*Article* **Geological Constraints on the Genesis of Jagpura Au-Cu Deposit NW India: Implications from Magnetite-Apatite Mineral Chemistry, Fluid Inclusion and Sulfur Isotope Study**

**Abhishek Anand 1,2, Sahendra Singh 2,\* , Arindam Gantait <sup>1</sup> , Amit Srivastava <sup>1</sup> , Girish Kumar Mayachar <sup>3</sup> and Manoj Kumar <sup>4</sup>**


**Abstract:** The Jagpura Au-Cu deposit is situated within the Aravalli craton in the northwestern part of India. In the present work, petrography, mineral chemistry, fluid inclusion and sulfur isotopic compositions were used to study the Jagpura Au-Cu deposit. The ore mineral association of the deposit is arsenopyrite, loellingite, chalcopyrite, pyrrhotite and pyrite, along with native gold, magnetite and apatite. The gold fineness ranges from 914–937‰ (avg. 927‰). The presence of Au-Bi-Te phases, pyrite (>1 Co/Ni ratio), magnetite (≥1 Ni/Cr ratio, <1 Co/Ni ratio) and apatite (>1 F/Cl ratio) suggest the hydrothermal origin Au-Cu mineralization. A fluid inclusion study indicates the different episodes of fluid immiscibility with the homogenization temperatures varying between 120–258 ◦C and salinities range within the 8.86–28.15 wt% NaCl eq. The sulfur isotopic composition of sulfides varies from 8.98 to 14.58‰ (avg. 11.16‰). It is inferred that the variation in the sulfur isotopic compositions of sulfides is due to the cooling and dilution of the metalliferous fluid of mixed origin, derived from the basement meta-sedimentary rocks and the high saline basinal fluid. The iron oxide-copper-gold-apatite associations, structural control of mineralization, pervasive hydrothermal alteration, fluid salinity and sulfur isotope compositions indicate that the Jagpura Au-Cu deposit is similar to the iron oxide-copper-gold (IOCG)-iron oxide-apatite (IOA)types of deposits. Based on the ore geochemistry and the trace elements systematic of magnetite, the deposit is further classified as an IOCG-IOA type: IOCG-Co (reduced) subtype.

**Keywords:** Jagpura Au-Cu deposit; Aravalli Craton; high fineness gold; hydrothermal magnetite; fluid inclusions; sulfur isotopic composition; IOCG-IOA type: IOCG-Co (reduced) subtype mineralization

### **1. Introduction**

Gold occurs mainly in a native state and often contains Ag, Cu, Hg and other impurities [1,2]. Native gold is an indicator mineral of gold deposits [2,3]. On the basis of their genesis, the gold deposits are classified into different types, viz. Orogenic lode gold, Carlin-type gold deposit, Porphyry type gold and Iron oxide-copper-gold (IOCG) type gold deposit [4–10]. The majority of these gold deposits is of hydrothermal origin and constitute a significant portion of the world's gold resources [11].In these deposits, gold mineralization is commonly associated with pyrite and magnetite. Magnetite is stable across a wide variety of physicochemical circumstances and contains various trace elements, including Al, Ti, Mg, Mn, Zn, Cr, V, Ni, Co, and Ga [12–16]. These elements are useful petrogenetic tools for modern-day exploration [15,17–22]. Accordingly, magnetite's trace element composition is used to distinguish between IOCG, Volcanogenic Massive Sulfide (VMS), copper porphyry, Cu-Fe skarn, magmatic Fe-Ti-V-Cr, Ni-Cu-PGE, Kiruna-type iron oxide-apatite (IOA) and BIF deposits [14,16,18,20,22–28]. Apatite is also a vital pathfinder

**Citation:** Anand, A.; Singh, S.; Gantait, A.; Srivastava, A.; Mayachar, G.K.; Kumar, M. Geological Constraints on the Genesis of Jagpura Au-Cu Deposit NW India: Implications from Magnetite-Apatite Mineral Chemistry, Fluid Inclusion and Sulfur Isotope Study. *Minerals* **2022**, *12*, 1345. https://doi.org/ 10.3390/min12111345

Academic Editor: Galina Palyanova

Received: 27 September 2022 Accepted: 19 October 2022 Published: 24 October 2022

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

mineral for IOCG/IOCG-IOA type deposits and is effectively used as an indicator mineral for IOCG system [29,30].

