stage (Ⅳ) Veinlet or reticulate Quartz, carbonate, and a small *3.1. 3D Geological Modeling*

Three-dimensional geological modeling technology uses the knowledge of geology, geostatistics, space science, and other fields to model the possible extent of geological objects in deep geological bodies based on surface geological data, underground drill-hole data [26,27], etc. Modeling software enables 3D visualization, spatial feature analysis, geological interpretation, and resource evaluation [26,27]. This study used SKUA-GOCAD 18.0 (18.0, Emerson, St. Louis, MI, USA) to establish a 3D geological model of the Zhaoxian gold deposit. In this work, the geological data used included a geological map, several exploration sections, and 19 drill holes of more than 1400 m depths. The four-step 3D geological modeling method is given as follows.

Intercalation of quartz

calcite veins No

(1) A 3D fault model is created based on 1:2000 exploration-line profile data. The image coordinates are corrected by MapGIS (6.7, Wuhan Zhongdi Information Engineering Co., Ltd., Wuhan, China) to obtain the fault-boundary lines, and then SKUA-GOCAD is used to connect the fault-boundary lines of adjacent profiles and perform surface smoothing.

(2) Based on the exploration-line profile and drill-hole data, the ore-body boundary vectorization is carried out to construct a 3D ore-body model of the developed gold deposit.

(3) According to the geological map, exploration-line profile, and drill-hole data, the formation surface profile is extracted. Based on the workflow of SKUA-GOCAD software, stratum modeling is carried out and the geological significance of curves is given. The block model is established to generate a 3D stratum model.

(4) A kriging spatial interpolation model is established using drill-hole geochemical data. The specific steps are to extract Au grade information first, then establish a grid model and generate ellipsoids using variogram analysis, and, finally, apply kriging for spatial interpolation.

#### *3.2. Spectral Analysis*

SWIR spectroscopy is based on the selective absorption characteristics of some specific groups in minerals to SWIR light. The spectral curves can be matched with the standard minerals or mineral assemblages in the spectral library through algorithms (such as The Spectral Assistant in Spectral Geologist (TSG8) software (TSGTM 8, CSIRO, North Ryde, Australia)) to identify minerals (Figure 3) [28,29]. When a sample is illuminated by light in a spectrometer, the molecular bonds in the minerals stretch and bend causing vibrations that result in the adsorption of certain wavelengths of light. In phyllosilicates (including white mica, kaolinite, and montmorillonite), the molecular bonds that cause such vibrations are mainly those in water and hydroxyl groups, including Al–OH, Mg–OH, and Fe–OH [30,31]. Furthermore, a scalar-extraction method has been constructed. This method takes the specific absorption characteristics of the spectrum as the research object (Figure 3), extracts the scalar in the spectral curve, and provides information about the mineral composition and displacement caused by changes in the cationic composition (for example, Tschermak substitution in muscovite) according to the scalar [32,33]. The use of scalars can improve traceability and comparability between different datasets [21]. *Minerals* **2022**, *12*, 1272 6 of 27

**Figure 3.** Common spectral profiles and absorption positions in short-wavelength infrared (SWIR) spectrometry (after GMEX, 2008 [30]). **Figure 3.** Common spectral profiles and absorption positions in short-wavelength infrared (SWIR) spectrometry (after GMEX, 2008 [30]).

locations are roughly equidistant, and intensive sampling was carried out near the mineralization. The sample locations included the surrounding rock, alteration zone, and mineralization center. The spectral analysis of these samples identifies the fluid migration and

**Figure 4.** Locations of short-wavelength infrared (SWIR) test holes at the mine site ((**a**)—top view;

The SWIR spectrometer used in the study area is an oreXpress mineral analyzer (oreXpressTM, Spectral Evolution, Haverhill, MA, USA). The effective test wavelength range of the instrument is 350–2500 nm, which has a good signal-to-noise ratio (SNR) [23]. When the contact probe is used to test the sample, real-time mineral identification is carried out

To comprehensively analyze the spectral characteristics of the study area and establish a 3D spectral model, the data involved in this work included five exploration lines in the Zhaoxian gold deposit area and a total of eight drill holes, of which the No. 88 Explo-

element migration in the study area.

(**b**)—side view).

To comprehensively analyze the spectral characteristics of the study area and establish a 3D spectral model, the data involved in this work included five exploration lines in the Zhaoxian gold deposit area and a total of eight drill holes, of which the No. 88 Exploration Line was mainly used for the scalar extraction of layered silicates (Figure 4). Sample locations are roughly equidistant, and intensive sampling was carried out near the mineralization. The sample locations included the surrounding rock, alteration zone, and mineralization center. The spectral analysis of these samples identifies the fluid migration and element migration in the study area. To comprehensively analyze the spectral characteristics of the study area and establish a 3D spectral model, the data involved in this work included five exploration lines in the Zhaoxian gold deposit area and a total of eight drill holes, of which the No. 88 Exploration Line was mainly used for the scalar extraction of layered silicates (Figure 4). Sample locations are roughly equidistant, and intensive sampling was carried out near the mineralization. The sample locations included the surrounding rock, alteration zone, and mineralization center. The spectral analysis of these samples identifies the fluid migration and element migration in the study area.

