5.1.3. Paragenesis Study

In the Jagpura deposit, the ore minerals are semi massive to massive type, fracture fill type, vein type, disseminations/stringers type, patchy and foliation parallel types. Based on ore and gangue minerals assemblages, the texture of ore minerals and their grain boundary relationship, three different stages of ore formation are recognized (Figure 9).

Stage-I: This stage is called the dissemination/stringer stage and is characterized by fine disseminations/stringers of magnetite, arsenopyrite, pyrrhotite and chalcopyrite grains within the host rocks (Figure 7G). The common gangue mineral assemblages of this stage are quartz, biotite, apatite, albite, tourmaline, muscovite, biotite, chlorite and sericite.

Stage -II: This is the shear stage marked by the regional D<sup>2</sup> phase of deformation and it is the most dominant phase of mineralization in the Jagpura deposit. Most hydrothermal alterations were formed during this stage, viz. chloritization, sericitization, silicification, ferruginization and iron oxide breccia. The common gangue mineral assemblages of this stage are quartz, chlorite, sericite, biotite, apatite, albite, tourmaline and muscovite. Semi-massive to massive type ore, foliation parallel ore and vein filled ore were formed during this stage. Pyrrhotite, pyrite, chalcopyrite, magnetite, arsenopyrite, loellingite, gold, maldonite and hedleyite mineral assemblages represent the shear stage.

Stage-III: This stage is the final ore formation stage, marked by the second phase of hydrothermal fluid activity. It exhibits mineralization along fracture planes and replaces early formed ores with later ones, i.e., arsenopyrite is replaced by pyrrhotite and chalcopyrite. Native gold was precipitated in this stage, showing stringers and patchy textures.

**Figure 9.** Trace elements plots of magnetite and geochemical discrimination diagrams suggesting IOCG type mineralization style in the study area. (**A**) Ti vs. Ni/Cr ratio of magnetite from reference [14] suggest hydrothermal nature of magnetite; (**B**) Ni/(Cr+Mn) vs. Ti+V plot from reference [18] **Figure 9.** Trace elements plots of magnetite and geochemical discrimination diagrams suggesting IOCG type mineralization style in the study area. (**A**) Ti vs. Ni/Cr ratio of magnetite from reference [14]

suggesting IOCG type deposit; (**C**) Ca+Al+Mn vs. Ti+V plot from reference [18] indicates IOCG type

suggest hydrothermal nature of magnetite; (**B**) Ni/(Cr+Mn) vs. Ti+V plot from reference [18] suggesting IOCG type deposit; (**C**) Ca+Al+Mn vs. Ti+V plot from reference [18] indicates IOCG type mineralization style; (**D**) Al+Mn vs. Ti+V plot from reference [26] also corroborate the IOCG affiliation based on magnetite EPMA data; (**E**) The IOCG-ISCG cube of the Jagpura deposit from reference [36] shows reduced mineralogical subtypes based on Fe-Cu-O-S mineral assemblages. (Key deposits are shown in red text: EH—Ernest Henry deposit, Elo—Eloise, OD—Olympic Dam, OE—Orlando East, Seq—Sequeirinho-Sossego); (**F**) The (Au g/t × 10,000)/ Cu ppm vs. (Co + Ni + 10\*Bi + 10\*Se + 50\*Te)/(U + La) IOCG discriminator diagram for geochemical subtypes of IOCG deposit from reference [36] indicates that the Jagpura deposit is IOCG-Co (reduced) subtype; (**G**) The La vs. Co discrimination diagram from reference [36] also indicates that the Jagpura deposit is IOCG-Co (reduced) subtype and unrelated to porphyry and skarn type deposit; (**H**) The Cu vs. Co + Ni + U + La discrimination diagram from reference [36] further suggest that the Jagpura deposit is IOCG type and unrelated with porphyry Cu-Au-Mo, skarn Fe-Cu-Zn-Au, greisen Sn-W-Mo and Intrusion-Related Gold (IRG) deposits).

#### *5.2. Fluid Inclusion Study*

#### 5.2.1. Fluid Inclusion Petrography

Fluid inclusions were investigated using fluid inclusion assemblage (FIA) methods [66]. The size of the inclusions varies from 2 to 30 µm. The size of water vapor/CO<sup>2</sup> bubbles varies from 0.50 to 6.85 µm. These inclusions are classified into four types based on the phases present: type-I primary monophase carbonic inclusions, type-II primary aqueous carbonic inclusions, type-III primary aqueous bi-phase inclusions, and type-IV secondary aqueous inclusions (Figure 10). Type-I inclusions are more common and abundant in mineralized quartz veins than any other type of inclusion. These inclusions have only one phase, but two phases have been observed at room temperature in some cases. The CO<sup>2</sup> vapor phase is perfectly circular, spherical, and occasionally oval in shape, and at room temperature, a few of the CO2vapor bubbles have a dark rim on the periphery due to the presence of a thin film of liquid CO<sup>2</sup> over vapor CO<sup>2</sup> and are homogenized into the liquid phase. Type-II inclusions are less common and appear in isolated patterns containing CO<sup>2</sup> (liquid) + CO<sup>2</sup> (gas) + H2O (liquid) + NaCl. Aqueous carbonic inclusions frequently have varying degrees of fill. In general, the vapor content ranges from 25% to 60% by volume. Type-III inclusions are more abundant than any other type of inclusion, and they occur as isolated inclusions and fluid inclusion assemblages (FIA). These are usually tiny, rounded, and irregular, with two phases: liquid (H2O+NaCl) and a vapor bubble H2O homogenized to liquid upon heating. The type-IV inclusions are secondary aqueous inclusions and are very similar to the aqueous inclusions of type-III.

