Radiometric Survey Research Articles

Effect of Natural Ionizing Radiation on Health Indicators in Region with Monazite Sand in Brazil

Abstract Objective This article compares the occurrence of cancer and germinal damage in the city of Guarapari-Espírito Santo (ES), an area with high natural ionizing radiation, with other coastal cities. Material and Methods The evaluated cities were: Guarapari (ES), Campos (Rio de Janeiro), Rio Grande (Rio Grande do Sul), and Ilhéus (Bahia); the following factors were considered: mortality rate % from tumors (2007–2017), mortality rate % from tumors up to 15 years of age (2007–2017), hospital morbidity rate % from tumors up to 15 years of age (2008–2018), and hospital morbidity rate % from congenital malformation and chromosomal anomalies (2008–2018). Radiometric surveys were conducted by the Applied Physics Group at Universidade Federal do Espírito Santo. Results The natural radiation levels recorded in Guarapari resulted in accumulated dose between 3.65 and 10.95 mSv/year, and 1 mSv in the other cities. The highest average cancer mortality rates were: Rio Grande = 22.4%; Guarapari = 17.6%; Campos = 16.7%; and Ilhéus = 11.8%. The proportional hospital mortality and morbidity rates for cancer up to 15 years of age are as follows: Ilhéus = 3.36 and 5.87%; Rio Grande = 0.79 and 7.38%; Guarapari = 0.64 and 7.25%; and Campos = 0.39 and 9.13%. The hospital morbidity rate due to congenital malformations and chromosomal anomalies was 0.72% for Campos, 0.63% for Rio Grande, 0.62% for Guarapari, and 0.43% for Ilhéus. Conclusion There was no increase in cases of cancer or germ damage in Guarapari. These results indicated a dose threshold in the induction of these damages, contradicting the current linear no-threshold theory.

Utilization of radiometric data for mapping primary and secondary sources of gamma radiation and radon/thoron release potentials in Ireland.

This paper presents a novel approach to predict and map radon and thoron levels. We developed separate radon and thoron prediction maps for Ireland and introduced a system for producing high-resolution 3D radiation maps which may be used for planning purposes in residential areas, recycling and demolishing waste depots, and quarries of building and construction material. Additionally, we highlight the critical need to monitor thoron alongside radon in indoor surveys, as thoron's shorter half-life and higher energy levels may pose a greater health risk. We utilized Tellus radiometric survey data and indoor radon measurement records to investigate the spatial correlation between elevated indoor radon activity and anomalies in radioelement concentrations. We also estimated the degree of thoron interference in indoor radon surveys conducted in Ireland using CR-39 detectors. Field and laboratory surveys were performed to produce high-resolution radiation maps for four Irish quarries and estimate the radon and thoron potential of these quarries. Our initial findings suggest that thoron may be the primary health issue in some parts of Ireland, surpassing radon. For example, our map shows that the expected thoron potential in county Donegal is significantly higher than that for radon. Our radon and thoron exhalation tests on building material samples from four random quarries confirm this. We also estimate that over 20% of the elevated indoor radon activity recorded by the EPA using CR-39 detectors may be attributed to thoron-related sources. This study contributes to a better understanding of the prevalence and impact of radon and thoron in Ireland, helping to determine the main radiological health issue related to indoor air quality in the country. Thoron's impact on indoor air quality and health has been understudied in Ireland, necessitating more comprehensive studies and monitoring programs to accurately assess the prevalence and impact of both radon and thoron.

A quantitative approach to determination of survey specification quality for airborne magnetic and radiometric surveys with relation to large-scale compilations

Regional and nationwide geophysical merges consisting of magnetic and radiometric datasets have become standard practice within Australia and some parts of the world. The best practice for geophysical merges is to ensure the highest quality survey data is incorporated in all given areas. However, the traditional means of accomplishing this determination is quite qualitative without a well-defined methodology. Here, a quantitative algorithmic approach is provided, reducing user “guesswork” regarding which survey supersedes others when occupying the same space within geophysical merges. This is accomplished by assessing a wide range of survey specifications and applying weighted scores to their relative importance. This algorithm is applied to 889 datasets flown in New South Wales between 1957 and 2023 and provides a clear efficacy in determination of data quality based on survey design. Results from this algorithm have demonstrated proficiency in ranking surveys from highest to lowest quality and have formed the basis of all statewide geophysical merges in NSW since 2020.

