Assinaturas radiométricas de plútons do magmatismo ediacarano no Domínio Rio Piranhas-Seridó, Província Borborema, NE do Brasil

The paper deals with natural radioactivity of metamorphic and igneous rocks and Palaeozoic sediments within the map sheet 14-33 Polička. Studied rocks belong to three geological units: the Hlinsko Zone (phyllites and quartzites of the Mrákotín Fm., flysch sediments of the Hlinsko-Rychmburk Fm.), the Svratka Crystalline Complex (mainly mica schists, paragneisses, orthogneisses and migmatites, also amphibolites, skarns, erlans and quartzites) and the Polička Crystalline Complex (mica schists, paragneisses to migmatites and the Variscan granitoids are dominant). Concentrations of potassium, uranium and thorium were measured using a laboratory gamma-ray spectrometer in 805 rock samples. Data are tabled and discussed. Natural radioactivity of rocks is evaluated on the basis of the calculated values of mass activity of 226Ra equivalent (am). Slightly increased am values were found in migmatites and orthogneisses of the Svratka Crystalline Complex (187 Bq.kg-1 on average), granites and granodiorites of the Budislav Pluton (216 Bq.kg-1), granodiorites and rocks of a tonalite suite of the Miřetín Pluton (199 and 194 Bq.kg-1). Increased concentrations of uranium and thorium were found in some samples of pegmatite and aplite. Radioactivity of rocks of the Hlinsko-Rychmburk and Mrákotín Fms. can be assessed as relatively low.

The granite pegmatites of Hmrat El Sorwhyia, situated in the northern Egyptian-Nubian Shield, are predominantly hosted within the central areas of syenogranitic bodies, with limited occurrences noted along the marginal sites. The Hmrat El Sorwhyia granitic pegmatites represent a notable example of rare-metal mineralisation. This study introduces novel bulk- rock compositions, including major, trace, and rare earth elements, to investigate and constrain the origin and mechanisms influencing the genesis of the Hmrat El Sorwhyia granitic pegmatites and their rare-metal mineralisation. The studied pegmatites exhibit diverse morphologies, featuring lenticular pockets that contain the highest radioelement concentrations. The maximum (equivalent uranium) eU value is 760 ppm while the maximum (equivalent thorium) eTh value is 5552 ppm. These pegmatites have granitic composition and peraluminous characteristics, indicative of A-type affinity associated with post-collisional tectonic settings, and are categorised as niobium–yttrium–fluorine-type pegmatites. The formation of granite pegmatites through fractional crystallisation during the late-stage magmatic processes involved the concentration of U, Th, rare earth elements, Zr, Y, and Nb. This concentration facilitated the crystallisation of thorite, uranothorite, columbite, cerianite, and zircon. Additionally, assimilation-fractional crystallisation mechanisms led to the exchange of accessory phases between successive injections of pegmatite and the surrounding wallrock, resulting in variable mineral concentrations. These open-system processes were responsible for the development of these pegmatites.

This study reports the natural radioactivity of characteristic rocks found in the historic Jeroným Mine of the Czech Republic as measured under the laboratory conditions. The rocks analyzed included granites and schists weathered to varying degrees and collected from different levels of the underground workings of the Jeroným Mine. The mine itself has been subject to metal extraction (mainly tin and tungsten) since the sixteenth century and has recently been developed as a cultural and scientific attraction open to the public. Activity concentrations of 40K, 232Th and 238U were measured from nine rock samples using gamma-ray spectrometry. The activity concentrations of 40K varied from 595 Bq kg−1 to 1244 Bq kg−1, while 232Th varied from 25 Bq kg−1 to 55 Bq kg−1. The activities associated with 238U ranged from 46 Bq kg−1 to 386 Bq kg−1. The measured activities were used to estimate two radiation hazard indices typically applied to building materials, the activity concentration index I and the external hazard index Hex. Mean respective values of 1.02 and 0.77 for I and Hex indicate that the rocks found in the Jeroným Mine meet radiological safety standards for building materials and do not pose a risk to potential tourists and staff.

A review of the geophysical knowledge of the Borborema Province, NE-Brazil, and tectonic implications

Spectrometric and remote sensing investigations of some granitic rocks in the Egyptian north Eastern Desert: Insights on environmental radiogenic heat production