#### 5.2.2. Microthermometry

The melting temperatures (TmCO2) of type-I inclusions range from −56.6 to −60.2 ◦C, with the maximum depression in TmCO<sup>2</sup> (−60.2 ◦C) indicating an admixture of other gases, most likely CH<sup>4</sup> or N<sup>2</sup> [67], and the melting temperatures (Tm, CO2) are graphically illustrated in histograms. The temperatures at which CO<sup>2</sup> was homogenized into the vapor phase ranged from 1.9 to 28.0 ◦C (density varies from 0.72 to 0.81 g/cm<sup>3</sup> ) and were graphically plotted in a histogram. The primary aqueous carbonic inclusions (type II) are less abundant and occur in isolated and cluster patterns. These are identified by the formation of vapor bubbles upon cooling, which corresponds to the composition CO<sup>2</sup> (liquid) + CO<sup>2</sup> (gas) + H2O (liquid) + NaCl. These aqueous carbonic inclusions frequently have varying degrees of fill and coexist with aqueous-rich inclusions, inferring that fluid immiscibility occurred later in the crystallization process [66]. The total homogenization temperature (Thtotal) ranges from 235 to 258 ◦C. The CO2clathrate temperature (Tmclath) ranges from 6 to 12 ◦C. The initial eutectic temperatures (Te) of ice melting range from −26.5 ◦C to −32.0 ◦C. This implies that the fluid system's main component in the aqueous phase is NaCl ± MgCl2. The melting temperatures of solid CO<sup>2</sup> range from −56.6 ◦C to 58.2 ◦C. The maximum melting temperature indicates a lesser amount of methane [68]

and the homogenization temperature of CO<sup>2</sup> varies from 2.5 to 4.2 ◦C. The density of aqueous the carbonic phase varies from 0.87 to 0.98 g/cm<sup>3</sup> . Type-III inclusions are aqueous inclusions that freeze at temperatures ranging from −52 to −72 ◦C. The homogenization temperature ranged from 146 to 252 ◦C, and the first melting (eutectic) temperatures (*Te*u) observed during the heating runs ranged from −51 to −30 ◦C, with an average of −41.65 ◦C, indicating that the major component in the fluid system is NaCl ± FeCl2. The presence of CaCl<sup>2</sup> ± FeCl<sup>2</sup> with NaCl and H2O may be indicated by the maximum eutectic temperature of −51 ◦C [69]. The final melting temperature of ice (*T*m, ice) ranges from −6.9 to −30.0 ◦C, with salinities ranging from 10.35 to 28.15 wt% NaCl equivalent. The density of the aqueous phase varies from 0.98 to 1.10 gms/cm<sup>3</sup> . The type-IV, secondary bi-phase inclusions are predominantly aqueous-rich. The first melting temperature (eutectic) varies from −22.5 to −44 ◦C with an average value of −32.1◦C. This suggests that the major component in the aqueous phase is MgCl<sup>2</sup> in the fluid system. The final ice melting temperatures range from −4.5 to −22.7 ◦C, corresponding to the wide range of salinity varying from 7.10 to 24.09 wt% NaCl equivalents. The total homogenization temperature (Th) varies from 120 to 238 ◦C. The density of inclusions varies from 0.93 to 1.11 gm/cm<sup>3</sup> (Figure 11), [Table 4]. *Minerals* **2022,** *12*, x FOR PEER REVIEW 22 of 36


**Figure 10.** Paragenetic sequence showing evolution of gold mineralization with respect to various oxide and sulfide minerals based on relationships between host rock mineral assemblages, ore textural and micro-structural relationships. **Figure 10.** Paragenetic sequence showing evolution of gold mineralization with respect to various oxide and sulfide minerals based on relationships between host rock mineral assemblages, ore textural and micro-structural relationships.

Fluid inclusions were investigated using fluid inclusion assemblage (FIA) methods [66]. The size of the inclusions varies from 2 to 30 µm. The size of water vapor/CO2 bubbles

carbonic inclusions, type-III primary aqueous bi-phase inclusions, and type-IV secondary aqueous inclusions (Figure 11).Type-I inclusions are more common and abundant in mineralized quartz veins than any other type of inclusion. These inclusions have only one phase, but two phases have been observed at room temperature in some cases. The CO2 vapor phase is perfectly circular, spherical, and occasionally oval in shape, and at room temperature, a few of the CO2vapor bubbles have a dark rim on the periphery due to the presence of a thin film of liquid CO2 over vapor CO2 and are homogenized into the liquid phase. Type-II inclusions are less common and appear in isolated patterns containing CO2 (liquid) + CO2 (gas) + H2O (liquid) + NaCl. Aqueous carbonic inclusions frequently have varying degrees of fill. In general, the vapor content ranges from 25% to 60% by volume. Type-III inclusions are more abundant than any other type of inclusion, and they occur as isolated inclusions and fluid inclusion assemblages (FIA). These are usually tiny, rounded, and irregular, with two phases: liquid (H2O+NaCl) and a vapor bubble H2O homogenized

*5.2. Fluid Inclusion Study* 

5.2.1. Fluid Inclusion Petrography

very similar to the aqueous inclusions of type-III.

