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Article

Soil Geochemical Characteristics and Prospecting Potential in the Nibao Carlin-Type Gold Deposit and Peripheral Areas, Southwestern Guizhou, China

by
Songtao Li
1,2,
Lijin Tan
3,
Zepeng Wang
2,3,
Rong Nie
3,
Minghua Meng
3,
Wenxin Han
3,
Chengfu Yang
2,3,
Junhai Li
2,3,
Bingqiang Zhang
3 and
Jianzhong Liu
2,4,*
1
School of Geography and Resources, Guizhou Education University, Guiyang 550018, China
2
Engineering Technology Innovation Center of Mineral Resources Explorations in Bedrock Zones, Ministry of Natural Resources of China, Guiyang 550081, China
3
105 Geological Team, Guizhou Bureau of Geology and Mineral Exploration and Development, Guiyang 550018, China
4
Guizhou Bureau of Geology and Mineral Resources, Guiyang 550004, China
*
Author to whom correspondence should be addressed.
Minerals 2025, 15(9), 922; https://doi.org/10.3390/min15090922
Submission received: 19 July 2025 / Revised: 22 August 2025 / Accepted: 27 August 2025 / Published: 29 August 2025
(This article belongs to the Section Mineral Deposits)
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Abstract

Carlin-type gold deposits in southwestern Guizhou, China require systematic exploration methods to identify deep and peripheral prospecting potential beyond known deposits. We conducted a 1:50,000-scale soil geochemical survey across 928 km2 in the Nibao gold deposit and its surrounding areas, with a total of 8842 samples collected. Fifteen elements were systematically analyzed, with particular focus on pathfinder elements associated with Carlin-type gold mineralization. Building on previous comparative analyses of soil geochemical and tectono-geochemical characteristics, this research systematically examines the enrichment patterns of soil geochemistry and their significance for ore prospecting. The results demonstrate that (1) elements such as Au, As, Sb, Hg, W, and Mo show significant positive correlation and strong enrichment patterns, indicating excellent metallogenic potential; (2) 176 and 12 single- and composite-element anomalies were delineated, respectively, with HS-2, HS-3, and HS-7 anomalies exhibiting high intensity and distinct concentration zonation, similar to those of the high factor score distribution of Au-As-Sb-Hg-W-Mo; (3) three prospecting targets were identified based on anomaly characteristics and geological conditions, including Nibao, Baogudi, and Sandaogou; (4) multiple mineralized bodies were revealed through engineering verification, indicating good prospecting potential in the deep and surrounding areas of the targets. These findings provide a scientific basis for further exploration of Carlin-type gold deposits in the study area and southwestern Guizhou.

1. Introduction

Carlin-type gold deposits (also known as fine disseminated gold deposits) are an important low-temperature class of hydrothermal ore systems, which account for ~6% of annual global Au production [1,2]. These deposits are predominantly found in Nevada, USA, as well as the Yunnan, Guizhou, and Guangxi Provinces, China (known as the Dian–Qian–Gui Golden Triangle), with some recently discovered deposits in the Nadaleen Trend of NW Canada [3,4,5,6,7,8]. Gold deposits are commonly controlled by gentle anticlines and their related reverse faults, and primarily hosted in carbonate-bearing sedimentary rocks [8,9,10,11]. According to ore body morphology and ore-controlling structures, gold mineralization can be categorized into fault-controlled and strata-bound types [2,3,4,5,6,7,8,9,10,11]. The deposits are dominantly characterized by Au-As-Sb-Hg-(Tl) assemblage, and low temperature (150–300 °C) and low salinity [3,4,5,6] (2–7 wt % NaCl equiv) ore fluids [11,12,13,14,15]. The hydrothermal alteration is dominated by decarbonization, silicification, and argillization [11,12,14,15,16,17,18]. Sulfidation is recognized to be the most important mechanism of gold deposition, whereby gold and pyrite precipitated together through reactions between H2S-rich, Fe-poor fluids and Fe-bearing minerals in the host rocks [12,15,16,17,18]. Gold in the deposits invisibly occurs as Au1+ in the structure of disseminated arsenian pyrite, while the gold-bearing pyrite generally exhibits multiple generations within its individual crystal grain [19,20,21,22,23]. In weathered soils from ores, gold occurs either as particulate Au0 or is absorbed by goethite and As-bearing goethite, as well as by siliceous matter and quartz, and occasionally by illite [24,25].
Geochemical prospecting methods primarily extract mineralization-related information from various media, including soil, stream sediments, rocks, and structural fillings, to analyze primary or secondary prospecting indicators for locating exploration targets [25,26,27,28,29,30,31,32,33,34,35]. A soil geochemical survey, as a mature geochemical prospecting method, features simplicity and efficiency [35,36,37]. This method investigates the spatial distribution of elements in soil, and analyzes their dispersion and enrichment patterns, thereby revealing their correlation with mineralization in the bedrock [38,39,40]. Earlier studies demonstrated that secondary anomalies extracted through soil geochemical surveys cover a much larger area than that of the actual ore body, allowing rapid and effective delineation of ore-prospecting targets [39,41].
Owing to the inherent characteristics of Carlin-type gold deposits (e.g., fine disseminated minerals, complex micro-texture of Au-bearing pyrite, sediment-hosted ore, low ore-forming temperature, and simple alteration assemblage), soil geochemistry has become an important prospecting method. From 1970 to 1990, large-scale soil geochemical surveys in Carlin-type gold trends in the U.S. identified anomalies of Au, As, Sb, and Hg, providing critical clues for regional gold exploration [4,42,43]. For instance, comprehensive soil anomaly analysis led to the discovery of the Goldbug-Rodeo deposit in 1987, while subtle soil As anomalies facilitated the identification of the Meikle deposit in 1989 [44]. As the earliest discovered region of Carlin-type gold deposits in China, southwestern Guizhou is a key component of the Dian–Qian–Gui Golden Triangle [45]. Soil geochemical surveys have played a crucial role in gold prospecting in southwestern Guizhou. Nearly all early-discovered gold deposits are located within composite soil geochemical anomalies of Au, As, Sb, and Hg delineated at the 1:200,000 scale [46,47,48,49,50,51,52].
The Nibao gold deposit is the third-largest Carlin-type gold deposit in the Dian–Qian–Gui Golden Triangle, which has both fault-controlled and strata-bound ore bodies [53]. This gold deposit is prominently characterized by basalt-hosted ore, distinguishing it from traditional sediment-hosted Carlin-type gold deposits [8,53,54]. Its metallogenic mechanism attracted widespread attention, but further research on prospecting methods and exploration potential remains necessary. Therefore, we systematically conducted a soil geochemical survey to investigate the spatial distribution of geochemical information and its relationship with mineralization. Although previous studies have reported the comparative results of soil geochemical and tectono-geochemical characteristics in this region [25], the enrichment patterns of soil geochemical anomalies and their implications for ore exploration remain uncertain. Therefore, we aimed to delineate priority geochemical targets, evaluate the prospecting potential in deep and peripheral areas, and to establish the geochemical signatures for regional gold prospecting.

