Ann: Colluli Project Update, page-10

It may reduce opex but a large increase in capex in my experience.
It usually requires drilling of at least a few large diameter holes over kilometres into the earth. The number of kilometres being dependent on the temperature profile and competence of the rock. There will be tax considerations and workarounds, like leasing power generation facilities, between capex and opex. However, depending on the tax regime of the country opex is usually favoured as generating NPAT compared with the CGT rules. Still, every case is different and in a country like Eritrea probably open to negotiation to some extent.

e.g It may be different at a place like Lihir Island where the mine is already very deep and sits on an upwelling of a volcanic magma. Lihir being one o the few I know of using geothermal. Certainly less than 1% of mines. IMVHO