Geoenvironmental characteristics of ferroniobium slag from the saint Lawrence columbium mine, Oka, Québec, Canada

Niobium (Nb) is a critical metal usually hosted in pyrochlore and mined from carbonatite deposits. The aluminothermic reduction of pyrochlore concentrate yields ferroniobium (FeNb) alloy and a slag waste. This study presents results from mineralogical, geochemical, and radiochemical investigations of FeNb slag found at the former Saint Lawrence Columbium mine in Oka, Québec, Canada. Slag casts exhibit a vertical zonation resulting from fractional crystallization and differentiation in the melt. Sampling of the slag was designed to characterize resulting chemical and mineralogical variations within casts. The median bulk composition of samples (n = 14) is dominated by Al2O3 (47%) and CaO (16%) from process reagents. The slag also contains significant TiO2 (4%) and trace elements including Zr (6763 ppm), U (601 ppm), and Th (1371 ppm) from pyrochlore that partition preferentially from concentrate to the slag. Based on radiochemical analyses of daughter products and assuming secular equilibrium, median (n = 3) activity concentrations for U and Th decay series are 213 and 111 Bq/g, respectively. A field spectral radiometric survey of the slag disposal area found median (n = 37) equivalent U and Th concentrations of 1069 and 2101 ppm, respectively. The primary mineralogy of the top and middle of slag casts is dominated by hibonite, grossite, and perovskite. Most of the U and Th is hosted by perovskite. The bottom of slag casts is an assemblage of mainly gehlenite, ferri-gehlenite, hercynite, grossite, and anorthite. The casts also contain a (Na,F,Ce) calcium-aluminate glass decreasing in abundance from top to bottom, and a (Na,F,Ce,Ti,Zr) calcium-aluminosilicate glass in the cast bottoms. The (Na,F,Ce) calcium-aluminate glass, grossite, and hibonite are the phases most susceptible to weathering. Perovskite, gehlenite, and hercynite show little or no signs of alteration. A leach test was performed on three columns filled with material from the top, middle, and bottom of casts. In the field, a parallel leach experiment was conducted with three barrels filled with undifferentiated slag material and open to atmospheric conditions. Column leachate was found to be highly alkaline, with pH in the top column reaching 13.2. Median pH values in column and barrel leachate were 10.4 and 9.2, respectively. The maximum U concentration in column leachate was 13 μg/L whereas in barrel leachate it was 65 μg/L. Maximum Th concentrations in column and barrel leachates were 7.65 and 0.2 μg/L, respectively. Median Al concentrations in column and barrel leachates were 74.9 and 3.9 mg/L, respectively. Slag from the production of FeNb is readily weathered and represents a technologically enhanced naturally occurring radioactive material (TENORM) requiring environmental management because of its radioactivity and the alkaline nature of its leachate.

Studies of radioactive minerals and geochemistry of uranium at the granitic rocks of Wadi Um Shillman Area, South Eastern Desert, Egypt