**Figure 11.** Types of fluid inclusions observed from study area. (**A**) Primary monophase carbonic (CO2) inclusions; (**B**) Primary aqueous carbonic inclusions; (**C**) Primary aqueous bi-phase inclusions; (**D**) Secondary aqueous bi-phase inclusions. **Figure 11.** Types of fluid inclusions observed from study area. (**A**) Primary monophase carbonic (CO<sup>2</sup> ) inclusions; (**B**) Primary aqueous carbonic inclusions; (**C**) Primary aqueous bi-phase inclusions; (**D**) Secondary aqueous bi-phase inclusions.

to liquid upon heating. The type-IV inclusions are secondary aqueous inclusions and are


The melting temperatures (TmCO2) of type-I inclusions range from −56.6 to −60.2 °C, **Table 4.** Fluid inclusion results of different inclusions from the Jagpura deposit.

#### + CO2 (gas) + H2O (liquid) + NaCl. These aqueous carbonic inclusions frequently have varying degrees of fill and coexist with aqueous-rich inclusions, inferring that fluid im-*5.3. Sulfur Isotopic Composition*

5.2.2. Microthermometry

miscibility occurred later in the crystallization process [66]. The total homogenization temperature (Thtotal) ranges from 235 to 258 °C. The CO2clathrate temperature (Tmclath) ranges from 6 to 12 °C. The initial eutectic temperatures (Te) of ice melting range from −26.5 °C to −32.0 °C. This implies that the fluid system's main component in the aqueous phase is NaCl ± MgCl2. The melting temperatures of solid CO2 range from −56.6 °C to 58.2 °C. The maximum melting temperature indicates a lesser amount of methane [68] and the homogenization temperature of CO2 varies from 2.5 to 4.2 °C. The density of aqueous the carbonic The δ <sup>34</sup>SVCDT (‰) values obtained from major sulfide minerals of the Jagpura deposit show a narrow range from +08.89 to +14.58‰ with an average value of +11.16‰ [Table 5]. The δ <sup>34</sup>S value of pyrite ranges from 10.28 to 11.05‰, pyrrhotite from 8.89to 12.34‰, chalcopyrite from 10.14to 12.14‰ and arsenopyrite from 10.98 to 14.58‰. The average δ <sup>34</sup>S values of pyrite, pyrrhotite, chalcopyrite and arsenopyrite are +10.60‰, +10.65‰, +11.15‰ and +12.31‰, respectively, in the increasing order of heavier isotope enrichment of δ <sup>34</sup>S values.

phase varies from 0.87 to 0.98 g/cm3. Type-III inclusions are aqueous inclusions that freeze at temperatures ranging from −52 to −72 °C. The homogenization temperature ranged from 146 to 252 °C, and the first melting (eutectic) temperatures (*Te*u) observed during the heating runs ranged from −51 to −30 °C, with an average of −41.65 °C, indicating that the


**Table 5.** δ <sup>34</sup>SVCDT (‰) values of various sulfide minerals of the Jagpura deposit.

#### *5.4. Geochemical Results*

The values of Fe in oxide range from 11.25 to 42.22 wt% and values of Fe in sulfide range from 4.27 to 22.37 wt%. The value of nickel ranges from 70 to 400 ppm, cobalt from 130 to 1600 ppm, Cu from 470 to 15,200 ppm, Cr from 155 to 348 ppm, Au from 0.20 to 18.60 ppm, Pb from 25 to 400 ppm, Zn from 10 to 100 ppm, La from 0.64 to 75.61 ppm and U from 2.42 to 3.84 ppm [Table 6]. The total REE varies from 76.64 to 346.38 ppm. The geochemical result shows enrichment of Co, Ni in Cu-Au ores and low values of REE and U.


**Table 6.** Geochemical results of samples from theJagpura deposit.

#### **6. Discussion**

#### *6.1. Nature and Control of Mineralization*

The mode of occurrence of mineralization as (1) semi-massive to massive type, (2) vein and fracture fill type, (3) foliation parallel disseminations/smears and (4) patchy and stringer type indicates hydrothermal origin of the mineralizing fluid. Textural investigations indicate the mineralization occurring as a fracture and open space-filling. The mineral boundary relationship, exsolution and the replacement and deformation textures further substantiate the hydrothermal nature of mineralization. This is further corroborated by the presence of iron oxide breccia, epigenetic quartz and pegmatite veins within the deposit. The ore mineralization is associated with pervasive hydrothermal Na-B alteration besides Fe-Mg-Ca-K alteration. Disseminated mineralization occurs parallel to S<sup>0</sup> II S<sup>1</sup> planes, related to the first deformation episodes. The ore mineralization is remobilized and concentrated within the hinge zone of F<sup>2</sup> folds and sympathetic shears (Figures 6E,F and 7F,H) during second phase of deformation. The NW-SE trending shear planes are parallel to F<sup>2</sup> axial planes of the second stage deformation event. The ore localization along these structures suggests distinct structural control of mineralization in the study area.

