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

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.

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 [4,5,6,7,8,9,10]. 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 [12,13,14,15,16]. These elements are useful petrogenetic tools for modern-day exploration [15,17,18,19,20,21,22]. 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 [14,16,18,20,22,23,24,25,26,27,28]. Apatite is also a vital pathfinder 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 source-transportation-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), [37,38,39,40,41]. 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].

The ADFB is composed of calcareous and argillaceous meta-sedimentary rocks, meta-volcano-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).

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].

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

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.

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.

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 S₂ 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 S₂ 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. F₁ type rootless, isoclinal folds represent D₁ phase deformation. The trends of the first-generation axial traces are NNW-SSE to NW-SE. D₂ phase deformation is marked by symmetrical to asymmetrical, tightly to openly inclined, moderately to steep plunging F₂ folds towards NW. F₂ 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 D₃ 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 D₂ deformation and shear plane is parallel with S₂ foliation. The ore microscopic studies show that the mineralization is localized along shear plane and fold hinges related to D₂ phase deformation event. In the study area, second-generation quartz veins occurring parallel to S₂ 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 D₂ 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 F₂ fold and F₂ axial planes parallel to the D₂ shear planes. The mineralization is also observed in epigenetic quartz and pegmatite veins (Figure 5G,H).

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 S₁ and S₂ foliation. However, quartz veins occurring parallel to the S₂ 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 S₂ 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.

4.2. Petrography and EPMA

Thin polished and polished sections of host rocks (n = 25) were studied for ore mineralogical and petrological studies using Leica DMRX advanced polarizing petrological microscope at the Regional Petrology Laboratory, the Geological Survey of India, Jaipur, India. Representative sections (n = 10) were studied to determine the mineral chemistry and to understand the nature of the gold and sulfide mineral phases using Electron Probe Micro Analyzer (EPMA), CAMECA SX-100 with five wave dispersive spectrometers (WDS) at National Centre of Excellence in Geoscience Research (NCEGR), GSI, Faridabad, India. The polished thin sections were examined using an optical microscope to characterize the mineralogical and textural relationship of the ore and associated gangue minerals. EPMA analysis was carried out using the operating column conditions of 20 kv accelerating voltage and a probe current of 15 nA. Analyses were carried out using a beam diameter of 1 µm. Peak and background counting times for major elements were 20 s and 10 s, respectively, whereas those for trace elements were 40 s and 20 s, respectively. Natural standards were run before and after analysis to determine the analytical error. Two sections were studied to determine the mineral chemistry of magnetite using Electron Probe Micro Analyzer (EPMA), CAMECA SX-5 at Central Research Facilities in Indian Institute of Technology (Indian School of Mines), Dhanbad, India. The analyses were carried out for Si, Ti, Al, Fe, Mn, Mg, Ca, Na, K, Ni, Co, V and Cr using the operating column conditions 15 kv accelerating voltage, probe current of 12 nA and beam diameter of 1 µm. Standards were run before and after analysis to determine the analytical error. The standards used for calibration of the instrument are as follows: spinel for Mg and Al, ilmenite for Ti, vanadium metal for V, chromite for Cr and Fe, and manganese oxide for Mn. Vanadium concentrations were corrected for the overlap between Ti Κ_β and V Κα peaks by analyzing V-free and Ti bearing standards of rutile and metallic Ti. Matrix correction was carried outusing the ZAF correction. The analytical inaccuracies and uncertainties of the analysis are negligible and as follows: <0.1% for Cr; <1% for Al, Si, K, Ca, Fe, Mg, Ti, Co, V; <2% for Mn and Na.

4.3. Fluid Inclusion Micro Thermometry

At the Fluid Inclusion Lab of NCEGR, GSI, Bengaluru, India, the fluid inclusions were observed under a microscope at high magnification and the temperatures of thermally induced phase transitions in fluid inclusions were evaluated using a calibrated LINKAM THMSG 600 heating/freezing stage. The heating and freezing stage is equipped with an Olympus BX-50 transmitted light microscope, an LNP-95-LTS liquid nitrogen chilling unit, and a digital video capturing system for temperature monitoring. LINKSYS is the program used to study fluid inclusions. The system was calibrated, and the reproducibility of measurements at room temperature was tested using natural fluid inclusion standards from quartz crystals tested in other established laboratories, as well as LINKAM’s standard CO₂ standards, with reproducibility achieved within the standard accepted error limits. The apparatus operates at temperatures ranging from 196 to 600 °C.

