Gamma-ray Spectrometric Evaluation in Watersheds With Gold Anomalies in Stream Sediments, Passo Feio Complex, Caçapava Do Sul Region (Brazil)

Gamma-ray Spectrometric Evaluation in Watersheds With Gold Anomalies in Stream Sediments, Passo Feio Complex, Caçapava Do Sul Region (Brazil) | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Gamma-ray Spectrometric Evaluation in Watersheds With Gold Anomalies in Stream Sediments, Passo Feio Complex, Caçapava Do Sul Region (Brazil) Luiza Lima Alves, César Augusto Moreira, Ana Flávia da Silva Araújo, and 5 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6214118/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 11 You are reading this latest preprint version Abstract This study utilizes gamma-ray spectrometry to identify source areas of gold recognized in geo-chemical prospecting work in stream sediments. The local geological context is represented by the Passo Feio Metamorphic Complex, which contains gold deposits possibly hosted in quartz veins concordant with metamorphic foliation, composed of quartzites, schists, and amphibolites. The study followed the sequence: geological reconnaissance, drone survey, and gamma-ray spectrometric acquisition. Field reconnaissance indicated an alternation of rocks oriented in a WNW/ENE direction, with recognition of quartz veins embedded concordantly with the foliation of quartzites. The drone data enabled the generation of a Digital Elevation Model (DEM) and served as a basis for planning the gamma-ray spectrometry work. A total of 715 gamma-ray spectrometric readings were taken, with an average spacing of 40 meters between points, followed by data processing and the generation of maps of K (0.5% – 2.5%) concentrations, eU (0.9–3.9 ppm), and eTh (2.8–24.4ppm). The data obtained regarding the K (%) concentration values reveal a clear anomaly in the central region with WNW/ENE orientation. The concentration data obtained for U (ppm) and Th (ppm) show a similar pattern concerning the WNW/ENE anomaly in the center of the area. The overlap of positive anomalies served as an indication of gold source areas in two river valleys. mineral exploration gold geophysics gamma-ray spectrometry Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1. Introduction The exponential increase in demand for mineral resources has justified various research projects and the discovery of multiple mineral deposits in Brazil, activities that have driven economic growth and social development. The global market demands a wide variety of mineral commodities, making Brazil a major exporter on a global scale. Consequently, maintaining this activity depends on constant research and discoveries. Gold is one of the oldest financial assets, offering high liquidity and security. It is widely used as a reserve during periods of international crises, leading to significant price increases on stock exchanges [ 1 , 2 ]. In May 2024, the price of gold reached a historical record, with the ounce value climbing to $ 2,300, a significant increase compared to its average price of around $ 1,500 per ounce [ 2 ]. Gold consumption in Brazil has increased alongside the population's purchasing power, appearing in jewelry, electronic components for computers, tablets, notebooks, and mobile phones, as well as parts for the automotive industry, healthcare, dentistry, and even some construction components [ 3 ]. New mineral commodities are discovered through several progressive and inter-connected steps, which involve and predict increased investment and decreased risk [ 4 , 5 ]. This process begins with the recognition of surface mineralization evidence, which may be associated with a subsurface ore body [ 5 ]. Geophysics is a highly mentioned tool in mineral exploration scenario for recognizing exploratory targets, since its field instruments allow for detecting contrasts between the physical properties of mineral deposits and their host rocks [ 6 , 7 , 8 , 9 , 10 , 11 ]. Gamma-ray spectrometry is a passive geophysical method, as it measures the in-herent radioactivity in the form of gamma rays from mineral species containing radi-oactive isotopes such as potassium ( 40 K), uranium ( 235 U e 238 U), and thorium ( 232 Th) [ 8 ]. This method enables rapid and easy data acquisition, allowing for extensive area coverage, though it is a shallow method with a maximum investigation depth of 50 to 100 cm [ 6 , 8 , 12 ]. Gamma-ray spectrometry offers several advantages in the analysis and quantification of elements in the soil compared to geochemical methods. In addition to the rapid acquisition of data, they can be easily processed using softwares, allowing results to be obtained shortly after the acquisition phase. In mineral research, gamma-ray spectrometry is mainly applied to characteristically radioactive deposits, such as uranium or hydrothermal origin deposits [ 13 , 14 , 15 , 16 ]. Few references exist for studies related to gold deposits, primarily resulting from airborne geophysical surveys [ 17 , 18 , 19 , 20 , 21 ]. This work involved field reconnaissance, drone investigation (Digital Elevation Model), and terrestrial gamma-ray spectrometry in a detailed survey conducted in two watersheds to identify outcropping occurrences of gold, based on prior indications from geochemical surveys of sediments conducted by the Geological Survey of Brazil in southernmost Brazil. 2. AREA LOCATION AND HISTORY The study area is located in the southernmost of Brazil, in the state of Rio Grande do Sul (RS). The occurrence studied is around 15 km from the urban area of the municipality of Caçapava do Sul, which is approximately 240 km from Porto Alegre, the state capital (Fig. 1 ). Evidence of mineralization was recognized from regional studies carried out by the CPRM (Companhia de Pesquisa de Recursos Minerais, currently the Geological Service of Brazil) through the National Gold Prospecting Program in 2000, where geological reconnaissance and geochemical prospecting were carried out on stream sediments in an area of 136000 ha [ 22 ]. The regional geochemical survey for gold conducted by the Brazilian Geological Survey involved the analysis of a total of 818 stream sediment samples and 553 heavy mineral concentrate samples from alluvial material. The sampling stations were located at the mouths of drainages associated with metavolcanic-sedimentary lithologies, known for hosting various mineralizations in the studied region. At each station, a volume of 20 liters of panned material was collected. The preparation and analysis of the samples for gold followed the routine below: (i) stream sediments were sieved to -120 mesh, pulverized in the laboratory to -200 mesh, and decomposed by fusion for analysis by plasma; (ii) heavy mineral concentrates were pulverized in the laboratory to -200 mesh, decomposed by fusion, and analyzed by atomic absorption. Two sub-basins with anomalous results for gold were selected as the target area for this study, based on the results of collecting samples of stream sediments and concentrates of heavy minerals in the alluvial material. There was a regional study on the area focused on defining anomalous basins, without detailing the origin of the gold [ 22 ]. Based on the premise of weathering in outcropping deposits, followed by the transport of gold particles to the mouth regions of the basins, this work sought to follow the opposite path, based on an analysis of gamma-spectrometric data, in an attempt to recognize primary gold deposits in the study area. 3. GEOLOGY AND METALLOGENETIC ORIGIN The study area encompasses rocks of the Caçapava do Sul Granitic Complex and the Passo Feio Metamorphic Complex, that are part of the igneous and metamorphic terrains that compose the Sul-Rio-Grandense Shield, formed during the Transamazonian (2.26–2.00 Ga) and Brasiliano (900–535 Ma) orogenic cycles [ 23 ]. The Caçapava do Sul Granitic Complex resulted from post-tectonic, calc-alkaline acidic magmatism, with its intrusion occurring at 562 ± 8 Ma during the late phases of the Brasiliano Orogeny evolution [ 22 , 24 ]. Three granite rock facies are present: biotite granitoids, leucogranitoids, transitional granitoids, with crystals elongated in the N34W direction, the same as the metamorphic foliation of the Passo Feio Complex, which hosts the granitic complex [ 25 ]. The Passo Feio Metamorphic Complex consists of pelitic schists, phyllites, amphibolites, and metavolcanoclastic rocks and can be divided into a Metasedimentary Association and a Metavolcanic Association [ 26 , 22 ]. It forms a doubly plunging antiform fold, with a sub-horizontal axis dipping towards NNE and SSW. The granitic complex intrudes its center, and the unit serves as the basement for the Camaquã Basin [ 24 , 27 , 28 ]. Due to a scarcity of studies conducted in the area covered by the Metamor-phic Complex, the most detailed geological map available was made by the Geological Survey of Brazil, in a scale of 1:100.000 (Fig. 2 ). The Metasedimentary Association is composed of metapelites and metavolcanoclastic rocks, represented by schists and phyllites containing muscovite, biotite, and/or chlorite, as well as minerals such as garnet, chloritoid, and staurolite. The foliation of these rocks is characterized by schistosity or slaty cleavage. The schist bands vary in thickness and are intercalated with amphibolites, quartz-feldspathic gneisses, and thin quartzite layers [ 26 ]. The Metavolcanic Association includes amphibolites, amphibole schists, amphibole gneisses, and massive amphibolites. These rocks exhibit planar and continuous structures with banding generated by metamorphic segregation or are massive [ 26 ]. The metapelites and amphibolites underwent two regional metamorphic events (M1 and M2) and three deformational phases (D1, D2, and D3), and among these, D3 