High Heat Producing Granites

Enhanced Geothermal Systems (EGS) or Hot Fractured Rock / HFR) geothermal energy relies on the presence of high heat production granites.

These granites have special naturally occurring radiogenic minerals which produce their own heat. The heat is trapped inside these granites by an overlying blanket of insulating rocks. Such a blanket has to be about 3km thick for the required >200^oC temperatures to be generated.

High heat production granites are quite common. For example, they occur at the surface near Stanthorpe in Queensland and near Tenterfield and Bathurst in New South Wales. At these locations, the granite is not hot enough, even at 6km depth, because the heat escapes into the atmosphere. There is no overlying insulating blanket to trap the heat.