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Article

Geochemical Survey in Mojiang Area of Yunnan Province, China: Geochemical Map and Geochemical Anomaly Map

by
Xianfu Zhu
1,
Peiyu Li
1,
Qingjie Gong
1,*,
Weixuan Gu
1,
Shengchao Xu
1 and
Taotao Yan
2,*
1
School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China
2
National Research Center for Geoanalysis, Beijing 100037, China
*
Authors to whom correspondence should be addressed.
Appl. Sci. 2025, 15(5), 2592; https://doi.org/10.3390/app15052592
Submission received: 6 January 2025 / Revised: 15 February 2025 / Accepted: 24 February 2025 / Published: 27 February 2025
(This article belongs to the Special Issue State-of-the-Art Earth Sciences and Geography in China)
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Abstract

:
The geochemical maps and geochemical anomaly maps produced based on the data in the databases of the Regional Geochemistry–National Reconnaissance (RGNR) and the National Multipurpose Regional Geochemistry Survey (NMPRGS) projects have played a crucial role in China’s geochemical exploration. A geochemical survey of the Mojiang area, Yunnan Province, China, has been completed and reveals potential new regions for Ni exploration related to occurrences of serpentinite melanges. The geochemical maps and geochemical anomaly maps need to be drawn in this area. Traditional geochemical maps, heavily dependent on data quantity, are less suitable for consistent comparisons across distinct regions and elements. Here, a fixed value method is proposed to contour the Ni geochemical map on 19 levels, which is convenient for the comparison among elements. On the geochemical maps, the two known Ni deposits are located in a region with Ni surely screening risk level (on the national standard of pollution risk of heavy metals in China) and a region with Ni economic level (Ni as an associate or main economic metal on the national standard of Ni deposit in China), respectively. In addition, we have determined that the Sn and Li levels in this area are at (low or high) background levels compared to other regions. Then, the method of seven levels of classification, which is also suitable for the comparison across different areas or elements, is used to draw the geochemical anomaly maps in the Mojiang area. On the anomaly maps, the two known Ni deposits are located in the regions with Ni anomaly levels not less than four, while the anomaly areas of Sn and Li are sporadic, with anomaly levels not larger than two in this area. These consistent results with the known facts of Ni, Sn, and Li deposits in the Mojiang area not only consolidate the roles of geochemical maps and geochemical anomaly maps but also illustrate the comparison among elements in mineral exploration. Furthermore, we predicted three Ni potential regions in the Mojiang area on the geochemical survey.

