The Indicative Significance of Interlayer-Sliding Fault Deformation in a Thrust–Fold Structure of the Huize Mine District to the Variation of Ore-Hosting Space: Insights from Analogue Modeling

Abstract

Interlayer-sliding faults play a crucial role in governing the distribution of metal deposits. Nevertheless, the mechanism by which these faults control the spatial arrangement of ore bodies throughout the evolution of fault–fold structures remains unclear. Here, we formulated three series of experimental models to explore variations in deformation and alterations in the mechanical characteristics of interlayer-sliding faults throughout the evolution of the thrust–fold structures. The experimental results indicate that the thrust faults formed in the three series of experiments all propagate in a piggyback propagation, displaying an imbricate thrust in cross-sections. Compared with Model 1 and Model 2, Model 3 demonstrates the longest transmission distance of the deformation front, the smallest thrust wedge taper angle, the fewest thrust faults with the largest spacing, and a reduction in the dip angle of the thrust fault. Particle image velocimetry (PIV) showed that in the top view, the position of minimum horizontal strain in each stage is the position of thrust faults. In the cross-sectional view, the development location of thrust faults shows the low-value area of the velocity field and surface strain field, and the development location of the interlayer-sliding fault and tensile space in the core of the fold displays the high-value area of velocity field and surface strain field. The structural characteristics of experiment 3 are highly similar to the actual geological model, indicating that there is a certain ore-hosting space in the Dengying Formation deep in the deposit. Although the expansion zone in the deep area is smaller than that in the shallow area, it still has favorable prospecting prospects.

1. Introduction

The thrust–fold structures are not only crucial for hydrocarbon reservoirs, but also closely related to metallic mineralization [1,2,3,4,5,6]. In particular, interlayer-sliding faults, situated within the framework of thrust–fold structures, exert a notable influence on the control of metal ore deposits. [7,8,9,10,11]. Interlayer-sliding fault refers to significant displacements between geological layers caused by variations in their competence under the influence of tectonic stress [12,13]. Large-scale, deep-seated interlayer-sliding faults are associated with global or widespread tectonic movements. For regional interlayer-sliding faults, their formation is generally linked to regional tectonic activity and folding. In thrust–fold structures, the types of interlayer-sliding interfaces are diverse, and, due to their low strength and high shear strain during sliding, these interlayer-sliding interfaces exhibit properties similar to fault planes. Therefore, they can also be referred to as interlayer-sliding faults. There is no distinct boundary between interlayer-sliding and layer-sliding faults. When interlayer-sliding reaches a certain scale, it transforms into interlayer-sliding faults [14]. Interlayer-sliding faults typically undergo three stages: layer sliding, thrusting, and reactivation [15]. Depending on the physical and chemical characteristics exhibited at diverse depths of the fault, interlayer-sliding faults can be categorized into three types: brittle interlayer-sliding faults, brittle-plastic interlayer-sliding faults, and plastic interlayer-sliding faults. Brittle interlayer-sliding faults are the most common type of fault and typically appear alongside the deformation, bending, and folding of rock layers subjected to compression [16]. In carbonate rock sequences, interlayer-sliding faults are a critical structural control, influencing the occurrence and positioning of gold–silver polymetallic deposits at regional and multi-scale levels [12].

Previous studies on the Huize transpressive oblique-slip fault–fold structures have primarily focused on its geometric characteristics, kinematics, dynamics, mechanics and the controlling effect of interlayer fault on mineralization is emphasized [17,18,19,20]. However, there is limited research on the changes in the mechanical mechanism of ore-hosting space caused by interlayer-sliding faults during the evolution of thrust–fold structures. Therefore, building upon previous work [9,16,17,18,19,20,21,22,23,24,25,26,27,28], we used analogue modeling to study the indicative significance of interlayer-sliding fault deformation in thrust–fold structures of Huize to the variation of ore-hosting space. Using Particle Image Velocimetry (PIV) technology, we conducted qualitative and quantitative studies on fold structures. We particularly discuss the impact of fold structures on the deformation of interlayer-sliding faults and the ore-hosting space.