#### *6.2. Geochemistry of Native Gold, Pyrite, Magnetite, Apatite and Their Implications*

EPMA analysis of gold indicates that Au concentration ranges from 89.25 to 94.72 wt% and it contains silver as minor impurity (6.15 to 8.46 wt%). Gold fineness ranges between 914–937‰ with an average value of 927‰ indicating high purity gold. The Co/Ni ratio of pyrite is >1 (1 to 2.54) suggests hydrothermal origin [64,69–71], [Table 1; Figure 8G].

The Co/Ni ratios [15], Ti and V concentrations [14,72,73] are important parameters to differentiate hydrothermal magnetite to magmatic magnetite. The hydrothermal magnetite is depleted in Ti (<2 wt%) and Al (<1 wt%), [14,15,18,20,26,74]. Low TiO<sup>2</sup> (0.01 to 0.11 wt%) and Al2O<sup>3</sup> (0.06 to 0.28 wt%) concentrations in magnetite indicates the presence of hydrothermal magnetite in the study area [Table 2]. The Ti vs. Al and Ti vs. Ni/Cr bivariate plot of magnetite from study area also indicates magnetite is hydrothermal in origin (Figures 8H and 12A). The Ni/(Cr + Mn) vs. Ti + V plot, Ca + Al + Mn vs. Ti + V and Al + Mn vs. Ti + V plot of magnetite suggest IOCG deposit style (Figure 12B–D). Apatite from study area is of fluorapatite variety with F content >1 wt% (4.23 to 5.97 wt%) and >1 F/Cl ratio [Table 3]. Apatite has a higher concentration of F and a lower concentration of Cl, FeO, and MnO, which indicate that it is hydrothermal in nature and is sourced from metavolcano-sedimentary units [75].

Mineralized Quartz veins

Mono phase carbonic inclusions

Aqueous carbonic inclusions

Aqueous in-

Secondary aqueous inclusions

of inclusions varies from 0.93 to 1.11 gm/cm3 (Figure 12), [Table 4].

**Figure 12.** Histograms showing the relationship between: (**A**) Melting temperature of CO2 (Tmco2) vs. frequency; (**B**) Homogenization temperature of CO2 (Thco2) vs. frequency; (**C**) Homogenization temperature (Thtotal) vs. Frequency; (**D**) Salinity (wt% NaCl equivalent) of the inclusion vs. frequency. **Figure 12.** Histograms showing the relationship between: (**A**) Melting temperature of CO<sup>2</sup> (Tmco<sup>2</sup> ) vs. frequency; (**B**) Homogenization temperature of CO<sup>2</sup> (Thco<sup>2</sup> ) vs. frequency; (**C**) Homogenization temperature (Thtotal) vs. Frequency; (**D**) Salinity (wt% NaCl equivalent) of the inclusion vs. frequency. [Table 3]. Apatite has a higher concentration of F and a lower concentration of Cl, FeO, and MnO, which indicate that it is hydrothermal in nature and is sourced from metavolcano-sedimentary units [72].

major component in the fluid system is NaCl ± FeCl2. The presence of CaCl2 ± FeCl2 with NaCl and H2O may be indicated by the maximum eutectic temperature of −51 °C [69]. The final melting temperature of ice (*T*m, ice) ranges from −6.9 to −30.0 °C, with salinities ranging from 10.35 to 28.15 wt% NaCl equivalent. The density of the aqueous phase varies from 0.98 to 1.10 gms/cm3. The type-IV, secondary bi-phase inclusions are predominantly aqueous-rich. The first melting temperature (eutectic) varies from −22.5 to −44 °C with an average value of −32.1°C. This suggests that the major component in the aqueous phase is MgCl2 in the fluid system. The final ice melting temperatures range from −4.5 to −22.7 °C, corresponding to the wide range of salinity varying from 7.10 to 24.09 wt% NaCl equivalents. The total homogenization temperature (Th) varies from 120 to 238 °C. The density

*Minerals* **2022,** *12*, x FOR PEER REVIEW 27 of 36

mineral boundary relationship, exsolution and the replacement and deformation textures further substantiate the hydrothermal nature of mineralization. This is further corroborated by the presence of iron oxide breccia, epigenetic quartz and pegmatite veins within the deposit. The ore mineralization is associated with pervasive hydrothermal Na-B alteration besides Fe-Mg-Ca-K alteration. Disseminated mineralization occurs parallel to S0 II

area is of fluorapatite variety with F content >1 wt% (4.23 to 5.97 wt%) and >1 F/Cl ratio