is not associated with regional metamorphism [ 26 , 29 ]. The D1 phase is preserved in quartz lenses, D2 formed the S2 foliation, and D3 created folds structuring the Passo Feio Metamorphic Complex. The M1 event was characterized by the presence of minerals in the staurolite zone (amphibolite facies) and andalusite, indicative of a low-pressure event [ 25 ]. Metapelites and amphibolites are associated with M1, while M2 was a retrogressive event in the greenschist facies [ 25 ]. The Caçapava Granite intrusion occurred between the D2-M2 interval, with the S2 foliation of metamorphic rocks correlating with that of the granite. The ages of M1 and M2 were estimated at 685 ± 12 Ma and 562 ± 8 Ma, respectively [ 24 ]. The Passo Feio Metamorphic Complex hosts Cu (Au) and Pb mineralizations. The target of this study is a disseminated gold occurrence hosted in quartz veins concord-ant with the foliation of the host rock and associated with shear zones, with its para-genesis consisting of quartz, gold, pyrite, arsenopyrite, and chalcopyrite, classified as epigenetic hydrothermal deposits [ 22 , 30 ]. The hydrothermal processes associated with the intrusion of the Caçapava do Sul Granitic Complex were responsible for the sulfide mineralization under study. Thermal fluids of magmatic origin mobilized metals from rocks adjacent to the Passo Feio Complex and deposited them in veins [ 24 ]. The deposits within the Metamorphic Complex are structurally controlled by NE-oriented strike-slip fault systems, formed during the Neoproterozoic collision processes involved in the formation of the Dom Feliciano Belt [ 31 ]. 4. METHODS This study was conducted through geological reconnaissance, drone surveys for elaboration of Digital Elevation Model (DEM), and gamma-ray spectrometry investigation. The work began with the geological reconnaissance of the region, conducted in a N-S direction along a road that crosses orthogonally to the foliation present in the outcrops. Simultaneously, structural measurements of fractures and metamorphic foliations were collected to identify a possible direct or indirect relationship between the measured structures and the occurrence of gold. Next, drone surveys were conducted using a DJI MAVIC 3T model, where two flights were performed: one over the higher terrain and another over the lower terrain, with both flying at an altitude of 120 meters (Fig. 3 A). The drone flight lines were conducted in the E/W direction to ensure efficient coverage of the study area. The spatial resolution achieved was 20 centimeters, allowing for a detailed analysis of the terrain's topographic features. The resulting images were combined using Agisoft Metashape software, which integrates the imported drone images. This process generated a digital point cloud that allowed for the measurement of altitude for each orthophoto. Through the interpolation of these altitude values, a Digital Elevation Model (DEM) was created. Based on the results of the drone surveys and after a topographic analysis based on the DEM, the investigation area was delineated for geophysical surveying. The method employed was gamma-ray spectrometry, using the RS-332 Multipurpose Gamma-Ray Spectrometer System by Radiation Solutions Inc. This device offers high sensitivity, thermal protection, ease of use, and an integrated GPS (Fig. 4 A). Additionally, the geophysical reading points were georeferenced using a differential GPS with 0.5 meter precision The RS-332 measures the inherent radioactivity that occurs naturally in the form of gamma rays emitted by mineral species containing radioactive isotopes such as cosmogenic nuclides like potassium ( 40 K), uranium ( 235 U and 238 U), and thorium ( 232 Th). The spectrometer operates with a BGO (Bismuth Germanate Oxide) detector, that operates within a measurement range of 30 keV to 3000 keV. The Limit of Detection (LOD) of the RS-332 is determined by the combination of the measurement time, background conditions and the detector measurement range, in a way that longer sampling periods and higher background radiation can elevate the LOD. The device's reading time can be configured as needed; for this study, it was set to 60 seconds. A study from 2014 determined that a 60 second reading time is reasonable for gamma-ray spectrometry analysis of volcanic rocks in the Paraná Basin using a similar device [ 32 ]. Similarly, another one effectively used 60 second reading time to identify potential zones for acid mine drainage generation in uranium mine waste piles [ 33 ]. The spectrometer has a screen that allows real-time monitoring of the measurements obtained for each analyzed element at each point investigated (Fig. 3 B). The elements U and Th are measured in ppm, while K is measured in percentage. The selected area for data acquisition covered approximately 88 hectares, mostly covered by low vegetation and forests limited to drainage areas, with some points of exposed rock. Measurements were taken by directly placing the device on the surface of dry soil. Approximately 715 data points were collected, distributed in a regular grid at 40 meter intervals, with differential GPS guidance in the field, which has an average error of 1 meter. After the data acquisition phase, processing was carried out using Geosoft's Oasis Montaj software to generate maps representing the radiometric distribution of eU, eTh, and K concentrations in the area. An interpolation of the collected data points was performed to create a two-dimensional representation of thorium, potassium, and uranium concentrations in terms of distance. The interpolation process involved a least-squares approximation to smooth the discrepancies between field data and software-calculated values. A theoretical two-dimensional model was generated by segmenting the subsurface into rectangular blocks. The software automatically distributed and sized these blocks based on the data points' spatial distribution. The program calculates the concentrations based on the block model created from the comparison between the measured and modeled values, the parameters of these blocks are adjusted interactively until the apparent value agrees with the values acquired in the field. The processed outputs were color-scaled maps representing each element's distribution, with potassium concentrations expressed as a percentage and eU and eTh concentrations in ppm. Additionally, ratio and ternary maps were generated and analyzed, however, they provided no further insights beyond those obtained from the original K, U, and Th maps. 5. RESULTS AND DISCUSSION The initial stage of geological reconnaissance followed a N-S direction and revealed an alternation of rocks, varying between quartzites, schists and amphibolites, with a repetitive pattern across the explored area (Figs. 4 B, 4 C and 4 D). Thus, it was expected that the geophysical data would show a standard pattern of alternation based on the local lithology, representing the area's background. Additionally, quartz veins were identified concordantly embedded in the quartzites' foliation, which are likely the hosts of the studied gold mineralization. The drone flights produced a high-resolution orthophoto of the study area, superior to freely available satellite images, and a Digital Elevation Model (DEM) (Fig. 5 ). These data were initially analyzed from a geomorphological perspective and later integrated with gamma-ray spectrometry data to assess the geochemical mobility of the analyzed elements. The primary source of gold is likely outcropping, and weathering processes with destruction of mineralized rocks and veins, have resulted in the release of gold particles, which were carried to the basin's mouth. The elevation difference in the study area is 127 meters, with the highest point in the southern portion (291 meters) and the lowest in the Passo Feio River region (164 meters). The gamma-ray spectrometric acquisition was conducted alongside differential GPS surveying. This equipment provides more precise coordinates than the GPS integrated into the RS-332, with a margin of error of only 0.5 meters, that provided a better result for the regular grid of 40 meter intervals. Thus, it enabled the creation of the point map for gamma-ray spectrometry analysis (Fig. 6 ). This study began interpreting the data using the altimetry values obtained from the DEM. These values were analyzed concerning terrain morphology, weathering, and element mobility in the geological environment, as these factors are crucial for assessing radioelement distribution at the Earth's surface. Naturally, sediment transport caused by erosion and physical weathering moves materials from higher elevations to lower areas, such as rivers floodplains. Geochemical element mobilization occurs through leaching and hydrothermal fluid activity, following the same patterns of movement as discussed before [ 34 , 35 , 36 ]. Potassium (K) is a lithophile, incompatible (especially during magma crystallization), and volatile element with high environmental mobility, primarily occurring in granitoids [ 37 , 35 ]. Uranium (U) becomes mobile under hydrothermal and supergenic conditions [ 37 , 35 ]. Thorium (Th) is less abundant in the crust and typically measured in ppb or ppm [ 38 , 35 ]. The chemical fractionation of U and Th series members occurs during magmatic processes [ 37 ]. Geomorphology, weathering, erosion, and the source rock collectively control the radioelement distribution in surface materials, creating differences from the bedrock background. Processes include K depletion during soil formation, K and Th enrichment through silicification in schists, and reduced K values during schist pedogenesis [ 35 ]. Generally, radioelement mobilization varies based on ground-water flow and leaching, with K being significantly more