The present study is part of the process of establishing national directives on the management of wastes from extractive industries, transposed into Cameroonian law by legal instruments applicable to environmental management a scribe to human development activities, protection of natural resources and environments. Law No. 2023/014 of December 19, 2023, relative to the Mining Code, prescribes in its article 4, the rules of mining art defined as the technical conditions and methods of exploration and exploitation to better valorize the potential of the deposit, as well as to optimize productivity and conditions of industrial safety, public safety and environmental protection. It also establishes in its article 11, the authorization to exploit mining wastes, hence the importance of this work. The importance of mineral resources exploitation is crucial in the development of a country. According to the 2017 statistical yearbook of the mining, industry and technological development sub-sector, the solid extractive sector has generated to the State of Cameroon, budgetary revenues of 35.39 billion FCFA compared to 406.58 billion FCFA for the liquid extractive sector (hydrocarbons), representing respectively 8.01% and 91.99% for a total of 441.97 billion FCFA. In 2023, the Cameroonian solid extractive sector contributed 719.36 kg of 24-carat gold to the state’s strategic reserve at BEAC, representing approximately 32.5 billion FCFA. Cameroon, like most African countries, relies on its mineral resources to ensure its development. However, this can only happen through a good knowledge of the geology and geochemistry of mineral resources throughout the national territory. In the field, mining companies are engaged in artisanal, semi-mechanized gold mining, implementing concentration techniques that do not guarantee maximum recovery of the substance. Furthermore, these companies don’t take account of other potential mineralization. As a result, other mineral substances often associated with gold mineralization such as platinum, silver, copper, etc., are generally of no importance for the operators to pay any attention. Not far from there, mining wastes consisting of gravel and sand resulting from washing, although being materials that can be used in construction and civil engineering, do not arouse any interest for the neighboring communities. For example, the work of Kitobo on mining waste from Kipushi enabled the identification of recoverable potential, whose processing would produce 80,950 tons of copper and 631,750 tons of zinc exploitable over 20 years . Other authors have worked on the characterization of mining wastes in Morocco, the Democratic Republic of Congo and Cameroon. This is the case of El Hachimi et al., who has work on mining wastes from the Zeïda mine in Morocco and highlighted the high contents of Pb and As with respective maximum values of 5547 g/t and 192.2 g/t in mining residues . According to Pahimi et al., in mining waste from artisanal mines in the locality of Bétaré-Oya it is possible to detect strong pollution by heavy metals and rare Earth elements (REE) whose concentrations are higher than the geochemical background . Ndjigui et al., demonstrated on the sediments of Tongo Gadima in Bétaré-Oya that alteration, erosion, transport and sedimentation strongly mobilize elements such as Ti, Zr, Th, Y, and REE, which are concentrated in sediments, thus increasing the exploitability potential of such sedimentary deposits . According to Tonang Zebaze et al., the studied mining wastes have acidic (2.8) to neutral (6.4) properties, therefore, the mobility of heavy metals is pronounced depending on the pH . The most illustrative cases are those of mining wastes from Mama Wassandé which has a lowest pH (2.8), and higher electrical conductivity of 1300 μS/cm and higher mineralization of Ni, Cu, Zn, Co, As, Sb, Cd, Cr, Se. This gigantism in terms of proportion is due to the fact that, the particles have recently been reworked and are therefore young compared to all other mining wastes in the locality. We are thus witnessing acidification of the waters and a release of heavy metals. That said, the main objective of this work is to characterize the mining waste from Fel and its surroundings on a geochemical level with to the main of determining its valorization potential.