The Jagpura Au-Cu deposit lies in the southern part of the Salumber-Ghatol Metallogenic Belt (SGMB), within the Paleoproterozoic Aravali Delhi Fold Belt (ADFB) Rajasthan, India. The Au-Cu mineralization of the SGMB, is hosted by carbonate rocks and albitite [27,31,32]. Previous workers advocated the magmatic-hydrothermal model for the origin of gold-sulfide mineralization within the Bhukia-Jagpura deposit [33]. However, recent investigations in the Jagpura deposit reveals that the Au-Cu lodes are hosted within the albitite and quartz-mica schist [34,35]. Since, the Jagpura Au-Cu deposit is a relatively recent finding; there are significant gaps in the understanding of the nature of the gold-sulfide mineralization, associated magnetite-apatite mineral chemistry, and sourcetransportation-precipitation mechanism of the ore bearing fluid to form the deposit. This requires a detailed investigation of the mineralization and hence, an integrated approach is attempted to constrain the genesis of gold-copper mineralization.

The present study was carried out with an aim to (i) characterize the gold mineralization associated with magnetite and apatite, (ii) understand the possible source of ore-bearing fluids and (iii) classify the Jagpura deposit in the light of the recent classification scheme for Cu-Au-Fe (CGI)/ IOCG deposits [36]. In this work, we present new data on the genetic aspects incorporating mineral chemistry of Au, Au-Bi, Bi-Te, Cu-sulfide phases, besides associated magnetite and apatite, the sulfur isotopic composition of major ore minerals, and fluid inclusion micro-thermometry of mineralized quartz veins of the Jagpura deposit. This study fills up the existing gaps in the understanding of the metallogeny of the Salumber-Ghatol Metallogenic Belt and has a broader exploration implication on this belt and allied areas of similar geological settings.

#### **2. Regional Geological Setting**

The Northwestern Indian shield is represented by 3.3–2.5 Ga Archean basement known as the Banded Gneissic Complex (BGC) and is overlain by 2.2–1.85 Ga Paleoproterozoic cover sequence of Aravalli-Delhi Fold Belt (ADFB), (Figure 1), [37–41]. The Archean basement consists of granite gneiss with meta-volcano-sedimentary rocks and intrusive rocks [38,39]. The BGC is in tectonic contact with or unconformably overlain by two Proterozoic supracrustal sequences, the Aravalli and Delhi supergroups [42]. The Aravalli Supergroup is widely distributed in the eastern and southeastern parts of the Aravalli-Delhi Fold Belt. The relationship between ADFB and BGC is unconformable along the entire Aravalli Fold Belt margin [42].

1

**Figure 1.** (**A**) Inset map showing the location of the Aravalli craton and Aravalli Delhi Fold Belt in Indian subcontinent, modified from reference [43]; (**B**) Geological map of the Aravalli–Delhi Fold Belt showing location of the basement Banded Gneissic Complex (BGC), Paleoproterozoic Aravalli Supergroup and Salumber-Ghatol metallogenic belt, modified from references [44].

The ADFB is composed of calcareous and argillaceous meta-sedimentary rocks, metavolcano-sedimentary rocks, and intrusive rocks. The Aravalli sequence belongs to the continental rift basin settings [45,46]. Geochronological studies showed that the Aravalli sedimentation period ranges from ~2.3 to ~1.6 Ga [47,48]. The 4–6 km wide and 70 km long Salumber-Ghatol Metallogenic Belt (SGMB) is exposed in the extreme southeastern part of the ADFB and forms a part of the eastern margin of the Debari Group of the Aravalli Supergroup. It extends from Salumber in the northwest to Ghatol in the southeast, exposing a meta-volcano-sedimentary sequence unconformably overlying the BGC (Figure 2), [49,50]. Staurolite schist is a part of the basement rock [51]. The contact between the staurolite schist of the BGC and the meta-sediments of the Jagpura Formation of the Debari Group is sheared and referred to as Ghatol Shear Zone [31]. The lithostratigraphic sequence of the Debari Group, exposed in the SGMB is classified into five formations viz., the Gurali Formation (Basal quartzite and conglomerate), Delwara Formation (metabasalt with intercalations of conglomerate, marble, quartzite and feldspathic schist), Jaisamand Formation (conglomerate, feldspathic quartzite, mica schist and dolomitic marble), Mukandpura Formation (dolomite, phyllite and carbonaceous phyllite with intercalations of mica schist) and Jagpura Formation (quartzite, quartz-mica schist, garnet-biotite schist, dolomitic marble, calc-silicate rock and amphibolite).