2. Materials and Methods

2.1. Regional Geology

The strata exposed in the Dian–Qian–Gui Golden Triangle primarily ranges from the Devonian to the Triassic, with the Triassic being the most dominant, followed by the Permian (Figure 1). Along the boundary from Guanling–Zhenfeng–Anlong (Guizhou) to Luoping (Yunnan), the Triassic strata can be divided into two dominant facies: a platform facies featured by carbonates and a slope/basin facies characterized by fine-grained clastic rocks [11]. Most of the lithological units can serve as host rocks for Carlin-type gold mineralization, indicating the diversity in ore-bearing rock types [8]. The southwestern Guizhou region dominantly develops three groups of structures in the northeast, northwest, and near east–west, which collectively form a complex fold-fault system resulting from multi-phase structural superimposition [25]. Structural alteration bodies (SBT) were formed along stratigraphic unconformities and lithological interfaces with significant physico-chemical contrasts, due to regional sedimentation, tectonic activities, and hydrothermal alteration processes [8].
Gold mineralization predominantly occurs within two distinct settings: (1) strata-bound ore bodies confined to SBT within ~1500 m around anticlinal cores, and (2) fault-controlled ore bodies localized in fracture zones along axial reverse faults on both flanks of the anticlines [25]. Based on the combination characteristics of multi-level SBT and ore-controlling faults in the region, the research team established a multi-level structural detachment metallogenic model for Carlin-type gold deposits (Figure 2), providing a theoretical basis for regional gold prospecting.

2.2. Geographical and Geological Setting

2.2.1. Geological Characteristics

The strata exposed in the study area mainly include the Middle Permian Maokou (P2m), Upper Permian Emeishan (P3β), Longtan (P3l) and Changxing (P3c), Lower Triassic Feixianguan (T1f) and Yongningzhen (T1yn), Middle Triassic Guanling (T2g), and Paleogene Shinao (E2–3s) formations, and Quaternary (Q) (Figure 3). The lithological characteristics of each stratigraphic unit were documented by [25]. The structures in the area are mainly NE-trending, followed by EW- and NW-trending structures. The NE-trending structures principally include the Erlongqiangbao, Dapingzi, and Sandaogou anticlines, Niujiaoshan Syncline and the Nibao (F1), Erlongqiangbao (F2), and Sandaogou (F3) faults. The EW-trending structures principally include the Baogudi and Dayakou anticlines, Yuzhang and Wantun synclines, and the Ganhe (F15), Dayakou (F19), and Sifangqiu (F20) faults. The NW-trending structures primarily include the Changerying Anticline, Xingren Syncline, Magudi Anticline, as well as the Banjiaohe (F16), Liushuigou (F17), and Yangsitun (F18) faults (Figure 3). Additionally, a structural alteration body (SBT) is developed between the P2m and P3l or P3β formations [22].
The study area hosts the Nibao gold deposit, with proven gold resources exceeding 70 tonnes, qualifying as a large-scale deposit [34]. The Nibao deposit contains numerous ore bodies, with diverse morphologies. These ore bodies average 2.68 × 10−6 in grade and 6.88 m in thickness [8]. Based on the occurrence characteristics, spatial distribution, and controlling factors, the gold ore bodies can be classified into fault-controlled, strata-bound, and residual-eluvial types (Figure 4). Among these, the fault-controlled type possesses the largest resource quantity, with individual ore bodies reaching the scale of medium-sized deposit, followed by the strata-bound type [8]. The hydrothermal alteration is predominantly characterized by low-temperature alteration assemblages, including sulfidation, silicification, carbonatization, decarbonatization, and argillization [54]. Based on cross-cutting, replacement, and paragenetic relationships among various minerals, the mineralization process is preliminarily divided into early (quartz + pyrite + arsenopyrite) and late (quartz + calcite + fluorite + stibnite + orpiment + realgar) ore stages [34].