The study area covers the villages of Fel, Kombo Laka, Mborguéné, Mama Wassandé, Ndoyong, Gbatoua and Ngazi, all in Meiganga Subdivision, Mbéré Division, and Adamawa Region. It is located about 152 km from Meiganga and about 10 km from the border with the Central African Republic (Figure 1). The topography of the study area is characterized by an altitude between 871 and 1155 m, with high altitudes covering the entire eastern part, and relatively lower altitudes for half of the western part. The hydrological network of the study area belongs to the Sanaga basin with the Lom as its main collector. In this sector, the drainage system is dendritic, evolving from watercourses of 1^st order to watercourses of 4^th order. The numerous rivers (Fel, Foum, Mama, Mifeck, Wantia, Moufeck, Mikila, Yoyo and Midal) and the main collector (Lom) are the areas of excellence for gold mining using semi-mechanized artisanal technics. From a lithological point of view, the study area is located in the central domain of the Central Africa Fold Belt (CAFB) (Figure 1). The Upper-Lom series in this area is dominated by undifferentiated schists, micaschists and quartzites which form bands of monoclinal arrangement, oriented in the NE-SW direction. In addition, the geological formations in the study area are crosscut by gold-bearing quartz veins whose size varies from few centimeters to tens of meters in the neighborhood of the granite intrusions . The rocks in this area were strongly mineralized by hydrothermal fluids circulating in a network of fractures developed during Neoproterozoic tectonic events . This is how gold and several other useful substances (Ag, Ba, Zn, Bi, As, B, Sb, W, diamond, rutile and graphite) have been reported . Primary mineralization is also premonitory of certain accumulations in weathering mantle sand detrital sediments, responsible for the emplacement of secondary metalliferous deposits . According to many authors, , the context of gold mineralization in that sector reveals that it is the pneumatolytic veins from the Pan-African granites rather than the granites themselves which carry the gold mineralization. Majority of exploited deposits are located in the Bétaré-Oya – Kombo-Laka corridor, in essentially granitic areas which contain pinched fragments of the shale formation of the Lom Serie. Previous studies carried out by BRGM in 1985 in the Upper-Lom series, revealed very strong mineralization in tungsten (W), Lead (Pb), Gold (Au) and Silver (Ag), perfectly highlighting certain geological entities . In the Lom basin, gold mineralization is accompanied by significantly high levels of Ag, Sb and Zn and numerous inclusions of pyrite and galena, emplaced within the granitoids of the Lom Series through a network of sulfide-rich hydrothermal quartz veins .

a) Pre-Mesozoic configuration of the Pan-African-Brazilian fold belt between NE Brazil and Cameroon ; b) Litho-structural map of Cameroon illustrating the main geotectonic domains (according to Toteu et al. and modified by Van Schmus et al.) . KCF, Kribi-Campos Fault; SF: Sanaga Fault; CCSZ: Central Cameroon Shear Zone; TBF: Tcholliré-Banyo Fault; GGSZ: Godé-Gormaya Shear Zone; MNSZ: Mayo-Nolti Shear Zone; SLC: Sào Luis Craton; SJD: Sériodo-Jaguaribé Domain.

The presence of certain chemical elements in the initial composition of an unaltered rock is a prerequisite for their monitoring during supergene processes, particularly their enrichment . These are generally certain MTEs and REEs trapped in the crystal structure of many rock minerals. Their enrichment in weathering products following the dissolution of host minerals depends on many factors. These include, among others, the crystallo-chemical characteristics of each element, the alterability of the host mineral, the physico-chemical conditions of the environment and the modalities of reincorporation of an element into neoformed secondary constituents . In the Lom series, many authors attest that tectonic event favored the establishment of a geochemical background characterized by mineralization indices of Cu, Pb, Zn, As, Sb, Mo, Ba, B, W, U and Au . Even if the latter are particularly enriched in the mineralized quartz joints and veins which cross-cut the surrounding rocks, their presence is reported in the shales, although in low concentrations. Hence, was addressed in this section the fate of useful elements in mining waste products from the shales of the Upper-Lom series in Fel and its environs. Mineral concentrations are neither accidents, nor anomalies related to a theory close to that of spontaneous generation. Geological agents capable of working on such enrichments are numerous and present in all geological cycles. Amongst them, the most important is hydrothermalism, fractional crystallization of magmas that separates and concentrates some minerals, metamorphism, erosion, differential weathering of rock minerals, and sedimentation. These mineral concentrations constitute deposits whatever their size, volume and value; while taking into account the technical, economic and social conditions of exploitation of the moment reclassifying these mineral concentrations as deposits.

