Origin of Fe–Ni–Cu (Co) sulfide and Fe–Ti oxide minerals in the c. 1.77 Ga dolerite dyke, Singhbhum Craton (eastern India)

Posted on 01.10.2021 - 11:25
Dolerite dyke swarms are widespread within the Singhbhum Craton (eastern India), which emplaced from the Neoarchean to Paleoproterozoic Era just after the stabilization of crust before c. 3 Ga. These dyke swarms are oriented in NE–SW to NNE–SSW, NW–SE to WNW–ESE, east–west and north–south directions. The WNW–ESE-trending c. 1.77 Ga Pipilia dyke swarm was sampled from the Satkosia area of Orissa state. The dyke shows a noticeable disparity in terms of the modal proportion and grain size of pyroxenes, plagioclase, Fe–Ti oxide minerals and texture across the trend. At places the primary silicates are altered to secondary hydrated mineral assemblages of amphibole, chlorite and sericite. Primary silicates are clinopyroxene (augite: Mg# = 65.7–82.6; En37–48Fs11–17Wo36–41), orthopyroxene (clinoenstatite: Mg# = 68.5–78; En63–70Fs20–29Wo4–5), plagioclase (An11–39Ab44–82Or1–7) and Fe–Ti oxides are titanomagnetite (FeO = 34.38–39.50 wt%, Fe2O3 = 48.26–56.21 wt%, TiO2 = 5.05–9.60 wt%) and ilmenite (FeO = 40.75–43.79 wt%, Fe2O3 = 3.54–10.03 wt%, TiO2 = 47.82–50.87 wt%). Application of two-pyroxene thermometry yields an equilibration temperature range of 1065°C to 978°C, and coexisting titanomagnetite–ilmenite pairs reveal 731.39°C to 573.37°C at the oxygen fugacity (fO2) condition NNO+0.3 to FMQ–1.03. The dyke contains disseminated sulfides at the interstices of Fe–Ti oxides, and silicates. Major sulfide minerals are pyrite, chalcopyrite and vaesite. Pyrite–vaesite assemblages occur in association with secondary silicate minerals. Pyrite grains contain variable concentrations of Co = 0.01–5.70 wt% and Ni = 0.02–1.95 wt%. Coexisting vaesite contains Co = 2.42–10.44 wt%, Ni = 26.40–47.88 wt%, and Fe = 7.32–26.55 wt%. Texture, sulfide–silicate assemblage, and presence of low metal/S sulfides, such as the pyrite–vaesite assemblage, indicate primary Fe–Ni sulfides (pyrrhotite–pentlandite) that segregated from immiscible sulfide liquid at high temperature were modified by late magmatic/hydrothermal fluid activities. Numerous sulfide-bearing deposits hosted in ultramafic–mafic intrusions of Paleoproterozoic age have been recorded globally and the occurrence of Fe–Ni sulfides in the c. 1.77 Ga Pipilia dyke swarm in the Singhbhum Craton enhances the exploration potential of this craton in eastern India.

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Dey, Arnab; Mondal, Sisir K. (2021): Origin of Fe–Ni–Cu (Co) sulfide and Fe–Ti oxide minerals in the c. 1.77 Ga dolerite dyke, Singhbhum Craton (eastern India). Geological Society of London. Collection. https://doi.org/10.6084/m9.figshare.c.5643989.v1
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