The northwestern part of Gabal Um Ara granitic pluton is represents a good example for uranium occurrence in the southeastern desert of Egypt. Among the different lithologies in the study area, the granitic rocks attract attention for more detailed geological, geochemical and radiometrical studies. Um Ara granitic masses cover an oval outline area of about 300 km2, which is characterised by moderate topography. The granitic rocks are classified as monzogranite and alkali feldspar granite. Both of them belong to the post-orogenic younger granite magmatic activity that intruded the Egyptian shield between 620 and 530 Ma. The intrusion of Um Ara monzogranite and alkali feldspar granite appears to have been controlled by deep-seated tectonic zones and block faulting. The studied area lies at southeast of Aswan City between 22ͦ 38′ 12˝–22ͦ 38′ 34˝ N and 33ͦ 47′ 27˝–33ͦ 48′ 14˝ E. Geochemically, the average concentration of the elements in North Um Ara granite shows that the relative abundance decreases gradually with decreasing incompatibility from Rb to Y. The common features are enrichment in more mobile elements Rb, Th and U. The monzogranite shows the lowest U and Th content, whereas the alkali-feldspar shows an enhanced contents of both elements, with average Th/U ratio = 3.0. the alkali-feldspar exhibits an expanded enrichment of Th relative to U. The U of the alkali-feldspar may be included within the structure of the refractory accessory minerals. The northern part of the Um Ara granitoids has subjected to different types of alterations. The radiometric survey of the northwestern part of Gabal Um area granitic pluton revealed the presence of several radioactive anomalies near the contact with the Dokhan volcanic and metavolcanic rocks in the north. Some visible uranium mineralisation of uranium minerals occur mainly along the NW, NE, E-W and N-S joints, of a highly sheared alkali feldspar-granite. Uranophane is visible secondary uranium mineral, characterised by bright yellow lemon colours and occurs mainly as filling fractures and joints associated with violet fluorite, iron and manganese oxides. The radioactive and accessory minerals studying and X-ray diffraction analysis that of the mineralised alkali feldspar-granite granite in the northwestern part of Gabal Um Ara granitic pluton revealed include the presence of fluorite, zircon, columbite, spessartine garnet whereas, the secondary uranium minerals are represented by uranophane, β-uranophane and kasolite. The hydrothermal origin was proposed as two possible alternatives for this uranium mineralisation.

On the detailed mapping of peat (raised bogs) using airborne radiometric data

This study concerns the applied use of the natural radioactivity in soils. The relevance of airborne radiometric (gamma ray) survey data to peat mapping is now well established and such data have been used in a stand-alone sense and as covariates in machine learning algorithms. Here we present a method to use these data to accurately map the boundaries of peat (raised bogs). This has the potential to assist with the estimation of carbon stocks using a property-based assessment of soil. The significance of such regionally-uniform survey data lies in the subsurface information carried by the measurement which contrasts with the surficial nature of many other covariates. Soils attenuate radiometric flux by virtue of their bulk density (and associated carbon content) and water saturation level. The high attenuation levels in low density, wet peat materials give rise to a distinctive soil response. Here an entirely physics-based assessment of flux attenuation is carried out both theoretically and empirically. Radiometric data from the ongoing Tellus airborne survey of Ireland are used. The study area is characterised by an extensive assemblage of discrete raised peat bogs in a framework of largely mineral soils. Peat is detected by a property contrast with adjacent soils and so we consider all soils within the study area. The relatively low lateral resolution of the airborne data is demonstrated by modelling and we examine the behaviour of a combined spatial derivative of the data. The procedure allows the identification of the edges of the 128 peat polygons considered and indicates other additional potential areas of subsurface peat. The data appear to resolve the differences that exist across three available soil/peat databases that are used for the validation of the results obtained.

A Multi-Method Approach to Geophysical Imaging of a Composite Pluton in North Portugal

Potassium (K), thorium (Th), and uranium (U) are good markers of magmatic or alteration processes and the surface concentrations of these radioelements can be mapped at the regional or local scale through radiometric (gamma) surveys. In this study, a radiometric survey was performed in a post-orogenic pluton located in North Portugal, namely the Lamas de Olo Pluton, composed by three granitic facies. This pluton has already been intensively studied, including magnetic susceptibility, gravimetric, geochemical, and petrographic studies. The main objective of this work is to evaluate the radiometric data and combine them with other characteristics, such as magnetic susceptibility, and gravimetry, as well as to elucidate structures such as faults and fractures, outline geological boundaries, and identify alteration zones within various granites of the pluton. The radiometric approach reveals the spatial distribution of radioelements, offering a more distinct portrayal of the geology in the studied area. The radioactive heat production rate was calculated for the studied pluton, showing that the mean value is 4.09 µW m−3, surpassing the known mean values for granites. Our study highlights that radiometric measurements unveil compositional variations within granitic pluton and aid in identifying feeder zones. Furthermore, these measurements can be correlated with each type of granites, demonstrating associations with surface concentrations of K-Th-U. Our findings indicate a spatial alignment between the NE feeder root and a U-rich granite (Barragem granite), as evidenced by its elevated concentration of this radioelement. Conversely, the other root displays a notable relative concentration of Th, consistent with the Th-rich characteristics observed of the two other granites (Lamas de Olo and Alto dos Cabeços granites).