Several field trips were carried out as part of this study. One of them in January 2017 aimed to identify rivers subject to semi-mechanized artisanal gold mining exploitation, identification of tailings dam sand to assess their extent in space. During this field trip, we were also able to appreciate the method of placers exploitation. The last field trip took place in April 2021, a period corresponding to the end of the dry season and in addition, a favorable time for accessibility and sampling. During this fieldwork, ten (10) wastes samples of different mining sites were collected for geochemical study, with seven (7) coming from washing wastes and three (3) from concentrated wastes.

The wastes of mining sites were progressively formed during the exploitation phase, which lasted only a few months and then remained accumulated for about five years. The heterogeneity of the environment is related to two main phenomena. Firstly, we have the granular classification using the density and size of the particles during decantation and the pulp flow from the point of supply to the water drainage weir. Secondly, we have the superposition of successive layers that reflects variations in the characteristics of production. Systematic sampling ensured good representativeness of the granulometric and geochemical characteristics of the wastes. Composite waste samples were taken from the pours of several mining sites namely Foum, Mama Wassande, Fel, Wantia, Mifeck, Moufek, upstream of the Lom River for the washed wastes, and Bondo, Wankoro and downstream of the Lom River at a place called Wakasso bridge for the concentrated wastes. Each composite sample was collected manually from several subsamples, taken from different locations and depths of the pours and packaged in clean plastic bags. The samples were dried, demolding, sieving through a stainless-steel sieve in five particle sizes (< 0,08 mm; 0,08 mm; 0,163 mm; 0,315 mm and 0,5mm) to study the effects of particle size on metal absorption , weighing, packaging, and then transported to the laboratory.

The geochemical analysis carried out covers 12 trace elements. The method usually consists of two steps including the extraction of the desired elements in solution and the determination of the elements by instrumental analysis of the solution. Extraction was total to measure the total abundance of elements of all minerals in the sample. The method of analysis used is the Inductively Coupled Plasma – Mass Spectrometry (ICP-MS) which measures the concentrations of the elements by counting the atoms for each element present in the solution. Generally, the ICP-MS analysis technique provides the widest range of elements associated with the lowest detection limits to ensure maximum exploration power. For the dosage of gold by atomic absorption, the threshold of 0.2 ppb, out of the five fractions was retained. Analysis of the MTE was performed on 10 ml aliquot fractions obtained by mineralization of the samples, with the addition of internal standards (indium, bismuth), HNO₃ 15N and H₂O milli-Q, obtained following a cold attack for 168 hours from 0.1 g to 1 g of each solid sample previously crushed. The attack was carried out with 20 ml of ultra-pure concentrated HNO₃ acid in polyethylene bottles. The results of analyses are compared with the normal average levels of MTE in the Earth's crust.

Mineralization is a generic term to designate an abnormally high natural concentration of chemical elements whose exploitation could be of economic interest. The mobilization of chemical elements during alteration processes is a major asset for the accumulation or enrichment of these elements in favorable environments, sometimes with high contents . This can lead to the emplacement of secondary mineralizations, because they are developed at the expense of a primary material. It may also result in the development of anomalies or indications of geochemical mineralization in altered materials. In this work, the determination of mineralized elements through their Mineralization Index (MI) in mining wastes was done using a comparative approach. This enabled to discriminate mineralized elements in each mining waste in the study area, even if there are exceptions due to the ease of extraction and/or available volume. An element is said to be mineralized when it has a content greater than that of its Clarke in a material on one hand, and if and only if the mineralization index of this element is greater than or equal to 2 on the other hand. In other words, the mineralization index is the ratio between the content of the mineralized element in a material by the Clarke of this mineralized element.

