## 4 Results and Discussion
### Geochemical Map on the 19-Level Fixed-Value Method  
To contour the geochemical maps, the elemental concentrations are converted into the 19 levels on the 19-level fixed-value method. So, the values of classified levels may range from 1 to 19, corresponding to the elemental concentrations ranging from the detection limit to the cutoff grade. Then, the data of elemental levels are gridded with an interval space of 2 km. The elemental grid data are contoured to derive the geochemical maps of Ni, Sn, and Li, respectively, with the same legend ranging from 1 to 19 (Figure 3) on the software of GeoExpl 2013 [7]. Figure 3: Geochemical maps of Ni (**a**), Sn (**b**), and Li (**c**) on the 19-level fixed-value method along with the geological map (**d**) in Mojiang area. Detailed legend information is in Figure 1 and Table 1.  
The concentrations of Ni in this area range from 8.3 \(\upmu\)g/g to 4580 \(\upmu\)g/g, corresponding to levels from 3 to 19. Therefore, only 17 levels are displayed for Ni in Figure 3a although the legend is on 19 levels. Figure 3a shows that the entire map area is dominated by a yellow tone representing high background values. The Jinchang Ni-Au deposit is located in the regions with gray tones and black color, which correspond to the regions of Ni mineralization as an associate and main economic metal, respectively. However, the Mili Ni deposit is located in the regions with red and pink tones, which correspond to the regions of Ni surely and maybe screening risk levels, respectively, on the Chinese national standard GB15618-2018 on the pollution risk of heavy metals on the agricultural soils. Additionally, three regions in black color and gray tones are delineated in Figure 3a, which are predicted as the Ni regions with economic potential because the concentrations of Ni in these three regions have reached the mineralization level of Ni as an associate economic metal. One is located in the northeast of Mengnong town, which is in the northwest of the Mojiang area. The second is in the north of Longba town, and the third is in the south of Longba town, which is in the southeast of the Mojiang area. The concentrations of Sn in this area range from 1 \(\upmu\)g/g to 9.3 \(\upmu\)g/g, corresponding to levels from 1 to 9 (Figure 3b). Figure 3b shows that the whole area is dominated by yellow and blue tones, which correspond to the high to low background levels. Till now, Sn deposit has not been discovered in this area, which is consistent with the results from the Sn geochemical map. For a comparison with the Gejju area in Yunnan province, in which the geochemical map of Sn was also contoured on the 19-level fixed-value method [11], the concentrations of Sn in the Gejju area range from 0.2 \(\upmu\)g/g to 7760 \(\upmu\)g/g, corresponding to levels 1 to 18. The discovered Sn deposits in the Gejju area are located in black color, gray, and red tones, corresponding to the hard-rock deposits, placer deposits, and high anomaly regions of Sn in the Gejju area. The concentrations of Li range from 7.8 \(\upmu\)g/g to 105 \(\upmu\)g/g, corresponding to levels 2 to 13. So, the level displayed in this area is only 12 levels (Figure 3c). Similar to those of the Sn geochemical map, the Li geochemical map is also dominated by yellow and blue tones, corresponding to the high and low background regions, respectively. Furthermore, no Li deposit has been discovered in this area till now. For a comparison with the Mufushan area, in which the geochemical map of Li was also contoured on the 19-level fixed-value method [12], the concentrations of Li in the Mufushan area range from 10.2 \(\upmu\)g/g to 279 \(\upmu\)g/g, corresponding to levels 3 to 16. The discovered Li deposits in the Mufushan area are located in the red tones, corresponding to high anomaly regions of Li, and three predicted potential regions are located in the grey tones, corresponding to the clay-type deposit of Li in the Mufushan area.