Arduino programming of an educational robotic platform applied in radiological accident simulation

This work aims to develop a robotic platform coupled to radiation detectors for application in radiological accident simulation experiments. To this end, a robot was assembled on a platform on six wheels with Arduino programming, seeking movement in different degrees of freedom. The robot was controlled by remote control and viewed by a camera so the operator could follow the path taken by the robotic platform. The radiation values were seen instantly from the display of the radiation monitor/detector (RadEye). This platform model used non-destructive tests with radioactive sources in the laboratory for an environmental radiometric survey simulating a radiological accident. The results showed the command synchronization between the controller and the platform in an environment with only the presence of the background and the visualization of the instantaneous dose rate in Sv/h. However, when faced with the radiation field, there was interference in the signals and communication controlling the robot's movements. However, due to the short exposure time to gamma rays, the electronic components did not show any damage. It can be concluded from this experience that the prototype should be improved by adding shielding to the electronic boards, which are sensitive to radioactivity. The relevance of this investigation lies in developing robotic platforms for exposure in environments that pose health risks and for the radiological protection of emergency teams in actions during radiological and nuclear accidents.

On methods for radiometric surveying in radiotherapy bunkers

Radiometric surveys in radiotherapy bunkers have been carried out in Brazil for many years, both by the same radiotherapy facility for verification of shielding as by the regulatory agency for licensing and control purposes. In recent years, the Intensity Modulated Radiation Therapy (IMRT) technique has been gradually incorporated into many facilities. Therefore, it has been necessary to consider the increased leakage component that has an important impact on the secondary walls. For that, a radiometric survey method has been used that considers an increased ‘time of beam—on’ for the secondary walls. In this work we discuss two methods of doing this: the first considers that this ‘time of beam—on’ affects the sum of the two components, leakage and scattered. In another method it is considered that only the leakage component is affected by this extended ‘time of beam—on’. We compare the methods and show that for secondary walls with U = 1 the first method overestimates dose rates by important percentages and for secondary walls with U < 1 it can both overestimate or underestimate the dose rates, depending on the parameters of the project. An optimized procedure is proposed, according to the use factor (U) of the secondary wall to be measured.

The history of airborne radiometric surveys over the nuclear test range at Maralinga and a call for a new survey

The history of airborne radiometric surveys over the nuclear test range at Maralinga and a call for a new survey

Radiometric survey of sediments and health risk assessments from the southern coastal area of Delta State, Nigeria

Over the years, the release of potential radiological components around the oil exploration environment has increased with potential health implications.Yet; the mechanism and health associated assessment have remained fuzzy to most experimental scientists. The current study determines the activity concentration of radionuclides in sediments and the corresponding health risk assessments from the hydrocarbon exploration environment of the southern coastal area of Delta State, Nigeria. A Sodium-iodide NaI(Tl) detector, with a well-calibrated multichannel analyzer (MCA) to ensure efficiency and energy was utilized. A total of seventy-five sediment samples (Five sediment samples each per community) were collected from the southern coastal area of Delta State, Nigeria. The mean activity concentrations of 40K, 238U, and 232Th of the sediment samples were 3361.48 ± 194.26 Bqkg−1, 40.11 ± 16.17 Bqkg−1, and 45.73 ± 19.27 Bqkg−1 respectively. The obtained mean values exceeded the world standard limit of 400 Bqkg−1, 35 Bqkg−1, and 30 Bqkg−1 respectively. Also, the computed mean radiological health hazard risk of radium equivalent activity (Raeq), representative level index (Iyr), external hazard index (Hex), internal hazard index (Hin), absorbed gamma dose rate (D), annual effective dose equivalent outdoor and indoor (AEDE) and lifetime cancer risk (ELCR) values are 363.94 ± 32.37 Bkgl−1, 2.9657 Bkgl−1, 0.9839, 1.0919, 175.82 nGyh−1, 2.1556 mSvyr−1, 0.8625 mSvyr−1, and 7.5447 mSvyr−1 respectively. The values were found to be slightly higher than the world standard limit. Therefore, the residents that are using the sediments of the southern coastal area for the construction of buildings as well as dwelling in houses built with such sediments are exposed to these radiological materials. This may pose a radiological health risk concern. The obtained results will serve as radiation and radiological baseline data for sediments of the southern coastal area of Delta State, Nigeria.