With X: the content of the element studied; Bg (PAAS): Background for a studied element x

According to Table 1, the MI values correspond to two mineralization conditions .

Enrichment, on the other hand, designates an increase in total contents, following anthropogenic contributions, without prejudging a negative change in the quality of the environment . The enrichment factor (EF) of provides information on the increase in the concentration of a chemical element in a material compared to a reference. The element of normalization chosen for this study is scandium. The Enrichment Factor (EF) has been proposed to discriminate between anthropogenic contributions from natural sources. The element chosen as reference must be closely associated with the finest particles and its concentration must not be altered by anthropogenic inputs . The metals Sc , Fe or Al , are elements often used as reference metals. In this study, scandium was chosen as the reference metal for its association with fine particles and its concentration which is very little or not altered by anthropogenic means. EF values between 0.5 and 1.5 indicate a natural origin of the metals, while those above 1.5 are attributed to anthropogenic contributions .

According to Table 2, the EF values correspond to several enrichment classes .

The enrichment factor is calculated following the formula from :

X: element studied; R: normalizing element.

Bg: background for a studied element x and the normalizing element. As part of this study, we will use the PAAS (Post-Archean Australian Shale) of .

From a morphological point of view, the residuum deposits are gray in color due to their richness in quartzo-feldspathic elements. In the shape of a fan or semi-circle, they occupy an area ranging from 300 to 1,300 m², located along the watercourses. There are approximately 13 (waste dumps) per kilometer. As for concentrate wastes, they only represent approximately 1% of the total volume of material treated and consequently, its storage is disseminated within the wastes from the washing process. Despite this low proportion, waste concentrations remain of very high value in geo-resources, since it is the latter which concentrates the economically exploitable mineral substances from the placers.

Geochemical response in different particle size fraction shows that fine-grained fraction tends to have relatively high metal contents, in part because of the high specific surface area of the smaller particles. For the MTEs in Mama Wassandé, Fel and High Lom, the trend clearly indicates a decrease in concentration with an increase in the granulometry of particles. The fraction with smaller size (< 80 μm) has the highest concentration, and the higher fraction (315-500 μm) has the lowest concentration . As part of this study, the contents of gold, silver, uranium, lead, copper, arsenic, thorium, antimony, bismuth, yttrium, selenium and platinum in the samples were compared to the PAAS for each element . The fine fractions (< 80µm) of concentrated wastes (CW) and washed wastes (WW) were selected for their best geochemical responses in terms of mineral concentration. This evaluation of the contents enabled to assess the mineralization indexes up to 2 (MI ≥ 2) and the severe to extremely severe enrichments (EF ≥ 10) and to define the mineral deposits for which there may be economic interest.

Figure 2a, 2b and 2c perfectly illustrates the enrichments in each of the sites for concentrated wastes. The elements taken into account in this figure only concern those whose mineralization index is greater than or equal to 2. It appears in Figure 2a at Wakasso that the elements Au, Ag, U, Th, Sb, Y, Se and Pt have enrichments ranging from severe to extremely severe, thus offering for this site a strong potential for valorization in these elements. With the exception of Cu, all other elements (Au, Ag, U, Pb, As, Th, Sb, Bi, Y, Se and Pt) present in the concentrated wastes from Wankoro concentrates (Figure 2b) show enrichments ranging from severe to extremely severe, also offering for this site a strong potential for valorization of these elements. Bondo concentrated wastes (Figure 2c) also follow the same trends with severe to extremely severe enrichments in Au, Ag, U, Pb, Th, Y, Se and Pt. Generally, the strong mineral association constituted by Au-Ag-Pt-Th-Se-(U)-(Pb)-(Y)-(Sb) is present in concentrated wastes, whatever the site and therefore, undeniably constitutes a valuable resource in such wastes. Among the mineralized trace elements, U and Pb are excellent radioactive and heat producers. They are of great interest as a source of nuclear energy, although used in several other fields such as geochronology. Au, Ag, Pt, Se and As also have multi-varied usages, particularly in the metallurgical industry as an alloy, in the chemical industry and in medicine.