2. Geological Background

The Huize Zn–Pb–(Ge–Ag) district is situated in Northeastern Yunnan, southwestern China, and it forms the central component of the Sichuan–Yunnan–Guizhou Triangular area (SYGT) known for its poly-metallic Zn–Pb mineralization. This district consists of two large-sized deposits including the Qilinchang and the Kuangshanchang deposits and a medium to small-scale Yinchangpo deposit (Figure 1c). The geological structure is predominantly controlled by the NE-trending Dongchuan–Zhenxiong thrust–fold structural zone, which has developed due to the sinistral shearing of the Xiaojiang fault and Zhaotong–Qujing concealed fault [21] (Figure 1a, b). Within the Huize district, three major faults—Kuangshanchang, Qilinchang, and Yinchangpo—demonstrate multiple movements and spatial associations with Zn–Pb–(Ge–Ag) ore bodies. During the mineralization period, these faults manifest as transpressive oblique-slip faults. [8,9,17,18,19,20,21,22]. The NE-trending interlayer-sliding fault derived from the Kuangshanchang and Qilinchang faults is the main ore-hosting structure, which specifically controls the spatial positioning of the ore body [17,18,19,20,21,22]. The ore bodies of the Huize Zn–Pb–(Ge–Ag) deposit are primarily located in the brittle interlayer-sliding faults at the lithological boundary between the dolomite and limestone of the Baizuo Formation [17,18,19,20,21,22,23].

3. Experimental Method

Analogue modeling has long been used to investigate the deformation mechanisms of thrust–fold structures as a powerful tool to evaluate and simulate the kinematics, mechanics, and dynamic processes of natural geological structures [29]. Due to practical constraints and limitations in the experimental setup, the intended simulation aimed at transpressive oblique-slip fault–fold structures was adapted to simulate thrust–fold structures. The experimental conditions, resources, and technical constraints guided this adjustment, with the acknowledgment that the simulated thrust–fold structures would provide valuable insights within the scope of this study’s objectives. We conducted three series of analogue models to explore the indicative significance of interlayer-sliding fault deformation in thrust–fold structures to the variation of ore-hosting space. Details of the models are listed as the following:

3.1. Experimental Materials and Scaling

There are various types of strata in the natural world, which can be primarily classified into two categories: brittle strata and ductile strata. Brittle strata encompass sedimentary rocks like limestone, sandstone, and crystalline rocks, among others. These materials deform following the Mohr–Coulomb rupture criteria. Dry quartz sand, with an internal friction angle of 31° to 40°, is a commonly used simulation material for brittle strata [30,31,32,33]. Glass microbeads, with an internal friction angle of approximately 25°, have lower frictional strength than quartz sand, making them suitable for simulating non-competent strata with low strength, such as mudstone and shale. They are normally used to simulate brittle deformation detachment layers in physical simulations of thrust–fold structures [34,35,36]. The predominant lithology in the study area consists of dolomite and limestone, with the focus being on the lithological interface between them. The dolomite and limestone are simulated by quartz sand, and glass microbeads simulate the interface between dolomite and limestone. Blue quartz sand is used as the marking layer to monitor the deformation. The mechanical properties remain unchanged. The sand maintained similar mechanical properties to the white sand. The quartz sand used in the experiment has a mesh number of 100 mesh and an internal friction angle of 35°. The mesh number of the glass microbeads is 100 mesh and the internal friction angle is 25°.

The design of the physical simulation experiment adheres to the principles of geometric similarity, kinematic similarity, and dynamic similarity. This approach allows for the revelation of the deformation process and controlling factors of natural geological structures [37,38,39].

The similarity calculations for the experiment are as follows:

(1) Geometric similarity:

$$L^{*}=\frac{L_m}{L_n}=\frac{0.5}{10000}=4.5\times {10}^{-4}$$

(1)

This means that 45 cm in the model represents 10 km in reality, equating to 1 cm in the actual model representing 222 m in nature.$L^{*}$ represents length scaling ratio,$L_m$ is model length,$L_n$ represents natural length.

(2) Dynamic similarity:

$${\sigma }^{*}={\rho }^{*}\times g^{*}\times L^{*}=0.56\times 1\times 4.5\times {10}^{-4}=2.52\times {10}^{-4}$$

(2)

Here, ${\sigma }^{*}$ represents the density similarity ratio, $g^{*}$ represents the gravity acceleration similarity ratio and ${\rho }^{*}$ is average density ratio.

(3) Kinematic similarity: Brittle Mohr–Coulomb materials like dry quartz sand and glass microbeads have deformation independent of strain rate [37]. Thus, the deformation rate does not need to be strictly proportional. After many experiments, it was found that at a speed of 0.2 mm/s, the evolutionary process was the most distinct, with minimal mixing between the marker layer and simulated stratigraphic layers. We set the movable wall compression displacement rate to 0.2 mm/s.