**Figure 2.** Geological map of Salumber-Ghatol metallogenic belt showing location of study area, modified from reference [51]. **Figure 2.** Geological map of Salumber-Ghatol metallogenic belt showing location of study area, modified from reference [51].

The general structural trend of the lithologic units of the SGMB is NNW-SSE with moderate to steep dips towards WSW. The rocks of the SGMB are affected by three phases of deformation events [33,52] and have undergone upper greenschist to middle amphibolite facies metamorphism [53]. The lower part of the Aravalli Supergroup i.e., Debari Group, lying close to the BGC, hosts several Au-Cu deposits/prospects in the SGMB viz. Bhukia, Jagpura, Delwara, Dagocha, Ghagri etc. [31]. The Geological Survey of India (GSI) has discovered gold-copper mineralization in the Bhukia area of SGMB in 1993 [49]. The subsequent exploration by the GSI has established 114.78 mt of gold resource with an average grade of 1.95 g/t gold, 0.15% associated copper, 93 g/t nickel and 130 g/t cobalt resource [54]. The interface of the BGC and the Aravalli Supergroup between Delwara and Ghatol in southeastern Rajasthan is mineralized (Cu-Au-iron oxide-graphite), [32]. In SGMB, the deposits/prospects situated in the southern part are more promising gold de-The general structural trend of the lithologic units of the SGMB is NNW-SSE with moderate to steep dips towards WSW. The rocks of the SGMB are affected by three phases of deformation events [33,52] and have undergone upper greenschist to middle amphibolite facies metamorphism [53]. The lower part of the Aravalli Supergroup i.e., Debari Group, lying close to the BGC, hosts several Au-Cu deposits/prospects in the SGMB viz. Bhukia, Jagpura, Delwara, Dagocha, Ghagri etc. [31]. The Geological Survey of India (GSI) has discovered gold-copper mineralization in the Bhukia area of SGMB in 1993 [49]. The subsequent exploration by the GSI has established 114.78 mt of gold resource with an average grade of 1.95 g/t gold, 0.15% associated copper, 93 g/t nickel and 130 g/t cobalt resource [54]. The interface of the BGC and the Aravalli Supergroup between Delwara and Ghatol in southeastern Rajasthan is mineralized (Cu-Au-iron oxide-graphite), [32]. In SGMB, the deposits/prospects situated in the southern part are more promising gold deposits in Western India [31,32,39,51,55].

posits in Western India [31,32,39,51,55]. The mineralization in this belt is represented by pyrrhotite, chalcopyrite, arsenopyrite, pyrite, loellingite along with magnetite, goethite and native gold. The host rock for aurifer-

ous mineralization is carbonate rocks and albitite. The U-Pb zircon ages of albite-rich rock from Bhukia deposit ranges from 1740 to 1820 Ma [56]. Gold-copper mineralization in this belt occurs as disseminations, massive ore, veins, stringers and smears along with shear fractures. The localization of ore is controlled by shears, genetically related to the D<sup>2</sup> phase of deformation. The ore is localized along with hinges of F<sup>2</sup> folds and F<sup>2</sup> axial plane which are parallel to D<sup>2</sup> shear planes. The associated alteration is characterized by pervasive Na-Ca-Mg-Fe-B-Ti alterations [31]. The present work is focused on Jagpura Au-Cu deposit, located in the southern part of the SGMB belongs to the Jagpura Formation of the Debari Group of the Aravalli Supergroup. auriferous mineralization is carbonate rocks and albitite. The U-Pb zircon ages of albiterich rock from Bhukia deposit ranges from 1740 to 1820 Ma [56]. Gold-copper mineralization in this belt occurs as disseminations, massive ore, veins, stringers and smears along with shear fractures. The localization of ore is controlled by shears, genetically related to the D2 phase of deformation. The ore is localized along with hinges of F2 folds and F2 axial plane which are parallel to D2 shear planes. The associated alteration is characterized by pervasive Na-Ca-Mg-Fe-B-Ti alterations [31]. The present work is focused on Jagpura Au-Cu deposit, located in the southern part of the SGMB belongs to the Jagpura Formation of the Debari Group of the Aravalli Supergroup.