mobile than U or Th in such scenarios [ 39 ]. A study characterized various mineral deposits using airborne gamma-ray spectrometry, including gold mineralization in metavolcanic/metasedimentary rocks with hydrothermal alteration (K enrichment), which resembles the present study area [ 40 ]. The geochemical dispersion halo is represented by abnormally high or low concentrations of chemical elements that constitute a mineralization or associated alteration [ 41 ]. It is generated by the processes of mineral deposit formation through the introduction and/or redistribution of elements in the environment (primary geochemical halo) or formed by supergene processes (secondary geochemical halo) [ 41 ]. Potassium concentrations, expressed as percentages (%), ranged from 0.5–2.5% (Fig. 7 A). A noticeable anomaly with high concentrations (1.2–2.5%) is present in the central region, oriented NE/SW, coinciding with the schists' metamorphic foliation direction. This area has undergone hydrothermal alteration due to the intrusion of the Caçapava do Sul Granitic Complex. Potassium is present in the micas forming the schists; therefore, potassium anomalies were associated with the schist lithotype. Additionally, a high K concentration area is evident in the northern region (Fig. 7 A). Uranium (U) and thorium (Th) concentrations, expressed in ppm, ranged from 0.9–3.9 ppm for U and 2.8–24.4 ppm for Th (Figs. 7 B and 7 C). Compared to the K values, both show anomalies with a NE/SW orientation positioned in the central region of the area, however, the anomalous areas are not superimposed, with the eU and eTh anomalous areas shifting northwards (Fig. 7 D). U and Th originate exclusively from hydrothermal processes, as they are more abundant in the mantle and concentrated in the crust through magma ascent [ 33 ]. In the study area, this correlates with the regional hydrothermal event responsible for mobilizing U and Th and their subsequent deposition in mineralized quartz veins embedded in metamorphic foliation. In this sense, U and Th exist only in the veins generated by the hydrothermal processes that are hosted within the quartzites, making them directly associated with the gold mineralization, and serving as a prospecting guide in the study area. An integrated analysis of K, U, and Th maps reveals differences in each element's dispersion halos on the surface. In terms of mobility, K is the most mobile, U is intermediate, and Th is the least mobile under weathering processes. Soil thickness is a critical factor for element mobility, as greater thickness allows higher K, U, and Th concentrations to become available for mobilization. Geological reconnaissance revealed underdeveloped soils (up to 30 cm thick) rich in rock fragments at several points. Under such conditions, gamma-ray spectrometry anomalies primarily reflect signatures associated with the underlying rocks, whether related to original mineral composition or hydrothermal processes. Two high K concentration regions or dispersion halos are evident. The Passo Feio River lies within a regional watershed, so the K anomaly in the floodplain consists of the sedimentation of fine suspended particles, predominantly clay minerals, may result from weathering in the study area's rocks or external factors, including the Caçapava do Sul Granitic Complex weathering. For U, the highest concentration (3.1–3.9 ppm) is central, with some dispersion around it. Th shows a smaller dispersion halo with higher values (14.5–24.4 ppm), potentially representing or delineating a zone with gold mineralization in quartz veins. To integrate the data, a map of anomalous halos for each element was generated and overlaid onto the DEM (Fig. 7 D). There is a coincidence between U and Th anomalies, with an absence of K in this domain, suggesting quartz vein emplacement in quartzites, which contain less K. Conversely, the K anomaly upstream of the U and Th halos may be associated with hydrothermalism in schists, a lithotype without quartz veins and likely barren of gold. Furthermore, the overlap of the anomalous halos proved effective in highlighting that they all share the same NE/SW orientation, consistent with the regional structural trend. This orientation aligns with the foliation of the rocks, quartz veins, fractures, and regional faults. The regional gold occurrences consist of quartz veins aligned concordantly with the foliation of the lithologies of the Metavolcanic-Sedimentary Belts, represented in the study area by the Passo Feio Metamorphic Complex [ 42 ]. There are several small prospects and deposits associated with the Caçapava do Sul Granitic Complex, hosted in the Passo Feio rocks, which include Cu (Au) and Pb sulfide veins of an epigenetic hydrothermal origin [ 24 ]. As discussed in [ 24 ], the region lacks prior studies, so the origin of the metal present in the mineralizing fluids of these deposits has not yet been investigated. Thus, the mineralizations hosted in the metasediments of the Passo Feio Meta-morphic Complex are associated with a remobilization or reconcentration of metallic elements, likely derived from adjacent rocks. The intrusion event of the Caçapava do Sul Granitic Complex resulted in local metamorphism and was responsible for providing the hydrothermal fluids that caused this remobilization and their deposition in the quartz veins. These veins were positioned along weakness planes, represented by the foliation and regional fractures, which have a NE/SW orientation 6. CONCLUSIONS Previous works that analyzed stream sediment geochemistry data revealed two sub-basins with potential for primary gold occurrences in the current study area. The data obtained in this study reveals the existence of a potentially mineralized area that crosses the two sub-basins, with an N70 orientation. Studies describing the metallogeny of gold in the study region suggest a magmatic/hydrothermal origin that may have occurred during the sedimentation of the host rocks or during the closure and deformation phase of the sedimentary basin in the Neoproterozoic. The Caçapava do Sul Granitic Complex is barren for gold but was possibly responsible for the last regional deformation of the Passo Feio Complex rocks, with reconcentration of gold in quartz veins embedded in the foliation and fractures of quartzites, previously contained in this geological unit. Since K was also found in large quantities in the river floodplain, this element was not used as a prospecting guide for the hydrothermal processes that generated the gold mineralization. The origin of K in the river may be related to the weathering of schists from the Passo Feio Complex or even to lithologies from outside the study area. In this context, anomalous K halos were associated with the schists, which showed low levels of U and Th, indicating gold sterility, perhaps due to the lack of spaces for the generation of quartz veins. The elements U and Th are abundant in the mantle and are exclusively related to hydrothermal processes. Thus, the surface anomalies of high U and Th values obtained in this study coincide with the mineralized quartz veins. In this sense, quartzites rep-resent the main lithotype or regional prospecting guide for gold searches. Although gamma spectrometry is widely used in mineral prospecting for the identification of radioactive deposits, this study highlights the application of the method for a hydrothermal-origin gold deposit. The association of U and Th with mineralization provides a new perspective for identifying potentially gold-bearing areas. The combined analysis of the digital terrain model with gamma spectrometry data has satisfactorily delimited potentially gold-mineralized targets, contained in a strip that crosses the two sub-basins recognized as anomalous in the geochemistry of stream sediments, and the probable primary outcropping source of gold. The combination of these methods has proven effective in refining targets from regional geochemical prospecting projects. It should be followed by detailed investigations using geophysical surveys, trenching, or borehole drilling, either to analyze the target architecture or to define its content. Declarations Author Contributions: Conceptualization, L.L.A and C.A.M; methodology, L.L.A and C.A.M; software, L.M.I.; investigation, L.L.A., C.A.M., A.F.S.A., L.M.I., S. K., M.A.F.H.; J.P.P.O.; H.M.; writing—original draft preparation, L.L.A.; Preparation of figures: L.L.A., C.A.M and J.P.P.O.; writing—review and editing, L.L.A., J.P.P.O., C.A.M.; supervision, C.A.M.; project administration, C.A.M. and H.M.;. Funding: This research was funded by FAPESP—Fundação de Amparo à Pesquisa do Estado de São Paulo (Process n. 2023/04732-8). Data Availability Statement: The data that support the findings of this study are available on request from the corresponding author, Luiza Lima Alves. Acknowledgments: The authors are especially grateful to the Fundação de Amparo à Pesquisa do Estado de São Paulo - FAPESP for funding the field trip of the Project. We also would like to thank the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) for financial support on the masterfs’ scholarship of Luiza Lima Alves. We are also thankful for the support provided by Universidade Federal do Pampa, Campus de Caçapava do Sul – UNIPAMPA. Conflicts of Interest: The authors declare no conflicts of interest. Ethics, Consent to Participate, and Consent to Publish declarations: not applicable. References IBRAM – Instituto Brasileiro De Mineração. Informações e Análises da Economia Mineral Brasileira, 2012. Available online: https://ibram.org.br/wp-content/uploads/2020/12/informacoes-sobre-a-economia-mineral-2017.pdf (Acessed on 30/06/2024). KITCO. Gold Price Today. Available online: https://www.kitco.com/gold-price-today-usa/ (Acessed on 10/07/2024). World Gold Council. 