#### *6.3. Evolution of Ore Fluids 6.3. Evolution of Ore Fluids*

**Table 4.** Fluid inclusion results of different inclusions from the Jagpura deposit. **Samples Descriptions Type Origin Size (µm) TmCO2 Te Tmice ThCO2 Th Total Salinity Density**  I Primary 2–15 −56.6 to −60.2°C - - 1.9 to 28°C - - 0.66 to 0.92 g/cc The characteristics of the mineralized quartz vein hosted fluid inclusions are listed in Table 4 and Figures 9 and 10. The homogenization temperature versus salinity diagram indicates that the mineralization within the Jagpura Au-Cu deposit is the result of the isothermal mixing of ore fluids with boiling/effervescence (Figure 13A), [76]. Most hydrothermal deposits have coexisting liquid rich, highly saline, and vapur rich low saline inclusions, indicating that the different phases are generated by immiscibility [77]. The characteristics of the mineralized quartz vein hosted fluid inclusions are listed in Table 4 and Figures 10 and 11. The homogenization temperature versus salinity diagram indicates that the mineralization within the Jagpura Au-Cu deposit is the result of the isothermal mixing of ore fluids with boiling/effervescence (Figure 13A), [76]. Most hydrothermal deposits have coexisting liquid rich, highly saline, and vapur rich low saline inclusions, indicating that the different phases are generated by immiscibility [77].

**Figure 13.** Homogenization temperature vs. salinity diagram of fluid inclusions from study area: (**A**) showing typical trends in homogenization temperature-salinity space due to various fluid evolution processes, from reference [78]; (**B**) Salinity vs. Homogenization temperature diagram from reference [79] indicates mixing of basinal brine, sea water and metamorphic fluids in ore fluid.

In the study area, type-III inclusions are liquid rich [(H2O + NaCl (l)] and highly saline (10.35–28.15 wt% NaCl equivalent); however, type-II inclusions are vapor rich and low saline (4.8–10.48 wt% NaCl equivalent). These data indicate that there is an immiscibility

of ore fluids. Generally, salinity of metamorphic fluids ranges between 3–10 wt% NaCl, with homogenization temperature varying between 150–425 ◦C and salinity of the basinal brine ranges between 5–40 wt% NaCl, with low homogenization temperature varying between 75–200 ◦C. In the Jagpura area, type-II inclusions match with the metamorphic fluids whereas type-III inclusions show similar character with basinal brine. Salinity versus homogenization temperature diagram indicates that the ore fluid is the result of the mixing of basinal brine, sea water and metamorphic fluids (Figure 13B), [80]. The high saline ore fluid transported metals in the system as metals chloride complex.

### *6.4. Source of Metals, Sulfur and Ore-Forming Fluids*

The δ <sup>34</sup>SVCDT values of sulfides from the Jagpura Au-Cu deposit are within the range of 8.98- to 14.58‰, with an average value of 11.16‰ (Figure 14A). This narrow range of sulfur isotopes indicates that (i) sulfur has originated from one uniform source under stable physicochemical condition or (ii) local disequilibrium between two phases of mineralization [81]. *Minerals* **2022,** *12*, x FOR PEER REVIEW 29 of 36

**Figure 14.** Sulfur isotope compositions of different sulfide minerals from the Jagpura deposit: (**A**) Histogram showing values of various sulfide minerals; (**B**) Range of δ34S for magmatic, sedimentary, metamorphic, seawater and evaporite systems from references [59,82]. Plot showing the variation in δ34S values of sulfides from the Jagpura IOCG deposit, and comparison of the δ34S values of sulfides from the Jagpura deposit with major geological sulfur reservoir and with various IOCG deposit worldwide from reference [24,83] and India from references [27,28,31,39,44,84]. The major gold bearing sulfide mineral within the Jagpura Au-Cu deposit is arseno-**Figure 14.** Sulfur isotope compositions of different sulfide minerals from the Jagpura deposit: (**A**) Histogram showing values of various sulfide minerals; (**B**) Range of δ <sup>34</sup>S for magmatic, sedimentary, metamorphic, seawater and evaporite systems from references [59,82]. Plot showing the variation in δ <sup>34</sup>S values of sulfides from the Jagpura IOCG deposit, and comparison of the δ <sup>34</sup>S values of sulfides from the Jagpura deposit with major geological sulfur reservoir and with various IOCG deposit worldwide from reference [24,83] and India from references [27,28,31,39,44,84].

pyrite and it contains a higher isotopic ratio than the other sulfide phases. The higher isotopic range in the sulfur isotope compositions imply that sulfide minerals are enriched

values of the sulfur isotope rule out magmatic (δ34S = 05), [85,86], mantle (δ34S = 01), [87], and seawater/biogenic sulfur sources (δ34S = > 20), [83]. The presence of relatively higher δ34S rich sulfides indicates that the possible source of heavy sulfurs is (i) seawater, (ii) evaporitic water and (iii) oxidized meta-sedimentary fluids [88,89]. Therefore, the

The major gold bearing sulfide mineral within the Jagpura Au-Cu deposit is arsenopyrite and it contains a higher isotopic ratio than the other sulfide phases. The higher isotopic range in the sulfur isotope compositions imply that sulfide minerals are enriched in heavy isotopes (Figure 14B). In various deposits around the world, isotopically heavy sulfur (δ <sup>34</sup>S > 5) suggests the presence of non-magmatic sulfur sources. Higher positive values of the sulfur isotope rule out magmatic (δ <sup>34</sup>S = 05), [85,86], mantle (δ <sup>34</sup>S = 01), [87], and seawater/biogenic sulfur sources (δ <sup>34</sup>S = > 20), [83]. The presence of relatively higher δ <sup>34</sup>S rich sulfides indicates that the possible source of heavy sulfurs is (i) seawater, (ii) evaporitic water and (iii) oxidized meta-sedimentary fluids [88,89]. Therefore, the moderately high δ <sup>34</sup>S values of the Jagpura deposit values suggest a meta-sedimentary source for sulfur.