The mineralization in this belt is represented by pyrrhotite, chalcopyrite, arsenopyrite, pyrite, loellingite along with magnetite, goethite and native gold. The host rock for

*Minerals* **2022,** *12*, x FOR PEER REVIEW 5 of 36

#### **3. Deposit Geology 3. Deposit Geology**

The lithologic units of the Jagpura deposit are classified into two different tectonostratigraphic domains: one is part of the Archean basement known as the Banded Gneissic Complex (BGC) and the other is part of Paleoproterozoic meta-sedimentary units of the Debari Group of the Aravalli Supergroup (Figure 3). The BGC is represented by medium grade staurolite schist, overlain by meta-sedimentary rock sequence comprising of dolomitic marble, amphibole quartzite, quartz-mica schist and albitite of the Jagpura Formation, Debari Group of the Aravalli Supergroup with a tectonic contact. The lithologic units of the Jagpura deposit are classified into two different tectonostratigraphic domains: one is part of the Archean basement known as the Banded Gneissic Complex (BGC) and the other is part of Paleoproterozoic meta-sedimentary units of the Debari Group of the Aravalli Supergroup (Figure 3). The BGC is represented by medium grade staurolite schist, overlain by meta-sedimentary rock sequence comprising of dolomitic marble, amphibole quartzite, quartz-mica schist and albitite of the Jagpura Formation, Debari Group of the Aravalli Supergroup with a tectonic contact.

**Figure 3.** (**A**) Geological map of the Jagpura deposit showing different litho-units and mineralized zones, modified from reference [57], Albitite is from reference [27]; (**B**) longitudinal borehole crosssection showing the position of ore lodes; (**C**) Geological cross-section along line A–B in Figure 3A. **Figure 3.** (**A**) Geological map of the Jagpura deposit showing different litho-units and mineralized zones, modified from reference [57], Albitite is from reference [27]; (**B**) longitudinal borehole crosssection showing the position of ore lodes; (**C**) Geological cross-section along line A–B in Figure 3A.

Staurolite schist is asilver-grey to dark grey colored fine to medium grained rock. The contact between staurolite schist and dolomitic marble is sheared, marked by various kinematic indicators in which sigma structure of quartz porphyroblast indicates a dextral sense of shearing. Dolomitic marble is medium to coarse-grained, fawn colored crystalline rock

and exhibits well-developed elephant skin weathering and saccharoidal texture. Amphibole quartzite is exposed in the southern part of the deposit and is brown to pink colored, medium grained, hard and compact rock. It is composed mainly of quartz, actinolite and K-feldspar. Quartz-mica schist is the most dominant lithologic unit in the deposit. It is abuff-grey to greenish-grey colored, fine-grained rock with a silvery sheen at places with more muscovite concentration. The rock shows the development of quartz porphyroblasts, crenulation cleavage, well-developed schistosity marked by a strong preferred orientation of muscovite, chlorite and biotite (Figure 4A). The rock is traversed by foliation parallel magnetite veins and highly ferruginized at places (Figure 4B–D). Albitite is a brown to brick-red colored, fine grained, hard and compact rock (Figure 4E). It occurs as competent bands within quartz-mica schist, contains foliation parallel tourmaline rich bands and ferruginized at places. sense of shearing. Dolomitic marble is medium to coarse-grained, fawn colored crystalline rock and exhibits well-developed elephant skin weathering and saccharoidal texture. Amphibole quartzite is exposed in the southern part of the deposit and is brown to pink colored, medium grained, hard and compact rock. It is composed mainly of quartz, actinolite and K-feldspar. Quartz-mica schist is the most dominant lithologic unit in the deposit. It is abuff-grey to greenish-grey colored, fine-grained rock with a silvery sheen at places with more muscovite concentration. The rock shows the development of quartz porphyroblasts, crenulation cleavage, well-developed schistosity marked by a strong preferred orientation of muscovite, chlorite and biotite (Figure 4A). The rock is traversed by foliation parallel magnetite veins and highly ferruginized at places (Figure 4B–D). Albitite is a brown to brick-red colored, fine grained, hard and compact rock (Figure 4E). It occurs as competent bands within quartz-mica schist, contains foliation parallel tourmaline rich bands and ferruginized at places.