4.4. Sulfur Isotopic Composition

A total of 31 sulfide samples were selected for conducting the sulfur isotope studies and the respective data were generated from the Isotope Ratio Mass Spectrometry (IRMS) laboratory, NCEGR, GSI, Bengaluru, India. Sulfide grains were separated by hand from gangue minerals under a stereomicroscope and then powdered avoiding any contamination. Using the ANCA GSL (Automated Nitrogen and Carbon Analyzer for Gas Solids and Liquid) peripheral system; the separated powdered samples were analyzed for sulfur isotopes in continuous flow mode using an Isotope Ratio Mass Spectrometer (Make: SerCon, Model: Geo 2020). Around 3550 mg powder of each sulfide mineral was manually packed into tin capsules and placed into the auto-sampler unit above the ANCA, with the positions noted. Each tin capsule was put one by one into a furnace at 1050 °C with an additional oxygen pulse during the analysis. In the presence of oxygen, the tin ignites and burns exothermally, raising the temperature to around 1800 °C and oxidizing the sample. Water is removed using a Nafion dryer and anhydrous magnesium perchlorate trap. Helium is the carrier gas used (99.99%). The gas stream is routed through a gas chromatograph, where sulfur is separated and injected into a mass spectrometer for isotope analysis of sulfur. Each sample’s total analysis time is 9 m 10 s. Analytical techniques and fractionation mechanism was followed in accordance with [59,60]. Each sample was analyzed three times in a batch, along with international reference (NBS) and internal laboratory standards. All sulfur-bearing samples are measured using the VCDT scale [61].

4.5. Geochemical Analysis

For geochemical analysis, drill core samples (n = 10) were collected from mineralized zone. The samples were crushed to −100 mesh size, sieved, coned and quartered, for major, trace, base metal and REE analysis. The geochemical analysis was carried out at NABL accredited (ISO/IEC17025:2005) chemical laboratory of Geological Survey of India, Western Region, Jaipur.The trace elements including REE were analyzed using Varian 820 Inductively Coupled Plasma Mass Spectrometry (ICP-MS instrument, following the closed digestion sample preparation technique). Standard reference materials (SRMs) were employed to estimate accuracy and precision of the instrument. Gold was analyzed using fire assay technique with ICPMS/GTAAS instrument. The base metal (Cu, Ni, Co, Pb, Zn) was analyzed using Flame Atomic Absorption Spectrophotometer (FAAS, Agilent Duo 280 AAS) instrument. The samples were pulverized to −200 mesh size using vibratory cup mill and taken in tightly packed zip plastic bag. For digestion, 0.2 g of the sample was weighed in a test tube and 5 mls of HNO3: HCl mixture in 1:2 ratios were added to it. The solution was heated over hotplate for 4 h and then made up with Type-I water and allowed to settle. The final solution was used for the determination of Cu, Ni, Co, Pb, Zn.

5. Results

5.1. Petrography and EPMA Study

5.1.1. Petrography of Host Rocks

Detailed petrographic studies of gangue and ore minerals of the host rocks were carried out to understand the relationship between gangue and ore minerals, nature of gold mineralization, microstructures, mineral paragenesis and hydrothermal alteration pattern. Quartz-mica schist is composed of muscovite, chlorite, sericite and quartz with an accessory amount of apatite, feldspar, tourmaline, biotite, ilmenite, rutile, hornblende, orthoclase and sphene (Figure 6A–F). A few sections also observe the alteration of biotite and amphibole to chlorite. The rock shows well-developed schistosity, marked by the parallel alignment of chlorite, muscovite, and sericite. S-C fabric, mica fish and pressure shadow are also observed within the rock. Orientation of mica fish and S-C fabric shows a dextral sense of shearing (Figure 6J) and alteration of feldspar to sericite. (Figure 6K). The rock shows well-developed crenulation cleavage and microfolds associated with the second phase of deformation. In chlorite, Fe/Fe+Mg ratio varies from 0.42 to 0.61 and Mg/Fe + Mg ratio ranges from 0.39 to 0.58. Most chlorites are ripidolite with few pynochlorite and diabantite (Figure 8E). Feldspar is mostly albite (Ab_98.6–91An_8.2–0.4Or_3–0.1) to oligoclase [(Ab_84.8–70.9An_27.1–14.6Or_2–0.3), (Figure 8F) and tourmaline is dravite variety.

Albitite comprises albite (Ab_98.7–90.8An_9.1–0.7) and tourmaline as major minerals (Figure 6D) along with apatite, biotite, muscovite, actinolite, quartz, orthoclase, rutile and ilmenite as accessory minerals. Albite occurs as subhedral, polygonal grains and generally untwined in nature. In some sections, albite constitutes up to 90% volume of the rock. Tourmaline occurs as euhedral to subhedral grains and shows strong pleochroism in brown shades. The concentration of tourmaline ranges from 5 to 50% volume of the rocks. A higher concentration of tourmaline is observed in the mineralized zones. Albite and tourmaline grains in albitite are elongated and aligned, parallel to the shear foliation close to the shear zone (Figure 6G,H).