1. Introduction

The Regional Geochemistry–National Reconnaissance (RGNR) project [1] covers over 7 million km2 of China’s land surface since its implementation in 1979, primarily focused on mountainous and hilly areas [2]. In the RGNR project, each sampling grid is 4 km2 corresponding to a scale of 1:200,000. In each grid, four sub-samples were collected in 1 km2 and then were combined to form a composite sample [3], and 39 geochemical items including major components (i.e., SiO2, Al2O3, Fe2O3, K2O, Na2O, CaO, MgO, Ti, P, and Mn) as well as Ni, Sn, Li, etc., were analyzed [4,5]. The Multi-Purpose Regional Geochemistry Survey (NMPRGS) project [6] has been implemented since 1999 in China, primarily focused on the basin and plain areas, and 54 geochemical items, including major components and Ni, Sn, Li, etc., were analyzed. The database compiled by these two projects [7] and the geochemical maps and geochemical anomaly maps produced based on the data have played significant roles in the exploration of mineral resources in China [8,9,10]. The Mojiang area in Yunnan Province, an important Ni ore gathering area in China, has completed relevant survey and data collection work. This paper draws geochemical maps and geochemical anomaly maps on Ni-based on these data, providing a reference for Ni deposit exploration in the areas.
Regarding geochemical maps which focus on the analytical values of elemental concentrations, there are three traditional methods commonly used: the cumulative frequency method, the logarithmic interval method, and the mean–standard deviation method [11]. As the scope of research areas and the accumulation of data continue to increase, the limitation of traditional methods that rely on the amount of data has gradually become apparent [12,13], which further results in the inability to compare across different areas and elements. In recent years, to overcome the limitations of traditional methods, An et al. [13] proposed a new approach to Cr geochemical map as the fixed-value method. Later, Xu et al. [11], Li et al. [12], and Jia et al. [14] further developed the fixed-value method for Sn, Li, and Mo on 19 levels, respectively. This 19-level fixed-value method is an objective method to classify elemental concentrations and facilitates the comparison across different elements and areas. However, the specific levels for Ni classification have not yet been proposed.
On geochemical anomaly maps which focus on the relatively high values (or the anomaly values) of elemental concentrations or other geochemical indices [15], the methods commonly used in determining anomalies can be divided into two types: the fixed-value method and the unfixed-value method [16]. Geochemical anomaly maps created using the fixed-value methods (e.g., the mean–standard deviation method, cumulative frequency method, fractal method, etc.), can be viewed as parts of the geochemical map (i.e., the background areas with low concentrations are covered) [12]. An apparent limitation of the fixed-value methods is that they ignore the influence of different lithologies on elemental concentrations [13]. Regarding the unfixed-value method, a method called seven levels classification [16,17] was proposed, which is an objective approach for determining anomalies not influenced by the lithologies and the weathering degrees of samples [4,5] and facilitates the comparisons across different elements and areas [11].
Based on the regional geochemical exploration data of the Mojiang area, which is rich in Ni resources in Yunnan province, China, this paper first proposes the 19-level fixed-value method for Ni. Then, this new method is used to draw geochemical maps and compare them with different elements. Subsequently, a seven-level classification method is used to create geochemical anomaly maps, also with a comparison among different elements. Finally, based on the geochemical maps and anomaly maps, we proposed potential targets for exploration in the Mojiang area.

2. Materials and Methods

2.1. Geological Settings

The Mojiang area is located in Yunnan province in the southwest of China. It extends ca. 56 km in the east–west corresponding to the longitude from E 101.44° to E 101.99° and ca. 65 km in the north–south corresponding to the latitude from N 23.24° to N 23.83°, covering an area of ca. 3626 km2 (Figure 1). Public network data indicates that the topography slopes from north to south, with significant elevation differences in this area. The landforms are characterized by medium-cut middle mountain hilly valleys. The climate features mild seasonal temperature differences, with no extreme heat in summer and no severe cold in winter. The average annual sunshine duration is ca. 90 days, and the average annual precipitation is ca. 1345 mm.
The exposed strata in the Mojiang area trend NW direction and include Paleoproterozoic, Silurian, Devonian, unclassified Paleozoic, Permian, Triassic, and Jurassic periods (Figure 1). The lithology of these strata is described briefly in Figure 1. The main magmatic rocks are felsic and ultramafic intrusions [18,19]. The felsic intrusions are mainly distributed in the northeast of the area and distributed in the NW direction. The ultramafic intrusions include four ophiolite bodies extending in an NNW direction [19,20]. The ultramafic ophiolite body located in the central is Jinchang ultramafic ophiolite body, which is mainly composed of serpentinized harzburgite [20,21].
The Mojiang area is located in the middle segment of the Ailaoshan orogenic belt, a region that has undergone complex tectonic evolution, extending northwest overall and fanning out southeast in a broom-like pattern [22,23]. The tectonic features within the area are dominated by faults, with northwest-trending faults being the most prominent, followed by north–northwest and nearly north–south orientations [23,24]. Several strike–slip faults paralleled in the NW direction have divided the Ailaoshan orogenic belt into elongated and narrow segments [25,26]. The mineral resources in the area are predominantly sulfide deposits of Ni, Au, Ag, Co, V, Cr, Mo, As, Sb, and Hg. The Jinchang Ni-Au deposit is located in the Jinchang ultramafic ophiolite body, whereas the Mili Ni deposit is situated within the Paleozoic strata [27].

