Our reactive transport models show that high-temperature fault-controlled dolomite can form from mixed convection and act as a sink for Mg in the circulating seawaters. This provides new perspectives to enhance understanding of mechanisms and controls on dolomitisation, geometry, and spatial distribution of dolomite bodies within faulted and fractured systems, which has important implications for modelling of systems ranging from geothermal resources to ore formation and carbonate diagenesis.