**Figure 3.** Common spectral profiles and absorption positions in short-wavelength infrared (SWIR)

spectrometry (after GMEX, 2008 [30]).

*Minerals* **2022**, *12*, 1272 6 of 27

**Figure 4.** Locations of short-wavelength infrared (SWIR) test holes at the mine site ((**a**)—top view; (**b**)—side view). **Figure 4.** Locations of short-wavelength infrared (SWIR) test holes at the mine site ((**a**)—top view; (**b**)—side view).

The SWIR spectrometer used in the study area is an oreXpress mineral analyzer (oreXpressTM, Spectral Evolution, Haverhill, MA, USA). The effective test wavelength range of the instrument is 350–2500 nm, which has a good signal-to-noise ratio (SNR) [23]. When the contact probe is used to test the sample, real-time mineral identification is carried out The SWIR spectrometer used in the study area is an oreXpress mineral analyzer (oreXpressTM, Spectral Evolution, Haverhill, MA, USA). The effective test wavelength range of the instrument is 350–2500 nm, which has a good signal-to-noise ratio (SNR) [23]. When the contact probe is used to test the sample, real-time mineral identification is carried out by spectral matching through proprietary EZ-ID spectral data acquisition software (1.4, Spectral Evolution, Haverhill, MA, USA), which has the United States Geological Survey and SpecMIN mineral libraries built in. The sampling bandwidth of the spectrometer is 1 nm, and the minimum scanning speed is 100 milliseconds. When performing spectral testing, the instrument needs to be preheated for 10–30 min, and then an international standard spectral whiteboard is used for calibration. During the testing process, the core was strictly guaranteed to be dry and clean.

Spectral Geologist software (TSG8) (TSGTM 8, CSIRO, North Ryde, Australia) was used to process the spectral data. The software matches the waveform of the spectral curve and the position of the absorption peak with the spectral library to determine mineral types and extract spectral information [34]. In the data processing, a Hull quotient removal of the spectral data was carried out. A baseline (Hull) was fitted to each reflectance spectrum. At each wavelength, the reflectance was divided by the corresponding value on the baseline (the Hull quotient) to remove the background effect [32,35]. The absorption characteristics of the spectrum can be enhanced by correcting the baseline [30].

This work adopted the PFIT (A TSG-provided method for extracting scalars to extract more accurate spectral feature parameters)processing method, which is based on the polynomial fitting of the spectral curve after removing the Hull quotient to extract the spectral features [9,10,36]. When analyzing layered silicate minerals in this work, the fourth derivative is calculated after removing the Hull quotient to obtain the fourth-derivative spectrum and extract the scalars. The minimum absorption peak position of Al–OH at 2200 nm and the absorption depths at 2200 nm, 1900 nm, and 2160 nm are extracted. The specific meanings are shown in Table 2.


**Table 2.** Scalar quantity and extraction used to identify white mica, chlorite, and kaolinite in TSG8 (modified by [37]).

#### **4. Results**

#### *4.1. 3D Geological Model*

The 3D geological model used for alteration modeling in the Zhaoxian mining area includes a 3D fault model and a 3D ore-body and grade-interpolation model. A 3D structural alteration-zone model is constructed to constrain the spatial range of the alteration-zone mineral parameters and the Au grade-interpolation modeling.

#### 4.1.1. 3D Fault Modeling

Using SKUA-GOCAD software, 3D ore-body and fault models of the Xincheng, Zhaoxian, Sizhuang, and Wang'ershan deposits were established from drill holes and geological sections, which can reflect the spatial location and geometry of the fault structures in the region, as well as the spatial correspondence between them and the main ore bodies. The 3D fault and ore-body model shown in Figure 5a was established by the location of the fault clay in the drill holes. The main fault surface is continuous and stable, extending from west to east; the fault controls the Xincheng, Zhaoxian, and Sizhuang gold deposits. The secondary faults in the footwall of the main fault zone, such as the Sanshandao and Wang'ershan faults, are relatively developed, and the occurrence changes of the main and secondary faults are in a gentle wave shape in the strike and tendency. The concave or convex zones in Figure 5a,b are the intrusion body boundaries of the Linglong-series monzogranite and the Guojialing-series granodiorite at depth. Additionally, the regional structure controls the distribution of gold ore bodies, keeping them close to the footwall with good continuity (Figure 5b).