2024. Available online: https://www.gold.org / (Acessed on: 05/11/2024). Moon, C.J.; Whateley, M.K. and Evans, A.M. 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Using of airborne gamma-ray spectrometric data to the exposure of potassic alteration -recognition of alteration relates to gold mineralization. Applied Radiation and Isotopes. 2022. 190, pp. 389–403. https://doi.org/10.1016/j.jafrearsci.2017.07.012 Saleh, A.; Salako, K.A.; Salawu, N.B. et al. Airborne magnetic and gamma-ray spectrometric pro-specting to delineate structures associated with gold mineralization—a case study in Yauri region, Northwestern, Nigeria. Arab J Geosci. 2023. 16, 308. https://doi.org/10.1007/s12517-023-11380-7 . CPRM – Companhia de Pesquisa de Recursos Minerais. Programa Nacional de Prospecção de Ouro. Resultados da prospecção para ouro na área RS-01 Lavras do Sul/Caçapava do Sul, Subárea Caçapava do Sul, Rio Grande do Sul. Porto Alegre. 2000. 14p. https://rigeo.sgb.gov.br/handle/doc/1589 . Soliani Junior, E.; Kawashita, K.; Baitelli, R. A Geologia Isotópica do Escudo Sul-rio-grandense - Parte I: métodos isotópicos e valor interpretativo. In: Geologia do Rio Grande do Sul, 1st ed.; M. Holz, & L. F. Deros. Universidade Federal do Rio Grande do Sul: Porto Alegre, Brasil, 2000. pp.161–174. Remus, M. V. D.; Hartmann, L. A.; Mcnaughton, N. J.; Groves, D. I. & Fletcher, I. R. The link be-tween hydrothermal epigenetic Copper mineralization and the Caçapava Granite of the Brasiliano Cy-cle in Southern Brazil. Journal of South American Earth Sciences. 2000. 13(3), pp. 191–216. https://doi.org/10.1016/S0895-9811(00)00017-1 . Nardi, L. V. S. & Bitencourt, M. F. Geologia, petrologia e geoquímica do Complexo Granítico de Caçapava do Sul, RS. Revista Brasileira de Geociências. 1989. 19(2), pp. 153–169. Bitencourt, M. F. Metamorfitos da região de Caçapava do Sul, RS – Geologia e Relações com o Corpo Granítico. In: Atas do 1º Simpósio Sul-Brasileiro de Geologia. 1983a. pp. 37–48 Paim, P. S. G.; Chemale Jr. F.; & Wildner, W. Estágios evolutivos da Bacia do Camaquã (RS). Ciência e Natura, Santa Maria. 2014. 36, pp. 183–193. Costa, E. O. Da; Bitencourt, M. F.; Tennholm, T.; Konopásek, J.; Moita, T. De F. P-T-D evolution of the southeast Passo Feio Complex and the meaning of the Caçapava Lineament, Dom Feliciano Belt, southernmost Brazil. Journal of South American Earth Sciences. 2021. 112(1), 103465. https://doi.org/10.1016/j.jsames.2021.103465 . Bitencourt, M. F. Geologia, Petrologia e Estrutura do Metamorfitos da Região de Caçapava do Sul, RS. Master Thesis, Programa de Pós-Graduação em Geociências, Instituto de Geociências, Univer-sidade Federal do Rio Grande do Sul, Porto Alegre, Brazil, 1983b. Toniolo, J. A.; Gil, C. A. A.; Sander, A. Projeto Baneo – Metalogenia das bacias neoproterozóico-eopaleozóicas do Sul do Brasil, Bacia do Camaquã. Serviço Geológico do Brasil: Porto Alegre, Brasil. 2007. pp. 138. Ribeiro, M.; Bocchi, P.R.; Figueiredo Filho, P.M.; Tessari, R.I. Geologia da quadrícula de Caçapava do Sul, RS, Brasil. Boletim da Divisão de Geologia e Mineralogia, DPM-DNPM. 1966. 127, pp. 1-232. Nardy, A. J. R.; Moreira, C.A.; Machado, F. B.; Luchetti, A. C. F.; Hansen, M. A. F.; Rossini, A. R.; Barbosa Jr, V. Gamma-Ray Spectometry Signature Of Paraná Volcanic Rocks: Preliminary Results. Geociências. 2014. 33(2), pp.216–227. Marques, A. C. G.; Moreira, C. A.; Casagrande, M. F. S.; Arcila, E. J. A. Gamma-ray spectrometry applied in the identification of potential acid mine drainage generation zones in waste rock pile with uranium ore and associated sulfides (Caldas, Brazil). Geofísica Internacional. 2022. 61(3), pp. 251–266. https://doi.org/10.22201/igeof.00167169p.2022.61.3.2207 . Mcsween, H. Y.; Richardson, S. M.; Uhle, M. E. Geochemistry: Pathways and Processes. 2. ed. Co-lumbia University Press: New York, United States, 2003; pp. 363. Gilmore, G. Practical Gamma-Ray Spectrometry. 1. ed. John Wiley & Sons, Ltd.: United Kingdom, 2008, pp. 387. Macheyeki, A. S.; Li, X.; Kafumu, D. P.; Yuan, F. Applied Geochemistry: Advances In Mineral Exploration Techniques. 1st. ed.; Elsevier Inc.: Amsterdam, Netherlands, 2020; pp. 210. International Atomic Energy Agency (IAEA). Guidelines for radioelement mapping using gamma ray spectrometry data. Viena, Áustria, 2003. 172p. Dickson, B.L.; Scott, K.M. Interpretation of aerial gamma ray surveys-adding the geochemical factors. AGSO Journal of Australian Geology & Geophysics. 1997. 17(2), pp. 187–200. Wilford, J.R.; Bierwirth, P.N.; Craig, M.A. Application of airborne gamma ray spectrometry in soil/regolith mapping and applied geomorphology. AGSO Journal of Australian Geology and Geophysics. 1997. 17(2), pp. 201–216. Shives, R.B.K.; Ford, K.L.; Charbonneau, B.W. Geological Survey of Canada Workshop Manual: Applications of Gamma ray Spectrometric/Magnetic/VLF-EM Surveys. Geological Survey of Canada. 1995. Open File 3061, pp. 85. LICHT, O. A. B. Prospecção Geoquímica: Princípios, Técnicas e Métodos. 1. ed. Rio de Janeiro: Companhia de Pesquisa de Recursos Minerais - CPRM, 1998. 236 p. PORCHER, C. A.; LEITES, S. R.; RAMGRAB, G. E.; CAMOZZATO, E. Passo do Salsinho, Folha SH.22-Y-A-I-4, Estado do Rio Grande do Sul. Brasília: Companhia de Pesquisa de Recursos Minerais – CPRM, 1995. (Programa Levantamentos Geológicos Básicos do Brasil). Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 09 May, 2025 Reviews received at journal 07 May, 2025 Reviewers agreed at journal 06 May, 2025 Reviewers agreed at journal 01 May, 2025 Reviews received at journal 27 Apr, 2025 Reviewers agreed at journal 05 Apr, 2025 Reviewers agreed at journal 04 Apr, 2025 Reviewers invited by journal 04 Apr, 2025 Editor assigned by journal 03 Apr, 2025 Submission checks completed at journal 03 Apr, 2025 First submitted to journal 12 Mar, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6214118","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":442669255,"identity":"d912394a-3b59-43dc-a67a-5f3b6c236f84","order_by":0,"name":"Luiza Lima Alves","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA0ElEQVRIiWNgGAWjYBACPgbGBiBlwcPAwHwAIiRBQAsbRIsEUAtbArFa4Mp4DIjUIpHc/OEHg4SMbvuZb9IFFXV5DNK9DwhoSWww7AE6zOxM7jbpGWcOFzPIHDcgqCWBB6TlAFALb9uBxAaJNEIOS2w4+Aek5fybZ9K8/+qI0tLYDLblRg6bNG8DMxFaeB42M8sYgLQ8M7bmOXa4mE3mGH4t/Ozpjz++qbCxNzuf/PA2T01dHr90G34tEIAURAlsxGhAAQkk6xgFo2AUjIJhDwCkCzo5xL8K0gAAAABJRU5ErkJggg==","orcid":"","institution":"São Paulo State University","correspondingAuthor":true,"prefix":"","firstName":"Luiza","middleName":"Lima","lastName":"Alves","suffix":""},{"id":442669256,"identity":"82b52c92-30fd-4896-8b19-43250cf5c91e","order_by":1,"name":"César Augusto Moreira","email":"","orcid":"","institution":"São Paulo State University","correspondingAuthor":false,"prefix":"","firstName":"César","middleName":"Augusto","lastName":"Moreira","suffix":""},{"id":442669257,"identity":"550516ae-671f-4b0c-90fb-fe5ff0679d94","order_by":2,"name":"Ana Flávia da Silva Araújo","email":"","orcid":"","institution":"São Paulo State University","correspondingAuthor":false,"prefix":"","firstName":"Ana","middleName":"Flávia da Silva","lastName":"Araújo","suffix":""},{"id":442669258,"identity":"b59108f8-9688-4156-9766-518574e7971b","order_by":3,"name":"Lenon Melo Ilha","email":"","orcid":"","institution":"Universidade Federal do Pampa","correspondingAuthor":false,"prefix":"","firstName":"Lenon","middleName":"Melo","lastName":"Ilha","suffix":""},{"id":442669259,"identity":"e57f20a3-965b-4f85-9115-2957382820fc","order_by":4,"name":"João Pedro Prado de Oliveira","email":"","orcid":"","institution":"São Paulo State University","correspondingAuthor":false,"prefix":"","firstName":"João","middleName":"Pedro Prado","lastName":"de Oliveira","suffix":""},{"id":442669260,"identity":"3d71f7fe-bd1d-4559-bdaf-b8e9dd141317","order_by":5,"name":"Sissa Kumaira","email":"","orcid":"","institution":"Universidade Federal do Pampa","correspondingAuthor":false,"prefix":"","firstName":"Sissa","middleName":"","lastName":"Kumaira","suffix":""},{"id":442669261,"identity":"2f403a7f-b1da-40c9-b9f4-0104d2b2fa08","order_by":6,"name":"Marco Antonio Fontoura Hansen","email":"","orcid":"","institution":"Universidade Federal do Pampa","correspondingAuthor":false,"prefix":"","firstName":"Marco","middleName":"Antonio Fontoura","lastName":"Hansen","suffix":""},{"id":442669262,"identity":"61a57d68-a85f-4734-ae8c-9ed66f008b5a","order_by":7,"name":"Henri Masquelin","email":"","orcid":"","institution":"Universidad de la Republica","correspondingAuthor":false,"prefix":"","firstName":"Henri","middleName":"","lastName":"Masquelin","suffix":""}],"badges":[],"createdAt":"2025-03-12 17:38:12","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6214118/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6214118/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":81368518,"identity":"a6ccbda5-1449-47be-a804-999edb2dfaac","added_by":"auto","created_at":"2025-04-25 09:59:04","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":25815191,"visible":true,"origin":"","legend":"\u003cp\u003eLocation of the study area in relation to Caçapava do Sul (RS)\u003c/p\u003e","description":"","filename":"Fig1.png","url":"https://assets-eu.researchsquare.com/files/rs-6214118/v1/e59231b723d978159128247f.png"},{"id":81368523,"identity":"dcad9011-2269-4b58-819d-a6710f543996","added_by":"auto","created_at":"2025-04-25 09:59:05","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1700489,"visible":true,"origin":"","legend":"\u003cp\u003eGeological map (Modified from [21])\u003c/p\u003e","description":"","filename":"Fig2.png","url":"https://assets-eu.researchsquare.com/files/rs-6214118/v1/b1d9fef2d56a4cb9eeab017b.png"},{"id":81368889,"identity":"ed46b748-333d-4870-8a71-73cb9303c0e9","added_by":"auto","created_at":"2025-04-25 