The lack of sulfate minerals in the Jagpura deposit indicates that the sulfur was present in the hydrothermal fluids as reduced sulfur (H2S). The potential source of reduced H2S was the basement rocks. The sulfur isotope compositions of sulfides from the Jagpura deposit are similar to the major geological sulfur reservoirs and other IOCG type deposits in India and the world (Figure 14B). External fluids, primarily basinal brines and modified seawater with high δ <sup>34</sup>Svalues (>+10), play an important role in IOCG ore-forming systems [90]. The sulfur isotope data indicate the mixed source of sulfur derived from the non-magmatic hydrothermal fluids, and the high saline brine (marine/evaporitic). Variation in the sulfur isotopic compositions of sulfides is the result of dilution and cooling of the metalliferous fluid derived from the basement meta-sedimentary rocks, which along with highly saline brine triggered the precipitation of Au along structural weak planes.

#### *6.5. Geochemical Characterization of the Jagpura Deposit*

There are three mineralogical subtypes of IOCG deposits based on dominant ore assemblages i.e., (i) oxidized (ii) intermediate-redox and (iii) reduced mineralogical subtypes [36]. The reduced mineralogical subtypes are represented by pyrrhotite and/or Fe-silicates and variable modal proportions of magnetite, pyrite, and chalcopyrite. The reduced IOCG-ISCG deposit group commonly includes phases hosting Co, Ni, As and Bi; however, REE, U, fluorite, barite or anhydrite phases are rare [36]. The Jagpura deposit is represented by the dominant ore assemblages of pyrrhotite-chalcopyrite-arsenopyritepyrite-magnetite. The deposit includes phases hosting Co, Ni, As and Bi; however, REE, U, fluorite and barite are not present. The IOCG-ISCG cube diagram based on Fe-Cu-O-S mineral assemblages (Figure 9E) suggests that the Jagpura deposit is characterized by reduced mineralogical subtypes. The geochemical result shows enrichment of Co, Ni in Cu-Au ores and low values of REE and U [Table 6]. The occurrence of >15% Fe in oxide, (Au g/t× 10,000)/ Cu ppm vs. (Co + Ni + 10\*Bi + 10\*Se + 50\*Te)/(U + La), La vs. Co and Cu vs. Co+Ni+U+La geochemical discrimination diagrams (Figure 12F–H) for geochemical subtypes of Cu-Au-Fe (± Co, REE) deposits including IOCG deposits indicates that the Jagpura is IOCG-Co (reduced) subtype deposit and unrelated to porphyry Cu-Au-Mo, skarn Fe-Cu-Zn-Au, greisen Sn-W-Mo, and intrusion-related gold (IRG) deposits.

#### *6.6. Genesis of the Jagpura Au-Cu Deposit*

The genesis of an ore deposits is closely related to the geological environments, i.e., pressure -temperature conditions, and the nature/source of the hydrothermal fluids [66,73,78,79]. Fluid inclusion study is a vital tool to understand the genetic aspects, whereas the sulfur isotope signatures help in the understanding of the nature and source of the mineralizing fluids of an ore deposit. [90–92]. Sulfur isotope data also provides the information about the source of metals in a deposit [59,93]. The sulfur isotope variations in an ore mineralizing systems are very complex and, hence, best understood in the context of the total geological framework of a deposit in conjunction with the fluid inclusion study.

Au-Cu sulfide mineralization within the Jagpura deposit is hosted by quartz-mica schist and albitite. The mineralization is localized along NW-SE trending D<sup>2</sup> shear planes parallel to F<sup>2</sup> axial planes and F<sup>2</sup> fold hinges and correlated to the second deformation phase (Figure 15). The ore mineral association is represented by the iron oxide (magnetite),

copper, gold and apatite. The mineralization includes arsenopyrite, loellingite, chalcopyrite, pyrrhotite and pyrite, along with the native gold and abundant magnetite. Further the maldonite and hedleyite occur as Au-Bi-Te phases. The mode of occurrence of mineralization as open space-filling, vein and fracture fill type indicates hydrothermal nature. The mineralization is associated with pervasive hydrothermal Na-B alteration besides Fe-Mg-Ca-K alteration. The occurrence of maldonite, hedleyite associated with gold lode, epigenetic quartz-pegmatite veins in host rocks and pervasive hydrothermal alteration indicate hydrothermal origin of ore fluids. *Minerals* **2022,** *12*, x FOR PEER REVIEW 31 of 36 epigenetic quartz-pegmatite veins in host rocks and pervasive hydrothermal alteration indicate hydrothermal origin of ore fluids.

**Figure 15.** Schematic diagram showing the stage of evolution of the structure and polymetallic mineralization at theJagpura deposit based on field and petrographic studies. **Figure 15.** Schematic diagram showing the stage of evolution of the structure and polymetallic mineralization at theJagpura deposit based on field and petrographic studies.