Geology, Petrography, and Geochemistry of Younger Granites and Related Radioactive Pegmatite from Gabal El Urf Area, North Eastern Desert, Egypt: Implications for the Evolution of the NYF-Type Rare-Elements Granitic Pegmatite

Gabal El Urf region is located in the northern Egyptian Eastern Desert and overlain essentially by older and younger granitoids of Late Proterozoic age. These granitoids contain numerous outcrops of pegmatites, mostly occurring as dikes and veins or huge separated masses. In the contrary, pegmatites form lens-like bodies enclosed within the younger granites along their margins. Previous radiometric surveys showed anomalous concentrations of radioactivity on pegmatite body, located to the south of the study region. The younger granites and the associated radioactive pegmatite are studied in details with the aim to describe this pegmatite, petrogenesis and its relation with the encolsing granite. The younger granites are monzogranite and syenogranite according to mineralogical and chemical classification. Petrographically, the two younger granitic phases are strikingly similar. Both consist of potash feldspar, plagioclase and biotite with some hornblende in the earlier phase. Gabal El Urf younger granites are categorized as highly fractionated I-type granites with metaluminous to mildly peraluminous characters, which emplaced at 600 ± 11 Ma in post-collisional environment. The radioactive pegmatite is located within the syenogranite and enriched with Zr, Nb, Ta, Y, Th, U and REEs; accordingly it was classified as NYF-type rare-elements pegmatite. Metal-bearing generations of minerals within the rare-elements pegmatite include zircon, uranothorite, betafite, aeschynite, fluorite, pyrite and ilmenite.

Radiation and Environmental Safety in the Exploration and Development of Metal Deposits in South Yakutia

Radiometric surveys of mining dumps on spent placers of gold, monazite and the exploited gold-uranium ore deposit in South Yakutia were carried out. It is established that the dumps of alluvial, overburden and waste rocks in terms of the effective specific activity of radionuclides when used in construction work are characterized by different degrees of tolerance. It is shown that stacked radioactive ore dumps at the “Lunnoye” deposit after heap leaching of gold become powerful uncontrolled sources of radioactive pollution of the environment. It is recommended to conduct periodic monitoring of their radioactivity levels by express methods of field radiometry for the safe use of mining dumps as building materials.

Empirical Relation Between Magnetic and Radiometric Survey in Bitumen Area, Ogun State, Nigeria

Abstract One of the vital roles played by both magnetic and radiometric surveys is identification and delineation of mineral deposits. The study area, Imeri, which lies between latitude 6 °45′N to 6 °48′N and longitude 3 °58′E to 3 °59′E, has been established for bitumen deposition. The responses of mineral deposition to different geophysical methods differ from place to place due to variation in climate and bedrock composition. In this study, two geophysical techniques—magnetic and radiometric methods—were adopted to investigate the magnetic anomalous and radiometric flux responses around the bitumen deposit area. The study also intends to establish a model-like relation between the radiometric parameters and the magnetic anomaly observed. Statistical inferences for the established relations were deduced using the t-test at 0.05 significance levels. The result obtained showed that uranium and thorium concentration responses along the two traverses were in good agreement with that of magnetic intensity. The claim was accounted for based on the correlation result, which ranged between 74%–79% and 84%–89% for uranium and thorium, respectively, with magnetic intensity along the two traverses. In order to validate the claim, the t-test was used. The result obtained showed that there exists no significant difference between the two geophysical methods; the result for the t-test has critical value &gt; calculated value (p-values &gt; 0.05). Based on this, the empirical relations were deduced for magnetic anomalous response and radiometric parameters. This work has therefore proven the two techniques to be versatile for bitumen prospecting in the study area.