Staurolite schist is asilver-grey to dark grey colored fine to medium grained rock. The

ematic indicators in which sigma structure of quartz porphyroblast indicates a dextral

*Minerals* **2022,** *12*, x FOR PEER REVIEW 6 of 36

**Figure 4.** Field photograph showing: (**A**) Well-developed foliation in quartz-mica schist; (**B**) Quartzmica schist is characterized by the presence of foliation parallel magnetite veins; (**C**) Magnetite veins within quartz-mica schist; (**D**) Intense Fe alteration in quartz-mica schist; (**E**) Albitite occurring within quartz-mica schist as competent bands; (**F**) Ferruginized quartz vein within quartz-mica schist; (**G**) Well developed gossan zone within quartz-mica schist; (**H**) Old workings at contact of quartz-mica schist and albitite; (**I**) Malachite staining in wall of old workings; (**J**) Hydrothermal **Figure 4.** Field photograph showing: (**A**) Well-developed foliation in quartz-mica schist; (**B**) Quartz-mica schist is characterized by the presence of foliation parallel magnetite veins; (**C**) Magnetite veins within quartz-mica schist; (**D**) Intense Fe alteration in quartz-mica schist; (**E**) Albitite occurring within quartz-mica schist as competent bands; (**F**) Ferruginized quartz vein within quartz-mica schist; (**G**) Well developed gossan zone within quartz-mica schist; (**H**) Old workings at contact of quartz-mica schist and albitite; (**I**) Malachite staining in wall of old workings; (**J**) Hydrothermal ferruginized breccias within quartz-mica schist indicate brecciation due to hydrothermal activity; (**K**) Na-B alteration marked by occurrence of albite and tourmaline veins; (**L**) Two generations of quartz veins occurring parallel to S<sup>1</sup> and S<sup>2</sup> foliation, depicting cross cutting relationship with each other.

Intrusive quartz veins are observed in all the lithologic units of the study area. Two generations of quartz veins are observed: the first-generation quartz veins are disposed of parallel to the S1foliation plane, the second-generation quartz veins are disposed parallel to the S<sup>2</sup> foliation plane and show a cross-cutting relationship with each other (Figure 4L). The second-generation quartz veins are prominent and associated with ore mineralization. The length of these quartz veins varies from 2 cm to 5 m and the width varies from 2 cm to 1 m. The quartz veins are ferruginized at places (Figure 4F). Quartz-mica schist and albitite are also traversed by pegmatite veins. The length of pegmatite veins varies from 5 cm to 4 m and the width varies from 2 to 15 cm. Calcite veins are present in quartz-mica schist, albitite and dolomitic marble lithologic unit and are variable in size ranging from 1 to 20 cm in length and 2 to 10 cm in width. Iron oxides in the deposit are represented by magnetite which occurs ubiquitously within quartz-mica schist and albitite as discontinuous veins parallel to the S<sup>2</sup> foliation plane (Figure 4B,C) and also as disseminations at places. The length of iron oxide veins varies from 15 cm to 2 m and the width varies from 1 to 10 cm.The mineral assemblages in different lithologic units of Jagpura deposit indicate upper greenschist to middle amphibolite facies of metamorphism.