2.2.2. Natural Geographic Features

The study area has a subtropical monsoon climate, with average annual precipitation and evaporation of 1328–1888 mm and 1368.1 mm, respectively, and an average annual temperature of 15.2 °C [25]. The topography is characterized by karst-erosion medium-to-low mountains, with elevations between 1000 and 2000 m. In the clastic rock distribution areas of the study area, stream gullies are well-developed and surface water resources are abundant, whereas in the carbonate rock distribution areas, surface water resources are scarce, and underground rivers are prevalent with abundant subsurface water resources. Clastic rock distribution areas are strongly weathered, with thick Quaternary cover and well-developed vegetation, while carbonate rock distribution areas comprise many exposed bedrocks with scarce vegetation.
The soil developed in the study area mainly includes siliceous ferrallitic yellow, red, and calcareous soils, with thicknesses ranging from a few centimeters to several meters. The soil profile primarily consists of humus (A), illuvial (B), and parent material (C) horizons. The A horizon is composed of topsoil, which is dark brown in color and has a higher organic matter content; the B horizon comprises clay and particulate materials leached from the A horizon, appearing lighter in color with lower organic matter content; the C horizon comprises residual coarse grains from weathered rock. In the valley bottoms of some areas, mixed materials of colluvial and residual origin are present, overlain by several meters of alluvial transported deposits.

2.3. Sampling and Analytical Methods

Based on the research objectives and the geological conditions of the study area, 1:50,000-scale soil geochemical mapping was conducted. According to the Chinese Specifications for Soil Geochemical Survey [55], a total of 8842 samples were collected within the 928 km2 survey area, with a sampling density of ~9.5 samples per square kilometer. Sampling points were designed on a grid with 500 m line spacing and 200 m point spacing, with transects oriented perpendicular to the main structural trends. Most were composite samples, mixed by subsamples collected within a 50 m radius of each designed point. The sampling layer was primarily the illuvial horizon (B horizon), generally at a depth greater than 20 cm. Sampling materials consisted of residual and slope-deposited soils, with plant roots and stones removed. Each individual sample weighed over 500 g, and after air drying and passing through a 60-mesh sieve, the remaining sample weight was greater than 200 g. Sampling locations were recorded using a Hi-Target Qcool GPS (Guangzhou Hi-Target Navigation Technology Co., Ltd., Guangzhou, China), with a positioning error typically less than 5 m. During the sampling process, three-tier quality management was implemented for sampling locations, materials, methods, records, and sample storage, with all meeting specified requirements. After field sampling, the collected samples were immediately air-dried at room temperature and ~200 g were weighed for subsequent analysis.
Sample preparation and testing were conducted at the Mineral Resources Testing Center in Guizhou. Samples were first ground to −0.076 mm (200 mesh), then digested using aqua regia. Thereafter, the solution was diluted quantitatively with deionized water for analysis. The analytical testing followed the technical requirements of the Chinese Geochemical Survey Specifications [55,56], with the analyzed elements including Au, As, Sb, Ag, Sn, Co, Cu, Pb, Hg, Ni, Cr, Zn, V, Mo, and W. The average reporting rate (proportion of samples with analytical data) for all elements was 99.91%. A total of 399 samples (4.41%) were randomly selected for duplicate analysis, and anomalously high concentrations (>99.97th percentile) were re-digested and re-analyzed. For Au analysis, four national-level-certified reference materials (GAu series) were inserted per 50 samples; for other elements, two GSS-series-certified reference materials were inserted per 50 samples. The relative standard deviation (RSD) for 12 certified reference materials was from 3.39 to 8.08%.