Physical Properties of Rocks - Fundamentals and Principles of Petrophysics

In order to enhance our knowledge about the tectonic processes responsible for the geological evolution of the Borborema Province and adjacent regions, the National Institute of Space Research (INPE) and the National Observatory (ON) are conducting Electromagnetic Induction studies in northeastern Brazil, which are being supported by the National Institute of Science & Technology for Tectonic Studies (INCTET) project during the past three years. Such studies contemplate the deep geophysical probing of this region with Magnetotelluric surveys (MT) and Transient Electromagnetic soundings (TEM) along several geoelectric transects and an array of Geomagnetic Depth Soundings (GDS), which complement other geophysical methods. The focus of this study is directed to the identification of geoelectric variations in electric conductivity at distinct lithospheric depths and associations of geoelectric strikes and anisotropy with structural grain and stress patterns, particularly in the long ubiquitous structural features that cross the province and that constitute major geoelectric heterogeneities, at the near surface crust and also in the lower crust and upper mantle. The preliminary results indicate a lithosphere with a very variable electrical resistivity. The upper-mid crust shows up as a very resistive layer, overlying a less resistive lower crust and upper mantle. In some areas the mantle is very resistive, characteristic of a cratonic origin. Exceptions to a resistive crust are found under the Serido belt, Jatoba rift basin and the Araripe intracratonic basin, marked by an underlying conductive crust. Laterally, the deeper portion of the crust and upper mantle is highly segmented in blocks with alternating juxtaposed higher and lower resistivities. This pattern is suggestive of highly deformed regions by transform dominated tectonic regimes, with the presence of contrasting mechanically strong cratonic-like keels against weaker zones likely subjected to delamination processes that might have produced magmatic related lithospheric re-fertilization by metasomatism. Introduction The National Institute of Science & Technology for Tectonic Studies congregates many geoscientists from several Brazilian research institutions with the purpose of studying the deep crust and upper mantle structures. It is multidisciplinary in its approach, merging different techniques and methodologies, which allow the study of the Earth’s interior based on different properties of its constituting rocks. The focus of this research is the study of the crust and upper mantle of the Borborema Province and adjoining Sao Francisco Craton and Parnaiba Basin. The Borborema Province is a complex association of crustal blocks with differing ages, origin and geologic evolution, and which were amalgamated during the last orogenic event that took place in what is now the Brazilian territory, namely the late Neoproterozoic-early Phanerozoic Brasiliano orogeny, composing the Gondwana supercontinent. Therefore, Electromagnetic Induction studies are being developed with the goal of making a major contribution to a better comprehension of the actual articulation of the amalgamated crustal blocks and the role of large transcurrent lineaments in bringing these blocks together, through an integrated multidisciplinary geophysical study.

Forty-eight uranium anomalies meet the minimum statistical requirements as defined in Volume I. These anomalies are tabulated and are shown on the Uranium Anomaly Interpretation Map, together with the interpretation of the magnetic data. Potassium (%K), equivalent Uranium (ppM eU), equivalent Thorium (ppM eT), eU/eT, eU/K, eT/K, and Magnetic Pseudo Contour maps are presented in Appendix E. Stacked Profiles showing geologic strip maps along each flight line, together with sensor data, and ancillary data are presented in Appendix F. All maps and profiles were prepared on a scale of 1:250,000, but have been reduced to 1:500,000 for presentation in Volume II.

Ten uranium anomalies meet the minimum statistical requirements as defined in Volume I. These anomalies are tabulated, and are shown on the Uranium Anomaly Interpretation Map, together with the interpretation of the magnetic data. Potassium (%K), equivalent Uranium (ppM, eU), equivalent Thorium (ppM, eT), eU/eT, eU/K, eT/K, and Magnetic Pseudo Contour Maps are presented in Appendix E. Stacked Profiles showing geologic strip maps along each flight line together with sensor data, and ancillary data are presented in Appendix F. All maps and profiles were prepared on a scale of 1:250,000, but have been reduced to 1:500,000 for presentation in Volume II.

Nineteen uranium anomalies meet the minimum statistical requirements as defined in Volume I. These anomalies are tabulated and are shown on the Uranium Anomaly Interpretation Map, together with the interpretation of the magnetic data. Potassium (%K), equivalent Uranium (ppM, eU), equivalent Thorium (ppM, eT), eU/eT, eU/K, eT/K, and Magnetic Pseudo Contour Maps are presented in Appendix E. Stacked Profiles showing geologic strip maps along each flight line together with sensor data, and ancillary data are presented in Appendix F. All maps and profiles were prepared on a scale of 1:250,000, but have been reduced to 1:500,000 for presentation in Volume II.

Ten uranium anomalies meet the minimum statistical requirements as defined in Volume I. These anomalies are tabulated and are shown on the Uranium Anomaly Interpretation Map, together with the interpretation of the magnetic data. Potassium (%K), equivalent Uranium (ppM eU), equivalent Thorium (ppM eT), eU/eT, eU/K, eT/K, and Magnetic Pseudo Contour Maps are presented in Appendix E. Stacked Profiles showing geologic strips maps along each flight line together with sensor data, and ancillary data are presented in Appendix F. All maps and profiles were prepared on a scale of 1:150,000, but have been reduced to 1:500,000 for presentation in Volume II. A number of short-wavelength magnetic anomalies are associated with ultrabasic intrusives. These intrusives crop out along the major northwest-trending fault zones that traverse the map area, and thus form a magnetic expression of the faults. Part of a long-wavelength anomaly that extends off the map area is present in the northeast corner of the quadrangle. The source of this anomaly is interpreted as a large, deep-seated magnetic body - possibly gabbro.

