*5.2. Mineral-Exploration Indications*

*5.2. Mineral-Exploration Indications*  The 3D alteration-zoning model (Figure 19) shows the location and geometric shape of each alteration zone and the gold mineralization and ore body [21,48]. The model clearly displays the spatial relationships among different alteration types and the ore bodies and fault structures and confirms the relative positions of alteration zones. The alteration zone is relatively continuous, and the phengite zone and underlying kaolinite zone are basically consistent with the ore body enrichment [34,48]. Based on the regional spreading of 3D fracture structures and ore bodies, the main Jiaojia fault was shown to be the key to conducting mineral exploration in the area. By developing a 3D model, it is possible to visualize the geological characteristics of the hanging wall and footwall of the ore body's occurrence stratum and their variations along the strike [49]. Understanding the spatial range of alteration-zone mineral assemblages and the relationship between the ore body and fault is of great significance for exploration around the deposit and is conducive to developing the mining plan [49]. In addition, based on the 3D geological model, the predecessors proposed a new method of building 3D mineral prospect with a convo-The 3D alteration-zoning model (Figure 19) shows the location and geometric shape of each alteration zone and the gold mineralization and ore body [21,48]. The model clearly displays the spatial relationships among different alteration types and the ore bodies and fault structures and confirms the relative positions of alteration zones. The alteration zone is relatively continuous, and the phengite zone and underlying kaolinite zone are basically consistent with the ore body enrichment [34,48]. Based on the regional spreading of 3D fracture structures and ore bodies, the main Jiaojia fault was shown to be the key to conducting mineral exploration in the area. By developing a 3D model, it is possible to visualize the geological characteristics of the hanging wall and footwall of the ore body's occurrence stratum and their variations along the strike [49]. Understanding the spatial range of alteration-zone mineral assemblages and the relationship between the ore body and fault is of great significance for exploration around the deposit and is conducive to developing the mining plan [49]. In addition, based on the 3D geological model, the predecessors proposed a new method of building 3D mineral prospect with a convolutional neural network (CNN), thus reducing the uncertainty of exploration targets [50].

lutional neural network (CNN), thus reducing the uncertainty of exploration targets [50]. When the quantity of alteration-zone mineral data in the study area is sparse, the mineralized center can be roughly determined through the IC value, which is associated with the sulfide ore-forming stage in the gold deposit, and then the characteristic IC parameters of muscovite can be introduced to delineate the high-temperature core zone of the gold deposit [16]. In the Zhaoxian gold deposit, the exploration targets can be accu-When the quantity of alteration-zone mineral data in the study area is sparse, the mineralized center can be roughly determined through the IC value, which is associated with the sulfide ore-forming stage in the gold deposit, and then the characteristic IC parameters of muscovite can be introduced to delineate the high-temperature core zone of the gold deposit [16]. In the Zhaoxian gold deposit, the exploration targets can be accurately

rately located along with datasets such as the distribution of Al–OH absorption characteristics of sericite (Pos2200 and IC) with pyritization alteration, sericite–kaolinite and

The results of alteration zoning provide an important reference for metallurgical test design. An accurate and comprehensive alteration combination diagram is crucial for optimizing the beneficiation process. The study of gold migration in the Zhaoxian gold deposit showed that each type of alteration accounts for different proportions of chalcopyrite and pyrite [25]. With the support of SWIR analysis, the alteration model established for the Zhaoxian gold deposit describes the precipitation characteristics of gold in different occurrence states, which is essential for the possible grinding and concentration processes in future prefeasibility work [21]. Additionally, because different layered silicate minerals have different flotation reactions, the layered silicate mineral assemblages identified by scalar extraction can help to understand the clay mineral content changes, thus helping to reduce the impact of clay minerals on flotation and bringing obvious economic

and microscopic identification, and geochemical data.

benefits to mineral processing [51].

located along with datasets such as the distribution of Al–OH absorption characteristics of sericite (Pos2200 and IC) with pyritization alteration, sericite–kaolinite and phengite alteration zones, the change in kaolinite crystallinity, hand specimen observation and microscopic identification, and geochemical data.

