**1. Introduction**

Multi-element geochemical mapping is useful for both, mineral exploration surveys and environmental studies as previously demonstrated [1–4]. For both applications, the unusually high concentrations (also known as anomalies) are strong pieces of evidence of a potential mineral deposit or a possible anthropogenic impact. Evaluating the spatial distribution of an element, in a given sampling medium (e.g., soils, sediments, water, and rocks), along with different geographic information (land cover and land use, hydrology, geomorphology, geology, and mineralized zones) may assist in accurately identifying the source of enrichment (for some authors, contamination), whether anthropic or not [5–7].

Traditional studies in environmental geochemistry usually carry out impact assessments separately for each sampling medium [8–10]. Taking this into consideration, an integrated assessment, using geochemical data from different sampling mediums, might be

**Citation:** Salomão, G.N.; Farias, D.d.L.; Sahoo, P.K.; Dall'Agnol, R.; Sarkar, D. Integrated Geochemical Assessment of Soils and Stream Sediments to Evaluate Source-Sink Relationships and Background Variations in the Parauapebas River Basin, Eastern Amazon. *Soil Syst.* **2021**, *5*, 21. https://doi.org/ 10.3390/soilsystems5010021

Academic Editors: Matteo Spagnuolo, Paola Adamo and Giovanni Garau

Received: 15 February 2021 Accepted: 17 March 2021 Published: 22 March 2021

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a powerful strategy for identifying source apportionment and evaluating the geochemical variability in terrestrial environments. In relation to the large geochemical data set, this strategy became more affordable due to recent advances in data analysis using a robust programming language in addition to geoprocessing techniques. Similar approaches have been conducted elsewhere [11–13].

Prior to conducting an integrated assessment methodology, it is indispensable to understand the limitations in terms of physicochemical properties and representativeness, regarding the medium of sampling [14]. For instance, soil samples have local representativeness and medium (A horizon) to low (B horizon) susceptibility in terms of changes in local conditions. In general, soils have a strong correlation to the parent geological material. In contrast, stream sediment samples have a wider representativeness, restricted to the whole upstream catchment area of the sampling point, and high susceptibility, not only due to the different lithologies occurring in the catchment area, but also due to changes in the hydrosedimentological dynamics, influenced by local seasonal variations, and changes in land cover and land use [15,16].

In addition, the determination of geochemical background is a mandatory approach for this assessment. The background concept has not been clearly established [17–19], but the term is often used as a naturally occurring concentration range of an element or chemical compound [20], determined by a given analytical method [21], which can be established by direct, indirect and integrated methods [6]. Some authors consider that the upper limit of the geochemical background, also known as the threshold value, can be used to distinguish between natural and anthropogenic influences [17]. The threshold concentration value is regularly used as a reference to define action levels in environmental legislation [22,23], whereas, the lower background limit has not been widely discussed, perhaps due to its low relevance for exploration and environmental purposes.

The Parauapebas River Basin (PB) is particularly relevant for geochemical studies because: (i) The basin is located in the Carajás Mineral Province, the largest mineral province of Brazil, and large open pit Fe (N4, N5 and S11D), Cu (Sossego) and Cu-Au (Antas North) mines, besides other mineral deposits, are situated on it (Figure 1d; (ii) The PB has protected areas that are covered by preserved tropical forest but most of it was deforested. Hence, the study area has strong contrasts of land use and cover; (iii) The possible impact in the environment related to mining activities and the effects of deforestation and increase of human occupation, with agricultural development and livestock production, should be evaluated. All these aspects can be evaluated by studying the spatial distribution of chemical elements particularly those of iron, the most voluminous mineral resource produced in the region, and Potentially Toxic Elements (PTE).

This study is associated with the Itacai únas Geochemical Mapping and Background Project (ItacGMBP), a large geochemical mapping project carried out by the Instituto Tecnológico Vale (ITV) in the entire Itacaiúnas River Watershed (IRW; Figure 1b). In the PB area (Figure 1c), a previous study about the soil [24] geochemistry has been conducted. However, an integrated and refined interpretation using soil and stream sediment geochemical data sets of the PB is presented here for the first time. To address the source apportionment and establishing geochemical threshold variations, a series of advanced data analyses were implemented, mainly by using geoprocessing techniques and traditional statistical methods. This integrated assessment of geochemical data is of grea<sup>t</sup> importance to fill the knowledge gaps identified in previous studies.

This study aims to handle an integrated evaluation of soil and stream sediment geochemical data to evaluate source apportionment and to establish geochemical threshold variations for Fe, Al, and 20 selected PTE (Ag, B, As, Ba, Bi, Cd, Co, Cr, Cu, Hg, Mn, Mo, Ni, Pb, Sb, Se, Sn, U, V, and Zn) in the PB. The study was designed to answer several questions:


#### **2. Study Area and Geological Setting**

The study area of the present research is the Parauapebas River Basin (PB), situated in the eastern Amazon Rainforest (Figure 1a). The PB is classified as one of the eight sub-basins of the IRW (Figure 1b), which covers an area of approximately 9600 km2, encompassing two main urban areas (Parauapebas and Canaã dos Carajás; Figure 1c), parts of conservation areas, represented mainly by the remaining preserved forest in the Center-West of the PB (Figure 1b), and active open-pit Fe (N4, N5, and S11D), Cu (Sossego) and Cu-Au (Antas North) mines (Figure 1d).

**Figure 1.** Location of the Parauapebas River Basin (PB) in the eastern Amazon region (**a**), situated in the Itacaiúnas River watershed (**b**). the land cover and land use map (**c**) and the geological map (**d**) are presented along with the sampling sites for soil and stream sediments. These two maps are overlaid on a shaded-relief digital elevation model (DEM). Inset shows the Northern (NPB) and Southern (SPB) PB. Map coordinates are in degrees (WGS84). Source: modified from [24].

> For the purpose of the present study, the geology of the PB can be simplified into three different domains (Figure 1d):

> • Rio Maria—Sapucaia—Canaã dos Carajás domains (RM-S-CC): It is restricted to the south of PB (Figure 1d), and is composed essentially of Mesoarchean tonalite— trondhjemite—granodiorite (TTG) series associated with greenstone belt sequences and calc-alkaline granites to tonalites and sanukitoids [25–28]. Neoarchean A-type like granitoids, charnockitic rocks, mafic-ultramafic bodies, and Paleoproterozoic anorogenic granites crosscut the Mesoarchean units [25,29–33].


## **3. Materials and Methods**