Figure 3a, 3b, 3c, 3d, 3e, 3f, 3g represents the enrichments of washed wastes in different sites and the elements taken into account, only concern those with mineralization index greater than or equal to 2. It appears that in the washed wastes of Moufeck (Figure 3a), we observe only one element (As) with an enrichment not reaching the severe threshold. In the Lom Amont washed wastes (Figure 3b), we observe just two elements (Au and As) with very severe and severe enrichments respectively. The Mifeck washed wastes (Figure 3c) show five elements of which three (As, Sb and Se) are severely enriched. The Wantia washed wastes (Figure 3d) show four elements, three of them (Au, As and Sb) have severe to very severe enrichments. Fel washed wastes (Figure 3e) exhibit four elements (Au, As, Sb and Se), all enriched from severe to extremely severe. The Mama Wassandé washed wastes (Figure 3f) are comparable to the Fel wastes with four elements (Au, As, Sb and Se) enriched from severe to extremely severe, and one element (Bi) moderately enriched. The Foum washed wastes (Figure 3g) show six elements of which only two (As and Sb) are severely to very severely enriched. Thus, we can remember that the mineral association constituted by Au-As-Sb-(Se) can constitute, depending on the site, mineral deposits in the washed wastes.

PAAS by .

C. Sam = Concentration of the Sample; MI = Mineralization Index; EF = Enrichment Factor

From the above, we can think that the remobilization and redistribution of chemical elements during supergene processes (weathering, transport and sedimentation) favored the accumulation of certain trace elements with concentrations greater than or equal to their Clarke. Subsequently, most of these elements present in the residual system were further remobilized in the gold ore processing process where some elements (Au, Ag and Pt) have been significantly enriched in the concentrated wastes. Generally, many of these MTEs are weakly concentrated in washed wastes, but highly concentrated in concentrated wastes. This is the case for Au, Ag, Pt, U, Pb, Y and Th. The best enrichments identified in mining wastes are classified into two groups, those which are represented in all fractions of wastes on the one hand, and those which are characteristic of a particular type of waste on the other hand. For the first case, i.e. the mineralization identified both in washing wastes and in concentrated wastes, we have in order of importance: Au-As-Sb-Se. For the second case, i.e. the mineralization identified only in concentrated wastes, we have in order of importance: Ag-Pt-Th-U-Y.

In short, concentrated wastes (CW) and washed wastes (WW) present potential in each of the following ten sites (Figure 4): The concentrated wastes at Wakasso show 09 mineralization out of the studied 12 elements. In order of importance, we cite Au-Ag-Pt-Th-Se-U-Sb-Y-Pb, ranging from extremely severe enrichments (Au, Ag, Pt, Th, Se) to moderate to severe enrichments (Pb), through very severe (U, Sb) and severe (Y) enrichments. Among all these elements, Au, Ag and Pt alone represent more than 99% of the enrichments. Concentrated wastes at Wankoro show 12 mineralization out of the studied 12 elements. In order of importance, we have Au-As-Ag-Sb-Th-Se-Pt-Bi-U-Y-Pb-Cu, ranging from extremely severe enrichments (Au, As, Ag, Sb, Th, Se) to moderate to severe enrichments (Cu), through severe enrichments (Pt, Bi, U, Y, Pb). Among these elements, Au, As and Ag alone represent more than 99% of the enrichments. The concentrated wastes at Bondo show 08 mineralization out of the studied 12 elements. In order of importance, we have Au-Pt-Ag-Th-Se-U-Y-Pb, ranging from extremely severe enrichments (Au, Pt, Ag, Th, Se) to severe enrichments (Pb, Y), through very severe enrichments (U). Among these elements, Au, Pt and Ag alone represent more than 99% of the enrichments. The washed wastes at Moufeck show only 01 mineralization out of the studied 12 elements. Arsenic (As) mineralization presents moderate to severe enrichment. The upstream Lom washed wastes present 02 mineralization out of the studied 12 elements. Au shows very severe enrichment while As shows severe enrichment;