#### 4.1.2. 3D Ore-Body and Au Grade-Interpolation Modeling

The 3D gold-deposit ore-body modeling of the area uses the traditional explicit modeling method, including roughly determining the ore-body range using the ore-body boundary line determined from mining engineering and drill-hole datasets (Figures 5a and 6). For this work, additional gold grade geochemistry datasets were acquired in the drill holes [18]. The constructed ore-body model is shown in Figure 6. The ore body has inclined veins and stable shape, and its occurrence is consistent with the fault (Figure 5b), most of which are distributed in the pyrite–sericite–quartz alteration zone (Figure 6). There is a close spatial and temporal relationship between the ore body and pyrite–sericite–quartz alteration zone.

**4. Results** 

*4.1. 3D Geological Model* 

4.1.1. 3D Fault Modeling

with good continuity (Figure 5b).

The 3D geological model used for alteration modeling in the Zhaoxian mining area includes a 3D fault model and a 3D ore-body and grade-interpolation model. A 3D structural alteration-zone model is constructed to constrain the spatial range of the alteration-

Using SKUA-GOCAD software, 3D ore-body and fault models of the Xincheng, Zhaoxian, Sizhuang, and Wang'ershan deposits were established from drill holes and geological sections, which can reflect the spatial location and geometry of the fault structures in the region, as well as the spatial correspondence between them and the main ore bodies. The 3D fault and ore-body model shown in Figure 5a was established by the location of the fault clay in the drill holes. The main fault surface is continuous and stable, extending from west to east; the fault controls the Xincheng, Zhaoxian, and Sizhuang gold deposits. The secondary faults in the footwall of the main fault zone, such as the Sanshandao and Wang'ershan faults, are relatively developed, and the occurrence changes of the main and secondary faults are in a gentle wave shape in the strike and tendency. The concave or convex zones in Figure 5a,b are the intrusion body boundaries of the Linglong-series monzogranite and the Guojialing-series granodiorite at depth. Additionally, the regional structure controls the distribution of gold ore bodies, keeping them close to the footwall

zone mineral parameters and the Au grade-interpolation modeling.

**Figure 5.** (**a**)—Northwestern Jiaodong Peninsula three-dimensional (3D) fault and ore-body model; (**b**)—3D ore-body and fault model of Zhaoxian gold deposit. **Figure 5.** (**a**)—Northwestern Jiaodong Peninsula three-dimensional (3D) fault and ore-body model; (**b**)—3D ore-body and fault model of Zhaoxian gold deposit.

4.1.2. 3D Ore-Body and Au Grade-Interpolation Modeling The 3D gold-deposit ore-body modeling of the area uses the traditional explicit modeling method, including roughly determining the ore-body range using the ore-body boundary line determined from mining engineering and drill-hole datasets (Figure 5a, Figure 6). For this work, additional gold grade geochemistry datasets were acquired in the drill holes [18]. The constructed ore-body model is shown in Figure 6. The ore body has inclined veins and stable shape, and its occurrence is consistent with the fault (Figure 5b), most of which are distributed in the pyrite–sericite–quartz alteration zone (Figure 6). There is a close spatial and temporal relationship between the ore body and pyrite–seric-To intuitively display the spatial distribution behavior of the gold grades in the study area, this study used the drill-hole datasets to perform 3D explicit modeling. Through the geostatistical analysis of the gold grade data at different depths in the drill hole and calculations of the variograms in different directions, each ore block is given a search radius ellipsoid. This process estimates the average-grade space allocation of each ore block (Figure 7a). The 3D grade-interpolation model is shown in Figure 7b. The 3D grade-interpolation model is constrained by the alteration zone. From the interpolation results, there are numerous high-grade ore areas within the alteration zone, and within the constrained range, the grade gradually increases from shallow to deep.

**Figure 6.** Three-dimensional (3D) ore-body modeling of Zhaoxian gold deposit.

To intuitively display the spatial distribution behavior of the gold grades in the study area, this study used the drill-hole datasets to perform 3D explicit modeling. Through the geostatistical analysis of the gold grade data at different depths in the drill hole and calculations of the variograms in different directions, each ore block is given a search radius

ite–quartz alteration zone.

(**b**)—3D ore-body and fault model of Zhaoxian gold deposit.

ite–quartz alteration zone.

4.1.2. 3D Ore-Body and Au Grade-Interpolation Modeling

**Figure 6.** Three-dimensional (3D) ore-body modeling of Zhaoxian gold deposit. **Figure 6.** Three-dimensional (3D) ore-body modeling of Zhaoxian gold deposit. range, the grade gradually increases from shallow to deep.