2.2. Analytical Method

This paper has collected geochemical survey sample data from the RGNR project [1], comprising a total of 957 stream sediment samples. In the RGNR project, the major components were determined using X-ray fluorescence (XRF) spectrometry, while the trace elements Ni and Li were measured by inductively coupled plasma mass spectrometry (ICP-MS), and Sn was determined by emission spectrometry. The detection limits were 2, 1, 5, 50, 10, and 10 µg/g for Ni, Sn, Li, Ti, P, and Mn, respectively, and 0.1% for other major oxides, the accuracy (≤0.05–0.10 ∆lgC for different concentrations) and precision (≤10–17% in relative standard deviation for different concentrations) of the analysis met the requirements of the RGNR project.

3. The Fixed-Value Method on Ni Geochemical Map

To create a more objective geochemical map, we adopt the 19-level fixed-value method to contour the geochemical map of Ni. In this method, the key task is to determine the 18 fixed values, which divided the concentrations into 19 levels further categorized into six major classes.
In the 19-level fixed-value method, Xu et al. [11] and others [12,14] determined 18 fixed values by relying on the different cumulative frequency values of stream sediments of the RGNR project [1] and soils of the NMPRGS project [28]. In this paper, these statistical parameters are also considered. Additionally, since Ni is one of the heavy metals [29,30], and there are different screening values on different pH values for Ni concentrations in agricultural land specified in the Chinese Standard GB15618-2018 [31], the Ni screening values in GB15618-2018 are also taken into consideration when determining these 18 fixed values.
In the 19-level fixed-value method, the first fixed value for Sn and Li were set at 1 μg/g and 5 μg/g corresponding to their detection limits in the RGNR and NMPRGS projects 12, respectively. Therefore, the first value for Ni is set at 2 μg/g which corresponds to the detection limits of Ni in the RGNR and NMPRGS projects.
The second value is set at 6 μg/g, which corresponds to three times the detection limit and is just right to the value of the 2% cumulative frequency in stream sediments of the RGNR project [7]. The third value is 10 μg/g, corresponding to the 15% cumulative frequency value in the stream sediments.
The fourth value is suggested to be 18 μg/g, which is the mean of the two values: the 25% cumulative frequency value of 14.5 μg/g in the stream sediments of the RGNR project and the 25% cumulative frequency value of 21 μg/g in soils in the NMPRGS project [28]. The fifth value is proposed as 25 μg/g, which is the mean of 23 μg/g of the 50% cumulative frequency value in the stream sediments and 27 μg/g of the 50% cumulative frequency value in the soils.
The sixth and seventh fixed values are set at 32 and 39 μg/g, respectively, which correspond to the 75% and 85% cumulative frequency values in stream sediments of the RGNR project. The eighth fixed value is suggested to be 48 μg/g, which is close to the 92% cumulative frequency value of 46 μg/g in stream sediments from the RGNR project.
The ninth fixed value is set at 60 μg/g, which corresponds to the minimum screening value for agricultural land in GB15618-2018 [31] and is equal to the mean of two values: the 97% cumulative frequency value of 68 μg/g in stream sediments of the RGNR project and the 97.5% cumulative frequency value of 52 μg/g in surface soils in the NMPRGS project.
The tenth fixed value is 70 μg/g, which corresponds to the intermediate screening value of 70 μg/g for agricultural land specified in GB15618-2018 [31]. The eleventh fixed value is proposed as 100 μg/g, which corresponds to the intermediate screening value for agricultural land of 100 μg/g in GB15618-2018 and is close to the 98.8% cumulative frequency value of 102 μg/g in stream sediments of the RGNR project.
The twelfth fixed value is set at 190 μg/g, which corresponds to the maximum screening value for agricultural land in GB15618-2018 [31].
In the 19-level fixed-value method, the fifteenth value of Sn is 200 μg/g, corresponding to the cutoff grade of the Sn placer [11], and the fifteenth value of Li is 232 μg/g, which is the cutoff grade of the clay-type Li deposit [12]. The cutoff grade for Ni as an associated economic metal in copper deposits (DZ/T0214-2002) [32] and iron-manganese deposits (DZ/T 0200-2020) [33] is 0.1%. Therefore, the fifteenth fixed value is suggested as 1000 μg/g, which corresponds to the concentration of Ni as an associated economic metal. Based on the twelfth and fifteenth fixed values, the thirteenth and fourteenth fixed values for Ni are interpolated to be 245 μg/g and 495 μg/g, respectively.
In the 19-level fixed-value method, the eighteenth values are 1000 μg/g for Sn and 1858 μg/g for Li, which correspond to their cutoff grades in hard rocks [11,12]. The cutoff grade for primary Ni ore specified in DZ/T0214-2002 [33] is 0.2%. Here, the eighteenth fixed value of 2000 μg/g for Ni is suggested. Based on the fifteenth and eighteenth fixed values, the sixteenth and seventeenth fixed values for Ni are interpolated to be 1260 μg/g and 1590 μg/g, respectively.
Based on the above 18 fixed values, the Ni concentration is divided into 19 levels to contour the Ni geochemical map. To better interpret these levels, the 19 levels are mapped on six color tones [11,12]. Levels 1 to 5 are assigned a blue tone for low background areas, corresponding to Ni concentrations less than 25 µg/g. Levels 6 to 9 are assigned a yellow tone for high background areas, corresponding to samples with Ni concentrations between 25 µg/g and 60 µg/g. Levels 10 to 12 are assigned a pink tone for maybe screening risk level areas, corresponding to samples with Ni concentrations between 60 µg/g and 190 µg/g. Levels 13 to 15 are assigned a red tone for surely screening risk level areas, corresponding to samples with Ni concentrations between 190 µg/g and 1000 µg/g. Levels 16 to 18 are assigned a gray tone for mineralization as an associate economic metal, corresponding to samples with Ni concentrations between 1000 µg/g and 2000 µg/g. The 19th level is assigned a black color for mineralization as the main economic metal in rocks, corresponding to samples with Ni concentrations above 2000 µg/g.
The specific 18 fixed values and 19 levels of Ni along with those of Sn, Li, and Mo are listed in Table 1 for a clear comparison.