### *3.1. Structure*

The lithologic units of the Jagpura deposit show NNW-SSE to N-S structural trends with moderate (50◦ ) to steep (82◦ ) dip towards WSW and ESE. Three distinct phases of deformation have been identified in the area. F<sup>1</sup> type rootless, isoclinal folds represent D<sup>1</sup> phase deformation. The trends of the first-generation axial traces are NNW-SSE to NW-SE. D<sup>2</sup> phase deformation is marked by symmetrical to asymmetrical, tightly to openly inclined, moderately to steep plunging F<sup>2</sup> folds towards NW. F<sup>2</sup> folds control the outcrop pattern of the area and axial traces strike towards NW-SE. Broad warps with widely spaced fracture cleavage and chevron folds represent the D<sup>3</sup> phase of deformation. The trends of the third-generation axial traces are ENE-WSW to E-W. The third generation of folds is less pervasive and has least affected the outcrop pattern of the area. The contact between basement and cover rock is traversed through a ductile shear zone which is evident from several kinematic indicators along with mylonitic foliation. The sense of shear is dextral. The NNW-SSE trending shear zone is exposed in the eastern side of the study area and is part of the regional Ghatol shear zone. The shear zone is sympathetic to the regional D<sup>2</sup> deformation and shear plane is parallel with S<sup>2</sup> foliation. The ore microscopic studies show that the mineralization is localized along shear plane and fold hinges related to D<sup>2</sup> phase deformation event. In the study area, second-generation quartz veins occurring parallel to S<sup>2</sup> foliation are prominent and associated with mineralization. The fluid inclusion study of mineralized quartz vein suggest that the high saline ore fluids injected during the D<sup>2</sup> phase of deformation is responsible for the transportation of metals in the ore system as metals chloride complex.

#### *3.2. Mineralization*

In the Jagpura deposit, surface indications of mineralization are gossan zones, old workings, malachite-azurite stains, hydrothermal alteration, veins and disseminations of iron oxide (magnetite), as well as the presence of visible sulfides (Figure 4G–I). In the study area, 12 old workings are present which are semi-circular in shape and open-pit type. The length of these old workings varies from 08 to10 m and the width varies from 2 to 5 m. Gossan zones are yellow, deep brown to brick-red, massive, hard and compact, and parallel to sub-parallel discontinuous bands. At places, native gold is seen as fine flakes and specks within the gossan zone. Albitite and quartz-mica schist are the host rocks for gold-copper mineralization. Three parallel gold-copper mineralized zones are exposed in the deposit. The cumulative strike length of the mineralized zones is about 1050 m (400 m, 350 m and 300 m), with the width varying from 20 to 30 m.The ore mineral association of the Au-Cu mineralization is native gold, arsenopyrite, loellingite and chalcopyrite with associated pyrrhotite, pyrite and abundant magnetite. Alongside these mineral associations, maldonite (Au2Bi) and hedleyite (Bi7Te3) are also observed as bismuth phases. Apatite, quartz, chlorite, biotite, albite, tourmaline and muscovite are common gangue minerals associated with the Au-Cu ore.

Subsurface mineralization is shallow in nature and all the three mineralized zones have been intersected in drillholes. Four different styles of mineralization are present in drillhole core samples i.e., (1) semi-massive to massive type, (2) vein and fracture fill type, (3) foliation parallel disseminations/smears and (4) patchy and stringer type (Figure 5A–F). The Geological Survey of India (GSI) has augmented a total resource of 6.07 mt gold with an average grade of 1.67 g/t Au and 8.05 mt copper with an average grade of 0.23% Cu [34,58]. Gold-copper mineralized zones occur along the hinges of F<sup>2</sup> fold and F<sup>2</sup> axial planes parallel to the D<sup>2</sup> shear planes. The mineralization is also observed in epigenetic quartz and pegmatite veins (Figure 5G,H). *Minerals* **2022,** *12*, x FOR PEER REVIEW 9 of 36

**Figure 5.** Photograph of drill core showing nature of sulfide mineralization in the Jagpura deposit. (**A**) Association of pyrrhotite, chalcopyrite and arsenopyrite in borehole core; (**B**) Massive to semi massive type pyrrhotite mineralization; (**C**) Foliation parallel semi massive arsenopyrite; (**D**) Vein and fracture filled chalcopyrite, pyrrhotite and arsenopyrite; (**E**) Euhedral coarse grained arsenopyrite specks of first generation; (**F**) Fine grained massive arsenopyrite of second generation; (**G**) Second generation arsenopyrite in quartz vein; (**H**) Stringers of pyrrhotite and disseminations of arse-**Figure 5.** Photograph of drill core showing nature of sulfide mineralization in the Jagpura deposit. (**A**) Association of pyrrhotite, chalcopyrite and arsenopyrite in borehole core; (**B**) Massive to semi massive type pyrrhotite mineralization; (**C**) Foliation parallel semi massive arsenopyrite; (**D**) Vein and fracture filled chalcopyrite, pyrrhotite and arsenopyrite; (**E**) Euhedral coarse grained arsenopyrite specks of first generation; (**F**) Fine grained massive arsenopyrite of second generation; (**G**) Second

