## 1 Introduction
### Sierra Pena Blanca, Deserts and Streams  
In the state of Chihuahua, around 40% of the proven uranium reserves in Mexico are reported, located approximately 50 km north of the capital at various points in the Sierra Pena Blanca (SPB) (Figure 1). The main uranium deposits in this area are Nopal I, Domitila, Puerto III, and Margaritas [16]. In the 1980s, the deposits were explored and exploited, and up to 300 tons of uranium ore were placed in the area in rock piles (repository), susceptible to weathering and erosion. Mineralization is associated with igneous rocks of volcanic origin (mainly hyrolitic tuffs), and the subsequent hydrothermal activity is presumed to be the event that mobilized and concentrated the mineral [17; 18]. In Nopal I, it is estimated that uranium was deposited in oxides such as uranium-pitchblende (UO\({}_{2}\)). In successive events,secondary minerals associated with uranium were formed, such as oxides, hydroxides, and silicates, represented mainly by the phases: schoepite ((UO)\({}_{2}\))4O(OH)\({}_{6}\cdot\)6H\({}_{2}\)O), weeksite K(UO)\({}_{2}\)(Si\({}_{5}\)O)\(\cdot\)4H\({}_{2}\)O, and uranophane (Ca(UO)\({}_{2}\))\({}_{2}\)Si\({}_{2}\)O\({}_{7}\)6H\({}_{2}\)O), which is predominant in the area [19; 20]. The SPB is located within the Chihuahuan Desert and is characterized by an arid climate, according to the Koppen climate classification modified by [21]. The average temperature is 18-22 \({}^{\circ}\)C, with extremes in summer around 40 \({}^{\circ}\)C [22]. The average rainfall is 235 mm, with variations of 150-400 mm, and is distinguished by being sporadic but intense [23]. Physiographically, the SPB is located in the province of Basins and Ranges of the North (PBRN). This is distinguished by the folding of marine sequences deposited during the Mesozoic, which outcrop to the northeast and south of the mountain range, as well as the filling of valleys with continental sediments (Laguna del Cuervo LC to the east), and sequences of extrusive igneous rocks of felsic composition superimposed on marine rocks of the Mesozoic. The PBRN comprises mountain ranges and valleys with elongated morphologies with a preferential northwest-southeast orientation. These characteristics led to closed endorheic basins, such as the Laguna Hormigas aquifer, where SPB and LC are located [24]. Streams within the SPB are dry most of the year but are well-developed in the high and mountainous parts. Main streams open downslope and deposit most of their sediment in fan-shaped bodies. The phase composition of the sediment is strongly controlled by the source rocks, crystalline tuffs and vitrophides of felsic composition, and mainly limestone sedimentary rocks. Grain sizes vary from conglomerates-fanglomerates to sections with well-sorted sand and layers of clay or mud [25]. Previous research has primarily focused on understanding the transport of uranium in the low-saturated zone through groundwater analysis [26; 27; 28; 29; 30]. However, the mechanisms of uranium transport in desert areas, especially surface transport, have not been widely studied. In the Pena Blanca area, the works of [31; 32] have shed some light on this issue. Sediment sampling was carried out along the Boca La Colorado and El Tigre streams, whose granulometries range from gravel to clay in different proportions. XRD established the mineralogical composition of these sediments as quartz, calcite, sanidine, natrolite,  
Figure 1: Location of the study area and sampling points at SPB. kaolinite, anorthite, and montmorillonite. These findings underscore the urgent need for further research in this area. The Boca La Colorado stream, whose sediments are representative of the minerals and granulometry of the area, originates in the central part of the SPB and flows a few meters from the repository area. During its course, it travels around 9 km, flowing into the flood plain of Laguna del Cuervo as an alluvial fan. Boca La Colorado was chosen as one of the leading research targets.