4. Results and Discussion

The statistical parameters for the concentrations of Ni, Sn, and Li, as well as the major components of the total of 957 records (or composite samples), are listed in Table 2. The concentrations of Ni, Sn, and Li range from 8.3 μg/g to 4580 μg/g, 1 μg/g to 9.3 μg/g, and 7.8 μg/g to 105 μg/g, respectively. The contents of SiO2, Al2O3, and TFe2O3 range from 37.4% to 68.1%, 3.6% to 13.2%, and 1.7% to 5.0%, respectively, which indicates that these samples are mainly silicate components. The contents of K2O, Na2O, CaO, and MgO range from 0.3% to 2.3%, 0.1% to 0.6%, 0.1% to 1.0%, and 0.3% to 1.4%, respectively, which indicates that these stream samples have undergone a chemical weathering process.
The lgNi, lgSn, and lgLi values for the 957 records from the Mojiang area are shown in Figure 2a–c as histograms with their box plots. The box plots are used to display the cumulative frequency.
To eliminate outliers, the mean ± 3 SD (standard deviation) method was employed [11]. In this method, when the data of lgNi, lgSn, and lgLi fell outside the range of mean ± 3 Std, they were excluded. This process to exclude values is repeated until no outliers are identified. The lgNi, lgSn, and lgLi data without outliers are presented in Figure 2d–f, and their statistical parameters are also listed in Table 2.
Although the statistical parameters are also listed in Table 2, they are not discussed further because the methods used on geochemical map (the 19-level fixed-value method) and geochemical anomaly map (the seven levels classification method) are irrelevant to the distribution of the data.