3.2. Experiment Setup

The ore body of the Huize Zn–Pb–(Ge–Ag) deposit mainly occurs in the interlayer-sliding faults between dolomite and limestone in the middle and upper parts of the Baizuo Formation (Figure 2a) [9,17,18,19,20,21,27,29]. According to the research of Han et al. (2006), the mechanical parameters of the ore-hosting surrounding rock of the Huize Zn–Pb–(Ge–Ag) mine district indicate that under the same conditions, the shear strength and compressive strength of limestone are greater than those of dolomite. Dolomite and limestone have different compressive and shear strength. Under tectonic stress, the boundary interface between the two rock types will form an interlayer-sliding fault [21]. Previous studies have shown that interlayer-sliding faults can facilitate the deformation, differentiation, and modification of rock layers, thereby influencing the formation, distribution, and enrichment of ore bodies [12,14]. In the fieldwork, it was found that compound folds and interlayer-sliding faults developed at level 1404 in the Kuangshanchang deposit of the Lower Sinian Dengying Formation. The ore body is hosted in the areas where interlayer-sliding faults (ZZW-42) and tensile space in the core of the fold developed (ZZW36-1) (Figure 2b).

After a comprehensive analysis of the ore field structure, structural mapping, and other relevant data in the mining district (Figure 1c, Figure 2,) [9,17,18,19,20,21,26,27,29], in combination with the position of the lithological interface in the stratigraphic column (Figure 3a) and the local interlayer-sliding fault noted in the tunnel catalog, a geological model for Huize with double lithological interfaces were established. The experiment aims to study the influence of thrust–fold structure on interlayer-sliding fault deformation and mineralization space. Three simplified model series were constructed, with the experimental model layout schematically illustrated in Figure 3b. The dimensions of these three models, in terms of length, width, and height, are 75 cm × 22 cm × 30 cm. Model 1 referrs to as the standard group, which consists of layers from bottom to top: 5 mm 90 mesh quartz sand, 3 mm 90 mesh quartz sand, 5 mm 90 mesh quartz sand, 3 mm 90 mesh quartz sand, and 5 mm 90 mesh quartz sand. This model does not include a lithological interface. In three models, glass microbeads are used to simulate the actual lithological interface between dolomite and limestone. The ore-hosting layer of the shallow Baizuo Formation is the lithological interface between dolomite and limestone. Model 2 single lithology interface model was established. Based on Model 1, the second layer of 3 mm quartz sand from bottom to top is replaced with 3 mm glass microbeads in Model 2. The deep Dengying Formation also has a lithological combination similar to the Baizuo Formation locally, and ore bodies have been discovered; therefore, model 3 is a double lithology interfaces model. Model 3 uses 3 mm glass microbeads to replace the second and fourth layers of 3 mm quartz sand in Model 1 from bottom to top (

Table 1. Expermental design parameters of the three experimental models.

Model	Model Size (cm)	Shortening (cm)	Time (min)	Lithological Interface I (cm)	Lithological Interface II (cm)
1	75 × 30 × 22	30	25	None	None
2	75 × 30 × 22	30	25	Glass microbead (0.3)	None
3	75 × 30 × 22	30	25	Glass microbead (0.3)	Glass microbead (0.3)

).

The sandbox body primarily comprises tempered glass and PVC boards. The basal PVC board has a friction coefficient of approximately 0.4, with an internal friction angle of around 22° [38]. The two lateral sides are constructed with transparent glass boards for capturing images and recording the experimental process. On the left end, there is a fixed wall, and the right end features a movable wall, which functions as a pusher. The right-end pusher gradually displaces the model towards the left end at a constant rate of 0.2 mm/s, inducing deformation in the model. The total compression shortening distance is set to 30 cm, and the compression process typically lasts about 25 min. Throughout the experiment, two cameras are employed to capture images of the model’s side and top at regular intervals, with photos taken approximately every 10 s. The top view facilitates quantitative monitoring of the superficial deformation during compression, while the cross-sectional view allows for the quantitative assessment of internal deformation within the model. The gray-level images obtained through photography are processed using particle image velocimetry (PIV). A Particle Image Velocimetry (PIV) device with data processing software MicroVec, was used to track the sand movement and to calculate the grain velocity ($\mathrm{V}$), horizontal strain ($E_{xx}$), and plane strain ($E_{xx}+E_{yy}$) during the deformation. Then, we put the processing results into Tecplot software to present better readability. This technique involves using high-resolution cameras to acquire a sequence of gray-level images, followed by intricate calculations and analysis to determine the velocity vector of each point on the image. This process yields the velocity field of the object being studied [40]. PIV is extensively applied in physical modeling to track and analyze structural deformations. Although previous researchers used PIV to calculate the velocity, vorticity, linear strain, and surface strain, they did not discuss the relationship with the location of the ore body [41,42,43].

