In the mixing zone, comprising an inorganic barrier precipitated at the interface of the two contrasting solutions, various redox reactions release free energy with the potential to drive endergonic reactions, assuming the involvement of coupling inorganic protoenzymes. Hydrogenotrophic methanogenesis and acetogenesis – long considered the most ancient forms of biological energy metabolisms – are able to achieve higher maximum energy yield (>0.5 kJ/kg hydrothermal fluid) than those in the modern serpentinization-associated seafloor hydrothermal systems (e.g., Kairei field). Furthermore, the recently proposed methanotrophic acetogenesis pathway was also thermodynamically investigated. It is known that methanotrophic acetogenesis would require additional exergonic reactions to compensate its most endergonic methane-to-methanol conversion reaction at the oxidative entry to the metabolic pathway. Our calculations support the view that this thermodynamic barrier could be overcome by the reduction of nitrate in seawater at low temperature, as previously suggested. However, the thermodynamic calculations also revealed that the reduction of ferric iron-bearing minerals would occur at the outer margin and within the hydrothermal chimney wall. The maximum available energy of iron-reducing methanotrophic acetogenesis was calculated to be 0.25–0.35 kJ/kg hydrothermal fluid. Although this value is lower than theoretically available through nitrate reduction, which approaches ∼0.45–1.25 kJ/kg hydrothermal fluid on the outer cool margins of a putative Hadean alkaline chimney, it is higher than that of sulfate-reducing anaerobic oxidation of methane in the Lost City field. These results suggest that iron reduction had the potential to drive methanotrophy and that the Hadean hydrothermal mixing zone was energetically more favorable to methanotrophy than previously thought. We conclude that iron oxidation and reduction in oxyhydroxides probably played important roles in the early evolution of energy metabolisms in the Hadean alkaline hydrothermal system.