The Co/Ni ratio of >1 in pyrite, gold-sulfide associated low TiO2, Al2O3 hydrothermal magnetite (Co/Ni ratio < 1 and Ni/Cr ≥ 1) and fluorapatite (>1 F/Cl ratio) support the hydrothermal origin of mineralization. Apatite has a higher F concentration and a lower concentration of Cl, FeO, and MnO, indicating its source from the metavolcano-sedimentary units. Fluid inclusions micro-thermometry indicates the presence of aqueous rich, mixed carbonic-aqueous and minor vapor rich aqueous inclusions. The FI's show episode of fluid immiscibility with the homogenization temperatures and salinities varying between 120–258 °C and 8.86–28.15 wt% NaCl eq., respectively. This data indicates that the high saline ore fluids are injected during the D2 phase of deformation. The high salinity ore fluid transport metals in the ore system as metals chloride complex. The Co/Ni ratio of >1 in pyrite, gold-sulfide associated low TiO2, Al2O<sup>3</sup> hydrothermal magnetite (Co/Ni ratio < 1 and Ni/Cr ≥ 1) and fluorapatite (>1 F/Cl ratio) support the hydrothermal origin of mineralization. Apatite has a higher F concentration and a lower concentration of Cl, FeO, and MnO, indicating its source from the metavolcano-sedimentary units. Fluid inclusions micro-thermometry indicates the presence of aqueous rich, mixed carbonic-aqueous and minor vapor rich aqueous inclusions. The FI's show episode of fluid immiscibility with the homogenization temperatures and salinities varying between 120–258 ◦C and 8.86–28.15 wt% NaCl eq., respectively. This data indicates that the high saline ore fluids are injected during the D<sup>2</sup> phase of deformation. The high salinity ore fluid transport metals in the ore system as metals chloride complex.

The iron oxide-copper-gold (IOCG) type deposits are characterized by abundant (>10%) hydrothermal iron oxides (magnetite or hematite) and economic grade Cu and/or Au. It also contains Ag, U, Th, F, Co, Bi, W, rare earth elements (REE) and other metals. These deposits are diverse in age (Neo-Archaean to the Cenozoic), tectonic setting, P–T conditions, characteristic Na-Ca-K alterations, host-rock package and mineralization style The iron oxide-copper-gold (IOCG) type deposits are characterized by abundant (>10%) hydrothermal iron oxides (magnetite or hematite) and economic grade Cu and/or Au. It also contains Ag, U, Th, F, Co, Bi, W, rare earth elements (REE) and other metals. These deposits are diverse in age (Neo-Archaean to the Cenozoic), tectonic setting, P–T conditions, characteristic Na-Ca-K alterations, host-rock package and mineralization

[36,90,94–98].The field characteristics, trace element geochemistry of pyrite, apatite and magnetite, fluid inclusion and sulfur isotope compositions of the Jagpura Au-Cu deposit are compared with the Epithermal gold deposit of high sulfidation and low sulfidation,

this suggeststhat the Jagpura gold-copper ore system is similar to the IOCG type. The Jagpura Au-Cu deposit indicate the: (i) iron oxide-copper-gold-apatite association of hydrothermal origin, (ii) distinct structural control of mineralization, (iii) Na-B-Mg-Fe-Ca-K style [36,90,94–98].The field characteristics, trace element geochemistry of pyrite, apatite and magnetite, fluid inclusion and sulfur isotope compositions of the Jagpura Au-Cu deposit are compared with the Epithermal gold deposit of high sulfidation and low sulfidation, Carlin type gold deposit, Orogenic lode gold and IOCG type Cu-Au deposits [4–10] and this suggeststhat the Jagpura gold-copper ore system is similar to the IOCG type. The Jagpura Au-Cu deposit indicate the: (i) iron oxide-copper-gold-apatite association of hydrothermal origin, (ii) distinct structural control of mineralization, (iii) Na-B-Mg-Fe-Ca-K hydrothermal alteration(dominant Na-B alteration), (iv) presence of iron oxide breccia, (v) abundant hydrothermal Fe oxides (>15%), (vi) trace element geochemistry of magnetite (Ti, Al + Mn, Ti + V concentrations and Ni/(Cr + Mn) vs. Ti + V, Ca + Al + Mn vs. Ti + V, Al + Mn vs. Ti + V ratios of magnetite Figure 8J–L) suggests IOCG style of mineralization, (vii) presence of late-stage sulfides with economic gold-copper resources, (viii) high saline ore fluid and sulfur isotope compositions within the range of IOCG deposits worldwide (−30 to +26‰) and (ix) The (Au g/t × 10,000)/ Cu ppm vs. (Co + Ni + 10\*Bi + 10\*Se + 50\*Te)/(U + La), La vs. Co and Cu vs. Co + Ni + U + La and discrimination diagrams (Figure 12F–H), [36] indicates a IOCG-Co (reduced) subtype deposit and is unrelated to porphyry Cu-Au-Mo, skarn Fe-Cu-Zn-Au, greisen Sn-W-Mo, and intrusion-related gold (IRG) deposits. These characters of the Jagpura deposit are well corroborated with the IOCG-IOA type and the IOCG-Co (reduced) subtype deposit.