10:07:05","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":42427745,"visible":true,"origin":"","legend":"\u003cp\u003e(A) Drone DJI MAVIC 3T; (B) RS-332 with results on the screen after measurement on Point 44\u003c/p\u003e","description":"","filename":"Fig3.png","url":"https://assets-eu.researchsquare.com/files/rs-6214118/v1/ebc9896bb054da756d5eeb05.png"},{"id":81368528,"identity":"9a2e8c11-eef4-4219-9012-54bf916a10ac","added_by":"auto","created_at":"2025-04-25 09:59:05","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":42351687,"visible":true,"origin":"","legend":"\u003cp\u003e(A) RS-332 conducting a measurement. (B) Quartzites with quartz veins embedded in metamorphic foliation. (C) Schists (D) Amphibolites\u003c/p\u003e","description":"","filename":"Fig4.png","url":"https://assets-eu.researchsquare.com/files/rs-6214118/v1/edbb8705253ccef54526964d.png"},{"id":81368521,"identity":"ed977aca-c2fd-4df5-8bca-f40e500b8130","added_by":"auto","created_at":"2025-04-25 09:59:05","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":33647067,"visible":true,"origin":"","legend":"\u003cp\u003eProducts from drone surveys and locations of [21] sampling points, showing the number of gold specks found in stream sediments. (A) Orthophoto of the study area. (B) DEM of the study area\u003c/p\u003e","description":"","filename":"Fig5.png","url":"https://assets-eu.researchsquare.com/files/rs-6214118/v1/a6f268efd88272fce628dad9.png"},{"id":81369812,"identity":"5115f8f3-4f00-48b5-ab72-ef5a3d859354","added_by":"auto","created_at":"2025-04-25 10:15:05","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":23051712,"visible":true,"origin":"","legend":"\u003cp\u003ePoint map for gamma-ray spectrometry\u003c/p\u003e","description":"","filename":"Fig6.png","url":"https://assets-eu.researchsquare.com/files/rs-6214118/v1/4542e2df60fa616c87f3b17a.png"},{"id":81369811,"identity":"7c9c2585-ed66-4a36-bec4-ef33cc150694","added_by":"auto","created_at":"2025-04-25 10:15:05","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":11491970,"visible":true,"origin":"","legend":"\u003cp\u003e(A) 2D interpolation map of K concentration, with the areas with the highest values highlighted in black. (B) 2D interpolation map of U concentration, with the areas with the highest values highlighted in black. (C) 2D interpolation map of Th concentration, with the areas with the highest values highlighted in black. (D) Areas with the highest element concentration values superimposed on the DEM\u003c/p\u003e","description":"","filename":"Fig7.png","url":"https://assets-eu.researchsquare.com/files/rs-6214118/v1/4aa458b887e68aed4fea8335.png"},{"id":81370722,"identity":"2edb70fd-1eb8-4def-85ed-32e42651eb2f","added_by":"auto","created_at":"2025-04-25 10:24:04","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":165973925,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6214118/v1/1a492134-7ad4-44fc-9f75-e55bf005d687.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"\u003cp\u003eGamma-ray Spectrometric Evaluation in Watersheds With Gold Anomalies in Stream Sediments, Passo Feio Complex, Caçapava Do Sul Region (Brazil)\u003c/p\u003e","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe exponential increase in demand for mineral resources has justified various research projects and the discovery of multiple mineral deposits in Brazil, activities that have driven economic growth and social development. The global market demands a wide variety of mineral commodities, making Brazil a major exporter on a global scale. Consequently, maintaining this activity depends on constant research and discoveries.\u003c/p\u003e \u003cp\u003eGold is one of the oldest financial assets, offering high liquidity and security. It is widely used as a reserve during periods of international crises, leading to significant price increases on stock exchanges [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. In May 2024, the price of gold reached a historical record, with the ounce value climbing to \u003cspan\u003e$\u003c/span\u003e2,300, a significant increase compared to its average price of around \u003cspan\u003e$\u003c/span\u003e1,500 per ounce [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eGold consumption in Brazil has increased alongside the population's purchasing power, appearing in jewelry, electronic components for computers, tablets, notebooks, and mobile phones, as well as parts for the automotive industry, healthcare, dentistry, and even some construction components [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eNew mineral commodities are discovered through several progressive and inter-connected steps, which involve and predict increased investment and decreased risk [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. This process begins with the recognition of surface mineralization evidence, which may be associated with a subsurface ore body [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eGeophysics is a highly mentioned tool in mineral exploration scenario for recognizing exploratory targets, since its field instruments allow for detecting contrasts between the physical properties of mineral deposits and their host rocks [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eGamma-ray spectrometry is a passive geophysical method, as it measures the in-herent radioactivity in the form of gamma rays from mineral species containing radi-oactive isotopes such as potassium (\u003csup\u003e40\u003c/sup\u003eK), uranium (\u003csup\u003e235\u003c/sup\u003eU e \u003csup\u003e238\u003c/sup\u003eU), and thorium (\u003csup\u003e232\u003c/sup\u003eTh) [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. This method enables rapid and easy data acquisition, allowing for extensive area coverage, though it is a shallow method with a maximum investigation depth of 50 to 100 cm [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Gamma-ray spectrometry offers several advantages in the analysis and quantification of elements in the soil compared to geochemical methods. In addition to the rapid acquisition of data, they can be easily processed using softwares, allowing results to be obtained shortly after the acquisition phase.\u003c/p\u003e \u003cp\u003eIn mineral research, gamma-ray spectrometry is mainly applied to characteristically radioactive deposits, such as uranium or hydrothermal origin deposits [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Few references exist for studies related to gold deposits, primarily resulting from airborne geophysical surveys [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThis work involved field reconnaissance, drone investigation (Digital Elevation Model), and terrestrial gamma-ray spectrometry in a detailed survey conducted in two watersheds to identify outcropping occurrences of gold, based on prior indications from geochemical surveys of sediments conducted by the Geological Survey of Brazil in southernmost Brazil.\u003c/p\u003e"},{"header":"2. AREA LOCATION AND HISTORY","content":"\u003cp\u003eThe study area is located in the southernmost of Brazil, in the state of Rio Grande do Sul (RS). The occurrence studied is around 15 km from the urban area of the municipality of Ca\u0026ccedil;apava do Sul, which is approximately 240 km from Porto Alegre, the state capital (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e\n\u003cp\u003eEvidence of mineralization was recognized from regional studies carried out by the CPRM (Companhia de Pesquisa de Recursos Minerais, currently the Geological Service of Brazil) through the National Gold Prospecting Program in 2000, where geological reconnaissance and geochemical prospecting were carried out on stream sediments in an area of 136000 ha [\u003cspan class=\"CitationRef\"\u003e22\u003c/span\u003e]. The regional geochemical survey for gold conducted by the Brazilian Geological Survey involved the analysis of a total of 818 stream sediment samples and 553 heavy mineral concentrate samples from alluvial material. The sampling stations were located at the mouths of drainages associated with metavolcanic-sedimentary lithologies, known for hosting various mineralizations in the studied region.\u003c/p\u003e\n\u003cp\u003eAt each station, a volume of 20 liters of panned material was collected. The preparation and analysis of the samples for gold followed the routine below: (i) stream sediments were sieved to -120 mesh, pulverized in the laboratory to -200 mesh, and decomposed by fusion for analysis by plasma; (ii) heavy mineral concentrates were pulverized in the laboratory to -200 mesh, decomposed by fusion, and analyzed by atomic absorption.\u003c/p\u003e\n\u003cp\u003eTwo sub-basins with anomalous results for gold were selected as the target area for this study, based on the results of collecting samples of stream sediments and concentrates of heavy minerals in the alluvial material. There was a regional study on the area focused on defining anomalous basins, without detailing the origin of the gold [\u003cspan class=\"CitationRef\"\u003e22\u003c/span\u003e]. Based on the premise of weathering in outcropping deposits, followed by the transport of gold particles to the mouth regions of the basins, this work sought to follow the opposite path, based on an analysis of gamma-spectrometric data, in an attempt to recognize primary gold deposits in the study area.