4.1. 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].
The concentrations of Ni in this area range from 8.3 μg/g to 4580 μg/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 μg/g to 9.3 μg/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 Gejiu 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 Gejiu area range from 0.2 μg/g to 7760 μg/g, corresponding to levels 1 to 18. The discovered Sn deposits in the Gejiu 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 Gejiu area.
The concentrations of Li range from 7.8 μg/g to 105 μg/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 μg/g to 279 μg/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.
In summary, the geochemical maps of Sn and Li are similar and mainly in yellow and blue tones (corresponding to the high and low background regions, respectively). The geochemical map of Ni shows clear regions in black color and grey tone, which correspond to the mineralization regions of Ni as an associate and main economic metal, respectively. Except for two known Ni deposits located in the Ni mineralization regions, three other regions are predicted for the Ni resource potential.

4.2. Geochemical Anomaly Map on Seven Levels Classification Method

To contour the geochemical anomaly maps, which focus on the relatively high values (or the anomaly values) of elemental concentrations or other geochemical indices, the elemental concentrations are converted on the method of seven levels of classification using GBAL 1.0 software [16] into nine levels ranging from −1 to 7. Here, the value of −1 indicates that the concentration is less than the background value of a sample, and 0 indicates that the concentration is between the background value and the first anomaly level. Values of 1 to 7 represent the first to seventh levels, and the 7th level indicates that the concentration is greater than or equal to the cutoff grade [16].
Then the data of anomaly levels are gridded with an interval space of 2 km. The grid parameters, including search radius, and interpolation method, were consistent with those used in the aforementioned 19-level fixed-value method for drawing the geochemical map. The anomaly grid data are contoured to derive the geochemical anomaly maps of Ni, Sn, and Li, respectively, with the same legend ranging from 1 to 7 (Figure 4). The background values (i.e., −1 and 0) are not illustrated in the geochemical anomaly maps.
In Figure 4a, the anomaly regions of Ni are distributed as a belt in the NNW direction. The maximum anomaly level reached 7, indicating that Ni concentrations in certain stream sediments exceeded the defined cutoff grade (i.e., 2000 μg/g). The anomaly belt is consistent with the outcropped regions of the four ultramafic ophiolite bodies. This consistency indicates that the mineralization of Ni in the Mojiang area is closely related to the ultramafic ophiolite bodies.
The two known Ni deposits, the Jinchang Ni-Au deposit, and the Mili Ni deposit, are located in the anomaly regions with the maximum anomaly levels of 6 and 4, respectively. However, in some regions with the anomaly level of 7, no Ni deposits have been reported till now although the Ni concentrations of stream sediments in these regions are higher than the cutoff grade.
In addition, three anomaly regions have been delineated with an anomaly level up to 7 (Figure 4a), whose locations are consistent with those delineated from the Ni geochemical map (Figure 3a). Therefore, the three anomaly regions can be predicted as the Ni resource potential, which is also spatially consistent with the outcropped regions of the other three ultramafic ophiolite bodies except the Jinchang ultramafic ophiolite body, which formed the Jinchang Ni-Au deposit. Due to the research conducted by numerous experts and scholars, it has been confirmed that the Jinchang ultramafic ophiolite body is the ore-bearing ophiolite body of the Jinchang Ni-Au deposit [18,19,20,21]. Therefore, the other three ultramafic ophiolite bodies that form an NNW linear distribution with the Jinchang ultramafic ophiolite body are predicted to be possible regions with Ni mineralization.
In Figure 4b,c, the anomaly regions of Sn and Li are delineated sporadically. The maximum anomaly level of Sn is only 1 (Figure 4b), and the maximum level of Li is only 2. The results of Sn and Li are consistent with the geological facts that no deposits of Sn and Li have been discovered in this area. For a comparison with the Mufushan area, in which a geochemical anomaly map of Li was also drawn on the seven levels classified method [12], the highest anomaly level reaches level 4, and all known Li deposits are located in areas with anomaly levels not less than level 2.
In a word, the four ultramafic ophiolite bodies are closely related to the Ni deposits. One of them, the Jinchang ultramafic ophiolite body, is closely associated with the Jinchang Ni-Au deposits, and the other three are related to the three predicted regions of Ni resource potential.
To sum up, the 19-level fixed-value method, as a new method for drawing geochemical maps, and the seven levels classification method, as a new method for drawing geochemical anomaly maps, provide new ideas for future geochemical work, especially mineral exploration in other geologically similar contexts, and can be used as a reference for related work.