3. Results and Discussion

3.1. Geochemical Parameters of Elements

The geochemical dataset focuses on the spatial distribution homogeneity, inter-element correlations, and anomaly intensities of trace elements within the study area, and is characterized by statistical parameters including mean value, coefficient of variation (CV), and enrichment factor (EF). Summary statistics are presented in Table 1.
Compared with those of the average crustal abundances (C.A.) [57], As, Sb, and Hg show significant enrichment with EFs of 5.2, 6.5, and 11.4, respectively. Lead and Sn exhibit moderate enrichment relative to crust values (EFs of 2 and 2.15, respectively), while other elements show low enrichment levels (EFs near 1), suggesting that As, Sb, and Hg may be mobile elements introduced by mineralization.
The coefficients of variation among geochemical data vary considerably. Gold, As, Sb, Hg, and Mo have high CVs (>3), indicating their strong potential for anomaly formation. Even after excluding outliers (extremely high or low values), Hg and Ag still exhibit background CVs greater than 2, demonstrating their highly heterogeneous distribution and strong enrichment potential. Contrastingly, other elements generally display background CV values below 0.2, suggesting that these elements have stable background values.
Skewness values among elements can be classified into low (Cu:0.74, Co:17.94), moderate (W:174.32, Sn:395.02), high (Hg:969.48, As:1754.12), and extremely high (Sb:4473.76, Mo:7900.28). All elements have positive kurtosis, with values covering low (Cu:0.24, Ni:0.67), moderate (Zn:1.31, Pb:1.9), high (W:10.87, As:33.93), and extremely high (Mo:86.65) kurtosis, where high/extremely high values indicate long-tailed distributions or the presence of outliers. Elements such as Au, As, Sb, Hg, W, Ag, and Sn show high skewness and kurtosis values, indicating that these elements have high variability.
Overall, Au, As, Sb, and Hg exhibit high enrichment factors, coefficients of variation, and skewness and kurtosis, generally manifesting as high anomalies and mineralization potential; these are followed by Pb, Ag, Sn, W, and Mo, which easily form weak anomalies, suggesting moderate mineralization possibility; Co, Cr, Cu, V, Ni, and Zn exhibit lower variation and enrichment coefficients, resulting in subdued anomaly gradients and limited mineralization potential.
The log-scale histograms of element concentrations (Figure 5) show that all elements roughly follow a log-normal distribution (with unimodal patterns), which is consistent with the results from the Q-Q plot. Gold, As, Sb, Hg, W, Mo, and Ag show wide distribution ranges and high dispersion, with the overall distribution pattern tilted toward the low value area on the left, indicating that the distribution frequency of low value is greater than that of high background values. From the soil-forming potential of the parent rock through weathering, no significant correlation existed between metallogenic elements (e.g., Au, As, Sb) and soil thickness; however, soils originated from ore-hosting layers show remarkably higher concentrations of these elements [57]. Chromium, Sn, Cu, Co, Ni, V, Pb, and Zn show more concentrated distributions, generally tilting toward the high value area on the right, indicating relatively elevated background levels for these elements.

3.2. Element Association Characteristics

The characteristic of correlation analysis lies in its use of correlation coefficients between variables to effectively identify combination relations among elements, thereby clarifying their intrinsic connections. The correlation coefficients were calculated based on the soil geochemical date, yielding the correlation matrix (Table 2). The results show that Au has a positive correlation (correlation coefficients between 0.3 and 0.5) with As, Sb, Hg, and W, while As, Sb, Hg, W, and Mo exhibit significant positive correlations with each other (correlation coefficients > 0.5), reflecting the characteristics of ‘not necessarily coexistent, but never far from its trace’ among ore elements. Chromium, Co, Ni, Cu, and Zn exhibit significant positive correlations among themselves, but show negative correlations with As, Sb, Hg, W, and Mo. This suggests that these elements may be naturally present in the original sedimentary rocks, and have subtle relationships with hydrothermal mineralization processes.
To further reveal the elemental associations, R-type cluster analysis was performed on the raw geochemical of 15 elements using SPSS 27 software, generating a dendrogram of element clustering (Figure 6). Using a distance coefficient threshold of 15, the elements can be divided into the following four clusters: (a) Au, As, Sb, Hg, W, and Mo represent the medium- and low-temperature element assemblage associated with Carlin-type gold mineralization [4,14]; (b) Ni, Zn, Co, Cu, V, and Cr likely reflect the elements characteristics of regional stratigraphic rocks or geological activities unrelated to gold mineralization; (c) Sn and Pb are commonly considered as elements associated with moderate- to high-temperature magmatic-hydrothermal activities [25]; (d) Ag forms an independent cluster with weak correlations with those of the other elements, possibly representing the background concentrations related to lithology. When the distance coefficient reaches 20, Au, As, Sb, Hg, W, and Mo, and Sn and Pb are grouped together, suggesting a potential genetic relationship between these two element assemblages.