The Borborema Province is located in Northeast Brazil and had its internal structure investigated by different geophysical methods (gravity, magnetic, seismic, etc). In this work we studied the behavior of the S wave velocity with depth in the Province crust, using dispersion characteristics of surface waves. The dispersion curves are calculated using the interstation method with two or three stations. This method allows to estimate S wave velocity in the region between the stations. The events arriving are located mainly at the edges of the South American, Nazca and North America plates. The inversions of dispersions were performed with Rayleigh waves. We used the knowledge of the depth of Moho under the stations as a constraint in the inversion. Our results shown that S waves velocities are similar in the profiles, there is a observation that the Moho is at a depth of about 33 km in the profiles with two stations and in the profile that passes through the Potiguar basin we observed a lower velocities.

Wadi El-Regeita area is located in the southern part of Sinai Peninsula, at the intersection of Lat. 28° 37′ 29′′ N and Long. 34° 05′ 15′′ E. The area acquired its importance since the discovery of significant copper mineralizations associated, in most cases, with some radioactive anomalies related to the increase in the uranium content. These mineralizations are related to intense post-magmatic, structurally controlled, hydrothermal activities in the area and the surroundings.This work deals with application of the gamma-ray spectrometry and self-potential methods to identify the content of the radioactive elements and delineate the mineralized zone in the area. The work also aims to explain if there is a relation or association between the mineralizations of uranium and copper, which could be useful in view of the exploratory processes in other areas.Data of the gamma-ray spectrometry revealed radioactivity levels ranging from 12.0 to 149.0 Ur, 0.3 to 130.0 ppm, 3.0 to 54.0 ppm and 0.5 to 9.8% for the total count of gamma rays, equivalent uranium, equivalent thorium and potassium, respectively. Interpretation of the constructed radioactivity maps, with the equivalent uranium false-color composite image, clearly reflect a sharp increase of the equivalent uranium concentrations along the NW-SE copper-mineralized shear zone in the area. Data of the self-potential survey also revealed a wide range of amplitudes (–106.7 to +55.4 mV), with the highest negative values recorded along the copper-mineralized shear zone. The quantitative interpretation revealed shallow depths to the centers of nine selected anomalies (ranging from 3.3 to 21.0 m and averaging 11.2 m), with half-widths ranging from 8.4 to 61.0 m and moderate dips toward the SW. The spatial distribution of the determined anomalies for equivalent uranium (> 37.5 ppm) and self-potential (> -60 mV) showed an excellent agreement, which indicates a very strong copper-uranium association and, therefore, methods of gamma-ray spectrometry can be considered as effective exploration tools for the copper mineralizations.

Borborema Province (BP) has a very complex history, but up to now, few geophysical data have been used to constrain its evolution history. This paper presents the first integrated gravity/magnetic/geological data interpretation of the tectonic framework of the province. BP is a Proterozoic fold belt extended between the Sao Luis - West Africa and Sao Francisco - Congo/Kasai cratons. Currently, as a result of an increase in geochronologic data, there is growing evidence that its evolution has occurred by a mechanism of terrane collage. This evolution model suggests that large crustal blocks were put together during Meso and Late-Proterozoic events, resulting in crust growing by the arrival of pieces of crust or by the addition of new crusts. Interpretation of regional magnetic and gravity maps revealed the boundaries between crust blocks or compartiments inside BP. As result of the integrated interpretation, it is proposed that BP is formed by the union of at least 11 crust blocks. Boundaries between these blocks form long lineaments in NE-SE direction, in some cases showing vergences to E-W direction. The major block to the south of BP is the Sao Francisco Craton. The boundary between BP and the craton is still a controversial question, but the geophysical data suggest that N-S lineaments, which occur inside the craton, prolong below Riacho do Pontal and Sergipano hrust fold belts, which are part of BP. In this way, the plate associated to the craton lies beyond its geologically mapped north limit.

This research focuses on hydrothermal alteration and mineral potential zones of the Bauchi area in northeastern Nigeria using the interpretation of aeroradiometric data. The high resolution aeroradiometric data were acquired and analyzed for possible areas of mineral potentials, lithologic units, and hydrothermal alteration. The radiometric data were interpreted by minimum curvature gridding techniques, arranged in three different grids as radioelement of percentage potassium (%K), equivalent thorium (eTh), and equivalent uranium (eU), and were displayed as pseudo[1]coloured images to reveal the surface concentration of each of the radioelements. The radioelement maps, K/eTh ratio map, and ternary image were used to recognize and interpret the radiometric signatures for mineral potential zones, lithological units, and identification of hydrothermal alteration zones in the study area. The relatively high eTh concentration (32.1274-54.8017 ppm) could be attributed to granitic rocks and high K/eTh ratio (0.285718-0.422418 wt%/ppm) indicates hydrothermally altered areas. The regions with high %K, high eTh and high eU coincide with the granitic rocks and this indicates that hydrothermal alteration and mineral potential zones are predominance in older granites and younger granites. The hydrothermal alteration zones are favorable areas for mineralization as observed from the K/eTh ratio map. The hydrothermally altered areas are underlain by granitic rocks and this attests that the hydrothermal alteration process is accompanied by granitic intrusions and emplacement of late intrusive rocks which provide the heat sources for hydrothermal solutions along fractures for the formation of minerals or react with the enclosing rock for hydrothermal alteration and subsequent mineralization.