5.1.2. Ore Petrography and Ore Chemistry

The sulfide mineral assemblages of the Jagpura deposit are represented by pyrrhotite, chalcopyrite, arsenopyrite, loellingite and pyrite in the order of abundance (Figure 7A–O). Moreover, native gold, maldonite (Au₂Bi) and hedleyite (Bi₇Te₃) are present as gold and bismuth ore, respectively (Figure 8D). The sulfide minerals occur as semi-massive to massive type, vein and fracture fill type, foliation parallel type, patchy and stringers type. Magnetite is the dominant oxide phase and is closely associated with gold-sulfide mineralization (Figure 7G,J,M); it is euhedral to subhedral in shape and occurs as disseminations and veins (Figure 7E,I,M and Figure 8A,B). Apatite is euhedral, hexagonal in shape and occurs as disseminations parallel to the foliation plane of host rocks (Figure 7L). Apatite is associated with magnetite and chalcopyrite at many places (Figure 7L and Figure 8C). The ore minerals indicate replacement, remobilization and deformational textures. Major sulfide phases show replacement textures. Two types of arsenopyrite are observed in the ore zones: one is coarse grained, granular and intensely fractured with cataclastic texture (Figure 7A) and the other is idiomorphic, euhedral, rhombic in shape, fine to medium grained without deformation texture (Figure 7B). The healing of fractures within the arsenopyrite by chalcopyrite shows that the former is replaced by the later (Figure 7C). The convexity of chalcopyrite grain boundary within pyrrhotite shows that pyrrhotite has formed earlier (Figure 7D). Occurrence of sulfides along weak planes viz. fractures, veins and shear planes (Figure 7H,K) and the hinge of F₂ folds represents ore remobilization (Figure 6E,F and Figure 7F). In mineralized zones, sulfide veins cross-cutting the albite-tourmaline grains (Figure 6I), deformed albite twin lamellae and cataclastic fragments of sulfide minerals indicate ore deformational textures (Figure 7K). Sulfide minerals such as pyrite and arsenopyrite are associated with gold [62]. Arsenopyrite has a higher gold content than pyrite, and the gold content of arsenian pyrites increases with arsenic content [63].

Ore petrography revealed that gold is mainly present within the arsenopyrite and loellingite. Within the arsenopyrite, gold occurs in association with loellingite, maldonite and hedleyite. Gold occurs as specks, fine flakes and films varying in size from a fraction of a micron to 40 microns (Figure 7N). Gold also occurs along the fractures within the arsenopyrite and loellingite. Epigenetic quartz vein within the host rocks also contains native gold (Figure 7O). Arsenopyrite and loellingite are intimately associated and form the main gold bearing minerals in the study area. EPMA analysis of native gold indicates that Au concentration ranges from 89.25 to 94.72 wt% and it contains silver as a minor impurity (6.15 to 8.46 wt%). Gold fineness ranges from 914–937‰, with average value of 927‰ (n = 6).

EPMA analysis of the sulfides also indicates the presence of invisible gold. Gold content ranges from 0.02 to 2.58 wt% in arsenopyrite, 0.02 to 0.20 wt% in chalcopyrite, 0.08 to 0.11wt% in pyrrhotite and up to 0.17 wt% in loellingite. The EPMA study reveals that loellingite and arsenopyrite occur as coexisting phase within the ore zones. However, loellingite is the preferred residence for gold mineralization compared to arsenopyrite (Figure 8D). Arsenic content is higher in loellingite (72.20 to 72.36 wt%) than arsenopyrite (47.07 to 51.05 wt%). Loellingite and arsenopyrite are also rich in nickel and cobalt wherein, loellingite shows higher values compared to arsenopyrite [

Table 1. EPMA data of Au, Au-Te, Au-Bi and sulfide phases (in Wt%) from the Jagpura gold-copper deposit, western India.