3.3. Distribution and Genesis of Geochemical Anomalies

3.3.1. Comprehensive Geochemical Anomalies

Background values (Co) and standard deviations (δ) of each element in the study area were determined after eliminating outliers using the iterative method. Subsequently, the anomaly threshold (Ca) for each element was calculated using the formula Ca = Co + kδ, where k generally ranges from 1 to 3. Based on comparative tests, a value of k = 2 was selected for this study. Finally, the anomaly threshold was calculated using the standard iterative method, with appropriate adjustments based on values obtained from the cumulative frequency method (90%–95%). The resulting anomaly thresholds were then rounded to establish the final classification boundaries (Table 3).
Based on soil geochemical analysis results, the anomaly thresholds were multiplied by one, two, and four times to define the outer, middle, and inner zones of anomalies, respectively. In total, 176 single-element anomalies were delineated for 15 elements. Building upon these single-element anomalies, a total of 12 comprehensive anomalies were identified, among which HS-2, HS-3, and HS-7 exhibited higher anomaly intensities and good overlapping of single-element anomalies. The detailed characteristics are as follows:
(a) The HS-2 anomaly is located in the western part of the study area and is elliptically distributed in a northeast direction, with a length of 7.32 km, a width of 3.8 km, and an anomaly area of 12.82 km2 (Table 4, Figure 7). This comprehensive anomaly is enclosed and primarily composed of Au, As, Sb, Hg, W, and Mo. These elements show good overlapping, with numerous anomaly points, extensive areal distribution, and high intensity. Gold, As, and Hg are particularly significant, with relatively high NAP values and contrast. The maximum concentrations of Au, As, Hg, and W are 351.3 × 10−9, 549 × 10−6, 114.3 × 10−6, and 45.48 × 10−6, respectively. The enrichment centers of Au, As, Hg, and W are obvious, displaying a three-level zoning of concentrations, whereas Sb and Mo display only outer and middle zone characteristics. The strata exposed in the anomaly area are principally the T1yn, P3l, P3c, and P3β. The structures are dominated by the NE-trending Erlongqiangbao Fault, and the Nibao and Erlongqiangbao anticlines (Figure 3). The Nibao gold deposit was discovered within this anomaly area and is located within the third-level anomaly range of the comprehensive element anomaly.
(b) The HS-3 anomaly is located in the central part of the study area and is elliptically and eccentrically distributed along the northeast direction, with a length of 9.01 km, a width of 3.29 km, and an area of 12.77 km2 (Table 5, Figure 8). This comprehensive anomaly is enclosed and primarily composed of Au, As, Sb, Hg, W, Mo, Ag, and Zn, with good overlapping anomalies among the elements. Among them, the Au, As, Sb, Hg, and W anomalies have a large number of anomaly points, large area, and high intensity, with the Au, As, and Hg anomalies being particularly significant, showing characteristics of high contrast and high NAP values. The maximum concentrations of Au, As, Sb, Hg, and W are 299.1 × 10−9, 12,736 × 10−6, 4796 × 10−6, 12.2 × 10−6, and 72.9 × 10−6, respectively, with obvious enrichment centers and three-level concentration zoning. Contrastingly, Mo, Ag, and Zn only have an outer zone. The strata exposed in the anomaly area dominantly include both the P2m and the T1yn. The structures are principally the NE-trending Sandaogou and Panjiazhuang faults and Nibao Anticline (Figure 3).
(c) The HS-7 anomaly is located in the eastern part of the study area and is elliptically distributed along a northeast direction, with a length of 8.23 km, width of 3.24 km, and an area of 12.49 km2 (Table 6, Figure 9). This anomaly is predominantly composed of Au, As, Sb, Hg, W, Mo, Ag, Sn, and V, with good overlapping among the elements and multiple enrichment centers. Gold, As, and Hg anomalies comprise numerous anomaly points, large area, and high intensity, with high contrast and NAP values. The maximum concentrations of Au, As, Sb, Hg, W, Mo, Ag, Sn, and V are 1200 × 10−9, 53.44 × 10−6, 2576 × 10−6, 23,490 × 10−6, 4796 × 10−6, 67.12 × 10−6, 1002 × 10−6, and 2.457 × 10−6, respectively. The enrichment centers of the aforementioned element are obvious, showing three-level concentration zoning, whereas Sn and V only have an outer zone. The strata exposed in the anomaly area are primarily the T1f, P3c, and P3l. The structures are principally the near EW-trending Dayakou and Goupijing anticlines, and Dayakou Fault (Figure 3).
These three comprehensive anomalies are all distributed along the axial faults proximal to anticline cores, showing obvious structural control characteristics. Additionally, in the Nibao gold ore district, these anomalies exhibit spatial consistency with the distribution of gold ore bodies (or mineralization) in fault fracture zones and SBT, which indicates that they may be ore-induced anomalies. The single-element components within the comprehensive anomaly zones are elliptically and eccentrically distributed, exhibiting characteristics of hydrothermal mineralization. Among the comprehensive anomalies, the front and the rear halo elements As and Sb and Mo and W, respectively, exhibit large-scale anomalies, clear concentration zoning, and good overlapping, suggesting that although the shallow ore (mineralization) bodies underwent erosion, parts of the gold ore (mineralization) bodies may still be preserved at depth.

3.3.2. Geochemical Combination Anomalies

Multi-element combinations can reveal subtle anomalies that single elements failed to determine and can exclude certain interferences, thereby highlighting mineralization-related information [58]. Correlation, cluster, and factor analyses [25] suggest that the ore-forming element combination in the study area is Au-As-Sb-Hg-W-Mo, indicating that this element combination can serve as an indicator for mineral exploration. Therefore, Au, As, Sb, Hg, W, and Mo were selected to plot the factor score contour maps.
The factor scores contour maps (Figure 10) indicate that the combination anomalies of Au-As-Sb-Hg-W-Mo are primarily distributed in the Nibao–Hongyan, Huomachong–Sandaogou, and Dayakou–Baogudi districts. These anomalies are concentrated at the intersections of NE- and NWW-trending structures. The anomalous areas are extensive and exhibit distinct concentration zoning, generally appearing in bead-like and elliptical patterns, whose morphology and scale are distinctly controlled by structure. Specifically, the Nibao–Hongyan anomaly area spatially corresponds to the HS-2 comprehensive anomaly, and matches well with that of the NE-trending Nibao and Erlongqiangbao anticlines and the axial Erlongqiangbao Fault; the Huomachong–Sandaogou anomaly area corresponds to the HS-3 comprehensive anomaly and aligns with that of the NE-trending Nibao Anticline as well as the axial Sandaogou and Panjiazhuang faults; the Dayakou–Baogudi anomaly area corresponds to the HS-17 comprehensive anomaly, and corresponds with that of approximately EW-trending Dayakou Anticline and its axial faults (F19 and F20). The NE-trending and SE-plunging anomalies in the Nibao–Hongyan area not only associate with those of the NE-trending structures (e.g., the Nibao and Erlongqiangbao anticlines and F1, F2, and F3 faults), but also coincide with the SE-dipping ore body in the Nibao gold deposit (Figure 10). Additionally, earlier studies demonstrated that the ore-forming substances of laterites (weathered soil) in southwest Guizhou did not directly originate from the bedrock strata, though they may be related to Carlin-type gold ores [24,25]. Therefore, the Au enrichment of soil within the Nibao–Hongyan area may be partly associated with Carlin-type gold mineralization, which accounts for the high anomalies observed in this area. According to the regional metallogenic model (Figure 2), in the anomaly concentration center of the extensive outcrops of the Maokou Formation in the Huomachong–Sandaogou area, the deep part of this area no longer possesses the favorable geological conditions for mineralization [8,45]. Additionally, three relatively weak anomaly areas were identified in the Xingren–Luguan, northeastern Panjiazhuang, and Yuzhang–Kongbai areas, exhibiting pronounced concentration zonation but limited to outer and middle zones only (Figure 10). Comprehensively, the anomalies weaken from west to east and decrease from south to north, which may indicate the migration direction of ore-forming fluids.
The three high integrated anomalies HS-2, HS-3, and HS-7 delineated by soil geochemical surveys correspond with those of the high factor score regions of the Au-As-Sb-Hg-W-Mo combination. Furthermore, they also align with ore-controlling structures, ore-hosting rocks, and alteration areas, indicating favorable prospects for exploration targeting. Both the 1:50,000 and 1:10,000 tectono-geochemical weak information extraction surveys demonstrate that primary geochemical halos display good correspondence with the three soil geochemical anomalies [25]. This suggests that the corresponding soil geochemical anomalies may be ore-induced.