The washed wastes at Mifeck show 05 mineralization out of the studied 12 elements. In order of importance, we have As-Sb-Se-Bi-Au, ranging from severe enrichments (As, Sb, Se) to moderate enrichments (Au). The washed wastes at Wantia show 04 mineralization out of the studied 12 elements. In order of importance, we have Sb-As-Au-Se, ranging from very severe enrichments (Sb) to moderate and severe enrichments (Se). The washed wastes at Fel show 04 mineralization out of the 12 elements studied. In order of importance, we have Au-As-Sb-Se, ranging from extremely severe enrichments (Au, As, Sb) to severe enrichments (Se). The washed wastes at Mama Wassandé show 05 mineralization out of the studied 12 elements. In order of importance, we have Sb-As-Se-Au-Bi, ranging from extremely severe enrichments (Sb, As) to moderate and severe enrichments (Bi). The washed wastes at Foum show 06 mineralization out of the studied 12 elements. In order of importance, we have As-Sb-Se-Bi-Au-Ag, ranging from very severe enrichments (As) to weak enrichments (Ag).

In fact, all elements that present mineralization indices ≥ 2 are potential metalliferous deposits. However, such elements must demonstrate accumulation and an optimal exploitation technique to militate in favor of their valorization. It should also be noted that in placer deposits, the mineral concentrations are already individualized and are located in the layers according to their density and size, and therefore, are easily exploitable by simple separation processes. Gold (Au) has significant enrichment in mining waste. This element is particularly enriched in concentrated wastes, with concentrations > 100,000 ppb, far higher than the average operating content in the deposit (1000 ppb). Most washed wastes also show concentrations higher than their Clarke. This trend is in agreement with many previous works () who documented the accumulation of this element in the alteration products of this large gold basin. For example, during the alteration of a mineralized structure, Au can be released from the primary gangue (sulphide minerals), then accumulate in a particular manner at the base of the sediment strata, in compliance with the normal granular classification system as demonstrated by many authors . The high concentrations of gold in this environment could be explained by such a process. This hypothesis is further reinforced here by the abundance of quartz veins in the area, and their artisanal or semi-mechanized artisanal exploitation by the local population and Chinese companies.

The main source of As and Sb in mining waste could be the alteration of arsenopyrite and stibnite respectively, which are satellite minerals associated with gold mineralization as demonstrated by the following authors . Accordingly, in Bétaré-Oya has also demonstrated high concentrations of arsenic in the soils, sediments and mining wastes in this mining area. This high geogenic As content is essentially linked to the presence of arsenopyrite which is strictly associated with the paragenesis of gold mineralization. The procession of mineralization constituted by Au-As-Sb-Se-(Ag)-(Pt)-(Th) which emerges from the present study is very close to that found in the Lom Series , in Dimako , in Kombo Laka , just to name few.

The behavior of REEs is generally marked by a strong accumulation in concentrated wastes. This can be confirmed here by the La/Y ratio which is high in concentrated wastes (from 11.9 to 19.7) and relatively low in washed wastes (from 1.98 to 4.25). This accumulation results from the remobilization and transport of REEs after hydrolysis of primary minerals, due to acidification of the environment . The enrichment of REEs in concentrated wastes is more marked for LREEs than for HREEs. All elements have concentrations higher than their Clarke with the exception of Lu which has concentration lower than its Clarke value. The enrichment factor has been determined. It varies from 3.87 for Lu to 101.79 for La in the Wakasso wastes (CW_WAKASSO), from 2.21 for Lu to 268.33 for Sm in Wankoro (CW_WANKORO) and from 4.25 for Lu to 186.59 for La in Bondo (CW_BONDO) (Table 4).

