Characterization of copper ± (gold) vein‐type mineralization along terrain boundary fault, Dubarpeth in Central India: Constraints from fluid inclusion, stable isotope, and in situ trace element geochemistry of sulphides
Authors: Nathala Kutumba Rao , Muduru Lachhana Dora , Deshmukh Manish S. , Malpe Deepak B. , Baswani Srinivas Rao , Sesha Sai V.V. , G Gopalakrishna , Ghosh Subhsish , Pati Pitambar , Meshram Tushar 
Published: December 2019

We present the findings on in situ trace element geochemistry of sulphides by LA‐ICPMS, sulphur isotope, and hydrothermal fluid evolution of copper ± gold mineralization at Dubarpeth, Central India. Mineralization is associated with chloritized‐silicified alteration zones, structurally localized along the terrain boundary fault between Archean TTG quartz diorite (2.5 Ga) of Western Bastar Craton and Paleo‐Mesoproterozoic cover sediments of Pranhita–Godavari (PG) Valley. Studies reveal that the Cu ± Au mineralization occurs in the form of dissemination, stringers, and veins along the microfaults and fractures. We infer three stages of mineralization based on the field observations and petrography studies. The early stage is characterized by the quartz–pyrite–chalcopyrite assemblage, while the middle stage is represented by quartz–chlorite–chalcopyrite ± pyrite. Calcite ± epidote is conspicuous in the late stage. Fluid inclusion microthermometry and Raman spectroscopy studies indicate that the early‐stage veins are mainly aqueous rich, mixed carbonic‐aqueous, and minor vapour‐rich aqueous inclusions. FIs in the early stage displayed evidence of vein formation during episode of fluid immiscibility with the homogenization temperatures and salinities up to 259°C and 27 wt.% NaCl equiv., respectively, indicating initial ore‐forming fluids of moderate temperature, moderate to high salinity in H2O–CO2–NaCl systems. Copper mineralization stage is liquid‐ and vapour‐rich (H2O–CO2–CH4 + N2) aqueous inclusions, with homogenization temperatures of 174–221°C and salinities of 6.37 to 13.9 wt.% NaCl equiv. This temperature range has been further supported by empirical chlorite thermometry based on Fe/Mg, AlIV, and AlV. The sulphur isotope values of pyrite and chalcopyrite showed δ34S interval of 2.29‰ to −10.85‰, characteristic of highly oxidized nature of the fluids and attributing sulphur source to magmatic origin. The ore‐forming fluids gradually became SO2−4 enriched and relatively oxidized during Cu mineralization. High Co–Ni trace element signatures of pyrite by LA‐ICPMS substantiate this observation, further indicating remobilization from a magmatic‐hydrothermal fluid. The presence of CH4 favours either a source of deep crustal nature or a mantle for the ore‐bearing fluid. We suggest that initial ore‐forming fluids are magmatic in origin that has been further cooled and diluted by mixing with meteoric water. Fluid boiling and mixing facilitated hydrothermal alteration and mineralization in the vicinity of the fault zone, which is perhaps activated during initiation of Paleo‐Mesoproterozoic segment of the Godavari Rift. The tectono‐magmatic setting, mineral assemblage, hydrothermal alteration, FIs, and trace element behaviour of pyrite (As–Co–Ni) suggest that the Dubarpeth Cu deposit is a high sulphidation epithermal vein type of deposit that is similar to those described for the shear/fault‐controlled epithermal deposits found elsewhere in the world.