**Figure 5.** (**a**)—Northwestern Jiaodong Peninsula three-dimensional (3D) fault and ore-body model;

The 3D gold-deposit ore-body modeling of the area uses the traditional explicit modeling method, including roughly determining the ore-body range using the ore-body boundary line determined from mining engineering and drill-hole datasets (Figure 5a, Figure 6). For this work, additional gold grade geochemistry datasets were acquired in the drill holes [18]. The constructed ore-body model is shown in Figure 6. The ore body has inclined veins and stable shape, and its occurrence is consistent with the fault (Figure 5b), most of which are distributed in the pyrite–sericite–quartz alteration zone (Figure 6). There is a close spatial and temporal relationship between the ore body and pyrite–seric-

**Figure 7.** Three-dimensional (3D) fault and grade-interpolation modeling of Zhaoxian gold deposit. (**a**)—Variograms in 3D environment in Jiaojia gold belt; (**b**)—3D grade-interpolation model of Zhaoxian gold deposit. **Figure 7.** Three-dimensional (3D) fault and grade-interpolation modeling of Zhaoxian gold deposit. (**a**)—Variograms in 3D environment in Jiaojia gold belt; (**b**)—3D grade-interpolation model of Zhaoxian gold deposit.

#### 4.1.3. 3D Alteration-Zone Modeling 4.1.3. 3D Alteration-Zone Modeling

Here, the alteration-zone model is constructed based on the pyrite–sericite–quartz alteration lithology that is symmetrically distributed on the hanging and lower walls of the fault[38]. The outline of the unit is extracted from the 1:2000 exploration-line profile. Here, the alteration-zone model is constructed based on the pyrite–sericite–quartz alteration lithology that is symmetrically distributed on the hanging and lower walls of the fault [38]. The outline of the unit is extracted from the 1:2000 exploration-line profile.

The structural morphology and spatial distribution of the altered zone can be described by the altered structure model. The final 3D alteration-zone model is shown in Figure 8.

the fault, and the morphology and distribution are controlled by the fracture. The range of the alteration zone is larger than the mineralization range, and its distribution is in the

form of a belt, intersected by the main fracture surface.

The structural morphology and spatial distribution of the altered zone can be described by the altered structure model. The final 3D alteration-zone model is shown in Figure 8. The 3D model can better demonstrate the spatial correlations among the fracture structure, ore body, and alteration zone. The gold ore is mainly distributed in the footwall of the fault, and the morphology and distribution are controlled by the fracture. The range of the alteration zone is larger than the mineralization range, and its distribution is in the form of a belt, intersected by the main fracture surface. *Minerals* **2022**, *12*, 1272 11 of 27

**Figure 8.** Three-dimensional tectonic alteration-zone and ore-body modeling.(**a**)—front view; **Figure 8.** Three-dimensional tectonic alteration-zone and ore-body modeling.(**a**)—front view; (**b**)—side view.

#### (**b**)—side view *4.2. Interpretation Based on SWIR Spectra*

*4.2. Interpretation Based on SWIR Spectra*  SWIR spectroscopy results identified the main alteration-mineral groups in the eight holes collected in the Zhaoxian gold deposit as white mica, carbonate (siderite and magnesite), kaolinite, smectite, and chlorite, with most minerals co-occurring with white mica. According to the spectral interpretation, the white mica of the Zhaoxian deposit mainly consists of muscovite, paragonite, phengite, muscovitic illlite, paragonitic illlite, and phengitic illlite; muscovitic illlite, for example, is an intermediate product of the conver-SWIR spectroscopy results identified the main alteration-mineral groups in the eight holes collected in the Zhaoxian gold deposit as white mica, carbonate (siderite and magnesite), kaolinite, smectite, and chlorite, with most minerals co-occurring with white mica. According to the spectral interpretation, the white mica of the Zhaoxian deposit mainly consists of muscovite, paragonite, phengite, muscovitic illlite, paragonitic illlite, and phengitic illlite; muscovitic illlite, for example, is an intermediate product of the conversion of muscovite to illite (the latter three are classified in this work as muscovite, paragonite, and phengite and not separately discussed).

sion of muscovite to illite (the latter three are classified in this work as muscovite, paragonite, and phengite and not separately discussed). Kaolinite is the most widely distributed clay mineral, an Al-rich silicate that forms through acidic alteration. The crystallinity of kaolinite can be identified by SWIR spectroscopy [34]. The mineral has typical double absorption peaks near 2160 nm and 2206 nm, the intensities of which depend on the type of kaolinite mineral and its crystallinity. Therefore, the influence of kaolinite on Pos2200 needs to be considered when a mixture of white mica and kaolinite is present [16,39,40]. In the Zhaoxian gold deposit, the kaolinite is mainly combined with white mica as a second major constituent, with only a small proportion being found as a single mineral.

In the Zhaoxian main ore-body zone, the chlorite is mainly found in deep granite in small quantities and always associated with muscovite and carbonate. Chlorite has diagnostic Fe–OH and Mg–OH absorptions centered at 2250 and 2350 nm. Because the Mg–OH in chlorite may be affected by the presence of carbonate, Fe–OH absorption is commonly used to determine the composition in the chlorite.

#### *4.3. Alteration Features and Zonation*

The ore bodies in the study area are controlled by the Jiaojia Fault and are mainly distributed in fractured, altered rocks [8]. Drill-hole cores are mainly concentrated in the northern part of the Zhaoxian gold deposit, and most of the ore bodies are present. The distribution of ore bodies along Line 88 is continuous, and their thicknesses are stable. Therefore, this study mainly focused on the Line 88 drill holes to study the cross-section of the ore body and host rock and to illustrate the spatial distribution of SWIR alterationzone minerals.