4. Experimental Results

In the three sets of experiments, the kinematic evolution profile is illustrated by five profiles of each shortening are explained. PIV is used to analyze the profile and plane. The profile includes sand velocity ($\mathrm{V}$) and plane strain ($E_{xx}+E_{yy}$) analysis and the plane includes sand velocity field ($\mathrm{V}$) and horizontal strain field ($E_{xx}$) to monitor structural deformation.

4.1. Model 1 (None)

The evolution of Model 1 with a total shortening of 30 cm (Figure 4a) can be divided into five deformation stages. The shortening amounts at each stage are (a) 4 cm, (b) 9 cm, (c) 14 cm, (d) 18 cm, and (e) 28 cm. Seven fore-thrusts develop in piggyback propagation, and the final thrust wedge shape is composed of seven fore-thrusts. The wedge length is 22 cm, and the taper angle of the thrust wedge is 19°. In terms of structural style, the main features are the formation of fore-thrusts and fault-related folds. The deformation of Model 1 was dominated by the fore-thrust propagating in a forward-breaking sequence toward the foreland, and showing imbricate thrusts. The early-formed thrust faults are passively uplifted and rotated, and their dip angles become larger and approach vertical. The spacing between the fore-thrust increases with the increase in compression.

According to the PIV velocity field analysis of the cross-sectional view of Model 1, the velocity of the fault footwall is zero, while the velocity of the hanging wall is larger and more concentrated. The velocity of the root zone and middle zone of the thrust–fold structures is larger, while the velocity of the front zone is smaller (Figure 4b). According to the PIV velocity field and horizontal strain field analysis of the plane view of Model 1, there is no obvious zoning of sand velocity, and the maximum sand velocity is concentrated in the root zone of the thrust plate compression end. The minimum horizontal strain position at each stage is the location where thrust faults develop. And the position of the low-value area of the velocity field is the development location of thrust faults (Figure 5).

4.2. Model 2 (Interlayer-Sliding Fault I)

Figure 6 shows the progressive evolution of Model 2 in five stages up to a maximum shortening of 30 cm. The shortening amounts at each stage are (a) 4.5 cm, (b) 10 cm, (c) 14 cm, (d) 19.5 cm, and (e) 29 cm. Five faults develop in piggyback propagation, and the final configuration of the thrust wedge comprises five fore-thrusts. The thrust wedge has a length of 24 cm and forms a wedge taper angle of about 17°. In terms of structural style, it still involves the formation of fore-thrusts and fault-related folds. The deformation of Model 2 was dominated by fore-thrusts propagating in a forward-breaking sequence towards the foreland basin. The dip angle of thrust faults gradually slows down toward the depth. Glass microbead layers become sliding weak surfaces. The glass microbead layer increases the distance between the thrust faults and at the same time propagates the strain long-distance in the foreland direction.

PIV analysis of Model 2 (Figure 6b) reveals that in the profile of Model 2, it is evident that the velocity of the fault’s foot wall is zero, while the velocity of the hanging wall is higher and more concentrated. The velocity is highest in the root zone of thrust–fold structures, and relatively lower in the middle zone and foreland zone. Analysis of the PIV velocity field and the horizontal strain field in the top view of Model 2 reveals that the boundary of maximum sand grain velocity is always the concentrated area of horizontal strain, and the position of the minimum horizontal strain moves forward with the position of the deformation front (Figure 7).

4.3. Model 3 (Interlayer-Sliding Fault I and II)

The progressive evolution of model 3 with a total shortening of 30 cm can be divided into 5 deformation stages (Figure 8). The shortening amounts at each stage are (a) 6 cm, (b) 8 cm, (c) 18 cm, (d) 23 cm, and (e) 29.5 cm. Three faults develop in piggyback propagation, and with the formation of new fore-thrusts, the early-formed fore-thrusts are continuously uplifted. The final configuration of the thrust wedge consists of three foreland-vergent thrusts. The thrust wedge has a length of 25 cm and has a taper angle of 16°. In terms of structural style, it primarily involves the formation of fore-thrusts and fault-related folds. The overall deformation characteristics of experiment 3 involve fore-thrusts propagating in a forward-breaking sequence towards the foreland basin. On cross-sections, fore-thrusts exhibit imbricate thrusts, the dip angle of the thrust fault gradually slows down toward the depth, and the two sets of glass microbead layers become sliding weak surfaces. The glass microbeads layer increases the distance between the thrust faults and at the same time propagates the strain long-distance in the foreland direction.