5. Conclusions

(1)
The 18 fixed values are proposed on the 19-level fixed-value method to classify the Ni concentrations for geochemical mapping.
(2)
The geochemical maps on the 19-level fixed-value method and the geochemical anomaly maps on the seven levels classification method can be compared among different elements, which are illustrated on the Ni, Sn, and Li in the Mojiang area.
(3)
Three regions of Ni resource potential are predicted on the geochemical map and geochemical anomaly map in the Mojiang area.

Author Contributions

X.Z.: conceptualization, data curation, writing—original draft. P.L.: data curation, formal analysis. W.G. and S.X.: data curation. Q.G. and T.Y.: conceptualization, methodology, writing—review and editing. All authors have read and agreed to the published version of the manuscript.

Funding

This work was financially supported by the Central Leading Local Science and Technology Development Fund Project (24ZYQF001).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The authors will make the raw data supporting this article’s conclusions available upon request.

Acknowledgments

We greatly appreciate the comments from the anonymous reviewers and editors for their valuable suggestions to improve the quality of this manuscript.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Regional geological map of the Mojiang area (after the 1:1,000,000 geological map of F47 by China Geological Survey). (1) Quaternary: sand, gravel, clay; (2) Pliocene: clay, clayey limestone; (3) Lower Cretaceous: yellow-gray, purplish-red sandstone interbedded with purplish-red and gray-green mudstone, gravelly sandstone, calcareous mudstone; (4) Upper Jurassic: yellow-gray, grayish-purple sandstone, purplish-red, gray-green mudstone, calcareous mudstone interbedded with mudstone-limestone; (5) Middle-Upper Jurassic: purplish-red mudstone, siltstone, calcareous mudstone interbedded with gray-green mudstone and mudstone-limestone, sandstone; (6) Middle Jurassic: yellow-gray sandstone, mudstone, purplish-red mudstone, interbedded with calcareous mudstone, mudstone-limestone; (7) Triassic–Jurassic: gray-white sandstone, black shale interbedded with limestone, purplish-red mudstone, siltstone interbedded with mudstone-limestone, fine sandstone; (8) Triassic: meta-conglomerate, sandstone, phyllite; (9) Upper Triassic: mudstone (slate), limestone, sandstone interbedded with siltstone, mudstone–limestone; (10) Upper Triassic Waigucun Formation: purplish-red, gray-green conglomerate, sandstone, mudstone, occasionally interbedded with mudstone-limestone; (11) Paleozoic: slate, phyllite, quartzite interbedded with green schist, crystalline limestone; (12) Upper Permian: Sandstone, siltstone, mudstone with coal seams, occasionally with tuff and volcanic rocks; (13) Middle-Upper Permian: sandstone, siltstone, mudstone with limestone, tuff, and andesite, locally containing coal; (14) Carboniferous-Devonian: sandstone, shale interbedded with thin layers of limestone and tuff; (15) Middle-Upper Devonian: quartz sandstone, graywacke interbedded with siltstone shale; (16) Silurian: black and gray-green shale, sandstone with a small amount of limestone; (17) Upper-middle parts of Kunyang Group of Mesoproterozoic: lower purple slate, dolomite, slate, metamorphic sandstone, upper dolomite interbedded with calcareous slate; (18) Dahongshan Group of Paleoproterozoic: microcrystalline schist, quartzite, marble with slate and metamorphosed intermediate-basic volcanic rocks; (19) Ailaoshan Group of Paleoproterozoic: gneiss, schist, marble interbedded with amphibolite, granulite, and graphite schist; (20) Granite; (21) Lherzolite; (22) Lithological boundary; (23) Fault; (24) Ni deposit.