#### 4.3.1. No. 88 Exploration Line

The No. 88 Exploration Line includes drill holes 88ZK01, 88ZK03, and 88ZK05 and crosses the hanging wall and footwall of the main fracture. The hanging wall of the main fracture is composed of medium-grained monzogranite and sericite-quartz altered rock. The ore bodies developed in the footwall of the fault zone, including most of the I, II-1, and II-2 ore bodies. Both ends of the ore bodies are pinched out, and their occurrence is controlled by the Jiaojia fault. From the center of the ore body to the outside, there is a symmetrical distribution of pyrite–sericite–quartz altered rock, pyrite-sericitized granitic altered rock, sericite–quartz altered rock" and medium-grained monzonitic granites (Figure 9). The ore body is relatively simple, with strong continuity, and has good metallogenic conditions [8,23]. Ore body I is present in the pyrite–sericite–quartz cataclastic rocks and sericite-quartz granitic cataclastic rocks. Ore body II mainly exists in sericite-quartz granitic cataclastic rocks. All the drill holes penetrated the intact alteration zone.

Drill-hole 88ZK01 is an oblique drill with a test depth of 905.46 m to 1594.99 m. SWIR spectroscopy indicates that it contains diorite and porphyrite interlayers. The lithology histogram can be described as follows. Five main alteration-zone mineral groups were extracted by SWIR spectroscopy, mainly white mica, kaolinite, smectite, carbonate, and other-Al–OH minerals; white mica was the main alteration-zone mineral (Figure 10). The mineralization is concentrated at approximately 1300 m to 1469 m. The type of sericite is muscovite, and its distribution basically corresponds to the mineralization. Kaolinite is less developed, and the muscovite–carbonate alteration zone is also developed. The distribution of alteration-zone minerals near the mineralization can be divided into five zones. The shallow depth of 1070 m is alteration-zone V, and the corresponding lithology is monzogranite. The main minerals are Al-rich sericite, carbonate, and a small quantity of montmorillonite, among which the carbonate is well-developed. The mineral assemblage can be preliminarily classified as the quartz–carbonate mineralization stage [23]. Alterationzone IV extends from 1070 m to 1300 m, where large quantities of Al-rich sericite–kaolinite alteration-zone minerals are developed, and montmorillonite and carbonate are generally developed. This layer has a unique kaolinite mineral with good crystallinity (kaolinite-wx). The 1469–1546.2 m deep mineralization is alteration-zone II, and the mineral assemblage is sericite–carbonate and a small quantity of low-crystallinity kaolinite (kaolinite-px). The Pos2200 value of sericite in this zone is lower than it is in zone IV. Chlorite is developed only in the monzonitic granite formation of alteration-zone I at 1546.2 m, and the mineral assemblage is sericite–carbonate–chlorite. Generally, sericite is widely distributed in drillhole 88ZK01, and there are obvious high Pos2200 values near the mineralization, which is developed in the pyrite–sericite–quartz cataclastic rock. The content of montmorillonite is low, there is no obvious regularity, and the carbonate alteration is relatively continuous (Figure 10).

Drill-hole 88ZK03 was vertically drilled and spectroscopically tested at depths of 870.39 m to 1679.77 m. There are gabbro interlayers near the mineralization, and potassic granite gneiss is developed in the deep part. There are tectonic cataclastic rocks near the Jiaojia fault zone. The lithology histogram is described as follows (Figure 11). The zoning of the mineral assemblages is the same as that of 88ZK01, where the shallow 870.39–1123.32 m area is alteration-zone V, and the corresponding lithology is monzogranite and sericite– quartz granite, mainly consisting of Al-rich muscovite and carbonate. Alteration-zone IV is located near the fault, with depths of 1123.32–1345.09 m, and the pyrite sericitization is obvious. The mineralization is roughly concentrated at 1345.0–1500 m in alterationzone II, and strong pyrite–sericite–quartz and sericite alterations are developed in the cataclastic rock (Figure 11). A large quantity of phengite appears in this layer, and kaolinite is rare. Alteration-zone I, which is developed in potassic granitic gneiss at depths of 1621–1679.77 m, contains unique chlorite minerals with relative contents higher than those of 88ZK01. *Minerals* **2022**, *12*, 1272 13 of 27

**Figure 9.** Cross-section of No. 88 Exploration Line of Zhaoxian gold deposit. (kaolinite-wx). The 1469–1546.2 m deep mineralization is alteration-zone II, and the **Figure 9.** Cross-section of No. 88 Exploration Line of Zhaoxian gold deposit.