\u003c/p\u003e\n"},{"header":"3. GEOLOGY AND METALLOGENETIC ORIGIN","content":"\u003cp\u003eThe study area encompasses rocks of the Ca\u0026ccedil;apava do Sul Granitic Complex and the Passo Feio Metamorphic Complex, that are part of the igneous and metamorphic terrains that compose the Sul-Rio-Grandense Shield, formed during the Transamazonian (2.26\u0026ndash;2.00 Ga) and Brasiliano (900\u0026ndash;535 Ma) orogenic cycles [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe Ca\u0026ccedil;apava do Sul Granitic Complex resulted from post-tectonic, calc-alkaline acidic magmatism, with its intrusion occurring at 562\u0026thinsp;\u0026plusmn;\u0026thinsp;8 Ma during the late phases of the Brasiliano Orogeny evolution [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. Three granite rock facies are present: biotite granitoids, leucogranitoids, transitional granitoids, with crystals elongated in the N34W direction, the same as the metamorphic foliation of the Passo Feio Complex, which hosts the granitic complex [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe Passo Feio Metamorphic Complex consists of pelitic schists, phyllites, amphibolites, and metavolcanoclastic rocks and can be divided into a Metasedimentary Association and a Metavolcanic Association [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. It forms a doubly plunging antiform fold, with a sub-horizontal axis dipping towards NNE and SSW. The granitic complex intrudes its center, and the unit serves as the basement for the Camaqu\u0026atilde; Basin [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. Due to a scarcity of studies conducted in the area covered by the Metamor-phic Complex, the most detailed geological map available was made by the Geological Survey of Brazil, in a scale of 1:100.000 (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe Metasedimentary Association is composed of metapelites and metavolcanoclastic rocks, represented by schists and phyllites containing muscovite, biotite, and/or chlorite, as well as minerals such as garnet, chloritoid, and staurolite. The foliation of these rocks is characterized by schistosity or slaty cleavage. The schist bands vary in thickness and are intercalated with amphibolites, quartz-feldspathic gneisses, and thin quartzite layers [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe Metavolcanic Association includes amphibolites, amphibole schists, amphibole gneisses, and massive amphibolites. These rocks exhibit planar and continuous structures with banding generated by metamorphic segregation or are massive [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe metapelites and amphibolites underwent two regional metamorphic events (M1 and M2) and three deformational phases (D1, D2, and D3), and among these, D3 is not associated with regional metamorphism [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. The D1 phase is preserved in quartz lenses, D2 formed the S2 foliation, and D3 created folds structuring the Passo Feio Metamorphic Complex.\u003c/p\u003e \u003cp\u003eThe M1 event was characterized by the presence of minerals in the staurolite zone (amphibolite facies) and andalusite, indicative of a low-pressure event [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Metapelites and amphibolites are associated with M1, while M2 was a retrogressive event in the greenschist facies [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. The Ca\u0026ccedil;apava Granite intrusion occurred between the D2-M2 interval, with the S2 foliation of metamorphic rocks correlating with that of the granite. The ages of M1 and M2 were estimated at 685\u0026thinsp;\u0026plusmn;\u0026thinsp;12 Ma and 562\u0026thinsp;\u0026plusmn;\u0026thinsp;8 Ma, respectively [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe Passo Feio Metamorphic Complex hosts Cu (Au) and Pb mineralizations. The target of this study is a disseminated gold occurrence hosted in quartz veins concord-ant with the foliation of the host rock and associated with shear zones, with its para-genesis consisting of quartz, gold, pyrite, arsenopyrite, and chalcopyrite, classified as epigenetic hydrothermal deposits [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe hydrothermal processes associated with the intrusion of the Ca\u0026ccedil;apava do Sul Granitic Complex were responsible for the sulfide mineralization under study. Thermal fluids of magmatic origin mobilized metals from rocks adjacent to the Passo Feio Complex and deposited them in veins [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. The deposits within the Metamorphic Complex are structurally controlled by NE-oriented strike-slip fault systems, formed during the Neoproterozoic collision processes involved in the formation of the Dom Feliciano Belt [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"4. METHODS","content":"\u003cp\u003eThis study was conducted through geological reconnaissance, drone surveys for elaboration of Digital Elevation Model (DEM), and gamma-ray spectrometry investigation. The work began with the geological reconnaissance of the region, conducted in a N-S direction along a road that crosses orthogonally to the foliation present in the outcrops. Simultaneously, structural measurements of fractures and metamorphic foliations were collected to identify a possible direct or indirect relationship between the measured structures and the occurrence of gold.\u003c/p\u003e \u003cp\u003eNext, drone surveys were conducted using a DJI MAVIC 3T model, where two flights were performed: one over the higher terrain and another over the lower terrain, with both flying at an altitude of 120 meters (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA). The drone flight lines were conducted in the E/W direction to ensure efficient coverage of the study area. The spatial resolution achieved was 20 centimeters, allowing for a detailed analysis of the terrain's topographic features.\u003c/p\u003e \u003cp\u003eThe resulting images were combined using Agisoft Metashape software, which integrates the imported drone images. This process generated a digital point cloud that allowed for the measurement of altitude for each orthophoto. Through the interpolation of these altitude values, a Digital Elevation Model (DEM) was created.\u003c/p\u003e \u003cp\u003eBased on the results of the drone surveys and after a topographic analysis based on the DEM, the investigation area was delineated for geophysical surveying. The method employed was gamma-ray spectrometry, using the RS-332 Multipurpose Gamma-Ray Spectrometer System by Radiation Solutions Inc. This device offers high sensitivity, thermal protection, ease of use, and an integrated GPS (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA). Additionally, the geophysical reading points were georeferenced using a differential GPS with 0.5 meter precision\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe RS-332 measures the inherent radioactivity that occurs naturally in the form of gamma rays emitted by mineral species containing radioactive isotopes such as cosmogenic nuclides like potassium (\u003csup\u003e40\u003c/sup\u003eK), uranium (\u003csup\u003e235\u003c/sup\u003eU and \u003csup\u003e238\u003c/sup\u003eU), and thorium (\u003csup\u003e232\u003c/sup\u003eTh). The spectrometer operates with a BGO (Bismuth Germanate Oxide) detector, that operates within a measurement range of 30 keV to 3000 keV. The Limit of Detection (LOD) of the RS-332 is determined by the combination of the measurement time, background conditions and the detector measurement range, in a way that longer sampling periods and higher background radiation can elevate the LOD.\u003c/p\u003e \u003cp\u003eThe device's reading time can be configured as needed; for this study, it was set to 60 seconds. A study from 2014 determined that a 60 second reading time is reasonable for gamma-ray spectrometry analysis of volcanic rocks in the Paran\u0026aacute; Basin using a similar device [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. Similarly, another one effectively used 60 second reading time to identify potential zones for acid mine drainage generation in uranium mine waste piles [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe spectrometer has a screen that allows real-time monitoring of the measurements obtained for each analyzed element at each point investigated (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB). The elements U and Th are measured in ppm, while K is measured in percentage.\u003c/p\u003e \u003cp\u003eThe selected area for data acquisition covered approximately 88 hectares, mostly covered by low vegetation and forests limited to drainage areas, with some points of exposed rock. Measurements were taken by directly placing the device on the surface of dry soil. Approximately 715 data points were collected, distributed in a regular grid at 40 meter intervals, with differential GPS guidance in the field, which has an average error of 1 meter.\u003c/p\u003e \u003cp\u003eAfter the data acquisition phase, processing was carried out using Geosoft's Oasis Montaj software to generate maps representing the radiometric distribution of eU, eTh, and K concentrations in the area. An interpolation of the collected data points was performed to create a two-dimensional representation of thorium, potassium, and uranium concentrations in terms of distance.\u003c/p\u003e \u003cp\u003eThe interpolation process involved a least-squares approximation to smooth the discrepancies between field data and software-calculated values. A theoretical two-dimensional model was generated by segmenting the subsurface into rectangular blocks. The software automatically distributed and sized these blocks based on the data points' spatial distribution. The program calculates the concentrations based on the block model created from the comparison between the measured and modeled values, the parameters of these blocks are adjusted interactively until the apparent value agrees with the values acquired in the field.\u003c/p\u003e \u003cp\u003eThe processed outputs were color-scaled maps representing each element's distribution, with potassium concentrations expressed as a percentage and eU and eTh concentrations in ppm. Additionally, ratio and ternary maps were generated and analyzed, however, they provided no further insights beyond those obtained from the original K, U, and Th maps.