the local environment and this paper reports the results for 226Ra and 210Pb. In farm soils, both nuclides have similar concentrations. The minimum values are comparable to those found in areas of normal radioactivity but the maximum concentrations are ten-fold higher. ‘Exchangeable’ radium in soils ranges from 2·3% to 34·5% of the total. No statistical correlation was found between the ‘exchangeable’ 226Ra and several physico-chemical soil parameters. In the vegetables analyzed, 226Ra concentrations are slightly higher than those of 210Pb and the maximum values are also one order of magnitude greater than in normal regions. For both radionuclides, the average soil-to-plant concentration factors are of the order of 10 −3 and 10 −2, when related to total and to ‘exchangeable’ contents in soils, respectively. For each vegetable, no statistical correlation was observed between the 226Ra or 210Pb concentrations in the plant (fresh weight) and concentrations in the soil, either total or ‘exchangeable’. The ‘exchangeable’ Ca in soils does not seem to influence radium uptake by plants in a defined way.

Migration of radium from the thorium ore deposit of Morro do Ferro, Poços de Caldas, Brazil

A large thorium ore deposit is located in Morro do Ferro, a hill in the Poços de Caldas Plateau, Minas Gerais, Brazil, which contains an estimated 30 000 t of Th and 100 t of U in a highly weathered matrix exposed to erosion and leaching. 228Ra and 226Ra were analyzed in surface waters collected at various points in the drainage basin and in groundwaters from wells drilled through and around the ore body. The concentrations in groundwater demonstrated that radium is markedly leached by rainwater percolating through the ore body. In its transit underground, radium is removed from groundwater by sorption on soil particles and this natural process greatly reduces the radium discharged to the environment. In dry weather, the concentration of dissolved 228Ra in the main stream draining the Morro do Ferro is 7·0 ± 1·1 mBq litre −1 and in a control stream 1·6 ± 0·3 mBq litre −1. The estimated 228Ra mobilization rate by solubilizations is of the order of 10 −7 y −1.

Pre-operational environmental survey at the uranium mine and mill site, Poços de Caldas, Minas Gerais, Brazil

The first Brazilian uranium mine and mill are located on the Poços de Caldas plateau, in the Central State of Minas Gerais. The pre-operational environmental survey was carried out over a period of two years by the Brazilian Nuclear Energy Commission (CNEN), through the Instituto de Radioproteção e Dosimetria (IRD). The selection of the materials to be monitored, the sampling points and the radionuclides to be analysed were based on critical parameters taking into account the meteorological and hydrological characteristics of the site as well as land use. The results obtained are sufficient to characterize the environmental background of the area, and will allow an assessment of the environmental impact due to the operation of the facility and an evaluation of the adequacy of the effluent emmission control measures. In relation to their contribution to the population dose, the results indicated that 226Ra and 210Pb will be the important radionuclides.

Energy Dispersive Analysis of Actinides, Lanthanides, and Other Elements in Soil and Sediment Samples

A model is under development at this laboratory to predict the mobilization of Th from an estimated 20,000 metric ton deposit, in place and weathering as long as 80 million years on the Morro do Ferro, a hill on the Pacos de Caldas plateau in Minas Gerais, Brazil. The significance of this deposit lies in the marked similarities, chemically, between Th and Pu with reference to the problem of Pu waste management from the nuclear fuel cycle. One of the objectives of this program is to determine the elemental composition of the Morro do Ferro soil and its relationship to the mobilization of Th from the deposit. X-ray fluorescence is used for the analysis of Th, U, Ba, La, Ce, Pr, Nd, Sm, Dy, Eu, Gd, Yb, Hf , Fe, Zr, N b , Mo and Pb. This paper describes the XRF system and methodology used for the determinations and presents the results of 72 core, soil and sediment sample analyses for the above 18 elements. Analyses of three United States Geological Survey (USGS) rock standards are also presented.

Studies of the Mobilization of Thoriun from the Norro Do Ferro

The Morro do Ferro1,2,3 is a hill on the Pocos de Caldas plateau in the state of of Minas Gerais, Brazil which, except for a few monazite beaches, may have the highest levels of natural radioactivity of any place on the surface of the earth (1–3 mK/hr). The radioactivity originates from an ore body located on the upper slopes of the hill (Fig. 1), which rises about 140 m above its surroundings to a maximum altitude of 1540 m. The ore body is estimated to contain about 20,000 metric tons of Th and a somewhat greater quantity of rare earths. The Morro do Ferro has been the site of a number of radiobiological studies conducted during the past 20 years.4,5,6,7

Rochas Clásticas do Planalto de Poços de Caldas

Rochas Clásticas do Planalto de Poços de Caldas