3.4. Implications for Mineral Exploration Targeting

Integrating soil geochemical anomalies with metallogenic geological conditions, three prospecting targets, including Nibao, Sandaogou, and Baogudi, were preliminarily delineated.
The Nibao target area contains the large-scale Nibao gold deposit, which is characterized by numerous ore bodies with diverse morphological types. Although some of the ore bodies in the Nibao deposit were already subjected to engineering control during exploration, most of the drilling depth remains shallow, and the deeper parts were not effectively constrained, especially the southern section dipping along the Erlongqiangbao Fault. Therefore, ore bodies may still exist in the deeper sections, as suggested by verification from individual deep holes within the area (Figure 3). Additionally, deep exploration conducted in the southern part of the Nibao deposit has revealed promising mineralization indicators, suggesting substantial ore-prospecting potential in the deeper and peripheral areas of the target.
In the Baogudi prospective target, a total of 29 trenches were excavated for verification, with 16 and 6 trenches intersecting ore bodies and revealing mineralization, respectively. The mineralized alteration zones exhibit large-scale variations, ranging 1–6450 m in length and 1–160 m in width. These zones are characterized by well-developed silicification, pyritization, and argillization. The ore thickness ranges from 1 to 8 m, with a maximum grade of 11.54 × 10−6 [25]. The gold mineralization exposed by the trenches is principally controlled by fault fracture zones and likely extend to greater depths, suggesting promising ore-prospecting potential in this target.
In the Sandaogou prospective target area, verification was conducted through three exploration trenches, all of which revealed mineralization. The maximum mineralized thickness reached 5.86 m, with a maximum grade of 4.53 × 10−6 [34]. The widely outcropping Maokou Formation within the Sandaoqou target area coincides with some of the geochemical anomaly concentration centers. However, recent metallogenic theories indicate that its deep mineralization potential may be limited, primarily due to complete weathering and erosion of the ores [8]. Consequently, the favorable exploration area should extend towards peripheral areas with younger stratigraphic units.

4. Conclusions

This systematic soil geochemical investigation successfully characterized element distribution patterns and identified prospecting targets in the Nibao gold deposit and peripheral areas, southwestern Guizhou, China.
(1)
Gold, As, Sb, Hg, W, and Mo exhibit significant positive correlations with high enrichment factors and extreme statistical parameters, forming a coherent pathfinder assemblage for Carlin-type gold exploration.
(2)
Based on the analysis of 15 elements, 176 and 12 single-element and integrated anomalies were delineated, respectively. Among them, HS-2, HS-3, and HS-7 have high anomaly intensity and are consistent with those of the concentrated anomaly zones shown in the Au-As-Sb-Hg-W-Mo factor score contour maps.
(3)
Combining geochemical anomalies with geological conditions, three favorable ore-prospecting target areas were delineated. The Nibao gold deposit lies in the Nibao target area, showing potential ore-prospecting space in the deep and peripheral zones of the gold deposits. Exploratory trenching in both the Baogudi and Sandaoqou prospective areas revealed mineralized zones. However, the Sandaogou target exhibits extensive outcrops of the Maokou Formation within anomalously enriched areas, suggesting that the deep mineralization potential may be limited.
These results demonstrate the practical applicability of soil geochemical surveys for mineral exploration, offering immediate exploration opportunities while establishing a methodology for regional application throughout the Dian–Qian–Gui Golden Triangle.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/min15090922/s1, Table S1: Soil geochemistry date (1:50,000) of the Nibao Carlin-type gold deposit and peripheral areas [25].

Author Contributions

Conceptualization, S.L. and J.L. (Jianzhong Liu); methodology, L.T., R.N., and M.M.; investigation, L.T., R.N., M.M., and W.H.; writing—original draft preparation, S.L.; writing—review and editing, J.L. (Jianzhong Liu), J.L. (Junhai Li), and C.Y.; visualization, B.Z.; supervision, Z.W. All authors have read and agreed to the published version of the manuscript.