Lithology: Albitite, Sample No. JGB-10
Mineral Name	Gold (Au)			Arsenopyrite (FeAsS)			Pyrrhotite (FeS)			Chalcopyrite (CuFeS2)
EPMA Analysis No.	1/1	1/2	1/3	1/4	1/5	1/6	1/7	1/8	1/9	1/10	1/11	1/12	1/13
S	0.09	0.02	0.02	17.74	17.70	17.33	38.27	39.04	39.17	34.14	34.18	34.03	33.88
Fe	0.68	0.12	0.12	31.10	31.60	34.68	59.85	58.75	59.22	30.08	29.35	30.02	29.92
Co	bdl	bdl	0.02	2.22	0.88	0.39	0.01	0.03	bdl	bdl	0.01	bdl	0.03
Ni	0.10	bdl	bdl	0.40	0.29	bdl	0.07	0.04	bdl	bdl	0.03	bdl	bdl
Cu	0.08	0.02	0.01	bdl	0.02	0.03	0.01	0.01	0.01	32.66	33.79	32.6	33.02
Zn	bdl	0.10	0.02	bdl	bdl	bdl	bdl	bdl	bdl	bdl	0.02	0.05	0.02
As	0.25	0.08	0.01	48.10	49.14	47.07	bdl	0.02	bdl	bdl	0.04	bdl	bdl
Mo	bdl	bdl	bdl	bdl	0.24	0.22	0.51	0.56	0.49	0.46	0.50	0.43	0.58
Ag	7.20	6.15	6.58	0.03	bdl	0.04	bdl	bdl	0.02	0.08	bdl	bdl	bdl
Cd	0.14	0.02	0.08	bdl	0.01	bdl	bdl	0.02	bdl	bdl	0.06	bdl	bdl
Te	bdl	bdl	bdl	bdl	bdl	bdl	bdl	0.02	bdl	2.44	bdl	2.42	2.19
Au	89.95	92.12	92.21	0.13	0.06	0.07	0.11	0.08	0.10	0.10	0.20	0.06	0.02
Pb	bdl	bdl	bdl	0.15	bdl	0.13	bdl	bdl	bdl	bdl	0.13	bdl	bdl
Bi	bdl	bdl	bdl	0.10	bdl	bdl	bdl	bdl	bdl	bdl	bdl	bdl	bdl
Total	98.49	98.63	99.07	99.97	99.94	99.96	98.83	98.57	99.01	99.96	98.31	99.61	99.66
Lithology: Quartz-mica schist, Sample No. JGB-7
Mineral Name	Gold (Au)			Loellingite (FeAs2)			Maldonite (Au2Bi)		Hedleyite (Bi7Te3)		Arsenopyrite (FeAsS)
EPMA Analysis No.	1/1	1/2	1/3	1/4	1/5	1/6	1/7	1/8	1/9	1/10	1/11	1/12
S	0.05	0.07	0.01	1.29	1.17	1.30	0.07	bdl	0.04	0.02	16.65	18.25
Fe	0.22	0.72	0.21	24.71	24.06	24.38	1.52	0.32	0.32	0.30	31.03	32.13
Co	bdl	bdl	bdl	1.08	1.44	1.41	0.06	0.04	0.07	0.09	0.69	0.67
Ni	0.01	0.11	0.05	2.45	2.50	2.10	0.11	0.06	0.14	0.15	0.29	0.18
Cu	0.03	0.07	0.04	bdl	bdl	bdl	bdl	bdl	bdl	bdl	bdl	bdl
Zn	bdl	bdl	bdl	bdl	bdl	bdl	bdl	bdl	bdl	bdl	bdl	0.02
As	0.08	0.21	0.03	70.36	70.20	70.34	0.32	0.22	0.49	0.42	47.55	48.32
Mo	bdl	bdl	bdl	0.02	bdl	0.04	bdl	bdl	bdl	bdl	0.19	0.28
Ag	8.46	7.60	7.12	bdl	0.08	bdl	0.12	0.09	bdl	bdl	0.02	bdl
Cd	0.03	0.12	bdl	bdl	bdl	bdl	0.19	0.12	bdl	bdl	bdl	0.07
Te	bdl	bdl	bdl	bdl	bdl	bdl	bdl	bdl	20.39	21.30	0.05	bdl
Au	89.93	89.25	91.12	bdl	bdl	0.17	64.71	66.47	bdl	bdl	2.58	0.02
Pb	bdl	bdl	bdl	bdl	bdl	0.11	bdl	bdl	0.10	0.08	bdl	bdl
Bi	bdl	bdl	bdl	bdl	bdl	bdl	32.68	31.52	78.11	77.18	0.80	bdl
Total	98.81	98.15	98.58	99.91	99.45	99.85	99.78	98.84	99.66	99.54	99.85	99.94
Lithology: Quartz-mica schist, Sample No. JGB-8
Mineral Name	Pyrite (FeS2)
EPMA Analysis No.	1/1	1/2	1/3	1/4	1/5	1/6	1/7	1/8	1/9	1/10	1/11
S	53.00	53.25	53.11	53.25	52.49	53.15	52.86	53.13	53.00	53.11	53.25
Fe	45.88	45.62	46.25	45.62	46.33	46.36	45.80	46.34	45.88	45.25	45.62
Co	0.06	0.15	0.10	0.15	0.04	0.03	0.19	0.07	0.06	0.10	0.15
Ni	0.03	0.06	0.04	0.06	0.03	0.02	0.10	0.06	0.03	0.03	0.06
Cu	bdl	bdl	0.02	bdl	bdl	0.02	0.02	0.01	bdl	0.02	bdl
Zn	bdl	0.04	bdl	0.04	0.03	bdl	bdl	bdl	bdl	bdl	0.04
As	bdl	0.01	bdl	0.01	bdl	0.01	0.01	0.02	bdl	bdl	0.01
Ag	0.01	0.02	0.04	0.02	bdl	0.04	bdl	0.03	0.01	0.04	0.02
Total	98.99	99.17	99.53	99.16	99.11	99.82	98.99	99.96	99.33	99.13	99.61
Co/Ni	1.96	2.54	2.40	2.54	1.17	1.76	1.89	1.17	1.96	3.20	2.54
S/Fe	1.16	1.17	1.15	1.17	1.13	1.15	1.15	1.15	1.16	1.17	1.17
Fe/(S+As)	0.87	0.86	0.87	0.86	0.88	0.87	0.87	0.87	0.87	0.85	0.86
bdl = below detection limit

]. The nickel and cobalt values in loellingite range from 2.10 to 2.45 wt% and 1.08 to 1.44 wt%, respectively. The nickel and cobalt values in arsenopyrite are 0.39 to 2.22 wt% and 0.18 to 0.40 wt%, respectively.