Figure 1. Regional geological map of the Mojiang area (after the 1:1,000,000 geological map of F47 by China Geological Survey). (1) Quaternary: sand, gravel, clay; (2) Pliocene: clay, clayey limestone; (3) Lower Cretaceous: yellow-gray, purplish-red sandstone interbedded with purplish-red and gray-green mudstone, gravelly sandstone, calcareous mudstone; (4) Upper Jurassic: yellow-gray, grayish-purple sandstone, purplish-red, gray-green mudstone, calcareous mudstone interbedded with mudstone-limestone; (5) Middle-Upper Jurassic: purplish-red mudstone, siltstone, calcareous mudstone interbedded with gray-green mudstone and mudstone-limestone, sandstone; (6) Middle Jurassic: yellow-gray sandstone, mudstone, purplish-red mudstone, interbedded with calcareous mudstone, mudstone-limestone; (7) Triassic–Jurassic: gray-white sandstone, black shale interbedded with limestone, purplish-red mudstone, siltstone interbedded with mudstone-limestone, fine sandstone; (8) Triassic: meta-conglomerate, sandstone, phyllite; (9) Upper Triassic: mudstone (slate), limestone, sandstone interbedded with siltstone, mudstone–limestone; (10) Upper Triassic Waigucun Formation: purplish-red, gray-green conglomerate, sandstone, mudstone, occasionally interbedded with mudstone-limestone; (11) Paleozoic: slate, phyllite, quartzite interbedded with green schist, crystalline limestone; (12) Upper Permian: Sandstone, siltstone, mudstone with coal seams, occasionally with tuff and volcanic rocks; (13) Middle-Upper Permian: sandstone, siltstone, mudstone with limestone, tuff, and andesite, locally containing coal; (14) Carboniferous-Devonian: sandstone, shale interbedded with thin layers of limestone and tuff; (15) Middle-Upper Devonian: quartz sandstone, graywacke interbedded with siltstone shale; (16) Silurian: black and gray-green shale, sandstone with a small amount of limestone; (17) Upper-middle parts of Kunyang Group of Mesoproterozoic: lower purple slate, dolomite, slate, metamorphic sandstone, upper dolomite interbedded with calcareous slate; (18) Dahongshan Group of Paleoproterozoic: microcrystalline schist, quartzite, marble with slate and metamorphosed intermediate-basic volcanic rocks; (19) Ailaoshan Group of Paleoproterozoic: gneiss, schist, marble interbedded with amphibolite, granulite, and graphite schist; (20) Granite; (21) Lherzolite; (22) Lithological boundary; (23) Fault; (24) Ni deposit.
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Figure 2. Histograms and boxplots (a–c) and (d–f) of sediment samples in the Mojiang area with and without outliers, including lgNi, lgSn, and lgLi.
Figure 2. Histograms and boxplots (a–c) and (d–f) of sediment samples in the Mojiang area with and without outliers, including lgNi, lgSn, and lgLi.
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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.
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.
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Figure 4. Geochemical anomaly map of Ni (a) Sn (b) and Li (c) on the method of seven levels classification along with the geological map (d) in the Mojiang area. Detailed legend information is in Figure 1.
Figure 4. Geochemical anomaly map of Ni (a) Sn (b) and Li (c) on the method of seven levels classification along with the geological map (d) in the Mojiang area. Detailed legend information is in Figure 1.