Funding

This study was jointly funded by the Guizhou Provincial Basic Research Program (Natural Science) (Nos. Qian Ke He Ji Chu ZD [2025] 032, Qian Ke He Ji Chu MS [2025] 011, Qian Ke He Ji Chu-ZK [2022] Yi Ban 336); the Guizhou Provincial Science and Technology Innovation Talent Team (No. Qian Ke He Ren Cai CXTD [2025] 002); Guizhou Provincial Program on Commercialization of Scientific and Technological Achievements (Qian Ke He Cheng Guo [2023] Zhong Da 006); and Scientific Research Fund Project of Guizhou Education University (No. 2024BS002).

Data Availability Statement

All data are contained within the article and Supplementary Materials.

Acknowledgments

We thank the reviewers and editors for their important comments and constructive suggestions which helped us significantly improve the quality of the manuscript. We also thank all staff from the previous First Exploration Department of the 105 Geological Team of the Guizhou Bureau of Geology and Mineral Exploration and Development for their support with field work, geochemical sampling, and sample preparation and for their assistance with data analysis, geochemical mapping, and interpretation of the results, particularly Liping Huang.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Regional geologic map showing the distribution of Carlin-type gold deposits in the Dian–Qian–Gui Golden Triangle, China (modifed from [25]).
Figure 1. Regional geologic map showing the distribution of Carlin-type gold deposits in the Dian–Qian–Gui Golden Triangle, China (modifed from [25]).
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Figure 2. Multi-level structural detachment metallogenic model of Carlin-type gold deposits in southern China (modified from [45]).
Figure 2. Multi-level structural detachment metallogenic model of Carlin-type gold deposits in southern China (modified from [45]).
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Figure 3. Geological map of the Nibao gold deposit and its surrounding area (modified from [25]).
Figure 3. Geological map of the Nibao gold deposit and its surrounding area (modified from [25]).
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Figure 4. Geological cross-section (A–A′) of the Nibao gold deposit (modified from [25]). The location of this section is shown in Figure 3.
Figure 4. Geological cross-section (A–A′) of the Nibao gold deposit (modified from [25]). The location of this section is shown in Figure 3.
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Figure 5. Element distribution patterns in soil geochemistry. Note: vertical axis = n (frequency), unit = count; horizontal axis = lgC, C = trace element concentration (Au in ppb, others in ppm).
Figure 5. Element distribution patterns in soil geochemistry. Note: vertical axis = n (frequency), unit = count; horizontal axis = lgC, C = trace element concentration (Au in ppb, others in ppm).
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Figure 6. R-type cluster analysis dendrogram of elements in soil geochemistry.
Figure 6. R-type cluster analysis dendrogram of elements in soil geochemistry.
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Figure 7. Analysis map of HS-2 geochemical anomaly, the corresponding geological content is shown in Figure 3.
Figure 7. Analysis map of HS-2 geochemical anomaly, the corresponding geological content is shown in Figure 3.
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Figure 8. Analysis map of HS-3 geochemical anomaly, the corresponding geological content is shown in Figure 3.
Figure 8. Analysis map of HS-3 geochemical anomaly, the corresponding geological content is shown in Figure 3.
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Figure 9. Analysis map of HS-7 geochemical anomaly, the corresponding geological content is shown in Figure 3.
Figure 9. Analysis map of HS-7 geochemical anomaly, the corresponding geological content is shown in Figure 3.
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Figure 10. Factor score contour map of Au-As-Sb-Hg-W-Mo showing the enrichment characteristics of this element assemblage, the low (blue) and high (red) factor scores represent depletion of this element assemblage and its enrichment, respectively.
Figure 10. Factor score contour map of Au-As-Sb-Hg-W-Mo showing the enrichment characteristics of this element assemblage, the low (blue) and high (red) factor scores represent depletion of this element assemblage and its enrichment, respectively.
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Table 1. Characteristic parameters of soil geochemical dataset.
Table 1. Characteristic parameters of soil geochemical dataset.
Elem.Min.Max.Avg.SDSkew.Kurt.CVCV *C.A.CF
Au0.210503.4117.9732.541573.575.2700.1381.31.23
As0.62310459.23377.8633.931754.126.380.0382.55.2
Sb0.1348395.5361.8861.614473.7611.1900.220.26.5
Hg0.0167.120.31.324.73969.484.3332.7810.0111.4
Ag0.022.750.070.0525.671140.320.7142.6190.0561.13
Sn151.824.41.1811.43395.020.2680.01922.15
Co0.22330.334017.241.7817.940.4310.004251.55
Cr11.65501.2185.1358.510.46−0.260.3160.0011001.77
Cu2.31491.81102.0542.370.240.740.4150.002551.69
Ni2.04480.1773.0129.810.675.160.4080.002750.95
Pb4.64160.8726.5610.261.99.180.3860.00612.52
V40.86722.8250.5162.890.551.140.251<0.0011351.8
Zn5.93588118.2538.271.3112.450.3240.00172.41.62
Mo0.3929.172.2810.1486.657900.284.4470.1451.51.13
W0.3168.192.242.4510.87174.321.0940.0731.51.2
Note: the CV * was calculated after continuously removing data other than that of the ‘mean values ±3 times the standard deviations’ (background data); enrichment factors were calculated as the arithmetic mean of raw data divided by crustal abundance; units: Au in ppb, and all others in ppm.
Table 2. Spearman correlation coefficient of trace elements from soil geochemistry.
Table 2. Spearman correlation coefficient of trace elements from soil geochemistry.
ElementsAuAsSbHgAgSnCoCrCuNiPbVZnMoW
Au1.00
As0.391.00
Sb0.320.761.00
Hg0.400.610.591.00
Ag0.120.070.190.201.00
Sn0.080.080.080.170.051.00
Co−0.25−0.54−0.41−0.350.03−0.101.00
Cr−0.09−0.51−0.32−0.110.010.040.471.00
Cu0.03−0.52−0.34−0.130.040.060.540.551.00
Ni−0.24−0.56−0.42−0.34−0.03−0.040.830.630.541.00
Pb−0.040.320.250.160.050.24−0.09−0.14−0.46−0.031.00
V0.17−0.23−0.070.100.110.130.200.500.670.18−0.431.00
Zn−0.18−0.38−0.25−0.230.10−0.010.770.390.460.830.090.141.00
Mo0.240.610.530.510.100.22−0.41−0.27−0.21−0.480.250.16−0.291.00
W0.460.670.620.540.100.14−0.50−0.32−0.36−0.470.21−0.08−0.370.451.00
Table 3. Threshold values for soil geochemical anomalies.
Table 3. Threshold values for soil geochemical anomalies.
ElementsAgAsAuCoCrCuHgMo
Calculated value0.1351274.6803332370.4885.34
Used value0.1351204.2803402300.55.2
ElementsNiPbSbSnVWZn
Calculated value151494.96.33983.3197
Used value150501064003.2200
Note: Au in PPb, others in ppm.
Table 4. Geochemical parameters of HS-2 anomaly.
Table 4. Geochemical parameters of HS-2 anomaly.
ElementsAuWSbAsHgMo
Area (km2)12.829.323.4710.3610.573.38
Maximum68043.1649.46422012.7619.97
Average43.88.7820.786901.2336.61
Contrast27.44.882.085310.83.89
Scale (NAP)351.345.487.22549114.313.2
Abnormal points2101525217216969
Residual element content42.26.9810.786771.1194.91
Areal metal productivity54165.0537.41701411.82816.6
Zone332331
Note: Au in ppb, and other elements in ppm.
Table 5. Geochemical parameters of HS-3 anomaly.
Table 5. Geochemical parameters of HS-3 anomaly.
ElementsAuSbWAsHgMoAgZn
Area (km2)6.8612.7710.0911.69.542.662.280.52
Maximum299.1479672.912,73612.26.640.217313
Average20.887.37.353721.4818.170.132231
Contrast138.74.1291310.692.12
Scale (NAP)89.2111.141.37336.412428.444.81
Abnormal points9718615116413446328
Residual element content19.277.35.553591.36619.870.069114
Areal metal productivity131.71987.1564164.413.0352.850.1659
Zone33333111
Note: Au in ppb, and other elements in ppm.
Table 6. Geochemical parameters of HS-7 anomaly.
Table 6. Geochemical parameters of HS-7 anomaly.
ElementsAuSbWAsHgMoAgSn
Area (km2)12.496.568.6112.4811.516.233.632.32
Maximum1200257653.4423,49067.1210022.45716.2
Average25.344.98.0465153.26318.1760.2546.5
Contrast15.84.54.474028.610.74.031.51
Scale (NAP)197.329.538.5499.2329.266.714.63.5
Abnormal points2111091502101951026736
Residual element content23.734.96.2465023.14916.4760.1912.2
Areal metal productivity29622953.8626536.2102.60.75.1
Zone33333331
Note: Au in ppb, and other elements in ppm.
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Li, S.; Tan, L.; Wang, Z.; Nie, R.; Meng, M.; Han, W.; Yang, C.; Li, J.; Zhang, B.; Liu, J. Soil Geochemical Characteristics and Prospecting Potential in the Nibao Carlin-Type Gold Deposit and Peripheral Areas, Southwestern Guizhou, China. Minerals 2025, 15, 922. https://doi.org/10.3390/min15090922