Figure 8. BSE images of magnetite-apatite-gold-sulfide mineral assemblages along with plots suggesting hydrothermal nature of pyrite and magnetite in the study area. (A) Magnetite megacryst in quartz-mica schist; (B) Disseminated magnetite within quartz mica-schist; (C) Subrounded to rounded apatite grains associated with chalcopyrite; (D) Association of gold, loellingite, arsenopyrite, maldonite and hedleyite; (E) Mineral composition classification diagram of chlorite, (Red = albitite, green = quartz-mica schist); (F) Or-Ab-An classification diagram of feldspar. (Red = albitite, green = quartz-mica schist); (G) Co vs. Ni plot of pyrite show hydrothermal signature, fields for pyrite composition from references [64]; (H) Ti vs. Al covariation plots of magnetite indicates magnetite is hydrothermal in nature, fields from reference [65]. (Apa = apatite, Mag = magnetite, Ccp = chalcopyrite, Au = gold, Mdl = maldonite, Lo = loellingite, Hed = hedleyite).

Figure 8. BSE images of magnetite-apatite-gold-sulfide mineral assemblages along with plots suggesting hydrothermal nature of pyrite and magnetite in the study area. (A) Magnetite megacryst in quartz-mica schist; (B) Disseminated magnetite within quartz mica-schist; (C) Subrounded to rounded apatite grains associated with chalcopyrite; (D) Association of gold, loellingite, arsenopyrite, maldonite and hedleyite; (E) Mineral composition classification diagram of chlorite, (Red = albitite, green = quartz-mica schist); (F) Or-Ab-An classification diagram of feldspar. (Red = albitite, green = quartz-mica schist); (G) Co vs. Ni plot of pyrite show hydrothermal signature, fields for pyrite composition from references [64]; (H) Ti vs. Al covariation plots of magnetite indicates magnetite is hydrothermal in nature, fields from reference [65]. (Apa = apatite, Mag = magnetite, Ccp = chalcopyrite, Au = gold, Mdl = maldonite, Lo = loellingite, Hed = hedleyite).

The EPMA study of magnetite from the study area reveals that the concentrations of TiO₂ ranges from(0.01 to 0.11 wt%), Al₂O₃ (0.06 to 0.28 wt%), MnO (up to 0.01 wt%), FeO (83.39 to 89.02 wt%), MgO (0.01 to 0.08 wt%), V₂O₃ (0.03 to 0.26 wt%), Cr₂O₃ (0.01 to 0.09 wt%), NiO (0.04 to 0.31 wt%), CoO (0.02 to 0.05 wt%) and CaO (0.01 to 0.08 wt%) [

Table 2. EPMA data of magnetite from the Jagpura gold-copper deposit, western India.