Drill-hole 88ZK01 is an oblique drill with a test depth of 905.46 m to 1594.99 m. SWIR

extracted by SWIR spectroscopy, mainly white mica, kaolinite, smectite, carbonate, and other-Al–OH minerals; white mica was the main alteration-zone mineral (Figure 10). The mineralization is concentrated at approximately 1300 m to 1469 m. The type of sericite is muscovite, and its distribution basically corresponds to the mineralization. Kaolinite is less developed, and the muscovite–carbonate alteration zone is also developed. The distribution of alteration-zone minerals near the mineralization can be divided into five zones. The shallow depth of 1070 m is alteration-zone V, and the corresponding lithology is monzogranite. The main minerals are Al-rich sericite, carbonate, and a small quantity of montmorillonite, among which the carbonate is well-developed. The mineral assemblage can be preliminarily classified as the quartz–carbonate mineralization stage [23]. Alteration-zone IV extends from 1070 m to 1300 m, where large quantities of Al-rich sericite– kaolinite alteration-zone minerals are developed, and montmorillonite and carbonate are generally developed. This layer has a unique kaolinite mineral with good crystallinity

mineral assemblage is sericite–carbonate and a small quantity of low-crystallinity kaolinite (kaolinite-px). The Pos2200 value of sericite in this zone is lower than it is in zone IV. Chlorite is developed only in the monzonitic granite formation of alteration-zone I at 1546.2 m, and the mineral assemblage is sericite–carbonate–chlorite. Generally, sericite is widely distributed in drill-hole 88ZK01, and there are obvious high Pos2200 values near the mineralization, which is developed in the pyrite–sericite–quartz cataclastic rock. The content of montmorillonite is low, there is no obvious regularity, and the carbonate alter-

ation is relatively continuous (Figure 10).

**Figure 10.** Distribution of alteration-zone minerals in drill-hole 88ZK01. ①—Sericite–quartz granitized cataclastic rock; ②—sericitized granite; ③—biotite monzogranite; ④—white diorite porphyrite; ⑤—sericite–quartz cataclastic rock; ⑥—pyrite–sericite–quartz granitic cataclastic rock; ⑦—pyrite–sericite–quartz cataclastic rock; ⑧—potassic sericite–quartz granitic cataclastic rock. 2200D indicates relative abundance of sericite minerals; 2160D indicates relative abundance of kaolinite; I—sericite–carbonate–chlorite alteration-zone; II—sericite–carbonate–kaolinite-px alterationzone; III—phengite–carbonate–kaolinite-wx alteration-zone; IV—phengite–carbonate alterationzone; V—sericite–carbonate alteration-zone. **Figure 10.** Distribution of alteration-zone minerals in drill-hole 88ZK01. <sup>1</sup> —Sericite–quartz granitized cataclastic rock; <sup>2</sup> —sericitized granite; <sup>3</sup> —biotite monzogranite; <sup>4</sup> —white diorite porphyrite; <sup>5</sup> —sericite–quartz cataclastic rock; <sup>6</sup> —pyrite–sericite–quartz granitic cataclastic rock; <sup>7</sup> —pyrite–sericite–quartz cataclastic rock; <sup>8</sup> —potassic sericite–quartz granitic cataclastic rock. 2200D indicates relative abundance of sericite minerals; 2160D indicates relative abundance of kaolinite; I—sericite–carbonate–chlorite alteration-zone; II—sericite–carbonate–kaolinite-px alterationzone; III—phengite–carbonate–kaolinite-wx alteration-zone; IV—phengite–carbonate alteration-zone; V—sericite–carbonate alteration-zone.

Drill-hole 88ZK03 was vertically drilled and spectroscopically tested at depths of 870.39 m to 1679.77 m. There are gabbro interlayers near the mineralization, and potassic granite gneiss is developed in the deep part. There are tectonic cataclastic rocks near the Jiaojia fault zone. The lithology histogram is described as follows (Figure 11). The zoning of the mineral assemblages is the same as that of 88ZK01, where the shallow 870.39– 1123.32 m area is alteration-zone V, and the corresponding lithology is monzogranite and sericite–quartz granite, mainly consisting of Al-rich muscovite and carbonate. Alterationzone IV is located near the fault, with depths of 1123.32–1345.09 m, and the pyrite The sampling depth of drill-hole 88ZK05 is deeper than that in the previous two drill holes, ranging from 1055.05 m to 1800 m. The drill hole passes through many ore veins, which pinch out on both sides. Compared with the previous two drill holes, the shallow area lacks pyrite–sericite–quartz granitoid cataclastic rock. The lithologic histogram for drillhole 88ZK05 can be described as follows (Figure 12). Owing to the increased acquisition depth, there was no alteration-zone V. Alteration-zone I is located in the granitic cataclastic rocks and sericite–quartz cataclastic rocks at 1774.5–1800 m. Compared with the other two drill holes, the content of montmorillonite in this alteration zone is relatively high. Alteration-zone II developed at 1599–1774.5 m. Alteration-zone III is the mineralized zone. Unlike the other drilling holes, there is a small quantity of kaolinite near the mineralization. Alteration-zone IV is shallower than 1475 m. The 88ZK05 drill hole is quite different from the previous two drill holes owing to the mineralized area and multiple ore bodies. A large quantity of sericite and carbonate are continuously distributed in the drill hole, with high relative contents, including abundant kaolinite-wx (Figure 12).