\u003c/p\u003e"},{"header":"5. RESULTS AND DISCUSSION","content":"\u003cp\u003eThe initial stage of geological reconnaissance followed a N-S direction and revealed an alternation of rocks, varying between quartzites, schists and amphibolites, with a repetitive pattern across the explored area (Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eB, \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eC and \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eD). Thus, it was expected that the geophysical data would show a standard pattern of alternation based on the local lithology, representing the area's background. Additionally, quartz veins were identified concordantly embedded in the quartzites' foliation, which are likely the hosts of the studied gold mineralization.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe drone flights produced a high-resolution orthophoto of the study area, superior to freely available satellite images, and a Digital Elevation Model (DEM) (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). These data were initially analyzed from a geomorphological perspective and later integrated with gamma-ray spectrometry data to assess the geochemical mobility of the analyzed elements. The primary source of gold is likely outcropping, and weathering processes with destruction of mineralized rocks and veins, have resulted in the release of gold particles, which were carried to the basin's mouth. The elevation difference in the study area is 127 meters, with the highest point in the southern portion (291 meters) and the lowest in the Passo Feio River region (164 meters).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe gamma-ray spectrometric acquisition was conducted alongside differential GPS surveying. This equipment provides more precise coordinates than the GPS integrated into the RS-332, with a margin of error of only 0.5 meters, that provided a better result for the regular grid of 40 meter intervals. Thus, it enabled the creation of the point map for gamma-ray spectrometry analysis (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThis study began interpreting the data using the altimetry values obtained from the DEM. These values were analyzed concerning terrain morphology, weathering, and element mobility in the geological environment, as these factors are crucial for assessing radioelement distribution at the Earth's surface. Naturally, sediment transport caused by erosion and physical weathering moves materials from higher elevations to lower areas, such as rivers floodplains. Geochemical element mobilization occurs through leaching and hydrothermal fluid activity, following the same patterns of movement as discussed before [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e].\u003c/p\u003e \u003cp\u003ePotassium (K) is a lithophile, incompatible (especially during magma crystallization), and volatile element with high environmental mobility, primarily occurring in granitoids [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. Uranium (U) becomes mobile under hydrothermal and supergenic conditions [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. Thorium (Th) is less abundant in the crust and typically measured in ppb or ppm [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. The chemical fractionation of U and Th series members occurs during magmatic processes [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eGeomorphology, weathering, erosion, and the source rock collectively control the radioelement distribution in surface materials, creating differences from the bedrock background. Processes include K depletion during soil formation, K and Th enrichment through silicification in schists, and reduced K values during schist pedogenesis [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. Generally, radioelement mobilization varies based on ground-water flow and leaching, with K being significantly more mobile than U or Th in such scenarios [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]. A study characterized various mineral deposits using airborne gamma-ray spectrometry, including gold mineralization in metavolcanic/metasedimentary rocks with hydrothermal alteration (K enrichment), which resembles the present study area [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe geochemical dispersion halo is represented by abnormally high or low concentrations of chemical elements that constitute a mineralization or associated alteration [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]. It is generated by the processes of mineral deposit formation through the introduction and/or redistribution of elements in the environment (primary geochemical halo) or formed by supergene processes (secondary geochemical halo) [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e].\u003c/p\u003e \u003cp\u003ePotassium concentrations, expressed as percentages (%), ranged from 0.5\u0026ndash;2.5% (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eA). A noticeable anomaly with high concentrations (1.2\u0026ndash;2.5%) is present in the central region, oriented NE/SW, coinciding with the schists' metamorphic foliation direction. This area has undergone hydrothermal alteration due to the intrusion of the Ca\u0026ccedil;apava do Sul Granitic Complex. Potassium is present in the micas forming the schists; therefore, potassium anomalies were associated with the schist lithotype. Additionally, a high K concentration area is evident in the northern region (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eA).\u003c/p\u003e \u003cp\u003eUranium (U) and thorium (Th) concentrations, expressed in ppm, ranged from 0.9\u0026ndash;3.9 ppm for U and 2.8\u0026ndash;24.4 ppm for Th (Figs.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eB and \u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eC). Compared to the K values, both show anomalies with a NE/SW orientation positioned in the central region of the area, however, the anomalous areas are not superimposed, with the eU and eTh anomalous areas shifting northwards (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eD). U and Th originate exclusively from hydrothermal processes, as they are more abundant in the mantle and concentrated in the crust through magma ascent [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. In the study area, this correlates with the regional hydrothermal event responsible for mobilizing U and Th and their subsequent deposition in mineralized quartz veins embedded in metamorphic foliation. In this sense, U and Th exist only in the veins generated by the hydrothermal processes that are hosted within the quartzites, making them directly associated with the gold mineralization, and serving as a prospecting guide in the study area.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAn integrated analysis of K, U, and Th maps reveals differences in each element's dispersion halos on the surface. In terms of mobility, K is the most mobile, U is intermediate, and Th is the least mobile under weathering processes. Soil thickness is a critical factor for element mobility, as greater thickness allows higher K, U, and Th concentrations to become available for mobilization. Geological reconnaissance revealed underdeveloped soils (up to 30 cm thick) rich in rock fragments at several points. Under such conditions, gamma-ray spectrometry anomalies primarily reflect signatures associated with the underlying rocks, whether related to original mineral composition or hydrothermal processes.\u003c/p\u003e \u003cp\u003eTwo high K concentration regions or dispersion halos are evident. The Passo Feio River lies within a regional watershed, so the K anomaly in the floodplain consists of the sedimentation of fine suspended particles, predominantly clay minerals, may result from weathering in the study area's rocks or external factors, including the Ca\u0026ccedil;apava do Sul Granitic Complex weathering.\u003c/p\u003e \u003cp\u003eFor U, the highest concentration (3.1\u0026ndash;3.9 ppm) is central, with some dispersion around it. Th shows a smaller dispersion halo with higher values (14.5\u0026ndash;24.4 ppm), potentially representing or delineating a zone with gold mineralization in quartz veins.\u003c/p\u003e \u003cp\u003eTo integrate the data, a map of anomalous halos for each element was generated and overlaid onto the DEM (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eD). There is a coincidence between U and Th anomalies, with an absence of K in this domain, suggesting quartz vein emplacement in quartzites, which contain less K. Conversely, the K anomaly upstream of the U and Th halos may be associated with hydrothermalism in schists, a lithotype without quartz veins and likely barren of gold. Furthermore, the overlap of the anomalous halos proved effective in highlighting that they all share the same NE/SW orientation, consistent with the regional structural trend. This orientation aligns with the foliation of the rocks, quartz veins, fractures, and regional faults.\u003c/p\u003e \u003cp\u003eThe regional gold occurrences consist of quartz veins aligned concordantly with the foliation of the lithologies of the Metavolcanic-Sedimentary Belts, represented in the study area by the Passo Feio Metamorphic Complex [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e]. There are several small prospects and deposits associated with the Ca\u0026ccedil;apava do Sul Granitic Complex, hosted in the Passo Feio rocks, which include Cu (Au) and Pb sulfide veins of an epigenetic hydrothermal origin [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. As discussed in [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e], the region lacks prior studies, so the origin of the metal present in the mineralizing fluids of these deposits has not yet been investigated.