Lithology: Quartz-mica Schist, Sample No. JGB-8
Mineral Name	Magnetite
EPMA Analysis No.	1/1	1/2	1/3	1/4	1/5	1/6	1/7	1/8	1/9	1/10
Wt%
SiO2	0.02	0.17	0.06	0.10	0.02	bdl	0.05	0.04	0.10	0.06
TiO2	0.05	0.01	0.05	0.07	0.01	0.10	0.05	0.09	0.01	0.05
Al2O3	0.12	0.14	0.13	0.11	0.10	0.28	0.15	0.27	0.26	0.21
Cr2O3	0.05	0.06	0.04	0.05	0.07	0.06	0.07	0.04	0.05	0.03
V2O3	0.20	0.17	0.18	0.07	0.17	0.15	0.08	0.15	0.19	0.17
FeO	89.02	87.69	88.49	87.88	87.82	83.39	83.82	88.57	86.63	88.98
MnO	bdl	0.06	bdl	0.06	bdl	0.01	0.03	bdl	bdl	bdl
MgO	0.05	0.08	bdl	bdl	0.03	bdl	0.01	bdl	bdl	bdl
CaO	bdl	0.03	bdl	bdl	bdl	0.01	0.02	bdl	0.02	bdl
Na2O	0.02	0.01	0.05	0.03	bdl	0.08	0.01	0.01	0.01	0.05
K2O	0.04	0.03	bdl	bdl	bdl	0.02	bdl	0.01	0.02	bdl
NiO	0.05	0.05	0.05	0.06	0.07	0.05	0.06	0.07	0.05	0.05
CoO	0.02	0.03	0.02	0.03	0.04	0.02	0.03	0.04	0.02	0.02
Total	89.64	88.53	89.07	88.46	88.33	84.17	84.38	89.29	87.36	89.62
apfu Number of ions on the basis of 4 (O)
Si	0.01	0.08	0.03	0.05	0.01	bdl	0.02	0.02	0.05	0.03
Ti	0.03	0.01	0.03	0.04	0.01	0.06	0.03	0.05	0.01	0.03
Al	0.06	0.07	0.07	0.06	0.05	0.15	0.08	0.14	0.14	0.11
Cr	0.03	0.04	0.03	0.03	0.05	0.04	0.05	0.03	0.03	0.02
V	0.11	0.10	0.10	0.04	0.10	0.08	0.04	0.08	0.11	0.10
Fe	69.20	68.16	68.78	68.31	68.26	64.82	65.15	68.85	67.34	69.17
Mn	bdl	0.05	bdl	0.05	bdl	0.01	0.02	bdl	bdl	bdl
Mg	0.03	0.05	bdl	bdl	0.02	bdl	0.01	bdl	bdl	bdl
Ca	bdl	0.02	bdl	bdl	bdl	0.01	0.01	bdl	0.01	bdl
Na	0.01	0.01	0.04	0.02	bdl	0.06	0.01	0.01	0.01	0.04
K	0.03	0.02	bdl	bdl	bdl	0.02	bdl	0.01	0.02	bdl
Ni	0.04	0.04	0.04	0.05	0.06	0.04	0.05	0.06	0.04	0.04
Co	0.01	0.02	0.01	0.02	0.03	0.01	0.02	0.03	0.01	0.01
Co/Ni	0.25	0.50	0.25	0.40	0.50	0.25	0.40	0.50	0.25	0.25
Ni/Cr	1.18	1.00	1.48	1.67	1.20	1.00	1.06	2.00	1.18	1.95
Lithology: Albitite No. JGB-10
Mineral name	Magnetite
EPMA Analysis No.	1/1	1/2	1/3	1/4	1/5	1/6	1/7	1/8	1/9
Wt%
SiO2	0.10	0.10	0.02	0.04	0.01	0.03	0.03	0.09	0.03
SiO2	0.10	0.10	0.02	0.04	0.01	0.03	0.03	0.09	0.03
TiO2	0.03	0.03	0.06	0.04	0.11	0.02	0.03	0.07	0.01
Al2O3	0.17	0.19	0.19	0.08	0.25	0.09	0.06	0.25	0.17
Cr2O3	0.04	0.08	0.07	0.01	0.06	0.09	0.04	0.09	0.09
V2O3	0.15	0.12	0.26	0.20	0.13	0.13	0.16	0.03	0.08
FeO	86.27	88.91	85.43	88.23	87.69	87.28	88.19	84.06	88.37
MnO	bdl	bdl	bdl	bdl	0.10	0.06	0.03	bdl	0.09
MgO	0.04	bdl	0.01	bdl	bdl	bdl	bdl	0.01	bdl
CaO	0.04	bdl	0.04	bdl	bdl	0.01	bdl	0.05	bdl
Na2O	bdl	0.08	0.03	0.03	0.02	bdl	0.01	0.02	0.01
K2O	bdl	bdl	0.02	bdl	bdl	0.01	0.03	bdl	0.01
NiO	0.04	0.07	0.09	0.05	0.09	0.09	0.04	0.31	0.14
CoO	0.02	0.05	0.02	0.03	0.05	0.04	0.02	0.02	0.04
Total	86.90	89.63	86.24	88.71	88.51	87.85	88.64	85.00	89.04
apfu Number of ions on the basis of 4 (O)
Si	0.05	0.05	0.01	0.02	bdl	0.01	0.01	0.04	0.01
Ti	0.02	0.02	0.04	0.02	0.07	0.01	0.02	0.04	0.01
Al	0.09	0.10	0.10	0.04	0.13	0.05	0.03	0.13	0.09
Cr	0.02	0.05	0.05	0.01	0.04	0.06	0.02	0.06	0.06
V	0.08	0.07	0.15	0.11	0.07	0.07	0.09	0.02	0.04
Fe	67.06	69.11	66.41	68.58	68.16	67.84	68.55	65.34	68.69
Mn	bdl	bdl	bdl	bdl	0.08	0.05	0.02	bdl	0.07
Mg	0.02	bdl	0.01	bdl	bdl	bdl	bdl	0.01	bdl
Ca	0.03	bdl	0.03	bdl	bdl	0.01	bdl	0.04	bdl
Na	bdl	0.06	0.02	0.02	0.01	bdl	0.01	0.01	0.01
K	bdl	bdl	0.02	bdl	bdl	0.01	0.02	bdl	0.01
Ni	0.03	0.06	0.07	0.04	0.07	0.07	0.03	0.24	0.11
Co	0.01	0.04	0.01	0.02	0.04	0.03	0.01	0.01	0.03
Co/Ni	0.33	0.67	0.14	0.50	0.57	0.43	0.33	0.04	0.27
Ni/Cr	1.50	1.20	1.40	4.00	1.75	1.17	1.50	4.00	1.83

]. Magnetite shows low concentrations of TiO₂ (0.01 to 0.11 wt%) and Al₂O₃ (0.06 to 0.28 wt%). The Co/Ni ratio of magnetite is <1 (0.04 to 0.67) and Ni/Cr ratio is ≥1 (1 to 4). Co/Ni ratio of pyrite from the study area is >1 (1 to 2.54, n = 22). The EPMA analysis of apatite reveals that apatite is of fluorapatite variety with F content >1 wt% and >1F/Cl ratio [

Table 3. EPMA data of apatite (in Wt%) from the Jagpura gold-copper deposit, western India. Lithology: Quartz-mica schist, Sample No. JGB-11.