AMA Style

Li S, Tan L, Wang Z, Nie R, Meng M, Han W, Yang C, Li J, Zhang B, Liu J. Soil Geochemical Characteristics and Prospecting Potential in the Nibao Carlin-Type Gold Deposit and Peripheral Areas, Southwestern Guizhou, China. Minerals. 2025; 15(9):922. https://doi.org/10.3390/min15090922

Chicago/Turabian Style

Li, Songtao, Lijin Tan, Zepeng Wang, Rong Nie, Minghua Meng, Wenxin Han, Chengfu Yang, Junhai Li, Bingqiang Zhang, and Jianzhong Liu. 2025. "Soil Geochemical Characteristics and Prospecting Potential in the Nibao Carlin-Type Gold Deposit and Peripheral Areas, Southwestern Guizhou, China" Minerals 15, no. 9: 922. https://doi.org/10.3390/min15090922

APA Style

Li, S., Tan, L., Wang, Z., Nie, R., Meng, M., Han, W., Yang, C., Li, J., Zhang, B., & Liu, J. (2025). Soil Geochemical Characteristics and Prospecting Potential in the Nibao Carlin-Type Gold Deposit and Peripheral Areas, Southwestern Guizhou, China. Minerals, 15(9), 922. https://doi.org/10.3390/min15090922

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