those of 88ZK01.

sericitization is obvious. The mineralization is roughly concentrated at 1345.0–1500 m in alteration-zone II, and strong pyrite–sericite–quartz and sericite alterations are developed in the cataclastic rock (Figure 11). A large quantity of phengite appears in this layer, and kaolinite is rare. Alteration-zone I, which is developed in potassic granitic gneiss at depths of 1621–1679.77 m, contains unique chlorite minerals with relative contents higher than

**Figure 11.** Distribution of alteration-zone minerals in drill-hole 88ZK03. ①—Biotite monzonitic granite; ②—sericite monzogranite; ③—pyrite–sericite–quartz granite; ④—pyrite–sericite–quartz granitic cataclastic rock; ⑤—tectonic cataclastic rock; ⑥—lithified cataclastic rock; ⑦—gabbro; ⑧—sericite–quartz cataclastic rock; ⑨—potassic granitic gneiss. 2200D indicates relative abundance of sericite-group minerals; ⑩—2160D indicates relative abundance of kaolinite; I—sericite– carbonate–chlorite alteration-zone; II—sericite–carbonate–kaolinite-px alteration-zone; III phengite–carbonate–kaolinite-wx alteration-zone; IV—phengite–carbonate alteration-zone; V—sericite–carbonate alteration-zone. **Figure 11.** Distribution of alteration-zone minerals in drill-hole 88ZK03. <sup>1</sup> —Biotite monzonitic granite; <sup>2</sup> —sericite monzogranite; <sup>3</sup> —pyrite–sericite–quartz granite; <sup>4</sup> —pyrite–sericite–quartz granitic cataclastic rock; <sup>5</sup> —tectonic cataclastic rock; <sup>6</sup> —lithified cataclastic rock; <sup>7</sup> —gabbro; <sup>8</sup> —sericite–quartz cataclastic rock; <sup>9</sup> —potassic granitic gneiss. 2200D indicates relative abundance of sericite-group minerals; <sup>10</sup>—2160D indicates relative abundance of kaolinite; I—sericite–carbonate–chlorite alterationzone; II—sericite–carbonate–kaolinite-px alteration-zone; III—phengite–carbonate–kaolinite-wx alteration-zone; IV—phengite–carbonate alteration-zone; V—sericite–carbonate alteration-zone.

The sampling depth of drill-hole 88ZK05 is deeper than that in the previous two drill 4.3.2. Spatial Distribution of Alteration-Zone Minerals in the Section of No. 88 Exploration Line

holes, ranging from 1055.05 m to 1800 m. The drill hole passes through many ore veins, which pinch out on both sides. Compared with the previous two drill holes, the shallow area lacks pyrite–sericite–quartz granitoid cataclastic rock. The lithologic histogram for drill-hole 88ZK05 can be described as follows (Figure 12). Owing to the increased acquisition depth, there was no alteration-zone V. Alteration-zone I is located in the granitic cataclastic rocks and sericite–quartz cataclastic rocks at 1774.5–1800 m. Compared with the other two drill holes, the content of montmorillonite in this alteration zone is relatively high. Alteration-zone II developed at 1599–1774.5 m. Alteration-zone III is the mineralized zone. Unlike the other drilling holes, there is a small quantity of kaolinite near the mineralization. Alteration-zone IV is shallower than 1475 m. The 88ZK05 drill hole is quite The No. 88 Exploration Line has obvious alteration zoning, clearly recording the mineralization and alteration characteristics of the deposit area, and the deep mineralization is typical. The SWIR results can be used to divide the alteration-zone mineralization into five alteration zones. Alteration-zone I, which is located in the monzogranite strata, consists of sericite–chlorite and only appears in the deep mineralization. Additionally, with increasing depth, the relative content of chlorite also increases. Alteration-zone II is a sericite–carbonate zone, containing a small quantity of kaolinite-px, usually near the intersection of the pyrite–sericite–quartz granitized cataclastic rock and deep potassic granite zone. Alteration-zone III is a mineralized zone with abundant pyritic sericite; its lithology is mainly pyrite–sericite–quartz cataclastic rock and pyrite–sericite–quartz granitic cataclastic rock. The alteration-zone minerals are phengite–carbonate, with a few other minerals. Alteration-zone IV is the sericite–kaolinite-wx–carbonate zone, which is located in the hanging wall of the fault zone, and is characterized by the development of unique kaolinite-wx. Alteration-zone V is the sericite–carbonate zone, containing small quantities of kaolinite and montmorillonite. Generally, the minerals have obvious zonal distribution, in which phengite is mostly developed near the mineralization (Figures 10–12).