Radiometric survey in microscopy laboratory

The objective of this paper was the radiometric survey at the Materials Engineering Laboratory of the Military Institute of Engineering, in Rio de Janeiro, Brazil. Properties of materials are analyzed in this laboratory using X-rays machines. For the development of that work, two scintillator detectors were used with their associated electronics. Detector “A” has NaI(Tl) as scintillator material and detector “B” has CeBr3. In addition to verifying whether the measured dose rate is in accordance with that provided by the CNEN standard, a comparison was made between the efficiencies of these radiation detection equipment.

Comparison of the response of two scintillator detectors used in an environmental and occupational radiometric survey during the operation of the Argonauta reactor

The Argonauta research reactor at the Institute of Nuclear Engineering - IEN operates, under normal conditions, at powers ranging from 1.7 to 340 W, developing activities of a scientific-technological nature in the areas of neutron radiography, radionuclide production and conduction from experimental practices to graduate courses at CNEN research institutions and other Brazilian institutes of science and technology. During some security operations, the presence of investigators, students and/or operators inside and around the main hall of the Argonauta is required. Therefore, it is important to assess normal occupational exposure conditions when the reactor is in critical condition. This makes it possible to verify in greater detail the equivalent doses of ambient gamma radiation contained by the combustion of the fuel element inside the reactor room and in the surrounding areas, according to the Radiation Protection Plan (RPP) of this installation. In this work, a didactic activity was carried out to familiarize the students of the first period of the Master's Course in Nuclear Engineering, at the Military Institute of Engineering, with the procedures involved in the radiometric survey of the free, controlled and subsequent locations of this nuclear installation. This practice aims to identify the doses to which Occupationally Exposed Workers (OEW) and the general public are admitted, verifying compliance with regulatory requirements regarding the monitoring of environmental and local activities, as well as a comparison between the radiation monitors used.

The Cs-137 radiological accident in Goiânia, Brazil: Conditions and results of the airborne radiometric survey

This paper describes the details of the aeroradiometric operations, the radiation detection system used and discusses the results. The low-altitude survey was carried out over Goiânia a few days after information of the accident was received by the national competent authority, the Brazilian Nuclear Energy Commission (CNEN). Given the little information at the time of the accident and the urgency to respond to the local and federal authorities, an aerial radiometric survey was proposed to evaluate the extent of the contamination and dispersion of the radioactive powder. The city's entire urban area and nearby dwellings centers, plus the two creeks crossing the city were surveyed in two days. The survey found only one additional contamination point 2.8 x 10-4 C/kg/h (1.1 R/h) that had not yet been identified by ground survey crews. Furthermore, no contamination was found along the margins of the Capim Puba Creek and Meia Ponte rivers which could be contaminated due to rainwater common at that time of the year. Detection tests conducted at different altitudes over the main contamination area showed that the Cs-137 gamma radiation could be detected even at altitudes of 350m above the ground. This was much higher than the 40 m - 70 m decided for the overflights. The survey demonstrated that the contamination was restricted to a few locations in the neighborhood of the metal scrap place where the source shield was broken. These locations were under the control of CNEN radiological emergency response personnel. Such a finding was an important indicator to calm down the population and the government authorities. This allowed concentrating attention on the remediation of the known points of high gamma activity.

Radiometric survey with Remotely Piloted Land Vehicle in Chemical, Biological, Radiological and Nuclear Defense operations

This article addresses the development of a remotely piloted vehicle for the chemical, biological, radiological, and nuclear army defense system, able itself to perform radiometric surveys remotely favoring the process of local mapping and investigation of possible dispersions of radioactive materials in radiological and nuclear accidents and incidents. Tests were carried out to verify the efficiency of the developed prototype and it can be verified that the vehicle has a great applicability and optimizes the radiological protection process.