### **7. Conclusions**

The Jagpura Au-Cu deposit shows pervasive hydrothermal alteration zones associated with the iron-oxide and sulfide mineralization along the brittle-ductile shear zone. The ore petrography and EPMA study show the presence of Au-Bi-Te phases, Co/Ni ratio of >1 in pyrite, gold-sulfide associated low TiO2, Al2O<sup>3</sup> hydrothermal magnetite (≥1 Ni/Cr ratio, <1 Co/Ni ratio). The presence of apatite with higher F concentration (>1 F/Cl ratio) and a lower concentration of Cl, FeO and MnO is consistent with its hydrothermal origin. Fluid inclusion microthermometric studies indicate the presence of aqueous rich, mixed carbonic-aqueous and minor vapor rich aqueous inclusions. The FI's show episodes of fluid immiscibility with the homogenization temperatures and salinities range of 120–258 ◦C and 8.86–28.15 wt% NaCl eq., respectively. These data indicate a mixture of highly saline ore fluid of basinal brine and metamorphic origin, responsible for the transport of metals in the system as metals chloride complex. The δ <sup>34</sup>S values of sulfides are within a narrow range of 8.98‰ to 14.58‰, with an average value of 11.16‰. This indicates the non-magmatic origin of sulfides. Variation in the sulfur isotopic compositions of sulfides resulted from the dilution and cooling of the metalliferous fluid derived from the basement rocks. The mixing of high saline brine triggered the gold precipitation along the structural discontinuities. The Ti, Al + Mn, Ti + V concentrations and Ni/(Cr + Mn) vs. Ti + V, Ca + Al + Mn vs. Ti + V, Al + Mn vs. Ti + Vratios of magnetite suggest an IOCG type of mineralization. The (Au g/t × 10,000)/ Cu ppm vs. (Co + Ni + 10\*Bi + 10\*Se + 50\*Te)/(U + La), La vs. Co and Cu vs. Co + Ni + U + La geochemical discrimination diagrams indicates that the Jagpura Au-Cu deposit is an IOCG-Co (reduced) subtype deposit. Iron oxide-copper-gold-apatite association of hydrothermal origin, nature and distinct structural control of mineralization, pervasive hydrothermal alteration, trace element characteristics of magnetite, pyrite and apatite, high saline ore fluid and sulfur isotope compositions suggest that the Jagpura deposit is an IOCG-IOA type and is similar to those described for the shear fault-controlled-IOCG deposits found elsewhere in the world. The classification of the Jagpura deposit as an IOCG-IOA type: IOCG-Co (reduced) subtype has significant implications for the deeper level sub-surface exploration in the Salumber Ghatol Metallogenic Belt within the Aravalli Craton.

**Author Contributions:** Conceptualization, A.A., S.S.; methodology, A.A., S.S., A.G.; validation, S.S., A.A., A.G.; investigation, A.A., A.S., M.K.; writing original draft preparation, A.A., A.G., M.K., G.K.M.; writing, review and editing, S.S., A.S.; visualization, A.A., A.G.; Formal analysis, A.A., G.K.M., M.K.; supervision, S.S., A.S. All authors have read and agreed to the published version of the manuscript.

**Funding:** This study is supported by the Geological Survey of India, Western Region, Jaipur.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The data presented in this study are mainly contained within the article and available in the references listed. To a minor degree, the data presented are not publicly available due to privacy and available on request from the first author.

**Acknowledgments:** The authors are extremely grateful to S. Raju, Director General, Geological Survey of India (GSI), Kolkata, Shri Jaya Lal, Addl. Director General &HoD, Western Region (WR), Jaipur and Sanjay Das, Deputy Director General, State Unit, Rajasthan, GSI, WR, Jaipur for their continuous encouragement and permission to publish this paper. AA extends sincere thanks to GSI for providing an opportunity to carry out research in the Jagpura area (project no.99) and extends sincere gratitude to Shri R. L. Jat, Shri Sanjay Singh, Shri Hemant Kumar Singh and Shri Lalit Mohan, GSI for providing help and guidance during field work. AA extends sincere thanks to M. L. Dora, GSI for their valuable suggestions and help to improve this manuscript. We also acknowledge and express sincere thanks to Shri Manish M. John, IRMS Lab, GSI, Bengaluru, Smt. Sonalika Joshi, EPMA Lab, GSI, Faridabad and personnel of EPMA Lab, IIT, ISM, Dhanbad for analyzing the samples. AA thanks Mohini S. Sathe, Geologist, GSI, WR for wholehearted support and encouragement during the writing of this article. The authors also acknowledge GSI's in house reviewers for their constructive and thoughtful comments, which helped in improving the quality of the manuscript. Authors extend their sincere thanks and gratitude to the Editor-in-Chief Paul Sylvester, Special Issue Editor Galina Palyanovaandanonymous reviewers for their continuous encouragement and kind suggestions for improving the quality of the manuscript.

**Conflicts of Interest:** The authors declare that they have no known competing financial interest or personal relationships that could have appeared to influence the work reported in this paper. There is no conflict of interest as this work is Ph.D work of first author, due acknowledgment has been given to pervious work. Author has intimated the competent authority of Geological Survey of India (GSI) to publish this work in the said journal.

### **References**