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Table 1. The information of the Ni geochemical map on the 19-level fixed-value method along with those of Sn, Li, and Mo.
Table 1. The information of the Ni geochemical map on the 19-level fixed-value method along with those of Sn, Li, and Mo.
Level No.12345678910111213141516171819References
Ni2610182532394860701001902454951000126015902000≥2000This study
lgNi0.3010.7781.0001.2551.3891.5051.5911.6811.7781.8452.0002.2792.3892.6953.0003.1003.2013.301-
ΔlgNi-0.4770.2220.2550.1430.1070.0860.0900.0970.0670.1550.2790.1100.3050.3050.1000.1010.100-
Sn11.31.82.73.44.36.07.910131728501002004006001000≥1000[11]
Li58172934405062707888991321752324609301858≥1858[12]
Mo0.30.370.450.550.6811.432.0733.84.86.19.120100144208300≥300[14]
Note: The concentration unit of Ni, Sn, Li, and Mo is μg/g; the 1st level corresponds to the detection limit of each element in the RGNR and NMPRGS project, and the 19th level corresponds to the cutoff grade of each element.
Table 2. Statistical concentration parameters of Ni, Sn, Li, and major components of samples in Mojiang area.
Table 2. Statistical concentration parameters of Ni, Sn, Li, and major components of samples in Mojiang area.
Statistical
Parameters		Data
Count		Minimum Q1: Lower
Quartile		Q2: Median
Quartile		Q3: Upper
Quartile		MaximumMeanStandard
Deviation
Ni (a)9578.323.530.540.4458036.6 2.4
lgNi (a)9570.9191.3711.4841.6063.6611.5630.380
lgNi (b)8670.9401.3581.4621.5682.9391.4610.175
Ni (b)8678.722.829.03786828.91.5
Sn (a)9571.02.32.73.39.32.81.4
lgSn (a)9570.0000.3620.4310.5190.9680.4470.146
lgSn (b)9480.0410.3620.4310.5190.8450.4450.135
Sn (b)9481.12.32.73.37.02.81.36
Li (a)9577.826.632.43910532.01.4
lgLi (a)9570.8921.4251.5111.5912.0211.5050.146
lgLi (b)9391.1551.4331.5131.5911.8401.5120.121
Li (b)93914.327.132.63969.232.51.32
SiO2 (a)95737.463.268.673.487.068.17.7
Al2O3 (a)9573.611.613.315.023.513.22.7
TFe2O3 (a)9571.74.04.75.617.85.01.8
K2O (a)9570.31.82.42.84.92.30.7
Na2O (a)8350.10.10.40.74.30.60.6
CaO (a)9220.10.20.61.314.81.01.3
MgO (a)9570.30.71.01.420.51.41.8
Ti (a)95713473520411547731678943331285
P (a)9571453444205251647462178
Mn (a)9572455806828222357725240
Note: The concentration units of Ni, Sn, Li, Ti, P, and Mn are in μg/g, and the oxides units are in %. (a) Original data; (b) data without outliers excluded on log-normal distribution.
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Zhu, X.; Li, P.; Gong, Q.; Gu, W.; Xu, S.; Yan, T. Geochemical Survey in Mojiang Area of Yunnan Province, China: Geochemical Map and Geochemical Anomaly Map. Appl. Sci. 2025, 15, 2592. https://doi.org/10.3390/app15052592

AMA Style

Zhu X, Li P, Gong Q, Gu W, Xu S, Yan T. Geochemical Survey in Mojiang Area of Yunnan Province, China: Geochemical Map and Geochemical Anomaly Map. Applied Sciences. 2025; 15(5):2592. https://doi.org/10.3390/app15052592

Chicago/Turabian Style

Zhu, Xianfu, Peiyu Li, Qingjie Gong, Weixuan Gu, Shengchao Xu, and Taotao Yan. 2025. "Geochemical Survey in Mojiang Area of Yunnan Province, China: Geochemical Map and Geochemical Anomaly Map" Applied Sciences 15, no. 5: 2592. https://doi.org/10.3390/app15052592

APA Style

Zhu, X., Li, P., Gong, Q., Gu, W., Xu, S., & Yan, T. (2025). Geochemical Survey in Mojiang Area of Yunnan Province, China: Geochemical Map and Geochemical Anomaly Map. Applied Sciences, 15(5), 2592. https://doi.org/10.3390/app15052592

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