\u003c/p\u003e \u003cp\u003eThus, the mineralizations hosted in the metasediments of the Passo Feio Meta-morphic Complex are associated with a remobilization or reconcentration of metallic elements, likely derived from adjacent rocks. The intrusion event of the Ca\u0026ccedil;apava do Sul Granitic Complex resulted in local metamorphism and was responsible for providing the hydrothermal fluids that caused this remobilization and their deposition in the quartz veins. These veins were positioned along weakness planes, represented by the foliation and regional fractures, which have a NE/SW orientation\u003c/p\u003e"},{"header":"6. CONCLUSIONS","content":"\u003cp\u003ePrevious works that analyzed stream sediment geochemistry data revealed two sub-basins with potential for primary gold occurrences in the current study area. The data obtained in this study reveals the existence of a potentially mineralized area that crosses the two sub-basins, with an N70 orientation.\u003c/p\u003e \u003cp\u003eStudies describing the metallogeny of gold in the study region suggest a magmatic/hydrothermal origin that may have occurred during the sedimentation of the host rocks or during the closure and deformation phase of the sedimentary basin in the Neoproterozoic. The Ca\u0026ccedil;apava do Sul Granitic Complex is barren for gold but was possibly responsible for the last regional deformation of the Passo Feio Complex rocks, with reconcentration of gold in quartz veins embedded in the foliation and fractures of quartzites, previously contained in this geological unit.\u003c/p\u003e \u003cp\u003eSince K was also found in large quantities in the river floodplain, this element was not used as a prospecting guide for the hydrothermal processes that generated the gold mineralization. The origin of K in the river may be related to the weathering of schists from the Passo Feio Complex or even to lithologies from outside the study area. In this context, anomalous K halos were associated with the schists, which showed low levels of U and Th, indicating gold sterility, perhaps due to the lack of spaces for the generation of quartz veins.\u003c/p\u003e \u003cp\u003eThe elements U and Th are abundant in the mantle and are exclusively related to hydrothermal processes. Thus, the surface anomalies of high U and Th values obtained in this study coincide with the mineralized quartz veins. In this sense, quartzites rep-resent the main lithotype or regional prospecting guide for gold searches.\u003c/p\u003e \u003cp\u003eAlthough gamma spectrometry is widely used in mineral prospecting for the identification of radioactive deposits, this study highlights the application of the method for a hydrothermal-origin gold deposit. The association of U and Th with mineralization provides a new perspective for identifying potentially gold-bearing areas.\u003c/p\u003e \u003cp\u003eThe combined analysis of the digital terrain model with gamma spectrometry data has satisfactorily delimited potentially gold-mineralized targets, contained in a strip that crosses the two sub-basins recognized as anomalous in the geochemistry of stream sediments, and the probable primary outcropping source of gold.\u003c/p\u003e \u003cp\u003eThe combination of these methods has proven effective in refining targets from regional geochemical prospecting projects. It should be followed by detailed investigations using geophysical surveys, trenching, or borehole drilling, either to analyze the target architecture or to define its content.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eAuthor Contributions:\u0026nbsp;Conceptualization, L.L.A and C.A.M; methodology, L.L.A and C.A.M; software, L.M.I.; investigation, L.L.A., C.A.M., A.F.S.A., L.M.I., S. K., M.A.F.H.;\u0026nbsp;J.P.P.O.;\u0026nbsp;H.M.; writing—original draft preparation, L.L.A.; Preparation of figures: L.L.A., C.A.M and J.P.P.O.; writing—review and editing, L.L.A.,\u0026nbsp;J.P.P.O.,\u0026nbsp;C.A.M.; supervision, C.A.M.; project administration, C.A.M. and H.M.;.\u003c/p\u003e\n\u003cp\u003eFunding:\u0026nbsp;This research was funded by FAPESP—Fundação de Amparo à Pesquisa do Estado de São Paulo (Process n. 2023/04732-8).\u003c/p\u003e\n\u003cp\u003eData Availability Statement:\u0026nbsp;The data that support the findings of this study are available on request from the corresponding author, Luiza Lima Alves.\u003c/p\u003e\n\u003cp\u003eAcknowledgments:\u0026nbsp;The authors are especially grateful to the Fundação de Amparo à Pesquisa do Estado de São Paulo - FAPESP for funding the field trip of the Project. We also would like to thank the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) for financial support on the masterfs’ scholarship of Luiza Lima Alves. We are also thankful for the support provided by Universidade Federal do Pampa, Campus de Caçapava do Sul – UNIPAMPA.\u003c/p\u003e\n\u003cp\u003eConflicts of Interest:\u0026nbsp;The authors declare no conflicts of interest.\u003c/p\u003e\n\u003cp\u003eEthics, Consent to Participate, and Consent to Publish declarations: not applicable.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eIBRAM \u0026ndash; Instituto Brasileiro De Minera\u0026ccedil;\u0026atilde;o. Informa\u0026ccedil;\u0026otilde;es e An\u0026aacute;lises da Economia Mineral Brasileira, 2012. 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(Programa Levantamentos Geol\u0026oacute;gicos B\u0026aacute;sicos do Brasil).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"discover-geoscience","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Discover Geoscience](https://www.springer.com/journal/44288)","snPcode":"44288","submissionUrl":"https://submission.nature.com/new-submission/44288","title":"Discover Geoscience","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Discover Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"mineral exploration, gold, geophysics, gamma-ray spectrometry","lastPublishedDoi":"10.21203/rs.3.rs-6214118/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6214118/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study utilizes gamma-ray spectrometry to identify source areas of gold recognized in geo-chemical prospecting work in stream sediments. The local geological context is represented by the Passo Feio Metamorphic Complex, which contains gold deposits possibly hosted in quartz veins concordant with metamorphic foliation, composed of quartzites, schists, and amphibolites. The study followed the sequence: geological reconnaissance, drone survey, and gamma-ray spectrometric acquisition. Field reconnaissance indicated an alternation of rocks oriented in a WNW/ENE direction, with recognition of quartz veins embedded concordantly with the foliation of quartzites. The drone data enabled the generation of a Digital Elevation Model (DEM) and served as a basis for planning the gamma-ray spectrometry work. A total of 715 gamma-ray spectrometric readings were taken, with an average spacing of 40 meters between points, followed by data processing and the generation of maps of K (0.5% \u0026ndash; 2.5%) concentrations, eU (0.9\u0026ndash;3.9 ppm), and eTh (2.8\u0026ndash;24.4ppm). The data obtained regarding the K (%) concentration values reveal a clear anomaly in the central region with WNW/ENE orientation. The concentration data obtained for U (ppm) and Th (ppm) show a similar pattern concerning the WNW/ENE anomaly in the center of the area. The overlap of positive anomalies served as an indication of gold source areas in two river valleys.\u003c/p\u003e","manuscriptTitle":"Gamma-ray Spectrometric Evaluation in Watersheds With Gold Anomalies in Stream Sediments, Passo Feio Complex, Caçapava Do Sul Region (Brazil)","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-04-25 09:58:59","doi":"10.21203/rs.3.rs-6214118/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-05-09T17:45:57+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-05-07T19:04:12+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"106571002566705058508440303264804534410","date":"2025-05-06T13:54:10+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"182187317760697414405704694679856345527","date":"2025-05-01T08:07:15+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-04-27T16:48:22+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"155086947064449624813054701817300040639","date":"2025-04-05T13:21:29+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"201311208060733224348617216764683505128","date":"2025-04-04T11:12:08+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-04-04T11:06:01+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-04-03T12:58:06+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-04-03T12:55:03+00:00","index":"","fulltext":""},{"type":"submitted","content":"Discover Geoscience","date":"2025-03-12T17:27:11+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"discover-geoscience","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Discover Geoscience](https://www.springer.com/journal/44288)","snPcode":"44288","submissionUrl":"https://submission.nature.com/new-submission/44288","title":"Discover Geoscience","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Discover Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"28743fd1-75b6-4e02-bc95-8dd4f34d8185","owner":[],"postedDate":"April 25th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2025-05-26T18:08:14+00:00","versionOfRecord":[],"versionCreatedAt":"2025-04-25 09:58:59","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6214118","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6214118","identity":"rs-6214118","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}