In the PIV velocity field analysis of the Model 3 profile, it is evident that the footwall of the fore-thrust exhibits zero velocity, while the hanging wall displays a higher and more dispersed velocity (Figure 8b). Analyzing the top view of Model 3 through the PIV velocity field and strain field, it is observed that the sand velocities do not exhibit clear zoning patterns. The maximum sand velocity is concentrated at the compressed end of the pushing plate and the frontal zone. The location of the minimum horizontal strain moves forward with the position of the deformation front, and the development location of the interlayer-sliding fault displays the high-value area of the velocity field (Figure 9).

5. Discussion

5.1. Influence of Interlayer-Sliding Fault on Thrust–Fold Structures

Based on the experimental findings from Model 2, we conducted a study on the influence of thrust–fold structure evolution on interlayer-sliding fault deformation under the presence of a single lithological interface on the deformation of thrust–fold structures. Deformation of Model 1 and Model 2 was dominated by thrusts propagating towards the foreland in piggyback propagation. We noted that the deformation front of Model 2 extended further. Specifically, the deformation fronts of the two models differed by approximately 2 cm, while the thrust wedge obtained a taper angle differed by 2° (Figure 10a). The development of interlayer-sliding faults along the lithological boundary between dolomite and limestone promotes the faster and farther propagation of deformation fronts. The thrust wedge taper angle decreases, and positive surface strain values are distributed along the lithological interface (Figure 10b), indicating the development of interlayer-sliding faults along the lithological boundary and the generation of spatial voids.

The experimental findings from Model 3 show the influence of thrust–fold structure evolution on interlayer-sliding fault deformation under the presence of double lithological interfaces on the deformation of thrust–fold structures. In Model 3, fore-thrusts propagate towards the foreland in piggyback propagation. The profile clearly displayed imbricate fore-thrusts. Comparing Model 3 with Model 1 and Model 2, we observed an increased wedge length, the farthest deformation front distance, the smallest taper angles, the fewest developed fore-thrusts, and the largest spacing between them. Additionally, the fore-thrust inclination angle decreased (Figure 10a). Based on the aforementioned experimental results, we can conclude that there exists a positive correlation between the number of interlayer-sliding faults and the propagation distance of the wedge with the number of lithological interfaces, while an inverse correlation can be observed with the wedge taper angle.

Particle Image Velocimetry (PIV) surface strain field analysis technology is utilized to accurately identify the spatial expansion area on the profile. When analyzing the velocity field ($\mathrm{V}$) and surface strain field ($E_{xx}+E_{yy}$) of the profile evolution diagrams of the three series of models in the final stage, minor errors were eliminated, and the area with a surface strain field value greater than 0.01 was selected to represent a positive plane strain field (expanded zones). At the same time, we will no longer consider positive outliers near the movable wall due to the interference of end effects (outliers caused by the accumulation of sand bodies near the movable wall). The results show that the interlayer-sliding faults develop in the high-value zone of the high-value zone of the plane strain field. As the lithological interface increases, the positive value range of surface strain becomes larger which may be more conducive to the formation of ore-holding space. The results of the strain field show that when there is no lithological interface, the distribution range of positive values of plane strain is small. The positive value area of the plane strain field ($E_{xx}+E_{yy}$) on the thrust–fold structures is relatively large; that is, the area of the spatial expansion zone on the profile increases, and the possibility of generating ore-hosting space becomes greater (Figure 10b).

