*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 K<sup>β</sup> and V Kα 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 CO<sup>2</sup> 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**