Kaolinite-wx develops on the hanging wall of the fault zone, and the position near the ore body contains almost no kaolinite. Moreover, chlorite only exists in the deep granite plutons far from the mineralization. different from the previous two drill holes owing to the mineralized area and multiple ore bodies. A large quantity of sericite and carbonate are continuously distributed in the drill hole, with high relative contents, including abundant kaolinite-wx (Figure 12).

**Figure 12.** Distribution of alteration-zone minerals in drill-hole 88ZK05. ①—Biotite monzonitic granite; ②—sericite–quartz granitic cataclastic rock; ③—diorite porphyrite; ④—sericite–quartz cataclastic rock; ⑤—pyrite–sericite–quartz granitic cataclastic rock; ⑥—pyrite–sericite–quartz cataclastic rock; ⑦—biotite-bearing monzonitic granitic cataclastic rock. 2200D indicates relative abundance of sericite-group minerals; 2160D indicates relative abundance of kaolinite; I—sericite– carbonate–chlorite alteration-zone; II—sericite–carbonate–kaolinite-px alteration-zone; III phengite–carbonate–kaolinite-wx alteration-zone; IV—phengite–carbonate alteration-zone. **Figure 12.** Distribution of alteration-zone minerals in drill-hole 88ZK05. <sup>1</sup> —Biotite monzonitic granite; <sup>2</sup> —sericite–quartz granitic cataclastic rock; <sup>3</sup> —diorite porphyrite; <sup>4</sup> —sericite–quartz cataclastic rock; <sup>5</sup> —pyrite–sericite–quartz granitic cataclastic rock; <sup>6</sup> —pyrite–sericite–quartz cataclastic rock; <sup>7</sup> —biotite-bearing monzonitic granitic cataclastic rock. 2200D indicates relative abundance of sericite-group minerals; 2160D indicates relative abundance of kaolinite; I—sericite–carbonate– chlorite alteration-zone; II—sericite–carbonate–kaolinite-px alteration-zone; III—phengite–carbonate– kaolinite-wx alteration-zone; IV—phengite–carbonate alteration-zone.

#### 4.3.2. Spatial Distribution of Alteration-Zone Minerals in the Section of No. 88 Exploration Line *4.4. Spectral Characteristics of Sericite*

The No. 88 Exploration Line has obvious alteration zoning, clearly recording the mineralization and alteration characteristics of the deposit area, and the deep mineralization is typical. The SWIR results can be used to divide the alteration-zone mineralization into five alteration zones. Alteration-zone I, which is located in the monzogranite strata, consists of sericite–chlorite and only appears in the deep mineralization. Additionally, with increasing depth, the relative content of chlorite also increases. Alteration-zone II is a sericite–carbonate zone, containing a small quantity of kaolinite-px, usually near the intersection of the pyrite–sericite–quartz granitized cataclastic rock and deep potassic granite zone. Alteration-zone III is a mineralized zone with abundant pyritic sericite; its lithology is mainly pyrite–sericite–quartz cataclastic rock and pyrite–sericite–quartz granitic cataclastic rock. The alteration-zone minerals are phengite–carbonate, with a few other minerals. Alteration-zone IV is the sericite–kaolinite-wx–carbonate zone, which is located in Sericitization is the main alteration type of the Zhaoxian deposit; sericite is distributed in the center of the alteration zone and is closely related to gold mineralization [3]. Sericite is commonly used to describe fine-grained white mica (muscovite, phengite, and/or illite) developed in hydrothermally altered rocks [28]. Muscovite is a dioctahedral layered silicate. When the octahedral coordination cation undergoes Tschermak substitution, the octahedral aluminum is replaced by other cations (such as iron and magnesium) to form three common end members: muscovite, paragonite, and phengite [28]. Tschermak displacement is common in phengite solid solutions and involves coupled displacement between tetrahedral and octahedral layers ((Al↔Si)tet = (Al)↔{Fe2+,Mg}oct) [9]. When the temperature and pressure are changed, the Al in the octahedral position is replaced by other cations, and the ratio of Si to Al becomes greater than 3; that is, Al-poor muscovite (phengite) is formed [41].

The muscovite group has a diagnostic Al–OH absorption signature centered at 2200 nm, which is associated with the vibrations of the octahedral coordination atoms, the wavelength positions of which provide information about the mineral composition and shifts owing to changes in the cationic composition [21,31,41]. A useful parameter is the wavelength of the Al–OH band (Table 2), which increases with a decrease in Alvi. Because montmorillonite has similar SWIR spectral characteristics (1900 nm and 2200 nm) to muscovite, illite crystallinity values (IC=2200D/1900D) are also widely used to evaluate muscovite and montmorillonite crystallinity [21,37]. Other octahedral silicate minerals, such as kaolinite and montmorillonite, also have absorption features near 2200 nm that overlap with many muscovite features, even though they can be identified and separated on the basis of other specific spectral properties.