Furthermore, mineralization will be defined for all REEs having a mineralization index greater than 2. The enrichment factor allows us to assess the degree of mineralization for each element. These criteria thus enable to define La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho and Er as being mineralized in concentrated wastes. The enrichment of these REEs evolves from weak enrichment (1 ˂ EF< 3) for Lu in Wankoro to extremely severe enrichment (EF> 50) for La, Ce, Pr, Nd, Sm, Gd in all sites (Figure 5).

Since the end of the 20th century, REEs have been actively sought after due to their growing importance in the technology industry . Furthermore, they are also very harmful elements for the health of living beings . However, just like trace elements, they are released into the environment during mining operations. This is the case in the present wastes where we certainly record, at a reduced volume, fairly significant accumulations and enrichments of these elements which could also be the subject of valorization.

It appears from Figure 5 that the REEs with extremely severe enrichment in mining wastes are La, Ce, Pr, Nd, Sm and Gd in all concentrated wastes, and Tb in Bondo and Wankoro wastes. These RREs can constitute metalliferous deposits. The REEs with very severely enriched in the wastes are among others Dy in all three wastes, Tb in Wakasso and Eu in Bondo. This level of enrichment in REEs can also constitute a metal deposit. The severely enriched REEs are Ho in all three wastes, Er in Bondo, Eu in Wankoro and Wakasso.

The moderately to weakly enriched REEs are Tm, Yb, Lu in all three sites, and Er at Wankoro and Wakasso. Specifically, these three elements do not constitute mineralization. Rare Earths (La-Ce-Pr-Nd-Sm-Gd-Tb-Dy) associated with Metallic Trace Elements (Au-Ag-Pt-Th-Se-U) in concentrated wastes can constitute metal deposits of 14 valuable elements. Figure 6 expresses the enrichments of the REEs in each of the three sites (Wakasso, Wankoro and Bondo). The resulting finding is marked by a high rate of enrichment of LREEs in the concentrated wastes from such sites. The HREEs show high enrichments for Gd, Tb and Dy, evolving from extremely severe enrichment to very severe enrichment; the others being moderately to weakly enriched.

PAAS: Taylor &McLennan (1985)

C. Sam = concentration of the sample; MI = Mineralization Index; EF = Enrichment Factor

The objective of this work was to appreciate mining wastes potential from gold exploitation in the locality of Fel and surrounding mining sites. To achieve this objective, direct observations and systematic sampling of mining wastes were conducted to determine their enrichment factor and mineralization index based on certain MTE (Au, Ag, U, Pb, Cu, As, Th, Sb, Bi, Y, Se, Pt) and REEs. The results from morphological analysis show washed wastes in the shape of a fan or semi-circle, each occupying an area ranging from 300 to 1,300 m². There are approximately 13 (waste dumps) per kilometer. Concentrated wastes only represent approximately 1% of the total volume of material processed. In the exploitation of placers, concentrated wastes constitute the most solicited phase because it concentrates economically exploitable mineral substances. The geochemistry perfectly highlights significant enrichments in Au, (As), (Sb) and Se both in the washed wastes and in the concentrated wastes, and Ag, Pt, Th, Pb, U and Y only in concentrated wastes. Bi and Cu doesn’t show any significant enrichment in either type of mining waste. Mineralization indexes ≥ 2 suggest that gold mineralization in the study area involves severe to extremely severe enrichments in Au-Ag-Pt-Th-Se-U in the wastes of mining concentrates. The REEs were also characterized by positive anomalies, with severe to extremely severe enrichments for La-Ce-Pr-Nd-Sm-Gd-Tb-Dy. For such ETM and REEs, these high enrichment rates constitute useful mineralization that can be valuable. Regarding the above results, it appears that the exploitation of mineral substances takes place without any respect for the standards in terms of sustainable exploitation of mineral resources, and this is how many potentially valuable ore minerals are abandoned in mining wastes.

The authors greatly appreciate comments of Editor and anonymous reviewers which help to improve the quality of paper.

The authors declare that they have no conflict of interest.