The results of alteration zoning provide an important reference for metallurgical test design. An accurate and comprehensive alteration combination diagram is crucial for optimizing the beneficiation process. The study of gold migration in the Zhaoxian gold deposit showed that each type of alteration accounts for different proportions of chalcopyrite and pyrite [25]. With the support of SWIR analysis, the alteration model established for the Zhaoxian gold deposit describes the precipitation characteristics of gold in different occurrence states, which is essential for the possible grinding and concentration processes in future prefeasibility work [21]. Additionally, because different layered silicate minerals have different flotation reactions, the layered silicate mineral assemblages identified by scalar extraction can help to understand the clay mineral content changes, thus helping to reduce the impact of clay minerals on flotation and bringing obvious economic benefits to mineral processing [51].

#### **6. Conclusions**

The analyses of the SWIR spectra show that muscovite, carbonate, kaolinite, montmorillonite, and chlorite are the main alteration-zone minerals in the Zhaoxian gold deposit, among which phengite is closely related to gold mineralization. The mineral assemblages in the study area have obvious zonality, and the changes between zones are gradual. Alteration-zone I consists of sericite–carbonate–chlorite and developed in deep granite. Phengite–carbonate zones are mainly distributed in alteration-zones II and III. Strong pyrite– sericite–quartz alteration is developed in alteration-zone III, and kaolinite is not developed, whereas alteration-zone II contains a small quantity of kaolinite-px. Sericite–carbonate– kaolinite-wx is developed in sericite–quartz granitized cataclastic rock (alteration-zone IV). Alteration-zone V (sericite–carbonate) is located in the monzogranite.

The 3D geological and spectral scalar models show that the study area has obvious tectonic control features, with spatial correlation between alteration zones, fracture structures, and ore bodies. The mineralization zone is a semiopen shear space and provides sufficient space for the water–rock metasomatic reaction of the fluid. The compressive torsional features and concave–convex section zone (depth 3000 m) are the main signs of 3D geological ore-body modeling in the Zhaoxian gold deposit for ore prospecting. A large quantity of high-crystallinity phengite was found near the mineralization and in the deep area, which indicates that a large quantity of gold in the fracture was precipitated in a hydrothermal environment with gradually lower temperatures and relatively higher pH.

The SWIR spectral features indicate that phengite is the proximal alteration-zone mineral to gold mineralization in a strong pyritic sericitization zone. Phengite with relatively high Pos2200 values (>2205 nm) as well as relatively high SWIR-IC values can correspond well to gold mineralization. Both Pos2200 and SWIR-IC can be used as mineralization indicators for the study area.

**Author Contributions:** Conceptualization, G.W.; methodology, B.L., X.L. and H.W.; software, B.L., X.L. and H.J.; validation, Y.P., X.Z. and H.W.; formal analysis, Y.P., X.Z., Z.Y. and H.W.; investigation, B.L. and G.W.; project administration, G.W. and X.L.; data curation, B.L., X.L. and G.W.; writing—original draft preparation, B.L.; writing—review and editing, G.W. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the open project of the Shandong Provincial Engineering Laboratory of Application and Development of Big Data for Deep Gold Exploration (Grant No. SDK202210) and National Key Research and Development Program of China (Grant No. 2022YFC2903604).

**Data Availability Statement:** The data presented in this study are available on request from the corresponding author. The data are not publicly available due to the confidentiality of some of the data.

**Acknowledgments:** The authors thank the Shandong Xincheng Gold Mining Co. Ltd. for its cooperation in field work. We are grateful to Ling Zuo for her constructive comments and discussion. We also thank Xuewei Shao for the improvements to the pictures.

**Conflicts of Interest:** The authors declare no conflict of interest.