5.2. Comparison to Examples from Huize Thrust–Fold Structures

The original intention was to simulate geological layers with non-horizontal orientations. However, due to practical constraints, specifically related to the limited viscosity between the experimental sand layers, attempting to simulate larger inclinations led to the occurrence of landslide-like phenomena. In response to these experimental challenges, the decision was made to adjust and simulate horizontal layers. It is important to note that, in the final presentation of results, the initial layer inclinations (about 15 degrees) [21] were overlaid to represent the intended non-horizontal geological conditions. This adaptation was made to provide a more realistic representation of the geological complexities within the experimental limitations. Among the three sets of experiments, Model 3 (double lithological interfaces model) exhibits similarity to the structural style revealed by the typical southeast regional structural section of the Huize Zn–Pb–(Ge–Ag mining district (Figure 11a,b). Nevertheless, due to the properties of the simulated material, the dip angle of the simulated result is smaller than the actual dip angle. The simulation results suggest the presence of regional interlayer-sliding faults in the deep Dengying Formation. In the root zone of the thrust–fold structures, the fault dip angle is relatively large, gradually decreasing towards the frontal zone, indicating fore-thrusts propagating in a forward-breaking sequence. Furthermore, the age of the fore-thrust gradually decreases from the orogen to the foreland basin [40]. F1 corresponds to the Yinchangpo fault, F2 corresponds to the Qilinchang fault, and F3 corresponds to the Kuangshanchang fault. The fore-thrust demonstrates variations in dip angle from shallow to deep and steep to gentle (Figure 11a,b). During the Indosinian–early Yanshan period, the Huize Zn–Pb–(Ge–Ag)mining district experienced compression in the NW-SE direction [44,45], resulting in the sequential formation of the Yinchangpo fault, Qilinchang fault, and Kuangshanchang fault. Through comprehensive analysis of analogue modeling and investigation of ore-controlling structures, their formation and development process can be divided into three stages: the embryonic stage of the Yinchangpo fault, the development of the Yinchangpo fault, and the incubation stage of the Qilinchang fault, and the development of the Qilinchang fault and the incubation stage of the Kuangshanchang fault. All three faults are developed in the basement and extend to the surface, serving as ore-controlling structures within the mining district. Additionally, the interlayer-sliding faults along one flank of the folds and the void spaces in the core of the folds serve as ore-hosting structures.

By integrating analogue modeling with PIV analysis, the cross-sectional view unveils distinct development locations of thrust faults and interlayer-sliding faults. Specifically, areas characterized by low values in the velocity field and surface strain field, as depicted in Figure 4b, Figure 6b, Figure 8b, and Figure 10b, correspond to zones where thrust faults are actively evolving. In contrast, the high-value areas in the velocity field and surface strain field align with the development locations of interlayer-sliding faults and tensile space in the core of the fold. Quantitative analyses based on the results of experiment 3 indicate that the dilation zones primarily concentrate in the shallow strata. Nevertheless, localized dilation phenomena have been observed in the deeper sections. This observation suggests that interlayer-sliding faults and dilation spaces near fold transition zones in the core of folds play a crucial role in providing necessary space for the regional occurrence of ore bodies in the deep strata. This presents promising research value for further exploration.

However, our study faces unresolved challenges associated with fluid migration, convergence, and mineralization reactions. In the realm of future research endeavors, there exist pivotal areas that warrant profound exploration within the sandbox modeling framework. A paramount focus should be directed toward enhancing the imaging of internal structures and fluid distributions, surmounting challenges such as sandbox sealing, and monitoring the entire process of ore-forming fluid migration, including chemical reactions and precipitation. Furthermore, forthcoming models ought to factor in density disparities in internal structural deformation and fluid charging, encompassing critical parameters like the temperature and velocity of ore-bearing fluids. An imperative facet of future investigations involves exploring the three-dimensional spatial variations in fault-fold structures during compression processes. The integration of three-dimensional discrete element numerical models with physical sandbox models stands out as a promising avenue, offering a holistic comprehension that transcends observable limitations and unveils intricate details.

6. Conclusions

This paper investigates the structural deformation characteristics of thrust–fold structures by means of analogue modeling, and obtains the following main insights by combining the PIV analysis technique:

(1) The ore-controlling thrust faults in the Huize mine district propagating towards the foreland in piggyback propagation. The number of interlayer-sliding faults correlates positively with the spacing of the thrust faults and negatively with their number and dip angle.

(2) Particle image velocimetry (PIV) showed that in the top view, the position of minimum horizontal strain in each stage is the position of thrust faults. In the cross-sectional view, the development location of thrust faults shows the low-value area of the velocity field and surface strain field, and the development location of the interlayer-sliding fault and tensile space in the core of the fold displays the high-value area of the velocity field and surface strain field.

(3) Model 3 (shallow Baizuo Formation and deep Dengying Formation) closely resembles the actual geological model, suggesting the possibility of mining area-scale interlayer-sliding faults in the deep Dengying Formation. However, it is essential to employ a combination of various methods to validate this observation thoroughly and gain a comprehensive understanding.