For petrography, mineral chemistry, fluid inclusion, and sulfur isotope study, samples were collected from the Jagpura deposit of the SGMB. Both surface and drill core samples of host rocks and ore zones were collected for analysis (Figure 3). Samples from all stages of ore formation, representing different ore and gangue mineral assemblages, were collected. These samples were used for petrographic study and representative samples were used for electron probe micro analyzer (EPMA). Auriferous quartz vein (n = 10) occurring parallel to S2 foliation was sampled for fluid inclusion study. A pure fraction of sulfides viz. pyrite, arsenopyrite, pyrrhotite and chalcopyrite were collected from the dif-

nopyrite in pegmatite vein. (Apy = arsenopyrite, Po = pyrrhotite, Ccp = chalcopyrite).

ferent ore zones for sulfur isotope analysis.

**4. Materials and Methods** 

*4.1. Sampling* 

generation arsenopyrite in quartz vein; (**H**) Stringers of pyrrhotite and disseminations of arsenopyrite in pegmatite vein. (Apy = arsenopyrite, Po = pyrrhotite, Ccp = chalcopyrite).

#### *3.3. Alteration Pattern*

Hydrothermal alteration in the Jagpura deposit is represented by pervasive Na-B alteration besides chloritization, sericitization, silicification, ferruginization and hydrothermal iron oxide breccias present close to the gold-copper mineralized zones. In the Jagpura deposit, hydrothermal alteration is dominated by Na-B metasomatism (Figure 4K), marked by the ubiquitous presence of albite and tourmaline in all the lithologic units of the Jagpura Formation [34,35]. In the study area, B metasomatism postdates Na metasomatism. Within quartz-mica schist, Na metasomatism was so intense that it has formed albitite rock. Silicification is present along the S<sup>1</sup> and S<sup>2</sup> foliation. However, quartz veins occurring parallel to the S<sup>2</sup> foliation are dominant and close to the ore zones. Chloritization (of biotite and amphibole) near sulfide mineralization is mainly associated with the shear zone Calcic alteration is marked by the presence of calcite veins besides tremolite, actinolite (calcic amphibole) and oligoclase, andesine mineral assemblages. A lesser degree of K-alteration is also observed along the shear planes marked by biotite enrichment and albite replacement by K-feldspar. Alteration of feldspar to sericite is noted throughout the host rocks Intense ferruginization (magnetite, goethite) is present in the quartz-mica schist, albitite and in quartz veins. Hydrothermal iron oxide breccia occurs in patches within the host rock. It is composed of rounded to angular clasts made up of polycrystalline quartz set in a ferruginized matrix (Figure 4J). The occurrence of albite, tourmaline, magnetite, chlorite, actinolite, tremolite, calcite and sphene represents Na-B-Fe-Mg-Ca-K alteration within the host rock proximal to Au-Cu ore zones.

#### **4. Materials and Methods**

#### *4.1. Sampling*

For petrography, mineral chemistry, fluid inclusion, and sulfur isotope study, samples were collected from the Jagpura deposit of the SGMB. Both surface and drill core samples of host rocks and ore zones were collected for analysis (Figure 3). Samples from all stages of ore formation, representing different ore and gangue mineral assemblages, were collected. These samples were used for petrographic study and representative samples were used for electron probe micro analyzer (EPMA). Auriferous quartz vein (n = 10) occurring parallel to S<sup>2</sup> foliation was sampled for fluid inclusion study. A pure fraction of sulfides viz. pyrite, arsenopyrite, pyrrhotite and chalcopyrite were collected from the different ore zones for sulfur isotope analysis.