Mineral Name	Apatite
EPMA Analysis No.	1/1	1/2	1/3	1/4	1/5	1/6	1/7
SiO2	0.04	0.21	0.04	0.06	0.53	0.04	0.23
TiO2	bdl	bdl	0.07	bdl	bdl	0.19	bdl
Al2O3	bdl	0.02	bdl	0.01	0.07	0.01	0.03
Cr2O3	bdl	0.12	0.03	bdl	bdl	bdl	bdl
FeO	0.15	0.01	0.04	0.04	0.28	0.13	bdl
MnO	bdl	bdl	0.07	0.05	0.01	bdl	bdl
MgO	bdl	bdl	bdl	bdl	bdl	bdl	bdl
CaO	54.42	53.55	54.34	54.10	53.45	54.46	53.23
Na2O	0.54	0.07	0.03	0.09	0.08	0.03	0.07
K2O	0.02	0.01	bdl	bdl	0.01	0.02	0.02
P2O5	38.10	39.91	39.92	41.05	41.14	38.99	41.12
F	5.89	5.20	4.74	4.32	4.23	5.97	5.10
Cl	0.73	0.14	0.12	0.29	0.16	0.08	0.16
Total	99.89	99.23	99.40	100.00	99.94	99.91	99.96
F/Cl	8.05	38.52	38.19	15.06	26.75	79.53	32.28
bdl = below detection limit

]. Apatite has a higher concentration of F (4.23 to 5.97 wt%, n = 10) and a lower concentration of Cl (0.08 to 0.73 wt%), FeO (0.01 to 0.28 wt%), and MnO (0.01 to 0.07 wt%).

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 D₂ 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.

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/CO₂ 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 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 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 (T_mCO₂) of type-I inclusions range from −56.6 to −60.2 °C, with the maximum depression in TmCO₂ (−60.2 °C) indicating an admixture of other gases, most likely CH₄ or N₂ [67], and the melting temperatures (Tm, CO₂) are graphically illustrated in histograms. The temperatures at which CO₂ was homogenized into the vapor phase ranged from 1.9 to 28.0 °C (density varies from 0.72 to 0.81 g/cm³) 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 CO₂ (liquid) + CO₂ (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 (Th_total) ranges from 235 to 258 °C. The CO₂clathrate temperature (Tm_clath) ranges from 6 to 12 °C. The initial eutectic temperatures (T_e) 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 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 (Teu) 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 CaCl₂ ± FeCl₂ with NaCl and H₂O may be indicated by the maximum eutectic temperature of −51 °C [69]. The final melting temperature of ice (Tm, 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 of inclusions varies from 0.93 to 1.11 gm/cm³ (Figure 11), [

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
Mineralized Quartz veins	Mono phase carbonic inclusions	I	Primary	2–15	−56.6 to −60.2 °C	-	-	1.9 to 28 °C	-	-	0.66 to 0.92 g/cc
	Aqueous carbonic inclusions	II	Primary	6–30	−56.6 to 58.8 °C	−26.5 to −32 °C	−3 to −7 °C	2.5 to 4.2 °C	235 to 258 °C	4.86 to 10.48	0.87 to 0.98 g/cc
	Aqueous inclusion	III	Primary	2–28		−30 to −51 °C	−6.9 to −30.0 °C	-	146 to 252 °C	10.35 to 28.15	0.98 to 1.10 g/cc
	Secondary aqueous inclusions	IV	Secondary	1–15		−22.5 to −44 °C	−4.5 to −22.7 °C	-	120 to 238 °C	7.10 to 24.09	0.93 to 1.11 g/cc

].

5.3. Sulfur Isotopic Composition

The δ³⁴S_VCDT (‰) 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. δ³⁴S_VCDT (‰) values of various sulfide minerals of the Jagpura deposit.

Sl. No.	Sample No.	δ34S VCDT‰	St. dev.	Sulfide Mineral Phase
1.	JPSI-1	8.89	0.20	Pyrrhotite
2.	JPSI-2	9.80	0.17
3.	JPSI-3	10.87	0.37
4.	JPSI-4	10.67	0.16
5.	JPSI-5	10.52	0.27
6.	JPSI-6	10.82	0.31
7.	JPSI-7	11.36	0.14
8.	JPSI-8	12.34	0.37
9.	JPSI-9	12.81	0.11	Arsenopyrite
10.	JPSI-10	10.98	0.20
11.	JPSI-11	11.00	0.07
12.	JPSI-12	11.42	0.13
13.	JPSI-13	11.73	0.16
14.	JPSI-14	13.68	0.11
15.	JPSI-15	14.58	0.08
16.	JPSI-16	10.77	0.10	Chalcopyrite
17.	JPSI-17	10.90	0.05
18.	JPSI-18	11.18	0.26
19.	JPSI-19	10.99	0.03
20.	JPSI-20	10.14	0.09
21.	JPSI-21	10.67	0.33
22.	JPSI-22	11.56	0.18
23.	JPSI-23	12.03	0.28
24.	JPSI-24	12.14	0.15
25.	JPSI-25	10.28	0.06	Pyrite
26.	JPSI-26	10.39	0.16
27.	JPSI-27	10.29	0.05
28.	JPSI-28	10.71	0.46
29.	JPSI-29	11.05	0.52
30.	JPSI-30	10.62	0.30
31.	JPSI-31	10.87	0.59

]. The δ³⁴S 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 δ³⁴S 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 δ³⁴S values.