Detailed Geogenic Radon Potential Mapping Using Geospatial Analysis of Multiple Geo-Variables—A Case Study from a High-Risk Area in SE Ireland

A detailed investigation of geogenic radon potential (GRP) was carried out near Graiguenamanagh town (County Kilkenny, Ireland) by performing a spatial regression analysis on radon-related variables to evaluate the exposure of people to natural radiation (i.e., radon, thoron and gamma radiation). The study area includes an offshoot of the Caledonian Leinster Granite, which is locally intruded into Ordovician metasediments. To model radon release potential at different points, an ordinary least squared (OLS) regression model was developed in which soil gas radon (SGR) concentrations were considered as the response value. Proxy variables such as radionuclide concentrations obtained from airborne radiometric surveys, soil gas permeability, distance from major faults and a digital terrain model were used as the input predictors. ArcGIS and QGIS software together with XLSTAT statistical software were used to visualise, analyse and validate the data and models. The proposed GRP models were validated through diagnostic tests. Empirical Bayesian kriging (EBK) was used to produce the map of the spatial distribution of predicted GRP values and to estimate the prediction uncertainty. The methodology described here can be extended for larger areas and the models could be utilised to estimate the GRPs of other areas where radon-related proxy values are available.

A RECENTLY DISCOVERED TRACHYTE-HOSTED RARE EARTH ELEMENT-NIOBIUM-ZIRCONIUM OCCURRENCE IN NORTHERN MAINE, USA

AbstractReported here are geological, geophysical, mineralogical, and geochemical data on a previously unknown trachyte-hosted rare earth element (REE)-Nb-Zr occurrence at Pennington Mountain in northern Maine, USA. This occurrence was newly discovered by a regional multiparameter, airborne radiometric survey that revealed anomalously high equivalent Th (eTh) and U (eU), confirmed by a detailed ground radiometric survey and by portable X-Ray fluorescence (pXRF) and whole-rock analyses of representative rock samples. The mineralized area occurs within an elongate trachyte body (~1.2 km2) that intrudes Ordovician volcanic rocks. Geologic constraints suggest that the trachyte is also Ordovician in age. The eastern lobe (~900 × ~400 m) of the trachyte is pervasively brecciated with a matrix containing seams, lenses, and veinlets composed mainly of potassium feldspar, albite, and fine-grained zircon and monazite. Barite is locally abundant. Minor minerals within the matrix include columbite, bastnäsite, euxenite, chlorite, pyrite, sphalerite, and magnetite. The pXRF analyses of 22 samples (App. Table A1) collected from the eastern lobe demonstrate that this entire part of the trachyte is highly mineralized. Whole-rock geochemical analyses for samples from the eastern lobe document high average contents of Zr (1.17 wt %), Nb (1,656 ppm), Ba (3,132 ppm), Y (1,140 ppm), Hf (324 ppm), Ta (122 ppm), Th (124 ppm), U (36.5 ppm), Zn (689 ppm), and Sn (106 ppm). Among light REE, the highest average concentrations are shown by La (763 ppm) and Ce (1,479 ppm). For heavy REE (HREE), Dy and Er are the most abundant on average (167 and 114 ppm, respectively). No HREE-rich minerals such as xenotime have been identified; the HREE may reside chiefly in monazite and bastnäsite, and within the fine-grained zircon. Very strong positive correlations (R2) of 0.92 to 0.98 exist between Th and Zr, Nb, Y, Ce, Yb, and Sn, indicating that the radiometric data for eTh are valid proxies for concentrations of these metals in the mineralized rocks.Trachyte-hosted REE-Nb-Zr deposits like the occurrence at Pennington Mountain also are known in eastern Australia and in the south Qinling belt of Central China. Based on comparisons with these deposits, and the lack of detailed geologic mapping in the Pennington Mountain region, we suggest that other rare-metal occurrences contained in trachyte may exist elsewhere in northern Maine, and more widely in the Appalachian-Caledonian orogen where volcanic and subvolcanic trachytes have been recognized.