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. Geochemical results of samples from theJagpura deposit.

Lithology: Quartz-Mica Schist
Trace Elements & REEs (ppm)
Ga	38	31	28	54	69	46	53	46	51	109
Sc	10	11	10	23	20	09	09	9	13	11
V	78	85	92	122	90	104	87	88	92	88
Th	20	21	30	27	26	30	23	21	27	22
Pb	120	400	70	40	50	30	25	25	25	40
Ni	300	140	100	90	130	70	80	100	70	400
Co	1100	950	480	860	480	730	290	330	840	1600
Cr	155	176	179	306	348	223	234	215	218	228
Sr	69	70	72	78	64	56	63	68	68	53
Zr	142	134	121	97	76	119	102	105	114	60
Cu	4600	2400	1200	15200	4700	4600	3100	7100	1100	4700
Zn	20	100	10	40	20	20	10	10	10	10
Be	3.88	4.30	3.47	2.67	2.94	3.00	2.34	1.82	2.48	1.54
Ge	1.64	1.72	1.52	1.03	0.98	1.32	1.23	1.31	1.42	1.11
Y	34.86	28.68	19.68	47.61	96.01	23.40	19.14	19.99	18.95	38.82
Mo	1.54	1.74	2.10	2.38	4.23	2.28	3.29	3.00	2.88	3.00
Sn	3.76	3.76	3.73	3.81	2.74	3.98	2.75	3.21	3.76	5.06
La	50.29	75.60	34.52	10.63	32.64	31.74	21.73	19.90	16.53	24.16
Ce	89.24	133.66	59.79	0.06	4.93	56.72	39.25	35.17	65.10	6.87
Pr	10.41	15.44	6.99	0.27	0.86	6.79	4.96	4.37	7.83	1.02
Nd	40.40	59.37	28.11	1.72	4.35	27.60	19.83	17.54	31.42	4.74
Sm	6.88	9.26	4.73	0.86	1.67	4.31	3.53	2.78	5.05	1.21
Eu	1.24	1.62	0.84	0.34	0.49	0.89	0.75	0.66	0.95	0.41
Gd	6.32	7.62	4.04	2.71	5.40	3.85	3.25	2.84	4.17	2.34
Tb	1.18	1.27	0.73	1.00	1.98	0.74	0.62	0.58	0.69	0.77
Dy	7.05	6.15	4.07	8.34	17.44	4.61	3.60	3.63	3.78	6.74
Ho	1.31	1.11	0.74	1.76	3.60	0.89	0.72	0.76	0.68	1.39
Er	3.72	3.09	2.23	4.84	9.88	2.61	2.01	2.17	2.00	3.91
Tm	0.58	0.45	0.31	0.71	1.40	0.37	0.28	0.31	0.27	0.56
Yb	3.39	2.65	2.04	3.93	7.50	2.42	1.74	2.02	1.82	3.26
Lu	0.46	0.38	0.30	0.52	0.95	0.31	0.25	0.29	0.26	0.45
Hf	4.36	4.20	4.15	3.27	2.83	4.61	3.80	3.88	3.89	2.82
Ta	1.27	1.14	1.16	1.46	0.66	1.26	1.14	1.11	1.06	0.88
W	27.00	6.42	6.47	6.76	4.76	14.72	11.26	11.41	11.70	10.11
U	3.15	3.31	2.42	3.62	2.98	3.83	3.48	3.39	3.16	2.89
Bi	0.16	0.27	0.38	2.65	2.94	1.31	2.17	2.33	1.05	5.46
Te	1.26	1.09	1.02	0.20	0.27	1.21	0.97	0.92	1.02	1.01
Se	0.20	0.20	0.20	0.20	0.20	0.20	0.20	0.20	0.20	0.20
Au	4.62	1.70	1.20	3.10	1.70	2.20	2.40	4.30	1.40	3.30

]. 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.

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 S₀ II S₁ planes, related to the first deformation episodes. The ore mineralization is remobilized and concentrated within the hinge zone of F₂ folds and sympathetic shears (Figure 6E,F and Figure 7F,H) during second phase of deformation. The NW-SE trending shear planes are parallel to F₂ 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 [64,69,70,71], [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 TiO₂ (0.01 to 0.11 wt%) and Al₂O₃ (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 (Figure 8H and Figure 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].

6.3. Evolution of Ore Fluids

The characteristics of the mineralized quartz vein hosted fluid inclusions are listed in Table 4 and Figure 9 and Figure 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].

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 δ³⁴S_VCDT 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].

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 (δ³⁴S > 5) suggests the presence of non-magmatic sulfur sources. Higher positive 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 moderately high δ³⁴S 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 δ³⁴Svalues (>+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-arsenopyrite-pyrite-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. [90,91,92]. 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 D₂ shear planes parallel to F₂ axial planes and F₂ 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.

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 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 [36,90,94,95,96,97,98].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 [4,5,6,7,8,9,10] 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 TiO_2, Al₂O₃ 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 δ³⁴S 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.